Electromagnetic wave shielding film and shielded printed wiring board

Abstract

Provided is an electromagnetic wave shielding film in which a shielding layer and a protective layer are unlikely to be detached even in a harsh environment such as a high temperature and high humidity environment. An electromagnetic wave shielding film according to the present invention comprises: a shielding layer that includes a metal layer; an anchor layer that is laminated on the shielding layer; and a protective layer that is laminated on the anchor layer on the side opposite to the shielding layer. The anchor layer contains a urethane resin having an acid value of 2800-5400 g / eq.

Description

Electromagnetic Wave Shielding Film and Shielded Printed Wiring Board

[0001] The present invention relates to an electromagnetic wave shielding film and a shielded printed wiring board.

[0002] Patent Document 1 discloses an electromagnetic wave shielding sheet including a conductive layer and an insulating layer, wherein the insulating layer contains a thermosetting resin, a curing agent, and a black colorant, and the black colorant has an average primary particle diameter of 20 to 100 nm.

[0003] Japanese Patent Application Laid-Open No. 2016-143751

[0004] Conventional electromagnetic wave shielding films such as the electromagnetic wave shielding sheet described in Patent Document 1 generally have a structure in which a shielding layer (in Patent Document 1, a conductive layer) and a protective layer (in Patent Document 1, an insulating layer) are laminated. And in the conventional electromagnetic wave shielding film, a metal layer such as copper may be used as the shielding layer.

[0005] However, in the conventional electromagnetic wave shielding film, there is a problem that peeling occurs between the shielding layer containing a metal layer and the protective layer, particularly in a harsh environment such as a high temperature and high humidity environment.

[0006] The present invention has been made to solve the above problems, and an object thereof is to provide an electromagnetic wave shielding film in which the shielding layer and the protective layer are less likely to peel even in a harsh environment such as a high temperature and high humidity environment. Further, an object of the present invention is to provide a shielded printed wiring board having an electromagnetic wave shielding film in which the shielding layer and the protective layer are less likely to peel even in a harsh environment such as a high temperature and high humidity environment.

[0007] The electromagnetic wave shielding film of the present invention is an electromagnetic wave shielding film including a shielding layer containing a metal layer, an anchor layer laminated on the shielding layer, and a protective layer laminated on the opposite side of the shielding layer of the anchor layer, wherein the anchor layer contains a urethane resin having an acid value of 2800 g / eq or more and 5400 g / eq or less.

[0008] In the electromagnetic shielding film of the present invention, since the anchor layer is provided between the shielding layer and the protective layer, contact between the shielding layer, which includes a metal layer, and the protective layer is avoided. Furthermore, in the electromagnetic shielding film of the present invention, the anchor layer contains a urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less. Therefore, even if the shielding layer includes a metal layer, the shielding layer and the anchor layer adhere more easily, and the protective layer and the anchor layer also adhere more easily. Thus, in the electromagnetic shielding film of the present invention, since both the shielding layer and the protective layer adhere closely to the anchor layer, the shielding layer and the protective layer are less likely to peel off from the anchor layer even in harsh environments such as high temperature and high humidity. In other words, in the electromagnetic shielding film of the present invention, the shielding layer and the protective layer are less likely to peel off even in harsh environments such as high temperature and high humidity.

[0009] If the acid value of the urethane resin contained in the anchor layer is lower than 2800 g / eq, the anchor layer hardens more easily, which reduces the adhesive performance of the anchor layer itself. As a result, the adhesion between the shield layer and the anchor layer, as well as the adhesion between the protective layer and the anchor layer, tends to decrease. Consequently, the shield layer and protective layer are more likely to peel off from the anchor layer, especially in harsh environments such as high temperature and high humidity.

[0010] If the acid value of the urethane resin contained in the anchor layer is higher than 5400 g / eq, the moisture and heat resistance of the anchor layer tends to decrease, and in particular, under harsh environments such as high temperature and high humidity, the shield layer and protective layer are more likely to peel off from the anchor layer.

[0011] In the electromagnetic wave shielding film of the present invention, it is preferable that the glass transition temperature (Tg) of the urethane resin contained in the anchor layer is 30°C or higher and 90°C or lower.

[0012] In the electromagnetic shielding film of the present invention, if the glass transition temperature of the urethane resin contained in the anchor layer is lower than 30°C, the anchor layer becomes too soft, making it difficult to obtain sufficient adhesion between the shielding layer and the anchor layer, and between the protective layer and the anchor layer. Furthermore, if the glass transition temperature of the urethane resin contained in the anchor layer is lower than 30°C, the viscosity of the urethane resin becomes too low, making it easier for the anchor layer to protrude from the shielding layer and the protective layer. For example, when cutting the electromagnetic shielding film, the anchor layer may adhere to the cut surfaces of the shielding layer and the protective layer, or to the cutting blade used during cutting, which can easily reduce the manufacturing efficiency of the shielded printed circuit board.

[0013] In the electromagnetic shielding film of the present invention, if the glass transition temperature of the urethane resin contained in the anchor layer is higher than 90°C, the anchor layer becomes less susceptible to thermal deformation, which can make it difficult to achieve sufficient adhesion between the shielding layer and the anchor layer. Furthermore, if the glass transition temperature of the urethane resin contained in the anchor layer is higher than 90°C, the anchor layer becomes less susceptible to thermal deformation, which can make it difficult for the electromagnetic shielding film of the present invention to conform to the stepped areas of the printed circuit board when using thermocompression bonding to place it on other components, such as a printed circuit board. Consequently, if the glass transition temperature of the urethane resin contained in the anchor layer is higher than 90°C, it becomes necessary to thermocompression bond the electromagnetic shielding film and the printed circuit board at high temperatures, which can easily increase manufacturing costs.

[0014] In the electromagnetic wave shielding film of the present invention, it is preferable that the number-average molecular weight (Mn) of the urethane resin contained in the anchor layer is 10,000 or more and 20,000 or less.

[0015] In the electromagnetic wave shielding film of the present invention, if the number-average molecular weight of the urethane resin contained in the anchor layer is less than 10,000, the moisture and heat resistance of the anchor layer tends to decrease. Therefore, in particular, under harsh environments such as high temperature and high humidity, the shielding layer may easily peel off from the anchor layer.

[0016] In the electromagnetic wave shielding film of the present invention, if the number-average molecular weight of the urethane resin contained in the anchor layer is greater than 20,000, the adhesion between the shielding layer and the anchor layer tends to decrease. Therefore, in particular, under harsh environments such as high temperature and high humidity, the shielding layer may easily peel off from the anchor layer.

[0017] In the electromagnetic wave shielding film of the present invention, the protective layer may contain at least one of a urethane resin and an amide resin.

[0018] In conventional electromagnetic shielding films, when laminating a shielding layer containing a metal layer onto a protective layer, if the protective layer contains at least one of urethane resin and amide resin, the adhesion between the metal layer and the protective layer may easily decrease, especially in harsh environments such as high temperature and high humidity. In contrast, in the electromagnetic shielding film of the present invention, since an anchor layer is provided between the shielding layer and the protective layer, contact between the metal layer and the protective layer can be avoided even if the protective layer contains at least one of urethane resin and amide resin. Furthermore, in the electromagnetic shielding film of the present invention, since an anchor layer containing urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less is used, the adhesion between the protective layer and the anchor layer is less likely to decrease even if the protective layer contains at least one of urethane resin and amide resin.

[0019] The shielded printed circuit board of the present invention comprises a printed circuit board having a base film, a printed circuit provided on the base film, and a coverlay provided to cover the printed circuit, and an electromagnetic wave shielding film provided on the coverlay side of the printed circuit board, wherein the electromagnetic wave shielding film is the electromagnetic wave shielding film of the present invention, and the side opposite to the protective layer faces the coverlay.

[0020] As described above, the electromagnetic shielding film of the present invention makes it difficult for the shielding layer and protective layer to peel off even in harsh environments such as high temperature and high humidity. Therefore, in the shielded printed circuit board of the present invention equipped with the electromagnetic shielding film of the present invention, the shielding layer and protective layer of the electromagnetic shielding film of the present invention are less likely to peel off even in harsh environments such as high temperature and high humidity.

[0021] In this specification, "film" is synonymous with "sheet," and the two are not distinguished by their thickness. In other words, "electromagnetic shielding film" is synonymous with "electromagnetic shielding sheet."

[0022] In this specification, a high-temperature, high-humidity environment is assumed to be, for example, an environment where the temperature is between 60°C and 85°C, and the humidity is between 85% and 95%.

[0023] According to the present invention, an electromagnetic wave shielding film can be provided in which the shielding layer and protective layer are less likely to peel off even under harsh conditions such as high temperature and high humidity. Furthermore, according to the present invention, a shielded printed circuit board having an electromagnetic wave shielding film in which the shielding layer and protective layer are less likely to peel off even under harsh conditions such as high temperature and high humidity can be provided.

[0024] Figure 1 is a schematic cross-sectional view showing an example of the electromagnetic wave shielding film of the present invention. Figure 2 is a schematic cross-sectional view showing an example of the shielded printed circuit board of the present invention.

[0025] The following describes specific examples of the electromagnetic shielding film and the shielded printed circuit board of the present invention. Note that the present invention is not limited to the following configurations and may be modified as appropriate without departing from the spirit of the invention. Furthermore, a combination of several of the preferred configurations described below also constitutes the present invention.

[0026] The drawings shown below are schematic representations, and their dimensions, aspect ratios, and scales may differ from those of the actual product.

[0027] In this specification, unless otherwise specified, terms describing relationships between elements (e.g., "parallel," "perpendicular," etc.) and terms describing the shape of elements mean not only their literal, exact form, but also a range that is substantially equivalent, for example, a range that includes differences of a few percent.

[0028] [Electromagnetic wave shielding film] Figure 1 is a schematic cross-sectional view showing an example of the electromagnetic wave shielding film of the present invention.

[0029] The electromagnetic wave shielding film 1 shown in Figure 1 has an adhesive layer 10, a shielding layer 20 including a metal layer, an anchor layer 25, and a protective layer 30.

[0030] The anchor layer 25 is laminated on the shield layer 20.

[0031] The protective layer 30 is laminated on the opposite side of the anchor layer 25 from the shield layer 20.

[0032] The adhesive layer 10 is laminated on the side of the shield layer 20 opposite to the anchor layer 25.

[0033] As described above, in the electromagnetic wave shielding film 1, the adhesive layer 10, the shielding layer 20, the anchor layer 25, and the protective layer 30 are laminated in that order.

[0034] In the electromagnetic shielding film 1, the anchor layer 25 contains a urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less. In this way, in the electromagnetic shielding film 1, the anchor layer 25 is provided between the shield layer 20 and the protective layer 30, so that contact between the shield layer 20, which contains a metal layer, and the protective layer 30 is avoided. Furthermore, in the electromagnetic shielding film 1, because the anchor layer 25 contains a urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less, even if the shield layer 20 contains a metal layer, the shield layer 20 and the anchor layer 25 adhere to each other more easily, and the protective layer 30 also adheres to the anchor layer 25 more easily. In this way, in the electromagnetic shielding film 1, because both the shield layer 20 and the protective layer 30 adhere to the anchor layer 25, the shield layer 20 and the protective layer 30 are less likely to peel off from the anchor layer 25 even in harsh environments such as high temperature and high humidity environments. In other words, with electromagnetic wave shielding film 1, the shielding layer 20 and the protective layer 30 are less likely to peel off even in harsh environments such as high temperature and high humidity.

[0035] If the acid value of the urethane resin contained in the anchor layer 25 is lower than 2800 g / eq, the anchor layer 25 hardens more easily, which reduces the adhesive performance of the anchor layer 25 itself. As a result, the adhesion between the shield layer 20 and the anchor layer 25 decreases, as does the adhesion between the protective layer 30 and the anchor layer 25. Consequently, the shield layer 20 and the protective layer 30 are more likely to peel off from the anchor layer 25, especially in harsh environments such as high temperature and high humidity.

[0036] If the acid value of the urethane resin contained in the anchor layer 25 is higher than 5400 g / eq, the moisture and heat resistance of the anchor layer 25 tends to decrease, and in particular, under harsh environments such as high temperature and high humidity, the shield layer 20 and protective layer 30 tend to peel off from the anchor layer 25.

[0037] The following describes each component of the electromagnetic wave shielding film 1.

[0038] <Shielding layer> The shielding layer 20 exhibits shielding performance for shielding electromagnetic waves. For example, when the electromagnetic wave shielding film 1 is mounted on mobile devices such as smartphones and tablet terminals, it is possible to shield electromagnetic waves generated from inside the mobile device and electromagnetic waves invading from outside the mobile device with the shielding layer 20.

[0039] The shielding layer 20 includes a metal layer. Thereby, it becomes easier for the shielding layer 20 to shield electromagnetic waves.

[0040] The shielding layer 20 is preferably a metal layer.

[0041] The constituent material of the metal layer is not particularly limited as long as it is a conductive material capable of shielding electromagnetic waves. For example, copper, silver, gold, aluminum, nickel, tin, palladium, chromium, titanium, zinc, alloys containing at least one of these, etc. may be mentioned. Among them, the constituent material of the metal layer is preferably copper. That is, the metal layer is preferably a copper layer. When the metal layer is a copper layer, the shielding performance of the shielding layer 20 is likely to be sufficiently exhibited even for high-frequency electromagnetic waves.

[0042] The thickness of the metal layer is preferably 0.1 μm or more and 50 μm or less.

[0043] When the thickness of the metal layer is less than 0.1 μm, the shielding performance of the metal layer may not be sufficiently exhibited. Further, when the thickness of the metal layer is less than 0.1 μm, the metal layer becomes too thin, so the strength of the metal layer may decrease. As a result, the bending resistance of the metal layer, and thus the bending resistance of the electromagnetic wave shielding film 1, may not be sufficiently obtained.

[0044] When the thickness of the metal layer is greater than 50 μm, the metal layer becomes too thick and difficult to handle, so the electromagnetic wave shielding film 1 may also become too thick and difficult to handle. Further, when the thickness of the metal layer is greater than 50 μm, the metal layer becomes too thick and difficult to bend, so the bending property of the metal layer, and thus the bending property of the electromagnetic wave shielding film 1, may not be sufficiently obtained.

[0045] The metal layer may be a metal foil layer.

[0046] In a conventional electromagnetic wave shielding film, when laminating a shield layer including a metal layer on a protective layer, if the metal foil layer as the metal layer is disposed on the protective layer, for example, compared with the case where the metal layer is formed on the protective layer by a vapor deposition method, the adhesion between the metal layer and the protective layer may easily decrease. In contrast, in the electromagnetic wave shielding film 1, since the anchor layer 25 is provided between the shield layer 20 and the protective layer 30, even if the metal layer included in the shield layer 20 is a metal foil layer, contact between the metal foil layer and the protective layer 30 can be avoided. Furthermore, in the electromagnetic wave shielding film 1, since the anchor layer 25 containing a urethane resin having an acid value of 2800 g / eq or more and 5400 g / eq or less is used, even if the metal layer included in the shield layer 20 is a metal foil layer, the adhesion between the metal foil layer and the anchor layer 25 is unlikely to decrease, and as a result, the adhesion between the shield layer 20 and the anchor layer 25 is unlikely to decrease.

[0047] The metal foil layer may be a copper foil layer.

[0048] In the electromagnetic wave shielding film 1, since the anchor layer 25 containing a urethane resin having an acid value of 2800 g / eq or more and 5400 g / eq or less is used, even if the metal foil layer included in the shield layer 20 is a copper foil layer containing copper, which is a difficult-to-adhere material, the adhesion between the copper foil layer and the anchor layer 25 is unlikely to decrease, and as a result, the adhesion between the shield layer 20 and the anchor layer 25 is unlikely to decrease.

[0049] The copper foil layer may be made of rolled copper foil or electrolytic copper foil.

[0050] Note that the metal foil layer may be other than a copper foil layer.

[0051] The metal layer may be other than a metal foil layer. In this case, the metal layer may be formed by methods such as vapor deposition (vacuum deposition, electron beam deposition, etc.), plating (electrolytic plating, electroless plating, etc.), sputtering, chemical vapor deposition (CVD), or metal-organic deposition. The metal layer may also be formed from materials such as metal nanoparticles or flaky metal particles.

[0052] When a metal layer is formed by vapor deposition, the metal layer becomes a metal vapor-deposited layer. For example, if a metal layer is formed by vapor deposition of copper, the metal layer becomes a copper vapor-deposited layer.

[0053] The thickness of the shield layer 20 is not particularly limited, but is preferably 0.1 μm or more and 50 μm or less, more preferably 0.5 μm or more and 10 μm or less, and even more preferably 1 μm or more and 6 μm or less.

[0054] If the thickness of the shielding layer 20 is less than 0.1 μm, the shielding performance of the shielding layer 20 may not be fully realized. Also, if the thickness of the shielding layer 20 is less than 0.1 μm, the shielding layer 20 may become too thin, which may reduce its strength. As a result, it may be difficult to obtain sufficient bending resistance for the shielding layer 20, and consequently, for the electromagnetic wave shielding film 1.

[0055] If the thickness of the shielding layer 20 is greater than 50 μm, the shielding layer 20 becomes too thick and difficult to handle, which may result in the electromagnetic wave shielding film 1 also becoming too thick and difficult to handle. Furthermore, if the thickness of the shielding layer 20 is greater than 50 μm, the shielding layer 20 becomes too thick and difficult to bend, which may result in insufficient flexibility of the shielding layer 20, and consequently, of the electromagnetic wave shielding film 1.

[0056] <Anchor layer> The anchor layer 25 contains a urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less.

[0057] The anchor layer 25 is preferably made of a urethane resin having an acid value of 2800 g / eq or more and 5400 g / eq or less.

[0058] The acid value of the urethane resin contained in the anchor layer 25 is preferably 2900 g / eq or more and 5300 g / eq or less, and more preferably 3000 g / eq or more and 5200 g / eq or less.

[0059] The glass transition temperature (Tg) of the urethane resin contained in the anchor layer 25 is preferably 30°C or higher and 90°C or lower, more preferably 30°C or higher and 80°C or lower, and even more preferably 35°C or higher and 70°C or lower.

[0060] If the glass transition temperature of the urethane resin contained in the anchor layer 25 is lower than 30°C, the anchor layer 25 may become too soft, making it difficult to achieve sufficient adhesion between the shield layer 20 and the anchor layer 25, and between the protective layer 30 and the anchor layer 25. Furthermore, if the glass transition temperature of the urethane resin contained in the anchor layer 25 is lower than 30°C, the viscosity of the urethane resin may become too low, making it easier for the anchor layer 25 to protrude from the shield layer 20 and the protective layer 30. For example, when cutting the electromagnetic wave shielding film 1, the anchor layer 25 may adhere to the cut surfaces of the shield layer 20 and the protective layer 30, or to the cutting blade used during cutting, which can easily reduce the manufacturing efficiency of the shielded printed circuit board.

[0061] If the glass transition temperature of the urethane resin contained in the anchor layer 25 is higher than 90°C, the anchor layer 25 becomes less susceptible to thermal deformation, which can make it difficult to achieve sufficient adhesion between the shielding layer 20 and the anchor layer 25. Furthermore, if the glass transition temperature of the urethane resin contained in the anchor layer 25 is higher than 90°C, the anchor layer 25 becomes less susceptible to thermal deformation, which can make it difficult for the electromagnetic shielding film 1 to conform to the stepped areas of the printed circuit board when using thermocompression bonding to place the electromagnetic shielding film 1 on another component, such as a printed circuit board. Consequently, if the glass transition temperature of the urethane resin contained in the anchor layer 25 is higher than 90°C, it becomes necessary to thermocompression bond the electromagnetic shielding film 1 and the printed circuit board at high temperatures, which can easily increase manufacturing costs.

[0062] The glass transition temperature of urethane resin is measured in accordance with differential scanning calorimetry (DSC) as defined in "JIS K 7121:1987".

[0063] The number-average molecular weight (Mn) of the urethane resin contained in the anchor layer 25 is preferably 10,000 or more and 20,000 or less, and more preferably 11,000 or more and 19,000 or less.

[0064] If the number-average molecular weight of the urethane resin contained in the anchor layer 25 is less than 10,000, the moisture and heat resistance of the anchor layer 25 tends to decrease, and in particular, under harsh environments such as high temperature and high humidity, the shield layer 20 may easily peel off from the anchor layer 25.

[0065] If the number-average molecular weight of the urethane resin contained in the anchor layer 25 is greater than 20,000, the adhesion between the shield layer 20 and the anchor layer 25 tends to decrease, and in particular, under harsh environments such as high temperature and high humidity, the shield layer 20 may easily peel off from the anchor layer 25.

[0066] The number-average molecular weight of urethane resin is measured by gel permeation chromatography (GPC) under the following conditions: Measuring instrument: Alliance GPC System (Waters Inc.) Column: Shodex® GPC KF-806L (Resonac Inc.) Column temperature: 40°C Sample concentration: 0.05 wt% / THF Injection volume: 10 μL Standard samples: Standard PS 500 (Tosoh Corporation), Shodex Standard PS SM-105 (Resonac Inc.) (set)

[0067] The urethane resin contained in the anchor layer 25 preferably has a carboxyl group.

[0068] If the urethane resin contained in the anchor layer 25 has carboxyl groups, the adhesive performance of the anchor layer 25 tends to improve, thus improving the adhesion between the shield layer 20 and the anchor layer 25, and between the protective layer 30 and the anchor layer 25. Furthermore, if the urethane resin contained in the anchor layer 25 has carboxyl groups, the heat and humidity resistance of the anchor layer 25 tends to improve, so the shield layer 20 and the protective layer 30 are less likely to peel off from the anchor layer 25 even in harsh environments such as high temperature and high humidity environments.

[0069] The anchor layer 25 may further contain other resins in addition to the urethane resin having an acid value of 2800 g / eq or more and 5400 g / eq or less. Examples of other resins include acrylic resin, core-shell type composite resin with urethane resin as the shell and acrylic resin as the core, epoxy resin, imide resin, amide resin, melamine resin, phenol resin, urea-formaldehyde resin, blocked isocyanate resin obtained by reacting polyisocyanate with a blocking agent such as phenol, polyvinyl alcohol resin, polyvinylpyrrolidone resin, polyester resin, and the like.

[0070] The thickness of the anchor layer 25 is not particularly limited, but it is preferably 1 μm or more and 3 μm or less.

[0071] If the thickness of the anchor layer 25 is less than 1 μm, the anchor layer 25 may become too thin, making it difficult to obtain sufficient adhesive performance of the anchor layer 25. As a result, it may be difficult to obtain sufficient adhesion between the shield layer 20 and the anchor layer 25, and between the protective layer 30 and the anchor layer 25.

[0072] If the thickness of the anchor layer 25 is greater than 3 μm, the anchor layer 25 becomes too thick, which can cause the electromagnetic shielding film 1 to become too thick and difficult to handle.

[0073] <Protective Layer> The protective layer 30 provides protection by protecting other layers such as the shield layer 20 and the anchor layer 25.

[0074] The constituent material of the protective layer 30 is not particularly limited as long as it is an insulating material capable of protecting the other layers, and examples include thermoplastic resin compositions, thermosetting resin compositions, and active energy ray curable compositions.

[0075] The thermoplastic resin composition is not particularly limited and includes, for example, amide resin compositions, styrene resin compositions, vinyl acetate resin compositions, polyester resin compositions, polyethylene resin compositions, polypropylene resin compositions, imide resin compositions, acrylic resin compositions, and the like.

[0076] The thermosetting resin composition is not particularly limited and includes, for example, urethane resin compositions, phenolic resin compositions, epoxy resin compositions, melamine resin compositions, alkyd resin compositions, polyester resin compositions, and the like.

[0077] The active energy ray curable composition is not particularly limited, and examples include polymerizable compounds having multiple (meth)acryloyloxy groups in the molecule.

[0078] The protective layer 30 may contain only one of the above compositions, or it may contain two or more.

[0079] The protective layer 30 may contain at least one of urethane resin and amide resin.

[0080] In conventional electromagnetic shielding films, when laminating a shielding layer containing a metal layer onto a protective layer, if the protective layer contains at least one of urethane resin and amide resin, the adhesion between the metal layer and the protective layer may easily decrease, especially in harsh environments such as high temperature and high humidity. In contrast, in electromagnetic shielding film 1, since the anchor layer 25 is provided between the shielding layer 20 and the protective layer 30, contact between the metal layer and the protective layer 30 can be avoided even if the protective layer 30 contains at least one of urethane resin and amide resin. Furthermore, in electromagnetic shielding film 1, the anchor layer 25 contains urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less, so even if the protective layer 30 contains at least one of urethane resin and amide resin, the adhesion between the protective layer 30 and the anchor layer 25 is less likely to decrease.

[0081] The protective layer 30 preferably contains urethane resin.

[0082] In the electromagnetic wave shielding film 1, an anchor layer 25 containing urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less is used. Therefore, when the protective layer 30 contains urethane resin, the materials contained in the protective layer 30 and the anchor layer 25 are both urethane resins, which makes it easier to achieve good adhesion between the protective layer 30 and the anchor layer 25.

[0083] The protective layer 30 may optionally contain curing accelerators, tackifiers, antioxidants, pigments, dyes, plasticizers, UV absorbers, defoamers, leveling agents, fillers, flame retardants, flame retardant aids, viscosity modifiers, anti-blocking agents, etc.

[0084] The thickness of the protective layer 30 is not particularly limited, but is preferably 1 μm or more and 15 μm or less, and more preferably 3 μm or more and 10 μm or less.

[0085] If the thickness of the protective layer 30 is less than 1 μm, the protective layer 30 may become too thin, making it difficult for the protective layer 30 to fully perform its protective function.

[0086] If the thickness of the protective layer 30 is greater than 15 μm, the protective layer 30 becomes too thick and difficult to bend, which can make it difficult to obtain sufficient flexibility for the protective layer 30, and consequently for the electromagnetic wave shielding film 1.

[0087] <Adhesive Layer> The electromagnetic wave shielding film 1 shown in Figure 1 has an adhesive layer 10 laminated on the side of the shielding layer 20 opposite to the anchor layer 25.

[0088] The adhesive layer 10 can be used when attaching (adhering) the electromagnetic shielding film 1 to other components, such as a printed circuit board. The adhesive layer 10 makes it easy to attach the electromagnetic shielding film 1 to other components, such as a printed circuit board, from the adhesive layer 10 side (opposite the protective layer 30). This makes it easy to manufacture a shielded printed circuit board in which the electromagnetic shielding film 1 is provided on the printed circuit board.

[0089] The constituent material of the adhesive layer 10 is not particularly limited, as long as it is an adhesive material that can attach (bond) the electromagnetic wave shielding film 1 to other components, such as a printed circuit board.

[0090] The adhesive layer 10 is preferably a conductive adhesive layer.

[0091] If the adhesive layer 10 is a conductive adhesive layer, for example, it becomes possible to electrically connect the shielding layer 20 of the electromagnetic shielding film 1 and the ground circuit included in the printed circuit of the printed wiring board via the conductive adhesive layer. As a result, the shielding characteristics of the electromagnetic shielding film 1 tend to improve.

[0092] The conductive adhesive layer may be an isotropic conductive adhesive layer or an anisotropic conductive adhesive layer. Among these, an anisotropic conductive adhesive layer is preferred.

[0093] When the conductive adhesive layer is an anisotropic conductive adhesive layer, the transmission characteristics of high-frequency signals transmitted in the signal circuits included in the printed circuit board tend to improve compared to when the conductive adhesive layer is an isotropic conductive adhesive layer.

[0094] If the adhesive layer 10 is a conductive adhesive layer, it is preferable that the adhesive layer 10 contains a conductive filler and an adhesive resin.

[0095] The conductive filler is not particularly limited and includes, for example, silver powder, copper powder, nickel powder, solder powder, aluminum powder, silver-plated copper powder, polymer microparticles, metal-coated microparticles such as glass beads coated with metal, carbon fiber, graphite, etc. Among these, from the viewpoint of manufacturing cost, copper powder or silver-plated copper powder is preferred as the conductive filler because it is inexpensive and readily available.

[0096] The adhesive layer 10 may contain only one type of the conductive filler described above, or it may contain two or more types.

[0097] The shape of the conductive filler is not particularly limited and can be spherical, flake-shaped, flaky, dendrite-shaped, rod-shaped, fibrous, etc. Among these, the shape of the conductive filler is preferably dendrite-shaped. When the shape of the conductive filler is dendrite-shaped, even if the electromagnetic wave shielding film 1 is bent, the conductive filler bends more easily, making it easier to maintain contact between the conductive fillers, and as a result the conductivity of the conductive adhesive layer does not decrease easily.

[0098] The average particle size of the conductive filler is not particularly limited, but is preferably 0.5 μm or more and 15 μm or less, and more preferably 5 μm or more and 13 μm or less.

[0099] If the average particle size of the conductive filler is smaller than 0.5 μm, it may be difficult to obtain sufficient conductivity in the conductive adhesive layer.

[0100] If the average particle size of the conductive filler is larger than 15 μm, the conductive adhesive layer may become too thick and difficult to bend, making it difficult to obtain sufficient flexibility for the conductive adhesive layer, and consequently for the electromagnetic shielding film 1.

[0101] The weight percentage of conductive filler in the conductive adhesive layer is preferably 10% by weight or more and 80% by weight or less.

[0102] When the conductive adhesive layer is an anisotropic conductive adhesive layer, the weight percentage of conductive filler in the conductive adhesive layer is preferably 5% by weight or more and 40% by weight or less, and more preferably 10% by weight or more and 35% by weight or less.

[0103] Examples of adhesive resins include thermoplastic resins and thermosetting resins.

[0104] Examples of thermoplastic resins include styrene resins, vinyl acetate resins, polyester resins, polyethylene resins, polypropylene resins, imide resins, amide resins, and acrylic resins.

[0105] Examples of thermosetting resins include phenolic resins, epoxy resins, urethane resins, melamine resins, alkyd resins, and polyester resins.

[0106] The adhesive layer 10 may contain only one type of adhesive resin, or it may contain two or more types.

[0107] The adhesive layer 10 does not have to be a conductive adhesive layer. Specifically, the adhesive layer 10 may be a non-conductive adhesive layer. In this case, the adhesive layer 10 may contain the above-mentioned adhesive resin without containing the above-mentioned conductive filler.

[0108] The thickness of the adhesive layer 10 is not particularly limited, but is preferably 0.5 μm or more and 30 μm or less.

[0109] If the thickness of the adhesive layer 10 is less than 0.5 μm, the adhesive layer 10 may become too thin, making it difficult to obtain sufficient adhesive performance.

[0110] If the thickness of the adhesive layer 10 is greater than 30 μm, the adhesive layer 10 becomes too thick and difficult to handle, which may also cause the electromagnetic wave shielding film 1 to become too thick and difficult to handle.

[0111] The electromagnetic shielding film of the present invention is not limited to the above-described form, and various applications and modifications can be made within the scope of the present invention regarding the structure, manufacturing conditions, etc. of the electromagnetic shielding film.

[0112] [Shielded Printed Wiring Board] Figure 2 is a schematic cross-sectional view showing an example of the shielded printed wiring board of the present invention.

[0113] The shielded printed circuit board 100 shown in Figure 2 comprises a printed circuit board 51 and an electromagnetic wave shielding film 1.

[0114] The following describes each component of the shielded printed circuit board 100.

[0115] <Printed Wiring Board> The printed wiring board 51 has a base film 60, a printed circuit 70, and a coverlay 80.

[0116] The printed circuit board 51 is preferably a flexible printed circuit board. In this case, the printed circuit board 51 can be easily bent, making the shielded printed circuit board 100 usable in a wider range of applications.

[0117] (Base film) The base film 60 preferably contains engineering plastic, and more preferably consists of engineering plastic.

[0118] Examples of engineering plastics included in the base film 60 include resins such as polypropylene, crosslinked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide.

[0119] (Printed circuit) The printed circuit 70 is provided on the base film 60.

[0120] The printed circuit 70 may be bonded to the base film 60 via an adhesive, or it may be joined without an adhesive, for example, in the same way as an adhesive-free copper-clad laminate.

[0121] The printed circuit 70 may include a ground circuit 71.

[0122] The printed circuit 70 may include a signal circuit (not shown).

[0123] The materials used to construct the printed circuit 70 are not particularly limited, and examples include circuit materials such as copper.

[0124] (Coverlay) The coverlay 80 is provided so as to cover the printed circuit 70.

[0125] The coverlay 80 may be provided with an exposure hole 81 that exposes the ground circuit 71 from the coverlay 80.

[0126] The coverlay 80 does not necessarily need to have an exposure hole 81.

[0127] The coverlay 80 preferably contains engineering plastic, and more preferably consists of engineering plastic.

[0128] Examples of engineering plastics included in Coverlay 80 include resins such as polypropylene, crosslinked polyethylene, polyester, polybenzimidazole, polyimide, polyimideamide, polyetherimide, and polyphenylene sulfide.

[0129] If the base film 60 and the coverlay 80 contain engineering plastics, the engineering plastics contained in them may be the same or different.

[0130] The coverlay 80 may be made by bonding multiple flexible insulating films together with an adhesive.

[0131] The coverlay 80 may be formed by a series of methods such as coating, drying, exposure, developing, and heat treatment of a photosensitive insulating resin.

[0132] <Electromagnetic wave shielding film> The electromagnetic wave shielding film 1 has the configuration described above (see Figure 1).

[0133] The electromagnetic shielding film 1 is provided on the coverlay 80 side of the printed circuit board 51.

[0134] The electromagnetic shielding film 1 has the side opposite the protective layer 30 facing the coverlay 80. In the example shown in Figure 2, the electromagnetic shielding film 1 is provided on the printed circuit board 51 such that the adhesive layer 10 located on the side opposite the protective layer 30 is in contact with the coverlay 80.

[0135] It is preferable that the adhesive layer 10 penetrates the exposed hole 81 while making contact with the ground circuit 71. In this case, it is more preferable that the adhesive layer 10 fills the inside of the exposed hole 81 while making contact with the ground circuit 71. In either case, if the adhesive layer 10 is a conductive adhesive layer, the shielding layer 20 and the ground circuit 71 will be electrically connected via the conductive adhesive layer. This makes it easier to improve the shielding characteristics of the electromagnetic shielding film 1.

[0136] The electromagnetic shielding film 1 is provided on the printed circuit board 51 by a conventionally known method. For example, it is preferable to place the electromagnetic shielding film 1 on the printed circuit board 51 such that the side opposite to the protective layer 30 (the adhesive layer 10 side in Figure 2) faces the coverlay 80 (in Figure 2, it is in contact with the coverlay 80), and then heat-press the electromagnetic shielding film 1 and the printed circuit board 51 together. The temperature during heat-pressure bonding is preferably 150°C or higher and 200°C or lower. The pressure during heat-pressure bonding is preferably 2 MPa or higher and 5 MPa or lower. The pressurizing time during heat-pressure bonding is preferably 1 minute or higher and 60 minutes or less.

[0137] As described above, in the electromagnetic wave shielding film 1, the shielding layer 20 and the protective layer 30 are less likely to peel off even in harsh environments such as high temperature and high humidity. Therefore, in the shielded printed circuit board 100 having the electromagnetic wave shielding film 1, the shielding layer 20 and the protective layer 30 of the electromagnetic wave shielding film 1 are less likely to peel off even in harsh environments such as high temperature and high humidity.

[0138] The shielded printed circuit board of the present invention is not limited to the above-described form, and various applications and modifications can be made within the scope of the present invention regarding the configuration, manufacturing conditions, etc., of the shielded printed circuit board.

[0139] The following are examples that more specifically disclose the electromagnetic shielding film of the present invention. However, the present invention is not limited to the following examples.

[0140] [Example 1] The electromagnetic shielding film of Example 1 was manufactured by the following method.

[0141] (Process for producing the protective layer) A protective layer composition containing urethane resin was applied to the transfer film, and then heated in an electric oven at 108°C for 3 minutes to produce the protective layer.

[0142] (Lamination process for anchor layer) An anchor layer composition containing a urethane resin having an acid value of 3200 g / eq, a glass transition temperature of 40°C, and a number average molecular weight of 15000 was applied to the protective layer, and then heated at 108°C for 3 minutes to create the anchor layer on the protective layer.

[0143] (Process for laminating the shield layer) By placing a copper foil with a thickness of 2 μm on the opposite side of the protective layer of the anchor layer, a shield layer made of copper foil was placed on the opposite side of the protective layer of the anchor layer. Then, using a laminator, the shield layer was laminated at 115°C, 0.5 MPa, and 20 rpm, thereby laminating the shield layer on the opposite side of the protective layer of the anchor layer.

[0144] (Process of laminating the adhesive layer) A conductive adhesive layer, which is a conductive adhesive layer, was laminated on the opposite side of the shield layer from the anchor layer by applying a conductive adhesive layer composition containing copper particles and urethane resin to the side of the shield layer opposite the anchor layer.

[0145] Based on the above, the electromagnetic wave shielding film of Example 1 was manufactured.

[0146] [Examples 2-5, Comparative Examples 1-5] The electromagnetic shielding films of Examples 2-5 and Comparative Examples 1-5 were manufactured in the same manner as the electromagnetic shielding film of Example 1, except that the material of the protective layer, the presence or absence of the anchor layer, the material of the anchor layer (if the anchor layer is present), the material (type) of the shielding layer, and the material of the adhesive layer were changed as shown in Tables 1 and 2.

[0147] [Evaluation] Peel tests were performed on the electromagnetic shielding films of Examples 1 to 5 and Comparative Examples 1 to 5 in accordance with the test method described in "Adhesion (Cross-cut method)" of "JIS K 5600-5-6:1999". The test conditions were a temperature of 85°C and a humidity of 85%. In addition, the number of cuts in each direction of the grid pattern was set to 10 (10 strips), and the tape was attached to the protective layer.

[0148] The above tests were conducted at initial time (0 hours), 500 hours, 1000 hours, and 1500 hours, respectively, while the electromagnetic shielding film was exposed to the above test conditions (temperature 85°C, humidity 85%).

[0149] The test results from the above tests were classified according to the classification method (classifications 0 to 5) described in "Adhesion (cross-cut method)" of "JIS K 5600-5-6:1999". The results are shown in Tables 1 and 2.

[0150]

[0151]

[0152] As shown in Tables 1 and 2, the electromagnetic shielding films of Examples 1 to 5, which used an anchor layer containing urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less, showed less peeling of the protective layer even after a long period of time under harsh conditions of 85°C and 85% humidity, compared to the electromagnetic shielding films of Comparative Examples 1 to 5, which did not use an anchor layer containing urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less. In particular, the electromagnetic shielding films of Examples 1, 4, and 5, which used a protective layer containing urethane resin, showed especially little peeling of the protective layer.

[0153] In the electromagnetic shielding film of Comparative Example 1, the protective layer was prone to peeling off because the anchor layer itself was not used.

[0154] In the electromagnetic shielding films of Comparative Examples 2 and 3, the anchor layer used contained a urethane resin with an acid value lower than 2800 g / eq, rather than a urethane resin with an acid value of 2800 g / eq or higher and 5400 g / eq or lower. As a result, the anchor layer hardened easily, reducing its adhesive performance, and making it difficult to adhere the shielding layer and protective layer to the anchor layer. Therefore, the above test could not be performed on the electromagnetic shielding films of Comparative Examples 2 and 3.

[0155] In the electromagnetic shielding film of Comparative Example 4, an anchor layer containing polyester resin was used instead of urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less, which made the protective layer prone to peeling.

[0156] In the electromagnetic shielding film of Comparative Example 5, instead of using a urethane resin with an acid value of 2800 g / eq or more and 5400 g / eq or less, an anchor layer containing a urethane resin with an acid value higher than 5400 g / eq was used. As a result, the moisture and heat resistance of the anchor layer was reduced, and the protective layer was prone to peeling off.

[0157] In the above tests, the tape was attached to the protective layer. However, the same results were obtained when the tape was attached to the shielding layer without an adhesive layer on the electromagnetic shielding film. Specifically, in the electromagnetic shielding films of Examples 1 to 5, the shielding layer was less likely to peel off even after a long period of time under harsh conditions of 85°C and 85% humidity, compared to the electromagnetic shielding films of Comparative Examples 1 to 5. In addition, in the electromagnetic shielding films of Examples 1 to 4, a shielding layer made of copper foil was used, but the shielding layer was less likely to peel off, similar to the electromagnetic shielding film of Example 5, which used a shielding layer made of a copper vapor-deposited layer formed by vapor deposition.

[0158] This specification discloses the following:

[0159] <1> An electromagnetic wave shielding film comprising: a shielding layer containing a metal layer; an anchor layer laminated on the shielding layer; and a protective layer laminated on the side of the anchor layer opposite to the shielding layer, wherein the anchor layer contains a urethane resin having an acid value of 2800 g / eq or more and 5400 g / eq or less.

[0160] <2> The electromagnetic wave shielding film according to <1>, wherein the glass transition temperature of the urethane resin contained in the anchor layer is 30°C or higher and 90°C or lower.

[0161] <3> The electromagnetic wave shielding film according to <1> or <2>, wherein the number average molecular weight of the urethane resin contained in the anchor layer is 10,000 or more and 20,000 or less.

[0162] <4> The electromagnetic wave shielding film according to any one of <1> to <3>, wherein the protective layer contains at least one of urethane resin and amide resin.

[0163] <5> A shielded printed circuit board comprising: a base film; a printed circuit provided on the base film; a coverlay provided to cover the printed circuit; and an electromagnetic wave shielding film provided on the coverlay side of the printed circuit board, wherein the electromagnetic wave shielding film is the electromagnetic wave shielding film described in any one of <1> to <4>, and the side opposite to the protective layer faces the coverlay.

[0164] 1 Electromagnetic shielding film 10 Adhesive layer 20 Shielding layer 25 Anchor layer 30 Protective layer 51 Printed circuit board 60 Base film 70 Printed circuit 71 Ground circuit 80 Coverlay 81 Exposed holes 100 Shielded printed circuit board

Claims

1. An electromagnetic wave shielding film comprising: a shielding layer containing a metal layer; an anchor layer laminated on the shielding layer; and a protective layer laminated on the side of the anchor layer opposite to the shielding layer, wherein the anchor layer contains a urethane resin having an acid value of 2800 g / eq or more and 5400 g / eq or less.

2. The electromagnetic wave shielding film according to claim 1, wherein the glass transition temperature of the urethane resin contained in the anchor layer is 30°C or higher and 90°C or lower.

3. The electromagnetic wave shielding film according to claim 1 or 2, wherein the number average molecular weight of the urethane resin contained in the anchor layer is 10,000 or more and 20,000 or less.

4. The electromagnetic wave shielding film according to any one of claims 1 to 3, wherein the protective layer comprises at least one of a urethane resin and an amide resin.

5. A shielded printed circuit board comprising: a base film; a printed circuit provided on the base film; a coverlay provided to cover the printed circuit; and an electromagnetic shielding film provided on the coverlay side of the printed circuit board, wherein the electromagnetic shielding film is the electromagnetic shielding film according to any one of claims 1 to 4, and the side opposite to the protective layer faces the coverlay.

Images