CN102762083A - Electromagnetic wave shielding material for FPC - Google Patents

Abstract

The invention provides an electromagnetic wave shielding material for FPC. The electromagnetic wave shielding material is flexible and thin. Even the electromagnetic wave shielding material is bent repeatedly and severely, the electromagnetic wave shielding performance does not degrade and thus the bending property is excellent. The electromagnetic wave shielding material (5) for FPC is characterized in that a base material (1) formed by coated dielectric thin resin film, a filmy adhesive layer (2), and an electrical conductivity layer (3) are laminated on a single face of a support body film (6), wherein the base material (1) is made of polyimide film formed by polyimide which is soluble through a solvent and is 1-9 microns thick.

Description

Electromagnetic wave shielding material for FPC

technical field

The present invention relates to an electromagnetic wave shielding material for FPC, which covers a flexible printed circuit board (hereinafter referred to as FPC) subjected to repeated bending operations, and is used for shielding electromagnetic waves.

Background technique

In portable electronic devices such as mobile phones, electronic components are integrated on printed circuit boards in order to reduce the size of the housing and control the size of the housing so that it can be carried easily. In addition, in order to reduce the external dimensions of the box, by dividing the printed circuit board into multiple parts, and using a flexible FPC for the connection wiring between the divided printed circuit boards, the printed circuit board can be folded, or the printed circuit board can be folded. It slides.

In addition, in recent years, important electronic components and FPCs are covered with electromagnetic wave shielding materials in order to prevent electronic equipment from malfunctioning due to the interference of electromagnetic waves received from the outside or the interference of electromagnetic waves received by internal electronic components.

Conventionally, as an electromagnetic wave shielding material used for the purpose of shielding such electromagnetic waves, a material having a pressure-sensitive adhesive layer provided on the surface of a metal foil such as rolled copper foil or soft aluminum foil has been used. An object to be shielded is covered with an electromagnetic wave shielding material composed of such a metal foil (for example, refer to Patent Documents 1 and 2).

Specifically, in order to shield important electronic components from electromagnetic waves, they are covered with metal foil or metal plates in the shape of a closed box. In addition, in order to shield the wiring of the bent FPC and prevent electromagnetic waves, an adhesive layer is provided on one surface of the metal foil, and bonding is carried out through the pressure-sensitive adhesive layer.

In recent years, mobile phones have rapidly spread as electronic devices that are carried around. It is preferable that the overall size of the mobile phone be reduced as much as possible when stored in a pocket or the like when not in use, and that the overall size be increased when in use. It is necessary to reduce the size and thickness of the mobile phone and improve the operability. As a means of solving these problems, a case structure in which a mobile phone is divided into two and folded to open and close or a slide to open and close is adopted.

In addition, in any housing structure in which the mobile phone is divided into two parts and folded and opened or opened and closed by slides, it is necessary to frequently open and close the operation screen (operation of starting and stopping). The frequency of opening and closing of the operation screen is performed at a frequency of tens of times/day or hundreds of times/day.

That is, the electromagnetic wave shielding material for FPC that shields the FPC used in the mobile phone and the FPC that covers the electromagnetic wave is subjected to repeated bending operations at a much higher frequency than conventional portable electronic devices. Therefore, the electromagnetic wave shielding material for FPC that realizes the electromagnetic wave shielding function of FPC is subjected to severe repeated stress. If the repeated stress cannot be withstood, eventually, the base material constituting the electromagnetic wave shielding material for FPC and the shielding material such as metal foil are damaged by fracture, peeling or the like. As a result, there is a concern that the electromagnetic wave shielding function of the electromagnetic wave shielding material for FPC will be reduced or lost.

Therefore, there is also known an electromagnetic wave shielding material for coping with such repeated bending motions (for example, refer to Patent Document 3).

prior art literature

patent documents

Patent Document 1: Japanese Publication No. 56-084221

Patent Document 2: Japanese Patent Laid-Open No. 61-222299

Patent Document 3: Japanese Patent Application Laid-Open No. 7-122883

Contents of the invention

(problem to be solved by the invention)

As disclosed in the above-mentioned Patent Documents 1 and 2, in the electromagnetic wave shielding material provided with a pressure-sensitive adhesive layer on the surface of metal foil such as rolled copper foil and soft aluminum foil, the number of bending operations is small and the time of use is small. In the short case, the shielding performance is trouble-free. However, there is a problem that the durability of the bending characteristics is insufficient when the time of use is as long as five to ten years and the number of bending operations increases. Such a conventional electromagnetic wave shielding material does not have a bending characteristic required for an FPC electromagnetic wave shielding material used in a recent mobile phone to pass a bending test of 1 million times or more.

的心轴(mandrel)的外周以180°的角度弯曲后恢复为直线的动作为1循环的弯曲试验，结果是没有损伤。In addition, Patent Document 3 discloses an electromagnetic wave shielding material in which a metal thin film such as metal vapor deposition is provided on one surface of a flexible film, and a conductive adhesive is laminated thereon. It is described that this electromagnetic wave shielding material can be used by covering electric wires subjected to repeated bending. According to the examples of Patent Document 3, a coating film of a conductive paint with silver powder added to a thickness of 0.5 μm is provided on one side of a polyester film with a thickness of 12 μm, and a polyester adhesive is mixed thereon. The conductive adhesive with nickel powder was heated and dried to form a conductive adhesive layer with a thickness of 30 μm. Also, it is documented that performing 500,000 cycles will

The outer circumference of the mandrel was bent at an angle of 180° and then returned to a straight line as a 1-cycle bending test. As a result, there was no damage.

However, in recent mobile phones, the external dimensions of the casing are reduced, and the thickness of the casing is reduced in units of 0.1 mm to make it as thin as possible. An electromagnetic wave shielding material for FPC that can be used in such a thin case requires excellent bending performance. For example, even if it is performed more than 1 million times, it will be along the outer diameter There was no damage in the bending test in which the outer periphery of the mandrel was bent at an angle of 180° and returned to a straight line as one cycle. Compared with the prior art, there is a need for an electromagnetic wave shielding material for FPC that can overcome a bending test performed under severe conditions.

In addition, in the electromagnetic wave shielding material described in the examples of Patent Document 3, a 0.5-μm-thick conductive paint coating film and a 30-μm-thick conductive adhesive layer are laminated on a 12-μm-thick resin film. The overall thickness of the electromagnetic wave shielding material exceeds 40 μm.

As described above, in order to reduce the external dimensions of the casing of the mobile phone as thin as possible, the overall thickness of the electromagnetic wave shielding material for FPC is required to be as thin as 30 μm or less. That is, compared with the conventional electromagnetic wave shielding material for FPC, the overall thickness is thinner, and the stronger electromagnetic wave shielding material for FPC which can withstand a severer bending test is demanded.

In addition, in order to impart conductivity to the pressure-sensitive adhesive layer, the conductive pressure-sensitive adhesive used for FPC electromagnetic wave shielding materials needs to add a considerable amount of conductive powder (metal fine particles or carbon fine particles). However, if the addition amount of the conductive powder is increased, the adhesive force of the pressure-sensitive adhesive layer will decrease.

In addition, in the electromagnetic wave shielding material for FPC used in mobile phones, etc., since the bending operation is repeated, the bonding interface between the base material and the conductive paste layer, and the layers between the conductive paste layer and the FPC is partially in the The layers are stripped. There is concern that the conductive paste layer may be broken at the peeled place, and the electromagnetic wave shielding performance may decrease over time.

In addition, in order for the base material of the electromagnetic wave shielding material for FPC to withstand repeated bending operations (for example, 1 million times of bending test) during the service life of electronic equipment, excellent bending characteristics are required.

It is an object of the present invention to provide an electromagnetic wave shielding material for FPC that is thin and flexible and does not degrade the electromagnetic wave shielding performance even if severe bending operations are repeated.

(Technical solutions to technical problems)

In the present invention, a substrate made of a heat-resistant resin film is used in order to withstand severe bending operations and firing of the conductive paste by high-temperature heating. In the present invention, an adhesive layer and a film layer of a conductive paste layer are sequentially laminated on a base material composed of a thin resin film of a dielectric to be applied to improve the adhesion between the base material and the conductive paste layer. Therefore, the technical idea of the present invention is to improve the bending performance while ensuring the electromagnetic wave shielding performance for FPC.

In addition, in the present invention, a thin resin film of a coated dielectric is used as the base material composed of a heat-resistant resin film in consideration of flexibility and heat resistance. Thereby, the whole thickness of the electromagnetic wave shielding material for FPC which removed the support body film 6 and the peeling film 7 can be reduced to 25 micrometers or less.

In addition, in the present invention, in order to increase the adhesive force between the conductive paste and the thin resin film composed of a polyimide film formed by using a solvent-soluble polyimide as the base material, the base material and the conductive paste layer An adhesive layer is provided between them.

Therefore, in order to solve the above-mentioned problems, the present invention provides an electromagnetic wave shielding material for FPC, in which a base material composed of a thin resin film of a coated dielectric, an adhesive layer of the film, Conductive paste layer.

In addition, the base material is composed of a polyimide film formed using a solvent-soluble polyimide, and its thickness is preferably 1 to 9 μm.

In addition, the adhesive layer of the film is formed by crosslinking a polyester resin composition having an epoxy group, and its thickness is preferably 0.05 to 1 μm.

In addition, the adhesive layer preferably further contains a light-absorbing material selected from the group consisting of carbon black, graphite, aniline black, cyanine black, titanium black, black iron oxide, chromium oxide, and manganese oxide. Composition of one or more black pigments or one or more colored pigments.

In addition, the conductive paste constituting the conductive paste layer preferably contains one or more conductive fillers selected from conductive metal fine particles, carbon nanotubes, and carbon nanofibers, and a binder resin composition.

In addition, the conductive paste layer is a conductive paste containing silver nanoparticles with an average particle diameter of 1-100 nm and a binder resin composition and fired at a temperature of 150-250° C., and the thickness is preferably 0.1-2 μm.

In addition, the dried volume resistivity of the conductive paste constituting the conductive paste layer is preferably 1.5×10 ⁻⁵ Ω·cm or less.

In addition, it is preferable to further laminate a conductive adhesive layer on the conductive paste layer.

In addition, it is preferable to further bond a release film subjected to release treatment to the conductive adhesive layer.

In addition, the present invention provides a mobile phone in which the above-mentioned electromagnetic wave shielding material for FPC is used as a member for electromagnetic wave shielding.

In addition, the present invention provides an electronic device in which the above-mentioned electromagnetic wave shielding material for FPC is used as a member for electromagnetic wave shielding.

(effect of invention)

The above-mentioned electromagnetic wave shielding material for FPC of the present invention uses a thin resin film (thickness: 1 to 9 μm) composed of a polyimide film formed using a solvent-soluble polyimide having high temperature heat resistance. The electromagnetic wave shielding material for FPC of the present invention can improve electrical conductivity by firing the conductive paste, and can obtain excellent bending characteristics that withstand severe bending operations.

In addition, by using a thin resin film (1 to 9 μm in thickness) made of a polyimide film formed using a solvent-soluble polyimide and a conductive paste layer, the thickness can be suppressed and electromagnetic wave shielding performance can be obtained.

Accordingly, the overall thickness of the FPC electromagnetic wave shielding material excluding the support film 6 and the peeling film 7 can be suppressed to 25 μm or less, and the overall thickness of mobile phones and electronic devices can be reduced.

One side of the electromagnetic shielding film can be colored in a specific color by mixing light-absorbing materials composed of one or more kinds of black pigments or colored pigments in the adhesive layer.

As described above, according to the present invention, it is possible to provide an electromagnetic wave shielding material for FPC that is flexible, thin, and does not degrade electromagnetic wave shielding performance even if severe bending operations are repeated.

Description of drawings

FIG. 1 is a schematic cross-sectional view showing an example of an FPC electromagnetic wave shielding material according to the present invention.

Fig. 2 is a schematic cross-sectional view showing another example of the electromagnetic wave shielding material for FPC according to the present invention.

3 is a schematic cross-sectional view showing a state in which the electromagnetic wave shielding material for FPC in FIG. 2 is removed and used, with a support film and a release film.

Symbol Description

1 substrate

2 adhesive layers

3 conductive paste layer

4 Conductive adhesive layer

5, 10, 11 Electromagnetic wave shielding materials for FPC

6 Support film

7 Peel off the film.

Detailed ways

Hereinafter, preferred embodiments of the present invention will be described.

When the electromagnetic wave shielding material for FPC of the present invention is bonded to FPC or the like as an adherend, the outer surface is a dielectric, and it is not necessary to bond an insulating film to the outer surface of the electromagnetic wave shielding material for FPC. In addition, the overall thickness of the electromagnetic wave shielding material for FPC of the present invention is reduced, and the bending performance against bending operation is improved.

As shown in Figure 1, the substrate 1 of the electromagnetic wave shielding material 5 for FPC of the present invention is a flexible thin resin film, which is formed by using a solvent-soluble polyimide with a thickness of 1 to 9 μm. Made of polyimide film. On one side of the substrate 1, a support film 6 is stacked, and on the other side of the substrate 1, an adhesive layer 2 for improving the adhesion between the conductive paste layer 3 and the substrate 1, a conductive paste layer containing conductive fine particles, and an adhesive agent layer 2 containing conductive fine particles are sequentially stacked. Sexual cream layer 3. As shown in FIG. 2 , another example of the electromagnetic wave shielding material 10 for FPC according to the present invention further laminates a conductive adhesive layer 4 and a release film 7 sequentially on a conductive paste layer 3 . This electromagnetic wave shielding material 10 for FPC can be used as the electromagnetic wave shielding material 11 for FPC which removed the two peeling films 6 and 7, as shown in FIG.

(polyimide film)

In the electromagnetic wave shielding materials 5, 10, and 11 for FPC according to the present invention, a thin resin film composed of a polyimide film formed by using a solvent-soluble polyimide as the base material 1 has a polyimide resin as the polyimide resin. Its characteristic high mechanical strength, heat resistance, insulation, and solvent resistance, and its chemical state is also very stable up to 260°C.

As the polyimide, there are a thermosetting polyimide produced by a dehydration condensation reaction of a polyamic acid by heating, and a solvent-soluble polyamic acid soluble in a non-dehydration condensation type solvent.

A generally known method for producing a polyimide film is to synthesize a polyamic acid as an imine precursor by reacting a diamine (diamin) and a carboxylic acid dianhydride (carbonic acid dianhydrate) in a polar solvent. Thereafter, the polyamic acid is heated or dehydrated and cyclized by using a catalyst to obtain a corresponding polyimide. However, the temperature of the heat treatment in the imidization step is preferably in the temperature range of 200°C to 300°C. If the heating temperature is lower than this temperature, imidization may not proceed, which is not preferable. If the heating temperature is higher than the above temperature, thermal decomposition of the compound may occur, so it is also not preferable.

In order to further improve the flexibility of the base material, the electromagnetic wave shielding material for FPC of the present invention uses an extremely thin polyimide film having a thickness of less than 10 μm.

Therefore, a thin polyimide film is laminated on one side of the support film 6 used as a reinforcing material for strength. However, the polyimide film itself has heat resistance for heat treatment at a heating temperature of 200°C to 250°C, and the support film 6 uses a general-purpose heat-resistant resin film, such as Polyethylene terephthalate (PET) resin film, therefore cannot adopt the method of forming polyimide from polyamic acid as imine precursor in the prior art.

The solvent-soluble polyimide has completed imidization of the polyimide and is soluble in a solvent. Therefore, film formation can be performed by volatilizing the solvent at a low temperature of less than 200° C. after coating the coating liquid dissolved in the solvent. The substrate 1 used in the electromagnetic wave shielding material for FPC of the present invention is a thin polyimide resin film, and the thin polyimide resin film is coated with a non-dehydration condensation type solvent-soluble resin film on one side of the support film 6. After the coating liquid of polyimide, it is made to dry at the heating temperature of temperature less than 200 degreeC, and it forms using solvent-soluble polyimide. By doing so, an extremely thin polyimide film having a thickness of 1 to 9 μm can be laminated on one surface of the support film 6 formed of a general-purpose heat-resistant resin film. The substrate 1 , the adhesive layer 2 , the conductive paste layer 3 , and the like can be continuously formed on the support film 6 while conveying the support film 6 in its longitudinal direction. The electromagnetic wave shielding material for FPC of the present invention can be produced by a roll-to-roll (roll to roll) production method.

The non-dehydration-condensation type solvent-soluble polyimide used in the present invention is not particularly limited, and a coating liquid of a generally sold solvent-soluble polyimide can be used. Commonly sold solvent-soluble polyimide coating liquids, specifically, Solpi-6,6-PI (Solpi-Industry), Q-IP-0895D (Pi-Ai Technology Research), PIQ (Hitachi Chemical Industries), SPI-200N (Nippon Steel Chemical), Rikacoat SN-20, Rikacoat PN-20 (Nippon Chemical), etc. The method of coating the coating solution of solvent-soluble polyimide on the support film is not particularly limited, for example, it can be coated by a metal die coater, a knife coater, a lip coater, etc. machine for coating.

The polyimide film used in the present invention preferably has a thickness of 1 to 9 μm. If the thickness of the polyimide film is less than 0.8 μm, it is technically difficult because the mechanical strength of the formed film is weak. In addition, if the thickness of the polyimide film exceeds 10 μm, electromagnetic wave shielding materials 5, 11 for FPC having excellent bending performance cannot be obtained.

(support film)

The base material of the support film 6 used in the present invention, for example, polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, Polyolefin films such as polypropylene and polyethylene.

The base material of the support film 6 is, for example, polyethylene terephthalate, etc., and when the base material has a certain degree of releasability, it is not necessary to perform a release treatment on the support film 6, but to directly laminate the coated film. A substrate formed of a thin resin film of a cloth dielectric. In addition, a peeling treatment for easy peeling may be performed on the support film 6 .

In addition, when the base film used as the above-mentioned support film 6 is not releasable, a release agent such as an amino alkyd resin or a silicone resin is applied and then subjected to a release treatment by heating and drying. Since the electromagnetic wave shielding materials 10 and 11 for FPC of this invention are bonded to FPC, it is preferable not to use silicone resin for this release agent. The reason is that if a silicone resin is used as a release agent, a part of the silicone resin moves on the surface of the substrate 1 that is in contact with the surface of the support film 6, and further passes through the electromagnetic wave shielding material 11 for FPC. Inside, there is a risk of movement from the substrate 1 to the conductive adhesive layer 4 . There is a risk that the silicone resin that migrates on the surface of the conductive adhesive layer 4 may weaken the adhesive force of the conductive adhesive layer 4 . The thickness of the support film 6 used in the present invention is not particularly limited since it is excluded from the overall thickness of the electromagnetic wave shielding material 11 for FPC when pasted on the FPC for use, and is usually about 12 to 150 μm.

(adhesive layer)

The adhesive layer 2 used in the FPC electromagnetic wave shielding materials 5, 10, and 11 of the present invention is to improve the electrical conductivity of the film composed of a polyimide film formed by using a solvent-soluble polyimide as the base material 1. The adhesive force of the adhesive paste layer 3 is set.

For the adhesive layer 2 , since the firing temperature of the conductive paste layer 3 provided thereon is 150 to 250° C., it is necessary to use an adhesive excellent in heat resistance. In addition, the adhesive layer 2 needs to have excellent adhesion to the polyimide film formed using a solvent-soluble polyimide as the base material 1 and the conductive paste layer 3 .

As the adhesive resin composition used for the adhesive layer 2, thermoplastic resins such as polyester resins, polyurethane resins, (meth)acrylic resins, polyethylene resins, polystyrene resins, and polyamide resins are preferably used. Alternatively, thermosetting resins such as epoxy resins, amino resins, polyimide resins, and (meth)acrylic resins may be used.

The adhesive resin composition of the adhesive layer 2 is particularly preferably an adhesive resin composition in which a polyester resin composition having an epoxy group is cross-linked, or an epoxy resin is mixed with polyurethane as a hardener. Resin-like adhesive resin composition. Therefore, the adhesive layer 2 has harder physical properties than the substrate 1 formed of a polyimide thin film coated with a solvent-soluble polyimide and laminated. The polyester resin composition having an epoxy group is not particularly limited, for example, an epoxy resin (uncured resin) having two or more epoxy groups in one molecule and an epoxy resin having two or more epoxy groups in one molecule The carboxyl polycarboxylic acid reaction etc. are obtained. Crosslinking of the polyester resin composition having epoxy groups is performed using a crosslinking agent for epoxy resins that reacts with epoxy groups.

In addition, the adhesive layer 2 may contain a light-absorbing material selected from the group consisting of carbon black, graphite, aniline black, cyanine black, titanium black, black iron oxide, chromium oxide, and manganese oxide. Composed of more than one black pigment or coloring pigment.

It is preferable to mix a black pigment such as carbon black into the adhesive layer 2 . The light-absorbing material composed of a black pigment or a color pigment is preferably contained in the adhesive layer 2 at 0.1 to 30% by weight. The black pigment or color pigment preferably has an average particle diameter of primary particles of about 0.02 to 0.1 μm as observed by SEM.

In addition, as a black pigment, there are cases where only the surface layer portion becomes black by immersing silica particles or the like in a black dye, or cases where the whole is formed from a black colored resin and becomes black. In addition, the black pigment includes particles of a color similar to black such as gray, black brown (黒つぽい brown), or black green (黒つぽい green) in addition to the case of being completely black, as long as it is difficult to reflect light. Dark colors can be used.

The thickness of the adhesive layer 2 is preferably about 0.05 to 1 μm, and with a film thickness of this level, sufficient adhesion of the conductive paste layer 3 can be obtained. When the thickness of the adhesive layer 2 is 0.05 μm or less, there is a risk that the fine particles of the light-absorbing material will be exposed, and the adhesion force between the base material 1 and the conductive paste layer 3 will decrease. In addition, even if the thickness of the adhesive layer 2 If the thickness exceeds 1 μm, there is no effect on the increase of the adhesive force of the substrate 1 or the conductive paste layer 3 formed of a polyimide film formed using a solvent-soluble polyimide. Therefore, when the thickness of the adhesive layer 2 exceeds 1 μm, the production cost increases, which is not preferable.

(conductive paste layer)

As the conductive paste layer 3 used in the present invention, a conductive paste obtained by mixing a conductive filler into a resin composition as a binder is used.

The conductive paste preferably contains one or more conductive fillers selected from conductive metal fine particles, carbon nanotubes, and carbon nanofibers, and a binder resin composition. As the conductive metal fine particles, fine metal powders of copper, silver, nickel, aluminum, etc. can be used, and it is preferable to use fine powders or nanoparticles of copper or silver which are highly conductive and inexpensive. In addition, carbon nanotubes and carbon nanofibers which are conductive carbon nanoparticles can also be used.

In order to suppress the firing temperature of the conductive paste to a low temperature in the temperature range of 150 to 250° C., the average particle diameter of the metal fine particles is preferably in the range of 1 to 100 nm, more preferably in the range of 1 to 60 nm.

It is desirable that the volume resistivity of the conductive paste layer 3 after drying is 1.5×10 ⁻⁵ Ω·cm or less.

The conductive paste layer 3 of the electromagnetic wave shielding materials 5, 10, and 11 for FPC according to the present invention, by containing such metal fine particles, not only can it be thinned, but thermal adhesion between the fine particles can also be achieved, and at the same time, the electrical conductivity can be improved. . The conductive paste used in the present invention is preferably such that, for example, metal fine particles having an average particle diameter in the range of 1 to 100 nm are uniformly dispersed in the dispersion solvent, and the surface of the metal fine particles is covered with an organic molecular layer to improve the dispersion performance in the solvent. . Finally, in the heating and firing step of the conductive paste, the metal microparticles are brought into surface contact with each other to obtain the conductivity of the conductive paste layer 3 . The heating and firing of the conductive paste is preferably performed at a temperature within the boiling point range of the organic molecular layer. This is because, for example, heating at a temperature of about 150 to 250° C. detaches and evaporates the organic molecular layer covering the surface of the metal fine particles. remove.

In the conductive paste, thermoplastic resins such as polyester resins, (meth)acrylic resins, polyethylene resins, polystyrene resins, and polyamide resins are preferably used as binder resin compositions mixed with conductive fillers. In addition, thermosetting resins such as epoxy resins, amino resins, polyimide resins, and (meth)acrylic resins can also be used.

For the conductive paste, after mixing conductive fillers such as conductive metal microparticles, carbon nanotubes, and carbon nanofibers into these binder resin compositions, the viscosity is adjusted by adding organic solvents such as ethanol or ether as needed. In addition, the viscosity of the conductive paste is adjusted by increasing or decreasing the amount of organic solvent added (mixing ratio).

The thickness after firing the conductive paste layer 3 is preferably about 0.1 to 2 μm, more preferably about 0.3 to 1 μm. If the thickness of the conductive paste layer 3 after firing is thinner than 0.1 μm, it will be difficult to obtain high electromagnetic wave shielding performance. On the other hand, if the conductive paste layer 3 after firing is thicker than 2 μm, the overall thickness of the FPC electromagnetic wave shielding material 11 excluding the support film 6 and release film 7 cannot be controlled to 25 μm or less.

(conductive adhesive layer)

In the electromagnetic wave shielding materials 10 and 11 for FPC according to the present invention, the conductive adhesive laminated on the conductive paste layer 3 uses acrylic adhesives, polyurethane adhesives, epoxy adhesives, rubber adhesives, etc. The quasi-adhesive, polysiloxane-based adhesive, etc. are not particularly limited in that commonly used thermosetting adhesives are mixed with conductive fine particles, ionic compounds such as quaternary ammonium salts, conductive polymers, and the like.

As the conductive adhesive, a pressure-sensitive adhesive exhibiting pressure-sensitive adhesiveness at room temperature was not used. The conductive adhesive of the present invention is an adhesive obtained by heating and pressing, and is preferably an adhesive whose adhesive force is hardly lowered against repeated bending.

The conductive fine particles mixed with the conductive adhesive layer 4 are not particularly limited, and conventionally known conductive fine particles can be used. Examples thereof include metal fine particles composed of carbon black and metals such as silver, nickel, copper, and aluminum, and composite metal fine particles in which the surfaces of these metal fine particles are covered with other metals. One kind or two or more kinds of these conductive fine particles are suitably selected and used.

In addition, in the above-mentioned conductive adhesive layer 4, in order to obtain excellent conductivity, the contact between the conductive fine particles and the contact between the particles and the conductive paste layer and the FPC as the adherend More preferably, if a large amount of conductive substance is contained, the adhesive force will decrease. On the other hand, if the content of conductive fine particles is reduced in order to improve the adhesive force, the contact between the conductive fine particles, the conductive paste layer, and the FPC as the adherend becomes insufficient, and the conductivity decreases. This opposite problem. Therefore, the compounding quantity of electroconductive fine particle is about 0.5-50 weight part normally with respect to 100 weight part of adhesive agents (solid content), More preferably, it is 2-10 weight part.

In addition, as the conductive adhesive constituting the conductive adhesive layer 4 of the present invention, an anisotropic conductive adhesive containing conductive fine particles is preferable, and known ones can be used. As the anisotropic conductive adhesive, for example, an adhesive having an insulating thermosetting resin such as an epoxy resin as a main component and in which conductive fine particles are dispersed can be used.

In addition, as the conductive fine particles used in the anisotropic conductive adhesive, for example, metal fine particles such as gold, silver, zinc, tin, and solder may be combined alone or two or more kinds thereof. In addition, resin particles plated with metal can be used as the conductive fine particles. The shape of the conductive fine particles preferably has a shape in which fine particles are connected in a linear chain, or a needle shape. With such a shape, when the FPC is heated and pressurized by the crimping member, the conductive fine particles can enter the conductor wiring of the FPC under low applied pressure.

The connection resistance value between the anisotropic conductive adhesive and FPC is preferably 5Ω/cm or less.

The adhesive strength of the conductive adhesive is not particularly limited, and its measurement method is based on the test method described in JIS Z 0237. The adhesive strength to the surface of the adherend is preferably in the range of 5 to 30 N/inch under the conditions of peeling off at a peeling angle of 180 degrees and a peeling speed of 300 mm/min. When the adhesive force is less than 5 N/inch, for example, the electromagnetic wave shielding material bonded to the FPC peels off from the FPC, resulting in a floating portion.

Conditions for heat and pressure bonding of FPC are not particularly limited, but are preferably, for example, a temperature of 160° C., a pressure of 2.54 MPa, and hot pressing for 30 minutes.

(peel film)

As the base material of the release film 7, for example, polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polypropylene or polypropylene Polyolefin films such as vinyl. After applying a release agent such as amino alkyd resin or silicone resin to these base films, a release treatment is performed by heating and drying. Since the electromagnetic wave shielding materials 10 and 11 for FPC of this invention are bonded to FPC, it is preferable not to use a silicone resin for this release agent. The reason is that if a silicone resin is used as a release agent, a part of the silicone resin moves on the surface of the conductive adhesive layer 4 that is in contact with the surface of the release film 7, and further passes through the FPC to shield the electromagnetic wave. There is a risk that the inside of the material 11 moves from the conductive adhesive layer 4 to the base material 1 . In addition, there is a possibility that the silicone resin migrated on the surface of the conductive adhesive layer 4 weakens the adhesive force of the conductive adhesive layer 4 . The thickness of the release film 7 used in the present invention is not particularly limited since it is excluded from the overall thickness of the FPC electromagnetic wave shielding material 11 when it is attached to an FPC for use, and is usually about 12 to 150 μm.

The electromagnetic wave shielding materials 5 , 10 , and 11 for FPCs of the present invention can be bonded to FPCs subjected to repeated bending operations, and are suitable for use as electromagnetic wave shielding materials for FPCs excellent in bending performance. Moreover, the electromagnetic wave shielding material for FPC of this invention can be used for a mobile phone or an electronic device as an electromagnetic wave shielding member.

Example

Hereinafter, the present invention will be specifically described based on examples.

(Example 1)

A polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product number: E5100) having a thickness of 50 μm was used as the support film 6 . On one side of the support film 6, a solvent-soluble polyimide coating liquid was cast-coated so that the thickness after drying became 4 μm, and dried to laminate a dielectric thin resin film. Substrate 1. On the formed base material 1, the paint for forming the adhesive bond layer 2 is applied so that the thickness after drying is 0.3 μm, and the adhesive bond layer 2 is laminated. Carbon black, which is a black pigment, is mixed with a polyester resin composition having a heat-resistant temperature of 260 to 280°C. On the adhesive layer 2, as a conductive filler, a conductive paste prepared by mixing silver particles with a primary average particle diameter of about 50 nm is used, and after drying, the thickness becomes 0.3 μm. It baked at 150 degreeC, the electroconductive paste layer 3 was formed, and the electromagnetic wave shielding material for FPC of Example 1 was obtained. The measured value of the volume resistivity of the dried conductive paste layer 3 was 1.5×10 ⁻⁵ Ω·cm or less.

(Example 2)

A polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product number: E5100) having a thickness of 50 μm was used as the support film 6 . On one side of the support film 6, a solvent-soluble polyimide coating liquid was cast-coated so that the thickness after drying became 8 μm, dried, and a thin resin film made of a dielectric was laminated. Substrate 1. On the formed base material 1, the paint for forming the adhesive bond layer 2 is applied so that the thickness after drying is 0.3 μm, and the adhesive bond layer 2 is laminated. Carbon black, which is a black pigment, is mixed with a polyester resin composition having a heat-resistant temperature of 260 to 280°C. On the adhesive layer 2, as a conductive filler, a conductive paste prepared by mixing silver particles with a primary average particle diameter of about 50 nm is used, and after drying, the thickness becomes 0.3 μm. It baked at 150 degreeC, the electroconductive paste layer 3 was formed, and the electromagnetic wave shielding material for FPC of Example 2 was obtained. The measured value of the volume resistivity of the dried conductive paste layer 3 was 1.5×10 ⁻⁵ Ω·cm or less.

(comparative example 1)

An electromagnetic wave shielding material for FPC of Comparative Example 1 was obtained in the same manner as in Example 1 except that the support film 6 was not used and a polyimide film made of thermosetting polyimide with a thickness of 10 μm was used as the base material 1 .

(Measurement method of surface resistivity of conductive paste layer 3)

According to the provisions of JIS-K-7194 "Resistivity test method using four-probe method for conductive plastics", the resistivity of the conductive paste layer 3 was measured by a resistivity meter (Loresta-GP T600 type) manufactured by Mitsubishi Chemical Co., Ltd. surface resistivity.

(Measurement method of bending test (1))

Using a thermosetting adhesive (manufactured by Three Bond, product number: 33A-798), adjust it so that the thickness after drying becomes 12 μm, apply it on the conductive paste layer 3, and apply the thermosetting adhesive The conductive paste layer 3 of the agent (Sribond, product number: 33A-798) is superimposed on the flexible printed circuit board provided with the test sample, and made to be in contact with the conductive adhesive layer 4 of the electromagnetic wave shielding material for FPC. The sides face each other, and after hot pressing at 160° C. and 2.54 MPa for 30 minutes, the test piece is cut into a size of 12.7 mm×160 mm.

According to the IPC standard TM-650 "TEST METHODS MANUAL" (JIS-C-6471 reference 3 "bending resistance"), the IPC bending test was performed using the cut test piece under the setting condition of R=1.5mm, and the conductivity was measured. The bending performance was evaluated by the number of bending tests when the resistance value of the conductive layer was doubled from the initial resistance value by repeated bending operations of the conductive layer.

Judgment of the bending test results is that the number of bending tests when the resistance value of the conductive paste layer is doubled from the initial resistance value due to repeated bending operations of the conductive layer exceeds 300,000 times. The case of less than 300,000 times is regarded as pass (○), and the case of less than 300,000 times is regarded as fail (×).

(Measurement method of bending test (2))

Using a thermosetting adhesive (manufactured by Three Bond, product number: 33A-798), adjust it so that the thickness after drying becomes 12 μm, apply it on the conductive paste layer 3, and apply the thermosetting adhesive The conductive paste layer 3 of the agent (Sribond, product number: 33A-798) is superimposed on the flexible printed circuit board provided with the test sample, and made to be in contact with the conductive adhesive layer 4 of the electromagnetic wave shielding material for FPC. The sides face each other, and after hot pressing at 160° C. and 2.54 MPa for 30 minutes, the test piece is cut into a size of 12.7 mm×160 mm.

According to IPC standard TM-650 "TEST METHODS MANUAL" (JIS-C-6471 reference 3 "bending resistance"), IPC bending test was carried out under the setting condition of R=1.0mm using the cut test piece, and the conductivity was measured. The bending performance was evaluated by the number of bending tests when the resistance value of the conductive paste layer doubled from the initial resistance value due to repeated bending operations of the conductive layer.

Judgment of the bending test results is that the number of bending tests when the resistance value of the conductive paste layer is doubled from the initial resistance value due to repeated bending operations of the conductive layer exceeds 300,000 times. The case of less than 300,000 times is regarded as pass (○), and the case of less than 300,000 times is regarded as fail (×).

(Measurement method of softness test)

Using a sample (width 17mm x length 160mm) for the bending test, install the sample on a ring stiffness tester (ル一プステイフネステステスタ) manufactured by Toyo Seiki Seisakusho Co., Ltd. to start the measurement, and bend the sample into a ring shape , According to the load when rolling along the diameter direction of the ring, the strength of elasticity (Koshi) is evaluated. Specifically, a ring with an outer circumference of 80 mm was produced by bending the sample used for the bending test into a ring shape to form an electromagnetic wave shielding material, and a force was applied at a speed of 3.3 mm/sec from the upper side of the ring until the end of the sample portion The distance of the minor axis was 1.5 mm, and the stress of the sample was measured when the state was maintained for 5 seconds.

(test results)

Regarding Examples 1 to 2 and Comparative Example 1, the surface resistivity, bending test, and flexibility test of the conductive paste layer were performed according to the above-mentioned test method, and Table 1 shows the obtained test results.

(Table 1)

From the results of the bending test shown in Table 1, it can be seen that the thickness of the polyimide film as the base material 1 has a large influence on the results of the flexibility test of the electromagnetic wave shielding material for FPC.

When using solvent-soluble polyimide to form a polyimide film with a thickness of 4 μm, since the electromagnetic wave shielding material for FPC is rich in flexibility, even if the bending radius is as small as R=1.0mm, excellent performance can be obtained. bending properties. In addition, when the thickness of the polyimide film formed by using solvent-soluble polyimide is 8 μm, if the bending radius is R=1.5mm, the bending performance is good, but if the bending radius is as small as R=1.0mm, then The bending performance is not good.

From these test results, it can be seen that the electromagnetic wave shielding material for FPC having excellent bending performance needs to form a film having a thickness of 1 to 9 μm as a base material composed of a polyimide film formed using a solvent-soluble polyimide. However, as the thickness of a polyimide film made of thermosetting polyimide currently sold in Japan, 7.5 μm is the thickness of the thinnest product. In the electromagnetic wave shielding material for FPC of this invention, it is necessary to use the polyimide film thinner than this thickness for a base material. Therefore, only by using a polyimide film having a thickness of 1 to 9 μm obtained by thinly casting a coating solution of a solvent-soluble polyimide in a base material, it is possible to obtain a film having excellent bending properties. Electromagnetic wave shielding material for FPC.

The electromagnetic wave shielding material for FPC of this invention can be used for various electronic equipments, such as a mobile phone, a notebook computer, and a portable terminal, as an electromagnetic wave shielding member.

Claims (10)

1. An electromagnetic wave shielding material for FPC, characterized in that, on one side of a support film, a base material composed of a thin resin film of a coated dielectric, an adhesive layer of a film, and a conductive paste layer are sequentially laminated . 2. FPC electromagnetic wave shielding material according to claim 1, is characterized in that, The base material is composed of a polyimide film formed by using solvent-soluble polyimide, and has a thickness of 1-9 μm. 3. The electromagnetic wave shielding material for FPC according to claim 1 or 2, characterized in that, The adhesive layer of the film is formed by cross-linking a polyester resin composition having an epoxy group, and has a thickness of 0.05-1 μm. 4. The electromagnetic wave shielding material for FPC according to claim 1 or 2, characterized in that, The adhesive layer further contains a light-absorbing material, and the light-absorbing material is one or more selected from the group consisting of carbon black, graphite, nigrosine black, cyanine black, titanium black, black iron oxide, chromium oxide, and manganese oxide. More than one type of black pigment or colored pigment. 5. The electromagnetic wave shielding material for FPC according to claim 1 or 2, characterized in that, The conductive paste layer is fired at a temperature of 150-250° C. and has a thickness of 0.1-2 μm by firing the conductive paste containing silver nanoparticles with an average particle diameter of 1-100 nm and a binder resin composition. 6. The electromagnetic wave shielding material for FPC according to claim 1 or 2, characterized in that, The conductive paste constituting the conductive paste layer has a dried volume resistivity of 1.5×10 ⁻⁵ Ω·cm or less. 7. The electromagnetic wave shielding material for FPC according to claim 1 or 2, characterized in that, A conductive adhesive layer is further laminated on the conductive paste layer. 8. FPC electromagnetic wave shielding material according to claim 7, is characterized in that, A release film subjected to release treatment was further bonded to the conductive adhesive layer. 9. A mobile phone characterized in that the electromagnetic wave shielding material for FPC according to any one of claims 1 to 8 is used as a member for electromagnetic wave shielding. 10. An electronic device, wherein the electromagnetic wave shielding material for FPC according to any one of claims 1 to 8 is used as a member for electromagnetic wave shielding.

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