JP2017115152A - Conductive adhesive layer and electromagnetic wave shielding material for FPC - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave shielding material for FPC excellent in adhesiveness with a substrate, a conductive paste layer and a conductive adhesive layer, having no partial delamination of an adhesive interface between the substrate and the conductive paste layer even with repeating flexure operation and suppressed reduction of electromagnetic shielding performance with time.SOLUTION: A conductive adhesive layer 4 laminated to an adherend by compression heating, containing a thermosetting adhesive, an epoxy resin with number average molecular weight of 1500 or less and conductive fine particles and concentration of the epoxy resin with the number average molecular weight of 1500 or less in the resin of the conductive adhesive is 15 wt.% to 50 wt.% of total resin component contained in the conductive adhesive layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electromagnetic wave shielding material for FPC that is used to shield an electromagnetic wave by covering a flexible printed circuit board (hereinafter referred to as FPC) that repeatedly receives a bending operation.

In portable electronic devices such as mobile phones and tablet terminals, electronic components are integrated on a printed circuit board in order to keep the outer dimensions of the housing small and facilitate carrying. Furthermore, in order to reduce the outer dimensions of the housing, the printed circuit board is divided into a plurality of parts, and the printed circuit board is folded by using a flexible FPC for connection wiring between the divided printed circuit boards, or It is done to slide.
In recent years, in order to prevent malfunction of electronic devices due to the effects of electromagnetic wave noise received from outside or electromagnetic wave noise mutually received between internal electronic components, important electronic components and FPCs can be prevented. Is covered with an electromagnetic shielding material.

Conventionally, as an electromagnetic shielding material used for the purpose of such electromagnetic shielding, what provided the adhesive layer on the surface of metal foil, such as rolled copper foil and soft aluminum foil, was used. Covering an object to be shielded using an electromagnetic shielding material made of such a metal foil has been performed (see, for example, Patent Documents 1 and 2).
Specifically, in order to shield an important electronic component from electromagnetic waves, a metal box or metal plate is used to form a sealed box and cover it. Further, in order to shield the bent FPC wiring from electromagnetic waves, a metal foil provided with an adhesive layer on one side is used and bonded through an adhesive layer.

In recent years, mobile phones, tablet terminals, and the like have rapidly spread as electronic devices carried around. In a cellular phone, it is preferable that the overall dimensions be as small as possible when stored in a pocket or the like without being used, and the overall dimensions can be increased when used. There is a need to reduce the size and thickness of mobile phones and to improve operability. In mobile phones, as a method of solving these problems, a folding / opening / sliding / opening / closing type housing structure is employed.
Moreover, in the case of a cellular phone, in both the folding open / close method and the slide open / close type housing structure, the operation screen is frequently opened and closed (start and stop operations) on a daily basis. It is performed at a frequency of several tens of times / day or several hundred times / day.

As a result, the FPC used in mobile phones and the electromagnetic wave shielding material for FPC that covers and shields the electromagnetic waves are repeatedly bent at a frequency exceeding the common sense of conventional portable electronic devices. Therefore, the electromagnetic shielding material for FPC which plays the role of electromagnetic shielding of FPC receives the severe repeated stress. If it becomes impossible to withstand the repeated stress, the base material constituting the FPC electromagnetic shielding material and the shielding material such as metal foil will eventually be damaged, such as rupture and peeling. There is a concern that the function as a shield material may be degraded or lost.
Therefore, an electromagnetic wave shielding material that copes with such repeated bending operations is also known (see, for example, Patent Document 3).

Japanese Utility Model Publication No. 56-084221 Japanese Patent Laid-Open No. 61-222299 Japanese Patent Laid-Open No. 7-122883

  In the electromagnetic wave shielding material provided with an adhesive layer on the surface of a metal foil such as rolled copper foil or soft aluminum foil as disclosed in the above-mentioned Patent Documents 1 and 2, the number of bending operations is small and it is used. There is no problem in shielding performance when the period is short. However, when the period of use is long from 5 to 10 years and the number of bending operations increases, there is a problem that the bending characteristics are lacking. Such an electromagnetic shielding material does not have an excellent bending characteristic that passes a bending test of 1 million times or more required for an electromagnetic shielding material for FPC used in recent mobile phones.

  Further, in the electromagnetic wave shielding material disclosed in Patent Document 3, in which a conductive paste layer such as metal vapor deposition is provided on one side of a flexible film and a conductive adhesive is laminated thereon, electric wires that are repeatedly bent It can be used as a coating. According to the example of Patent Document 3, a conductive film in which a conductive coating material containing silver powder having a thickness of 0.5 μm is provided on one side of a polyester film having a thickness of 12 μm and a polyester adhesive and nickel powder are mixed thereon is provided. The adhesive is heated and dried to provide a conductive adhesive layer having a thickness of 30 μm. In addition, it is said that it was confirmed that there was no damage by conducting a bending test with one cycle of bending at an angle of 180 ° along the outer periphery of a mandrel having an outer diameter of 10 mmφ and returning it to a straight line for one cycle.

  However, recent mobile phones are required to be as thin as possible by reducing the thickness of the outer dimensions of the casing in units of 0.1 mm. An electromagnetic wave shielding material for FPC having bending performance that can be used in such a thin casing is, for example, bent at an angle of 180 ° along the outer periphery of a mandrel having an outer diameter of 2 mmφ and returned to a straight line as one cycle. It is required that the bending test is not damaged even if it is carried out 1 million times or more. There is a need for an electromagnetic wave shielding material for FPC that can overcome a bending test under harsh conditions as compared with the prior art.

In addition, the electromagnetic wave shielding material described in the example of Patent Document 3 has a resin film having a thickness of 12 μm, a coating film of a conductive paint having a thickness of 0.5 μm, and a conductive adhesive layer having a thickness of 30 μm. The total thickness of the electromagnetic shielding material exceeds 40 μm.
As described above, in order to make the outer dimensions of the casing of the mobile phone as thin as possible, the electromagnetic shielding material for FPC is required to have a total thickness of 30 μm or less. That is, there is a demand for a strong FPC electromagnetic shielding material that is thinner than the conventional FPC electromagnetic shielding material and that can withstand severer bending tests.

Moreover, in the conductive adhesive used for the electromagnetic wave shielding material for FPC, in order to make the adhesive layer conductive, it is necessary to add a considerable amount of conductive powder (metal fine particles or carbon fine particles). Then, conversely, the adhesive strength of the adhesive layer is reduced.
In addition, in an electromagnetic wave shielding material for FPC in a cellular phone, the adhesive strength between the base material and the conductive paste layer is weak, so that the followability to a step when bonded to an uneven surface is poor, or it breaks. Since the bending operation is repeated, the adhesive interface between the base material and the conductive paste layer is partially delaminated, and the conductive paste layer is broken at this peeling site, and the electromagnetic shielding performance is deteriorated over time. There is concern.
In addition, the base material itself is required to have excellent bending characteristics enough to withstand repeated bending operations (for example, one million bending tests) during the lifetime of the electronic device.

  An object of the present invention is to provide a thin substrate with flexibility, followability to a step, and prevent deterioration of electromagnetic wave shielding performance even when severe bending operation is repeatedly performed. Excellent adhesion to the adhesive layer, and even if the bending operation is repeated, the adhesion interface between the base material and the conductive paste layer is not partially delaminated, and the electromagnetic wave shielding performance decreases over time. An object of the present invention is to provide a suppressed electromagnetic wave shielding material for FPC.

In the present invention, a base material made of a thin film of heat-resistant resin is used in order to withstand a severe bending operation and to have followability to a step. In the present invention, an anchor coat layer, a conductive paste layer, and a conductive adhesive layer are sequentially laminated on a base material made of a coated dielectric thin film resin film, and the conductive adhesive layer has several layers. By including an epoxy resin having an average molecular weight of 1500 or less, the adhesion between the substrate, the conductive paste layer and the conductive adhesive layer is improved, and the electromagnetic wave shielding performance for FPC is secured, and the bending performance and the follow-up to the step are also ensured. The technical idea is to improve the performance.
Also, in the present invention, a coated dielectric thin film resin film is used as a substrate made of a heat resistant resin thin film in consideration of flexibility and heat resistance, and the support film and the release film are removed. In addition, the entire thickness of the electromagnetic shielding material for FPC can be reduced to 25 μm or less.
Moreover, in this invention, in order to increase the adhesive force of the thin film resin film of the polyimide film formed using the solvent soluble polyimide which is a base material, and an electroconductive paste layer, it is anchored between a base material and an electroconductive paste layer. A coat layer is provided.

  Therefore, in the present invention, in order to solve the above-mentioned problems, a substrate made of a thin film resin film of a dielectric material applied on one side of a support film, an anchor coat layer, a conductive paste layer, a conductive material An adhesive layer is laminated in order, and a component that penetrates and cures into the anchor coat layer and / or the conductive paste layer in a part of the composition forming the conductive adhesive layer. The electromagnetic wave shielding material for FPC characterized by including is provided.

  In addition, the conductive adhesive layer includes an epoxy resin having a number average molecular weight of 1500 or less, and at least a part of the epoxy resin penetrates into the anchor coat layer and / or the conductive paste layer to be half. Preferably it is cured.

  The conductive adhesive layer preferably contains a flame retardant polyurethane resin and an epoxy resin having a number average molecular weight of 1500 or less.

  Moreover, it is preferable that the said base material consists of a polyimide film formed using the solvent soluble polyimide, and thickness is 1-9 micrometers.

  Moreover, it is preferable that the said anchor coat layer bridge | crosslinks the resin composition which consists of a polyester-type resin which has an epoxy group, and the thickness of the said anchor coat layer is 0.05-1 micrometer.

  Further, the anchor coat layer is further one or more black pigments or colored pigments selected from the group consisting of carbon black, graphite, aniline black, cyanine black, titanium black, black iron oxide, chromium oxide, and manganese oxide. It is preferable that the light absorption material which consists of 1 or more types of these is included.

  Moreover, the conductive paste layer is fired at a temperature of 150 to 250 ° C., and a thickness of 0.1 to 120 nm. The conductive paste contains silver nanoparticles having an average particle diameter of 1 to 120 nm and a binder resin composition. It is preferable that it is 2 micrometers.

The volume resistivity of the conductive paste layer is preferably 1.5 × 10 ⁻⁵ Ω · cm or less.

  Moreover, it is preferable that a release film subjected to a release treatment is further bonded onto the conductive adhesive layer.

  The present invention also provides a mobile phone in which the FPC electromagnetic shielding material described above is used as an electromagnetic shielding member.

  The present invention also provides an electronic device in which the electromagnetic wave shielding material for FPC described above is used as a member for shielding electromagnetic waves.

According to the electromagnetic wave shielding material for FPC of the present invention, an anchor coat layer, a conductive paste layer, and a conductive adhesive layer are laminated in this order on a substrate made of a coated dielectric thin film resin film. The composition for forming the conductive adhesive layer includes an epoxy resin having a number average molecular weight of 1500 or less, thereby improving the adhesion between the substrate, the conductive paste layer, and the conductive adhesive layer. It becomes possible. The conductive adhesive layer includes an epoxy resin having a number average molecular weight of 1500 or less, and the epoxy resin penetrates into the anchor coat layer and / or the conductive paste layer and is semi-cured. Thus, it is completely cured after heating and pressure bonding to the flexible circuit board, and the adhesion between the base material, the conductive paste layer, and the conductive adhesive layer can be improved.
Moreover, the adhesion of a base material and a conductive paste layer is achieved by using a thin film resin film (thickness of 1 to 9 μm) of a polyimide film formed using a solvent-soluble polyimide, an anchor coat layer, and a conductive paste layer. In addition to improving the properties, it is possible to obtain electromagnetic wave shielding performance while suppressing the thickness.
By this, the whole thickness of the electromagnetic wave shielding material for FPC excluding the support film and the release film can be suppressed to 25 μm or less, which can contribute to reducing the overall thickness of the mobile phone and the electronic device.
By mixing a light absorbing material composed of one or more kinds of black pigments or colored pigments in the anchor coat layer, specific coloring can be performed on one side of the shield film.
As described above, according to the present invention, the electromagnetic wave shielding material for FPCs is excellent in bending characteristics, which is flexible and thin, and does not deteriorate the electromagnetic wave shielding performance even when severe bending operation is repeated. Can be provided.

It is a schematic sectional drawing which shows an example of the electromagnetic wave shielding material for FPC concerning this invention. It is a schematic sectional drawing which shows another example of the electromagnetic wave shielding material for FPC concerning this invention.

Hereinafter, preferred embodiments of the present invention will be described.
When the FPC electromagnetic shielding material of the present invention is bonded to an adherend FPC or the like, the outer surface is a dielectric, and an insulating film needs to be bonded to the outer surface of the FPC electromagnetic shielding material. There is no. In addition, the electromagnetic shielding material for FPC of the present invention has a reduced overall thickness in order to improve the bending characteristics with respect to the bending operation.

  The electromagnetic wave shielding material 10 for FPC of the present invention shown in FIG. 1 is formed using a dielectric material (preferably having a flexible thickness of 1 to 9 μm and having a thickness of 1 to 9 μm) to which a base material 1 is applied. Polyimide film). The support film 6 is laminated on one surface of the base material 1, and the anchor coat layer 2 and the conductive paste that improve the adhesion between the conductive paste layer 3 and the base material 1 on the other surface of the base material 1. Layer 3 and conductive adhesive layer 4 are sequentially laminated. In the electromagnetic wave shielding material 11 for FPC of the present invention according to another example shown in FIG. 2, a release film 7 is further laminated in order on the conductive adhesive layer 4. This FPC electromagnetic shielding material 11 can be used as an FPC electromagnetic shielding material from which the support film 6 and the release film 7 are removed.

(Base material made of dielectric thin film resin film)
As the base material 1 of the electromagnetic wave shielding materials 10 and 11 for FPC according to the present invention, a dielectric thin film resin film formed by coating on one side of a support film 6 is used. In particular, a polyimide resin thin film resin film formed using a solvent-soluble polyimide has high mechanical strength, heat resistance, insulation, and solvent resistance, which are the characteristics of polyimide resin. It is said to be stable.
Examples of polyimide include thermosetting polyimide that is generated by a dehydration condensation reaction by heating polyamic acid, and solvent-soluble polyimide that is soluble in a non-dehydration condensation type solvent.
A generally known method for producing a polyimide film is to synthesize polyamic acid, which is an imide precursor, by reacting diamine and carboxylic dianhydride in a polar solvent, and heat the polyamic acid. Alternatively, a corresponding polyimide is formed by dehydration cyclization by using a catalyst. However, the temperature of the heat treatment in this imidization step is preferably a temperature range of 200 ° C. to 300 ° C., and 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, the compound may be thermally decomposed, which is not preferable.

In the electromagnetic wave shielding material for FPC of the present invention, it is preferable to use a very thin polyimide film having a thickness of less than 10 μm in order to further improve the flexibility of the substrate.
For this reason, it is necessary to laminate and form a thin polyimide film on one side of the support film 6 used as a reinforcing material for strength. However, although the polyimide film itself has heat resistance against heat treatment at a heating temperature of 200 ° C. to 250 ° C., the support film 6 is a general-purpose heat resistance because of the balance between price and heat resistance temperature performance. Since a resin film, for example, a polyethylene terephthalate (PET) resin film is used, a method of forming polyimide from polyamic acid which is a conventional imide precursor cannot be employed.
The solvent-soluble polyimide is complete in imidization of the polyimide and is soluble in the solvent. After applying the coating solution dissolved in the solvent, the solvent is volatilized at a low temperature of less than 200 ° C. A film can be formed. For this reason, the base material 1 used for the electromagnetic wave shielding material for FPC of the present invention is coated with a non-dehydration-condensation solvent-soluble polyimide coating solution on one surface of the support film 6, and then the temperature is 200. It is possible to form a thin film resin film of a polyimide film formed using a solvent-soluble polyimide by drying at a heating temperature of less than ° C. By carrying out like this, the very thin polyimide film whose thickness is 1-9 micrometers can be laminated | stacked on the single side | surface of the support body film 6 which consists of a general purpose heat resistant resin film. Since the base material 1, the anchor coat layer 2, the conductive paste layer 3 and the like can be continuously formed on the support film 6 along its longitudinal direction, production on a roll-to-roll basis is possible. Is also possible.

The solvent-soluble polyimide that is a non-dehydrating condensation type used in the present invention is not particularly limited, but a commercially available coating solution for solvent-soluble polyimide can be used. Specific examples of commercially available solvent-soluble polyimide coating solutions include Solpy 6,6-PI (Solpy Industry), Q-IP-0895D (PI Engineering), PIQ (Hitachi Chemical Industry), SPI-200N (Nippon Steel Chemical). ), Rika Coat SN-20, Rika Coat PN-20 (New Nippon Rika) and the like. The method for applying the solvent-soluble polyamide coating solution on the support film 6 is not particularly limited, and for example, it can be applied by a coater such as a die coater, a knife coater, or a lip coater.
The thickness of the polyimide film used in the present invention is preferably 1 to 9 μm. Forming a polyimide film with a thickness of less than 0.8 μm is technically difficult because the mechanical strength of the formed film is weak. Moreover, when the thickness of a polyimide film exceeds 10 micrometers, it will become difficult to obtain the electromagnetic wave shielding materials 10 and 11 for FPC which have the outstanding bending | flexion performance.

(Support film)
Examples of the substrate of the support film 6 used in the present invention include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene.
When the base material of the support film 6 has a certain degree of peelability on the base material itself, such as polyethylene terephthalate, for example, it is directly applied to the support film 6 without performing a peeling treatment. The base material 1 made of an applied dielectric thin film resin film may be laminated, or the surface of the support film 6 may be subjected to a peeling treatment for making the base material 1 easier to peel off.
Moreover, when the base film used as the support film 6 does not have releasability, a release treatment such as amino alkyd resin or silicone resin is applied and then dried by heating. Applied. Since the electromagnetic wave shielding materials 10 and 11 for FPC of the present invention are bonded to the FPC, it is desirable not to use a silicone resin for this release agent. This is because when a silicone resin is used as a release agent, a part of the silicone resin is transferred to the surface of the substrate 1 in contact with the surface of the support film 6, and further from the substrate 1 through the inside of the electromagnetic wave shielding material 11 for FPC. There is a risk of transition to the conductive adhesive layer 4. This is because the silicone resin transferred to 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 because it is excluded from the total thickness of the electromagnetic wave shielding material 11 for FPC when used by being attached to an FPC. It is about 150 μm.

(Anchor coat layer)
The anchor coat layer 2 used for the electromagnetic wave shielding materials 10 and 11 for FPC of the present invention has an adhesive force between a thin film of a polyimide film formed using a solvent-soluble polyimide as the base material 1 and the conductive paste layer 3. It is provided in order to improve the above.
The anchor coat layer 2 needs to use a resin having excellent heat resistance in order to form the conductive paste layer 3 applied thereon by a heating and baking process of the applied conductive paste.
In addition, the anchor coat layer 2 needs to have excellent adhesion to the dielectric thin film resin film (for example, a polyimide film formed using a solvent-soluble polyimide) serving as the substrate 1 and the conductive paste layer 3. is there.
The resin used for the anchor coat layer 2 is at least one resin selected from the group consisting of acrylic resins, polyurethane resins, polyester resins, cellulose resins, epoxy resins, and polyamide resins. It is preferable to include.
Particularly preferred as the adhesive resin composition for the anchor coat layer 2 is an adhesive resin composition for crosslinking a polyester resin composition having an epoxy group, or an adhesive resin obtained by mixing an epoxy resin as a curing agent with a polyurethane resin. It is a composition. For this reason, the anchor coat layer 2 has harder physical properties than the base material 1 made of a polyimide thin film laminated by applying a solvent-soluble polyimide. The polyester-based resin composition having an epoxy group is not particularly limited. For example, an epoxy resin having two or more epoxy groups per molecule (its uncured resin) and two or more carboxyls per molecule. It can be obtained by reaction with a polyvalent carboxylic acid having a group. For crosslinking of the polyester-based resin composition having an epoxy group, a crosslinking agent for epoxy resin that reacts with the epoxy group can be used.

The anchor coat layer 2 is composed of one or more black pigments selected from the group consisting of carbon black, graphite, aniline black, cyanine black, titanium black, black iron oxide, chromium oxide, and manganese oxide, or colored pigments (coloring A light absorbing material comprising one or more of (pigment) may be included. Among these light absorbing materials, it is preferable to mix a black pigment such as carbon black. The light absorbing material made of a black pigment or a colored pigment is preferably contained in the anchor coat layer 2 at 0.1 to 30% by weight. The black pigment or the colored pigment preferably has an average primary particle size of about 0.02 to 0.1 μm by SEM observation.
Moreover, as a black pigment, a silica particle etc. may be immersed in a black color material, and only a surface layer part may be made black, and it may be formed from a black colored resin etc. and may become black over the whole. Further, the black pigment includes particles exhibiting a color similar to black, such as gray, dark brown, or dark green, in addition to true black, and can be used as long as it is a dark color that hardly reflects light.
The thickness of the anchor coat layer 2 is preferably about 0.05 to 1 μm, and sufficient adhesive strength of the conductive paste layer 3 can be obtained with this thickness. When the thickness of the anchor coat layer 2 is 0.05 μm or less, fine particles of the light absorbing material are exposed, and the adhesion between the substrate 1 and the conductive paste layer 3 may be reduced. Further, even if the thickness of the anchor coat layer 2 exceeds 1 μm, there is no effect in increasing the adhesive force to the base material 1 and the conductive paste layer 3 made of a polyimide film formed using a solvent-soluble polyimide. It is not preferable that the thickness of the coat layer 2 exceeds 1 μm because the cost increases.

(Conductive paste layer)
As the conductive paste layer 3 used in the present invention, a conductive paste in which a conductive filler is mixed in a resin composition serving as a binder is used. The conductive paste preferably contains one or more selected from the group of conductive fillers composed of conductive metal fine particles, carbon nanotubes, and carbon nanofibers, and a binder resin composition. As the conductive metal fine particles, fine metal powders such as copper, silver, nickel, and aluminum are used. However, since the conductive performance is high and the price is low, copper or silver fine powder or nanoparticles (copper nanoparticles, Silver nanoparticles etc. are preferably used. In addition, carbon nanotubes and carbon nanofibers, which are carbon nanoparticles having conductivity, can also be used.
The volume resistivity of the conductive paste layer 3 after firing is desirably 1.5 × 10 ⁻⁵ Ω · cm or less. Further, the surface resistivity after firing of the conductive paste layer 3 is desirably 0.2Ω / □ or less.

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 120 nm, and more preferably in the range of 1 to 100 nm.
The conductive paste layer 3 of the electromagnetic wave shielding materials 10 and 11 for FPC according to the present invention can not only cope with the thin film by containing such metal fine particles, but also the fine particles are fused. Thus, the conductivity can be improved at the same time. In the conductive paste used in the present invention, for example, in order to uniformly disperse metal fine particles having an average particle diameter of 1 to 120 nm in a dispersion solvent, the surface of the metal fine particles is coated with an organic molecular layer, It is preferable to improve the dispersion performance in a solvent. Finally, in the step of heating and baking the conductive paste, the metal fine particles can be brought into contact with each other to obtain the conductivity of the conductive paste layer 3.
The conductive paste is heated and fired, for example, by heating to about 150 to 250 ° C., the organic molecular layer covering the surface of the metal fine particles is separated and evaporated to remove the organic paste. Preferably, the boiling point is within the range.
As described above, the polyimide film itself serving as the base material 1 has heat resistance to heat treatment at a heating temperature of 200 ° C. to 250 ° C., but the support film 6 is inferior in heat resistance, and thus the support film. When 6 is used, it is preferable that the firing temperature is lower.
The firing temperature of the conductive paste is preferably 150 to 180 ° C., whereby the appearance defect due to thermal deterioration of the support film 6 can be suppressed.

As the binder resin composition used by mixing the conductive paste with the conductive filler, a thermoplastic resin such as a polyester resin, a (meth) acrylic resin, a polyethylene resin, a polystyrene resin, or a polyamide resin is preferably used. Moreover, thermosetting resins, such as an epoxy resin, an amino resin, a polyimide resin, and a (meth) acrylic resin, may be sufficient. The conductive paste is mixed with these binder resin compositions with conductive fillers such as conductive metal fine particles, carbon nanotubes, and carbon nanofibers, and then added with an organic solvent such as alcohol or ether as necessary. Make adjustments.
Viscosity adjustment can be performed by the addition amount (compounding ratio) of an organic solvent. The thickness of the conductive paste layer 3 after firing is preferably about 0.1 to 2 μm. More preferably, the thickness is about 0.3 to 1 μm. When the thickness of the conductive paste layer 3 after firing is thinner than 0.1 μm, it is difficult to obtain high electromagnetic shielding performance. On the other hand, if the thickness of the conductive paste layer 3 after firing is greater than 2 μm, the entire thickness of the FPC electromagnetic wave shielding material 11 excluding the support film 6 and the release film 7 can be suppressed to 25 μm or less. It becomes difficult.

(Conductive adhesive layer)
As the conductive adhesive layer laminated on the conductive paste layer 3 of the electromagnetic wave shielding materials 10 and 11 for FPC according to the present invention, acrylic adhesive, polyurethane adhesive, epoxy adhesive, rubber-based adhesive Thermosetting adhesive imparting flame retardancy to adhesives, silicone adhesives, etc., and an epoxy resin having a number average molecular weight of 1500 or less that can penetrate and cure inside the anchor coat layer and / or conductive paste layer Conductive by mixing one or more kinds of conductive materials selected from conductive materials such as conductive fine particles, ionic compounds such as quaternary ammonium salts, conductive polymers, etc. Although what gave nature is used, it is not specifically limited.
It is preferable that the conductive adhesive layer is not a pressure-sensitive adhesive layer exhibiting pressure-sensitive adhesiveness at room temperature, but an adhesive layer formed by heating and pressurization because the adhesive force hardly decreases with respect to repeated bending.

The flame retardant resin (flame retardant thermosetting adhesive) to be blended in the conductive adhesive layer 4 is not particularly limited, and a conventionally known one can be applied, but it penetrates into a layer having fine voids. It is preferable that the acid value is higher so that the epoxy resin having a number average molecular weight of 1500 or less, which is a component to be cured, can be easily crosslinked. The acid value of the flame retardant resin is preferably 5 or more, and more preferably 10 or more. When the acid value of the flame retardant resin is less than the above lower limit value, for example, less than 5, sufficient heat resistance may not be obtained.
Component that blends into conductive adhesive layer 4 and penetrates and hardens into a layer having fine voids (resin component that penetrates into anchor coat layer 2 and / or conductive paste layer 3 made of the conductive paste) Is preferably an epoxy resin having a number average molecular weight of 1500 or less. Examples of such epoxy resins include bisphenol A type epoxy resins, bisphenol F type epoxy resins, phenol novolac type epoxy resins, and the like. Among these, bisphenol A type epoxy resin is preferable. Among the bisphenol A type epoxy resins, commercially available liquid bisphenol A type epoxy resins include, for example, jER828EL, jER834 (Mitsubishi Chemical Corporation), EPICLON840, EPICLON850 (DIC Corporation), YD-127, Examples thereof include YD-128 (Nippon Steel & Sumikin Chemical Co., Ltd.), but are not particularly limited. Examples of commercially available solid bisphenol A resins include jER1001, jER1002 (Mitsubishi Chemical Corporation), YDF-2001 (Nippon Steel & Sumikin Chemical Co., Ltd.), EPICLON1050 (DIC Corporation), There is no particular limitation.

In addition, the blending ratio of the flame retardant resin in the resin of the conductive adhesive layer is determined by the concentration of the flame retardant component. For example, in the flame retardant resin in which a phosphorus flame retardant is introduced, the phosphorus concentration in the total resin content Is preferably 1.0% by weight or more. If the phosphorus concentration in the total resin content is less than 1.0% by weight, sufficient flame retardancy may not be obtained. The concentration of the epoxy resin having a number average molecular weight of 1500 or less in the resin of the conductive adhesive layer is the total resin content contained in the conductive adhesive layer (when the curing agent is combined with the resin to be polymerized). The amount of the curing agent is also included in the total resin content.) Is preferably 15% by weight or more, particularly preferably 20% by weight or more. When the concentration of the epoxy resin having a number average molecular weight of 1500 or less in the resin of the conductive adhesive layer is less than the above lower limit value, for example, less than 15% by weight, the fineness of the anchor coat layer, the conductive paste layer, etc. A sufficient amount does not penetrate into the layer having a void, and the effect of increasing the adhesive force is difficult to obtain. Further, the upper limit value of the concentration of the epoxy resin having a number average molecular weight of 1500 or less in the resin of the conductive adhesive layer is not particularly limited. For example, about 30% by weight, about 40% by weight, about 50% by weight, etc. However, in order to ensure flame retardancy, the blending amount of the component that penetrates and cures is moderated, or a component that penetrates and cures having flame retardancy, such as a flame retardant epoxy resin, is added. It is preferable to use it.
A component (for example, a curable component such as an epoxy resin having a number average molecular weight of 1500 or less) that penetrates into a layer having fine voids and is mixed in the conductive adhesive layer 4 is cured by the conductive adhesive layer 4. Is laminated on the anchor coat layer 2 and the conductive paste layer 3, and then penetrates into these layers (at least inside the conductive paste layer 3, preferably further to the inside of the anchor coat layer 2). This is because the conductive paste layer 3 has fine voids compared to a dense metal vapor deposition layer. Preferably, the component that penetrates and hardens into the layer having fine voids of the conductive adhesive layer 4 applied on the conductive paste layer 3 is penetrated into the anchor coat layer 2 and the conductive paste layer 3. Then, it is cured. The component contained in the conductive adhesive layer 4 that penetrates and cures the layer having fine voids may be semi-cured or cured before being bonded to an adherend such as an FPC, or cured after being bonded. May be. For example, it can be cured in a heating step such as hot pressing. The molecular weight of the epoxy resin after penetrating into the layer having fine voids and curing may be a high molecular weight of 10,000 or more.

The electroconductive fine particles mix | blended with the electroconductive adhesive layer 4 are not specifically limited, A conventionally well-known thing can be applied. Examples thereof include metal fine particles made of metal such as carbon black, silver, nickel, copper, and aluminum, and composite metal fine particles obtained by coating the surface of the metal fine particles with other metals. Can be appropriately selected and used.
Further, in the above conductive adhesive, in order to obtain excellent conductivity, the contact between the conductive material particles and the contact between the particles, the conductive paste layer, and the FPC as the adherend are improved. In addition, if a large amount of conductive material is contained, the adhesive strength is reduced. On the other hand, when the content of the conductive material is reduced in order to increase the adhesive force, the contact between the conductive material and the conductive paste layer and the FPC that is the adherend becomes insufficient, and the conductivity decreases. There are conflicting problems. For this reason, the compounding quantity of electroconductive fine particles is about 0.5-150 weight part normally with respect to 100 weight part of adhesive agents (solid content), More preferably, it is 25-75 weight part.

  Moreover, as a conductive adhesive which comprises the conductive adhesive layer 4 of this invention, the anisotropic conductive adhesive containing conductive fine particles is preferable, and a well-known thing can be used. For example, in the same manner as the conductive adhesive, a thermosetting adhesive that imparts flame retardancy to an acrylic adhesive, a polyurethane adhesive, an epoxy adhesive, a rubber adhesive, a silicone adhesive, etc. A resin component composed of an epoxy resin having a number average molecular weight of 1500 or less that penetrates and cures inside the anchor coat layer and the conductive paste layer, an ionic compound such as conductive fine particles and quaternary ammonium salt, a conductive polymer A material obtained by mixing one or more conductive materials selected from a group of conductive materials such as those having conductivity is used, but is not particularly limited.

In addition, as the conductive fine particles used for the anisotropic conductive adhesive, for example, single or two or more kinds of metal fine particles such as gold, silver, zinc, tin, and solder may be combined. Further, as the conductive fine particles, resin particles plated with metal can be used. The shape of the conductive fine particles is preferably a shape in which fine particles are connected in a straight chain or a needle shape. If it is such a shape, when heat-pressing processing with respect to FPC by a crimping | compression-bonding member, it will become possible for electroconductive fine particles to bite into the conductor wiring of FPC with a low pressurizing force.
The anisotropic conductive adhesive preferably has a connection resistance value with the FPC of 5 Ω / cm or less, and more preferably 1 Ω / cm or less.
The adhesive strength of the conductive adhesive is not particularly limited, but the measurement method is in accordance with the test method described in JIS C 6471 method 8.1.1. The range of 5 to 30 N / cm is preferable under the condition that the adhesive strength to the adherend surface has a peeling angle of 90 ° peel and a peeling speed of 50 mm / min. When the adhesive force is less than 5 N / cm, for example, the electromagnetic shielding material bonded to the FPC may peel off or float.
The conditions for heat and pressure adhesion to the FPC are not particularly limited, but for example, it is preferable to heat press for 60 minutes at a temperature of 160 ° C. and a pressure of 4.5 MPa.

(Peeling film)
Examples of the substrate of the release film 7 include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene. After applying a release agent such as amino alkyd resin or silicone resin to these base films, the release treatment is performed by drying by heating. Since the electromagnetic wave shielding materials 10 and 11 for FPC of the present invention are bonded to the FPC, it is desirable not to use a silicone resin for this release agent. This is because when a silicone resin is used as a release agent, a part of the silicone resin is transferred to the surface of the conductive adhesive layer 4 in contact with the surface of the release film 7 and further conductively bonded through the inside of the electromagnetic shielding material 11 for FPC. There is a risk of migration from the agent layer 4 to the substrate 1. This is because the silicone resin transferred to the surface of the conductive adhesive layer 4 may weaken 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 because it is excluded from the total thickness of the electromagnetic wave shielding material 11 for FPC when used by being attached to an FPC, but is usually about 12 to 150 μm. It is.

  The electromagnetic wave shielding materials 10 and 11 for FPC of the present invention have excellent followability with respect to a level difference when bonded to an uneven surface, and can be used by being bonded to an FPC that is repeatedly bent. It can be suitably used as an excellent electromagnetic shielding material for FPC. Moreover, the electromagnetic wave shielding material for FPC of this invention can be used for a mobile telephone or an electronic device as an electromagnetic wave shielding member.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not restrict | limited at all by this Example.
Example 1
A polyethylene terephthalate (PET) film having a thickness of 50 μm and subjected to a peeling treatment on one side was used as the support film 6. A substrate 1 made of a dielectric thin film resin film is applied by casting and drying a solvent-soluble polyimide coating solution on the release-treated surface of the support film 6 so that the thickness after drying is 4 μm. Were laminated. Coating for forming an anchor coat layer 2 in which carbon black as a black pigment of a light absorbing material and a polyester resin composition having a heat resistant temperature of 260 to 280 ° C. are mixed on the formed substrate 1. The liquid was used to coat the anchor coat layer 2 so that the thickness after drying was 0.3 μm. After applying to the anchor coat layer 2 using a conductive paste prepared by mixing silver particles having a primary average particle diameter of about 50 nm as a conductive filler so that the thickness after drying is 0.3 μm. The conductive paste layer 3 was formed by drying and baking at a temperature of 150 ° C. The value obtained by measuring the volume resistivity of the dried conductive paste layer 3 was 1.5 × 10 ⁻⁵ Ω · cm or less.
Separately, with respect to 250 parts by weight of a 40% solution of flame retardant polyurethane resin (A-1), 15 parts by weight of a curing agent 70% solution (B-1) and an epoxy resin having a number average molecular weight of 1500 or less (C-1) ) 60 parts by weight, equivalent of curing agent (D-1) (19.5 parts by weight), fused silica having an average particle diameter of 16 nm, 40% solution of flame retardant polyurethane resin (A-1), curing agent 70% Silver-coated copper having 10% by weight and an average particle diameter of 6 μm with respect to the total amount of solids (ie, total resin content) of the solution (B-1), epoxy resin (C-1), and curing agent (D-1). Was added so as to be 50% by weight of the total solid content including fused silica, diluted with methyl ethyl ketone and toluene, and stirred and kneaded to obtain a conductive adhesive solution. The obtained conductive adhesive solution was applied on the conductive paste layer 3 so that the thickness after drying was 12 μm as measured with a dial gauge, and was heat-dried at 130 ° C. for 3 minutes to be semi-cured. The electromagnetic wave shielding material for FPC of Example 1 was obtained.

(Examples 2 to 4)
An electromagnetic wave shielding material for FPC was obtained in the same manner as in Example 1 except that the epoxy resin having a number average molecular weight of 1500 or less was changed as shown in Table 1.
(Examples 5-7)
An electromagnetic wave shielding material for FPC was obtained in the same manner as in Example 1 except that the compounding amount of the epoxy resin having a number average molecular weight of 1500 or less was changed as shown in Table 1.

(Comparative Examples 1-2)
An electromagnetic wave shielding material for FPC was obtained in the same manner as in Example 1 except that an epoxy resin having a number average molecular weight of 1500 or more was blended as shown in Table 2 instead of the epoxy resin having a number average molecular weight of 1500 or less.
(Comparative Example 3)
(C-1) An electromagnetic shielding material for FPC was obtained in the same manner as in Example 1 except that no epoxy resin was blended.
(Comparative Example 4)
An electromagnetic wave shielding material for FPC was obtained in the same manner as in Example 1 except that the compounding amount of the epoxy resin having a number average molecular weight of 1500 or less was changed as shown in Table 2.

(Measurement method of adhesive strength)
A 50 μm-thick polyimide film (manufactured by Toray DuPont Co., Ltd., product number: 200H) was overlapped with the conductive adhesive layer 4 side of the electromagnetic shielding material for FPC facing each other, and hot-pressed at 160 ° C. and 4.5 MPa for 60 minutes. Then, the support body film 6 was peeled and cut | judged to 50 mm x 120 mm. A commercially available bonding sheet and a polyimide film having a thickness of 12.5 μm (product number: 50H, manufactured by Toray DuPont Co., Ltd.) are stacked in this order so as to face the substrate 1 of the cut film, and hot pressed at 160 ° C. and 4.5 MPa for 60 minutes. A test piece was obtained. In accordance with JIS-C-6471 “Testing method for copper-clad laminates for flexible printed wiring boards” in 8.1.1, method A (90 ° direction peeling), the polyimide film side with a thickness of 50 μm is fixed to the support bracket. Then, the anchor coat layer 2, the substrate 1, the bonding sheet, and the polyimide film having a thickness of 12.5 μm were peeled together, and the adhesive force between the anchor coat layer 2 and the conductive paste layer 3 was measured.

(Flame retardancy evaluation method)
A 12.5 μm-thick polyimide film (manufactured by Toray DuPont Co., Ltd., product number: 50H) is overlapped with the conductive adhesive layer 4 side of the electromagnetic shielding material for FPC facing each other, and heated at 160 ° C. and 4.5 MPa for 60 minutes. After pressing, the support film 6 was peeled off and cut into 50 mm × 200 mm to obtain test pieces.
The obtained test piece was evaluated for flame retardancy according to its combustion behavior according to a thin material vertical combustion test (ASTM D4804).

(Test results)
About Examples 1-7 and Comparative Examples 1-4, the adhesive test of the electrically conductive paste layer was done with said test method, and the obtained test result was shown to Tables 1-2. The abbreviations in Tables 1 and 2 indicate the following.
40% solution of flame retardant polyurethane resin (A-1): 40% solution of flame retardant polyurethane resin having a phosphorus content of 2.4% by weight, a number average molecular weight of about 15000 and an acid value of 32 KOHmg / g % Solution (B-1): Toyobo product name “HY-30” (curing agent for flame-retardant polyurethane resin)
-Epoxy resin (C-1): Mitsubishi Chemical product name "jER828EL" (epoxy equivalent 189 g / equivalent, number average molecular weight 370)
Epoxy resin (C-2): Mitsubishi Chemical product name “jER834” (epoxy equivalent 250 g / equivalent, number average molecular weight of about 470)
Epoxy resin (C-3): Mitsubishi Chemical product name “jER1001” (epoxy equivalent 475 g / equivalent, number average molecular weight 900)
-Epoxy resin (C-4): Mitsubishi Chemical product name “jER1002” (epoxy equivalent 642 g / equivalent, number average molecular weight approximately 1200)
Epoxy resin (C-5): Mitsubishi Chemical product name “jER1004” (epoxy equivalent 950 g / equivalent, number average molecular weight approximately 1650)
-Epoxy resin (C-6): Mitsubishi Chemical product name "jER1007" (epoxy equivalent 1975 g / equivalent, number average molecular weight about 2900)
Curing agent (D-1): Wakayama Seika Kogyo Co., Ltd. Trade name “Seika Cure S” (Curing agent for epoxy resin with amine equivalent of 62.1: 4,4′-diaminodiphenyl sulfone)
In Tables 1 and 2, the numerical values shown in the columns “A-1”, “B-1”, “C-1” to “C-6”, “D-1” are described in the first embodiment. Thus, the weight part of each component is shown. “-” Means that the component is not included.

According to the results of the adhesive strength test shown in Tables 1 and 2, the number average molecular weight of the epoxy resin blended in the conductive adhesive layer depends on the adhesive strength between the anchor coat layer and the conductive paste layer of the electromagnetic wave shielding material for FPC. It can be seen that it has a big influence.
In Examples 1 to 7, an epoxy resin having a number average molecular weight of 1500 or less is blended, and the effect of enhancing the adhesive force is sufficiently recognized as compared with Comparative Example 3 in which no epoxy resin is blended.
In Comparative Examples 1 and 2, since an epoxy resin that has a large number average molecular weight and does not easily penetrate into the anchor coat layer and / or the conductive paste layer is blended, the effect of enhancing the adhesive strength is small.
Moreover, when things using the same epoxy resin (C-1) are compared with each other, in Examples 1, 5, 6, and 7, a sufficient adhesion enhancement effect is recognized, but the amount of the epoxy resin is small. In Example 4, the amount of the epoxy resin penetrating the anchor coat layer and / or the inside of the conductive paste layer is also reduced, and the effect of enhancing the adhesive force is not sufficient.
From these test results, an electromagnetic wave shielding material for FPC having excellent adhesion between the respective layers is a base material made of a dielectric thin film resin film (for example, a base made of a polyimide film formed using a solvent-soluble polyimide). The thickness of the material is a thin film having a thickness of 1 to 9 μm, and an anchor coat layer, a conductive paste layer, and a conductive adhesive layer are sequentially laminated on the base material), and a part of the conductive adhesive layer is electrically conductive. It is necessary that it penetrates and hardens inside the conductive paste layer (more preferably inside the anchor coat layer). For this purpose, it is desirable that the conductive adhesive layer contains an epoxy resin having a number average molecular weight of 1500 or less.
Currently, the electromagnetic shielding material for FPC commercially available in Japan uses a deposited metal thin film as a conductive layer, but since the deposited metal thin film is a dense film, the adhesive component from the conductive adhesive layer penetrates. It is difficult to expect an increase in interlayer adhesion due to the adhesive component penetrating into the metal thin film and curing.
On the other hand, in the electromagnetic wave shielding material for FPC of the present invention, a dielectric thin film resin film (for example, a polyimide film having a thickness of 1 to 9 μm obtained by thinly applying a solvent-soluble polyimide coating solution) In order to improve the adhesion with the anchor coat layer and the conductive paste layer, the anchor coat layer, the conductive paste layer and the conductive adhesive layer are laminated in order, and the conductive adhesive layer has a number average molecular weight. The epoxy resin of 1500 or less is mix | blended. Therefore, according to the present invention, the adhesion between each layer is excellent, and even when the bending operation is repeated, the adhesion interface between the substrate and the conductive paste layer is not partially delaminated, and the electromagnetic wave shielding performance Thus, it is possible to obtain an electromagnetic wave shielding material for FPC in which the deterioration with time is suppressed.

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

DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... Anchor coat layer, 3 ... Conductive paste layer, 4 ... Conductive adhesive layer, 10, 11 ... Electromagnetic wave shielding material for FPC, 6 ... Support film, 7 ... Release film.

Claims (5)

A conductive adhesive layer bonded to the adherend by pressure heating,
The conductive adhesive layer contains a thermosetting adhesive, an epoxy resin having a number average molecular weight of 1500 or less, and conductive fine particles, and the number average molecular weight in the resin of the conductive adhesive layer. The conductive adhesive layer, wherein the concentration of the epoxy resin of 1500 or less is 15 wt% or more and 50 wt% or less of the total resin contained in the conductive adhesive layer.   The conductive adhesive layer according to claim 1, wherein the acid value of the thermosetting adhesive is 5 or more, and the thermosetting adhesive is a flame retardant polyurethane resin.   The conductive fine particles are at least one selected from the group of conductive fine particles composed of metal fine particles of silver, nickel, copper, and aluminum, and composite metal fine particles in which the surface of the metal fine particles is coated with another metal. The conductive adhesive layer according to claim 1 or 2.   An electromagnetic wave shielding material for FPC, comprising the conductive adhesive layer according to claim 1.   An FPC comprising the conductive adhesive layer according to claim 1.

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