JP6920796B2 - Conductive adhesive sheet for FPC and FPC - Google Patents

Description

The present invention relates to a conductive adhesive sheet for FPC and an FPC using the same.

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 external dimensions of the housing small and easy to carry. Further, in order to reduce the external dimensions of the housing, the printed circuit board is divided into a plurality of parts, and the divided printed circuit boards are connected and wired using a flexible FPC to fold the printed circuit board. Or, it is being slid.
Further, in recent years, the electronic device malfunctions due to the influence of the electromagnetic wave noise received from the outside of the electronic device or the electromagnetic wave noise received between the electronic components arranged inside the electronic device. In order to prevent this, important electronic components and FPCs are covered with an electromagnetic wave shielding material.
A conductive adhesive sheet is used to connect the electromagnetic wave shielding material to the conductive circuit of the FPC. Further, in order to impart electromagnetic wave shielding property to the metal reinforcing plate, a conductive adhesive sheet is used for connecting the metal reinforcing plate and the conductor circuit of the FPC.

As a technique related to the above-mentioned conductive adhesive sheet, for example, Patent Document 1 describes a curable conductive adhesive composition containing a polyurethane resin, an epoxy resin, a conductive filler, and an additive. Have been described. It is described that the curable conductive adhesive composition described in Patent Document 1 can impart appropriate fluidity at the time of adhesion and can secure excellent adhesiveness by adopting the above configuration.

International Publication No. 2014/010524

In recent years, the conductive adhesive sheet used for FPC is required to have high flame retardancy in addition to good conductivity. In order to impart flame retardancy to the conductive adhesive sheet, it can be recalled that a flame retardant is added to the conductive adhesive composition used for the conductive adhesive sheet.
However, when the present inventors added a flame retardant to the conductive adhesive composition, it was found that both conductivity and flame retardancy could not be achieved at the same time.
The present invention has been made in view of the above circumstances, and is a conductive adhesive sheet for FPC capable of satisfying both conductivity and flame retardancy, and further satisfying higher flame retardancy than before, and a conductive adhesive sheet for FPC. An object of the present invention is to provide an FPC using a conductive adhesive sheet for FPC.

As a result of repeated studies to achieve the above object, the present inventors have achieved both conductivity and flame retardancy by using a conductive adhesive composition containing a resin material and a conductive material in a specific ratio. It has been found that a conductive adhesive sheet for FPC that satisfies the requirements can be obtained.

That is, the present invention has adopted the following configuration.
[1] The support film has a conductive adhesive layer laminated on one surface of the support film, and the conductive adhesive layer includes a phosphorus-containing resin, silver-coated copper particles, and the like. The conductive adhesive composition containing the above is used as a forming material, and the conductive adhesive composition contains 100 parts by mass or more and 200 parts by mass or less of the silver-coated copper particles with respect to 100 parts by mass of the phosphorus-containing resin. The phosphorus-containing resin contains 0.2 parts by mass or more of phosphorus with respect to 100 parts by mass of the phosphorus-containing resin, and the silver-coated copper particles have a silver coating ratio of 80% or more for FPC. Conductive adhesive sheet.
[2] The conductive adhesive sheet for FPC according to [1], wherein the combustion time is less than 5 seconds in the flame retardancy evaluation performed under the following conditions.
<Conditions>
≪Preparation of measurement sample≫
Ten conductive adhesive sheets for FPC are cut out to a size of 50 mm × 200 mm and placed at 23 ° C. and 50% humidity for 48 hours to prepare a measurement sample.
≪Evaluation conditions≫
The measurement sample prepared by the above method is wound around a rod having a diameter of 12.7 mm. Then, of the sample wound in a cylindrical shape, the inside of the portion within 75 mm from the upper end is fastened with pressure-sensitive tape, and the rod is pulled out. After that, the upper end of the measurement sample is closed so that there is no chimney effect during the measurement. Then, the measurement sample is placed vertically, and cotton wool is placed 300 mm below the measurement sample. After that, the burner is arranged so that the cylinder of the burner is located 10 mm from the lower end of the measurement sample. Then, a blue flame is indirectly flamed in the center of the lower end of the sample for 3 seconds, and the burning time of the measurement sample after deflaming is measured. The burning time of 10 measurement samples is performed in the same manner, and the average value of the burning time is calculated.
[3] The conductive adhesive sheet for FPC according to [1] or [2], wherein the silver coating ratio of the silver-coated copper particles is 95% or more.
[4] The conductive adhesive sheet for FPC according to any one of [1] to [3], wherein the silver-coated copper particles are dendritic.
[5] The conductive adhesive sheet for FPC according to any one of [1] to [4], wherein the silver-coated copper particles have an average particle size of 15 μm or more and 20 μm or less.
[6] The conductive adhesive sheet for FPC according to any one of [1] to [5], wherein the phosphorus-containing resin is a phosphorus-containing polyurethane resin.
[7] The conductive adhesive sheet for FPC according to [6], wherein the phosphorus concentration of the phosphorus-containing polyurethane resin is 1% by weight or more based on the total amount of the phosphorus-containing polyurethane resin.
[8] The conductive adhesive sheet for FPC according to any one of [1] to [7], wherein the conductive adhesive resin composition contains silica particles.
[9] The conductive adhesive sheet for FPC according to any one of [1] to [8], wherein the primary particle size of the silica particles is 10 nm or more and 20 nm or less.
[10] The conductive adhesive sheet for FPC according to any one of [1] to [9], which contains 1 part by mass or more and 15 parts by mass or less of the silica particles with respect to 100 parts by mass of the phosphorus-containing resin.
[11] The conductive adhesive sheet for FPC according to any one of [1] to [10], wherein the conductive adhesive resin composition contains a silane coupling agent.
[12] The FPC in which the conductive adhesive sheet for FPC according to any one of [1] to [11] is used to attach a metal reinforcing plate to the surface of the FPC.

According to the present invention, it is possible to provide a conductive adhesive sheet for FPC capable of satisfying both conductivity and flame retardancy, and an FPC using the conductive adhesive sheet for FPC.

It is schematic cross-sectional view which shows an example of the conductive adhesive sheet for FPC which concerns on this invention. It is schematic cross-sectional view which shows an example which the reinforcing plate was attached to FPC via the conductive adhesive sheet for FPC which concerns on this invention. FIG. 5 is a schematic cross-sectional view showing a conductive adhesive sheet with a metal reinforcing plate, in which the conductive adhesive sheet for FPC of the present invention is laminated on a metal reinforcing plate via a conductive adhesive layer. (A) is a schematic plan view of a simulated flexible substrate used in the method for evaluating conductivity, and (b) is a cross-sectional view taken along the line AA of FIG. 4 (a). (A) is a schematic plan view of a test piece for evaluating conductivity used in the method for evaluating conductivity, and (b) is a cross-sectional view taken along the line BB of FIG. 5 (a). It is a schematic diagram which shows the measurement sample used for flame retardancy evaluation. It is a schematic diagram of the test table for performing flame retardancy evaluation.

Hereinafter, the present invention will be described based on preferred embodiments.

<Conductive adhesive sheet for FPC>
The conductive adhesive sheet for FPC used in FPC of the present invention has a support film and a conductive adhesive layer laminated on one surface of the support film, and the conductive adhesive. The layer uses a conductive adhesive composition containing phosphorus-containing resin and silver-coated copper particles (hereinafter, referred to as "adhesive composition") as a forming material, and the conductive adhesive composition is The silver-coated copper particles are contained in an amount of 100 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the phosphorus-containing resin, and the phosphorus-containing resin contains 0.2 parts by mass of phosphorus with respect to 100 parts by mass of the phosphorus-containing resin. Including the above, the silver-coated copper particles are characterized by having a silver coating ratio of 80% or more.
Since the conductive adhesive sheet for FPC of the present invention is formed by using an adhesive composition containing a phosphorus-containing resin, it has high flame retardancy. Further, since silver-coated copper particles having a high coating ratio of 80% or more are used, they have high conductivity. Further, since the phosphorus-containing resin and the silver-coated copper particles are contained in a specific ratio, it is possible to provide a conductive adhesive sheet for FPC that satisfies both flame retardancy and conductivity.

FIG. 1 is a schematic cross-sectional view showing an example of a conductive adhesive sheet for FPC according to the present invention.
FIG. 2 is a schematic cross-sectional view showing an example in which a reinforcing plate is attached to an FPC via a conductive adhesive sheet for FPC according to the present invention.
FIG. 3 is a schematic cross-sectional view showing a conductive adhesive sheet with a metal reinforcing plate in which the conductive adhesive sheet for FPC of the present invention is laminated on a metal reinforcing plate via a conductive adhesive layer.

The conductive adhesive sheet 5 for FPC of the present invention shown in FIG. 1 is formed by laminating the conductive adhesive layer 4 on the peeled surface of the support film 1 whose one side has been peeled. The conductive adhesive layer 4 contains a phosphorus-containing resin 2 and silver-coated copper particles 3. Further, as shown in FIG. 3, the conductive adhesive sheet 5 for FPC is laminated on the metal reinforcing plate 6 via the conductive adhesive layer 4, then cut to a predetermined size, and is conductive with the metal reinforcing plate. As the sex-adhesive sheet 30, the support film 1 is removed and stored in a stacked state. The conductive adhesive sheet 30 with a metal reinforcing plate is a laminate of the metal reinforcing plate 6 and the conductive adhesive layer 4, and can be used as an electromagnetic wave shielding reinforcing plate for FPC in the embodiment of FIG. .. In FIG. 2, the FPC 20 has a mounting component 7 and a ground circuit 9 on a substrate film 8, and the ground circuit 9 is protected by a coverlay 12 provided with an insulating adhesive layer 10 on the insulating film 11. Is. A through hole 14 is provided in the coverlay 12, and the conductive adhesive layer 4 of the conductive adhesive sheet 30 with a metal reinforcing plate comes into contact with the ground circuit 9 through the through hole 14, whereby the metal reinforcing plate 6 shields the electromagnetic wave. Functions as a material.

The conductive adhesive sheet for FPC of the present invention has high flame retardancy.
Specifically, in the flame retardancy evaluation performed under the following conditions, the combustion time is preferably less than 5 seconds.
<Conditions>
≪Preparation of measurement sample≫
Ten conductive adhesive sheets for FPC were cut out to a size of 50 mm × 200 mm and placed under the condition of 23 ° C. and 50% humidity for 48 hours to prepare a measurement sample.
≪Evaluation conditions≫
The measurement sample prepared by the above method is wound around a rod having a diameter of 12.7 mm.
Then, of the sample wound in a cylindrical shape, the inside of the portion within 75 mm from the upper end is fastened with pressure-sensitive tape, and the rod is pulled out.
After that, the upper end of the measurement sample is closed so that there is no chimney effect during the measurement.
Then, the measurement sample is placed vertically, and cotton wool is placed 300 mm below the measurement sample.
After that, the burner is arranged so that the cylinder of the burner is located 10 mm from the lower end of the measurement sample.
Then, a blue flame is indirectly flamed in the center of the lower end of the sample for 3 seconds, and the burning time of the measurement sample after deflaming is measured.
The burning time of 10 measurement samples is performed in the same manner, and the average value of the burning time is calculated.

The evaluation method of flame retardancy evaluation will be described with reference to the drawings.
FIG. 6 shows a schematic diagram of a measurement sample used for flame retardancy evaluation. A conductive adhesive sheet for FPC is cut into a size of 50 mm × 200 mm, and 10 measurement samples 61 are prepared. It is preferable that the mark 62 is marked on the measurement sample 61 at a position 125 mm in length. The measurement sample prepared in this manner is placed under the condition of 23 ° C. and 50% humidity for 48 hours to be used as the measurement sample 61.
As shown in FIG. 6, the measurement sample is firmly wound in a cylindrical shape around the rod 63 having a diameter of 12.7 mm indicated by reference numeral 64.
The inside of the portion 75 mm from the upper end of the cylindrical measurement sample 61 thus obtained is firmly fastened with the pressure-sensitive tape 74, and then the rod 63 is pulled out. The upper end of the measurement sample 61 is closed so that there is no chimney effect during the measurement.

FIG. 7 shows a schematic view of the test table 71 for performing flame retardancy evaluation. A cylindrical measurement sample is vertically placed on the clamp 72 located at the tip of the arm 73.
The absorbent cotton 78 is placed 300 mm below the measurement sample 61, and the burner 75 is placed so that the burner cylinder is located 10 mm from the lower end of the measurement sample 61 (the position indicated by reference numeral 76 in FIG. 7), and the lower end of the sample is placed. Indirect flame of blue flame for 3 seconds in the center of.
Then, the flame was released, and the burning time of the measurement sample after the flame was released was measured. The burning time of 10 measurement samples is performed in the same manner, and the average value of the burning time is calculated.

In the present invention, the burning time measured by the above method is preferably within 5 seconds.
From the viewpoint of achieving higher flame retardancy, the time until extinguishing the flame is more preferably within 4 seconds, and particularly preferably within 3 seconds.
The result of flame retardancy calculated by this evaluation method indicates that the flame retardancy is higher than that of VTM-0, which is a criterion for determining flame retardancy according to the UL94 standard.

Hereinafter, each material used for the conductive adhesive sheet for FPC of the present invention will be described.

(Support film)
Examples of the support film 1 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 support film 1 is, for example, polyethylene terephthalate and the support film itself has a certain degree of peelability, the support film 1 is directly peeled off without being subjected to a peeling treatment. The conductive adhesive layer 4 may be laminated on the surface. Further, the surface of the support film 1 may be subjected to a peeling treatment for making it easier to peel the conductive adhesive layer 4 from the support film 1.
When the resin film used as the support film 1 does not have peelability, a peeling treatment is performed by applying a peeling agent such as an amino alkyd resin or a silicone resin and then heating and drying. Will be done. Since the conductive adhesive sheet 5 for FPC of the present invention is bonded to FPC, it is desirable not to use a silicone resin as this release agent. This is because when the silicone resin is used as the 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 support film 1, and further, it is conductive through the inside of the conductive adhesive layer 4. This is because there is a risk of migrating to the other surface of the sex adhesive layer 4. The silicone resin transferred to the surface of the conductive adhesive layer 4 may weaken the adhesive force of the conductive adhesive layer 4 to the metal reinforcing plate 6.
The thickness of the support film 1 used in the present invention is not particularly limited because it is excluded from the thickness of the conductive adhesive layer 4 when it is attached to the FPC and used, but it is usually about 12 μm to 150 μm. Is.

(Release film)
In the conductive adhesive sheet 5 for FPC according to the present invention shown in FIG. 1, a conductive adhesive layer 4 is laminated on one surface of a support film 1. Further, the conductive adhesive sheet 5 for FPC according to the present invention is a release film in which a conductive adhesive layer 4 is laminated on one surface of a support film 1 and a release agent layer is laminated on one surface of a base material. The structure may be such that the conductive adhesive layer 4 is bonded to the conductive adhesive layer 4 via the release agent layer.
Examples of the base material of the release film include polyester films such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene. A release agent such as an aminoalkyd resin or a silicone resin is applied to these resin films and then heat-dried to perform a release treatment. Since the conductive adhesive sheet for FPC of the present invention is bonded to FPC, it is desirable not to use a silicone resin as this release agent. This is because when the silicone resin is used as the release agent, a part of the silicone resin is transferred to the surface of the conductive adhesive layer in contact with the surface of the release film, and further, the conductive adhesive layer is passed through the inside of the conductive adhesive sheet for FPC. This is because there is a risk of shifting from the support film 1 to the support film 1. The silicone resin transferred to the surface of the conductive adhesive layer may weaken the adhesive force of the conductive adhesive layer. The thickness of the release film used in the present invention is not particularly limited, but is usually about 12 μm to 150 μm.

≪Conductive adhesive composition≫
The conductive adhesive composition used for forming the conductive adhesive layer of the conductive adhesive sheet for FPC of the present invention will be described. The adhesive composition contains a phosphorus-containing resin and silver-coated copper particles in a specific ratio.

[Phosphorus-containing resin]
The phosphorus-containing resin used in the present invention may be a phosphorus-containing resin containing phosphorus in the molecule (hereinafter, referred to as “introduction type”), and a phosphorus-containing resin obtained by adding a low molecular weight phosphorus-containing compound to the resin. (Hereinafter, referred to as "blend type") may be used.
The introduction-type phosphorus-containing resin means a resin having a structure in which a phosphorus atom is introduced into a main chain structure or a side chain structure.
For example, phosphorus-containing polyester resin, phosphorus-containing polyurethane resin, phosphorus-containing epoxy resin and the like derived from a compound containing phosphorus in the structure can be mentioned. Among these, a phosphorus-containing polyurethane resin is preferable.

From the viewpoint of obtaining higher flame retardancy, the introduction type phosphorus-containing resin contains 0.2 parts by mass or more of phosphorus with respect to 100 parts by mass of the phosphorus-containing resin, and is 1% by weight or more in 100 parts by mass of the phosphorus-containing resin. It is preferably 1.5% by mass or more, and particularly preferably 2.0% by mass or more. The upper limit is preferably 10% by weight or less, and more preferably 5% or less. If the phosphorus content is less than the above lower limit, flame retardancy cannot be sufficiently exhibited, and it becomes difficult to obtain a flame retardant conductive adhesive sheet for FPC.
As used herein, the term "phosphorus content" means the weight ratio of the phosphorus element itself in the resin.

Examples of the blend type phosphorus-containing resin include resins such as epoxy resin, acrylic resin, polyester resin, polyimide resin, and polyurethane resin to which a phosphorus-based flame retardant is added, and among these, phosphorus-based polyurethane resin is used. A phosphorus-containing resin to which a flame retardant is added is preferable.
In the present invention, a phosphorus-containing resin containing phosphorus in the molecule is preferable, and a phosphorus-containing polyurethane resin is particularly preferable, because higher flame retardancy can be imparted.

From the viewpoint of obtaining higher flame retardancy, the blend type phosphorus-containing resin contains 0.2 parts by mass or more of a phosphorus-based flame retardant with respect to 100 parts by mass of the phosphorus-containing resin, and 1 weight in 100 parts by mass of the phosphorus-containing resin. % Or more, more preferably 1.5% by mass or more, and particularly preferably 2.0% by mass or more. If the content of the phosphorus-based flame retardant is less than the above lower limit value, the flame retardant cannot be sufficiently exhibited, and it becomes difficult to obtain a flame-retardant conductive adhesive sheet for FPC.

[Silver-coated copper particles]
The silver-coated copper particles used in the present invention have a silver coating ratio of 80% or more, and are preferably 90% or more, more preferably 95% or more, from the viewpoint of obtaining higher conductivity.
Here, the term "silver-coated copper particles" means particles having a core-shell structure in the present invention, in which the core does not substantially contain silver while the shell is made of silver. In silver-coated copper particles, the silver shell is a coating or layer that at least partially covers the core.
The silver-coated copper particles used in the present invention are conductive particulate materials and can have various shapes such as spherical, flat, flake-like, and dendritic-like. In the present invention, the silver-coated copper particles are preferably dendritic.

As a method of setting the silver coverage of the silver-coated copper particles in the above-mentioned specific range, a silver-coated copper particle material that achieves the above-mentioned specific silver coverage may be purchased, or when the copper particles are coated with silver. By controlling the silver precipitation time, silver-coated copper particles that achieve the above-mentioned specific silver coverage may be obtained.

In the present invention, the average particle size of the silver-coated copper particles is preferably 15 μm or more and 20 μm or less.
In the present invention, the "average particle size" is a value obtained by measuring the size of particles in a suspension or emulsion of silver-coated copper particles using diffraction of a laser beam.
When the silver-coated copper particles are spherical, the average particle size can be calculated from the measured value of the diameter of the sphere, and when the silver-coated copper particles are shaped like flat, flake, or dendritic, the longest diameter is measured. The average particle size can be calculated.

In the present invention, the adhesive composition contains 100 parts by mass or more and 200 parts by mass or less of the silver-coated particles with respect to 100 parts by mass of the phosphorus-containing resin, and 110 parts by mass or more and 190 parts by mass or less. It is preferably 115 parts by mass or more and 185 parts by mass or less.
The conductive adhesive sheet for FPC of the present invention has both conductivity and flame retardancy by using an adhesive composition in which the ratio of the phosphorus-containing resin and the silver-coated copper particles is in the above-mentioned specific range. be able to.

[Silica particles]
In the present invention, it is preferable that the adhesive resin composition contains silica particles. When the adhesive resin composition contains silica particles, it is possible to prevent the silver-coated copper particles from settling. Further, since the cohesive force of the adhesive resin composition can be improved, the heat resistance of the conductive adhesive sheet for FPC and the adhesion to the substrate can also be improved.
In the present invention, the primary particle size of the silica particles is preferably 10 nm or more and 20 nm or less, and more preferably 12 nm or more and 18 nm or less.

The content of silica particles in the adhesive composition is preferably 1 part by mass or more and 15 parts by mass or less, and more preferably 5 parts by mass or more and 14 parts by mass or less with respect to 100 parts by mass of the phosphorus-containing resin.

[Silane coupling agent]
In the present invention, it is preferable that the adhesive resin composition contains a silane coupling agent. When the adhesive resin composition contains a silane coupling agent, the adhesive performance can be improved.

[Other ingredients]
In the present invention, other thermosetting resins, thermoplastic resins and the like can be added in addition to the above-mentioned components. Further, additives such as a curing accelerator, a polymerization inhibitor, a sensitizer, a flame retardant, and a thixotropic agent may be contained.
Among the above, as the cross-linking agent, a bifunctional or higher functional epoxy resin is preferable. Examples of such an epoxy resin include a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a phenol novolac type epoxy resin, and a glycidylamine type. Among them, a polyfunctional epoxy resin is preferable from the viewpoint of heat resistance. Examples of such a polyfunctional epoxy resin include jER (registered trademark) 154, jER157, jER1031, jER1032 (Mitsubishi Chemical Co., Ltd.), EPICLON (registered trademark) N-740, and EPICLON N-770 (DIC Corporation). , YDPN-638, YDCN-700, YH-434 (Nippon Steel & Sumikin Chemical Co., Ltd.), TETRAD (registered trademark) -X, TETRAD-C (Mitsubishi Gas Chemical Co., Ltd.), and the like, but are not particularly limited.

<FPC>
In the FPC of the present invention, the conductive adhesive sheet for FPC of the present invention is used to attach a metal reinforcing plate to the surface of the FPC.
The conductive adhesive sheet for FPC of the present invention can improve the efficiency of the work process of attaching the conductive adhesive sheet with a metal reinforcing plate to the FPC, and can contribute to the improvement of productivity, and is industrially effective. The utility value of is great.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these examples.

<Preparation of conductive adhesive composition>
Each component shown in Table 1 below was mixed to obtain a conductive adhesive composition of Compositions 1 to 9 and Comparative Compositions 1 to 4.
Specifically, the silver-coated copper particles, the silane coupling agent, the silica particles, and the cross-linking agent of each compounding ratio shown in Table 1 are added to 250 parts by mass of a 40% solution of the phosphorus-containing resin (resin component is 100 parts by mass). In addition, it was diluted with methyl ethyl ketone and toluene and mixed with stirring to obtain a conductive adhesive composition.

In Table 1, each component means the following materials. The values in [] in Table 1 are the compounding ratio (parts by mass). In Table 1, the "phosphorus content" is the weight ratio of the phosphorus element itself to the total amount of the phosphorus-containing polyurethane resin.
(A) -1: Phosphorus-containing polyurethane (manufactured by Toyobo Co., Ltd., trade name "UR-3575" (flame-retardant polyurethane resin, phosphorus-containing concentration: 2.5%, acid value: 10 KOHmg / g)).
-(A) -2: Phosphorus-containing resin obtained by adding a phosphorus-based flame retardant to polyurethane.
-(A) -3: Polyurethane.
-Silver-coated copper particles: Silver-coated copper (manufactured by Toda Kogyo Co., Ltd., product name: RM-D10).
・ Silane coupling agent: KBM-403 manufactured by Shin-Etsu Chemical Co., Ltd.
-Silica particles: manufactured by Nippon Aerosil Co., Ltd., trade name "R972" (hydrophobic fumed silica)
-Crosslinking agent: Toyobo, trade name "HY-30".

<Manufacturing of conductive adhesive sheets for FPC>
A polyethylene terephthalate (PET) film having a thickness of 50 μm, which had been peeled off on one side, was used as the support film 1.
The thickness of each of the conductive adhesive compositions of Compositions 1 to 9 and Comparative Compositions 1 to 4 obtained above was measured on the peeling-treated surface of the support film 1 with a dial gauge after drying. The film was applied so as to have a thickness of 40 μm, dried by heating at 150 ° C. for 3 minutes, and semi-cured to obtain conductive adhesive sheets for FPC of Examples 1 to 9 and Comparative Examples 1 to 4.

≪Evaluation of conductive adhesive sheet for FPC≫
The obtained conductive adhesive sheets for FPC of Examples 1 to 9 and Comparative Examples 1 to 4 were evaluated as follows.

[Flame retardation evaluation]
Combustion tests were carried out on the conductive adhesive sheets for FPC of Examples 1 to 9 and Comparative Examples 1 to 4.
As shown in FIG. 6, the conductive adhesive sheet for FPC was cut into a size of 50 mm × 200 mm, and 10 measurement samples 61 were prepared. The measurement sample 61 has a mark 62 at a position 125 mm in length. The prepared measurement sample was placed at 23 ° C. and 50% humidity for 48 hours to prepare a measurement sample 61.
As shown in FIG. 6, the measurement sample was firmly wound around a rod 63 having a diameter of 12.7 mm indicated by reference numeral 64 in a cylindrical shape.
The inside of the portion 75 mm from the upper end of the cylindrical measurement sample 61 was firmly fastened with the pressure-sensitive tape 74, and then the rod 63 was pulled out. The upper end of the measurement sample 61 was closed so that there was no chimney effect during the measurement.

A cylindrical measurement sample was vertically placed on the clamp 72 located at the tip of the arm 73 of the test table 71 shown in FIG.
The absorbent cotton 78 is placed 300 mm below the measurement sample 61, and the burner 75 is placed so that the burner cylinder is located 10 mm from the lower end of the measurement sample 61 (the position indicated by reference numeral 76 in FIG. 7), and the lower end of the sample is placed. A blue flame was indirectly burned in the center of the body for 3 seconds.
Then, the flame was released, and the burning time of the measurement sample after the flame was released was measured. The burning time of 10 measurement samples was performed in the same manner, the average value of the burning time was calculated, and the evaluation was performed according to the following evaluation criteria.
〇: The average value of the burning time was 3 seconds or less.
Δ: The average value of the burning time was longer than 3 seconds and 5 seconds or less.
X: The average value of the burning time was longer than 5 seconds.

[Adhesion]
A metal reinforcing plate made of SUS foil (manufactured by Nissin Steel Co., Ltd., material: SUS304) having a thickness of 30 μm is laminated with the conductive adhesive layer 4 side of the conductive adhesive sheet for FPC facing each other at 140 ° C., 1 m. After heat laminating under the condition of / min, the support film 1 was peeled off, and the conductive adhesive sheet for FPC was cut into dimensions of 50 mm × 120 mm. A polyimide film with a thickness of 50 μm (manufactured by Toray DuPont Co., Ltd., product number: 200H) was laminated so as to face the conductive adhesive layer side of the cut conductive adhesive sheet with a metal reinforcing plate, and 60 at 160 ° C. and 2.5 MPa. Specimens were obtained by hot pressing for minutes. Fix the SUS foil side with a thickness of 30 μm to the support bracket according to Method A (90 ° direction peeling) of 8.1.1 of JIS-C-6471 "Copper-clad laminate test method for flexible printed wiring board". Then, the polyimide film having a thickness of 50 μm that was adhered later was peeled off and the peeling force (N / cm) was measured. The sample of (Δ) was designated as “Δ”, and the sample of less than 5 N / cm was designated as “x”, and the samples were shown in Table 2.

[Conductivity]
A metal reinforcing plate 6 made of SUS foil (manufactured by Nissin Steel Co., Ltd., material: SUS304) having a thickness of 30 μm is overlaid with the conductive adhesive layer 4 side of the conductive adhesive sheet 5 for FPC facing each other. After heat laminating under the conditions of 140 ° C. and 1 m / min, it was cut into dimensions of width 15 mm × length 100 mm, and then the support film 1 was peeled off to obtain a conductive adhesive sheet 30 with a metal reinforcing plate.
Next, as shown in FIG. 4, strip-shaped copper foil pieces 9 having a width of 5 mm and a length of 50 mm are arranged in a row at a pitch interval of 30 mm on a substrate film 8 made of a polyimide film, and a plurality of copper foils are arranged. The pieces were placed to create a simulated flexible substrate.
Next, as shown in FIG. 5, a part of the strip-shaped copper foil piece 9 of the simulated flexible substrate is covered with a coverlay film 12 having a through hole 14 having a diameter of 1.5 mm, and further, the through hole is further covered. A conductive adhesive sheet 30 with a metal reinforcing plate is temporarily fixed via a conductive adhesive layer 4 so as to cover 14, and heat-pressed at 160 ° C. and 2.5 MPa for 60 minutes to evaluate conductivity. Got Next, the electrical resistance between the exposed portion of the copper foil piece 9 of the simulated flexible substrate and the metal reinforcing plate 6 of the conductive adhesive sheet 30 with the metal reinforcing plate is measured by a digital multimeter (TFF Caseley Co., Ltd.). Measured with Instruments, model: 2100/100), samples with electrical resistance of less than 0.5Ω (○), samples of 0.5Ω or more and less than 1.0Ω (△), samples of 1.0Ω or more Was (x).

[Resin flowability]
Whether or not there was resin flow from the end of the simulated flexible substrate obtained by the evaluation of conductivity was confirmed using a microscope at a magnification of 200 times. Samples with a resin flow protrusion of less than 100 μm (○), samples with a resin flow protrusion of 100 μm or more and less than 150 μm (Δ), and samples with a resin flow protrusion of 150 μm or more (×) bottom.

[Blocking resistance]
A polyimide film with a thickness of 25 μm (manufactured by Toray DuPont Co., Ltd., product number: 100H) is laminated with the conductive adhesive layer 4 side of the conductive adhesive sheet for FPC facing each other, and heat-laminated at 140 ° C. and 1 m / min. After that, the support film 1 was peeled off and cut into a size of 90 mm × 140 mm. A conductive adhesive sheet with a cut polyimide film was fixed to a SUS plate, a weight of 5 kg was placed on it, and the mixture was left at room temperature for 1 hour to prepare a sample. Draw a conductive adhesive sheet with a polyimide film from the SUS plate according to Method B (180 ° direction peeling) of 8.1.1 of JIS-C-6471 "Copper-clad laminate test method for flexible printed wiring board". It was peeled off and the peeling force (mN / 50 mm) was measured. A sample having a peeling force of less than 100 mN / 50 mm was marked with ◯, and a sample having a peeling force of less than 100 mN / 50 mm was marked with x.
In this evaluation method, as a model of the blocking phenomenon caused when two conductive adhesive sheets with metal reinforcing plates are stacked, one conductive adhesive sheet with metal reinforcing plates (on the side of the conductive adhesive layer) is used. A conductive adhesive sheet with a polyimide film is used as a substitute, and another conductive adhesive sheet with a metal reinforcing plate (on the side of the metal reinforcing plate) is replaced by a SUS plate.

As shown in the above results, the conductive adhesive sheets for FPCs of Examples 1 to 9 to which the present invention was applied had both flame retardancy and conductivity, and also had good adhesion.
Although the evaluation could be performed in Example 8, the overall evaluation was set to "Δ" because the particle size of the silver-coated copper particles was large and the formed adhesive layer contained air.
Examples 1 to 8 using phosphorus-containing polyurethane containing phosphorus in the molecule showed higher flame retardancy than Example 9 using a phosphorus-containing resin in which a phosphorus-based flame retardant was added to polyurethane.
On the other hand, in Comparative Example 1, the amount of silver-coated copper particles blended was large, and the adhesion was remarkably poor. Further, Comparative Examples 2 to 4 did not have good flame retardancy. In Comparative Examples 1 to 4 to which the present invention is not applied, both flame retardancy and conductivity could not be achieved at the same time.

1 ... Support film, 2 ... Phosphorus-containing resin, 3 ... Silver-coated copper particles, 4 ... Conductive adhesive layer, 5 ... Conductive adhesive sheet for FPC, 6 ... Metal reinforcing plate, 7 ... Mounting parts, 8 ... Substrate Film, 9 ... Earth circuit (copper foil piece), 10 ... Insulating adhesive layer, 11 ... Insulating film, 12 ... Coverlay, 14 ... Through hole, 20 ... FPC, 30 ... Conductive adhesive sheet with metal reinforcing plate, 61 ... Measurement sample, 62 ... Mark, 63 ... Rod, 64 ... Rod diameter, 74 ... Pressure sensitive tape, 71 ... Test table, 72 ... Clamp, 73 ... Arm, 78 ... Degreased cotton, 76 ... Flame contact position, 75 ... burner.

Claims (11)

It has a support film and a conductive adhesive layer laminated on one surface of the support film, and the conductive adhesive layer contains a phosphorus-containing resin and silver-coated copper particles. The conductive adhesive composition is used as a forming material, and the conductive adhesive composition contains 100 parts by mass or more and 200 parts by mass or less of the silver-coated copper particles with respect to 100 parts by mass of the phosphorus-containing resin, and contains the phosphorus. The resin contains 0.2 parts by mass or more of phosphorus with respect to 100 parts by mass of the phosphorus-containing resin, and the silver-coated copper particles have a silver coating ratio of 80% or more. A conductive adhesive sheet for FPC, characterized in that the burning time is less than 5 seconds.
<Conditions>
≪Preparation of measurement sample≫
Ten conductive adhesive sheets for FPC are cut out to a size of 50 mm × 200 mm and placed at 23 ° C. and 50% humidity for 48 hours to prepare a measurement sample.
≪Evaluation conditions≫
The measurement sample prepared by the above method is wound around a rod having a diameter of 12.7 mm.
Then, of the sample wound in a cylindrical shape, the inside of the portion within 75 mm from the upper end is fastened with pressure-sensitive tape, and the rod is pulled out.
After that, the upper end of the measurement sample is closed so that there is no chimney effect during the measurement.
Then, the measurement sample is placed vertically, and cotton wool is placed 300 mm below the measurement sample.
After that, the burner is arranged so that the cylinder of the burner is located 10 mm from the lower end of the measurement sample.
Then, a blue flame is indirectly flamed in the center of the lower end of the sample for 3 seconds, and the burning time of the measurement sample after deflaming is measured.
The burning time of 10 measurement samples is performed in the same manner, and the average value of the burning time is calculated. The conductive adhesive sheet for FPC according to claim 1, wherein the silver coating ratio of the silver-coated copper particles is 95% or more. The conductive adhesive sheet for FPC according to claim 1 or 2 , wherein the silver-coated copper particles are dendritic. The conductive adhesive sheet for FPC according to any one of claims 1 to 3 , wherein the silver-coated copper particles have an average particle size of 15 μm or more and 20 μm or less. The conductive adhesive sheet for FPC according to any one of claims 1 to 4 , wherein the phosphorus-containing resin is a phosphorus-containing polyurethane resin. The conductive adhesive sheet for FPC according to claim 5 , wherein the phosphorus concentration of the phosphorus-containing polyurethane resin is 1% by weight or more based on the total amount of the phosphorus-containing polyurethane resin. The conductive adhesive sheet for FPC according to any one of claims 1 to 6 , wherein the conductive adhesive resin composition contains silica particles. The conductive adhesive sheet for FPC according to claim 7 , wherein the primary particle size of the silica particles is 10 nm or more and 20 nm or less. The conductive adhesive sheet for FPC according to any one of claims 1 to 8 , wherein the silica particles are contained in an amount of 1 part by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the phosphorus-containing resin. The conductive adhesive sheet for FPC according to any one of claims 1 to 9 , wherein the conductive adhesive resin composition contains a silane coupling agent. The FPC in which the conductive adhesive sheet for FPC according to any one of claims 1 to 10 is used for adhering a metal reinforcing plate to the surface of the FPC.

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