JP2018010889A - Electromagnetic shielding material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave shielding material having excellent followability even with a high step. SOLUTION: A conductive adhesive layer 13 which does not contain a flame retardant different from a resin component is laminated on one side of a base material 11 made of a dielectric resin film, and the tensile elongation of the base material 11 is high. It is 100% or more. Further, the tensile elongation of the base material 11 is 100% or more and 300% or less. Further, the base material 11 is made of a solvent-soluble polyimide film. Further, the base material 11 is made of a polyimide film formed by using a polyimide material having an aliphatic unit having 3 or more carbon atoms between aromatic units. [Selection diagram] Fig. 1

Description

  The present invention relates to an electromagnetic shielding material that can be used for electromagnetic shielding such as a printed circuit board.

In portable electronic devices such as mobile phones, printed circuit boards on which electronic components are integrated are widely used. Further, an electromagnetic shielding material is used in order to prevent malfunction of the electronic device due to the influence of electromagnetic noise.
For example, Patent Document 1 discloses a shield in which a metal layer and an anisotropic conductive adhesive layer containing a heat-resistant phosphorus-containing thermosetting resin, a flame retardant, and a conductive filler are sequentially provided on one surface of an insulating layer. A film is described.
Patent Document 2 describes a curable electromagnetic shielding adhesive film having a curable conductive polyurethane polyurea adhesive layer containing a conductive filler and a film-like curable insulating polyurethane polyurea resin composition. Has been.

Japanese Patent No. 4914262 Japanese Patent No. 5104778

  As the printed board, a rigid board in which the insulating board is hard, a flexible board in which the insulating board is flexible, a rigid flexible board (flex rigid board) including a flexible part and a hard part, and the like are known. When there is a high step at the boundary between different parts of the board thickness, when the electromagnetic wave shielding material is stuck on the printed circuit board, if the electromagnetic wave shielding material does not sufficiently follow the printed circuit board step, there will be a gap in the level difference. There are problems such as electromagnetic wave intrusion or leakage, moisture intrusion, and dust adhesion. If the electromagnetic wave shielding material is forced to follow the step, the electromagnetic wave shielding characteristics may be deteriorated due to breakage or damage of the conductive layer constituting the electromagnetic wave shielding material.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the electromagnetic wave shielding material excellent in followable | trackability also with respect to a high level | step difference.

In order to solve the above-mentioned problems, the present invention is such that a conductive adhesive layer not containing a flame retardant different from a resin component is laminated on one side of a base material made of a dielectric resin film, An electromagnetic shielding material characterized by having a tensile elongation of 100% or more is provided.
It is preferable that the tensile elongation of the base material is 100% or more and 300% or less.

The substrate is preferably made of a solvent-soluble polyimide film.
The base material is preferably made of a polyimide film formed using a polyimide material having an aliphatic unit having 3 or more carbon atoms between aromatic units.

The conductive adhesive layer preferably has a thickness of 5 to 20 μm.
It is preferable that the conductive adhesive layer is an isotropic conductive adhesive layer.
The conductive adhesive layer preferably includes polyurethane.

The total thickness from the base material to the conductive adhesive layer is preferably 12 to 25 μm.
It is preferable that the base material is supported on a surface opposite to the side on which the conductive adhesive layer is laminated by a support film that can be peeled from the base material.

Moreover, this invention provides a mobile telephone provided with the said electromagnetic wave shielding material.
Moreover, this invention provides an electronic device provided with the said electromagnetic wave shielding material.

  According to the electromagnetic shielding material of the present invention, it is possible to provide an electromagnetic shielding material that is excellent in followability even with respect to a high level difference.

It is a schematic sectional drawing which shows an example of the electromagnetic wave shielding material of this invention. It is a schematic sectional drawing explaining the evaluation method of the level | step difference followable | trackability in an Example.

Hereinafter, preferred embodiments of the present invention will be described.
In FIG. 1, the schematic sectional drawing of the electromagnetic wave shielding material of this embodiment is shown. The electromagnetic wave shielding material 10 has a configuration in which a conductive adhesive layer 13 is laminated in this order in the thickness direction of the base material 11 on one surface of the base material 11 made of a dielectric resin film. When the electromagnetic shielding material 10 is attached to a printed circuit board or the like, which is an adherend, the outer surface is the dielectric base material 11, so that it is not necessary to further provide an electrically insulating coating material on the outer surface.

(Base material)
The substrate 11 is an insulating layer made of a dielectric resin film. Examples of the resin film constituting the substrate 11 include a polyimide resin film, a polyester resin film, and a polyamide resin film. When the substrate 11 is made of a polyimide resin film, it has high mechanical strength, heat resistance, insulation, and solvent resistance, which are characteristics of the polyimide resin, and is chemically stable up to about 260 ° C. Therefore, it is preferable.

  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 then heat the polyamic acid with a catalyst. By using it, it is dehydrated and made into a corresponding polyimide. However, the temperature of the heat treatment in the imidizing step is preferably in the temperature range of 200 ° C to 300 ° C. If the heating temperature is lower than this temperature, imidization may not proceed, which is not preferable. When the heating temperature is higher than the above temperature, the compound may be thermally decomposed, which is not preferable.

  In order to further improve the flexibility of the substrate 11, a very thin polyimide film having a thickness of less than 10 μm is preferable. Forming the base material 11 by laminating a thin polyimide film on one surface of the support film 21 is preferable because continuous conveyance along the longitudinal direction is facilitated even if the mechanical strength of the polyimide film itself is low. . The support film 21 is preferably a general-purpose resin film, for example, a polyethylene terephthalate (PET) resin film, in view of the balance between price and heat-resistant temperature performance. However, since the heat resistant temperature of PET is not as high as that of polyimide, it is not possible to adopt a method of applying an imide precursor and imidizing polyamic acid on PET.

  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, when the base material 11 consists of a solvent-soluble polyimide film, after apply | coating the coating liquid of the solvent-soluble polyimide which is a non-dehydration condensation type | mold on the single side | surface of the support body film 21, temperature is less than 200 degreeC heating temperature. It is possible to form a thin film resin film of a polyimide film by the method of drying with. Moreover, the anchor layer 12, the conductive adhesive layer 13, etc. can be continuously formed on one side of the support film 21 while the same support film 21 is conveyed along the longitudinal direction. Thereby, it is also possible to produce the electromagnetic shielding material 10 by a roll to roll, and it is excellent in workability and productivity.

  The non-dehydrating condensation type solvent-soluble polyimide used for the substrate 11 is not particularly limited, but a commercially available solvent-soluble polyimide coating solution 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 21 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 substrate 11 (for example, the thickness of the polyimide film) is preferably 1 to 9 μm. It is technically difficult to form a polyimide film with a thickness of less than 0.8 μm because the mechanical strength of the formed film is weak. Moreover, when the thickness of the base material 11 exceeds 10 μm, it is difficult to obtain the electromagnetic wave shielding material 10 that is thin and has excellent step following ability. Moreover, when the thickness of the base material 11 is thinner than about 7 μm, it is difficult to adjust the tension when winding on a roll. For this reason, it is preferable that a thin polyimide film is laminated on one side of the support film 21. Alternatively, it is preferable to form the base material 11 after the conductive adhesive layer 13 and the anchor layer 12 are formed on the release film 22 in advance.
The thickness in the case of using the substrate 11 made of only a thin polyimide film without using the support film 21 is preferably about 1 to 9 μm.

  Moreover, since the base material 11 of this embodiment improves the followable | trackability with respect to the level | step difference of the printed circuit board which is a to-be-adhered body, it is preferable that tensile elongation is high. The tensile elongation of the substrate 11 is preferably 100% or more. Moreover, although the upper limit of the tensile elongation of the base material 11 is not specifically limited, 300% or less can be illustrated. It is preferable that the elastic modulus of the base material 11 is 1.0 GPa or more and 2.5 GPa or less. When the substrate 11 having a high tensile elongation is composed of a polyimide film, for example, a polyimide film formed using a polyimide material having an aliphatic unit having 3 or more carbon atoms between aromatic units is preferable. Further, the aliphatic unit preferably contains a polyalkyleneoxy group having an alkylene group having about 1 to 10 carbon atoms.

Moreover, the water vapor permeability of the polyimide film used in the substrate 11 of the present embodiment is preferably 500 g / m ² · day or more. In the case where the water vapor permeability is lower than 500 g / m ² · day, in the heating process such as solder reflow after coating the printed circuit board with the electromagnetic wave shielding material 10, outgas from the residual solvent and adhesive of each layer, There is a possibility that the respective layers may be separated by water vapor generated by suddenly heating the moisture in the film. There is no particular upper limit to the water vapor transmission rate, but as long as the same material is used, the water vapor transmission rate is inversely proportional to the thickness. Therefore, when the water vapor transmission rate is increased by reducing the thickness, the water vapor transmission rate falls within the above range. It is preferable.

(Support film)
The support film 21 can be peeled off from the substrate 11 when the electromagnetic shielding material 10 is used. Examples of the substrate of the support film 21 include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene. The thickness of the support film 21 is not particularly limited because it is excluded from the total thickness of the electromagnetic wave shielding material 10 when it is used while being coated on a printed circuit board, but is usually about 12 to 150 μm.

  When the base material of the support film 21 has a certain degree of peelability on the base material itself, such as polyethylene terephthalate (PET), for example, the release treatment is not performed on the support film 21. The base material 11 made of the applied dielectric thin film resin film may be directly laminated, or the surface of the support film 21 is subjected to a peeling treatment for facilitating the peeling of the base material 11. Also good. Moreover, when the base material of the support film 21 does not have releasability, a release treatment such as amino alkyd resin or silicone resin can be applied and then dried by heating to perform a release treatment. It is desirable not to use a silicone resin for the release agent applied to the support film 21. When the silicone resin is used as a release agent, a part of the silicone resin is transferred to the surface of the base material 11 in contact with the surface of the support film 21, and further to the surface of the conductive adhesive layer 13 through the inside of the electromagnetic wave shielding material 10. The silicone resin may migrate and weaken the adhesive force of the conductive adhesive layer 13.

(Anchor layer)
In the electromagnetic wave shielding material 10 of the present embodiment, the anchor layer 12 can be used in order to improve the adhesion between the base material 11 and the conductive adhesive layer 13. The anchor layer 12 is a thin film adhesive layer that bonds the substrate 11 and the conductive adhesive layer 13 together. When the adhesiveness of the conductive adhesive layer 13 to the base material 11 is sufficient, the anchor layer 12 can be omitted.

  The adhesive resin used for the anchor layer 12 is preferably a polyester resin, polyurethane resin, (meth) acrylic resin, polyethylene resin, polystyrene resin, polyamide resin or other thermoplastic resin, epoxy resin, amino resin, polyimide resin, ( A thermosetting resin such as (meth) acrylic resin may be used. Particularly preferable as the adhesive resin for the anchor layer 12 is an adhesive resin composition for crosslinking a polyester resin composition having an epoxy group, or an adhesive resin composition in which an epoxy resin is mixed as a curing agent with a polyurethane resin. is there. For this reason, the anchor layer 12 has a harder physical property than the base material 11 which consists of a thin film of a polyimide film. 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 thickness of the anchor layer 12 is preferably about 0.05 to 1 μm. With such a film thickness, sufficient adhesion with the conductive adhesive layer 13 can be obtained. When the thickness of the anchor layer 12 is 0.05 μm or less, the adhesion between the base material 11 and the conductive adhesive layer 13 may be reduced. Moreover, since the cost will increase when the thickness of the anchor layer 12 exceeds 1 μm, it is not preferable.

(Conductive adhesive layer)
The conductive adhesive layer 13 is an adhesive layer for adhering the electromagnetic shielding material 10 to an adherend such as a printed board. The conductive adhesive layer 13 is preferably not a pressure-sensitive adhesive layer exhibiting pressure-sensitive adhesive properties at room temperature, but a thermosetting adhesive layer by heating and pressing. Thereby, even when the printed circuit board is repeatedly bent, the adhesive force is unlikely to decrease.

  As the thermosetting adhesive used for the conductive adhesive layer 13, generally used are acrylic adhesive, polyurethane adhesive, epoxy adhesive, rubber adhesive, silicone adhesive, and the like. A thermosetting adhesive. However, in addition to the resin component, a thermosetting adhesive that is made flame retardant by mixing a flame retardant such as phosphorous or bromine, etc., causes the conductive adhesive layer 13 to be too soft, and follows the step. Since there is a possibility that the electrical conductivity of the resin may deteriorate, it is not preferable. A polyurethane resin containing phosphorus in the molecular structure of the resin can be used as a thermosetting adhesive by using a phosphorus-containing compound as a polyol compound or polyisocyanate compound as a raw material of polyurethane. It is preferable that the thermosetting conductive adhesive layer 13 includes a phosphorus-containing polyurethane resin composition and an epoxy resin.

The electroconductive fine particles mix | blended with the electroconductive adhesive layer 13 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 in which other metal is coated on the surface of these metal fine particles. Can be appropriately selected and used.
Further, in the above-described conductive adhesive, conductivity is exhibited by contact between the conductive particles and contact between the conductive particles and the printed circuit board as the adherend. For this reason, when a large amount of a conductive material is contained, excellent conductivity can be obtained. However, the adhesive strength is reduced, and when the content of the conductive material is reduced, the adhesive strength is improved. There is a conflicting problem of lowering. For this reason, the compounding quantity of electroconductive fine particles is about 100-500 weight part normally with respect to 100 weight part of adhesive agents (solid content), More preferably, it is 150-450 weight part.

  Moreover, as a conductive adhesive which comprises the conductive adhesive layer 13, an isotropic conductive adhesive containing conductive fine particles is preferable. As this isotropic conductive adhesive, a known one can be used. For example, an adhesive having an insulating thermosetting resin such as an epoxy resin as a main component and conductive fine particles dispersed therein can be used. Examples of the conductive fine particles used in the isotropic conductive adhesive include one or more metal fine particles such as gold, silver, zinc, tin, and solder, or resin particles plated with a metal. . It is preferable that the conductive fine particles have a dendritic shape or a needle shape. With such a shape, when heat and pressure treatment is performed on the printed circuit board of the adherend by the pressure bonding member, the conductive fine particles bite into the conductor wiring of the printed circuit board with a low pressure, and isotropic conductivity. It becomes possible to reduce the electrical resistance between the adhesive layer and the conductor wiring.

  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 Z 0237. A range of 5 to 30 N / inch is preferable under the condition that the adhesive strength to the adherend surface is a peeling angle of 180 ° peel and a peeling speed of 300 mm / min. When the adhesive force is less than 5 N / inch, for example, the electromagnetic shielding material 10 attached to the printed circuit board may be peeled off or floated. The conditions for heat and pressure adhesion to the printed circuit board 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.

  The thickness of the conductive adhesive layer 13 is preferably 5 to 20 μm. Thereby, the total thickness of the electromagnetic wave shielding material 10 including the thickness of the conductive adhesive layer 13 is reduced, and the step following property is improved. If the thickness of the conductive adhesive layer 13 is less than 5 μm, the function of the electromagnetic wave shielding material 10 as a conductive layer is not preferable. If the thickness of the conductive adhesive layer 13 is thicker than 20 μm, it cannot cope with the recent thinning of the information terminal and the cost increases, which is not preferable.

(Light absorber)
In order to impart light shielding properties to the electromagnetic wave shielding material 10, a light absorbing material may be included in any layer constituting the electromagnetic wave shielding material 10 excluding the support film 21 and the release film 22. Examples of the layer that can contain a light absorbing material for this purpose include any one layer or two or more layers of the substrate 11, the anchor layer 12, and the conductive adhesive layer 13. Examples of the light absorber include one or more black pigments or colored pigments selected from the group consisting of non-conductive carbon black, graphite, aniline black, cyanine black, titanium black, black iron oxide, chromium oxide, and manganese oxide. It is done. For the purpose of improving the appearance in a state where the electromagnetic wave shielding material 10 is attached to an adherend such as a printed circuit board, one or both of the base material 11 and the anchor layer 12 which are outside the electromagnetic wave shielding material 10 are light absorbing materials. It is preferable to contain.

  The light transmittance of the electromagnetic wave shielding material 10 excluding the support film 21 and the release film 22 is preferably 5% or less. Examples of the light transmittance include visible light transmittance and total light transmittance. When the base material 11 is comprised from a solvent soluble polyimide film, the base material 11 may contain a light absorber.

  In order to effectively reduce the light transmittance, a black pigment such as carbon black is preferable among the light absorbing materials. The light absorbing material composed of a black pigment or a colored pigment is preferably contained at 0.1 to 30% by weight in any layer. 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. The thickness of the layer containing the light absorber is preferably larger than the particle size of the light absorber so that the fine particles of the light absorber are not exposed. 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.

(Peeling film)
A release film 22 can be provided on the surface of the conductive adhesive layer 13 in order to protect the conductive adhesive layer 13. The release film 22 can be peeled from the conductive adhesive layer 13 when the electromagnetic wave shielding material 10 is used. Examples of the base material of the release film 22 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. It is desirable not to use a silicone resin for the release agent applied to the release film 22. If silicone resin is used as a release agent, the adhesive strength of the conductive adhesive layer 13 may be weakened. The thickness of the release film 22 is not particularly limited because it is excluded from the total thickness of the electromagnetic wave shielding material 10 when used by being attached to a printed circuit board, but is usually about 12 to 150 μm.

  The total thickness of the electromagnetic wave shielding material 10 is preferably in the range of 12 to 25 μm, and more preferably 12 to 16 μm. Here, the total thickness of the electromagnetic wave shielding material 10 means the total thickness from the base material 11 to the conductive adhesive layer 13, and includes the thickness of the base material 11 and the thickness of the conductive adhesive layer 13.

(Printed board)
As a printed circuit board in which the electromagnetic wave shield of the present invention is used, a rigid substrate having a hard insulating substrate, a flexible substrate having a flexible insulating substrate, a rigid flexible substrate including a flexible portion and a hard portion (flex rigid substrate) Substrate). Examples of the step include 50 μm or more, and further 300 μm or more.

  The electromagnetic wave shielding material laminate 20 in which one or both of the support film 21 and the release film 22 are laminated on one side or both sides of the electromagnetic wave shielding material 10 is excellent in handleability even if the total thickness of the electromagnetic wave shielding material 10 is thin. . When adhering the electromagnetic shielding material 10 to the printed circuit board of the adherend, at least the release film 22 is peeled off and the surface of the conductive adhesive layer 13 is made to face the adherend. When step followability is required, the electromagnetic wave shielding material 10 is superposed on the adherend in a state where the total thickness is thin except for the support film 21 and the release film 22. Thereafter, preferably, the conductive adhesive layer 13 is thermally cured by heating and pressing, and the electromagnetic shielding material 10 is adhered to the adherend.

  The electronic device in which the electromagnetic wave shield of the present invention is used is not particularly limited, and examples thereof include a mobile phone, a notebook computer, a mobile terminal, and a tablet terminal. These electronic devices can include a printed circuit board to which the electromagnetic wave shield of the present invention is attached.

  Hereinafter, the present invention will be described specifically by way of examples.

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 a support film. Solvent-soluble, comprising 1% by weight of non-conductive carbon black as a light absorbing material black pigment on one side of the support film, based on a solid content of solvent-soluble polyimide having a tensile elongation of 170% after drying. The polyimide coating solution was cast and dried so that the thickness after drying was 4 μm, and a base material made of a dielectric thin film resin film was laminated. In addition, in order to measure the tensile elongation of the base material, a base material for measuring the tensile elongation was prepared in the same manner as in the production of the electromagnetic shielding material, and the base material was peeled off from the support film. −650 According to the method of 2.4.19, the tensile elongation was measured and found to be 170%.
Separately, 3.9 parts by weight of a polyfunctional epoxy resin 70% solution (Toyobo: HY-30) with an average particle diameter of 16 nm is 100 parts by weight of a 40% solution of phosphorus-containing polyurethane resin (Toyobo: UR3575). 2.1 parts by weight of fumed silica (manufactured by Nippon Aerosil Co., Ltd .: R972), 0.42 parts by weight of silane coupling agent (manufactured by Shin-Etsu Chemical Co., Ltd .: KBM-403) as an additive, silver hybrid copper (Fukuda Metals) 192 parts by weight of Foil Powder Industrial Co., Ltd .: FCC-TBX) were sequentially added, diluted with methyl ethyl ketone and toluene, and stirred and kneaded to obtain a conductive adhesive solution. The ratio of silver hybrid copper to 100 parts by weight of the adhesive (solid content) obtained by adding the phosphorus-containing polyurethane resin and the polyfunctional epoxy resin is about 449 parts by weight. Example 1 was obtained by laminating the conductive adhesive layer on the base material laminated on one side of the support film so that the thickness after drying was 10 μm. An electromagnetic shielding material was obtained.

(Example 2)
The electromagnetic wave shielding material of Example 2 was obtained in the same manner as in Example 1 except that a base material was formed by adding non-conductive carbon black to a solvent-soluble polyimide coating solution having a tensile elongation of 120% after drying. Obtained.

(Example 3)
Without adding non-conductive carbon black to a solvent-soluble polyimide coating solution having a tensile elongation of 170% after drying, the substrate was formed so that the thickness after drying was 4 μm. On top of this, a non-conductive carbon black as a black pigment for the light absorbing material and a polyester resin composition having a heat resistant temperature of 260 to 280 ° C. are mixed and dried using a coating liquid for forming an anchor layer. The electromagnetic wave shielding material of Example 3 was applied in the same manner as in Example 1 except that a conductive adhesive layer was formed on the anchor layer after applying and laminating the anchor layer so that the subsequent thickness was 1 μm. Obtained.

Example 4
Without adding non-conductive carbon black to the solvent-soluble polyimide coating solution having a tensile elongation of 120% after drying, the substrate is formed so that the thickness after drying becomes 4 μm, and is added to the conductive adhesive solution. An electromagnetic wave shielding material of Example 4 was obtained in the same manner as in Example 1 except that nonconductive carbon black was mixed to form a conductive adhesive layer.

(Example 5)
An electromagnetic wave shielding material of Example 5 was obtained in the same manner as in Example 1 except that the conductive adhesive layer was formed using a polyurethane resin not containing phosphorus.

(Comparative Example 1)
The electromagnetic wave shielding material of Comparative Example 1 was prepared in the same manner as in Example 1 except that a base material was formed by adding non-conductive carbon black to a solvent-soluble polyimide coating solution having a tensile elongation of 50% after drying. Obtained.

(Comparative Example 2)
The electromagnetic wave shielding material of Comparative Example 2 was used in the same manner as in Example 3 except that a support film was not used and a polyimide film made of a thermosetting polyimide having a thickness of 10 μm and a tensile elongation of 62% was used as the base material. Got.

(Comparative Example 3)
A conductive adhesive layer is formed using a conductive adhesive solution in which 15% by weight of a phosphorus-based flame retardant (Fushimi Pharmaceutical: FP-110) is added to a polyurethane resin not containing phosphorus. An electromagnetic wave shielding material of Comparative Example 3 was obtained in the same manner as Example 5 except that.

(Evaluation method for step following ability)
As shown in FIG. 2, a test substrate 30 provided with a hard substrate portion 33 and a terminal portion 31 on a flexible substrate portion 32 was prepared, and the electromagnetic wave shielding material 10 was stacked thereon. The length between the terminal portions 31 formed on both ends of the flexible substrate portion 32 is 50 mm. The step formed by the hard substrate portion 33 with respect to the flexible substrate portion 32 has a height of 0.3 mm (300 μm) and a width of 30 mm. The length of the hard substrate portion 33 is 30 mm, and the length of the opening 35 between the terminal portion 31 and the hard substrate portion 33 is 10 mm on each of the left and right sides.

  The exposed portion 34 for measuring the inter-terminal resistance on the terminal portion 31 is left, and the end portion of the electromagnetic wave shielding material 10 covers a part on the terminal portion 31, and the surface of the electromagnetic shielding material 10 has a conductive adhesive surface. It piled up so that the opening part 35 might be covered, and it hot-pressed on 160 degreeC, 2.5 Mpa, and the conditions for 65 minutes, and obtained the evaluation sample of followable | trackability. Observe the cross section of the obtained sample. If the electromagnetic shielding material follows the center step, it will be “Yes”. If the electromagnetic shielding material does not follow, the electromagnetic shielding material will float from the test substrate, creating a gap. The case where the film of the electromagnetic wave shielding material was cut at the corner of “「 ”was marked“ x ”.

(Conductivity evaluation method)
The resistance between terminals at both ends of the sample obtained by the step follow-up evaluation method is measured with a digital multimeter (TFF Keithley Instruments, model: 2100/100). “Δ”, 2Ω or more was defined as “x”.

(Flame retardancy evaluation method)
The obtained electromagnetic shielding material was hot-pressed on a polyimide film having a thickness of 25 μm under conditions of 160 ° C., 4.5 MPa, 65 minutes, and then a sample for evaluation of flame retardancy was obtained. In addition, when the electromagnetic wave shielding material had a support body film, it heat-pressed to the polyimide film, having laminated | stacked on the electromagnetic wave shielding material, Then, the support body film was peeled off.
The flame retardancy is evaluated according to the method of UL-94 Thin Material Vertical Combustion Test (ASTM D4804). When the flame retardancy is equivalent to VTM-0, “◯”, when not flame retardancy (VTM-2) Non-conformity) was set to “x”.

(Method for evaluating heat resistance)
The obtained electromagnetic shielding material was hot-pressed on a polyimide film having a thickness of 25 μm under the conditions of 160 ° C., 2.5 MPa, and 65 minutes to obtain a sample for heat resistance evaluation. A test piece was cut to a size of 2.5 cm × 5 cm, dipped in a solder bath at 290 ° C. for 10 seconds, and then pulled up. The external appearance of the electromagnetic shielding material after immersion in the solder bath is visually inspected for abnormalities such as deformation or shrinkage. did.

(Test results)
About Examples 1-6 and Comparative Examples 1-2, evaluation of the electromagnetic wave shielding material was performed by the above evaluation method, and the obtained evaluation results are shown in Tables 1-2. “None” written in the thickness column means that the layer is not provided. In the column of polyimide material of the polyimide base material, “PI1”, “PI2”, “PI3”, and “PI4” are polyimides used in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, respectively. means. In the column of the adhesive resin of the conductive adhesive layer, “PU1” means a heat-adhesive adhesive containing the flame-retardant polyurethane used in Example 1, and “PU2” It means a heat-adhesive adhesive containing the polyurethane used. Moreover, the phosphorus content rate of a conductive adhesive layer represents content of the phosphorus atom with respect to resin content.

  According to the results of the followability test shown in Tables 1 and 2, it can be seen that when the tensile elongation of the substrate is 100% or more, the followability and conductivity are improved. In other words, when the tensile elongation of the base material is 100% or less, it cannot follow the level difference of the test substrate, and a gap is formed between the test substrate and the conductive adhesive layer breaks down. And conductivity deteriorated. Furthermore, according to Examples 1-4, favorable flame retardance was securable by using phosphorus containing flame retardant resin for a conductive adhesive.

Furthermore, as shown in Comparative Example 3, when a commercially available phosphorus-based flame retardant was added to a polyurethane resin not containing phosphorus, although the flame retardancy and followability could be secured, the conductive adhesive layer was too soft. As a result, the conductive adhesive layer was pushed out at the corner of the step, and the conductivity deteriorated. That is, by using a phosphorus-containing polyurethane resin, it was possible to obtain an electromagnetic wave shielding material for FPC having good flame retardancy, followability, and conductivity.
Further, in the case of Comparative Example 1 using a solvent-soluble polyimide having a tensile elongation of 50%, water vapor caused by moisture in the base film, unreacted substances, Outgas due to low molecular components cannot pass, resulting in poor appearance such as foaming. That is, when a solvent-soluble polyimide having a tensile elongation of 100% or more as in Examples 1 to 5 was adopted, the gas permeability of the substrate was high, and the moisture and outgas mentioned above passed through and heated rapidly. Even in this case, it was possible to obtain an electromagnetic wave shielding material with good heat resistance that does not cause poor appearance such as foaming.

DESCRIPTION OF SYMBOLS 10 ... Electromagnetic shielding material, 11 ... Base material, 12 ... Anchor layer, 13 ... Conductive adhesive layer, 20 ... Electromagnetic shielding material laminated body, 21 ... Support film, 22 ... Release film, 30 ... Test substrate, 31 ... Terminal part, 32 ... Flexible substrate part, 33 ... Hard substrate part.

Claims (11)

  A conductive adhesive layer that does not contain a flame retardant different from the resin component is laminated on one side of a base material made of a dielectric resin film, and the tensile elongation of the base material is 100% or more. An electromagnetic shielding material characterized by   The electromagnetic shielding material according to claim 1, wherein the tensile elongation of the substrate is 100% or more and 300% or less.   The electromagnetic shielding material according to claim 1, wherein the substrate is made of a solvent-soluble polyimide film.   The said base material consists of a polyimide film formed using the polyimide material which has a C3 or more aliphatic unit between aromatic units, The any one of Claims 1-3 characterized by the above-mentioned. The electromagnetic wave shielding material as described in 2.   The electromagnetic shielding material according to claim 1, wherein the conductive adhesive layer has a thickness of 5 to 20 μm.   The electromagnetic shielding material according to claim 1, wherein the conductive adhesive layer is an isotropic conductive adhesive layer.   The electromagnetic shielding material according to claim 1, wherein the conductive adhesive layer contains polyurethane.   The electromagnetic wave shielding material according to any one of claims 1 to 7, wherein a total thickness from the base material to the conductive adhesive layer is 12 to 25 µm.   The said base material is supported by the support body film which can be peeled from the said base material in the surface on the opposite side to the side on which the said conductive adhesive layer was laminated | stacked. 2. The electromagnetic shielding material according to item 1.   A mobile phone comprising the electromagnetic shielding material according to claim 1.   An electronic device provided with the electromagnetic wave shielding material according to claim 1.

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