JPH0799796B2 - Composite plate for electromagnetic wave shielding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has a thermoplastic resin film or sheet containing a small amount of conductive carbon black, which is integrally laminated on one or both sides of a metal foil or a metal plate. Between electronic circuit boards in electronic devices, whose surface has antistatic and insulating properties, and also has excellent mechanical strength, rigidity, impact resistance, folding resistance, etc. The present invention relates to a composite board suitable for electromagnetic wave shielding applications.

[Conventional technology]

Various electronic elements attached to an electronic circuit board in an electronic device may radiate unnecessary electromagnetic waves to the surroundings as they operate, causing malfunctions and noise in adjacent electronic elements.

Therefore, conventionally, in order to prevent a short circuit, a housing is formed of a sheet metal having a thermoplastic resin film or sheet attached to the surface thereof, and electromagnetic waves are shielded, or a sheet metal having a thermoplastic resin film or sheet attached to both surfaces thereof, or By inserting a metal foil between electronic circuit boards, capacitive coupling between the circuit boards is prevented.

However, generally, the thermoplastic resin film or sheet has both a high volume resistivity and a high surface resistivity value and is suitable as an insulating material, but due to the high surface resistivity value, it is very easily charged by friction or contact, When this is used as an electromagnetic wave shielding sheet metal or an insulating layer of a metal foil, the function of the IC attached to the electronic circuit board is destroyed by electrostatic discharge, so various methods for improving it have been proposed.

For example, (1) a method of applying an antistatic agent on the surface of a thermoplastic resin film or sheet.

(2) A method of applying a conductive paint on the surface of a thermoplastic resin film or sheet.

(3) As disclosed in JP-A-57-205145, there is a method of laminating a conductive layer on the surface of a thermoplastic resin film or sheet by coextrusion.

However, the method (1) has an antistatic effect immediately after coating, but it may flow out due to moisture during long use, or the antistatic agent may be removed by friction on the surface.
This is not a preferable method because it loses the antistatic effect and causes corrosion to the IC and the metal case.

In the method (2), the resin necessary for the adhesion of the base resin is limited, the coating is likely to be non-uniform, the surface layer is vulnerable to peeling, and the antistatic effect is lost. This is an unsuitable method because it may cause a fire.

On the other hand, the method (3) is very effective in maintaining the antistatic effect, but the surface resistivity is low and the insulation between the electronic circuit boards is maintained, but the insulation between the IC terminals is maintained. No, it's not the right way.

[Problems to be solved by the invention]

The present invention is to solve such drawbacks, one or both sides of a metal foil or a metal plate, a thermoplastic resin film or sheet containing a small amount of conductive carbon rack is integrally laminated, the surface of which is electrostatic and Suitable for electromagnetic wave shielding applications such as between electronic circuit boards in electronic devices, which have insulating properties, and also have excellent mechanical strength, rigidity, impact resistance, folding resistance, etc. It is intended to provide a composite board.

[Means for solving problems]

That is, the present invention contains 2 to 20 parts by weight of conductive carbon rack to 100 parts by weight of resin on one or both sides of a metal foil or a metal plate having a thickness of 20 to 2000 μm, and has a surface specific resistance value of 10 ¹⁰ It is characterized by integrally laminating a thermoplastic resin film or sheet having an Ω to 10 ¹⁶ Ω.

The present invention will be described in more detail below.

Metal foil or metal plate of the present invention (hereinafter referred to as electromagnetic wave shielding layer)
Is copper, zinc, brass, beryllium, tin, iron, steel, permalloy, or the like, and preferably a metal foil or a metal plate having a magnetic permeability of more than 100 is used in consideration of magnetic field shielding in the near field.

The thickness of the metal foil or metal plate is 20 to 2000 μm, preferably 30
If it is less than 20 μm, a sufficient electromagnetic wave shielding effect cannot be obtained. On the other hand, if it exceeds 2000 μm, it cannot be used for applications requiring lightweight and small size. When the metal foil or metal plate of the present invention which is easily oxidized is used, it is preferable to use a surface-treated one such as chromate treatment or zinc plating treatment for the purpose of preventing oxidation. Next, examples of the resin of the thermoplastic resin film or sheet (hereinafter referred to as the surface antistatic insulating layer) used in the present invention include general-purpose thermoplastic resins such as polyethylene resin, polypropylene resin, polystyrene resin, ABS resin, polyethylene terephthalate resin. And heat-resistant thermoplastic resins such as aromatic polyether resin, polycarbonate resin, polyether sulfone, and polyimide. Among them, polyethylene resin, polypropylene resin, polystyrene resin, and ABS resin, which have a small tan δ, are the most preferable in order to reduce the dielectric loss in the high frequency region.

Since the surface antistatic insulating layer of the present invention can impart physical properties such as mechanical strength, rigidity, impact resistance and folding strength by the metal foil or metal plate of the electromagnetic wave shielding layer, Such physical properties are not so strongly required, and it is important to sufficiently enhance the adhesiveness between the electromagnetic wave shielding layer and the adhesive layer.

For this purpose, the surface antistatic insulating layer may be added with an additive or another resin component, or a known means such as corona treatment or application of a pretreatment agent may be used.

The carbon black used in the present invention is, for example, a conductive carbon black satisfying the following characteristics.

 The structure is well developed.

 The particle size is small.

 Large surface area (large number of pores).

 There are few impurities that trap large electrons.

 Graphite conversion is progressing.

Further, the addition amount is 2 to 20 parts by weight, preferably 7 to 15 parts by weight. If it is less than 2 parts by weight, the surface specific resistance value of the surface antistatic insulating layer increases and the dielectric loss factor value further decreases. In addition, the antistatic performance is impaired, and it is not suitable for use as an insulating plate that electrically insulates an electronic circuit board in an electronic device from a metal housing.
If the amount exceeds 20 parts by weight, the surface specific resistance value decreases,
Insulation between IC terminals cannot be maintained, which is also not suitable for use as an insulating plate.

Next, in order to produce the product of the present invention, first, a thermoplastic resin film or sheet containing a small amount of conductive carbon black is prepared by a method such as T-die molding method inflation molding method / calender method and solvent cast method. After being formed, it can be obtained by integrating with a metal foil or a metal plate by a method such as extrusion lamination, dry lamination, and emulsion lamination.

Obtained by such a method, the total thickness of the electromagnetic shielding composite plate of the present invention having antistatic and insulating properties is 0.1 to 10 mm,
The thickness is preferably about 0.2 to 2 mm, and if the wall thickness is less than 0.1 mm, the strength as an insulating plate is insufficient, while if the wall thickness exceeds 10 mm, it is not preferable because the insertion space is limited.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 The impact-resistant polystyrene resin used was Denka Styrol HI-E-4, a trade name of Denki Kagaku Kogyo Co., Ltd., and the carbon black was Denka acetylene black, a trade name of Denka Kagaku Kogyo Co., Ltd. Acid is added and blended in the composition shown in the table, and the blended mixture is put into a Banbury mixer heated to 140 ° C. and melt-kneaded to form a mixture of 19
When it reached 0 ° C, it was taken out, immediately cooled into a sheet with a mixing roll, and pulverized into a pellet. This is the diameter
It is supplied into the extruder through the 40m / m extruder (L / D = 24) supply port, melted and supplied to a 200 ° C single-layer sheet die, with a wall thickness of 0.5m /
After forming a surface antistatic insulating sheet of m, one side of the sheet and 20 μm thick steel foil (TOYO STEEL CO., LTD. product name Ironfoil IF) are dry-laminated with urethane thread adhesive and integrated. As a result, the total thickness of the board is 0.
A 52 m / m composite plate was obtained. The adhesive force between the two layers of the obtained composite plate was sufficient and peeling was impossible. As shown in the table, this composite plate was excellent in all properties such as antistatic property, insulating electromagnetic shielding effect, and mechanical strength.

Example 2 A copper foil having a thickness of 20 μm similar to that of Example 1 was provided on both sides with a thickness of 0.25
Working under the same conditions as in Example 1 except that the m / m surface antistatic insulating sheet was dry laminated with a urethane thread adhesive to form a three-layer structure with a total composite plate thickness of 0.52 m / m. The composite plate was obtained.

As shown in the table, this composite plate was excellent in all properties such as antistatic property, insulating property and mechanical strength.

Example 3 As a carbon black to be mixed in the conductive layer, KETCHEN BLACK Japan EC Co., Ltd., trade name "KETCHEN BLACK E
C "was mixed in the composition shown in the table, and the same operation as in Example 1 was carried out to obtain a composite plate having a wall thickness of 0.52 m / m. As shown in the table, this composite plate was excellent in all properties such as antistatic property, insulating property, electromagnetic shielding effect and mechanical strength.

Example 4 In place of the impact-resistant polystyrene resin as the resin component of the surface antistatic insulating sheet, Denka Chemical Industry Co., Ltd. trade name "Denka ABS GR-2000" was used as the ABS resin, except that
Work was performed under the same conditions as in Example 1 to obtain a sheet having a wall thickness of 0.52 m / m. As shown in the table, this sheet was excellent in all properties such as antistatic property, insulating electromagnetic shielding effect and mechanical strength.

Example 5 A composite plate was obtained under the same conditions as in Example 1 except that a steel plate having a thickness of 1000 μm was used as the electromagnetic wave shielding layer and the total thickness of the composite plate was 1.5 m / m.

As shown in the table, this composite plate was excellent in all properties such as antistatic property, insulating property, electromagnetic shielding effect and mechanical strength.

Comparative Examples 1 and 2 The impact-resistant polystyrene resin is Denka Styrol HI-E-4, a trade name of Denki Kagaku Kogyo KK, and the carbon black is Denka acetylene black, a trade name of Denki Kagaku Kogyo Co., Ltd. Stearic acid was added and blended in the composition shown in the table. The blended mixture was put into a Banbury mixer heated to 140 ° C, and melt-kneaded to obtain a mixture of 190
When the temperature reached ℃, it was taken out, immediately cooled with a mixing roll into a sheet and crushed into pellets. Diameter 40
It is fed into the extruder from the feed port of the m / m extruder (L / D = 24), melted and fed to a 200 ° C single layer sheet die, with a wall thickness of 0.5 m / m
After forming the surface anti-static insulating sheet of, the iron foil with a thickness of 20 μm (product name: Ironfoil IF, manufactured by Toyo Steel Co., Ltd.) and urethane thread adhesive are dry laminated and integrated to form the entire plate. A composite plate with a thickness of 0.52 m / m was obtained.

The antistatic property, insulating property, electromagnetic shielding effect and physical property measurement results of this composite plate are shown in the table.

Comparative Example 3 A composite plate was obtained under the same conditions as in Comparative Example 1 except that a steel plate having a thickness of 5000 μm was used as the electromagnetic wave shielding layer and the total thickness of the composite plate was 5.5 m / m.

The antistatic property, insulating property, electromagnetic wave shielding effect and physical property measurement results of this composite plate are shown in the table.

The test methods in Examples and Comparative Examples were as follows.

1.Surface resistivity: JIS K-6911 compliant, Kawaguchi Denki Co., Ltd., room temperature measuring box, super insulation meter used 2. Dielectric loss factor: JIS K-6911 compliant, Ando Electric Co., Ltd. dielectric loss Using the measuring device 3. Charged charge: Rub the surface of the resin sheet with a dry cotton cloth (20 strokes) and measure the generated charge in the Faraday cage.

4. Electromagnetic wave shielding effect: As shown in the drawing, the sample was set in a conductive tube and the electromagnetic wave shielding effect due to impedance mismatch was measured.

5. Tensile strength: In accordance with JIS K-6734, a tensile test was performed with an Instron at a tensile speed of 50 mm for 1 minute, and the maximum load until breakage was measured and defined as the tensile strength.

6. Folding endurance: JIS-P-8115 MIT test of paper and paperboard was performed according to the folding endurance test method. Tension 500g,
It was bent at a speed of 175 times per minute, and the bending angle was 75 degrees. The test piece with the sample in the sheet flow direction is the vertical direction, and the test piece with the sample in the sheet flow direction is the horizontal direction, and the average value is determined according to JIS-Z-8401 (Rounding number). Indicated.

〔The invention's effect〕

As described above, the present invention is a metal foil or a metal plate, and a thermoplastic resin film or sheet containing a small amount of conductive carbon black, by integrally laminated, antistatic properties, insulation, electromagnetic wave shielding effect and There is an effect that a composite plate having excellent mechanical strength can be obtained.

[Brief description of drawings]

The drawings are schematic illustrations of an apparatus for measuring an electromagnetic wave shielding effect. 1 ... Waveguide, 2 ... Sample, 3 ... 50Ω coaxial cable, 4 ... Spectrum analyzer, 5 ... Tracking generator

Claims (1)

[Claims] 1. A metal foil or metal plate having a thickness of 20 to 2000 μm contains 2 to 20 parts by weight of a conductive carbon black with respect to 100 parts by weight of a resin, and has a surface specific resistance value of 10 ^10. A composite plate for electromagnetic wave shielding having an antistatic property and an insulating property, which is obtained by integrally laminating a thermoplastic resin film or a sheet having an Ω to 10 ¹⁶ Ω.