Compositions – Electrically conductive or emissive compositions – Elemental carbon containing
Reexamination Certificate
2000-04-03
2002-02-05
Lam, Cathy (Department: 1775)
Compositions
Electrically conductive or emissive compositions
Elemental carbon containing
C252S512000, C442S006000, C442S117000
Reexamination Certificate
active
06344155
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrically conductive adhesive composition and an electrically conductive adhesive sheet having flexibility and folding endurance feasible for use as a shield against electromagnetic waves in a flexible printed circuit (FPC), an electromagnetic wave shield material formed by integrating these with an electrically conductive fiber sheet, and an electromagnetic-wave-shield-functioning flexible printed wiring board formed by laminating the electromagnetic wave shield material on a flexible substrate.
DESCRIPTION OF THE PRIOR ART
With regard to an electromagnetic wave shield of a cable for connecting electronic machines or devices, conventionally, a group of shield cables obtained by braiding individual conductive cables is used. Since, however, a group of bundled shield cables in a larger number is used, it is difficult to attain a decrease in size and thickness.
Electronic machines, devices and peripheral hardware are recently decreasing in size and thickness, and it is accordingly required to decrease the size and thickness of the cables per se. Hand-held computers in particular appreciably tend to be downsized and decreased in thickness together with versatile functions and higher performances. The system of interface cables for connecting a computer and a display is changing from a system of a group of bundled cables to a system of flat cables and further to a system of a flexible printed wiring board (FPC) having a small thickness. Moreover, for faster transmission of information, frequency in a higher frequency band comes to be used, and FPC comes to be required to have higher electromagnetic wave shield property than it has so far had. Specifically, useless electromagnetic waves from inside FPC are generated from a pattern used for a basic clock, and electromagnetic waves having a frequency of 150 to 700 MHz are mainly included at present. As measures for electromagnetic wave shield of FPC, a solid grounding plate is formed by bonding a copper foil to one surface or each surface of FPC. However, there are caused problems that the electromagnetic wave shield function is poor since the copper foil is generally attached with an adhesive having the level of an insulator having a volume resistivity of 10
7
&OHgr;cm or more as an electric resistance, and that the copper foil is not sufficiently durable in a bending test and undergoes brittle fracture.
FPC is increasingly used as electronic machines and devices are decreased in size and thickness as described above, and FPC accordingly comes to be required to have high electromagnetic wave shield properties in addition to flexibility, a lighter weight, a smaller thickness and electric properties. The present inventors have therefore proposed a metal fiber sheet for shielding against electromagnetic wave, as a method of attaining effective acrylonitrile-butadiene copolymer (a) has a relatively high nitrile content of 10 to 45%, preferably 20 to 45% and a molecular weight of 3,000 to 1,000,000, preferably 3,000 to 10,000, or 50,000 to 500,000. Such an acrylonitrile-butadiene copolymer is preferred in the present invention.
The above electromagnetic wave shield method is excellent, while it is not yet fully satisfactory as far as flame retardancy is concerned. That is, UL-94 which is the combustion test standard of plastic materials for parts is applied to electronic machines and devices for which the above electromagnetic wave shield material is used, and the electromagnetic wave shield material is required to have flame retardancy grades of a V-1 or V-0 level. There is therefore demanded an electromagnetic wave shield method which accomplishes excellent flame retardancy of the above standard levels.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electrically conductive adhesive composition and an electrically conductive adhesive sheet, having excellent flame retardancy without impairing excellent electric conductivity.
It is another object of the present invention to provide an electromagnetic wave shield material formed by integrating an electrically conductive adhesive composition or an electrically conductive adhesive sheet with an electrically conductive fiber sheet or metal foil, which electromagnetic wave shield material has flexibility and folding endurance feasible particularly for use as an electromagnetic wave shield of a flexible printed wiring board (FPC).
It is further another object of the present invention to provide an electromagnetic-wave-shield-functioning flexible printed wiring board having the property of electromagnetic wave shield, formed by applying the above electromagnetic wave shield material to a flexible printed wiring board.
According to the present invention, there is provided an electrically conductive adhesive composition comprising 100 parts by weight of (a) an acrylonitrile-butadiene copolymer, 20 to 500 parts by weight of (b) a phenolic resin and/or an epoxy resin, 1 to 100 parts by weight, per 100 parts by weight of the components (a) and (b) in total, of (c) an electrically conductive filler and 1 to 50 parts by weight, per 100 parts by weight of the components (a) and (b) in total, of (d) a bromine-containing flame retardant.
According to the present invention, there is also provided an electrically conductive adhesive composition according to the above, wherein the bromine-containing flame retardant contains at least 50% by weight of brome and has a melting point of at least 100° C.
According to the present invention, there is also provided an electrically conductive adhesive composition according to the above, wherein the bromine-containing flame retardant is a tetrabromobisphenol A derivative of the following formulas.
or
According to the present invention, there is also provided an electrically conductive adhesive composition according to the above, which further contains 1 to 10 parts by weight, per 100 parts by weight of the components (a) and (b) in total, of (e) a stabilizer.
According to the present invention, there is also provided an electrically conductive adhesive sheet formed of the above electrically conductive adhesive composition in the form of a sheet.
According to the present invention, there is also provided an electromagnetic shield material formed of the above electrically conductive adhesive composition and an electrically conductive fiber sheet having a surface resistivity of 1 &OHgr;/□ or less, wherein the electrically conductive fiber sheet is impregnated with the electrically conductive adhesive composition or the electrically conductive adhesive composition is applied to the electrically conductive fiber sheet.
According to the present invention, there is also provided an electromagnetic shield material formed of a laminate of the above electrically conductive adhesive sheet and an electrically conductive fiber sheet or metal foil having a surface resistivity of 1 &OHgr;/□ or less, wherein the electrically conductive adhesive sheet is laminated on one surface, or each surface, of the electrically conductive fiber sheet or metal foil and the electromagnetic shield material is shaped under pressure.
According to the present invention, there is also provided an electromagnetic-wave-shield-functioning flexible printed wiring board formed of the above electromagnetic wave shield material and a flexible printed wiring board, wherein the electromagnetic wave shield material is laminated on one surface, or each surface, of the flexible printed wiring board.
DETAILED DESCRIPTION OF THE INVENTION
The components for constituting the electrically conductive adhesive composition of the present invention will be explained first. The acrylonitrile-butadiene copolymer (a) is an essential component for imparting the electrically conductive adhesive composition with flexibility and also works to improve the adhesion of the composition to a substrate. The acrylonitrile-butadiene copolymer is selected from many elastomer materials by taking into account cold resistance, oil
Higashi Kensaku
Kitahara Hiroshi
Lam Cathy
Tomoegawa Paper Co. Ltd.
Wenderoth Lind & Ponack LLP
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