JP2000031688A - Electromagnetic wave shielding material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave shielding material which is superior in both electromagnetic wave shielding effect and machinability. SOLUTION: This electromagnetic wave shielding material contains coil-like carbon fibers encapsulated in a microcapsule. The microcapsule comprises a core substance 21 composed of coil-like carbon fibers 22 and a dispersant 23 therefor, and a shell substance 24 covering the core substance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave shielding material which is regarded as important in the field of electronic devices such as personal computers, audio products, home electric appliances, and mobile phones. The present invention relates to an electromagnetic wave shielding material having excellent characteristics.

[0002]

2. Description of the Related Art Conventionally, as an electromagnetic wave shielding material, a low-resistance metal sheet or metal foil, a metal plating, a metal plating, a metal or a metal oxide, an electrostatic shield generally used for an electronic device main body, and a high frequency. There is a magnetic shield made of a magnetic material or the like having a high magnetic permeability, which is used depending on the application.

[0003] Specifically, indium oxide, gold,
There are known copper, silver, tin oxide, indium oxide, and the like formed into a thin film by vapor deposition. However, these have problems that the manufacturing process is complicated and the cost is high.

[0004] As another form, there is known a conductive powder, flake, or fiber such as silver, copper, nickel, aluminum, carbon, metal fiber, carbon fiber, or metal glass fiber mixed in a resin. ing. These are low-cost and the manufacturing process is simple, but the electromagnetic wave shielding effect is insufficient.

Further, as another form, for example,
-104927, JP-A-3-227412, JP-A-4-222228, JP-A-10-37
As described in Japanese Patent Application Publication No. 024, a coiled fiber is known instead of a linear fiber. In particular, the coiled carbon fibers generate an induced current and have a high effect of completely absorbing electromagnetic waves.

However, when this is processed as an electromagnetic wave shielding material, a method of mixing it into a resin is used. However, there is a disadvantage that the coil-shaped material is broken at the time of mixing.

[0007]

As described above, the conventional electromagnetic wave shielding material has a shielding effect but is poor in workability when a metal or metal oxide film is used, and has good workability when conductive particles are used. When conductive fibers having a low shielding effect and a high shielding effect were used, the workability was poor. Accordingly, an object of the present invention is to provide an electromagnetic wave shielding material having both an electromagnetic wave shielding effect and good workability.

[0008]

Means for Solving the Problems The present invention has been made to achieve the above-mentioned object, and the invention according to claim 1 is an electromagnetic wave shielding material containing coiled carbon fibers. An electromagnetic wave shielding material characterized in that fibers are microencapsulated.

According to a second aspect of the present invention, there is provided the electromagnetic wave shielding material according to the first aspect, wherein the microcapsules comprise a core material comprising at least a coiled carbon fiber and a dispersion medium for dispersing the same, and a shell material covering the core material. It is characterized by consisting of.

A third aspect of the present invention is the electromagnetic wave shielding material according to the first or second aspect, wherein the microcapsules are dispersed and arranged in a binder.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the drawings showing embodiments. FIG. 1 is a cross-sectional view showing one embodiment of the electromagnetic wave shielding material of the present invention, and FIG. 2 is a cross-sectional view showing one embodiment of a microcapsule used in the present invention.

FIG. 1 shows a configuration of an electromagnetic wave shielding material 1 of the present invention, in which microcapsules 11 containing coiled carbon fibers and the like are dispersed in a binder 12.

FIG. 2 is a cross-sectional view showing one embodiment of the microcapsule used in the present invention. The microcapsule 11 is composed mainly of a suspension in which coiled carbon fibers 22 are dispersed in a dispersion medium 23. The core material 21 is encapsulated with a shell material 24 made of a polymer or the like.

As the coiled carbon fiber 22, various coiled carbide fibers such as carbon, silicon carbide (SiC) and titanium carbide (TiC) can be used.
5 μm fiber, the coil outer diameter is 2 to 10 times the fiber diameter, and the number of turns is 5 to 50 times the reciprocal of the coil outer diameter per 10 μm.
The one in the double range is good. Here, in order to stably disperse the coiled carbon fibers 22 in the dispersion medium 23, it is preferable to perform a fatty acid treatment, a higher ester treatment, a silane coupling treatment, and a coating treatment with various resins.

As the dispersion medium 23, generally known organic solvents such as aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, aliphatic esters, aromatic esters, and alcohols which are liquid at ordinary temperature are used alone. Alternatively, they can be mixed and used as appropriate.

Alternatively, natural waxes which are solid at ordinary temperature, such as paraffin wax and carnauba wax, or synthetic waxes such as carboxylic acid wax, fatty acid wax, and petrolatum can be used alone or in combination as appropriate.

Further, a UV-curable resin or an electron beam-curable resin can be used. UV-curable resins are compounds having an ethylenically unsaturated group capable of free radical addition polymerization or crosslinkable, and having at least one ethylenically unsaturated group, for example, a monomer having a vinyl group or an allyl group, An oligomer, a polymer having an ethylenically unsaturated group at a terminal or a side chain, or the like can be used. In addition, a compound that can be radically polymerized, an epoxy compound that can be cationically polymerized, an oxetane compound, a vinyl ether compound, or a generally known resin that can be crosslinked with a crosslinking agent can be used. As the compound capable of undergoing radical polymerization, a compound having at least one ethylenically unsaturated double bond in a molecule is preferable.
As the epoxy compound, compounds formed by a condensation reaction of various phenol compounds such as bisphenol A, bisphenol AD, bisphenol B and bisphenol S with epichlorohydrin can be used. As the oxetane compound, xylylene oxetane, oxetane alcohol and the like can be used. As the vinyl ether compound, diglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, polyethylene glycol diglycidyl ether, vinyl-n-butyl ether, trimethylolethanetrivinyl ether, and the like can be used.

The above-mentioned coiled carbon fiber 22, dispersion medium 2
The core material 21 mainly composed of 3 or the like is converted into a shell material 2 such as a polymer.
Cover with 4 and microencapsulate. Examples of the shell material 24 include commonly used resins, for example, an organic material such as an acrylic resin, a methacrylic resin, a polystyrene, a polyester resin, a polyurethane resin, a polyurea resin, a polyamide resin, an epoxy resin, and a natural resin, or an inorganic material. May be used alone or in combination of two or more. In particular, a material having high conductivity is preferable.

Microcapsule 1 having the above-mentioned shell material
The production method of 1 includes a phase separation method of separating a concentrated phase of a polymer around a core substance dispersed in a polymer solution,
In-liquid curing coating method, in which the polymer is cured around the core substance in the polymer solution with a polymer curing test agent, etc., and monomers or polymerization catalysts are supplied from either the emulsion in which the core substance is dispersed or the external phase. Microencapsulation techniques such as in-situ polymerization, in which the surface of the core material is covered with a polymer, and interfacial polymerization, in which monomers are supplied from both the internal and external phases of the emulsion in which the core material is dispersed, are preferred. However, the present invention is not limited to this.

In particular, by manufacturing by using an in-situ polymerization method of supplying a monomer from the outer phase of a suspension in which a coiled carbon fiber 22 as a core substance 21 is uniformly dispersed in a dispersion medium 23, or a phase separation method, The microcapsules 11 in which the coiled carbon fibers 22 are efficiently arranged in the microcapsules can be manufactured. As the polymerizable monomer used here, acrylates, methacrylates, styrene and derivatives thereof, isocyanates, various amines, compounds having an epoxy group, and the like are preferable.

When the coiled carbon fiber is microencapsulated, it can be processed without breaking the coil shape when used in a dispersed state in a resin solution.

Next, the electromagnetic wave shielding material 1 of the present invention is shown in FIG.
Microcapsule 11 having the above configuration as shown in FIG.
Is dispersed in the binder 12.

Examples of the binder 12 include polyvinyl alcohol, polyvinylpyrrolidone, polysodium acrylate, polyacrylamide, polyethyleneimine,
Aqueous binders such as gelatin, gum arabic, cellulose derivatives, sodium alginate, melamine, and urea resins; solvent-based binders such as acrylic resins, urethane resins, polystyrene, polyvinyl chloride, and styrene-maleic acid resins; and styrene-maleic acid Emulsion binders such as a polymer, a latex such as a methyl methacrylate-to-butadiene copolymer, a latex of an acrylic polymer, and a latex of a vinyl polymer are appropriately used.

By dispersing the microcapsules in the binder solution to form an ink, the coating can be performed irrespective of the shape of the adherend requiring the electromagnetic wave shielding material,
It is possible to form a layer made of an electromagnetic wave shielding material.

As a method of forming the electromagnetic wave shielding material, for example, a known printing method such as a gravure printing method, an offset printing method, a silk screen printing method, or a coating method such as a dip method, a spray method, a roll method, and a knife edge method. Can be appropriately selected from the above-described methods according to the shape, application, quantity, and the like of the adherend to be produced.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to specific embodiments. <Example 1> Fifteen parts by weight of coiled carbon fiber subjected to silane coupling treatment was heated to 60 ° C and melted, and 50 parts by weight of stearyl stearate, 15 parts by weight of diisopropylnaphthalene, 15 parts by weight of dibutyl phthalate, and ethyl cellulose 1 were used. The dispersion is uniformly dispersed in 80 parts by weight of a mixed solvent of 80 parts by weight, and the dispersion is dispersed in 200 parts by weight of a 5% aqueous solution of polyvinyl alcohol heated to 60 ° C., and has an average particle diameter of 75 μm at a rotation speed of 2,000 rpm using a homogenizer. For about 5 minutes. 100 parts by weight of a melamine-formalin prepolymer aqueous solution was mixed with the obtained dispersion, and a 20% acetic acid aqueous solution was added dropwise to adjust the pH to 6.
Thereafter, the temperature of the solution was raised to 65 ° C., and a polymerization reaction was performed for 6 hours to produce microcapsules having a melamine-formalin wall.

A coating liquid in which the obtained microcapsules were uniformly dispersed in an aqueous polyvinyl alcohol solution was applied to a PET film to form a layer made of an electromagnetic wave shielding material.

When the electromagnetic wave shielding effect of the formed electromagnetic wave shielding material was measured, it was found that the frequency was 30 MHz to 500 MHz.
, The electric field attenuation of -35 dB was exhibited.

[0029]

According to the electromagnetic wave shielding material of the present invention, in the electromagnetic wave shielding material containing coiled carbon fiber,
Since the coiled carbon fiber having a high electromagnetic wave shielding effect is used, the electromagnetic wave shielding is high. In particular, since the coiled carbon fiber is microencapsulated, it becomes possible to perform processing without breaking the coil shape when used by dispersing in a resin solution.

Further, by dispersing the microcapsules in a binder solution to form an ink, coating can be performed regardless of the shape of the adherend requiring an electromagnetic wave shielding material, and a layer made of the electromagnetic wave shielding material can be formed. It is.

[0031]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of an electromagnetic wave shielding material of the present invention.

FIG. 2 is a sectional view showing one embodiment of a microcapsule used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electromagnetic wave shielding material 11 Microcapsule 12 Binder 21 Core material 22 Coiled carbon fiber 23 Dispersion medium 24 Shell material

Claims (3)

[Claims] 1. An electromagnetic wave shielding material containing a coiled carbon fiber, wherein the coiled carbon fiber is microencapsulated. 2. The electromagnetic wave shielding material according to claim 1, wherein said microcapsules are composed of at least a core material composed of at least a coiled carbon fiber and a dispersion medium for dispersing the same, and a shell material covering the core material. . 3. The electromagnetic wave shielding material according to claim 1, wherein the microcapsules are dispersed in a binder.