JPH036898A - Shield material - Google Patents

Abstract

PURPOSE:To shield wide range of and many kinds of noise and to obtain high processability by maintaining ferrite powder and specific carbon fibers by a binder, and forming them into a specified shape. CONSTITUTION:A compound shield plate 1 is the one where shield plates 3, 5, and 7 metallic layers 13, 15, and 17, which cover each surface of these shield plates 3, 5, and 7, are laminated on parent material 2 such as plastic plate, etc. The shield plates 3, 5, and 7 are formed in thin plate shapes by heat-fusing, the shield material wherein ABS resin as a binder, ferrite powder about 4-10mum in grain diameter, and specified carbon fibers are mixed. The carbon fibers are created by vapor phase method wherein benzene is decomposed by heat in the furnace of 950-1300 deg.C, and those are the substances 0.1-0.5mum in diameter and 0.1-1.0mum in length which are grown with the iron powder 0.02-0.03mum in grain diameter as a growth starting part. Moreover, if the thickness t of the compound shield plate 1 is 2 to 3mum or more, it displays excellent shield effect by the change of crystal structure near the interface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a shielding material that is disposed at a portion to be shielded from an electric field, an electromagnetic field, or a magnetic field.

[Background Art] In recent years, with the advancement of electronic technology, many devices that utilize electronics, electricity, and radio waves have come into use. These devices may unintentionally emit unnecessary electromagnetic waves, etc., which may affect other electronic devices, causing malfunctions, noise generation, and various other malfunctions.

Therefore, in order to prevent the occurrence of functional failure due to noise such as electric fields, magnetic fields, electromagnetic waves, etc., it has been conventional practice to provide a shield to the noise source side or to provide a shield to the affected equipment.

Such shields can vary depending on the shielding material used.
The principles for preventing noise are different, including electric field shielding that prevents coupling due to stray capacitance, electromagnetic shielding due to electromagnetic induced currents, and magnetic field shielding that utilizes low reactance circuits.

That is, each shield prevents noise based on the principle shown below, and uses a respective shield material to achieve this.

Electric field shielding takes advantage of the fact that by surrounding equipment with a good conductor, the effects of electric fields will hardly reach the equipment. Therefore, a shielding material with good conductivity is used for the electric field shield.

Electromagnetic shielding utilizes the effect of current induced in a shield member by electromagnetic induction (reflection and absorption of electromagnetic fields). Therefore, a good conductor such as a metal plate is used as a shielding material for electromagnetic shielding.

Magnetic shielding is aimed at low-frequency magnetic fields, and obtains a shielding effect by deflecting the magnetic field using a high magnetic permeability material. Therefore, a magnetic substance is used as a shielding material for a magnetic shield.

[Problems to be Solved by the Invention] However, in the conventional technology, different shielding materials must be used depending on the target of shielding or the frequency of noise, and in order to prevent noise over a wide range, it is necessary to use different shielding materials. , multiple shielding materials had to be used in combination.

For this reason, conventionally, there have been problems in that the shielding member becomes large and the number of parts and man-hours required for processing increase.

An object of the present invention is to solve the above-mentioned problems, thereby shielding a wide range of noises from many types of noise, and achieving high workability.

[Means for Solving the Problems] As a means for achieving the above object, the shielding material of the present invention is formed into a predetermined shape, and is applied to an electric field.

A shielding material placed in a part where electromagnetic or magnetic fields are to be shielded.It is produced by a vapor phase method by thermal decomposition of ferrite powder and hydrocarbon in a binder such as resin or rubber, and has a high melting point. The gist is that carbon fibers grown using ultrafine powder of a metal and/or a compound of the metal as a growth starting part are added.

[Function] The shielding material of the present invention is made by holding ferrite powder and specific carbon fibers together with a binder and molding them into a predetermined shape. This consists of ferrite powder, which is a magnetic material, and
Carbon fiber, which is a good conductor, shields the electric field, electromagnetic field, or magnetic field of the disposed portion.

Polyester resins and vinyl resins are used as binders that hold the ferrite powder and carbon fibers together.

Examples include synthetic resins such as polyamide resins, glue, rubber, and casein.

Unlike polyacrylonitrile-based carbon fibers or pitch-based carbon fibers, the carbon fibers used in this invention are produced in the form of whiskers with a minute diameter approximately equal to the diameter of ultrafine powder of a high-melting point metal and/or its compound. be.

The high melting point metal that serves as the starting point for carbon fiber growth is a metal that does not vaporize at 950°C to 1300°C, which is the temperature for thermal decomposition of hydrocarbons, and is Ti.

Group 4a of the periodic table such as Zr, Group 5a such as V, Nb,
Group 6a such as Or, MO, Group 7a such as Mn, Fe, C
Group 8 elements such as O are suitable, with Fe and C being particularly desirable.
o, Ni, v, Nb, Ta.

They are Ti and Zr. Compounds of such metals include their oxides, nitrides, and geothermal compounds.

In the present invention, the whisker-like carbon fibers have excellent adhesion and dispersibility with the binder, and are distributed uniformly throughout all parts of the binder used.

Furthermore, this carbon fiber is based on a regular graphite crystal layer with few lattice defects, and has a small electrical resistivity, that is, good electrical conductivity, and excellent mechanical properties such as tensile strength. Therefore, they are dispersed and held in a chain form in the binder, imparting electrical conductivity to the shielding material of the present invention and also improving its mechanical properties.

The degree of electrical conductivity, ie, electrical resistivity, of the shielding material is determined by the amount of addition, which is the degree of chaining of the carbon fibers. Furthermore, when the amount of carbon fiber added reaches a predetermined amount necessary for mutual contact between the carbon fibers, the electrical resistivity of the shielding material becomes close to the electrical resistivity of the carbon fiber alone. This predetermined amount is approximately 40% by volume of the binder used. In other words, it is preferable that the amount of carbon fiber added exceeds about 20% by volume of the binder because the electrical resistivity decreases. The shielding material imparted with conductivity in this manner reflects and absorbs electromagnetic noise when used as an electromagnetic shielding member.

In the shielding material of the present invention, the carbon fibers are dispersed and held in the binder, improving the mechanical properties of the shielding material, so that the ferrite powder is dispersed and held while maintaining the strength of the shielding material. As a result, the shielding material to which the ferrite powder is added has the high magnetic permeability of the ferrite powder itself. Therefore, it has a function of shielding magnetic fields.

The ferrite powders dispersed and held in the binder have high magnetic permeability even if they are not in contact with each other, so the amount added should be determined appropriately, and if the amount exceeds about 2% by volume of the binder, preferable.

[Example] Next, examples of the shielding material of the present invention will be described.

The composite shield plate 1 of this embodiment includes shield plates 3, 5.7 on a base material 2 such as a plastic plate, and these shield plates 3.
．． A metal layer 13 and a metal layer 15.17 are laminated to cover the surfaces of each of the elements 5.7 and 15.17.

The shield plate 3.5.7 is made by heating and melting a shielding material that is a mixture of ABS resin as a binder, ferrite powder with a particle size of about 4 to 10 μm, and carbon fiber manufactured as shown below. , molded into a thin plate shape.

Carbon R fibers are produced by a gas phase method of thermally decomposing benzene in a furnace at 950°C to 1300'C, and have a particle size of 0.0
Diameter 0.1μm-0.5μm, length 0.11IIJ grown using 2μm-0.03μm iron powder as growth starting point
It is an object of n~1M.

ABS resin that constitutes the shield plate 3.5.7.

The physical property values of the ferrite powder and carbon fiber are as shown in Table 1 below.

Table 2 Umbrella 1... Composition ratio of ferrite powder 2... Composition ratio of charcoal jK fiber or carbon black particles 3... Shielding effect in an electric field of 500 MHz or magnetic field of 10 KI-1z, and shield plate 3.5 The composition ratio of .7 is ABS resin 7 and 20% by volume of fiber.

Table 2 shows the measurement results regarding the physical properties of shield plate 3.5.7 (test piece A). Moreover, the shield plate 3 of this embodiment
In order to compare with v 5 * 7, Table 2 also shows the physical property values of a conventional shield plate (test piece B) in which carbon black particles were added to ABS resin. In addition, for the test, JIS
A No. 1 test piece described in K 7113 was used.

From this result, the shield plates 3 and 5 of this example.

7 (test piece A) compared to the conventional one (test piece B),
It has a low volume resistivity (Ω·c/n) and a high magnetic field shielding effect. It also has a sufficient electric field shielding effect.

The metal layers 13, 15, 17 cover each shield plate 3, 5.
Different metals on the surface of 7, for example nickel.

It is coated with copper, aluminum, etc.

The composite shielding plate 1 described above has a thickness t of the composite shielding plate 1, in addition to the electromagnetic field and magnetic field shielding effect of each shielding plate 3, 5.7 and the metal layer 13, 15.17 themselves.
If it is 2 to 3 μm or more, an excellent shielding effect can be achieved due to changes in the crystal structure near the interface.

Moreover, the composite shield plate 1 can adjust the reflection and absorption characteristics of the incident electromagnetic field by appropriately selecting the material or thickness of each metal layer 13, 15.degree. 17. Therefore, the electromagnetic field in a desired frequency band can be attenuated by a desired amount, and the shielding characteristics can be easily adjusted, which is an excellent effect.

Furthermore, by appropriately selecting the amount of ferrite added to each shield plate 3,5.7 or the magnetic permeability, it is possible to adjust the characteristics of each shield plate 3.5.7 as a magnetic material. can.

In addition, the composite shield plate 1 has high workability and strength due to carbon fiber, and is difficult to crack even when bent at an acute angle, so it can be bent and bonded to the corner of a box as is. .

Note that the carbon fibers added to the shield plates 3, 5.7 may be plated with metal. As a result, shield plates 3 and 5
．． The volume resistivity of No. 7 becomes smaller, and the electromagnetic wave shielding ability improves.

Next, a second embodiment will be explained.

The electromagnetic wave shielding core 21 of this embodiment is made by molding a shielding material having a composition ratio of 6 strands of ABS resin and 30% by volume into a tubular shape as shown in FIG.

The measurement results regarding the physical property values of the electromagnetic shielding core 21 (test piece C) are shown in Table 3 below.

Table 3 *1 Composition of ferrite powder Stop wheel 2 Composition ratio of carbon fiber Book 3 Shielding effect in a 500 MHz electric field or 10 KHz magnetic field From these results, the electromagnetic shielding core 21 of this example ( Test piece C) has a much better shielding effect against electric and magnetic fields than the conventional one (test piece B shown in Table 2 already mentioned).

Since the electromagnetic shielding core 21 described above is a tubular member having high magnetic permeability, the conducting wire 25 passing through the hole 23
Cuts off high frequency current.

Further, the electromagnetic wave shielding core 21 is formed into a long pipe shape, and is cut as appropriate in consideration of the frequency band to be blocked and the amount of attenuation. Therefore, an excellent effect is achieved in that extremely high versatility can be obtained.

Next, a third embodiment will be described.

As shown in FIG. 3, the electromagnetic shielding component 35 of this embodiment consists of a collar portion 31 and a tube portion 33, and a hole portion 37 is formed in the tube portion 33.

This electromagnetic shield component 35 is made of rubber as a binder, ferrite powder, and carbon fiber. Therefore, the electromagnetic shield component 35 has high elasticity due to the rubber, good conductivity due to the carbon mt'i, and high magnetic permeability due to the ferrite powder.

As shown in FIG. 4, the electromagnetic shield component 35 is used by being inserted into an opening 43 in a box 41 of a computer or the like.

As a result, heat dissipation inside the box body 41 or extraction of signal lines, etc. is performed through the hole 37 of the electromagnetic shielding component 35.
Electromagnetic waves do not leak outside via 7. That is,
The electromagnetic waves generated inside the box body 41 are transmitted through the conductive pipe section 3.
3. Further, the high frequency waves induced in the signal line or the like passing through the hole 37 are attenuated by the magnetic tube 33.

Further, the tube portion 33 is pressed against the opening 43 of the box body 41 due to its elastic force and comes into close contact with the opening 43, and the collar portion 31 closes the gap created between the tube portion 33 and the opening 43. Therefore, electromagnetic waves will not leak from the part where the electromagnetic wave shield component 35 is inserted into the box body 41.

As explained above, the electromagnetic wave shielding component 35 has an extremely excellent effect in that it has a high ability to prevent electromagnetic waves from leaking from the opening 43 of the box body 41.

Note that the hole 37 in the N magnetic wave shield component 35 may be formed in a straight pipe shape or in a spiral shape.

[Effects of the Invention] As explained above, in the shielding material of the present invention, the binder disperses and holds ferrite powder having high magnetic permeability and specific carbon fibers having excellent mechanical properties and conductivity. For this reason, it has a high degree of freedom in molding shape, and also has high magnetic permeability imparted by ferrite powder and good conductivity imparted by specific carbon fibers, and has improved mechanical properties due to specific carbon fibers. It becomes a shielding material.

Therefore, by molding the shielding material of the present invention into various shapes by injection molding, vacuum forming, etc., electric fields can be removed from external space.
Shields electromagnetism and also shields low frequency magnetic fields from external space.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of a composite shield plate 1 of the first embodiment, FIG. 2 is a perspective view of the electromagnetic shielding core 21 of the second embodiment, and FIG. 3 is an electromagnetic shielding component 35 of the third embodiment.
FIG. 4 is a sectional view of the device in use.

Claims (1)

[Scope of Claims] A shielding material formed into a predetermined shape and disposed in a part intended to shield an electric field, an electromagnetic field, or a magnetic field, which comprises ferrite powder in a binder such as resin or rubber; A shielding material produced by a gas phase method using thermal decomposition of hydrocarbons, and to which carbon fibers grown using ultrafine powder of a high melting point metal and/or a compound of the metal as a growth starting point are added.