JPS6178873A - Electromagnetic shielding material and its preparation - Google Patents

Abstract

PURPOSE:An electromagnetic shielding material which well absorbs waves in a low-frequency region (about 1GHs or lower), made by dispersing the laminar particles of a ferrite containing excessive iron in a polymer matrix. CONSTITUTION:The laminar paticles (B) of a ferrite containing excessive iron which has a spinel-type structure, is shown by the formula [wherein M is at least one divalent metal; X>0.5 (especially 0.8<=X<=0.501)], and has an average length d of particles of 0.5-500mum, the proportion of the particles having the diameter of 0.3-3.4 d of 90wt% or more, and an aspect ratio (length/thickness) of 3 or higher, in an amount of about 20-65vol%, are added to a polymer matrix (A) (e.g., an epoxy resin or a styrene resin) to be mixed, and the mixture is heated to disperse the particles in the matrix. This compound is then molded into a desired form, giving a sheet, a housing, etc., having excellent electromagnetic shielding properties.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Background Technical Field of the Invention The present invention relates to an electromagnetic shielding material and a method for manufacturing the same.

Prior art and its problems Plate-shaped ferrite particles exhibit excellent properties as radio wave absorbing materials and electromagnetic shielding materials in the low frequency range, which cannot be achieved with ordinary ferrite particles (48F Application No. 58-19
7595 and Japanese Patent Application No. 199206)
.

The crystal system of ferrite particles is cubic system.
If growth with 11 shapes occurs, it will not become plate-like.

However, if synthesis is performed using the flux method.

The plate-shaped hematite-shaped ferrite-on r used for the material can be made into 71#. In other words, when flux is added to raw materials and heated, the flux becomes a melt at temperatures above its melting point and dissolves the raw materials. At this time, oxides other than hematite with a small particle size are first dissolved, transported, and react with hematite to form ferrite particles (Japanese Journal).

1981, No. 9 F1391 N1394).

By using this method, plate-shaped nickel-zinc ferrite particles have been obtained (described in Japanese Patent Application No. 19795-1982 and Japanese Patent Application No. 199206-1983).

That is, Franks, which is a mixture of 5 mo1% of Na25043B and 5 mo1% of Li250463, was mixed with plate-shaped hematite, nickel oxide, and the oxide material of the refractory bone box, and heat-treated at 900°C in air. It is something to do.

In the case of iron-deficient and chemically stoichiometric ferrite particles such as Enkel-1F lead-based particles, the ferrite formation reaction does not involve the entry and exit of oxygen, and can be synthesized relatively easily.

Manganese-111 lead-based and other iron-excess ferrite particles, which are most commonly used as high B materials as L- and LA-based materials, are synthesized because it is difficult to determine the oxygen content in ferrite. It has not been.

If this synthesis is successful, it is expected that its properties will be utilized to create an excellent electromagnetic shielding material.

II. OBJECTS OF THE INVENTION The object of the present invention is to provide a plate-shaped ferrite powder that has a wide range of uses as a magnetic material and has excellent performance.

The object of the present invention is to realize a manufacturing method thereof and use the same to provide an electromagnetic shielding material having excellent Nhund properties and a manufacturing method thereof.

Such purposes include: iS1. This is achieved by the second and third inventions.

That is, the first invention is an electromagnetic shield that absorbs electromagnetic waves, characterized in that it is made of iron-rich ferrite particles with a spinel-type structure, and is made by dispersing ferrite powder, which has a flat plate shape, in a polymer matrix. It is a material.

The second invention is to mix plate-shaped hematite and oxide, or a material that becomes an oxide through heat treatment, with one or more sulfates in the amount of 7 lux, and heat the mixture at 1000°C to After heat-treating at 300°C and cooling sufficiently in an inert gas atmosphere, it is washed with water to remove the fluff, dried, and made into an iron-rich Ferra with a spinel structure (
) A method for producing an electromagnetic shielding material capable of absorbing electromagnetic waves, characterized by obtaining ferrite powder having a flat plate shape and dispersing it in a polymer matrix.

Specific structure of the old invention Hereinafter, a specific configuration of the present invention will be explained in detail.

The ferrite powder of the present invention is an aggregate of iron-rich ferrite particles having a spinel structure.

Further, the ferrite powder of the present invention is mainly composed of particles having a tabular shape. Usually, 90% by weight or more of the total amount of particles forming the powder is in the form of a flat plate.

The average major axis J of ferrite particles is 50 at 0.54 m or more.
This is because when J is less than 0.5 μm, the plate-like characteristics are lost, and when J exceeds 500 μm, the ferritization reaction becomes inhomogeneous.

Particularly favorable results are obtained when J is 1 to lo μm.

90 of the total amount of ferrite particles forming the ferrite powder
% by weight or more means particles having a particle size in the range of 0.3J to 3.41.

This is because if the grain size 4j becomes broader than this, the orientation will deteriorate.

In addition, more than 90% by weight of the total amount of ferrite particles is 0
．． It is more preferable to have a particle size in the range of 5H to 2.71.

Moreover, it is preferable that the 7 spectral ratio (major axis/thickness) of the ferrite particles is 3 or more.

This is because when the number is less than 3, the plate-like effect disappears.

That is, the ferrite of the present invention is of an iron-rich type, and its composition is (MO) (Fez 03 ) [where M is -
x 1 of divalent metal! It is more than fI. ], x>0.5, especially 0.8≧X≧0.50'1.

In such a case, the type of MO mentioned above is not limited, but the following ones, especially the following Mn-based, Mn-Zn-based, Ni-based,
Ni-Zn type and Zn type are preferred.

l) F e203; greater than 50 mol%.

70 mol% or more, ZnO; O ~ 30 mol%, remainder M n
0 2) F C203: More than 50 mol%, 80 mol% or less, Zn0O to less than 50 mol%, remaining NiO In addition to these main components, one or more of Ca, Si, etc. is present in the form of an oxide. It may be contained in an amount of 500 pμm or less of the synthetic material.

Ferrite powder with such a composition and shape is
It exhibits high saturation magnetization of 60 emu/g or more up to 100 emu/g.

It should be noted that among conventional ferrite powders, there is no iron-rich type that is mainly composed of flat plate-shaped ferrite particles.

This is because it is difficult to control oxygen-containing acids in ferrite.

The ferrite particles of the present invention have improved this point! The A method is shown below.

That is, a flux is mixed with plate-shaped hematite (iron oxide) and a material 1 which becomes an oxide or a oxide by heat treatment, and '9. This is a method of synthesis by heat treatment in an inert scum such as raw material.

At this time, manganese oxide, such as manganese tetroxide, or materials that become mancan oxide when heat treated, such as manganese carbonate, zinc oxide, or materials that become zinc oxide when heat treated, are particles that are smaller than iron oxide particles. .

The long axis of the iron oxide used is 0.5 to 5004 m, and the thickness is 0.
．． 01-1. The size of subcomponent materials such as manganese carbonate and zinc oxide is usually spherical, and each particle has a particle size of 13%0.
A length of 1 to 0.54 m is preferable.

For mixing, a method is used that uniformly mixes the iron oxide without destroying its shape.

Also, /A is not treated, and it is carried out in an inert gas at a melting point of 7 lux or higher.

The inert gas used is usually nitrogen, and its oxygen partial pressure is 0.01% or less.

The manufacturing method of M n -Z n system will be briefly explained below.
I will explain to iT 1ill+.

Dendritic hematite (α-Fe203) and manocan oxide (
Mn304) or a material that becomes manganese oxide by heat treatment (for example, Mn30.+, MnC
Oxide (ZnO, etc.) and zinc oxide (ZnO) or a material that becomes 1F lead through heat treatment are mixed with one or more types of sulfur! After heat treatment at 1000°C to 1300°C and sufficient cooling in an inert gas atmosphere such as nitrogen, the product is washed with water to remove flux and dried.

It is preferable to use a flux consisting of one type or two or more types of acid m salts having a melting point of 1000° C. or higher.

These include high melting point fluxes such as 1 to 2304, C52SOa.

Rb2SO4 etc. may be used alone.

Also, Li2504, Na2504.

A mixture of K250.1, CC2S04, and Rb2SO4'J with a melting point of 1000°C or higher may be used.

:jrI1 diagram shows the melting point of the flux and the Mn-Zn ferrite powder Fe20325 when the flux was heat-treated at 1150°C for 1 hour in a nitrogen atmosphere.
mol%, M n 025 mol%.

The relationship with the saturation magnetization of Zn022 mol %) is shown.

As a result, the melting point of the flux is 800℃ and 1000℃.
It can be seen that the m-sum magnetization rapidly increases at point C.

These temperatures correspond to the temperatures at which m elements are released from the oxide material.

Therefore, by using a flux with a high melting point, oxygen in the ferrite, which lowers the saturation magnetization of the ferrite, is removed during ferrite formation. In other words, it is difficult for oxygen to move in the liquid phase, so
The m-element release is completed before the flux is dissolved, and the oxygen in Zena, Cl, and the like is removed.

The amount of flux contained in the three types of oxides described in 1111 (hereinafter expressed as total moles of flux t!t/total number of moles of oxide) is based on the expected saturation magnetization of the ferrite product. Although it varies depending on the value, it is preferably from 0.4 to 4.0, and in particular, from 06 to 0.8, high saturation magnetization will be impaired.

If the flux amount is less than 0.4, the oxide particles will not be sufficiently wetted, and if it is greater than 4.0, the oxide particles will settle.

Further, the mixing molar ratio of a-Fe203, MnO and ZnO may be arbitrary as long as iron is excessive, but considering the use of ferrite products, especially a-F
e20352-54 moles6. It is preferable that MnO is 21 to 38 mol% and ZnO is 1O to 25 mol%.

Such ferrite powder is i! Used for magnetic shielding materials.

The electromagnetic shielding material is made by dispersing the ferrite powder of the present invention in a polymer matrix or lath.

Dispersed hani is 20-65 m01%, especially 40-60 vo
1% is preferable.

If M lj exceeds 65%, the moldability becomes poor and the properties of the resin deteriorate. Also, it becomes a ball.

Note that when the variance 1+1 becomes 20 Ma01%, the shielding effect becomes small, so 20 Ma01%, especially 4
It is preferable that it is 07015 or more.

Various types of polymer matrices and glues can be used for the IL material to be dispersed. That is, thermosetting resins such as epoxy resins, unsaturated polyester resins, and polyimide resins, or thermoplastic resins such as polyamide resins, polyvinyl chloride resins, polyolefin resins, and styrene resins are selected as appropriate depending on the intended use. You can use it as

Note that the matrine lath may further contain powders, flakes, farpers, etc. of other conductive materials or magnetic materials.

Such a shielding material is produced by heating a thermoplastic resin with a roll heated to around the softening point of the resin.
It is also possible to add and mix m, etc., and then extrude using a T-die extruder or the like to form a sheet.

Similarly, after mixing, a molded product such as a housing may be made using an injection molding machine or the like.

In general, when using a thermosetting resin, an organic solvent and fibers may be added and mixed, and then the organic solvent may be removed and molded under pressure and heat to form a molded product such as a housing.

In addition, a sealing member can be obtained by adding a resin and fiber to an organic solvent, injecting the mixture, and curing the mixture.

In addition, in the electromagnetic shielding material, it is preferable to orient the main surface of the plate-shaped ferrite so as to be perpendicular to the incident direction of the 7rL magnetic wave in terms of electromagnetic wave absorption characteristics.

For this purpose, a magnetic field may be applied during molding.

■ Physical effects of the invention The ferrite powder used in the present invention consists of flat iron-rich particles, so when it is dispersed in a polymer matrix, it has a natural resonance frequency in the low frequency region. It is extremely useful as an electromagnetic shielding material that satisfactorily absorbs radio waves in the low frequency region (lGHz or less).

By the way, normal electromagnetic shielding materials are made of conductive materials such as metals. In such cases, although some of the electromagnetic waves are absorbed due to ohmic loss, most of them are reflected, and as a result, electromagnetic waves are prevented from leaking out of the equipment, but unnecessary electromagnetic waves are trapped inside the equipment and Not only is interference between internal circuits more likely to occur, but also noise leaks from inadequately shielded connectors and cables.

The electromagnetic shielding material of the present invention has absorptive properties.

In other words, by utilizing the magnetic loss of flat ferrite, it not only prevents noise leakage due to the transmission of electromagnetic waves, but also reduces the electromagnetic field strength inside the device by absorbing electromagnetic waves, thereby preventing interference between one circuit. - What to do? # sign.

Furthermore, the ferrite powder used in the present invention is as follows.

By applying the flux method using high-melting point flux and controlling the oxygen concentration in ferrite, it is possible to produce high saturation magnetism and magnetism, making it extremely easy to produce electromagnetic shielding materials. It is advantageous.

(2) Specific Examples of the Invention Below, five specific synthesis examples and examples of the present invention will be shown to explain the present invention in further detail.

Synthesis Example 1 Table-shaped iron oxide, manganese dioxide, and zinc oxide with a major axis of 10 μm are mixed in an aqueous solution so that Fe20353 mo1%, MnO2501%, and Zn022 O1% are mixed in an aqueous solution, filtered, and dehydrated. did.

Add 2SO4 (melting point 1069) to this material as a flux.
℃) was added and mixed in a dry manner.
This was heated at 1150°C in nitrogen at lO! ? It was held for a while and then heat treated.

Next, after appropriately crushing in a mortar, ultrasonic cleaning in water 1.
This was then filtered to remove the flux. The second scanning electron IIO micrograph of the plate-like ferrite after dry storage.
As shown in the figure.

Average g=io tiles m, The average aspect ratio was 10.

On the other hand, for comparison, the same ntr& oxide was mixed and heat treated at 1150° C. for 1 hour to strip the ferrite.

This scanning electron micrograph is shown as the third factor.

It can be seen from the m3 diagram that the elite particles form a neck with each other.

The saturation magnetization of both was measured using a vibrating magnetometer. The results are shown below.

(uninvented) 74.09e abuse u/g (comparison L)
73, 68 emu/g Synthesis Example 2 Tabular iron oxide, manganese dioxide and zinc oxide were mixed in an aqueous solution so that Fe20353 mo1%, Mn034 mo1% and ZnO13 mo1% were mixed, filtered and dehydrated.

Add 2 soa to this material as flux to 118.0
5 wt% was added and mixed in a dry manner.

This was held at 1150°C for 1 hour in nitrogen λ.

Heat treated. Next, the mixture was crushed appropriately in a mortar, and then subjected to ultrasonic cleaning in water. This was filtered to remove the flux. A scanning electron micrograph of the plate-like ferrite after drying is shown in FIG.

Average H=IOμm.

The average aspect ratio was 10.

For comparison, we mixed oxides with the same composition,
Ferrite was obtained by heat treatment at 1200° C. for 1 hour.

The saturation magnetization of both was measured using a vibrating magnetometer. The results are shown below.

(Invention) 84.37e meeting u/g (Comparison 2)
84, l 8! mu/g Synthesis Example 3 Tabular iron oxide, manganese trioxide and zinc oxide were mixed in an aqueous solution so as to have Fe20353 mo1%, Mn025ma1% and Zn022a+o1%, and the mixture was filtered and dehydrated.

This material contains 70.83% heavy clay as a flux.
Soa and 14.05% by weight of Na2SO4 were added and mixed in a dry manner. This was heat-treated by holding it at 1150° C. for 1 hour in nitrogen. Then, it was ground to ia in a mortar and washed in water. This was filtered to remove the flux. When this plate-like ferrite was measured with a vibrating magnetic crab 1, the saturation magnetization was 72,04 emu/g.
There was a time.

Average H = 10 tiles m.

The average aspect ratio was 10.

From the above synthesis examples 1 to 3, the ferrite of the present invention is ^゛6
It can be seen that because it was produced using a melting point flux, there was no decrease in saturation magnetization compared to 7Elite produced without using a flux.

Therefore, in the ferrite synthesis method in the present invention, M n
-Z This can be said to be a failed method for producing iron-rich type plate-shaped ferrite such as n-based ferrite.

Example Using the flat plate-shaped blow powder of the present invention.

A ferrite-resin mixture was prepared as follows and evaluated as an electromagnetic shielding material.

To 46.8 g of ferrite powder and 10.8 g of epoxy resin, 3.6 g of carbon powder was added to supplement electrical conductivity and mixed with a kneader. At this time, about 2 g of tenker thinner was added to facilitate dispersion.

The mixture was poured into a mold made of Teflon and molded into the desired shape.

In this case, a magnetic field was applied to orient the plate-shaped ferrite so that its surface was perpendicular to the direction of incidence of the electromagnetic wave nozzle. The shape of the sample is outer diameter 40.5I1m, inner diameter 15m, thickness 3Il11.
It has a toroidal shape, and was inserted into a coaxial tube to measure the electromagnetic wave transmission ♀ and reflection layer.

In this case, the dispersion value of the ferrite powder is 45 mm.01%.

Transmission lit of the powders of Synthesis Examples 1 to 3 and each comparative example
When the reflection rt was measured, the results shown in Table 1 below were obtained.

Table 1 500MHz 100100O
Transmission tS'1) (dB) Reflection amount (dB) Transmission amount (dB) Reflection (dB) Synthesis example 1 25
3.1 25 3.7 Comparative Example 1 20
17 21 2.0 Synthesis Example 2 2
3 2.0 25 5.8 Comparative Example 2
19 1.3 '20 2.6
]°i Example 3 24 3.0 25
3.8 Comparative Example 3 19 1.5 2
1 2.1 From the results shown in Table 1, the effects of the present invention are clear.

[Brief explanation of drawings]

: The JSI diagram is a graph showing the ratio A between the melting point of the flux and the saturation magnetization of ferrite when the flux is heat-treated at 1150°C for 1 hour in a nitrogen atmosphere. By flux method (FeO)
・(MnO) ・(ZnO)i22 353
, 25 A scanning electron micrograph at a magnification of 5000 times of M′i-formed plate-like ferrite.
3-CMno) T (Zno) Scanning electron microscope at 5000x magnification of 7x light with composition of 22'!
r*, 'jS 4 Figure a and Figure 4b are 1 by the Flagsno people of the present invention (F e 203) ・(M n
0) 34. (Z n O) + magnification of plate-like ferrite with composition of a
This is a scanning electron micrograph at magnification. FIG, 1 Flux f) Melting point (°C) Drawing engraving (Contents (no change)) 'T0.2 11 No. II[] Drawing engraving: ', inside circle; no change 1'J (3,3 TO □--1 101 Uni 1 - Hair System Complete 1j Correct - 1 (Method) February 19, 1985 Manabu Shiga, Commissioner of the Patent Office 1, Display electromagnetic shielding material and its manufacturing method 3, Relationship with the terms of the person making the amendments Patent application colonel Location 13-1 Nihonbashi-chome, Chuo-ku, Tokyo Name (306) TDC Co., Ltd. Representative Kan Otoshi 4, Agent Lot Address Chiyoda, Tokyo 4th floor, Chiyoda Iwamoto Building, 3-2-2 Iwaki-cho, Ward January 29, 1985 (Delivery) "Figures 2, 3, 4a and 4b are substitutes for drawings showing the particle structure of ferrite. Insert "in the photograph." Nidojo, Tanichi S. S. (self-motivated) August 5, 1985 + V + mark 1959 Patent Application No. 200310 2 Title of invention Electromagnetic shielding material and manufacture thereof Method 3, Amendment 1-Relationship with Route 11 Patent Application Director Office
Hikibashi, Chuo-ku, Tokyo - Shimome 13-1 Name
(306) Representative of TEC-DK Co., Ltd.
Address: 1-11-11 Takaido Higashi, Suginami-ku, Tokyo
Name: Takashi Yamaguchi 4, Agent 101 Address: 4th floor, Chiyoda Iwamoto Building, 3-2-2 Iwamotocho, Chiyoda-ku, Tokyo 21864-4498 Fax: 864-62806
．． 7+li Positive contents (1) "rsooo times" in the 8th line, 12th line, and 2nd line from the bottom on page 29 of Specification-1 is corrected to "approximately 4000 times." (2) "r1000x" in the second line from the bottom of page 29,
Correct it to "approximately 800 times." (3) Figures 2, 3, and 4 of the drawings will be replaced as shown in the attached sheet.

Claims (8)

[Claims] (1) An electromagnetic shielding material capable of absorbing electromagnetic waves, characterized in that it consists of iron-rich ferrite particles with a spinel-type structure, and ferrite powder having a flat plate shape is dispersed in a polymer matrix. (2) The electromagnetic shielding material according to claim 1, wherein the ferrite particles are Mn-based, Mn-Zn-based, Ni-based, or Ni-Zn-based. (3) When the average major axis of the particles is @d@, @d@ is 0.
5 μm or more and 500 μm or less, and 90% by weight or more of the total amount has a particle size in the range of 0.3@d@ to 3.4@d@ Electromagnetic shielding material. (4) The electromagnetic shielding material according to any one of claims 1 to 3, which mainly comprises particles having an aspect ratio (major axis/thickness) of 3 or more. (5) The electromagnetic shielding material according to any one of claims 1 to 4, wherein the amount of ferrite powder dispersed is 20 to 65 vol%. (6) The electromagnetic shielding material according to any one of claims 1 to 5, wherein the main plane of the ferrite powder is oriented substantially perpendicular to the direction of incidence of electromagnetic waves. (7) One or more types of sulfate is mixed as a flux with plate-shaped hematite and oxide, or a material that becomes an oxide through heat treatment, and the mixture is heated in an inert gas atmosphere.
After heat treatment at 000°C to 1300°C and sufficient cooling in an inert gas atmosphere, washing with water to remove flux and drying produces ferrite consisting of iron-rich ferrite particles with a spinel structure and a flat plate shape. A method for producing an electromagnetic shielding material capable of absorbing electromagnetic waves, characterized by obtaining powder and dispersing it in a polymer matrix. (8) Claim 7, in which the melting point of the flux made of one or more sulfates is 1000°C or higher.
The method for manufacturing the electromagnetic shielding material described in Section 1.