JP2003229694A - Electromagnetic wave absorbent and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorbent which is improved in complex permeability and superior in electromagnetic wave absorbing properties, and to provide its manufacturing method. <P>SOLUTION: A magnetic paint mainly composed of flat soft magnetic metal material and a high-molecular binder dissolved into an organic solvent is applied onto a separable support 13 with a blade 11 while a magnetic field is applied to the support 13 in a plane direction, and the applied magnetic paint is dried out into an electromagnetic wave absorbing layer. The flat soft magnetic metal material contains 40 to 100 pts.wt. particles which are each 100 to 300 μm in diameter and in the aspect ratio (diameter/thickness) of 70 or above: 1. The number average molecular weight of the high-molecular binder is 30,000 or above, and an aromatic component contained in the molecule is 40 wt.% or above. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended for electronic equipment, communication devices, etc., to absorb noises from the outside, such as electromagnetic waves leaking from the outside, to prevent noise and electromagnetic interference, and to achieve stable functions. The present invention relates to an electromagnetic wave absorber used in and a manufacturing method thereof.

[0002]

2. Description of the Related Art In electronic equipment or communication devices,
BACKGROUND ART An electromagnetic wave absorber is used for the purpose of absorbing noises such as disturbances from the outside and electromagnetic waves leaking from the inside to prevent noise and electromagnetic interference, and achieving a stable function. BACKGROUND ART Conventionally, an electromagnetic wave absorber which has a spinel type ferrite sintered body or a flat type soft magnetic metal as particles and is mixed with a resin to form a composite has been put into practical use. This electromagnetic wave absorber is several MH
It absorbs electromagnetic waves in the range of several GHz from z.

The material parameter relating to the characteristics of such an electromagnetic wave absorber is a complex magnetic permeability μ (= μ'-j
μ ″ which is an imaginary component of μ ″) is involved in the electromagnetic wave absorber. However, the spinel type ferrite sintered body has a demagnetizing field due to its indefinite shape, and the saturation magnetization is low due to the ferrite being an oxide. The body cannot expect high magnetic permeability, which is an important characteristic due to noise suppression. This is expressed by the following equation (1).

Complex permeability μ∝ (Ms) ² / (aK + bλσ) (1) where Ms: saturation magnetization, K: magnetic anisotropy, λ: magnetostriction,
σ: stress, a, b: constant.

In the case of the flat type soft magnetic metal, the saturation magnetization is increased by using the soft magnetic metal. Further, by adopting a flat shape, it is possible to reduce the influence of the demagnetizing field. By arranging the flat metal in the plane of the composite, a composite having a high complex magnetic permeability μ has been provided.

On the other hand, since the electromagnetic wave absorber is used in electronic equipment, it is required to have heat resistance against heat generated by the electronic equipment as well as flame retardancy from the viewpoint of safety.

As a conventional technique for imparting flame retardancy, there is a method of using a polymer binder having high flame retardancy. That is, it is a method of using a halogen resin typified by a polyvinyl chloride resin or a chlorinated polyethylene resin. There is also a method of adding a halogen compound represented by a bromine compound as a flame retardant material separately from the polymer binder. These halogen-based compounds and halogen-based flame retardants have a flame-retardant mechanism in which radicals generated during a combustion reaction are captured by halogens and inactivated. These halogen-based compounds are being reconsidered for their effects on safety during use of electronic equipment, heating at the time of disposal and incineration treatment, or on the global environment.

On the other hand, as the non-halogen flame retardant, there are metal oxide, crystal water type, expansion type, phosphorus type and the like.

Examples of the metal oxides include antimony oxide, molybdenum oxide, manganese oxide, chromium oxide, iron oxide and the like. These are often used as auxiliary agents for halogen-based flame retardants, and the flame retardant effect alone is poor. Also, from the viewpoint of heavy metal pollution, there is a tendency to limit the use in the world.

Examples of the water of crystallization include chemicals containing a large amount of water of crystallization such as calcium hydroxide, magnesium hydroxide and silica gel, which are inexpensive. However, in order to obtain the flame retardant effect equivalent to halogen-based flame retardants, 1 to 2 times the weight of the target product is required.
It is necessary to mix a double amount. In some cases, the weight ratio of the flat type soft magnetic metal material is reduced, and the original performance of the electromagnetic wave absorber is degraded.

On the contrary, the expansion system is expected to prevent the spread of fire due to its adiabatic effect or oxygen-blocking effect, by conversely burning itself to rapidly expand its volume. However, it is not suitable for the purpose of preventing the initial combustion of the electromagnetic wave absorber itself.

Therefore, any flame-retardant polymer bond or flame-retardant was insufficient for the next-generation electronic device application.

[0013]

In recent years, electronic devices have been downsized, and noise radiated from a printed circuit board may adversely affect other devices or electromagnetic waves from the outside may cause malfunctions. The problem is getting serious.
Therefore, in order to save the space and obtain the absorption characteristics equivalent to or better than those of the conventional products, it is necessary to further improve the imaginary number component μ ″ of the complex magnetic permeability of the composite.

It can be understood from the fact that the absorption amount in the electromagnetic wave absorber sheet is proportional to the product of the imaginary number component μ "of the complex magnetic permeability and the sheet thickness as shown in the following equation (2).

Absorption characteristics of electromagnetic wave absorber ∝ Complex magnetic permeability imaginary number component μ "× sheet thickness (2) From this, the complex permeability imaginary number component μ" is increased and the flame retardancy of the sheet is also increased. The need to secure is increasing.

The present invention has been made in view of the above points, and an object thereof is to provide an electromagnetic wave absorber having a high complex magnetic permeability and excellent electromagnetic wave absorbability, and a method for producing the same.

[0017]

The electromagnetic wave absorber of the present invention is an electromagnetic wave absorber mainly composed of a flat type soft magnetic metal material having a large particle size, a polymer binder and a flame retardant plasticizer,
The flat soft magnetic metal material has a particle size of 100 μm or more and an aspect ratio of 70 or more, and the polymer binder has a number average molecular weight of 30,000 or more,
The aromatic component in the molecule is 40% by weight or more.

The method for producing an electromagnetic wave absorber of the present invention is
A magnetic paint prepared by mixing a flat soft magnetic metal material and a polymer material in an organic solvent is applied and dried to form an electromagnetic wave absorbing layer.

In order to increase the complex magnetic permeability μ of the composite, the flat type soft magnetic metal material is made to be huge to narrow the interval between the particles, and the flat type aspect ratio is further increased to improve the antipermeability of the composite. Obtained by reducing the influence of the magnetic field.

In particular, in order to distinguish the enlarging flat type soft magnetic metal material from the current average particle diameter of several tens of μm, the specific surface area is 0.3 m ² / g or less and the aspect ratio is 75 or more. Is characterized by.

However, it is not easy to densely fill the polymer softener with the enlarging flat type soft magnetic metal. Especially if you knead a huge flat soft magnetic metal powder material using a polymer binder, the flat soft magnetic metal material will be broken into a knuckle by the load during kneading because the aspect ratio is high, Or it will be subject to great distortion. The destroyed flat type soft magnetic metal material can no longer benefit from the enlargement. Further, in the strained flat type soft magnetic metal material, the stress term represented by the formula (1) increases and the complex magnetic permeability decreases.

Therefore, the flat soft magnetic metal material and the polymer binder are mixed by using a polymer binder dissolved in a solvent and mixing the metal material without applying a load. The metal material and a polymer binder dissolved in a solvent are mixed, and a magnetic field is applied to the mixture to coat the support.

By applying a magnetic field, the effect of orienting and arranging the flat soft magnetic metal in the in-plane direction can be obtained during coating and after coating, and it is possible to fill the soft magnetic material at a high density. Orientation of flat type soft magnetic metal without magnetic field
The array is subjected to natural orientation after coating, but the packing density does not increase and the orientation state cannot be optimized. As a result, the magnetic permeability of the electromagnetic wave absorber sheet as a whole is lowered, and the electromagnetic wave absorption characteristics are lowered.

Further, the coating thickness is 0.2 mm after drying.
By keeping the amount below, it is possible to accelerate the evaporation of the solvent and form an electromagnetic wave absorber sheet having few pores, which is a problem in coating. When the coating thickness is 0.2 mm or more, the solvent evaporative gas is occluded by the binder film and the giant flat type soft magnetic metal formed on the first main surface which has been dried previously, and the evaporative gas is accumulated inside. Therefore, it is not a preferable method for densely filling the soft magnetic material in order to generate pores.

After coating, two electromagnetic wave absorber sheets are firstly placed.
By adhering the main surfaces to each other and applying pressure, an electromagnetic wave absorber sheet with few pores and high packing density can be obtained. When the main surfaces are bonded to each other and the main surfaces are dry, if a solvent is applied and bonded later, the effect of reducing voids is high. By bonding the principal surfaces to each other, the second principal surface on the releasable support appears on both surfaces, so that it also has the effect of reducing the surface roughness.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The electromagnetic wave absorber of the present invention will be described below in detail with reference to the drawings. The basic configuration of the electromagnetic wave absorber of the present invention is shown in the schematic sectional view of FIG. Two electromagnetic wave absorber sheets 15 are laminated on the peelable support 13. Although the drawing shows the stacking boundary line, the stacking boundary line does not occur in those actually stacked.

FIG. 2 shows a sheet obtained by stacking a plurality of the electromagnetic wave absorber sheets 15 of the present invention. A solvent, an adhesive or the like is used for the lamination, and a pressure-bonding method is used. By laminating a plurality of sheets in this way, it is possible to improve the electromagnetic wave absorption characteristics. In FIG. 1 and FIG. 2, 17 is a flat type soft magnetic metal material used for an electromagnetic wave absorber.

The releasable support 13 is paper, paper laminated with a polymer resin such as polyolefin, polymer resin,
Cloth, non-woven fabric, metal, glass, etc. are used. Of these, thin and strong polymer resins are preferably used. The polymer resin is not particularly limited, but polyesters such as polyethylene phthalate, polyethylene-2, and 6-naphthalate, polyolefins such as polyethylene and polypropylene, and fluorine obtained by substituting a part or all of hydrogen of these polyolefins with a fluororesin. Resin, cellulose triacetate, cellulose derivative such as cellulose diacetate, vinyl resin such as polyvinyl chloride, vinylidene resin such as polyvinylidene chloride, polycarbonate, polyphenylene sulfide, polyamide imide,
Examples include polyimide. Further, the surface of these polymer resins may be subjected to a release treatment with a release agent such as silicone resin. These polymer resins are preferably plate-shaped or film-shaped. In the case of a plate, the thickness is about several hundred μm to several mm, and in the case of a film, the thickness is about several μm to several mm.

The composition of the flat soft magnetic metal material 17 is not particularly limited, and may be FeSi, FeNi, FeSiA.
1, iron-based soft magnetic metals such as FeNiSiB and FeSiB, and cobalt-based soft magnetic metals such as CoFeSiB. The particle size of these flat soft magnetic metal materials is 100 to 3
Those containing 40 to 100 parts by weight of a particle size of 00 μm and an aspect ratio of 70 or more are adopted.

The binder used in the electromagnetic wave absorber is not particularly limited either, but either a thermosetting resin or a reactive resin can be used. As the molecular weight of the resin, one having a number average molecular weight of 30,000 or more is adopted.

Examples of the thermosetting resin and the reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea formaldehyde resin, melamine resin, alkyd resin, silicone resin, polyamine resin, high molecular polyester resin and isocyanate prepolymer. Examples include mixtures of polymers, mixtures of polyester polyols and polyisocyanates, mixtures of low molecular weight glycols, polymeric diols and isocyanates, and mixtures of these resins. Among these resins, it is preferable to use a polyurethane resin, a polycarbonate resin, a polyester resin, an acrylonitrile-butadiene copolymer, etc., which are supposed to give flexibility.

These resins are dispersions of flat type soft magnetic metal.
-SO to improve₃M, -OSO₃M, -COO
M, or -PO (OM ')₂Contains polar functional groups such as
(However, M is H, Li, K
a, an alkali metal such as Na, M'is H or Li, K
Represents an alkali metal such as a, Na or an alkyl group
). Other polar functional groups include -NR₁R₂, -NR
₁R₂R₃ ⁺X^-Side chain type having an end group of₁R
₂ ⁺X^-Main chain type, etc. (where R₁, R₂, R ₃Is
A hydrogen atom or a hydrocarbon group, X^-Is fluorine, charcoal
Halogen ions such as elemental, bromine and iodine, or inorganic,
Represents machine ion). In addition to this, -OH, -SH, -C
It may be a polar functional group such as N or an epoxy group. these
The content of polar functional groups is 10^-1-10^-8mol / g
, Preferably 10^-2-10^-6It is mol / g. this
Although the organic binder can be used alone,
It is also possible to use two or more types together.

Among the above-mentioned binders and binders, for example, polyisocyanate or the like can be added as a curing agent for crosslinking and curing the curable resin. Polyisocyanates include trimethylolpropane and 2,4-
An adduct of tolylene diisocyanate (TDI) (for example, trade name Coronate L-50) is generally used.
-Alkylene diisocyanate adducts such as diphenylmethane diisocyanate (MDI) and hexane diisocyanate (HDI) may be used. In addition, tetraglycidyl metaxylenediamine, tetraglycidyl-1,3-bisaminomethylcyclohexane, tetraglycidylaminodiphenylmethane, triglycidyl-p
-A polyglycidylamine compound such as aminophenol,
2-dibutylamino-4,6-dimercapto-substituted triandi and other polyol compounds, triglycidyl isocyanate and other epoxy compounds, epoxy compound and isocyanate compound mixtures, epoxy compound and oxazoline compound mixtures, imidazole compound and isocyanate compound mixtures, anhydrous Any of methylnazic acid and conventionally known ones can be used. The mixing ratio of these curing agents to the curable resin is 0.5 to 80 parts by weight, preferably 5 to 50 parts by weight, based on 100 parts by weight of the curable resin. By adding the curing agent within this range, the bondability with the flat soft magnetic metal material is enhanced, and the mechanical strength of the electromagnetic wave absorber is improved. These isocyanate compounds may be applied to the surface of the coating film after forming the coating film of the electromagnetic wave absorber. In this case, the surface layer of the electromagnetic wave absorber is hardened to prevent the flat soft magnetic metal from falling off from the binder.

In any of the polymer binders, it is desirable that the aromatic component in the molecule is 40% by weight or more. Those having no aromatic ring in the molecule may be blended with another polymer binder having an aromatic ring to achieve this value.

The electromagnetic wave absorber of the present invention may contain an organic silane compound. The organosilane compound enhances the reinforcing effect at the interface between the flat soft magnetic metal material and the polymer binder, and enhances the mechanical strength of the electromagnetic wave absorber. Examples of the organic silane compound include vinyltrichlorosilane and vinyltris (β-
(Methoxyethoxy) silane, vinyltriethoxysilane, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylethoxysilane, β- (3,4epoxycyclohexyl) ethyltrimethoxysilane, γ-glycid Xypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β- (aminoethyl) γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) γ-aminopropylmethyldimethoxysilane, γ -Aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane and the like are exemplified. It is not limited to these.

If necessary, other additives such as a lubricant, a reinforcing pigment, conductive particles, an antistatic agent, a surfactant and a stabilizer may be used in the electromagnetic wave absorber. For these additives, conventional general materials and compounding ratios can be adopted.

Lubricants include graphite, molybdenum disulfide, tungsten disulfide, fatty acids having up to about 2 to 26 carbon atoms, fatty acid esters consisting of fatty acids and alcohols having up to about 2 to 26 carbon atoms, terpene compounds, and the like. All of the conventionally known compounds such as oligomers, silicone oils, and fluorine lubricants are included.

Examples of the reinforcing pigment include inorganic pigments such as silicone oxide, aluminum oxide, calcium carbonate, carbon fiber and glass fiber. The amount of the reinforcing pigment added is 20 parts by weight or less, preferably 5 parts by weight or less, based on 100 parts by weight of the soft magnetic metal.

As conductive particles and antistatic agents, carbon black, graphite, metal particles, tin oxide, ITO (I
A conductive oxide such as ndium tin oxide) or a surfactant is used.

As the surfactant, any of conventionally known nonionic, cationic, anionic or amphoteric compounds may be used.

There are no particular restrictions on the solvent used to prepare the coating composition containing the soft magnetic metal material, polymer binder and organic silane compound as the main components, and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc. , Alcohols such as methanol, ethanol, propanol, butanol, esters such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl lactate, ethyl glycol acetate, diethylene glycol dimethyl ether, 2-ethoxyethanol,
Ethers such as tetrahydrofuran and dioxane, aromatic hydrocarbon compounds such as benzene, toluene and xylene,
Halogenated hydrocarbon compounds such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and chlorobenzene can be used. Again, it is preferable to use a solvent containing no chlorine from the viewpoint of safety.

A kneader, agitator, ball mill, sound mill, roll mill, extruder, homogenizer, ultrasonic disperser and the like can be used as a dispersing and kneading device for adjusting the coating material. Among these dispersing and mixing devices, an agitator, a ball mill, a roll mill, a homogenizer, and an ultrasonic disperser which do not break or strain the soft magnetic metal material are preferable.

The coating method for forming the electromagnetic wave absorbing layer on the support is not particularly limited, and may be an air doctor coat,
Blade coat, wire bar coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, extrusion coat,
Any conventional method such as die coating or spin coating can be adopted. By using these types of coating equipment,
It can be coated on one side or both sides of the support.

As a method of magnetic field orientation of the electromagnetic wave absorber, there are magnetic field directions such as an in-plane magnetic field and a vertical magnetic field. The orientation by the magnetic field holds the magnetic field in the direction for orienting the flat soft magnetic metal material. The strength of the magnetic field varies depending on the polymer binder dispersed in the solvent and the flat type soft magnetic metal material, but a range of 30 to 300 kA / m is generally selected.

The method for laminating and pressing the electromagnetic wave absorber is
Molding, pressure thermoforming, molding with adhesives and adhesives, etc.
Used. Add the solvent after impregnating and swelling the electromagnetic wave absorbing layer with a solvent.
It may be pressure-formed. Pressurization conditions depend on the type of polymer binder
Type, presence or absence of heating, heating temperature, number of electromagnetic wave absorbers, thickness
Generally, 0.1-500 kg / cm
²The range of is selected. 250 ° C or less for heat molding
Is desirable. For pressure molding and pressure thermoforming,
Ordinary press equipment and roll laminators are used.
It

(Embodiment Examples) Hereinafter, preferred embodiment examples of the present invention will be described in more detail with appropriate comparison examples, but the present invention is not limited to these embodiment examples. [Embodiment 1] As a flat type soft magnetic metal material, CoFeSiB having the following characteristics was adopted.

Particle size Thickness 1 μm, Diameter 25 to 300 μm (Aspect ratio 25 to 300) Particle size distribution 25 to 50 15% by weight 50 to 100 25% by weight 100 to 300 60% by weight Specific surface area 0.2 m ² / g Saturation magnetic flux density 75 Am ² / kg The particle size of the flat soft magnetic metal material was the thickness and diameter of 500 unit particles of the soft magnetic metal randomly extracted by observation with a transmission electron microscope. Particle size distribution is 2 each
Using a sieve having a mesh size of 5, 50, 100 or 300 μm, the weight in each size was measured and used as the particle size distribution.
The specific surface area was measured by the BET method. For the saturation magnetic flux density, the saturation magnetic flux density at 12 MA / m was measured with a VMS measuring machine.

(Preparation of paint for electromagnetic wave absorber) Polyurethane resin (Vylon manufactured by Toyobo Co., Ltd.) (polymer binder: number average molecular weight 30,000, aromatic component in the molecule 45 weight) %) And a phosphoric acid ester oil and fat as a phosphorus compound (CR manufactured by Daihachi Chemical Industry Co., Ltd.
-741) (2% by weight of phosphorus element in phosphoric acid compound) was mixed by a ball mill and uniformly dispersed to form a coating material.
The compounding composition is shown below.

CoFe-based flat type soft magnetic metal material 100 parts by weight Polyurethane resin 9 parts by weight (Byron manufactured by Toyobo Co., Ltd.) Phosphate ester fats and oils 2 parts by weight (CR-741 manufactured by Daihachi Chemical Industry Co., Ltd.) γ-amino Propylethoxysilane 0.1 part by weight (A1100 manufactured by Nippon Unicar Co., Ltd.) Methyl ethyl ketone 25 parts by weight Toluene 2 parts by weight The composition made into a paint has 0.5 parts by weight of polyisocyanate (Coronate HL manufactured by Nippon Polyurethane Co.) immediately before coating. In addition, the mixture was further mixed to obtain a coating material for the electromagnetic wave absorber layer.

(Molding of Electromagnetic Wave Absorbing Layer) FIG. 3 shows a state of molding the electromagnetic wave absorber sheet. As an example, thickness is 50 μm
A sheet was coated with a doctor blade 11 on the one main surface side of the peelable support 13 made of the polypropylene film described above. In FIG. 3, 10 is a paint for an electromagnetic wave absorber, 12 is a magnetic field, 13 is a peelable support, and 14 is a magnetic field.

The coating thickness of the paint 10 is 0.4 m when wet.
m and 0.15 mm after drying. Immediately after coating, a magnetic field 12 of 25 MA / m is applied in the traveling direction to orient the flat soft magnetic metal.

The two sheets oriented in the magnetic field are attached to each other with their first main surfaces bonded to each other, and the electromagnetic wave absorber sheet is pressure-molded through the compression molding machine shown in FIG. In FIG. 4, 13 is a peelable support, 15 is an electromagnetic wave absorber sheet, and 16 is a roll press. At this time, if the main surface is dry, a solvent is applied later and pressure is applied.

In the present embodiment, in order to measure the pores of the electromagnetic wave absorber, the density of the sheet was measured with a density measuring machine (made by Shimadzu Corporation) using the Archimedes method to determine the pores in the sheet. . Regarding the electromagnetic wave absorption characteristics, μ ″, which is an imaginary number component of complex magnetic permeability, was measured and evaluated by an impedance analyzer. [Embodiment Examples 1 to 4] employs a flat type soft magnetic metal material having the same composition as that of Embodiment Example 1. Then, except that the particle size distribution was changed, the electromagnetic wave absorber sheets of Embodiments 1 to 4 were obtained according to the above Embodiment 1. [Prior Art 1 to
3] employs a flat type soft magnetic metal material having the same composition as that of the first embodiment and changes the particle size distribution to a range that is more preferable in the conventional sheet production. According to the above, the electromagnetic wave absorber sheets of Conventional Examples 1 to 3 were obtained. Reference Examples 1 and 2 are the same as those of Embodiment 1 except that a flat soft magnetic metal material having the same composition as that of Embodiment 1 is used and the particle size distribution and aspect ratio are changed. The electromagnetic wave absorber sheet 2 was obtained. [Embodiment 5]
Is an electromagnetic wave absorber of the type (n = 3) shown in FIG. 2 in which only the electromagnetic wave absorbing layer is laminated in the same manner as in Embodiment 1,
The peelable support 13 was peeled off to obtain the electromagnetic wave absorber of Example 5 having only three electromagnetic wave absorbing layers.

Table 1 shows the production results of the electromagnetic wave absorbers of Embodiments 1 to 5, Conventional Examples 1 to 3 and Reference Examples 1 and 2.

[0055]

[Table 1]

(Study of Particle Size Distribution of Flat Soft Magnetic Metal) A series of samples of Embodiment Examples 1 to 4, Conventional Examples 1 to 3 and Reference Example 1 showed that the particle shape of the flat soft magnetic metal was an electromagnetic wave absorber. We investigated how it affects the imaginary components of porosity and complex permeability. From the results of Embodiments 1 to 4, the particle size is 1
When it is contained in an amount of 00 μm to 300 μm and 40 parts by weight or more, it is preferable that it is 15 or more higher than the imaginary number component μ ″ 12 of the complex magnetic permeability when a large number of particle diameters 100 μm or less shown in Conventional Examples 1 to 3 are used. Recognize.

(Study of Aspect Ratio of Flat Soft Magnetic Metal) Embodiments 1 to 4, Conventional Examples 1 to 3 and Reference Examples 1 and 2
A series of samples were examined to see how the aspect ratio of the flat type soft magnetic metal affects the porosity and the imaginary component of the complex magnetic permeability of the electromagnetic wave absorber.

FIG. 5 is a graph showing the relationship between the aspect ratio and the imaginary number component μ ″ of the complex magnetic permeability. From this graph, the imaginary number component μ ″ of the complex permeability is 70 or more and the imaginary number component μ ″ of the complex magnetic permeability is 15 ”.
It turns out that it is above. On the other hand, the aspect ratio is 7
If it is less than 0, the imaginary number component μ ″ of the complex magnetic permeability does not reach 15. Therefore, it is understood that the aspect ratio of 70 or more is preferable.

FIG. 6 is a graph showing the relationship between the aspect ratio and the sheet porosity.

(Effects when a plurality of electromagnetic wave absorber sheets are superposed) From the samples of Embodiment 1 and Embodiment 5, when a plurality of electromagnetic wave absorber sheets are superposed, the porosity of the electromagnetic wave absorber is And how it affects the imaginary component of complex permeability.

As a result, even if a plurality of electromagnetic wave absorber sheets were stacked, there was no effect on the imaginary component of the complex magnetic permeability. However,
By increasing the number of sheets, the absorption characteristics of the electromagnetic wave absorber are improved according to the formula (2). [Embodiment 6] employs the same flat type soft magnetic metal material as that of Embodiment 1, while using as the polymer binder a polyurethane resin having a number average molecular weight of 30,000 and an aromatic component concentration of 40% by weight in the molecule. Adopted, and others
An electromagnetic wave absorber sheet was obtained according to the first embodiment. [Embodiment 7] has a number average molecular weight of the polymer binder of 40,000.
An electromagnetic wave absorber sheet was obtained in the same manner as in Example 6 except that the above was changed. In [Embodiment 8], an electromagnetic wave absorber sheet was obtained according to Embodiment 6 except that the addition amount of the phosphoric acid compound was changed to 1 part by weight. [Embodiment 9] is different from the phosphoric acid compound used as the flame retardant in the solid form of ammonium polyphosphate in that the original addition amount was changed to 5 parts by weight.
An electromagnetic wave absorber sheet was obtained according to the sixth embodiment.
[Embodiment 10] is the same as Embodiment 9, except that the phosphoric acid compound is changed to a solid-state ammonium polyphosphate salt similar to Embodiment 9, and the original addition amount is changed to 4 parts by weight. According to 6, an electromagnetic wave absorber sheet was obtained. In [Reference Example 3], an electromagnetic wave absorber sheet was obtained according to Embodiment 6 except that the addition amount of the phosphoric acid compound was changed to 0.5 part by weight. Reference Example 3 is below the desired concentration as a liquid phosphoric acid compound. In addition, Embodiments 6 and 8 and Reference Example 3 are a series of samples in which the addition amount of the liquid phosphorus compound is changed. In [Reference Example 4], the phosphoric acid compound as a flame retardant was changed to the same solid ammonium polyphosphate salt as in the embodiment, and the addition amount was changed to 3, and the electromagnetic wave absorber sheet was prepared according to the above-mentioned Embodiment 3. Got Reference Example 4 has a concentration lower than the desired concentration as a solid phosphoric acid compound. The embodiment examples 9 and 10 and the reference example 4 are a series of samples in which the addition amount of the solid phosphorus compound is changed. In [Comparative Example 1], the same flat type soft magnetic metal material as that of Embodiment 1 was adopted. On the other hand, as the polymer binder, an electromagnetic wave absorber sheet was obtained in the same manner as in Example 1 except that a polyurethane resin having a number average molecular weight of 30,000 and an aromatic component concentration of 35% by weight in the molecule was used.
The aromatic component concentration of the polymer binder of Comparative Example 1 is lower than the polymer binder aromatic component concentration proposed by the present invention. In [Comparative Example 2], the same flat type soft magnetic metal material as that of Embodiment 1 was adopted. On the other hand, as the polymer binder, an electromagnetic wave absorber sheet was obtained according to the first embodiment except that a polyurethane resin having a number average molecular weight of 20,000 and an aromatic component concentration of 40% by weight in the molecule was used. The number average molecular weight of the polymer binder of Comparative Example 2 is lower than the number average molecular weight of the polymer binder proposed by the present invention. [Comparative Example 3] is the first embodiment.
The same flat type soft magnetic metal material as was used. On the other hand, a chlorinated polyethylene resin having a number average molecular weight of 20,000 was adopted as the polymer binder. An electromagnetic wave absorber sheet was obtained according to the first embodiment except that no flame retardant was used.
The polymer binder of Comparative Example 3 is a resin containing halogen.

As described above, Embodiments 1, 6 to 10 and Reference Example 3,
Table 2 shows the production results of the electromagnetic wave absorbers of Example 4 and Comparative Examples 1 to 3.

[0063]

[Table 2]

Next, regarding the flame retardant performance evaluation method, UL-
According to the 94 flame resistance test method (20 mm vertical combustion test method), the same sample was tested 5 times, and the total combustion time was measured to obtain V-
It was evaluated by classifying it as 0, V-1 and V-2. This test method is described in detail in "UL94 Safety Standards, Combustion Testing of Plastics Materials for Equipment Parts, Fifth Edition, October 29, 1996".

(Regarding the number average molecular weight of the polymer binder)
From the samples of Embodiments 6 and 7 and Comparative Example 2, when the number average molecular weight of the polyurethane resin is 30,000 or more, good results such as V-0 are obtained, but the number average molecular weight of 20,0.
It can be seen that with 00, the flame retardancy is inferior to V-1.

(Concentration of Aromatic Component in Polymer Binder) From the samples of Embodiments 1 and 6 and Comparative Example 1, when the aromatic component concentration of the polyurethane resin is 40% by weight or more, V-
Although a good result of 0 was obtained, it was found that when the aromatic component concentration was 35% by weight, the flame retardancy was significantly inferior to V-2 or less.

(Regarding Addition Amount of Liquid Flame Retardant) From the samples of Examples 6 and 8 and Reference Example 3, when the addition amount of the liquid flame retardant was 1 part by weight or more, good results equivalent to V-0 were obtained. However, it can be seen that when the amount added is 0.5 part by weight, the flame retardancy is inferior to V-1.

(Regarding Addition Amount of Solid Flame Retardant) From the samples of Examples 9 and 10 and Reference Example 4, when the addition amount of the liquid flame retardant was 4 parts by weight or more, good results equivalent to V-0 were obtained. However, it can be seen that the flame retardancy is inferior to V-1 when the amount added is 3 parts by weight. In [Comparative Example 4], a magnetic field was not applied from the electromagnetic wave absorber of Embodiment 1 during sheet formation, and an electromagnetic wave absorber of Comparative Example 4 was obtained in the same manner as in Embodiment 1 except for the above. [Comparative Example 5] does not use a method in which two sheets, which are magnetically oriented from the electromagnetic wave absorber of Embodiment 1, are bonded to each other at their first main surfaces and the sheets are pressed through the compression molding machine shown in FIG. In other cases, an electromagnetic wave absorber of Comparative Example 5 was obtained in the same manner as in Example 1 except for the above. [Comparative Example 6] has been partially described above, but the manufacturing method will be described again.
A general method other than mixing the flat-type soft magnetic metal and the binder dissolved in a solvent from the electromagnetic wave absorber of Embodiment 1 and coating the mixture on a peelable support while applying a magnetic field in the in-plane direction. I did. First, a flat soft magnetic metal and chlorinated polyethylene as a thermoplastic elastomer were mixed with a two-roll mill and uniformly dispersed. The compounding composition is shown below.

CoFe-based soft magnetic metal 100 parts by weight Chlorinated polyethylene resin 11 parts by weight (manufactured by Showa Denko) Epoxidized soybean oil 0.3 double parts Molding was performed in a two-roll machine until the molding thickness was 0.
It was adjusted to be 15 mm. At this time, no magnetic field is applied. An electromagnetic wave absorber of Comparative Example 6 was obtained according to the first embodiment except for the above. Comparative Example 7 is Comparative Example 6
In the same manner as in Example 1, except that the flat soft magnetic metal and the binder dissolved in the solvent are mixed from the electromagnetic wave absorber of Embodiment 1 and coating is performed on the peelable support while applying a magnetic field in the in-plane direction. Was done. First, a flat soft magnetic metal and a silicone rubber as a thermoplastic elastomer were mixed with a two-roll mill and uniformly dispersed. The compounding composition is shown below.

CoFe-based soft magnetic metal 100 parts by weight Silicone rubber 11 parts by weight Molding was carried out in a two-roll machine until the molding thickness was 0.
It was adjusted to be 15 mm. At this time, no magnetic field is applied. As described above, an electromagnetic wave absorber of Comparative Example 7 was obtained according to the first embodiment except for the above.

Table 3 shows the production results of the electromagnetic wave absorbers of Embodiment 1 and Comparative Examples 4 to 7.

[0072]

[Table 3]

(Magnetic field orientation during coating) How the magnetic field orientation during coating affects the porosity and the imaginary component of the complex magnetic permeability of the electromagnetic wave absorber by the samples of Embodiment 1 and Comparative Example 4 Examined.

As a result, when no magnetic field is applied, the number of holes increases and the imaginary component of the complex magnetic permeability remains low. From this fact, the magnetic field orientation during coating is effective.

(Effects of Bonding the First Main Surfaces and Pressurizing) The samples of Embodiment 1 and Comparative Example 5
It was examined how bonding the first main surfaces of the electromagnetic wave absorber sheet to each other and pressurizing the same has an effect on the porosity and the imaginary component of the complex magnetic permeability of the electromagnetic wave absorber.

As a result, as in Comparative Example 5, when the principal surfaces were adhered to each other and pressure was not applied, the number of holes increased,
The imaginary component of the complex magnetic permeability is also low. From this, it is preferable that the first main surfaces of the electromagnetic wave absorber sheet are adhered to each other and pressed.

(Effect of Using Binder Dissolved in Solvent) According to the samples of Embodiment 1 and Comparative Examples 6 and 7, the binder dissolved in the solvent shows the porosity and complex magnetic permeability of the electromagnetic wave absorber. I investigated how it affects the imaginary component.

As a result, when the thermoplastic elastomer is used, the value of the imaginary component of the complex magnetic permeability is small, although the sheet porosity is small. From the result of the observation with the optical microscope, it can be seen that the cause is that the flat soft magnetic metal is broken or distorted and the characteristics are deteriorated. From this, when forming a flat type soft magnetic metal sheet having a large particle size, it is necessary to use a binder dissolved in a solvent. [Embodiment 11
12] are coating thicknesses of 100 and 200, respectively.
This is the case of μm, and the electromagnetic wave absorbers of Embodiments 11 and 12 were obtained according to Embodiment 1 otherwise. [Comparative Example 8] is a case where the coating thickness is larger than the desired coating
An electromagnetic wave absorber of Comparative Example 8 was obtained in the same manner as in Example 1 except for the above. In [Comparative Example 9], the electromagnetic wave absorber of Comparative Example 9 was obtained according to the first embodiment except that the coating thickness was smaller than the desired thickness.

Table 4 shows the production results of the electromagnetic wave absorbers of Embodiments 1, 11 and 12 and Comparative Examples 8 and 9.

[0080]

[Table 4]

(Study on Thickness at Coating)
From the series of samples of Embodiment Examples 1, 11, and 12 and Comparative Examples 8 and 9, it was examined how the coating thickness affects the porosity and the imaginary component of the complex magnetic permeability of the electromagnetic wave absorber. .

FIG. 7 is a graph showing the relationship between the coating thickness and the imaginary number component μ ″ of the complex magnetic permeability. From this graph, it can be seen that the coating thickness is 200 or more or less than 100 and the imaginary number component μ ″ of the complex magnetic permeability is 15 or less. You can see.
On the other hand, when the coating thickness is in the range of 100 to 200, the imaginary number component μ ″ of the complex magnetic permeability becomes 15 or more.
It can be seen that mm is preferable.

FIG. 8 is a graph showing the relationship between coating thickness and sheet porosity. From this graph, the coating porosity is 2 when the coating thickness is 200 or more or less than 100.
It turns out that it becomes 2 or more. On the other hand, since the sheet porosity is 22 or less in the coating thickness range of 100 to 200, it is understood that the coating thickness is preferably 100 to 200 mm after the sheet is dried.

Therefore, it is understood that the coating thickness is preferably 100 to 200 mm after the sheet is dried.

The detailed description of the method for producing the electromagnetic wave absorber of the present invention has been given above, but these are merely examples, and the present invention is not limited to these experimental examples. That is, it goes without saying that the size of the particle diameter, the aspect ratio, the type of soft magnetic metal or binder, the molecular weight, the type of flame retardant, the laminated structure, and the coating method can be appropriately changed. In addition to a film-shaped or plate-shaped support as the support, the support can be applied to a casing of various electronic devices.

[0086]

As described above, according to the present invention as set forth in claims 1 to 12, a sheet is produced at a high density without breaking or straining a flat type soft magnetic metal having a large grain size. It is possible to do Further, a high electromagnetic wave absorbing effect can be expected while avoiding the use of a halogen-based material as the polymer binder and ensuring flame retardancy. As a result, it is possible to provide an electromagnetic wave absorber that is preferable as an environmental measure and that is light and thin and that has sufficient characteristics. (2) According to the present invention as set forth in claims 5 to 8, since the electromagnetic wave absorbing layer is formed while applying a magnetic field, an effect of orienting and arranging the flat soft magnetic metal in the in-plane direction can be obtained.
The soft magnetic metal material is densely packed. Therefore, it is possible to manufacture an electromagnetic wave absorber having a high complex magnetic permeability and excellent electromagnetic wave absorption characteristics. (3) According to the present invention as set forth in claim 9, the polymer binder can be mixed without applying a load to the flat soft magnetic metal material. It is possible to increase the magnetic susceptibility and manufacture an electromagnetic wave absorber having more excellent electromagnetic wave absorption characteristics. (4) According to the present invention of claim 10, since evaporation of the solvent is promoted, it is possible to manufacture an electromagnetic wave absorption layer having few pores during coating, and the soft magnetic metal material is packed at a high density. It Therefore, it is possible to manufacture an electromagnetic wave absorber having a high complex magnetic permeability and excellent electromagnetic wave absorption characteristics. (5) Further, according to the present invention described in claim 11, it is possible to manufacture an electromagnetic wave absorbing layer with few holes, and the soft magnetic metal material is packed at a high density. Therefore, it is possible to manufacture an electromagnetic wave absorber having a high complex magnetic permeability and excellent electromagnetic wave absorption characteristics. Further, by adhering the main surfaces of the electromagnetic wave absorbing layer to each other, the second main surface on the releasable support appears on both surfaces, so that the surface roughness of the surface can be reduced. (6) According to the present invention of claim 12, the electromagnetic wave absorption characteristics of the electromagnetic wave absorber can be further improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a basic configuration of an electromagnetic wave absorber sheet according to the present invention.

FIG. 2 is a perspective view showing a laminated electromagnetic wave absorber sheet according to the present invention.

FIG. 3 is an explanatory view showing a state of coating in an embodiment of the present invention.

FIG. 4 is an explanatory view showing a state of compression molding in an embodiment of the present invention.

FIG. 5 is a graph showing a relationship between an aspect ratio and an imaginary component of complex magnetic permeability in an electromagnetic wave absorber.

FIG. 6 is a graph showing the relationship between the aspect ratio and the sheet porosity in the electromagnetic wave absorber.

FIG. 7 is a graph showing the relationship between the sheet thickness and the imaginary component of complex magnetic permeability in the electromagnetic wave absorber.

FIG. 8 is a graph showing the relationship between the sheet thickness and the sheet porosity in the electromagnetic wave absorber.

[Explanation of symbols]

10 ... Paint, 11 ... Blade, 12 ... Magnetic field, 13 ... Peelable support, 14 ... Magnetic field, 15 ... Electromagnetic wave absorber sheet, 1
6 ... Roll press, 17 ... Flat soft magnetic metal material.

Claims (12)

[Claims] 1. An electromagnetic wave absorber comprising an electromagnetic wave absorbing layer mainly composed of a flat soft magnetic metal material and a polymer binder, wherein the flat soft magnetic metal material has a particle diameter of 100 to 300 μm.
An electromagnetic wave absorber containing 40 to 100 parts by weight of a particle diameter of m and having an aspect ratio (diameter / thickness ratio) of 70 or more. 2. The number average molecular weight of the polymer binder is 3
The electromagnetic wave absorber according to claim 1, characterized in that the amount of aromatic component in the molecule is 40% by weight or more, while the amount is 2,000 or more. 3. The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorbing layer further contains a phosphorus compound in one of a liquid state and a solid state. 4. The amount of elemental phosphorus in the phosphorus compound is 1.0 part by weight or more with respect to 100 parts by weight of the flat soft magnetic metal material in the case of a liquid phosphorus compound, and the amount of the phosphorus compound in a solid state. On the other hand, the amount is 4.0 parts by weight or more.
The electromagnetic wave absorber according to. 5. A magnetic paint mainly composed of a flat soft magnetic metal material and a polymer binder dissolved in an organic solvent is applied and dried on a releasable support while applying a magnetic field in the in-plane direction. The flat soft magnetic metal material has a particle size of 100 to 300 μm.
A method for producing an electromagnetic wave absorber, which comprises 40 to 100 parts by weight of a particle diameter of m and has an aspect ratio (diameter / thickness ratio) of 70 or more. 6. The number average molecular weight of the polymer binder is 3
The method for producing an electromagnetic wave absorber according to claim 5, wherein the amount of aromatic component in the molecule is 40% by weight or more while the amount is 2,000 or more. 7. The method of manufacturing an electromagnetic wave absorber according to claim 5, wherein the electromagnetic wave absorbing layer contains a phosphorus compound in one of a liquid state and a solid state. 8. The amount of elemental phosphorus in the phosphorus compound is 1.0 part by weight or more with respect to 100 parts by weight of the flat type soft magnetic metal material in the case of a liquid phosphorus compound, and is relative to the solid phosphorus compound. 8. The method for producing an electromagnetic wave absorber according to claim 7, wherein the total amount is 4.0 parts by weight or more. 9. The electromagnetic wave absorber according to claim 5, wherein the magnetic paint is formed by mixing the flat soft magnetic metal material and a polymer binder dissolved in an organic solvent. Body manufacturing method. 10. The method for producing an electromagnetic wave absorber according to claim 5, wherein the coating thickness of the magnetic paint is 0.2 mm or less after the sheet of the electromagnetic wave absorption layer is dried. 11. The method of manufacturing an electromagnetic wave absorber according to claim 5, further comprising a step of adhering and pressing the electromagnetic wave absorbing layers. 12. The method of manufacturing an electromagnetic wave absorber according to claim 5, further comprising a step of laminating a plurality of the electromagnetic wave absorption layers.