HK1098631B - Electromagnetic wave absorber - Google Patents

Description

Electromagnetic wave absorber

Technical Field

The present invention relates to an electromagnetic wave absorber, an electromagnetic wave absorber having a wide band frequency characteristic, and a laminated electromagnetic wave absorber. In particular, the present invention relates to an electromagnetic wave absorber which is excellent in electromagnetic wave absorbability, thermal conductivity, flame retardancy, small temperature dependency, flexibility, excellent adhesion strength, high electric resistance, high insulation property, and no adhesion limitation; an electromagnetic wave absorber having a wide band frequency characteristic, and a laminated electromagnetic wave absorber having excellent electromagnetic wave absorbability and electromagnetic wave shielding properties, which can be attached to the top surface of a case and also to a radioactive source of unnecessary electromagnetic waves such as a high-speed computing element.

Background

With the recent development of electromagnetic wave applications such as broadcasting, mobile communication, radar, mobile phone, wireless LAN, and the like, electromagnetic waves are scattered in a living space, and problems such as electromagnetic wave failure and erroneous operation of electronic equipment occur at a high frequency. In particular, unnecessary electromagnetic waves (noise) radiated from internal elements of an apparatus or a printed circuit board pattern generating electromagnetic waves cause interference or resonance phenomena, resulting in deterioration of the performance and reliability of the apparatus, and measures against such electromagnetic waves in the vicinity of the electromagnetic field and measures against heat generation due to an increase in the speed of the computing element are urgently required.

As a method for solving these problems, a reflection method of reflecting the generated noise to be restored to the generation source, a bypass method of guiding the noise to a potential stabilizing surface (a ground portion or the like), a shielding method, or the like are mainly adopted.

Recently, however, the mounting density has been increased due to the demand for smaller and lighter devices, and accordingly, the space for mounting noise coping parts has become smaller; since the low voltage of the element drive is required to save electric energy, it follows that the high frequency electromagnetic wave from other media is easily received in the power supply system; according to the requirement of rapidly increasing the operation processing speed, the synchronous pulse signal becomes narrow, and is easily influenced by high-frequency electromagnetic waves; with the rapid popularization of resin shells, a structure which is easy to leak electromagnetic waves is formed; for these reasons, the reflection method, the bypass method, the shielding method, and other methods cannot be used as methods that can sufficiently satisfy both the requirements for the electromagnetic wave of the proximity electromagnetic field and the heat radiation at the same time, and this is the current situation.

Further, with the high speed of operation of digital functional elements, digital circuit units, and the like, frequencies exceeding 1GHz have been involved in this tendency.

In order to solve these problems, electromagnetic wave absorbers have been used which convert noise generated from elements and printed circuit board patterns in a resin case into thermal energy. The electromagnetic wave absorber is required to have a function of absorbing electromagnetic wave energy of generated noise by utilizing magnetic loss characteristics, converting the electromagnetic wave energy into thermal energy, and suppressing reflection and transmission of noise in the case, and a function of reducing an electromagnetic energy level by adding impedance to electromagnetic energy emitted as an antenna to the substrate pattern or the element terminal, thereby deteriorating an antenna effect.

Further, an electromagnetic wave absorber which exhibits an effect in a wide high-frequency band region of 1 to 10GHz is preferable.

As a method for dealing with these problems, a flexible and thin electromagnetic wave absorber has been proposed in which a flexible sheet-like electromagnetic wave absorbing layer formed by mixing an electromagnetic wave energy loss material and a holding material and an electromagnetic wave reflecting layer formed by electroless plating a highly conductive metal material on an organic fiber cloth are laminated (patent document 1).

In addition, in order to prevent electromagnetic waves from leaking to the outside of the device, a method of providing a metal plate as an electromagnetic wave shielding material and a method of providing electromagnetic wave shielding performance by providing a case with conductivity are adopted, but since such a shielding material causes reflected and scattered electromagnetic waves to fill the inside of the device, there are problems of promoting electromagnetic interference and electromagnetic interference between a plurality of substrates provided inside the device. In order to solve these problems, an electromagnetic interference suppressor in the form of an insulating soft magnetic layer containing a conductive support, soft magnetic powder, and an organic binder has been proposed (patent document 2).

An electromagnetic wave absorber characterized by laminating an electromagnetic wave absorbing layer in which an electromagnetic wave absorbing filler is dispersed in a silicone resin on at least one surface of an electromagnetic wave reflecting layer in which a conductive filler is dispersed in a silicone resin is also disclosed (patent document 3), which has high electromagnetic wave absorbing performance and high electromagnetic wave shielding performance, can exhibit the properties of the silicone resin itself, and is excellent in processability, flexibility, weather resistance, and heat resistance. Further, there is disclosed an electromagnetic wave absorbing and heat conducting silicone gel-molded sheet formed from a silicone gel composition containing metal oxide magnetic particles such as ferrite and a heat conducting filler such as metal oxide (patent document 4).

Also disclosed is a method for producing a composite magnetic body, wherein a film is formed from a slurry mixture containing a flat soft magnetic powder, a binder and a solvent (patent document 5). In this method, it is difficult to increase the volume occupancy of the flat soft magnetic powder material, and it is not expected that a high magnetic permeability is obtained in the high-frequency electromagnetic wave range of 1GHz or more. Further, there is disclosed a curable silicone composition which can form a composite soft magnetic material having excellent moldability even when a soft magnetic powder is highly filled in order to obtain a composite soft magnetic material having excellent electromagnetic wave absorption characteristics (patent documents 6 and 7). However, these compositions have a problem that the filling amount thereof is insufficient and the moldability is poor. Further, there is disclosed a composite magnetic body for electromagnetic wave absorption, which contains a flat soft magnetic powder having an excellent balance between complex permeability and complex permittivity, a flat soft magnetic powder having a planar aspect ratio of 20 or more, a ferrite powder having a particle size of 100 μm or less, and a resin binder, in converting high-frequency noise into thermal energy (patent document 8).

However, in any of the above-mentioned techniques, the electromagnetic wave absorber has a structure in which a powder of a magnetic loss material such as ferrite and a powder of a dielectric loss material such as carbon are uniformly filled in rubber, plastic, or the like, but the electromagnetic wave absorber has a limited degree of filling and has a problem in flexibility in order to cope with various shapes of a structure to be mounted.

In particular, as an electromagnetic wave absorber for a highly densified and highly integrated portion of an electronic device element in an electronic device, a material having an electromagnetic wave absorbing performance, a high electric resistance, a high insulating property, and a thermal conductive property is required. However, there is no material having these three properties, and in such applications, flexibility, heat resistance, flame retardancy, and the like are required. In particular, in an absorber having an electromagnetic wave reflection function, the installation place is limited, and the absorber cannot be installed well on, for example, the top surface of a resin case.

In both of these techniques, the electromagnetic wave absorber has a structure having a limited degree of filling with flat soft magnetic powder or the like, and has a problem in flexibility in order to cope with various shapes of the mounted structure. In particular, there is no material having the same effect in the MHz to 10GHz range, and having electromagnetic wave absorption performance, high resistance, high insulation performance, and thermal conductivity, and in such applications, flexibility, heat resistance, flame retardancy, and the like are also required, but there is no material that can satisfy these performance requirements at the same time.

Patent document 1: japanese patent application laid-open No. 3097343

Patent document 2: japanese unexamined patent publication Hei 7-212079

Patent document 3: japanese laid-open patent publication No. 2002-329995

Patent document 4: japanese unexamined patent publication No. 11-335472

Patent document 5: japanese laid-open patent publication No. 2000-243615

Patent document 6: japanese unexamined patent application publication No. 2001-294752

Patent document 7: japanese laid-open patent publication No. 2001-119189

Patent document 8: japanese laid-open patent publication No. 2002-15905

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide an electromagnetic wave absorber which can be highly filled with a magnetic loss material, is excellent in electromagnetic wave absorbability, thermal conductivity and flame retardancy, has small temperature dependency, is flexible, has excellent adhesion strength, has high resistance and high insulation properties, and has no adhesion limitation, and which has stable energy conversion efficiency in a wide frequency band of MHz to 10GHz, particularly in a high frequency band; and a laminated electromagnetic wave absorber in which unnecessary electromagnetic waves from the inside and outside of the resin case are absorbed by using these electromagnetic wave absorbers and a conductive electromagnetic wave reflecting layer is laminated on the electromagnetic wave absorbing layer, wherein the laminated electromagnetic wave absorber has an adhesive force with which it can be attached to an unnecessary electromagnetic wave radiation source such as a high-speed computing element and the like, and has an adhesive force with which it does not fall off even if it is attached to the top surface of the horizontal glass surface shape of the resin case.

The present inventors have made intensive studies in order to solve the above problems and found that by using a surface-treated soft ferrite as a filler for a magnetic loss material, using a flat soft magnetic metal powder having a good electromagnetic wave absorption effect in a high frequency range, using magnetite as a flame retardancy-improving agent and a thermal conductivity-improving agent, and using silicone as a material having flexibility and excellent adhesion strength, and blending these materials at a specific ratio, it is possible to obtain an electromagnetic wave absorbing layer having excellent electromagnetic wave absorption, thermal conductivity and flame retardancy, small temperature dependence, flexibility, excellent adhesion strength, high electrical resistance and high insulation properties, stable energy conversion efficiency in a wide frequency band frequency range of MHz to 10GHz, and further, an electromagnetic wave absorbing layer containing at least an adhesive having adhesion to an unnecessary electromagnetic wave emitting source such as a high-speed computing element, and an adhesive layer having at least a top surface that is adhered to a horizontal glass surface shape of a resin case, and a laminated electromagnetic wave absorber having an adhesive force that does not fall off, and the present invention has been completed.

That is, according to the invention of claim 1, there is provided an electromagnetic wave absorber, characterized in that: contains (a) 60 to 90 wt% of soft ferrite surface-treated with a non-functional group silane compound, (c) 3 to 25 wt% of magnetite, and (c) 7 to 15 wt% of silicone.

By the invention of claim 2, there is provided an electromagnetic wave absorber, characterized in that: contains (a) 40 to 60 wt% of soft ferrite surface-treated with a non-functional group silane compound, (b) 20 to 30 wt% of flat soft magnetic metal powder, (c) 3 to 10 wt% of magnetite, and (d) 7 to 25 wt% of silicone.

According to the invention of claim 3, there is provided the electromagnetic wave absorber as set forth in claim 2, characterized in that: (a) the weight mixing ratio of the soft ferrite surface-treated with the non-functional group silane compound to the flat soft magnetic metal powder (b) is 1.8-2.3: 1.

According to the 4 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 1 st to 3, wherein: (a) the soft ferrite surface-treated with the non-functional group-based silane compound is a soft ferrite surface-treated with dimethyldimethoxysilane or methyltrimethoxysilane.

According to the 5 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 1 st to 4 th aspects, wherein: (a) the pH of the soft ferrite surface-treated with the non-energy group silane compound is 8.5 or less.

According to the 6 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 1 st to 5 th aspects, wherein: soft ferrite particle size distribution D used in (a) soft ferrite surface-treated with a non-functional group-based silane compound₅₀1 to 30 μm.

According to the 7 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 1 st to 6 th aspects, wherein: the soft ferrite used in (a) the soft ferrite surface-treated with the non-functional group-based silane compound is a Ni — Zn-based ferrite.

According to the 8 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 2 nd to 7 th aspects, wherein: (b) the flat soft magnetic metal is a low-self-oxidizing flat soft magnetic metal having a weight change rate of 0.3 wt% or less in an exposure test in an atmosphere under heating.

According to the 9 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 2 nd to 8 th aspects, wherein: (b) the specific surface area of the flat soft magnetic metal powder is 0.8 to 1.2m²/g。

According to the 10 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 2 nd to 9 th aspects, wherein: (b) particle size distribution D of flat soft magnetic metal powder₅₀8 to 42 μm.

According to the 11 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 1 st to 9 th aspects, wherein: (b) the flat soft magnetic metal powder is microencapsulated.

According to the 12 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 1 st to 11 th aspects, wherein: (c) particle size distribution D of magnetite₅₀0.1 to 0.4 μm.

According to the 13 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 1 st to 12 th aspects, wherein: (c) magnetite is an octahedral shape microparticle.

According to the 14 th aspect of the present invention, there is provided the electromagnetic wave absorber according to any one of the 1 st to 13, wherein: (d) the silicone is a silicone gel having a penetration of 5 to 200 according to JIS K2207-1980(50g load).

According to the 15 th aspect of the present invention, there is provided a laminated electromagnetic wave absorber in which a conductor reflection layer is laminated on the electromagnetic wave absorber according to any one of the 1 st to 14 th aspects, wherein: an insulating layer is arranged outside the reflecting layer.

According to the 16 th aspect of the present invention, there is provided the laminated electromagnetic wave absorber according to the 15 th aspect of the present invention, which is a laminated electromagnetic wave absorber in which an unnecessary electromagnetic wave from the inside and outside of a resin case is absorbed, a conductive electromagnetic wave reflecting layer is laminated on an electromagnetic wave absorbing layer body, an adhesive layer is laminated on the outside of the electromagnetic wave reflecting layer through an insulating layer, and a peeling film layer is laminated on each of the outside of the electromagnetic wave absorbing layer and the outside of the adhesive layer, wherein: the electromagnetic wave absorber layer has at least adhesiveness to be attached to the high-speed operation element, and the adhesive layer has at least adhesive force to be attached to the top surface of the horizontal glass without falling off.

According to the 17 th aspect of the present invention, there is provided the laminated electromagnetic wave absorber according to any one of the 15 th or 16 th aspects, wherein: an insulator layer is provided between the electromagnetic wave absorber layer and the electromagnetic wave reflection layer.

According to the 18 th aspect of the present invention, there is provided the laminated electromagnetic wave absorber according to any one of the 15 th to 17, wherein: the electromagnetic wave reflecting layer is an aluminum metal layer.

According to the 19 th aspect of the present invention, there is provided the laminated electromagnetic wave absorber according to any one of the 15 th to 18 th aspects, wherein: the adhesive layer is an acrylic adhesive layer.

According to the 20 th aspect of the present invention, there is provided the laminated electromagnetic wave absorber according to any one of the 15 th to 19 th aspects, wherein: the insulator layer is a polyethylene terephthalate resin layer.

The electromagnetic wave absorber of the present invention is excellent in electromagnetic wave absorbability, thermal conductivity, flame retardancy, small temperature dependency, flexibility, excellent adhesion strength, high electric resistance, high insulation property, and no adhesion limitation.

The electromagnetic absorber of the present invention exhibits a stable energy conversion efficiency in a wide frequency range of MHz to 10GHz, and is excellent in electromagnetic wave absorption, thermal conductivity, and flame retardancy, has a small temperature dependence, is flexible, has excellent adhesion strength, and has high-resistance and high-insulation properties.

The laminated electromagnetic wave absorber of the present invention is laminated in the order of the release film layer, the electromagnetic wave absorbing layer, the electromagnetic wave reflecting layer, the insulator layer, the adhesive layer, and the release film layer, and therefore can be applied to any product of one form, for example, can be attached to the top surface of a case, can be attached to a high-speed computing element, or the like, and exhibits excellent effects in electromagnetic wave absorption and electromagnetic wave shielding properties.

Drawings

FIG. 1 is a graph showing the results of measurement of magnetic loss of electromagnetic wave absorbers in examples and comparative examples.

FIG. 2 is a cross-sectional view of an example of a laminated electromagnetic wave absorber.

FIG. 3 is a view for explaining an example of a method of using a laminated absorbent body.

FIG. 4 is a view for explaining an example of a method of using a laminated absorbent body.

FIG. 5 is a view for explaining an example of a method of using a laminated absorbent body.

FIG. 6 is a graph showing the result of measuring the absorption rate of an electromagnetic wave of an adjacent electromagnetic field in the example.

Description of the symbols

1 electromagnetic wave absorbing layer

2 electromagnetic wave reflecting layer

3 insulator layer

4 adhesive layer

5, 6 peeling film layer

10, 10', 15 substrate

11, 11 ', 12, 12' high-speed arithmetic element

20 casing

21 top surface of the housing

Detailed Description

The present invention relates to an electromagnetic wave absorber containing (a) soft ferrite, (c) magnetite and (d) silicone; an electromagnetic wave absorber containing (a) a soft ferrite, (b) a flat soft magnetic metal powder, (c) a magnetite and (d) a silicone gel; the electromagnetic wave absorber includes an electromagnetic wave absorbing layer containing the electromagnetic wave absorber and an electromagnetic wave reflecting layer containing a conductor, and is a laminated electromagnetic wave absorber in which a release film layer, an electromagnetic wave absorbing layer, an electromagnetic wave reflecting layer, an insulator layer, an adhesive layer, and a release film layer are laminated in this order. The respective constituent components, production methods, and the like will be described in detail below.

1. Constituent component of electromagnetic wave absorber

(a) Soft ferrites

The soft ferrite used in the electromagnetic wave absorber of the present invention is a substance that can exhibit a magnetic function even under a weak excitation current. The soft ferrite is not particularly limited, and examples thereof include Ni-Zn ferrite, Mn-Mg ferrite, Cu-Zn ferrite, Ni-Zn-Cu ferrite, Fe-Mg-Zn-Cu ferrite, Fe-Mn-Zn ferrite and the like, and among these ferrites, Ni-Zn ferrite is preferable in terms of the balance of electromagnetic wave absorption characteristics, thermal conductivity, price and the like.

The shape of the soft ferrite is not particularly limited, and the soft ferrite can be formed into a desired shape such as a spherical shape, a fibrous shape, an irregular shape, and the like. In the present invention, in order to enable filling with a high filling density and to obtain higher thermal conductivity, the shape of the soft ferrite is preferably spherical. When the soft ferrite has a spherical shape, the particle size can be filled at a high filling density, and the aggregation of particles can be prevented, thereby facilitating the compounding operation.

By using Ni — Zn ferrite in such a shape, the silicone gel material can exhibit a certain degree of thermal conductivity without causing the later-described inhibition of curing of the silicone gel, and has excellent dispersibility in the silicone gel material.

Further, soft ironParticle size distribution D of the ferrite₅₀1 to 30 μm, preferably 10 to 30 μm. In addition, in the electromagnetic wave absorber using the flat soft magnetic metal powder (b), 1 to 10 μm is more preferable. If the particle size distribution D of the soft ferrite₅₀When the particle size is less than 1 μm, the electromagnetic wave absorption performance tends to be lowered in a low frequency band of 500MHz or less; if it exceeds 30 μm, the smoothness of the electromagnetic wave absorber is not preferable.

Here, the particle diameter distribution D₅₀The particle size ranges from a value obtained by a particle size distribution analyzer, in which the particle size is small, to a value obtained when the cumulative weight of particles reaches 50%.

In order to suppress the influence of the residual alkali ions present on the surface of the soft ferrite, the soft ferrite used in the present invention must be treated with a non-functional group-based silane compound. The soft ferrite is used in combination with silicone described later, but the residual alkali ions present on the surface of the soft ferrite sometimes become a factor of curing inhibition in the condensation type or addition curing mechanism of silicone, and if curing inhibition occurs, the soft ferrite cannot be highly filled, and the filled soft ferrite is not sufficiently dispersed.

The pH of the soft ferrite surface-treated with the nonfunctional silane compound is 8.5 or less, preferably 8.2 or less, more preferably 7.8 to 8.2 by treating the surface of the soft ferrite with the nonfunctional silane compound. By making the pH of the soft ferrite 8.5 or less, the curing inhibition of silicone can be suppressed, and it is applicable to any silicone. Further, the soft ferrite has good affinity with silicone, and as a result, the filling amount of the soft ferrite in silicone can be increased, and the mixing property with the thermally conductive filler can be improved, and a uniform molded body can be obtained.

Examples of the nonfunctional silane compound for the surface treatment of soft ferrites which can be used in the present invention include methyltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, isobutyltrimethoxysilane and decyltrimethoxysilane. Among them, dimethyldimethoxysilane and methyltrimethoxysilane are preferable. These non-functional group silane compounds may be used alone or in combination of two or more.

When a silane coupling agent having a functional group, such as epoxy silane compound or vinyl silane compound, which is generally used for surface treatment of the soft ferrite of the present invention, is used as a silane compound for surface treatment of the filler, a change in hardness due to an increase in hardness in a heating environment test causes cracks due to thermal decomposition, and the like, and thus the shape cannot be maintained, and the appearance is impaired, which is not preferable.

The method of treating the surface of the soft ferrite with the above-mentioned non-functional group-containing silane compound is not particularly limited, and an inorganic compound surface treatment method using a general silane compound or the like can be used. For example, the soft ferrite is obtained by immersing and mixing the soft ferrite in a methanol solution of about 5% by weight of dimethyldimethoxysilane, adding water to the solution, hydrolyzing the mixture, and pulverizing and mixing the resulting treated product with a Henschel mixer or the like. The non-functional group silane compound is preferably about 0.2 to 10 wt% with respect to the soft ferrite.

In the electromagnetic wave absorber containing (a), (c), and (d) of the present invention, the amount of the soft ferrite is 60 to 90% by weight, preferably 75 to 85% by weight. By setting the blending amount of the soft ferrite within this range, sufficient electromagnetic wave absorption, thermal conductivity and electrical insulation properties can be imparted, and good moldability can be ensured. If the blending amount of the soft ferrite is less than 60 wt%, sufficient electromagnetic wave absorption performance cannot be obtained; if it exceeds 90% by weight, it becomes difficult to form a sheet.

In the electromagnetic wave absorber containing (a), (b), (c), and (d) of the present invention, the amount of the soft ferrite is 40 to 60% by weight, preferably 45 to 55% by weight. By setting the blending amount of the soft ferrite within this range, sufficient electromagnetic wave absorption, thermal conductivity and electrical insulation properties can be imparted, and good moldability can be ensured. If the blending amount of the soft ferrite is less than 40 wt%, sufficient electromagnetic wave absorption performance cannot be obtained; if it exceeds 60% by weight, it becomes difficult to form a sheet.

(b) Flat soft magnetic metal powder

The flat soft magnetic metal powder (b) that can be used in the electromagnetic wave absorber of the present invention is a material having a stable energy conversion efficiency effect in a high frequency band range.

The flat soft magnetic metal powder (b) is not particularly limited, and any metal powder may be used as long as it exhibits soft magnetism and can be flattened by mechanical treatment. It is preferable that the magnetic material has a high magnetic permeability, a low self-oxidizing property, and a high aspect ratio (a value obtained by dividing the average particle diameter by the average thickness) in terms of shape. Specific examples of the metal powder include soft magnetic metals such as Fe-Ni alloy system, Fe-Ni-Mo alloy system, Fe-Ni-Si-B alloy system, Fe-Si-Al alloy system, Fe-Si-B alloy system, Fe-Cr-Si alloy system, Co-Fe-Si-B alloy system, Al-Ni-Cr-Fe alloy system, and Si-Ni-Cr-Fe alloy system, and among them, Al or Si-Ni-Cr-Fe alloy system is preferable from the viewpoint of low self-oxidation. These alloys may be used in 1 kind, or 2 or more kinds may be mixed and used.

The autoxidability was determined from the rate of change in weight of the sample by conducting an exposure test in a heated atmosphere. Preferably a substance whose weight change rate is 0.3% or less when exposed to an atmosphere of 200 ℃ for 300 hours. If the flat soft magnetic metal powder has low self-oxidizing properties, it is characterized in that even if a silicone gel or the like having high permeability is used as the binder resin, the deterioration of magnetic properties with age due to changes in ambient environmental conditions such as humidity does not occur. Thus, there is an advantage in that any adhesive resin can be used.

Further, if the self-oxidizing property is low, there is no risk of dust explosion, and the product can be handled as a non-hazardous substance and stored in a large amount, and therefore, the product is easy to use and can be produced at high efficiency.

The aspect ratio of the flat soft magnetic metal powder is preferably 10 to 150, and more preferably 17 to 20; the bulk density is preferably 0.55 to 0.75 g/ml. Further, the surface of these metallic magnetic flat powders is preferably subjected to an antioxidant treatment.

The average thickness of the flat soft magnetic metal powder is preferably 0.01 to 1 μm. When the thickness is smaller than 0.01. mu.m, the dispersibility in the resin is deteriorated, and the particles cannot be aligned in one direction sufficiently even if the orientation treatment with an external magnetic field is applied. Even if the materials have the same composition, magnetic properties such as magnetic permeability are reduced, and magnetic shielding properties are also reduced. In contrast, if the average thickness exceeds 1 μm, the filling ratio decreases. Further, the influence of the diamagnetic field becomes large when the aspect ratio is small, and the magnetic permeability is lowered, so that the shielding property is insufficient.

Also, the particle size distribution D of the flat soft magnetic metal powder₅₀Preferably 8 to 42 μm. If the particle size distribution D₅₀Below 8 μm, the energy conversion efficiency is reduced; if it exceeds 42 μm, the mechanical strength of the particles is lowered, and the particles are easily broken when mechanically mixed.

Here, the particle diameter distribution D₅₀The particle size ranges from a value at which the particle size obtained by a particle size distribution analyzer is small to a value at which the cumulative weight reaches 50%.

The specific surface area of the flat soft magnetic metal powder is preferably 0.8 to 1.2m²(ii) in terms of/g. Since flat soft magnetic metal powder is a material that realizes an energy conversion function by electromagnetic induction, high energy conversion efficiency can be maintained as the specific surface area is larger, but the mechanical strength is weaker as the specific surface area is larger. It is therefore necessary to select the optimum range. If the specific surface area is less than 0.8m²(iv)/g, then high fill can be done, but the energy exchange function is reduced; if it exceeds 1.2m²When the amount is/g, the powder is easily broken during mechanical mixing, and it is difficult to maintain the shape, and even if high filling is possible, the energy exchange function is reduced.

The specific surface area herein is a value measured by a BET measuring apparatus.

The flat soft magnetic metal powder used in the present invention is preferably used after microencapsulation treatment. When flat soft magnetic metal powder and soft ferrite are compositely filled, the volume resistance and dielectric breakdown strength are likely to be reduced. The microencapsulation treatment can prevent the dielectric breakdown strength from being lowered and can improve the strength.

The method of microencapsulation is not particularly limited, and any method may be used as long as the method is a method of coating the surface of the flat soft magnetic metal powder with a constant thickness and treating the surface with a material that does not affect the energy conversion function of the flat soft magnetic metal powder.

For example, as a material for coating the surface of the flat soft magnetic metal powder, a flat soft magnetic metal powder in which soft magnetic metal powder is coated and encapsulated with gelatin can be obtained by dispersing soft magnetic metal powder in a toluene solution in which gelatin is dissolved and then evaporating and removing toluene. In this case, for example, a material having a particle size of about 100 μm can be obtained by microencapsulating a material in which the weight ratio of gelatin is about 20% and the weight ratio of flat soft magnetic metal powder is about 80%, and the dielectric breakdown strength of the electromagnetic wave absorber using the material can be increased by about 2 times as much as that when microencapsulating is not performed.

In the electromagnetic wave absorber containing (a), (b), (c), and (d) of the present invention, the amount of flat soft magnetic metal powder (b) is 20 to 30% by weight. By setting the amount of the flat soft magnetic metal powder (b) to be blended within this range, high energy conversion efficiency can be maintained. If the amount of flat soft magnetic metal powder compounded is less than 20 wt%, the energy conversion efficiency becomes poor; if it exceeds 30% by weight, mixing becomes difficult.

In the electromagnetic wave absorber of the present invention, the weight mixing ratio of (a) the soft ferrite and (b) the flat soft magnetic metal powder is preferably 1.8 to 2.3: 1.0, and more preferably 1.9 to 2.2: 1.0. If the weight mixing ratio of (a) and (b) is out of the above range, the balance between the energy conversion efficiency and the sheet formability cannot be maintained.

(c) Magnetite

The magnetite (c) in the electromagnetic wave absorber of the present invention is iron oxide (Fe)₃O₄) By using the soft ferrite, the electromagnetic wave absorber can be provided with flame retardancy and the thermal conductivity can be improved, and further, the magnetic properties of magnetite are added to provide a synergistic effect, and the electromagnetic wave absorbing effect of the electromagnetic wave absorber as a whole can be improved.

Particle size distribution D of magnetite₅₀Preferably 0.1 to 0.4 μm. By making the particle size distribution D of magnetite₅₀To achieve the soft ferrite grain diameter distribution D₅₀About 1/10, a highly filled soft ferrite can be obtained. In addition, if the particle size distribution D of magnetite is₅₀Less than 0.1 μm, handling becomes difficult; if it exceeds 0.4 μm, high filling with soft ferrite cannot be performed.

Here, the particle diameter distribution D₅₀The particle size ranges from a value at which the particle size obtained by a particle size distribution analyzer is small to a value at which the cumulative weight reaches 50%.

The shape of the magnetite is not particularly limited, and the magnetite may be formed into a desired shape such as a spherical shape, a fibrous shape, an indefinite shape, and the like. In the present invention, octahedral fine particles are preferable for obtaining high flame retardancy. When magnetite is fine particles in the shape of octahedron, the specific surface area is large, and the effect of imparting flame retardancy is good.

The amount of magnetite added to the electromagnetic wave absorber containing (a), (c), and (d) of the present invention is 3 to 25% by weight, preferably 5 to 10% by weight. If the amount of magnetite added is less than 3 wt%, a sufficient flame retardant effect cannot be obtained; if the content exceeds 25% by weight, the electromagnetic wave absorber becomes magnetic, and adversely affects peripheral electronic devices.

In the electromagnetic wave absorber containing (a), (b), (c), and (d) of the present invention, the amount of magnetite added is 3 to 25% by weight, preferably 3 to 10% by weight. If the amount of magnetite added is less than 3 wt%, a sufficient flame retardant effect cannot be obtained; if the content exceeds 25% by weight, the electromagnetic wave absorber becomes magnetic, and adversely affects peripheral electronic devices.

(d) Silicone

The silicone (d) in the electromagnetic wave absorber of the present invention functions as a binder for the soft ferrite, the flat soft magnetic metal powder, and the magnetite, and also has a function of reducing the temperature dependence of the electromagnetic wave absorber and enabling use in a wide temperature range of 20 to 150 ℃. The silicone (d) may be any conventionally known silicone material generally used as various commercially available silicone materials. Therefore, any material such as heat-curable or room-temperature-curable silicone, and condensation-type or addition-type silicone as a curing mechanism can be used. The group bonded to the silicon atom is not particularly limited, and examples thereof include an alkyl group such as a methyl group, an ethyl group and a propyl group, a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, an alkenyl group such as a vinyl group and an allyl group, and an aryl group such as a phenyl group and a tolyl group, and further include those in which a part of hydrogen atoms of these groups is substituted with another atom or a bonding group.

The silicone used in the electromagnetic wave absorber of the present invention may be a silicone in a gel state, and for example, a silicone gel having a penetration of 5 to 200 in JIS K2207-1980(50g load) after curing may be used. When a silicone gel having such a degree of flexibility is used, it is advantageous in terms of adhesion when used as a molded article. By using such silicone, the electromagnetic wave absorbing layer used in the present invention can have at least adhesiveness to a high-speed operation element.

In the electromagnetic wave absorber containing (a), (b), and (d) of the present invention, the amount of silicone is 7 to 15% by weight, preferably 10 to 14% by weight. If the compounding amount of the silicone is less than 7% by weight, it is difficult to form a sheet shape; if it exceeds 15% by weight, the electromagnetic wave absorption performance is not obtained. In the electromagnetic wave absorber containing (a), (b), (c), and (d) of the present invention, the amount of silicone is 7 to 25% by weight, preferably 15 to 25% by weight. If the compounding amount of the silicone is less than 7% by weight, it is difficult to form a sheet shape; if it exceeds 25% by weight, the electromagnetic wave absorption performance is not obtained.

In the electromagnetic wave absorber of the present invention, other components may be added in the range of the kind and amount thereof not impairing the object of the present invention. Examples of such other components include catalysts, curing inhibitors, curing accelerators, and colorants.

2. Production of electromagnetic wave absorber

The electromagnetic wave absorber of the present invention is a composite material layer in which the silicone resin (d) contains the soft ferrite (a), the flat soft magnetic metal powder (b), and the magnetite (c). These (a) to (d) may be combined according to the intended purpose. For example, (i) an electromagnetic wave absorber for the purpose of high resistance and high insulation is preferably a combination comprising (a), (c), and (d); (ii) an electromagnetic wave absorber for the purpose of high electromagnetic wave absorbability in the 2 to 4GHz frequency band, preferably comprising a combination of (b), (c) and (d); (iii) the electromagnetic wave absorber for the purpose of broadband frequency characteristics preferably includes a combination of (a), (b), (c), and (d).

In the electromagnetic wave absorbing layer containing (a), (c) and (d) for the purpose of (i), the composition ratio of each component is preferably such that the composition contains 60 to 90% by weight of (a) soft ferrite surface-treated with a non-functional group-based silane compound, (c) 3 to 25% by weight of magnetite and (d) 7 to 15% by weight of silicone. In the electromagnetic wave absorbing layer containing (b), (c) and (d) for the purpose of (ii), the composition ratio of each component is preferably such that it contains 60 to 70% by weight of (b) flat soft magnetic metal powder, (c) 3 to 10% by weight of magnetite and (d) 20 to 37% by weight of silicone. In the electromagnetic wave absorbing layer containing (a), (b), (c) and (d) for the purpose of (iii), the composition ratio of each component is preferably such that the composition contains 40 to 60% by weight of (a) soft ferrite surface-treated with a non-functional group silane compound, (b) 20 to 30% by weight of flat soft magnetic metal powder, (c) 3 to 10% by weight of magnetite and (d) 7 to 25% by weight of silicone.

The electromagnetic wave absorber used in the present invention is obtained by highly filling a mixture of soft ferrite, flat soft magnetic metal powder, magnetite, and the like in silicone as described above, but generally, if an inorganic filler such as ferrite, flat soft magnetic metal powder, magnetite, and the like is highly filled in silicone rubber, the viscosity increases, and roll kneading, banbury kneading, or kneader kneading becomes difficult to perform. Even if kneading is possible, the viscosity of the compound is high, and a uniform thickness cannot be obtained by compression molding. However, if the silicone gel is used, even if the filling is high, kneading by a chemical mixer (ケミカルミキサ A) is easy, and sheet molding with a uniform thickness is easy by a general sheet molding machine. Further, since the surface of the soft ferrite is treated with a non-functional group-based silane compound, there is an effect that kneading can be easily performed. Further, in general, if the silicone is highly filled with ferrite and kneaded with a roll, the silicone has insufficient holding strength for the ferrite, and the ferrite cannot be aggregated with each other, and the compound adheres to the roll, and a uniform compound cannot be formed. Further, when a substance obtained by microencapsulating flat soft magnetic metal powder is used, the effect of easier kneading is obtained.

The electromagnetic wave absorber containing (a), (c), and (d) of the present invention is excellent in electromagnetic wave absorbability, thermal conductivity, and flame retardancy, has small temperature dependence, is flexible, has excellent adhesion strength, has high electrical resistance and high insulation properties, and is particularly excellent in the balance between high electrical resistance, high insulation properties, thermal conductivity, and electromagnetic wave absorbability, so that it is not necessary to use adhesion restriction such as adhesion that can be applied only to a specific noise generating source, and has a characteristic that it can be applied to any noise source. Therefore, the present invention can be used in any case where the noise generation source is a cable, a high-speed computing element, a printed circuit board pattern, or the like.

3. Laminated electromagnetic wave absorber

The laminated electromagnetic wave absorber of the present invention is a laminate comprising an electromagnetic wave absorbing layer containing the above electromagnetic wave absorber and a conductive reflecting layer laminated thereon, and preferably capable of absorbing unnecessary electromagnetic waves from the inside and outside of a resin case, wherein the conductive electromagnetic wave reflecting layer is laminated on the electromagnetic wave absorbing layer, an adhesive layer is laminated on the outside of the electromagnetic wave reflecting layer via an insulating layer, and a peeling film layer is laminated on the outside of the electromagnetic wave absorbing layer and the outside of the adhesive layer, respectively, wherein the electromagnetic wave absorbing layer has at least adhesiveness to a high-speed computing element, and the adhesive layer has at least an adhesive strength capable of adhering to the top surface of a horizontal glass without falling off.

(1) Electromagnetic wave absorber layer

The electromagnetic wave absorber layer used in the laminated electromagnetic wave absorber of the present invention is a layer in which the above-described (a) soft ferrite, (b) flat soft magnetic metal powder, (c) magnetite, and the like are contained in the silicone resin (d), and the layers (a) to (d) are used in combination according to the purpose.

The shape of the electromagnetic wave absorber layer is not particularly limited, and may be formed into a desired shape according to the application. For example, when the sheet is formed, the thickness is preferably 0.5mm to 5.0mm, and the sheet can be used alone or 2 to 3 sheets can be used by laminating.

(2) Electromagnetic wave reflecting layer

In the laminated electromagnetic wave absorber of the present invention, by providing the electromagnetic wave absorbing layer and the reflective layer, the electromagnetic energy attenuation performance can be improved simply and inexpensively, and even in the case of a sheet product, by continuous reflection attenuation due to the shielding effect and thermal energy conversion of the electromagnetic wave absorbing layer. The electromagnetic wave reflecting layer is not particularly limited, and a conductor such as aluminum, copper, or stainless steel may be used, and may be an aluminum foil or an aluminum layer deposited on a resin film or the like.

The reflective layer used in the present invention may be directly laminated on the electromagnetic wave absorbing layer, or may be laminated on the electromagnetic wave absorbing layer through an insulator layer.

(3) Insulator layer

In the laminated electromagnetic wave absorber of the present invention, it is necessary to provide an insulator layer on the electromagnetic wave reflecting layer laminated on the electromagnetic wave absorbing layer. The insulator layer is made of an insulating material such as a polyethylene terephthalate (PET) resin film, a polypropylene resin film, or a polystyrene resin film, and can improve the strength of the electromagnetic wave absorber while suppressing a decrease in dielectric breakdown strength.

In addition, the insulator layer may be provided between the electromagnetic wave absorbing layer and the electromagnetic wave reflecting layer as necessary.

The thickness of the insulator layer is preferably 25 to 75 μm.

In addition, an acrylic resin adhesive or the like may be used for lamination of the insulator layer.

(4) Adhesive layer

In the laminated electromagnetic wave absorber of the present invention, an adhesive layer having an adhesive force that does not fall off when it is attached to at least the top surface of the horizontal glass surface shape is provided outside the insulator layer laminated on the electromagnetic wave reflecting layer. By providing such an adhesive layer, the adhesive layer can be applied to the top surface and the side surface of the housing, and the range of application thereof can be expanded.

The adhesive of the adhesive layer is not particularly limited, and an acrylic resin adhesive can be used.

Further, it is preferable that an adhesive layer/release film is provided on one side of an insulator layer such as a PET film, and the adhesive layer/release film is integrally molded.

(5) Stripping film layer

In the laminated electromagnetic wave absorber of the present invention, the release film layer is provided outside the electromagnetic wave absorbing layer and outside the adhesive layer. The release film layer may be an insulating film such as a PET resin film, a polypropylene resin film, or a polystyrene resin film, and preferably has a thickness of 20 to 30 μm. The release film layer is laminated by the adhesiveness of the silicone gel of the electromagnetic wave absorbing layer and the adhesive force of the adhesive layer.

4. Layer construction and methods of use of laminates

The laminated electromagnetic wave absorber of the present invention is obtained by laminating the above-described layers, and for example, a laminate having a cross-sectional view shown in fig. 2 is formed. In fig. 2, 1 is an electromagnetic wave absorbing layer, 2 is an electromagnetic wave reflecting layer, 3 is an insulator layer, 4 is an adhesive layer, and 5 and 6 are release film layers.

In using the laminated electromagnetic wave absorber of the present invention, it is often used in the order of lamination of the electromagnetic wave absorbing layer/electromagnetic wave reflecting layer with respect to the incident direction of the unnecessary electromagnetic wave. Examples of the use thereof will be described with reference to FIGS. 3 to 5. For example, in the case where the unnecessary electromagnetic wave radiation source from a high-speed computing element, a cable, a pattern, or the like can be specified, that is, in the case where the high-speed computing element 11 on the substrate 10 in fig. 3 is specified as the unnecessary electromagnetic wave radiation source, the peeling film 5 on the outer side of the electromagnetic wave absorbing layer 1 is peeled off from the high-speed computing element 11, and the peeled film is directly attached to the upper surface of the high-speed computing element in the arrow direction (enlarged view of 11) by the tackiness of the electromagnetic wave absorbing layer 1. When the unnecessary electromagnetic wave emitting source cannot be specified, in the case where the attachment to the substrate is possible, the peeling film 5 on the outer side of the electromagnetic wave absorbing layer 1 may be peeled off and attached to the substrate. In the case of a multilayer structure, the adhesive layer 4 may be laminated between the substrates, for example, when the adhesive layer is attached to the lower side of the substrate positioned on the upper side, that is, between the substrates 10 and 10 ' in fig. 4, in order to prevent the influence of unnecessary electromagnetic waves from the high-speed computing elements 11 and 12 of the substrate 10 on the substrate 10 ', the adhesive layer 4 is attached to the lower side of the substrate 10 ' in the direction of the arrow by peeling the release film 6 on the outer side of the adhesive layer 4. Further, in the case where it is not possible to specify the source of unnecessary electromagnetic waves and to attach the same to the substrate, that is, in fig. 5, it is not possible to specify which of the cables, patterns, elements, and the like on the substrate 15 in the case 20 is the source of unnecessary electromagnetic waves and to attach the same in terms of shape, the release film 6 on the outer side of the adhesive layer 4 can be peeled off and the adhesive layer 4 can be attached to the case top plate 21 in the direction of the arrow for use, thereby preventing the unnecessary electromagnetic waves from being reflected and transmitted to the outer side of the case. Thus, the laminated electromagnetic wave absorber of the present invention is a product of one form, but can be applied to all cases where an electromagnetic wave radiation source is unnecessary.

Examples

The present invention will be described in detail with reference to examples, but the present invention is not limited to these examples. The physical property values and evaluations in the examples were measured by the following methods.

(1) Penetration degree: determined according to JIS K2207-1980.

(2) Magnetic loss (magnetic permeability): the magnetic permeability and the inductivity (inductivity) were measured by using an S-parameter system coaxial tube (μ r measuring instrument system) manufactured by Anritsu & Keycom.

(3) Volume resistance: measured according to JIS K6249.

(4) Dielectric breakdown strength: measured according to JIS K6249.

(5) Coefficient of thermal conductivity: obtained according to the QTM method (Kyoto electronics industries Co., Ltd.).

(6) Flame retardancy: measured according to UL 94.

(7) Heat resistance: after leaving at a constant temperature of 150 ℃, the penetration and the thermal conductivity were measured, and the time-dependent change was observed, and the value which did not change for 1000 hours or more was rated as "O" and the value which changed was rated as "X".

(8) Appearance: the color was judged by visually observing the color of the surface. Here, black is a color due to addition of magnetite.

(9) Formability (mass productivity): the number of sheets that could be formed was determined as "O" and the number of sheets that could not be formed was determined as "X" by the sheet forming machine.

(10) Absorption rate: the measurement was carried out using an electromagnetic wave absorbing material measuring apparatus (manufactured by Keycom corporation) for the near field.

(11) Self-oxidizing: about 10g of metal powder was placed on a phi 100 petri dish, and the plate was left to stand in an oven at 200 ℃ for 300 hours, and then the plate was taken out, cooled to room temperature, and the weight was measured with an electronic balance, and the weight change rate was determined from the difference in weight before and after exposure.

(example 1)

Using methyltrimethoxysilane to regulate the particle size distribution D₅₀A soft ferrite having a particle size distribution D of 83 wt% and surface-treated with Ni-Zn soft ferrite (BSN-828 (trade name) manufactured by Koita industries, Ltd.) of 10 to 30 μm₅₀The magnetic particles (KN-320 (trade name) of octahedral magnetite fine particles of 0.1 to 0.4 μm, manufactured by Konta industries, Ltd.) were mixed in an amount of 5 wt%, and a Silicone gel (CF-5106 (trade name) manufactured by Toray Dow Corning, Silicone, Ltd.) of JIS K2207-1980(50g load) having a penetration of 150 was mixed in an amount of 12 wt%, vacuum defoamed, poured between glass plates without air mixing, heated at 70 ℃ for 60 minutes, and press molded to obtain a molded article having a smooth surface and a thickness of 1 mm. The evaluation results of the molded article are shown in table 1.

(example 2)

The same operation as in example 1 was carried out except that the blending amounts of magnetite and silicone gel were changed to amounts shown in table 1 to obtain molded bodies, and the evaluation results of the molded bodies are shown in table 1.

Comparative example 1

A molded body was obtained in the same manner as in example 1, except that soft ferrite without surface treatment was used and magnetite was not blended, and the amount of silicone was changed to the blending amount shown in table 1. If soft ferrite without surface treatment is used, the silicone is filled with only 20% by weight, which may inhibit curing of the silicone and may not give a sufficient molded article. The evaluation results are shown in table 1.

Comparative example 2

A molded body was obtained in the same manner as in example 1 except that the surface treatment of the soft ferrite was performed with epoxytrimethoxysilane which was a silane compound having a functional group. The evaluation results of the molded articles are shown in Table 1. The obtained molded article was poor in heat resistance.

Comparative example 3

A molded article was obtained in the same manner as in example 1 except that the surface treatment of the soft ferrite was performed with vinyltrimethoxysilane which was a silane compound having a functional group. The evaluation results of the molded articles are shown in Table 1. The obtained molded article was poor in heat resistance.

Comparative example 4

A molded body was obtained in the same manner as in example 1 except that the blending amount of magnetite was changed to be less than the range of the present invention and the blending amount of soft ferrite and silicone was changed to the amount shown in table 1. The evaluation results of the molded articles are shown in Table 1. The resulting molded article was poor in flame retardancy.

Comparative example 5

A molded body was obtained by performing the same operation as in example 1 except that the amount of silicone blended was changed to be equal to or more than the range of the present invention and the amount of soft ferrite blended was changed to the amount described in table 1. The evaluation results of the molded articles are shown in Table 1. The resulting molded article has poor electromagnetic wave absorption performance.

Comparative example 6

A molded body was obtained in the same manner as in example 1, except that the blending amount of silicone was set to be less than the range of the present invention and the blending amounts of soft ferrite and magnetite were changed to the amounts shown in table 1. The evaluation results of the molded articles are shown in Table 1. The obtained molded article was poor in moldability.

Comparative example 7

A molded body was obtained in the same manner as in example 1, except that the blending amount of magnetite was changed to be higher than the range of the present invention, and the blending amount of soft ferrite and silicone was changed to the amount shown in table 1. The evaluation results of the molded articles are shown in Table 1. The resulting molded article had poor electromagnetic wave absorption performance and also had magnetic residue.

[ Table 1]

(example 3)

Using methyltrimethoxysilane to regulate the particle size distribution D₅₀50 wt% of Ni-Zn soft ferrite (BSN-714) (product name) made by Suitan industries, Ltd.) having a particle size distribution D of 1 to 10 μm₅₀25 wt% of flat soft magnetic metal powder (JEM-M, manufactured by Jemco, Inc.) having a particle size distribution D of 8 to 42 μ M and a self-oxidizing property of 0.26 wt%₅₀5 wt% of octahedral magnetite fine particles (KN-320 (trade name) manufactured by Kothereto industries, Ltd.) having a particle size of 0.1 to 0.4 μm and 20 wt% of Silicone gel (CF-5106 (trade name) manufactured by Toray Dow Corning, Silicone, Ltd.) having a penetration of 150 according to JIS K2207-1980(50g load) were mixed, vacuum defoamed, poured between glass plates without air mixing, heated at 70 ℃ for 60 minutes and press molded to obtain a surface-smooth molded body having a thickness of 1 mm. The evaluation results of the molded article are shown in Table 2.

Further, the magnetic loss was measured in the range of 0.5 to 10GHz and was shown as A in FIG. 1.

(example 4)

A molded body was obtained in the same manner as in example 3, except that the flat soft magnetic metal powder used in example 3 was dispersed in a gelatin 20 wt% solution dissolved in toluene, and then toluene was evaporated and removed to obtain a microencapsulated flat soft magnetic metal powder (gelatin 20 wt%, flat soft magnetic metal powder 80 wt%) whose surface was coated with gelatin. The evaluation results of the molded articles are shown in Table 2.

(example 5)

A PET film insulating layer having a thickness of 50 μm was laminated on the molded article obtained in example 3 to obtain an electromagnetic wave absorber. The evaluation results of the molded articles are shown in Table 2. Further, the PET film is used to improve dielectric breakdown strength.

(example 6)

A molded body was obtained in the same manner as in example 3, except that the amounts of soft ferrite, flat soft magnetic metal powder, and silicone were changed to the amounts shown in table 1. The evaluation results of the molded articles are shown in Table 1. Further, the magnetic loss was measured in the range of 0.5 to 10GHz, and it was B shown in FIG. 1.

Comparative example 8

A molded body was obtained in the same manner as in example 3, except that the soft ferrite without surface treatment was used and the flat magnetic metal powder and magnetite were not blended so that the amount of silicone was adjusted to the blending amount shown in table 2. If soft ferrite without surface treatment is used, the silicone is filled with only 20% by weight, which inhibits curing of the silicone and prevents a sufficient molded body from being obtained. The evaluation results are shown in table 2.

Comparative example 9

A molded body was obtained in the same manner as in example 3, except that the soft ferrite was surface-treated with epoxytrimethoxysilane which was a silane compound having a functional group. The evaluation results of the molded articles are shown in Table 2. The obtained molded article was poor in heat resistance.

Comparative example 10

A molded body was obtained in the same manner as in example 3, except that the soft ferrite was surface-treated with vinyltrimethoxysilane, which is a silane compound having a functional group. The evaluation results of the molded article are shown in Table 2. The obtained molded article was poor in heat resistance.

Comparative example 11

A molded body was obtained in the same manner as in example 3, except that the amount of magnetite added was changed to be less than the range of the present invention and the amount of soft ferrite shown in table 2 was changed. The evaluation results of the molded articles are shown in Table 2. The resulting molded article was poor in flame retardancy.

Comparative example 12

A molded body was obtained in the same manner as in example 3, except that the flat soft magnetic metal powder was not blended, and the blending amounts of soft ferrite and silicone were changed to amounts shown in table 2. The evaluation results of the molded articles are shown in Table 2. Further, the magnetic loss was measured in the range of 0.5 to 10GHz and was shown as D in FIG. 1. In the high frequency band range of 1GHz or higher, the magnetic loss is small and the electromagnetic wave absorption performance is poor.

Comparative example 13

A molded body was obtained in the same manner as in example 3, except that the amount of flat soft magnetic metal powder and silicone were changed to the amounts shown in table 2 without blending soft ferrite. The evaluation results of the molded articles are shown in Table 2. Further, the magnetic loss was measured in the range of 0.5 to 10GHz, and it was C shown in FIG. 1. The magnetic loss is excellent at 2 to 4GHz, but the magnetic loss is small in a high frequency band such as 10GHz, and the electromagnetic wave absorption performance is poor.

[ Table 2]

(example 7)

Using methyltrimethoxysilane to regulate the particle size distribution D₅₀A soft ferrite of Ni-Zn series (BSE-828 (trade name) made by Koita Kogyo Co., Ltd.) having a particle size distribution D of 83 wt% and having a surface treated surface of 10 to 30 μm₅₀5 wt% of octahedral magnetite fine particles (KN-320 (trade name) manufactured by Kothereto industries, Ltd.) having a thickness of 0.1 to 0.4 μm and 12 wt% of Silicone gel (CF-5106 (trade name) manufactured by Toray Dow Corning silicon, Ltd.) having a penetration of 150 according to JIS K2207-1980(50g load) were mixed, vacuum defoamed, poured between glass plates without air mixing, heated at 70 ℃ for 60 minutes and press-molded to obtain an electromagnetic wave absorbing sheet having a smooth surface with a thickness of 1 mm.

Then, using the obtained electromagnetic wave absorbing sheet, a PET film release film having a thickness of 20 μm, an electromagnetic wave absorbing sheet, an aluminum foil, a PET film having a thickness of 50 μm, an adhesive layer having a thickness of 1 μm, and a PET film release film having a thickness of 20 μm were laminated in this order to obtain a laminated electromagnetic wave absorber. The absorption rate of the electromagnetic wave of the proximity electromagnetic field of the laminated electromagnetic wave absorber is measured. The result is a shown in fig. 6. In fig. 6, for comparison, the value of the near-field electromagnetic wave absorption rate of the electromagnetic wave absorber in which no aluminum foil is laminated is shown as B.

The properties of the obtained laminated electromagnetic wave absorber were as follows, magnetic loss μ ″ (1 GHz): 4.0; volume resistance: 2X 10¹¹Omega.m; dielectric breakdown strength: 4.5 kV/mm; coefficient of thermal conductivity: 1.2W/m.K; specific gravity: 2.8 of; penetration degree: 60, adding a solvent to the mixture; flame retardancy (UL 94): corresponds to V-0; heat resistance: 1000 hours or more.

Industrial applicability of the invention

The electromagnetic wave absorber of the present invention is excellent in electromagnetic wave absorbability, thermal conductivity, flame retardancy, small temperature dependency, flexibility, excellent adhesion strength, high electric resistance and high insulation property, and particularly excellent in the balance of high electric resistance, high insulation property, thermal conductivity and electromagnetic wave absorbability, and can be used by being attached to any of a cable, a high-speed computing element, a printed circuit board pattern, and the like.

The electromagnetic wave absorber of the present invention can exhibit the effect of stable energy conversion efficiency in a wide frequency band of MHz to 10GHz, is excellent in electromagnetic wave absorption, thermal conductivity, and flame retardancy, has small temperature dependence, is flexible, has excellent adhesion strength, has high-resistance and high-insulation properties, and can be used by being attached to any of a cable, a high-speed computing element, a printed circuit board pattern, and the like, particularly because it is excellent in the balance of high-resistance and high-insulation properties, thermal conductivity, and electromagnetic wave absorption.

Further, the laminated electromagnetic wave absorber of the present invention is laminated in the order of the release film layer, the electromagnetic wave absorbing layer, the electromagnetic wave reflecting layer, the insulator layer, the adhesive layer, and the release film layer, and therefore can be attached to the top surface of the case, or to a high-speed computing element or the like, and exhibits excellent effects in electromagnetic wave absorption and electromagnetic wave shielding properties, and is particularly useful for applications of absorbing unnecessary electromagnetic waves in the vicinity of electromagnetic fields such as broadcasting, mobile phones, and wireless LANs.

Claims (20)

1. An electromagnetic wave absorber, characterized in that: the composition comprises (a) 60 to 90% by weight of soft ferrite surface-treated with a non-functional group silane compound, (c) 3 to 25% by weight of magnetite and (d) 7 to 15% by weight of silicone.

2. An electromagnetic wave absorber, characterized in that: the soft magnetic powder comprises (a) 40 to 60% by weight of soft ferrite surface-treated with a non-functional group silane compound, (b) 20 to 30% by weight of flat soft magnetic metal powder, (c) 3 to 10% by weight of magnetite, and (d) 7 to 25% by weight of silicone.

3. An electromagnetic wave absorber as set forth in claim 2, wherein: (a) the weight mixing ratio of the soft ferrite surface-treated with the non-functional group silane compound to the flat soft magnetic metal powder (b) is 1.8-2.3: 1.

4. An electromagnetic wave absorber as set forth in claim 1 or 2, wherein: (a) the soft ferrite surface-treated with the non-functional group-based silane compound is a soft ferrite surface-treated with dimethyldimethoxysilane or methyltrimethoxysilane.

5. An electromagnetic wave absorber as set forth in claim 1 or 2, wherein: (a) the pH of the soft ferrite surface-treated with the non-functional group-based silane compound is 8.5 or less.

6. An electromagnetic wave absorber as set forth in claim 1 or 2, wherein: particle size distribution D of soft ferrite used in (a) soft ferrite surface-treated with non-functional group-based silane compound₅₀1 to 30 μm.

7. An electromagnetic wave absorber as set forth in claim 1 or 2, wherein: the soft ferrite used in (a) the soft ferrite surface-treated with the non-functional group-based silane compound is a Ni — Zn-based ferrite.

8. An electromagnetic wave absorber as set forth in claim 2, wherein: (b) the flat soft magnetic metal is a low self-oxidizing flat soft magnetic metal having a weight change rate of 0.3% by weight or less in an exposure test in an atmosphere under heating.

9. According to claimThe electromagnetic wave absorber according to claim 2, wherein: (b) the specific surface area of the flat soft magnetic metal powder is 0.8 to 1.2m²/g。

10. An electromagnetic wave absorber as set forth in claim 2, wherein: (b) particle size distribution D of flat soft magnetic metal powder₅₀8 to 42 μm.

11. An electromagnetic wave absorber as set forth in claim 2, wherein: (b) the flat soft magnetic metal powder is microencapsulated.

12. An electromagnetic wave absorber as set forth in claim 1 or 2, wherein: (c) particle size distribution D of magnetite₅₀0.1 to 0.4 μm.

13. An electromagnetic wave absorber as set forth in claim 1 or 2, wherein: (c) magnetite is an octahedral shape microparticle.

14. An electromagnetic wave absorber as set forth in claim 1 or 2, wherein: (d) the silicone is a silicone gel having a penetration of 5 to 200 according to JIS K2207-1980 under a load of 50 g.

15. A laminated electromagnetic wave absorber in which a conductor reflective layer is laminated on the electromagnetic wave absorber according to claim 1 or 2, characterized in that: an insulating layer is arranged outside the reflecting layer.

16. The laminated electromagnetic wave absorber according to claim 15, which absorbs unnecessary electromagnetic waves from the inside and outside of a resin case, wherein a conductive electromagnetic wave reflecting layer is laminated on the electromagnetic wave absorbing layer, an adhesive layer is laminated on the outside of the electromagnetic wave reflecting layer via an insulating layer, and a peeling film layer is laminated on the outside of the electromagnetic wave absorbing layer and the outside of the adhesive layer, respectively, wherein: the electromagnetic wave absorber layer has at least adhesiveness to be attached to the high-speed operation element, and the adhesive layer has at least adhesive force to be attached to the horizontal glass ceiling surface without falling off.

17. A laminated electromagnetic wave absorber as claimed in claim 15, wherein: an insulator layer is provided between the electromagnetic wave absorber layer and the electromagnetic wave reflection layer.

18. A laminated electromagnetic wave absorber as claimed in claim 15, wherein: the electromagnetic wave reflecting layer is an aluminum metal layer.

19. A laminated electromagnetic wave absorber as claimed in claim 16, wherein: the adhesive layer is an acrylic adhesive layer.

20. A laminated electromagnetic wave absorber as claimed in claim 15, wherein: the insulator layer is a polyethylene terephthalate resin layer.