JP2007042907A - Electromagnetic wave shielding composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave shielding composition capable of sufficiently shielding high frequency electromagnetic waves. <P>SOLUTION: The electromagnetic wave shielding composition is composed of (A) a resin binder and (B) a thin film of sendust. The thin film of sendust is included in a solid content of the electromagnetic wave shielding composition by 40-60 vol.%. The aspect ratio of the sendust is 5-15, and the particle distribution D (50%) of the sendust measured by a laser diffraction particle distribution measuring device is in a range of 30-50 μm. Since loss caused by an eddy current in a high frequency region is small although a particle diameter is large, the magnetic permeability of a resin composition is high. In addition, since a peak frequency of the resin composition is at a high frequency side, excellent electromagnetic wave shielding effects can be obtained in the high frequency region. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electromagnetic wave shielding composition that exhibits a high electromagnetic wave shielding effect even in a high frequency region.

  In recent years, various electronic devices such as personal computers and televisions have spread rapidly in general homes and offices, and the operating frequency of electronic devices has been increasing with the increase in functionality of the devices. There are also concerns about the effects of electromagnetic waves leaking from electronic devices on the human body. For this reason, various electromagnetic shielding materials have been developed in order to prevent electromagnetic waves generated inside the electronic device from leaking to the outside of the device and from being affected by electromagnetic waves from the outside.

In general, an electric field and a magnetic field are oscillated at a constant frequency orthogonal to each other. However, in the propagation of electromagnetic waves, a soft magnetic material having a high magnetic permeability and a low coercive force is suitable in the low frequency region. In addition, in the high frequency region, the influence of the electric field component is large, and a material having high conductivity has been considered suitable. For example, silicon steel, sendust, permalloy, and ferrite-based oxides are listed as soft magnetic materials, and conductive metals such as copper, silver, nickel, gold, and palladium are listed as materials having high conductivity.
JP 2002-198683 A Japanese Patent Laid-Open No. 11-354773 JP 2003-158003 A

In fact, as an electromagnetic shielding material for the high frequency region, metallic magnetic materials such as Sendust (Fe-Si-Al alloy) and Permalloy (Fe-Ni alloy) that can obtain a high magnetic flux density in a small volume are used. There are many. In order to improve the performance of the electromagnetic shielding material filled with these metal magnetic materials, various measures have been taken to increase the magnetic permeability, such as increasing the particle size and aspect ratio of the metal magnetic material, In some cases, the metal magnetic material is forcibly arranged by reducing the oxygen content of the metal magnetic material, filling the metal magnetic material with high density, or applying external pressure to form the metal magnetic material. However, with these measures, the electrical resistance of the electromagnetic wave shielding material is reduced as a result of easy contact between metal magnetic bodies having an electrical resistivity of about 10 ⁻⁶ to 10 ⁻⁵ Ωcm. While the magnetic permeability is improved, there is a drawback that high permeability cannot be obtained due to eddy current loss in a high frequency region.

In addition, when Ni—Zn ferrite or Co ferrite having a very high electric resistivity of 10 ⁶ Ωcm or more is used, an electromagnetic wave shielding material having a large electric resistance can be obtained. Therefore, it is preferably used as a countermeasure material in a high frequency region. ing. However, since ferrite is an oxide magnetic material exhibiting ferrimagnetism, the saturation magnetization value is usually as small as about 0.3 to 0.5 T, so that it is easily saturated. Furthermore, since the magnetic permeability is low, in order to obtain a high electromagnetic wave shielding effect as an electromagnetic wave shielding material, there is a drawback that the filler must be highly filled and the volume must be increased.

  In general, a filler having a large aspect ratio has a high shielding effect, but has a drawback that the bulk density of the filler is very small, so that the resin cannot be highly filled.

  The present invention has been studied in view of such a situation, and aims to exhibit an excellent shielding effect against electromagnetic waves in a high frequency region, and is characterized by the following. That is, the invention described in claim 1 is an electromagnetic wave shielding composition comprising (A) a resin binder and (B) flaky sendust, wherein the flaky sendust is 40 to 40% in the solid content of the electromagnetic wave shield composition. 60% by volume, the flaky sendust has an aspect ratio of 5 to 15, and the flaky sendust has a particle size distribution D (50%) measured by a laser diffraction particle size distribution measuring device of 30 to 50 μm. An electromagnetic wave shielding composition.

  When Sendust is used in a flaky shape with an aspect ratio of 5 to 15 and a particle size distribution D (50%) of 30 to 50 μm, the loss due to eddy currents in the high frequency region is small despite the large particle size. The magnetic permeability of the composition is high, and the peak frequency of the resin composition exists on the high frequency side. Therefore, the electromagnetic wave shielding effect in the high frequency region is high. Hereinafter, the present invention will be described in detail.

  The (A) resin binder used in the present invention is not particularly limited, and is appropriately selected in consideration of work efficiency, use conditions, etc. in addition to miscibility and insulation. In particular, a resin having high cohesive strength is desirable.

  For example, epoxy resin, styrene / butadiene rubber (SBR), styrene / isoprene / styrene rubber (SIS), styrene / isoprene / butadiene / styrene rubber (SIBS), styrene / butadiene / styrene rubber (SBS), acrylonitrile / butadiene rubber ( NBR), methyl methacrylate / butadiene rubber (MBR), styrene / ethylene / propylene / styrene rubber (SEPS), styrene / ethylene / butadiene / styrene rubber (SEBS), styrene / ethylene / ethylene / propylene / styrene rubber (SEEPS) , Ethylene vinyl acetate resin, polyamide resin, solvent resin (acrylic resin), vinyl acetate or vinyl acetate resin in which vinyl acetate and acrylate are copolymerized, vinyl chloride and vinyl acetate, ethylene, acrylic resin Vinyl chloride resin copolymerized with acid ester, styrene resin copolymerized with styrene and acrylate, ethylene / vinyl acetate copolymer resin, urethane resin, acrylic urethane resin, polyester polyurethane resin, modified silicone resin And water-dispersed resin-based materials (specific examples of synthetic rubber-based latexes such as styrene / butadiene rubber latex and acrylonitrile / butadiene rubber), carboxyl-modified ones such as methyl methacrylate / butadiene rubber and chloroprene rubber.

  Among the binders exemplified above, acrylic urethane is a reaction product of acrylic polyol and polyfunctional isocyanate, and acrylic polyol is hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxypropyl methacrylate, polyethylene. It is a copolymer of (meth) acrylates having a hydroxyl group such as glycol monoacrylate, polyethylene glycol monomethacrylate, polypropylene glycol monoacrylate, polypropylene glycol monomethacrylate, glycerol monomethacrylate and other unsaturated compounds. The polyester polyurethane resin refers to a resin produced by further subjecting a polyester polyol produced by a condensation polymerization reaction of a polyol and a polycarboxylic acid to a urethane reaction via a polyisocyanate.

  In addition, acrylic resin emulsions prepared using acrylic monomers such as various acrylic esters, which are synthetic resin emulsions, and vinyl acetate or vinyl acetate and comonomers such as acrylic esters and Veova were copolymerized. Vinyl acetate resin emulsions, vinyl chloride resin emulsions in which vinyl chloride and vinyl acetate, ethylene, acrylic acid ester and other comonomer are polymerized, styrene resin emulsions in which styrene and acrylic acid ester and other comonomer are copolymerized, ethylene Examples include vinyl acetate copolymer emulsion.

  Moreover, the modified silicone resin, cyanoacrylate resin, urethane resin etc. which are moisture hardening type resins are also mentioned.

  Sendust (Fe-Al-Si alloy) used in the present invention was directly pulverized from molten alloy powder by atomizing method, powder obtained by pulverizing Sendust alloy ingot or reaction sintered body by general mechanical pulverization method, etc. The thing by various pulverization methods, such as a powder, can be used. The alloy composition is an alloy in which Si is 8.5 wt% to 10.5 wt%, Al is 4.5 wt% to 6.5 wt%, and the balance is Fe. The complex relative permeability of the resin composition is also high frequency region of about 100 MHz. There is little decrease in the imaginary term of the magnetic susceptibility, and it can be suitably used.

Here, the complex relative permeability means that the magnetic flux density induced in the magnetic material cannot keep up with the change of the magnetic field in the high-frequency AC magnetic field, and the phase of the magnetic field wave is delayed. The real term is related to the magnetic flux density component having the same phase as the magnetic field, and the imaginary term is an index including a phase delay and corresponds to the loss of magnetic energy. When the generation of high-frequency current is suppressed, the equivalent resistance component size depends on the size of μ ”of the complex relative permeability μ = μ′−jμ ″ of the magnetic material, and the area of the magnetic material is constant. Is known to be substantially proportional to the magnitude of the imaginary component μ ″.
The complex relative permeability μ = μ′−jμ ″ is often expressed by frequency dependence, and the frequency at which μ ″ is maximum is defined as the peak frequency. In a region where μ ″ is low at a frequency sufficiently lower than this peak frequency, it is widely used as a magnetic core material as a low-loss material, while on the other hand, an electromagnetic wave absorbing material is utilized by utilizing a large magnetic loss in a high frequency region above the peak frequency. It is used as.

  Examples of the shape include, for example, a spherical shape, a scale shape, a fiber shape, and the like. In particular, a thin piece having a small aspect ratio can be contained in a large amount in the resin binder, and is included in the resin binder. It is preferable because the magnetic permeability of the resin composition is increased when the flaky sendusts are aligned in parallel in the same direction.

  The particle size distribution of the flaky sendust was measured by a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, SALD-200V-WJA1: V1.01, refractive index 2.70-0.20i). (50%) is preferably 30 to 50 μm, more preferably D (25%) is 25 to 35 μm, D (50%) is 30 to 50 μm, and D (75%) is 50 to 60 μm, and D (50 %) Is less than the lower limit, the magnetic permeability of the resin composition is lowered. When the upper limit is exceeded, the peak frequency of the resin composition is on the low frequency side. Incidentally, D (50%) means a 50% cumulative distribution particle size.

  The aspect ratio of the flaky sendust is 5 to 15, preferably 6 to 10. If the aspect ratio is less than the lower limit, the magnetic permeability of the resin composition is low. When the upper limit is exceeded, the peak frequency of the resin composition is on the low frequency side. More preferably, the average thickness is 3 μm to 10 μm, and D (50%) is 30 μm to 50 μm.

  The electromagnetic wave shielding composition of the present invention contains the resin binder and flaky sendust powder as main components, and if necessary, a dispersant, a surfactant, a curing agent, a plasticizer, an antistatic agent, a lubricant, and a polishing agent. An agent, an antirust agent, an organic solvent, etc. can be blended. Various types of mixing, kneading, and dispersing machines can be used for the adjustment. For example, a two-roll mill, a three-roll mill, a ball mill, a sand mill, a Henschel mixer, a planetary mixer, a pressure kneader, an extruder, an attritor, and a high-speed mixer can be used.

  The electromagnetic wave shielding composition prepared by the above method can be applied by a generally known method and dried to form an electromagnetic wave shielding layer. Examples of the coating method include gravure coating, gravure reverse coating, Reverse roll coating, roll coating, die coating, wire bar coating, doctor blade coating, dip coating, air knife coating, kiss coating, slot coating, spray coating, screen printing, metal mask printing, dispenser coating, dipping, spray coating, etc. Can be mentioned.

  Hereinafter, although an Example and a comparative example are demonstrated, a capacity | capacitance part is a value of solid content.

Example 1
Flaky sendust powder (manufactured by Toho Zinc Co., Ltd.) 60 parts by volume (composition Fe: 85.6 wt%, Al: 5.3 wt%, Si: 9.1 wt%,
Aspect ratio 7
Particle size distribution D (50%) 37μm)
Polyester polyurethane resin (solid content 30% by weight) 40 parts by volume (UR-5537 manufactured by Toyobo Co., Ltd.); solvent composition: methyl ethyl ketone: toluene = 50: 50, including sulfonic acid sodium salt as a polar functional group, molecular weight 20000, Tg 34 ° C. Hydroxyl value 16-18 / KOHmg / g, acid value less than 1 KOHmg / g)
Was put into a planetary mixer and dispersed and mixed for 3 hours to obtain an electromagnetic wave shielding composition.

Example 2
Flaky sendust powder (manufactured by Toho Zinc Co., Ltd.) 60 parts by volume (composition Fe: 85.6 wt%, Al: 5.3 wt%, Si: 9.1 wt%,
Aspect ratio 8
Particle size distribution D (50%) 43 μm)
Polyester polyurethane resin (same as in Example 1) 40 parts by volume were placed in a planetary mixer and dispersed and mixed for 3 hours to obtain an electromagnetic wave shielding composition.

Comparative Example 1 (when the blending ratio of flaky sendust is less than the lower limit)
Flaky Sendust powder (manufactured by Toho Zinc Co., Ltd.) 30 parts by volume (composition Fe: 85.6 wt%, Al: 5.3 wt%, Si: 9.1 wt%,
Aspect ratio 7
Particle size distribution D (50%) 37μm)
Polyester polyurethane resin (same as in Example 1) 70 parts by volume were placed in a planetary mixer and dispersed and mixed for 3 hours to obtain an electromagnetic wave shielding composition.

Comparative Example 2 (When the proportion of flaky sendust exceeds the upper limit)
Flaky Sendust powder (manufactured by Toho Zinc Co., Ltd.) 70 parts by volume (composition Fe: 85.6 wt%, Al: 5.3 wt%, Si: 9.1 wt%,
Aspect ratio 7
Particle size distribution D (50%) 37μm)
Polyester polyurethane resin (same as in Example 1) 30 parts by volume were put into a planetary mixer and dispersed and mixed for 3 hours to obtain an electromagnetic wave shielding composition.

Comparative Example 3 (when the aspect ratio of flaky sendust is less than the lower limit)
Flaky sendust powder (manufactured by Toho Zinc Co., Ltd.) 60 parts by volume (composition Fe: 85.6 wt%, Al: 5.3 wt%, Si: 9.1 wt%,
Aspect ratio 4
Particle size distribution D (50%) 33 μm)
Polyester polyurethane resin (same as in Example 1) 40 parts by volume were placed in a planetary mixer and dispersed and mixed for 3 hours to obtain an electromagnetic wave shielding composition.

Comparative Example 4 (When the aspect ratio of flaky sendust exceeds the upper limit)
The flaky Sendust powder (manufactured by Toho Zinc Co., Ltd.) was flattened with a wet bead mill to obtain the following flaky Sendust powder.
60 parts by volume of flaky sendust powder (composition Fe: 85.6 wt%, Al: 5.3 wt%, Si: 9.1 wt%,
Aspect ratio 40
Particle size distribution D (50%) 40 μm)
Polyester polyurethane resin (same as in Example 1) 40 parts by volume were placed in a planetary mixer and dispersed and mixed for 3 hours to obtain an electromagnetic wave shielding composition.

Comparative Example 5 (When the particle size distribution D (50%) of flaky sendust is less than the lower limit)
The following flaky sendust powder was obtained by air classification of flaky sendust powder (manufactured by Toho Zinc Co., Ltd.).

60 parts by volume of flaky sendust powder (composition Fe: 85.6 wt%, Al: 5.3 wt%, Si: 9.1 wt%,
Aspect ratio 8
Particle size distribution D (50%) 14 μm)
Polyester polyurethane resin (same as in Example 1) 40 parts by volume were placed in a planetary mixer and dispersed and mixed for 3 hours to obtain an electromagnetic wave shielding composition.

Comparative Example 6 (When the particle size distribution D (50%) of flaky sendust exceeds the upper limit)
The following flaky sendust powder was obtained by air classification of flaky sendust powder (manufactured by Toho Zinc Co., Ltd.).

60 parts by volume of flaky sendust powder (composition Fe: 85.6 wt%, Al: 5.3 wt%, Si: 9.1 wt%,
Aspect ratio 8
Particle size distribution D (50%) 60μm)
Polyester polyurethane resin (same as in Example 1) 40 parts by volume were placed in a planetary mixer and dispersed and mixed for 3 hours to obtain an electromagnetic wave shielding composition.

The test methods were as follows. Resins obtained by the methods of Examples 1 and 2 and Comparative Examples 1 to 6 were made into sheets. The electromagnetic shielding performance was confirmed by measuring the complex relative permeability of this resin composition. Furthermore, each surface resistance value was measured by the JIS-K6911 conformity method.
Complex relative magnetic permeability; manufactured by Agilent Technologies, Inc. Model number: Impedance analyzer E4991A and test fixture 1645A were used and measured at a measurement frequency of 1 MHz to 1 GHz.
Surface resistance value: manufactured by Advantest Co., Ltd., model number: digital ultrahigh resistance / microammeter R8340A, resiliency chamber R12704A (internal electrode φ50 mm, external electrode φ83 mm) was measured at an applied voltage of 500V.

  The evaluation results are shown in Table 1.

The evaluation results were as follows.

  In Table 1, in Examples 1 and 2, it was confirmed that the real number term of the complex relative permeability was as large as 27 or more, and the imaginary term of the complex relative permeability had a high peak value of around 15 near 300 MHz. Furthermore, even though the particle size is relatively large, flaky flaky sendust having an appropriate aspect ratio is used and mixed at an appropriate blending ratio, so that the surface resistance value is high, and the complex relative permeability on the high frequency side. We also confirmed that there exists a maximum value of the imaginary term. From these results, it was judged that a resin composition having a high shielding effect in the high frequency region was obtained.

  In Table 1, in Comparative Example 1 (the blending ratio of flaky Sendust is less than the lower limit), the ratio of the resin that is an insulator is increased (the surface resistance value of the resin composition is high), so the peak frequency is 1 GHz or more. However, the permeability in the low frequency region is low, indicating that the electromagnetic shielding effect is small. That is, it was judged that the target electromagnetic shielding material was not obtained.

  In Table 1, in Comparative Example 2 (when the blending ratio of the flaky sendust exceeds the upper limit), the filling amount of the flaky sendust with respect to the resin binder is too high. The sheet for evaluation was not obtained. That is, it was judged that the target electromagnetic shielding material was not obtained.

  In Table 1, in Comparative Example 3 (when the aspect ratio of the flaky sendust is less than the lower limit), the peak frequency of the resin composition is 1 GHz or higher, which is on the high frequency side, but both the real and imaginary terms are low. This indicates that a sufficient shielding effect cannot be exhibited unless the aspect ratio is low, that is, the aspect ratio is 5 or more. That is, it was judged that the target electromagnetic shielding material was not obtained.

  In Table 1, in Comparative Example 4 (when the aspect ratio of flaky sendust exceeds the upper limit), the resin composition has a large real permeability term, but the peak frequency is as low as 32.2 MHz, and the shielding effect in a higher frequency region. Is low. The low peak frequency is supported by the surface resistance value. That is, it was judged that the target electromagnetic shielding material was not obtained.

  In Table 1, Comparative Example 5 (when the particle size distribution D (50%) of the flaky sendust is less than the lower limit) has a low complex relative permeability of the resin composition because the particle size of the flaky sendust is small, and the shielding effect Is low. That is, it was judged that the target electromagnetic shielding material was not obtained.

  In Table 1, in Comparative Example 6 (when the particle size distribution D (50%) of the flaky sendust exceeds the upper limit), the resin composition has a very high complex relative permeability because the particle size of the flaky sendust is large. Although it was predicted that a composition would be obtained, it was difficult to fill the resin binder in a high amount. As a result, the obtained resin composition was lacking in coating suitability, and a sheet for evaluation could not be obtained. That is, it was judged that the target electromagnetic shielding material was not obtained.

Claims (1)

An electromagnetic shielding composition comprising (A) a resin binder and (B) flaky sendust, wherein the flaky sendust is contained in an amount of 40 to 60% by volume in the solid content of the electromagnetic shield composition, An electromagnetic shielding composition, wherein the sendust has an aspect ratio of 5 to 15 and a particle size distribution D (50%) of the flaky sendust measured by a laser diffraction particle size distribution analyzer is in the range of 30 to 50 μm.