JP6706569B2 - Electromagnetic field shield sheet - Google Patents

Description

The present invention relates to an electromagnetic field shield sheet having both an electric field shield property and a magnetic field shield property, and particularly to an electromagnetic field shield sheet that is thin but provides high shield property.

In a shield member that absorbs energy of passing electromagnetic waves and attenuates it, by forming it in a sheet shape, it can be given along the inner surface of the casing of the electronic device, and can be applied from the substrate inside the electronic device. It is possible to prevent the electromagnetic wave from leaking to the outside of the housing or protect the electronic device from the electromagnetic wave outside the housing. By making such an electromagnetic field shield sheet thinner, it becomes possible to mount it inside a small electronic device, and it becomes easier to cover a large area, and it has practically high versatility. It will be.

For example, Patent Document 1 discloses an electromagnetic wave shield cloth for use in protective clothing for working against electromagnetic waves in which a coating material containing soft magnetic alloy powder is applied to the surface of a thin cloth containing metal-coated fibers. Such an electromagnetic wave shielding cloth is obtained by applying a soft magnetic alloy powder made of Fe-Al-Si or Fe-Ni mixed with a vinyl chloride adhesive to the surface of a non-woven fabric made of fibers coated with silver, and further applying a vinyl chloride series cloth. It is said that it will be manufactured by bonding it to a soft vinyl chloride sheet with an adhesive.

Further, Patent Document 2 discloses an electromagnetic interference suppressor including a laminated sheet in which magnetic sheets made of a soft magnetic material powder and a binder are attached to both surfaces of a conductive sheet. It is said that the magnetic sheet absorbs electromagnetic waves, and the electromagnetic waves that have passed through the magnetic sheet are reflected by the conductive sheet toward the magnetic sheet to have a high electromagnetic wave absorbing ability. The magnetic sheet is obtained by using elastomer such as chlorinated polyethylene as an organic binder and dispersing soft magnetic powder in the organic binder to form a sheet with a rolling roll or the like. Here, the conductive sheet is a Ni-plated mesh-like woven fabric, and since it has a plurality of holes, it is said that the adhesive strength in the rolling lamination with the magnetic sheet is increased.

JP-A-5-186966 JP, 10-79595, A

In the electromagnetic field shield sheet, simply stacking the electric field shield sheet and the magnetic field shield sheet increases the thickness. Further, in order to enhance the transmission attenuation capability of the electromagnetic field, it can be considered that the thickness is larger. On the other hand, when the thickness is made larger, the flexibility as a sheet is lost, and when the soft magnetic metal powder is dispersed in the sheet, the soft magnetic metal powder falls off by bending or the like, and the sheet May decrease in strength. On the contrary, in order to maintain the flexibility, the content density of the soft magnetic metal powder must be lowered, and as a result, the sheet thickness must be increased to obtain the same transmission attenuation ability. I will end up.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electromagnetic field shield sheet that is thin but has high shielding properties.

The electromagnetic field shield sheet according to the present invention is an electromagnetic field shield sheet having both an electric field shield property and a magnetic field shield property, and imparts an electric field shield property along the main surface of a flexible insulating resin sheet body. A flat soft magnetic metal powder that is embedded with a mesh made of a conductive material and that imparts magnetic field shielding properties to the resin sheet body inside and outside the mesh of the mesh so as to be substantially parallel to the main surface. Are oriented and dispersed.

According to such an invention, a high electric field shielding property and magnetic field shielding property are provided by compounding a mesh made of a conductive metal that imparts an electric field shielding property and a flat soft magnetic metal powder that imparts a magnetic field shielding property. .. In addition, regarding the resin sheet body in which the flat soft magnetic metal powder which imparts the magnetic field shielding property is dispersed, the net-like body made of the conductive metal which imparts the electric field shielding property provides the composite reinforcement and the flexibility of the resin sheet body. To maintain.

In the above invention, the resin sheet body may include 80 to 90 parts by mass of the soft magnetic metal powder in 100 parts by mass. According to this invention, the filling rate of the soft magnetic metal powder can be further increased to provide a higher magnetic field shielding property.

In the above invention, the resin sheet body may be made of urethane resin. According to such an invention, it is possible to increase the filling rate of the soft magnetic metal powder inside and outside the mesh and increase the orientation thereof, so that a higher magnetic field shielding property can be provided. In other words, due to the follow-up deformability of the urethane resin, even if the flat soft magnetic metal powder is highly filled and oriented and dispersed in the resin, it can be prevented from falling off and the flexibility can be maintained.

In the above invention, the soft magnetic metal powder has a flat shape with an average particle size D50 of 20 μm or more and 100 μm or less and a flatness of 20 or more, and the mesh of the reticulate body is more than the average particle size D50. It may be characterized by being large. Further, in the above invention, the mesh may have an aperture ratio of 20% or more. According to this invention, the orientation of the soft magnetic metal powder in the mesh can be enhanced, and a higher magnetic field shielding property can be provided.

In the above invention, the mesh may have an opening of 0.05 mm or more and 1 mm or less. According to this invention, the orientation of the soft magnetic metal powder in the mesh can be enhanced while maintaining the electric field shielding property, and higher electric field shielding property and magnetic field shielding property can be provided.

In the above invention, the soft magnetic metal powder may be made of an Fe-Ni based alloy, an Fe-Si based alloy, an Fe-Si-Cr based alloy, or an Fe-Si-Al based alloy. According to this invention, a high magnetic field shielding property can be provided.

FIG. 3A is a perspective view and FIG. 2B is a partial sectional view of an electromagnetic field shield sheet according to the present invention. It is a partial top view of the net-like body used for an electromagnetic field shield sheet. FIG. 6 is a partial sectional view of another electromagnetic field shield sheet according to the present invention. It is a table which shows the component composition of the alloy used for the soft magnetic alloy powder. It is a figure of the measurement result of the attenuation rate about the electric field of electromagnetic waves. It is a figure of the measurement result of the attenuation rate about the magnetic field of an electromagnetic wave. Measurement result of 10 MHz electromagnetic wave attenuation factor ((a) electric field shield (b) magnetic field shield) Measurement result of 100MHz electromagnetic wave attenuation factor ((a) electric field shield (b) magnetic field shield) It is a list of the measurement results of the configuration and the attenuation rate of the electromagnetic field shield sheet. It is a microscope observation photograph of the cross section of an electromagnetic field shield sheet.

An electromagnetic field shield sheet as one example according to the present invention will be described with reference to FIGS. 1 to 3.

As shown in FIG. 1, a sheet body 10 which is an electromagnetic field shield sheet has a mesh body 1 embedded inside a resin 2 which is an insulating resin sheet body arranged over the entire area in the thickness direction, and further has a mesh shape. A powder 3 of a soft magnetic alloy powder made of a soft magnetic alloy is dispersed inside and outside the mesh of the body 1 and throughout the resin sheet body. The powder 3 has a flat shape and is oriented so as to be substantially parallel to the main surface of the sheet body 10. As a result, in the main surface direction of the sheet body 10 of the mesh body 1, the powder 3 disposed between the meshes improves the conductivity in the main surface direction and further improves the electric field shielding property originally possessed by the mesh body 1. Become. Further, the powders 3 that are oriented and dispersed in the entire sheet body 10 including the inside of the mesh are appropriately insulated from each other by the resin 2, and the eddy current generated in the entire sheet body 10 can be suppressed. In particular, a higher magnetic field shielding property can be obtained in a high frequency region.

Referring also to FIG. 2, in the mesh body 1, the metal wire 11 made of a conductive metal is plain-woven, and the respective contacts of the metal wires 11 are electrically connected to each other. That is, in the mesh body 1, conduction is secured except for the openings by the mesh 12. As the metal wire 11, a copper-based alloy such as copper, aluminum, or stainless steel can be used, and can be used regardless of its magnetism. Note that the mesh body 1 is not limited to this, and may be a metal wire 11 woven in another way, or may be a metal sheet such as punched metal with a large number of holes opened, and the mesh is made of a conductive material. It may be a woven fiber made of a resin coated with a metal or a resin containing a conductive filler. As the conductive filler contained in the fiber, carbon black or conductive metal powder such as copper or aluminum can be used. In this way, the net-like body 1 is made of a conductive material to ensure electrical continuity other than the openings such as the mesh 12.

Since the net-like body 1 mainly imparts the electric field shielding property, the mesh 12 is made fine so that the energy of the electromagnetic wave passing therethrough can be attenuated. Further, it is necessary to orient and disperse the powder 3 in the mesh 12 to obtain the effect of magnetic field shielding. Therefore, the mesh 12 is preferably larger than the average particle diameter D50 of the powder 3 described later. In other words, from the viewpoint of arranging the powder 3 in the mesh 12 by orienting the powder 3 substantially parallel to the main surface of the sheet body 10, it is preferable to make the mesh 12 large. Considering these, for example, the mesh opening of the mesh 12 is preferably in the range of 0.05 mm or more and 1 mm or less in equivalent circle diameter, and the aperture ratio is in the range of 20% or more and 85% or less. preferable.

The resin 2 is a binder that disperses and orients the powder 3 in the sheet body 10 before forming the sheet body 10. As such a resin 2, for example, urethane resin, acrylic resin, polyester resin, epoxy resin, polyimide resin, silicone resin or the like can be used. It is also preferable that the adhesion to the reticulate body 1 and the powder 3 is high.

In particular, urethane resin is preferable because the orientation of the powder 3 can be increased. For example, when the soft magnetic paint made of urethane resin containing the powder 3 is applied to the reticulate body 1 during the manufacture of the sheet body 10, the flat powder 3 naturally moves in the direction along the main surface of the sheet body 10. It has been confirmed to be oriented. Further, the follow-up deformability of the urethane resin is preferable because the adhesion to the reticulate body 1 and the powder 3 can be increased and breakage of the sheet body 10 during deformation can be suppressed. Further, even if the flat powder 3 is oriented and dispersed at a high filling rate, it can be prevented from falling off. The other details of the resin 2 are the same as those described in JP-A-2016-21490 and are as follows.

The urethane resin is obtained by reacting a polyol with a polyisocyanate compound. Examples of the urethane resin include polyether polyurethane, polycarbonate polyurethane, and polyester polyurethane. Among them, polyester-based polyurethane is preferable in terms of high elongation at break and excellent flexibility, and can impart high flexibility to the sheet body 10.

Polyether polyurethane is a reaction product of a polyether polyol and a polyisocyanate compound. Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like.

Polycarbonate polyurethane is a reaction product of a polycarbonate polyol and a polyisocyanate compound. Examples of the polycarbonate polyol include diols (ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, Examples thereof include polycarbonate diol obtained by reacting neopentyl glycol) with a carbonate (dimethyl carbonate, diphenyl carbonate, ethylene carbonate, phosgene, etc.).

Polyester polyurethane is a reaction product of a polyester polyol and a polyisocyanate compound. Examples of polyester polyols include dicarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, adipic acid, sebacic acid, etc.) and polyhydric alcohols (ethylene glycol, propylene glycol, tetramethylene glycol, 1, 4-butanediol, 1,6-hexanediol, neopentyl glycol, trimethylolpropane, pentaerythritol, etc.) and the like.

Examples of the polyisocyanate compound include hexamethylene diisocyanate, tolylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, norbornene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, a trimer of isophorone diisocyanate, hydrogenated xylylene diisocyanate, Examples thereof include hydrogenated diphenylmethane diisocyanate.

The weight average molecular weight of the urethane resin is preferably 1,000 to 100,000, and more preferably 5,000 to 50,000. If the weight average molecular weight of the urethane resin is less than 1000, the durability of the sheet body 1 tends to decrease, and the magnetic field shielding property due to the insulation property tends to deteriorate. On the other hand, when the weight average molecular weight of the urethane resin exceeds 100,000, the flexibility of the sheet body 1 and the adhesiveness with the reticulate body 1 are reduced, and the orientation of the powder 3 tends to be reduced.

The powder 3 is particles of the soft magnetic alloy powder that is oriented and dispersed in the sheet body 10, and mainly imparts the magnetic field shielding property to the sheet body 10. The powder 3 is a soft magnetic material having a flat shape as described above, and it is preferable that a high magnetic permeability can be imparted in the direction along the main surface of the sheet body 10. Therefore, it is preferable that the filling rate of the resin 2 can be increased. Further, as described above, the powder 3 is also oriented inside the mesh 12. Considering these, the average particle diameter D50 of the powder 3 is preferably 20 μm or more and 100 μm or less, and the flatness described later is preferably 20 or more. Further, it is preferable that 80 to 90 parts by mass of the powder 3 be contained in 100 parts by mass of the resin 2 which is the resin sheet body in total.

Further, as the soft magnetic alloy which is the material of the powder 3, Fe-Ni based alloy, Fe-Si based alloy, Fe-Si-Cr based alloy, Fe-Si-Al based alloy or the like is preferable. These can be mixed and used. These alloys can impart the above-mentioned high magnetic permeability to the sheet body 10 and can easily be processed into a flat shape. In addition, it is preferable that the powder 3 has conductivity because the electric field shielding property can be enhanced by the synergistic effect with the mesh body 1.

The flatness is measured and defined as follows. First, the powder 3 is embedded in a resin and polished, and the thickness direction of the powder 3 is observed with an optical microscope to obtain a maximum thickness tmax and a minimum thickness tmin, which is an average value (tmax+tmin)/ 2 is the average thickness ta. Ta was calculated for 100 powders 3, and the average value thereof was divided by the average particle diameter D50 to obtain the flatness.

Such a sheet body 10 can be obtained by applying a soft magnetic paint obtained by mixing a soft magnetic alloy powder of the powder 3 with a raw material of the resin 2 to the mesh body 1 and drying it. The raw material of the resin 2 is obtained, for example, by mixing a urethane resin with a dispersant, an organic solvent, an antifoaming agent, or the like. Examples of the coating method include a spray method, a screen printing method, a brush coating method, and a dipping method.

Referring to FIG. 1 again, the sheet body 10 is coated with the soft magnetic paint obtained by mixing the raw material of the resin 2 and the powder 3 from one surface of the net body 1 at the time of manufacturing the sheet body 10. There is a portion where the resin 2 and the powder 3 are not arranged.

On the other hand, as shown in FIG. 3, the sheet body 11 is coated with the soft magnetic paint from both sides of the reticulated body 1 at the time of manufacturing, and the resin 2 and the powder 3 are applied to both sides of the reticulated body 1. Are placed. The electromagnetic field shield sheet may be the sheet body 11 formed by such double-sided coating.

According to the electromagnetic field shield sheet including the sheet body 10 or 11 as described above, the electric field shield property mainly by the conductive mesh body 1 and the magnetic field shield property mainly by the powder 3 can be imparted, and the electromagnetic field shield can be provided. Can be used as. In particular, since the powder 3 is oriented and dispersed inside the mesh 12 of the mesh body 1, it is possible to give the sheet body 10 a high shielding property even though it is thin. Further, the resin sheet body in which the powder 3 is dispersed in the resin 2 is compounded and strengthened by embedding the mesh body 1 inside, and the applicable range of the sheet body 10 can be widened based on the obtained flexibility. As described above, the sheet body 10 or 11 is imparted with a high shielding property and is given, for example, along the inner surface of the housing of the electronic device, while reducing the influence of electromagnetic waves emitted from the electronic device on the outside. It is possible to improve the so-called electromagnetic compatibility by reducing the influence of electromagnetic waves from the outside on the inside of the electronic device.

A specific example of manufacturing the sheet body 11 as the electromagnetic field shield sheet will be described with reference to FIGS. 4 to 10.

First, a raw material powder was manufactured by an atomizing method in which a molten alloy having the composition shown in FIG. 4 was sprayed in a nitrogen atmosphere.

Next, the raw material powder of the FeSiAl alloy is subjected to a heat treatment of holding it at a temperature of 900 to 1000° C. for 5 hours in a hydrogen atmosphere to adjust the crystal grain size. The FeSiCr alloy raw material powder is not heat treated.

A flattening treatment is applied to each alloy powder. Specifically, in an attritor device, about 35 kg of the raw material powder, 50 liters of a solvent made of a naphthene-based solvent, 550 kg of a grinding medium made of high carbon chromium bearing steel and having a diameter of 4.8 mm, and a weight ratio to the raw material powder of 0.08. A lubricant made of zinc stearate of about 1.6% by mass is added, and the raw material powder is crushed while being flatly deformed to be flattened. The FeSiAl alloy was a soft magnetic alloy powder having a flatness of 20 or 40, and the FeSiCr alloy was a soft magnetic alloy powder having a flatness of 40.

The flattened soft magnetic alloy powder is dried by a heat treatment of holding it at a temperature of 810 to 830° C. for 3 hours. Further, only the soft magnetic alloy powder made of FeSiAl alloy is subjected to the phosphoric acid film treatment. The obtained soft magnetic alloy powder was measured by a laser diffraction/scattering type particle size distribution measuring device to obtain a particle size D50 with a volume distribution of 50%.

The soft magnetic alloy powder contains 38.28 parts by mass of urethane resin (polyester-based polyurethane, weight average molecular weight of 30,000) 22.97 parts by mass, phosphoric acid polyester-based dispersant 0.31 part by mass, and an organic solvent. A soft magnetic coating material was obtained by mixing 38.28 parts by mass of toluene and 0.15 parts by mass of a non-silicone defoaming agent as a defoaming agent using a disper. The soft magnetic paint was applied to one surface or both surfaces of the conductive net-like body at a pressure of 4.0 kg/cm ² using a spray gun having a gun diameter of 1.5 mm and dried. As the mesh body, a commercially available product having a thickness of 50 μm, an aperture ratio of 60% and an opening of 190 μm was used. The soft magnetic paint has a nonvolatile content of 45% and a viscosity of 5.0 dPa·s, and the solid content after drying is composed of 16 parts by mass of a binder made of urethane resin and 84 parts by mass of soft magnetic alloy powder. The electromagnetic field shield sheet was manufactured as described above.

Next, with respect to each of the obtained electromagnetic field shield sheets, in order to evaluate the electric field shield property and the magnetic field shield property, the attenuation factor of the electric field and the magnetic field for each frequency of the electromagnetic wave was measured using the KEC method. The measurement results are shown in FIGS. 6 and 7. In addition, in the measurement of the attenuation rate, as a comparative example, a noise suppression sheet (commercially available product) having a thickness of 100, 200, and 300 μm, which is a magnetic field shield sheet, and a net body used for manufacturing the electromagnetic field shield sheet are also combined. Used.

As shown in FIG. 5, with respect to the electric field shielding property, the attenuation rate is higher in the “conductive mesh sheet 50 μm only” which is a simple net body compared to the “noise suppressing sheet 300 μm thick”, and the electromagnetic field shielding sheet "A conductive mesh sheet 50 µm + soft magnetic paint 80 µm" and "A conductive mesh sheet + soft magnetic paint (double-sided coating 135 + 135 µm)" resulted in a higher attenuation rate.

As shown in FIG. 6, as for the magnetic field shielding property, the electromagnetic field shielding sheet (sheet body 10 or 11) has an equivalent or higher level in a wide frequency band as compared with “only the conductive mesh sheet 50 μm” which is a single mesh body. It had a decay rate. Compared to the “noise suppression sheet 300 μm thick”, the attenuation factor was higher in the electromagnetic field shield sheet (sheet body 10 or 11) in the high frequency region from around 10 MHz.

That is, the electromagnetic field shield sheet (sheet body 10 or 11) having a thickness of 130 μm or 270 μm exhibited high electric field shielding property and magnetic field shielding property in a wide frequency band.

Also, regarding the attenuation rate of the electromagnetic wave having a frequency of 10 MHz, a. Reticulate body (single body), b. A noise suppression sheet having a thickness of 300 μm, c. A laminate in which these are stacked, d. FIG. 7 shows the measurement results of the electric field shielding property and the magnetic field shielding property of each of the electromagnetic field shielding sheets (coated on both sides, thickness: 270 μm). Similarly, FIG. 8 shows the measurement result of the attenuation rate of 100 MHz electromagnetic wave. Note that the corresponding measurement results for “a”, “b”, and “d” are extracted from the measurement results in FIGS. 5 and 6 described above. The frequencies of electromagnetic waves, 10 MHz and 100 MHz, are typical numerical values evaluated for improving so-called electromagnetic compatibility.

As shown in FIG. 7 and FIG. 8, in each case, the electromagnetic field shield sheet (d) obtained an attenuation rate equal to or higher than that of the laminate (c) of the net-like body and the noise suppression sheet. That is, the thinner electromagnetic field shield sheet (d) having a thickness of 270 μm has the same or higher high electric field shielding property and magnetic field shielding property as compared with the laminated body (c) having a thickness of 350 μm. That is, the electromagnetic field shield (sheet body) in this embodiment has a high electromagnetic field shielding property even though it is thin.

In addition, FIG. 9 shows the noise suppressing sheet, the net-like body, and the laminate of both as Comparative Examples 1, 2 and 3, respectively, and the electric field shielding property and the magnetic field shielding property together with the electromagnetic field shielding sheets of Examples 1 to 10. The decay rate was measured for evaluation. In all of Examples 1 to 10, an attenuation rate equal to or higher than that of the comparative example was obtained.

Note that FIG. 10 shows a photograph of a cross section of the sheet body of Example 1 observed under a microscope. In particular, it is observed that the powder 3 is dispersed and arranged in the mesh of the left and right mesh bodies 1.

Although the representative embodiments of the present invention have been described above, the present invention is not necessarily limited to these, and a person skilled in the art can deviate from the gist of the present invention or the scope of the appended claims. , It will be possible to find various alternatives and modifications.

1 reticulated body 2 resin 3 powder (soft magnetic metal powder)
10 sheet body (electromagnetic field shield sheet)

Claims (6)

An electromagnetic field shielding sheet having both electric field shielding property and magnetic field shielding property,
A mesh made of a conductive material that imparts an electric field shielding property is embedded along the main surface of a flexible insulating resin sheet, and the opening ratio of the mesh is 60 to 85% . An electromagnetic field shield sheet, characterized in that a flat soft magnetic metal powder for imparting a magnetic field shield property is oriented and dispersed in the resin sheet body inside and outside the mesh so as to be substantially parallel to the main surface. The electromagnetic field shield sheet according to claim 1, wherein the resin sheet body contains 80 to 90 parts by mass of the soft magnetic metal powder in 100 parts by mass. The electromagnetic field shield sheet according to claim 2, wherein the resin sheet body is made of urethane resin. The soft magnetic metal powder has a flat shape with an average particle size D50 of 20 μm or more and 100 μm or less and a flatness of 20 or more, and the mesh of the mesh body is larger than the average particle size D50. The electromagnetic field shield sheet according to any one of claims 1 to 3. The electromagnetic field shield sheet according to claim 4, wherein the mesh has an opening of 0.05 mm or more and 1 mm or less. The soft magnetic metal powder is made of an Fe-Ni-based alloy, an Fe-Si-based alloy, an Fe-Si-Cr-based alloy, or an Fe-Si-Al-based alloy, according to any one of claims 1 to 5. The electromagnetic field shield sheet described in 1.