JP2011192714A - Electromagnetic wave shielding material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain superior electromagnetic wave shielding performance of an electromagnetic wave shielding material over a wide frequency range while minimizing a blending amount of conductive fibers which are expensive and cause friction against a member, a metal mold, etc., of a molding machine. <P>SOLUTION: An electromagnetic wave shielding material 10 has only conductive fibers 3 dispersed in synthetic resin 2, so conductive circuits are formed only by mutual contacting of the conductive fibers 3 and a sufficient number of conductive circuits are not formed. An electromagnetic shielding material 11 has conductive particles 4 dispersed in synthetic resin 2 together with conductive fibers 3 and conductive circuits are thereby easily formed, but the number thereof is insufficient. Alternatively, an electromagnetic shielding material 1 includes a certain volume of inexpensive non-conductive particles 5 in synthetic resin 2 as compared with conductive fibers 3 and conductive particles 4, so there is a great number of places where the conductive fibers 3 or conductive fibers 3 and conductive particles 4 come into contact with each other are obtained to form many conductive circuits, thereby sufficiently large electromagnetic wave shielding performance is obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electromagnetic wave shielding material mainly composed of a synthetic resin having high electromagnetic wave shielding characteristics while maintaining excellent moldability, lightness and low cost equivalent to those of a synthetic resin material. In the present specification and claims, the term “fiber” means a fiber in which single fibers are bundled except for the term “single fiber”.

  In recent years, with the development of IT (information technology), IT and OA devices such as personal computers (hereinafter referred to as “personal computers”) have rapidly spread, and even in normal home and work environments, The influence of electromagnetic waves radiated from IT equipment / OA equipment on the human body has become a problem. In particular, portable electronic devices represented by mobile phones, notebook computers, electronic notebooks, video cameras, etc. have been widely used, and the housings (housings) of these electronic devices are external to electromagnetic waves generated inside the electronic devices. In order to prevent leakage to the surface, conductivity (electromagnetic wave shielding property) is required.

Also, vehicles such as automobiles are equipped with a large number of electronic control units (ECU) such as engine control system, steering system, drive system, air conditioning system, various sensors, actuators, etc. Electromagnetic shielding properties are also required for the casings of these in-vehicle electronic devices.
Here, with respect to the casings of the above portable electronic devices and in-vehicle electronic devices, since there are demands such as downsizing, weight reduction, cost reduction and freedom of shape design, synthetic resin has been mainly used conventionally. The product is used.

For example, in Patent Document 1, for the purpose of application to an electromagnetic wave shielding cabinet or the like of the above electronic devices, a woven fabric composed of a composite elastic yarn in which metal fibers are spirally wound around an elastic fiber is thermoplastic. The present invention discloses a device for shielding an electromagnetic wave that is sandwiched between synthetic resin sheets.
However, in the technique described in Patent Document 1, a woven fabric configured using metal fibers is sandwiched between thermoplastic synthetic resin sheets, and the productivity is extremely poor, resulting in high costs. In addition, the degree of freedom in shape design is very limited, and the electromagnetic wave shielding performance is 57 dB at a frequency of 30 MHz and 42 dB at 1000 MHz (1 GHz), and a remarkably large value is not obtained.

Moreover, in patent document 2, for the purpose of application to various uses where electromagnetic wave shielding properties such as housings of electronic devices are required, 100 parts by mass of thermoplastic resin, 1 to 20 parts by mass of carbon fiber, and metal The invention discloses an invention of a conductive resin composition containing 1 to 20 parts by mass of fibers and having a volume resistivity of 10 ³ Ω · cm or less. This conductive resin composition can be subjected to extrusion molding and injection molding, and is superior to the technique described in Patent Document 1 in the productivity of the electromagnetic shielding material.

  However, even in the technique described in Patent Document 2, the electromagnetic wave shielding performance is 10 dB to 53 dB at a frequency of 10 MHz, and 8 dB to 40 dB at 1 GHz, as shown in Table 1 of the same document. Not obtained. The reason for this is that any of the techniques forms a conductive circuit (a conductive portion having a certain length or more effective for shielding electromagnetic waves, also referred to as a conductive path) inside the electromagnetic wave shielding material. This is probably because only the conductive fibers are in contact with each other, and the fibers are not sufficiently in contact with each other, so that a large number of conductive circuits cannot be formed inside the electromagnetic wave shielding material.

  On the other hand, Patent Document 3 discloses a resin composition in which a compounding material containing 3 to 10% by weight of stainless fiber and 15 to 40% by weight of talc is blended in a polypropylene resin at 18 to 50% by weight. The invention of an in-vehicle electromagnetic wave shielding case integrally formed with an elastically deformable locking portion is disclosed, and as a second invention, 10-30 wt% carbon black is blended with the above resin composition Is disclosed. As a result, an electromagnetic wave shielding case having a sufficient shielding effect for an electronic component mounted on a vehicle and having excellent moldability can be obtained.

No. 3-40595 JP 2006-045330 A Japanese Patent No. 3099146

  However, as shown in Table 1 of Patent Document 3, when the blending amount of the stainless fiber is 3% by weight as the lower limit, only a small value of 30 dB can be obtained as the initial shielding effect, whereas the stainless fiber When the blending amount is 10% by weight as the upper limit, a large initial shielding effect of 70 dB has been obtained, but when the blending amount of the stainless fiber is increased in this way, the stainless fiber is expensive, resulting in high cost. Furthermore, there has been a problem that the wear of screws, cylinders and molds of molding machines such as extrusion molding machines and injection molding machines becomes severe.

  Therefore, the present invention has been made to solve such a problem, and can meet the demands for freedom in downsizing, weight reduction, and shape design, and is expensive, such as a molding machine member or mold. An object of the present invention is to provide an electromagnetic shielding material capable of obtaining excellent electromagnetic shielding performance in a wide frequency range while minimizing the blending amount of conductive fibers such as stainless fibers that cause wear.

  The electromagnetic wave shielding material according to the invention of claim 1 contains a synthetic resin, a conductive material, and non-conductive particles or bubbles that increase contact between the conductive materials.

Here, as the “synthetic resin”, general-purpose resins such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, acrylic resin, polytetrafluoroethylene, polyamide-based resin, aramid resin, and ABS resin are used. Thermoplastic resins such as phenolic resins, epoxy resins, melamine resins, urea resins, unsaturated polyester resins, alkyd resins, polyurethanes, thermosetting polyimides, etc. Materials can be used.
“Conductive materials” include conductive fibers such as carbon fiber, copper fiber, iron fiber, aluminum fiber, stainless steel fiber, etc., copper powder, iron powder, aluminum powder, zinc powder, carbon black, graphite One or a combination of one or more conductive particles such as powder (graphite powder) can be used.

Furthermore, as the “non-conductive particles”, particles of inorganic compounds can be used. For example, silica particles, alumina particles, zircon particles, glass beads, ceramic crushed particles, zeolite crushed particles, talc, mica One or a combination of one or more such as (mica) can be used.
In addition, “bubbles” are generally “microscopic parts containing gas in a liquid or solid. (Shinmura, edited by “Kojien (4th edition)”, page 641, published by Iwanami Shoten Co., Ltd. on November 15, 1991). However, in the present specification and claims, it may or may not contain gas. Regardless, it shall be used to mean “a void in a liquid or solid”.
Further, as a method of incorporating bubbles in the synthetic resin, for example, a mechanism for retracting a part of the mold (core) is provided in an injection mold or press mold, and the core is retracted during molding. There is a so-called core back molding method in which a synthetic resin is foamed by rapidly expanding the size of the mold cavity, a method of generating gas by mixing a synthetic resin with a foaming agent, and heating, etc. One or a combination of one or more of diazoaminobenzene, sodium hydrogen carbonate, aluminum acetate, ammonium carbonate and the like can be used.

  The electromagnetic shielding material according to the invention of claim 2 is the structure of claim 1, wherein the volume ratio of the non-conductive particles or the bubbles to the electromagnetic shielding material is in the range of 10 vol% to 50 vol%, more preferably. It is within the range of 15 vol% to 42 vol%, more preferably within the range of 30 vol% to 40 vol%.

An electromagnetic wave shielding material according to a third aspect of the present invention is the electromagnetic shielding material according to the first or second aspect, wherein the average particle diameter measured by the Coulter principle of the non-conductive particles is in the range of 10 μm to 500 μm or the size of the bubbles. Is in the range of 10 μm to 500 μm, more preferably in the range of 50 μm to 100 μm.
Here, the “Coulter principle” is a particle measurement principle using electrical resistance invented by WHCoulter. As a particle size distribution measuring apparatus based on this principle, for example, Multisizer 3 (trade name) manufactured by Beckman Coulter, Inc. Multisizer 4 (trade name), Coulter counter model ZBI (trade name), and the like.

An electromagnetic wave shielding material according to a fourth aspect of the present invention is the electromagnetic wave shielding material according to any one of the first to third aspects, wherein the conductive material is at least a conductive fiber.
Here, as the “conductive fiber”, carbon fiber, metal fiber such as copper fiber, iron fiber, aluminum fiber, stainless steel fiber (especially stainless steel fiber is preferable), synthetic fiber is made of conductive material such as carbon or metal. One or a combination of one or more such as those coated with can be used.

An electromagnetic wave shielding material according to a fifth aspect of the present invention is the electromagnetic wave shielding material according to the fourth aspect, wherein the conductive material includes conductive fibers and conductive particles.
Here, as the “conductive particles”, one or one of metal powder such as copper powder, iron powder, aluminum powder and zinc powder, carbon powder such as carbon black and graphite powder (graphite powder), etc. Combinations of the above can be used.

  The electromagnetic wave shielding material according to the invention of claim 1 contains a synthetic resin, a conductive material, and non-conductive particles or bubbles that increase the contact between the conductive materials. As a result, non-conductive particles or bubbles that are less expensive than the conductive material occupy a certain volume in the synthetic resin, so the volume occupied by the conductive material in the synthetic resin is limited, and the presence of the conductive material As the density of the parts to be increased increases, the number of places where the conductive materials come into contact with each other increases so that a large number of conductive circuits within the electromagnetic wave shielding material (a certain length that is effective for shielding electromagnetic waves) A portion having electrical conductivity).

  Therefore, it becomes possible to form a large number of conductive circuits in a synthetic resin without using a large amount of expensive conductive material, and short conductive fibers or granular conductive particles as a conductive material, Since long conductive circuits in continuous contact can coexist in the synthetic resin, it is possible to effectively shield electromagnetic waves having a short frequency to electromagnetic waves having a long frequency. And since there is little content of an electroconductive material, also when shape | molding as an electromagnetic wave shielding material, abrasion of the member of a molding machine, a metal mold | die, etc. can be suppressed to the minimum.

  In this way, it is possible to meet the demands for freedom in miniaturization, weight reduction, and shape design, and the amount of conductive materials such as stainless steel fibers that cause wear on molding machine parts and molds is minimized. An electromagnetic shielding material capable of obtaining excellent electromagnetic shielding performance in a wide frequency range while suppressing to the limit.

In the electromagnetic shielding material which concerns on invention of Claim 2, the ratio of the volume which occupies for the electromagnetic shielding material of a nonelectroconductive particle or a bubble exists in the range of 10 vol%-50 vol%.
The inventor has conducted extensive experimental research on the ratio of the volume of non-conductive particles or bubbles to the electromagnetic wave shielding material optimal for improving the shielding performance of the electromagnetic shielding material. The inventors have found that the shielding performance is further improved when the volume ratio in the electromagnetic shielding material is in the range of 10 vol% to 50 vol%, and have completed the present invention based on this finding.

That is, if the volume ratio of the non-conductive particles or bubbles to the electromagnetic shielding material is less than 10 vol%, the density of the portion where the conductive material exists becomes low, and the number of places where the conductive materials are in contact with each other is reduced. As a result, the effect of forming a large number of conductive circuits inside the electromagnetic wave shielding material is reduced, and sufficient shielding performance cannot be obtained. On the other hand, when the proportion of the volume of the non-conductive particles or bubbles in the electromagnetic shielding material exceeds 50 vol%, the proportion of the synthetic resin volume decreases, the moldability deteriorates, and the electromagnetic shielding material can be produced with a high yield. It becomes difficult, or the strength of the electromagnetic wave shielding material is reduced, or the ratio of the conductive material is reduced, and sufficient shielding performance cannot be obtained.
Therefore, the volume ratio of the non-conductive particles or bubbles to the electromagnetic wave shielding material is preferably in the range of 10 vol% to 50 vol%.

  In addition, it is more preferable that the proportion of the volume of the non-conductive particles or bubbles in the electromagnetic shielding material is in the range of 15 vol% to 42 vol%, because more excellent electromagnetic shielding performance can be obtained more surely, and 30 vol% to 40 vol%. It is more preferable that it is within the range because a better electromagnetic shielding performance can be obtained.

  The electromagnetic shielding material according to the invention of claim 3 has an average particle diameter measured by the Coulter principle of non-conductive particles within a range of 10 μm to 500 μm or a bubble size within a range of 10 μm to 500 μm.

  As a result of earnest experiment research on the appropriate size of non-conductive particles and bubbles in the electromagnetic wave shielding material, the present inventor has obtained an average particle diameter measured by the Coulter principle, that is, a particle measuring device based on electric resistance (Coulter counter). In addition to the effect of the invention according to claim 1 or claim 2, when the average particle diameter measured by the method is within the range of 10 μm to 500 μm and when the size of the bubbles is within the range of 10 μm to 500 μm, The present inventors have found that an excellent electromagnetic shielding effect can be obtained more reliably, and have completed the present invention based on this finding.

That is, if the average particle diameter or bubble size of the non-conductive particles measured by a particle measuring instrument based on electric resistance is less than 10 μm, the non-conductive particles or bubbles are too fine, and a certain volume in the synthetic resin is obtained. Since the effect of facilitating the formation of a conductive circuit is reduced by occupying it, it becomes difficult to obtain excellent electromagnetic shielding performance. On the other hand, the average particle diameter or bubbles of non-conductive particles measured by a particle measuring instrument based on electric resistance If the size exceeds 500 μm, the non-conductive particles or bubbles are too large and the moldability is deteriorated or the strength is lowered, and it is difficult to enter between the conductive materials, so that it is easy to form a conductive circuit. It will decline.
Therefore, the size of the non-conductive particles or bubbles is preferably such that the average particle diameter of the non-conductive particles or the size of the bubbles measured by a particle measuring instrument based on electric resistance is in the range of 10 μm to 500 μm.

  In the case of non-conductive particles, when the size of the non-conductive particles or bubbles is within the range of 50 μm to 100 μm, the average particle diameter or bubble size measured by a particle measuring instrument based on electrical resistance. Is more preferable because it is easier to disperse uniformly in the synthetic resin, and in the case of bubbles, it is easier to form, so that better electromagnetic shielding performance can be obtained more easily.

  In the electromagnetic wave shielding material according to the invention of claim 4, since the conductive material is at least a conductive fiber, in addition to the effects of the invention according to claims 1 to 3, the contact between the conductive fibers. Thus, a long conductive circuit is formed, and an electromagnetic wave shielding material having excellent electromagnetic wave shielding performance even in a low frequency region is obtained.

  In the electromagnetic wave shielding material according to the invention of claim 5, since the conductive material contains conductive fibers and conductive particles, in addition to the effect of the invention of claim 4, the conductive particles 4 Enters between the conductive fibers 3, so that a conductive circuit is easily formed, and a better electromagnetic shielding performance can be obtained.

  In addition, when the non-conductive particles are hollow particles having a space inside, the hollow particles have a smaller mass than the solid particles even with the same outer diameter, so the electromagnetic wave shielding performance of the electromagnetic wave shielding material is maintained. However, the electromagnetic shielding material can be further reduced in weight.

  In addition, as a result of earnest experiment research on the appropriate content ratio of the synthetic resin, conductive fiber, and conductive particles in the electromagnetic wave shielding material, the present inventor has obtained a synthetic resin content of 25 wt% to 70 wt%. When the content is within the range, the conductive fiber content is within the range of 3% by weight to 9% by weight, and the conductive particle content is within the range of 9% by weight to 40% by weight, it is more reliably superior. It has been found that the effect of electromagnetic wave shielding can be obtained.

That is, when the content of the synthetic resin is less than 25% by weight, the amount of the synthetic resin is too small, the moldability is deteriorated, and it is difficult to produce an electromagnetic shielding material with a high yield. If it exceeds 70% by weight, the content of conductive fibers and conductive particles decreases, making it difficult to obtain excellent electromagnetic shielding performance.
Further, when the content of the conductive fiber is less than 3% by weight, it is difficult to obtain excellent electromagnetic shielding performance because the conductive fiber is too small, while the content of the conductive fiber exceeds 9% by weight. Then, when the electromagnetic wave shielding material is molded, wear of a molding machine member or a mold is likely to occur.

Furthermore, when the content of the conductive particles is less than 9% by weight, it is difficult to obtain excellent electromagnetic wave shielding performance due to too few conductive particles, while the content of the conductive particles exceeds 40% by weight. Then, the synthetic resin is reduced, the moldability is deteriorated, and the cost of the electromagnetic shielding material is increased.
Therefore, the content of the synthetic resin is in the range of 25 wt% to 70 wt%, the content of the conductive fiber is in the range of 3 wt% to 9 wt%, and the content of the conductive particles is 9 wt% to It is preferable to be within the range of 40% by weight.

  The content of the synthetic resin is in the range of 30% to 50% by weight, the content of the conductive fiber is in the range of 4% to 7% by weight, and the content of the conductive particles is 15% to When it is within the range of 30% by weight, it is more preferable because a further excellent electromagnetic shielding performance can be obtained.

  Further, as a result of earnest experimental research on the appropriate fiber diameter and fiber length of the conductive fiber in the electromagnetic wave shielding material, the present inventor has made the fiber diameter within the range of 1 μm to 20 μm and the fiber length of 1 mm to It has been found that when it is within the range of 10 mm, an excellent electromagnetic shielding effect can be obtained more reliably.

That is, when the fiber diameter of the conductive fiber is less than 1 μm, the conductive fiber is too thin and becomes easy to cut at the time of molding, and it becomes difficult to obtain excellent electromagnetic shielding performance. When the diameter exceeds 20 μm, the conductive fibers are too thick and the moldability is deteriorated, and at the same time, the members of the molding machine and the mold are easily worn.
Moreover, if the fiber length of the conductive fiber is less than 1 mm, it is difficult to obtain excellent electromagnetic wave shielding performance because the conductive fiber is too short, while the fiber length of the conductive fiber exceeds 10 mm, Although the electromagnetic shielding performance is improved, the variation of the content ratio in the electromagnetic shielding material is increased, and when the electromagnetic shielding material is molded, wear of a molding machine member or a mold is likely to occur.
Therefore, it is preferable that the fiber diameter of the conductive fiber is in the range of 1 μm to 20 μm and the fiber length is in the range of 1 mm to 10 mm.

  In addition, when the fiber diameter of the conductive fiber is in the range of 5 μm to 15 μm and the fiber length is in the range of 3 mm to 6 mm, more excellent electromagnetic wave shielding performance can be obtained, which is more preferable.

  In addition, as a result of earnest experiment research on the appropriate size of the conductive particles in the electromagnetic wave shielding material, the present inventor found that the average particle diameter measured by the laser diffraction / scattering method was in the range of 10 μm to 100 μm or sieved. It has been found that when the particle size distribution measured by the test method is such that particles of 45 μm or less are 70% by weight or more, an excellent electromagnetic shielding effect can be obtained more reliably.

That is, when the average particle diameter measured by the laser diffraction / scattering method is less than 10 μm, the conductive particles are too fine to form a conductive circuit, making it difficult to obtain excellent electromagnetic shielding performance. When the average particle diameter measured by the laser diffraction / scattering method exceeds 100 μm and the particle size distribution measured by the sieve test method is less than 70% by weight, the conductive particles are too large and the moldability is high. And the wear of molding machine members and molds is likely to occur during molding.
Therefore, the size of the conductive particles is such that the average particle diameter measured by the laser diffraction / scattering method is within the range of 10 μm to 100 μm, or the particle size distribution measured by the sieving test method is such that particles of 45 μm or less are 70% by weight or more. It is preferable.

  The size of the conductive particles is such that the average particle diameter measured by the laser diffraction / scattering method is in the range of 20 μm to 50 μm, or the particle size distribution measured by the sieve test method is 45% or less of particles of 90% by weight or more. In this case, more excellent electromagnetic wave shielding performance can be obtained, which is more preferable.

  Moreover, as a manufacturing method of an electromagnetic wave shielding material, a thermosetting resin or a two-part epoxy resin is used as a synthetic resin, and a synthetic resin, conductive fibers, conductive particles, and non-conductive particles are mixed and mixed liquid and A mixing step, a pouring step of pouring the mixed liquid into a lower die of a press die having an upper die and a lower die, and a pressing step of fitting the upper die to the lower die of the press die and pressing at a predetermined pressure And a curing method for curing a thermosetting resin or a two-part epoxy resin.

  As a result, a thermosetting resin or two-part epoxy resin that has fluidity at room temperature is used as the synthetic resin, so the synthetic resin, conductive fibers, conductive particles, and non-conductive particles are uniformly distributed in the mixing process. Can be mixed into the press mold while maintaining uniformity in the casting process, and the dispersion state of the conductive fibers, conductive particles and non-conductive particles in the electromagnetic wave shielding material to be manufactured is ensured. Can be made uniform.

In addition, since the molding process is performed by a pressing process, almost no shearing force is applied at the time of molding, so that the conductive fiber is not cut short by the shearing force and maintains high electromagnetic shielding performance generated from the long conductive fiber. be able to. Therefore, excellent electromagnetic shielding performance can be obtained by using a minimum amount of conductive fibers.
Furthermore, due to the presence of the conductive particles, a large electromagnetic shielding performance can be obtained even in a high frequency region.

  In addition, as another method for producing an electromagnetic shielding material, there are a mixing step of mixing synthetic resin, conductive fibers, conductive particles and non-conductive particles to form a mixed material, and injection of the mixed material with a low shear screw. Some have an injection molding process of injection molding using a molding machine or a pre-plunger type injection molding machine.

  Here, the “low shear screw” is a general in-line injection molding machine that measures, plasticizes, and extrudes (injects) a synthetic resin (injection molding material) with a single screw. It is a special screw designed not to apply a shearing force to the synthetic resin as much as possible. Specifically, for example, there are special screws for long fiber reinforced resin manufactured by Mitsubishi Heavy Industries Plastic Technology Co., Ltd., F screws for high viscosity resin, conical twin screws and parallel twin screws manufactured by Guangzhou Impulse Electric Technology Co., Ltd. .

  The “pre-plunger type injection molding machine” is an injection molding machine in which a plasticizing screw and an injection cylinder are separately provided, unlike the above-described general inline type injection molding machine. This is an injection molding machine in which the synthetic resin (injection molding material) is plasticized, moved to the injection cylinder, and injected from the injection cylinder with a plunger, so that no shear force is applied to the synthetic resin.

  As a result, the mixed material uniformly mixed by stirring and kneading in the mixing process is formed into the electromagnetic shielding material by the injection molding method in the injection molding process, so that the electromagnetic shielding material having a more complicated shape than the press molding method. Can be mass-produced, can meet the demand for the degree of freedom in shape design, and can further reduce the cost.

In the injection molding process, injection molding is performed using an injection molding machine equipped with a low shear screw or a pre-plunger type injection molding machine, so that a large shearing force as in a conventional inline type injection molding machine is applied to the mixed material. It does not hang and the conductive fiber is not cut short by shearing force, and high electromagnetic shielding performance generated from the long conductive fiber can be maintained. Therefore, excellent electromagnetic shielding performance can be obtained by using a minimum amount of conductive fibers.
Furthermore, due to the presence of the conductive particles, a large electromagnetic shielding performance can be obtained even in a high frequency region.

1A is a schematic diagram showing the internal structure of the electromagnetic shielding material of Comparative Example 2, FIG. 1B is a schematic diagram showing the internal structure of the electromagnetic shielding material of Comparative Example 1, and FIG. It is a schematic diagram which shows the internal structure of the electromagnetic wave shielding material which concerns on the form 1. FIG. 2 is a flowchart showing a method of manufacturing the electromagnetic shielding material according to Embodiment 1 of the present invention. FIG. 3 is a characteristic diagram showing the electromagnetic wave shielding effect of the electromagnetic wave shielding material according to Example 1 to Example 3 of Embodiment 1 of the present invention in comparison with the electromagnetic wave shielding effect of the electromagnetic wave shielding material of Comparative Example 1. FIG. 4 is a characteristic diagram showing a comparison of the electromagnetic wave shielding effects of the electromagnetic wave shielding materials according to Examples 4 to 7 of Embodiment 1 of the present invention. FIG. 5 is a characteristic diagram comparing the electromagnetic wave shielding effects of the electromagnetic wave shielding materials according to Example 8 and Example 9 of Embodiment 1 of the present invention. 6 compares the electromagnetic wave shielding effect of the electromagnetic wave shielding material according to Example 8, Example 10, Example 11 and Example 12 of Embodiment 1 of the present invention with the electromagnetic wave shielding effect of the electromagnetic wave shielding material of Comparative Example 2. FIG. FIG. 7 is a flowchart showing a method of manufacturing the electromagnetic shielding material according to Embodiment 2 of the present invention.

In order to implement the electromagnetic wave shielding material according to the present invention, a synthetic resin, a conductive material, a non-conductive particle, or a method of introducing bubbles is required.
Here, as the synthetic resin, thermoplastic resins such as general-purpose resins, engineering plastics (hereinafter also referred to as “engineer plastics”), super engineering plastics, and thermosetting resins can be used. Those having as high a fluidity as possible are preferred. This is because when the fluidity is higher, conductive fibers, conductive particles, non-conductive particles, or bubbles can be more uniformly dispersed in the synthetic resin.

  As a synthetic resin having high fluidity in the molding stage of the electromagnetic shielding material, specifically, a polyalkylene resin (polyethylene, polypropylene, etc.) for a thermoplastic resin, an acrylic resin, a phenol resin, an epoxy resin or a two-component for a thermosetting resin An epoxy resin is preferable. In particular, a phenol resin, an epoxy resin, and a two-component epoxy resin are more preferable because they have fluidity close to a liquid state even at room temperature, unlike thermoplastic resins.

In addition, as the conductive material, conductive fibers, conductive particles, and the like can be used. As the conductive fibers, carbon fibers, metal fibers such as copper fibers, iron fibers, aluminum fibers, stainless fibers, and synthetic fibers are used. Can be used, such as carbon or metal coated with a conductive material, but iron fibers and stainless steel fibers are preferable in that they are ferromagnetic and have excellent electromagnetic shielding performance.
Furthermore, as the length of the conductive fiber, the longer the electromagnetic shielding performance is improved, the longer the length of the conductive fiber, the greater the variation in the content in the synthetic resin. In order to easily cause wear of a mold or the like, it is preferably within a range of 1 mm to 10 mm, and more preferably within a range of 3 mm to 6 mm.

In addition, as the conductive particles, metal powder such as copper powder, iron powder, aluminum powder and zinc powder, carbon powder such as carbon black, graphite powder (graphite powder), etc. can be used. Copper powder and graphite powder are preferable in terms of enhancing the hardness.
Further, as the size of the conductive particles, if the conductive particles are too fine, it is difficult to form a conductive circuit, and if the conductive particles are too large, the moldability is deteriorated and the molding machine member, mold, etc. For metal powder such as copper powder, it is preferable that the average particle diameter measured by the laser diffraction / scattering method is in the range of 10 μm to 100 μm, and for carbon powder such as graphite powder, It is preferable that particles having a diameter of about 45 μm or less are 70% by weight or more in the particle size distribution measured by a sieve test method.

Non-conductive particles include inorganic compound particles such as silica particles, alumina particles, zircon particles, glass beads, ceramic pulverized particles, zeolite pulverized particles, talc, mica (mica), etc. Alternatively, one or more combinations can be used, but silica particles, glass beads, and talc are preferable because they are inexpensive and easily available.
Furthermore, in the present invention, since the electromagnetic shielding material is mainly composed of a synthetic resin for the purpose of reducing the weight, one of the foamed inorganic compound particles, hollow silica particles, glass balloons and the like which are hollow particles is used. Alternatively, it is preferable to use one or more combinations because they can contribute to weight reduction.

  In addition, as the size of the non-conductive particles, if the non-conductive particles are too fine, the effect of occupying a certain volume in the synthetic resin and facilitating the formation of a conductive circuit is reduced, and if the non-conductive particles are too large The average particle diameter measured by the laser diffraction / scattering method is in the range of 10 μm to 500 μm because the effect of facilitating the formation of the conductive circuit is reduced because the moldability is deteriorated and it is difficult to enter between the conductive fibers. It is preferable that it is in the range of 50 μm to 100 μm.

  In addition, as a method of introducing bubbles into the synthetic resin, a core back molding method in which a mechanism for retreating the core of the mold is provided, a method of generating a gas by mixing a synthetic resin with a foaming agent, and heating, etc. However, in terms of cost reduction of the mold, a method using a foaming agent is preferable. As the foaming agent, diazoaminobenzene, sodium hydrogen carbonate, aluminum acetate, ammonium carbonate, or the like can be used.

  Hereinafter, embodiments of an electromagnetic wave shielding material according to the present invention will be described with reference to the drawings.

[Embodiment 1]
First, Embodiment 1 of the electromagnetic wave shielding material according to the present invention will be described with reference to FIGS.

First, the reason why the electromagnetic shielding material according to Embodiment 1 of the present invention has excellent electromagnetic shielding performance is compared with the electromagnetic shielding materials of Comparative Example 1 and Comparative Example 2, and referring to the schematic diagram of FIG. I will explain.
As shown in FIG. 1A, the electromagnetic shielding material 10 of Comparative Example 2 is obtained by dispersing only conductive fibers 3 in a synthetic resin 2. In such a configuration, a conductive circuit (a conductive portion having a certain length or more effective for shielding electromagnetic waves) is formed only from contact between the conductive fibers 3, so that FIG. As shown, a sufficient number of conductive circuits are not formed.

In order to form a sufficient number of conductive circuits with such a configuration, the content of the conductive fiber 3 must be extremely increased, the content of the synthetic resin 2 is decreased, and the moldability is inferior. Costs are increased, and further, there is a drawback that wear of screws, cylinders, molds and the like of molding machines such as extrusion molding machines and injection molding machines becomes severe.
Such an electromagnetic wave shielding material 10 of Comparative Example 2 shown in FIG. 1A corresponds to the technique described in Patent Document 2 described in the above section [Background Art].

As shown in FIG. 1B, the electromagnetic wave shielding material 11 of Comparative Example 1 is obtained by dispersing conductive particles 4 together with conductive fibers 3 in a synthetic resin 2. In such a configuration, since the conductive particles 4 enter between the conductive fibers 3, a conductive circuit is easily formed. As shown in FIG. 1B, the conductive particles 4 are more than the electromagnetic wave shielding material 10 of the comparative example 2. A conductive circuit is formed.
However, even in the configuration of Comparative Example 1, the number of conductive circuits is still insufficient, and a sufficiently large electromagnetic shielding performance cannot be obtained.

On the other hand, as shown in FIG. 1C, the electromagnetic wave shielding material 1 according to the first embodiment includes a non-conductive particle 5 in a synthetic resin 2 and a conductive fiber 3 as a conductive material. The conductive particles 4 are dispersed together with the conductive fibers 3 as necessary, or the conductive fibers 4 as the conductive material in the synthetic resin 2 and the conductive particles 4 together with the conductive fibers 3 as necessary. Are dispersed and bubbles 5 are formed in the synthetic resin 2.
As a result, the non-conductive particles 5 and the bubbles 5 which are cheaper than the conductive fibers 3 and the conductive particles 4 occupy a certain volume in the synthetic resin 2, and as shown in FIG. The volume occupied by the conductive fibers 3 and the conductive particles 4 in the synthetic resin 2 is limited, and the density of the portions where the conductive fibers 3 and the conductive particles 4 are present increases, so that the conductive fibers 3 or the conductive fibers 3 are electrically connected. Since the number of places where the conductive fibers 3 and the conductive particles 4 come into contact with each other is extremely large, a large number of conductive circuits are formed inside the electromagnetic wave shielding material 1. Therefore, a sufficiently large electromagnetic shielding performance can be obtained.

  Next, the manufacturing method of the electromagnetic wave shielding material 1 according to the first embodiment will be described with reference to the flowchart of FIG. In the manufacturing method of the electromagnetic wave shielding material 1 according to the first embodiment, a two-component epoxy resin is used as the synthetic resin.

  As shown in FIG. 2, first, the curing agent 2Ab is added to the base 2Aa of the two-component epoxy resin 2A, and the conductive fibers 3, the conductive particles 4, and the non-conductive material are added to the two-component epoxy resin 2A. A mixing step in which the particles 5 are mixed is performed (step S10). In addition, the mixing procedure in the mixing step is not limited to this, and after mixing the conductive fibers 3, the conductive particles 4, and the non-conductive particles 5 with the base 2Aa of the two-component epoxy resin 2A, the curing agent 2Ab May be added. As a result, a mixed solution 6 is obtained, and a pouring process is performed in which the mixed solution 6 is poured into the lower mold of the press mold (step S11).

  When the pouring process is completed, a pressing process is performed in which the upper mold of the press mold is fitted to the lower mold of the press mold into which the mixed liquid 6 has been poured and pressed at a predetermined pressure (step S12). ). In Embodiment 1, using a press die having a flat plate-shaped cavity for producing a specimen, the mixed liquid 6 in the cavity was compressed by hand until the predetermined thickness (3 mm) was reached. Therefore, the “predetermined pressure” in the method for manufacturing the electromagnetic wave shielding material 1 according to the first embodiment is a pressure necessary for setting the thickness of the cavity of the press mold into which the mixed liquid 6 is poured to 3 mm. is there.

After that, a curing process for curing the mixed liquid 6 in the press mold is performed (step S13). In Embodiment 1, since a two-component epoxy resin is used as the synthetic resin, it is left to cure at room temperature for about 8 hours. As a result, the electromagnetic shielding material 1 according to the first embodiment was obtained.
In Embodiment 1, the non-conductive particles 5 are arranged on the electromagnetic wave shielding material 1 using a two-component epoxy resin that is cured at room temperature. However, thermosetting properties such as heat-cured epoxy resin as a synthetic resin are used. By using the resin, it is possible to produce the electromagnetic shielding material 1 in which bubbles are formed by adding a foaming agent in advance and foaming the foaming agent by heating at the time of curing.

According to the above steps, the characteristics / blending amounts of the blending components are changed to produce the electromagnetic shielding material 1 according to Examples 1 to 12 of the first embodiment, and the electromagnetic shielding performance is evaluated. It was. For comparison, the electromagnetic shielding materials of Comparative Example 1 and Comparative Example 2 were also manufactured, their electromagnetic shielding performance was evaluated, and the electromagnetic shielding materials 1 according to Examples 1 to 12 were compared and evaluated. .
The composition of the electromagnetic shielding material according to Examples 1 to 12 and the electromagnetic shielding material of Comparative Examples 1 and 2 is shown in the upper part of Table 1.

As shown in Table 1 and as described above, the two-component epoxy resin is used as the synthetic resin 2. Specifically, a two-part epoxy resin Epofix (trade name) manufactured by Marumoto Struers Co., Ltd. was used as the two-part epoxy resin.
In addition, as the conductive fiber 3, three types having different fiber lengths using stainless steel fibers (hereinafter also referred to as “SUS fibers”) were used. Specifically, as a SUS short fiber having a fiber length of 0.3 mm, an SMF grade (fiber length: 300 μm, fiber diameter: φ10 μm) manufactured by JFE Steel Corporation is used, and the fiber length is 1 mm and As a 3 mm SUS long fiber, a product of Nippon Seisen Co., Ltd. was used.

Further, as shown in Table 1, as the conductive particles 4, two types of copper powder as metal particles and graphite powder as carbon particles were used. Specifically, FCC-115 (product number) manufactured by Fukuda Metal Foil Powder Industry Co., Ltd. is used as the copper powder, and CGC-50 of the spheroidized graphite powder series manufactured by Nippon Graphite Industry Co., Ltd. is used as the graphite powder. (Product name) was used.
And when copper powder FCC-115 was measured by MPIF (Metal Powder Industries Federation) standard 05 which is a sieve test method, particles of 45 μm or less are 90% by weight or more, and particles of 45 μm to 63 μm are less than 10% by weight, The particle size distribution was such that particles of 63 μm to 75 μm were less than 2% by weight, and particles of 75 μm or more were 0% by weight.

  Further, the graphite powder CGC-50 had an average particle diameter of 50 μm as measured by a laser diffraction / scattering method using a laser diffraction particle size distribution analyzer.

  Further, as the non-conductive particles 5, as shown in Table 1, four types of glass beads having different particle diameters were used. As glass beads, M-4-20PN (average particle size: 0.5 mm), M-7-20PN (average particle size: 0.3 mm), M-11-20PN (average particle size) manufactured by Potters Ballotini Co., Ltd. Diameter 0.1 mm) and GB301S (average particle diameter 0.05 mm) were used. In addition, the value of an average particle diameter is measured with the particle | grain measuring device by an electrical resistance, ie, a Coulter counter.

  Using each formulation of Example 1 to Example 12 and Comparative Example 1 and Comparative Example 2 shown in Table 1, based on the manufacturing process shown in the flowchart of FIG. Each was manufactured. The size of the specimen was 110 mm × 110 mm × 3 mm (thickness). The near-field electromagnetic wave shielding performance was measured for five frequencies of 10 MHz, 100 MHZ, 300 MHz, 500 MHz, and 1000 MHz (1 GHz) by the KEC method.

The “KEC method” is a measurement method using an electromagnetic shielding effect measuring device developed by the Kansai Electronics Industry Promotion Center (KEC). The effect is measured and evaluated. Briefly, the shielding effect at a place where an electromagnetic wave is generated is evaluated by dividing it into an electric field and a magnetic field. That is, the KEC method is divided into a transmitting jig and a receiving jig, and a shielding material is inserted between them to evaluate how much the signal is attenuated on the receiving side. The signal output from the signal generator is input to the transmission side jig through the attenuator. On the receiving side, the signal reaching the jig is amplified by a preamplifier, and then the signal level is measured by a spectrum analyzer. At this time, the amount of attenuation when the measurement sample is inserted is evaluated in decibels with reference to the state where there is no sample.
The measurement results by the KEC method are shown in the lower part of Table 1 and in FIGS.

The characteristic diagram of FIG. 3 clarifies the relationship between the amount of glass beads added as the non-conductive particles 5 and the electromagnetic shielding performance.
As shown in the upper part of Table 1, in the formulation of Example 1, the addition amount of glass beads was 13.0% by weight (15.3 vol% in volume%), and in the formulation of Example 2, the addition amount of glass beads was 25. 0.0% by weight (30.0 vol%), and in the formulation of Example 3, the amount of glass beads added was gradually increased to 34.4% by weight (41.8 vol%). In contrast, as shown in the upper part of Table 1, the glass beads were not added to the formulation of Comparative Example 1.

As a result, as shown in the lower part of FIG. 3 and Table 1, it can be seen that the electromagnetic shielding effect increases as the amount of glass beads added increases. This is because the volume (vol%) of glass beads occupying in the electromagnetic wave shielding material 1 of glass beads increases as the amount of glass beads added increases, so that the conductive material relatively occupied in the electromagnetic wave shielding material 1. The volume of (SUS fiber and copper powder) decreases, and the electromagnetic wave shielding effect increases as the decrease in volume increases. Therefore, as described above, when the volume of the conductive material in the electromagnetic shielding material 1 is limited, the density of the conductive material in the occupied volume increases and the number of contact points between the conductive materials increases. It was proved that the shielding effect was improved.
The difference in electromagnetic wave shielding performance between Example 1 to Example 3 and Comparative Example 1 is small at high frequencies and the overall electromagnetic wave shielding performance is as small as less than 20 dB. This is because a fiber having a fiber length of 0.3 mm which is too short is used.

The characteristic diagram of FIG. 4 clarifies the relationship between the size (average particle diameter) of the glass beads as the nonconductive particles 5 and the electromagnetic wave shielding performance.
As shown in the upper part of Table 1, the composition of Example 4 has a glass bead size of 0.5 mm, the composition of Example 5 has a glass bead size of 0.3 mm, and the composition of Example 6 has a glass bead. The size of the glass beads was gradually reduced to φ0.05 mm. In addition, the addition amount of a glass bead is unified with 37.0 weight% (39.5 vol%).

  As a result, as shown in FIG. 4 and the lower part of Table 1, it can be seen that the electromagnetic shielding effect increases as the size of the glass beads decreases. Here, in the first embodiment, glass beads with an average particle diameter of φ0.5 mm or less are used, and as can be seen from the results of Example 4, the largest glass beads with φ0.5 mm are used. The shielding effect of 20 dB or more is exhibited in the frequency range of 10 MHz to 1000 MHz. Therefore, the size of the glass beads as the non-conductive particles 5 is such that the average particle diameter is φ0.5 mm or less, more preferably the average particle diameter is φ0.1 mm or less.

The characteristic diagram of FIG. 5 clarifies the relationship between the fiber length of the SUS fiber as the conductive fiber 3 and the electromagnetic shielding performance. As shown in the upper part of Table 1, the formulation of Example 8 has a fiber length of SUS fiber of 3 mm, and the formulation of Example 9 has a fiber length of SUS fiber of 1 mm.
As a result of comparison between the two, as shown in the lower part of FIG. 5 and Table 1, it can be seen that the electromagnetic shielding effect is increased when the fiber length of the SUS fiber is longer. Moreover, from the results of Table 1, Examples 1 to 3 in which the fiber length of the SUS fiber is 0.3 mm are compared with Examples 4, 8 and 9 in which the fiber length of the SUS fiber is 1 mm or more. And the shield effect of Example 4, Example 8, and Example 9 is more excellent. Therefore, the fiber length of the SUS fiber as the conductive fiber 3 is preferably 1 mm or more, and more preferably 3 mm or more.

In particular, as shown in the lower part of Table 1, the electromagnetic shielding material 1 according to the formulation of Example 8 is 82.08 dB at 10 MHz, and the electromagnetic shielding material mainly composed of synthetic resin is more electromagnetic than ever. The shielding performance is remarkably large, and even at 1000 MHz (1 GHz), the remarkably large value is 71.2 dB.
That is, it can be said that the electromagnetic wave shielding material 1 according to Example 8 of the first embodiment is a particularly excellent electromagnetic wave shielding material.

The characteristic diagram of FIG. 6 shows the electromagnetic wave shielding material 1 according to the formulation of Example 8, the electromagnetic shielding material of the case of changing the kind of the conductive particles 4, the case of the Example 12 and the formulation of Comparative Example 2. Are compared in electromagnetic wave shielding performance.
As shown in the upper part of Table 1, the formulation of Example 10 is obtained by adding 9.7% by weight of graphite powder instead of copper powder as the conductive particles 4, and the formulation of Example 11 is 27% of graphite powder. .7% added. Further, in the formulation of Example 12, glass beads were added in a relatively large amount of 46.2% by weight (42.0 vol%), but the conductive particles 4 were not added at all.

  On the other hand, the composition of Comparative Example 2 does not add any glass beads as the conductive particles 4 and the non-conductive particles 5, and is 85.0% by weight of the two-component epoxy resin as the synthetic resin 2. It is manufactured only from 15.0% by weight of SUS fiber as the conductive fiber 3.

  As a result, as shown in the lower part of FIG. 6 and Table 1, in the formulation according to Example 10 in which the amount of graphite powder added as the conductive particles 4 is as small as 9.7% by weight, it is 60.6 dB at a frequency of 100 MHz. Although the electromagnetic shielding performance is relatively large, the electromagnetic shielding performance is 46.84 dB at a frequency of 1000 MHz (1 GHz), which is considerably smaller than the formulation according to Example 8.

On the other hand, in the formulation according to Example 11 where the amount of graphite powder added as the conductive particles 4 is as high as 27.7% by weight, 70.6 dB at a frequency of 100 MHz and 67.24 dB at a frequency of 1000 MHz (1 GHz). 8 shows excellent electromagnetic shielding performance equivalent to the formulation according to No. 8.
Therefore, it has been clarified that even when carbon particles such as graphite powder are used as the conductive particles 4, electromagnetic wave shielding performance equivalent to that obtained when metal particles such as copper powder is used can be obtained.

  Moreover, as shown in the lower part of FIG. 6 and Table 1, Example 12 shows a shielding effect substantially equivalent to that of Comparative Example 2, and the addition amount of expensive SUS fiber is reduced by adding inexpensive glass beads. It can be reduced. Furthermore, from the results of Example 8, Example 10, Example 11 in which conductive particles 4 were added and Example 12 in which conductive particles 4 were not added, in addition to SUS fibers as conductive fibers, conductive particles 4 ( It can be seen that the shielding effect is improved by arranging copper powder or graphite powder.

  From the above examination results, in order to obtain excellent electromagnetic shielding performance in the electromagnetic shielding material mainly composed of the synthetic resin 2, the conductive fibers 3 and the nonconductive particles 5 are essential components, and the fibers of the conductive fibers 3 It has been revealed that the length is preferably 1 mm or more, more preferably 3 mm or more, and the average particle diameter of the nonconductive particles 5 is preferably φ0.5 mm or less, and more preferably φ0.1 mm or less.

  Thus, in the electromagnetic wave shielding material according to the first embodiment, it is possible to meet demands for freedom in size reduction, weight reduction, and shape design, which is expensive and is a member of a molding machine, a mold, or the like. Excellent electromagnetic shielding performance can be obtained in a wide frequency range while minimizing the blending amount of stainless steel fibers or the like as conductive fibers that cause wear.

[Embodiment 2]
Next, Embodiment 2 of the electromagnetic wave shielding material according to the present invention will be described with reference to FIG. In the manufacturing method of the electromagnetic wave shielding material 1 according to the second embodiment, an injection molding method is used as a molding method.

  First, the manufacturing method of the electromagnetic wave shielding material which concerns on Embodiment 2 of this invention is demonstrated with reference to the flowchart of FIG. As shown in FIG. 7, a mixing process is first performed in which the conductive particles 4 and the nonconductive particles 5 are mixed with the synthetic resin 2B (step S20). Specifically, as the mixing step, when a thermoplastic resin is used as the synthetic resin 2B, there is a method of heating to the softening temperature of the thermoplastic resin using a kneader or the like and kneading, etc. When a curable resin is used, there is a method of stirring according to the viscosity of the thermosetting resin at room temperature.

  In parallel with this, a fiber pellet molding process by pultrusion molding for covering the conductive fibers 3 with the synthetic resin 2B is performed (step S21). As a result, the long fiber pellets 8 aligned in a certain direction can be obtained without cutting the conductive fibers 3.

A dry blending step is performed in which the long fiber pellet 8 is mixed by dry blending with a mixture 7 obtained by uniformly mixing the synthetic resin 2B, the conductive particles 4, and the nonconductive particles 5 in the mixing step (step S22). ). And the injection molding process which performs injection molding using the injection molding machine or pre-plunger type injection molding machine provided with the low shear screw at least is implemented (step S23).
Thereby, the electromagnetic wave shielding material 1A having various shapes according to the cavity shape of the injection mold can be obtained.

  In the second embodiment, specifically, a polyamide PA6 (nylon 6, melting point 225 ° C.), which is a thermoplastic resin, is used as the synthetic resin 2B. SUS fiber) is measured by a laser diffraction / scattering method using a spheroidized graphite powder series CGC-50 (laser diffraction type particle size distribution measuring apparatus) manufactured by Nippon Graphite Industry Co., Ltd., which is a graphite powder as the conductive particles 4. The average particle diameter was 50 μm), glass beads were used as the non-conductive particles 5, the fiber length of the SUS fibers was 6 mm, and the size of the glass beads was an average measured by a particle measuring instrument based on electric resistance, that is, a Coulter counter. The particle diameter was 0.05 mm.

In addition, in the mixture 7, polyamide PA6 was 26.34% by weight (34.97 vol% in volume%), graphite powder was 30.33% by weight (21.67 vol%), and glass beads were 43.34. It was set as weight% (43.35 vol%). On the other hand, in the long fiber pellet 8, the polyamide PA6 is 25.0% by weight and the SUS fiber is 75.0% by weight. In the dry blending process, the mixture 7 is 91.5% by weight and the long fiber pellet 8 is 8.5. Dry blending was carried out at a weight percentage and injection molding was performed.
As a result, the blending ratio in the obtained electromagnetic shielding material 1A was as follows: polyamide PA6 was 26.2 wt% (36.45 vol%), graphite powder was 27.8 wt% (20.76 vol%), and glass beads were 6. 4 weight% (41.53 vol%) and SUS fiber became 39.7 weight% (1.25 vol%).

In the mixing step, the above ingredients are kneaded and mixed at a rotation speed of 24 rpm for 5 minutes at a temperature of 250 ° C. with a heating kneader, and the mixed material is taken out and cooled to near room temperature. Then, the cooled mixed material was reheated and extruded from a jig having a hole having a diameter of φ2.0 and cut to produce a rod-shaped pellet (mixture 7). In addition, this mixing process can implement from kneading | mixing to pelletization at once by using a twin-screw extruder.
The dry blend material of the mixture 7 and the long fiber pellet 8 was put into a hopper of a pre-plunger type injection molding machine equipped with a low shear screw manufactured by Sodick, and injection molding was performed. The cavity shape of the injection mold was 110 mm × 110 mm × 3 mm.

  The electromagnetic shielding performance of the electromagnetic shielding material having the dimensions of 110 mm × 110 mm × 3 mm obtained in this way was measured by the KEC method. It became clear that it has an electromagnetic wave shielding performance substantially equivalent to the electromagnetic wave shielding material by the composition of Example 8 of the first embodiment shown in the lower part.

  Thus, in the electromagnetic wave shielding material according to the second embodiment, it is possible to meet the demands for freedom in miniaturization, weight reduction, and shape design, which are expensive, and are members of a molding machine, molds, etc. Excellent electromagnetic shielding performance can be obtained in a wide frequency range while minimizing the blending amount of stainless steel fibers or the like as conductive fibers that cause wear.

  In each of the above embodiments, only the case where a two-component epoxy resin or polyamide PA6 is used as the synthetic resin has been described. However, the synthetic resin is not limited to these, and a thermoplastic resin other than polyamide PA6, A thermosetting resin can be used.

  Further, in each of the above-described embodiments, only the electromagnetic wave shielding material and the manufacturing method thereof that can obtain excellent electromagnetic wave shielding performance by including non-conductive particles in the synthetic resin have been described. By containing conductive fibers and conductive particles in the resin, adding a foaming agent to the synthetic resin, heating, performing core back molding, etc., by including bubbles in the synthetic resin, An electromagnetic shielding material having excellent electromagnetic shielding performance can be obtained.

Further, in each of the above-described embodiments, only the case where a 110 mm × 110 mm × 3 mm plate-shaped molded body is formed as the electromagnetic wave shielding material has been described, but this is a specimen for measuring electromagnetic wave shielding performance by the KEC method. Therefore, any other shape of electromagnetic shielding material can be formed.
In particular, the injection molding method according to Embodiment 2 has an advantage that the degree of freedom in shape design is extremely large.

  In each of the above embodiments, the case where glass beads that are solid particles are used as non-conductive particles has been described. However, hollow particles can also be used as non-conductive particles. There is an advantage that the weight is further reduced and the heat insulation is improved. As such hollow particles, foamed inorganic compound particles, hollow silica particles, glass balloons and the like can be used.

  In practicing the present invention, the component, configuration, shape, quantity, material, size, connection relationship, manufacturing method, etc. of other parts of the electromagnetic shielding material, and other steps of the electromagnetic shielding material manufacturing method are also included. The invention is not limited to the above embodiments. The numerical values given in the embodiment of the present invention are not all critical values, and certain numerical values indicate appropriate values suitable for implementation. The implementation is not denied.

1, 1A Electromagnetic wave shielding material 2, 2A, 2B Synthetic resin 3 Conductive fiber 4 Conductive particle 5 Non-conductive particle

Claims (5)

  An electromagnetic wave shielding material comprising a synthetic resin, a conductive material, and nonconductive particles or bubbles that increase contact between the conductive materials.   2. The electromagnetic shielding material according to claim 1, wherein a volume ratio of the non-conductive particles or the bubbles to the electromagnetic shielding material is 10 vol% to 50 vol%.   The average particle diameter measured by the Coulter principle of the non-conductive particles is in the range of 10 μm to 500 μm, or the size of the bubbles is in the range of 10 μm to 500 μm. Electromagnetic shielding material.   The electromagnetic shielding material according to any one of claims 1 to 3, wherein the conductive material is at least a conductive fiber.   The electromagnetic wave shielding material according to claim 4, wherein the conductive material contains conductive fibers and conductive particles.

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