JP2012151502A - Composite filler for mixing resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite filler that is used by being mixed with a resin composition and that is excellent in insulation properties, electromagnetic wave absorptivity and heat dissipation.SOLUTION: A composite particle, which comprises a soft magnetic metal particle and an inorganic oxide particle and in which a diameter of the metal particle is 10 times or more larger than that of the inorganic oxide particle, has a structure in which the inorganic oxide particle coats a surface of the metal particle in such a manner as to stick thereinto. Flat plate-like soft magnetic metal powder having an aspect ratio of 5 or more and the inorganic oxide particles are alternately stacked to constitute the one composite particle. Additionally, a composite filler for mixing a resin is coated with inorganic oxide particles that do not constitute the composite particle.

Description

  The present invention relates to a composite filler for resin mixing used by mixing with a resin or the like.

  It is possible to mix a filler such as metal powder with the resin composition to obtain a resin composite having electromagnetic wave absorption characteristics and heat dissipation. However, the metal powder has poor wettability with respect to the resin composition, has a higher density than the resin composition, and easily aggregates when highly filled, resulting in uneven dispersion of the filler. Therefore, it is difficult to increase the filling amount of the filler made of metal powder.

  Japanese Unexamined Patent Publication No. 2000-223984 (Patent Document 1) discloses an electromagnetic wave absorber excellent in corrosion resistance, in which a powder 2 made of a soft magnetic metal material and surface-treated with a nonmetallic substance 6 is dispersed in a rubber 4. Is provided. As the surface treatment, it is described that a solution / melt of a non-metallic substance is adhered to the surface of the metal powder.

  Japanese Patent Application Laid-Open No. 2001-358493 (Patent Document 2) describes an electromagnetic wave absorber in which composite magnetic particles in which magnetic metal particles and ceramics are integrated are dispersed in a material having a high electrical resistivity. As the composite magnetic particles, there are described particles in which a plurality of magnetic metal particles and ceramics are integrated, particles in which a plurality of magnetic metal particles are surrounded by ceramics, and the like.

Japanese Patent Laid-Open No. 2000-223984 JP 2001-358493 A

  However, the composite filler as described above has a problem that it has a high bulk density and is difficult to mix with the resin composition. The subject of this invention is providing the resin molded product obtained by mixing the composite filler for resin which eliminates the said problem, and the said composite filler and a resin composition.

  The present invention for solving the above-described problems is as described in the claims. The present invention is characterized by using composite particles including an aggregate of metal particles and inorganic oxide particles sufficiently smaller than the metal particles. The average particle size of the final inorganic oxide particles is preferably 5 μm or less, and the composite particle size is 10 to 40 μm. The metal powder is flaky. It is preferable to use a powder having a maximum diameter of 5 or more (an aspect ratio of 5 or more) with respect to the thickness. As the metal powder, soft magnetic metal powder, particularly iron, nickel, manganese, silicon, samarium or cobalt can be used. In particular, the frequency characteristics of electromagnetic wave absorption are improved by alloying them. When mixed with resin or the like, high frequencies can be absorbed.

  In addition to using the composite particle as a filler, the coating layer that can be provided with an inorganic coating layer and an insulating layer on the composite particle may be either an inorganic particle layer or an inorganic coating layer. In particular, it is preferable to cover the periphery with inorganic oxide particles that do not constitute composite particles. By using a filler in which composite particles and inorganic oxide particles that do not constitute composite particles are dispersed, the insulating properties of the resin molded body can be maintained even when the composite particles are cracked during the molding process or by kneading with a solid resin. Can be maintained. The average particle diameter of the inorganic oxide particles not constituting the composite particles is preferably 5 μm or less. Moreover, it is preferable that the particle diameter of the composite particles has a size of 5 times or more as compared with the size of the inorganic oxide particles existing in a mixture with the composite particles.

  Such a composite filler has a metal ratio of 30 to 55% with respect to 45 to 70% of silica in terms of molar ratio (when iron or silica is used, 20 to 50% by weight of silica by weight ratio, iron 50 to 80% by weight) is preferable in order to satisfy electromagnetic wave absorption performance, thermal conductivity, and insulation. In particular, it is easy to use for a member that requires insulation by increasing the content molar ratio of silica to metal.

  In addition, the resin composite material of the present invention is configured by mixing the composite filler and a resin composition. According to the composite filler as described above, it is possible to increase the filling amount when the resin is filled. Therefore, when the composite filler and the resin composition are mixed and the molded body is used as an electromagnetic wave absorbing material or used as a sheet-shaped electromagnetic wave absorbing sheet, the electromagnetic wave absorbing performance can be improved. In particular, if the soft magnetic metal powder has a high density filling of 50 vol% or more by volume percentage, an improvement in electromagnetic wave absorption performance can be expected. It is possible to absorb electromagnetic waves in the frequency band range of 800 megahertz to 10 gigahertz. Further, by using the molded body of the composite filler and the resin composition for a member that requires heat dissipation, for example, a semiconductor integrated circuit (IC) sealing material, heat dissipation can be improved.

  According to the present invention, when mixed with an appropriate resin composition, it is possible to increase the filling amount of the composite filler into the resin.

The schematic diagram of a composite particle. SEM image photograph of reduced iron powder. The schematic diagram of a composite particle. The example of a composite particle manufacturing apparatus. An example of a composite particle manufacturing process. SEM image photograph of composite particles. The single peak size distribution map of a composite particle. The SEM-EDX elemental analysis of the silica particle of the composite particle which expressed electroconductivity. FIB-TEM image of TEOS coating powder particles. The double peak size distribution map of a composite particle and a silica particle. The schematic diagram of the composite particle entirely covered with the alumina nitride. The FIB-TEM image of the composite particle which mixed the copper powder.

  The electromagnetic wave absorbing material is used in the vicinity of a device that emits an electromagnetic wave, and is required to have an electrical insulation property together with the electromagnetic wave absorbing performance. The objective of this invention is providing the filler for electromagnetic wave absorbers which can improve the insulation of an electromagnetic wave absorber further.

  The characteristics of the composite particles are composite particles including metal particles and inorganic oxide particles that are sufficiently smaller than the metal particles, and have a structure in which the inorganic oxide particles cover the surface of the metal particles. There is. According to the invention of the present application, an electromagnetic wave absorbing material with high insulation can be provided by mixing with an appropriate resin.

  The average major axis of the metal particles is preferably at least 10 times the average major axis of the inorganic oxide particles. According to the said structure, when an insulating layer with a thick inorganic oxide particle is formed around a metal particle, and an electromagnetic wave absorbing material is formed, it is possible to maintain high electrical insulation. Moreover, according to the said structure, it is prevented that the surface of a metal particle is oxidized, and deterioration of electromagnetic wave absorption performance is prevented.

  The composite particles of the present invention include an inorganic powder such as silica or aluminum nitride and a soft magnetic metal powder such as iron powder, nickel, manganese, silicon, samarium or cobalt. The soft magnetic metal powder has a flat shape and has a structure in which it is laminated with an inorganic oxide powder.

  When attaching the inorganic oxide particles to the metal particles, it is preferable to use ceramic sputtering or mechanical alloying (mechanical alloying, MA method). Here, the impact by the mechanical alloying method (mechanical alloying, MA method) is referred to as external stimulation. In the MA method, the inorganic oxide particles are pulverized and refined, and the metal particles are also expanded into a flat plate shape, so that the fine particles and the flat plate metal are stacked on each other. The MA microstructure has a basic structure in which a soft magnetic metal, which is spherical or granular as a starting material, is flattened by impact and is covered with fine ceramic particles, and the basic structure is further laminated. It is a structure in which one composite particle is formed. The structure of this composite particle is shown in FIG.

  Sputtering is a method of coating an inorganic oxide on metal particles using an inorganic oxide such as silica as a target. In this case, the core is a metal, and composite particles having a shape in which a ceramic such as silica, which is an inorganic oxide, is coated on the outer periphery thereof. In the sputtering method, the amount of silica coating can be adjusted freely. On the other hand, silica coated particles covered with iron powder by a sputtering method have a simple layer structure, and when broken, iron particles are easily exposed.

The specific gravity of the metal particles of the composite particles is large, and the specific gravity of the inorganic oxide particles is small. Therefore, changing the ratio of the particle diameters changes the manner in which the inorganic oxide particles adhere, and the density of the filler can be adjusted. Moreover, the density of a filler can be suitably adjusted with 4-7 g / cm < ³ > by changing the mixing ratio of a metal particle and an inorganic oxide particle.

  Metal particles have a large coefficient of thermal expansion, and inorganic oxide particles have a small coefficient of thermal expansion. Therefore, the coefficient of thermal expansion of the composite particles can be adjusted by coating the surfaces of the metal particles with inorganic oxide particles.

  The iron powder preferably has a particle size of 10 to 100 μm. In the iron powder having a size of 2 to 10 μm, the difference from the size of the silica particles is small, and the silica particles are difficult to adhere to the iron powder. Moreover, since the particle becomes closer to a sphere as the particle size of the iron powder is smaller, it is expected that the contact with the silica particle is reduced and the silica particle is less likely to adhere. Therefore, it is preferable to use a powder in which particles of iron powder having a particle size of 10 to 75 μm account for 75% or more.

  Also, metal powder such as nickel powder and cobalt powder other than iron can be used in the same manner. Various powders having a size in the range of about 1 to 120 μm are commercially available in various shapes such as flakes, spikes, and spheres, even nickel powder and cobalt powder. Nickel powder and cobalt powder have the advantage of being less rusting than iron powder, but iron powder is easier to adjust the density.

  The closer the iron powder is to a true spherical shape, the more difficult it is for silica particles to adhere. Accordingly, when the iron powder has a flat shape (FIG. 2) or a complicated shape such as a twist, the amount of silica particles attached is large, and the mixing ratio of silica and iron powder can be easily adjusted.

  Furthermore, the amount of silica attached can be increased by using iron powder having large irregularities (rough surface). FIG. 2 is an SEM image of reduced iron powder having a flat shape. It can be confirmed that the surface has irregularities with a height of about 0.1 μm. The size of the irregularities on the surface of the iron powder (surface roughness) is preferably about 0.15 to 0.5 μm.

  An inorganic oxide such as alumina may be used instead of silica, and the same effect as in the case of silica is expected. Further, ceramics such as carbide and nitride may be used instead of the inorganic oxide.

  Said composite particle is used as a molding material as a filler mixed with resin. As the resin, generally known thermosetting resins and thermoplastic resins can be appropriately used depending on the purpose. When used with a thermosetting resin such as an epoxy resin, the resin composition before curing and the filler are mixed at a low temperature such as room temperature, and the mixed paste-like material is shaped and heated, It becomes a molding material such as an electromagnetic wave absorbing sheet. On the other hand, a thermoplastic resin can be mixed with a filler while heating a cured resin, shaping the mixed paste-like substance, and cooling to form a molding material.

  When a thick sheet mixed with a thermoplastic resin is produced, a thin sheet is produced, and hot pressing is performed while laminating thin sheets to obtain a sheet adjusted to a desired thickness integrally. be able to.

  Moreover, the thermal expansion coefficient of the filler containing the composite particles of iron powder and inorganic oxide can be changed depending on the blending ratio of the raw material iron powder and inorganic oxide.

  The thermal expansion coefficient of the filler containing composite particles of iron powder and silica is very small compared to iron powder. Therefore, by using a molding material such as a sheet in which such composite particles are mixed in the vicinity of the device, thermal expansion during a change in heat can be suppressed. Also, the greater the amount of silica deposited, the smaller the thermal expansion coefficient.

  Moreover, the thermal expansion coefficient can be increased by using alumina particles instead of silica particles. The thermal expansion coefficient of alumina is about twice that of silica, and the use of alumina makes it possible to make the thermal expansion coefficient of the filler closer to that of a metal. By increasing the thermal expansion coefficient of the filler, there is an effect of alleviating thermal strain in the low temperature part and the high temperature part. Therefore, performance degradation such as peeling can be prevented by using the sheet of the present invention as an insert material between a device that may generate a high temperature and a heat radiating portion such as a metal heat radiating fin or a metal heat radiating plate.

The density (specific gravity) of the filler containing composite particles of iron powder and silica or the like can be changed depending on the blending ratio of the raw material iron powder and silica particles. Ceramics and resins such as silica have low thermal conductivity and high heat insulation effect. Therefore, the thermal conductivity of the sheet increases in proportion to the iron powder content. In order to increase the amount of filler contained in the sheet, it is necessary to equalize the resin and filler density. The density of iron powder is high, about 7~8g / cm ^3, the density of the resin is generally 4-6 g / cm ^3. In order to provide a sheet with high thermal conductivity, it is necessary to increase the amount of iron powder used. Filler is mixed with resin by increasing the amount of silica (specific gravity 2-3 g / cm ³ ) adhering to iron powder and reducing the filler density to 3.5-6.5 g / cm ³ to match the resin. As a result, the amount of iron powder in the sheet can be increased.

  In addition, the technique of carrying out silica coating (thickness of about several nm) by a coupling process to iron powder is known. However, the silica coating is thin and it is very difficult to reduce the filler density to the same level as the resin. The density, which was difficult to adjust by silane coupling, can be adjusted by changing the mixing ratio of iron powder and ceramic powder.

  The composite particle of the present invention is used as a filler for mixing with a resin, such as an electromagnetic wave absorbing sheet or a semiconductor integrated circuit sealing material. The composite particles preferably have an average particle size of 100 μm or less. When the filler diameter exceeds 100 μm, the thickness of the molding material becomes 500 μm or more in order to suppress surface irregularities when it is mixed with a resin and molded into a sheet or the like, and it is difficult to produce a thin molding material It is to become. Moreover, the compounding ratio of iron and silica in the composite particles is preferably about 70 to 45% of silica with respect to 30 to 55% of iron in terms of molar ratio. When the ratio falls within this range, composite particles that maintain a good balance between insulation and thermal conductivity can be provided.

The above composite particles are also suitable as a filler material kneaded into a resin for mounting a semiconductor integrated circuit. While maintaining the same insulating property (10 ¹³ Ωm or more) as when only particles made of silica alone are kneaded, the thermal conductivity can be improved twice or more. Specifically, it can be set to 1.2 W / m · K or more.

  Furthermore, electromagnetic waves generated from the IC can be reduced. The resin used for the IC sealing material preferably has insulating properties, thermal conductivity, and electromagnetic wave absorption characteristics. With the development of new ICs that increase the calculation speed and density required for miniaturization, the temperature of ICs in recent years has increased, and the heat resistance and thermal conductivity of sealing materials such as epoxy resins have improved. Required. Therefore, a sealing material with good thermal conductivity is effective. Further, in the mobile IC, an electromagnetic wave shield with a metal cap has been conventionally provided. However, as the clock frequency increases, the function of the metal cap as an antenna becomes a problem. Therefore, a sealing material that absorbs electromagnetic waves is effective. Use of a resin sealing material having an electromagnetic wave absorbing function as the sealing material is effective for space saving.

  When used as an electromagnetic wave absorber, it is required to absorb electromagnetic waves in the frequency band of 800 megahertz to 10 gigahertz.

The mixture of resin and filler used as the IC sealing material is preferably a resin containing at least two types of particles, in addition to composite particles, in which insulating particles such as silica particles are present. The particle size distribution of the composite filler containing these particles has a peak of silica particles and a peak of composite particles. Silica particles have a fine particle size on the order of microns or less, and composite particles have a particle size distribution with a large particle size on the order of 10 microns. By providing two kinds of particle size distributions with such a two-peak particle size distribution, even when the composite particles are crushed under stress, such as during kneading with a resin, the insulating silica particles In order to compensate the periphery of the composite particles, it is difficult to reduce the insulation required for the IC sealing material. When aluminum nitride is used as the insulating particles mixed with the composite particles, the volume efficiency is lower than that of silica (about 10 ¹² Ωm), but high thermal conductivity (1.5 W / m · K or more) ) Can be achieved, which is preferable for use as an IC sealing material or the like.

  When the inorganic oxide particles are adhered to the metal particles, it is preferable to use a mechanical alloying method (mechanical alloying). The inorganic oxide particles are embedded in the surface of the metal particles by an external impact. Although the mechanical alloying method is used, the metal particles and the inorganic oxide particles are hardly alloyed and the method is carried out at a temperature lower than the temperature at which these materials are alloyed. There was no alloying of the particles.

  As for the diameter of the filler containing composite particles, the average particle diameter is preferably 100 μm or less. This is because if the filler diameter exceeds 100 μm, the sheet thickness becomes 500 μm or more in order to suppress surface irregularities, making it difficult to produce a thin sheet. FIG. 3 is a schematic view of a filler in which the silica particles entirely cover the surface of the reduced iron powder. The filler of the present invention can increase the amount of silica adhering to the surface portion as compared with conventional products, and can enhance the insulating properties of the filler. As a result, the insulating property of the electromagnetic wave absorber is also increased.

  In addition, since the particles can be made large and mixed with the electromagnetic wave absorber by adjusting the specific gravity as in the present invention, the thermal conductivity of the electromagnetic wave absorber can be increased.

  The ratio of iron and silica in the composite particles is preferably about 1: 1.4 to 1.8 with respect to iron, as compared with weight. When the ratio falls within this range, composite particles that maintain a good balance between insulation and thermal conductivity can be provided. Further, although the reason is unknown, electromagnetic wave absorption characteristics are good in this range. The present inventors examined using composite particles of Fe: Si = 3: 7, 7: 3 and 8: 2 by weight ratio. In addition, the ratio of silica further increases in volume ratio.

  Hereinafter, description will be made using examples.

  The composite particles of this embodiment include inorganic oxide particles such as silica and alumina and metal powders such as iron powder. Inorganic oxide particles adhere around the metal powder to form an insulating layer. The composite particles of the present invention are used as a filler for an electromagnetic wave absorbing sheet, mixed with a resin, and formed into a sheet shape.

  The filler of the present invention was produced by the following method. A mechanical alloying method (mechanical alloying) is used for manufacturing the filler. Mechanical alloying refers to a treatment in which powder containing metal particles and inorganic oxide particles is placed in a container, and a steel ball or a steel rod is placed in the container to vibrate the powder, thereby causing the powders to collide with each other. As a result, the inorganic oxide particles can be adhered to the periphery of the metal particles, and a treatment can be performed to obtain composite particles of iron powder and silica.

An example of a manufacturing apparatus is shown in FIG. Here, the case where reduced iron powder is used for the metal particles and silica particles are used for the inorganic oxide particles will be described as one embodiment. After putting steel balls, iron powder, and silica particles in a stainless steel container, it is evacuated to a ^10-3 Pa digit by a rotary pump from the exhaust port attached to the stainless steel container lid, and placed on the stainless steel container lid. Inert gas was blown from the attached suction port to replace the atmosphere with inert gas. Replacement with an inert gas was performed twice.

  The step of purifying the filler is considered to occur as follows (FIG. 5). Silica particles are pulverized to a powder of about 10 to 100 nm by putting silica particles of about 10 μm and iron powder of 10 to 20 μm into a mechanical alloying device and colliding with a steel ball. The pulverized silica particles adhere to pierce the iron powder. Silica particles added in an excessive amount to the iron powder or to iron powder in which a plurality of iron powders are integrated further adhere to form a thick silica particle layer.

  In the case of producing composite particles containing iron powder and silica particles, the time for performing the treatment step is preferably about 5 hours. Comparing the case of 5 hours and 50 hours, the electromagnetic wave absorbing ability of the filler was slightly reduced by the treatment for 50 hours. The reason is that the insulating layer containing silica particles formed on the surface is easily peeled off by impact during long-time treatment, and the exposed metal parts after peeling are bonded and integrated by a mechanical alloying method. This is probably because the absorption efficiency of the metal particles decreased as a result of the increase in the size of the particles. This tendency becomes more prominent as the metal weight ratio increases.

  The reason why the atmosphere is an inert gas is to suppress oxidation of the iron powder. When iron powder is oxidized, it becomes iron oxide, and physical properties such as insulation, thermal conductivity, and thermal expansion change. By mixing the iron oxide powder, the properties as a filler deteriorate. By sufficiently replacing the atmosphere in the container with an inert gas, the iron powder can be prevented from being oxidized and the characteristics can be maintained.

  As the iron powder, those having an irregular shape and a relatively large particle size are preferable. This is because the iron particles are relatively large relative to the silica particles, and the silica particles are easily attached by increasing the contact range with the silica particles. In this example, as the iron powder, a powder having a particle size of 1 to 100 μm and a powder having a particle size dispersion center value of about 25 μm was used.

  Further, reduced iron powder was used as the iron powder. The metal particles are preferably reduced iron powder. The reduced iron powder includes particles having various shapes, and has a feature that, for example, the particle diameter is larger than that of carbonyl iron powder and the surface is rough. Accordingly, the inorganic oxide particles are easily attached, and are suitable for use in the present invention.

  The unevenness present on the surface of the metal particles preferably has a depth of 0.1 μm or more.

  The average particle diameter of the inorganic oxide particles is preferably 0.01 to 1 μm. In particular, those having an average particle size of about 10 to 100 nm are preferable.

  Silica particles having an average particle diameter of about 19.6 μm were used. In order to adhere the silica particles so as to pierce the iron powder without gaps by the mechanical alloying method, the silica particles need to have a sufficiently small diameter with respect to the iron powder. When the average diameter of the iron powder is 50 μm, the average diameter of the silica particles needs to be 5 μm or less (1/10 or less). In addition, good results were obtained when the particle size distribution of the silica particles was inclined to 1 μm or less. The initial average particle diameter of silica was about 19.6 μm, and 90% of the particle diameter was 43 μm or less. Silica particles were pulverized during compounding using a mechanical alloying method, and most of them became powders of 1 μm or less, and adhered to the surface of the reduced iron powder in several layers.

  The composite particles produced from the above iron powder and silica particles had a median particle size distribution (a value at which the amount of particles smaller than the median is 50%) of 26 μm. The size of iron particles was partially reduced by mechanical alloying.

  In the electromagnetic wave absorbing material, the resin connects fillers and functions as an insulating material, and determines the shape of the molding material. The metal particles are high thermal conductors and have an action of absorbing electromagnetic waves. The inorganic oxide particles are a binder of metal and resin, and have a function of adjusting the density of the composite particles. When these are mixed at different ratios to obtain an electromagnetic wave absorber, the insulating property and the thermal conductivity are in a contradictory relationship. In addition, the amount of filler mixed in the electromagnetic wave absorber is preferably 40 to 80 vol% by volume ratio. Moreover, 80 to 90 wt% is preferable in weight ratio. The inventors of the present application have made a study by setting the weight ratio of resin, iron, and silica in the case of producing an electromagnetic wave absorbing material to approximately resin: iron: silica = 2: 3: 5.

  FIG. 6 shows an example in which silica particles are adhered to the entire surface of the reduced iron powder by the mechanical alloying method.

  FIG. 7 shows the particle size distribution of the composite particles in which the molar ratio of iron and silica is 7: 3. When mechanical alloying was performed for 5 hours, the particle size distribution had a single distribution with a peak of about 27 μm. By changing the blending ratio and mechanical alloying time, the size of the composite particles changes. When mechanical alloying is performed for a long time or when the compounding ratio of silica is increased, the particle size becomes small. In order to obtain surface smoothness when mixed with a resin, the particle size of the composite particles is preferably 30 μm or less.

This composite particle is dry-blended with biphenyl resin powder made by Japan Epoxy Resin, added with a curing agent made by Gunei Chemical Industry, and roll-kneaded using two rolls for kneading, and the resulting kneaded resin is crushed. And made a tablet. As a result, the volume resistivity was 10 ² to 10 ³ Ωcm. Roll kneading is a method of kneading particles with great stress. When the composite particles are kneaded with a solid resin such as epoxy, a stress that is pushed into a narrow gap of the roll is generated, and thus the composite particles may be stressed. In this case, since a stress is applied to the method of crushing the composite particles by the rotation of the roll, the composite particles are crushed. Then, the composite particle exposes the metal in the core part to the particle surface and becomes conductive between the particles, which may impair insulation.

  In FIG. 8, the cross-sectional structure observation photograph of the sample which measured volume resistivity, and the result of an elemental analysis are shown. From the cross-sectional structure observation photograph, a structure in which silica powder is alternately laminated with long-stretched iron is observed. As a result of elemental analysis, iron was detected on the surface of the silica particles.

  From the results of the cross-sectional structure and elemental analysis, when the compounding ratio is 7: 3 with iron to silica and roll kneading with a solid resin, metallic iron to be a core material partially adheres to the surface of the silica particles. However, it is considered that metallic electrical conductivity is generated due to the adhesion of the metal, and the insulating property is adversely affected. Therefore, when the ratio of iron: silica is 7: 3, the composite particles and the solid resin are mixed by a method that does not apply a load to the composite particles (such as mixing with a liquid resin as described above). It is considered necessary.

  When mixed with thermoplastic polypropylene, the composite particles cracked when stirred with a high-shearing blade, resulting in the same problems as kneading with the solid resin. On the other hand, when a liquid silicone resin was mixed with the composite particles and solidified, a resin composite material maintaining the form of the composite particles was obtained. The resin composite material has high electromagnetic wave absorption performance and high thermal conductivity.

  Example 2 shows an example of composite particles that include inorganic particles such as silica or aluminum nitride and soft magnetic metal powders such as iron powder and the periphery is coated with a silicon compound.

  First, in the same manner as in Example 1, the molar mixing ratio of iron and silica was set to 7: 3, and the particles were formed by mechanical alloying (mechanical alloying, MA method).

Next, by using a hydrolysis reaction of tetraethoxysilane (C ₂ H ₅ O) ₄ Si (hereinafter abbreviated as TEOS), the surface of the iron powder exposed by the separation of the silica in the MA process was exposed to the silica. Protected with a coating layer containing Hydroxyl groups are present on the iron powder surface, TEOS in contact with the hydroxyl groups is hydrolyzed, and the silica compound adheres to the iron powder surface. The reaction formula is shown below. This is a so-called sol-gel reaction and is often used when silica is generated at a low temperature.

(C ₂ H ₅ O) ₄ Si + 4H ₂ O → Si (OH) ₄ + 4C ₂ H ₅ OH (1)
Si (OH) ₄ →-(OSiO) _-n + 4H ₂ O (2)
As TEOS, a new one or a sufficiently dried one was used. The drying method is as follows. First, the molecular sieve was air-dried overnight to remove the residual organic solvent, and dried under reduced pressure at 120 ° C. Using the dried molecular sieve, TEOS was dehydrated with molecular sieve 3A, and then deethanol was performed with 4A. The TEOS used for coating the composite particles can also be dried and used again.

  Samples were prepared under the following conditions (1) to (3) using 100 g of composite particles.

  Condition (1): The particles after MA were stirred and mixed with 208 g of TEOS by hand. The iron powder after the reaction was filtered off, air-dried to remove residual TEOS, and dried at 60 ° C. under reduced pressure for 1 minute and at 110 ° C. under reduced pressure for 2 hours.

  Condition (2): The particles after MA were mixed with 270 g of TEOS, 60 g of ethanol and 94 ml of water, and left for 1 hour under ultrasonic irradiation. The iron powder after the reaction was filtered off, air-dried to remove residual TEOS, and dried at 60 ° C. under reduced pressure for 1 minute and at 220 ° C. under reduced pressure for 2 hours.

  Condition (3): The particles after MA were mixed with 270 g of TEOS, 60 g of ethanol and 94 ml of water, left under ultrasonic irradiation for 4 hours, and allowed to stand overnight. The iron powder after the reaction was filtered off, air-dried to remove residual TEOS, and dried at 60 ° C. under reduced pressure for 1 minute and at 220 ° C. under reduced pressure for 2 hours.

  In the sol-gel method, the composite particles are gelled to vitrify depending on the conditions. Therefore, in the conditions (1) to (3), the decomposition reaction of TEOS is suppressed to such an extent that the gelation does not proceed. In addition, the surface element distribution of the particles after the MA process was measured by Auger spectroscopic elemental analysis (AGS), and the amount of soft magnetic metal was 1/3, so the amount of TEOS was 1/3 molar equivalent of the raw iron powder. It was set as the quantity for making it react.

The composite particles provided with TEOS coating are dry blended with biphenyl resin powder made by Japan Epoxy Resin, added with a curing agent made by Gunei Chemical Industry, and roll kneaded using two rolls for kneading. The resin was crushed and tableted. The volume resistivity was improved by an order of magnitude, from 10 ³ to 10 ⁴ Ωcm.

  FIG. 9 shows FIB microsampling and TEM observation results for the powder part in the resin. In TEOS coating, a thin metal layer on the order of nanometers is attached to the surface of the surface silica layer, which is considered to have formed during the coating process. When mixed with a solid resin, the TEOS coating cannot withstand the stress generated during roll kneading, and the composite particles are crushed and conduction between the composite particles occurs, resulting in a lower insulating property than in the case of the liquid resin. It is thought.

  In addition, when mixed with thermoplastic polypropylene, the composite particles cracked when agitated with a high shearing blade, resulting in the same problem as in the case of roll kneading with the solid resin. On the other hand, when a liquid silicone resin was mixed with the composite particles and solidified, a resin composite material maintaining the form of the composite particles was obtained. The resin composite material of the liquid silicone resin and the composite filler had high electromagnetic wave absorption performance and high thermal conductivity.

  Example 3 shows an example in which composite particles containing inorganic particles such as silica or aluminum nitride and soft magnetic metal powders such as iron powder and silica particles not constituting the composite particles are used together and mixed with a resin. In this example, the mixing ratio of iron and silicon was set at a molar ratio of 5: 5, and composite particles were produced by mechanical alloying. This is an example. Some silica was separated as particles. A strong insulating layer is formed by the silica particle layer (silica coating) provided on the surface of the composite particle, and the insulation is improved.

  FIG. 10 shows the size distribution of the composite filler containing composite particles when the blending ratio (iron to silica) is 5: 5. The peak distribution of the particle diameter of the composite particles was about 20 μm, the peak distribution of the particles of the silica alone was about 2 μm, and the particle diameter distribution had two peaks.

  Next, the composite particles mixed with the silica particles were blended with a biphenyl resin powder made from Japan Epoxy Resin, and roll kneaded to form a tablet. Table 1 shows a comparison of the characteristics of the resin containing the composite particles and the silica particles and the resin containing only the silica particles.

The volume resistivity was improved to 1.6 × 10 ¹⁷ Ωcm. Since the volume resistivity that we are developing is 10 ¹³ Ωcm or more, a filler having an insulating property exceeding the target value could be obtained. In addition, compared with the case where the same amount of silica particles were kneaded with the same amount of resin, the volume resistivity was about two orders of magnitude better, and the thermal conductivity was about 2.8 times higher. This result shows that even if the composite particles are crushed during roll kneading, the fine silica particles cover the exposed core material, so that the metal electrical conductivity is suppressed and the kneading resin has excellent insulation. It is thought that it became. Moreover, since the diameter of the composite particles is reduced by crushing, it is considered that the finer particles can be used for thinning the IC.

  Unlike the silica coating layer produced by TEOS, the insulating property of the filler could be maintained in this example. By mixing silica particles finer than the composite particles alone, the amount of silica adhering to the surface portion can be sufficiently increased even if the composite particles are crushed, so that the insulating properties of the filler can be enhanced. As a result, even when mixed with a resin as a composite filler for an electromagnetic wave absorber and applied to the electromagnetic wave absorber, the imaginary part of the complex permeability can be maintained from 800 MHz to a high frequency in the vicinity of 10 GHz. By mixing inorganic particles having a small diameter as compared with such composite particles, the peak of the small filler is about 0.5 to 5 μm, and the peak of the large filler is about 10 to 40 μm. Kneading can be performed. In particular, when the diameters of the large peak and the small peak are compared, the dimensional ratio is preferably 5 to 10.

  In this example, an example in which the surface of the composite particle of Example 1 is provided with an aluminum nitride layer having good thermal conductivity will be described. FIG. 11 is a schematic view of a filler in which the composite particle powder is entirely covered with aluminum nitride. Since the outermost layer is coated with alumina nitride having good thermal conductivity, it is possible to maintain the insulating properties at the alumina nitride level while maintaining the electromagnetic wave absorption characteristics, and to further increase the thermal conductivity.

  The surface of the composite particles was coated with aluminum nitride by sputtering. As a result, the thickness of the aluminum nitride coating layer was 0.5 μm or more. By providing the aluminum nitride layer, the thermal conductivity of the composite particles could be further increased. The electromagnetic wave absorption characteristics were maintained. As in Example 3, it seems effective to change the coating layer around the composite particles to aluminum nitride particles, and kneading with a solid resin is also possible. Further, the inorganic oxide powder constituting the composite particles can be used by changing to aluminum nitride particles.

  Aluminum nitride has a lower insulating property and higher thermal conductivity than silica. Therefore, when used by kneading with a resin, a composite material of a resin and a filler having a lower insulating property and a higher thermal conductivity can be formed. Moreover, it can use for adjustment of insulation and heat conductivity by using together with a silica.

(Comparative Example 1)
An example of adding composite particles and copper powder as the third element for the purpose of improving thermal conductivity is shown. These composite fillers were kneaded with a solid resin.

  FIG. 12 shows the results of FIB microsampling and TEM observation of single particles when composite particles are synthesized by the MA method. The ternary composite particles showed a completely different form from the binary composite particles of the soft magnetic metal and the inorganic oxide. That is, the third element, copper, was kneaded with the soft magnetic metal and integrated, and contained silica powder. Therefore, since it has metal-level thermal conductivity and conductivity, insulation cannot be obtained.

  Thus, in the filler containing the composite particles having a shape in which the inorganic oxide particles are covered with a metal, the insulating properties when kneaded with the resin cannot be obtained.

  The filler of the present invention can be mixed with a resin composition and used to produce a resin molded product such as an electromagnetic wave absorber having high insulation.

Claims (13)

  A composite filler for resin mixing comprising composite particles containing two types of inorganic oxide powder and metal powder, and a coating layer containing an inorganic oxide covering the composite particles, wherein the metal powder has an aspect ratio of 5 A composite filler for resin mixing, wherein the composite particles have the structure in which the inorganic oxide powder and the reduced iron powder are laminated.   The composite filler for resin mixing according to claim 1, wherein the inorganic oxide powder is silica.   The composite filler for resin mixing according to claim 1, wherein the coating layer is a silica particle layer or a silica film layer.   The composite filler for resin mixing according to claim 1, wherein the composite filler for resin mixing is an aggregate of particles having at least two peaks in the particle size distribution, and two of the particle size distributions. The composite filler for resin mixing, wherein the peaks are 0.5 to 5 μm and 10 to 40 μm.   A composite filler for resin mixing composed of composite particles containing two types of silica powder and metal powder, and silica particles containing silica, wherein the composite particles have a structure in which the silica powder and metal powder are laminated. The metal powder is a plate-like reduced iron powder having an aspect ratio of 5 or more, and the composite filler for resin mixing is an aggregate of particles having two peaks in the particle size distribution. For resin mixing, wherein the peak size ratio is 5 or more, and the smaller one of the two peaks of the particle size distribution is mainly composed of the silica particles, and the larger one is mainly composed of the composite particles. Composite filler.   The composite filler for resin mixing according to claim 5, wherein the silica particles and the silica powder have an average particle size of 5 μm or less, and the composite particles have an average particle size of 10 to 40 μm. Composite filler for resin mixing.   6. The composite filler for resin mixing according to claim 5, wherein a component ratio of the composite filler for resin mixing is 45 to 70 mol% of silica and 30 to 55 mol% of metal.   The composite filler for resin mixing according to claim 5, wherein the composite filler for resin mixing has a silica molar ratio larger than that of metal.   6. The composite filler for resin mixing according to claim 5, wherein the metal powder contains iron as a main component, and the component ratio of the composite filler for resin mixing is 20 to 50% by weight of silica and 50 to 80% by weight of iron. There is a composite filler for resin mixing.   The composite filler for resin mixing according to claim 5, wherein the silica powder or the silica particles are replaced with alumina nitride powder or alumina nitride particles. A resin composite material comprising the composite filler for resin mixing according to any one of claims 1 to 10 and a resin composition, wherein the volume resistivity of the resin composite material is 10 ¹³ Ωcm or more. Resin composite material.   The resin composite material according to claim 11, wherein the resin is an epoxy resin, and the thermal conductivity of the resin composite material is 1.2 W / m · K or more.   A method for producing a filler for an electromagnetic wave absorber comprising composite particles comprising metal particles and inorganic oxide particles attached to the surface of the metal particles, wherein the metal particles are reduced iron powder, and the inorganic oxide An average major axis of the particles is 1/10 or less of an average major axis of the metal particles, and a part of the inorganic oxide is embedded in the metal particles by an external stimulus.

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