JP5229526B2 - Magnetic ultrafine particles and method for producing the same - Google Patents

Description

  The present invention relates to magnetic iron ultrafine particles, a method for producing the same, and a composite material, magnetic recording material, electromagnetic wave absorber, and biological material extraction carrier using magnetic iron ultrafine particles.

  Metallic magnetic powder made of magnetic metal particles extracts magnetic powder for magnetic recording, electromagnetic wave absorber powder for absorbing electromagnetic waves that cause noise, and biological materials such as nucleic acids, protein components, and cells. It is used as a carrier. Composite materials combining magnetic metal particles and other materials are used as electromagnetic wave absorber materials. The description will be divided into three parts: magnetic powder for magnetic recording, electromagnetic wave absorber material, and carrier.

  First, magnetic powder for magnetic recording is used in recording media used in audio devices, video devices, computer devices, and the like. As the recording medium, a magnetic coating prepared by dispersing and kneading magnetic powder, binders and various additives in an organic solvent and applying the coating onto a nonmagnetic support and drying to form a magnetic layer is a so-called coating type. Magnetic recording media are dominant because of their excellent productivity and versatility. In the various magnetic recording / reproducing apparatuses described above, in recent years, miniaturization and weight reduction, higher image quality, and longer time have been promoted, and accordingly, high-density recording has also been achieved for the coating type magnetic recording medium. It has come to be requested.

  In order to improve the characteristics in the high-density recording region of the coating type magnetic recording medium, it is important to first select a magnetic powder having a large saturation magnetization. Therefore, instead of the conventionally used iron oxide magnetic powder, a metal magnetic powder containing iron as a main component is used as a magnetic powder to be contained in the magnetic layer.

  However, the fine metal magnetic powder containing iron as a main component may not only deteriorate characteristics but also cause a serious accident if it comes into contact with oxygen in the air. In so-called nanoparticles, such a risk is remarkable, and the same applies to metal magnetic powders composed of particles having the most excellent magnetic properties and an average particle diameter of 20 nm to 100 nm.

  Therefore, a method of providing an iron oxide layer on the surface layer by gradually oxidizing metal magnetic powder with a gas having a low oxygen concentration has been proposed and widely used (for example, see Patent Document 1).

  Next, powders for electromagnetic wave absorbers, composite materials in which magnetic metal particles are combined with other materials, and composite materials in which magnetic metal particles are combined with other materials are used as electromagnetic wave absorbers. In various electronic devices, various electromagnetic wave absorbers have been put into practical use for the purpose of preventing the influence of external electromagnetic waves or suppressing the emission of external electromagnetic waves. One of the most prominent types is one in which a magnetic metal powder mainly composed of iron is dispersed in a resin and formed into a sheet or other shape. The magnetic metal powder mainly composed of iron includes atomization, that is, metal powder obtained by atomizing a molten metal with water or gas by an atomization method of about 50 μm, and metal powder of about several millimeters obtained by mechanically cutting a metal lump. Is used.

  In recent years, electronic devices and information devices such as personal computers and mobile phones have been rapidly spread and developed, and thin, light and high performance are required, and an electromagnetic wave absorber that can be used in the GHz range is required. However, the above-mentioned magnetic iron particles having a size of several tens of μm or more, or an oxide having a size of several hundreds of nm to several tens of μm and an average particle size having the most excellent magnetic properties of 20 nm to 100 nm. Iron fine particles do not achieve the required electromagnetic wave absorption characteristics.

  The electromagnetic wave absorption characteristics are governed by the permeability value, and the permeability value is governed by the saturation magnetization. When the oxidation resistance is low, the saturation magnetization and the magnetic permeability are lowered. Therefore, iron alloy fine particles containing silicon have been proposed as a method for improving oxidation resistance (see, for example, Patent Document 2). Further, fine particles in which iron fine particle nuclei are coated with an iron nitride layer have been proposed (see, for example, Patent Document 3). In addition, fine particles in which iron fine particles are coated with magnetic spinel ferrite (iron oxide) have been proposed (see, for example, Patent Document 4).

  In order to make it possible to apply iron-based particle powders to electromagnetic wave absorbers, not only increase the saturation magnetization and magnetic permeability of the raw material powder used but also improve oxidation resistance, It is also important to make a resin composite material having a high particle concentration while maintaining insulation. This is because an electromagnetic wave absorber having a high particle concentration has a high electromagnetic wave absorption effect. On the other hand, metal magnetic powder generally has a low specific resistance, so when the particle concentration becomes high, the particles come into contact with each other, the eddy current loss increases, the electromagnetic wave absorption effect decreases, and the noise suppression characteristics deteriorate. End up. In addition, if a resin composite material in which the particles constituting the metal magnetic powder come into contact with each other is placed on an electronic circuit or the like, a problem such as a short circuit occurs, so that electrical insulation is maintained. is important.

  In order to increase the specific resistance, it has been proposed to coat the surface of the metal magnetic powder with ferrite, which is a magnetic iron oxide. This also leads to an improvement in oxidation resistance (see, for example, Patent Document 4). Further, iron powder having a size of 0.1 μm to 10 μm was previously mixed with ceramic powder and resin to form secondary particles coated with an insulating material, and then the particles and resin were mixed and formed. It is a composite material with a resin, and a material containing 29 to 52% by volume of iron has been proposed (see, for example, Patent Document 5). Excellent magnetic properties are realized by dispersing the particles at a high particle concentration in the resin.

  Next, carriers for extracting biological substances such as nucleic acids, protein components, and cells are used to efficiently isolate biological substances from materials containing biological substances. For example, as a diagnostic agent carrier, cell separation carrier, nucleic acid separation carrier, immobilized enzyme carrier used for extracting and purifying nucleic acid from a specimen, sample, or material containing nucleic acid, or purifying a nucleic acid amplification product, Magnetic fine particles are used. A biological material such as a nucleic acid, a protein component, or a cell is adsorbed on the surface of the magnetic fine particle, and then the biological material is collected and dispersed by using a magnetic force.

Proposals of biomaterial extraction carriers include those using superparamagnetic metal oxides as magnetic fine particles (see, for example, Patent Document 6), and those using carbonyl iron with higher magnetic force (for example, see Patent Document 7). Has been. Further, in order to bind diffusion in the biological sample to the surface of the magnetic fine particle, it is necessary to cover the surface with a material that can bind to nucleic acid. Silicon oxide is suitable as the surface coating material, and as the coating method, a silicon alkoxide is used, and a plurality of multi-domains are formed in silica particles having a specific surface area of 0.1 m ² / g or more and less than 100 m ² / g. A method of containing core fine particles of metal or metal oxide has been proposed (see, for example, Patent Document 8). In addition, a surface modification layer containing the magnetic metal and silicon is provided on the magnetic metal fine particles by surface modification using a silane coupling agent in an organic solvent, and the surface modification layer is formed using a silicon alkoxide. A method of coating with silicon oxide has been proposed (see, for example, Patent Document 9).

JP-A-9-302404 (Claims 1 to 4) JP 2002-158482 A (Claim 1) JP 2001-308582 A (Claim 1) JP 2005-268363 A (Claim 2) JP 2004-143347 A (0042 paragraph) JP 2001-78761 A (Claim 1) JP 2004-135678 A (paragraph 0014) JP 2000-256388 (paragraph 0022) JP 2006-249528 A (paragraph 0005)

  However, in the oxidation protective film layer composed of iron oxide described in Patent Document 1, when ultrafine particles having a nanoparticle size are used, if the oxygen in the air is touched even at room temperature, the oxidation progresses and the magnetic field is increased. There was a problem that the characteristics deteriorated. Further, even in the methods proposed in Patent Documents 2, 3 and 4, when ultrafine particles are used, the oxidation resistance is not sufficient, and if the oxygen in the air is touched at room temperature, the oxidation progresses and the magnetic properties are improved. There was a problem of deterioration. In other words, the methods for improving oxidation resistance disclosed in Patent Documents 1, 2, 3, and 4 are not dense films, so that when they come into contact with oxygen in the air at room temperature, they do not cause deterioration of magnetic properties. It has not yet been achieved.

  Furthermore, the methods proposed in Patent Documents 4 and 5 do not provide a composite material of magnetic iron ultrafine particles having a high particle concentration and a resin. In addition, ultrafine particles with a particle size smaller than that of submicron-sized particles, when the amount exceeds approximately 5% by volume, the interparticle attractive force becomes extremely large, which makes it very easy to agglomerate, making it difficult to control the aggregation / dispersion behavior. However, there is a problem that it is very difficult to uniformly disperse and dispose the fine particles at a high particle concentration in the resin. With oxides such as iron oxide having a hydrophilic surface, it is possible to disperse and arrange even ultrafine particles even to some extent in recent years by adsorbing organic polymers and modifying the surface. However, since the surface of ultrafine particles of metal such as pure iron is hydrophobic, the above method is not effective, and no method for uniformly dispersing and arranging it has been found.

  In the method proposed in Patent Document 8, when pure metal fine particles are used as core fine particles, the surface of the pure metal fine particles is hydrophobic and therefore does not adsorb hydrophilic silicon oxide. It is extremely difficult to control and coat the oxide. In the scope of research conducted by the inventors using ultrafine particles, in pure metal ultrafine particles, even if silicon alkoxide is used, in the state where no surface modification is performed, pure metal ultrafine particles are used as core fine particles to form silicon oxide. Silica particles provided with a controlled coating could not be obtained. With magnetic metal oxide fine particles having a hydrophilic surface, it is possible to apply a silicon oxide coating with controlled thickness and uniformity by this proposed method, but the magnetic properties are inferior to magnetic metal ultrafine particles. There was a problem.

  In the ultrafine particles, the technique proposed in Patent Document 9 has a layer containing the metal and Si on the surface constituted by the hydrophobicity of the metal fine particle nucleus, and a silicon oxide layer is provided thereon. However, there is a problem that it is not easy to control and install the silicon oxide layer. It is known that the so-called nano-particle level ultrafine particles having a size of 100 nm or less and the microparticles having a size of several μm have completely different surface characteristics. Of course, the difficulty of handling in the process also differs. Since the silane coupling agent does not sufficiently adsorb on the hydrophobic surface, even when the surface is modified with the silane coupling agent, especially at the nanoparticle level, the thickness and uniformity of the silicon alkoxide are subsequently increased. It has been found by the inventors' research that it is difficult to coat silicon oxide with no deterioration in magnetic properties even when it is in contact with oxygen in the air. As described above, in the conventionally proposed technology, the silicon oxide having excellent oxidation characteristics and the finest ultrafine metal particles mainly composed of iron, which is excellent in magnetic characteristics, and which is dense and controlled in thickness and uniformity. Has not been successfully coated.

  As an electromagnetic wave absorber, it is necessary to maintain a high specific resistance, thus maintaining high electrical insulation, and to disperse magnetic metal fine particles uniformly in the resin at a high particle concentration, and there is no crack. However, in the conventional method of applying a paint in which magnetic metal fine particles are dispersed in an organic solvent or the method disclosed in Patent Document 5, the electrical insulation is maintained at a high particle concentration. A composite material in which particles are uniformly dispersed in a resin cannot be obtained. In addition, cracks and pores are likely to occur.

  The present invention has been made in view of such conventional problems. A first object of the present invention is to provide magnetic iron ultrafine particles having high saturation magnetization and high oxidation resistance. A second object of the present invention is to provide a method for producing magnetic iron ultrafine particles capable of producing ultrafine particles mainly composed of iron having high oxidation resistance and high magnetic properties.

  A third object of the present invention is to provide a composite material of magnetic iron ultrafine particles and a resin that maintains electrical insulation, has excellent magnetic properties, and has a high electromagnetic wave absorption effect. A fourth object of the present invention is to provide a composite material manufacturing method capable of manufacturing a composite material that maintains electrical insulation, is excellent in magnetic characteristics, and has a high electromagnetic wave absorption effect.

  A fifth object of the present invention is to provide a magnetic recording body that has excellent magnetic characteristics and enables high density recording. A sixth object of the present invention is to provide an electromagnetic wave absorber that has a high electromagnetic wave absorption effect and can be used in the GHz range. A seventh object of the present invention is to provide a biological substance extraction carrier that has excellent magnetic properties and can perform a nucleic acid magnetic separation operation in a short time.

In order to achieve the first object, the first aspect of the present invention comprises an ultrafine particle nucleus mainly composed of iron, an iron oxide layer formed on the surface of the ultrafine particle nucleus, and an alkoxide of silicon. Magnetic iron ultrafine particles formed of silicon oxide chemically deposited by hydrolysis reaction and comprising a silicon oxide layer covering the iron oxide layer are heated at 400 ° C. to 600 ° C. in an atmosphere containing hydrogen gas. Magnetic iron ultrafine particles obtained by heat treatment below, comprising ultrafine particle nuclei mainly composed of iron and a silicon oxide layer covering the ultrafine particle nuclei, wherein the ultrafine particle nuclei have a major axis of 100 nm. The acicular particles having a short axis of 20 nm or more and 50 nm or less and a short axis of 500 nm or less, or the ultrafine particle nuclei are particles other than acicular particles, and the average particle diameter is 20 nm or more and 100 nm or less, and the silicon The thickness of the oxide layer is 1n Providing magnetic iron ultrafine particles, characterized in der Rukoto than 10nm or less. In the present application, ultrafine particles refer to particles having a minor axis length of nano-size (1 nm or more and 100 nm or less) in the case of acicular particles, and in the case of other than acicular particles, the average particle diameter is nano-size (1 nm). Or more than 100 nm).

The nanoparticle nuclei, or minor axis in the long axis is 100nm or 500nm or less is acicular particles is 20nm or more 50nm or less, or the nanoparticle nuclei, a grain other than acicular, average particle diameter If it is 20nm or 100nm or less, it shows a high saturation magnetization and magnetic permeability. An average particle size of less than 20 nm is not preferable because it becomes superparamagnetic and loses magnetic properties. If the average particle size is larger than 100 nm, the magnetic properties are not sufficient. Spherical nanoparticles or acicular nanoparticles exhibiting magnetic anisotropy are suitable as magnetic powders used as magnetic recording materials, electromagnetic wave absorbers, and biological separation carriers. In particular, it is considered that the magnetic powder for magnetic recording material is most preferably spherical ultrafine particles having an average particle diameter of 20 nm or more and 100 nm or less and containing iron as a main component.

  According to the first aspect of the present invention, the saturation magnetization is high and the oxidation resistance is high. Therefore, the first aspect of the present invention is suitable as a magnetic powder for magnetic recording. Moreover, it is suitable as an electromagnetic wave absorber powder for absorbing electromagnetic waves that cause noise and the like. Moreover, it is suitable as a carrier for extracting biological substances such as nucleic acids, protein components and cells.

The second aspect of the present invention is the method for producing magnetic iron ultrafine particles according to the first aspect of the present invention described above, in order to achieve the second object, wherein the ultrafine particles are mainly composed of iron. Slow oxidation of the nuclei to form an iron oxide layer on the surface of the ultrafine particle nuclei, a step of dispersing in an organic solvent, and a silicon oxide chemically deposited by a hydrolysis reaction of silicon alkoxide step of the covering of the iron oxide layer of a silicon oxide layer, in an atmosphere containing hydrogen gas, characterized by the step of reducing the iron oxide layer was heat-treated at 400 ° C. or higher 600 ° C. or less A method for producing magnetic iron ultrafine particles is provided . According to the second aspect of the present invention, it is possible to produce ultrafine particles mainly composed of iron having high oxidation resistance and high magnetic properties. Also, magnetic iron ultrafine particles can be produced safely by preventing rapid oxidation reaction.

  According to a third aspect of the present invention, there is provided a composite material of magnetic iron ultrafine particles and a resin for achieving the third object, wherein the magnetic iron ultrafine particles of the first aspect of the present invention described above are combined. Provided is a composite material characterized in that it is a particle in which a resin monomer is adsorbed on the surface and further graft-polymerized to coat the resin. Furthermore, the composite material is preferably molded by heating in pressure.

  According to a fourth aspect of the present invention, there is provided a method for producing a composite material of magnetic iron ultrafine particles and a resin in order to achieve the fourth object, wherein the magnetic iron according to the first aspect of the present invention described above. A step of hydrophobizing magnetic iron ultrafine particles, which are particles obtained by adsorbing resin monomers on the surface of the ultrafine particles and further graft-polymerizing and coating the resin with a silane coupling agent, and resin on the surface of the magnetic iron ultrafine particles A method for producing a composite material, comprising the steps of adsorbing the monomer and further carrying out a resin coating by graft polymerization.

  It is preferable that the above-described composite material manufacturing method further includes a step of heating and molding in pressurization after coating the resin. According to such a method, it is possible to disperse magnetic metal fine particles having high magnetic properties in a resin at a high particle concentration without cracks and pores while maintaining a high specific resistance.

  In addition, the fifth aspect of the present invention includes a magnetic layer formed by applying the magnetic paint containing the magnetic iron ultrafine particles of the first aspect of the present invention described above in order to achieve the fifth object. There is provided a magnetic recording medium characterized by the above. According to the fifth aspect of the present invention, it has extremely effective insulation.

  In order to achieve the sixth object, the sixth aspect of the present invention is a composite material of the magnetic iron ultrafine particles of the first aspect of the present invention described above or the particles of the third aspect of the present invention described above. An electromagnetic wave absorber characterized in that is dispersed in an insulating substrate. It may be composed of the molded composite material of the third aspect of the present invention described above.

Further, a seventh aspect of the present invention is characterized in that, in order to achieve the seventh object, the magnetic iron ultrafine particles of the first aspect of the present invention described above are contained and nucleic acid is extracted. A biological substance extraction carrier is provided.

  According to the magnetic iron ultrafine particles of the present invention, the saturation magnetization is high and the oxidation resistance is high. Further, according to the method for producing magnetic iron ultrafine particles of the present invention, ultrafine particles mainly composed of iron having high oxidation resistance and high magnetic properties can be produced.

  According to the composite material of the present invention, the electrical insulation is maintained, the magnetic characteristics are excellent, and the electromagnetic wave absorption effect is high. Moreover, according to the composite material manufacturing method of the present invention, it is possible to manufacture a composite material that maintains electrical insulation, is excellent in magnetic characteristics, and has a high electromagnetic wave absorption effect.

  Also, the magnetic recording material of the present invention has excellent magnetic characteristics and enables high density recording. Moreover, according to the electromagnetic wave absorber of the present invention, the electromagnetic wave absorption effect is high, and the use in the GHz region is possible. Moreover, according to the biological substance extraction carrier of the present invention, it is excellent in magnetic properties and enables nucleic acid magnetic separation operation to be performed in a short time.

<Magnetic iron ultrafine particles>
FIG. 1 is a schematic view showing a first embodiment of magnetic iron ultrafine particles of the present invention. The magnetic iron ultrafine particles shown in FIG. 1 are composed of an ultrafine particle nucleus 1 containing iron as a main component, an iron oxide layer 2 covering the core, and a silicon oxide layer 3 covering the core. FIG. 2 is a schematic view showing a second embodiment of the magnetic iron ultrafine particles of the present invention. The magnetic iron ultrafine particles shown in FIG. 2 are composed of an ultrafine particle nucleus 1 mainly composed of iron and a silicon oxide layer 3 covering the ultrafine particle nucleus 1. In the second embodiment of the magnetic iron ultrafine particles of the present invention, the magnetic properties and oxidation resistance properties are further improved as compared to the first embodiment.

  The magnetic iron ultrafine particles of the first embodiment of the present invention include metal ultrafine particle nuclei mainly composed of iron, an iron oxide film layer formed on the surface thereof, and a silicon oxide covering the iron oxide film layer. Consists of layers. Alternatively, the magnetic iron ultrafine particles are composed of metal ultrafine particle nuclei containing iron as a main component by a reduction heat treatment in an atmosphere containing hydrogen gas, and a silicon oxide layer whose surface is densely coated. The ultrafine metal particle core containing iron as a main component may contain cobalt (Co), nickel (Ni), or the like. In particular, an iron alloy containing Co is more preferable because it exhibits high saturation magnetization. High saturation magnetization is effective as a magnetic powder for carriers that extract magnetic recording materials and biological substances, and high saturation magnetization and magnetic permeability are effective as magnetic powder for electromagnetic wave absorbers.

  The electromagnetic wave absorber can take in electromagnetic energy into the absorber and convert it into heat energy for consumption. In order to obtain a high absorption effect in the vicinity of a substrate in an electronic device, one having a high complex permeability loss at a high frequency is suitable. For high-frequency magnetic fields extending to several GHz, it is said that the magnetization rotation dominates the value of magnetic permeability, and according to this assumption, those with high saturation magnetization have high magnetic permeability. The saturation magnetization is larger for metals such as iron and cobalt compared to iron oxide-based materials such as ferrite. In particular, iron is known to have high saturation magnetization. However, in the case of metal, since the electrical resistance is low, most of the high-frequency magnetic field does not function effectively as a magnetic material due to the skin effect caused by eddy currents. The oxide particles were larger than the particles. Therefore, metal particles have been considered unsuitable as an electromagnetic wave absorber material. Therefore, in order to obtain an electrical insulation state between iron particles, a structure that is uniformly dispersed in a resin has been proposed. However, in the magnetic iron ultrafine particles of the first embodiment of the present invention, since the surface of the magnetic iron ultrafine particles is coated with silicon oxide, no eddy current is generated even in a high-frequency magnetic field, and thus the saturation magnetization is high. The thing fits the theory that the permeability increases. Since the magnetic iron ultrafine particles of the first embodiment of the present invention have a high saturation magnetization value, the magnetic permeability is also high.

As the metal ultrafine particle nucleus mainly composed of iron, vapor phase synthesis in which carbonyl iron or iron oxide is reduced at a high temperature can be obtained. Of course, it may be a commercial product. The size of ultrafine particles as a main component the above iron, if the form of particles of acicular, ranging the long axis is less than 5 nm or more 1 nm, a minor axis of 50nm or less in the range above 20 nm, the form of particles In the case other than the needle shape, the average particle diameter is preferably in the range of 20 nm to 100 nm. In order to show higher saturation magnetization and magnetic permeability, the size of the ultrafine particles is set in the above range. The form of the ultrafine particles may be acicular or spherical. The recording material is more preferably an acicular shape exhibiting magnetic anisotropy, and the electromagnetic wave absorber and the biological separation carrier are more preferably spherical particles.

  The surface modified layer of this embodiment is formed by a method by slow oxidation of ultrafine metal particles containing iron as a main component. As a result, there is no danger of burning due to a rapid oxidation reaction during handling in the process. This surface modification layer is indispensable for coating silicon oxide with silicon alkoxide. The hydrophilic group formed by the hydrolysis reaction of silicon alkoxide can be adsorbed because it is a hydrophilic surface of iron oxide, and the surface cannot be adsorbed to ultrafine metal particles having hydrophobic properties.

  The iron oxide layer formed by gradual oxidation is preferably in the range of 1 nm to 10 nm. If the surface iron oxide layer is smaller than 1 nm, the hydrophilicity of the surface cannot be said to be sufficient, and stable coating of silicon oxide becomes difficult, and as a result, it is difficult to control the thickness and uniformity of the silicon oxide coating. End up. If the surface modification layer is larger than 10 nm, the ratio of iron oxide is increased, so that magnetic properties such as saturation magnetization and permeability are inferior.

  The silicon oxide layer covering the iron oxide layer is preferably in the range of 1 nm to 10 nm. If the silicon oxide coating layer has a thickness of 10 nm or more, the magnetic properties are deteriorated, which is not preferable. If it is 1 nm or less, the oxidation resistance is not sufficient, which is not preferable.

  In the first embodiment of the magnetic iron ultrafine particles of the present invention, a step of gradually oxidizing an ultrafine particle nucleus mainly composed of iron to form an iron oxide layer on the surface of the ultrafine particle nucleus (gradual oxidation step), By sequentially performing each step of dispersing in an organic solvent (dispersing step) and covering the surface iron oxide layer with a silicon oxide layer by a hydrolysis reaction of silicon alkoxide (silicon oxide coating step) Can be manufactured.

  The magnetic iron ultrafine particles of the present invention comprising the ultrafine particle nuclei and the silicon oxide layer covering the ultrafine particle nuclei obtained by heat-treating the magnetic iron ultrafine particles of the first embodiment of the present invention described above. In the second embodiment, the iron oxide layer is subjected to heat treatment at 400 ° C. or more and 600 ° C. or less in an atmosphere containing hydrogen gas after sequentially performing the gradual oxidation step, the dispersion step, and the silicon oxide coating step. Can be manufactured by performing a step of reducing (reduction step).

(Slow oxidation step)
Slow oxidation is achieved by a method of leaving at room temperature using a neutral gas or a reducing gas containing a small amount of oxygen. Control of the thickness of the surface oxide layer can be achieved by changing the standing time. After the predetermined iron oxide layer is formed, it is preferable to quickly hold and store in a vacuum, a reducing gas or a neutral gas stream. When left in the air, even if the ultrafine metal particles are provided with an iron oxide layer by gradual oxidation, the oxidation gradually proceeds until all of them become oxides. The iron oxide layer formed on this surface is distinguished from ultrafine particle nuclei containing iron as a main component with contrast by observation with a transmission electron microscope.

(Distributed step)
The ultrafine metal particles mainly composed of iron on which an iron oxide layer is formed by slow oxidation are loosened and dispersed in an organic solvent such as alcohol, and then coated with silicon oxide. This dispersion process is important because if it is not highly dispersed, the particles are adhered to each other and silicon oxide is coated in a state where the particles are adhered to each other, so that magnetic properties such as saturation magnetization and magnetic permeability are deteriorated. Since the silicon oxide coating is achieved by a hydrolysis reaction of silicon alkoxide, the dispersion medium is preferably an alcohol. Examples of the alcohol solution include lower alcohols such as ethanol, methanol, and isopropyl alcohol. In a highly dispersed state, a fatty acid such as oleic acid or stearic acid is added as a dispersing agent in an amount of 1.0 mg / m ² or more and 5.0 mg / m ² or less per iron ultrafine particle surface area, and a frequency of 20 KHz, 1200 W. Can be obtained by irradiating the above ultrasonic wave in water cooling for 30 minutes or more, or by performing a bead mill treatment with a bead diameter of 50 μm and a peripheral speed of 8 m / s or more for 1 hour or more. In any of the dispersion methods, it is necessary to handle ultrafine particles in a non-oxidizing atmosphere.

(Silicon oxide coating step)
Ultrafine particle nuclei containing iron as a main component and having iron oxide formed on a surface highly dispersed in alcohol can be coated with silicon oxide by hydrolysis reaction using silicon alkoxide. Specific examples of silicon alkoxides include tetramethoxysilane, tetraethoxysilane, tetraproxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, tetrapropoxysilane, and phenyltriethoxy. Silane is suitable.

A method for forming a silicon oxide coating layer will be described by taking tetraethoxysilane as an example. By adding tetraethoxysilane, ammonia and water to the ultrafine particles mainly composed of iron in which the iron oxide layer is formed on the surface by slow oxidation, which is highly dispersed in the above-mentioned alcohol, for example, ethanol A silicon oxide coating layer can be formed. Iron ultrafine particles with a total surface area of 15 to 30 m ² per liter of ethanol are suitable. When ultrafine particles having a total surface area of 30 m ² or more are added, a silicon oxide coating layer is formed while the iron ultrafine particles are aggregated. Any amount of 15 m ² or less may be used, but it is not preferable because efficiency is deteriorated. Tetraethoxysilane is added in an amount necessary for forming a silicon oxide coating layer of 1 nm to 10 nm on the surface layer of ultrafine particles. Regarding the addition amount of water, it is preferable that the addition amount of water is 2 mol or more with respect to 1 mol of tetraethoxysilane. The amount of ammonia added is preferably 10 to 100 parts by weight with respect to 100 parts by weight of tetraethoxysilane when, for example, the concentration of ammonia water is 28%. When the amount is 10 parts by weight or less, the effect as a catalyst is not sufficiently exhibited. When the amount is 100 parts by weight or more, spherical particles isolated from silicon oxide are formed, and thus the above range is preferable. The hydrolysis reaction can be obtained, for example, by stirring for 24 hours using a rotary spring of 300 rpm to 500 rpm. The thickness of the silicon oxide layer can be determined from the contrast obtained by observation with a transmission electron microscope. However, since the layer determined by contrast is a layer in which the silicon oxide layer and the iron oxide layer are combined, it is necessary to determine the thickness of the iron oxide layer in advance. The silicon oxide layer can be confirmed by elemental analysis by energy dispersive X-ray fluorescence analysis and detection of silicon and oxygen. The average particle size is desirably determined by image analysis of about 1000 particles by electron microscope observation.

(Reduction step)
Furthermore, in order to improve the magnetic properties and the oxidation resistance properties, the iron ultrafine particle nucleus containing iron as a main component, the iron oxide layer formed on the surface of the ultrafine particle nucleus, and the surface It is desirable to heat-treat magnetic iron ultrafine particles composed of a silicon oxide layer covering the iron oxide layer in a range of 400 ° C. to 600 ° C. in an atmosphere containing hydrogen gas. Examples of the gas containing hydrogen gas include a mixed gas of 4% hydrogen and 96% nitrogen. If the heat treatment is performed at 500 ° C., the iron oxide layer is completely reduced after the treatment for 5 hours. become. Furthermore, the silicon oxide layer can be densified to significantly reduce the oxygen diffusivity.

(Hydrophobicization step)
Alcohol alone may be used, but it is more preferable to add water in order to promote the hydrolysis reaction. Examples of the alcohol include lower alcohols such as ethanol, methanol, and isopropyl alcohol. As the silane coupling agent, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2- (3,4-epoxycyclohexylethyltrimethoxysilane), 3-glycidoxypropyltrimethoxysilane, 3- Glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylyoriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyl Diethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2- (aminoethyl) -3-aminopropylmethyldimethoxysilane, N-2- (aminoethyl) 3-aminopropyltrimethoxysilane, N-2- (aminoethyl) -3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N- ( 1,3-dimethyl-butylidene) propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N- (vinylbenzyl) -2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, and the like. The addition amount of the silane coupling agent is preferably 20% by weight to 40% by weight with respect to the magnetic ultrafine particles. When the amount is less than 20% by weight, the surface hydrophobization treatment of the ultrafine particles cannot be sufficiently performed.

  After adding the silane coupling agent, the mixture is first mixed and stirred for 30 minutes using a stirring spring of 300 rpm to 500 rpm, and further mixed for 60 minutes in the range of 60 ° C. to 90 ° C. using a planetary ball mill using zirconia balls. . More preferably, 80 ° C to 90 ° C is suitable. By setting the temperature within this range, the hydrolysis reaction can be promoted. By this treatment, the surface is hydrophobized, and ultrafine particles mainly composed of iron dispersed in alcohol are precipitated. This is because the surface is hydrophobized. This precipitate is washed several times with ethanol to obtain ultrafine particles that have been subjected to a hydrophobic treatment.

(Resin coating step)
1 to 5 parts by weight of ultrafine particles mainly composed of hydrophobically-treated iron prepared as described above, 100 parts by weight of ethanol and 0.5 to 1.0 parts by weight of an initiator such as advisonitrile, In addition, one of the monomers of the resin such as methyl methacrylate (MMA), styrene, epoxy resin, phenol resin, urethane resin, for example, 5 to 15 parts by weight of methyl methacrylate (MMA) that is a monomer of methacrylic resin. Part is added to adsorb MMA on the surface of the ultrafine particles.

  The ultrafine particles having MMA adsorbed on the surface are further stirred in nitrogen in the range of 300 rpm to 500 rpm at 65 ° C. for 24 hours using a stirring spring to graft polymerize the resin monomers. When the amount of ultrafine particles is less than 1 part by weight, the efficiency is poor, and when it exceeds 5 parts by weight, the above range is preferable because the ultrafine particles are aggregated. If the initiator is less than 0.5 parts by weight, a sufficient effect cannot be achieved, and if it exceeds 5 parts by weight, an unnecessary initiator remains. If the addition amount of the resin monomer is less than 5 parts by weight, the resin component is small, and cracking occurs during the heat molding described later, and if it exceeds 15 parts by weight, a composite material with a resin having a high particle concentration cannot be obtained. . Ultrafine particles mainly composed of iron grafted with a resin monomer are washed several times with toluene, and then dried in air at 100 ° C. for 24 hours. It is possible to obtain a composite material that is an ultrafine particle.

(Molding step)
Furthermore, it is desirable to manufacture a composite material with a resin containing ultrafine metal particles having a high particle concentration by forming the composite material by heating in pressure. The first embodiment of the composite material of the present invention is uniaxially pressed at 150 ° C., for example.

<Magnetic recording material>
The magnetic recording body of the present invention preferably contains a magnetic layer formed by applying a magnetic paint containing the magnetic iron ultrafine particles of the first embodiment of the present invention. More preferably, the magnetic iron ultrafine particles contained are needle-shaped magnetic iron ultrafine particles. The magnetic recording body of the present invention further preferably includes a magnetic layer formed by applying a magnetic paint containing the magnetic iron ultrafine particles of the second embodiment of the present invention.

<Electromagnetic wave absorber>
The electromagnetic wave absorber of the present invention is an insulating material of the magnetic iron ultrafine particles of the first embodiment of the present invention, the magnetic iron ultrafine particles of the second embodiment, or the composite material of the first embodiment of the present invention. It is preferable that the base material is dispersed and contained. Or it consists of the composite material of the 2nd Embodiment of this invention. The magnetic iron ultrafine particles are more preferably spherical magnetic iron ultrafine particles having an average particle diameter of 20 nm to 50 nm. By molding such an electromagnetic wave absorber into various shapes, it is effective as a member used for mobile phones, wireless LANs, automatic highway billing, in-vehicle short-range radar, satellite broadcasting, and the like.

<Biological substance extraction carrier>
The biological material extraction carrier of the present invention preferably contains the magnetic iron ultrafine particles of the first embodiment of the present invention or the magnetic iron ultrafine particles of the second embodiment, and extracts nucleic acid. The magnetic iron ultrafine particles are more preferably spherical magnetic iron ultrafine particles having an average particle diameter of 20 nm to 50 nm.

  Hereinafter, the magnetic iron ultrafine particles of the present invention and the production method thereof, and the composite material, magnetic recording material, and biological substance extraction carrier using the magnetic iron ultrafine particles will be described in detail with reference to examples. Is not limited to these.

[Example 1: Magnetic iron ultrafine particles]
The magnetic iron ultrafine particles of Example 1 of the present invention include ultrafine particle nuclei mainly composed of iron, an iron oxide layer formed on the surface of the ultrafine particle nuclei, and silicon covering the surface iron oxide layer. It consists of an oxide layer. Pure iron needle-like ultrafine particles having a major axis of about 200 nm and a minor axis of about 20 nm were used as starting materials. The starting material has been slowly oxidized. FIG. 3 is a transmission electron micrograph of acicular ultrafine particles containing iron as a main component with iron oxide formed on the surface by gradual oxidation. As shown in FIG. 3, the pure iron needle-shaped ultrafine particles are formed on the surface of the ultrafine particle nuclei mainly formed of iron and the ultrafine particle nuclei by gradual oxidation according to the contrast of observation with a transmission electron microscope. It can be seen that it has a 3 nm iron oxide layer. Furthermore, there were no detection elements other than iron and oxygen by energy dispersive fluorescent X-rays.

As described above, pure iron needle-shaped ultrafine particles having an iron oxide layer formed on the surface thereof are 0.085% by volume with respect to 1 liter of ethanol, and oleic acid as a dispersant is 3.0 mg / per surface area of the ultrafine particles. m ² was added. Dispersion was carried out using a 20 KHz, 1200 W ultrasonic oscillator for 30 minutes in water cooling to obtain a highly dispersed acicular magnetic iron ultrafine particle suspension. Furthermore, 0.015 mol of tetraethoxysilane, 36.5 mol of water, and 1.5 mol of 25% strength ammonia water were added, and the mixture was stirred for 24 hours using a 300 rpm stirring spring to cause a hydrolysis reaction. It was confirmed by observation with a transmission electron microscope that the obtained ultrafine particles were in contrast and the thickness of the silicon oxide coating layer was about 5 nm. Furthermore, it was confirmed by energy dispersive X-ray fluorescence analysis that it was formed of silicon, oxygen and iron. The obtained ultrafine particles were washed with ethanol three times and then vacuum dried at 50 ° C. to obtain magnetic iron ultrafine particles of Example 1 of the present invention. FIG. 4 is a transmission electron micrograph of acicular ultrafine particles mainly composed of iron coated with silicon oxide. FIG. 4 shows the magnetic iron ultrafine particles of Example 1 of the present invention, and the surface composition confirmed by the method by energy dispersive X-ray fluorescence analysis attached to the transmission electron microscope. In addition to iron, silicon and oxygen were detected at both the end (A) and the center (B) of the needle-like particles. The end (A) has less iron than the center (B). This indicates that the outer surface of magnetic iron ultrafine particles, which are core ultrafine particles, is coated with silicon oxide.

[Example 2: Magnetic iron ultrafine particles]
The magnetic iron ultrafine particle of Example 2 of the present invention comprises an iron ultrafine particle nucleus and a silicon oxide layer covering the ultrafine particle nucleus. The magnetic iron ultrafine particles of Example 1 of the present invention were heat-treated at 500 ° C. for 5 hours using a mixed gas of 4% hydrogen and 96% nitrogen to obtain magnetic iron ultrafine particles of Example 2 of the present invention.

[Comparative Example 1: Magnetic iron ultrafine particles]
Pure iron needle ultrafine particles (manufactured by Dowa Mining Co., Ltd.) having a major axis of about 200 nm and a minor axis of about 20 nm on which an iron oxide layer of about 3 nm was formed on the surface were used as magnetic iron ultrafine particles of Comparative Example 1.

[Example 3: Magnetic iron ultrafine particles]
The magnetic iron ultrafine particles of Example 3 of the present invention include ultrafine particle nuclei mainly composed of iron, an iron oxide layer formed on the surface of the ultrafine particle nuclei, and silicon that covers the surface iron oxide layer. It consists of an oxide layer. A 500 ml flask was charged with 80 g of kerosene, 11 g of a surfactant, and 70 g of an Fe (CO) ₅ solution, and oxygen was removed by bubbling with nitrogen gas. Then, it was left for 1 hour at 80 ° C. in a mixed gas stream of high purity ammonia 400 cm ³ / min and nitrogen 40 cm ³ / min. Then, it cooled to room temperature and obtained the pure iron nanoparticle. The particle diameter of the pure iron nanoparticles obtained by the dynamic light scattering method was measured, and it was confirmed that the average particle diameter was 30 nm. The ultrafine particles dispersed in the kerosene were gradually oxidized by treating them at 30 ° C. for 30 minutes in a stream of mixed gas of oxygen 5% argon 95%. The obtained iron oxide layer was about 2 nm. The ultrafine particles were added to 0.085% by volume with respect to 1 liter of ethanol, and oleic acid as a dispersant was added at 3.0 mg / m ² per surface area of the ultrafine particles. Dispersion was performed using a 20 KHz, 1200 W ultrasonic oscillator for 30 minutes in water cooling to obtain a highly dispersed magnetic iron ultrafine particle suspension. Further, 0.015 mol of tetraethoxysilane, 36.5 mol of water, and 1.5 mol of 25% strength ammonia water were added, and the mixture was stirred for 24 hours using a stirring spring of 300 rpm, and subjected to a hydrolysis reaction. The obtained ultrafine particles were washed three times with ethanol and then vacuum dried at 50 ° C. to obtain magnetic iron ultrafine particles of Example 3 of the present invention. The magnetic iron ultrafine particles of Example 3 of the present invention were coated with a silicon oxide layer of about 5 nm from the contrast observed with a transmission electron microscope.

[Example 4: Magnetic iron ultrafine particles]
The magnetic iron ultrafine particle of Example 4 of the present invention comprises an iron ultrafine particle nucleus and a silicon oxide layer covering the ultrafine particle nucleus. The ultrafine particles containing iron as a main component, which is the magnetic iron ultrafine particles of Example 3 of the present invention, were heat-treated at 500 ° C. for 5 hours using a mixed gas of 4% hydrogen and 96% nitrogen, and the examples of the present invention. 4 magnetic iron ultrafine particles were obtained.

[Comparative Example 2: Magnetic iron ultrafine particles]
Pure iron nanoparticles were synthesized by the method shown in Example 3 of the present invention. The particle diameter was measured by a dynamic light scattering method, and it was confirmed that the average particle diameter was 30 nm. The ultrafine particles containing iron as a main component dispersed in kerosene are treated at 30 ° C. for 30 minutes in a stream of mixed gas of 5% oxygen and 95% oxygen to form an iron oxide layer on the surface by a method of slow oxidation. The magnetic iron ultrafine particles of Comparative Example 2 were formed. The iron oxide layer was about 2 nm.

[Experimental results: magnetic iron ultrafine particles of Examples 1 to 4 and Comparative Examples 1 and 2]
The magnetic iron ultrafine particles of Examples 1 to 4 of the present invention and the magnetic iron ultrafine particles of Comparative Examples 1 and 2 were left in an environment of 90% humidity and 80 ° C. for 7 days, respectively. Table 1 shows the results obtained by measuring with a vibrating sample magnetometer and evaluating the oxidation resistance by the reduction rate of the saturation magnetization obtained.

  As shown in Table 1, with respect to oxidation resistance, the magnetic iron ultrafine particles of Comparative Examples 1 and 2 were allowed to stand for 7 days in an environment of 90% humidity and 60 ° C., so that the saturation magnetization was 10% due to oxidation. On the other hand, in the magnetic iron ultrafine particles of Examples 1 and 3 of the present invention, the saturation magnetization was decreased by only 2% under the same conditions. In the magnetic iron ultrafine particle No. 4, the saturation magnetization was not reduced at all, indicating that the oxidation resistance was remarkably improved. The reason why the oxidation resistance is improved is that the magnetic iron ultrafine particles of Examples 1 and 3 of the present invention are coated with silicon oxide as compared with the magnetic iron ultrafine particles of Comparative Examples 1 and 2, and thus the present invention is further improved. This is because the magnetic iron ultrafine particles of Examples 2 and 4 were subjected to hydrogen reduction treatment, whereby the silicon oxide layer was densified to form an oxidation-resistant protective film in which oxygen does not diffuse.

Examples 1, 3 of the present invention, as compared with the magnetic iron ultrafine particles of Comparative Examples 1 and 2, the magnetic iron ultrafine particles of Examples 2 and 4 of the present invention is remarkable saturation magnetization, residual magnetization, coercive magnetic force is large As a result, the magnetic properties were improved. This is because the iron oxide layer of the intermediate layer applied to coat the iron ultrafine particles with silicon oxide was reduced by the hydrogen reduction treatment.

Therefore, according to the magnetic iron ultrafine particles of Examples 1 to 4 of the present invention, the saturation magnetization, residual magnetization, coercive magnetic force is high, and high oxidation resistance. In particular, magnetic iron ultrafine particles of Examples 2 and 4 of the present invention, the saturation magnetization, residual magnetization, coercive magnetic force is remarkably high, very high oxidation resistance. In the magnetic iron ultrafine particles of Examples 1 to 4 of the present invention, as described above, since the eddy current is not generated and the magnetic permeability is governed by the saturation magnetization, it can be said that the magnetic permeability is also high.

[Example 5: Composite material]
In the composite material of Example 5 of the present invention, the surface of the magnetic iron ultrafine particles of Example 4 of the present invention consisting of ultrafine particle nuclei and a silicon oxide layer covering the ultrafine particle nuclei was added with resin. It is a molded product formed by heating in pressure. Such magnetic iron ultrafine particles include magnetic iron comprising spherical ultrafine particle nuclei containing iron as a main component, an iron oxide layer formed on the surface of the ultrafine particle nuclei, and a silicon oxide layer covering the surface iron oxide layer. It is obtained by heat treating ultrafine particles at 400 ° C. or more and 600 ° C. or less in an atmosphere containing hydrogen gas.

  To a solution composed of 118 g of pure water, 18 g of ammonia, and 160 g of ethanol containing 0.5 g of spherical magnetic iron ultrafine particles having an average particle diameter of 30 nm in Example 4 of the present invention, 3-methacryloxypropyltriethoxy 0.094 g of silane was added, and the mixture was treated for 30 minutes at 85 ° C. with a planetary ball mill using zirconia balls. Washed 3 times with ethanol and dried in vacuum at 50 ° C. Furthermore, 100 g of ethanol was added to 3.0 g of the ultrafine particles obtained, and 0.6 g of adzobenzonitrile and 4.5 g of MMA were added as initiators, followed by stirring in a nitrogen stream at 350 rpm and 65 ° C. for 24 hours. did. After drying in vacuum at 50 ° C., the surface was hydrophobized with a silane coupling agent, and MMA, which is a monomer of methacrylic resin, was graft-polymerized to obtain particles coated with methacrylic resin. The obtained particles were uniaxially pressed at 150 ° C. and 100 MPa to obtain a composite material of Example 5 of the present invention which is a composite material with a resin.

[Examples 6 to 8: Composite material]
In the composite material of Example 6 of the present invention, particles coated with methacrylic resin were obtained by the same method as the composite material of Example 5, and 50 parts by volume of methacrylic resin was added to 50 parts by volume of the obtained particles. A film having a thickness of 0.5 mm was formed by using a formula extruder. The composite material of Example 6 of the present invention is a composite material of magnetic iron ultrafine particles and a resin. The composite material of Example 7 of the present invention was produced in the same manner as the composite material of Example 6 of the present invention, except that 70 parts by volume of methacrylic resin was added to 30 parts by volume of the obtained particles. The composite material of Example 8 of the present invention was produced in the same manner as the composite material of Example 6 of the present invention, except that 90 parts by volume of methacrylic resin was added to 10 parts by volume of the obtained particles.

[Comparative Examples 3 to 5: Composite Material]
The composite material of Comparative Example 3 is a composite material of magnetic iron particles and resin. First, acicular ferrite particles are kept at 500 ° C. for 1 hour and then at 700 ° C. for 1 hour using a mixed gas having a volume ratio of H ₂ : NH ₃ = 7: 3. Iron particles having a particle diameter of 1.5 μm were prepared. When nano-sized particles are combined with a resin, they are oxidized and burned, so that the composite material itself cannot be produced. According to X-ray diffraction, the iron particles contained a slight amount of iron nitride. This iron nitride is formed on the outer surface of the iron particles and contributes as an oxidation-resistant protective film. Next, Comparative Example 3 which is a composite material with resin by adding 50 parts by volume of methacrylic acid resin to 50 parts by volume of the iron particles and forming a film having a thickness of 0.5 mm using a screw type extruder. It was set as the composite material. The composite material of Comparative Example 4 was produced in the same manner as the composite material of Comparative Example 3 except that 70 parts by volume of methacrylic acid resin was added to 30 parts by volume of the iron particles. The composite material of Comparative Example 5 was produced in the same manner as the composite material of Comparative Example 3, except that 90 parts by volume of methacrylic acid resin was added to 10 parts by volume of the iron particles.

[Experimental results: composite materials of Examples 5 to 8 and Comparative Examples 3 to 5]
Regarding the composite materials of Examples 5 to 8 of the present invention and the composite materials of Comparative Examples 3 to 5, each cross section was observed with an SEM, and the presence or absence of cracks and pores, as well as problems in the fine structure such as the uniform dispersibility of the magnetic particles The points were compared. Furthermore, the area occupancy of the iron powder was measured by a method of image analysis of the obtained SEM image, and the particle concentration (volume%) was evaluated. The obtained sheet-like composite material was measured for specific resistance by a four-terminal method, and further by measuring the attenuation in an electromagnetic wave absorption characteristic by a free space method in a frequency band of 1 GHz to 20 GHz. The results obtained are summarized in Table 2.

In Table 2, symbols in the SEM observation microstructure column are
Pore: ○ No pore, × Pore with sharpness: ○ Without crease, Δ Slightly fine crease, × Dispersed and uniformly dispersed structure: ○ Highly dispersed, Δ Slightly agglomerated, × Highly agglomerated.

  In the composite material of Example 5 of the present invention, the iron ultrafine particles are uniformly dispersed while maintaining a high specific resistance, and no iron or nanoparticles are contained at a high particle concentration of 50% by volume without cracks and pores. Contains. The electromagnetic wave absorption characteristics were also excellent. Resin monomers are uniformly adsorbed and polymerized on iron ultrafine particles coated with silicon oxide, and the polymer adsorbed in the step of uniaxial pressing during heating is melted and filled in the pores.

  The magnetic iron ultrafine particles of the present invention represented by the magnetic iron ultrafine particles of Example 4 of the present invention are coated with silicon oxide and have been widely used in the past as shown in the composite materials of Examples 6-8. It can also be molded using a conventional extruder. As can be seen from the result of the composite material of Example 6, this method is slightly inferior in terms of the presence or absence of pores and cracks compared to the method of the composite material of Example 5, but maintains a high specific resistance because of the surface modification. Thus, a composite material in which magnetic iron ultrafine particles are uniformly dispersed at a high particle concentration can be obtained. Further, as can be seen from the results of the composite materials of Examples 7 and 8, if the particle concentration is low or medium, the ultrafine iron particles are uniformly dispersed while maintaining a high specific resistance, and cracks and pores are maintained. In addition, a material having good insulation and electromagnetic wave absorption characteristics can be obtained. In the composite materials of Examples 6 to 8, the magnetic iron ultrafine particles were uniformly dispersed because the magnetic iron ultrafine particles adsorbed and polymerized the resin monomer and had good wettability with the resin to be added. The composite materials of Examples 5, 7, and 8 of the present invention were almost insulators because it was difficult to measure specific resistance by the four probe method.

  On the other hand, from the results of the composite materials of Examples 6 to 8 of the present invention and the composite materials of Comparative Examples 3 to 5, the composite material formed by adding resin to micron particles was formed by adding resin to nanoparticles. Compared with the composite material, the uniform dispersibility of the iron particles was poor even at the same particle concentration. In addition, pores and cracks were generated even at a medium particle concentration, and the insulation and electromagnetic wave absorption characteristics were poor. When a composite material of magnetic iron ultrafine particles and a resin is prototyped by the method shown in the composite material of Comparative Example 3, oxidation progresses significantly in the process. Therefore, the comparative experiment used micron particles instead of nanoparticles. In the composite materials of Comparative Examples 3 to 5, since the iron particles are not coated with silica, the iron particles are easily in contact with each other and inferior in uniform dispersibility, so that the iron particles are in contact with each other. Compared with the composite material of 8, the specific resistance was small. In the case of micron particles, the particle concentration is 10 vol% or less in terms of specific resistance. In the composite material of Comparative Example 3, eddy current was generated in the high frequency band, and the attenuation in the absorption characteristics was remarkably reduced. In Comparative Examples 4 and 5, the eddy current was small, but the attenuation in the absorption characteristics was remarkably small. On the other hand, the composite materials of Examples 5, 7, and 8 of the present invention showed a large attenuation. In particular, the amount of attenuation was large in the composite material of Example 5 of the present invention.

  Therefore, according to the composite materials of Examples 5, 7, and 8 of the present invention, the magnetic properties are excellent and the electromagnetic wave absorption effect is high. According to the method for producing the composite material of the present invention shown in Example 5 of the present invention, the magnetic metal fine particles having high magnetic properties in the resin are maintained in a state of maintaining a high specific resistance at an extremely high particle concentration. It can be dispersed without cracks or pores. According to the composite material manufacturing method of the present invention shown in Examples 6 to 8 of the present invention, magnetic metal fine particles having high magnetic properties can be uniformly dispersed in the resin while maintaining a high specific resistance. it can. At medium and low particle concentrations, it can be further dispersed without cracks and pores, and has good electromagnetic wave absorption characteristics.

[Example 9: Magnetic recording body]
The magnetic recording material of Example 9 of the present invention was formed by applying a magnetic coating material including the magnetic iron ultrafine particles of Example 2 of the present invention consisting of ultrafine particle nuclei and a silicon oxide layer covering the ultrafine particle nuclei. Contains a magnetic layer. Such magnetic iron ultrafine particles are composed of acicular ultrafine particle nuclei mainly composed of iron, an iron oxide layer formed on the surface of the ultrafine particle nuclei, and a silicon oxide layer covering the surface iron oxide layer. It is obtained by heat-treating iron ultrafine particles at 400 ° C. or more and 600 ° C. or less in an atmosphere containing hydrogen gas.

  100 parts by weight of magnetic iron ultrafine particles of Example 2 of the present invention, 20 parts by weight of polyurethane resin and vinyl chloride resin combined as binder, 3 parts by weight of alumina as abrasive, and 2 parts by weight of carbon black as antistatic agent , 100 parts by weight of methyl ethyl ketone, 100 parts by weight of toluene, 50 parts by weight of cyclohexanone, and 1 part by weight of oleic acid were mixed and dispersed to prepare a magnetic coating material. A magnetic layer is formed by orienting ultrafine particles in one direction and applying and drying. Since the magnetic layer of the magnetic recording material of Example 9 of the present invention has excellent oxidation resistance, the magnetic recording material of Example 9 of the present invention is effective as a magnetic recording material with very little characteristic deterioration.

  Therefore, according to the magnetic recording medium of Example 9 of the present invention, it is excellent in magnetic characteristics and enables high density recording.

[Example 10: Carrier for extracting biological material]
The biological material extraction carrier of Example 10 of the present invention contains the magnetic iron ultrafine particles of Example 4 of the present invention consisting of ultrafine particle nuclei and a silicon oxide layer covering the ultrafine particle nuclei, and extracts nucleic acids. Is. Such magnetic iron ultrafine particles include magnetic iron comprising spherical ultrafine particle nuclei containing iron as a main component, an iron oxide layer formed on the surface of the ultrafine particle nuclei, and a silicon oxide layer covering the surface iron oxide layer. It is obtained by heat treating ultrafine particles at 400 ° C. or more and 600 ° C. or less in an atmosphere containing hydrogen gas. The biological material extraction carrier of Example 10 of the present invention extracts nucleic acids as follows.

  First, the biological material extraction carrier of Example 10 of the present invention consisting of magnetic iron ultrafine particles of Example 4 of the present invention was used as a guanidine acid, sodium isothiocyanate, potassium iodide, urea, sodium peroxide hydrochloride, chromium peroxide. The nucleic acid is bound to the silicon oxide on the surface by contacting the nucleic acid-containing material in a solution for nucleic acid extraction such as sodium acid.

  Next, the magnetic iron ultrafine particles coated with silicon oxide to which nucleic acids are bound are separated from the nucleic acid extraction solution by magnetism.

  Thereafter, the nucleic acid is dissociated from the magnetic iron ultrafine particles coated with silicon oxide in a dissociation solution such as Tris buffer or phosphate buffer.

  As described above, since the isolated nucleic acid has high purity, it can be used as it is in the medical field such as gene analysis including nucleic acid amplification. Since the biological substance extraction carrier of Example 10 of the present invention is an ultrafine particle and has excellent magnetic properties, it can separate nucleic acids with high accuracy.

  Therefore, according to the biological substance extraction carrier of Example 10 of the present invention, the nucleic acid magnetic separation operation can be performed in a short time with excellent magnetic properties.

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention. In addition, the constituent elements of the above embodiments can be arbitrarily combined without departing from the spirit of the invention.

It is a schematic diagram which shows 1st Embodiment of the magnetic iron ultrafine particle of this invention. It is a schematic diagram which shows 2nd Embodiment of the magnetic iron ultrafine particle of this invention. 2 is a transmission electron micrograph of acicular ultrafine particles mainly composed of iron having iron oxide formed on the surface by slow oxidation. 2 is a transmission electron micrograph of acicular ultrafine particles mainly composed of iron coated with silicon oxide.

Explanation of symbols

1 Ultrafine particle nucleus mainly composed of iron 2 Iron oxide layer 3 Silicon oxide layer

Claims (10)

The iron oxide formed by ultrafine particle nuclei mainly composed of iron, an iron oxide layer formed on the surface of the ultrafine particle nuclei, and silicon oxide chemically precipitated by hydrolysis reaction of silicon alkoxide. Magnetic iron ultrafine particles obtained by heat-treating magnetic iron ultrafine particles comprising a silicon oxide layer covering a physical layer in an atmosphere containing hydrogen gas at 400 ° C. or higher and 600 ° C. or lower, comprising iron as a main component Whether or not the ultrafine particle nucleus is a needle-like particle having a major axis of 100 nm to 500 nm and a minor axis of 20 nm to 50 nm. Alternatively, the magnetic iron is characterized in that the ultrafine particle nuclei are particles other than needle-like particles, the average particle diameter is 20 nm or more and 100 nm or less, and the thickness of the silicon oxide layer is 1 nm or more and 10 nm or less. Ultrafine . The method for producing magnetic iron ultrafine particles according to claim 1, wherein a step of gradually oxidizing an ultrafine particle nucleus mainly composed of iron to form an iron oxide layer on a surface of the ultrafine particle nucleus, in an organic solvent A step of dispersing the iron oxide layer with a silicon oxide layer formed from a silicon oxide chemically precipitated by a hydrolysis reaction of silicon alkoxide, in an atmosphere containing hydrogen gas at 400 ° C. A method for producing magnetic iron ultrafine particles, comprising the step of reducing the iron oxide layer by heat treatment at 600 ° C. or lower . A composite material of magnetic iron ultrafine particles and a resin, wherein the resin iron monomer is adsorbed on the surface of the magnetic iron ultrafine particles according to claim 1 and further graft-polymerized to coat the resin. And composite materials. A composite material, wherein the composite material according to claim 3 is molded by heating in pressure. A method for producing a composite material of magnetic iron ultrafine particles and a resin, comprising hydrophobizing the magnetic iron ultrafine particles according to claim 1 with a silane coupling agent, and a resin monomer on the surface of the magnetic iron ultrafine particles A composite material manufacturing method comprising the steps of adsorbing and further graft-polymerizing the resin. 6. The method for producing a composite material according to claim 5 , further comprising a step of heating and molding in pressure after coating the resin. A magnetic recording material comprising a magnetic layer formed by applying a magnetic paint containing the magnetic iron ultrafine particles according to claim 1 . Electromagnetic wave absorber characterized in that the composite material according dispersed contained in the insulating base material to the magnetic ultra-fine iron particles or claim 3 according to claim 1. An electromagnetic wave absorber comprising the composite material according to claim 4 . A biomaterial extraction carrier comprising the magnetic iron ultrafine particles according to claim 1 and extracting nucleic acid.