Magnetic body, magnetic fluid, particle size distribution measurement standard sample, method for manufacturing magnetic body, and method for manufacturing magnetic fluid

Abstract

This invention addresses the issues of preservation and safety of magnetic fluids based on polar organic solvents, and provides a magnetic body, a magnetic fluid, a standard sample for particle size distribution determination, a method for manufacturing the magnetic body, and a method for manufacturing the magnetic fluid. Even when a second magnetic fluid is prepared by adding a polar organic solvent to a magnetic body obtained by removing the dispersion medium contained in a first magnetic fluid, the generation of secondary particles from the magnetic particles in the magnetic fluid can be effectively suppressed. A magnetic body comprises: magnetic particles with an average particle size of 10–50 nm, a saturated fatty acid or its salt or an unsaturated fatty acid or its salt with 10–24 carbon atoms, and an alkoxylate formed by adding an epoxide with 2–4 carbon atoms to an alcohol with 1–3 carbon atoms.

Description

Technical Field

[0001] This invention relates to magnetic materials, magnetic fluids, standard samples for particle size distribution determination, methods for manufacturing magnetic materials, and methods for manufacturing magnetic fluids. Background Technology

[0002] In recent years, magnetic fluids have attracted attention as magnetic materials that do not exhibit hysteresis and can be used in magnetic cores, rectifiers, current sensors, etc. (e.g., Patent Document 1). Magnetic fluids are magnetic materials that exhibit superparamagnetism by dispersing magnetic powders such as ferrite particles and magnetite particles with a particle size in the range of 3–50 nm in a dispersion medium. To exhibit superparamagnetism, the particle size of the magnetic particles needs to be in the nanometer range. Furthermore, polar organic solvents such as water, hydrocarbon oils, and alcohols can be used as the dispersion medium.

[0003] Furthermore, in order to uniformly disperse nanoscale magnetic particles in a dispersion medium, at least a portion of the surface of the magnetic particles is typically coated with a dispersant selected from surfactants (such as sodium oleate). For example, Patent Document 2 discloses an alcohol-based magnetic fluid containing particles of an alcohol, a surfactant, a liquid crystal compound that is liquid at a specified temperature, a magnetic metal oxide, and / or a magnetic metal. Furthermore, examples are disclosed using polyoxyethylene nonylphenyl ether as the surfactant, a cyanobiphenyl liquid crystal compound as the liquid crystal compound, and magnetite as the magnetic metal compound.

[0004] Existing technical documents Patent documents Patent Document 1: International Publication No. 2010 / 041340 Patent Document 2: Japanese Patent Application Publication No. 9-40983 However, the safety of magnetic fluids based on polar organic solvents, such as alcohols, needs to be considered during storage and transportation. To address this issue, one could consider removing some or all of the polar organic solvent from the magnetic fluid and then magnetically pulverizing it. However, in such cases, the magnetic nanoparticles will aggregate to form secondary particles. Because the magnetic nanoparticles are strongly aggregated, even if polar organic solvents are added to the magnetic powder to restore it to the same state as the magnetic fluid before the removal of the organic solvents, the magnetic nanoparticles will not revert to primary particles but will exist as secondary particles, thus exhibiting hysteresis. Therefore, it is difficult to apply them to magnetic cores, rectifiers, current sensors, etc. Therefore, those skilled in the art are looking to develop magnetic fluids that can suppress the formation of secondary particles from magnetic nanoparticles even when organic solvents are added again to the magnetic material obtained after removing the organic solvents from the magnetic fluid for magnetic fluidization.

[0005] On the other hand, the particle size determination results of nanoparticles dispersed in a liquid depend on the measurement principle and conditions. Therefore, standard samples can be used to evaluate the appropriateness of the nanoparticle particle size determination results. As a standard sample, it is required to be a substance similar to the sample being measured. However, commercially available standard samples for nanoparticle determination are aqueous dispersions of organic or metallic nanoparticles; there are no samples in polar organic solvents that can be diluted at any concentration. Furthermore, when using a polar organic solvent dispersion of magnetic nanoparticles as a standard sample, good control of the iron oxide particle size and excellent dispersion stability are required, but magnetic nanoparticle standard samples have not been sufficiently developed / researched to date. Therefore, if a magnetic fluid can be developed that can suppress the generation of secondary particles of magnetic nanoparticles even when a polar organic solvent is added again to the composition obtained after removing the polar organic solvent from the magnetic fluid for magnetic fluidization, it can be expected to be used as a standard sample. Summary of the Invention

[0006] This invention was made with regard to the above aspects, and its purpose is to solve the problems of preservation and safety of magnetic fluids based on polar organic solvents. It also provides a magnetic body, a magnetic fluid, a standard sample for particle size distribution determination, a method for manufacturing the magnetic body, and a method for manufacturing the magnetic fluid. The magnetic body can effectively suppress the generation of secondary particles of magnetic particles in the magnetic fluid, even when a second magnetic fluid is made by adding a polar organic solvent to the magnetic body obtained by removing the dispersion medium contained in the first magnetic fluid.

[0007] In order to solve the above-mentioned technical problems, the present invention has determined the following [1] to [7].

[0008] [1] A magnetic material comprising: magnetic particles with an average particle size of 10 to 50 nm, a saturated fatty acid or its salt having 10 to 24 carbon atoms, or an unsaturated fatty acid or its salt, and an alkoxylate formed by adding an epoxide having 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms.

[0009] [2] According to the magnetic body described in [1], wherein the magnetic body is in the form of a paste.

[0010] [3] A magnetic fluid comprising a magnetic body as described in [1] or [2] and a polar organic solvent.

[0011] [4] A standard sample for particle size distribution determination, comprising a magnetic material and a polar organic solvent as described in [1] or [2], wherein the magnetic particles contain 0.5 to 3% by mass.

[0012] [5] A method for manufacturing a magnetic body, comprising the step of removing the polar organic solvent from the magnetic fluid as described in [3] to obtain the magnetic body, wherein the content of the polar organic solvent in the magnetic body obtained by removing the polar organic solvent is less than 1% by mass.

[0013] [6] A method for manufacturing a magnetic material, comprising: a step of obtaining a first magnetic fluid, the first magnetic fluid comprising magnetic particles, a saturated fatty acid or its salt having a carbon number of 10 to 24 or an unsaturated fatty acid or its salt, and water or a nonpolar solvent; a step of mixing an alkoxylate in the first magnetic fluid, the alkoxylate being formed by adding an epoxide having a carbon number of 2 to 4 to an alcohol having a carbon number of 1 to 3; and a step of removing the water or nonpolar solvent.

[0014] [7] A method for manufacturing a magnetic fluid, comprising: a step of obtaining a second magnetic fluid by mixing a polar organic solvent into a magnetic body obtained by the manufacturing method described in [6].

[0015] Invention Effects According to embodiments of the present invention, the problems of preservation and safety of magnetic fluids based on polar organic solvents can be solved, and magnetic bodies, magnetic fluids, standard samples for particle size distribution determination, methods for manufacturing magnetic bodies, and methods for manufacturing magnetic fluids can be provided. Even when a second magnetic fluid is prepared by adding a polar organic solvent to a magnetic body obtained by removing the dispersion medium contained in a first magnetic fluid, the generation of secondary particles of magnetic particles in the magnetic fluid can be well suppressed. Attached Figure Description

[0016] Figure 1 The results are the particle size distribution determination results of the magnetic particles in the standard sample of Example 7.

[0017] Figure 2 The results are from the particle size distribution determination of the magnetic particles in the sample of Comparative Example 14. Detailed Implementation

[0018] The following describes embodiments of the magnetic body, magnetic fluid, particle size distribution determination standard sample, manufacturing method of the magnetic body, and manufacturing method of the magnetic fluid of the present invention. However, the present invention is not limited thereto. Various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art without departing from the scope of the present invention.

[0019] It should be noted that in this specification, the "~" indicating a numerical range means a range that includes both the upper and lower limits of the values ​​listed. Furthermore, if only the upper limit of the numerical range is specified with a unit, it means that the lower limit has the same unit as the upper limit.

[0020] In the numerical ranges described in this specification, the upper or lower limit of a certain numerical range can be replaced by the upper or lower limit of other numerical ranges described in different periods.

[0021] Furthermore, within the numerical ranges described in this specification, the upper or lower limit value within a certain numerical range may be replaced with the values ​​shown in the embodiments.

[0022] In this specification, the content or percentage of each component in the composition refers to the total content or percentage of the various substances present in the composition, unless otherwise specified.

[0023] (Magnetic material) The magnetic material of this embodiment comprises: magnetic particles with an average particle size of 10 to 50 nm, a saturated fatty acid or its salt having 10 to 24 carbon atoms, or an unsaturated fatty acid or its salt, and an alkoxylate formed by adding an epoxide having 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms. The components contained in the magnetic material will be described below.

[0024] 1. Magnetic particles The magnetic material in this embodiment comprises magnetic particles. Examples of magnetic particles include: strongly magnetic oxides; strongly magnetic metals; and metal nitrides. Examples of strongly magnetic oxides include: magnetite (Fe3O4), γ-iron oxide, manganese ferrite, cobalt ferrite, or composite ferrites of these with zinc or nickel, and barium ferrite. Examples of strongly magnetic metals include: iron, cobalt, and rare earth elements. From a mass production perspective, magnetite is preferred as the magnetic particle. It should be noted that the average particle size of the magnetic particles used in this embodiment is 10–50 nm, preferably 10–40 nm. One type of magnetic particle can be used alone, or two or more can be used in combination. To facilitate dispersion, the shape of the magnetic particles is preferably spherical or approximately spherical.

[0025] The content of magnetic particles relative to the total mass of the magnetic body is preferably in the range of 45 to 85% by mass, and more preferably 55 to 75% by mass.

[0026] 2. Saturated fatty acids or their salts with 10 to 24 carbon atoms, or unsaturated fatty acids or their salts. The magnetic material of this embodiment comprises a saturated fatty acid or its salt, or an unsaturated fatty acid or its salt, having 10 to 24 carbon atoms. Examples of saturated fatty acids or their salts, or unsaturated fatty acids or their salts, having 10 to 24 carbon atoms include: lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, linolenic acid, linoleic acid, erucic acid, arachidonic acid, behenic acid, creosotenic acid, etc., which are saturated fatty acids or their salts, or unsaturated fatty acids or their salts, having 10 to 24 carbon atoms. Among these, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, linolenic acid, linoleic acid, arachidonic acid, etc., which are saturated fatty acids or their salts, or unsaturated fatty acids or their salts, having 12 to 20 carbon atoms are preferred. From the viewpoint of being inexpensive and readily available, sodium salt of oleic acid (hereinafter, sometimes referred to as sodium oleate) is particularly preferred. It should be noted that in this specification, saturated fatty acids or their salts with 10 to 24 carbon atoms or unsaturated fatty acids or their salts are sometimes referred to as the first surfactant.

[0027] Saturated fatty acids or their salts, or unsaturated fatty acids or their salts, having 10 to 24 carbon atoms, can be used alone or in combination with two or more. The total content of saturated fatty acids or their salts, or unsaturated fatty acids or their salts, having 10 to 24 carbon atoms in the magnetic material is not particularly limited, as long as it prevents the magnetic particles from agglomerating; it can be appropriately selected according to the intended use. The content of saturated fatty acids or their salts, or unsaturated fatty acids or their salts, having 10 to 24 carbon atoms, relative to the total amount of the magnetic material, is preferably 5 to 25% by mass, more preferably 10 to 20% by mass.

[0028] 3. Alkoxylated compounds formed by adding an epoxide with 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms. The magnetic material of this embodiment comprises an alkoxylate formed by adding an epoxide with 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms. It should be noted that, in this specification, the alkoxylate formed by adding an epoxide with 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms is sometimes referred to as a second surfactant. The magnetic material contains such a second surfactant, which then adheres to the first surfactant adhering to the surface of the magnetic particles. As a result, the problems of storage and safety of the magnetic fluid are solved, and even when a polar organic solvent is added again to the magnetic material for magnetic fluidization, the aggregation of magnetic particles in the magnetic fluid can be well suppressed.

[0029] The content of the alkoxylated compound formed by adding an epoxide with 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms is preferably 10 to 30% by mass relative to the total amount of magnetic material, more preferably 15 to 25% by mass.

[0030] Examples of alcohols having 1 to 3 carbon atoms include methanol, ethanol, and propanol. Methanol is preferred. Examples of alkyl oxides having 2 to 4 carbon atoms include ethylene oxide, propylene oxide, 1,2-epoxybutane, 2,3-epoxybutane, and 2-methyl-1,2-epoxypropane (isobutene oxide). Ethylene oxide and propylene oxide are preferred, and ethylene oxide is more preferred. Alcohols having 1 to 3 carbon atoms and alkyl oxides having 2 to 4 carbon atoms can be used individually or in combination of two or more. The method for producing alkoxylates by adding alkyl oxides having 2 to 4 carbon atoms to alcohols having 1 to 3 carbon atoms will be described later.

[0031] The magnetic material of this embodiment may further include the polar organic solvent described below. From the viewpoint of storing and transporting the magnetic material, the content of the polar organic solvent relative to the total amount of the magnetic material is preferably 1% by mass or less, more preferably 0.8% by mass or less, and even more preferably 0.6% by mass or less.

[0032] The magnetic material in this embodiment is preferably in the form of a paste. When the content of the polar organic solvent relative to the total amount of the magnetic material is 1% by mass or less, it is preferable, for example, that the form remains a paste from the state containing the polar organic solvent until the polar organic solvent is removed. Magnetic fluids containing polar organic solvents pose a hazard during transport and storage; therefore, safety is improved by transporting and storing them in a paste-like form after removing the polar organic solvent. Furthermore, as described later, the magnetic fluid of this embodiment, even when a polar organic solvent is added again to the paste for magnetic fluidization, can suppress the aggregation of magnetic particles within the magnetic fluid and effectively suppress the generation of secondary particles.

[0033] (Method for manufacturing magnetic materials) In the case of the magnetic material of this embodiment, after obtaining the first magnetic fluid described below, an alkoxylate formed by adding an epoxide with 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms is mixed in the first magnetic fluid. Next, the material can be manufactured by removing water or a non-polar solvent, which serves as the dispersion medium, using methods such as heating or vacuum heating. The removal of water or the non-polar solvent can be performed, for example, by heating at 40 to 50°C or by drying under reduced pressure.

[0034] Alternatively, the magnetic body can be manufactured by removing the polar organic solvent from the magnetic fluid (second magnetic fluid) described later. In this case, the content of the polar organic solvent in the magnetic body is preferably 1% by mass or less, more preferably 0.8% by mass or less, and even more preferably 0.6% by mass or less.

[0035] (Magnetic fluid) The magnetic fluid of this embodiment comprises: magnetic particles with an average particle size of 10 to 50 nm, a saturated fatty acid or its salt having 10 to 24 carbon atoms, or an unsaturated fatty acid or its salt, an alkoxylate formed by adding an epoxide having 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms, and a polar organic solvent. In this specification, this magnetic fluid is sometimes referred to as a second magnetic fluid.

[0036] Furthermore, in this specification, a magnetic fluid comprising magnetic particles with an average particle size of 10 to 50 nm, saturated fatty acids or their salts with 10 to 24 carbon atoms or unsaturated fatty acids or their salts, and water or a nonpolar solvent is sometimes referred to as a first magnetic fluid.

[0037] In the magnetic material of this embodiment, saturated fatty acids or their salts having 10 to 24 carbon atoms, or unsaturated fatty acids or their salts, are present as alkoxylates formed by adding an epoxide having 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms, and are attached to the surface of the magnetic particles in this order. When this is the case, even when a second magnetic fluid is prepared by mixing a polar organic solvent into the magnetic material, the aggregation of magnetic particles in the magnetic fluid can be suppressed, and the generation of secondary particles from the magnetic particles can be effectively suppressed.

[0038] Furthermore, even when a polar organic solvent is added again to the composition obtained after removing the polar organic solvent contained in the second magnetic fluid for re-magnetization, the aggregation of magnetic particles in the magnetic fluid can be suppressed, and the generation of secondary particles of magnetic particles can be effectively suppressed. Taking advantage of this effect, from the perspective of storage and safety, the magnetic fluid obtained by adding a polar organic solvent again after removing the polar organic solvent from the second magnetic fluid does not deteriorate. Therefore, the magnetic fluid of this embodiment solves the conventional problems of storage and safety.

[0039] The components contained in the first and second magnetic fluids will be described below.

[0040] (First magnetic fluid) The magnetic particles with an average particle size of 10 to 50 nm, saturated fatty acids or their salts with 10 to 24 carbon atoms, or unsaturated fatty acids or their salts contained in the first magnetic fluid are the same as the substances described in the magnetic body of this embodiment.

[0041] The first magnetic fluid further comprises water or a nonpolar solvent. This water or nonpolar solvent is added as a dispersion medium for the magnetic particles contained in the magnetic fluid. Examples of nonpolar solvents include aromatic hydrocarbons and aliphatic hydrocarbons. Examples of aromatic hydrocarbons include benzene, toluene, and xylene. Examples of aliphatic hydrocarbons include isoparaffins, kerosene, hexane, and heptane. Water or a nonpolar solvent can be used alone or in combination with two or more. It should be noted that when water is used as the dispersion medium, it is preferable to further add a hydrophilic dispersant.

[0042] The content of magnetic particles relative to the total amount of the first magnetic fluid is preferably in the range of 25 to 70% by mass, more preferably 28 to 60% by mass. By setting the content of magnetic particles relative to the total amount of the first magnetic fluid to the range of 25 to 70% by mass, the dispersibility of the magnetic particles can be maintained, thus maintaining the function as a fluid and functioning as a magnetic material when a magnetic field is applied.

[0043] (Second magnetic fluid) The second magnetic fluid contains magnetic particles with an average particle size of 10-50 nm, saturated fatty acids or their salts or unsaturated fatty acids or their salts with 10-24 carbon atoms, and alkoxylated compounds formed by adding an epoxide with 2-4 carbon atoms to an alcohol with 1-3 carbon atoms, which are the same substances described in the magnetic material of this embodiment. Furthermore, the content of magnetic particles can be appropriately adjusted according to the intended use of the second magnetic fluid. In the second magnetic fluid, substances with extremely low magnetic particle content are referred to as particle size distribution measurement standard samples. It should be noted that the magnetic particle content of the particle size distribution measurement standard samples will be described later. The magnetic particle content of the second magnetic fluid (except in the case of particle size distribution measurement standard samples) is preferably within the same range as the magnetic particle content of the first magnetic fluid.

[0044] (Polar organic solvents) The magnetic fluid (second magnetic fluid) of this embodiment contains a polar organic solvent. The polar organic solvent is added as a dispersion medium for the magnetic particles contained in the magnetic fluid. Examples of polar organic solvents include: alcohols such as methanol, ethanol, and propanol; cresol; N,N-dimethylacetamide (DMAc); N-methyl-2-pyrrolidone (NMP); dimethyl sulfoxide (DMSO); 1,3-dimethylimidazolinone (DMI); N,N-dimethylformamide (DMF); butyl cellosolve (BCS); and γ-butyrolactone (GBL). One polar organic solvent may be used alone, or two or more may be used in combination. Alcohols are particularly preferred.

[0045] (Other ingredients) In addition to the components described herein, the magnetic fluid of this embodiment may be further combined with various other components according to the purpose, without compromising the effectiveness of this embodiment.

[0046] Other components include, for example, viscosity index improvers, surfactants, viscosity modifiers, rust inhibitors, antioxidants, corrosion inhibitors, metal passivators, and defoamers.

[0047] Examples of viscosity modifiers include: polybutene, polyalphaolefin, castor oil, hydrogenated castor oil, fatty acid amide, beeswax, carnauba wax, benzyl sorbitol, metal soap, oxidized polyethylene, sulfate-based anionic surfactants, (meth)acrylates, polyisobutylene, and polyalkylstyrene.

[0048] Viscosity modifiers can be used alone or in combination with two or more.

[0049] (use) The magnetic fluid of this embodiment can be used for a variety of conventional applications. For example, it can be used in electronic devices such as speakers, vibration motors, and portable terminals that use them.

[0050] Furthermore, the magnetic fluid of this embodiment can be used as a magnetic fluid seal. Examples of magnetic fluid seals include vacuum seals, dust seals, and gas seals.

[0051] Mechanical devices that utilize magnetic fluid seals include: reduced pressure CVD (LPCVD) equipment, roller coaters, rotary chucks, turntables, substrate transport robots, ion implantation equipment, vacuum heat treatment equipment, and silicon pulling equipment.

[0052] Furthermore, the magnetic fluid of this embodiment has the characteristic of effectively suppressing the generation of secondary particles of magnetic particles in the magnetic fluid even when a polar organic solvent is added again to the composition obtained by removing the polar solvent from the magnetic fluid for magnetic fluidization, and therefore can be used as a standard sample for particle size distribution determination.

[0053] (Methods for manufacturing the first and second magnetic fluids) 1. Method for manufacturing the first magnetic fluid The first magnetic fluid of this embodiment can be prepared by adding magnetic particles, saturated fatty acids or their salts having 10 to 24 carbon atoms, or unsaturated fatty acids or their salts, and dispersing them in water or a nonpolar solvent.

[0054] The first magnetic fluid can be prepared or commercially available products can be used.

[0055] 2. Method for manufacturing the second magnetic fluid The manufacturing method of the second magnetic fluid according to this embodiment will be described. It should be noted that, in the manufacturing of the magnetic fluid, heating or cooling, or pressurization, can be performed as needed.

[0056] First, an alkoxylated compound with 2 to 4 carbon atoms is formed by adding an epoxide to an alcohol having 1 to 3 carbon atoms in a first magnetic fluid.

[0057] In preparing the aforementioned first magnetic fluid, the preparation methods include: methods for subdividing macroscopic magnetic particles to colloidal size; and methods for agglomerating atoms or ions to obtain magnetic microparticles. Methods for subdividing magnetic particles include: pulverization and spark erosion. Methods for agglomerating atoms or ions include: chemical coprecipitation (wet method), thermal decomposition of metal carbonyl groups, and vacuum evaporation. In particular, from the viewpoint of superior productivity, chemical coprecipitation is preferred. For example, firstly, sodium oleate, which is a saturated fatty acid or its salt with 10 to 24 carbon atoms, or an unsaturated fatty acid or its salt, is added to a magnetite slurry prepared from an aqueous solution of ferrous sulfate and an aqueous solution of ferric sulfate, so that oleic acid ions adhere to the surface of the magnetite particles to form particles. This yields the first magnetic fluid.

[0058] Alkoxylated compounds, which are formed by adding an epoxide with 2 to 4 carbon atoms to an alcohol with 1 to 3 carbon atoms, can be produced by reacting an alcohol with 1 to 3 carbon atoms and an epoxide with 2 to 4 carbon atoms using an alkaline catalyst.

[0059] Examples of alkaline catalysts include: alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal hydrides, alkaline earth metal hydrides, alkali metal carboxylates, and / or alkaline earth metal carboxylates. Alkali metals are selected from the group consisting of Li, Na, K, Rb, and Cs, while alkaline earth metals are selected from the group consisting of Be, Ca, Mg, Sr, and Ba.

[0060] In addition, organic basic catalysts (e.g., amines) can be used as basic catalysts. Examples of organic basic catalysts include: N,N-dimethylbenzylamine, dimethylaminoethanol, dimethylaminopropanol, N-methyldiethanolamine, trimethylamine, triethylamine, N,N-dimethylcyclohexylamine, N-methylpyrrolidine, N,N,N',N'-tetramethylethylenediamine, diazabicyclo[2.2.2]octane, aliphatic amines or alkanolamines such as 1,4-dimethylpiperazine or N-methylmorpholine, aromatic amines such as imidazole and alkyl-substituted imidazole derivatives, N,N-dimethylaniline, 4-(N,N-dimethyl)aminopyridine, and copolymers of 4-vinylpyridine or vinylimidazolium with divinylbenzene through partial crosslinking.

[0061] Sodium hydroxide, potassium hydroxide, and / or cesium hydroxide are preferred as alkali metal hydroxides, with potassium hydroxide being particularly preferred.

[0062] An organic compound containing active hydrogen and an alkyl oxide, along with a basic catalyst, can be placed in a reaction apparatus and reacted at a temperature of 80–180°C, preferably 100–170°C, under an inert gas atmosphere. This yields an alkoxylated compound formed by adding an alkyl oxide with 2–4 carbon atoms to an alcohol having 1–3 carbon atoms.

[0063] As described above, after mixing an alkoxylate formed by adding an epoxide with 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms into a first magnetic fluid, the dispersion medium (water or a non-polar solvent) contained in the first magnetic fluid is removed, thereby obtaining a magnetic body. Next, a polar organic solvent is mixed into the magnetic body, thereby obtaining the second magnetic fluid of this embodiment.

[0064] (Standard sample for particle size distribution determination) The particle size distribution determination standard sample of this embodiment comprises a magnetic material and a polar organic solvent. The magnetic material comprises: magnetic particles with an average particle size of 10–50 nm, a saturated fatty acid or its salt or an unsaturated fatty acid or its salt with 10–24 carbon atoms, and an alkoxylate formed by adding an epoxide with 2–4 carbon atoms to an alcohol with 1–3 carbon atoms. The magnetic particles, the saturated fatty acid or its salt or an unsaturated fatty acid or its salt with 10–24 carbon atoms, the alkoxylate formed by adding an epoxide with 2–4 carbon atoms to an alcohol with 1–3 carbon atoms, and the polar organic solvent contained in the particle size distribution determination standard sample can be substances used in the magnetic fluid of this embodiment described above.

[0065] The content of magnetic particles in the standard sample for particle size distribution determination in this embodiment is preferably 0.5 to 3% by mass. More preferably, the content of magnetic particles in the standard sample for particle size distribution determination in this embodiment is 1 to 1.8% by mass, and even more preferably 1 to 1.4% by mass.

[0066] When using magnetic fluid as a standard sample for particle size distribution determination, the content of polar organic solvent relative to the total amount of magnetic fluid is preferably 97 to 99.5% by mass, more preferably 98 to 99% by mass.

[0067] The particle size distribution measurement standard sample of this embodiment can be used as a reference for particle size correction in the determination of the particle size distribution of magnetic particles. The particle size distribution measurement standard sample of this embodiment can be prepared as described above by adding a polar organic solvent to the magnetic body of this embodiment. Even when a polar organic solvent is added again to the magnetic body for magnetic fluidization, the generation of secondary particles of magnetic particles in the magnetic fluid can be well suppressed, and the issues of storage and safety of the magnetic fluid are simultaneously resolved. Therefore, it has excellent properties as a particle size distribution measurement standard sample.

[0068] Example The following are embodiments of the present invention, but these embodiments are provided to better understand the invention and its advantages and are not intended to limit the invention. It should be noted that, unless otherwise specified, "%" hereafter means "mass %".

[0069] The raw materials used in the examples and comparative examples are as follows.

[0070] [First Magnetic Fluid 1] • Magnetic particles: magnetite (average particle size: 30 nm); saturated fatty acids or their salts with 10-24 carbon atoms, or unsaturated fatty acids or their salts: sodium oleate; dispersion medium: heptane; magnetic particle content: 50% by mass.

[0071] [First Magnetic Fluid 2] • Magnetic particles: magnetite (average particle size: 30 nm); saturated fatty acids or their salts with 10-24 carbon atoms, or unsaturated fatty acids or their salts: sodium oleate; dispersion medium: isoparaffins; magnetic particle content: 60% by mass.

[0072] [Magnetic particles] • Magnetite (average particle size: 20 nm), saturated fatty acids or their salts with 10 to 24 carbon atoms, or unsaturated fatty acids or their salts: sodium oleate.

[0073] [Alkoxylate 1] Alkoxylated products formed by the addition of ethylene oxide to methanol: the alcohol has 1 carbon atom.

[0074] [Alkoxylate 2] Alkoxylated compounds formed by the addition of ethylene oxide or propylene oxide to 1-hexadecyl alcohol or stearyl alcohol: the alcohol has 16 or 18 carbon atoms.

[0075] [Alkoxylate 3] Alkoxylated compounds formed by the addition of ethylene oxide to 2-butyl-1-octanol: the alcohol has 12 carbon atoms.

[0076] [Alkoxylate 4] Alkoxylated compounds formed by the addition of ethylene oxide to isotrexol: the alcohol has 13 carbon atoms.

[0077] [Polyester-based dispersant 1] • Polyhydroxystearic acid dispersants [Polyester-based dispersant 2] Polycaprolactone-based dispersants [Polar organic solvents] · Ethanol <Example 1> 1. Preparation of the first magnetic fluid 1 Magnetite slurry is produced by the well-known chemical coprecipitation method.

[0078] After adjusting the pH to 3 by adding 3N (equivalent) of HClaq (hydrochloric acid aqueous solution) to the magnetite slurry, sodium oleate was added as a dispersant, and the mixture was stirred at 60°C for 30 minutes. This process allows the dispersant to adsorb onto the surface of the magnetite particles. Next, the mixture was allowed to stand, allowing the magnetite particles in the liquid to agglomerate and settle, and the supernatant was discarded. Then, fresh water was added, stirred, and allowed to stand, and the supernatant was discarded. This water washing process was repeated several times to remove electrolytes from the aqueous solution. The mixture was then filtered, dehydrated, and dried to produce powdered magnetite particles coated with sodium oleate as a dispersant.

[0079] Next, hexane, a low-boiling-point organic solvent, was added to the powdered magnetite particles and the mixture was thoroughly shaken, thus obtaining an intermediate medium in which the magnetite particles were dispersed in hexane. Then, methanol, a low-boiling-point polar organic solvent, was added to the slurry to cause the particles to agglomerate and precipitate once, and the supernatant was discarded. This removed excess dispersant, except for the dispersant molecules adsorbed onto the magnetite particles. The precipitated magnetite particles were then redispersed in hexane to obtain an intermediate medium containing dispersed magnetite particles.

[0080] The intermediate medium was placed in a centrifuge and centrifuged at 8000G for 30 minutes to remove larger, poorly dispersed magnetite particles by sedimentation. Next, the supernatant containing the unsettled magnetite particles was transferred to a rotary evaporator and maintained at 90°C to evaporate and remove the low-boiling-point organic solvent, hexane, yielding oleophilic magnetite particles (average particle size: 20 nm) coated with sodium oleate as a dispersant through monomolecular adsorption. It should be noted that the mass ratio of magnetite to sodium oleate was 4:1.

[0081] 6.5g of the magnetite particles were taken and dispersed in 6.5g of heptane to obtain the first magnetic fluid 1.

[0082] 2. Preparation of the magnetic material in Example 1 Next, 5g of alkoxylate 1 was added to 10g of the magnetic body, and then the mixture was dried under reduced pressure to remove heptane, thus obtaining the magnetic body of Example 1.

[0083] <Example 2> For the preparation of the first magnetic fluid 1 in Example 1, isoparaffin was used instead of heptane, and its addition amount was changed to 4.3g. Otherwise, the magnetic body of Example 2 was obtained in the same manner as in Example 1.

[0084] <Example 3> In Example 1, the first magnetic fluid 2 was used instead of the first magnetic fluid 1, and otherwise the same magnetic body as in Example 1 was obtained in Example 3.

[0085] <Comparative Example 1> Heptane was removed by depressurized drying of the first magnetic fluid 1 in Example 1, and a magnetic material of Comparative Example 1 was obtained.

[0086] <Comparative Example 2> In Example 1, alkoxylate 1 was replaced with alkoxylate 2, and otherwise the magnetic material of Comparative Example 2 was obtained in the same manner as in Example 1.

[0087] <Comparative Example 3> In Example 1, alkoxy compound 1 was replaced with alkoxy compound 3, and otherwise the magnetic material of Comparative Example 3 was obtained in the same manner as in Example 1.

[0088] <Comparative Example 4> In Example 1, alkoxy compound 1 was replaced with alkoxy compound 4, and otherwise the magnetic material of Comparative Example 4 was obtained in the same manner as in Example 1.

[0089] <Comparative Example 5> In Example 1, alkoxylate 1 was replaced with polyester dispersant 1, and otherwise the magnetic material of Comparative Example 5 was obtained in the same manner as in Example 1.

[0090] <Comparative Example 6> In Example 1, alkoxylate 1 was replaced with polyester dispersant 2, and otherwise the magnetic material of Comparative Example 6 was obtained in the same manner as in Example 1.

[0091] <Comparative Example 7> In Example 3, alkoxy compound 1 was replaced with alkoxy compound 2, and otherwise the same magnetic material as in Example 3 was obtained for Comparative Example 7.

[0092] <Example 4> Ethanol was added to the magnetic material in Example 1 to obtain a second magnetic fluid 1 with a magnetic particle content of 30% by mass.

[0093] <Example 5> Ethanol was added to the magnetic material in Example 3 to obtain a second magnetic fluid 2 with a magnetic particle content of 30% by mass.

[0094] <Comparative Example 8> An attempt was made to add ethanol to the magnetic material of Comparative Example 2 to prepare a magnetic fluid.

[0095] <Comparative Example 9> An attempt was made to prepare a magnetic fluid by adding ethanol to the magnetic material of Comparative Example 3.

[0096] <Comparative Example 10> An attempt was made to prepare a magnetic fluid by adding ethanol to the magnetic material of Comparative Example 4.

[0097] <Comparative Example 11> An attempt was made to prepare a magnetic fluid by adding ethanol to the magnetic material of Comparative Example 5.

[0098] <Comparative Example 12> An attempt was made to prepare a magnetic fluid by adding ethanol to the magnetic material of Comparative Example 6.

[0099] <Comparative Example 13> An attempt was made to prepare a magnetic fluid by adding ethanol to the magnetic material of Comparative Example 7.

[0100] <Example 6> A composition was obtained by removing ethanol from the magnetic fluid of Example 4. Ethanol was then added to this composition to obtain a second magnetic fluid 3 with a magnetic particle content of 30% by mass.

[0101] <Example 7> Ethanol was added to the magnetic material in Example 1 to obtain a standard sample 1 for particle size distribution determination with a magnetic particle content of 1% by mass.

[0102] <Comparative Example 14> Ethanol was added to the magnetic material of Comparative Example 1 to obtain Particle Size Distribution Test Sample 2, which contained 1% by mass of magnetic particles.

[0103] <Status Evaluation of Magnetic Materials> The state of the magnetic bodies in Examples 1-3 and Comparative Examples 1-7 was visually observed and evaluated using the following criteria A-D. The evaluation results are shown in Table 1.

[0104] A: Paste-like (flowing).

[0105] B: Clay-like (non-flowing).

[0106] C: liquid.

[0107] D: Solid-liquid separation.

[0108] <Evaluation of superparamagnetism> Ten g each of the second magnetic fluids from Examples 4-6 and the compositions from Comparative Examples 8-13 were placed in petri dishes. When a permanent magnet (6 overlapping 240mT neodymium magnets) was brought close to the glass surface of the petri dish, the presence of spikes was visually evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 2.

[0109] If there is a spike phenomenon, it indicates that the magnetic particles in the second magnetic fluid are superparamagnetic.

[0110] A: There is a spike phenomenon.

[0111] B: No spike phenomenon.

[0112] <Evaluation of dispersibility in polar organic solvents> The state of the second magnetic fluids of Examples 4-6 and the compositions of Comparative Examples 8-13 was visually evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 2.

[0113] A: It becomes a magnetic fluid, with magnetic particles dispersed in ethanol.

[0114] B: It did not become a magnetic fluid, but separated into a magnetic material and ethanol.

[0115] <Particle Size Evaluation of Magnetic Particles> The particle size distribution results of the magnetic particles in the standard sample for particle size distribution determination of Example 7 and the sample for particle size distribution determination of Comparative Example 14 are shown below. Figure 1 and Figure 2 The particle size was measured using a dynamic light scattering particle size distribution measuring device (product name: SZ-100SZ, manufactured by Horiba Manufacturing Co., Ltd.).

[0116] like Figure 1 As shown, the peak value of the particle size distribution of magnetic particles in the standard sample of Example 7 was approximately 30 nm. (Inspection) The magnetic materials of Examples 1 to 3 contain magnetic particles with an average particle size of 10 to 50 nm, saturated fatty acids or their salts or unsaturated fatty acids or their salts with 10 to 24 carbon atoms, and alkoxylates formed by adding an epoxide with 2 to 4 carbon atoms to an alcohol with 1 to 3 carbon atoms. Therefore, as described in Table 1, they all become magnetic materials with a fluid paste-like consistency.

[0117] On the other hand, the magnetic materials of Comparative Examples 1 to 7 do not contain any of the following: saturated fatty acids or their salts having 10 to 24 carbon atoms, unsaturated fatty acids or their salts, or alkoxylates formed by adding an epoxide having 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms. Therefore, as described in Table 1, none of them became a magnetic material with a fluid paste-like consistency.

[0118] The second magnetic bodies in Examples 4 to 6 are magnetic bodies formed by adding polar organic solvents to the magnetic bodies in Examples 1 to 3. As shown in Table 2, they have superparamagnetism and good dispersibility in polar organic solvents.

[0119] On the other hand, the compositions of Comparative Examples 8 to 13 were compositions formed by adding a polar organic solvent to the magnetic body of Comparative Examples 2 to 7. As shown in Table 2, they did not have superparamagnetism, did not become magnetic fluids, and separated into magnetic body and ethanol, and did not become magnetic fluids.

[0120] According to the results of Examples 1 to 7, the particle sizes of the magnetic particles in the first magnetic fluid 1 and the magnetic particles in the first magnetic fluid 2 are both 20 nm. On the other hand, the peak value of the particle distribution of the magnetic particles in the particle size distribution measurement standard sample 1 is about 30 nm. Therefore, it can be considered that this difference in particle size is caused by the second surfactant adhering to the first surfactant.

[0121] That is, as can be seen from the results of Examples 1 to 7, by including a second surfactant, which is an alkoxylated compound formed by adding an epoxide with 2 to 4 carbon atoms to an alcohol with 1 to 3 carbon atoms, and the second surfactant adhering to the first surfactant adhering to the surface of the magnetic particles, the problems of storage and safety of magnetic fluid are solved, and even when a polar organic solvent is added to the magnetic body again for magnetic fluidization, the aggregation of magnetic particles in the magnetic fluid can be well suppressed.

Claims

1. A magnetic material comprising: magnetic particles with an average particle size of 10-50 nm, a saturated fatty acid or its salt having 10-24 carbon atoms, or an unsaturated fatty acid or its salt, and an alkoxylate formed by adding an epoxide having 2-4 carbon atoms to an alcohol having 1-3 carbon atoms.

2. The magnetic body according to claim 1, wherein, The magnetic material is in the form of a paste.

3. A magnetic fluid comprising a magnetic material as described in claim 1 or 2 and a polar organic solvent.

4. A standard sample for particle size distribution determination, comprising a magnetic material as described in claim 1 or 2 and a polar organic solvent, wherein the magnetic particles contain 0.5 to 3% by mass.

5. A method for manufacturing a magnetic material, comprising the step of removing the polar organic solvent from the magnetic fluid as described in claim 3 to obtain the magnetic material. The polar organic solvent content in the magnetic material obtained by removing the polar organic solvent is less than 1% by mass.

6. A method for manufacturing a magnetic material, comprising: The process of obtaining a first magnetic fluid, wherein the first magnetic fluid comprises magnetic particles, a saturated fatty acid or its salt having a carbon number of 10 to 24, or an unsaturated fatty acid or its salt, and water or a nonpolar solvent. In the step of mixing an alkoxylate in the first magnetic fluid, the alkoxylate is formed by adding an epoxide with 2 to 4 carbon atoms to an alcohol having 1 to 3 carbon atoms; and The process of removing the water or nonpolar solvent.

7. A method for manufacturing a magnetic fluid, comprising: a step of obtaining a second magnetic fluid by mixing a polar organic solvent into a magnetic body obtained by the manufacturing method of claim 6.

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