Semi-hard magnetic powder having high value of color and method for synthesizing the same

Abstract

To provide a semi-hard magnetic white powder having properties suitable for use as a security pigment, such as a magnetic powder contained in magnetic ink used in MICR.SOLUTION: Provided is a white powder having a titanium oxide film and a silver metal film disposed, in this order, on the surface of base particles formed from an alnico alloy that is a semi-hard magnet.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a white semi-hard magnetic powder, such as an alnico alloy (Fe-Al-Ni-Co) powder, characterized by high brightness (whiteness). In particular, the invention relates to a white powder that can be used as a pigment for security purposes, such as magnetic powder contained in magnetic ink used in magnetic ink character recognition (MICR). [Background technology]

[0002] Magnetic ink character recognition (MICR) is a system that uses magnetic ink to print an identification mark on specified media such as securities, and then uses a dedicated reader to read information such as the shape and magnetic information of the identification mark, in order to prevent the media from being altered or counterfeited after it has been circulated on the market.The system then uses the read information to determine whether the media is genuine or not. The magnetic ink used in MICR contains magnetic powder, which is required to be capable of forming identification marks that are highly durable and easy to read. The present invention relates to a white powder that is particularly suitable for use in such magnetic ink for security purposes.

[0003] Generally, the properties required for magnetic powder used in magnetic ink include sufficient dispersibility in the ink and sufficient magnetism imparted to the ink. In MICR magnetic inks, good dispersibility of the magnetic powder in the ink results in good fixation of the magnetic ink, and a high remanent magnetic moment results in good sensitivity as a magnetic ink, which contributes to improving the image quality of printed identification marks. Patent Document 1 describes a magnetic ink in which magnetic properties are adjusted by the shape anisotropy (acicular shape) of the magnetic particles by using a magnetic powder consisting of acicular magnetic particle powder and non-acicular magnetic particle powder.

[0004] Alnico alloys are alloys whose main components are Al, Ni, and Co or Al and Ni, with the remainder essentially consisting of Fe. They are generally manufactured by casting, but because they are hard and brittle, cutting is extremely difficult, so small magnets with complex shapes are manufactured using powder metallurgy and powder molding. On the other hand, the widely used method for producing alloy powder is to produce molten alloy by atomization, such as water atomization or gas atomization. However, the atomization of Alnico alloys has problems such as difficulty in production due to the high Al and Ti content, which makes the molten alloy pouring nozzle prone to clogging during spraying, low yield and high production costs, limiting mass production. Patent Document 2 discloses a technology for producing Alnico alloy powder by atomization, which prevents the clogging of the pouring nozzle by adding Si to the molten metal.

[0005] Furthermore, magnetic powders are generally often black, and even if a colored layer is provided on the surface, the overall color becomes dark, making it impossible to obtain a vividly colored color magnetic ink. Patent Document 3 describes a technology for obtaining a bright white powder by forming a titanium oxide film and a metallic silver film in this order on the surface of base particles mainly made of soft magnetic powder. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-211446 [Patent Document 2] Japanese Patent Application Publication No. 10-280011 [Patent Document 3] Patent No. 4113045 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide a semi-hard magnetic white powder having properties suitable for use as a pigment for security purposes, such as the magnetic powder contained in magnetic ink used in MICR. That is, the object of the present invention is to provide a magnetic powder that has semi-hard magnetic properties and has been subjected to a whitening treatment to increase brightness. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention has the following configuration. [1] A white powder comprising base particles made of an alnico alloy having semi-hard magnetic properties, and a titanium oxide film and a metallic silver film on the surface of the base particles made of the alnico alloy, in that order from the surface to the outside. [2] The composition of the base particles made of the alnico alloy is, based on the total weight of the base particles made of the alnico alloy, The white powder according to [1], which is composed of Al: 7 to 13 wt %, Ni: 14 to 25 wt %, Co: 0 to 38 wt %, Cu: 0 to 4 wt %, Ti: 0 to 8 wt %, and the remainder being Fe and unavoidable impurity components. [3] The white powder according to [1] or [2], wherein the base particles made of the alnico alloy are atomized powder formed by a spraying method. [4] The white powder according to any one of [1] to [3], wherein the semi-hard magnetic property of the white powder is a remanent magnetic moment of 15 emu / g or more. [5] The white powder according to [4], wherein the semi-hard magnetic properties of the white powder are such that the residual magnetic moment is 15 emu / g or more and the coercive force is less than 500 Oe. [6] The white powder has an average particle size of 1 to 100 μm and a specific surface area of ​​0.01 to 20 m 2 / g and a lightness L* of 75 or more. [7] A magnetic ink containing the white powder according to any one of [1] to [6]. [8] A method for producing a white powder made of an alnico alloy, in which a titanium oxide film and a metallic silver film are formed on the surface of the alnico alloy powder in that order from the surface outward. [9] The composition of the alnico alloy powder is, based on the total weight of the alnico alloy powder, [8] A method for producing a white powder according to [8], comprising Al: 7 to 13 wt%, Ni: 14 to 25 wt%, Co: 0 to 38 wt%, Cu: 0 to 4 wt%, Ti: 0 to 8 wt%, and the remainder consisting of Fe and unavoidable impurity components.

[10] The method for producing a white powder according to [8] or [9], wherein the alnico alloy powder is produced by an atomization method.

[11] The alnico alloy powder formed by the atomization method has an average particle size of 1 to 100 μm and a specific surface area of ​​0.01 to 5.0 m 2 / g

[10] The method for producing a white powder according to

[10] .

[12] A method for producing a white powder according to any one of [8] to

[11] , comprising heat-treating an alnico alloy powder to form a semi-hard magnetic powder having a remanence moment of 15 emu / g or more, and then forming a titanium oxide film and a metallic silver film in this order.

[13] The method for producing a white powder according to

[12] , wherein the heat treatment is performed in an inert atmosphere at 750°C to 1000°C for 0 to 30 minutes. [Effects of the Invention]

[0009] The white powder of the present invention has semi-hard magnetic properties, making it suitable for use in magnetic inks used in MICR. Furthermore, because it has been subjected to a whitening treatment to enhance its brightness, when a colored layer is applied on top of it, it can be used to create vividly colored magnetic inks. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an SEM photograph of alnico metal powder coated with titanium oxide and silver. DETAILED DESCRIPTION OF THE INVENTION

[0011] (semi-hard magnetic) The present invention is characterized in that semi-hard magnetic powder is used as the magnetic powder for use in MICR and the like. Generally, ferromagnetic materials are classified into hard and soft magnetic materials according to their magnetization characteristics. Here, whether a magnetic material is hard or soft is generally determined by the magnitude of its coercive force. Hard magnetic materials are materials with both large coercive force and remanent magnetic moment, while soft magnetic materials are materials with both small coercive force and remanent magnetic moment. In this regard, when magnetic powder is used for security pigments such as MICR, if the magnetic powder is hard magnetic with a large coercive force, a large amount of external energy is required for magnetization, and a large-scale magnetization device is required.On the other hand, if the magnetic powder is soft magnetic with a small coercive force, the magnetic properties of the medium after magnetization will be below the readability limit of a magnetic information reader, which means that accurate magnetic information cannot be read.

[0012] Therefore, the inventors of the present invention have focused on semi-hard magnetic materials as magnetic powders, which have magnetic properties intermediate between hard and soft magnetic properties. In the case of semi-hard magnetic materials, the coercive force is intermediate between that of hard and soft magnetic materials, so the above-mentioned problems can be avoided. In addition, since semi-hard magnetic materials have lower coercive force and remanent magnetic moment than hard magnetic materials, they are less likely to aggregate in liquid magnetic ink, which improves the dispersibility and dispersion stability of the magnetic particles. The alnico alloy powder of the present invention has a small coercive force but a remanent magnetic moment intermediate between hard and soft, making it a magnetic powder with characteristics suitable for use as a pigment for security purposes.

[0013] (Alnico alloy powder produced by atomization) The alnico alloy powder of the present invention is produced by atomization, so that it is possible to form spherical powder with a fairly uniform particle size. This further improves dispersibility in magnetic ink. Furthermore, fluidity is also improved, leading to improved printing characteristics. Furthermore, because the particles are spherical, they can be used in the subsequent whitening process, forming uniform, thin TiO2 or metallic silver films, which is advantageous from the standpoint of magnetic properties.

[0014] (size of alnico alloy powder) The alnico alloy powder preferably has a volume average particle diameter D50 of 1 to 100 μm, more preferably 5 to 20 μm, as measured by a laser diffraction / scattering method. In addition, considering that the alnico alloy powder will be whitened in a later process, the thickness of the powder should be 0.01 to 5.0 m. 2 It is desirable that the specific surface area is 5.0 m / g. 2 If the specific surface area is greater than 0.01 m / g, it is necessary to use a larger amount of metallic silver to conceal the surface of the magnetic particles, but if the amount of metallic silver is too large, the magnetic properties of the magnetic powder will deteriorate, which is not preferable. 2 If the density is less than 1 / g, the size of the magnetic particles becomes too large, which is unsuitable for printing security materials, and is therefore undesirable. In order to adjust the magnetic powder to a preferred specific surface area, it is preferable to classify the alnico alloy powder after producing it by the atomization method.

[0015] (Composition of Alnico Alloy Powder) In general, it is said that in an alnico alloy, a decrease in Ni content increases the residual magnetic flux density and decreases the coercive force, while an increase in Al content decreases the coercive force. In the present invention, the alloy composition of the alnico alloy powder is in the following range. This makes it possible to achieve a coercive force suitable for magnetic ink applications. The composition of the alnico alloy powder used in the present invention is, based on the total weight of the alnico alloy powder, 7 to 13 weight percent Al, 14 to 25 weight percent Ni, 0 to 38 weight percent Co, 0 to 4 weight percent Cu, and 0 to 8 weight percent Ti, with the remainder being Fe and unavoidable impurities.

[0016] (Magnetic treatment of Alnico alloy powder) The formed alnico powder is magnetized to the desired magnetic material by aging heat treatment, which involves heating at 750 to 1000°C for 0 to 30 minutes in an inert atmosphere. By carrying out such an aging heat treatment, the remanent magnetic moment can be increased to a desired value.

[0017] (whitening method) The whitening of the alnico alloy powder is achieved by forming a titanium oxide film and a metallic silver film in this order on the surface of the powder. The titanium oxide film is mainly made of tetravalent titanium oxide (TiO2), but divalent or trivalent titanium oxide may also be used. The film may be formed by hydrolyzing titanium alkoxide or by forming an aqueous film from an aqueous titanium salt solution and then oxidizing it. The method for forming the metallic silver film is not particularly limited, and any known method such as electroless plating may be used. According to this whitening method, the titanium oxide film is interposed between the magnetic powder and the silver film, which significantly improves the brightness of the magnetic powder. In addition, the thickness of the metallic silver film can be made thinner than that of conventional metallic silver-coated white powders, which improves the magnetic properties of the white powder.

[0018] The magnetic properties of the produced white powder are preferably a residual magnetic moment Mr of 15 emu / g or more and a coercive force Hc of less than 500 Oe. As for the shape, the average particle diameter (volume average D50) is 1 to 100 μm, and the specific surface area is 0.01 to 20 m. 2 / g, and the lightness L* is preferably 75 or more. [Example]

[0019] (Alnico alloy powder) An iron-aluminum-nickel-cobalt alloy (Al: 12.9 wt%, Ni: 20.9 wt%, Co: 4.9 wt%, Cu: 3.0 wt%, Mr: 2.1 emu / g, Hc: 0.02 Oe, lightness L*: 52) manufactured by Epson Atmix was prepared by the atomization method. The alloy was classified using an air classifier.10 : 4.3 μm, D 50 :9.6μm, D 95 A metal powder with a particle size distribution of 24.7 μm was obtained. The specific surface area was 0.08 m. 2 / g. (Magnetic treatment) The metal powder obtained by the classification was heat-treated in a nitrogen atmosphere at a temperature increase rate of 15°C / min, and after the core temperature of the powder reached 850°C, it was air-cooled to obtain a magnetic powder with Mr: 20.4 emu / g and Hc: 354 Oe. (whitening) A yellow, transparent peroxotitanic acid solution was prepared by mixing 2.2 mL of titanium tetrachloride solution (16.0-17.0% asTi), 5.84 g of ammonia water, and 10.0 g of hydrogen peroxide water with 19.8 g of deionized water. 9.92 g of boric anhydride, 11.72 g of potassium chloride, and 2.55 g of sodium hydroxide were dissolved in 535.81 g of deionized water, and 167.5 g of the magnetic powder was suspended in the solution. The peroxotitanic acid solution was added dropwise while stirring the suspension, and the suspension was then dried to obtain titanium oxide-coated powder. A reducing solution was prepared by dissolving 1.2g of glucose, 0.12g of tartaric acid, and 2.12g of ethanol in 26.56g of deionized water. A silver ammine complex solution was prepared by mixing 1.25g of sodium hydroxide, 1.75g ​​of silver nitrate, and 3g of ammonia water with 90g of deionized water, and 10.0g of titanium oxide-coated powder was suspended in this solution. The reducing solution was mixed into the suspension while irradiating it with ultrasound, and the suspension was dried to obtain silver film-coated powder. (white powder) The obtained white powder had a lightness L* of 80.0, Mr: 21.6 emu / g, Hc: 362 Oe, D 50 : 13.5 μm, specific surface area is 0.1 m 2 / g. [Industrial Applicability]

[0020] The white powder made of the alnico alloy powder produced according to the present invention has semi-hard magnetic properties and significantly improved brightness, and is therefore expected to be used as a very useful security pigment in industry.

Claims

1. base particles made of an alnico alloy having semi-hard magnetic properties; The surface of the base particle made of the alnico alloy is coated with a titanium oxide film, a metallic silver film, and a silver film in this order from the surface to the outside. A white powder having the formula:

2. The composition of the base particles made of the alnico alloy is, based on the total weight of the base particles made of the alnico alloy, Al: 7-13% by weight, Ni: 14 to 25% by weight, Co: 0 to 38% by weight, Cu: 0 to 4% by weight, Ti: 0 to 8% by weight, 2. The white powder according to claim 1, wherein the balance consists of Fe and unavoidable impurities.

3. 3. The white powder according to claim 1, wherein the base particles made of the alnico alloy are atomized powder formed by a spraying method.

4. 4. The white powder according to claim 1, wherein the semi-hard magnetic property of the white powder is such that the remanent magnetic moment is 15 emu / g or more.

5. 5. The white powder according to claim 4, wherein the semi-hard magnetic properties of the white powder are such that the remanent magnetic moment is 15 emu / g or more and the coercive force is less than 500 Oe.

6. The white powder has an average particle size of 1 to 100 μm and a specific surface area of ​​0.01 to 20 m ２ / g and a lightness L* of 75 or more.

7. A magnetic ink containing the white powder according to any one of claims 1 to 6.

8. A method for producing a white powder made of an alnico alloy A method for producing a white powder, comprising forming a titanium oxide film and a metallic silver film on the surface of an alnico alloy powder in that order from the surface outward.

9. The composition of the alnico alloy powder is, based on the total weight of the alnico alloy powder, Al: 7-13% by weight, Ni: 14 to 25% by weight, Co: 0 to 38% by weight, Cu: 0 to 4% by weight, Ti: 0 to 8% by weight, and the remainder consists of Fe and unavoidable impurities.

10. 10. The method for producing a white powder according to claim 8, wherein the alnico alloy powder is produced by an atomization method.

11. The alnico alloy powder formed by the atomization method has an average particle size of 1 to 100 μm and a specific surface area of ​​0.01 to 5.0 m ２ The method for producing a white powder according to claim 10, characterized in that the molecular weight of the white powder is 1 / g.

12. The method for producing a white powder according to any one of claims 8 to 11, characterized in that the Alnico alloy powder is subjected to a heat treatment to obtain a semi-hard magnetic powder having a remanent magnetic moment of 15 emu / g or more, and then a titanium oxide film and a metallic silver film are formed in this order.

13. 13. The method for producing a white powder according to claim 12, wherein the heat treatment is performed in an inert atmosphere at a temperature of 750 to 1000° C. for 0 to 30 minutes.

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