AlNICO-based magnetic particles for security inks

Abstract

To provide AlNiCo-based magnetic particles with improved security. The AlNiCo-based magnetic particles are hard magnetic particles comprising a core particle containing Al, Ni, and Co, and an inorganic shell surrounding the core particle, and the core particle has a particle diameter D corresponding to 50% of the cumulative particle diameter distribution of the core particles. 50 The core particles are ultrafine particles having a particle size of 12 μm or less, and the core particles have compositional uniformity as defined by the following formulas 1, 2, and 3: Formula 1: 10≦UNF(Al), Formula 2: 10≦UNF(Ni), and Formula 3: 10≦UNF(Co). In formula 1, UNF(Al) is the value obtained by dividing the average Al composition among core particles by the standard deviation of the Al composition based on the weight percent composition, in formula 2, UNF(Ni) is the value obtained by dividing the average Ni composition among core particles by the standard deviation of the Ni composition based on the weight percent composition, and in formula 3, UNF(Co) is the value obtained by dividing the average Co composition among core particles by the standard deviation of the Co composition based on the weight percent composition.

Description

[Technical Field]

[0001] The present invention relates to AlNiCo-based magnetic particles for security inks and security inks containing the same, and more particularly to AlNiCo-based magnetic particles for security inks and security inks containing the same, in which the magnetic particles have excellent composition uniformity according to pre-designed values, thereby enabling them to have uniform hard magnetic properties and improved security. [Background technology]

[0002] Security materials are essential in areas where counterfeiting and falsification must be prevented. For example, in the field of security printing, security materials are used for valuable documents such as checks, stamps, gift certificates, certificate stamps, and bonds.

[0003] Currently, magnetic particles with a core-shell structure formed by coating a magnetic material with an inorganic material are known as security materials. It is known that the magnetic material is coated with an inorganic material to lighten the dark color of the magnetic material, or that other types of inorganic materials are further coated to improve the mechanical properties of the magnetic particles (Patent Document 1).

[0004] Recently, research has been conducted to maximize the security of security products using security materials. As a preliminary step, it has been shown that the security of security products can be maximized by mixing ferromagnetic particles with relatively high coercivity and soft magnetic particles with relatively low coercivity and forming them into a specific shape or pattern, as a method of positioning the coercivity and magnetization density of magnetic particles within a specific region.

[0005] However, with the evolution of highly developed measurement equipment, if the security material has a simple pattern or the difference in coercivity of the mixed magnetic particles is too large, it may be easily recognized by general equipment, so it is necessary for the security material to have a specific window of coercivity and magnetization density so that it can be recognized only by expensive high-resolution recognition equipment (hereinafter referred to as ``expensive recognition equipment'').

[0006] However, existing magnetic particles still have the following problems in solving these problems: 1) If the magnetization density of the magnetic particles is too large or too small, it will be difficult for expensive recognition equipment to measure the unique signal of the magnetic particles. 2) If the size of the magnetic particles is too large or too small, the magnetic particles will not be able to effectively reflect sunlight, making it difficult to conceal the originally dark color of the magnetic particles. This not only drastically reduces the security, but may also cause problems such as printing defects during the security printing process.

[0007] Proposals to solve this problem include: i) a method of producing relatively small nanoparticles by agglomerating them with a binder; and ii) a method of crushing relatively large particles to a desired size.

[0008] However, the binder aggregation method (i) can cause the problem of the binder swelling when agglomerating with the magnetic particles, making it difficult to produce magnetic particles for security purposes having a specific size and shape.

[0009] The pulverization method ii) is advantageous in terms of coercive force, magnetization density, purity, cost, etc., compared to the binder aggregation method i) because no binder is added.

[0010] However, in the pulverization method (ii), magnetic particles are generally produced by a crushing method, which we have found to be difficult to control particle size to the several micron level.Furthermore, when powders are made from starting materials with relatively large coercive force, the coercive force also decreases significantly as the particle size decreases.

[0011] In addition to these two methods, atomizing is known as a method for producing magnetic particles of a specific size. Atomizing methods are divided into gas atomization, water injection, and mixed atomization, depending on the type of cooling medium. In general, atomizing involves spraying molten alloy into a cooling medium through a nozzle or the like, and then cooling the molten alloy droplets by colliding them with the cooling medium, thereby producing fine magnetic particles with a particle size of tens or hundreds of micrometers.

[0012] However, the water atomization process uses water (H2O) as the main cooling medium, which poses a significant problem of oxidation of the powder produced.

[0013] In addition, the gas atomization method uses inert gases (N2, Ar, He) or air as a cooling medium, which reduces the problems of oxidation and impurity contamination during powder production, making it possible to produce high-quality powder. However, the cooling effect is relatively low, which can lead to the risk of fine segregation during the production process, making it technically inconvenient for producing magnetic particles of specific shapes, and the yield is very low at around 5%, making it very unsuitable for commercial use.

[0014] Therefore, the applicant has provided a manufacturing technology for AlNiCo-based magnetic particles that can effectively reflect sunlight to conceal dark-colored magnetic particles, have magnetic properties that enable them to function as strong security elements, and are suitable for printing (Patent Document 2).After conducting more in-depth research on this, the applicant has established a manufacturing technology for AlNiCo-based magnetic particles that has improved yield and further improved security, and has filed the present invention. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Korean Patent Publication No. 2013-0072444 [Patent Document 2] Korean Patent Registration No. 1718505 Summary of the Invention [Problem to be solved by the invention]

[0016] An object of the present invention is to provide AlNiCo-based magnetic particles with improved security.

[0017] In particular, the present invention aims to provide AlNiCo-based magnetic particles that have magnetic properties that allow magnetic particles and paramagnetic particles to be distinguished using expensive recognition equipment, have bright colors, have excellent printability, and have a designed and extremely uniform composition that allows for stable formation of fine linear security patterns. [Means for solving the problem]

[0018] The AlNiCo-based magnetic particles (I) according to one embodiment of the present invention are hard magnetic particles comprising a core particle containing Al, Ni, and Co, and an inorganic shell surrounding the core particle, and the core particle has a particle diameter D corresponding to 50% of the cumulative particle diameter distribution of the core particles. 50 The core particles are ultrafine particles having a particle diameter of 12 μm or less, and the core particles have composition uniformity represented by the following formulas 1, 2 and 3. Formula 1: 10≦UNF(Al) Formula 2: 10≦UNF(Ni) Formula 3: 10≦UNF(Co) In formula 1, UNF(Al) is the value obtained by dividing the average Al composition between core particles by the standard deviation of the Al composition, based on the weight percent composition; in formula 2, UNF(Ni) is the value obtained by dividing the average Ni composition between core particles by the standard deviation of the Ni composition, based on the weight percent composition; and in formula 3, UNF(Co) is the value obtained by dividing the average Co composition between core particles by the standard deviation of the Co composition, based on the weight percent composition.

[0019] The AlNiCo-based magnetic particles (II) according to another embodiment of the present invention are hard magnetic particles comprising a core particle containing Al, Ni, and Co, and an inorganic shell surrounding the core particle, and the core particle has a particle diameter D corresponding to 50% of the cumulative particle diameter distribution of the core particles. 50 The core particles are ultrafine particles having a particle diameter of 12 μm or less, and are produced by an atomizing method using a coolant containing at least water, and satisfy the following formulas 4, 5, and 6 based on a design composition, which is the composition of a molten alloy containing Al, Ni, and Co used during atomizing.

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[0020] In the AlNiCo-based magnetic particles (I, II) according to one embodiment of the present invention, the core particle can further satisfy the following formulas 7 and 8. Equation 7: 3μm≦D 50 ≦12μm Formula 8: 10μm≦D 90 ≦20μm In formula 7, D 50 is the particle size corresponding to 50% in the cumulative particle size distribution of the core particles, and in Equation 8, D 90 is the particle size corresponding to 90% of the cumulative particle size distribution of core particles.

[0021] In the AlNiCo-based magnetic particles (I, II) according to one embodiment of the present invention, the inorganic shell includes a metal shell, and the metal shell can satisfy the following formulas 9 and 10. Formula 9: 50nm≦t m ≦100nm Equation 10: σ t ≦30nm In equation 9, t m is the average thickness of the metal shell, and in Eq. 10, σ t is the standard deviation of the metal shell thickness.

[0022] In the AlNiCo-based magnetic particles (I, II) according to one embodiment of the present invention, the inorganic shell may further include a dielectric shell located below or above the metal shell.

[0023] In the AlNiCo-based magnetic particles (I, II) according to one embodiment of the present invention, the saturation magnetization (Ms) of the magnetic particles may be 50 to 150 emu / g, and the remanence (Mr) may be 10 to 40 emu / g.

[0024] In the AlNiCo-based magnetic particles (I, II) according to one embodiment of the present invention, the coercive force of the magnetic particles may be 100 to 500 Oe.

[0025] In the AlNiCo-based magnetic particles (I, II) according to one embodiment of the present invention, the core particle may further contain one or more quaternary elements selected from Cu, Ti, Fe, and Si.

[0026] In the AlNiCo-based magnetic particles (I, II) according to one embodiment of the present invention, the core particles may have a composition in weight percent such that the average composition of the fourth element among the core particles divided by the standard deviation of the composition of the fourth element is 10 or more.

[0027] In the AlNiCo-based magnetic particles (I, II) according to one embodiment of the present invention, the core particle further contains Ti, Fe, and Cu, and may contain, on a weight percent basis, 4 to 12% Al, 10 to 20% Ni, 15 to 25% Co, 1 to 10% Ti, 0.5 to 5% Cu, with the remainder being Fe and other unavoidable impurities.

[0028] The AlNiCo-based magnetic particles (I, II) according to one embodiment of the present invention can have an infrared reflectance of 60% or more at a wavelength of 900 nm.

[0029] The present invention includes a security ink containing the above-mentioned AlNiCo-based magnetic particles (I, II).

[0030] The present invention includes a valuable instrument containing the above-mentioned AlNiCo-based magnetic particles (I, II). [Effects of the Invention]

[0031] The AlNiCo-based magnetic particles for security purposes according to the present invention are 50 The ultra-fine particles, with a particle size of 12 μm or less, and the precisely designed composition of the particles provide improved security.

[0032] The AlNiCo-based magnetic particles for security purposes according to the present invention are 50 The ultra-fine particles, with a diameter of 12 μm or less, and the extremely small compositional variation, allow each particle to have uniform magnetic properties, making it possible to realize security elements with sophisticated shapes.

[0033] The AlNiCo-based magnetic particles according to one embodiment of the present invention have a light color characteristic that can conceal dark colored magnetic particles, have enhanced security that can be distinguished from hard magnetic materials using only expensive recognition equipment, and are printable, which has the advantage that conventional methods for manufacturing security elements using inks can be used as is without any significant changes.

[0034] The AlNiCo-based magnetic particles according to one embodiment of the present invention have significantly improved infrared reflectivity, and therefore have the advantage of enabling multiple security features based on different and independent elements such as magnetic properties that are difficult to distinguish from hard magnetic particles, infrared reflectivity properties, and advanced shaping. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a scanning electron microscope photograph of AlNiCo-based magnetic particles produced according to one embodiment of the present invention. [Figure 2] 1A and 1B are scanning electron microscope photographs of the cross section of an AlNiCo-based magnetic particle manufactured according to one embodiment of the present invention, and a graph showing the thickness distribution of the silver shell measured. [Figure 3] FIG. 1 shows optical images, soft magnetic images, hard magnetic images, and infrared images of security elements formed using a security ink containing AlNiCo-based magnetic particles manufactured according to one embodiment of the present invention and a security ink containing general soft magnetic particles. DETAILED DESCRIPTION OF THE INVENTION

[0036] The AlNiCo-based magnetic particles of the present invention will be described in detail below. In this regard, unless otherwise defined, the technical and scientific terms used have the meanings that are commonly understood by those skilled in the art to which the present invention pertains, and descriptions of known functions and configurations that may obscure the gist of the present invention will be omitted in the following description and accompanying drawings.

[0037] The present applicant has found that when designing a security element in the form of a fine line using fine AlNiCo-based hard magnetic particles with a size on the order of micrometers to fabricate a security element on a valuable document, even expensive recognition equipment cannot distinguish and recognize the security element from a paramagnetic particle-based security element with a high degree of reproducibility, and that the shape of the designed security element cannot be recognized with a high degree of reproducibility. After extensive research to solve these problems, the applicant has found that uniform compositional characteristics among the AlNiCo-based magnetic particles are essential to stably realize a fine linear security element. In other words, it is essential to suppress compositional variations among the magnetic particles being manufactured. As a result of long-term research to ensure uniform compositional characteristics, the company discovered that the conventional gas injection method (atomizing method using gas as a cooling medium) has the limitation of being unable to prevent segregation that induces aluminum-rich phases or iron-rich phases due to the slow cooling rate. However, by using water as a cooling medium to induce rapid cooling and prevent oxidation of easily oxidized elements (e.g., Al, Ti, etc.) during the cooling process, it was discovered that compositional variation can be suppressed, resulting in uniform magnetic properties and the production of particles with a composition substantially identical to the designed composition, which led to the filing of the present invention.

[0038] Therefore, the present invention includes one embodiment of magnetic particles (I) in which compositional variation among particles is suppressed, and another embodiment of magnetic particles (II) having a designed composition, i.e., a composition substantially identical to the composition of the molten metal used during atomization. In describing the present invention in detail, unless specifically described in relation to one embodiment, all of the detailed description corresponds to one embodiment (magnetic particles (I)) and another embodiment (magnetic particles (II)).

[0039] In describing the present invention in detail, "AlNiCo-based" refers to an alloy containing Al, Ni, and Co, and "AlNiCo-based magnetic particles" refers to hard magnetic alloy particles containing Al, Ni, and Co, and may refer to security magnetic particles used for the security of valuable documents. Hard magnetic particles are difficult to magnetize, but once magnetized, are difficult to demagnetize and have higher coercive force (Hc) and residual magnetization density (Mr) than soft magnetic particles. In AlNiCo-based magnetic particles, "hard magnetic" refers to magnetic properties with a coercive force of 100 to 500 Oe. On the other hand, "soft magnetic particles" refer to particles that are easily magnetized by a relatively weak magnetic field, but that rapidly lose magnetization over time when the external magnetic field is removed. "Soft magnetic" refers to magnetic properties with a coercive force of 10 to 90 Oe.

[0040] In describing the present invention in detail, the aqueous atomizing method may refer to a process or manufacturing method in which a coolant containing water is used when a molten alloy is sprayed through a nozzle, etc. In this regard, the aqueous atomizing method should not be interpreted as being limited to a method in which only water is used as a coolant, but should also be interpreted as including a case in which water and a gas (e.g., an inert gas such as N2, Ar, He, or Ne) are used simultaneously as a coolant.

[0041] In describing the present invention in detail, the term "AlNiCo-based magnetic particles" can refer to a magnetic particle group, i.e., an aggregate of individual magnetic particles, or a group of independent individual magnetic particles excluding aggregates of magnetic particles or aggregates of core particles. In this context, the term "group" refers to a number at least large enough that the average magnetic properties do not change depending on the number of magnetic particles constituting the group. In other words, the term "group" can refer to a group of magnetic particles large enough in size (number) that the magnetic properties of the magnetic particle group can be consistently exhibited. In another sense, the term "group" can refer to a particle group having a size large enough to obtain reliable average size, average composition, and dispersion. In this respect, the term "AlNiCo-based magnetic particles" can refer to a group of at least 50 magnetic particles, specifically at least 100 magnetic particles, more specifically at least 300 magnetic particles, even more specifically at least 500 magnetic particles, and even more specifically at least 1000 magnetic particles. In terms of manufacturing method, AlNiCo-based magnetic particles can mean a group of magnetic particles manufactured using particle(s) obtained as a core particle by atomizing an AlNiCo-based alloy melt having a designed composition using a coolant containing water, that is, particle(s) obtained as a core particle by a single water-based injection method.

[0042] The Al-based magnetic particles (I) according to one embodiment of the present invention are magnetic particles in which the compositional variation among magnetic particles is suppressed. Specifically, the AlNiCo-based magnetic particles (I) according to the present invention are hard magnetic particles comprising core particles containing Al, Ni, and Co, and an inorganic shell surrounding the core particles, and the core particles have a particle diameter D corresponding to 50% in the cumulative particle diameter distribution of the core particles. 50 The core particles are ultrafine particles having a particle diameter of 12 μm or less, and the core particles have composition uniformity represented by the following formulas 1, 2 and 3. Formula 1: 10≦UNF(Al) Formula 2: 10≦UNF(Ni) Formula 3: 10≦UNF(Co) In formula 1, UNF(Al) is the value obtained by dividing the average Al composition between core particles by the standard deviation of the Al composition, based on the weight percent composition; in formula 2, UNF(Ni) is the value obtained by dividing the average Ni composition between core particles by the standard deviation of the Ni composition, based on the weight percent composition; and in formula 3, UNF(Co) is the value obtained by dividing the average Co composition between core particles by the standard deviation of the Co composition, based on the weight percent composition.

[0043] That is, UNF(Al) is the value obtained by dividing the average Al composition (average Al weight %) between core particles by the standard deviation of the Al composition (standard deviation of Al weight % between core particles) based on the weight % composition when the total weight of the core particle is 100%, UNF(Ni) is the value obtained by dividing the average Ni composition (average Ni weight %) between core particles by the standard deviation of the Ni composition (standard deviation of Ni weight % between core particles) based on the weight % composition when the total weight of the core particle is 100%, and UNF(Co) is the value obtained by dividing the average Co composition (average Co weight %) between core particles by the standard deviation of the Co composition (standard deviation of Co weight % between core particles) based on the weight % composition when the total weight of the core particle is 100%.

[0044] As mentioned above, the magnetic particles may refer to a magnetic particle group, and in Formulas 1, 2, and 3, the average Al composition (or Ni composition or Co composition) of the core particles may refer to the average value of the Al composition (or Ni composition or Co composition) based on the weight percent Al content of each of the core particles of the magnetic particles constituting the magnetic particle group, and it goes without saying that the standard deviation of the Al composition (or Ni composition or Co composition) may refer to the standard deviation of the Al composition (or Ni composition or Co composition) of each of the core particles of the magnetic particles constituting the magnetic particle group. Furthermore, since the UNF of any given element increases as the composition becomes more uniform, it is meaningless to limit the upper limit of the UNF, but in practice, the upper limit of the UNF can reach 200.

[0045] The compositional uniformity of AlNiCo-based magnetic particles that satisfy Equations 1, 2, and 3 is a compositional uniformity of AlNiCo-based particles that cannot be obtained by conventionally known gas atomization processes or conventional water atomization processes that cause oxidation by water. This compositional uniformity has never been reported for AlNiCo-based magnetic particles with average particles on the order of several micrometers, which have hard magnetic properties that cannot be distinguished from soft magnetic particles using general recognition equipment and can be detected and distinguished from soft magnetic particles using expensive recognition equipment.

[0046] As described above, the AlNiCo-based magnetic particles according to the present invention have a core particle of D 50 The AlNiCo-based magnetic particles are characterized by being ultrafine particles with a particle size of 12 μm or less, and by having compositional uniformity, which is the main factor determining the magnetic uniformity of AlNiCo-based magnetic particles, satisfying Equations 1, 2, and 3, resulting in a magnetic particle aggregate with extremely low compositional variation. This allows for stable and reproducible recognition even when fine linear security elements are designed, without the design shape of the security elements being damaged by expensive recognition equipment. Furthermore, even when fine linear security elements are mixed with paramagnetic particle-based security elements, they can be stably distinguished and recognized, significantly improving security. In a more distinctive and advantageous example, the AlNiCo-based magnetic particles can satisfy UNF(Al) of 11 or more, UNF(Ni) of 40 or more, and UNF(Co) of 30 or more. This high degree of compositional uniformity allows the AlNiCo-based magnetic particles to exhibit highly uniform magnetic properties.

[0047] In addition to or independently of the above-mentioned embodiment, magnetic particles according to another embodiment of the present invention are magnetic particles (II) having a designed composition, i.e., a composition substantially identical to the composition of the molten metal used during atomization. Specifically, the magnetic particles (II) according to another embodiment of the present invention are hard magnetic particles including a core particle containing Al, Ni, and Co and an inorganic shell surrounding the core particle, and the core particle has a particle diameter D corresponding to 50% of the cumulative particle diameter distribution of the core particle. 50The core particles are ultrafine particles having a particle diameter of 12 μm or less, and are produced by an atomizing method using a coolant containing at least water, and satisfy the following formulas 4, 5, and 6 based on a design composition which is the composition of the molten alloy containing Al, Ni, and Co used during atomizing.

[0048]

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[0049] In formula 4, C m (Al) is the average Al composition between core particles based on the weight percent composition, and C O (Al) is the Al composition of the designed composition based on the weight percent composition, Cm(Ni) is the average Ni composition between the core particles based on the weight percent composition, and C O (Ni) is the Ni composition of the designed composition based on the weight percent composition, and C m (Co) is the average Co composition between core particles based on the weight percent composition, and C O (Co) is the Co composition of the designed composition based on the weight percent composition. That is, in Formula 4, C m (Al) corresponds to the average Al composition described above for Formula 1, and in Formula 5, C m (Ni) corresponds to the average Ni composition described above for formula 2, and in formula 6, C m (Co) corresponds to the average Co composition defined in Equation 3. O (Al) may be the weight percent of Al contained in the molten AlNiCo alloy used for atomizing, and C O (Ni) may be the Ni weight percent contained in the molten AlNiCo alloy used for atomizing, and C O(Co) may be the Co weight percent contained in the molten AlNiCo alloy used for atomizing. In this case, to improve compositional uniformity, it is advantageous to produce an ingot by melting and solidifying metal powders of an alloy having a predetermined composition in an inert atmosphere, and then melting the produced ingot in an inert atmosphere. In such an advantageous example, the design composition of the molten alloy may be a composition based on a mixture of metal powders that form the alloy for ingot production. However, it goes without saying that the design composition should not be interpreted as being limited to the composition based on the mixture of raw metal powders, but may also refer to the composition of the ingot itself or the composition of the ingot (molten alloy) itself melted for atomizing.

[0050] As shown in Relational Formulas 4, 5, and 6, the AlNiCo-based magnetic particles according to the present invention are characterized in that the composition of the core particles, which determines the magnetic properties, is substantially similar to the designed composition, and variation from the designed composition is suppressed.

[0051] In terms of manufacturing method, it is only when the ingots and molten metal are produced in an inert atmosphere, the molten metal is rapidly cooled with an aqueous coolant (a coolant containing water) during spraying to prevent segregation, and an antioxidant contained in the aqueous coolant prevents changes in composition due to oxidation during the spraying process, particularly changes in inter-particle composition due to oxidation of highly oxidizable elements such as Al, that core particles having a composition substantially identical to the designed composition, which satisfies Relations 4, 5, and 6, can be produced, and furthermore, compositional uniformity which satisfies Relations 1, 2, and 3 can be ensured.

[0052] In terms of both variations from the designed composition and variations in composition between particles, the magnetic particles according to the present invention can include the two aspects described above, but these two aspects should not be interpreted as being solely independent of each other, and it goes without saying that the present invention should be interpreted as including magnetic particles belonging to both the first and second aspects.

[0053] That is, the magnetic particles according to one example of the present invention are hard magnetic particles including a core particle containing Al, Ni, and Co and an inorganic shell surrounding the core particle, and the core particle has a particle diameter D corresponding to 50% in the cumulative particle diameter distribution of the core particles. 50 The core particles are ultrafine particles having a particle size of 12 μm or less, and the core particles have the compositional uniformity of the above-mentioned formulas 1, 2, and 3. The core particles are produced by an atomizing method using a coolant containing at least water, and the core particles can have a composition that satisfies the above-mentioned formulas 4, 5, and 6 based on a design composition, which is the composition of the molten alloy containing Al, Ni, and Co used during atomizing.

[0054] The core particles may be made of an alloy containing aluminum (Al), nickel (Ni), and cobalt (Co), which has excellent coercive force, saturation magnetization, and remanence. As a specific example, the core particles may contain one or more quaternary elements selected from Fe, Cu, Ti, and Si, as well as other unavoidable impurities. As a practical example, the core particles may be made of an AlNiCo-based alloy containing Al, Ni, and Co, and including one or more non-ferrous elements selected from the group consisting of Cu, Si, and Ti, an iron-based element containing Fe, and other unavoidable impurities.

[0055] Similar to the compositional uniformity of Al, Ni, and Co, AlNiCo-based magnetic particles are characterized by extremely uniform content of the quaternary element. Specifically, the core particles have a compositional uniformity such that the value obtained by dividing the average quaternary element composition (average content based on weight %) among the core particles by the standard deviation of the quaternary element composition, based on the composition in weight %, is 10 or more. That is, UNF (quaternary element) may be 10 or more, or UNF (quaternary element) may be the value obtained by dividing the average quaternary element composition (average quaternary element weight %) among the core particles by the standard deviation of the quaternary element composition (standard deviation of quaternary element weight %), based on the composition in weight %, and when the quaternary element is two or more elements, UNF (quaternary element) may be 10 or more for each of the two or more elements. In this case, it goes without saying that the average fourth element composition among core particles can mean the average value of the fourth element composition of each core particle of the magnetic particles that make up the magnetic particle group, and the standard deviation of the fourth element composition can mean the standard deviation of the fourth element composition of each core particle of the magnetic particles that make up the magnetic particle group.

[0056] As a substantial example, the core particle may further contain Ti, Fe, and Cu in addition to Al, Ni, and Co, and UNF(Ti) where the fourth element is Ti, NF(Fe) where the fourth element is Fe, and UNF(Cu) where the fourth element is Cu may each be 10 or more. As a more substantial example, UNF(Ti) may be 15 or more, UNF(Fe) may be 35 or more, and UNF(Cu) may be 30 or more.

[0057] That is, in one substantial and advantageous example, the core particles may contain Ti, Fe, and Cu, along with Al, Ni, and Co, and may have a high degree of compositional uniformity satisfying UNF(Al) of 11 or more, UNF(Ni) of 40 or more, UNF(Co) of 30 or more, UNF(Ti) of 15 or more, UNF(Fe) of 35 or more, and UNF(Cu) of 30 or more.

[0058] In one substantial and advantageous example of an AlNiCo-based magnetic particle, the core particle may contain, based on the weight percent of the total weight of the core particle being 100%, 4-12% Al, 10-20% Ni, 15-25% Co, 1-10% Ti, 0.5-5% Cu, and the remainder being Fe and other unavoidable impurities. In another substantial and advantageous example of an AlNiCo-based magnetic particle, the core particle may contain, based on the weight percent of the total weight of the core particle being 100%, 4-12% Al, 10-20% Ni, 15-25% Co, 1-10% Ti, 0.5-5% Cu, 0.1-1% Si, and the remainder being Fe and other unavoidable impurities. In this case, the composition of the core particle refers to the average weight percent of the individual elements contained in each core particle of the magnetic particles constituting the magnetic particle group, and may correspond to the average composition of one element used in the UNF definition of one element.

[0059] The core particles may contain 4 to 12 wt %, preferably 5 to 10 wt %, and more preferably 6 to 9 wt % Al. When the aluminum content falls within this composition range, the effect of preventing sintering during subsequent heat treatment for eliminating segregation and controlling magnetic properties is sufficient, the shape of the fine particles secured by the water atomization method can be maintained, and deterioration of the mechanical properties of the core particles can be prevented, which is advantageous, as can improving saturation magnetization and remanent magnetization.

[0060] The core particles may contain 10 to 20 wt %, preferably 12 to 18 wt %, and more preferably 13 to 16 wt % of Ni. When the nickel content falls within this composition range, it is advantageous to be able to simultaneously increase the coercive force and remanence.

[0061] The core particles can contain 15 to 25 wt %, preferably 17 to 25 wt %, and more preferably 17 to 23 wt % of Co. When the cobalt content falls within this composition range, it is advantageous in that the coercive force can be increased and costs can be reduced.

[0062] Ti and Cu can further improve the coercivity of the Al-Ni-Co alloy. To prevent a decrease in remanence and improve the coercivity, the core particles may contain 1 to 10 wt% Ti, preferably 2 to 8 wt%, and more preferably 3 to 6 wt% Ti. To prevent a decrease in remanence and improve the coercivity, the core particles may contain 0.5 to 5 wt% Cu, preferably 1 to 4 wt%, and more preferably 1 to 3 wt% Cu.

[0063] The core particles may contain 0.1 wt. % or more of Si, which is advantageous for deoxidation during molten metal production and for stabilizing the shape of the microparticles when the molten metal is sprayed. However, it is preferable to contain 1 wt. % or less of Si to prevent degradation of magnetic properties. Specifically, the core particles may contain 0.4 to 0.7 wt. % of Si to deoxidize the microparticles, maintain their shape, and prevent degradation of magnetic properties. However, as shown in the embodiment, if an ingot is produced in an inert atmosphere, the ingot is melted in an inert atmosphere to produce the molten metal, and a refrigerant (coolant) containing an antioxidant is used together with water when spraying the molten metal, oxidation during the molten metal particle formation process can be sufficiently suppressed. This allows the molten metal to be free of deoxidizing agents such as Si, which degrade magnetic properties, and magnetic particles having the above-mentioned compositional uniformity and substantially the same composition as the designed composition can be produced.

[0064] In the AlNiCo-based magnetic particle according to one embodiment of the present invention, the core particle can further satisfy the following formulas 7 and 8.

[0065] Equation 7: 3μm≦D 50 ≦12μm Formula 8: 10μm≦D 90 ≦20μm

[0066] D in Equation 7 50 As described above, D is the particle size corresponding to 50% in the cumulative particle size distribution of the core particles. 90 is the particle size corresponding to 90% of the cumulative particle size distribution of the core particles. 50 may be 3 to 9 μm, and D 90The thickness may be 10 to 15 μm.

[0067] The core particle is D 50 In the case of ultrafine particles with a particle size of 12 μm or less, the particle size distribution can also affect the magnetic properties. When AlNiCo-based magnetic particles satisfy formulas 7 and 8, printability is ensured, and not only are print defects such as nozzle clogging reduced during the printing process, but changes in magnetic properties due to size variation can be suppressed, allowing AlNiCo-based magnetic particles to have more uniform magnetic properties.

[0068] In order to use a magnetic material as a security element, the inherent dark color of the magnetic particles needs to be concealed. Therefore, as proposed by the present applicant, the inherent dark color of the magnetic particles can be concealed by using a technology to lighten the color of the magnetic material by encasing the magnetic material in a metal shell (see Korean Patent Registration No. 1341150).

[0069] In the AlNiCo-based magnetic particles, the inorganic shell can play a role in hiding the dark color inherent to the core particle containing Al, Ni, and Co, and causing the AlNiCo-based magnetic particles to have a light color.

[0070] Specifically, the inorganic shell may include a metal shell and may further include a dielectric shell located on the top of the metal shell (i.e., on the surface side of the metal shell) and / or on the bottom of the metal shell (on the core particle side of the metal shell). The dielectric shell may improve the bonding strength between the metal shell and the core particle or protect the metal shell from the outside to improve durability.

[0071] Through various long-term preliminary experiments, it was confirmed that the uniformity of the metal shell, which is the main component for lightening the color, as well as the uniformity of the core particle composition and particle size distribution, have a significant impact on the magnetic properties of AlNiCo-based magnetic particles.

[0072] Thus, in the AlNiCo-based magnetic particle according to one embodiment of the present invention, the inorganic shell may include a metal shell, and the metal shell may have a thickness uniformity that satisfies the following formulas 9 and 10.

[0073] Formula 9: 50nm≦t m ≦100nm Equation 10: σ t ≦30nm

[0074] In equation 9, t m is the average thickness of the metal shell, and in Eq. 10, σ t is the standard deviation of the metal shell thickness. In this case, the average thickness and standard deviation of thickness in Equations 9 and 10 are the average thickness at the position of one metal shell surrounding one core particle based on one magnetic particle, and the deviation is also the standard deviation of the thickness at one metal shell. Magnetic particles belonging to the AlNiCo-based magnetic particle group can satisfy Equations 9 and 10, respectively.

[0075] That is, the magnetic particles belonging to the AlNiCo-based magnetic particle group may each have an average metal shell thickness of 50 to 100 nm, and the deviation in the thickness of the metal shell of each magnetic particle belonging to the AlNiCo-based magnetic particle group may be within 30 nm, substantially 1 nm to 10 nm.

[0076] The metal shell may be one or more metals selected from copper, nickel, gold, platinum, silver, aluminum, and chromium, with silver being more effective for lightening and moreover, being more advantageous since the silver shell can impart infrared reflectivity to the AlNiCo-based magnetic particles.

[0077] The dielectric shells located above, below, or both above and below the metal shell may be one or more dielectric materials selected from titanium oxide, silicon oxide, aluminum oxide, zinc oxide, zirconium oxide, calcium carbonate, magnesium fluoride, and zinc sulfide. The thickness of the dielectric shell may be, but is not limited to, 10 to 100 nm in order to stably improve durability and further improve color lightening.

[0078] The AlNiCo-based magnetic particles according to one embodiment of the present invention may have a coercive force of 100 to 500 Oe, a saturation magnetization (Ms) of 50 to 150 emu / g, and a remanent magnetization (Mr) of 10 to 40 emu / g. Specifically, the AlNiCo-based magnetic particles may have a coercive force of 100 to 500 Oe, a saturation magnetization (Ms) of 50 to 70 emu / g, and a remanent magnetization (Mr) of 15 to 30 emu / g. These magnetic properties of coercive force, saturation magnetization, and remanent magnetization are indistinguishable from soft magnetic particles using general recognition equipment, but can be detected and distinguished from soft magnetic particles using expensive recognition equipment, ensuring enhanced security.

[0079] The AlNiCo-based magnetic particles have a composition that is strictly designed to ensure the above-mentioned uniformity of composition and the planned magnetism. Advantageously, the uniformity of composition, the designed composition, the uniformity of particle diameter, and the uniformity of metal shell thickness allow security elements designed with sophisticated shapes such as fine wires to be reproducibly and stably detected and distinguished from soft magnetic particles using expensive recognition equipment, thereby significantly improving security properties.

[0080] Furthermore, while magnetic particles generally have infrared absorption properties, the AlNiCo-based magnetic particles according to an advantageous embodiment of the present invention can also reflect infrared rays. Furthermore, the AlNiCo-based magnetic particles according to an advantageous embodiment of the present invention have a metal shell with uniform thickness and very low surface roughness, resulting in excellent infrared reflectivity, reflecting more than 60% of infrared rays (infrared rays with a wavelength of 900 nm) based on a wavelength of 900 nm. This means that the magnetic particles according to an embodiment of the present invention have magnetic properties that are indistinguishable from soft magnetic particles using conventional recognition equipment, and can realize security elements with highly shaped features, including fine lines, and have security properties such as high infrared reflectivity. In other words, multifaceted security features, including magnetic properties, security patterns (security element shapes), and infrared rays, can be achieved using a single material, the AlNiCo-based magnetic particles. In particular, the AlNiCo-based magnetic particles according to an embodiment of the present invention can achieve soft magnetic properties with substantially the same composition, and conventional composition analysis devices and conventional magnetic recognition devices cannot distinguish them from soft magnetic particles, making counterfeiting security elements virtually impossible.

[0081] The present invention includes the above-mentioned method for producing AlNiCo-based magnetic particles. The production method according to the present invention includes all of the details described above for the AlNiCo-based magnetic particles.

[0082] In the manufacturing method of the present invention, terms such as "cooling medium containing water," "water-based spray" and / or "water-based cooling medium" should be interpreted as meaning that they include at least water, and should not be interpreted as meaning that the cooling medium is composed of a liquid, but should also be interpreted as including cases where the cooling medium contains a gas phase of an inert gas together with water.

[0083] The method for producing AlNiCo-based magnetic particles according to the present invention includes the steps of: a) melting and solidifying raw materials containing Al, Ni, and Co in an inert atmosphere to produce an ingot; b) melting the produced ingot in an inert atmosphere and spraying it with a cooling medium containing water and an antioxidant to produce fine particles; c) heat-treating the produced fine particles; and d) air-classifying the heat-treated fine particles to produce D. 50 and e) forming an inorganic shell on the AlNiCo-based core particle.

[0084] As mentioned above, when using the gas atomization method, the cooling rate is slow, making it practically very difficult to produce particles with uniform magnetic properties. Furthermore, the size required for printing (for example, D 50 However, the yield of ultrafine particles (≦12 μm) is only around 5%, making it unsuitable for mass production.

[0085] The production method according to the present invention uses a cooling medium containing water, which allows rapid cooling and prevents segregation, making it possible to produce ultrafine particles with a dense structure at an extremely high yield (for example, 35% or more).The cooling medium contains an antioxidant, which prevents the uneven oxidation of specific elements that are highly oxidizable in particles produced using water, making it possible to produce core particles with a designed composition with excellent compositional uniformity (low compositional variation) as described above.

[0086] Since compositional variations occur due to the uneven oxidation of highly oxidizing elements (e.g., Al, Ti, etc.), the occurrence of compositional variations up to the step immediately prior to spraying can be suppressed by performing (step a)) ingot formation by melting the raw materials in an inert gas atmosphere and (step b)) remelting the ingot for spraying in an inert atmosphere, and the occurrence of compositional variations during the spraying process can be suppressed by using a water-based cooling medium containing an antioxidant during spraying.

[0087] Next, the fine particles produced by atomization can be heat-treated to improve the coercive force, and the heat-treated fine particles can be air-classified to improve the D 50 is 12 μm or less, preferably D 50 and D 90 It is possible to produce core particles having a very narrow size distribution that satisfies Equations 7 and 8, and that have an ultrafine size.

[0088] Furthermore, when a metal shell is formed in the inorganic shell formation step after the core particles are produced, the metal shell is formed using electroless plating. In this case, by performing the electroless plating at a low temperature of 5°C or less, specifically 1 to 5°C, a thin, uniform metal film having very low surface roughness that satisfies Equations 9 and 10 can be produced.

[0089] The detailed manufacturing method will be described below, and in describing the manufacturing method in detail, the size, distribution, composition, element content, magnetic properties of the core particles, and the material and thickness of the inorganic shell are similar to or equivalent to those described in detail above for the AlNiCo-based magnetic particles. Thus, the manufacturing method of the AlNiCo-based magnetic particles includes all of the relevant configurations described in detail above for the AlNiCo-based magnetic particles.

[0090] The ingot can be produced by melting a raw material containing a mixture of powders of elements including Al, Ni, and Co in an inert atmosphere to produce a molten metal having the same composition as the designed core particles, and then cooling the molten metal in an inert atmosphere. However, if the core particles contain iron, heavy carbon steel (iron containing 0.15 to 0.3 wt. % C) with its antioxidant effect can be used instead of the iron powder. However, since the ingot formation and melting are performed in an inert atmosphere and the ingot is sprayed with a water-based coolant containing an antioxidant, heavy carbon steel is not necessarily required and can be used selectively. Therefore, it goes without saying that the present invention is not limited by the type of iron raw material. Therefore, the ingot can be an AlNiCo alloy ingot containing Al, Ni, and Co. Specifically, it can be an AlNiCo alloy ingot containing Al, Ni, and Co, as well as one or more elements selected from Fe, Cu, Si, and Ti, and other unavoidable impurities. More substantially, the ingot may be an AlNiCo alloy ingot containing Ti, Fe, Cu and other inevitable impurities along with Al, Ni and Co. As another substantial example, the ingot may be an AlNiCo alloy ingot containing Ti, Fe, Cu, Si and other inevitable impurities along with Al, Ni and Co.

[0091] According to one substantial and advantageous example, the composition of the raw material, the composition of the ingot, or the composition of the molten metal corresponding to the design composition may, based on weight percent, include 4-12% Al, 10-20% Ni, 15-25% Co, 1-10% Ti, 0.5-5% Cu, with the balance being Fe and other unavoidable impurities. According to another substantial and advantageous example, the composition of the raw material, the composition of the ingot, or the composition of the molten metal corresponding to the design composition may, based on weight percent, include 4-12% Al, 10-20% Ni, 15-25% Co, 1-10% Ti, 0.5-5% Cu, 0.1-1% Si, with the balance being Fe and other unavoidable impurities, with the total weight of the core particles being 100%.

[0092] In this case, the raw material composition, ingot composition, or molten metal composition corresponding to the designed composition may contain 4 to 12 wt%, preferably 5 to 10 wt%, and more preferably 6 to 9 wt% Al. The raw material composition, ingot composition, or molten metal composition corresponding to the designed composition may contain 10 to 20 wt%, preferably 12 to 18 wt%, and more preferably 13 to 16 wt% Ni. The raw material composition, ingot composition, or molten metal composition corresponding to the designed composition may contain 15 to 25 wt%, preferably 17 to 25 wt%, and more preferably 17 to 23 wt% Co. The raw material composition, ingot composition, or molten metal composition corresponding to the designed composition may contain 1 to 10 wt%, preferably 2 to 8 wt%, and more preferably 3 to 6 wt% Ti. Furthermore, the raw material composition, ingot composition, or molten metal composition corresponding to the designed composition may contain 0.5 to 5 wt. % Cu, preferably 1 to 4 wt. % Cu, and more preferably 1 to 3 wt. % Cu. The raw material composition, ingot composition, or molten metal composition corresponding to the designed composition may contain 0.1 wt. % or more Si, specifically 0.4 to 0.7 wt. % Si, but Si can be selectively used as needed, for the same reasons as detailed above for carbon steel.

[0093] The ingot melting step b) may be a process of melting the ingot in an inert atmosphere, specifically, a process of melting the ingot by high-frequency induction heating in an inert atmosphere, but is not limited to a specific heating method as long as the melting is performed in an inert atmosphere that prevents oxidation. A specific, non-limiting example is a temperature of 1300 to 1800°C during high-frequency melting in an inert atmosphere.

[0094] The spraying in step b) may be performed using a water-based cooling medium containing water and an antioxidant, or may be performed by spraying the water-based cooling medium through a ring-shaped spray nozzle.

[0095] When the ingot melted for atomization is an AlNiCo-based molten metal, the water-based coolant can contain water and an antioxidant to suppress oxidation during the granulation of the AlNiCo-based molten metal using a water-based fluid, and the antioxidant can contain one or more selected from a reducing organic solvent and a reducing organic compound. In particular, the antioxidant can contain a reducing organic compound including urea, and when atomization is performed using a water-based coolant containing urea and water, heterogeneous oxidation during the granulation of the AlNiCo-based molten metal can be significantly suppressed, making it possible to produce core particles that satisfy the above-mentioned Relations 1, 2, and 3. Furthermore, oxidation itself during granulation can be significantly suppressed, making it possible to produce core particles that substantially match the design composition and satisfy Relations 4, 5, and 6.

[0096] Specifically, the cooling medium may contain 10 to 100 parts by weight of urea, advantageously 15 to 100 parts by weight of urea, and more advantageously 20 to 100 parts by weight of urea, relative to 100 parts by weight of water. Such a urea content is a content that can substantially completely suppress oxidation by water and non-uniform oxidation by water during the particulation of the AlNiCo-based molten metal.

[0097] However, in the present invention, the antioxidant contained in the cooling medium should not be interpreted as being limited to urea alone, and it goes without saying that the cooling medium may further contain a reducing organic solvent in addition to the above-mentioned reducing organic compound containing urea, as necessary. As the reducing organic solvent, an alkanolamine having excellent miscibility with water, a high boiling point, and excellent reducing properties is advantageous. The alkanolamine may include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), monoisopropylamine (MIPA), diisopropylamine (DIPA), or a mixture thereof, but the present invention is not limited thereto.

[0098] When the cooling medium further contains a reducing organic solvent, in order not to inhibit the rapid cooling effect of water, the cooling medium may contain 30 parts by weight or less of the reducing organic solvent, specifically 1 to 30 parts by weight, more specifically 5 to 20 parts by weight, per 100 parts by weight of water, but the present invention is not limited thereto.

[0099] Furthermore, when the cooling medium further contains a gas phase containing an inert gas, the volume ratio of water to the gas phase containing an inert gas is advantageously in the range of 1:0.05 to 0.3 so as to maintain the rapid cooling effect of water, which prevents segregation and the formation of undesired heterogeneous phases (for example, aluminum-rich phases).

[0100] During spraying, the spray pressure of the cooling medium containing water and antioxidants must be 500 bar or more. 50 This is advantageous for producing ultrafine particles with a particle size of 12 μm or less. 50 In order to obtain ultrafine particles with a diameter of 12 μm or less with a good yield, the injection pressure of the cooling medium may be 500 to 1000 bar, more particularly 500 to 800 bar.

[0101] The AlNiCo-based particles can be obtained by the above-described atomization process, and then a step of heat-treating the AlNiCo-based particles produced by atomization can be performed. In the case of gas atomization, heat treatment is required to improve the magnetic properties and remove segregation and undesired heterophases (e.g., γ phase) caused by slow cooling. However, in the case of AlNiCo-based particles obtained by a manufacturing method according to one embodiment of the present invention, rapid cooling prevents segregation and phase separation (formation of heterophases), so heat treatment under conditions favorable for improving the magnetic properties of the AlNiCo-based particles is sufficient. Specifically, the heat treatment in step c) can be performed at a temperature of 700 to 800°C in a typical inert or reducing atmosphere. The heat treatment time may be sufficient to achieve the desired improvement in magnetic properties without causing the AlNiCo-based particles to strongly bond together. For example, the heat treatment time may be 30 minutes to 2 hours, but the present invention is not limited by the specific heat treatment time.

[0102] If necessary, a multi-stage heat treatment may be performed, including a first heat treatment at 700 to 800°C, a second heat treatment at a temperature relatively lower than that of the first heat treatment, and a third heat treatment at a temperature relatively lower than that of the second heat treatment, and this multi-stage heat treatment can further improve the coercivity of the AlNiCo-based particles. Specifically, if necessary, a first heat treatment at 700 to 800°C may be performed, followed by a second heat treatment at a temperature of 600 to 700°C (excluding 700°C) for 2 to 4 hours, and then a third heat treatment at 550 to 600°C (excluding 600°C) for 10 to 15 hours.

[0103] In step d), the heat-treated particles are subjected to air classification, and D 50 The cyclone-type air classification may be a step of producing core particles having a particle size of 12 μm or less. As is well known, in cyclone-type air classification, coarse particles move to the outer wall of the classifier by the centrifugal force and fluid drag of the high-speed airflow, circulating along the wall and being collected, while fine particles move to the center (inside) of the classifier, circulating with the air, and being exhausted and collected. The adjustment of the classification point can be mainly controlled by the rotation speed of the classifier and the amount of air injected. Air classification is very suitable in the present invention because it allows for precise classification of very fine particles and the classified particles have a very narrow particle size distribution. As a specific, non-limiting example, D is obtained by air classification of a differential that has been subjected to gas atomization and multi-stage heat treatment. 50 In order to classify and recover core particles having a particle diameter of 12 μm or less, preferably particles satisfying formulas 7 and 8, the rotation speed during air classification may be 2500 to 8000 rpm, and the air injection amount may be 2 to 10 m 3 However, it is obvious to those skilled in the art of controlling particle size distribution by air classification that the detailed construction of various commercially available air classifiers will allow them to control the main variables of the known classifiers to obtain particles having a desired average size and distribution, thereby achieving the desired classification.

[0104] Obtained by airflow classification, D 50Core particles having a particle diameter of 12 μm or less, preferably particles satisfying formulas 7 and 8, are highly suitable for printing fine linear patterns, and are advantageous in that they can prevent problems such as printing defects that may occur during the printing process and can prevent changes in magnetic properties due to variations in particle diameter.

[0105] Step e) is a step of forming a shell on the core particles obtained by air classification, and step e) may include a step of forming a metal shell. Specifically, step e) may include a step of forming a dielectric shell on the core particles and a step of forming a metal shell on the dielectric shell. However, it goes without saying that, if necessary, a step of forming a dielectric shell of the same or different type on the metal shell to protect the metal shell may be further performed.

[0106] The dielectric shell formation step may be performed using any method commonly used for coating a dielectric on particles, but a sol-gel method is advantageous in terms of forming a thin and uniform film. Specifically, an alkoxide sol-gel method or a colloid sol-gel method may be used depending on the dielectric material of the shell to be formed. As a specific, non-limiting example, when a titanium oxide shell is to be formed, core particles dispersed in a dispersing medium containing water may be mixed with a titanium sol in which a titanium precursor such as titanium tetrabutoxide is dissolved, and the core particles may then be separated, collected, and dried to produce core particles with a titanium oxide shell formed thereon.

[0107] The metal shell formation step can be performed using any method commonly used for coating metals on particles. However, electroless plating is advantageous for forming a thin, uniform film. In particular, low-temperature electroless plating at 5°C or below, specifically 1 to 5°C, is advantageous for forming a thin, uniform metal film that satisfies Equations 9 and 10, enabling the production of magnetic particles with low surface roughness and excellent infrared reflectance of 60% or more at a wavelength of 900 nm. Various electroless plating solutions can be used depending on the metal material of the metal shell. In one advantageous example, when a silver shell is to be formed as the metal shell, the plating bath for electroless plating can include a silver precursor (e.g., silver nitrate), a pH adjuster (e.g., potassium hydroxide), an adhesive (e.g., aqueous ammonia, ammonium salt), a solvent, and a reducing agent. In this case, the reducing agent may include monosaccharides, glucose, fructose, galactose, seignette salt, sodium tartrate, potassium tartrate, sodium potassium tartrate, calcium tartrate, stearyl tartrate, formaldehyde, etc. In this case, the pH of the plating bath can be adjusted to 7 to 10 using a pH adjuster, and the plating bath may further contain known additives for uniform plating.

[0108] The present invention includes AlNiCo-based magnetic particles produced by the above-described production method.

[0109] The present invention includes a security ink containing the above-mentioned AlNiCo-based magnetic particles, and it goes without saying that the security ink may be used for valuable documents.

[0110] In a security ink according to one embodiment of the present invention, the security ink may contain the above-mentioned AlNiCo-based magnetic particles, varnish, pigment, surfactant, wax, and solvent.

[0111] In detail, the security ink may contain, but is not limited to, 5-15 wt% AlNiCo-based magnetic particles, 20-40 wt% varnish, 30-50 wt% pigment, 5-10 wt% surfactant, 1-10 wt% wax and 2-10 wt% solvent.

[0112] Examples of varnishes include thermoplastic resins, thermosetting resins, and photocurable resins, and are not limited to those that can be dissolved in organic solvents. Specific examples of varnishes include thermoplastic resins such as petroleum resins, casein, shellac, rosin-modified maleic acid resins, rosin-modified phenolic resins, nitrocellulose, cellulose acetate butyrate, vulcanized rubber, chlorinated rubber, oxidized rubber, hydrochloric acid rubber, phenolic resins, alkyd resins, polyester resins, unsaturated polyester resins, amino resins, epoxy resins, vinyl resins, vinyl chloride resins, vinylidene chloride resins, vinyl chloride acetate resins, ethylene vinyl acetate resins, acrylic resins, methacrylic resins, polyurethane resins, silicone resins, fluororesins, drying oils, synthetic drying oils, styrene-maleic acid resins, styrene-acrylic resins, polyamide resins, and butyral resins. Specific examples of thermosetting resins include epoxy resins, phenolic resins, benzoguanamine resins, melamine resins, and urea resins. Photocurable resins (photosensitive resins) include those prepared by reacting a linear polymer having reactive substituents such as hydroxyl, carboxyl, or amino groups with a (meth)acrylic compound having reactive substituents such as isocyanate, aldehyde, or epoxy groups, or with cinnamic acid, thereby introducing photocrosslinkable groups such as (meth)acryloyl or styryl groups into the linear polymer. It is also possible to use linear polymers containing acid anhydrides, such as styrene-maleic anhydride copolymers or α-olefin-maleic anhydride copolymers, that are half-esterified with (meth)acrylic compounds having hydroxyl groups, such as hydroxyalkyl (meth)acrylates.

[0113] The pigment is not particularly limited, and examples thereof include soluble azo pigments, insoluble azo pigments, phthalocyanine pigments, halogenated phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, isoindoline pigments, perylene pigments, perinone pigments, dioxazine pigments, anthraquinone pigments, dianthraquinonyl pigments, anthrapyrimidine pigments, andanthrone pigments, indanthrone pigments, flavanthrone pigments, pyranthrone pigments, and diketopyrrolopyrrole pigments.

[0114] The surfactant is not limited to a specific type, and examples thereof include one or more selected from the group consisting of fluorinated surfactants, polymerizable fluorinated surfactants, siloxane surfactants, polymerizable siloxane surfactants, polyoxyethylene surfactants, and derivatives thereof.

[0115] The wax is not limited to any particular type as long as it is in powder form and has the effect of reducing the stickiness of the resin. Examples of waxes include, but are not limited to, one or more selected from polyethylene wax, amide wax, erucamide wax, polypropylene wax, paraffin wax, Teflon (registered trademark), and carnauba wax.

[0116] The solvent is not limited to a specific type as long as it is a general organic solvent that can uniformly mix substances such as wax, pigment, varnish, etc. Specific examples of usable solvents include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, xylene, acetone, hexane, methyl ethyl ketone, cyclohexanone, propylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether acetate, diethylene glycol monoethyl acetate, and diethylene glycol monobutyl ether acetate.

[0117] The present invention includes a valuable instrument containing the above-described AlNiCo-based magnetic particles.

[0118] In particular, the present invention includes valuable instruments such as banknotes, checks, stamps, gift certificates, certificates, bonds, etc., which contain the above-mentioned AlNiCo-based magnetic particles as security elements. In this case, it goes without saying that the security elements containing the AlNiCo-based magnetic particles can have shapes designed for security purposes, such as images (including part of the shapes that form the images), numbers, letters, geometric patterns, etc. [Example]

[0119] (Example) Raw powders (aluminum, nickel, cobalt, titanium, copper, and iron, with a purity of ≥99.9%) were mixed according to the design composition: 6 wt% Al, 15 wt% Ni, 22 wt% Co, 4 wt% Ti, 3 wt% Cu, and 50 wt% Fe. The raw powders were melted in an inert atmosphere and solidified to produce ingots. One kilogram of the resulting ingot was placed in a crucible heated by a high-frequency generator and placed under an inert atmosphere. The temperature was maintained at 1650°C to form an AlNiCo-based molten metal. To atomize the molten metal, the molten metal was poured into a vacuum atomization confinement, and a cooling medium (a 25 wt% urea solution in water) was sprayed at 600 bar through an annular spray nozzle.

[0120] The produced particles were heat treated at 750°C for 1 hour in an argon gas atmosphere.

[0121] After the heat treatment, the particles were collected at a rotation speed of 7500 rpm and an air injection volume of 2.8 m 3 / min, and the airflow is classified by the cyclone method. 50 is 7.8 μm, and D 90 The core particles obtained by air classification were washed twice with ethanol and then dried at 60°C.

[0122] Approximately 1 g of the core particles were randomly sampled, and the central region of the particle cross section was subjected to elemental analysis (10 kV, 100 sec) using EDS (Energy Dispersive X-Ray Spectroscopy, FEI company, Magellan 400). Elemental analysis was performed on each of the 50 particles, and the average composition and standard deviation of the composition by element were calculated. The results are summarized in Table 1 (Table 1-1: Al, Ni, Co analysis results, Table 1-2: Ti, Cu, Fe analysis results). The values ​​specified in Equations 4, 5, and 6, i.e., the degree of deviation from the design composition, are referred to as "DEV," and are summarized and illustrated in Table 2.

[0123] Separately, 1 g of washed core particles, 1 ml of TBOT (tetrabutoxytitanium) (Aldrich), and 1 ml of distilled water were added to 170 ml of ethanol and stirred at 300 rpm for 2 hours at 85°C to coat the surfaces of the core particles with a titanium oxide shell (50 nm thick). The core particles coated with the titanium oxide shell were separated and collected with a magnet, then washed twice with ethanol and dried.

[0124] Next, 21 g of silver nitrate (AgNO3) and 4 g of sodium hydroxide (NaOH) were added to 1200 ml of distilled water, followed by 34 ml of ammonium hydroxide (NH4OH) and stirring until the brown precipitate turned into a transparent silver amine complex solution. 60 g of titanium dioxide shell-coated core particles were added to the silver amine complex solution maintained at 3°C ​​and stirred at 300 rpm for 30 minutes. A solution (3°C) of 20 g of glucose and 1.5 g of potassium tartrate dissolved in 400 ml of distilled water was added to the silver amine complex solution (3°C) containing the titanium dioxide shell-coated core particles and stirred at 300 rpm for 1 hour. A 58.4 nm thick silver shell was formed on the titanium dioxide shell-coated core particles, producing AlNiCo-based magnetic particles. The magnetic particles were then separated using a magnet, washed twice with ethanol, and dried at 60°C.

[0125] The coercive force, saturation magnetization (Ms), and remanent magnetization (Mr) of the produced magnetic particles were measured using a VSM (vibrating sample magnetometer, Lakeshore, 7400 series), and the results are summarized in Table 3.

[0126] (Comparative Example 1) The procedure was the same as in Example 1, except that water was used as a cooling medium during spraying. Core particles were then produced in the same manner as in Example 1, and magnetic particles were then produced in the same manner as in Example 1, except that a room temperature solution was used during the production of the silver shell.

[0127] The composition uniformity of the core particles produced in Comparative Example 1 was also confirmed in the same manner as in Example 1, and the results are summarized and shown in Table 1. In addition, the values ​​defined in Equations 4, 5, and 6, i.e., the degree of deviation from the designed composition, were designated as "DEV" and are summarized and shown in Table 2. The magnetic properties of the produced magnetic particles were also measured in the same manner as in Example 1, and the results are summarized and shown in Table 3.

[0128] [Table 1-1]

[0129] [Table 1-2]

[0130] In Table 1 (Table 1-1 and Table 1-2), C m (A) is the average weight percent of element A in the core particles, σ(A) is the standard deviation of element A among core particles (based on weight percent), and UNF(A) is the C m (A) / σ(A). In addition, in Table 1, C between elements m The reason the sum does not equal 100 is due to unavoidable impurities.

[0131] As shown in Table 1, the AlNiCo-based magnetic particles according to the present invention have significantly improved composition uniformity and the D 50is 7.8 μm, and D 90 It can be seen that the particle size is extremely fine, with a very narrow particle size distribution of 14.1 μm.

[0132] [Table 2]

[0133] As shown in Table 2, in the case of the core particles produced in the examples, it can be seen that magnetic particles having substantially the same composition as the composition of the designed raw materials are produced.

[0134] [Table 3]

[0135] As shown in Table 3, rapid cooling prevents segregation and heterogeneous phases, and prevents compositional variations due to oxidation. As a result, a simple and very short heat treatment at 750°C for 1 hour produces hard magnetic particles with magnetic properties that are indistinguishable from soft magnetic particles using ordinary measuring equipment, ensuring improved security.

[0136] Figure 1 is a scanning electron microscope photograph of the AlNiCo-based magnetic particles prepared in Example 1. As shown in Figure 1, it can be seen that substantially spherical particles were prepared, and it can be confirmed that a uniform and stable silver shell was formed by low-temperature electroless plating at 3°C.

[0137] Figure 2 shows a scanning electron microscope image of the cross section of the manufactured AlNiCo-based magnetic particles, along with a graph illustrating the measured thickness distribution of the silver shell. As shown in Figure 2, the particles have an extremely uniform silver shell, with an average thickness of 58.4 nm and a standard deviation of only 7.9 nm. Furthermore, as in the concentration uniformity test, 50 AlNiCo-based magnetic particles were randomly selected and the thickness and thickness distribution of the formed silver shells were measured by cross-sectional observation. The average silver shell thickness (average thickness of the silver shell for each magnetic particle) for all measured AlNiCo-based magnetic particles was in the range of 56.2 to 59.7 nm, and the standard deviation of the silver shell thickness (standard deviation of the silver shell thickness for each magnetic particle) was in the range of 7.1 to 8.3 nm.

[0138] Furthermore, the infrared reflectance of the magnetic particles produced by irradiating them with a 900 nm laser was measured using a spectrophotometer (Carry 5000), and it was confirmed that the reflectance was 64%.

[0139] Example 2 A security ink for valuable documents (hereinafter referred to as hard magnetic ink) was prepared using the AlNiCo-based magnetic particles prepared in Example 1. Specifically, 18 wt% of the first varnish (Jevisco, KR-KU), 14 wt% of the second varnish (Jevisco, KR-KA), 10 wt% of the prepared AlNiCo-based magnetic particles, 41 wt% of the extender pigment (Donghao Calcium, TL-2000), 6 wt% of the mixed wax (Micro Powders, Polyfluo 540XF), 2 wt% of the aliphatic hydrocarbon (SK Chemicals, YK-D130), 2 wt% of the solvent (diethylene glycol monobutyl ether), 5 wt% of the surfactant (Hannong Chemical, Koremul-263Na), and 2 wt% of the desiccant were mixed and then placed in a kneader and kneaded 4 to 5 times to prepare the security ink.

[0140] A paramagnetic ink was prepared using the same materials and composition as the hard magnetic ink described above, except that 10% by weight of magnetic pigment (BASF, 025) was mixed in place of 10% by weight of the AlNiCo-based magnetic particles prepared in Example 1.

[0141] FIG. 3 shows optical images, soft magnetic images, ferromagnetic images and infrared images of security elements produced by printing the hard magnetic ink and paramagnetic ink.

[0142] As shown in the optical photograph of Figure 3, while conventional magnetic particles have a dark color inherent to magnetic particles, it can be seen that the ink containing the AlNiCo-based magnetic particles of the present invention can achieve a bright color in printed areas. Furthermore, as shown in the soft magnetic image taken in soft magnetic mode using a magnetic image measuring device (G&D), the ink containing the AlNiCo-based magnetic particles of the present invention has magnetic properties similar to those of conventional soft magnetic pigments in soft magnetic mode, making them virtually indistinguishable. However, as shown in the hard magnetic image taken in hard magnetic mode using the same magnetic image measuring device, the AlNiCo-based magnetic particles of the present invention are stably detected in hard magnetic mode, forming a clear image, while conventional soft magnetic pigments are not. Furthermore, as shown in the infrared image taken using an infrared image measuring device (VSC 4 PLUS, manufactured by Foster & Freeman), the AlNiCo-based magnetic particles of the present invention do not appear in an image due to their infrared reflection properties, while conventional soft magnetic pigments form an image due to their infrared absorption properties.

[0143] The present invention has been described above using specific and limited examples and drawings, but these are provided to facilitate a general understanding of the present invention. The present invention is not limited to the above examples, and various modifications and variations can be made from such descriptions by those having ordinary knowledge in the field to which the present invention pertains.

[0144] Therefore, the concept of the present invention should not be limited to the above-described embodiments, and it can be said that not only the scope of the claims described below, but also all modifications that are equivalent to or equivalent to the scope of the claims fall within the scope of the concept of the present invention.

Claims

1. A hard magnetic particle comprising a core particle containing Al, Ni, and Co, and an inorganic shell surrounding the core particle, The core particles have a particle diameter D corresponding to 50% of the particle diameter cumulative distribution of the core particles. ５０ are ultrafine particles having a particle size of 12 μm or less, The core particle is an AlNiCo-based magnetic particle that further satisfies the following formulas 7 and 8: Formula 7: 3 μm ≦ D ５０ ≦12μm Formula 8: 10 μm ≦ D ９０ ≦20μm (In formula 7, D ５０ is the particle diameter corresponding to 50% in the cumulative particle diameter distribution of the core particles, and in Equation 8, D ９０ is the particle size corresponding to 90% in the cumulative particle size distribution of the core particles.) The AlNiCo-based magnetic particles have a saturation magnetization (Ms) of 50 to 150 emu / g and a remanent magnetization (Mr) of 10 to 40 emu / g, The inorganic shell includes a silver shell, and the silver shell satisfies the following formulas 9 and 10 and has an infrared reflectance of 60% or more based on a wavelength of 900 nm: Formula 9: 50nm≦tm≦100nm Formula 10: σt≦30nm (In Equation 9, tm is the average thickness of the silver shell, and in Equation 10, σt is the standard deviation of the silver shell thickness.) AlNiCo magnetic particles.

2. The inorganic shell further includes a dielectric shell located below the silver shell, 2. The AlNiCo-based magnetic particle according to claim 1, wherein the dielectric material of the dielectric shell is one selected from the group consisting of titanium oxide, silicon oxide, aluminum oxide, zinc oxide, zirconium oxide, calcium carbonate, magnesium fluoride, and zinc sulfide.

3. 2. The AlNiCo-based magnetic particles according to claim 1, wherein the coercive force of the magnetic particles is 100 to 500 Oe.

4. the core particle further contains one or more quaternary elements selected from Cu, Ti, Fe, and Si; 2. The AlNiCo-based magnetic particle according to claim 1, wherein the core particle has a composition in weight percent where the average composition of the fourth element among the core particles divided by the standard deviation of the composition of the fourth element is 15 or more.

5. A security ink comprising the AlNiCo-based magnetic particles according to claim 1.

6. A valuable document comprising the AlNiCo-based magnetic particles according to claim 1.

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