JP6164396B2 - Spinel ferrimagnetic particle powder and magnetic recording medium for magnetic recording medium - Google Patents

Description

  The present invention relates to a spinel-type ferrimagnetic particle powder for magnetic recording media, and more specifically, a magnetic powder having an average particle size of 5 to 70 nm and a powder SFD of 1.4 or less. The present invention relates to a spinel-type ferrimagnetic particle powder effective for reducing noise in a recording medium and a magnetic recording medium using the spinel-type ferrimagnetic particle powder.

  Conventionally, magnetic recording technology has been widely used in various fields including audio, video, and computer. In recent years, there has been a demand for smaller and lighter devices, longer recording time, increased recording capacity, and the like, and further improvement in recording density is desired for recording media.

  In order to perform high-density recording on a conventional magnetic recording medium, a high C / N ratio is required, noise (N) is low, and reproduction output (C) is required to be high. In recent years, high-sensitivity heads such as magnetoresistive heads (MR heads) and giant magnetoresistive heads (GMR heads) have been developed in place of the inductive magnetic heads used so far. Since it is easy to obtain a reproduction output as compared with the head, in order to obtain a high C / N ratio, it is more important to reduce the noise than to increase the output.

  The noise of the magnetic recording medium is roughly divided into particulate noise and surface noise generated due to the surface property of the magnetic recording medium. In the case of particulate noise, the influence of the particle size is large, and the finer the particle, the better the noise reduction. Therefore, the magnetic particle powder used in the magnetic recording medium needs to be as small as possible. Since the particle volume is reduced by miniaturization, the ratio of magnetic anisotropy energy and thermal energy (KuV / kT) representing the thermal stability of magnetization (Ku: magnetic anisotropy constant, V: particle volume) , K: Boltzmann constant, T: absolute temperature) becomes small, and is susceptible to thermal fluctuations.

  In general, as magnetic particles having fine particles and a high coercive force value, metal magnetic particle powder containing iron as a main component, hexagonal ferrite particle powder, spinel ferrimagnetic particle powder, and the like are known.

  However, in the magnetic metal particle powder mainly composed of iron, the coercive force (Hc) and the saturation magnetization value (σs) decrease as the particle size decreases because the mechanism of magnetization is derived from shape magnetic anisotropy. Tend to. Further, the hexagonal ferrite particle powder has σs (saturation magnetization value) of about ½ of that of the metal magnetic particle powder, and Ku (Ku is obtained by Hk · σs / 2) (Hk: anisotropic magnetic field) ) Is difficult to increase, and the influence of thermal fluctuation tends to be larger than that of metal magnetic particle powder. Furthermore, in the case of hexagonal ferrite particle powder, the SFD tends to increase because the crystal growth is suppressed by setting the crystallization temperature low in order to reduce the particle size, and the high output due to the influence of self-demagnetization. It is known that it is difficult to obtain.

  Up to now, spinel ferrimagnetic particles with high dispersibility and chemical stability having high coercive force (Hc) and large saturation magnetization value (σs) as a high-density magnetic recording material, although the particle diameter is fine Are known (Patent Documents 1 to 3).

JP 2004-231460 A International Publication WO 2004/100190 JP 2006-229037 A

  In the above-mentioned patent documents 1 to 3, spinel ferrimagnetism having an average particle diameter of 5 to 30 nm in which the particle surface is coated with a hydroxide of one or more metals selected from the group of Si, Al, P and Zn. Although particle powder is described, it is difficult to obtain excellent output characteristics because the powder SFD is large and the noise of the magnetic recording medium is high, as shown in a comparative example.

  Therefore, the present invention provides a technique for obtaining a spinel-type ferrimagnetic particle powder having an average particle diameter of 5 to 70 nm and a powder SFD of 1.4 or less, which is effective for reducing noise in a magnetic recording medium. As an objective.

  The technical problem can be achieved by the present invention as follows.

That is, the present invention is a magnetic recording comprising spinel-type ferrimagnetic particles represented by the following general formula, having an average particle diameter of 5 to 70 nm, and a powder SFD of 1.4 or less. It is a spinel type ferrimagnetic particle powder for a medium (Invention 1).
_{(CoO) x (NiO) y} (MO) z · n / 2 (Fe 2 O 3)
(M: divalent to pentavalent metal element) (2.05 ≦ n ≦ 3.0)
(X: 0.15 to 0.60, y: 0.15 to 0.60, z: 0 to 0.3)
(X + y + az / 2 = 1) (a: valence of metal element)

  In the present invention, the divalent to pentavalent metal element M is Zn, Mn, Mg, Sn, Cu, Si, Pd, Cr, Al, La, Ce, Y, Sc, Sb, Rh, Nd, B, It is a spinel type ferrimagnetic particle powder for a magnetic recording medium according to the first aspect of the present invention comprising one or more selected from the group of Ru, Pr, Bi, Zr, Ti, Ge, Mo, Nb, P and Re. Invention 2).

In addition, the present invention provides the spinel ferrimagnetic material of the present invention 1 or the present invention 2 having a coercive force (Hc) of 159.2 to 397.9 kA / m and a saturation magnetization value (σs) of 40 to 70 Am ² / kg. Magnetic particle powder (Invention 3).

  The present invention also provides a magnetic recording medium comprising a magnetic recording layer comprising a magnetic particle powder and a binder resin formed on a nonmagnetic support, wherein the magnetic particle powder is any one of the present inventions 1 to 3. 2 is a magnetic recording medium using spinel-type ferrimagnetic particle powder for magnetic recording medium (invention 4).

  The spinel-type ferrimagnetic particle powder according to the present invention can further reduce noise of the magnetic recording medium because the powder SFD is 1.4 or less despite the fine average particle diameter of 5 to 70 nm. Therefore, it is suitable as a magnetic particle powder for a high-density magnetic recording medium.

  The configuration of the present invention will be described in more detail as follows.

  First, the spinel ferrimagnetic particle powder for magnetic recording media according to the present invention will be described.

The spinel-type ferrimagnetic particle powder for magnetic recording media according to the present invention comprises a spinel-type ferrimagnetic particle powder represented by the following general formula, has an average particle diameter of 5 to 70 nm, and a powder SFD of 1. 4 or less.
_{(CoO) x (NiO) y} (MO) z · n / 2 (Fe 2 O 3)
(M: divalent to pentavalent metal element) (2.05 ≦ n ≦ 3.0)
(X: 0.15 to 0.60, y: 0.15 to 0.60, z: 0 to 0.3)
(X + y + az / 2 = 1) (a: valence of metal element)

The composition of the spinel type ferrimagnetic particle powder for magnetic recording media according to the present invention is represented by the formula: (CoO) _x (NiO) _y (MO) _z · n / 2 (Fe ₂ O ₃ ). In the formula, M is a divalent to pentavalent metal element, specifically, Zn, Mn, Mg, Sn, Cu, Si, Pd, Cr, Al, La, Ce, Y, Sc, Sb, One or more metal elements selected from the group of Rh, Nd, B, Ru, Pr, Bi, Zr, Ti, Ge, Mo, Nb, P and Re. Considering the magnetic properties of the obtained spinel ferrimagnetic particle powder, M is preferably a divalent metal element, more preferably Zn, Mn, and Cu.

  In the above composition formula of the spinel type ferrimagnetic particle powder for magnetic recording media according to the present invention, n is a value larger than the stoichiometric amount of the spinel type ferrite, specifically, a range of 2.05 to 3.0. It is preferable that When n is out of the above range, the coercive force (Hc) is remarkably lowered, which is not preferable. A more preferable value of n is 2.1 to 2.9.

In the above composition formula of the spinel-type ferrimagnetic particle powder for magnetic recording media according to the present invention, x, y and z are usually 0.15 to 0.60, preferably 0.20 to 0.55, y Is usually 0.15 to 0.60, preferably 0.20 to 0.55, and z
Is usually 0 to 0.3, preferably 0.01 to 0.3, and x + y + az / 2 = 1.

  The average particle diameter of the spinel type ferrimagnetic particle powder for magnetic recording media according to the present invention is 5 to 70 nm, preferably 9 to 60 nm, and more preferably 10 to 50 nm. When the average particle diameter is less than 5 nm, the saturation magnetization value of the spinel ferrimagnetic particle powder becomes low, and it becomes difficult to obtain sufficient characteristics as a magnetic material. Moreover, since the influence of the thermal fluctuation accompanying refinement | miniaturization of magnetic particle powder becomes large, it is not preferable. If it exceeds 70 nm, it is difficult to reduce the particle noise because the particle size is large, and it becomes difficult to obtain a magnetic recording medium having a high C / N ratio.

BET specific surface area of the magnetic recording medium for the spinel-type ferrimagnetic particles according to the present invention is preferably 15~250m ² / g, more preferably 20~150m ² / g, even more preferably at 25~130m ² / g is there. When the BET specific surface area value is less than 15 m ² / g, the magnetic fine particle powder for a magnetic recording medium is coarse, so that the surface smoothness of the magnetic recording medium obtained using this decreases, and the particulate noise Is unfavorable because of an increase. On the other hand, when the BET specific surface area value exceeds 250 m ² / g, aggregation is likely to occur due to an increase in intermolecular force due to finer particles, so that the dispersibility in the vehicle during the production of the magnetic coating material is lowered.

The magnetic properties of the spinel-type ferrimagnetic particle powder for magnetic recording media according to the present invention are preferably such that the coercive force (Hc) is 159.2 to 397.9 kA / m, more preferably 159.2 to 358.1 kA / m. The saturation magnetization value is preferably 40 to 70 Am ² / kg, more preferably 45 to 70 Am ² / kg.

  The powder SFD of the spinel ferrimagnetic particle powder for magnetic recording media according to the present invention is 1.4 or less. When the powder SFD exceeds 1.4, since the powder SFD is large and the noise of the magnetic recording medium is high, it is difficult to obtain excellent output characteristics. A preferable powder SFD is 1.2 or less.

  The spinel-type ferrimagnetic particle powder for magnetic recording media according to the present invention, if necessary, the surface of the spinel-type ferrimagnetic particle powder is one or more hydroxides selected from the group of Si, Al, P and Zn, or You may coat | cover with an oxide. When it is dispersed in a magnetic paint by coating with one or more hydroxides or oxides selected from the group consisting of Si, Al, P, and Zn, it has good compatibility with the binder resin. The degree of dispersion is more easily obtained.

  Next, the magnetic recording medium according to the present invention will be described.

  The magnetic recording medium according to the present invention has a magnetic recording layer containing the spinel-type ferrimagnetic particle powder according to the present invention and a binder resin formed on a nonmagnetic support. Further, if necessary, a nonmagnetic underlayer may be formed between the nonmagnetic support and the magnetic recording layer, and further, with respect to the magnetic recording layer formed on one surface of the nonmagnetic support, A back coat layer may be formed on the other surface of the nonmagnetic support. In particular, in the case of a backup tape for computer recording, it is preferable to provide a nonmagnetic underlayer or a backcoat layer from the viewpoint of preventing winding disturbance and improving running durability.

  As the nonmagnetic support in the present invention, polyesters such as polyethylene terephthalate and polyethylene naphthalate that are currently widely used in magnetic recording media, polyolefins such as polyethylene and polypropylene, polycarbonate, polyamide, polyamideimide, polyimide, aromatic Synthetic resin films such as polyamide, aromatic polyimide, aromatic polyamideimide, polysulfone, cellulose triacetate, and polybenzoxazole, metal foils and plates such as aluminum and stainless steel, and various papers can be used.

  As the binder resin, a thermoplastic resin, a thermosetting resin, an electron beam curable resin, etc. that are widely used in the production of magnetic recording media can be used alone or in combination.

  In the magnetic recording medium of the present invention, when a nonmagnetic underlayer is formed between the nonmagnetic support and the magnetic recording layer, the nonmagnetic underlayer contains nonmagnetic particle powder and a binder.

  Nonmagnetic particle powders used for the nonmagnetic underlayer include alumina, hematite, goethite, titanium oxide, silica, chromium oxide, cerium oxide, zinc oxide, silicon nitride, boron nitride, silicon carbide, calcium carbonate, and barium sulfate. Can be used alone or in combination. Hematite, goethite and titanium oxide are preferred, and hematite is more preferred.

  The particle shape of the non-magnetic particle powder may be any shape such as needle shape, spindle shape, rice grain shape, spherical shape, granular shape, polyhedron shape, flake shape, scale shape and plate shape. The particle size is preferably 0.005 to 0.30 μm, more preferably 0.010 to 0.25 μm. If necessary, the particle surface may be coated with one or more compounds selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide. Compared with the case of not coating, dispersibility in the nonmagnetic paint can be improved.

  As the binder resin, the binder resin used for producing the magnetic recording layer can be used.

  In the magnetic recording medium of the present invention, when a backcoat layer is formed on the other surface of the nonmagnetic support relative to the magnetic recording layer formed on one surface of the nonmagnetic support, It is preferable to contain an antistatic agent and inorganic particle powder together with the binder resin for the purpose of improving the surface electrical resistance value and strength of the backcoat layer.

  As the inorganic powder, one or more selected from alumina, hematite, goethite, titanium oxide, silica, chromium oxide, cerium oxide, zinc oxide, silicon nitride, boron nitride, silicon carbide, calcium carbonate, barium sulfate, etc. Can be used. The particle size is preferably 0.005 to 1.0 [mu] m, more preferably 0.010 to 0.5 [mu] m.

  As the antistatic agent, conductive powder such as carbon black, graphite, tin oxide, titanium oxide-tin oxide-antimony oxide, a surfactant, and the like can be used. In addition to antistatic properties, carbon black is preferably used as the antistatic agent since effects such as reduction of the friction coefficient and improvement of the strength of the magnetic recording medium can be expected.

  As the binder resin, the binder resin used for producing the magnetic recording layer and the nonmagnetic underlayer can be used.

  In the magnetic recording layer, nonmagnetic underlayer and backcoat layer in the present invention, lubricants, abrasives, dispersants, antistatic agents, etc., which are usually used in the production of magnetic recording media are added as necessary. May be.

  The magnetic recording medium according to the present invention has a coercive force value of 159.2 to 397.9 kA / m, preferably 159.2 to 358.1 kA / m, and a coercive force distribution SFD (Switching Field Distribution) of 1.2 or less. , Preferably 1.1 or less.

  Next, a method for producing a spinel ferrimagnetic particle powder for a magnetic recording medium according to the present invention will be described.

  The method for producing spinel-type ferrimagnetic particle powder for magnetic recording media according to the present invention includes the following steps: Preparation step (however, the divalent to pentavalent metal element M is mixed with an aqueous M-containing solution or Fe-containing Ni-containing aqueous solution or Co-containing aqueous solution as necessary); (2) Fe, Ni (3) Fe, Ni, Co-containing coprecipitation adding Co-containing raw material aqueous solution to the Fe, Ni-containing coprecipitate precipitate-containing liquid Step for producing precipitate-containing liquid; (4) Step for producing black particles by heat-treating the Fe, Ni, Co-containing coprecipitate-containing liquid at 80 to 120 ° C .; And removing the ultrafine particle component by adding acid to the black particle etching step; and (6) after filtering and washing the black particles obtained in (5), drying at a temperature of 120 ° C. or lower, It consists of a step of pulverization and heat treatment at 160 to 250 ° C.

First, in the raw material aqueous solution preparation step (1), water-soluble metal salts of Fe, Ni, Co, and M (divalent to pentavalent metal elements) that are raw materials are dissolved in water, respectively, to obtain a metal salt having a predetermined concentration. Each aqueous solution containing (Fe ³⁺ , Ni ²⁺ , Co ²⁺ and M ^{a +} (a: 2 to 5)) is prepared. Next, the Fe-containing aqueous solution and the Ni-containing aqueous solution are mixed to prepare an Fe and Ni-containing raw material aqueous solution. The M (divalent to pentavalent metal element) -containing aqueous solution is mixed with an Fe, Ni-containing raw material aqueous solution, or a Co-containing raw material aqueous solution as necessary.

  Examples of the iron compound used in the present invention include one or two selected from water-soluble iron salts such as halides such as chloride, bromide and iodide, nitrates, sulfates, carbonates, organic acid salts and complex salts. The above can be used. Considering solubility in water and economy, ferric chloride and ferric nitrate are preferable.

  As a metal salt selected from Ni compounds, Co compounds, and M (divalent to pentavalent metal elements) used in the present invention, water-soluble chlorides, bromides, iodides and other halides or nitrates may be used. it can. Specific examples of M (divalent to pentavalent metal elements) include Zn, Mn, Mg, Ti, Sn, Zr, Cu, Mo, La, Ce, V, Si, Sc, Sb, Y, Rh, Pd, Cr, Nd, Nb, B, P, Ge, Al, Ru, Pr, Bi, W, Re, or the like can be used.

  The concentration of the alkaline aqueous solution is preferably adjusted so that the alkali concentration in the reaction solution after adding the Co-containing raw material aqueous solution to the Fe, Ni-containing coprecipitate precipitate-containing liquid is 0.1 to 10 mol / L. More preferably, it is 0.2-8 mol / L. When the alkali concentration is less than 0.1 mol / L, crystallization of spinel ferrimagnetic particles is incomplete, which is not preferable. Moreover, since the coercive force falls remarkably when the density | concentration of aqueous alkali solution exceeds 10 mol / L, it is not preferable.

  Examples of the alkali to be used include water-soluble alkalis such as sodium hydroxide, potassium hydroxide and aqueous ammonia. Moreover, it is preferable to heat and raise the temperature of aqueous alkali solution beforehand in the range of 60 to 110 degreeC.

  Addition of the Fe and Ni-containing raw material aqueous solution to the alkaline aqueous solution is performed while stirring at a temperature of 60 to 110 ° C., preferably 80 to 100 ° C., and then, while maintaining the temperature of 60 to 110 ° C. Stirring is performed for min-2 hours to obtain a Fe, Ni-containing coprecipitate-containing liquid.

  In the step of producing the Fe, Ni-containing coprecipitate precipitate-containing liquid, when the temperature of the mixed solution of the alkaline aqueous solution and the Fe, Ni-containing raw material aqueous solution is less than 60 ° C, the particle size of the produced coprecipitate precipitate is large. Thus, it is difficult to achieve the object of the present invention. Further, when the temperature of the mixed liquid is 110 ° C. or higher, a special device such as an autoclave is required, which is not economical.

  Addition of the Co-containing raw material aqueous solution to the Fe and Ni-containing coprecipitate precipitate-containing liquid obtained above is carried out with stirring at a temperature of 60 ° C to 110 ° C, preferably 80 to 100 ° C.

  Next, in the black particle production step (4), the reaction is carried out at a temperature of 80 to 120 ° C., preferably 85 to 110 ° C. for 30 minutes to 20 hours, preferably 1 to 15 hours, and contains Fe, Ni and Co. A liquid containing a coprecipitate precipitate (black particles) is obtained. When the reaction temperature in the step of generating the Fe, Ni, Co-containing coprecipitate-containing precipitate-containing liquid is less than 80 ° C., ultrafine particles are generated, and the spinel-type ferrimagnetic particle powder having the particle size and magnetic properties intended by the present invention Is difficult to get. Moreover, when it exceeds 120 degreeC, it exists in the tendency for a particle size to become large, and it is difficult to achieve the objective of this invention.

  The metal ion concentration in the coprecipitate precipitate-containing liquid is usually 0.05 to 0.5 mol / L, preferably 0.1 to 0.4 mol / L. When the metal ion concentration is less than 0.05 mol / L, the concentration of the coprecipitate precipitate becomes too low, which is not economical. On the other hand, when the metal ion concentration exceeds 0.5 mol / L, the particle size distribution of the generated spinel ferrimagnetic particles becomes large, and it is difficult to achieve the object of the present invention.

  In the black particle etching step (5), the obtained black particles are washed to remove alkali, and then an acid is added to remove ultrafine components. As a cleaning method, it can be performed by a known method. The washing is preferably performed until the filtrate has an electric conductivity of 1 mS / cm or less.

  In the acid etching method for black particles, for example, an acid equivalent corresponding to usually 5 to 200 mol%, preferably 15 to 100 mol% is added to the number of moles of metal ions contained in the black particles. Become. The etching temperature is usually 5 to 90 ° C., preferably 20 to 50 ° C. The etching time is usually 1 to 48 hours, preferably 2 to 20 hours. As the acid to be added, hydrochloric acid, sulfuric acid, nitric acid, oxalic acid and the like can be used. The method for adding the acid is not particularly limited, and for example, batch addition or sequential addition may be used.

  When the acid equivalent is less than 5 mol%, a large amount of ultrafine components remain, making it difficult to obtain a spinel ferrimagnetic particle powder having a good SFD. On the other hand, when the acid equivalent exceeds 200 mol%, the yield of the obtained particles is lowered, which is not industrially preferable.

  Since the black particle-containing liquid after the black particle etching step (5) contains a soluble metal salt, the soluble metal salt is removed by washing. As a cleaning method, it can be performed by a known method. The washing is preferably performed until the electric conductivity of the filtrate is 50 μS / cm or less. However, when the particle surface is coated with a metal hydroxide or metal oxide by adding one or more metal-containing aqueous solutions selected from the group of Si, Al, P, and Zn after etching with an acid, Cleaning may be performed until the electric conductivity of the liquid becomes 1 mS / cm or less.

  After washing, filtration, drying and pulverization are performed, followed by heating and firing to obtain spinel ferrimagnetic particle powder. The drying temperature is usually 60 to 120 ° C., preferably 60 to 100 ° C., and the drying time is usually 2 to 20 hours.

  The heating and baking temperature after drying is 160 ° C. to 250 ° C., preferably 180 ° C. to 240 ° C., and the heating and baking time is 15 minutes to 3 hours, preferably 30 minutes to 2 hours. When the heating and baking treatment is less than 160 ° C., the coercive force Hc exceeds 397.9 kA / m, which is not preferable. On the other hand, when the heating and baking treatment exceeds 250 ° C., the coercive force Hc is less than 159.2 kA / m, which is not preferable.

  After cleaning and filtering the etched black particles, one or more metal-containing aqueous solutions selected from the group of Si, Al, P, and Zn are added to coat the particle surface with metal hydroxide or metal oxide May be.

  The surface coating treatment is performed by adding an aqueous solution in which the metal water-soluble salt is dissolved to the washed black particle-containing liquid and mixing and stirring, or, if necessary, adjusting the pH value after mixing and stirring. The surface of the black particles is coated, and then filtered, washed, dried, pulverized, and then heated and fired.

  Examples of the silicon compound include water-soluble salts such as sodium silicate and potassium silicate. Examples of the aluminum compound include water-soluble salts such as aluminum sulfate and sodium aluminate. Examples of the phosphorus compound include disodium hydrogen phosphate, Water-soluble salts such as orthophosphoric acid are exemplified, and examples of the zinc compound include water-soluble salts such as zinc chloride and zinc sulfate. Examples of the alkali include water-soluble alkalis such as sodium hydroxide, potassium hydroxide, and aqueous ammonia.

  Next, a method for manufacturing a magnetic recording medium in the present invention will be described.

  Solvents used in forming the nonmagnetic underlayer, magnetic recording layer, and backcoat layer include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and tetrahydrofuran, toluene, xylene, and the like that are widely used in magnetic recording media. Aromatic hydrocarbons, alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol and isopropyl alcohol, esters such as methyl acetate, butyl acetate, isobutyl acetate and glycol acetate, glycol dimethyl ether, glycol monoethyl ether and dioxane Glycol ethers and mixtures thereof can be used.

  The nonmagnetic underlayer, the magnetic recording layer, and the backcoat layer are kneaded and dispersed with a kneader and a disperser that generally use components and solvents that constitute each layer, thereby preparing each paint. Using each of the coating materials, a nonmagnetic underlayer and a magnetic recording layer are applied in this order on one surface of the nonmagnetic support, dried, and then calendared. As a coating method at that time, either the Wet on Wet method in which the magnetic layer and the nonmagnetic layer are applied almost simultaneously, or the Wet on Dry method in which the nonmagnetic underlayer is applied and dried and then the magnetic recording layer is applied thereon. But you can. If necessary, if a backcoat layer is provided, a backcoat layer coating is applied on the nonmagnetic support opposite to the nonmagnetic underlayer and the magnetic recording layer, dried, calendered, and magnetically treated. A recording medium is obtained.

<Action>
The most important point in the present invention is that the spinel-type ferrimagnetic particle powder according to the present invention has an average particle diameter of 5 to 70 nm and a powder SFD of 1.4 or less, This is the fact that a magnetic recording medium capable of higher density recording can be obtained because the noise of the magnetic recording medium can be further reduced.

  The present inventor considers the reason why the spinel-type ferrimagnetic particle powder for magnetic recording media according to the present invention can further reduce the noise of the magnetic recording media as follows.

  That is, although the conventional spinel type ferrimagnetic particle powder is fine with an average particle diameter of 5 to 30 nm, the powder SFD is large, and it is difficult to reduce noise in the magnetic recording medium. The present inventors have found that the coercive force Hc is sharply distributed by improving the addition method of the raw material solution and performing the heat-firing treatment after the drying / pulverization step, and as a result, the distribution of the coercive force Hc is sharp. Therefore, it is considered that the noise of the magnetic recording medium could be further reduced because the powder SFD could be reduced.

  Examples of the present invention are shown below, and the present invention will be specifically described.

  The average particle diameter of the spinel ferrimagnetic particles is obtained by taking a photograph of the particles in a plurality of fields using a transmission electron microscope, measuring the particle diameter of 360 or more particles using the photograph, and calculating the average value of the particles. The average particle diameter was shown.

  The content of various elements contained in the spinel ferrimagnetic particle powder was measured using an “inductively coupled plasma emission spectroscopic analyzer SPS4000” (manufactured by Seiko Denshi Kogyo Co., Ltd.).

  The specific surface area was shown by the value measured by BET method using “Monosorb MS-11” (manufactured by Kantachrome Co., Ltd.).

  The magnetic properties of the spinel-type ferrimagnetic particle powder and the magnetic tape were measured using a “vibrating sample magnetometer VSM SSM-5-15” (manufactured by Toei Kogyo Co., Ltd.) under an external magnetic field of 1193.7 kA / m. . The powder SFD and the SFD of the magnetic tape have a sweep speed of 79.6 (kA / m) / min when the applied magnetic field is in the range of 0 to 397.9 kA / m, and is 397.9 to 1,193.7 kA / min. In the range of m, the sweep rate was measured as 397.9 (kA / m) / min.

  The glossiness of the coating film surface of the magnetic tape is a value measured at an incident angle of 45 ° using “Gloss meter UGV-5D” (manufactured by Suga Test Instruments Co., Ltd.), and the standard plate gloss is 86.3%. The hour value is shown in%.

  Surface roughness Ra measured the centerline average roughness of the coating film using "ZYGO NewView600S" (made by ZYGO Corporation).

  The thickness of each layer of the nonmagnetic support and the magnetic recording layer constituting the magnetic recording medium was measured using a digital electronic micrometer K351C (manufactured by Anritsu Electric Co., Ltd.).

  The electromagnetic conversion characteristics of the magnetic tape were measured using a drum tester, a MIG head as a recording head, and an MR head as a reproducing head. The relative speed between the head and the magnetic tape is 2.5 m / sec. The reproduction signal output (C) at a recording frequency of 10 MHz and the output at a recording frequency of 9 MHz are noise signal outputs (N). The relative value with respect to the reference tape was determined as 0 dB (reference tape). C / N is shown using these reproduction signal output (C) and noise signal output (N).

<Example 1-1: Production of spinel-type ferrimagnetic particle powder>
As metal salts, ferric chloride hexahydrate, cobalt chloride hexahydrate, nickel chloride hexahydrate, and manganese chloride tetrahydrate are each dissolved in pure water in a 5-liter resin beaker, and 2.00 [mol / L] Fe ³⁺ aqueous solution, 0.29 [mol / l] Co ²⁺ aqueous solution, 0.24 [mol / l] Ni ²⁺ aqueous solution and 0.24 [mol / l] Mn ²⁺ aqueous solution 10 liters each It was adjusted. A resin container equipped with a stirrer and a thermometer and having a volume of 10 liters was ^{charged with} 1.2 liters of Fe ³⁺ aqueous solution, 2.0 liters of Ni ²⁺ aqueous solution and 0.8 liters of Mn ²⁺ aqueous solution, mixed and stirred, and Fe, Ni , A mixed solution containing Mn was prepared (A liquid). Next, 7.0 liters (solution B) of an aqueous sodium hydroxide solution having a concentration of 6.50 [mol / l] was charged into a stainless steel reaction vessel (15 liters) and heated to 95 ° C. with stirring. The solution A was added to an aqueous sodium hydroxide solution with stirring, and reacted at 95 ° C. for 60 minutes to obtain a Fe, Ni, Mn-containing coprecipitate-containing solution.

Next, 1.0 liter of a Co ²⁺ aqueous solution is added to the Fe, Ni, Mn-containing coprecipitation precipitate-containing liquid obtained above while stirring, and the reaction is performed at 95 ° C. for 60 minutes to contain Fe, Ni, Mn, and Co. A liquid containing a coprecipitate precipitate was obtained.

  The Fe-, Ni-, Mn-, and Co-containing coprecipitate-containing solution obtained above is washed thoroughly with pure water using pure water until the filtrate has an electric conductivity of 1 mS / cm or less, and then Fe, Ni Then, 0.20 liter of 70 mass% sulfuric acid solution was added to 12 liters (30 ° C.) of the slurry containing the coprecipitation precipitate containing Mn and Co with stirring, and etching treatment with acid was performed at 30 ° C. for 3 hours.

  The acid-etched Fe, Ni, Mn, and Co-containing slurry containing the coprecipitate precipitate obtained above is sufficiently washed with pure water until the electrical conductivity of the filtrate is 20 μS / cm or less using pure water. After filtration, it was dried at 70 ° C. for 12 hours. The obtained dry powder was pulverized and then heated and fired at 200 ° C. for 1 hour to obtain a spinel-type ferrimagnetic particle powder of Example 1-1.

The obtained spinel-type ferrimagnetic particle powder has a spinel-type structure as a result of X-ray diffraction measurement, the shape is granular, the average particle diameter is 28.9 nm, and the BET specific surface area value is 46.7 m ² / g, the coercive force value (Hc) was 248.9 kA / m, the saturation magnetization (σs) was 62.2 Am ² / kg, and the powder SFD was 0.744. The Fe content is 46.74 wt%, the Ni content is 9.74 wt%, the Co content is 5.89 wt%, the Mn content is 3.65 wt%, and n in the following composition formula is 2.518, x was 0.301, y was 0.499, and z was 0.200.
_{(CoO) x (NiO) y} (MO) z · n / 2 (Fe 2 O 3)

<Example 2-1: Production of magnetic recording medium>
Nonmagnetic coating composition for nonmagnetic underlayer formation 100.0 parts by weight of hematite particle powder for nonmagnetic underlayer,
11.8 parts by weight of a vinyl chloride copolymer resin having a potassium sulfonate group,
11.8 parts by weight of a polyurethane resin having a sodium sulfonate group,
78.3 parts by weight of cyclohexanone,
195.8 parts by weight of methyl ethyl ketone,
117.5 parts by weight of toluene,
Curing agent (polyisocyanate) 3.0 parts by weight,
Lubricant (butyl stearate) 1.0 part by weight.

  A non-magnetic underlayer hematite particle powder, a binder resin solution (vinyl chloride copolymer resin having potassium sulfonate group 30 wt% and cyclohexanone 70 wt%) and cyclohexanone are mixed so that the solid content is 72 wt%; A kneaded product was obtained by kneading for 30 minutes using an automatic mortar.

  Next, the kneaded product and an additional binder resin solution (30% by weight of a polyurethane resin having a sodium sulfonate group, 70% by weight of a solvent (methyl ethyl ketone: toluene = 1: 1)) so that the nonmagnetic coating composition is obtained. , Cyclohexanone, methyl ethyl ketone and 95 g of toluene 1.5 mmφ glass beads were added to a 140 ml glass bottle and mixed and dispersed for 6 hours with a paint shaker to obtain a nonmagnetic coating composition. Thereafter, a lubricant and a curing agent were added, and further mixed and dispersed for 15 minutes with a paint shaker, followed by filtration using a filter having an average pore diameter of 3 μm to prepare a nonmagnetic paint for a nonmagnetic underlayer.

  The nonmagnetic coating for the nonmagnetic underlayer was applied onto an aromatic polyamide film having a thickness of 4.5 μm, and then dried to form a nonmagnetic underlayer.

Magnetic coating composition for forming a magnetic recording layer 100.0 parts by weight of spinel-type ferrimagnetic particle powder,
12.5 parts by weight of a vinyl chloride copolymer resin having a potassium sulfonate group,
7.5 parts by weight of a polyurethane resin having a sodium sulfonate group,
Abrasive (AKP-50) 5.0 parts by weight,
2.0 parts by weight of carbon black,
Lubricant (myristic acid: butyl stearate = 1: 2) 3.0 parts by weight,
Curing agent (polyisocyanate) 5.0 parts by weight,
170.0 parts by weight of cyclohexanone,
170.0 parts by weight of methyl ethyl ketone.

  Spinel-type ferrimagnetic particle powder, abrasive, carbon black, binder resin solution (30% by weight of vinyl chloride copolymer resin having potassium sulfonate group and 70% by weight of cyclohexanone) and cyclohexanone have a solid content of 76% by weight. And kneaded for 40 minutes using an automatic mortar to obtain a kneaded product.

  Next, the kneaded product and an additional binder resin solution (30% by weight of a polyurethane resin having a sodium sulfonate group, 70% by weight of a solvent (methyl ethyl ketone: toluene = 1: 1)) so that the magnetic coating composition is obtained, A magnetic coating composition was obtained by adding to a 140 ml glass bottle together with 95 g of cyclohexanone, methyl ethyl ketone and toluene 1.5 mmφ glass beads, and mixing and dispersing for 6 hours with a paint shaker. Thereafter, a lubricant and a curing agent were added, and further mixed and dispersed for 15 minutes with a paint shaker, followed by filtration using a filter having an average pore diameter of 3 μm to prepare a magnetic coating material for a magnetic recording layer.

  The magnetic recording layer coating composition was applied on the nonmagnetic underlayer so that the thickness after drying was 1.5 μm, and then oriented and dried in a magnetic field. Thereafter, a curing reaction was performed at 60 ° C. for 24 hours, and a magnetic recording medium was obtained by slitting to a width of 12.7 mm.

  The obtained magnetic recording medium had a coercive force value Hc of 254.3 kA / m, a Br / Bm of 0.81, a coercive force distribution SFD of 0.725, a glossiness of 164%, and a surface roughness Ra of 14.2 nm. The reproduction output (C) was +0.2 dB and C / N was +1.6 dB.

  Spinel-type ferrimagnetic particle powder and a magnetic recording medium were prepared according to Example 1-1 and Example 2-1. Various production conditions and various properties of the obtained spinel-type ferrimagnetic particle powder and magnetic recording medium are shown.

<Manufacture of spinel ferrimagnetic particle powder>
Examples 1-2 to 1-5 and Comparative Example 1-1

  A spinel type ferrimagnetic particle powder was obtained in the same manner as in Example 1-1 except that the conditions for producing the spinel type ferrimagnetic particle powder were variously changed.

  Production conditions at this time are shown in Tables 1 and 2, and various properties of the obtained spinel-type ferrimagnetic particle powder are shown in Table 3.

Example 1-6:
Half of the Fe-, Ni-, Mn-, and Co-containing coprecipitation precipitate-containing slurry obtained in Example 1-1 after acid etching was extracted, and the electrical conductivity of the filtrate was 1 mS / cm ² or less using pure water by a conventional method. The slurry was sufficiently washed with water, and an aqueous sodium hydroxide solution was added to the slurry to adjust the pH value to 9. Then, the slurry was heated to 60 ° C. In this slurry, 9.75 g of 20 wt% aqueous sodium aluminate solution (spinel (Corresponding to 1.3% by weight in terms of Al) with respect to the type ferrimagnetic particle powder, and maintained for 30 minutes, and then the pH value was adjusted to 9 using acetic acid. After maintaining for 30 minutes in this state, filtration, washing, drying and pulverization were performed to obtain a spinel-type ferrimagnetic particle powder of Example 1-6 in which the particle surface was coated with an aluminum hydroxide or the like. Table 3 shows various characteristics of the spinel-type ferrimagnetic particle powder whose surface is coated with aluminum hydroxide or the like.

Comparative Example 1-2:
As metal salts, ferric chloride hexahydrate, nickel chloride hexahydrate, cobalt chloride hexahydrate, and manganese chloride tetrahydrate were each dissolved in pure water in a 10-liter resin beaker to obtain 2.00 [mol / L] Fe ³⁺ aqueous solution, 0.24 [mol / l] Ni ²⁺ aqueous solution, 0.29 [mol / l] Co ²⁺ aqueous solution and 0.24 [mol / l] Mn ²⁺ aqueous solution of 10 liters each. It was adjusted. A resin container equipped with a stirrer and a thermometer with a capacity of 10 liters is ^{charged with} 1.2 liters of Fe ³⁺ aqueous solution, 2.0 liters of Ni ²⁺ aqueous solution, 0.8 liters of Mn ²⁺ aqueous solution, and 1.0 liter of Co ²⁺ aqueous solution. Then, a mixed solution containing Fe, Ni, Mn, and Co was prepared by mixing and stirring (solution A). Next, 7.0 liters (solution B) of an aqueous sodium hydroxide solution having a concentration of 6.50 [mol / l] was charged into a stainless steel reaction vessel (15 liters) and heated to 95 ° C. with stirring. The above solution A was stirred into an aqueous sodium hydroxide solution and reacted at 95 ° C. for 60 minutes to obtain a Fe, Ni, Mn, Co-containing coprecipitate precipitate-containing liquid. Table 3 shows various characteristics of the obtained magnetic particle powder.

  The Fe, Ni, Mn, Co-containing coprecipitate precipitate-containing liquid obtained above was washed, acid-etched, washed / filtered, dried / pulverized in the same manner as in Example 1-1, and Comparative Example 1-2 Magnetic particle powder was obtained.

Comparative Example 1-3:
As metal salts, ferric chloride hexahydrate, nickel chloride hexahydrate, cobalt chloride hexahydrate, and manganese chloride tetrahydrate were each dissolved in pure water in a 10-liter resin beaker to obtain 3.00 mol / L] Fe ³⁺ aqueous solution, 0.36 [mol / l] Ni ²⁺ aqueous solution, 0.68 [mol / l] Co ²⁺ aqueous solution and 0.045 [mol / l] Mn ²⁺ aqueous solution 10 liters each It was adjusted. A resin container equipped with a stirrer and a thermometer with a capacity of 10 liters is ^{charged with} 1.2 liters of Fe ³⁺ aqueous solution, 2.0 liters of Ni ²⁺ aqueous solution, 0.8 liters of Mn ²⁺ aqueous solution, and 1.0 liter of Co ²⁺ aqueous solution. Then, a mixed solution containing Fe, Ni, Mn, and Co was prepared by mixing and stirring (solution A). Next, 7.0 liters (solution B) of an aqueous sodium hydroxide solution having a concentration of 7.1 [mol / l] was put into a stainless steel reaction vessel (15 liters) and heated to 95 ° C. with stirring. The above solution A was stirred into an aqueous sodium hydroxide solution and reacted at 95 ° C. for 60 minutes to obtain a Fe, Ni, Mn, Co-containing coprecipitate precipitate-containing liquid.

  The Fe-, Ni-, Mn-, and Co-containing coprecipitate-containing solution obtained above was washed, acid-etched, washed / filtered, dried / pulverized, and heated and fired in the same manner as in Example 1-1. -3 magnetic particle powder was obtained. Table 3 shows various characteristics of the obtained magnetic particle powder.

<Manufacture of magnetic recording media>
Examples 2-2 to 2-7, comparative examples 2-1 to 2-3:
A magnetic recording medium was manufactured according to the method for manufacturing a magnetic recording medium of Example 2-1 except that the type of spinel ferrimagnetic particle powder was changed variously.

  Table 4 shows various characteristics of the obtained magnetic recording medium.

  From the above examples, the spinel-type ferrimagnetic particle powder obtained according to the present invention has an average particle diameter of 5 to 70 nm and a powder SFD of 1.4 or less. It can be seen that noise is further reduced.

The spinel-type ferrimagnetic particle powder according to the present invention can further reduce noise of the magnetic recording medium because the powder SFD is 1.4 or less despite the fine average particle diameter of 5 to 70 nm. Therefore, it is suitable as a magnetic particle powder for a high-density magnetic recording medium.

Claims (2)

It consists of spinel-type ferrimagnetic particles represented by the following general formula, the average particle size is 10 to 50 nm, the powder SFD is 1.2 or less, and the divalent to pentavalent metal element M is Zn , Mn, Cu, Ti, one or more selected from the group, coercive force (Hc) is 159.2 to 358.1 kA / m, and saturation magnetization value σs is 45 to 70 Am ² / kg. spinel-type ferrimagnetic particles for magnetic recording medium characterized Oh Rukoto.
_{(CoO) x (NiO) y} (MO) z · n / 2 (Fe 2 O 3)
(M: divalent to pentavalent metal element) ( 2.1 ≦ n ≦ 2.9 )
(X: 0.2~0.55, y: 0.2~0.55 , z: 0.01 ~0.3)
(X + y + az / 2 = 1) (a: valence of metal element) In the magnetic recording medium comprising a magnetic recording layer containing magnetic particles is formed on a nonmagnetic support binder resin, the magnetic particles as claimed in claim 1 Symbol placement of the magnetic recording medium for the spinel-type ferrimagnetic particles A magnetic recording medium characterized by using.