JP2011181161A - Hexagonal ferrite particle powder for magnetic recording medium, and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide hexagonal ferrite particle powder for a magnetic recording medium which can reduce the noise of the magnetic recording medium and can suppress the deterioration of the magnetic recording medium. <P>SOLUTION: The hexagonal ferrite particle power for the magnetic recording medium has an average plate surface diameter of 10 to 30 nm. The proportion of large particles having a plate surface diameter of 50 nm or larger relative to all particles is 3.0% or smaller. The total amount of platinum group elements (ruthenium, rhodium, palladium, osmium, iridium, and platinum) contained in the hexagonal ferrite particle power is 10 ppm or smaller. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a hexagonal ferrite particle powder for magnetic recording media. Specifically, the average plate surface diameter is 10 to 30 nm, and the presence ratio of large particles having a plate surface diameter of 50 nm or more with respect to all particles. The present invention relates to a hexagonal ferrite particle powder that is 3.0% or less and is effective for reducing noise in a magnetic recording medium.

  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.

  In order to reduce noise of the magnetic recording medium, it is effective to increase the density of the magnetic particle powder per unit volume. As a method for improving the density of magnetic particle powder per unit volume, a method for increasing the volume ratio of magnetic particles in the magnetic layer and a method for reducing the particle volume of magnetic particles are known.

  In order to reduce the volume of the magnetic particles, it is only necessary to refine the magnetic particle powder. However, since the particle volume of the magnetic particles acts as a square to a cube of the particle size, the average particle size is small. However, the noise reduction effect is reduced when the presence ratio of coarse magnetic particles is large.

  Generally, as magnetic particles having fine particles and a high coercive force value, metal magnetic particle powders mainly composed of iron, hexagonal ferrite particle powders, and the like are known, and hexagonal ferrite particle powders are acicular metal. Compared with magnetic particle powder, it has a feature that a high output can be obtained in a short wavelength region, and is very promising as a magnetic powder for high-density recording magnetic recording media using an MR head or GMR head for reproduction.

  So far, hexagonal ferrite particle powder in which the abundance of fine particle components in hexagonal ferrite particle powder is limited to 3 to 5% or less for the purpose of improving SFD of hexagonal ferrite particle powder (Patent Document 1 and Patent Document 2). Etc. are known.

JP-A-10-92618 JP 2005-329309 A

  Patent Document 1 and Patent Document 2 described above describe a method of removing fine particle components by treating the obtained hexagonal ferrite particle powder with an aqueous solution of a strong acid, but the large particle components are considered. In addition, as shown in a comparative example to be described later, since the noise of the magnetic recording medium is increased due to the high ratio of large particles, it is difficult to obtain excellent output characteristics. Further, Patent Document 2 synthesizes hexagonal ferrite particle powder by a glass crystallization method, and uses a crucible such as platinum at the time of glass melting. Therefore, a metal having catalytic activity such as platinum in the obtained hexagonal ferrite particle powder. There is a problem of containing elements.

  Therefore, the present invention provides an hexagonal ferrite particle powder having an average plate surface diameter of 10 to 30 nm and a ratio of large particles having a plate surface diameter of 50 nm or more to the total particles of 3.0% or less. Another object of the present invention is to obtain hexagonal ferrite particle powder that is effective in reducing noise in magnetic recording media.

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

  That is, the present invention has an average plate surface diameter of hexagonal ferrite particle powder of 10 to 30 nm, and the presence ratio of large particles having a plate surface diameter of 50 nm or more with respect to all particles is 3.0% or less, A hexagonal ferrite particle for a magnetic recording medium, wherein the total amount of platinum group elements (ruthenium, rhodium, palladium, osmium, iridium and platinum) contained in the hexagonal ferrite particle powder is 10 ppm or less It is a powder (Invention 1).

  In the present invention, the average plate surface diameter of the hexagonal ferrite particle powder is 10 to 25 nm, and the presence ratio of large particles having a plate surface diameter of 40 nm or more with respect to all particles is 3.0% or less. A hexagonal ferrite particle for a magnetic recording medium, wherein the total amount of platinum group elements (ruthenium, rhodium, palladium, osmium, iridium and platinum) contained in the hexagonal ferrite particle powder is 10 ppm or less It is a powder (Invention 2).

  Further, the present invention is the hexagonal ferrite particle powder for magnetic recording media according to the present invention 1 or 2, wherein the coercive force (Hc) is 95.5 kA / m or more (Invention 3). .

  Further, the present invention provides a magnetic recording medium comprising a magnetic recording layer comprising a magnetic particle powder and a binder resin formed on a nonmagnetic support, and the magnetic particle powder is any one of the present inventions 1 to 3. A magnetic recording medium comprising the hexagonal ferrite particle powder for magnetic recording medium described in (4).

  The hexagonal ferrite particle powder for magnetic recording media according to the present invention has an average plate surface diameter of 10 to 30 nm, and the ratio of large particles having a plate surface diameter of 50 nm or more to all particles is 3.0% or less, Since the total amount of each element of the platinum group element is 10 ppm or less, the noise of the magnetic recording medium can be further reduced and the deterioration of the magnetic recording medium can be suppressed, so that the magnetic particle powder of the high-density magnetic recording medium It is suitable as.

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

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

  The hexagonal ferrite particle powder for magnetic recording media according to the present invention has an average plate surface diameter of 10 to 30 nm, and the ratio of large particles having a plate surface diameter of 50 nm or more to all particles is 3.0% or less, The total amount of each platinum group element is 10 ppm or less.

  The hexagonal ferrite particle powder for magnetic recording media according to the present invention is a magnetoplumbite type (M type) ferrite fine particle powder or W type ferrite fine particle containing one or more elements selected from Ba, Sr and Ca. It is a powder or a hexagonal ferrite particle powder in which some of the atoms are substituted with other elements. Specific examples of substitution elements include Co, Ni, Zn, Mn, Mg, Ti, Sn, Zr, Cu, Mo, La, Ce, V, Si, S, Sc, Sb, Y, Rh, Pd, and Nd. Nb, B, P, Ge, Al, Ag, Au, Ru, Pr, Bi, W, Re, Te, or the like can be used alone or in combination.

  The average plate surface diameter of the hexagonal ferrite particles for magnetic recording media according to the present invention is 10 to 30 nm, preferably 10 to 28 nm, and more preferably 10 to 25 nm. When the average plate surface diameter of the hexagonal ferrite particle powder exceeds 30 nm, the particle size is large, so that it is difficult to further reduce the particulate noise, and it is difficult to obtain a magnetic recording medium having a high C / N ratio. It becomes. Moreover, when the average plate surface diameter is less than 10 nm, the influence of thermal fluctuation accompanying the miniaturization of the magnetic particle powder increases, which is not preferable.

  The plate ratio (average plate surface diameter to average thickness) (hereinafter referred to as “plate ratio”) of the hexagonal ferrite particles for magnetic recording media according to the present invention is preferably 1.5 to 10.0, More preferably, it is 1.75 to 8.0, and still more preferably 2.0 to 6.0. When the plate ratio exceeds 10, stacking between particles increases, dispersibility in the vehicle during production of the magnetic coating material decreases, and viscosity may increase, which is not preferable.

BET specific surface area of the magnetic recording medium for the hexagonal ferrite particles according to the present invention is preferably 20 to 200 m ² / g, more preferably 25~200m ² / g, still more preferably is 30 to 150 m ² / g . When the BET specific surface area value is less than 20 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 by using this decreases, resulting in that It becomes difficult to improve the output. In addition, the saturation magnetization value and the coercive force value in the short wavelength region are decreased, and particle noise is increased, which is not preferable. When the BET specific surface area value exceeds 200 m ² / g, aggregation tends 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 decreases.

  In the hexagonal ferrite particles for magnetic recording media according to the present invention, the ratio of large particles having a plate surface diameter of 50 nm or more to the total particles is 3.0% or less, preferably 2.0% or less. Preferably it is 1.0% or less. When the proportion of large particles having a plate surface diameter of 50 nm or more with respect to all particles exceeds 3.0%, since the proportion of coarse magnetic particles is large, it is difficult to further reduce particulate noise. It becomes difficult to obtain a magnetic recording medium having a high C / N ratio.

  The hexagonal ferrite particle powder for magnetic recording media according to the present invention is a large particle having a plate surface diameter of 40 nm or more with respect to all particles, particularly when the average plate surface diameter is in the range of 10 to 25 nm. Is 3.0% or less, preferably 2.0% or less, more preferably 1.0% or less. When the average plate surface diameter is in the range of 10 to 25 nm and the presence ratio of large particles having a plate surface diameter of 40 nm or more with respect to all particles exceeds 3.0%, the presence ratio of coarse magnetic particles is large. Therefore, it is difficult to reduce particulate noise, and it is difficult to obtain a magnetic recording medium having a high C / N ratio.

  The total of the platinum group elements (ruthenium, rhodium, palladium, osmium, iridium and platinum) contained in the hexagonal ferrite particles for magnetic recording media according to the present invention is 10 ppm or less, preferably 8 ppm or less, more preferably. Is 5 ppm or less. When the content of the platinum group element exceeds 10 ppm, it is preferable because an organic solvent or a resin contained in a magnetic paint or a magnetic recording medium produced using the platinum group element is easily deteriorated by a metal having catalytic activity such as platinum. Absent.

As for the magnetic properties of the hexagonal ferrite particles for magnetic recording media according to the present invention, the coercive force (Hc) is preferably 95.5 to 397.9 kA / m, more preferably 119.4 to 318.3 kA / m. The saturation magnetization value is preferably 40 to 70 Am ² / kg, more preferably 45 to 70 Am ² / kg.

  The hexagonal ferrite particle powder for magnetic recording media according to the present invention, if necessary, the surface of the hexagonal ferrite particle powder is made of aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide. You may coat | cover with the 1 type (s) or 2 or more types of selected compound (henceforth "aluminum hydroxide etc."). By carrying out a coating treatment with aluminum hydroxide or the like, when dispersed in a magnetic paint, it is well-familiar with the binder resin and a desired 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 is formed by forming a magnetic recording layer containing the hexagonal ferrite particle powder according to the present invention and a binder resin 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 95.5 to 358.1 kA / m, preferably 51.7 to 318.3 kA / m, and a coercive force distribution SFD (Switching Field Distribution) of 0.70 or less. , Preferably 0.67 or less, more preferably 0.65 or less.

  Next, a method for producing hexagonal ferrite particles for magnetic recording media according to the present invention will be described.

  The production method for obtaining the hexagonal ferrite particle powder for magnetic recording media according to the present invention is not particularly limited as long as it satisfies the above-mentioned characteristics, but the glass crystallization method is usually performed from platinum during firing. Since the resulting crucible is used, the platinum group element content of the obtained hexagonal ferrite particle powder exceeds 10 ppm, which is not preferable. Preferred are wet methods such as a hydrothermal synthesis method and a coprecipitation-calcination method.

  Specifically, the coprecipitation-firing method is selected from metal salts and iron compounds containing at least one metal element selected from barium, strontium, and calcium, and divalent to pentavalent metal elements. A suspension in which one or more metal salts are mixed is gradually added to an alkaline aqueous solution over 20 minutes, and then reacted in a temperature range of 60 to 100 ° C., and the resulting coprecipitate is filtered off. -It can obtain by removing a flux after drying and then baking at the temperature of 600-800 degreeC in presence of a flux.

  Specifically, the hydrothermal synthesis method is selected from a metal salt and an iron compound containing at least one metal element selected from barium, strontium, and calcium, and a divalent to pentavalent metal element. A suspension in which seeds or two or more kinds of metal salts are mixed is gradually added to an alkaline aqueous solution over 20 minutes, and then reacted in a temperature range of 100 to 300 ° C., and the obtained hexagonal ferrite precursor is obtained. It can be obtained by filtering and drying, and then baking at a temperature of 600 to 800 ° C. in the presence of a flux and then removing the flux.

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

  Solvents used in the formation of 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, etc. 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 the fact that the hexagonal ferrite particle powder for a magnetic recording medium according to the present invention can further reduce noise of the magnetic recording medium and suppress deterioration of the magnetic recording medium. .

  The present inventor considers the reason why the hexagonal ferrite 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, to reduce the noise of the magnetic recording medium, it is effective to increase the density of the magnetic particle powder per unit volume, and a method for reducing the particle volume of the magnetic particles is known. In order to reduce the volume of the magnetic particles, it is only necessary to refine the magnetic particle powder. However, since the particle volume of the magnetic particles acts as a square to a cube of the particle size, the average particle size is small. However, the noise reduction effect is reduced when the presence ratio of coarse magnetic particles is large. In the present invention, the present inventor believes that the noise reduction of the magnetic recording medium can be achieved by setting the proportion of coarse hexagonal ferrite particle powder that affects noise reduction to 3.0% or less. .

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

  The average plate surface diameter and average thickness of the hexagonal ferrite particle powder are obtained by taking a photograph of particles in a plurality of fields of view using a transmission electron microscope, and using the photograph, the plate surface diameter and thickness of 360 or more particles. Were measured, and the average plate surface diameter and average thickness of the particles were shown by their average values. In addition, as selection criteria of the particle | grains at the time of calculating | requiring an average board surface diameter and average thickness, the particle | grains have overlapped and the thing where the boundary is not clear shall not be measured.

  The ratio of the large particles in the hexagonal ferrite particles is determined by selecting a field of view of more than about 1000 particles from the above-mentioned photographs taken using the transmission electron microscope and calculating the number of all particles in the field of view. Then, the number of large particles having a plate surface diameter exceeding 50 nm or 40 nm was measured and expressed as a ratio (%) to the total number of particles.

  The plate ratio was shown as the ratio between the average plate surface diameter and the average thickness.

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

  The content of various elements contained in the hexagonal ferrite particle powder is measured using a “fluorescence X-ray analyzer 3063M type” (manufactured by Rigaku Denki Kogyo Co., Ltd.) according to “General X-ray fluorescence analysis rules” of JIS K0119. did.

  The content of the platinum group element contained in the hexagonal ferrite particle powder is 0.2 g of sample and 10 ml of aqua regia placed in a 100 ml fluororesin beaker and stirred, and held at 240 ° C. for 20 minutes to dissolve, This solution was measured using an “inductively coupled plasma optical emission spectrometer SPS4000” (manufactured by Seiko Denshi Kogyo Co., Ltd.).

  The magnetic properties of the hexagonal ferrite 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 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).

  The deterioration of the magnetic tape is the same condition as when the magnetic tape was stored for 14 days in an environment of a temperature of 60 ° C. and a relative humidity of 90%, and the electromagnetic conversion characteristics were measured for each of the magnetic tape before and after storage. From the envelope obtained in step 1, the number of dropouts per unit time was counted and indicated by the amount of increase in dropout after storage compared to before storage.

<Example 1-1: Production of hexagonal ferrite particle powder for magnetic recording medium>
Pure water was added and dissolved in 0.817 mol of BaCl ₂ · 2H ₂ O, 6.00 mol of FeCl ₃ · 6H ₂ O, 0.36 mol of NiCl _{2 and} 0.18 mol of TiCl ₄ to prepare a 7 L mixed solution. Next, while stirring 5 L of 18.55 mol / L NaOH aqueous solution, the mixed solution was stirred at 200 mL / min. Was added to an aqueous NaOH solution at a flow rate of 80 ° C. and then reacted at 80 ° C. for 6 hours. Next, after sufficiently washing with pure water to make a 10 L slurry containing coprecipitate, 30 parts by weight of NaCl as a flux is added to 100 parts by weight of the coprecipitate of hexagonal ferrite particles, Filtration and drying gave a coprecipitate.

  Subsequently, the obtained coprecipitate was baked at a temperature of 690 ° C. for 2 hours in an air atmosphere, and 1 L of pure water was added to the obtained baked product to obtain a dispersed slurry. The obtained slurry was adjusted to pH value 2 with hydrochloric acid and maintained for 60 minutes for acid treatment, adjusted to pH value 5 with aqueous sodium hydroxide solution, washed with water, filtered, dried, By pulverizing, the hexagonal ferrite particle powder of Example 1-1 was obtained.

The obtained hexagonal ferrite particle powder has a plate shape, an average plate surface diameter of 20.8 nm, an average thickness of 6.2 nm, a plate ratio of 3.4, and a BET specific surface area value (measured value) of 77.5 m. ² / g, the abundance of large particles with a plate surface diameter of 50 nm or more (> 50 nm) is 0.26%, the abundance of large particles with a plate surface diameter of 40 nm or more (> 40 nm) is 0.79%, platinum group The coercive force value (Hc) was 203.3 kA / m, and the saturation magnetization (σs) was 49.8 Am ² / kg.

<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 magnetic recording layer formation Hexagonal ferrite particle powder 100.0 parts by weight,
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.

  Hexagonal ferrite particles, 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 so that the solid content becomes 76% by weight. They were mixed 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, The mixture was added to a 140 ml glass bottle together with 95 g of cyclohexanone, methyl ethyl ketone and toluene 1.5 mmφ glass beads, 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 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 212.9 kA / m, a Br / Bm of 0.82, a coercive force distribution SFD of 0.58, a glossiness of 173%, and a surface roughness Ra of 10.3 nm. The reproduction output (C) was +1.3 dB, C / N was 2.5 dB, and the amount of increase in dropout was 2 / msec.

  A hexagonal ferrite 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 hexagonal ferrite particle powder and magnetic recording medium are shown.

Example 1-2:
Pure water was added and dissolved in 0.817 mol of BaCl ₂ · 2H ₂ O, 6.00 mol of FeCl ₃ · 6H ₂ O, 0.36 mol of NiCl _{2 and} 0.18 mol of TiCl ₄ to prepare a 7 L mixed solution. Next, while stirring 5 L of 18.55 mol / L NaOH aqueous solution, the mixed solution was stirred at 200 mL / min. Was added to an aqueous NaOH solution at a flow rate of 5 ° C., followed by reaction at 65 ° C. for 6 hours. Next, after sufficiently washing with pure water to make a 10 L slurry containing coprecipitate, 30 parts by weight of NaCl as a flux is added to 100 parts by weight of the coprecipitate of hexagonal ferrite particles, Filtration and drying gave a coprecipitate.

  Subsequently, the obtained coprecipitate was baked at a temperature of 670 ° C. for 2 hours in an air atmosphere, and 1 L of pure water was added to the obtained baked product to obtain a dispersed slurry. The obtained slurry was adjusted to pH value 2 with hydrochloric acid and maintained for 60 minutes for acid treatment, adjusted to pH value 5 with aqueous sodium hydroxide solution, washed with water, filtered, dried, By grinding, the hexagonal ferrite particle powder of Example 1-2 was obtained. Table 1 shows various properties of the obtained hexagonal ferrite particle powder.

Example 1-3:
Pure water was added and dissolved in BaCl ₂ .2H ₂ O 0.08 mol, FeCl ₃ .6H ₂ O 0.60 mol, NiCl ₂ 0.018 mol, TiCl ₄ 0.018 mol to prepare a 0.7 L mixed solution. Next, while stirring 0.5 L of 18.55 mol / L NaOH aqueous solution, the mixed solution was added at 20 mL / min. Was added to an aqueous NaOH solution at a flow rate of 35 minutes, reacted at 130 ° C. for 6 hours using an autoclave, and then cooled to room temperature.

  Next, the obtained reaction solution was sufficiently washed with pure water to obtain a 1 L slurry containing a precursor of hexagonal ferrite particles, and then the pH value was adjusted to 8.5 using hydrochloric acid, After stirring for 10 minutes using an ultrasonic homogenizer (Sonifier II model 450D manufactured by BRANSON Corporation), 30 parts by weight of NaCl as a flux is added to 100 parts by weight of the hexagonal ferrite particle precursor, filtered and dried. A precursor of hexagonal ferrite particles was obtained.

  The precursor of the hexagonal ferrite particles obtained above was calcined for 120 minutes at a temperature of 690 ° C. in an air atmosphere, and 1 L of pure water was added to the obtained calcined product to obtain a dispersed slurry. The obtained slurry was wet crushed, adjusted to pH value 2 with hydrochloric acid and acid-treated, adjusted to pH value 5 with aqueous sodium hydroxide solution, washed with water, filtered, dried, By grinding, the hexagonal ferrite particle powder of Example 1-3 was obtained. Table 1 shows various properties of the obtained hexagonal ferrite particle powder.

Example 1-4:
Pure water was added and dissolved in 0.810 mol of BaCl ₂ · 2H ₂ O, 6.00 mol of FeCl ₃ · 6H ₂ O, 0.24 mol of NiCl _{2 and} 0.24 mol of TiCl ₄ to prepare a 7 L mixed solution. Next, while stirring 5 L of 18.55 mol / L NaOH aqueous solution, the mixed solution was stirred at 200 mL / min. Was added to an aqueous NaOH solution at a flow rate of 1, and then reacted at 100 ° C. for 6 hours. Next, after sufficiently washing with pure water to make a 10 L slurry containing coprecipitate, 30 parts by weight of NaCl as a flux is added to 100 parts by weight of the coprecipitate of hexagonal ferrite particles, Filtration and drying gave a coprecipitate.

  Subsequently, the obtained coprecipitate was baked at a temperature of 710 ° C. for 2 hours in an air atmosphere, and 1 L of pure water was added to the obtained baked product to obtain a dispersed slurry. The obtained slurry was adjusted to pH value 2 with hydrochloric acid and maintained for 60 minutes for acid treatment, adjusted to pH value 5 with aqueous sodium hydroxide solution, washed with water, filtered, dried, By grinding, the hexagonal ferrite particle powder of Example 1-4 was obtained. Table 1 shows various properties of the obtained hexagonal ferrite particle powder.

Example 1-5:
A dispersion slurry was prepared using 200 g of hexagonal ferrite particle powder of Example 1-1 and 1500 ml of water, and after adding a sodium hydroxide aqueous solution to adjust the pH value to 9, water was added to the slurry to adjust the slurry concentration. The amount was 98 g / l. 150 L of this slurry was heated to 60 ° C., and 54.44 ml of 1.0 mol / l sodium aluminate solution (corresponding to 1.2% by weight in terms of Al with respect to hexagonal ferrite particle powder) was added to this slurry. In addition, after maintaining for 30 minutes, 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 hexagonal ferrite particle powder of Example 1-5 in which the particle surface was coated with aluminum hydroxide or the like. Table 1 shows properties of the obtained hexagonal ferrite particle powder whose surface is coated with aluminum hydroxide or the like.

Comparative Example 1-1
Pure water was added and dissolved in 1.134 mol of BaCl ₂ · 2H ₂ O, 8.40 mol of FeCl ₃ · 6H ₂ O, 0.336 mol of NiCl _{2 and} 0.336 mol of TiCl ₄ to prepare a 7 L mixed solution. Next, while stirring 5 L of 18.55 mol / L NaOH aqueous solution, the mixed solution was stirred at 200 mL / min. Was added to an aqueous NaOH solution at a flow rate of 1, and then reacted at 100 ° C. for 6 hours. Next, after sufficiently washing with pure water to make a 10 L slurry containing coprecipitate, 30 parts by weight of NaCl as a flux is added to 100 parts by weight of the coprecipitate of hexagonal ferrite particles, Filtration and drying gave a coprecipitate.

  Subsequently, the obtained coprecipitate was baked at a temperature of 710 ° C. for 2 hours in an air atmosphere, and 1 L of pure water was added to the obtained baked product to obtain a dispersed slurry. The obtained slurry was adjusted to pH value 2 with hydrochloric acid and maintained for 60 minutes for acid treatment, adjusted to pH value 5 with aqueous sodium hydroxide solution, washed with water, filtered, dried, By grinding, the hexagonal ferrite particle powder of Comparative Example 1-1 was obtained. Table 1 shows various properties of the obtained hexagonal ferrite particle powder.

Glass crystallization method comparative example 1-2:
BaCO ₃ 24.7mmol, H ₃ BO ₃ 34.1mmol, Fe ₂ O ₃ 19.8mmol, Co ₃ O ₄ 0.35mmol, ZnO 0.72mmol, Nb ₂ O ₅ 0.28mmol, ZrO ₂ 0.42mmol enough The mixed raw material was put into a platinum crucible, heated and melted at 1330 ° C., and then the (homogenized) melt was quenched (rolled) to produce an amorphous body. The obtained amorphous body was kept at 600 ° C. for 3 hours to precipitate hexagonal ferrite crystals. After pulverizing the precipitate, acid treatment was performed by stirring for 4 hours in a 10% acetic acid solution while controlling the solution temperature at 80 ° C. or higher to dissolve BaO and B ₂ O ₃ . Subsequently, water washing was repeated to remove these BaO and B ₂ O ₃ components and the acid component, and then the slurry was dried to obtain hexagonal ferrite particle powder of Comparative Example 1-2. Table 1 shows various properties of the obtained hexagonal ferrite particle powder.

<Manufacture of magnetic recording media>
Examples 2-2 to 2-5, comparative examples 2-1 and 2-2:
A magnetic tape was produced according to the method for producing a magnetic recording medium of Example 2-1 except that the type of hexagonal ferrite particle powder was variously changed.

  Table 2 shows the characteristics of the obtained magnetic tape.

  From the above examples, the hexagonal ferrite particle powder obtained by the present invention has an average plate surface diameter of 10 to 30 nm, and the ratio of large particles having a plate surface diameter of 50 nm or more to the total particle is 3.0. %, And the total amount of each element of the platinum group element is 10 ppm or less, the magnetic recording medium obtained by using these elements has further reduced noise and the deterioration of the magnetic recording medium. It turns out that it is suppressed.

The hexagonal ferrite particle powder for magnetic recording media according to the present invention has an average plate surface diameter of 10 to 30 nm, and the presence ratio of large particles having a plate surface diameter of 50 nm or more with respect to all particles is 3.0% or less. In addition, since the total amount of each element of the platinum group element is 10 ppm or less, noise of the magnetic recording medium can be further reduced and deterioration of the magnetic recording medium can be suppressed. Suitable as magnetic particle powder.

Claims (4)

The hexagonal ferrite particle powder has an average plate surface diameter of 10 to 30 nm, and the ratio of large particles having a plate surface diameter of 50 nm or more to all particles is 3.0% or less. A hexagonal ferrite particle powder for a magnetic recording medium, wherein the total amount of each element of platinum group elements (ruthenium, rhodium, palladium, osmium, iridium and platinum) contained in is 10 ppm or less. The hexagonal ferrite particle powder has an average plate surface diameter of 10 to 25 nm, the proportion of large particles having a plate surface diameter of 40 nm or more with respect to all particles is 3.0% or less, and the hexagonal ferrite particle powder. A hexagonal ferrite particle powder for a magnetic recording medium, wherein the total amount of each element of platinum group elements (ruthenium, rhodium, palladium, osmium, iridium and platinum) contained in is 10 ppm or less. The hexagonal ferrite particle powder for a magnetic recording medium according to claim 1 or 2, wherein the coercive force (Hc) is 95.5 kA / m or more. 4. The magnetic recording medium according to claim 1, wherein the magnetic particle powder is a magnetic recording medium comprising a magnetic recording layer including a magnetic particle powder formed on a nonmagnetic support and a binder resin. A magnetic recording medium comprising a hexagonal ferrite particle powder for a recording medium.