JP2011018423A - Hexagonal ferrite particle powder for magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide hexagonal ferrite particle powders highly dispersible in magnetic paint and capable of reducing noise of the magnetic recording medium more.SOLUTION: The hexagonal ferrite particle powders for a magnetic medium is prepared in a manner that an average plate surface diameter (L) among hexagonal ferrite particle powders is 10 to 20.5 nm, and a relationship between the average plate surface diameter (L) and a BET specific surface area value (SSA) is represented by following expression: (1) SSA(m/g)≥-2.3×L(nm)+127.

Description

  The present invention relates to a hexagonal ferrite particle powder for a magnetic recording medium. Specifically, the average plate surface diameter (L) is 10 to 20 nm, the average plate surface diameter (L) and the BET specific surface area value (SSA). ) Has a specific relationship and relates to a hexagonal ferrite particle powder excellent in dispersibility.

  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 classified 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 more advantageous the noise reduction. Therefore, the particle size of the magnetic particle powder used for the magnetic recording medium is required to be as small as possible.

  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.

  The method for producing hexagonal ferrite particle powder is to melt the raw material and glass-forming substance mixed so as to have a desired ferrite composition, rapidly cool to an amorphous body, and then reheat, wash and grind. Glass crystallization method to obtain hexagonal ferrite particle powder (Patent Document 1), alkaline suspension of desired ferrite composition is liquid phase heated above 100 ° C, washed and dried, then heat treated at around 900 ° C and pulverized Hydrothermal synthesis method to obtain hexagonal ferrite particle powder (Patent Document 2), metal salt solution of desired ferrite composition was neutralized with alkali, and the resulting coprecipitate of iron salt and barium salt was washed with water and dried Thereafter, heat treatment at 800 ° C. and pulverization to obtain hexagonal ferrite particles powder (Patent Document 3) and coprecipitation-firing method in which the coprecipitate is formed by the reverse micelle method (Patent Document 4) Etc. are known That.

JP 2006-5299 A Japanese Patent Laid-Open No. 2-9723 JP-A-7-172839 JP 2007-91517 A

The average plate surface diameter (L) is 10 to 20 nm, and the average plate surface diameter (L) (nm) and BET specific surface area value (SSA) (m ² / g) are in the relationship of the following formula (1). A hexagonal ferrite particle powder for recording media has not yet been obtained.
SSA (m ² /g)≧−2.3×L (nm) +127 (1)

  That is, the hexagonal ferrite particle powders described in the aforementioned Patent Documents 1 to 4 each have an average plate surface diameter (L) of 10 to 20 nm and an average plate surface diameter (L) that the present invention is preferable. The BET specific surface area value (SSA) is not satisfied.

  Accordingly, the present invention provides a hexagonal crystal having excellent dispersibility, in which the average plate surface diameter (L) is 10 to 20 nm, and the average plate surface diameter (L) and the BET specific surface area value (SSA) have a specific relationship. Obtaining ferrite particle powder is a technical problem.

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

That is, in the present invention, the average plate surface diameter (L) of the hexagonal ferrite particle powder is 10 to 20 nm, and the average plate surface diameter (L) (nm) of the hexagonal ferrite particle powder and the BET specific surface area value ( SSA) (m ² / g) is a hexagonal ferrite particle powder for magnetic recording media characterized by the following formula (1) (Invention 1).
SSA (m ² /g)≧−2.3×L (nm) +127 (1)

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

  The hexagonal ferrite particle powder for magnetic recording media according to the present invention has an average plate surface diameter (L) of 10 to 20 nm, and the average plate surface diameter (L) and the BET specific surface area value (SSA) have a specific relationship. In addition to being excellent in dispersibility in the magnetic coating material, and when used as a magnetic particle powder of a magnetic recording medium, noise of the magnetic recording medium can be further reduced, so that the magnetic particle powder of a 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 (L) of 10 to 20 nm, an average plate surface diameter (L) (nm) and a BET specific surface area value (SSA) (m ² / g) is in the relationship of the following formula (1).
SSA (m ² /g)≧−2.3×L (nm) +127 (1)

  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 20 nm, preferably 11 to 20 nm, and more preferably 12 to 20 nm. When the average plate surface diameter of the hexagonal ferrite particle powder exceeds 20 nm, the particle size is large, so that it is difficult to 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 10 nm or less, the influence of thermal fluctuation accompanying the miniaturization of the magnetic particle powder becomes large, 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.

The relationship between the average plate surface diameter (L) (nm) and the BET specific surface area value (SSA) (m ² / g) of the hexagonal ferrite particles for magnetic recording media according to the present invention is expressed by the following formula (1). The
SSA (m ² /g)≧−2.3×L (nm) +127 (1)

  When the relationship between the average plate surface diameter (L) and the BET specific surface area value (SSA) is in the range of the above formula (1), the dispersibility in the magnetic coating material is improved when a magnetic recording medium is produced using this. Therefore, a magnetic recording medium having excellent surface properties can be obtained.

The lower limit value of the BET specific surface area value of the magnetic fine particle powder for magnetic recording media according to the present invention is a value represented by the above-mentioned formula (1). Moreover, it is preferable that the upper limit is 170 m < ² > / g, More preferably, it is 160 m < ² > / g, More preferably, it is 150 m < ² > / g. When the BET specific surface area value exceeds 170 m ² / g, aggregation is likely to occur due to an increase in intermolecular force due to finer particles, so that dispersibility in the vehicle during the production of the magnetic coating material is reduced.

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.

  As a manufacturing method for obtaining a hexagonal ferrite particle powder for magnetic recording media according to the present invention, the raw material and the glass-forming substance mixed so as to have a desired ferrite composition are melted and rapidly cooled to an amorphous body, Next, after reheating treatment, glass crystallization method to obtain hexagonal ferrite particle powder by washing and pulverizing, liquid phase heating of alkaline suspension of desired ferrite composition at 100 ° C. or higher, washing and drying, 900 ° C. Hydrothermal synthesis method to obtain hexagonal ferrite particle powder by heat treatment before and after grinding, neutralize metal salt solution of desired ferrite composition with alkali, wash the resulting iron salt and barium salt coprecipitate with water There is a coprecipitation-firing method in which, after drying, heat treatment at 800 ° C. and pulverization to obtain hexagonal ferrite particle powder, there is no particular limitation as long as it satisfies the aforementioned characteristics.

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

  The average plate surface diameter and the average thickness of the hexagonal ferrite particle powder were obtained by taking a photograph of the particles using a transmission electron microscope and measuring the plate surface diameter and thickness of each of 360 or more particles using the photograph. The average plate surface diameter and average thickness of the particles are shown by the average value. In addition, as a selection criterion for particles, particles that overlap each other and whose boundaries are not clear are not measured.

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

  The specific surface area value was represented by a 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 magnetic properties of the hexagonal ferrite particle powder 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.

  In order to evaluate and confirm the characteristics of the hexagonal ferrite particles for magnetic recording media according to the present invention in the magnetic recording media, magnetic tapes were prepared and evaluated by the following methods.

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.

100.0 parts by weight of a magnetic coating composition hexagonal ferrite particle powder for forming a magnetic recording layer,
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 tape was obtained by slitting to a width of 12.7 mm.

  Among the magnetic properties of the magnetic tape, the coercive force value Hc and the squareness ratio Br / Bm were measured using an “oscillating sample magnetometer VSM SSM-5-15” (manufactured by Toei Kogyo Co., Ltd.) and an external magnetic field of 1193.7 kA / m It measured on condition of this.

  Among the magnetic properties of the magnetic tape, the coercive force distribution SFD has a range of 0 to 397.9 kA / m applied magnetic field using “vibrating sample magnetometer VSM SSM-5-15” (manufactured by Toei Kogyo Co., Ltd.). Then, the sweep speed was 79.6 (kA / m) / min, and the sweep speed was measured at 397.9 (kA / m) / min in the range of 397.9 to 1,193.7 kA / m.

  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 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%.

  The surface roughness Ra of the coating film of the magnetic tape was determined by measuring the center line average roughness of the coating film using “ZYGO NewView 600S” (manufactured by ZYGO Corporation).

  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 the noise signal output (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: Production of hexagonal ferrite particle powder for magnetic recording medium>
Pure water was added and dissolved in 0.798 mol of BaCl ₂ · 2H ₂ O, 6.00 mol of FeCl ₃ · 6H ₂ O, 0.18 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, 100 g of BaCl ₂ · 2H ₂ O as a flux is added to 1 L of the slurry, filtered and dried, I got a deposit.

  Subsequently, the obtained coprecipitate was baked at a temperature of 720 ° C. for 4 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 was obtained.

The obtained hexagonal ferrite particle powder has a plate shape, an average plate surface diameter of 18.9 nm, an average thickness of 5.8 nm, a plate ratio of 3.3, and a BET specific surface area value (actual measurement value) of 88.8 m. ^The coercive force value (Hc) was 165.6 kA / m, and the saturation magnetization (σs) was 46.5 Am ² / kg.

Example 2:
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 0.024 mol, TiCl ₄ 0.024 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 1, and the reaction was carried out at 150 ° C. for 6 hours using an autoclave, and then cooled to room temperature. After stirring the reaction solution for 10 minutes using “Ultrasonic Homogenizer Sonifier II model 450D” (manufactured by BRANSON Co., Ltd.) and thoroughly washing with pure water to obtain a 1 L slurry containing seed crystals of hexagonal ferrite particles Then, 100 g of BaCl ₂ .2H ₂ O as a flux was added to 1 L of the slurry, and filtered and dried to obtain seed crystals of hexagonal ferrite particles.

  Subsequently, the seed crystals of the obtained hexagonal ferrite particles were fired in an air atmosphere at a temperature of 720 ° C. for 4 hours, and 1 L of pure water was added to the fired 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, The hexagonal ferrite particle powder of Example 2 was obtained by pulverization. Table 1 shows various properties of the obtained hexagonal ferrite particle powder.

Example 3:
BaCO ₃ 24.7mmol, H ₃ BO ₃ 34.1mmol, Fe ₂ O ₃ 19.8mmol, Co ₃ O ₄ 0.44mmol, ZnO 1.12mmol, Nb ₂ O ₅ 0.28mmol, ZrO ₂ 0.14mmol 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 Example 3. Table 1 shows various properties of the obtained hexagonal ferrite particle powder.

Example 4:

The hexagonal ferrite particle powder of Example 4 was obtained in the same manner as in Example 1 except that the coprecipitate obtained in Example 1 was fired at 690 ° C. and fired for 3.5 hours. Table 1 shows various properties of the obtained hexagonal ferrite particle powder.

Example 5:
A dispersion slurry was prepared using 200 g of the hexagonal ferrite particle powder of Example 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 obtain a slurry concentration of 98 g / L. 150 l of this slurry was heated to 60 ° C., and 9.8 mL of No. 3 water glass (corresponding to 0.9% by weight in terms of Si with respect to hexagonal ferrite particle powder) was added to this slurry and held for 30 minutes. Thereafter, the pH value was adjusted to 9 using acetic acid. After maintaining for 30 minutes in this state, filtration, washing with water, drying and pulverization were performed to obtain hexagonal ferrite particle powder of Example 5 in which the particle surface was coated with a silicon compound. Table 1 shows various properties of the obtained hexagonal ferrite particle powder.

Comparative Example 1 (Follow-up test according to Example 5 of JP 2007-91517 A):
An alkane solution in which 108 g of aerosol OT and 800 ml of decane were mixed was added to an aqueous solution in which 80 mmol of NaOH was dissolved in 160 ml of pure water to prepare a reverse micelle solution (I).

BaCl ₂ · 2H ₂ O 2 mmol, FeCl ₃ · 6H ₂ O 22.7 mmol, CoCl ₂ · 6H ₂ O 0.56 mmol, ZnCl ₂ 0.50 mmol, Nb (NO ₃ ) ₃ 0.24 mmol were dissolved in 140 ml of pure water. To the aqueous metal salt solution, an alkane solution in which 54 g of aerosol OT and 500 ml of decane were mixed was added and mixed to prepare a reverse micelle solution (II).

  While the reverse micelle solution (I) was stirred at a high speed with an “ultrasonic homogenizer Sonifier II model 450D” (manufactured by BRANSON) at 22 ° C., the reverse micelle solution (II) was added at 22 ° C. over 3 minutes, and magnetic After stirring for 8 minutes with a stirrer, the temperature was raised to 50 ° C., aged for 30 minutes, cooled to room temperature, and taken out into the atmosphere. In order to destroy the reverse micelle, a mixed solution of 500 ml of water and 500 ml of methanol is added to separate into an aqueous phase and an oil phase, and the oil phase side in which the coprecipitated particles are dispersed is mixed with 600 ml of water and 200 ml of methanol. Then, 2000 ml of methanol was added to cause co-precipitation particles to flocculate and settle. After removing the supernatant, 100 ml of heptane was added and redispersed.

Further, precipitation by adding 1000 ml of methanol and precipitation dispersion of 100 ml of heptane were repeated twice, and methanol was added to precipitate the coprecipitated particles. The supernatant was removed, and then 1000 ml of water was added to disperse, settle and remove the supernatant twice. The coprecipitate obtained was redispersed in 1 L of pure water, 0.1 mol of CaCl ₂ · 6H ₂ O dissolved in pure water was added, and then neutralized with NH ₄ OH, hexagonal crystal A coating of Ca (OH) ₂ was formed on the surface of the ferrite composition particles. The precipitate was filtered and washed with water, and then dried at 120 ° C., and then the dried product was pulverized.

  The pulverized dried product was heated in air at 600 ° C. to convert the surface coating into an oxide, and further heat treated at 700 ° C. for 2 hours to obtain hexagonal ferrite particle powder. The product was placed in a 5% aqueous acetic acid solution to remove the surface coating, and the hexagonal ferrite particle powder of Comparative Example 1 was obtained. Table 1 shows various properties of the obtained hexagonal ferrite particle powder.

<Manufacture of magnetic tape>
Magnetic tape 1-5, comparative magnetic tape 1:
A magnetic tape was manufactured according to the magnetic tape manufacturing method of the above example except that the type of hexagonal ferrite particles was variously changed.

Table 2 shows the characteristics of the obtained magnetic tape.

  As can be seen from the above examples, the hexagonal ferrite particle powder obtained by the present invention has an average plate surface diameter (L) of 10 to 20.5 nm, and the average plate surface diameter (L) and BET specific surface area value. When (SSA) is in a specific relationship, the dispersibility in the magnetic paint is excellent, and thus the magnetic recording medium obtained using these has a reduced noise and a high C / N.

  The hexagonal ferrite particle powder for magnetic recording media according to the present invention has an average plate surface diameter (L) of 10 to 20.5 nm, and a specific plate surface diameter (L) and BET specific surface area value (SSA) are specific. Due to this relationship, the dispersibility in the magnetic paint is excellent, and when this is used as the magnetic particle powder of the magnetic recording medium, the noise of the magnetic recording medium can be further reduced. Suitable as particle powder.

Claims (2)

The hexagonal ferrite particle powder has an average plate surface diameter (L) of 10 to 20 nm, and the hexagonal ferrite particle powder has an average plate surface diameter (L) (nm) and a BET specific surface area value (SSA) (m ² / A hexagonal ferrite particle powder for magnetic recording media, wherein g) is in the relationship of the following formula (1):
SSA (m ² /g)≧−2.3×L (nm) +127 (1) 2. The hexagonal ferrite particle powder for magnetic recording media according to claim 1, wherein the coercive force (Hc) is 95.5 kA / m or more.