Method for producing magnetic powder and method for producing magnetic recording medium

Abstract

Provided is a method for producing a magnetic powder, wherein degradation of magnetic characteristics can be suppressed.　This method for producing a magnetic powder includes: a step for cooling a melt of a granluar raw material to form amorphous bodies including crystal nuclei; a step for classifying the amorphous bodies; and a step for firing the classified amorphous bodies to precipitate hexagonal ferrite particles.

Description

Manufacturing method of magnetic powder and manufacturing method of magnetic recording medium

[0001] The present disclosure relates to a method for producing magnetic powder and a method for producing a magnetic recording medium.

[0002] In recent years, hexagonal ferrite particles have been used in various technical fields, including magnetic recording media, and further improvements in the properties of hexagonal ferrite particles are desired. Therefore, from the viewpoint of improving the properties of hexagonal ferrite particles, various studies have been conducted on techniques for producing hexagonal ferrite particles. For example, Patent Document 1 discloses a technique for producing hexagonal ferrite particles by a glass crystallization method.

[0003] Japanese Patent Application Laid-Open No. 2019-164876

[0004] However, when magnetic powder of hexagonal ferrite particles is produced by the glass crystallization method, the magnetic properties of the magnetic powder may be deteriorated. ３ When producing a magnetic powder having the following properties, the magnetic properties of the magnetic powder tend to deteriorate significantly.

[0005] An object of the present disclosure is to provide a method for producing magnetic powder and a method for producing a magnetic recording medium that can suppress deterioration of magnetic properties.

[0006] In order to solve the above-mentioned problems, the method for producing magnetic powder according to the present disclosure includes the steps of: forming an amorphous body containing crystal nuclei; classifying the amorphous body; and firing the classified amorphous body to precipitate hexagonal ferrite particles.

[0007] The method for manufacturing a magnetic recording medium according to the present disclosure includes the steps of: forming an amorphous body containing crystalline nuclei; classifying the amorphous body; firing the classified amorphous body to precipitate hexagonal ferrite particles; preparing a coating material containing the hexagonal ferrite particles; and preparing a magnetic layer using the coating material.

[0008] The method for producing magnetic powder according to the present disclosure includes the steps of: cooling a melt of particle raw material to form an amorphous body; classifying the amorphous body; and firing the classified amorphous body to precipitate hexagonal ferrite particles.

[0009] FIG. 1 is a manufacturing process diagram illustrating an example of a method for manufacturing a magnetic powder according to a first embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of an electric furnace. FIG. 3 is a cross-sectional view showing an example of the configuration of a tape-shaped magnetic recording medium. FIG. 4 is a schematic view showing an example of the layout of a data band and a servo band. FIG. 5A is an enlarged view showing an example of the configuration of a data band. FIG. 5B is an enlarged view showing an example of a data track in a shingled magnetic recording system. FIG. 6 is an enlarged view showing an example of the configuration of a servo band. FIG. 7 is a graph showing the measurement results of the particle size distribution of a magnetic powder. FIG. 8A is a graph showing the relationship between the particle size of barium ferrite particles (containing no strontium) and the half-width Ha of an SFD (Switching Field Distribution) curve. FIG. 8B is a graph showing the relationship between the particle size of barium ferrite particles (containing no strontium) and the coercive force Hc. FIG. 9A is a graph showing the relationship between the particle size of barium ferrite particles (containing no strontium) and the half-width Ha of an SFD curve. 9B is a graph showing the relationship between particle size and coercive force Hc of barium ferrite particles (containing strontium). FIG. 10 is a graph showing the measurement results of an SFD curve of barium ferrite particles (not containing strontium). FIG. 11 is a graph showing the particle volume V of barium ferrite particles. XRD 12A is a graph showing the relationship between the position where the sample was taken (the position in the depth direction of the crucible) and the coercive force Hc of the precipitated hexagonal ferrite particles. FIG. 12B is a graph showing the relationship between the position where the sample was taken (the position in the depth direction of the crucible) and the actual temperature of the sample during crystallization annealing. FIG. 12C is a graph showing the relationship between the position where the sample was taken (the position in the depth direction of the crucible) and the particle volume V of the hexagonal ferrite particles precipitated by crystallization annealing. XRD 10 is a graph showing the relationship between

[0010] The embodiments of the present disclosure will be described in the following order: 1. General description of the method for manufacturing magnetic powder according to the present disclosure 2. Background leading to the creation of the embodiments of the present disclosure 3. First embodiment 3.1 Magnetic powder 3.2 Method for manufacturing magnetic powder 3.3 Effects 3.4 Modifications 4. Second embodiment 4.1 Structure of magnetic tape 4.2 Method for manufacturing magnetic tape 4.3 Effects 5. Experimental examples 5.1 Consideration of particle size distribution of magnetic powder 5.2 Consideration of classification process 5.3 Consideration of variation in magnetic powder properties caused during firing 5.4 Consideration of effect of spacer during firing 5.5 Consideration of firing amount

[0011] In this specification, unless a measurement environment is specifically stated in connection with the explanation of the measurement method and evaluation method, the measurement and evaluation are performed in an environment of 25°C ± 2°C and 50% RH ± 5% RH.

[0012] <1. General Description of the Method for Producing Magnetic Powder According to the Present Disclosure> In the present disclosure, classification refers to separation according to particle size, and includes, for example, at least one of sieve classification and air classification.

[0013] In the present disclosure, the expression "amorphous bodies having a particle size of 300 μm or less are removed" not only means that all amorphous bodies having a particle size of 300 μm or less are removed, but also includes that a portion of the amorphous bodies having a particle size of 300 μm or less are removed.

[0014] 2. Background to the Creation of the Embodiments of the Present Disclosure The present inventors have conducted extensive research into a method for producing a magnetic powder that can suppress deterioration of the magnetic properties of hexagonal ferrite particles. The details of this research are described below. Specific examples of the magnetic properties include at least one of the coercive force Hc of the magnetic powder and the half-width Ha of the main peak of the SFD curve.

[0015] One possible method for preventing the deterioration of the magnetic properties of hexagonal ferrite particles is to classify the finished magnetic powder to remove fine particles that may cause deterioration of the magnetic properties. However, in order to achieve high recording densities in magnetic recording media, magnetic powders these days generally have a nanoscale size, making it difficult to remove fine particles below a certain particle size from the magnetic powder by classification.

[0016] Specifically, classification methods include dry classification such as sieving and air classification, and wet classification. However, with either method, it is difficult to remove fine particles below a certain particle size from magnetic powder. In other words, with sieving, it is difficult to achieve a nanoscale mesh size for the sieve mesh used for classification, making it unrealistic to classify nanoscale hexagonal ferrite particles by sieving. Even if it were possible to achieve a nanoscale mesh size for the sieve mesh, nanoscale hexagonal ferrite particles tend to aggregate, making it difficult for them to pass through the mesh. With air classification, it is difficult to classify hexagonal ferrite particles in the form of primary particles because nanoscale hexagonal ferrite particles tend to aggregate. With wet classification, hexagonal ferrite particles are dispersed in a liquid and then centrifuged, but it is difficult to prepare a nanoparticle dispersion, and the dispersion process is time-consuming, which may result in reduced productivity.

[0017] Therefore, the inventors conducted extensive research into a technique for suppressing the deterioration of the magnetic properties of magnetic powders by a method other than classifying the finished magnetic powder. As a result, they discovered a technique for suppressing the deterioration of the magnetic properties of magnetic powders by classifying the amorphous material before sintering (before crystallization annealing), removing minute amorphous material, and then sintering the amorphous material. Hexagonal ferrite particles have a particle size on the order of nanometers, while amorphous material has a particle size on the order of several hundred microns. Therefore, it is easier to remove amorphous material below a certain size by classification than to remove hexagonal ferrite particles below a certain size by classification.

[0018] <3 First embodiment> [3.1 Magnetic powder] A magnetic powder according to a first embodiment of the present disclosure will be described below. The magnetic powder according to the first embodiment is a magnetic powder for tape-shaped magnetic recording media, and includes magnetic particles containing hexagonal ferrite as a main phase (hereinafter sometimes referred to as "hexagonal ferrite particles"). In this specification, magnetic powder containing hexagonal ferrite particles may be referred to as hexagonal ferrite magnetic powder. Furthermore, magnetic powder containing barium ferrite particles may be referred to as barium ferrite magnetic powder.

[0019] In the present disclosure, the term "magnetic powder" refers to an aggregate of a plurality of magnetic particles. An aggregate of a plurality of magnetic particles refers to an aggregate in which the magnetic particles are in direct contact with each other, as well as an aggregate in which a binder, lubricant, additive, or the like is present between the magnetic particles.

[0020] The hexagonal ferrite particles have, for example, a plate shape such as a hexagonal plate or a columnar shape such as a hexagonal pillar (where the thickness or height is smaller than the major axis of the plate surface or base). In the present disclosure, the term "hexagonal plate" includes a substantially hexagonal plate shape. The term "hexagonal pillar" also includes a substantially hexagonal pillar shape.

[0021] The hexagonal ferrite particles contain Fe and a metal M1 other than Fe. The metal M1 contains, for example, at least one alkaline earth metal. The at least one alkaline earth metal contains, for example, at least one selected from the group consisting of Ba, Sr, and Ca. Among these alkaline earth metals, it is preferable to contain at least one of Ba and Sr. The metal M1 may contain Pb in addition to the alkaline earth metal.

[0022] The hexagonal ferrite particles may further contain a metal M2 in addition to Fe and metal M1. The metal M2 is preferably capable of substituting a portion of the Fe sites in the crystal structure of the hexagonal ferrite. The metal M2 includes, for example, at least one selected from the group consisting of rare earth elements, transition metal elements other than Fe, and metal elements of Group 13 of the periodic table, and among these, at least one selected from the group consisting of Ti, Al, and Nd is preferred.

[0023] In the present disclosure, rare earth elements are defined as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Transition metal elements other than Fe are defined as Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Hf, Ta, and W. Metal elements of Group 13 of the periodic table are defined as Al, Ga, In, and Tl.

[0024] Specifically, the hexagonal ferrite particles may be, for example, barium ferrite particles or strontium ferrite particles. In the present disclosure, strontium ferrite particles refer to hexagonal ferrite particles in which the average atomic ratio of Sr to metal M1 (Sr / M1) is 50 atomic % or more. Therefore, hexagonal ferrite particles containing Sr and a metal M1 other than Sr are included in strontium ferrite particles if the average atomic ratio of Sr to metal M1 (Sr / M1) is 50 atomic % or more. For example, if metal M1 contains Sr and Ba, hexagonal ferrite particles in which the average atomic ratio of Sr to the total amount of Sr and Ba (Sr / (Sr+Ba)) is 50 atomic % or more are called strontium ferrite particles.

[0025] In the present disclosure, barium ferrite particles refer to hexagonal ferrite particles in which the average atomic ratio of Ba to metal M1 (Ba / M1) is 50 atomic % or more. Therefore, hexagonal ferrite particles containing Ba and a metal M1 other than Ba ​​are included in barium ferrite particles if the average atomic ratio of Ba to metal M1 (Ba / M1) is 50 atomic % or more. For example, when metal M1 contains Sr and Ba, hexagonal ferrite particles in which the average atomic ratio of Ba to the total amount of Sr and Ba (Ba / (Sr+Ba)) is 50 atomic % or more are called barium ferrite particles.

[0026] When the hexagonal ferrite particles contain Ba and Sr as alkaline earth metals, the average atomic ratio of Sr to the total amount of Ba and Sr ((Sr / (Ba+Sr))) is preferably 0.1 or more and less than 1. When the average atomic ratio ((Sr / (Ba+Sr)))) is 0.1 or more, it is possible to suppress a decrease in the effect of adding Sr to improve magnetic properties (for example, the effect of improving thermal stability (Ku) derived from strontium ferrite). When the average atomic ratio ((Sr / (Ba+Sr)))) is less than 1, it is possible to suppress variation in the magnetic properties of the magnetic powder.

[0027] More specifically, the hexagonal ferrite may have an average composition represented by the following general formula (A): Sr （１－ｘ） Ba ｘ Fe （１２－ｙ） Ti ｙ O １９ ...(A) (wherein, in formula (A), x represents 0.5<x≦1, preferably 0.5<x<1, and y represents 0≦y<1.)

[0028] More specifically, the hexagonal ferrite may have an average composition represented by the following general formula (B): （１－ｖ） Ba ｖ Fe （１２－ｗ） β ｗ O １９ ...(B) (In formula (B), α represents at least one element selected from the group consisting of Sr, Ca, and Pb. β represents at least one element selected from the group consisting of rare earth elements, transition metal elements other than Fe, and metal elements of Group 13 of the periodic table, more specifically, for example, at least one element selected from the group consisting of Ti, Nd, Al, Ta, La, and Co. v represents 0.5<v≦1, preferably 0.5<v<1. w represents 0≦w<1.)

[0029] The ratio of each element in the magnetic powder is calculated from the analytical values ​​of inductively coupled plasma atomic emission spectroscopy (ICP-AES) as follows. First, 0.1 g of sample is wet decomposed using acid, and then the solution is diluted to 100 ml. This is used as the sample solution and quantitatively analyzed using ICP-AES. A blank sample is prepared by performing the same procedure as the sample using water. Next, the ratio of each element is calculated, with the Fe concentration obtained from this measurement set to 100%. When the hexagonal ferrite contains Sr and Ba, the atomic ratio of Sr to the total amount of Sr and Ba [atomic %] and the atomic ratio of Ba to the total amount of Sr and Ba [atomic %] are calculated using the calculation results.

[0030] (Particle volume of magnetic powder V XRD ) Particle volume V of magnetic powder XRD The upper limit of the ３ or less, more preferably 1300 nm ３ or less, more preferably 1200 nm ３ Below, 1100nm ３ Below, 1000nm ３ Below, 950nm ３ or below 900 nm ３ The particle volume V of the magnetic powder is as follows: XRD is 1400 nm ３ If the magnetic powder is used in the production of a magnetic tape, a sufficient number of magnetic particles can be contained in a unit area, thereby improving the electrical characteristic conversion characteristics of the magnetic tape.

[0031] Particle volume V of magnetic powder XRD The lower limit of the ３ More preferably, 800 nm or more ３ More preferably, 900 nm or more ３ That's all. The particle volume V of the magnetic powder XRD is 700 nm ３ If the above is the case, when a magnetic tape is produced using the magnetic powder, deterioration of the reproduced signal due to thermal fluctuation can be suppressed, and therefore the electromagnetic conversion characteristics of the magnetic tape can be improved.

[0032] Particle volume V of magnetic particles XRDThe numerical range may be defined by any of the above upper limit values ​​and any of the above lower limit values, and is preferably 700 nm ３ More than 1400 nm ３ Less than 700 nm, more preferably ３ 1300nm or more ３ More preferably, 700 nm or less ３ 1200nm or more ３ Below, 700nm ３ 1100nm or more ３ or below 700 nm ３ 1000nm or more ３ It may be the following:

[0033] In the present disclosure, the particle volume V of the magnetic powder XRD The particle volume V of the magnetic powder is determined by measuring the magnetic powder using X-ray diffraction (XRD). XRD is determined as follows: First, a measurement sample is prepared by placing magnetic powder in a recess (square, 1.8 cm x 2.0 cm) of a non-reflective silicon sample plate for XRD and leveling it with a glass plate. Next, the X-ray diffraction pattern of the measurement sample is measured using the focusing method.

[0034] Composition formula: BaFe １２ O １９ For hexagonal ferrite represented by the formula (1), the crystallite size D obtained from the diffraction peak of the (0,0,6) plane is １ For hexagonal ferrite containing Sr, the crystallite size D was calculated by multiplying the crystallite size obtained from the diffraction peak of the (1,1,4) plane by a correction coefficient of 0.5406. １ Here, the crystallite size D １ is a value corresponding to the plate thickness of the particle. １ Plate thickness D １ This is what happens.

[0035] In addition, since the strength of the (0,0,6) plane of hexagonal ferrite containing Sr is weak, the crystallite size D is calculated by applying a correction coefficient to the (1,1,4) plane, which has a relatively high strength. １ Also, the crystallite size D is calculated from the diffraction peak of the (2,2,0) plane.２ Here, the crystallite size D ２ is a value corresponding to the particle size (plate diameter) of the particle. ２ particle size D ２ Or plate diameter D ２ Crystallite size D １ and crystallite size D ２ The following Scherrer formula is used to calculate the value of Dx: Scherrer formula: Dx = Kλ / B cos θ, where Dx is the crystallite size (nm), λ is the wavelength of the measured X-ray (nm), B is the broadening of the diffraction line due to the size of the crystallite (half-width of the diffraction peak), θ is the angle at which the diffraction peak appears, and K is the Scherrer constant (=0.94).

[0036] The X-ray diffraction measurement conditions were as follows: Instrument used: XRD (Ultima IV, manufactured by Rigaku) ​​Measurement mode: Focusing method Radiation source: Co (CoKα radiation, wavelength λ=0.179 nm) Voltage: 40 kV Current: 40 mA Divergence slit: 1 / 2° Divergence vertical limiting slit: 5 mm Scattering slit: 8 mm Receiving slit: Open Step width: 0.02° Scan speed: 1° / min Scan range: 20° to 80° Analysis software: PDXL2

[0037] Next, the particle volume (crystallite volume) V of the magnetic powder is calculated using the following formula: ＸＲＤ Ask for. However, D １ is the composition formula BaFe １２ O １９ In the case of hexagonal ferrite represented by the formula D, the crystallite size is calculated from the diffraction peak of the (0,0,6) plane, and in the case of hexagonal ferrite containing Sr, the crystallite size is calculated by multiplying the crystallite size obtained from the diffraction peak of the (1,1,4) plane by a correction coefficient of 0.5406. ２ is the crystallite size calculated from the diffraction peak of the (2,2,0) plane.

[0038] (Particle size of magnetic powder (plate diameter) D ２ ) Magnetic powder particle size (plate diameter) D ２From the viewpoint of improving the linear recording density of the magnetic tape, the upper limit of is preferably 19.0 nm or less, more preferably 18.0 nm or less, and even more preferably 17.0 nm or less, 16.0 nm or less, or 15.0 nm or less.

[0039] Magnetic powder particle size (plate diameter) D ２ The lower limit of the thickness is preferably 13.0 nm or more, and more preferably 14.0 nm or more, from the viewpoint of improving the dispersibility of the magnetic particles and improving the electromagnetic conversion characteristics of the magnetic tape (for example, SNR (Signal-to-Noise Ratio)).

[0040] The numerical range of the particle size (plate diameter) of the magnetic powder may be defined by any of the above upper limits and any of the above lower limits, and is preferably 13.0 nm or more and 19.0 nm or less, more preferably 13.0 nm or more and 18.0 nm or less, even more preferably 13.0 nm or more and 17.0 nm or less, 14.0 nm or more and 17.0 nm or less, or 14.0 nm or more and 16.0 nm or less.

[0041] The aspect ratio of the magnetic powder is preferably 1.0 or more and 3.0 or less, more preferably 1.5 or more and 2.8 or less, and even more preferably 1.8 or more and 2.7 or less. When the aspect ratio of the magnetic powder is within the range of 1.0 or more and 3.0 or less, aggregation of the hexagonal ferrite particles can be suppressed. Furthermore, when the hexagonal ferrite particles are vertically oriented in the magnetic layer formation process, the resistance applied to the hexagonal ferrite particles can be suppressed. Therefore, the vertical orientation of the hexagonal ferrite particles can be improved. In the present disclosure, the aspect ratio of the magnetic powder refers to the plate thickness D of the magnetic powder. １ The particle size (plate diameter) of the magnetic powder D ２ The ratio (D ２ / D １ ) refers to

[0042] Magnetic powder thickness D １ and the particle size (plate diameter) of the magnetic powder D ２ The method for measuring the particle volume V of the magnetic powder XRD This is as explained in the measurement method.

[0043] (Coercive force Hc) The upper limit of the coercive force Hc of the magnetic powder is preferably 3000 Oe or less, more preferably 2900 Oe or less, and even more preferably 2800 Oe or less. When the coercive force Hc of the magnetic powder is 3000 Oe or less, saturation recording by a recording head is facilitated when a magnetic tape is produced using the magnetic powder, and excellent electromagnetic conversion characteristics can be obtained.

[0044] The lower limit of the coercive force Hc of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT is preferably 1800 Oe or more, more preferably 2000 Oe or more, and even more preferably 2200 Oe or more. If the lower limit of the coercive force Hc is 1800 Oe or more, when a magnetic tape is produced using the magnetic powder, it is possible to prevent the loss of written data due to the influence of thermal fluctuation.

[0045] The coercive force Hc of magnetic powder is calculated as follows. First, a magnetic powder sample is prepared by compressing the magnetic powder into a resin capsule with an inner diameter of 6 mm and a depth of 2.5 mm and then closing the lid. The magnetic powder must be sufficiently fixed within the capsule. If the magnetic powder is not sufficiently fixed, the magnetic powder may move during magnetic property measurement, resulting in a low measured coercive force Hc. Next, the M-H loop of the magnetic powder sample is measured using a vibrating sample magnetometer (VSM). The coercive force Hc is calculated from the obtained M-H loop. This calculation uses the measurement and analysis program included with the VSM-P7-15. Note that the above M-H loop measurement is performed at 25°C ± 2°C and 50% RH ± 5% RH.

[0046] The M-H loop of the magnetic powder sample is measured using a high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by Toei Kogyo Co., Ltd. The measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 12 bits, time constant of locking amp: 0.03 sec, waiting time: 0.1 sec, number of MH averages: 20.

[0047] (Half width Ha) From the viewpoint of suppressing noise in magnetic tapes, the half width Ha of the main peak of the SFD (Switching Field Distribution) curve of the magnetic powder is preferably 3000 Oe or less, more preferably 2500 Oe or less, even more preferably 2400 Oe or less, and particularly preferably 2300 Oe or less. Here, the half width Ha represents the full width at half maximum (FWHM).

[0048] The half-value width Ha is determined as follows. First, a magnetic powder sample is prepared in the same manner as in measuring the coercive force Hc, and its M-H loop is measured. Next, an SFD curve (a differential curve of the M-H loop) is determined from the M-H loop, and then the half-value width (full width at half maximum) Ha of the main peak of the SFD curve is determined. The measurement and analysis program included with the "VSM-P7-15" is used to calculate the SFD curve and half-value width Ha.

[0049] [3.2 Manufacturing Method of Magnetic Powder] Hereinafter, an example of a manufacturing method of magnetic powder according to the first embodiment of the present disclosure will be described with reference to Fig. 1. This manufacturing method of magnetic powder uses a so-called glass crystallization method.

[0050] (Raw Material Mixing Step) First, in step S1, hexagonal ferrite-forming components (magnetic powder raw materials) and glass-forming components (glass raw materials) are mixed. For example, the hexagonal ferrite-forming components and the magnetic raw materials containing the glass-forming components are placed in a container such as a plastic container, and then mixed for a predetermined time (e.g., 60 minutes) using a powder mixer.

[0051] The glass-forming component is a glass raw material that exhibits a glass transition phenomenon and can be amorphized, that is, a glass raw material that can be vitrified. The glass-forming component is, for example, sodium tetraborate (Na ２ B ４ O ７ ) and boric acid (B ２ O ３ ) and at least one of them.

[0052] The hexagonal ferrite forming component is a compound containing atoms that are constituent atoms of the crystalline structure of hexagonal ferrite, and includes, for example, metal carbonate and iron oxide. The metal carbonate includes at least strontium carbonate (SrCO ３ Metal carbonates further include barium carbonate (BaCO ３ The iron oxide may further include, for example, ferric oxide (Fe ２ O ３ ) in the hexagonal ferrite forming component SrCO ３ The content of is preferably higher than the content of iron oxide in the hexagonal ferrite forming components.

[0053] The content of each component in the raw material mixture is determined depending on the composition of the hexagonal ferrite particles to be obtained. For example, the content of the glass-forming component in the raw material mixture is 30 mol% or less. The raw material mixture can be prepared by weighing and then mixing the various components.

[0054] During the mixing, an oxide of the metal M2 may be further mixed, if necessary. The oxide of the metal M2 may be, for example, titanium oxide (TiO ２ ), aluminum oxide (Al ２ O ３ ) and neodymium oxide (Nd ２ O ３ ) and the like.

[0055] (Melting Step) Next, in step S2, the raw material mixture is melted to obtain a melt. The raw material mixture can be melted, for example, in a glass melting furnace. For example, the raw material mixture is placed in a crucible of the glass melting furnace and melted at a melting temperature of, for example, 1300°C or higher and 1500°C or lower. The melting time may be appropriately set so that the raw material mixture is sufficiently melted. For example, when 1 kg of raw material mixture is placed in the glass melting furnace, the melting time may be, for example, 80 minutes. It is also preferable to melt the raw material mixture in the melting furnace while stirring it with a stirrer. This is to reduce temperature unevenness in the melting furnace and promote the amorphization of the melt obtained by melting the raw material mixture. When the content of glass raw materials in the raw material mixture is low, for example, to 30 mol% or lower, the content of iron oxide (Fe２ O ３ In this case, the content of components containing molten metal is increased. In this case, the melting point of the raw material mixture increases, so stirring is important to homogenize the temperature distribution in the furnace and eliminate uneven melting. In addition, stirring can prevent the melt from clogging the outlet when it is discharged from the melting furnace. The stirring device should be set to a rotation speed of, for example, 30 rpm or more.

[0056] (Quenching Process) Next, in step S3, the melt obtained by melting the raw material mixture is quenched to produce an amorphous mass containing crystal nuclei. This quenching can be performed in the same manner as the quenching process typically performed to obtain an amorphous mass by glass crystallization. For example, a method in which the melt is quenched while being rolled using a pair of chill rolls rotated at high speed is preferred. The pair of chill rolls may be configured to maintain a constant surface temperature, for example, by circulating cooling water through an internal flow path. This is to stabilize the quenching efficiency and promote the amorphization of the melt. The surface temperature of the chill rolls is set to, for example, 20°C. The gap between the pair of chill rolls is, for example, 1 mm or less, and the discharge rate is, for example, 0.5 g / sec or more and 1.0 g / sec or less. Note that "quenching" refers to rapidly cooling the molten raw material mixture to near room temperature to transform the melt into a disordered state (hereinafter referred to as an amorphous state). It is believed that one condition for achieving an amorphous state is that the cooling rate exceeds the crystal growth rate. By achieving an amorphous state, it is possible to control the growth and particle size of nanoparticles. If the cooling rate is slower than the crystal growth rate, crystal growth of the particles occurs before the transition to an amorphous state, resulting in a mixture of amorphous and crystalline states in the melt. Therefore, if rapid cooling is not successful and the melt of the raw material mixture does not become sufficiently amorphous, the amorphous and crystalline states will be mixed in the melt. As a result, particles that grow from the amorphous state in the subsequent firing process and particles that grow from a crystalline state of a certain size in the firing process will be mixed in the magnetic powder (hexagonal ferrite magnetic powder). This is thought to result in variations in the particle size distribution and magnetic properties of the resulting magnetic powder (hexagonal ferrite magnetic powder).

[0057] (Pulverization Step) Next, in step S4, the amorphous mass is pulverized using, for example, a pulverizer to obtain an amorphous powder containing crystalline nuclei. Here, the amorphous powder containing crystalline nuclei refers to an aggregate of amorphous particles containing crystalline nuclei. Examples of pulverizers that can be used include, but are not limited to, roller mills, jet mills, high-speed rotary pulverizers, and container-driven mills.

[0058] (Classification Process) Next, in step S5, the amorphous powder is classified. The classification process may be repeated multiple times as necessary. By the classification process, the amorphous powder is divided into multiple groups based on particle size range, and it is preferable to remove the amorphous powder in the group with the smallest particle size range from the multiple groups. This is because the hexagonal ferrite powder obtained by firing the amorphous powder in the group with the smallest particle size range is likely to contain many hexagonal ferrite particles with low magnetic properties (for example, hexagonal ferrite particles with a coercive force Hc of approximately zero).

[0059] The amorphous powder removed by classification preferably contains amorphous particles with a particle size of 300 μm or less. This is because hexagonal ferrite powder obtained by firing amorphous powder with a particle size of 300 μm or less is likely to contain a large number of hexagonal ferrite particles with particularly low magnetic properties (e.g., hexagonal ferrite particles with a coercive force Hc of approximately zero). For example, when sieving is used for classification, the removal of amorphous particles with a particle size of 300 μm or less by classification can be confirmed by the size of the sieve openings.

[0060] The classification can be performed by wet classification or dry classification, with dry classification being preferred. This is because wet classification may cause the amorphous powder to dissolve when the classification process is performed in a liquid such as water. As the dry classification, sieving or air classification may be used, or a combination of both may be used. As the air classification, gravity classification, inertial classification, or centrifugal classification may be used, or a combination of two or more of these classifications may be used.

[0061] When sieving is used for classification, the sieve used for sieving preferably has a mesh size of 300 μm or less. This allows amorphous powder with a particle size of 300 μm or less to be removed by classification. Here, the sieve mesh size is the mesh size specified in JIS Z 8801-1:2019.

[0062] (Firing Process) Next, in step S6, the amorphous powder is placed in a crucible, and the crucible is then placed in a predetermined position in an electric furnace. The crucible is an example of a firing container. Examples of materials for the crucible include ceramics such as alumina (aluminum oxide), magnesia (magnesium oxide), zirconia (zirconium oxide), SiC (silicon carbide), and AlN (aluminum nitride). Among these materials, SiC (silicon carbide) and AlN (aluminum nitride) are preferred from the viewpoint of improving the thermal conductivity of the crucible.

[0063] Next, the temperature inside the furnace is raised from room temperature to a predetermined temperature, and after reaching the predetermined temperature, the furnace is maintained at the predetermined temperature for a predetermined time, thereby firing the amorphous powder and obtaining a fired body. During this process, crystals grow from the crystal nuclei within the amorphous particles. That is, hexagonal ferrite particles are precipitated within the amorphous particles. The particle size of the precipitated hexagonal ferrite particles can be controlled by the firing conditions. Increasing the firing temperature for crystallization (crystallization temperature) may result in an increase in the particle size of the precipitated hexagonal ferrite particles. Therefore, it is preferable that the temperature be as low as possible but above the temperature at which crystallization of hexagonal ferrite occurs. Specifically, it is preferable to generate crystals by firing the amorphous powder at a firing temperature of 570°C or higher and 630°C or lower. The firing time for crystallization (holding time at the crystallization temperature) is, for example, 1 hour or higher and 48 hours or lower, and preferably, for example, 8 hours or higher. The rate of temperature rise until the firing temperature is reached is, for example, 1.0° C. / min to 10.0° C. / min, specifically, for example, 5.0° C. / min or less. The firing treatment may be carried out in one or two stages, or in three or more stages.

[0064] (Acid Treatment / Water Washing Step) Next, in step S7, the sintered body is subjected to an acid treatment. This dissolves the glass component surrounding the hexagonal ferrite particles, and a powder of hexagonal ferrite particles is extracted. The acid treatment may be performed, for example, by putting the sintered body into an acid such as acetic acid and washing it with a ball mill. Next, the extracted powder of hexagonal ferrite particles is washed with pure water.

[0065] (Separation Treatment Step) Next, in step S8, the borate glass and hexagonal ferrite particles dissolved in water by the acid treatment are separated (decanted) using a centrifuge, thereby removing impurities such as glass components.

[0066] (Drying Process) Next, in step S9, the powder of hexagonal ferrite particles from which the glass component has been removed is washed with water and then dried. It is preferable to subject the sintered body to a pulverization process before the acid treatment. This is to increase the efficiency of the acid treatment. The pulverization process may be performed by either a dry or wet method. This allows the desired magnetic powder to be obtained.

[0067] In the above-mentioned method for producing magnetic powder, Na is used as a glass raw material. ２ B ４ O ７ and B ２ O ３ At least one of the following is used, and Na is used as a glass raw material in the raw material mixture. ２ B ４ O ７ and B ２ O ３ It is preferable that the content of at least one of the above is 30 mol% or less. By keeping the content of the glass raw material in the raw material mixture low in this way, the number of nucleation particles that become the nuclei of hexagonal ferrite particles in the raw material mixture increases relatively. The nucleation particles are, for example, SrCO as a magnetic raw material. ３ Sr atoms and Fe atoms contained in ２ O ３ It is believed that the relative increase in the number of nucleation particles leads to the generation of a large number of hexagonal ferrite particles, and the coarsening of individual hexagonal ferrite particles is suppressed.２ B ４ O ７ and B ２ O ３ By using at least one of the following, for example, H ３ BO ３ Compared with the case where H is used, it has the following advantages: ３ BO ３ The boiling point of H is very low at 300°C. ３ BO ３ This may cause evaporation, which increases the melting point of the melt and makes it difficult to dissolve. ２ B ４ O ７ The boiling point of ２ O ３ Since the boiling point of Na is relatively high at 1680°C, the raw material mixture is charged into the melting furnace. ２ B ４ O ７ Therefore, the melting point of the melt can be kept low and the raw material mixture can be sufficiently dissolved. ２ B ４ O ７ and B ２ O ３ By using at least one of the following, H ３ BO ３ Compared to when using , the melt is more likely to become amorphous during rapid cooling, which has the effect of suppressing the variation in particle growth and particle coarsening during firing.

[0068] In the above-mentioned method for producing magnetic powder, the magnetic raw material is SrCO ３ The content (molar ratio) of Fe in the magnetic material raw material ２ O ３It is preferable that the Sr content (molar ratio) is higher than the Fe content (molar ratio). That is, it is preferable that the Sr content (molar ratio) is higher than the Fe content (molar ratio). This results in the generation of a large number of hexagonal ferrite particles. Therefore, it is thought that the coarsening of individual hexagonal ferrite particles is suppressed. Strontium has a high tendency to ionize and dissolves in the glass to a certain extent. Therefore, if the Sr content (molar ratio) is equal to or lower than the Fe content (molar ratio), there will be a shortage of strontium, and the number of hexagonal ferrite particles generated will decrease. As a result, individual hexagonal ferrite particles tend to coarsen easily.

[0069] [3.3 Effects] As described above, the method for producing magnetic powder according to the first embodiment of the present disclosure includes a step of classifying the amorphous powder containing crystalline nuclei after the pulverization step and before the firing step. This reduces the number of small amorphous particles that can produce a large number of hexagonal ferrite particles with excessively low magnetic properties (e.g., coercive force Hc). This prevents the magnetic powder from deteriorating. It also prevents the particle size distribution of the magnetic powder from widening.

[0070] [3.4 Modifications] (Modification 1) In the firing step, as shown in FIG. 2, a plurality of spacers 83 may be disposed between the bottom of the heating chamber 81 of the electric furnace 80 and the bottom of the crucible 82. In this case, heat from a heater (heat source) 84 disposed on the side of the heating chamber 81 can flow into the gap formed between the bottom of the heating chamber 81 of the electric furnace 80 and the bottom of the crucible 82. This makes it easier for the heat from the heater 84 to be conducted from the bottom side of the crucible 82 to the amorphous powder 85 in the crucible 82, thereby suppressing temperature variations in the depth direction within the crucible 82 during firing. Therefore, the magnetic properties (e.g., coercive force Hc) and particle properties (e.g., particle volume V) of the magnetic powder can be improved. XRD When crucible 82 is a rectangular crucible, four spacers 83 may be disposed at the corners of the bottom surface of crucible 82. The ratio of the contact area S2 between the bottom surface of crucible 82 and spacers 83 to the area S1 of the bottom surface of crucible 82 ((S2 / S1)×100) is preferably 20% or less.

[0071] (Variation 2) In the firing step, the amorphous powder may be fired so that the temperature difference of the amorphous powder in the crucible is 5°C or less. In this case, it is possible to suppress the variation in size of the hexagonal ferrite particles obtained by firing. Therefore, it is possible to suppress the variation in the magnetic properties (e.g., coercive force Hc) of the magnetic powder obtained in one lot.

[0072] Here, the temperature difference refers to the difference between the maximum temperature of the amorphous powder in the crucible and the minimum temperature of the amorphous powder in the crucible. The maximum temperature and the minimum temperature are calculated from the coercive force Hc of the hexagonal ferrite particles obtained by firing. Details of the calculation method for the maximum temperature and the minimum temperature will be explained in the experimental examples below. The temperature difference may be the temperature difference in the depth direction of the crucible.

[0073] (Variation 3) The thermal conductivity of the crucible in which the amorphous powder is housed may be 60 W / m·K or more. If the thermal conductivity of the crucible is 60 W / m·K or more, the temperature difference of the amorphous powder in the crucible can be suppressed. Therefore, the magnetic properties (e.g., coercive force Hc) and particle properties (e.g., particle volume V) of the magnetic powder obtained in one lot can be reduced. XRD ) can be suppressed.

[0074] The thermal conductivity is measured in accordance with the standard JIS R 1611: 2010. Examples of crucibles having a thermal conductivity of 60 W / m·K or more include, but are not limited to, crucibles made of SiC (silicon carbide) or AlN (aluminum nitride).

[0075] 4. Second Embodiment [4.1 Configuration of Magnetic Tape] FIG. 3 is a cross-sectional view showing an example of the configuration of a magnetic tape MT according to a second embodiment of the present disclosure. The magnetic tape MT includes a long substrate 41, an underlayer 42 provided on one main surface (first main surface) of the substrate 41, a magnetic layer 43 provided on the underlayer 42, and a back layer 44 provided on the other main surface (second main surface) of the substrate 41. The underlayer 42 and the back layer 44 are provided as needed and may be omitted. The magnetic tape MT is preferably a perpendicular recording magnetic recording medium. From the viewpoint of improving running performance, the magnetic tape MT preferably includes a lubricant. The lubricant may be contained in at least one of the underlayer 42 and the magnetic layer 43. The magnetic tape MT may further include a lubricant layer provided on the surface of the magnetic layer 43 (hereinafter referred to as the "magnetic surface"). The magnetic tape MT may be housed in a cartridge.

[0076] The magnetic tape MT may conform to the LTO standard, or may conform to a standard other than the LTO standard. The width of the magnetic tape MT may be 1 / 2 inch, or may be wider than 1 / 2 inch. If the magnetic tape MT conforms to the LTO standard, the width of the magnetic tape MT is 1 / 2 inch. The magnetic tape MT may have a configuration that allows the width of the magnetic tape MT to be kept constant or approximately constant by adjusting the tension applied to the magnetic tape MT in the longitudinal direction during running using a recording / playback device (drive).

[0077] The magnetic tape MT has a long shape and runs longitudinally during recording and playback. The magnetic tape MT is preferably used in a recording and playback device equipped with a ring-type head as a recording head. The magnetic tape MT is configured to be capable of recording signals at a linear recording density D. From the viewpoint of achieving high recording capacity, the lower limit of the linear recording density D of signals recordable on the magnetic tape MT is preferably 545 kfci or more, more preferably 549 kfci or more, even more preferably 550 kfci or more, 552 kfci or more, 577 kfci or more, 600 kfci or more, or 635 kfci or more. The upper limit of the linear recording density D of data recordable on the magnetic tape MT is preferably 1270 kfci or less, taking into account the magnetic particle size.

[0078] The magnetic tape MT is preferably reproduced by a reproducing head using a TMR element. The signal reproduced by the reproducing head using the TMR may be data recorded in the data band DB (see FIG. 4) or a servo pattern (servo signal) recorded in the servo band SB (see FIG. 4).

[0079] (Substrate) The substrate 41 is a non-magnetic support that supports the underlayer 42 and the magnetic layer 43. The substrate 41 has a long film shape. From the viewpoint of improving the recording capacity that can be recorded on one data cartridge, the upper limit of the average thickness of the substrate 41 is preferably 4.40 μm or less, more preferably 4.20 μm or less, even more preferably 4.00 μm or less, 3.80 μm or less, or 3.40 μm or less. From the viewpoint of suppressing a decrease in the strength of the substrate 41, the lower limit of the average thickness of the substrate 41 is preferably 3.00 μm or more, more preferably 3.20 μm or more, even more preferably 3.80 μm or more, or 3.9 μm or more. The numerical range of the average thickness of the substrate 41 may be defined by any of the above upper limits and any of the above lower limits, and is preferably 3.80 μm or more and 4.40 μm or less, more preferably 3.90 μm or more and 4.40 μm or less.

[0080] The average thickness of the substrate 41 is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and a sample is prepared by cutting the magnetic tape MT into a length of 250 mm at a position 30 to 40 m longitudinally from one end of the magnetic tape MT on the outer periphery. In this specification, the term "longitudinal direction from one end of the magnetic tape MT on the outer periphery" refers to the direction from one end of the magnetic tape MT on the outer periphery toward the other end on the inner periphery.

[0081] Next, the layers of the sample other than the substrate 41 (i.e., the underlayer 42, magnetic layer 43, and backing layer 44) are removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, the thickness of the sample (substrate 41) is measured at five positions, and the measured values ​​are simply averaged (arithmetic mean) to calculate the average thickness of the substrate 41. Note that the five measurement positions are selected randomly from the sample so that they are each different from the others in the longitudinal direction of the magnetic tape MT.

[0082] From the viewpoint of cost reduction, the base 41 preferably contains a polyester-based resin as a main component. Examples of polyester-based resins include at least one selected from the group consisting of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene p-oxybenzoate), and polyethylene bisphenoxycarboxylate. When the base 41 contains two or more polyester-based resins, these two or more polyester-based resins may be mixed, copolymerized, or laminated. At least one of the terminals and side chains of the polyester-based resin may be modified. In addition to the polyester-based resin, the base 41 may also contain a resin other than the polyester-based resin described below.

[0083] In this specification, the term "main component" refers to the component that has the highest content ratio among the components that constitute the base 41. For example, when the main component of the base 41 is a polyester-based resin, the content ratio of the polyester-based resin in the base 41 may be, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more relative to the mass of the base 41, or the base 41 may be composed only of a polyester-based resin.

[0084] The inclusion of a polyester-based resin in the substrate 41 can be confirmed, for example, as follows. First, similar to the method for measuring the average thickness of the substrate 41, a magnetic tape MT is prepared and cut into a length of 250 mm to prepare a sample, and then layers other than the substrate 41 of the sample are removed. Next, an IR spectrum of the sample (substrate 41) is obtained by infrared absorption spectrometry (IR). Based on this IR spectrum, it can be confirmed that the substrate 41 contains a polyester-based resin.

[0085] The substrate 41 preferably contains a polyester-based resin. By including a polyester-based resin in the substrate 41, the Young's modulus in the longitudinal direction of the substrate 41 can be reduced preferably to 2.5 GPa or more and 7.8 GPa or less, more preferably to 3.0 GPa or more and 7.0 GPa or less. Therefore, by adjusting the tension in the longitudinal direction of the magnetic tape MT during running using a recording / reproducing device, the width of the magnetic tape MT can be kept constant or approximately constant. A method for measuring the Young's modulus in the longitudinal direction of the substrate 41 will be described later.

[0086] The base 41 may contain a resin other than a polyester-based resin. In this case, the resin other than a polyester-based resin may be the main component of the base 41's constituent material. When a resin other than a polyester-based resin is the main component of the base 41's constituent material, the content of the resin other than a polyester-based resin in the base 41 may be, for example, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 98% by mass or more relative to the mass of the base 41. Alternatively, the base 41 may be composed solely of a resin other than a polyester-based resin. The resin other than a polyester-based resin may include, for example, at least one selected from the group consisting of polyolefin-based resins, cellulose derivatives, vinyl-based resins, and other polymer resins. When the base 41 contains two or more of these resins, the two or more materials may be mixed, copolymerized, or laminated.

[0087] The polyolefin resin includes, for example, at least one selected from the group consisting of PE (polyethylene) and PP (polypropylene). The cellulose derivative includes, for example, at least one selected from the group consisting of cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate), and CAP (cellulose acetate propionate). The vinyl resin includes, for example, at least one selected from the group consisting of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).

[0088] Examples of other polymer resins include at least one selected from the group consisting of PEEK (polyether ether ketone), PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, for example, Zylon (registered trademark)), polyether, PEK (polyether ketone), polyether ester, PES (polyethersulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane). Specifically, for example, the base 41 may contain, as a main component, PEEK (polyether ether ketone), PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, for example, Zylon (registered trademark)), polyether, PEK (polyether ketone), polyether ester, PES (polyethersulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), or PU (polyurethane).

[0089] The substrate 41 may be biaxially stretched in the longitudinal direction and the width direction. The polymer resin contained in the substrate 41 is preferably oriented in a direction oblique to the width direction of the substrate 41.

[0090] (Magnetic Layer) The magnetic layer 43 is configured to be capable of recording signals using a magnetization pattern. The magnetic layer 43 is preferably a perpendicular recording type recording layer. The magnetic layer 43 contains, for example, magnetic powder, a binder, carbon particles, and a lubricant. If necessary, the magnetic layer 43 may further contain at least one additive selected from the group consisting of abrasive particles, antistatic agents, hardeners, rust inhibitors, and non-magnetic reinforcing particles. The magnetic layer 43 may have multiple protrusions on the surface (magnetic surface) facing the magnetic layer 43. The multiple protrusions are formed, for example, by carbon particles and abrasive particles protruding from the magnetic surface.

[0091] The magnetic layer 43 may have a plurality of holes on its surface. A lubricant may be stored in the holes. In this case, the supply of the lubricant to the magnetic surface can be improved. From the viewpoint of improving the supply of the lubricant to the magnetic surface, it is preferable that the holes extend in a direction perpendicular to the magnetic surface.

[0092] As shown in FIG. 4, the magnetic layer 43 may have a plurality of servo bands SB and a plurality of data bands DB in advance. The plurality of servo bands SB are arranged at equal intervals in the width direction of the magnetic tape MT. A data band DB is provided between adjacent servo bands SB. The servo bands SB are used to guide the head unit (magnetic head) 56 (specifically, servo read heads 56A and 56B) when recording or reproducing data. Servo patterns (servo signals) for tracking control of the head unit 56 are written in advance in the servo bands SB. User data is recorded in the data bands DB.

[0093] In order to read asymmetric servo stripes 113 (see FIG. 6 ), which will be described later, the head unit 56 may be configured to be able to maintain an inclined position with respect to an axis Ax parallel to the width direction of the magnetic tape MT during data recording and reproduction, as shown in FIG. 4 . Alternatively, the head unit 56 may be configured to follow the meandering or deformation of the magnetic tape MT and become inclined with respect to the axis Ax during data recording and reproduction. The inclination angle of the head unit 56 with respect to the axis Ax parallel to the width direction of the magnetic tape MT is preferably 3° to 18°, more preferably 5° to 15°.

[0094] The total area S of the plurality of servo bands SB relative to the area S of the magnetic surface (surface on the magnetic layer 43 side) ＳＢ Ratio R Ｓ (=(S ＳＢ From the viewpoint of ensuring a high recording capacity, the upper limit of the ratio (S / S) × 100) is preferably 4.0% or less, more preferably 3.5% or less, and even more preferably 3.0% or less. ＳＢ Ratio R Ｓ The lower limit of is preferably 1.0% or more from the viewpoint of ensuring 5 or more servo bands SB.

[0095] The total area S of the plurality of servo bands SB relative to the area S of the entire magnetic surface ＳＢ Ratio R Ｓ The magnetic tape MT is developed using a ferricolloid developer (Sigma Marker Q, manufactured by Sigma High Chemical Co., Ltd.), and the developed magnetic tape MT is then observed under an optical microscope to determine the servo bandwidth W ＳＢ and the number of servo bands SB. Next, the ratio R is calculated from the following formula: Ｓ Calculate the ratio R Ｓ [%] = (((Servo bandwidth W ＳＢ ) × (number of servo bands SB)) / (width of magnetic tape MT)) × 100

[0096] The number of servo bands SB is, for example, 5+4n (where n is an integer greater than or equal to 0) or more. The number of servo bands SB is preferably 5 or more, and more preferably 9 or more. If the number of servo bands SB is 5 or more, the effect on the servo signal due to dimensional changes in the width direction of the magnetic tape MT can be suppressed, and stable recording and reproduction characteristics with less off-track can be ensured. The upper limit of the number of servo bands SB is not particularly limited, but is, for example, 33 or less.

[0097] The number of servo bands SB is determined by the above ratio R Ｓ It can be calculated in the same way as

[0098] Servo Bandwidth W ＳＢ From the viewpoint of ensuring a high recording capacity, the upper limit of the servo bandwidth W is preferably 95 μm or less, more preferably 65 μm or less, and even more preferably 50 μm or less. ＳＢ The lower limit of the servo bandwidth W is preferably 10 μm or more. ＳＢ It is difficult to manufacture a magnetic head that can read such servo signals.

[0099] Servo Bandwidth W ＳＢ The width of the ratio R Ｓ It can be calculated in the same way as

[0100] 5A, the magnetic layer 43 is configured to allow multiple data tracks Tk to be formed in the data band DB. From the viewpoint of improving track recording density and ensuring high recording capacity, the upper limit of the data track width W is preferably 1200 nm or less, more preferably 1000 nm or less, and even more preferably 850 nm or less, 800 nm or less, or 600 nm or less. The lower limit of the data track width W is preferably 20 nm or more, taking into account the magnetic grain size.

[0101] The data track width W is calculated as follows. First, a cartridge 10 is prepared with data recorded on the entire surface of the magnetic tape MT. The magnetic tape MT is unwound from the cartridge 10, and a 250 mm sample is cut from the magnetic tape MT at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the data recording pattern in the data band DB portion of the magnetic layer 43 of the sample is observed using a magnetic force microscope (MFM) to obtain an MFM image. The MFM used is a Digital Instruments Dimension3100 and its analysis software. The measurement area of ​​the MFM image is 10 μm × 10 μm, and this 10 μm × 10 μm measurement area is divided into 512 × 512 (= 262,144) measurement points. Three 10 μm × 10 μm measurement areas in different locations are measured using the MFM, resulting in three MFM images. The track width was measured at 10 locations on each of the three MFM images obtained, for a total of 30 measurement values, and the average value (simple average) of the 30 measurement values ​​was calculated. This average value is the data track width W. The analysis software included with the Dimension3100 was used to measure the track width. The MFM measurement conditions were: sweep speed: 1 Hz, tip used: MFMR-20, lift height: 20 nm, and correction: Flatten order 3.

[0102] 5A shows an example in which adjacent data tracks Tk are recorded so as not to overlap, but the recording method for the data tracks Tk is not limited to this example. For example, as shown in FIG. 5B, adjacent data tracks Tk may be recorded so as to partially overlap each other in the width direction of the magnetic tape MT by using shingled magnetic recording (SMR).

[0103] 5B, head 61 and head 62 represent a recording head and a reproducing head, respectively. In the case of the shingled magnetic recording method, the data track width W is the recording track width W ＲTherefore, in the case of shingled magnetic recording, the width of the read head 62 is narrower than the width of the write head 61. As described above, in the shingled magnetic recording, the data track width W is narrower than the recording track width W Ｒ Since the recording track width W is narrower than the recording track width W, it is advantageous in terms of improving the recording density. Ｒ represents the track width when writing data. When shingled magnetic recording is used as the recording method, the recording track width W Ｒ represents the track width before overwriting (the track width when data is written).

[0104] The magnetic layer 43 has a minimum magnetization reversal distance L min The minimum distance between magnetization reversals L min From the viewpoint of achieving high recording capacity, the upper limit of the distance L is preferably 46.6 nm or less, more preferably 46.3 nm or less, and even more preferably 46.2 nm or less, 46.0 nm or less, 44.0 nm or less, 42.3 nm or less, or 40.0 nm or less. min Considering the size of the magnetic particles, the lower limit is preferably 20.0 nm or more.

[0105] Minimum distance between magnetization reversals L minis calculated as follows. First, a sample is prepared using the same method as for measuring the data track width W. Next, the data recording pattern in the data band DB portion of the magnetic layer 43 of the sample is observed using a magnetic force microscope (MFM) to obtain an MFM image. The MFM used is a Dimension3100 manufactured by Digital Instruments and its analysis software. The measurement area of ​​the MFM image is 2 μm × 2 μm, and this 2 μm × 2 μm measurement area is divided into 512 × 512 (= 262,144) measurement points. Three 2 μm × 2 μm measurement areas in different locations are measured using the MFM, resulting in three MFM images. Fifty inter-bit distances are measured from a two-dimensional concavo-convex chart of the recording pattern of the obtained MFM image. The inter-bit distances are measured using the analysis software provided with the Dimension3100. The value that is approximately the greatest common divisor of the 50 measured inter-bit distances is set as the minimum value L of the inter-magnetic reversal distance. min The measurement conditions are: sweep rate: 1 Hz, tip used: MFMR-20, lift height: 20 nm, correction: Flatten order 3.

[0106] The magnetic layer 43 is configured to be able to record signals in the data band DB with a bit length (1 bit length) T. From the viewpoint of improving the linear recording density D of the magnetic tape MT, the upper limit of the bit length T of the signal recordable in the data band DB is preferably 46.6 nm or less, more preferably 46.3 nm or less, and even more preferably 46.2 nm or less, 46.0 nm or less, 44.0 nm or less, 42.3 nm or less, or 40.0 nm or less. Taking the magnetic particle size into consideration, the lower limit of the bit length T of the signal recordable in the data band DB is preferably 20.0 nm or more.

[0107] The bit length T of the signal that can be recorded in the data band DB is the minimum value L min It can be determined in the same manner as in the measurement method of

[0108] The bit area of ​​the signal that can be recorded on the data band DB is preferably 53000 nm from the viewpoint of improving the linear recording density D of the magnetic tape MT. ２or less, more preferably 45,000 nm ２ or less, more preferably 37,000 nm ２ Below 30,000 nm, particularly preferably ２ The following is the result.

[0109] The bit area of ​​a signal recordable on the data band DB can be calculated as follows: First, three MFM images are obtained in the same manner as in the method for measuring the data track width W. Next, the data track width W and bit length T are calculated in the same manner as in the method for measuring the data track width W and bit length T. Next, the bit area (W x T) of a signal recordable on the data band DB is calculated using the data track width W and bit length T.

[0110] The servo patterns are magnetized regions, and are formed by magnetizing specific regions of the magnetic layer 43 in specific directions using a servo write head during magnetic tape manufacturing. The regions of the servo bands SB where no servo patterns are formed (hereinafter referred to as "non-pattern regions") may be magnetized regions where the magnetic layer 43 is magnetized, or may be non-magnetized regions where the magnetic layer 43 is not magnetized. When the non-pattern regions are magnetized regions, the servo pattern forming regions and the non-pattern regions are magnetized in different directions (e.g., opposite directions).

[0111] In the LTO standard, a servo pattern is formed on the servo band SB, as shown in FIG. 6, consisting of a plurality of servo stripes (linear magnetized regions) 113 inclined with respect to an axis Ax parallel to the width direction of the magnetic tape MT.

[0112] The servo band SB includes a plurality of servo frames 110. Each servo frame 110 is made up of 18 servo stripes 113. Specifically, each servo frame 110 is made up of a servo subframe 1 (111) and a servo subframe 2 (112).

[0113] Servo subframe 1 (111) is composed of an A burst 111A and a B burst 111B. The B burst 111B is arranged adjacent to the A burst 111A. The A burst 111A is inclined at a predetermined angle θ with respect to an axis Ax parallel to the width direction of the magnetic tape MT.１ 6, these five servo stripes 113 are inclined at a regular interval from the EOT (End Of Tape) to the BOT (Beginning Of Tape) of the magnetic tape MT, and are labeled with the symbol A. １ , A ２ , A ３ , A ４ , A ５ are indicated with .

[0114] The B burst 111B is at a predetermined angle θ with respect to an axis Ax parallel to the width direction of the magnetic tape MT. ２ 6, these five servo stripes 113 are inclined at regular intervals from the EOT to the BOT of the magnetic tape MT. １ , B ２ , B ３ , B ４ , B ５ are indicated with .

[0115] The servo stripes 113 of the B burst 111B are inclined in the opposite direction to the servo stripes 113 of the A burst 111A. The servo stripes 113 of the A burst 111A and the servo stripes 113 of the B burst 111B are asymmetric with respect to the axis Ax, which is parallel to the width direction of the magnetic tape MT. That is, the servo stripes 113 of the A burst 111A and the servo stripes 113 of the B burst 111B are arranged in a substantially V-shape. Because the servo stripes 113 of the A burst 111A and the servo stripes 113 of the B burst 111B are asymmetric with respect to the axis Ax, when the head unit 56 is tilted obliquely with respect to the axis Ax, there exists a state in which the servo stripes 113 of the A burst 111A and the servo stripes 113 of the B burst 111B are substantially symmetric with respect to the central axis of the sliding surface of the head unit 56. By changing the tilt of the head unit 56 based on this state, it is possible to adjust the distance between the servo read heads 56A and 56B in the width direction of the magnetic tape MT. Therefore, in both cases where the width of the magnetic tape MT is increased and where the width of the magnetic tape MT is decreased, the servo read heads 56A and 56B can be made to face the specified positions of the servo bands SB. Note that the central axis of the sliding surface of the head unit 56 refers to the axis that passes through the centers of the multiple servo read heads 56A and 56B on the sliding surface of the head unit 56.

[0116] A predetermined angle θ, which is the inclination angle of the servo stripe 113 of the A burst 111A １ and a predetermined angle θ which is the inclination angle of the servo stripe 113 of the B burst 111B. ２ More specifically, the predetermined angle θ of the servo stripe 113 of the A burst 111A is different from １ However, the predetermined angle θ of the servo stripe 113 of the B burst 111B ２ , or the predetermined angle θ of the servo stripe 113 of the B burst 111B. ２ However, the predetermined angle θ of the servo stripe 113 of the A burst 111A １That is, the inclination of the servo stripes 113 of the A burst 111A may be larger than the inclination of the servo stripes 113 of the B burst 111B, or the inclination of the servo stripes 113 of the B burst 111B may be larger than the inclination of the servo stripes 113 of the A burst 111A. Note that in FIG. 6, the predetermined angle θ of the servo stripes 113 of the A burst 111A １ However, the predetermined angle θ of the servo stripe 113 of the B burst 111B ２ In the following, the predetermined angle θ of the servo stripe 113 of the A burst 111A is shown. １ However, the predetermined angle θ of the servo stripe 113 of the B burst 111B ２ The case where it is larger than

[0117] Servo subframe 2 (112) is composed of a C burst 112C and a D burst 112D. The D burst 112D is arranged adjacent to the C burst 112C. The C burst 112C is inclined at a predetermined angle θ with respect to an axis Ax parallel to the width direction of the magnetic tape MT. １ 6, the four servo stripes 113 are inclined at a predetermined interval from the EOT to the BOT of the magnetic tape MT and are marked with the symbol C １ , C ２ , C ３ , C ４ are indicated with .

[0118] The D burst 112D is at a predetermined angle θ with respect to an axis Ax parallel to the width direction of the magnetic tape MT. ２ 6, the four servo stripes 113 are inclined at a predetermined interval from the EOT to the BOT of the magnetic tape MT and are indicated by the symbol D. １ , D ２ , D ３ , D ４ are indicated with .

[0119] The servo stripes 113 of the D burst 112D are inclined in the opposite direction to the servo stripes 113 of the C burst 112C. The servo stripes 113 of the C burst 112C and the servo stripes 113 of the D burst 112D are asymmetric with respect to the axis Ax, which is parallel to the width direction of the magnetic tape MT. That is, the servo stripes 113 of the C burst 112C and the servo stripes 113 of the D burst 112D are arranged in a generally V-shape. Because the servo stripes 113 of the C burst 112C and the servo stripes 113 of the D burst 112D are asymmetric with respect to the axis Ax, when the head unit 56 is tilted obliquely with respect to the axis Ax, there exists a state in which the servo stripes 113 of the C burst 112C and the servo stripes 113 of the D burst 112D are generally symmetric with respect to the central axis of the head unit 56. By changing the tilt of the head unit 56 based on this state, it is possible to adjust the servo distance.

[0120] The predetermined angle θ is the inclination angle of the servo stripe 113 of the C burst 112C. １ and a predetermined angle θ which is the inclination angle of the servo stripe 113 of the D burst 112D. ２ More specifically, the predetermined angle θ of the servo stripe 113 of the C burst 112C is different from １ However, the predetermined angle θ of the servo stripe 113 of the D burst 112D ２ , or the predetermined angle θ of the servo stripe 113 of the D burst 112D. ２ However, the predetermined angle θ of the servo stripe 113 of the C burst 112C １ That is, the inclination of the servo stripes 113 of the C burst 112C may be larger than the inclination of the servo stripes 113 of the D burst 112D, or the inclination of the servo stripes 113 of the D burst 112D may be larger than the inclination of the servo stripes 113 of the C burst 112C. Note that in FIG. 6, the predetermined angle θ of the servo stripes 113 of the C burst 112C １ However, the predetermined angle θ of the servo stripe 113 of the D burst 112D ２In the following, the predetermined angle θ of the servo stripe 113 of the C burst 112C is １ However, the predetermined angle θ of the servo stripe 113 of the D burst 112D ２ The case where it is larger than

[0121] The predetermined angle θ of the servo stripe 113 in the A burst 111A and the C burst 112C １ is preferably 18° or more and 28° or less, and more preferably 18° or more and 26° or less. ２ is preferably -4° or more and 6° or less, and more preferably -2° or more and 6° or less. The servo stripes 113 in the A burst 111A and the C burst 112C are an example of a first magnetization region. The servo stripes 113 in the B burst 111B and the D burst 112D are an example of a second magnetization region.

[0122] Reading the servo bands SB with the head unit 56 provides information for determining the tape speed and the longitudinal position of the head unit 56. The tape speed is calculated from the times between four timing signals (A1-C1, A2-C2, A3-C3, A4-C4). The head position is calculated from the times between the aforementioned four timing signals and another four timing signals (A1-B1, A2-B2, A3-B3, A4-B4). The servo pattern may have a shape including two parallel lines.

[0123] 6, the servo patterns (i.e., the plurality of servo stripes 113) are preferably arranged linearly in the longitudinal direction of the magnetic tape MT. That is, the servo bands SB preferably have a linear shape in the longitudinal direction of the magnetic tape MT.

[0124] The average thickness t of the magnetic layer 43 ２ The upper limit of the average thickness t of the magnetic layer 43 is preferably 0.080 μm or less, more preferably 0.070 μm or less, even more preferably 0.060 μm or less, and particularly preferably 0.050 μm or less. ２If the upper limit value is 0.080 μm or less, when a ring-type head is used as the recording head, the influence of the demagnetizing field can be reduced, and therefore, even better electromagnetic conversion characteristics can be obtained.

[0125] The average thickness t of the magnetic layer 43 ２ The lower limit of the average thickness t of the magnetic layer 43 is preferably 0.035 μm or more. ２ If the lower limit is 0.035 μm or more, when an MR type head is used as the reproducing head, output can be ensured, and therefore even better electromagnetic conversion characteristics can be obtained.

[0126] The average thickness t of the magnetic layer 43 ２ is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and three 250 mm samples are cut from the magnetic tape MT at positions 10 m to 20 m, 30 m to 40 m, and 50 m to 60 m from one end of the outer periphery of the magnetic tape MT in the longitudinal direction, respectively. Each sample is then thinned using a method such as FIB (Focused Ion Beam). When using the FIB method, a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below. The carbon layer is formed by vapor deposition on the surface of the magnetic tape MT facing the magnetic layer 43 and the surface facing the back layer 44, and the tungsten layer is then further formed by vapor deposition or sputtering on the surface facing the magnetic layer 43. The thinning is performed along the longitudinal direction of the magnetic tape MT. That is, the thinning process forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape MT.

[0127] The cross section of each obtained thinned sample was observed under the following conditions using a transmission electron microscope (TEM) to obtain a TEM image of each thinned sample. Note that the magnification and acceleration voltage may be adjusted appropriately depending on the type of device. Device: TEM (H9000NAR manufactured by Hitachi, Ltd.) Acceleration voltage: 300 kV Magnification: 100,000 times

[0128] Next, using the TEM image of each obtained thinned sample, the thickness of the magnetic layer 43 is measured at 10 positions on each thinned sample. The 10 measurement positions on each thinned sample are randomly selected from the sample so that they are different positions in the longitudinal direction of the magnetic tape MT. The measured values ​​of each obtained thinned sample (thickness of the magnetic layer 43 at 30 points in total) are simply averaged (arithmetic average) to obtain an average value, which is the average thickness t of the magnetic layer 43. ２ Let [nm].

[0129] (Magnetic Powder) The magnetic powder is the magnetic powder according to the first embodiment. It is preferable that the magnetic powder has a crystal orientation preferentially in the perpendicular direction of the magnetic tape MT. In this specification, the perpendicular direction (thickness direction) of the magnetic tape MT refers to the thickness direction of the magnetic tape MT.

[0130] (Binder) The binder includes, for example, a thermoplastic resin, and may further include a thermosetting resin or a reactive resin.

[0131] The thermoplastic resin includes, for example, a first thermoplastic resin (first binder) containing chlorine atoms and a second thermoplastic resin (second binder) containing nitrogen atoms. More specifically, the thermoplastic resin includes a vinyl chloride resin and a urethane resin. In this specification, the vinyl chloride resin refers to a polymer containing a structural unit derived from vinyl chloride. More specifically, for example, the vinyl chloride resin refers to a homopolymer of vinyl chloride, a polymer of vinyl chloride and a comonomer copolymerizable therewith, and a mixture of these polymers.

[0132] The vinyl chloride resin includes, for example, at least one selected from the group consisting of vinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-vinyl chloride-vinylidene chloride copolymer, and methacrylic acid ester-vinyl chloride copolymer.

[0133] The term "urethane-based resin" refers to a resin containing a urethane bond in at least a portion of the molecular chain constituting the resin, and may be a urethane resin or a copolymer containing a urethane bond in a portion of the molecular chain. The urethane-based resin may be, for example, one obtained by reacting a polyisocyanate with a polyol. Alternatively, the urethane-based resin may be, for example, one obtained by reacting a polyester with a polyol. In this specification, the term "urethane-based resin" also includes one obtained by reaction with a curing agent.

[0134] The polyisocyanate includes, for example, at least one selected from the group consisting of diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), 1,5-pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). In this specification, polyisocyanate refers to a compound having two or more isocyanate groups in the molecule. The polyisocyanate may be the polyisocyanate contained in the curing agent.

[0135] Any suitable polyol having two or more OH groups can be used as the polyol. The polyol may include, for example, at least one selected from the group consisting of a polyol (diol) having two OH groups, a polyol (triol) having three OH groups, a polyol (tetraol) having four OH groups, a polyol (pentaol) having five OH groups, and a polyol (hexaol) having six OH groups. Specific examples of the polyol include at least one selected from the group consisting of polyester polyols, polyether polyols, polycarbonate polyols, polyesteramide polyols, and acrylate polyols.

[0136] The polyester includes, for example, at least one selected from the group consisting of phthalic acid polyesters and aliphatic polyesters.

[0137] The thermoplastic resin may further include a thermoplastic resin other than a vinyl chloride resin or a urethane resin. Examples of such a thermoplastic resin include at least one selected from the group consisting of vinyl acetate, an acrylic acid ester-acrylonitrile copolymer, an acrylic acid ester-acrylonitrile copolymer, an acrylic acid ester-vinylidene chloride copolymer, a methacrylic acid ester-vinylidene chloride copolymer, a methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, a vinylidene chloride-acrylonitrile copolymer, an acrylonitrile-butadiene copolymer, a polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), a styrene-butadiene copolymer, a polyester resin, an amino resin, and synthetic rubber.

[0138] The thermosetting resin includes at least one selected from the group consisting of, for example, phenolic resin, epoxy resin, polyurethane curing resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, and urea formaldehyde resin.

[0139] All of the above binders contain -SO ３ M, -OSO ３ M, -COOM, P=O(OM) ２ (wherein M represents a hydrogen atom or an alkali metal such as lithium, potassium, or sodium), or -NR1R2, -NR1R2R3 ＋ X － a side chain amine having a terminal group represented by >NR1R2 ＋ X － (wherein R1, R2, and R3 represent a hydrogen atom or a hydrocarbon group, and X － represents a halogen element ion such as fluorine, chlorine, bromine, or iodine, or an inorganic ion or an organic ion.) Polar functional groups such as -OH, -SH, -CN, and epoxy groups may also be introduced. The amount of these polar functional groups introduced into the binder is 10 －１ 10 above －８ It is preferably 10 mol / g or less.－２ 10 above －６ It is more preferably mol / g or less.

[0140] (Carbon Particles) Some of the carbon particles contained in the magnetic layer 43 may protrude from the magnetic surface, forming multiple protrusions. The carbon particles forming the multiple protrusions reduce the electrical resistance of the magnetic surface, suppressing charging of the magnetic surface. This also reduces dynamic friction between the head unit 56 and the magnetic surface while the magnetic tape MT is running.

[0141] The carbon particles may function as an antistatic agent and a solid lubricant. The carbon particles preferably have an average primary particle size of 100.0 nm or less. When the carbon particles have an average primary particle size of 100.0 nm or less, even when the carbon particles are particles with a wide particle size distribution (e.g., carbon black), the inclusion of particles that are excessively large relative to the thickness of the magnetic layer 43 is suppressed.

[0142] The carbon particles may be, for example, one or more selected from the group consisting of carbon black, acetylene black, ketjen black, carbon nanotubes, and graphene, and among these carbon particles, carbon black is preferably used. Examples of carbon black that can be used include Seast TA manufactured by Tokai Carbon Co., Ltd., and Asahi #15 and #15HS manufactured by Asahi Carbon Co., Ltd.

[0143] The magnetic layer 43 may contain hybrid particles instead of carbon particles, or may contain hybrid particles together with carbon particles. The hybrid particles contain carbon and a material other than carbon. The material other than carbon is, for example, an organic material or an inorganic material. The hybrid particles may be hybrid particles in which carbon is attached to the surface of inorganic particles. Specifically, for example, they may be hybrid carbon in which carbon is attached to the surface of silica particles.

[0144] (Lubricant) The lubricant may be a liquid lubricant. The lubricant may be, for example, at least one selected from a fatty acid and a fatty acid ester, preferably both a fatty acid and a fatty acid ester. The inclusion of a lubricant in the magnetic layer 43, particularly the inclusion of both a fatty acid and a fatty acid ester in the magnetic layer 43, contributes to improving the running stability of the magnetic tape MT. More particularly, the magnetic layer 43 containing a lubricant and having pores achieves good running stability. This improvement in running stability is thought to be due to the lubricant adjusting the dynamic friction coefficient of the magnetic layer 43-side surface of the magnetic tape MT to a value suitable for running the magnetic tape MT.

[0145] The fatty acid may preferably be a compound represented by the following general formula (1) or (2). For example, the fatty acid may contain either or both of the compound represented by the following general formula (1) and the compound represented by the general formula (2).

[0146] The fatty acid ester may preferably be a compound represented by the following general formula (3), (4), or (5). For example, the fatty acid ester may contain one, two, or three of the compounds represented by the following general formula (3), (4), and (5).

[0147] By including in the lubricant one or both of the compound represented by general formula (1) and the compound represented by general formula (2), and one, two or three of the compound represented by general formula (3), the compound represented by general formula (4) and the compound represented by general formula (5), it is possible to suppress an increase in the coefficient of dynamic friction due to repeated recording or reproduction of the magnetic tape MT.

[0148] CH3 (CH2) k COOH (1) (In general formula (1), k is an integer selected from the range of 14 to 22, more preferably from the range of 14 to 18.)

[0149] CH3 (CH2) n CH=CH(CH2) mCOOH (2) (In the general formula (2), the sum of n and m is an integer selected from the range of 12 to 20, more preferably from the range of 14 to 18.)

[0150] CH3 (CH2) p COO(CH2) q CH3 (3) (wherein, in general formula (3), p is an integer selected from the range of 14 or more and 22 or less, more preferably 14 or more and 18 or less, and q is an integer selected from the range of 2 or more and 5 or less, more preferably 2 or more and 4 or less.)

[0151] CH3 (CH2) r COO-(CH2) s CH(CH3)2 (4) (In the general formula (4), r is an integer selected from the range of 14 to 22, and s is an integer selected from the range of 1 to 3.)

[0152] CH3 (CH2) ｔ COO-(CH)(CH3)CH2(CH3) ｕ ...(5) (In general formula (5), t is an integer selected from the range of 14 to 22, and u is an integer selected from the range of 1 to 3.)

[0153] (Abrasive particles) Some of the abrasive particles contained in the magnetic layer 43 may protrude from the magnetic surface to form multiple protrusions. When the head unit 56 slides over the magnetic tape MT, the protrusions formed by the abrasive particles can come into contact with the head unit 56.

[0154] The lower limit of the Mohs hardness of the abrasive particles is preferably 7.0 or more, more preferably 7.5 or more, even more preferably 8.0 or more, and particularly preferably 8.5 or more, from the viewpoint of suppressing deformation due to contact with the head unit 56. The upper limit of the Mohs hardness of the abrasive particles is preferably 9.5 or less, from the viewpoint of suppressing wear of the head unit 56.

[0155] The abrasive particles are preferably inorganic particles. Examples of inorganic particles include α-alumina with an α-conversion rate of 90% or more, β-alumina, γ-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, acicular α-iron oxide obtained by dehydrating and annealing magnetic iron oxide raw materials, optionally surface-treated with aluminum and / or silica, and diamond powder. Examples of inorganic particles that are preferably used include alumina particles such as α-alumina, β-alumina, and γ-alumina, and silicon carbide. The abrasive particles may be acicular, spherical, or cubic, but those with angular shapes are preferred because they have high abrasiveness.

[0156] (Antistatic Agent) The antistatic agent reduces the electrical resistance of the magnetic surface and can suppress charging of the magnetic surface. The antistatic agent includes, for example, at least one selected from the group consisting of natural surfactants, nonionic surfactants, and cationic surfactants.

[0157] (Curing Agent) The curing agent includes, for example, polyisocyanate. The polyisocyanate may include, for example, diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), xylylene diisocyanate (XDI), 1,5-pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), or isophorone diisocyanate (IPDI) as an isocyanate source. The polyisocyanate may have a TMP adduct structure, an isocyanurate structure, a biuret structure, an allophanate structure, or the like.

[0158] Specific examples of polyisocyanates include aromatic polyisocyanates such as an adduct of tolylene diisocyanate (TDI) and an active hydrogen compound, and aliphatic polyisocyanates such as an adduct of hexamethylene diisocyanate (HMDI) and an active hydrogen compound. The weight average molecular weight of these polyisocyanates is preferably in the range of 100 to 3,000.

[0159] (Rust inhibitor) Examples of the rust inhibitor include phenols, naphthols, quinones, heterocyclic compounds containing a nitrogen atom, heterocyclic compounds containing an oxygen atom, and heterocyclic compounds containing a sulfur atom.

[0160] (Non-magnetic reinforcing particles) Examples of non-magnetic reinforcing particles include aluminum oxide (α-, β-, or γ-alumina), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, and titanium oxide (rutile or anatase titanium oxide).

[0161] (Underlayer) The underlayer 42 is intended to reduce the unevenness of the surface of the substrate 41 and adjust the unevenness of the magnetic surface. The underlayer 42 is a non-magnetic layer containing non-magnetic particles, a binder, and a lubricant. The underlayer 42 supplies the lubricant to the magnetic surface. If necessary, the underlayer 42 may further contain at least one additive selected from the group consisting of an antistatic agent, a hardener, an anti-rust agent, etc.

[0162] The underlayer 42 may have a plurality of holes. A lubricant may be stored in the holes. In this case, the supply of the lubricant to the magnetic surface can be improved. From the viewpoint of improving the supply of the lubricant to the magnetic surface, it is preferable that the holes extend in a direction perpendicular to the magnetic surface. From the viewpoint of improving the supply of the lubricant to the magnetic surface, it is preferable that the holes in the underlayer 42 and the holes in the magnetic layer 43 are connected to each other.

[0163] Average thickness t of the underlayer 42 ３ The upper limit of the average thickness t of the underlayer 42 is preferably 0.90 μm or less, more preferably 0.80 μm or less, even more preferably 0.70 μm or less, and particularly preferably 0.60 μm or less.３ When the average thickness t of the underlayer 42 is 0.90 μm or less, the amount of binder that comes out onto the magnetic surface can be suppressed, and therefore, an increase in running friction between the head and the magnetic tape MT can be suppressed. ３ The lower limit of the thickness is preferably 0.30 μm or more from the viewpoint of reducing the unevenness on the surface of the substrate 41 .

[0164] Average thickness t of the underlayer 42 ３ is the average thickness t of the magnetic layer 43 ２ However, the magnification of the TEM image is adjusted appropriately depending on the thickness of the underlayer 42.

[0165] Average thickness t of the substrate 41 １ Whereas, the average thickness t ２ and the average thickness t of the underlayer 42 ３ If the total thickness of the substrate 41 is too large, the bending rigidity will increase, and the stability of contact between the magnetic tape MT and the head may decrease. １ Whereas, the average thickness t ２ and the average thickness t of the underlayer 42 ３ If the total thickness of the substrate 41 is too small, the surface properties of the magnetic surface of the magnetic tape MT may be reduced. １ The average thickness t of the magnetic layer 43 ２ and the average thickness t of the underlayer 42 ３ The ratio of the total thickness ((t ２ +t ３ ) / t １ ) is preferably 0.19 or more and 0.28 or less.

[0166] The underlayer 42 preferably has a plurality of holes. By storing lubricant in these holes, it is possible to further suppress a decrease in the amount of lubricant supplied between the magnetic surface and the head unit 56, even after repeated recording or reproduction (i.e., after repeated running with the head unit 56 in contact with the surface of the magnetic tape MT). This further suppresses an increase in the dynamic friction coefficient. In other words, even better running stability can be obtained.

[0167] (Non-magnetic particles) Non-magnetic particles include, for example, at least one of inorganic particles and organic particles. Non-magnetic particles may also be carbon particles such as carbon black. One type of non-magnetic particle may be used alone, or two or more types of non-magnetic particles may be used in combination. Inorganic particles include, for example, metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, or metal sulfides. The shapes of non-magnetic particles include, for example, various shapes such as needles, spheres, cubes, and plates, but are not limited to these shapes.

[0168] (Binder, Lubricant) The binder and lubricant are the same as those in the magnetic layer 43 described above.

[0169] (Additives) The antistatic agent, hardener, and anticorrosive agent are the same as those in the magnetic layer 43 described above.

[0170] (Back Layer) The back layer 44 contains a binder and non-magnetic particles. If necessary, the back layer 44 may further contain at least one additive selected from the group consisting of a lubricant, a hardener, an antistatic agent, etc. The binder and non-magnetic particles are the same as those in the underlayer 42 described above. The hardener and antistatic agent are the same as those in the magnetic layer 43 described above.

[0171] The average particle size of the non-magnetic particles is preferably 10.0 nm or more and 150.0 nm or less, more preferably 15.0 nm or more and 110.0 nm or less. The average particle size of the non-magnetic particles is determined in the same manner as the average particle size of the magnetic particles. The non-magnetic particles may include non-magnetic particles having two or more particle size distributions.

[0172] Average thickness t of the back layer 44 ４ The upper limit of the average thickness t of the back layer 44 is preferably 0.60 μm or less. ４ When the upper limit of the average thickness t of the backing layer 44 is 0.60 μm or less, the thickness of the underlayer 42 and the substrate 41 can be kept thick even when the average thickness t of the magnetic tape MT is 5.30 μm or less, so that the running stability of the magnetic tape MT in a recording / reproducing device can be maintained. ４ The lower limit of the thickness is not particularly limited, but is, for example, 0.20 μm or more.

[0173] Average thickness t of the back layer 44 ４ is calculated as follows: First, the average thickness t of the magnetic tape MT Ｔ Measure the average thickness t Ｔ The method for measuring the average thickness of the magnetic tape is as described below in "Average Thickness of Magnetic Tape." Next, the magnetic tape MT housed in the cartridge 10 is unwound, and a sample is prepared by cutting the magnetic tape MT into a length of 250 mm at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the back layer 44 of the sample is removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid. Next, the thickness of the sample is measured at five positions using a laser hologram gauge (LGH-110C) manufactured by Mitutoyo Corporation, and the measured values ​​are simply averaged (arithmetic mean) to obtain the average thickness t Ｂ Then, the average thickness t of the back layer 44 is calculated using the following formula: ４ The five measurement positions are selected at random from the sample so that they are different positions in the longitudinal direction of the magnetic tape MT. ４ [μm] = t Ｔ [μm]-t Ｂ [μm]

[0174] (Lubricant Layer) The lubricant layer contains a lubricant. The lubricant is the same as the lubricant contained in the magnetic layer 43. The lubricant layer may be formed from a lubricant supplied to the magnetic surface from the magnetic layer 43 and the underlayer 42.

[0175] (Average thickness of magnetic tape) Average thickness (average total thickness) t of magnetic tape MT Ｔ The upper limit of the average thickness t of the magnetic tape MT is preferably 5.30 μm or less, more preferably 5.10 μm or less, even more preferably 4.90 μm or less, and particularly preferably 4.70 μm or less. Ｔ When the average thickness t of the magnetic tape MT is 5.30 μm or less, the recording capacity that can be recorded in one data cartridge can be increased compared to that of a general magnetic tape. Ｔ The lower limit of the thickness is not particularly limited, but is, for example, 3.50 μm or more.

[0176] Average thickness t of magnetic tape MT Ｔ is obtained as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and a sample is cut out of the magnetic tape MT at a length of 250 mm at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the thickness of the sample is measured at five positions using a Mitutoyo Laser Hologram (LGH-110C) as a measuring device, and the measured values ​​are simply averaged (arithmetic mean) to obtain the average thickness t Ｔ The five measurement positions are selected at random from the sample so that they are different positions in the longitudinal direction of the magnetic tape MT.

[0177] (Coercive force Hc2) The upper limit of the coercive force Hc2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT is preferably 2000 Oe or less, more preferably 1900 Oe or less, and even more preferably 1800 Oe or less. If the coercive force Hc2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT is 2000 Oe or less, sufficient electromagnetic conversion characteristics can be obtained even at high recording densities.

[0178] The lower limit of the coercive force Hc2 of the magnetic layer 43 measured in the longitudinal direction of the magnetic tape MT is preferably 1000 Oe or more. When the coercive force Hc2 of the magnetic layer 43 measured in the longitudinal direction of the magnetic tape MT is 1000 Oe or more, demagnetization due to leakage flux from the recording head can be suppressed.

[0179] The coercive force Hc2 is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and six magnetic tape MTs are cut out at positions 30 to 40 meters longitudinally from one end of the outer periphery of the magnetic tape MT. At this time, markings are made with any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic tape MT can be identified. Next, the three cut-out magnetic tape MTs are stacked with double-sided tape so that the longitudinal direction of the three cut-out magnetic tape MTs is the same, and then punched out with a φ6.39 mm punch to prepare a measurement sample. Next, the M-H loop of the measurement sample (the entire magnetic tape MT) corresponding to the longitudinal direction (running direction) of the magnetic tape MT is measured using a vibrating sample magnetometer (VSM). Next, the coatings (underlayer 42, magnetic layer 43, back layer 44, etc.) of the remaining three cut-out magnetic tape MTs are wiped off using acetone, ethanol, or the like, leaving only the substrate 41. Three of the obtained substrates 41 are then stacked together with double-sided tape, and punched out with a φ6.39 mm punch to prepare a sample for background correction (hereinafter simply referred to as a "correction sample"). Thereafter, the M-H loop of the correction sample (substrate 41) corresponding to the longitudinal direction of the substrate 41 (the longitudinal direction of the magnetic tape MT) is measured using a VSM.

[0180] The MH loop of the measurement sample (the entire magnetic tape MT) and the MH loop of the correction sample (substrate 41) are measured using a high-sensitivity vibrating sample magnetometer "VSM-P7-15" manufactured by Toei Kogyo Co., Ltd. The measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, number of MH averages: 20.

[0181] After obtaining the M-H loop of the measurement sample (the entire magnetic tape MT) and the M-H loop of the correction sample (substrate 41), background correction is performed by subtracting the M-H loop of the correction sample (substrate 41) from the M-H loop of the measurement sample (the entire magnetic tape MT), thereby obtaining the background-corrected M-H loop. This background correction calculation is performed using the measurement and analysis program included with the VSM-P7-15. The coercive force Hc2 is calculated from the obtained background-corrected M-H loop. Note that this calculation is performed using the measurement and analysis program included with the VSM-P7-15. Note that all of the above M-H loop measurements are performed at 25°C ± 2°C and 50% RH ± 5% RH. Furthermore, "demagnetization field correction" is not performed when measuring the M-H loop in the longitudinal direction of the magnetic tape MT.

[0182] (Squareness Ratio) The lower limit of the squareness ratio S1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT is preferably 0.62 or more, more preferably 0.65 or more, and even more preferably 0.68 or more, 0.72 or more, or 0.75 or more. When the squareness ratio S1 is 0.62 or more, the perpendicular orientation of the magnetic particles is sufficiently high, thereby improving the electromagnetic conversion characteristics.

[0183] When the magnetic powder contains hexagonal ferrite particles, the upper limit of the squareness ratio S1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT is preferably 0.85 or less, more preferably 0.80 or less. When the upper limit of the squareness ratio S1 is 0.85 or less, it is possible to prevent the plate faces of the hexagonal ferrite particles from being excessively aligned on the surface of the magnetic layer 43. Therefore, it is possible to suppress running friction between the magnetic tape MT and the head.

[0184] When the magnetic powder contains hexagonal ferrite particles, the numerical range of the squareness ratio S1 of the magnetic layer 43 may be defined by any of the above lower limit values ​​and any of the above upper limit values, and is preferably 0.62 or more and 0.85 or less, more preferably 0.65 or more and 0.85 or less, even more preferably 0.68 or more and 0.85 or less, 0.72 or more and 0.80 or less, or 0.75 or more and 0.80 or less.

[0185] The squareness ratio S1 in the perpendicular direction of the magnetic tape MT is determined as follows. First, a measurement sample is prepared in the same manner as in the above-described method for measuring the coercive force Hc2. Next, an M-H loop of the measurement sample (the entire magnetic tape MT) corresponding to the perpendicular direction of the magnetic tape MT (the perpendicular direction of the magnetic tape MT) is measured using a VSM. Next, a correction sample is prepared in the same manner as in the above-described method for measuring the coercive force Hc2. Thereafter, an M-H loop of the correction sample (substrate 41) corresponding to the perpendicular direction of the substrate 41 (the perpendicular direction of the magnetic tape MT) is measured using a VSM.

[0186] After obtaining the M-H loop of the measurement sample (the entire magnetic tape MT) and the M-H loop of the correction sample (substrate 41), background correction is performed by subtracting the M-H loop of the correction sample (substrate 41) from the M-H loop of the measurement sample (the entire magnetic tape MT), thereby obtaining the M-H loop after background correction. This background correction calculation is performed using the measurement and analysis program included with the "VSM-P7-15 Model."

[0187] The saturation magnetization Ms (emu) and residual magnetization Mr (emu) of the M-H loop after background correction are substituted into the following formula to calculate the squareness ratio S1 (%). Note that all of the above M-H loop measurements are performed at 25°C ± 2°C and 50% RH ± 5% RH. Also, no "demagnetizing field correction" is performed when measuring the M-H loop in the perpendicular direction to the magnetic tape MT. Note that this calculation uses the measurement and analysis program included with the "VSM-P7-15 model." Squareness ratio S1 = (Mr / Ms)

[0188] The upper limit of the squareness ratio S2 of the magnetic layer 43 in the longitudinal direction (running direction) of the magnetic tape MT is preferably 0.35 or less, more preferably 0.30 or less, and even more preferably 0.29 or less, 0.25 or less, 0.20 or less, or 0.15 or less. When the squareness ratio S2 is 0.35 or less, the perpendicular orientation of the magnetic particles is sufficiently high, thereby improving the electromagnetic conversion characteristics.

[0189] When the magnetic powder contains hexagonal ferrite particles, the lower limit of the squareness ratio S2 of the magnetic layer 43 in the longitudinal direction (running direction) of the magnetic tape MT is preferably 0.26 or more. When the lower limit of the squareness ratio S2 is 0.26 or more, it is possible to prevent the plate faces of the hexagonal ferrite particles from being excessively aligned on the surface of the magnetic layer 43. Therefore, it is possible to suppress running friction between the magnetic tape MT and the head.

[0190] When the magnetic powder contains hexagonal ferrite particles, the numerical range of the squareness ratio S2 of the magnetic layer 43 may be defined by any of the above upper limits and the above lower limit, and is preferably 0.26 or more and 0.35 or less, more preferably 0.26 or more and 0.30 or less, and even more preferably 0.26 or more and 0.29 or less.

[0191] One of the squareness ratio S1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT and the squareness ratio S2 of the magnetic layer 43 in the longitudinal direction (running direction) of the magnetic tape MT may be within the above-mentioned preferred range, while the other may be outside the above-mentioned preferred range. Alternatively, both the squareness ratio S1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT and the squareness ratio S2 of the magnetic layer 43 in the longitudinal direction (running direction) of the magnetic tape MT may be within the above-mentioned preferred range.

[0192] The squareness ratio S2 in the longitudinal direction of the magnetic tape MT is determined in the same manner as the squareness ratio S1, except that the MH loop is measured in the longitudinal direction (running direction) of the magnetic tape MT and the substrate 41.

[0193] (Ratio Hc2 / Hc1) The ratio Hc2 / Hc1 of the coercive force Hc1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT to the coercive force Hc2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT preferably satisfies the relationship Hc2 / Hc1≦0.8, more preferably Hc2 / Hc1≦0.75, and even more preferably Hc2 / Hc1≦0.7, H2 / Hc1≦0.65, or H2 / Hc1≦0.6. When the coercive forces Hc1 and Hc2 satisfy the relationship Hc2 / Hc1≦0.8, the degree of perpendicular orientation of the magnetic particles can be increased. Therefore, the magnetization transition width can be reduced and a high-output signal can be obtained during signal reproduction, resulting in even better electromagnetic conversion characteristics. As described above, a small Hc2 allows the magnetization to respond more sensitively to the perpendicular magnetic field from the recording head, thereby forming a good recording pattern.

[0194] When the ratio Hc2 / Hc1 is Hc2 / Hc1≦0.8, the average thickness t ２ It is particularly effective that the average thickness t of the magnetic layer 43 is 90 nm or less. ２ If the thickness exceeds 90 nm, when a ring-type head is used as the recording head, the lower region of the magnetic layer 43 (the region on the underlayer 42 side) may be magnetized in the longitudinal direction of the magnetic tape MT, which may prevent uniform magnetization of the magnetic layer 43 in the thickness direction. Therefore, even if the ratio Hc2 / Hc1 is set to Hc2 / Hc1≦0.8 (i.e., even if the degree of perpendicular orientation of the magnetic particles is increased), there is a risk that even better electromagnetic conversion characteristics may not be obtained.

[0195] The lower limit of Hc2 / Hc1 is not particularly limited, but for example, it is 0.5≦Hc2 / Hc1. Note that Hc2 / Hc1 represents the degree of perpendicular orientation of the magnetic grains, and the smaller Hc2 / Hc1, the higher the degree of perpendicular orientation of the magnetic grains.

[0196] The method for calculating the coercive force Hc2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT is as described above. The coercive force Hc1 of the magnetic layer 43 in the perpendicular direction of the magnetic tape MT is determined in the same manner as the coercive force Hc2 of the magnetic layer 43 in the longitudinal direction of the magnetic tape MT, except that the M-H loop is measured in the perpendicular direction (thickness direction) of the magnetic tape MT and the substrate 41.

[0197] (Activation volume V ａｃｔ ) Activation volume V ａｃｔ However, preferably 8000 nm ３ Less than 6000 nm, more preferably ３ or less, more preferably 5000 nm ３ Below, 4000nm ３ or below 3000 nm ３ The activation volume V is ａｃｔ is 8000 nm ３ If the magnetic grains are dispersed at or below this value, the bit inversion region can be made steeper, and the magnetic signal recorded on the adjacent track can be prevented from being degraded by the leakage magnetic field from the recording head, thereby achieving even better electromagnetic conversion characteristics.

[0198] The activation volume V ａｃｔ is calculated by the following formula derived by Street & Woolley: ａｃｔ (nm ３ ) = k Ｂ ×T×X ｉｒｒ / (μ ０ × Ms × S) (where k Ｂ : Boltzmann constant (1.38 × 10 －２３ J / K), T: temperature (K), Χ ｉｒｒ : Irreversible magnetic susceptibility, μ ０ : magnetic permeability of vacuum, S: magnetic viscosity coefficient, Ms: saturation magnetization (emu / cm ３ ))

[0199] Irreversible magnetic susceptibility X substituted into the above formula ｉｒｒ The saturation magnetization Ms and magnetic viscosity coefficient S are determined using a VSM as follows. The measurement direction using the VSM is the perpendicular direction (thickness direction) of the magnetic tape MT. Measurement using the VSM is performed on a measurement sample cut out from a long magnetic tape MT at 25°C ± 2°C and 50% RH ± 5% RH. When measuring the M-H loop in the perpendicular direction (thickness direction) of the magnetic tape MT, no "demagnetizing field correction" is performed.

[0200] (irreversible magnetic susceptibility Χ ｉｒｒ ) Irreversible magnetic susceptibility Χ ｉｒｒis defined as the slope of the remanent magnetization curve (DCD curve) near the remanent coercivity Hr. First, a magnetic field of -1193 kA / m (15 kOe) is applied to the entire magnetic tape MT, and the magnetic field is returned to zero, resulting in a remanent magnetization state. Then, a magnetic field of approximately 15.9 kA / m (200 Oe) is applied in the opposite direction, and the magnetic field is returned to zero again, and the amount of remanent magnetization is measured. After that, similar measurements are repeated, applying a magnetic field 15.9 kA / m greater than the previously applied magnetic field and returning it to zero, and the amount of remanent magnetization is plotted against the applied magnetic field to measure the DCD curve. From the obtained DCD curve, the point where the amount of magnetization is zero is taken as the remanent coercivity Hr, and the DCD curve is further differentiated to determine the slope of the DCD curve at each magnetic field. In the slope of this DCD curve, the slope near the remanent coercivity Hr is X. ｉｒｒ This becomes:

[0201] (Saturation magnetization Ms) First, an M-H loop after background correction is obtained in the same manner as in the measurement method for the squareness ratio S1 described above. Next, the value of the saturation magnetization Ms (emu) of the obtained M-H loop and the volume (cm ３ ) to Ms (emu / cm ３ The volume of the magnetic layer 43 is calculated by multiplying the area of ​​the measurement sample by the average thickness t ２ The average thickness t of the magnetic layer 43 required to calculate the volume of the magnetic layer 43 is ２ The calculation method is as described above.

[0202] (Magnetic viscosity coefficient S) First, a magnetic field of -1193 kA / m (15 kOe) is applied to the entire magnetic tape MT (measurement sample), and the magnetic field is returned to zero to create a state of remanent magnetization. Then, a magnetic field equivalent to the value of the remanent coercivity Hr obtained from the DCD curve is applied in the opposite direction. With the magnetic field applied, the amount of magnetization is continuously measured at regular time intervals for 1000 seconds. The relationship between time t and amount of magnetization M(t) obtained in this way is compared with the following formula to calculate the magnetic viscosity coefficient S: M(t) = M0 + S × ln(t) (where M(t): amount of magnetization at time t, M0: initial amount of magnetization, S: magnetic viscosity coefficient, ln(t): natural logarithm of time)

[0203] (Surface roughness R of the back surface ｂ) Surface roughness of the back surface (surface roughness of the back layer 44) R ｂ The upper limit of the surface roughness R of the back surface is preferably 7.5 nm or less, more preferably 7.2 nm or less, and even more preferably 7.0 nm or less, 6.5 nm or less, 6.3 nm or less, or 6.0 nm or less. ｂ When the surface roughness R of the back surface is 7.5 nm or less, the influence of the unevenness of the back surface on the surface of the magnetic layer 43 during winding of the magnetic tape MT can be reduced, and adverse effects on the electromagnetic conversion characteristics can be suppressed. ｂ The lower limit of is preferably 3.0 nm or more, more preferably 3.2 nm or more, and even more preferably 3.4 nm or more.

[0204] Surface roughness R of the back surface ｂ is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and a sample is prepared by cutting the magnetic tape MT to a length of 100 mm at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the sample is placed on a slide glass with the surface to be measured (the surface on the magnetic layer 43 side) facing up, and the end of the sample is fixed with mending tape. The surface shape is measured using a VertScan (20x objective lens) as a measuring device, and the surface roughness R of the back surface is calculated from the following formula based on the ISO 25178 standard. ｂ The measurement conditions are as follows: Equipment: Non-contact roughness meter using optical interference (Non-contact surface / layer cross-sectional shape measurement system VertScan R5500GL-M100-AC, manufactured by Ryoka Systems Co., Ltd.) Objective lens: 20x Measurement area: 640 x 480 pixels (field of view: approximately 237 μm x 178 μm field of view) Measurement mode: phase Wavelength filter: 520 nm CCD: 1 / 3 inch Noise reduction filter: smoothing 3 x 3 Surface correction: correction using quadratic polynomial approximation surface Measurement software: VS-Measure Version 5.5.2 Analysis software: VS-viewer Version 5.5.5 As described above, after measuring the surface roughness at five positions in the longitudinal direction of the magnetic tape MT, the arithmetic mean roughness Sａ (nm) is the surface roughness R ｂ (nm).

[0205] (Young's modulus in the longitudinal direction of the magnetic tape) The upper limit of the Young's modulus in the longitudinal direction of the magnetic tape MT is preferably 9.0 GPa or less, more preferably 8.0 GPa or less, even more preferably 7.5 GPa or less, and particularly preferably 7.1 GPa or less. When the Young's modulus in the longitudinal direction of the magnetic tape MT is 9.0 GPa or less, the elasticity of the magnetic tape MT due to external forces is further increased, making it easier to adjust the width of the magnetic tape MT by adjusting the tension. Therefore, off-track can be more appropriately suppressed, and data recorded on the magnetic tape MT can be more accurately reproduced. The lower limit of the Young's modulus in the longitudinal direction of the magnetic tape MT is preferably 3.0 GPa or more, more preferably 4.0 GPa or more. When the lower limit of the Young's modulus in the longitudinal direction of the magnetic tape MT is 3.0 GPa or more, deterioration of running stability can be suppressed.

[0206] The Young's modulus in the longitudinal direction of the magnetic tape MT is a value that indicates the resistance of the magnetic tape MT to expansion and contraction in the longitudinal direction due to external forces; the larger this value, the less the magnetic tape MT is able to expand and contract in the longitudinal direction due to external forces, and the smaller this value, the more easily the magnetic tape MT is able to expand and contract in the longitudinal direction due to external forces.

[0207] The Young's modulus in the longitudinal direction of the magnetic tape MT is a value related to the longitudinal direction of the magnetic tape MT, but it also correlates with the resistance to expansion and contraction in the width direction of the magnetic tape MT. In other words, the larger this value, the less the magnetic tape MT is susceptible to expansion and contraction in the width direction due to external forces, and the smaller this value, the more the magnetic tape MT is susceptible to expansion and contraction in the width direction due to external forces. Therefore, from the viewpoint of tension adjustment, it is advantageous for the Young's modulus in the longitudinal direction of the magnetic tape MT to be small as described above, 9.0 GPa or less.

[0208] A tensile tester (AG-100D, manufactured by Shimadzu Corporation) is used to measure Young's modulus in the longitudinal direction of the tape. When measuring Young's modulus in the longitudinal direction of the tape, the magnetic tape MT housed in the cartridge 10 is unwound and cut into a length of 180 mm at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT to prepare a measurement sample. A jig capable of fixing the tape width (1 / 2 inch) is attached to the tensile tester, and the top and bottom of the tape width are fixed. The distance (length of tape between chucks) is set to 100 mm. After chucking the tape sample, stress is gradually applied in the direction of pulling the sample. The pulling speed is set to 0.1 mm / min. Young's modulus is calculated from the change in stress and the amount of elongation at this time using the following formula: E (N / m ２ )=((ΔN / S) / (Δx / L))×10 ６ ΔN: Change in stress (N) S: Cross-sectional area of ​​test piece (mm ２ ) Δx: elongation (mm) L: distance between gripping jigs (mm) The cross-sectional area S of the measurement sample 10S is the cross-sectional area before the pulling operation and is calculated by multiplying the width (½ inch) of the measurement sample 10S by the thickness of the measurement sample 10S. The range of tensile stress during measurement is set to a linear region of tensile stress depending on the thickness of the magnetic tape MT, etc. Here, the stress range is set to 0.2 N to 0.7 N, and the stress change (ΔN) and elongation (Δx) at this time are used for calculation. The above Young's modulus measurement is performed at 25°C ± 2°C and 50% RH ± 5% RH.

[0209] (Young's modulus in the longitudinal direction of the substrate) The Young's modulus of the substrate 41 in the longitudinal direction is preferably 7.8 GPa or less, more preferably 7.0 GPa or less, even more preferably 6.6 GPa or less, and particularly preferably 6.4 GPa or less. When the Young's modulus of the substrate 41 in the longitudinal direction is 7.8 GPa or less, the elasticity of the magnetic tape MT due to external forces is further increased, making it easier to adjust the width of the magnetic tape MT by adjusting the tension. Therefore, off-track can be more appropriately suppressed, and data recorded on the magnetic tape MT can be more accurately reproduced. The lower limit of the Young's modulus of the substrate 41 in the longitudinal direction is preferably 2.5 GPa or more, more preferably 3.0 GPa or more. When the lower limit of the Young's modulus of the substrate 41 in the longitudinal direction is 2.5 GPa or more, deterioration of running stability can be suppressed.

[0210] The Young's modulus in the longitudinal direction of the substrate 41 is determined as follows. First, the magnetic tape MT housed in the cartridge 10 is unwound, and the magnetic tape MT is cut into a length of 180 mm at a position 30 to 40 m longitudinally from one end of the outer periphery of the magnetic tape MT. Next, the underlayer 42, magnetic layer 43, and back layer 44 are removed from the cut magnetic tape MT to obtain the substrate 41. Using this substrate 41, the Young's modulus in the longitudinal direction of the substrate 41 is determined using the same procedure as for the Young's modulus in the longitudinal direction of the magnetic tape MT.

[0211] The thickness of the substrate 41 accounts for more than half of the total thickness of the magnetic tape MT. Therefore, the Young's modulus in the longitudinal direction of the substrate 41 correlates with the resistance of the magnetic tape MT to expansion and contraction due to external forces, and the larger this value, the less the magnetic tape MT is able to expand and contract in the width direction due to external forces, and the smaller this value, the more the magnetic tape MT is able to expand and contract in the width direction due to external forces.

[0212] The Young's modulus of the substrate 41 in the longitudinal direction is a value related to the longitudinal direction of the magnetic tape MT, but it also correlates with the resistance to expansion and contraction of the magnetic tape MT in the width direction. In other words, the larger this value, the less the magnetic tape MT is susceptible to expansion and contraction in the width direction due to external forces, and the smaller this value, the more the magnetic tape MT is susceptible to expansion and contraction in the width direction due to external forces. Therefore, from the perspective of tension adjustment, it is advantageous for the Young's modulus of the substrate 41 in the longitudinal direction to be small, as described above, at 7.8 GPa or less.

[0213] [4.2 Manufacturing Method of Magnetic Tape] Next, an example of a manufacturing method of the magnetic tape MT having the above-described configuration will be described.

[0214] (Paint preparation process) First, the paint for forming the base layer is prepared by kneading and dispersing non-magnetic particles, a binder, etc. in a solvent. Next, the paint for forming the magnetic layer is prepared by kneading and dispersing magnetic powder, a binder, etc. in a solvent. For example, the following solvents, dispersing devices, and kneading devices can be used to prepare the paint for forming the magnetic layer and the paint for forming the base layer.

[0215] Examples of solvents used in preparing the coating material include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, alcohol solvents such as methanol, ethanol, and propanol, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, and ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, and halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene. These may be used alone or in appropriate combinations.

[0216] Examples of the kneading apparatus used in preparing the above coating material include, but are not limited to, a continuous twin-screw kneader, a continuous twin-screw kneader capable of multi-stage dilution, a kneader, a pressure kneader, a roll kneader, etc. Examples of the dispersing apparatus used in preparing the above coating material include, but are not limited to, a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, a pearl mill (e.g., the "DCP Mill" manufactured by Eirich), a homogenizer, an ultrasonic disperser, etc.

[0217] (Coating Process) Next, a base layer forming paint is applied to one main surface of the substrate 41 and dried to form the base layer 42. Subsequently, a magnetic layer forming paint is applied to the base layer 42 and dried to form the magnetic layer 43 on the base layer 42. During drying, the magnetic particles may be magnetically oriented in the thickness direction of the substrate 41, for example, using a permanent magnet. After the magnetic layer 43 is formed, a back layer 44 is formed on the other main surface of the substrate 41. This results in a magnetic tape MT. The order in which the base layer 42, magnetic layer 43, and back layer 44 are formed is not limited to the above example. For example, the back layer 44 may be formed on the other main surface of the substrate 41, and then the base layer 42 and magnetic layer 43 may be formed in that order on one main surface of the substrate 41.

[0218] The squareness ratios S1 and S2 can be set to desired values ​​by, for example, adjusting the strength of the magnetic field applied to the coating film of the magnetic layer-forming paint, the concentration of solids in the magnetic layer-forming paint, and the drying conditions (drying temperature and drying time) of the coating film of the magnetic layer-forming paint. The strength of the magnetic field applied to the coating film is preferably between two and three times the coercive force of the magnetic particles. To further increase the squareness ratio S1 (i.e., to further reduce the squareness ratio S2), it is preferable to improve the dispersion state of the magnetic particles in the magnetic layer-forming paint. To further increase the squareness ratio S1, it is also effective to magnetize the magnetic particles before the magnetic layer-forming paint enters an orientation device for magnetically orienting the magnetic particles. The above methods for adjusting the squareness ratios S1 and S2 may be used alone or in combination.

[0219] (Hardening Step) Next, after the magnetic tape MT is wound into a roll, the magnetic tape MT is subjected to a heat treatment in this state, thereby hardening the underlayer 42 and the magnetic layer 43 .

[0220] (Calendering Process) Next, the obtained magnetic tape MT is subjected to a calendering process to smooth the magnetic surface.

[0221] (Aging Step) Next, if necessary, the obtained magnetic tape MT is subjected to an aging treatment.

[0222] (Cutting Step) Next, the magnetic tape MT is cut to a predetermined width (for example, 1 / 2 inch width). In this way, the magnetic tape MT is obtained.

[0223] (Servo Write Process) Next, if necessary, the magnetic tape MT may be demagnetized and then a servo pattern may be written onto the magnetic tape MT.

[0224] [4.3 Effects] As described above, the magnetic tape MT according to the second embodiment includes a magnetic layer 43 containing magnetic powder produced by the magnetic powder production method according to the first embodiment. The magnetic powder produced by the magnetic powder production method according to the first embodiment contains a reduced amount of hexagonal ferrite particles, which have excessively low magnetic properties (e.g., coercive force Hc). This can improve the electromagnetic conversion properties of the magnetic tape.

[0225] <5. Experimental Examples> Hereinafter, the present disclosure will be specifically explained using experimental examples, but the present disclosure is not limited to these experimental examples.

[0226] Table 1 shows the composition of the raw materials used in the following experimental examples.

[0227]

[0228] [5.1 Consideration of particle size distribution of magnetic powder] Two types of magnetic powder (barium ferrite magnetic powder) with different particle size distributions were prepared, and their particle size distributions were evaluated.

[0229] [Experimental Example 1-1] (Raw Material Mixing Process) First, sodium tetraborate (Na ２ B ４ O７ ), α-iron oxide (Fe ２ O ３ ), barium carbonate (BaCO ３ ) and titanium oxide (TiO ２ ) were mixed in a powder mixer to obtain a raw material mixture. The composition of each raw material was as shown in Composition 4 in Table 1. The mixing time was 60 minutes.

[0230] (Melting step) Next, 1 kg of the raw material mixture was placed in a crucible of a glass melting furnace and melted to obtain a melt. The melting temperature was 1400°C, and the melting time was 80 minutes. During the melting, the raw material mixture placed in the crucible was stirred with a stirring rod rotating at 30 rpm.

[0231] (Quenching step) Next, the melt was quenched while flowing out of the crucible to produce an amorphous mass containing crystal nuclei. Here, the melt was quenched while rolling using a pair of chill rolls whose surface temperature was set to 20° C. The gap between the pair of chill rolls was 1 mm or less, and the discharge rate was 0.5 g / sec or more and 1.0 g / sec or less.

[0232] (Pulverization Step) Next, the amorphous body was pulverized using a molar mill to obtain an amorphous body powder containing crystal nuclei (amorphous particle powder).

[0233] (Firing Process) Next, 30 g of amorphous powder was placed in a crucible, which was then placed in a muffle furnace and fired. No spacers were placed between the bottom of the crucible and the bottom of the heating chamber. A rectangular alumina crucible measuring 15 cm in length, 15 cm in width, and 7 cm in height was used as the crucible. The firing process was carried out as follows: The furnace was heated from room temperature to a firing temperature of 590°C at a heating rate of 5°C / min. Once the firing temperature reached 590°C, the firing temperature of 590°C was maintained for 8 hours (firing time). The heater of the muffle furnace was then turned off, and the muffle furnace was left with the door closed. After the temperature in the furnace had sufficiently decreased, the fired body containing barium ferrite particles was removed from the muffle furnace. The firing temperature described in the firing process refers to the set temperature of the furnace. Similarly, in the following experimental examples, the firing temperatures described in the firing steps represent the set temperatures of the firing furnaces.

[0234] (Acid Treatment / Water Washing Step) Next, the obtained sintered body was subjected to acid treatment to remove glass components and extract a powder of barium ferrite particles. The acid treatment was performed by putting the sintered body into acetic acid and washing it with a ball mill. Next, the extracted powder of barium ferrite particles was washed with pure water.

[0235] (Separation Treatment Step) Thereafter, the mixture was centrifuged using a centrifugal separator and decanted to obtain a powder of barium ferrite particles.

[0236] (Drying step) Finally, the barium ferrite particle powder was placed in an electric furnace and dried in an environment of 120° C. until the moisture content of the powder reached 2.0 (wt %) or less, thereby obtaining the desired barium ferrite magnetic powder.

[0237] [Experimental Example 1-2] Barium ferrite magnetic powder was obtained by carrying out the same steps as in Experimental Example 1-1 except for the raw material mixing step and the firing step. The raw material mixing step and the firing step in Experimental Example 1-2 were as follows.

[0238] (Raw material mixing process) Sodium tetraborate (Na ２ B ４ O ７ ), α-iron oxide (Fe ２ O ３ ), barium carbonate (BaCO ３ ), titanium oxide (TiO ２ ) and aluminum oxide (Al ２ O ３ ) were mixed in a powder mixer to obtain a raw material mixture. The composition of each raw material was as shown in Composition 3 in Table 1. The mixing time was 60 minutes.

[0239] (Firing Step) The firing step was carried out in the same manner as in Example 1-1, except that the firing temperature was changed from 590°C to 570°C.

[0240] [Evaluation] Particle size distribution, average plate diameter D, standard deviation σ, coefficient of variation, and maximum plate diameter D of magnetic powders in Experimental Examples 1-1 and 1-2 max and minimum plate diameter D minwas determined as follows: The coefficient of variation of the particle size of the magnetic powder is expressed by the following formula: Coefficient of variation [%] = (σ / D) × 100 In the above formula, σ represents the standard deviation of the distribution of the plate diameter (particle size) [nm] of the magnetic powder, and D represents the average plate diameter (average particle size) [nm] of the magnetic powder.

[0241] First, the magnetic powder was observed using a scanning transmission electron microscope (STEM) to obtain a STEM image. The STEM used and the observation conditions are as follows: Apparatus: STEM (Hitachi S4800) Acceleration voltage: 30 kV Measurement magnification: 200,000 times

[0242] Next, 300 barium ferrite particles were selected from the obtained STEM image using the following selection criteria. The length of each particle horizontally relative to the STEM image was determined, and this length was used as the plate diameter (particle size). If it is not possible to measure 300 particles from one STEM image, two or more STEM images may be used. <Particle Selection Criteria> [1] Particles with parts outside the field of view of the photograph are not measured. [2] Particles with clear outlines and existing in isolation are measured. [3] Even if a particle deviates from the average particle shape, particles that are independent and can be measured as individual particles are measured. [4] Particles that overlap but have clear boundaries and whose overall shape can be determined are measured as individual particles. [5] Particles that overlap with unclear boundaries and whose overall shape cannot be determined are not measured, as their shape cannot be determined.

[0243] Next, the maximum plate diameter D max and minimum plate diameter D minwere selected. Next, the average plate diameter D [nm] and standard deviation σ of the magnetic powder were calculated from the obtained plate diameter (particle size) values, and then these were used to calculate the coefficient of variation σ / D [%] of the particle diameter of the magnetic powder. The average plate diameter is the average particle size, and is the sum of the measured 300 plate diameters (particle sizes) divided by 300. The standard deviation σ is the unbiased standard deviation of the obtained data of the 300 plate diameters (particle sizes). From the above, the coefficient of variation σ / D represents the number-based distribution variation in particle size. The above evaluation results are shown in Table 2. Furthermore, Figure 7 shows the particle size distribution of the magnetic powders of Experimental Examples 1-1 and 1-2.

[0244]

[0245] In order to improve the recording density (linear recording density) of magnetic tape, it is necessary to make the barium ferrite particles finer. However, from the above evaluation results, it can be seen that when the barium ferrite particles are made finer, the proportion of barium ferrite particles with a plate diameter of 9 nm or less, where the coercive force Hc is Hc≈0, increases. Therefore, it can be seen that in order to suppress the decrease in coercive force Hc, it is desirable to remove barium ferrite particles with a small plate diameter. Note that in Experimental Example 1-1, the particle volume V XRD is 800 nm ３ The magnetic powder in Experimental Example 1-2 was produced with the aim of achieving a particle volume V XRD is 1600 nm ３ This magnetic powder was created with the aim of achieving this.

[0246] [5.2 Consideration of Classification Treatment] After the amorphous powder was classified, the amorphous powder was fired to produce barium ferrite magnetic powder, and its magnetic properties and particle properties were evaluated.

[0247] [Experimental Example 2-1] By carrying out the steps from the raw material mixing step to the drying step in the same manner as in Experimental Example 1-2, barium ferrite magnetic powder (BaFe １１．５ Ti ０．５ O １９ A magnetic powder of particles was obtained.

[0248] [Experimental Examples 2-2 to 2-5] (Raw Material Mixing Step to Pulverization Step) First, the steps from the raw material mixing step to the pulverization step were carried out in the same manner as in Experimental Example 2-1 to obtain an amorphous powder.

[0249] (Classification step) Next, the amorphous powder was classified into four groups (groups (1) to (4)) based on particle size D by sieving classification (dry classification). The particle size D ranges of groups (1) to (4) were as follows: Group (1): 500 μm<D Group (2): 300 μm<D≦500 μm Group (3): 200 μm<D≦300 μm Group (4): D≦200 μm

[0250] The conditions for sieving and classification were as follows: Sieve: Test sieve specified in JIS Z 8801-1 (2006) First sieve from the bottom: 200 μm mesh, second sieve from the bottom: 300 μm mesh, third sieve from the bottom: 500 μm mesh, frame diameter: 200 mm, depth: 45 mm, plain weave Classifier: Electric sieve (ANF-30, manufactured by Nitto Kagaku Co., Ltd.) Sieving time: 60 sec Amount charged per run: 100 g The classification process was carried out until the mass of the amorphous powder in each of groups (1) to (4) reached 30 g or more.

[0251] (From the firing process to the drying process) Next, the amorphous powders of each of Groups (1) to (4) were subjected to the firing process to the drying process in the same manner as in Experimental Example 2-1, thereby obtaining barium ferrite magnetic powders of Experimental Examples 2-2 to 2-5.

[0252] [Experimental Example 3-1] By carrying out the same steps as in Experimental Example 2-1 except for the raw material mixing step and the firing step, barium ferrite magnetic powder (Ba ０．５４ Sr ０．４６ Fe １１．７ Ti ０．３ O １９ The raw material mixing step and the firing step in Experimental Example 3-1 were as follows.

[0253] (Raw material mixing process) Boric acid (B ２ O ３), α-iron oxide (Fe ２ O ３ ), barium carbonate (BaCO ３ ), strontium carbonate (SrCO ３ ) and titanium oxide (TiO ２ ) were mixed in a powder mixer to obtain a raw material mixture. The composition of each raw material was as shown in Composition 2 in Table 1. The mixing time was 60 minutes.

[0254] (Firing step) 30 g of the classified amorphous powder was placed in a crucible, and the crucible was placed in a muffle furnace and fired. The firing process was carried out as follows. The temperature inside the furnace was raised from room temperature at a temperature increase rate of 5°C / min until a firing temperature of 610°C was reached. Once the firing temperature reached 610°C, the firing temperature of 610°C was maintained for 8 hours (firing time). Thereafter, the firing process in the muffle furnace was stopped, and the muffle furnace was left with the door closed. After waiting for the temperature inside the furnace to drop sufficiently, the fired body containing barium ferrite particles was removed from the muffle furnace.

[0255] [Experimental Examples 3-2 to 3-5] (Raw Material Mixing Step to Pulverization Step) First, the steps from the raw material mixing step to the pulverization step were carried out in the same manner as in Experimental Example 3-1 to obtain an amorphous powder.

[0256] (Classification Step) Next, the amorphous powder was classified into four groups, group (1) to group (4), based on the particle size D by carrying out the same classification process as in Experimental Examples 2-2 to 2-5.

[0257] (From the firing process to the drying process) Next, the amorphous powders of each of Groups (1) to (4) were subjected to the firing process to the drying process in the same manner as in Experimental Example 3-1, thereby obtaining barium ferrite magnetic powders of Experimental Examples 3-2 to 3-5.

[0258] [Evaluation] The magnetic powders of Experimental Examples 2-1 to 2-5 and 3-1 to 3-5 were evaluated as follows.

[0259] (Magnetic Properties) First, the coercive force Hc and half-width Ha of the magnetic powder were measured using the same method as described in the first embodiment. Furthermore, when measuring the coercive force Hc and half-width Ha, the mass magnetization σs, squareness ratio Rs, and SFD were also measured from the M-H loop. These measurements were performed using the measurement and analysis program included with the "VSM-P7-15 model." The SFD is the value obtained by normalizing the half-width Ha by the coercive force Hc (Ha / Hc).

[0260] Figure 8A shows the measurement results of the half-value width Ha of the magnetic powders of Experimental Examples 2-1 to 2-5. Figure 8B shows the measurement results of the coercive force Hc of the magnetic powders of Experimental Examples 2-1 to 2-5. Figure 9A shows the measurement results of the half-value width Ha of the magnetic powders of Experimental Examples 3-1 to 2-5. Figure 9B shows the measurement results of the coercive force Hc of the magnetic powders of Experimental Examples 3-1 to 2-5. Figure 10 shows the SFD curves of the magnetic powders of Experimental Examples 2-1, 2-2, and 2-5.

[0261] (Particle Characteristics) The plate thickness D of the barium ferrite particles described in the first embodiment １ , plate diameter D ２ , aspect ratio D ２ / D １ and particle volume V XRD These were measured by the measurement method described above.

[0262]

[0263]

[0264] 8A reveals the following about the barium ferrite magnetic powder (containing no strontium): The half-width Ha of the magnetic powders of Experimental Examples 3-2 and 3-3 (classified group (1): 500 μm<D, classified group (2): 300 μm<D≦500 μm) is narrower than the half-width Ha of the magnetic powder of Experimental Example 3-1 (no classification treatment). On the other hand, the half-width Ha of the magnetic powders of Experimental Examples 3-4 and 3-5 (classified group (3): 200 μm<D≦300 μm, classified group (4): D≦200 μm) is wider than the half-width Ha of the magnetic powder of Experimental Example 3-1 (no classification treatment). Therefore, from the viewpoint of improving the half-value width Ha of the magnetic powder (i.e., from the viewpoint of suppressing noise in the magnetic tape), it is preferable to remove amorphous particles of 200 μm or less by classification, and it is more preferable to remove amorphous particles of 300 μm or less.

[0265] 8B reveals the following about the barium ferrite magnetic powder (containing no strontium): The coercive force Hc of the magnetic powders of Experimental Examples 3-2 and 3-3 (classification treatment group (1): 500 μm < D, classification treatment group (2): 300 μm < D ≦ 500 μm) is higher than the coercive force Hc of the magnetic powder of Experimental Example 3-1 (no classification treatment). On the other hand, the coercive force Hc of the magnetic powders of Experimental Examples 3-4 and 3-5 (classification treatment group (3): 200 μm < D ≦ 300 μm, classification treatment group (4): D ≦ 200 μm) is lower than the coercive force Hc of the magnetic powder of Experimental Example 3-1 (no classification treatment). Therefore, from the viewpoint of improving the coercive force Hc of the magnetic powder, it is preferable to remove amorphous particles with a particle size of 200 μm or less by classification treatment, and it is more preferable to remove amorphous particles with a particle size of 300 μm or less.

[0266] 9A reveals the following about the barium ferrite magnetic powder (containing strontium): The half-value width Ha of the magnetic powder increases in the order of Experimental Examples 3-1, 3-2, 3-3, 3-4, and 3-5. Therefore, from the viewpoint of improving the half-value width Ha of the magnetic powder (i.e., from the viewpoint of suppressing noise in the magnetic tape), it is preferable to remove amorphous particles with a particle size of 200 μm or less by classification, more preferably to remove amorphous particles with a particle size of 300 μm or less, and even more preferably to remove amorphous particles with a particle size of 500 μm or less.

[0267] 9B reveals the following about the barium ferrite magnetic powder (containing strontium): The coercive force Hc of the magnetic powder decreases in the order of Experimental Examples 3-1, 3-2, 3-3, 3-4, and 3-5. Therefore, from the viewpoint of improving the coercive force Hc of the magnetic powder, it is preferable to remove amorphous particles with a particle size of 200 μm or less by classification, more preferably to remove amorphous particles with a particle size of 300 μm or less, and even more preferably to remove amorphous particles with a particle size of 500 μm or less.

[0268] [5.3 Study on Variation in Magnetic Powder Properties Generated During Sintering] Barium ferrite particles were taken as samples from the lower, middle and upper layers of the sintered body, and the differences in their magnetic properties were evaluated.

[0269] [Experimental Examples 4-1 to 4-3] (Raw Material Mixing Step) First, sodium tetraborate (Na ２ B ４ O ７ ), α-iron oxide (Fe ２ O ３ ), barium carbonate (BaCO ３ ), strontium carbonate (SrCO ３ ) and aluminum oxide (Al ２ O ３ ) were mixed in a powder mixer to obtain a raw material mixture. The composition of each raw material was as shown in Composition 1 in Table 1. The mixing time was 60 minutes.

[0270] (Dissolving Step to Pulverizing Step) Next, the steps from the dissolving step to the pulverizing step were carried out in the same manner as in Experimental Example 1-1, thereby obtaining an amorphous powder.

[0271] (Firing Process) Next, 500 g of the pulverized amorphous powder was placed in a crucible, and the crucible was placed in an industrial rapid heating electric furnace (Superburn, manufactured by Motoyama Corporation) and fired. No spacers were placed between the bottom of the crucible and the bottom of the heating chamber. A rectangular alumina crucible measuring 15 cm in length, 15 cm in width, and 7 cm in height was used as the crucible. The firing process was carried out as follows. The temperature inside the furnace was increased from room temperature to a firing temperature (crystallization temperature) of 555°C at a heating rate of 5°C / min. Once the firing temperature reached 555°C, the firing temperature of 555°C was maintained for 8 hours (firing time). The firing process in the rapid heating electric furnace was then stopped, and the door of the rapid heating electric furnace was left closed. After waiting for the temperature inside the furnace to drop sufficiently, the sintered body containing the barium ferrite particles was removed from the rapid heating electric furnace.

[0272] (Sample Collection Step) Next, the sintered body was removed from the crucible, and 30 g of the lower layer of the sintered body, 440 g of the middle layer of the sintered body, and 30 g of the upper layer of the sintered body were collected, respectively, to obtain powders of the sintered bodies of Experimental Examples 4-1, 4-2, and 4-3. The powders of the lower and upper layers of the sintered body were collected by scraping off the upper and lower sides of the crystallized product, respectively, and the powder of the middle layer of the sintered body was collected as the remaining portion after the upper and lower sides were scraped off. Here, the lower layer of the sintered body was the layer located on the bottom side of the container part of the crucible, and the upper layer of the sintered body was the layer located on the opening side of the container part of the crucible.

[0273] [Experimental Examples 5-1 to 5-3] The sintered powders of Experimental Examples 4-1, 4-2, and 4-3 were subjected to the same processes as Experimental Example 1-1, from the acid treatment and water washing process to the drying process, to obtain barium ferrite magnetic powders of Experimental Examples 5-1, 5-2, and 5-3.

[0274] [Evaluation] The sintered powders of Experimental Examples 4-1 to 4-3 and the barium ferrite magnetic powders of Experimental Examples 5-1 to 5-3 were evaluated as follows.

[0275] (Magnetic Properties) The coercive force Hc, squareness ratio Rs, SFD, and half-width Ha of the sintered powder were determined in the same manner as in the evaluation of the magnetic powders of Experimental Examples 2-1 to 2-5 and 3-1 to 3-5. The mass magnetization σs, coercive force Hc, squareness ratio Rs, SFD, and half-width Ha of the barium ferrite magnetic powder were also determined. The results of these measurements are shown in Table 5.

[0276]

[0277] The above evaluation results reveal the following. When a large amount of amorphous powder is sintered in a crucible, variations in the sintering of the amorphous powder occur within the crucible. This results in variations in the magnetic properties of the sintered powder and barium ferrite magnetic powder obtained by sintering the amorphous powder. The upper layer of the sintered body is more crystallized than the lower and middle layers of the sintered body. In other words, the upper layer of the sintered body has higher magnetic properties than the lower and middle layers of the sintered body.

[0278] [5.4 Consideration of the effect of spacers during firing] A spacer was placed between the bottom of the crucible and the bottom of the heating chamber, and the effect of the spacer placement on the magnetic properties and particle properties of barium fairite particles was evaluated.

[0279] [Experimental Examples 6-1 to 6-3] (Raw Material Mixing Step to Firing Step) First, the steps from the raw material mixing step to the firing step were carried out in the same manner as in Experimental Examples 4-1 to 4-3 to obtain fired bodies.

[0280] (Sample Collection Step) Next, powder of the sintered body was collected from three positions, 1.0 mm, 9.0 mm, and 17.0 mm from the bottom surface of the sintered body (i.e., the bottom surface of the container part of the crucible).

[0281] (From the acid treatment / water washing process to the drying process) Next, the processes from the acid treatment / water washing process to the drying process were carried out on each of the sintered powders collected from the three locations in the same manner as in Experimental Example 1-1, thereby obtaining barium ferrite magnetic powders of Experimental Examples 6-1, 6-2, and 6-3.

[0282] [Experimental Examples 7-1 to 7-3] Barium ferrite magnetic powders of Experimental Examples 7-1 to 7-3 were obtained in the same manner as Experimental Examples 6-1 to 6-3, except that spacers were placed between each corner of the bottom of the crucible and the bottom of the heating chamber in the firing process. The spacers used were ceramic cubes with sides each measuring approximately 3.5 cm.

[0283] [Evaluation] The magnetic powders of Experimental Examples 6-1 to 6-3 and 7-1 to 7-3 were evaluated as follows.

[0284] (Magnetic Properties) The mass magnetization σs, coercive force Hc, squareness ratio Rs, SFD, and half-width Ha of the magnetic powder were evaluated in the same manner as in the evaluation of the magnetic powders of Experimental Examples 2-1 to 2-5 and 3-1 to 3-5 above. The firing temperature of each experimental example was calculated from the coercive force Hc. The evaluation results are shown in Table 6.

[0285] Specifically, the firing temperature was calculated from the coercive force Hc as follows. (1) A glass sample with the same composition as that used in the experimental example was prepared, and five samples, weighing 30 g, were placed in SiC crucibles. (2) The firing furnace temperature was set to -20°C, -10°C, ±0°C, +10°C, and +20°C from the set temperature of the firing furnace in the experimental example, and one sample of (1) was placed in each furnace and fired. (Firing conditions: firing started at room temperature, temperature increase rate 5°C / min, holding time 8 hours, natural temperature decrease, spacer present). (3) The fired sample was recovered, acid-treated, and washed with water. (4) The magnetic properties (coercive force Hc) of the sample (3) were measured. The measurement method was the same as the method for measuring coercive force Hc described in the first embodiment above. (5) Based on the measurement results of (4), a graph was plotted with the X axis representing the actual temperature in the firing furnace and the Y axis representing coercive force Hc. The relationship between the sintering temperature and the coercive force Hc was obtained by linear approximation of the plotted graph. (6) The sample temperature was estimated using the approximate equation obtained in (5) from the magnetic properties (coercive force Hc) obtained in the experimental example. Note that the amount of sintered sample was 30 g, which is a small amount and the sample spreads flat on the bottom of the crucible, so the heat generated during the crystallization reaction can be almost ignored. The actual temperature of the sample during sintering and the actual temperature of the atmosphere in the sintering furnace are approximately the same.

[0286] (Particle characteristics) In the same manner as in the evaluation of the magnetic powders of Experimental Examples 2-1 to 2-5 and 3-1 to 3-5, the plate thickness D of the magnetic powder was measured. １ , plate diameter D ２, aspect ratio (D ２ / D １ ) and particle volume V XRD The results of the evaluation are shown in Table 6. Also, FIG. 11 shows the particle volume V of the barium ferrite particles. XRD and coercive force Hc.

[0287]

[0288] The above evaluation results reveal the following: The particle volume V of barium ferrite particles was found to be higher in the following order: samples taken from the 17.0 mm position (Experimental Examples 6-1 and 7-1), samples taken from the 9.0 mm position (Experimental Examples 6-2 and 7-2), and samples taken from the 1.0 mm position (Experimental Examples 6-3 and 7-3). XRD The particle volume V of the barium ferrite particles tends to decrease depending on the sample collection position. XRD By placing a spacer between the bottom of the crucible and the bottom of the heating chamber, the particle volume V XRD Furthermore, the variation in coercive force Hc can be suppressed.

[0289] [5.5 Consideration of firing amount] The changes in the magnetic properties and particle properties of the magnetic powder due to differences in firing amount were evaluated. In addition, samples were taken from different positions in the thickness direction of the sintered body, and the magnetic properties and particle properties of each sample were evaluated.

[0290] [Experimental Example 8-1] (Raw Material Mixing Step to Pulverization Step) First, the steps from the raw material mixing step to the pulverization step were carried out in the same manner as in Experimental Examples 3-1 to 3-5, thereby obtaining a powder of a fired body.

[0291] (Firing Process) Next, 30 g of amorphous powder was placed in a crucible, and the crucible was placed in an industrial rapid heating electric furnace (Superburn, manufactured by Motoyama Corporation) and fired. No spacers were placed between the bottom of the crucible and the bottom of the heating chamber. A rectangular alumina crucible measuring 15 cm in length, 15 cm in width, and 7 cm in height was used as the crucible. The firing process was carried out as follows. The temperature inside the furnace was increased from room temperature to a firing temperature (crystallization temperature) of 610°C at a heating rate of 5°C / min. Once the firing temperature reached 610°C, the firing temperature of 610°C was maintained for 8 hours (firing time). The firing process in the rapid heating electric furnace was then stopped, and the door of the rapid heating electric furnace was left closed. After waiting for the temperature inside the furnace to drop sufficiently, the sintered body containing the barium ferrite particles was removed from the rapid heating electric furnace.

[0292] (Acid Treatment / Water Washing Step to Drying Step) Next, the obtained sintered powder was subjected to the steps from the acid treatment / water washing step to the drying step in the same manner as in Experimental Example 1-1, thereby obtaining barium ferrite magnetic powder.

[0293] (Evaluation process of magnetic properties and particle properties) Next, in the same manner as in the evaluation of the magnetic powders of Experimental Examples 2-1 to 2-5 and 3-1 to 3-5, the magnetic properties (mass magnetization σs, coercive force Hc, squareness ratio Rs, SFD and half width Ha) and particle properties (plate thickness D １ , plate diameter D ２ , aspect ratio D ２ / D １ and particle volume V XRD The firing temperature was calculated from the coercive force Hc in the same manner as in Experimental Examples 6-1 to 6-3 and 7-1 to 7-3. The evaluation results are shown in Tables 7 and 8.

[0294] [Experimental Examples 9-1 to 9-3] (From the raw material mixing step to the firing step) First, a fired body was obtained by carrying out the steps from the raw material mixing step to the firing step in the same manner as in Experimental Example 8-1, except that in the firing step, 500 g of amorphous powder was placed in the crucible.

[0295] (Sample Collection Step) Next, the fired body was removed from the crucible, and the fired body was scraped off at three positions 15.0 mm, 9.0 mm, and 3.0 mm from the bottom surface of the fired body, to collect powder of the fired body.

[0296] (From the acid treatment / water washing process to the drying process) Next, the processes from the acid treatment / water washing process to the drying process were carried out on each of the sintered powders collected from the three locations in the same manner as in Experimental Example 1-1, thereby obtaining barium ferrite magnetic powders of Experimental Examples 9-1 to 9-3.

[0297] (Evaluation process of magnetic properties and particle properties) Next, in the same manner as the evaluation of the magnetic powder of Experimental Example 8-1, the magnetic properties (mass magnetization σs, coercive force Hc, squareness ratio Rs, SFD and half width Ha) and particle properties (plate thickness D １ , plate diameter D ２ , aspect ratio D ２ / D １ and particle volume V XRD ) were evaluated. In addition, the firing temperature was calculated from the coercive force Hc in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. The evaluation results are shown in Table 7, Figures 12A, 12B, and 12C. Next, the magnetic properties of the magnetic powders of Experimental Examples 9-1 to 9-3 were simply averaged. The average values ​​are shown in Table 8. In addition, the particle properties of the magnetic powders of Experimental Examples 9-1 to 9-3 were simply averaged. The average values ​​are shown in Table 8.

[0298] [Experimental Examples 10-1 to 10-5] First, barium ferrite magnetic powders of Experimental Examples 10-1 to 10-5 were obtained in the same manner as Experimental Examples 9-1 to 9-3, except for the following points. In the firing step, 1000 g of amorphous powder was placed in a crucible. In the sample collection step, the fired body was scraped off from five positions, 31.5 mm, 24.5 mm, 17.5 mm, 10.5 mm, and 3.5 mm from the bottom surface of the fired body, and powder of the fired body was collected.

[0299] Next, the magnetic properties and particle properties of each of the magnetic powders of Experimental Examples 10-1 to 10-5 were evaluated in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. Furthermore, the firing temperature was calculated from the coercive force Hc in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. These evaluation results are shown in Table 7, Figures 12A, 12B, and 12C. Next, the magnetic properties of the magnetic powders of Experimental Examples 10-1 to 10-5 were simply averaged. The average values ​​are shown in Table 8. Furthermore, the particle properties of the magnetic powders of Experimental Examples 10-1 to 10-5 were simply averaged. The average values ​​are shown in Table 8.

[0300] [Experimental Example 11-1] First, barium ferrite magnetic powder of Experimental Example 11-1 was obtained in the same manner as Experimental Example 8-1, except for the following points: In the firing step, a square crucible made of SiC (silicon carbide) with dimensions of 15 cm in length, 15 cm in width, and 7 cm in height was used.

[0301] Next, the magnetic properties and particle properties of the magnetic powder of Experimental Example 11-1 were evaluated in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. The sintering temperature was calculated from the coercive force Hc in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. The evaluation results are shown in Tables 7 and 8, and in Figures 12A, 12B, and 12C.

[0302] [Experimental Examples 12-1 to 12-3] First, barium ferrite magnetic powders of Experimental Examples 12-1 to 12-3 were obtained in the same manner as Experimental Examples 9-1 to 9-3, except for the following points: In the firing step, a square crucible made of SiC (silicon carbide) with dimensions of 15 cm in length, 15 cm in width, and 7 cm in height was used.

[0303] Next, the magnetic properties and particle properties of each of the magnetic powders of Experimental Examples 12-1 to 12-3 were evaluated in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. The firing temperature was calculated from the coercive force Hc in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. The evaluation results are shown in Table 7, Figures 12A, 12B, and 12C. The magnetic properties of the magnetic powders of Experimental Examples 12-1 to 12-3 were then simply averaged. The average values ​​are shown in Table 8. The particle properties of the magnetic powders of Experimental Examples 12-1 to 12-3 were also simply averaged. The average values ​​are shown in Table 8.

[0304] [Experimental Examples 13-1 to 13-5] First, barium ferrite magnetic powders of Experimental Examples 13-1 to 13-5 were obtained in the same manner as Experimental Examples 10-1 to 10-5, except for the following points: In the firing step, a square crucible made of SiC (silicon carbide) with dimensions of 15 cm in length, 15 cm in width, and 7 cm in height was used.

[0305] Next, the magnetic properties and particle properties of each of the magnetic powders of Experimental Examples 13-1 to 13-5 were evaluated in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. Furthermore, the firing temperature was calculated from the coercive force Hc in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. These evaluation results are shown in Table 7, Figures 12A, 12B, and 12C. Next, the magnetic properties of the magnetic powders of Experimental Examples 13-1 to 13-5 were simply averaged. The average values ​​are shown in Table 8. Furthermore, the particle properties of the magnetic powders of Experimental Examples 13-1 to 13-5 were simply averaged. The average values ​​are shown in Table 8.

[0306] [Experimental Examples 14-1 to 14-10] (From the raw material mixing step to the firing step) First, a fired body was obtained by carrying out the steps from the raw material mixing step to the firing step in the same manner as in Experimental Example 11-1, except that in the firing step, 2000 g of amorphous powder was placed in the crucible.

[0307] (Sample Collection Step) Next, the sintered body was removed from the crucible, and the sintered body was scraped off from each of 10 positions, 66.5 mm, 59.5 mm, 52.5 mm, 45.5 mm, 38.5 mm, 31.5 mm, 24.5 mm, 17.5 mm, 10.5 mm, and 3.5 mm from the bottom surface of the sintered body, to collect powder of the sintered body.

[0308] (From the acid treatment / water washing process to the drying process) Next, the processes from the acid treatment / water washing process to the drying process were carried out on each of the sintered powders collected from the 10 locations in the same manner as in Experimental Example 1-1, thereby obtaining barium ferrite magnetic powders of Experimental Examples 14-1 to 14-10.

[0309] (Step of Evaluating Magnetic Properties and Particle Properties) Next, the magnetic properties and particle properties of each of the magnetic powders of Experimental Examples 14-1 to 14-10 were evaluated in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. Furthermore, the firing temperature was calculated from the coercive force Hc in the same manner as in the evaluation of the magnetic powder of Experimental Example 8-1. These evaluation results are shown in Table 7, FIGS. 12A, 12B, and 12C. Next, the magnetic properties of the magnetic powders of Experimental Examples 14-1 to 14-10 were simply averaged. The average values ​​are shown in Table 8. Furthermore, the particle properties of the magnetic powders of Experimental Examples 14-1 to 14-10 were simply averaged. The average values ​​are shown in Table 8.

[0310]

[0311]

[0312] Table 9 shows the maximum and minimum firing temperatures calculated from the coercive force Hc, as well as the temperature difference between them. It also shows the maximum and minimum coercive forces Hc, as well as the difference between them.

[0313]

[0314] 12A, 12B, 12C, etc., the following can be seen: The more amorphous powder is charged into the electric furnace, i.e., the greater the bulk of the amorphous powder contained in the crucible, the greater the difference in properties tends to be within the sintered body.

[0315] The following can be seen from Figures 12A and 12B, etc.: The changes in coercive force Hc and sample temperature (the firing temperature of the sample calculated from the coercive force Hc) relative to the sample collection position differ depending on the crucible material. With a SiC crucible, the coercive force Hc and sample temperature tend to be higher at the center of the fired body, while with an alumina crucible, the coercive force Hc and sample temperature tend to be higher on the surface of the fired body. This is thought to be due to the difference in thermal conductivity of the crucible material. From Table 9, etc., it can be seen that in order to keep the coercive force Hc variation within a lot within 150 Oe, it is preferable to keep the firing temperature difference in the depth direction of the crucible within 5°C.

[0316] The following can be seen from Figure 12B and other figures. The holding temperature during crystallization annealing is 610°C, but the actual temperature of the sample tends to be higher than 610°C due to the heat of reaction when hexagonal ferrite particles are generated or grown within the amorphous particles. This tendency is particularly pronounced in the SiC crucible, where heat is less likely to escape from the center of the sample. In both the SiC crucible and the alumina crucible, the actual temperature of the sample located on the bottom side of the crucible tends to be less likely to rise because heat is easily absorbed by the crucible itself.

[0317] The following can be seen from Figure 12C etc.: The particle volume V XRD In the case of an alumina crucible, the change in the particle volume V of the magnetic powder from the opening side of the container part of the crucible to the bottom side (i.e., from the top side to the bottom side of the sintered body) XRD This is thought to be because the thermal conductivity of the alumina crucible is lower than that of the SiC crucible, making it difficult for heat to be transferred from the bottom of the alumina crucible to the amorphous powder during firing. On the other hand, in the SiC crucible, the particle volume V of the magnetic powder tends to decrease as it approaches the center of the container part of the crucible. XRD This is thought to be because, in a SiC crucible, the temperature tends to rise more easily at a position closer to the center of the container portion of the crucible due to heat generated during crystallization.

[0318] Although the embodiments and modifications of the present disclosure have been specifically described above, the present disclosure is not limited to the above embodiments and modifications, and various modifications based on the technical concepts of the present disclosure are possible. For example, the configurations, methods, steps, shapes, materials, and numerical values ​​described in the above embodiments and modifications are merely examples, and different configurations, methods, steps, shapes, materials, and numerical values ​​may be used as necessary. The configurations, methods, steps, shapes, materials, and numerical values ​​of the above embodiments and modifications can be combined with each other as long as they do not deviate from the spirit of the present disclosure.

[0319] The chemical formulas of the compounds exemplified in the above embodiments and modifications are representative, and are not limited to the valences described, etc., as long as they are the general names of the same compounds. In the numerical ranges described in stages in the above embodiments and modifications, the upper or lower limit of a numerical range in one stage may be replaced with the upper or lower limit of a numerical range in another stage. Unless otherwise specified, the materials exemplified in the above embodiments and modifications can be used alone or in combination of two or more.

[0320] The present disclosure can also employ the following configurations. (1) A method for producing a magnetic powder, comprising: forming an amorphous body containing crystal nuclei; classifying the amorphous body; and firing the classified amorphous body to precipitate hexagonal ferrite particles. (2) The method for producing a magnetic powder according to (1), in which the classification removes amorphous bodies having a particle size of 300 μm or less. (3) The method for producing a magnetic powder according to (1), in which the classification separates the amorphous bodies into a plurality of groups based on particle size ranges, and removes the amorphous bodies in the group with the smallest particle size range among the plurality of groups. (4) The method for producing a magnetic powder according to any one of (1) to (3), in which the classification includes dry classification. (5) The method for producing a magnetic powder according to any one of (1) to (3), in which the classification includes sieve classification. (6) The method for producing a magnetic powder according to (5), wherein the sieve classification is carried out using a sieve with an opening of 300 μm or less. ３(8) The method for producing a magnetic powder according to any one of (1) to (6), wherein the coercive force of the hexagonal ferrite particles is 1,800 Oe or more. (9) The method for producing a magnetic powder according to any one of (1) to (8), wherein the half width at half maximum of a main peak of an SFD (Switching Field Distribution) curve of the hexagonal ferrite particles is 3,000 Oe or less. (10) The method for producing a magnetic powder according to any one of (1) to (7), wherein the coercive force of the hexagonal ferrite particles is 2,000 Oe or more and the half width at half maximum of a main peak of an SFD (Switching Field Distribution) curve of the hexagonal ferrite particles is 2,500 Oe or less. (11) The method for producing a magnetic powder according to any one of (1) to (10), wherein the hexagonal ferrite particles contain barium (Ba). (12) The method for producing a magnetic powder according to (11), wherein the hexagonal ferrite particles further contain strontium (Sr). (13) The method for producing a magnetic powder according to (12), wherein the average atomic ratio of the strontium (Sr) to the total amount of the barium (Ba) and the strontium (Sr) ((Sr / (Ba+Sr))) is 0.1 or more and less than 1. (14) The method for producing a magnetic powder according to any one of (11) to (13), wherein the hexagonal ferrite particles further contain at least one element selected from the group consisting of titanium (Ti), neodymium (Nd), aluminum (Al), tantalum (Ta), lanthanum (La), and cobalt (Co). (15) The method for producing a magnetic powder according to any one of (1) to (14), further comprising a step of pulverizing the amorphous body after the step of forming the amorphous body and before the step of classifying the amorphous body. (16) The method for producing a magnetic powder according to any one of (1) to (15), wherein in the sintering step, the classified amorphous body is placed in a sintering container, and the classified amorphous body is sintered in a state in which a spacer is disposed between a bottom surface of the sintering container and a bottom surface of a heating chamber of a heating furnace.(17) The method for producing a magnetic powder according to any one of (1) to (16), wherein in the firing step, the classified amorphous body is placed in a firing container and fired such that a temperature difference of the amorphous body in the firing container is 5°C or less. (18) The method for producing a magnetic powder according to any one of (1) to (17), wherein in the firing step, the classified amorphous body is placed in a firing container having a thermal conductivity of 60 W / m·K or more and fired. (19) A method for producing a magnetic recording medium, comprising: a step of forming an amorphous body containing crystal nuclei; a step of classifying the amorphous body; a step of firing the classified amorphous body to precipitate hexagonal ferrite particles; a step of preparing a coating material containing the hexagonal ferrite particles; and a step of preparing a magnetic layer using the coating material. (20) A method for producing a magnetic powder, comprising: a step of cooling a melt of a particle raw material to form an amorphous body, a step of classifying the amorphous body, and a step of firing the classified amorphous body to precipitate hexagonal ferrite particles. (21) A method for producing a magnetic recording medium, comprising: a step of cooling a melt of a particle raw material to form an amorphous body, a step of classifying the amorphous body, and a step of firing the classified amorphous body to precipitate hexagonal ferrite particles, a step of preparing a coating material containing the hexagonal ferrite particles, and a step of preparing a magnetic layer using the coating material.

[0321] 41 substrate 42 underlayer 43 magnetic layer 44 back layer 56 head unit 56A, 56B servo read head 61, 62 head 110 servo frame 111 servo subframe 1 112 servo subframe 2 113 servo stripe 111A A burst 111B B burst 112C C burst 112D D burst MT magnetic tape SB servo band DB data band Tk data track

Claims

forming an amorphous body containing crystal nuclei; classifying the amorphous body; a step of firing the classified amorphous body to precipitate hexagonal ferrite particles; Including, Method for manufacturing magnetic powder. 　 By the classification, the amorphous bodies having a particle size of 300 μm or less are removed. A method for producing the magnetic powder according to claim 1. 　 By the classification, the amorphous bodies are divided into a plurality of groups based on particle size ranges, and the amorphous bodies in the group with the smallest particle size range among the plurality of groups are removed. A method for producing the magnetic powder according to claim 1. 　 The classification includes dry classification. A method for producing the magnetic powder according to claim 1. 　 The classification includes sieve classification. A method for producing the magnetic powder according to claim 1. 　 The sieve classification is carried out using a sieve with an opening of 300 μm or less. The method for producing the magnetic powder according to claim 5 . 　 The particle volume of the hexagonal ferrite particles is 1400 nm ３ Below is the A method for producing the magnetic powder according to claim 1. 　 The coercive force of the hexagonal ferrite particles is 1800 Oe or more. A method for producing the magnetic powder according to claim 1. 　 the half-value width of the main peak of the SFD (Switching Field Distribution) curve of the hexagonal ferrite particles is 3000 Oe or less; A method for producing the magnetic powder according to claim 1. 　 The coercive force of the hexagonal ferrite particles is 2000 Oe or more. the half-value width of the main peak of the SFD (Switching Field Distribution) curve of the hexagonal ferrite particles is 2500 Oe or less; A method for producing the magnetic powder according to claim 1. 　 The hexagonal ferrite particles contain barium (Ba). A method for producing the magnetic powder according to claim 1. 　 The hexagonal ferrite particles further contain strontium (Sr). The method for producing the magnetic powder according to claim 11. 　 an average atomic ratio ((Sr / (Ba+Sr))) of the strontium (Sr) to the total amount of the barium (Ba) and the strontium (Sr) is 0.1 or more and less than 1; The method for producing the magnetic powder according to claim 12. 　 The hexagonal ferrite particles further contain at least one element selected from the group consisting of titanium (Ti), neodymium (Nd), aluminum (Al), tantalum (Ta), lanthanum (La), and cobalt (Co). The method for producing the magnetic powder according to claim 11. 　 The method further comprises a step of pulverizing the amorphous body after the step of forming the amorphous body and before the step of classifying the amorphous body. A method for producing the magnetic powder according to claim 1. 　 In the firing step, the classified amorphous body is placed in a firing container, and the classified amorphous body is fired in a state in which a spacer is disposed between a bottom surface of the firing container and a bottom surface of a heating chamber of a heating furnace. A method for producing the magnetic powder according to claim 1. 　 In the firing step, the classified amorphous body is placed in a firing container, and the classified amorphous body is fired in such a manner that the temperature difference of the amorphous body in the firing container is 5°C or less. A method for producing the magnetic powder according to claim 1. 　 In the firing step, the classified amorphous body is placed in a firing container having a thermal conductivity of 60 W / m K or more, and the classified amorphous body is fired. A method for producing the magnetic powder according to claim 1. 　 forming an amorphous body containing crystal nuclei; classifying the amorphous body; a step of firing the classified amorphous body to precipitate hexagonal ferrite particles; preparing a paint containing the hexagonal ferrite particles; a step of preparing a magnetic layer using the paint; Including, A method for manufacturing a magnetic recording medium. 　 cooling the melt of the particle raw material to form an amorphous body; classifying the amorphous body; a step of firing the classified amorphous body to precipitate hexagonal ferrite particles; Including, Method for manufacturing magnetic powder.

Images