JP6592042B2 - Magnetic tape - Google Patents

Description

  The present invention relates to a magnetic tape.

  There are two types of magnetic recording media, tape-shaped and disk-shaped. For data storage applications such as data backup, tape-shaped magnetic recording media, ie magnetic tape, are mainly used. In recent years, data transfer techniques for transmitting information at high speed have been remarkably developed, and it has become possible to transfer images and data having a large amount of information. Along with the development of this data transfer technology, magnetic tapes for recording, storing and reproducing information are being recorded at higher density. Accordingly, it is required to improve the electromagnetic conversion characteristics of the magnetic tape in order to reproduce information recorded at high density with high sensitivity (see, for example, Patent Document 1).

JP-A-11-31320

  Recording and / or reproduction of a signal on the magnetic tape is usually performed by causing the magnetic tape to travel in the drive and causing the magnetic tape surface (magnetic layer surface) and the magnetic head to contact and slide. For example, by repeatedly running the magnetic tape in the drive (hereinafter also simply referred to as “repeated running”), the signal recorded on the magnetic tape can be reproduced continuously or intermittently. In order to increase the reliability of the magnetic tape in the data storage application, it is desirable to suppress the deterioration of the electromagnetic conversion characteristics in such repeated running. This is because a magnetic tape with little deterioration in electromagnetic conversion characteristics during repeated running can continue to exhibit excellent electromagnetic conversion characteristics even when running continuously or intermittently in the drive.

  Furthermore, in order to increase the reliability of the magnetic tape in data storage applications, it is desirable to suppress the disappearance of part of the signal recorded on the magnetic tape during storage of the magnetic tape. For this purpose, it is desirable to suppress demagnetization during storage of the magnetic tape (generally referred to as “improving thermal stability”).

  As described above, it is desirable for a magnetic tape to improve electromagnetic conversion characteristics, suppress a decrease in electromagnetic conversion characteristics during repeated running, and improve thermal stability. On the other hand, for improving the performance of the magnetic recording medium, it has been conventionally proposed to adjust the magnetic characteristics such as the squareness ratio (see, for example, Patent Document 1).

  Incidentally, in the magnetic recording field, high density recording is desired in order to cope with an increase in the amount of information. In this regard, it is generally said that among the various ferromagnetic powders, the ferromagnetic hexagonal ferrite powder is suitable for high density recording. Therefore, the present inventor has repeatedly studied magnetic tapes containing ferromagnetic hexagonal ferrite powder in the magnetic layer. As a result of the adjustment of magnetic characteristics as previously proposed, improvement of electromagnetic conversion characteristics, electromagnetic conversion in repeated running, etc. It has become clear that it is not easy to achieve both suppression of deterioration of characteristics and improvement of thermal stability.

  Therefore, an object of the present invention is a magnetic tape containing a ferromagnetic hexagonal ferrite powder in a magnetic layer, which can exhibit excellent electromagnetic conversion characteristics and thermal stability, and decrease in electromagnetic conversion characteristics in repeated running. It is to provide a magnetic tape with a small amount.

One embodiment of the present invention provides:
A magnetic tape having a magnetic layer comprising a ferromagnetic powder and a binder on a non-magnetic support,
The ferromagnetic powder is a ferromagnetic hexagonal ferrite powder,
In a vibrating sample magnetometer, at least one of a vertical squareness ratio and a longitudinal squareness ratio obtained by a measurement performed by sweeping an external magnetic field on a magnetic tape in a range of magnetic field strength of −1197 kA / m to 1197 kA / m. A magnetic tape having a mold ratio of 0.70 or more and 1.00 or less, and A calculated by the following formula 1 is 5.0% or less.

(In Equation 1, n represents the number of measurement points performed in the range of -40 kA / m to 40 kA / m during the sweep, n = 52, and Mr (Hex) is the magnetization measured at the magnetic field strength Hex. (Μ represents an arithmetic average of Mr (Hex) obtained by measurement performed in the range of −40 kA / m to 40 kA / m of magnetic field intensity during the above sweep.)

Regarding the magnetic field strength, the conversion coefficient of the unit Oe (Oersted) to the SI unit A / m is 10 ³ / 4π. The range of −1197 kA / m to 1197 kA / m is synonymous with the range of −15 kAOe to 15 kOe, and the range of −40 kA / m to 40 kA / m is synonymous with the range of −500 Oe to 500 Oe. In addition, Mr (Hex) and μ adopt the same unit system. The unit of magnetization is A / m or J / (T · m ³ ) in the SI unit system.

In the present invention and the present specification, the measurement performed using the vibrating sample type magnetometer is performed at a measurement temperature of 24 ° C. ± 1 ° C. The sweep of the external magnetic field is performed by using the tape sample cut out from the magnetic tape to be measured according to the sweep condition shown in Table 2 to be described later, with the average number at each step = 1. By sweeping the external magnetic field in this way, a hysteresis curve (referred to as “MH curve”) is obtained in the range of −1197 kA / m to 1197 kA / m. Hereinafter, an MH curve obtained by measurement performed by placing the tape sample on the vibrating sample type magnetometer so that the application direction of the external magnetic field and the longitudinal direction of the tape sample are orthogonal to each other is referred to as “vertical MH curve”. " The MH curve obtained by the measurement performed by placing the tape sample on the vibrating sample magnetometer so that the application direction of the external magnetic field and the longitudinal direction of the tape sample are parallel to each other is referred to as “longitudinal MH curve”. Call. The longitudinal direction of the tape sample refers to the direction that was the longitudinal direction of the magnetic tape from which the tape sample was cut. The same applies to the width direction of the tape sample. The measurement value is obtained as a value obtained by subtracting the magnetization of the sample probe of the vibrating sample magnetometer as background noise. The squareness ratio is a squareness ratio without demagnetizing field correction. As a vibrating sample magnetometer (VSM), a known device such as a device used in an example described later can be used. In the tape sample, the saturation magnetization obtained from the MH curve thus obtained is in the range of 5 × 10 ⁻⁶ to 10 × 10 ⁻⁶ A · m ² (5 × 10 ⁻³ to 10 × 10 ⁻³ emu). The size and shape are not limited as long as saturation magnetization in this range can be obtained.

  In the present invention and this specification, the vertical squareness ratio is a squareness ratio measured in the vertical direction of the magnetic tape, and the vertical direction means a direction orthogonal to the longitudinal direction of the magnetic tape. The longitudinal squareness ratio is a squareness ratio measured in the longitudinal direction of the magnetic tape. The vertical squareness ratio is obtained from a vertical MH curve. The longitudinal squareness ratio is determined from the longitudinal MH curve. Further, in the present invention and the present specification, descriptions relating to directions and angles (for example, orthogonal) include a range of errors allowed in the technical field to which the present invention belongs. The range of the error means, for example, a range less than a strict angle ± 10 °, preferably within a strict angle ± 5 °, and more preferably within ± 3 °.

  In the present invention and the present specification, the “ferromagnetic hexagonal ferrite powder” means an aggregate of a plurality of ferromagnetic hexagonal ferrite particles. Hereinafter, the particles constituting the ferromagnetic hexagonal ferrite powder (ferromagnetic hexagonal ferrite particles) are also referred to as “hexagonal ferrite particles” or simply “particles”. The term “aggregation” is not limited to an aspect in which particles constituting the aggregation are in direct contact with each other, and an aspect in which a binder, an additive, and the like are interposed between particles is also included. The same applies to various powders such as the non-magnetic powder in the present invention and the present specification.

  In one embodiment, A is 1.5% or more and 5.0% or less.

  In one embodiment, A is 1.5% or more and 3.9% or less.

  In one embodiment, at least one of the perpendicular squareness ratio and the longitudinal squareness ratio of the magnetic layer is 0.75 or more and 1.00 or less.

  In one embodiment, the magnetic tape has a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer.

  In one aspect, the magnetic tape has a backcoat layer containing a nonmagnetic powder and a binder on the surface side opposite to the surface side having the magnetic layer of the nonmagnetic support.

  According to one aspect of the present invention, a magnetic tape containing ferromagnetic hexagonal ferrite powder in a magnetic layer, which can maintain excellent electromagnetic conversion characteristics during repeated running, and is excellent in thermal stability Can be provided.

The transmission electron microscope image of the particle | grains contained in the ferromagnetic hexagonal ferrite powder 1 used in the Example is shown. The transmission electron microscope image of the particle | grains contained in the ferromagnetic hexagonal ferrite powder 1 used in the Example is shown. 3 is a graph produced by taking X (ωt) measured for the particles shown in FIGS. 1 and 2 on the vertical axis and polar coordinates ωt on the horizontal axis. The hysteresis curve (MH curve) obtained about Example 2 and Comparative Example 6 is shown.

  One aspect of the present invention is a magnetic tape having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support, wherein the ferromagnetic powder is a ferromagnetic hexagonal ferrite powder, and a vibrating sample magnetometer At least one of the perpendicular squareness ratio and the longitudinal squareness ratio (hereinafter, referred to as “longitudinal squareness ratio”) obtained by a measurement performed by sweeping an external magnetic field on the magnetic tape in a range of magnetic field strength of −1197 kA / m to 1197 kA / m. It is simply referred to as “square ratio”.) Is 0.70 or more and 1.00 or less, and A calculated by the following formula 1 is 5.0% or less.

(In Equation 1, n represents the number of measurement points performed in the range of -40 kA / m to 40 kA / m during the sweep, n = 52, and Mr (Hex) is the magnetization measured at the magnetic field strength Hex. (Μ represents an arithmetic average of Mr (Hex) obtained by measurement performed in the range of −40 kA / m to 40 kA / m of magnetic field intensity during the above sweep.)

  The inventor of the present invention controls the magnetic characteristics obtained from the hysteresis curve (MH curve) obtained by sweeping the external magnetic field as described above, so that the magnetic tape containing the ferromagnetic hexagonal ferrite powder in the magnetic layer is controlled. It has been newly found that it is possible to improve electromagnetic conversion characteristics, suppress deterioration of electromagnetic conversion characteristics in repeated running, and improve thermal stability. The inventors' inference regarding the magnetic tape is described below.

The squareness ratio of the magnetic tape being 0.70 or more and 1.00 or less can mainly contribute to the magnetic tape being able to exhibit excellent electromagnetic conversion characteristics. In addition, this inventor has guessed that presence of the fine particle demonstrated below may interfere with an output improvement and may reduce an electromagnetic conversion characteristic.
However, the present inventor considers that the squareness ratio is usually a value greatly affected by the shape of the MH curve in the range of 40 kA / m to 1197 kA / m in the magnetic field strength in the MH curve. Yes. On the other hand, in order to obtain a magnetic tape that exhibits excellent thermal stability in addition to excellent electromagnetic conversion characteristics and has little deterioration in electromagnetic conversion characteristics during repeated running, the inventor of the MH curve It was considered that the magnetic characteristics affected by the shape of the MH curve in the range where the magnetic field strength is less than 40 kA / m should be controlled. This is because such a component that affects the magnetic characteristics is considered to cause a decrease in thermal stability and a decrease in electromagnetic conversion characteristics in repeated running. Specifically, the component that affects the magnetic characteristics is considered to be fine particles. Such fine particles are presumed to be generated by, for example, chipping of the ferromagnetic hexagonal ferrite powder partly due to the dispersion treatment in the preparation process of the magnetic layer forming composition. However, such fine particles cannot be magnetized by an external magnetic field and cannot contribute to recording, or even if they can be magnetized, recorded information tends to be lost due to so-called thermal fluctuation. The present inventors speculate that the presence of such fine particles causes a decrease in thermal stability. Furthermore, when the proportion of fine particles in the ferromagnetic hexagonal ferrite powder contained in the magnetic layer increases, organic substances such as binders and ferromagnetic hexagonal ferrite powders that are estimated to have lower strength than these organic substances The present inventor believes that the strength of the magnetic layer tends to decrease due to an increase in the interface with the particles. If the magnetic layer surface is scraped when the magnetic layer surface of the magnetic tape and the magnetic head slide during repeated running with the strength of the magnetic layer being lowered, the magnetic layer is caused by foreign matter generated by scraping and adhering to the magnetic head. This increases the spacing (spacing) between the surface and the magnetic head. This is considered to cause a decrease in output called so-called spacing loss, and as a result, the electromagnetic conversion characteristics are deteriorated in repeated running.
With regard to the above points, the present inventor repeatedly examined, and the value of A calculated by the above-described formula 1 has a correlation with the amount of fine particles in the magnetic layer, and the value of A is small. We thought that it showed that there were few fine particles. As a result of further studies, it has been newly found that by setting A to 5.0% or less, it is possible to improve thermal stability and / or suppress deterioration of electromagnetic conversion characteristics in repeated running. .
However, the present invention is not limited to the above estimation. Further, the present specification includes the inference of the present inventors such as the above description. The present invention is not limited to such inference.

  Hereinafter, the magnetic tape will be described in more detail.

[Square ratio]
The magnetic tape has a vertical squareness ratio and a longitudinal squareness ratio obtained by measurement performed by sweeping an external magnetic field in the range of magnetic field strength of −1197 kA / m to 1197 kA / m on the magnetic tape in a vibrating sample magnetometer. The squareness ratio of at least one of is 0.70 or more and 1.00 or less. The squareness ratio of at least one of the vertical squareness ratio and the longitudinal squareness ratio may be 0.70 or more and 1.00 or less. In one embodiment, the vertical squareness ratio is 0.70 or more and 1.00 or less, and the longitudinal squareness ratio is less than 0.70. In another aspect, the longitudinal squareness ratio is 0.70 or more and 1.00 or less, and the vertical squareness ratio is less than 0.70. In another embodiment, the vertical squareness ratio and the longitudinal squareness ratio are 0.70 or more and 1.00 or less. From the viewpoint of improving electromagnetic conversion characteristics, the higher the squareness ratio in the range of 0.70 to 1.00, the better. From this viewpoint, the squareness ratio in the range of 0.70 or more and 1.00 or less is preferably 0.75 or more, more preferably 0.80 or more, and 0.85 or more. Further preferred. The squareness ratio has a maximum value of 1.00 in principle. The squareness ratio in the range of 0.70 or more and 1.00 or less can be 0.98 or less, 0.95 or less, or 0.93 or less. However, since the squareness ratio is preferably as high as possible from the viewpoint of improving the electromagnetic conversion characteristics, it may exceed these exemplified upper limits. The squareness ratio can be controlled by, for example, the alignment conditions of the alignment treatment. Examples of the orientation conditions include the strength of the magnet used for the orientation treatment, the magnetic field application time, and the like. The vertical squareness ratio can be preferably controlled by performing a vertical alignment process and adjusting the alignment conditions of the vertical alignment process. The longitudinal squareness ratio can be preferably controlled by performing a longitudinal alignment treatment and adjusting the alignment conditions of the longitudinal alignment treatment.

[A calculated by Equation 1]
The magnetic tape is calculated by the following formula 1 using a measurement value obtained by a measurement performed by sweeping an external magnetic field on the magnetic tape in a vibration sample type magnetometer in a range of magnetic field strength of −1197 kA / m to 1197 kA / m. A is 5.0% or less.

  In Equation 1, n represents the number of measurement points performed in the range of the magnetic field intensity −40 kA / m to 40 kA / m during the sweep, n = 52, and Mr (Hex) is the amount of magnetization measured at the magnetic field intensity Hex. Μ represents an arithmetic average of Mr (Hex) obtained by measurement performed in the range of −40 kA / m to 40 kA / m of the magnetic field intensity during the sweep. For magnetic tapes with different vertical squareness ratios and longitudinal squareness ratios, the MH curve used to determine A is the MH curve obtained for the direction with the higher squareness ratio. That is, for a magnetic tape having a vertical squareness ratio greater than the longitudinal squareness ratio, A is obtained using the vertical MH curve. For a magnetic tape having a longitudinal squareness ratio greater than the vertical squareness ratio, A is determined using the longitudinal MH curve. For magnetic tapes having the same vertical squareness ratio and longitudinal squareness ratio, A is obtained using a vertical MH curve.

  With respect to A obtained by Equation 1, the present inventor has shown that A is a value that serves as an index of variation in the amount of magnetization in a magnetic field intensity range of −40 kA / m to 40 kA / m. It is considered that the proportion of the fine particles described above in the ferromagnetic hexagonal ferrite powder contained is small. On the other hand, the inventor believes that the squareness ratio is a value greatly influenced by the shape of the MH curve in the range of the magnetic field strength of 40 kA / m to 1197 kA / m. Therefore, it is considered that it is difficult to sufficiently control the magnetic characteristics of the magnetic tape affected by the fine particles only by the squareness ratio. On the other hand, as a result of intensive studies, the present inventor has come to control A obtained by the above equation 1. A smaller value of A is preferable because the proportion of the fine particles in the ferromagnetic hexagonal ferrite powder contained in the magnetic layer is considered to be small. In this respect, A is preferably 4.8% or less, more preferably 4.5% or less, further preferably 4.2% or less, and 4.0% or less. Is more preferable, and it is still more preferable that it is 3.9% or less, and it is still more preferable that it is 3.5% or less. Further, A can be, for example, 1.0% or more, 1.5% or more, 2.0% or more, or 2.5% or more. However, since it is preferable that the value is smaller, the above A may be lower than these exemplified lower limits. The present inventor believes that A can be reduced by suppressing the generation of fine particles (chipping) in the process of preparing the magnetic layer forming composition. Specific means for suppressing the generation (chipping) of the fine particles will be described later.

[Ferromagnetic hexagonal ferrite powder]
The magnetic layer of the magnetic tape contains ferromagnetic hexagonal ferrite powder. Regarding the ferromagnetic hexagonal ferrite powder, the crystal structure of hexagonal ferrite is known to be magnetoplumbite type (also called “M type”), W type, Y type and Z type. The ferromagnetic hexagonal ferrite powder contained in the magnetic layer may take any crystal structure. Further, the crystal structure of hexagonal ferrite includes iron atoms and divalent metal atoms as constituent atoms. The divalent metal atom is a metal atom that can be a divalent cation as an ion, and examples thereof include an alkaline earth metal atom such as a barium atom, a strontium atom, and a calcium atom, and a lead atom. For example, hexagonal ferrite containing barium atoms as divalent metal atoms is barium ferrite, and hexagonal ferrite containing strontium atoms is strontium ferrite. The hexagonal ferrite may be a mixed crystal of two or more kinds of hexagonal ferrite. As an example of the mixed crystal, a mixed crystal of barium ferrite and strontium ferrite can be given.

  Use of a ferromagnetic powder having a small average particle size as the ferromagnetic powder contained in the magnetic layer of the magnetic tape is preferable from the viewpoint of improving the recording density of the magnetic tape. In this respect, the average particle size of the ferromagnetic hexagonal ferrite powder is preferably 50 nm or less, more preferably 40 nm or less, further preferably 35 nm or less, and further preferably 30 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic hexagonal ferrite powder is preferably 10 nm or more, and more preferably 15 nm or more.

The average particle size of various powders in the present invention and the present specification is a value measured by the following method using a transmission electron microscope.
The powder is photographed at a photographing magnification of 100,000 using a transmission electron microscope. Using image analysis software, the contour of the particle is traced in the transmission electron microscope image obtained by the above photographing, and the size of the particle (primary particle) is measured. Primary particles refer to independent particles without agglomeration.
The above measurements are performed on 500 randomly extracted particles. The arithmetic average of the particle sizes of the 500 particles thus obtained is taken as the average particle size of the powder. As the transmission electron microscope, for example, JEM-2100 Plus manufactured by JEOL Ltd. can be used. The particle size can be measured using a known image analysis software such as ImageJ (National Institutes of Health, Open Source).
In the present invention and the present specification, the average particle size of the ferromagnetic hexagonal ferrite powder and other powders means the average particle size obtained by the above method unless otherwise specified. Measurement of the average particle size shown in Examples described later was performed using JEM-2100 Plus manufactured by JEOL as a transmission electron microscope and ImageJ as image analysis software.

In the present invention and the present specification, the size of the particles constituting the powder (hereinafter referred to as “particle size”) is the shape of the particles observed in the above-mentioned particle photograph.
(1) In the case of needle shape, spindle shape, columnar shape (however, the height is larger than the maximum major axis of the bottom surface), it is represented by the length of the major axis constituting the particle, that is, the major axis length,
(2) In the case of plate shape or columnar shape (thickness or height is smaller than the maximum major axis of the plate surface or bottom surface), it is represented by the maximum major axis of the plate surface or bottom surface,
(3) In the case of a spherical shape, a polyhedral shape, an unspecified shape, etc., and the major axis constituting the particle cannot be specified from the shape, it is represented by an equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.

The average acicular ratio of the powder is determined by measuring the length of the minor axis of the particle, that is, the minor axis length in the above measurement, and obtaining the value of (major axis length / minor axis length) of each particle. Refers to the arithmetic average of the values obtained for the particles. Here, the short axis length refers to the length of the short axis constituting the particle in the case of (1) in the definition of the particle size, and the thickness or the height in the case of (2), In the case of (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience.
And when the shape of the particle is specific, for example, in the case of definition (1) of the above particle size, the average particle size is the average major axis length, and in the case of definition (2), the average particle size is the average plate diameter. The average plate ratio is an arithmetic average of (maximum major axis / thickness or height). In the case of the same definition (3), the average particle size is an average diameter (also referred to as an average particle diameter or an average particle diameter).

  As a method of collecting sample powder such as ferromagnetic powder from the magnetic tape for particle size measurement, for example, the method described in paragraph 0015 of JP2011-048878A can be employed. The average particle size of the ferromagnetic hexagonal ferrite powder used in the preparation of the magnetic layer forming composition may be the same as or different from the average particle size of the ferromagnetic hexagonal ferrite powder contained in the magnetic layer. . Hereinafter, the ferromagnetic hexagonal ferrite powder used for preparing the composition for forming a magnetic layer is also referred to as “raw material powder”, and the hexagonal ferrite particles contained in the raw material powder are also referred to as “raw material particles” or simply “particles”.

  As the particle shape of the hexagonal ferrite particles contained in the ferromagnetic hexagonal ferrite powder, there has conventionally been a knowledge that a hexagonal plate shape is preferable. On the other hand, the inventor believes that the shape of the raw material particles contained in the raw material powder is preferably close to a disk shape when viewed in plan in the direction perpendicular to the easy axis direction. This is because the hexagonal ferrite particles having such a shape are unlikely to cause chipping in the dispersion treatment performed in the preparation process of the magnetic layer forming composition. From the viewpoint of suppressing the occurrence of chipping, the raw material powder used in the preparation of the magnetic layer forming composition has an arithmetic average of 30.0 T of 500 raw material particles calculated by the following formula 2 (unit:%). % Or less is preferable.

Each value in Equation 2 is determined using a transmission electron microscope image taken by the method described above for measuring the average particle size. However, the transmission electron microscope image described above regarding the measurement of the average particle size is taken without subjecting the powder to be photographed to orientation processing. On the other hand, the transmission electron microscope image for obtaining the above T is obtained by subjecting an imaging sample prepared using the raw material powder to be measured to an orientation process in the vertical direction (direction perpendicular to the horizontal plane). Shoot after shooting. From the viewpoint of facilitating observation of the particle shape of the hexagonal ferrite particles contained in the raw material powder to be measured, the photographing sample is preferably prepared by a method capable of suppressing particle aggregation. An example of such a preparation method will be described later in Examples. The magnetic field strength in the alignment treatment applied to the imaging sample is not limited. An example will be described later in Examples. By performing the orientation treatment in the vertical direction, a planar view image of the particles in the direction perpendicular to the easy magnetization axis can be taken using a transmission electron microscope. X (ωt) is the distance from the center of the circumscribed circle of the particle in the polar coordinate ωt direction to the contour (edge) of the particle, and X (ωt) is changed from 0 to 2πrad. Measured at a total of m points in the range of. m = 360, and the interval between the measurement points is 5.6 × 10 ⁻³ πrad. And ρ is an arithmetic average of X (ωt) measured at a total of m locations. The unit of X (ωt) and ρ may be any unit as long as it represents a distance. However, the unit of X (ωt) and ρ is the same unit. The T is preferably 30.0% or less, more preferably 25.0% or less, still more preferably 20.0% or less, and even more preferably 15.0% or less. Further, the T can be, for example, 5.0% or more. However, as the value of T is smaller, the shape of the raw material particles contained in the raw material powder is more preferable to be close to a disk shape. Therefore, T may be less than 5.0%.

  As a method for producing the ferromagnetic hexagonal ferrite powder, a glass crystallization method, a coprecipitation method, a reverse micelle method, a hydrothermal synthesis method, and the like are known. All of the above production methods are known. The particle shape of the raw material powder can be controlled by manufacturing conditions. As an example, the glass crystallization method will be described below. However, the raw material powder is not limited to those produced by the glass crystallization method.

A manufacturing process for manufacturing a ferromagnetic hexagonal ferrite powder by a glass crystallization method generally includes the following processes.
(1) A step of melting a raw material mixture containing a hexagonal ferrite forming component (optionally including a coercive force adjusting component) and a glass forming component to obtain a melt (melting step);
(2) A step of rapidly cooling the melt to obtain an amorphous body (amorphization step);
(3) A step of heat-treating the amorphous body to precipitate hexagonal ferrite particles (crystallization step);
(4) A step of collecting hexagonal ferrite particles precipitated from the heat-treated product (particle collection step).

One means for obtaining a raw material powder containing particles having the preferred particle shape described above is to adjust the composition of the raw material mixture. As described above, the raw material mixture used in the glass crystallization method includes a hexagonal ferrite forming component (optionally including a coercive force adjusting component) and a glass forming component. Here, the glass-forming component is a component that exhibits a glass transition phenomenon and can be made amorphous (vitrified), and a B ₂ O ₃ component is used in a normal glass crystallization method. In addition, each component contained in the raw material mixture in the glass crystallization method exists as an oxide or various salts that can be converted into an oxide in a process such as melting. For example, “B ₂ O ₃ component” includes B ₂ O ₃ itself and various salts such as H ₃ BO _{3 that} can be changed to B ₂ O ₃ during the process. The same applies to the other components described below. In addition, the composition of the raw material mixture described below is shown as a composition in terms of oxide. Examples of the glass forming component other than the B ₂ O ₃ component include a SiO ₂ component, a P ₂ O ₅ component, a GeO ₂ component, and an Al ₂ O ₃ component.

The hexagonal ferrite forming component contained in the raw material mixture is a component that is a constituent component of hexagonal ferrite particles, and includes metal oxides such as Fe ₂ O ₃ , BaO, SrO, and PbO. For example, barium ferrite can be obtained by using a BaO component as the main component of the hexagonal ferrite forming component.

  Hexagonal ferrite particles can also be obtained in which part of Fe is replaced by another metal element for coercive force adjustment. JP, 2014-192256, A paragraph 0022 can be referred to for a coercive force adjustment component containing a substitution element.

Regarding the particle shape control, the higher the content of the hexagonal ferrite-forming component (for example, Fe ₂ O ₃ component) in the raw material mixture, the higher the shape of the raw material particles in a plan view is observed. It is also preferable to use a raw material mixture containing an Al ₂ O ₃ component in order to obtain raw material particles whose plan view shape is close to a disk shape. When using a material containing an Al ₂ O ₃ component as the raw material mixture, the higher the content of the Al ₂ O ₃ component in the raw material mixture, the more the shape of the raw material particles tends to be closer to a disk shape. .
From the above points, regarding the composition of the raw material mixture, the content of the Fe ₂ O ₃ component in the raw material mixture (wherein the Fe ₂ O ₃ component may be partially replaced by a coercive force adjusting component) is as follows. The total amount of the raw material mixture is preferably 20.0 mol% or more, more preferably 25.0 mol% or more, and further preferably 30.0 mol% or more. The content of the _Fe 2 _{O 3} component can be, for example, 50.0 mol% or less. However, it may exceed 50.0 mol%. On the other hand, the content of the Al ₂ O ₃ component in the raw material mixture is preferably 0.5 mol% or more, more preferably 1.0 mol% or more with respect to 100 mol% of the total amount of the raw material mixture, It is further preferably 2.0 mol% or more, more preferably 3.0 mol% or more, and even more preferably 4.0 mol% or more. The content of the _Al 2 _{O 3} component can be, for example, 10.0 mol% or less. However, it may exceed 10.0 mol%. The raw material particles thus obtained can contain, for example, about 1.5 to 20.0 atomic percent of Al with respect to Fe.

  Further, as one of means for obtaining the raw material powder containing the particles having the preferred particle shape described above, in the production process of producing the ferromagnetic hexagonal ferrite powder by the glass crystallization method, the ferromagnetic hexagonal ferrite particles Therefore, it is also possible to perform a process of removing a portion that is easily chipped. For example, even if the shape of the particles obtained in the particle collection step (step (4) described above) of the glass crystallization method is a shape in which T calculated by the above formula 2 exceeds 30.0% By removing a portion that is easily chipped such as a corner from particles having such a shape, particles having T of 30.0% or less can be obtained. Therefore, in the case of performing a treatment for removing a portion that tends to be chipped from the ferromagnetic hexagonal ferrite particles, even if a raw material mixture having a composition deviating from the above-described composition is used as a preferred composition for particle shape control, the above formula 2 Thus, a ferromagnetic hexagonal ferrite powder having an arithmetic average of 500 particles of T calculated by the following can be easily obtained.

A specific embodiment of the treatment for removing a portion that is easily chipped from the ferromagnetic hexagonal ferrite particles will be described below.
The manufacturing process for manufacturing the ferromagnetic hexagonal ferrite powder by the glass crystallization method includes the steps (1) to (4) described above. The heat-treated product obtained in the crystallization step of step (3) usually contains a glass component together with ferromagnetic hexagonal ferrite particles. In the particle collection step of step (4), ferromagnetic hexagonal ferrite particles can be obtained by removing the glass component from the heat-treated product. The removal of the glass component can be performed by various treatments generally performed by a glass crystallization method such as acid treatment under heating. By subjecting the particles obtained by removing the glass component to a treatment similar to the dispersion treatment performed in the magnetic layer forming composition preparation step, there is a possibility of lacking in the magnetic layer forming composition preparation step. The portion, that is, the portion that can cause generation of fine particles by chipping can be removed or reduced. An example of such treatment is bead dispersion. Bead dispersion is a dispersion process using beads (dispersed beads) as a dispersion medium. In the bead dispersion, a dispersion liquid can be obtained by dispersing a solution containing particles to be dispersed and dispersed beads with a disperser. As a disperser, for example, a sand mill can be used. The filling rate of the dispersed beads in the disperser is preferably about 30 to 80% by volume, the rotation speed in the disperser is preferably about 1000 to 3000 rpm (revolution per minute), and the dispersion time (dispersion time) The residence time in the apparatus is preferably 60 to 360 minutes. The bead diameter of the dispersed beads is preferably about 0.03 to 1.0 mm. Further, as the dispersed beads, zirconia beads are preferable.
Thereafter, by subjecting the dispersion obtained by the above dispersion treatment to, for example, a centrifugal separation treatment, fine particles generated by part of the particles being lost by the dispersion treatment can be removed. Thereafter, through a drying treatment, a ferromagnetic hexagonal ferrite powder having an arithmetic average of 500 T particles calculated by the above formula 2 of 30.0% or less can be obtained.

  For the details regarding other glass crystallization methods, known techniques can be applied without any limitation. For details of each of the above steps in the glass crystallization method, reference can be made to, for example, paragraphs 0018 to 0029 of JP2014-192256A, paragraphs 0011 to 0025 of JP2010-24113A, and the like.

  However, the ferromagnetic hexagonal ferrite powder contained in the magnetic layer of the magnetic tape is not limited to those produced by the glass crystallization method. For example, the ferromagnetic hexagonal ferrite powder contained in the magnetic layer of the magnetic tape can be produced by a hydrothermal synthesis method. For the hydrothermal synthesis method, reference can be made, for example, to paragraphs 0037 to 0103 of JP-A No. 2015-201246 and the description of Examples in the publication.

  Hereinafter, the magnetic tape will be described in more detail.

[Magnetic layer]
<Ferromagnetic powder>
The ferromagnetic powder contained in the magnetic layer is as described above. The content (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass. Components other than the ferromagnetic powder of the magnetic layer are at least a binder, and optionally one or more additives may be included. A high filling rate of the ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving the recording density.

<Binder, curing agent>
The magnetic layer of the magnetic tape contains a binder together with ferromagnetic powder. A binder is one or more resins. The resin may be a homopolymer or a copolymer. As binders contained in the magnetic layer, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, styrene, acrylonitrile, acrylic resin copolymerized with methyl methacrylate, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, Those selected from polyvinyl alkylal resins such as polyvinyl acetal and polyvinyl butyral can be used alone, or a plurality of resins can be mixed and used. Among these, preferred are polyurethane resin, acrylic resin, cellulose resin and vinyl chloride resin. These resins can also be used as a binder in the nonmagnetic layer and / or backcoat layer described below. As for the above binder, paragraphs 0029 to 0031 of JP2010-24113A can be referred to. The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less as the weight average molecular weight. The weight average molecular weight in the present invention and the present specification is a value obtained by converting a value measured by gel permeation chromatography (GPC) into polystyrene. The following conditions can be mentioned as measurement conditions. The weight average molecular weight shown in the Examples described later is a value obtained by converting a value measured under the following measurement conditions into polystyrene.
GPC device: HLC-8120 (manufactured by Tosoh Corporation)
Column: TSK gel Multipore HXL-M (Tosoh Corporation, 7.8 mm ID (Inner Diameter) × 30.0 cm)
Eluent: Tetrahydrofuran (THF)

  Further, when forming the magnetic layer, a curing agent can be used together with the resin that can be used as the binder. In one aspect, the curing agent can be a thermosetting compound that is a compound that undergoes a curing reaction (crosslinking reaction) by heating, and in another aspect, photocuring in which a curing reaction (crosslinking reaction) proceeds by light irradiation. It can be a sex compound. The curing agent may be included in the magnetic layer in a state of being reacted (crosslinked) with other components such as a binder as the curing reaction proceeds in the magnetic tape manufacturing process. A preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. JP, 2011-216149, A paragraphs 0124-0125 can be referred to for the details of polyisocyanate. The curing agent is, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder in the composition for forming a magnetic layer, and preferably 50.0 to 80. It can be added and used in an amount of 0 parts by weight.

<Additives>
The magnetic layer can contain one or more additives as required. One example of the additive is the above-described curing agent. Additives that can be included in the magnetic layer include non-magnetic powders (for example, abrasives or protrusion-forming agents that can form protrusions that can contribute to controlling friction characteristics on the magnetic layer surface), lubricants, dispersants, dispersion aids. Agents, antifungal agents, antistatic agents, antioxidants, carbon black and the like. As the additive, a commercially available product or one produced by a known method can be appropriately selected and used depending on the desired properties. As an example, preferable dispersants include compounds containing a polyalkyleneimine chain and a polyester chain described in, for example, JP-A-2015-28830. For details of such compounds, reference can be made to paragraphs 0026 to 0071 of JP-A-2015-28830 and the description of Examples in the publication. However, the said compound is an example and can use well-known various additives as an additive.

[Nonmagnetic layer]
Next, the nonmagnetic layer will be described.
The magnetic tape may have a magnetic layer directly on the surface of the nonmagnetic support, and a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. Also good. The nonmagnetic powder contained in the nonmagnetic layer may be an inorganic powder or an organic powder. Carbon black or the like can also be used. Examples of the inorganic powder include powders of metal, metal oxide, metal carbonate, metal sulfate, metal nitride, metal carbide, metal sulfide, and the like. These nonmagnetic powders are available as commercial products, and can also be produced by a known method. Details thereof can be referred to paragraphs 0036 to 0039 of JP 2010-24113 A. The content (filling rate) of the nonmagnetic powder in the nonmagnetic layer is preferably in the range of 50 to 90 mass%, more preferably in the range of 60 to 90 mass%.

  For other details such as binders and additives for the nonmagnetic layer, known techniques relating to the nonmagnetic layer can be applied. Further, for example, with respect to the type and content of the binder, the type and content of the additive, etc., known techniques relating to the magnetic layer can be applied.

  The nonmagnetic layer of the present invention and the present specification shall include a substantially nonmagnetic layer containing a small amount of ferromagnetic powder together with the nonmagnetic powder, for example, as an impurity or intentionally. Here, the substantially non-magnetic layer means that the residual magnetic flux density of this layer is 10 mT or less, the coercive force is 7.96 kA / m (100 Oe) or less, or the residual magnetic flux density is 10 mT or less. And a layer having a coercive force of 7.96 kA / m (100 Oe) or less. The nonmagnetic layer preferably has no residual magnetic flux density and no coercive force.

[Non-magnetic support]
Nonmagnetic supports (hereinafter also simply referred to as “supports”) are known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide (eg, aramid). Is mentioned. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable. These supports may be subjected in advance to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like.

[Back coat layer]
The magnetic tape may have a backcoat layer containing a nonmagnetic powder and a binder on the surface side opposite to the surface side having the magnetic layer of the nonmagnetic support. The back coat layer preferably contains one or both of carbon black and inorganic powder. For the binder contained in the backcoat layer and various additives that can optionally be contained, known techniques relating to the formulation of the magnetic layer and / or the nonmagnetic layer can be applied.

[Various thicknesses]
Regarding the thickness of the nonmagnetic support and each layer of the magnetic tape, the thickness of the nonmagnetic support is preferably 3.00 to 6.00 μm, more preferably 3.00 to 4.50 μm.
The thickness of the magnetic layer can be optimized according to the saturation magnetization of the magnetic head used, the head gap length, the band of the recording signal, and the like. The thickness of the magnetic layer is generally 10 nm to 150 nm, preferably 20 nm to 120 nm, more preferably 30 nm to 100 nm, from the viewpoint of high density recording. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied. The thickness of the magnetic layer when separating into two or more layers is the total thickness of these layers.
The thickness of the nonmagnetic layer is, for example, 0.01 to 3.00 μm, preferably 0.05 to 2.00 μm, and more preferably 0.05 to 1.50 μm.
The thickness of the back coat layer is preferably 0.90 μm or less, and more preferably 0.10 to 0.70 μm.

  The thickness of each layer of the magnetic tape and the nonmagnetic support can be determined by a known film thickness measurement method. As an example, for example, after a cross section in the thickness direction of the magnetic tape is exposed by a known method such as an ion beam or a microtome, the exposed cross section is observed with a scanning electron microscope. Various thicknesses can be obtained as an arithmetic average of thicknesses obtained at one location in the thickness direction in cross-sectional observation, or at two or more locations randomly extracted, for example, at two locations. Alternatively, the thickness of each layer may be determined as a design thickness calculated from manufacturing conditions.

[Magnetic tape manufacturing process]
The process for producing a composition for forming a magnetic layer, a nonmagnetic layer or a backcoat layer usually includes at least a kneading process, a dispersing process, and a mixing process provided before and after these processes. Each process may be divided into two or more stages. Various components may be added at the beginning or middle of any step. Individual components may be divided and added in two or more steps. For example, the binder may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to manufacture the magnetic recording medium, a conventionally known manufacturing technique can be used for some or all of the processes. In the kneading step, it is preferable to use a material having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. JP-A-1-106338 and JP-A-1-79274 can be referred to for details of these kneading treatments. Further, in order to disperse the composition for forming each layer, glass beads can be used as the dispersed beads. Further, as the dispersed beads, zirconia beads, titania beads, and steel beads, which are high specific gravity dispersed beads, are also suitable. The particle diameter (bead diameter) and filling rate of these dispersed beads can be optimized and used. A well-known thing can be used for a disperser.

In the process of preparing the composition for forming a magnetic layer, a magnetic liquid containing a ferromagnetic hexagonal ferrite powder, a binder, and a solvent (however, containing substantially no abrasive), an abrasive and a solvent are included. The abrasive liquid is preferably prepared in separate steps. Thus, the dispersibility of the ferromagnetic hexagonal ferrite powder in the magnetic layer forming composition can be improved by separately dispersing the ferromagnetic hexagonal ferrite powder and the abrasive after mixing. The above “substantially free of abrasive” means that it is not added as a component of the magnetic liquid, and it is acceptable that a trace amount of abrasive is present as an unintentionally mixed impurity. Shall be. The abrasive refers to a nonmagnetic powder having a Mohs hardness of more than 8 and is preferably a nonmagnetic powder having a Mohs hardness of 9 or more. The maximum Mohs hardness is 10 for diamond. Specifically, examples of the abrasive include powders such as alumina (Al ₂ O ₃ ), silicon carbide, boron carbide (B ₄ C), TiC, cerium oxide, zirconium oxide (ZrO ₂ ), and diamond. Of these, alumina powder is preferred. Regarding the particle size of the abrasive, the BET (Brunauer-Emmett-Teller) specific surface area, which is an index of particle size, is, for example, 14 m ² / g or more, preferably 16 m ² / g or more, more preferably 18 m ² / g. That's it. Moreover, the BET specific surface area of an abrasive | polishing agent can be 40 m < ² > / g or less, for example. The BET specific surface area is a specific surface area measured for primary particles by the BET method.

  The magnetic liquid preparation process preferably includes one or more dispersion treatments. High dispersibility of the ferromagnetic hexagonal ferrite powder in the magnetic layer is preferable for increasing the squareness ratio by the orientation treatment. For this purpose, it is preferable to increase the dispersibility of the ferromagnetic hexagonal ferrite powder in the magnetic liquid by a dispersion treatment. From the viewpoint of improving the dispersibility, it is preferable to perform a dispersion process using at least a dispersion medium as the dispersion process of the magnetic liquid. Dispersion treatment using a dispersion medium is generally stronger in magnetic liquids because it has a higher strength to break up the aggregation of ferromagnetic hexagonal ferrite powder particles than dispersion treatment without dispersion media (for example, ultrasonic dispersion). This is because it is effective in improving the dispersibility of the magnetic hexagonal ferrite powder. However, the chipping of the ferromagnetic hexagonal ferrite powder particles caused by the dispersion treatment generates fine particles that are considered to be a factor that increases A calculated by Equation 1. As a result, a decrease in thermal stability and / or a decrease in electromagnetic conversion characteristics in repeated running occurs. Therefore, the dispersion treatment of the magnetic liquid is preferably performed so as to reduce the damage given to the particles of the ferromagnetic hexagonal ferrite powder, but to flocculate the particles. From the above points, a preferable dispersion treatment is bead dispersion. Further, the bead dispersion is such that E calculated by the following formula 3 is 10000 nJ or less and W calculated by the following formula 4 is 1.0 J · min. 30.0 J · min. It is particularly preferable to carry out under the following conditions.

In Formula 3, the unit of E is nJ, a represents the total mass (unit: g) of the beads used for bead dispersion, and v is the motion speed of the beads during bead dispersion (unit: m / sec.). Represents. As the bead movement speed v, for example, the value of the linear velocity at the outermost periphery of the rotor calculated from the rotor radius of the disperser and the rotor rotational speed set in the disperser can be applied.
In Equation 4, E is obtained from Equation 3. The unit of W is J · min. And b represents the number of beads used per 1 cm ³ of the magnetic liquid in bead dispersion, and is also referred to as a bead number density (unit: pieces / cm ³ ) below. t represents the dispersion time (unit: min.) of bead dispersion.

A larger E calculated by Equation 3 means that the collision energy of the dispersed beads is larger. It is preferable that E is 10000 nJ or less from the viewpoint of suppressing occurrence of chipping in the raw material particles due to collision with the dispersed beads. The E is preferably 7000 nJ or less, more preferably 5000 nJ or less, still more preferably 3000 nJ or less, still more preferably 2000 nJ or less, and even more preferably 1000 nJ or less. , 500 nJ or less is even more preferable, and 100 nJ or less is even more preferable. The E can be, for example, 20 nJ or more or 30 nJ or more. However, it may be lower than the exemplified lower limit.
On the other hand, the W calculated by Expression 4 is 30.0 J · min. The following also means that the collision energy of the dispersed beads is not too high, which is preferable from the viewpoint of suppressing chipping. The W is 20.0 J · min. More preferably, it is 15.0 J · min. More preferably, it is 10.0 J · min. More preferably, it is as follows. The W is 1.0 J · min. The above is preferable for enhancing the dispersibility of the ferromagnetic hexagonal ferrite powder in the magnetic liquid. The above W is 2.0 J · min. Or more, preferably 3.0 J · min. More preferably, it is 5.0 J · min. It is still more preferable that it is above.

Regarding the dispersed beads used for dispersing the beads of the magnetic liquid, the density of the dispersed beads is preferably more than 3.7 g / cm ^{3, and} more preferably 3.8 g / cm ³ or more. Further, the density of the dispersed beads is, for example, 7.0 g / cm ³ or less, or may be more than 7.0 g / cm ³ . Here, the density is obtained by dividing the mass of the dispersed beads (unit: g) by the volume of the dispersed beads (unit: cm ³ ). The measurement is performed by the Archimedes method. As the dispersed beads, it is preferable to use zirconia, alumina, or stainless steel beads alone, or a mixture of two or more of these. The dispersed beads used for dispersing the magnetic liquid beads preferably have a bead diameter in the range of 0.01 to 0.50 mm. The bead diameter is a value measured by the same method as the method for measuring the average particle size of the powder described above for the dispersed beads used for the dispersion treatment. The filling rate of the dispersed beads in the disperser can be, for example, 30 to 80% by volume, preferably 50 to 80% by volume, based on the volume. The dispersion time (retention time in the disperser) is preferably 10 to 180 minutes, and more preferably 10 to 120 minutes.

  A magnetic layer-forming composition can be prepared by mixing the magnetic liquid after beads dispersion with other components as necessary, and then simultaneously or sequentially mixing with other components such as an abrasive liquid. . With respect to other details such as the preparation of the abrasive liquid, known techniques relating to the preparation of the magnetic layer forming composition can be applied without any limitation.

  For other details of the method for manufacturing the magnetic recording medium, reference can also be made to paragraphs 0051 to 0057 of JP 2010-24113 A, for example. For example, with respect to the alignment treatment, reference can be made to paragraph 0052 of JP2010-24113A.

  The magnetic tape is a magnetic tape containing ferromagnetic hexagonal ferrite powder in the magnetic layer, can exhibit excellent electromagnetic conversion characteristics, can suppress the electromagnetic conversion characteristics in repeated running, and is excellent. Thermal stability can also be shown.

Hereinafter, the present invention will be described based on examples. However, this invention is not limited to the aspect shown in the Example. Unless otherwise specified, “parts” and “%” described below indicate “parts by mass” and “% by mass”.
Unless otherwise specified, the following processes and evaluations were performed in a room temperature (20 to 25 ° C.) environment.

[Preparation example of ferromagnetic hexagonal ferrite powder (preparation of ferromagnetic hexagonal ferrite powders 1 to 5)]
So that the raw material compositions shown in Table 1 in terms of _oxide, B 2 _{O 3} component _{(H 3 BO 3), Al} 2 O 3 component _{(Al (OH) 3),} BaO component _(BaCO 3), _Fe 2 O ₃ and a predetermined amount of Ta ₂ O ₅ corresponding to element Ta for substituting Fe and adjusting the coercive force were weighed and mixed in a mixer to prepare a raw material mixture. The prepared raw material mixture was charged into a platinum crucible having a capacity of 2 L, and after melting, the melt was continuously poured onto a water-cooled roll and cooled with a water-cooled roll to obtain an amorphous body.
600 g of the obtained amorphous body was charged into an electric furnace, heated to the temperature shown in Table 1 (crystallization temperature) over 3 hours, and kept at the same temperature for 5 hours to crystallize hexagonal ferrite.
Next, the crystallized product containing hexagonal ferrite was coarsely pulverized in a mortar, placed in a 3 L pot mill, and pulverized in a ball mill for 4 hours together with 5 kg of 5 mm diameter ZrO ₂ balls and 1.2 kg of pure water. Thereafter, the pulverized liquid was separated from the ZrO ₂ balls and placed in a stainless beaker having a capacity of 5 L. The pulverized liquid was added to an 8% by mass acetic acid solution and kept at a liquid temperature of 85 ° C. for 2 hours, and then decantation washing was repeated to remove unnecessary glass components, followed by drying to obtain a powder. The obtained powder was subjected to X-ray diffraction analysis and confirmed to have a hexagonal ferrite crystal structure. In this way, ferromagnetic hexagonal ferrite powders (ferromagnetic hexagonal barium ferrite powders) 1 to 5 were obtained.

[Preparation Example of Ferromagnetic Hexagonal Ferrite Powder (Preparation of Ferromagnetic Hexagonal Ferrite Powder 6)]
So that the raw material compositions shown in Table 1 in terms of _oxide, B 2 _{O 3} component _{(H 3 BO 3), Al} 2 O 3 component _{(Al (OH) 3),} BaO component _(BaCO 3), _Fe 2 O ₃ and a predetermined amount of Ta ₂ O ₅ corresponding to element Ta for substituting Fe and adjusting the coercive force were weighed and mixed in a mixer to prepare a raw material mixture. The prepared raw material mixture was charged into a platinum crucible having a capacity of 2 L, and after melting, the melt was continuously poured onto a water-cooled roll and cooled with a water-cooled roll to obtain an amorphous body.
600 g of the obtained amorphous body was charged into an electric furnace, heated to the temperature shown in Table 1 (crystallization temperature) over 3 hours, and kept at the same temperature for 5 hours to crystallize hexagonal ferrite.
Next, the crystallized product containing hexagonal ferrite was coarsely pulverized in a mortar, placed in a 3 L pot mill, and pulverized in a ball mill for 4 hours together with 5 kg of 5 mm diameter ZrO ₂ balls and 1.2 kg of pure water. Thereafter, the pulverized liquid was separated from the ZrO ₂ balls and placed in a stainless beaker having a capacity of 5 L. The crushed liquid was added to an 8% by mass acetic acid solution and kept at a liquid temperature of 85 ° C. for 2 hours, and then decantation washing was repeated to remove unnecessary glass components. The washed solution is passed through a horizontal sand mill (bead filling rate: 50% by volume, dispersed beads: zirconia beads having a bead diameter of 0.5 mm) with a pump, and dispersed for 180 minutes at a rotational speed of 2000 rpm (bead dispersion). Went. The dispersion obtained by the bead dispersion was subjected to a centrifugal separation process to remove fine particles generated in the bead dispersion and then dried to obtain a powder. The obtained powder was subjected to X-ray diffraction analysis and confirmed to have a hexagonal ferrite crystal structure. In this way, a ferromagnetic hexagonal ferrite powder (ferromagnetic hexagonal barium ferrite powder) 6 was obtained.

[Evaluation of ferromagnetic hexagonal ferrite powder]
(1) Average particle size The average particle size of the ferromagnetic hexagonal ferrite powders 1 to 6 was determined by the method described above.

(2) T calculated by Equation 2
With respect to the ferromagnetic hexagonal ferrite powders 1 to 6, T calculated by Equation 2 was determined by the following method.
Ferromagnetic hexagonal ferrite powder (powder to be photographed) is put into pure water and subjected to ultrasonic dispersion (ultrasonic treatment device: UIS250V manufactured by Heelscher, operating conditions of ultrasonic treatment device: intermittent operation (frequency 0.5 kHz operation) Then, the suspension was stopped for 0.5 seconds) and repeated for 6 hours to prepare a dispersion (solid content concentration 0.01%).
Acetic acid was added to the prepared dispersion so that the concentration of acetic acid in the dispersion was 1%. Thereafter, the dispersion was ultrasonically dispersed using the same apparatus and the same operating conditions as described above.
Gelatin was added to the dispersion after ultrasonic dispersion so that the gelatin concentration was 0.03%.
The sample solution prepared by the above method is dropped on a grid mesh (mesh sample pan), and an external magnetic field of 478 kA / m (6 kOe) is applied in a direction perpendicular to the horizontal plane (that is, orientation treatment in the vertical direction). The sample for photography was obtained by drying.
The photographing sample was photographed at a magnification of 100,000 using a transmission electron microscope (JEM-2100 Plus manufactured by JEOL Ltd.) to obtain a transmission electron microscope image.
Using the obtained transmission electron microscope image, various values for calculating T by Equation 2 were obtained. As an example, FIGS. 1 and 2 show transmission electron microscope images of particles contained in the ferromagnetic hexagonal ferrite powder 1. In FIG. 2, a circumscribed circle, a center C of the circumscribed circle, and lines for explanation in the polar coordinate ωt direction are added to the transmission electron microscope image of the particle shown in FIG. The measurement location m = 360, and the interval between the measurement locations is 5.6 × 10 ⁻³ πrad. It was. FIG. 3 is a graph prepared by taking X (ωt) measured for the particles shown in FIGS. 1 and 2 on the vertical axis and polar coordinates ωt on the horizontal axis. T was calculated | required as an arithmetic average of the value obtained by performing such a measurement about each of 500 particles about the ferromagnetic hexagonal ferrite powders 1-5.

  The results are shown in Table 1.

[Example 1]
1. Preparation of Alumina Dispersion (Abrasive Liquid) About 100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) having an alpha conversion rate of about 65% and a BET specific surface area of 20 m ² / g, 3.0 parts of 2, A 32-% solution of 3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd.) and a polyester polyurethane resin having a SO ₃ Na group as a polar group (UR-4800 manufactured by Toyobo Co., Ltd. (polar group amount: 80 meq / kg)) (solvents are methyl ethyl ketone and toluene) 31.3 parts) and 570.0 parts of a mixed solution of methyl ethyl ketone and cyclohexanone 1: 1 (mass ratio) as a solvent were mixed and dispersed in a paint shaker for 5 hours in the presence of zirconia beads. After dispersion, the dispersion and beads were separated with a mesh to obtain an alumina dispersion.

2. Formulation of magnetic layer forming composition (magnetic liquid)
Ferromagnetic hexagonal ferrite powder 1 100.0 parts SO ₃ Na group-containing vinyl chloride copolymer 10.0 parts Weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g
SO ₃ Na group-containing polyurethane resin 4.0 parts Weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g
Polyalkyleneimine derivative (J-2) obtained by the method described in Synthesis Example 22 described in JP-A-2015-28830 10.0 parts cyclohexanone 150.0 parts methyl ethyl ketone 170.0 parts (polishing liquid)
Above 1. 6.0 parts (silica sol) of alumina dispersion prepared in
Colloidal silica 2.0 parts Average particle size: 100 nm
(Other ingredients)
Stearic acid 2.0 parts Butyl stearate 6.0 parts Polyisocyanate (Tosoh Coronate (registered trademark)) 2.5 parts (finishing additive solvent)
Cyclohexanone 300.0 parts Methyl ethyl ketone 140.0 parts

3. Formulation of composition for forming nonmagnetic layer Carbon black 100.0 parts Average particle size: 20 nm
SO ₃ Na group-containing vinyl chloride copolymer 10.0 parts Weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g
SO ₃ Na group-containing polyurethane resin 4.0 parts Weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g
Trioctylamine 5.0 parts Stearic acid 2.0 parts Butyl stearate 2.0 parts Cyclohexanone 450.0 parts Methyl ethyl ketone 450.0 parts

4). Formulation of composition for forming backcoat layer Nonmagnetic inorganic powder: 80.0 parts of α-iron oxide Average particle size (average major axis length): 0.15 μm, average needle ratio: 7, BET specific surface area: 52 m ² / g
Carbon black 20.0 parts Average particle size: 20 nm
Vinyl chloride copolymer 13.0 parts Polysulfonate resin containing sulfonate group 6.0 parts Phenylphosphonic acid 3.0 parts Cyclohexanone 355.0 parts Methyl ethyl ketone 155.0 parts Stearic acid 3.0 parts Butyl stearate 3.0 parts Poly Isocyanate 5.0 parts

5. Preparation of Composition for Forming Each Layer A composition for forming a magnetic layer was prepared by the following method.
Each component of the magnetic liquid was mixed using a homogenizer, and then beads were dispersed using a continuous horizontal bead mill. Table 3 shows processing conditions for bead dispersion. The bead movement speed v during bead dispersion shown in Table 3 is a linear velocity at the outermost periphery of the rotor calculated from the rotor radius of the bead mill and the rotor rotational speed set in the bead mill.
Using the above bead mill, the prepared magnetic liquid is mixed with the above-mentioned abrasive liquid and other components (silica sol, other components and finishing additive solvent), and then for 0.5 minutes with a batch ultrasonic device (20 kHz, 300 W). Treatment (ultrasonic dispersion) was performed. Then, it filtered using the filter which has an average hole diameter of 0.5 micrometer, and prepared the composition for magnetic layer formation.
A composition for forming a nonmagnetic layer was prepared by the following method.
Each component except stearic acid and butyl stearate was dispersed for 12 hours using a batch type vertical sand mill to obtain a dispersion. As the dispersion beads, zirconia beads having a bead diameter of 0.1 mm were used. Thereafter, the remaining components were added to the obtained dispersion and stirred with a disper. The dispersion thus obtained was filtered using a filter having an average pore size of 0.5 μm to prepare a composition for a nonmagnetic layer.
A composition for forming a backcoat layer was prepared by the following method.
Each component excluding stearic acid, butyl stearate, polyisocyanate and cyclohexanone was kneaded and diluted with an open kneader, then using a horizontal bead mill with zirconia beads having a bead diameter of 1 mm, a bead filling rate of 80% by volume, and the circumference of the rotor tip Speed 10m / sec. Then, the 1-pass residence time was set to 2 minutes, and 12-pass dispersion processing was performed. Thereafter, the remaining components were added to the obtained dispersion and stirred with a disper. The dispersion thus obtained was filtered using a filter having an average pore size of 1 μm to prepare a composition for forming a backcoat layer.

6). 5. Preparation of magnetic tape 5. On the surface of an aramid support having a thickness of 3.60 μm, the thickness described above is adjusted to 0.10 μm after drying. The composition for forming a nonmagnetic layer prepared in (1) was applied and dried to form a nonmagnetic layer. The above-mentioned 5. so that the thickness after drying is 70 nm on the surface of the formed nonmagnetic layer. The composition for forming a magnetic layer prepared in (1) was applied to form a coating layer. While the coating layer was in an undried state, a magnetic field having a magnetic field strength of 0.4 T was applied in the vertical direction or the longitudinal direction with respect to the surface of the coating layer to perform orientation treatment. Thereafter, the coating layer was dried.
Then, on the surface opposite to the surface on which the nonmagnetic layer and the magnetic layer of the aramid support are formed, the thickness after drying is 0.40 μm. The backcoat layer forming composition prepared in (1) was applied and dried.
Then, the surface smoothing process (calendar process) was performed at a speed of 100 m / s, a linear pressure of 300 kg / cm (294 kN / m), and a calender roll surface temperature of 100 ° C. with a calendar composed of only metal rolls.
Thereafter, heat treatment was performed for 36 hours in an environment with an ambient temperature of 70 ° C., and then slitted to a width of ½ inch (0.0127 meter) to obtain a magnetic tape.
The thickness of each of the layers is a design thickness calculated from manufacturing conditions.

7). Measurement with a vibrating sample magnetometer Three tape samples having a size of 12 mm short side × 32 mm long side were cut out from the produced magnetic tape. Each tape sample was diffracted once at the short side and twice at the long side and folded into a size of 6 mm × 8 mm. The three tape samples folded in this way were stacked and placed in a vibrating sample magnetometer. The three tape samples were stacked so that the directions of the tape samples (longitudinal direction and width direction of the tape sample) coincided.
A TEM-WF82.5R-152 manufactured by Toei Kogyo Co., Ltd. was used as a vibrating sample type magnetometer, and an external magnetic field was swept at a measurement temperature of 24 ° C. to obtain a hysteresis curve (MH curve). The measurement for obtaining the vertical MH curve was performed by placing the tape sample on the vibrating sample type magnetometer so that the magnetic field application direction and the longitudinal direction of the tape sample were orthogonal to each other. The measurement for obtaining the longitudinal MH curve was performed by placing the tape sample on the vibrating sample type magnetometer so that the magnetic field application direction and the longitudinal direction of the tape sample were parallel. The external magnetic field was swept according to the sweep conditions shown in Table 2, with the average number at each step = 1, starting from a magnetic field intensity of 1197 kA / m to -1197 kA / m and again up to 1197 kA / m. The sweep conditions shown in Table 2 were sequentially performed from the top to the bottom. The total sweep time was 312 seconds. In addition, the amount of magnetization of only the measurement sample probe was measured in advance and subtracted as background noise during measurement. For each tape sample, the saturation magnetization obtained from the perpendicular MH curve thus obtained and the saturation magnetization obtained from the longitudinal MH curve are both 5 × 10 ⁻⁶ to 10 × 10 ⁻⁶ A. · ^m was in the range of ^{2 (5 × 10 -3 ~10 ×} 10 -3 emu).

8). Evaluation of magnetic tape (1) Square ratio (SQ)
Above 7. From the vertical MH curve and the longitudinal MH curve obtained by the measurement in (1), the perpendicular squareness ratio and longitudinal squareness ratio of the magnetic tape were determined.

(2) A calculated by Equation 1
Above 7. Various values for calculating A according to Equation 1 were obtained from the results of the measurements.

(3) Electromagnetic conversion characteristics (Signal-to-Noise-Ratio; SNR)
The SNR of the magnetic tape was measured by the following method.
Using a linear head, a signal of 27.6 MHz (linear recording density 350 kfci) was recorded and reproduced while running the magnetic tape by the following running method. The reproduction signal was inputted to U3741 manufactured by Advantest, and the signal output (S) of the peak signal of 27.6 Hz and the integrated noise (N) in the range of 1 MHz to 54.9 MHz excluding 27.6 MHz ± 0.3 MHz were measured. . These ratios (S / N) were taken as SNR. The SNR is shown as a relative value where the SNR obtained by the above method for Comparative Example 1 described later is 0 dB. If the SNR is 1.0 dB or more, it can be determined that the electromagnetic conversion characteristics are excellent.
(Driving method)
A magnetic tape having a total length of 90 cm is looped and attached to a loop type recording / reproducing apparatus, and the relative speed (running speed) between the head and the magnetic tape is 2 m / sec. The vehicle was run with a back tension of 0.7 N and a lap angle of 3 °.

(4) Thermal stability Using a magnetic tape tester (reel tester), a signal is recorded at a linear recording density of 30 kfci by the following running method, and the output when the recorded signal is reproduced is set to an initial value of 100% for 2 weeks. The same track was reproduced on the magnetic tape after storage at room temperature, and the decrease in output from the initial value was shown in Table 3 as a percentage of demagnetization. If the demagnetization factor is within -5.0%, it can be determined that the thermal stability is excellent.
(Driving method)
The relative speed (running speed) between the head and the magnetic tape is 4 m / sec while winding and feeding the magnetic tape between the reels. A magnetic tape having a total length of 1000 m was run with a back tension of 0.7 N and a wrap angle of 3 °.

(5) Changes in electromagnetic conversion characteristics during repeated travel (SNR reduction)
The SNR after a 3000 m long magnetic tape was reciprocated by the same method as in (4) above was determined. From the SNR obtained here and the SNR obtained in (3) above, the SNR decrease (SNR after the reciprocating travel) − (SNR obtained in (3) above) was calculated. If the SNR decrease is within -1.0 dB, it can be determined that the magnetic tape has little decrease in electromagnetic conversion characteristics in repeated running.

[Examples 2 to 12, Comparative Examples 1 to 12]
A magnetic tape was obtained by the same method as in Example 1 except that the manufacturing conditions of the magnetic tape were changed as shown in Table 3.
The obtained magnetic tape was evaluated in the same manner as in Example 1.
FIG. 4 is a hysteresis curve (MH curve) obtained by measurement with a vibrating sample magnetometer for the magnetic tape of Example 2 and the magnetic tape of Comparative Example 6.
In FIG. 4, the shape of the MH curve of Example 2 is a smooth curve shape as compared with the MH curve of Comparative Example 6 in the range of magnetic field strength −40 kA / m to 40 kA / m. Can be confirmed. On the other hand, in the MH curve of Comparative Example 6, for example, a step-shaped non-uniform portion is seen at a magnetic field strength of 0 kA / m.
The difference in the shape of the MH curve described above is due to the fact that the magnetic tape of Comparative Example 6 contains more fine particles as described above in the magnetic layer than the magnetic tape of Example 2. This is thought to have occurred.
On the other hand, in the magnetic tape of Comparative Example 8, since the strength of the magnetic layer was low, the magnetic layer was broken during running by the above running method, and various evaluations could not be performed. The main reason is that the strength of the magnetic layer is reduced due to the generation of a large number of fine particles due to chipping in bead dispersion of the magnetic liquid.

  The results are shown in Table 3.

  From the results shown in Table 3, it was confirmed that the magnetic tapes of the examples were excellent in electromagnetic conversion characteristics and thermal stability, and there was little decrease in the electromagnetic conversion characteristics in repeated running.

  The present invention is useful in the technical field of data storage magnetic tapes such as data backup tapes.

Claims (6)

A magnetic tape having a magnetic layer comprising a ferromagnetic powder and a binder on a non-magnetic support,
The ferromagnetic powder is a ferromagnetic hexagonal ferrite powder,
In the vibrating sample type magnetometer, the vertical squareness ratio obtained without demagnetizing field correction is 0.70 or more and 1 obtained by measurement performed by sweeping an external magnetic field on the magnetic tape in the range of magnetic field strength of −1197 kA / m to 1197 kA / m. A magnetic tape that is 0.000 or less and A calculated by the following formula 1 is 5.0% or less;
In Equation 1, n represents the number of measurement points performed in the range of the magnetic field intensity −40 kA / m to 40 kA / m during the sweep, n = 52, and Mr (Hex) is the amount of magnetization measured at the magnetic field intensity Hex. Μ represents an arithmetic average of Mr (Hex) obtained by measurement performed in the range of −40 kA / m to 40 kA / m of magnetic field intensity during the sweep. The magnetic tape according to claim 1, wherein A is 1.5% or more and 5.0% or less. The magnetic tape according to claim 1 or 2, wherein A is 1.5% or more and 3.9% or less. Upper Kishide straight direction squareness ratio is 0.75 to 1.00, the magnetic tape according to any one of claims 1 to 3. The magnetic tape of any one of Claims 1-4 which has a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. The magnetic tape according to any one of claims 1 to 5, further comprising a backcoat layer containing a nonmagnetic powder and a binder on the surface side opposite to the surface side having the magnetic layer of the nonmagnetic support. .