Magnetic recording medium, magnetic tape cartridge, and magnetic recording reproduction device

Abstract

Provided are a magnetic recording medium including a non-magnetic support and a magnetic layer containing a ferromagnetic powder, a magnetic tape cartridge including the magnetic recording medium, and a magnetic recording reproduction device. The magnetic field 0.3 of the magnetic recording medium is between 4.0 kOe and 8.0 kOe (both inclusive). The magnetic recording medium is a magnetic tape or a magnetic disk. The magnetic field 0.3 is a value on the high magnetic field side of the two values on the horizontal axis at which the value on the vertical axis is 0.3, in a graph in which the residual magnetization obtained by measurement with a vibrating sample magnetometer as the vertical axis value is plotted against the value of the applied magnetic field in the longitudinal direction of the magnetic tape or in the radial direction of the magnetic disk on the horizontal axis, and the differential curve obtained by differentiating these plots is normalized to a maximum value of 1 on the vertical axis.

Description

Magnetic recording media, magnetic tape cartridges, and magnetic recording / recovery devices

[0001] The present invention relates to a magnetic recording medium, a magnetic tape cartridge, and a magnetic recording and playback device.

[0002] Magnetic recording media are widely used as recording media for recording and storing various types of data (see, for example, Patent Document 1).

[0003] Japanese Patent Publication No. 2021-28859

[0004] As the information society progresses, there is a growing demand for higher capacity magnetic recording media for archiving purposes. One way to achieve this is to increase the recording density. And to increase the recording density, it is necessary to improve the electromagnetic conversion characteristics of the magnetic recording media.

[0005] One aspect of the present invention aims to provide a magnetic recording medium that can exhibit excellent electromagnetic conversion characteristics.

[0006] Japanese Patent Publication No. 2021-28859 (Patent Document 1), mentioned above, proposes improving electromagnetic conversion characteristics by controlling the anisotropic magnetic field and anisotropic magnetic field distribution of a magnetic recording medium. In contrast, the present inventors, through repeated studies, came to believe that the magnetic field component on the high-magnetic-field side, which had not been previously considered, affects the electromagnetic conversion characteristics, and further diligent studies were conducted. As a result, the magnetic field described in detail below ０．３ We have newly discovered that by controlling this, it is possible to further improve the electromagnetic conversion characteristics of magnetic recording media.

[0007] One embodiment of the present invention is as follows: [1] A magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the magnetic field of the magnetic recording medium ０．３ The magnetic recording medium is 4.0 kOe or more and 8.0 kOe or less, and the magnetic recording medium is a magnetic tape or a magnetic disk, and the magnetic field ０．３[2] A magnetic recording medium in which the remanent magnetization obtained by measurement with a vibrating sample type magnetometer is plotted on the vertical axis against the applied magnetic field value in the longitudinal direction of the magnetic tape or the radial direction of the magnetic disk on the horizontal axis, and the differential curve obtained by differentiating these plots is normalized to the maximum value of the vertical axis to 1, and the value on the horizontal axis is the higher magnetic field value of the two values ​​on the horizontal axis that result in a value of 0.3. [2] The magnetic recording medium according to [1], wherein the ferromagnetic powder is a hexagonal strontium ferrite powder with an average particle size of 9 nm or more and 19 nm or less. [3] The magnetic field ０．３ The magnetic recording medium according to [1] or [2], wherein the magnetic field is 4.0 kOe or more and 5.4 kOe or less. [4] The magnetic recording medium according to any one of [1] to [3], further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. [5] The magnetic recording medium according to any one of [1] to [4], further comprising a back coat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer. [6] The magnetic recording medium according to any one of [1] to [5], wherein the thickness of the magnetic recording medium is 5.0 μm or less. [7] The magnetic recording medium according to any one of [1] to [6], wherein the non-magnetic support is an aromatic polyamide support. [8] The magnetic recording medium according to any one of [1] to [7], wherein the magnetic recording medium is a magnetic tape. [9] The ferromagnetic powder is a hexagonal strontium ferrite powder with an average particle size of 9 nm or more and 19 nm or less, and the magnetic field ０．３ The magnetic recording medium according to any one of [1] to [8], wherein the magnetic layer is 4.0 kOe or more and 5.4 kOe or less, and further comprises a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer, and further comprises a back coat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer, and the thickness of the magnetic recording medium is 5.0 μm or less, and the magnetic recording medium is a magnetic tape. A magnetic tape cartridge comprising the magnetic tape according to

[10] , [8] or [9]. A magnetic recording and playback device comprising the magnetic recording medium according to any one of [1] to [9].

[0008] According to one aspect of the present invention, a magnetic recording medium capable of exhibiting excellent electromagnetic conversion characteristics can be provided. Further, according to one aspect of the present invention, a magnetic tape cartridge and a magnetic recording and reproducing apparatus including the magnetic recording medium can be provided.

[0009] Magnetic field ０．３ An example of a graph for obtaining is shown.

[0010] [Magnetic Recording Medium] One aspect of the present invention relates to a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder. The magnetic field of the magnetic recording medium ０．３ is 4.0 kOe or more and 8.0 kOe or less. The magnetic recording medium is a magnetic tape or a magnetic disk, and the magnetic field ０．３ is the residual magnetization obtained by measurement with a vibrating sample magnetometer as the value on the vertical axis, plotted against the value of the applied magnetic field in the longitudinal direction of the magnetic tape or the radial direction of the magnetic disk on the horizontal axis, and the differential curve obtained by differentiating these plots is normalized so that the maximum value on the vertical axis is 1. In the graph, it is the value on the high magnetic field side of the two values on the horizontal axis where the value on the vertical axis becomes 0.3.

[0011] <Magnetic field ０．３ > The "magnetic field ０．３The value is determined by the remanence method using a vibrating sample magnetometer (VSM) as follows: The measurement is performed at a sample temperature of 23°C. By setting the ambient temperature around the sample to 23°C, temperature equilibrium is achieved, allowing the sample temperature to be set to 23°C. A biaxial VSM capable of measuring magnetization in two directions (x and y directions) is used. The "y direction" is the thickness direction of the magnetic recording medium, and the "x direction" is the longitudinal direction for tape-shaped magnetic recording mediums (i.e., magnetic tapes) and the radial direction for disk-shaped magnetic recording mediums (i.e., magnetic disks). A sample of a size that can be introduced into the VSM is cut from the magnetic recording medium to be measured, and this sample is attached to the VSM's sample rod for measurement. First, an external magnetic field Hm is applied in the x-direction to saturate the sample (i.e., the sample magnetic field in the y-direction is reduced to zero), and then the applied magnetic field is reduced to zero and the remanent magnetization in the y-direction is measured. The external magnetic field Hm applied above should be a value that can saturate the sample. Next, an external magnetic field H1 is applied from an angle 15° different from the x-direction, and then the applied magnetic field is reduced to zero and the remanent magnetization in the y-direction is measured. Here, H1 is smaller than Hm. Next, an external magnetic field H2 is applied from an angle 15° different from the x-direction, and then the applied magnetic field is reduced to zero and the remanent magnetization in the y-direction is measured. Here, H2 is larger than H1. Next, an external magnetic field H3 is applied from an angle 15° different from the x-direction, and then the applied magnetic field is reduced to zero and the remanent magnetization in the y-direction is measured. Here, H3 is larger than H2. In this way, the applied magnetic field in the x-direction is changed from H1 → 0 → H2 → 0 → H3 → 0... and the remanent magnetization in the y-direction is measured sequentially. The magnetic field applied in the x-direction for each measurement is larger than the magnetic field applied for the previous measurement. The magnetic field applied in the x-direction for the final measurement can be set arbitrarily. The remanent magnetization in the y-direction measured as described above is plotted on a graph (vertical axis: value of remanent magnetization in the y-direction, horizontal axis: value of applied magnetic field in the x-direction). In the differential curve obtained by differentiating these plots, if the applied magnetic field is denoted as H and the remanent magnetic field as M, the vertical axis can be expressed as dM / dH. This differential curve is normalized so that the maximum value on the vertical axis is 1.A graph is created in which the normalized remanent magnetization value in the y-direction is the value on the vertical axis and the applied magnetic field value in the x-direction is the value on the horizontal axis. Figure 1 shows the graph created in this way (i.e., the magnetic field). ０．３ An example of a graph for determining the magnetic field is shown. However, the graph shown in Figure 1 is illustrative and does not limit the present invention. The graph created as described above takes the shape of having one peak, as shown in Figure 1, for example, so there are two values ​​on the horizontal axis for which the value on the vertical axis is 0.3. Of these two values, the value on the high magnetic field side is called the "magnetic field". ０．３ "

[0012] The inventors of this invention have found a magnetic field ０．３ This value is considered to be an indicator of the magnetic field component on the high-magnetic-field side. The magnetic field of the above magnetic recording medium. ０．３ From the viewpoint of improving electromagnetic conversion characteristics, the value is between 4.0 kOe and 8.0 kOe. 1 [kOe] = 10 ６ The magnetic field is 4π [A / m]. ０．３ For example, it can be 4.1 kOe or higher or 4.2 kOe or higher. From the viewpoint of further improving electromagnetic conversion characteristics, the magnetic field ０．３ The magnetic field is preferably 7.5 kOe or less, more preferably 7.0 kOe or less, and even more preferably in the order of 6.5 kOe or less, 6.0 kOe or less, 5.8 kOe or less, 5.6 kOe or less, 5.4 kOe or less, and 5.2 kOe or less. The inventors of this invention have found that the magnetic field is 7.5 kOe or less, more preferably 7.0 kOe or less, and more preferably 6.5 kOe or less, 6.0 kOe or less, 5.8 kOe or less, 5.6 kOe or less, 5.4 kOe or less, and 5.2 kOe or less. ０．３ Regarding this, we surmise that the following trends exist. However, the present invention is not limited to the surmise described herein. Magnetic field ０．３ The specific control methods will be described later. If there is a high frequency of particles with low magnetism and / or small particle size in the ferromagnetic powder contained in the magnetic layer, the magnetic field ０．３ The value of becomes smaller. If there is a high frequency of highly magnetic particles and / or coarse particles in the ferromagnetic powder contained in the magnetic layer, the magnetic field ０．３ The value of becomes larger. The more aligned the orientation of the ferromagnetic powder particles in the magnetic layer, the stronger the magnetic field becomes. ０．３ The value will increase.

[0013] The magnetic recording medium described above will be explained in more detail below.

[0014] <Magnetic Layer> (Ferromagnetic Powder) As the ferromagnetic powder included in the magnetic layer, one or more known ferromagnetic powders used in the magnetic layers of various magnetic recording media can be used in combination. Using a ferromagnetic powder with a small average particle size is preferable from the viewpoint of improving recording density. From this viewpoint, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, even more preferably 40 nm or less, even more preferably 35 nm or less, even more preferably 30 nm or less, even more preferably 25 nm or less, and still even more preferably 20 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 8 nm or more, even more preferably 10 nm or more, even more preferably 15 nm or more, and even more preferably 20 nm or more. Magnetic field of magnetic recording media ０．３ From the viewpoint of controlling the value to the range described above, it is preferable that the average particle size of the ferromagnetic powder be between 9 nm and 19 nm.

[0015] A specific example of hexagonal ferrite powder ferromagnetic powder is hexagonal ferrite powder. For details on hexagonal ferrite powder, see, for example, paragraphs 0012 to 0030 of Japanese Patent Publication No. 2011-225417, paragraphs 0134 to 0136 of Japanese Patent Publication No. 2011-216149, paragraphs 0013 to 0030 of Japanese Patent Publication No. 2012-204726, and paragraphs 0029 to 0084 of Japanese Patent Publication No. 2015-127985.

[0016] In the present invention and this specification, "hexagonal ferrite powder" refers to a ferromagnetic powder in which a hexagonal ferrite crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to the structure to which the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis belongs. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the hexagonal ferrite crystal structure, it shall be determined that the hexagonal ferrite crystal structure has been detected as the main phase. If only a single structure is detected by X-ray diffraction analysis, this detected structure shall be considered the main phase. The hexagonal ferrite crystal structure contains at least iron atoms, divalent metal atoms, and oxygen atoms as constituent atoms. Divalent metal atoms are metal atoms that can become divalent cations as ions, and examples include strontium atoms, barium atoms, alkaline earth metal atoms such as calcium atoms, and lead atoms. In the present invention and this specification, hexagonal strontium ferrite powder refers to powder in which the main divalent metal atom contained is strontium, and hexagonal barium ferrite powder refers to powder in which the main divalent metal atom contained is barium. The main divalent metal atom refers to the divalent metal atom that accounts for the largest proportion on an atomic percentage basis among the divalent metal atoms contained in the powder. However, rare earth atoms are not included in the above divalent metal atoms. In the present invention and this specification, "rare earth atoms" are selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanide atoms. Lanthanide atoms are selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0017] Below, we will describe hexagonal strontium ferrite powder, a form of hexagonal ferrite powder, in more detail.

[0018] The activation volume of the hexagonal strontium ferrite powder is preferably 800 to 1600 nm. ３ The activation volume is within the range described above. Finely milled hexagonal strontium ferrite powder exhibiting an activation volume within the above range is suitable for the fabrication of magnetic recording media that exhibit excellent electromagnetic conversion properties. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm. ３ That's all, for example, 850 nm ３ It can also be the above. Furthermore, from the viewpoint of further improving electromagnetic conversion characteristics, the activation volume of hexagonal strontium ferrite powder is 1500 nm. ３ The following is more preferable: 1400 nm ３ It is even more preferable that the following occur: 1300 nm ３ It is even more preferable that the following conditions are met: 1200 nm ３ It is even more preferable that the following conditions apply: 1100 nm ３ It is even more preferable that the following conditions be met. The same applies to the activation volume of the hexagonal barium ferrite powder.

[0019] "Activation volume" is a unit of magnetization reversal and an indicator of the magnetic size of a particle. The activation volume and the anisotropy constant Ku described herein and below are values ​​obtained from the following relationship between Hc and activation volume V, measured using a vibrating sample type magnetometer at magnetic field sweep speeds of 3 minutes and 30 minutes in the coercivity Hc measurement section (measurement temperature: 23°C ± 1°C). Regarding the unit of the anisotropy constant Ku, 1 erg / cc = 1.0 × 10⁻⁶ －１ J / m ３ Therefore, Hc = 2Ku / Ms{1 - [(kT / KuV)ln(At / 0.693)] １／２} [In the above formula, Ku: anisotropy constant (unit: J / m) ３ ), Ms: Saturation magnetization (unit: kA / m), k: Boltzmann constant, T: Absolute temperature (unit: K), V: Activation volume (unit: cm ３ ), A: Spin precession frequency (unit: s) －１ ), t: magnetic field reversal time (unit: s)]

[0020] As an indicator of reducing thermal fluctuations, or in other words, improving thermal stability, the anisotropy constant Ku can be cited. The hexagonal strontium ferrite powder is preferably 1.8 × 10⁻⁶ ５ J / m ３ It can have a Ku of the above, and more preferably 2.0 × 10 ５ J / m ３ It can have a Ku of the above. Also, the Ku of hexagonal strontium ferrite powder is, for example, 2.5 × 10 ５ J / m ３ The following values ​​are possible. However, since a higher Ku value is preferable as it indicates higher thermal stability, the values ​​are not limited to those exemplified above.

[0021] Hexagonal strontium ferrite powder may or may not contain rare earth atoms. When hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the rare earth atoms are present at a concentration of 0.5 to 5.0 atomic percent (bulk concentration) per 100 atomic percent of iron atoms. In one embodiment, hexagonal strontium ferrite powder containing rare earth atoms may have a surface layer segregation of rare earth atoms. In the present invention and this specification, "rare earth atom surface segregation" means that the rare earth atom content relative to 100% of iron atoms in a solution obtained by partially dissolving hexagonal strontium ferrite powder with acid (hereinafter referred to as "rare earth atom surface content" or simply "surface content" with respect to rare earth atoms) satisfies the ratio of rare earth atom surface content / rare earth atom bulk content > 1.0 with respect to rare earth atoms in a solution obtained by completely dissolving hexagonal strontium ferrite powder with acid (hereinafter referred to as "rare earth atom bulk content" or simply "bulk content" with respect to rare earth atoms). The rare earth atom content of hexagonal strontium ferrite powder described later is synonymous with the rare earth atom bulk content. In contrast, partial dissolution using acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder. Therefore, the rare earth atom content in the solution obtained by partial dissolution is the rare earth atom content in the surface layer of the particles constituting the hexagonal strontium ferrite powder. When the rare earth atom surface layer content satisfies the ratio "rare earth atom surface layer content / rare earth atom bulk content > 1.0", it means that in the particles constituting the hexagonal strontium ferrite powder, rare earth atoms are concentrated in the surface layer (i.e., there are more of them in the surface layer than in the interior). In this invention and specification, the surface layer refers to a part of the region extending from the surface to the interior of the particles constituting the hexagonal strontium ferrite powder.

[0022] When hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 atomic percent relative to 100 atomic percent of iron atoms. It is believed that containing rare earth atoms at the bulk content within the above range, and having the rare earth atoms unevenly distributed on the surface of the particles constituting the hexagonal strontium ferrite powder, contributes to suppressing the decrease in regeneration output during repeated regeneration. This is presumed to be because the anisotropy constant Ku can be increased by containing rare earth atoms at the bulk content within the above range, and having the rare earth atoms unevenly distributed on the surface of the particles constituting the hexagonal strontium ferrite powder. The higher the value of the anisotropy constant Ku, the more it is possible to suppress the occurrence of a phenomenon called thermal fluctuation (in other words, improve thermal stability). By suppressing the occurrence of thermal fluctuation, the decrease in regeneration output during repeated regeneration can be suppressed. It is speculated that the uneven distribution of rare earth atoms on the surface of hexagonal strontium ferrite powder particles contributes to stabilizing the spin of iron (Fe) sites in the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. Furthermore, it is speculated that using hexagonal strontium ferrite powder with uneven distribution of rare earth atoms on the surface as the ferromagnetic powder for a magnetic layer contributes to suppressing wear on the magnetic layer surface due to sliding with the magnetic head. In other words, it is speculated that hexagonal strontium ferrite powder with uneven distribution of rare earth atoms on the surface may also contribute to improving the running durability of magnetic recording media. This is speculated to be because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder contributes to improved interaction between the particle surface and organic substances (e.g., binders and / or additives) contained in the magnetic layer, resulting in improved strength of the magnetic layer. From the viewpoint of suppressing a decrease in regeneration output during repeated regeneration and / or further improving running durability, the rare earth atom content (bulk content) is more preferably in the range of 0.5 to 4.5 atomic percent, even more preferably in the range of 1.0 to 4.5 atomic percent, and even more preferably in the range of 1.5 to 4.5 atomic percent.

[0023] The bulk content mentioned above is the content obtained by completely dissolving the hexagonal strontium ferrite powder. In this invention and specification, unless otherwise specified, the content of atoms refers to the bulk content obtained by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one type of rare earth atom, or it may contain two or more types of rare earth atoms. When two or more types of rare earth atoms are included, the bulk content mentioned above is determined for the sum of the two or more types of rare earth atoms. This also applies to other components in this invention and specification. That is, unless otherwise specified, one type of component may be used, or two or more types may be used. When two or more types are used, the content or content refers to the sum of the two or more types.

[0024] When hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms included may be one or more of any type of rare earth atom. From the viewpoint of suppressing a decrease in regeneration output during repeated regeneration, preferred rare earth atoms include neodymium atoms, samarium atoms, yttrium atoms, and dysprosium atoms, with neodymium atoms, samarium atoms, and yttrium atoms being more preferred, and neodymium atoms being even more preferred.

[0025] In hexagonal strontium ferrite powder having a rare-earth atom surface segregation, the rare-earth atoms only need to be segregated in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of segregation is not limited. For example, in hexagonal strontium ferrite powder having a rare-earth atom surface segregation, the ratio of the rare-earth atom surface content obtained by partial dissolution under the dissolution conditions described later to the rare-earth atom bulk content obtained by total dissolution under the dissolution conditions described later, "surface content / bulk content," is greater than 1.0 and can be 1.5 or greater. A "surface content / bulk content" greater than 1.0 means that in the particles constituting the hexagonal strontium ferrite powder, the rare-earth atoms are segregated in the surface layer (i.e., there are more of them in the surface layer than in the interior). Furthermore, the ratio of the surface content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content of rare earth atoms obtained by total dissolution under the dissolution conditions described later, "surface content / bulk content," can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in hexagonal strontium ferrite powder having a rare earth atom surface distribution bias, the rare earth atoms only need to be biased towards the surface of the particles constituting the hexagonal strontium ferrite powder, and the above "surface content / bulk content" is not limited to the upper or lower limits exemplified.

[0026] The partial and total dissolution of hexagonal strontium ferrite powder is described below. For hexagonal strontium ferrite powder existing as a powder, the sample powders to be partially and completely dissolved are taken from the same lot of powder. On the other hand, for hexagonal strontium ferrite powder contained in the magnetic layer of a magnetic recording medium, a portion of the hexagonal strontium ferrite powder extracted from the magnetic layer is subjected to partial dissolution, and another portion is subjected to total dissolution. The extraction of hexagonal strontium ferrite powder from the magnetic layer can be performed, for example, by the method described in paragraph 0032 of Japanese Patent Application Publication No. 2015-91747. Partial dissolution refers to dissolving to the extent that residual hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. For example, partial dissolution can dissolve a region of 10 to 20% by mass of the particles constituting the hexagonal strontium ferrite powder, with the total particles being 100% by mass. On the other hand, total dissolution refers to dissolution to the point where no residue of hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. The measurement of partial dissolution and surface layer content is performed, for example, by the following method. However, the dissolution conditions such as the amount of sample powder below are examples, and any dissolution conditions that enable partial and total dissolution can be arbitrarily adopted. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 1 mol / L hydrochloric acid is held on a hot plate at a set temperature of 70°C for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the resulting filtrate is performed using an inductively coupled plasma (ICP) analyzer. In this way, the surface layer content of rare earth atoms relative to 100 atomic percent of iron atoms can be determined. If multiple types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer content. This also applies to the measurement of bulk content. On the other hand, the measurement of total dissolution and bulk content is performed, for example, by the following method: A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 4 mol / L hydrochloric acid is held on a hot plate at a set temperature of 80°C for 3 hours.Subsequently, the bulk content relative to 100 atomic percent of iron atoms can be determined by performing the same procedure as described above for partial dissolution and surface layer content measurement.

[0027] From the perspective of increasing the playback output when reproducing data recorded on a magnetic recording medium, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic recording medium to be high. In this regard, hexagonal strontium ferrite powder containing rare earth atoms but lacking surface segregation of rare earth atoms tended to have a significantly lower σs compared to hexagonal strontium ferrite powder that does not contain rare earth atoms. In contrast, hexagonal strontium ferrite powder having surface segregation of rare earth atoms is considered preferable in order to suppress such a large decrease in σs. In one embodiment, the σs of hexagonal strontium ferrite powder is 45 A·m ２ It can be 47 A·m or more per kg. ２ It can also be greater than / kg. On the other hand, σs is 80 A·m from the viewpoint of noise reduction. ２ It is preferable that the value be less than or equal to 60 A·m / kg. ２ It is more preferable that it be less than or equal to / kg. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In the present invention and this specification, unless otherwise specified, the mass magnetization σs is the value measured at a magnetic field strength of 15 kOe.

[0028] Regarding the constituent atom content (bulk content) of hexagonal strontium ferrite powder, the strontium atom content can be in the range of, for example, 2.0 to 15.0 atomic percent relative to 100 atomic percent of iron atoms. In one embodiment, the hexagonal strontium ferrite powder may contain only strontium atoms as divalent metal atoms. In another embodiment, the hexagonal strontium ferrite powder may contain one or more other divalent metal atoms in addition to strontium atoms. For example, it may contain barium atoms and / or calcium atoms. When other divalent metal atoms besides strontium atoms are included, the barium atom content and calcium atom content in the hexagonal strontium ferrite powder can be in the range of, for example, 0.05 to 5.0 atomic percent relative to 100 atomic percent of iron atoms.

[0029] The known crystal structures of hexagonal ferrites include magnetoplumbite (also called "M-type"), W-type, Y-type, and Z-type. Hexagonal strontium ferrite powder may have any of these crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. Hexagonal strontium ferrite powder may show a single crystal structure or two or more crystal structures by X-ray diffraction analysis. For example, in one embodiment, hexagonal strontium ferrite powder may show only the M-type crystal structure by X-ray diffraction analysis. For example, M-type hexagonal ferrite is AFe １２ O １９It is represented by the following compositional formula: Here, A represents a divalent metal atom, and if the hexagonal strontium ferrite powder is of type M, A is either only a strontium atom (Sr), or if A contains multiple divalent metal atoms, then as described above, strontium atoms (Sr) make up the largest proportion on an atomic percentage basis. The divalent metal atom content of hexagonal strontium ferrite powder is usually determined by the type of crystal structure of the hexagonal ferrite and is not particularly limited. The same applies to the iron atom content and oxygen atom content. Hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms and oxygen atoms, and may also contain rare earth atoms. Furthermore, hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, hexagonal strontium ferrite powder may contain aluminum atoms (Al). The aluminum atom content can be, for example, 0.5 to 10.0 atomic percent relative to 100 atomic percent of iron atoms. From the viewpoint of suppressing a decrease in regeneration output during repeated regeneration, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms, and rare earth atoms, and the content of atoms other than these atoms is preferably 10.0 atomic percent or less, more preferably in the range of 0 to 5.0 atomic percent, and may even be 0 atomic percent, relative to 100 atomic percent of iron atoms. That is, in one embodiment, the hexagonal strontium ferrite powder does not need to contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The above content expressed in atomic percent is obtained by converting the content of each atom (unit: mass%) obtained by completely dissolving the hexagonal strontium ferrite powder into an atomic percent value using the atomic weight of each atom. Furthermore, in the present invention and this specification, "does not contain" for a certain atom means that the content measured by an ICP analyzer after complete dissolution is 0 mass%. The detection limit of an ICP analyzer is typically 0.01 ppm (parts per million) or less by mass. The term "does not contain" above is used to include the presence of substances in amounts below the detection limit of the ICP analyzer.Hexagonal strontium ferrite powder can, in one form, be bismuth atom-free (Bi).

[0030] For example, methods for producing hexagonal ferrite powder include glass crystallization, coprecipitation, reverse micelle, and hydrothermal synthesis.

[0031] As an example, the glass crystallization method generally includes the following steps. For each step, see, for example, paragraphs 0035 to 0041 of Japanese Patent Publication No. 2021-28859 (Patent Document 1). (1) A step of melting a raw material mixture containing at least a hexagonal ferrite-forming component and a glass-forming component to obtain a molten product (melting step); (2) A step of rapidly cooling the molten product to obtain an amorphous product (amorphization step); (3) A step of heat-treating the amorphous product to obtain a crystalline product containing hexagonal ferrite particles precipitated by the heat treatment and crystallized glass components (crystallization step); (4) A step of collecting hexagonal ferrite particles from the crystalline product (particle collection step).

[0032] The crystallized material obtained in the crystallization process contains hexagonal ferrite particles and crystallized glass components. Therefore, when the crystallized material is treated with acid, the crystallized glass components surrounding the hexagonal ferrite particles are dissolved and removed, allowing the hexagonal ferrite particles to be collected. Prior to the above acid treatment, it is preferable to perform coarse grinding to improve the efficiency of the acid treatment. Coarse grinding may be performed by either a dry or wet method. The conditions for coarse grinding can be set according to known methods. The acid treatment for particle collection can be performed by methods commonly used in glass crystallization methods, such as heated acid treatment. After that, hexagonal ferrite powder can be obtained by performing post-treatment such as classification (e.g., centrifugation, decantation, magnetic separation), washing with water, and drying as needed. For example, the average particle size of the obtained hexagonal ferrite powder can be controlled by adjusting the classification conditions (e.g., number of treatments, treatment time, centrifugal force applied in centrifugation, magnetic field strength in magnetic separation, frequency in the case of an AC magnetic field, etc.). Controlling the average particle size of hexagonal ferrite powder is important for the magnetic field of magnetic recording media fabricated using the resulting hexagonal ferrite powder. ０．３This can contribute to controlling the value of the magnetic field of a magnetic recording medium. ０．３ From the viewpoint of controlling the value to the range described above, hexagonal ferrite powder with an average particle size of 9 nm to 19 nm is preferred, and hexagonal strontium ferrite powder with an average particle size of 9 nm to 19 nm is more preferred.

[0033] Specific examples of metal powder ferromagnetic powders include ferromagnetic metal powders. For details on ferromagnetic metal powders, see, for example, paragraphs 0137 to 0141 of Japanese Patent Publication No. 2011-216149 and paragraphs 0009 to 0023 of Japanese Patent Publication No. 2005-251351.

[0034] ε-iron oxide powder can also be cited as a specific example of ε-iron oxide powder ferromagnetic powder. In the present invention and this specification, "ε-iron oxide powder" refers to ferromagnetic powder in which the crystal structure of ε-iron oxide is detected as the main phase by X-ray diffraction analysis. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the crystal structure of ε-iron oxide, it shall be determined that the crystal structure of ε-iron oxide has been detected as the main phase. Methods for producing ε-iron oxide powder include methods from goethite and the reverse micelle method. All of the above production methods are publicly known. Furthermore, for a method of producing ε-iron oxide powder in which a portion of Fe is substituted with substituted atoms such as Ga, Co, Ti, Al, and Rh, see, for example, J. Jpn. Soc. Powder Metallurgy Vol. 61 Supply, No. S1, pp. See S280-S284, J. Mater. Chem. C, 2013, 1, pp. 5200-5206, etc. However, the method for producing ε-iron oxide powder that can be used as ferromagnetic powder in the magnetic layer of the above magnetic recording medium is not limited to the method listed herein.

[0035] The activation volume of ε-iron oxide powder is preferably 300 to 1500 nm. ３The activation volume is within the range described above. Finely milled ε-iron oxide powder exhibiting an activation volume within this range is suitable for the fabrication of magnetic recording media that exhibit excellent electromagnetic conversion properties. The activation volume of the ε-iron oxide powder is preferably 300 nm. ３ That's all, for example, 500 nm ３ It can also be the above. Furthermore, from the viewpoint of further improving electromagnetic conversion characteristics, the activation volume of ε-iron oxide powder is 1400 nm. ３ The following is more preferable: 1300 nm ３ It is even more preferable that the following conditions apply: 1200 nm ３ It is even more preferable that the following conditions be met: 1100 nm ３ The following is even more preferable.

[0036] The anisotropy constant Ku can be cited as an indicator of the reduction of thermal fluctuations, or in other words, the improvement of thermal stability. The ε-iron oxide powder is preferably 3.0 × 10 ４ J / m ３ It can have a Ku of the above, and more preferably 8.0 × 10 ４ J / m ３ It is possible to have the above Ku content. Also, the Ku content of ε-iron oxide powder is, for example, 3.0 × 10 ５ J / m ３ The following values ​​are possible. However, a higher Ku value indicates higher thermal stability, which is preferable, so the values ​​are not limited to those exemplified above.

[0037] From the perspective of increasing the playback output when reproducing data recorded on a magnetic recording medium, it is desirable for the mass magnetization σs of the ferromagnetic powder contained in the magnetic recording medium to be high. In this regard, in one embodiment, the σs of ε-iron oxide powder is 8 A·m ２ It can be 12 A·m or more per kg. ２ It can also be more than / kg. On the other hand, the σs of ε-iron oxide powder is 40 A·m from the viewpoint of noise reduction. ２ It is preferable that it be less than or equal to 35 A·m / kg. ２ It is more preferable that the amount is less than or equal to / kg.

[0038] In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powder shall be the value measured using a transmission electron microscope by the following method: The powder is photographed using a transmission electron microscope at a magnification of 100,000x, and the resulting image is printed on photographic paper or displayed on a screen to obtain a photograph of the particles constituting the powder, with a total magnification of 500,000x. The target particles are selected from the obtained photographs of the particles, and their contours are traced with a digitizer to measure the size of the particles (primary particles). Primary particles refer to independent particles that do not aggregate. The above measurement is performed on 500 randomly selected particles. The arithmetic mean of the particle sizes of these 500 particles is taken as the average particle size of the powder. As the above-mentioned transmission electron microscope, for example, a Hitachi H-9000 transmission electron microscope can be used. Furthermore, the particle size measurement can be performed using known image analysis software, for example, Carl Zeiss KS-400 image analysis software. The average particle sizes shown in the Examples section below were measured using a Hitachi H-9000 transmission electron microscope and Carl Zeiss KS-400 image analysis software, unless otherwise specified. In the present invention and this specification, "powder" means an aggregate of multiple particles. For example, ferromagnetic powder means an aggregate of multiple ferromagnetic particles. Furthermore, an aggregate of multiple particles is not limited to a form in which the particles constituting the aggregate are in direct contact, but also includes forms in which binders, additives, etc., described later, are interposed between the particles. The word "particle" is sometimes used to refer to powder.

[0039] As a method for collecting sample powder from a magnetic recording medium for particle size measurement, for example, the method described in paragraph 0015 of Japanese Patent Application Publication No. 2011-048878 can be employed.

[0040] In the present invention and this specification, unless otherwise specified, the size of the particles constituting the powder (particle size) is expressed as follows: (1) If the shape of the particles observed in the above particle photograph is needle-shaped, spindle-shaped, columnar (however, the height is greater than the longest major axis of the base), it is expressed as the length of the long axis constituting the particle, i.e., the long axis length; (2) If the shape is plate-shaped or columnar (however, the thickness or height is less than the longest major axis of the plate surface or base), it is expressed as the longest major axis of the plate surface or base; (3) If the shape is spherical, polyhedral, irregular, etc., and the long axis constituting the particle cannot be determined from the shape, it is expressed as the equivalent circle diameter. The equivalent circle diameter refers to the diameter determined by the circular projection method.

[0041] Furthermore, the average needle-shape ratio of the powder refers to the arithmetic mean of the values ​​obtained for the 500 particles by measuring the length of the short axis of each particle in the above measurement, i.e., the short axis length, and determining the (long axis length / short axis length) value for each particle. Here, unless otherwise specified, the short axis length refers to the length of the short axis constituting the particle in the definition of particle size above (1), the thickness or height in the definition of (2), and in the case of (3), since there is no distinction between the long axis and the short axis, (long axis length / short axis length) is considered to be 1 for convenience. And unless otherwise specified, when the shape of the particle is specific, for example, in the definition of particle size above (1), the average particle size is the average long axis length, and in the definition of (2), the average particle size is the average plate diameter. In the definition of (3), the average particle size is the average diameter (also called the average particle size or average particle diameter).

[0042] The content (filling rate) of ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass, relative to the total mass of the magnetic layer. A high filling rate of ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving recording density.

[0043] (Binding Agent) The above magnetic recording medium can be a coated magnetic recording medium, and the magnetic layer may contain a binding agent. The binding agent is one or more resins. Various resins commonly used as binding agents for coated magnetic recording media can be used as binding agents. For example, as binding agents, a resin selected from polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, polyvinyl alkylal resin such as polyvinyl butyral, etc. can be used alone or in mixture of multiple resins. Among these, polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin are preferred. These resins may be homopolymers or copolymers. These resins can also be used as binding agents in the non-magnetic layer and / or back coat layer described later. For more information on the binding agents, refer to paragraphs 0028 to 0031 of Japanese Patent Application Publication No. 2010-24113. Furthermore, the binder may be a radiation-curable resin such as an electron beam-curable resin. For radiation-curable resins, refer to paragraphs 0044 to 0045 of Japanese Patent Application Publication No. 2011-048878. The average molecular weight of the resin used as a binder can be, for example, 10,000 or more and 200,000 or less as a weight-average molecular weight. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass per 100.0 parts by mass of ferromagnetic powder.

[0044] (Curing agent) A curing agent can also be used together with the binder. In one form, the curing agent can be a thermosetting compound, which undergoes a curing reaction (crosslinking reaction) by heating, and in another form, it can be a photocurable compound, which undergoes a curing reaction (crosslinking reaction) by light irradiation. As the curing reaction progresses during the manufacturing process of the magnetic recording medium, at least a portion of the curing agent may be included in the magnetic layer in a state where it has reacted (crosslinked) with other components such as the binder. A preferred curing agent is a thermosetting compound, and polyisocyanate is preferred. For details on polyisocyanate, refer to paragraphs 0124 to 0125 of Japanese Patent Application Publication No. 2011-216149. The curing agent can be used in the magnetic layer forming composition in an amount of, for example, 0 to 80.0 parts by mass per 100.0 parts by mass of the binder, and preferably 50.0 to 80.0 parts by mass from the viewpoint of improving the strength of each layer such as the magnetic layer.

[0045] (Other components) The magnetic layer may contain one or more additives as needed. Commercially available additives can be appropriately selected and used according to the desired properties. Alternatively, compounds synthesized by known methods can be used as additives. An example of an additive is the curing agent mentioned above. Other additives that may be included in the magnetic layer include non-magnetic fillers, lubricants, dispersants, dispersion aids, antifungal agents, antistatic agents, antioxidants, etc. Non-magnetic fillers are synonymous with non-magnetic particles or non-magnetic powders. Examples of non-magnetic fillers include non-magnetic fillers that can function as protrusion-forming agents and non-magnetic fillers that can function as abrasives. Other known additives, such as various polymers described in paragraphs 0030 to 0080 of Japanese Patent Application Publication No. 2016-051493, can also be used.

[0046] As a protrusion-forming agent, which is a form of non-magnetic filler, inorganic particles, organic particles, or composite particles of inorganic and organic substances can be used. Carbon black can also be used. Examples of inorganic substances include inorganic oxides such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides, with inorganic oxides being preferred. In one form, the protrusion-forming agent can be inorganic oxide-based particles. Here, "system" is used to mean "containing". One form of inorganic oxide-based particles is particles made of inorganic oxides. Another form of inorganic oxide-based particles is composite particles of inorganic oxides and organic substances, and a specific example is composite particles of inorganic oxides and polymers. For example, such particles include particles in which a polymer is bonded to the surface of inorganic oxide particles.

[0047] The average particle size of the protrusion-forming agent can be, for example, 30 to 300 nm, and preferably 40 to 200 nm.

[0048] Another form of nonmagnetic filler, the abrasive, is preferably a nonmagnetic powder with a Mohs hardness greater than 8, and more preferably a nonmagnetic powder with a Mohs hardness of 9 or higher. In contrast, the Mohs hardness of the protrusion-forming agent can be, for example, 8 or less, or 7 or less. The maximum Mohs hardness is 10, which is diamond. Specifically, as an abrasive, alumina (e.g., Al ２ O ３ ), silicon carbide, boron carbide (e.g., B ４ C), SiO ２ TiC, chromium oxide (Cr ２ O ３ ), cerium oxide, zirconium oxide (e.g., ZrO) ２ Examples of abrasives include iron oxide and diamond powders, with alumina powder such as α-alumina and silicon carbide powder being preferred. The average particle size of the abrasive can be in the range of 30 to 300 nm, and is preferably in the range of 50 to 200 nm.

[0049] Furthermore, from the viewpoint of enabling the protrusion-forming agent and abrasive to exhibit their functions more effectively, the content of the protrusion-forming agent in the magnetic layer is preferably 0.1 to 4.0 parts by mass, more preferably 0.3 to 3.5 parts by mass, and even more preferably 0.5 to 2.5 parts by mass, per 100.0 parts by mass of ferromagnetic powder. On the other hand, the content of the abrasive in the magnetic layer is preferably 1.0 to 20.0 parts by mass, more preferably 3.0 to 15.0 parts by mass, and even more preferably 4.0 to 10.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder.

[0050] An example of an additive that can be used in a magnetic layer containing an abrasive is the dispersant described in paragraphs 0012 to 0022 of Japanese Patent Application Publication No. 2013-131285, which can be used as a dispersant to improve the dispersibility of the abrasive in a magnetic layer forming composition. For more information on dispersants, see paragraphs 0061 and 0071 of Japanese Patent Application Publication No. 2012-133837. The dispersant may also be included in the non-magnetic layer. For more information on dispersants that can be included in the non-magnetic layer, see paragraph 0061 of Japanese Patent Application Publication No. 2012-133837.

[0051] Furthermore, one form of additive that may be included in the magnetic layer is a compound having an ammonium salt structure of an alkyl ester anion represented by the following formula 1.

[0052]

[0053] (In Formula 1, R represents an alkyl group having 7 or more carbon atoms or a fluorinated alkyl group having 7 or more carbon atoms, Z ＋ (This represents an ammonium cation.)

[0054] The inventors believe that the above compound can function as a lubricant. The above compound will be described in more detail below.

[0055] In the present invention and this specification, unless otherwise specified, the groups described may or may not have substituents. Furthermore, with respect to substituted groups, "number of carbon atoms" means the number of carbon atoms excluding the substituents, unless otherwise specified. In the present invention and this specification, examples of substituents include alkyl groups (e.g., alkyl groups having 1 to 6 carbon atoms), hydroxyl groups, alkoxy groups (e.g., alkoxy groups having 1 to 6 carbon atoms), halogen atoms (e.g., fluorine atoms, chlorine atoms, bromine atoms, etc.), cyano groups, amino groups, nitro groups, acyl groups, carboxyl groups, salts of carboxyl groups, sulfonic acid groups, salts of sulfonic acid groups, and the like.

[0056] Compounds having an ammonium salt structure of an alkyl ester anion represented by Formula 1 can form a liquid film on the surface of the magnetic layer, with at least a portion contained within the magnetic layer, and a portion that can move to the surface of the magnetic layer and form a liquid film when sliding with the magnetic head, etc. Furthermore, a portion can be contained in the non-magnetic layer described later, and can move to the magnetic layer and then to the surface of the magnetic layer to form a liquid film. Note that "alkyl ester anion" can also be called "alkyl carboxylate anion".

[0057] In Formula 1, R represents an alkyl group having 7 or more carbon atoms or a fluorinated alkyl group having 7 or more carbon atoms. A fluorinated alkyl group has a structure in which some or all of the hydrogen atoms constituting the alkyl group are substituted with fluorine atoms. The alkyl group or fluorinated alkyl group represented by R may have a linear structure, a branched structure, or a cyclic alkyl group or fluorinated alkyl group, but a linear structure is preferred. The alkyl group or fluorinated alkyl group represented by R may have substituents or be unsubstituted, but it is preferred to be unsubstituted. The alkyl group represented by R is, for example, C ｎ H ２ｎ＋１ It can be represented by -. Here, n represents an integer greater than or equal to 7. Also, the alkyl fluoride represented by R is, for example, C ｎ H ２ｎ＋１The alkyl group represented by - may have a structure in which some or all of the hydrogen atoms constituting the alkyl group are substituted with fluorine atoms. The number of carbon atoms in the alkyl group or alkyl fluoride represented by R is 7 or more, preferably 8 or more, more preferably 9 or more, even more preferably 10 or more, even more preferably 11 or more, even more preferably 12 or more, and even more preferably 13 or more. Furthermore, the number of carbon atoms in the alkyl group or alkyl fluoride represented by R is preferably 20 or less, more preferably 19 or less, and even more preferably 18 or less.

[0058] In formula 1, Z ＋ represents an ammonium cation. The ammonium cation has, in detail, the following structure. In this invention and specification, an asterisk in a formula representing a part of a compound indicates the bond position between the part of the structure and an adjacent atom.

[0059]

[0060] Nitrogen cation of ammonium cation N ＋ and the oxygen anion O in Equation 1 － These can form a salt crosslinking group, creating an ammonium salt structure of the alkyl ester anion represented by formula 1. The presence of a compound having an ammonium salt structure of the alkyl ester anion represented by formula 1 in the magnetic layer can be confirmed by analyzing the magnetic recording medium using X-ray photoelectron spectroscopy (ESCA), infrared spectroscopy (IR), etc.

[0061] In one form, Z ＋The ammonium cation represented by can be brought about, for example, by the nitrogen atom of a nitrogen-containing polymer becoming a cation. A nitrogen-containing polymer means a polymer containing a nitrogen atom. In the present invention and this specification, the terms "polymer" and "polymerized product" are used in a meaning that includes homopolymers and copolymers. The nitrogen atom can be included as an atom constituting the main chain of the polymer in one form, and can also be included as an atom constituting the side chain of the polymer in one form.

[0062] As one form of the nitrogen-containing polymer, polyalkyleneimine can be mentioned. Polyalkyleneimine is a ring-opening polymer of alkyleneimine and is a polymer having a plurality of repeating units represented by the following formula 2.

[0063]

[0064] The nitrogen atom N constituting the main chain in formula 2 becomes a nitrogen cation N ＋ and can bring about the ammonium cation represented by Z ＋ in formula 1. And an alkyl ester anion can form an ammonium salt structure, for example, as follows.

[0065]

[0066] Hereinafter, formula 2 will be described in more detail.

[0067] In formula 2, R １ and R ２ each independently represent a hydrogen atom or an alkyl group, and n1 represents an integer of 2 or more.

[0068] As the alkyl group represented by R １ or R ２ , for example, an alkyl group having 1 to 6 carbon atoms can be mentioned, preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group, and still more preferably a methyl group. The alkyl group represented by R １ or R ２ is preferably an unsubstituted alkyl group. R １ and R ２The combinations include a form in which one is a hydrogen atom and the other is an alkyl group, a form in which both are hydrogen atoms, and a form in which both are alkyl groups (identical or different alkyl groups), with the form in which both are hydrogen atoms being preferred. As an alkylene imine that yields a polyalkylene imine, the structure with the fewest number of carbon atoms constituting the ring is ethyleneimine, and the number of carbon atoms in the main chain of the alkylene imine (ethyleneimine) obtained by ring-opening of ethyleneimine is 2. Therefore, n1 in formula 2 is 2 or more. n1 in formula 2 can be, for example, 10 or less, 8 or less, 6 or less, or 4 or less. The polyalkylene imine may be a homopolymer containing only the same structure as the repeating structure represented by formula 2, or it may be a copolymer containing two or more different structures as the repeating structure represented by formula 2. The number-average molecular weight of the polyalkylene imine that can be used to form a compound having an ammonium salt structure of an alkyl ester anion represented by formula 1 can be, for example, 200 or more, and preferably 300 or more. Furthermore, the number-average molecular weight of the polyalkyleneimine can be, for example, 10,000 or less, preferably 5,000 or less, and more preferably 2,000 or less.

[0069] In the present invention and this specification, average molecular weight (weight-average molecular weight and number-average molecular weight) refers to the value obtained by measuring by gel permeation chromatography (GPC) and converting it to standard polystyrene equivalent. Unless otherwise specified, the average molecular weights shown in the Examples section below are values ​​obtained by converting the values ​​measured using GPC under the following measurement conditions to standard polystyrene equivalent (polystyrene equivalent value). GPC instrument: HLC-8220 (Tosoh Corporation) Guard column: TSKguardcolumn Super HZM-H Columns: TSKgel Super HZ2000, TSKgel Super HZ 4000, TSKgel Super HZ-M (Tosoh Corporation, 4.6 mm (inner diameter) x 15.0 cm, 3 columns connected in series) Eluent: Tetrahydrofuran (THF), stabilizer (2,6-di-t-butyl-4-methylphenol) Eluent flow rate: 0.35 mL / min Column temperature: 40°C Inlet temperature: 40°C Refractive index (RI) measurement temperature: 40°C Sample concentration: 0.3% by mass Sample injection volume: 10 μL

[0070] Another form of nitrogen-containing polymer is polyallylamine. Polyallylamine is a polymer of allylamine, having multiple repeating units represented by the following formula 3.

[0071]

[0072] In formula 3, the nitrogen atom N constituting the amino group of the side chain is a nitrogen cation N ＋ And so Z in equation 1 ＋ An ammonium cation represented by [formula] can be obtained. Then, with an alkyl ester anion, it can form an ammonium salt structure, for example, as shown below.

[0073]

[0074] The weight-average molecular weight of the polyallylamine that can be used to form a compound having an ammonium salt structure of an alkyl ester anion represented by Formula 1 can be, for example, 200 or more, preferably 1,000 or more, and more preferably 1,500 or more. Furthermore, the weight-average molecular weight of the polyallylamine can be, for example, 15,000 or less, preferably 10,000 or less, and more preferably 8,000 or less.

[0075] The fact that compounds having an ammonium salt structure of an alkyl ester anion represented by Formula 1 include compounds having structures derived from polyalkylene imines or polyallylamines can be confirmed, for example, by analyzing the surface of the magnetic layer using time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0076] A compound having an ammonium salt structure of an alkyl ester anion represented by formula 1 can be a salt of a nitrogen-containing polymer and one or more fatty acids selected from the group consisting of fatty acids having 7 or more carbon atoms and fluorinated fatty acids having 7 or more carbon atoms. The nitrogen-containing polymer that forms the salt can be one or more nitrogen-containing polymers, for example, a nitrogen-containing polymer selected from the group consisting of polyalkylene imines and polyallylamines. The fatty acids that form the salt can be one or more fatty acids selected from the group consisting of fatty acids having 7 or more carbon atoms and fluorinated fatty acids having 7 or more carbon atoms. Fluorinated fatty acids have a structure in which some or all of the hydrogen atoms constituting the alkyl group bonded to the carboxyl group COOH in the fatty acid are replaced with fluorine atoms. For example, the salt formation reaction can easily proceed by mixing the nitrogen-containing polymer and the above fatty acids at room temperature. Room temperature is, for example, about 20 to 25°C. In one embodiment, one or more nitrogen-containing polymers and one or more fatty acids can be used as components of a magnetic layer forming composition, and the salt formation reaction can be carried out by mixing them in the preparation step of the magnetic layer forming composition. In one embodiment, before preparing the magnetic layer-forming composition, one or more nitrogen-containing polymers and one or more fatty acids can be mixed to form a salt, and this salt can then be used as a component of the magnetic layer-forming composition to prepare the magnetic layer-forming composition. This also applies when forming a non-magnetic layer containing a compound having an ammonium salt structure of an alkyl ester anion represented by formula 1. For example, with respect to the magnetic layer, 0.1 to 10.0 parts by mass of nitrogen-containing polymer can be used per 100.0 parts by mass of ferromagnetic powder, and it is preferable to use 0.3 to 8.0 parts by mass of nitrogen-containing polymer. The above fatty acids can be used, for example, 0.05 to 10.0 parts by mass per 100.0 parts by mass of ferromagnetic powder, and it is preferable to use 0.1 to 5.0 parts by mass. With respect to the non-magnetic layer, 0.1 to 10.0 parts by mass of nitrogen-containing polymer can be used per 100.0 parts by mass of non-magnetic powder, and it is preferable to use 0.3 to 8.0 parts by mass of nitrogen-containing polymer.The above fatty acids can be used in amounts of, for example, 0.05 to 10.0 parts by mass per 100.0 parts by mass of non-magnetic powder, and preferably in amounts of 0.1 to 5.0 parts by mass. When mixing the nitrogen-containing polymer and the above fatty acids to form an ammonium salt of the alkyl ester anion represented by formula 1, the nitrogen atoms constituting the nitrogen-containing polymer may also react with the carboxyl groups of the above fatty acids to form the following structure, and forms including such a structure are also included in the above compound.

[0077]

[0078] Examples of the above fatty acids include fatty acids having the alkyl group previously described as R in Formula 1, and fluorinated fatty acids having the fluorinated alkyl group previously described as R in Formula 1.

[0079] The mixing ratio of the nitrogen-containing polymer used to form the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 to the above fatty acids is preferably 10:90 to 90:10, more preferably 20:80 to 85:15, and even more preferably 30:70 to 80:20, as the mass ratio of nitrogen-containing polymer to the above fatty acids. Furthermore, the compound having the ammonium salt structure of the alkyl ester anion represented by Formula 1 is preferably contained in the magnetic layer in an amount of 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100.0 parts by mass of ferromagnetic powder. Here, the content of the above compound in the magnetic layer refers to the total amount of the amount forming a liquid film on the surface of the magnetic layer and the amount contained inside the magnetic layer. On the other hand, a high content of ferromagnetic powder in the magnetic layer is preferable from the viewpoint of high-density recording. Therefore, from the viewpoint of high-density recording, a low content of components other than ferromagnetic powder is preferable. From this viewpoint, the content of the above compound in the magnetic layer is preferably 15.0 parts by mass or less, more preferably 10.0 parts by mass or less, and even more preferably 8.0 parts by mass or less, per 100.0 parts by mass of ferromagnetic powder. The same applies to the preferred range of content of the above compound in the magnetic layer forming composition used to form the magnetic layer.

[0080] As lubricants, esters and / or amides of fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid can also be used. Specific examples of fatty acid esters include butyl myristate, butyl palmitate, butyl stearate, neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl stearate, isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate, and butoxyethyl stearate. Specific examples of fatty acid amides include lauric acid amide, myristic acid amide, palmitic acid amide, and stearic acid amide. The content of fatty acid esters in the magnetic layer or magnetic layer-forming composition is, for example, 0 to 10.0 parts by mass, preferably 0.5 to 7.0 parts by mass, per 100.0 parts by mass of ferromagnetic powder. The content of fatty acid amides in the magnetic layer or magnetic layer-forming composition is, for example, 0 to 1.0 part by mass, preferably 0.1 to 1.0 part by mass, per 100.0 parts by mass of ferromagnetic powder. For the content of fatty acid esters and fatty acid amides in the non-magnetic layer or non-magnetic layer-forming composition, the above description can be applied by replacing the ferromagnetic powder with non-magnetic powder.

[0081] <Non-magnetic layer> Next, the non-magnetic layer will be described. The magnetic recording medium described above may have a magnetic layer directly on a non-magnetic support, or it may have a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. The non-magnetic powder used in the non-magnetic layer may be an inorganic powder or an organic powder. Carbon black can also be used. Examples of inorganic substances include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These non-magnetic powders are available commercially and can also be manufactured by known methods. For details, see paragraphs 0146 to 0150 of Japanese Patent Application Publication No. 2011-216149. For carbon black that can be used in the non-magnetic layer, see paragraphs 0040 to 0041 of Japanese Patent Application Publication No. 2010-24113. The content (filling rate) of non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass, relative to the total mass of the non-magnetic layer.

[0082] The non-magnetic layer may contain a binder and may also contain additives. Regarding other details of the binder, additives, etc., of the non-magnetic layer, known technology relating to non-magnetic layers can be applied. Furthermore, regarding, for example, the type and content of the binder, the type and content of the additives, known technology relating to magnetic layers can also be applied.

[0083] The non-magnetic layer of the above magnetic recording medium shall also include a substantially non-magnetic layer containing a small amount of ferromagnetic powder, for example as an impurity or intentionally, along with non-magnetic powder. Here, a substantially non-magnetic layer means a layer in which the remanent magnetic flux density is 10 mT or less, or the coercivity is 7.96 kA / m (100 Oe) or less, or the remanent magnetic flux density is 10 mT or less and the coercivity is 7.96 kA / m (100 Oe) or less. It is preferable that the non-magnetic layer has no remanent magnetic flux density and coercivity.

[0084] <Non-magnetic support> Next, non-magnetic support will be described. Examples of non-magnetic support (hereinafter also simply referred to as "support") include known materials such as biaxially oriented polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamide-imide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These support may be subjected to corona discharge, plasma treatment, easy-adhesion treatment, heat treatment, etc. in advance.

[0085] In one embodiment, the non-magnetic support of the above-mentioned magnetic recording medium may be an aromatic polyester support. In the present invention and this specification, "aromatic polyester" means a resin containing an aromatic skeleton and a plurality of ester bonds, and "aromatic polyester support" means a support containing at least one layer of aromatic polyester film. "Aromatic polyester film" means a film in which the component that constitutes the film and which accounts for the largest amount by mass is aromatic polyester. In the present invention and this specification, "aromatic polyester support" includes both a support in which all the resin films contained therein are aromatic polyester films and a support containing aromatic polyester films and other resin films. Specific forms of aromatic polyester support include a single layer of aromatic polyester film, a laminated film of two or more layers of aromatic polyester films with the same constituent components, a laminated film of two or more layers of aromatic polyester films with different constituent components, a laminated film containing one or more layers of aromatic polyester film and one or more layers of resin films other than aromatic polyester, etc. In a laminated film, an adhesive layer or the like may be optionally included between two adjacent layers. Furthermore, the aromatic polyester support may optionally include a metal film and / or a metal oxide film formed by vapor deposition or the like on one or both surfaces. The same applies to the "polyethylene terephthalate support" and "polyethylene naphthalate support" in the present invention and this specification.

[0086] The aromatic rings contained in the aromatic skeleton of an aromatic polyester are not particularly limited. Specific examples of aromatic rings include, for example, benzene rings and naphthalene rings. For example, polyethylene terephthalate (PET) is a polyester containing a benzene ring and is a resin obtained by polycondensation of ethylene glycol with terephthalic acid and / or dimethyl terephthalate. In the present invention and this specification, "polyethylene terephthalate" also includes structures having one or more other components in addition to the above components (e.g., copolymer components, components introduced into the terminals or side chains, etc.). Polyethylene naphthalate (PEN) is a polyester containing a naphthalene ring and is a resin obtained by esterification of dimethyl 2,6-naphthalenedicarboxylate with ethylene glycol, followed by transesterification and polycondensation reactions. In the present invention and this specification, "polyethylene naphthalate" also includes structures having one or more other components in addition to the above components (e.g., copolymer components, components introduced into the terminals or side chains, etc.).

[0087] In one embodiment, the non-magnetic support of the magnetic recording medium described above may be an aromatic polyamide support. In the present invention and this specification, "aromatic polyamide" means a resin containing an aromatic skeleton and a plurality of amide bonds. The aromatic rings contained in the aromatic skeleton of the aromatic polyamide are not particularly limited. Specific examples of aromatic rings include, for example, benzene rings. "Aromatic polyamide support" means a support containing at least one layer of aromatic polyamide film. "Aromatic polyamide film" means a film in which the component that constitutes the film by mass is aromatic polyamide. In the present invention and this specification, "aromatic polyamide support" includes both a support in which all the resin films contained are aromatic polyamide films and a support containing aromatic polyamide films and other resin films. Specific forms of aromatic polyamide support include a single layer of aromatic polyamide film, a laminated film of two or more layers of aromatic polyamide films with the same constituent components, a laminated film of two or more layers of aromatic polyamide films with different constituent components, and a laminated film containing one or more layers of aromatic polyamide film and one or more layers of resin films other than aromatic polyamide. In the laminated film, an adhesive layer or the like may be optionally included between two adjacent layers. Furthermore, the aromatic polyamide support may optionally include a metal film and / or a metal oxide film formed by vapor deposition or the like on one or both surfaces.

[0088] Furthermore, as mentioned above, the non-magnetic support can be a biaxially oriented film, and may be a film that has undergone corona discharge, plasma treatment, easy adhesion treatment, heat treatment, etc.

[0089] One indicator of the physical properties of a non-magnetic support is, for example, its moisture content. In the present invention and this specification, the moisture content of a non-magnetic support is a value obtained by the following method. A sample piece (for example, a sample piece with a mass of several grams) cut from the non-magnetic support to be measured for moisture content is dried in a vacuum dryer at a temperature of 180°C and a pressure of 100 Pa (Pascals) or less until a constant weight is reached. The mass of the dried sample piece is denoted as W1. W1 is a value measured within 30 seconds after removal from the vacuum dryer in a measurement environment of 23°C and 50% relative humidity. Next, the mass of this sample piece after being placed in an environment of 25°C and 75% relative humidity for 48 hours is denoted as W2. W2 is a value measured within 30 seconds after removal from the above environment in a measurement environment of 23°C and 50% relative humidity. The moisture content is calculated by the following formula. Water content (%) = [(W2 - W1) / W1] × 100 For example, after removing parts other than the non-magnetic support, such as the magnetic layer, from the magnetic recording medium by a known method (e.g., defilm removal using an organic solvent), the water content of the non-magnetic support can also be determined by the above method.

[0090] In one embodiment, the non-magnetic support of the magnetic recording medium preferably has a water content of 2.0% or less, more preferably 1.8% or less, even more preferably 1.6% or less, even more preferably 1.4% or less, even more preferably 1.2% or less, and even more preferably 1.0% or less. Furthermore, the water content of the non-magnetic support of the magnetic recording medium can be 0%, 0% or more, greater than 0%, or 0.1% or more.

[0091] Young's modulus is also an indicator of the physical properties of a non-magnetic support. In the present invention and this specification, the Young's modulus of a non-magnetic support contained in a magnetic tape is a value measured by the following method in a measurement environment of 23°C and 50% relative humidity. A sample piece cut from the non-magnetic support to be measured is pulled in a universal tensile testing apparatus under the conditions of a chuck distance of 100 mm, a tensile speed of 10 mm / min, and a chart speed of 500 mm / min. As the universal tensile testing apparatus, for example, a commercially available universal tensile testing apparatus such as the Tensilon manufactured by Toyo Baldwin Co., Ltd. or a universal tensile testing apparatus with a known configuration can be used. From the tangent of the rising portion of the load-elongation curve thus obtained, the Young's modulus in the longitudinal and width directions of the sample piece is calculated, respectively. Here, the longitudinal and width directions of the sample piece refer to the longitudinal and width directions when this sample piece was contained in a magnetic tape. For example, after removing parts other than the non-magnetic support, such as the magnetic layer, from the magnetic tape using a known method (e.g., defilm removal using an organic solvent), the Young's modulus in the longitudinal and width directions of the non-magnetic support can be determined using the method described above.

[0092] In one embodiment, the Young's modulus of the non-magnetic support contained in the magnetic tape is preferably 3000 MPa or more, more preferably 4000 MPa or more, even more preferably 5000 MPa or more, and even more preferably 6000 MPa or more in the longitudinal direction. The Young's modulus of the non-magnetic support contained in the magnetic tape can also be 15000 MPa or less, 13000 MPa or less, or 12000 MPa or less. In the width direction, the Young's modulus of the non-magnetic support contained in the magnetic tape is preferably 2000 MPa or more, more preferably 3000 MPa or more, even more preferably 4000 MPa or more, and even more preferably 5000 MPa or more in the width direction. The Young's modulus of the non-magnetic support contained in the magnetic tape can also be 12000 MPa or less, 11000 MPa or less, or 10000 MPa or less. During the manufacture of magnetic tape, the non-magnetic support is typically used with the machine direction (MD) of the film as the longitudinal direction and the transverse direction (TD) as the width direction. In one embodiment, it is preferable that the Young's modulus in the longitudinal direction is greater than the Young's modulus in the width direction, and it is more preferable that the difference (Young's modulus in the longitudinal direction - Young's modulus in the width direction) is in the range of 800 to 3000 MPa.

[0093] The water content and Young's modulus of a non-magnetic support can be controlled by the type and mixing ratio of the components constituting the support, the manufacturing conditions of the support, etc. For example, by adjusting the stretching ratio in each direction during biaxial stretching, the Young's modulus in the longitudinal direction and the Young's modulus in the width direction can be controlled, respectively.

[0094] <Backcoat Layer> The magnetic recording medium described above may or may not have a backcoat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support. Preferably, the backcoat layer contains either or both carbon black and inorganic powder. The backcoat layer may contain a binder and may also contain additives. For details of the non-magnetic powder, binder, additives, etc. of the backcoat layer, known technology relating to backcoat layers may be applied, and known technology relating to magnetic layers and / or non-magnetic layers may also be applied. For example, paragraphs 0018 to 0020 of Japanese Patent Application Publication No. 2006-331625 and lines 65 to 38 of column 5 of U.S. Patent No. 7,029,774 can be referenced regarding the backcoat layer.

[0095] <Various Thicknesses> Regarding the thickness (total thickness) of magnetic recording media, with the enormous increase in the amount of information in recent years, there is a demand for increased recording capacity (higher capacity) in magnetic recording media. Means for increasing capacity include, for example, for magnetic tape, reducing the thickness of the magnetic tape and increasing the length of magnetic tape that can be stored in one reel of magnetic tape cartridge. From the viewpoint of increasing capacity, the thickness (total thickness) of the above magnetic recording media is preferably 5.6 μm or less, more preferably 5.5 μm or less, more preferably 5.4 μm or less, even more preferably 5.3 μm or less, even more preferably 5.2 μm or less, and even more preferably 5.0 μm or less. Furthermore, from the viewpoint of ease of handling, the thickness of the magnetic recording media is preferably 3.0 μm or more, and more preferably 3.5 μm or more.

[0096] For example, the thickness (total thickness) of a magnetic tape can be measured by the following method: Ten tape samples (e.g., 5-10 cm in length) are cut from any part of the magnetic tape, and the thickness is measured by stacking these tape samples. The measured thickness is divided by ten to obtain the value obtained (thickness per tape sample), which is taken as the tape thickness. The above thickness measurement can be performed using a known measuring instrument capable of measuring thickness to the order of 0.1 μm.

[0097] The thickness of the non-magnetic support is preferably 2.0 to 5.0 μm, more preferably 3.0 to 5.0 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 bandwidth of the recording signal, etc., and is generally 0.01 μm to 0.15 μm, preferably 0.02 μm to 0.12 μm, and even more preferably 0.03 μm to 0.1 μm, from the viewpoint of high-density recording. There should be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic properties, and known configurations for multilayer magnetic layers can be applied. When separated into two or more layers, the thickness of the magnetic layer is the total thickness of these layers. The thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm, preferably 0.1 to 1.0 μm, and more preferably 0.1 to 0.7 μm. The thickness of the back coat layer is preferably 0.9 μm or less, and even more preferably 0.1 to 0.7 μm. Various thicknesses, such as the thickness of the magnetic layer, can be determined by the following method: After exposing the cross-section of the magnetic recording medium in the thickness direction using an ion beam, the exposed cross-section is observed using a scanning electron microscope or a transmission electron microscope. Various thicknesses can be determined as the arithmetic mean of the thicknesses obtained at any two locations in the cross-sectional observation. Alternatively, various thicknesses can be determined as design thicknesses calculated from manufacturing conditions, etc.

[0098] <Manufacturing Method> (Preparation of Composition for Forming Each Layer)The composition for forming a magnetic layer, a non-magnetic layer, or a backcoat layer generally contains a solvent together with the various components described above. As the solvent, various organic solvents commonly used for manufacturing a coated magnetic recording medium can be used. Among them, from the viewpoint of the solubility of the binder usually used for the coated magnetic recording medium, the composition for forming each layer preferably contains one or more of ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, and tetrahydrofuran. The amount of the solvent in the composition for forming each layer is not particularly limited and can be the same as that of the composition for forming each layer of a normal coated magnetic recording medium. Further, the step of preparing the composition for forming each layer can usually include at least a kneading step, a dispersion step, and a mixing step provided as necessary before and after these steps. Each individual step may be divided into two or more stages. The components used for preparing the composition for forming each layer may be added at the beginning or during any step. The individual components may be added in portions over two or more steps. For example, the binder may be added in portions in the kneading step, the dispersion step, and the mixing step for adjusting the viscosity after dispersion. For example, in the step of preparing the composition for forming a magnetic layer, if the dispersion time in the preparation of a dispersion liquid containing ferromagnetic powder (hereinafter referred to as "magnetic liquid") is increased, the magnetic field of the manufactured magnetic recording medium ０．３The value of tends to decrease. Also, as described above, one or more nitrogen-containing polymers and one or more of the above fatty acids can be used as components of the magnetic layer forming composition, and the salt formation reaction can be carried out by mixing them in the preparation step of the magnetic layer forming composition. In one embodiment, one or more nitrogen-containing polymers and one or more of the fatty acids can be mixed to form a salt before preparing the magnetic layer forming composition, and then this salt can be used as a component of the magnetic layer forming composition to prepare the magnetic layer forming composition. This also applies to the preparation step of the non-magnetic layer forming composition. In one embodiment, in the step of preparing the magnetic layer forming composition, a dispersion containing a protrusion-forming agent (hereinafter referred to as "protrusion-forming agent solution") can be prepared, and then this protrusion-forming agent solution can be mixed with one or more of the other components of the magnetic layer forming composition. For example, the protrusion-forming agent solution can be prepared by a known dispersion treatment such as ultrasonic treatment. Ultrasonic treatment can be performed, for example, with 200 cc (1 cc = 1 cm). ３ This can be performed for 1 to 300 minutes at an ultrasonic output of approximately 10 to 2000 watts per unit. Filtration may also be performed after the dispersion treatment. For information on filters to be used for filtration, please refer to the following description.

[0099] In the manufacturing process of the magnetic recording medium described above, some or all of the conventional known manufacturing techniques can be used in some or all of the processes. In the kneading process, it is preferable to use a kneader with strong kneading force, such as an open kneader, continuous kneader, pressure kneader, or extruder. Details of these kneading processes are described in Japanese Patent Publication No. 1-106338 and Japanese Patent Publication No. 1-79274. In addition, glass beads and / or other beads can be used to disperse each layer-forming composition. Suitable dispersion beads include high-density dispersion beads such as zirconia beads, titania beads, and steel beads. It is preferable to optimize the particle size (bead diameter) and packing rate of these dispersion beads. Known dispersers can be used. Each layer-forming composition may be filtered by a known method before being subjected to the coating process. Filtration can be performed, for example, by filter filtration. As filters used for filtration, for example, filters with a pore size of 0.01 to 3 μm (e.g., glass fiber filters, polypropylene filters, etc.) can be used.

[0100] (Coating Process) The magnetic layer can be formed by, for example, directly coating a magnetic layer-forming composition onto a non-magnetic support, or by sequentially or simultaneously overcoating it with the non-magnetic layer-forming composition. When orientation processing is performed, the orientation processing is carried out on the coated layer in the orientation zone while the coated layer of the magnetic layer-forming composition is wet. Various known techniques, including the one described in paragraph 0052 of Japanese Patent Application Publication No. 2010-24113, can be applied to the orientation processing. For example, vertical orientation processing can be performed by known methods such as using opposite-polarity opposing magnets. In the orientation zone, the drying speed of the coated layer can be controlled by the temperature and volume of the drying air and / or the transport speed in the orientation zone. Alternatively, the coated layer may be pre-dried before being transported to the orientation zone. The back coat layer can be formed by coating a back coat-forming composition on the side of the non-magnetic support opposite to the side that has (or will subsequently have) the magnetic layer. For details on coating for each layer formation, refer to paragraph 0066 of Japanese Patent Application Publication No. 2010-231843.

[0101] magnetic field ０．３ Regarding control, the slower the transport speed of the non-magnetic support during coating, orientation, and drying in the coating process, the more the magnetic field of the manufactured magnetic recording medium will be affected. ０．３ The value of tends to decrease. Also, the lower the drying temperature during drying after orientation processing, the lower the magnetic field of the manufactured magnetic recording medium. ０．３ The value tends to be small.

[0102] (Other processes) After the above coating process, the magnetic recording medium is usually calendered to improve its surface smoothness. Regarding the calendering conditions, the calendering pressure is, for example, 200 to 500 kN / m, preferably 250 to 350 kN / m; the calendering temperature (more specifically, the surface temperature of the calender roll) is preferably 90 to 120°C, more preferably 100 to 120°C; and the calendering speed (more specifically, the transport speed of the non-magnetic support in the calendering process) is, for example, 50 to 300 m / min, preferably 80 to 200 m / min. For other various processes for manufacturing magnetic recording media, refer to paragraphs 0067 to 0070 of Japanese Patent Application Publication No. 2010-231843. By going through various processes, a long magnetic recording medium raw material can be obtained. The obtained magnetic recording medium raw material is cut into tape or disc shapes using a known cutting machine. For example, it is cut (slit) to the width of a magnetic tape to be housed in a magnetic tape cartridge. The above width can be determined according to the standard and is usually 1 / 2 inch. A servo pattern is usually formed on the magnetic tape obtained by slitting.

[0103] (Formation of servo patterns) "Formation of servo patterns" can also be described as "recording of servo signals." The formation of servo patterns will be explained below using magnetic tape as an example.

[0104] Servo patterns are typically formed along the longitudinal direction of the magnetic tape. Examples of control methods that utilize servo signals (servo control) include timing-based servo (TBS), amplitude servo, and frequency servo.

[0105] As indicated in ECMA (European Computer Manufacturers Association)-319 (June 2001), magnetic tapes conforming to the LTO (Linear Tape-Open) standard (commonly referred to as "LTO tapes") employ a timing-based servo system. In this timing-based servo system, the servo pattern is composed of multiple pairs of non-parallel magnetic stripes (also called "servo stripes") arranged continuously in the longitudinal direction of the magnetic tape. In the present invention and this specification, "timing-based servo pattern" refers to a servo pattern that enables head tracking in a timing-based servo system. As described above, the reason why the servo pattern is composed of pairs of non-parallel magnetic stripes is to inform the servo signal reading element passing over the servo pattern of its position. Specifically, the pair of magnetic stripes described above are formed such that their spacing changes continuously along the width of the magnetic tape, and the servo signal reading element reads this spacing to determine the relative position between the servo pattern and the servo signal reading element. This relative position information enables the tracking of data tracks. For this purpose, multiple servo tracks are typically set up on the servo pattern along the width of the magnetic tape.

[0106] A servo band consists of a servo pattern that runs continuously along the longitudinal direction of the magnetic tape. Typically, multiple servo bands are provided on a magnetic tape. For example, in an LTO tape, there are five. The area between two adjacent servo bands is the data band. A data band consists of multiple data tracks, each corresponding to a servo track.

[0107] In one embodiment, as shown in Japanese Patent Publication No. 2004-318983, each servo band has embedded information indicating the servo band number (also called "servo band ID (identification)" or "UDIM (Unique DataBand Identification Method) information"). This servo band ID is recorded by shifting a specific pair of servo stripes within a servo band so that its position is displaced relative to the longitudinal direction of the magnetic tape. Specifically, the method of shifting a specific pair of servo stripes is changed for each servo band. As a result, the recorded servo band ID is unique for each servo band, so that a servo band can be uniquely identified by reading it with a servo signal reading element.

[0108] Furthermore, one method for uniquely identifying a servo band is the staggered method, as described in ECMA-319 (June 2001). In this staggered method, a group of non-parallel magnetic stripes (servo stripes) arranged continuously along the longitudinal direction of the magnetic tape are recorded in a manner that shifts each servo band along the longitudinal direction of the magnetic tape. Since the combination of this shift between adjacent servo bands is unique across the entire magnetic tape, it is possible to uniquely identify a servo band when reading the servo pattern using two servo signal reading elements.

[0109] Furthermore, each servo band typically has embedded information indicating its position along the longitudinal direction of the magnetic tape (also known as "LPOS (Longitudinal Position) information"), as shown in ECMA-319 (June 2001). This LPOS information, like the UDIM information, is recorded by shifting the positions of a pair of servo stripes along the longitudinal direction of the magnetic tape. However, unlike the UDIM information, the same signal is recorded for each servo band in this LPOS information.

[0110] It is also possible to embed information other than the UDIM and LPOS information described above into the servo bands. In this case, the embedded information may be different for each servo band, like the UDIM information, or it may be common to all servo bands, like the LPOS information. Furthermore, methods other than those described above can be used to embed information into the servo bands. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of servo stripes.

[0111] A servo pattern forming head is called a servo light head. A servo light head typically has a pair of gaps corresponding to the pair of magnetic stripes mentioned above, for each servo band. Typically, a core and a coil are connected to each pair of gaps, and by supplying current pulses to the coils, the magnetic field generated in the core can create a leakage magnetic field in the pair of gaps. When forming a servo pattern, by inputting current pulses while running a magnetic tape over the servo light head, the magnetic patterns corresponding to the pair of gaps are transferred to the magnetic tape, thereby forming the servo pattern. The width of each gap can be appropriately set according to the density of the servo pattern to be formed. For example, the width of each gap can be set to 1 μm or less, 1 to 10 μm, 10 μm or more, etc.

[0112] Before forming a servo pattern on a magnetic tape, it is usually demagnetized (erased). This erasing process can be performed by applying a uniform magnetic field to the magnetic tape using a DC or AC magnet. There are two types of erasing: DC (Direct Current) erasing and AC (Alternating Current) erasing. AC erasing is performed by gradually reducing the strength of the magnetic field while reversing the direction of the magnetic field applied to the magnetic tape. On the other hand, DC erasing is performed by applying a unidirectional magnetic field to the magnetic tape. There are two further methods of DC erasing. The first method is horizontal DC erasing, which applies a unidirectional magnetic field along the longitudinal direction of the magnetic tape. The second method is vertical DC erasing, which applies a unidirectional magnetic field along the thickness direction of the magnetic tape. The erasing process may be performed on the entire magnetic tape or on each servo band of the magnetic tape.

[0113] The direction of the magnetic field of the formed servo pattern is determined according to the direction of the erase. For example, when a magnetic tape is horizontally DC erased, the servo pattern is formed such that the direction of the magnetic field is opposite to the direction of the erase. This makes it possible to increase the output of the servo signal obtained by reading the servo pattern. As shown in Japanese Patent Application Publication No. 2012-53940, when a magnetic pattern using the above gap is transferred to a vertically DC erased magnetic tape, the servo signal obtained by reading the formed servo pattern is in the shape of a single-pole pulse. On the other hand, when a magnetic pattern using the above gap is transferred to a horizontally DC erased magnetic tape, the servo signal obtained by reading the formed servo pattern is in the shape of a double-pole pulse.

[0114] [Magnetic Tape Cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the above-mentioned tape-shaped magnetic recording medium (i.e., magnetic tape).

[0115] Details of the magnetic tape included in the above magnetic tape cartridge are as described above.

[0116] In a magnetic tape cartridge, the magnetic tape is generally housed inside the cartridge body, wound onto a reel. The reel is rotatably mounted inside the cartridge body. Two types of magnetic tape cartridges are widely used: single-reel cartridges, which have one reel inside the cartridge body, and double-reel cartridges, which have two reels inside the cartridge body. When a single-reel magnetic tape cartridge is mounted in a magnetic recording / reproduction device for recording and / or reproducing data onto magnetic tape, the magnetic tape is pulled out of the cartridge and wound onto the reel on the magnetic recording / reproduction device side. A magnetic head is positioned in the magnetic tape transport path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed and rewound between the reel on the magnetic tape cartridge side (supply reel) and the reel on the magnetic recording / reproduction device side (take-up reel). During this time, the magnetic head and the surface of the magnetic layer of the magnetic tape come into contact and slide against each other, enabling data recording and / or reproduction. In contrast, a dual-reel magnetic tape cartridge has both a supply reel and a take-up reel housed inside the magnetic tape cartridge. The magnetic tape cartridge may be either a single-reel or dual-reel type. The magnetic tape cartridge may contain a magnetic tape according to one aspect of the present invention, and other aspects may be based on known technology. The total length of the magnetic tape housed in the magnetic tape cartridge can be, for example, 800 m or more, and may be in the range of 800 m to 2000 m. A longer total length of tape housed in the magnetic tape cartridge is preferable from the viewpoint of increasing the capacity of the magnetic tape cartridge.

[0117] [Magnetic Recording and Reproducing Device] One aspect of the present invention relates to a magnetic recording and reproducing device including the above-mentioned magnetic recording medium.

[0118] In the present invention and this specification, "magnetic recording and reproduction device" means a device capable of recording data onto a magnetic recording medium and reproducing data recorded on a magnetic recording medium, or at least one of the latter. Such a device is generally called a drive. The magnetic recording and reproduction device may be, for example, a sliding type magnetic recording and reproduction device. A sliding type magnetic recording and reproduction device is a device in which the surface of the magnetic layer and the magnetic head come into contact and slide when recording data onto a magnetic recording medium and / or reproducing recorded data. For example, the magnetic recording and reproduction device may include a magnetic tape cartridge that can be detachably attached.

[0119] The above magnetic recording and playback device may include a magnetic head. The magnetic head may be a recording head capable of recording data onto a magnetic tape, or a playback head capable of playing back data recorded on the magnetic tape. In one embodiment, the magnetic recording and playback device may include both a recording head and a playback head as separate magnetic heads. In another embodiment, the magnetic head included in the magnetic recording and playback device may have a configuration in which both an element for recording data (recording element) and an element for playing back data (playback element) are provided on a single magnetic head. The recording head may be an in-plane recording magnetic head or a vertical recording magnetic head. For in-plane recording magnetic heads and vertical recording magnetic heads, known technology relating to those heads can be applied. For example, the magnetic recording medium can exhibit excellent electromagnetic conversion characteristics when playing back data recorded in an in-plane recording method. In one embodiment, the recording head included in the magnetic recording and playback device may be an in-plane recording magnetic head. As the playback head, a magnetic head (MR head) that includes a magnetoresistive (MR) element as a playback element, which can read data recorded on magnetic tape with high sensitivity, is preferred. As the MR head, various known MR heads such as AMR (Anisotropic Magnetoresistive) heads, GMR (Giant Magnetoresistive) heads, and TMR (Tunnel Magnetoresistive) heads can be used. In addition, the magnetic head that records and / or plays back data may include a servo signal reading element. Alternatively, a magnetic head (servo head) equipped with a servo signal reading element may be included in the magnetic recording and / or playback device as a separate head from the magnetic head that records and / or plays back data. For example, a magnetic head that records and / or plays back recorded data (hereinafter also referred to as the "recording / playback head") may include two servo signal reading elements, each of which can simultaneously read two adjacent servo bands.One or more data elements can be placed between two servo signal reading elements. Elements for recording and reproducing data are collectively referred to as "data elements."

[0120] In the above-described magnetic recording and reproduction apparatus, recording data onto a magnetic recording medium and / or reproducing data recorded on the magnetic recording medium can be performed, for example, by bringing the magnetic layer surface of the magnetic recording medium into contact with a magnetic head and sliding it. The above-described magnetic recording and reproduction apparatus may include a magnetic recording medium according to one aspect of the present invention, and prior art can be applied for other aspects.

[0121] For example, when recording data and / or playing back recorded data, tracking using servo signals is performed first. That is, by making the servo signal reading element follow a predetermined servo track, the data element is controlled to pass over the target data track. The movement of the data track is achieved by changing the servo track read by the servo signal reading element in the tape width direction. The recording / playback head can also record and / or play back data on other data bands. In this case, the UDIM information described above is used to move the servo signal reading element to a predetermined servo band, and tracking for that servo band is started.

[0122] The present invention will be described below based on examples. However, the present invention is not limited to the embodiments shown in the examples. Unless otherwise specified, "parts" and "%" in the following description refer to "parts by mass". Furthermore, unless otherwise specified, the processes and evaluations described below were carried out in an environment with a temperature of 23°C ± 1°C. "eq" in the following description refers to equivalent weight and is a unit that cannot be converted to SI units.

[0123] [Ferromagnetic Powders] In Table 1, "BaFe" is an abbreviation for hexagonal barium ferrite powder. In Table 1, "SrFe" is an abbreviation for hexagonal strontium ferrite powder. The average particle size of the ferromagnetic powders shown in Table 1 was measured using a Hitachi H-9000 transmission electron microscope and Carl Zeiss KS-400 image analysis software.

[0124] [Non-magnetic support] In Table 1, "PEN" indicates a polyethylene naphthalate support, and "PA" indicates an aromatic polyamide support.

[0125] [Example 1] <Preparation of ferromagnetic powder (hexagonal ferrite powder SrFe1)> SrCO ３ 1736g, H ３ BO ３ 662g, Fe ２ O ３ 1340g of Al(OH) ３ 52g of CaCO2 ３ 35g of BaCO ３146 g each was weighed and mixed in a mixer to obtain a raw material mixture. The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1420°C. While stirring the molten material, the outlet at the bottom of the platinum crucible was heated, and the molten material was dispensed in a rod shape at approximately 6 g / second. The dispensed material was rapidly cooled and rolled using a water-cooled twin roll to produce an amorphous material. 280 g of the obtained amorphous material was placed in an electric furnace, heated to 645°C (crystallization temperature), and held at the same temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. Next, the crystalline material obtained above, containing the hexagonal strontium ferrite particles, was coarsely ground in a mortar and placed in a glass bottle. 1000 g of 1 mm particle size zirconia beads and 800 ml of 1% acetic acid aqueous solution were added to this glass bottle and dispersed in a paint shaker for 3 hours. After that, the dispersion was separated from the beads and placed in a stainless steel beaker. The dispersion was allowed to stand at a liquid temperature of 95°C for 3.5 hours to dissolve the glass components, then it was washed by repeated decantation after sedimentation using a centrifuge, and dried in a heating furnace at a furnace temperature of 110°C for 6 hours. The powder after drying was subjected to classification by the following method. In the classification process, among the particles contained in the liquid subjected to centrifugation, the particles with a small particle size dispersed in the supernatant after centrifugation, while the particles with a large particle size precipitated. 10 g of the dried powder, 3.5 g of citric acid, 300 g of zirconia beads, and 55 g of pure water were placed in a sealed container and dispersed in a paint shaker for 3.8 hours. Then, 360 g of pure water was added to separate the beads from the liquid, and after centrifugation to settle the powder, the supernatant was removed. Subsequently, 380 g of pure water was added, and the mixture was redispersed using a homogenizer. The pH was adjusted to 9.6 with 25% aqueous ammonia to obtain dispersion A containing dispersed hexagonal strontium ferrite powder particles. Dispersion A was subjected to a first centrifugation at 15200 G (G: acceleration due to gravity) for 190 minutes, after which the precipitate and supernatant were separated by decantation. Next, the obtained supernatant was subjected to a second centrifugation at 15200 G for 275 minutes, after which the supernatant and precipitate were separated by decantation. The obtained precipitate was dried in a heating furnace at a furnace temperature of 95°C for 6 hours to obtain hexagonal strontium ferrite powder SrFe1.

[0126] <Composition for forming a magnetic layer> (Magnetic liquid) Ferromagnetic powder (see Table 1): 100.0 parts Oleic acid: 2.0 parts Vinyl chloride copolymer (Kaneka Corporation MR-104): 10.0 parts SO ３ Na group-containing polyurethane resin: 4.0 parts (weight-average molecular weight 70,000, SO ３ Na group: 0.07 meq / g) Additive A: 10.0 parts Methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts (Abrasive liquid) α-alumina (average particle size: 110 nm): 6.0 parts Vinyl chloride copolymer (Kaneka Corporation MR110): 0.7 parts Cyclohexanone: 20.0 parts (Protrusion-forming agent liquid) Protrusion-forming agent (Asahi Carbon Co., Ltd. Asahi #50 (carbon black), average particle size 60 nm): 1.0 part Methyl ethyl ketone: 9.0 parts Cyclohexanone: 6.0 parts (Other components) Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd., number average molecular weight 300): 0.3 parts Stearic acid: 0.3 parts Stearamide: 0.3 parts Butyl stearate: 6.0 parts Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate (Tosoh Corporation, Coronate® L): 3.0 parts

[0127] The additive A described above is a polymer synthesized by the method described in paragraphs 0115 to 0123 of Japanese Patent Publication No. 2016-051493.

[0128] <Nonmagnetic layer forming composition> Nonmagnetic inorganic powder (α-iron oxide): 80.0 parts (average particle size: 0.15 μm, average acicular ratio: 7, BET (Brunauer-Emmett-Teller) specific surface area: 52 m ２ ( / g) Carbon black (average particle size: 20 nm): 20.0 parts Electron beam curable vinyl chloride copolymer: 13.0 parts Electron beam curable polyurethane resin: 6.0 parts Phenylephosphonic acid: 3.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Butyl stearate: 2.0 parts Stearic acid: 1.0 part

[0129] <Composition for forming the backcoat layer> Non-magnetic inorganic powder (α-iron oxide): 80.0 parts (average particle size: 0.15 μm, average needle-like ratio: 7, BET specific surface area: 52 m²) ２( / g) Carbon black (average particle size: 20 nm): 20.0 parts Carbon black (average particle size: 100 nm): 3.0 parts Vinyl chloride copolymer: 13.0 parts Sulfonic acid group-containing polyurethane resin: 6.0 parts Phenylephosphonic acid: 3.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Stearic acid: 3.0 parts Polyisocyanate (Tosoh Corporation's Coronate® L): 5.0 parts Methyl ethyl ketone: 400.0 parts

[0130] <Preparation of Compositions for Forming Each Layer> The magnetic layer-forming compositions were prepared by the following method. After kneading and diluting the components of the magnetic liquid in an open kneader, zirconia (ZrO) with a particle size of 0.5 mm was dispersed in a vessel-type bead mill disperser. ２ Using Zr beads (hereinafter referred to as "Zr beads"), a dispersion treatment was performed for 720 minutes at a bead filling rate of 80% by volume and a stirring spring peripheral speed of 2000 rpm (revolutions per minute). The abrasive liquid was prepared by mixing the components of the abrasive liquid above, then placing it in a vertical sand mill disperser together with 1 mm particle Zr beads, adjusting the ratio to 100 × bead volume / (abrasive liquid volume + bead volume) to 60%, and performing a sand mill dispersion treatment for 180 minutes. After treatment, the liquid was removed and subjected to ultrasonic dispersion filtration using a flow-type ultrasonic dispersion filtration device. The protrusion-forming agent liquid was prepared by mixing the components of the protrusion-forming agent liquid above, then ultrasonically treating (dispersing) the resulting dispersion with a horn-type ultrasonic disperser at an ultrasonic output of 500 watts per 200 cc for 60 minutes, and filtering the resulting dispersion through a filter with a pore size of 0.5 μm. The magnetic liquid, abrasive liquid, protrusion-forming agent liquid, and the other components mentioned above were introduced into a dissolver stirrer and stirred at a peripheral speed of 10 m / s for 30 minutes. After that, the mixture was subjected to three passes at a flow rate of 7.5 kg / min using a flow-type ultrasonic disperser, and then filtered through a filter with a pore size of 1 μm to prepare a composition for forming a magnetic layer.

[0131] The non-magnetic layer-forming composition was prepared by the following method. The above components, excluding the lubricants (butyl stearate and stearic acid), were kneaded and diluted using an open kneader, and then dispersed using a horizontal bead mill disperser for the dispersion time shown in Table 1. After that, the lubricants (butyl stearate and stearic acid) were added and mixed using a dissolver stirrer to prepare the non-magnetic layer-forming composition.

[0132] The backcoat layer forming composition was prepared by the following method: The above components, excluding the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts), were kneaded and diluted in an open kneader, and then dispersed in a horizontal bead mill disperser. Subsequently, the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts) were added and mixed in a dissolver stirrer to prepare the backcoat layer forming composition.

[0133] <Fabrication of Magnetic Tape and Magnetic Tape Cartridge> A biaxially oriented polyethylene naphthalate (PEN) support with a thickness of 4.0 μm was transported while a non-magnetic layer-forming composition was applied and dried so that the thickness after drying was 0.6 μm. Then, it was irradiated with an electron beam at an accelerating voltage of 125 kV to an energy of 40 kGy. While the support was transported, a magnetic layer-forming composition was applied on the non-magnetic layer formed by electron beam irradiation so that the thickness after drying was 0.1 μm to form a coated layer. While this coated layer was still wet, a magnetic field with a magnetic field strength of 0.5 T was applied perpendicularly to the surface of the coated layer of the magnetic layer-forming composition in the orientation zone to perform a vertical orientation treatment. Then, the coated layer was dried at a drying temperature of 70°C (listed in the "Coating Conditions" column in Table 1). Furthermore, a back coat layer-forming composition was applied to the surface of the support opposite to the surface where the non-magnetic layer and magnetic layer were formed so that the thickness after drying was 0.3 μm, and it was dried. The conveying speed of the support in the above process was 150 m / min (as indicated in the "Coating Conditions" column in Table 1). Subsequently, calendering was performed using a seven-stage calender roll consisting only of metal rolls, at a calendering speed (conveying speed of the non-magnetic support in the calendering process) of 80 m / min, a linear pressure of 320 kN / m, and a calendering temperature (surface temperature of the calender roll) of 100°C. After that, heat treatment was performed for 36 hours in an ambient temperature of 70°C. After the heat treatment, the material was slit to a width of 1 / 2 inch, and the surface of the magnetic layer was cleaned using a tape cleaning device equipped with a feed and winding device for the slit material, in which a nonwoven fabric and a razor blade were attached so as to press against the surface of the magnetic layer, thereby obtaining a magnetic tape. By recording servo signals on the magnetic layer of the obtained magnetic tape using a commercially available servo writer, a magnetic tape was obtained having data bands, servo bands, and guide bands arranged in accordance with the LTO (Linear Tape-Open) Ultrium format, and having a servo pattern (timing-based servo pattern) on the servo band in an arrangement and shape in accordance with the LTO Ultrium format.The servo pattern thus formed conforms to the specifications of JIS (Japanese Industrial Standards) X6175:2006 and Standard ECMA-319 (June 2001). The total number of servo bands is 5, and the total number of data bands is 4. The magnetic tape (960 m in length) on which the servo signals were recorded was wound onto a reel of a magnetic tape cartridge (LTO Ultrium 8 data cartridge). In this way, a magnetic tape cartridge with the magnetic tape wound onto a reel was manufactured.

[0134] [Examples 2-15, Comparative Examples 1-10] Except for the changes shown in Table 1 to the items shown in Table 1, magnetic tapes and magnetic tape cartridges were manufactured using the method previously described for Example 1. In the production of "BaFe1" and "BaFe2", SrCO2 was used. ３ Instead, BaCO ３ I used it.

[0135] For each of Examples 1 to 15 and Comparative Examples 1 to 10, multiple magnetic tape cartridges were manufactured and used for the evaluations described below.

[0136] [Evaluation Method] <Magnetic Field> ０．３ Measurement of magnetic field > For the magnetic tapes removed from each magnetic tape cartridge in Examples 1 to 15 and Comparative Examples 1 to 10, the magnetic field was measured using the method described above. ０．３ They sought it.

[0137] <Magnetic Tape Thickness> Ten tape samples (5 cm in length) were cut from arbitrary sections of the magnetic tape taken from each magnetic tape cartridge in the examples and comparative examples, and the thickness of these tape samples was measured by stacking them. The thickness was measured using a digital thickness meter consisting of a MARH Millimar 1240 compact amplifier and a Millimar 1301 inductive probe. The measured thickness was divided by 10 to obtain the value obtained (thickness per tape sample), which was defined as the tape thickness. For each magnetic tape in Examples 1 to 12 and Comparative Examples 1 to 5, the tape thickness was 5.0 μm. The tape thicknesses of each magnetic tape in Examples 13 to 15 were as follows: Example 13: 4.6 μm, Example 14: 4.0 μm, Example 15: 3.4 μm.

[0138] <Electromagnetic Conversion Characteristics> Under ambient temperature of 23°C ± 1°C and relative humidity of 50%, a recording head (MIG (Metal-in-gap) head, gap length 0.15 μm, 1.8 T) and a playback GMR (Giant Magnetoresistive) head (playback track width 1 μm) were attached to a loop tester, and a signal with a linear recording density of 350 kfci was recorded using an in-plane recording method (a recording method in which the direction of the recording magnetic field applied to the recording layer for magnetization reversal is controlled to be horizontal with respect to the in-plane direction). Subsequently, the playback signal was measured using an Advantest spectrum analyzer. Note that the unit kfci is the unit of linear recording density (cannot be converted to the SI unit system). The ratio of the output value of the carrier signal to the integrated noise across the entire spectral band was defined as the SNR (Signal-to-Noise Ratio). For SNR measurement, the signal was used from the portion of the magnetic tape where the signal had stabilized sufficiently after the tape began to run. The resulting SNR was then calculated as a relative value with the value of Comparative Example 10 as the reference (0.0 dB), and the electromagnetic conversion characteristics were evaluated according to the following evaluation criteria: A: 1.0 dB or more B: 0.6 dB or more and less than 1.0 dB C: 0.3 dB or more and less than 0.6 dB D: 0.0 dB or more and less than 0.3 dB

[0139] The results are shown in Table 1 (Tables 1-1 to 1-5).

[0140]

[0141]

[0142]

[0143]

[0144]

[0145] The results shown in Table 1 confirm that the magnetic tapes of Examples 1 to 15 exhibited excellent electromagnetic conversion characteristics.

[0146] One aspect of the present invention is useful in the technical field of various data storage technologies.

Claims

1. A magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the magnetic field of the magnetic recording medium ０．３ The magnetic field is 4.0 kOe or more and 8.0 kOe or less, the magnetic recording medium is a magnetic tape or a magnetic disk, and the magnetic field ０．３ This refers to a magnetic recording medium in which the remanent magnetization, obtained by measurement with a vibrating sample type magnetometer, is plotted on the vertical axis against the applied magnetic field value in the longitudinal direction of the magnetic tape or the radial direction of the magnetic disk on the horizontal axis, and the differential curve obtained by differentiating this plot is normalized to a maximum value of 1 on the vertical axis, and the value on the horizontal axis is the higher magnetic field value of the two values ​​on the horizontal axis that result in a value of 0.

3.

2. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is a hexagonal strontium ferrite powder having an average particle size of 9 nm or more and 19 nm or less.

3. The aforementioned magnetic field ０．３ The magnetic recording medium according to claim 1, wherein the coefficient of kOe is 4.0 kOe or more and 5.4 kOe or less.

4. The magnetic recording medium according to claim 1, further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

5. The magnetic recording medium according to claim 1, further comprising a back coat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer.

6. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic recording medium is 5.0 μm or less.

7. The magnetic recording medium according to claim 1, wherein the non-magnetic support is an aromatic polyamide support.

8. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a magnetic tape.

9. The ferromagnetic powder is a hexagonal strontium ferrite powder with an average particle size of 9 nm or more and 19 nm or less, and the magnetic field ０．３ The magnetic recording medium according to claim 1, wherein the magnetic layer is 4.0 kOe or more and 5.4 kOe or less, and further comprises a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer, and further comprises a back coat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer, and the thickness of the magnetic recording medium is 5.0 μm or less, and the magnetic recording medium is a magnetic tape.

10. A magnetic tape cartridge comprising the magnetic tape according to claim 8 or 9.

11. A magnetic recording and reproducing apparatus including a magnetic recording medium according to any one of claims 1 to 9.

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