Magnetic recording medium, magnetic tape cartridge, and magnetic recording / reproducing device

Abstract

To provide a magnetic recording medium capable of exhibiting excellent durability and reducing head wearing.SOLUTION: There is provided a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder, in which the magnetic layer contains an abrasive, the abrasive is a carbide, an average primary particle size of the abrasive is 10 nm or more and 100 nm or less, and a ratio of an area occupied by the abrasive present in an aggregated state with a maximum Feret diameter of 0.2 μm or more is 50% or more, when a total area occupied by the abrasive in an electron microscope image of a surface of the magnetic layer is 100%. There are also provided a magnetic tape cartridge and a magnetic recording / reproducing device containing the magnetic recording medium.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a magnetic recording medium, a magnetic tape cartridge, and a magnetic recording / reproducing device. [Background technology]

[0002] BACKGROUND ART Magnetic recording media are widely used as recording media for recording various types of data (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-26564 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-286074 Summary of the Invention [Problem to be solved by the invention]

[0004] Data is recorded on a magnetic recording medium and reproduced by, for example, contacting and sliding a magnetic head (hereinafter also referred to simply as "head") against the magnetic layer surface of the magnetic recording medium. The phenomenon in which the distance between the magnetic layer surface and the head increases is generally called spacing loss, and the greater this distance, the more the electromagnetic conversion characteristics tend to deteriorate.

[0005] There are two causes of spacing loss: The first cause is shavings generated when the magnetic recording medium (e.g., the magnetic layer) is scraped away by the sliding contact with the head. Such shavings are generally called debris. When debris adheres to the head, the distance between the magnetic layer surface and the head increases. The second cause is wear of the head due to sliding contact with the magnetic layer surface. When the head wears, the distance between the head and the magnetic layer surface increases in the worn area.

[0006] One way to address the first cause is to provide the magnetic layer surface with the ability to remove debris from the head, which has traditionally been achieved by incorporating an abrasive into the magnetic layer (see, for example, Patent Documents 1 and 2). However, if the abrasive wears the head significantly when the magnetic layer surface slides over the head, the electromagnetic conversion characteristics are more likely to deteriorate due to spacing loss.

[0007] In view of the above, it is desirable for a magnetic recording medium to be able to achieve the following two goals at the same time. First, it must be highly durable, because a highly durable magnetic recording medium is less likely to produce debris when it slides against the head. Second, the head is less likely to be worn out even when it slides against the head (that is, head wear is reduced).

[0008] An object of one aspect of the present invention is to provide a magnetic recording medium that can exhibit excellent durability and reduce head wear. [Means for solving the problem]

[0009] One aspect of the present invention is A magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder, the magnetic layer contains an abrasive; The abrasive is a carbide, The average primary particle size of the abrasive is 10 nm or more and 100 nm or less, and a magnetic recording medium in which, in an electron microscope image of the surface of the magnetic layer, the ratio of the area occupied by the abrasive in an aggregated state with a maximum Feret diameter of 0.2 μm or more (hereinafter also referred to as "abrasive aggregate ratio") is 50% or more, with the total area occupied by the abrasive being 100%; Regarding.

[0010] In one embodiment, the magnetic recording medium can further include one or more non-magnetic layers containing non-magnetic powder between the non-magnetic support and the magnetic layer.

[0011] In one embodiment, when the total number of non-magnetic layers in the magnetic recording medium is one, the thickness of this one non-magnetic layer can be less than 1.0 μm.

[0012] In one embodiment, when the total number of non-magnetic layers in the magnetic recording medium is two or more, the total thickness of these two or more non-magnetic layers can be less than 1.0 μm.

[0013] In one embodiment, the carbide can be one or more selected from the group consisting of titanium carbide, tungsten carbide, zirconium carbide, silicon carbide, boron carbide, and vanadium carbide.

[0014] In one embodiment, the proportion of the area occupied by the abrasive present in an aggregated state with a maximum Feret diameter of 0.2 μm or more can be 50% or more and 95% or less.

[0015] In one embodiment, the proportion of the area occupied by the abrasive present in an agglomerated state with a maximum Feret diameter of 0.2 μm or more can be 60% or more and 95% or less.

[0016] In one embodiment, the proportion of the area occupied by the abrasive present in an aggregated state with a maximum Feret diameter of 0.2 μm or more can be 80% or more and 95% or less.

[0017] In one embodiment, the magnetic recording medium can further have a backcoat layer containing nonmagnetic powder on the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is formed.

[0018] In one embodiment, the magnetic recording medium can be a magnetic tape.

[0019] One aspect of the present invention relates to a magnetic tape cartridge including the above-mentioned magnetic tape.

[0020] One aspect of the present invention relates to a magnetic recording and reproducing device including the above magnetic recording medium. [Effects of the Invention]

[0021] According to one aspect of the present invention, it is possible to provide a magnetic recording medium that exhibits excellent durability and enables reduced head wear, and also to provide a magnetic tape cartridge and a magnetic recording / reproducing device that include such a magnetic recording medium. [Brief explanation of the drawings]

[0022] [Figure 1] 1 shows an example of the arrangement of data bands and servo bands. [Figure 2] An example of servo pattern layout for an LTO (Linear Tape-Open) Ultrium format tape is shown below. DETAILED DESCRIPTION OF THE INVENTION

[0023] [Magnetic recording media] One aspect of the present invention relates to a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the magnetic layer contains an abrasive, the abrasive is a carbide, the average primary particle diameter of the abrasive is 10 nm or more and 100 nm or less, and in an electron microscope image of the surface of the magnetic layer, the proportion of the area occupied by the abrasive in an aggregated state with a maximum Feret diameter of 0.2 μm or more is 50% or more, with the total area occupied by the abrasive being 100%.

[0024] The present inventors speculate as follows as to why the above magnetic recording medium is able to exhibit excellent durability and reduce head wear. The magnetic recording medium described above uses a carbide abrasive (hereinafter also referred to as "carbide abrasive"). Through extensive research into carbide abrasives, the present inventors have inferred that the presence of carbide abrasives in the magnetic layer as aggregates contributes to mitigating the impact that the magnetic layer surface receives from the head when the magnetic layer surface slides over the head. In this specification and the present invention, "magnetic layer surface" is synonymous with the magnetic layer surface of the magnetic recording medium. Further extensive research led the present inventors to conclude that the inclusion of a certain proportion or more of carbide abrasives in the magnetic layer in this state enables both excellent durability and reduced head wear. An aggregate is an aggregate of primary particles. The present inventors believe that the presence of carbide abrasives in the magnetic layer can be determined as aggregates that contribute to mitigating the impact that the magnetic layer surface receives from the head when the magnetic layer surface slides over the head. The present inventors believe that the presence of carbide abrasives in the magnetic layer can be determined as aggregates that contribute to mitigating the impact that the magnetic layer surface receives from the head when the magnetic layer surface slides over the head when the magnetic layer surface slides over the head. The present inventors have newly discovered that magnetic recording media containing 50% or more of such carbide abrasives present as aggregates relative to the total amount of carbide abrasives observed on the magnetic layer surface can exhibit excellent durability and reduce head wear. The present inventors speculate that in carbide abrasive aggregates, amorphous carbon contained as an impurity in the carbide particles is present between the primary particles that make up the aggregates, and that the amorphous carbon between the particles deforms when the magnetic layer surface slides against the head, thereby mitigating the impact that the magnetic layer surface receives from the head. However, the present invention is not limited to the speculations described in this specification.

[0025] <Carbide abrasives> In the present invention and this specification, the term "abrasive" refers to inorganic particles having a Mohs hardness of at least 6. Inorganic particles are particles of an inorganic substance.

[0026] The abrasive contained in the magnetic layer of the magnetic recording medium is a carbide. The magnetic recording medium can contain one or more carbides as abrasives in the magnetic layer in any ratio. Examples of carbides include titanium carbide, tungsten carbide, zirconium carbide, silicon carbide, boron carbide, and vanadium carbide. Regarding the composition formula, titanium carbide can be expressed by the composition formula TiC, tungsten carbide can be expressed by the composition formula WC, zirconium carbide can be expressed by the composition formula ZrC, silicon carbide can be expressed by the composition formula SiC, and vanadium carbide can be expressed by the composition formula VC. Boron carbide can be expressed by the composition formula B4C, etc. Regarding the Mohs hardness, TiC, WC, ZrC, SiC, VC, and B4C all have a Mohs hardness of 9.5. The Mohs hardness of the carbide abrasive is 6 or more, preferably 7 or more, more preferably 8 or more, even more preferably 9 or more, and even more preferably greater than 9. The Mohs hardness of the carbide abrasive is 10 or less, and preferably less than 10.

[0027] (Average primary particle size) The average primary particle size of the carbide abrasive contained in the magnetic layer of the magnetic recording medium is 10 nm or more and 100 nm or less. In the present invention and this specification, the average primary particle size of the carbide abrasive is a value determined by the following method. The carbide abrasive is photographed using a transmission electron microscope, and the photographed particle photograph is printed on photographic paper or displayed on a display, etc. The particle photograph can be taken, for example, using a Hitachi H-9000 transmission electron microscope at a magnification of about 50,000 to 100,000 times. From the particle photograph, 50 primary particles are randomly selected, and the outline of each primary particle is traced using a digitizer. Primary particles are independent particles without agglomerations. The diameter of a circle with the same area as the traced region (i.e., the equivalent circle diameter) is calculated. The arithmetic mean of the equivalent circle diameters of the 50 particles calculated in this way is taken as the average primary particle diameter of the carbide abrasive. The equivalent circle diameter can be calculated using known image analysis software. An example of such image analysis software is the Carl Zeiss KS-400 image analysis software. Furthermore, to calculate the equivalent circle diameter, scale correction can be performed using, for example, a circle with a diameter of 1 cm when capturing and analyzing images from a scanner. The average primary particle diameters of the various abrasives described in the Examples section below were determined using a Hitachi H-9000 transmission electron microscope at a magnification of approximately 50,000 to 100,000 times, and Carl Zeiss KS-400 image analysis software, with scale correction performed using a circle with a diameter of 1 cm when capturing images from a scanner and analyzing the images to calculate the circle equivalent diameter. The particles to be imaged may be sample particles collected from the magnetic layer, raw material particles before they are used to form the magnetic layer, or particles from the same lot as the raw material particles used to form the magnetic layer may be used if they are available. The method for collecting sample particles from a magnetic recording medium can be, for example, the method described in paragraph 0015 of JP 2011-048878 A.

[0028] The average primary particle diameter of the carbide abrasive contained in the magnetic layer of the magnetic recording medium is 10 nm or more, and can be 20 nm or more or 30 nm or more. The average primary particle diameter of the carbide abrasive is 100 nm or less, and can be 90 nm or less, 80 nm or less, or 70 nm or less. As mentioned above, the present inventors believe that the presence of aggregates can be determined by observing a collection of primary particles with an average primary particle diameter of 10 nm to 100 nm with a maximum Feret diameter of 0.2 μm or more.

[0029] (abrasive aggregate ratio) In the present invention and this specification, the abrasive aggregate ratio is a value determined by the following method. The maximum Feret diameter is the maximum value of the straight line length connecting two points on the circumference of a particle, and in the case of an aggregate in which multiple primary particles are aggregated, it is the maximum value of the straight line length connecting two points on the outer edge of the aggregate. The maximum Feret diameter and area of ​​an aggregate can be measured by the following procedure.

[0030] (1) Obtaining electron microscope images A field emission scanning electron microscope (FE-SEM) is used as the electron microscope. For example, the S-4800 manufactured by Hitachi High-Technologies Corporation can be used as the FE-SEM. The FE-SEM is used to observe the planar surface of the magnetic layer of the magnetic recording medium to be measured, and an electron microscope image is obtained. The electron microscope image is obtained under the following conditions. Accelerating voltage: 2 kV Working distance (WD): 4mm Magnification: 13,000x Simultaneous detection of secondary electrons and backscattered electrons Resolution: 2560 pixels x 1920 pixels

[0031] (2) Image analysis The electron microscope image obtained in (1) above was imported into image analysis software. (i) binarization processing, and (ii) calculating the total area of ​​the carbide portion in the binarized image, identifying the portion of the carbide portion with a maximum Feret diameter of 0.2 μm or more (i.e., aggregates), and calculating the total area of ​​the portion of the carbide portion with a maximum Feret diameter of 0.2 μm or more (i.e., aggregates); The binarization process allows the carbide portions to be distinguished from other portions by their shades in the binarized image. That is, in the binarized image, the carbide portions can be distinguished from other portions as bright (i.e., white) or dark (i.e., black) regions. Furthermore, in the binarized image, portions where multiple primary particles aggregate, i.e., aggregates, are displayed as regions surrounded by an outer edge. Therefore, within the region surrounded by the outer edge, regions with a maximum Feret diameter of 0.2 μm or greater can be identified as regions where carbide exists in an aggregated state with a maximum Feret diameter of 0.2 μm or greater. Carbide abrasives may exist in the magnetic layer in the form of aggregates or primary particles, where primary particles aggregate. The binarized image may contain only a portion of the aggregates or only a portion of the primary particles. In such cases, the total area of ​​the carbide portions and the total area of ​​the portions with a maximum Feret diameter of 0.2 μm or greater are calculated without including the aggregates or primary particles. As image analysis software, free software ImageJ can be used. For example, in Example 1 described below, ImageJ was used to carry out the above steps (i) and (ii) under the following conditions: noise reduction process Despeckle was performed, Enhance Contrast was performed, Threshold was set to 0-100, and Analyze Particle was set to 500-pixel. The threshold setting for the binarization conditions is preferably adjusted depending on the type of carbide. For carbides that appear as black areas in the binarized image, a threshold of approximately 0 to 100 is appropriate. On the other hand, for carbides that appear as white areas in the binarized image, a threshold of approximately 150 to 255 is appropriate. Furthermore, carbide portions that should be distinguished by their shade in a binarized image can be identified on the image if they can be clearly identified on the electron microscope image before binarization, or they can be identified by performing component analysis using a known method such as SEM component analysis (e.g., obtaining a component map), energy dispersive X-ray spectrometry (EDS), or Auger electron spectroscopy (AES).

[0032] In the magnetic recording medium, the abrasive agglomerate ratio is 50% or more, preferably 55% or more, more preferably 60% or more, and even more preferably 65% ​​or more, 70% or more, 75% or more, and 80% or more in that order, from the viewpoint of improving the durability of the magnetic recording medium and reducing head wear. Furthermore, the abrasive agglomerate ratio can be 100% or less, less than 100%, 99% or less, or 95% or less. A high abrasive agglomerate ratio is preferred from the viewpoint of further improving the durability of the magnetic recording medium and further reducing head wear.

[0033] In order to control the abrasive agglomerate ratio to 50% or more, it is preferable to actively generate and increase the agglomerates by adopting preparation conditions and / or preparation methods that facilitate aggregation of the carbide abrasive in the preparation of the magnetic layer-forming composition. For example, the abrasive agglomerate ratio can be controlled to 50% or more by any combination of one or more of the following: shortening the dispersion time of the carbide abrasive dispersion, slowing the dispersion peripheral speed, leaving the dispersion standing for several days, concentrating the dispersion by heating, freezing and then thawing the dispersion, and centrifuging the dispersion to obtain a precipitate and then redispersing it.

[0034] The content of the carbide abrasive in the magnetic layer of the magnetic recording medium is, for example, preferably 1.0 to 20.0 parts by mass, and more preferably 1.0 to 10.0 parts by mass, per 100 parts by mass of the ferromagnetic powder.

[0035] The above magnetic recording medium will now be described in more detail.

[0036] <Magnetic layer> (Ferromagnetic powder) The ferromagnetic powder contained in the magnetic layer can be one or a combination of two or more known ferromagnetic powders used in the magnetic layers of various magnetic recording media. 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 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.

[0037] Regarding the particle size of the ferromagnetic powder, the average particle volume can also be used as an index of particle size. From the viewpoint of improving recording density, the average particle volume is set to 2500 nm 3 Preferably, it is 2300 nm or less. 3 More preferably, it is 2000 nm or less. 3 More preferably, it is 1500 nm or less. 3 From the viewpoint of magnetization stability, the average particle volume of the ferromagnetic powder is more preferably 500 nm or less. 3 It is preferable that the thickness is 600 nm or more. 3 More preferably, it is 650 nm or more. 3 More preferably, it is 700 nm or more. 3 The above average particle volume is a value determined as a sphere-equivalent volume from the average particle size determined by the method described below.

[0038] Hexagonal ferrite powder A preferred example of the ferromagnetic powder is hexagonal ferrite powder. For details of the hexagonal ferrite powder, see, for example, JP 2011-225417 A, paragraphs 0012 to 0030, JP 2011-216149 A, paragraphs 0134 to 0136, JP 2012-204726 A, paragraphs 0013 to 0030, and JP 2015-127985 A, paragraphs 0029 to 0084.

[0039] 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 diffraction peak belongs in the X-ray diffraction spectrum obtained by X-ray diffraction analysis. For example, if the highest diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is assigned to the hexagonal ferrite crystal structure, it is 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 is considered to be 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 of such atoms include alkaline earth metal atoms such as strontium atoms, barium atoms, and calcium atoms, and lead atoms. In the present invention and this specification, "hexagonal strontium ferrite powder" refers to a powder in which the main divalent metal atom contained therein is strontium atom, and "hexagonal barium ferrite powder" refers to a powder in which the main divalent metal atom contained therein is barium atom. "Main divalent metal atom" refers to the divalent metal atom that is the most abundant, on an atomic % 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 atom" refers to a powder selected from the group consisting of scandium atom (Sc), yttrium atom (Y), and lanthanoid atom. The lanthanoid atom is selected from the group consisting of lanthanum atom (La), cerium atom (Ce), praseodymium atom (Pr), neodymium atom (Nd), promethium atom (Pm), samarium atom (Sm), europium atom (Eu), gadolinium atom (Gd), terbium atom (Tb), dysprosium atom (Dy), holmium atom (Ho), erbium atom (Er), thulium atom (Tm), ytterbium atom (Yb), and lutetium atom (Lu).

[0040] Hereinafter, hexagonal strontium ferrite powder, which is one form of hexagonal ferrite powder, will be described in more detail.

[0041] The activation volume of the hexagonal strontium ferrite powder is preferably 800 to 1600 nm 3 The finely divided hexagonal strontium ferrite powder exhibiting an activation volume in the above range is suitable for producing a magnetic recording medium that exhibits excellent electromagnetic conversion characteristics. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm 3 or more, for example, 850 nm 3 From the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the hexagonal strontium ferrite powder can be 1500 nm or more. 3 More preferably, it is 1400 nm or less. 3 More preferably, it is 1300 nm or less. 3 More preferably, it is 1200 nm or less. 3 It is even more preferable that the value is equal to or less than 1100 nm. 3 It is even more preferable that the activation volume of the hexagonal barium ferrite powder is equal to or less than 10 ...

[0042] "Activation volume" is a unit of magnetization reversal and is an index showing the magnetic size of a particle. The activation volume described in this invention and this specification and the anisotropy constant Ku described below are values ​​obtained by measuring the coercive force Hc using a vibrating sample magnetometer at magnetic field sweep rates of 3 minutes and 30 minutes (measurement temperature: 23°C ± 1°C) in the coercive force Hc measurement section, and then calculating from the following relational expression between Hc and activation volume V. The unit of the anisotropy constant Ku is 1 erg / cc = 1.0 x 10 -1 J / m 3 is. 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)]

[0043] The anisotropy constant Ku can be used as an index for reducing thermal fluctuation, in other words, improving thermal stability. The hexagonal strontium ferrite powder preferably has an anisotropy constant of 1.8×10 5 J / m 3 and more preferably 2.0×10 5 J / m 3 The Ku of the hexagonal strontium ferrite powder can be, for example, 2.5×10 5 J / m 3 However, since a higher Ku value means higher thermal stability and is therefore preferred, the Ku value is not limited to the above-mentioned values.

[0044] The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the rare earth atoms are contained at a content (bulk content) of 0.5 to 5.0 atomic % relative to 100 atomic % of iron atoms. In one embodiment, the hexagonal strontium ferrite powder containing rare earth atoms can have rare earth atoms unevenly distributed in the surface layer portion. In the present invention and this specification, the term "surface layer distribution of rare earth atoms" refers to the ratio of the rare earth atom content relative to 100 atomic % of iron atoms in a solution obtained by partially dissolving a hexagonal strontium ferrite powder in an acid (hereinafter referred to as "surface layer content of rare earth atoms" or simply "surface layer content" with respect to rare earth atoms) to the ratio of the rare earth atom content relative to 100 atomic % of iron atoms in a solution obtained by completely dissolving a hexagonal strontium ferrite powder in an acid (hereinafter referred to as "bulk content of rare earth atoms" or simply "bulk content" with respect to rare earth atoms), Rare earth atom surface content / rare earth atom bulk content > 1.0 This means that the ratio of "surface rare earth atom content / bulk rare earth atom content > 1.0" is satisfied. The rare earth atom content of the hexagonal strontium ferrite powder described below is synonymous with the rare earth atom bulk content. In contrast, partial dissolution using an acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder, so 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 surface rare earth atom content satisfies the ratio "surface rare earth atom content / bulk rare earth atom content > 1.0", this means that the rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder (i.e., present in greater amounts in the surface layer than in the interior). In the present invention and this specification, the surface layer refers to a partial region extending from the surface toward the interior of the particles constituting the hexagonal strontium ferrite powder.

[0045] When the 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. Having rare earth atoms in the above-mentioned bulk content range and having the rare earth atoms unevenly distributed in the surface layers of the particles constituting the hexagonal strontium ferrite powder is thought to contribute to suppressing a decrease in playback output during repeated playback. This is presumably because the hexagonal strontium ferrite powder contains rare earth atoms in the above-mentioned bulk content range and having the rare earth atoms unevenly distributed in the surface layers of the particles constituting the hexagonal strontium ferrite powder can increase the anisotropy constant Ku. The higher the anisotropy constant Ku, the more the occurrence of a phenomenon known as thermal fluctuation can be suppressed (in other words, thermal stability can be improved). By suppressing the occurrence of thermal fluctuation, the decrease in playback output during repeated playback can be suppressed. It is speculated that the uneven distribution of rare earth atoms in the surface layer of hexagonal strontium ferrite powder particles contributes to stabilizing the spin of the iron (Fe) sites in the crystal lattice in the surface layer, thereby increasing the anisotropy constant Ku. Furthermore, it is believed that using hexagonal strontium ferrite powder with rare earth atoms unevenly distributed on the surface as the ferromagnetic powder for the magnetic layer also contributes to further suppressing the abrasion of the magnetic layer surface due to sliding with the magnetic head. This is believed to be because the uneven distribution of rare earth atoms on the surfaces of the particles that make up the hexagonal strontium ferrite powder contributes to improving the interaction between the particle surfaces and the 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 further suppressing a decrease in reproduction output during repeated reproduction 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 %, even more preferably in the range of 1.0 to 4.5 atomic %, and even more preferably in the range of 1.5 to 4.5 atomic %.

[0046] The bulk content is the content determined by completely dissolving the hexagonal strontium ferrite powder. In the present invention and this specification, unless otherwise specified, the content of an atom refers to the bulk content determined by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one rare earth atom or two or more rare earth atoms. When two or more rare earth atoms are contained, the bulk content is determined for the total of the two or more rare earth atoms. This also applies to other components in the present invention and this specification. That is, unless otherwise specified, a certain component may be used alone or in combination with two or more. When two or more components are used, the content or content refers to the total of the two or more components.

[0047] When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms may be any one or more of rare earth atoms. From the viewpoint of further suppressing the decrease in playback output during repeated playback, 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.

[0048] In a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, the rare earth atoms need only be unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of uneven distribution is not limited. For example, for a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, the ratio of the surface content of rare earth atoms determined by partial dissolution under the dissolution conditions described below to the bulk content of rare earth atoms determined by complete dissolution under the dissolution conditions described below, i.e., "surface content / bulk content," is greater than 1.0 and can be 1.5 or greater. A "surface content / bulk content" ratio greater than 1.0 means that the rare earth atoms are unevenly distributed in the surface layer (i.e., present in greater amounts than in the interior) in the particles constituting the hexagonal strontium ferrite powder. Furthermore, the ratio of the surface content of rare earth atoms determined by partial dissolution under the dissolution conditions described below to the bulk content of rare earth atoms determined by complete dissolution under the dissolution conditions described below, i.e., "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 a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layers, it is sufficient that the rare earth atoms are unevenly distributed in the surface layers of the particles constituting the hexagonal strontium ferrite powder, and the above "surface content / bulk content" is not limited to the exemplified upper or lower limits.

[0049] The partial and total dissolution of hexagonal strontium ferrite powder is described below. For hexagonal strontium ferrite powder present as a powder, sample powders to be partially and completely dissolved are collected from the same powder lot. 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 removed from the magnetic layer is subjected to partial dissolution, and another portion is subjected to total dissolution. The hexagonal strontium ferrite powder can be removed from the magnetic layer by, for example, the method described in paragraph 0032 of JP 2015-91747 A. The term "partial dissolution" as used herein refers to dissolving the hexagonal strontium ferrite powder to such an extent that the remaining hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. For example, partial dissolution can dissolve 10 to 20 mass% of the particles constituting the hexagonal strontium ferrite powder, with the total particles being 100 mass%. On the other hand, the term "complete dissolution" as used herein refers to dissolving the hexagonal strontium ferrite powder to such an extent that the remaining hexagonal strontium ferrite powder cannot be visually confirmed in the liquid at the end of dissolution. The partial dissolution and measurement of the surface layer content are carried out, for example, by the following method. Note that the dissolution conditions such as the amount of sample powder described below are merely examples, and any dissolution conditions that allow partial or complete dissolution can be adopted. A container (e.g., a beaker) containing 12 mg of sample powder and 10 mL of 1 mol / L hydrochloric acid is placed on a hot plate set at 70°C for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the filtrate is performed using an inductively coupled plasma (ICP) analyzer. This allows the surface content of rare earth atoms relative to 100 atomic percent iron atoms to 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 content. This also applies to measurements of bulk content. On the other hand, the total dissolved and bulk contents are measured, 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 placed on a hot plate set at 80°C for 3 hours. After that, the bulk content relative to 100 atomic % of iron atoms can be determined by carrying out the same procedures as for the partial dissolution and surface layer content measurements described above.

[0050] From the viewpoint of increasing the reproduction output when reproducing data recorded on a magnetic recording medium, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic recording medium is high. In this regard, hexagonal strontium ferrite powder that contains rare earth atoms but does not have the rare earth atoms unevenly distributed in the surface layer tends to have a significantly lower σs than hexagonal strontium ferrite powder that does not contain rare earth atoms. On the other hand, hexagonal strontium ferrite powder that has the rare earth atoms unevenly distributed in the surface layer is considered preferable in order to suppress such a large decrease in σs. In one embodiment, the σs of the hexagonal strontium ferrite powder is 45 A·m 2 / kg or more, and 47A·m 2 / kg or more. On the other hand, from the viewpoint of noise reduction, σs is 80A·m 2 / kg or less is preferable, and 60A·m 2 / kg or less is more preferable. 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 a value measured at a magnetic field strength of 15 kOe. 1 [kOe] = 10 6 / 4π[A / m].

[0051] Regarding the content (bulk content) of constituent atoms of the hexagonal strontium ferrite powder, the strontium atom content can be, for example, in the range of 2.0 to 15.0 atomic % relative to 100 atomic % of iron atoms. In one embodiment, the hexagonal strontium ferrite powder can contain only strontium atoms as divalent metal atoms. In another embodiment, the hexagonal strontium ferrite powder can contain one or more other divalent metal atoms in addition to strontium atoms. For example, barium atoms and / or calcium atoms can be contained. When divalent metal atoms other than strontium atoms are contained, the barium atom content and calcium atom content in the hexagonal strontium ferrite powder can each be, for example, in the range of 0.05 to 5.0 atomic % relative to 100 atomic % of iron atoms.

[0052] Known crystal structures of hexagonal ferrite include magnetoplumbite type (also called "M type"), W type, Y type, and Z type. The hexagonal strontium ferrite powder may have any of these crystal structures. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder may be one in which a single crystal structure or two or more types of crystal structures are detected by X-ray diffraction analysis. For example, in one embodiment, the hexagonal strontium ferrite powder may be one in which only the M-type crystal structure is detected by X-ray diffraction analysis. For example, the M-type hexagonal ferrite is AFe 12 O 19The composition formula is represented by the formula: where A represents a divalent metal atom. When the hexagonal strontium ferrite powder is of M type, A is only strontium atom (Sr). Alternatively, when A contains multiple divalent metal atoms, strontium atom (Sr) accounts for the largest proportion on an atomic % basis, as described above. The divalent metal atom content of the hexagonal strontium ferrite powder is usually determined by the type of crystalline structure of the hexagonal ferrite and is not particularly limited. The same applies to the iron atom content and oxygen atom content. The hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms, and oxygen atoms, and may further contain rare earth atoms. Furthermore, the hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may contain aluminum atoms (Al). The content of aluminum atoms can be, for example, 0.5 to 10.0 atomic % relative to 100 atomic % of iron atoms. From the viewpoint of further suppressing a decrease in playback output during repeated playback, 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 % or less, more preferably 0 to 5.0 atomic %, relative to 100 atomic % of iron atoms, and may even be 0 atomic %. That is, in one embodiment, the hexagonal strontium ferrite powder may contain no atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The content expressed in atomic % above is determined by converting the content (unit: mass %) of each atom obtained by completely dissolving the hexagonal strontium ferrite powder into a value expressed in atomic % using the atomic weight of each atom. Furthermore, in the present invention and this specification, "not containing" a certain atom means that the content is 0 mass % when completely dissolved and measured by an ICP analyzer. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less by mass. The above term "free from" is used to mean that the substance is contained in an amount below the detection limit of the ICP analyzer.In one form, the hexagonal strontium ferrite powder can be one that does not contain bismuth atoms (Bi).

[0053] metal powder A preferred example of the ferromagnetic powder is ferromagnetic metal powder. For details of the ferromagnetic metal powder, see, for example, paragraphs 0137 to 0141 of JP-A No. 2011-216149 and paragraphs 0009 to 0023 of JP-A No. 2005-251351.

[0054] ε-iron oxide powder A preferred example of the ferromagnetic powder is ε-iron oxide powder. In the present invention and this specification, the term "ε-iron oxide powder" refers to a ferromagnetic powder in which an ε-iron oxide crystalline structure is detected as the main phase by X-ray diffraction analysis. For example, if the highest intensity diffraction peak in an X-ray diffraction spectrum obtained by X-ray diffraction analysis is assigned to the ε-iron oxide crystalline structure, it is determined that the ε-iron oxide crystalline structure is detected as the main phase. Known methods for producing ε-iron oxide powder include a method using goethite and a reverse micelle method. All of these production methods are publicly known. For a method for producing ε-iron oxide powder in which part of the Fe atoms are replaced by atoms such as Ga, Co, Ti, Al, or Rh, see, for example, J. Jpn. Soc. Powder Metallurgy, Vol. 61, Supplement, No. S1, pp. S280-S284 and J. Mater. Chem. C, 2013, 1, pp. 5200-5206. However, the method for producing the ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer of the magnetic recording medium is not limited to the method given here.

[0055] The activation volume of the ε-iron oxide powder is preferably 300 to 1500 nm 3 The activation volume of the ε-iron oxide powder is preferably in the range of 300 nm. The ε-iron oxide powder having an activation volume in the above range is suitable for producing a magnetic recording medium that exhibits excellent electromagnetic conversion characteristics. The activation volume of the ε-iron oxide powder is preferably in the range of 300 nm. 3or more, for example, 500 nm 3 From the viewpoint of further improving the electromagnetic conversion characteristics, the activation volume of the ε-iron oxide powder can be 1400 nm or more. 3 More preferably, it is 1300 nm or less. 3 More preferably, it is 1200 nm or less. 3 More preferably, it is 1100 nm or less. 3 It is even more preferred that:

[0056] The anisotropy constant Ku can be used as an index of the reduction in thermal fluctuation, in other words, the improvement in thermal stability. The ε-iron oxide powder is preferably 3.0×10 4 J / m 3 and more preferably 8.0×10 4 J / m 3 The Ku of the ε-iron oxide powder can be, for example, 3.0×10 5 J / m 3 However, since a higher Ku value means higher thermal stability and is therefore preferred, the Ku value is not limited to the above-mentioned values.

[0057] From the viewpoint of increasing the reproduction output when reproducing data recorded on the magnetic recording medium, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic recording medium is high. In this regard, in one embodiment, the σs of the ε-iron oxide powder is 8 A m 2 / kg or more, and 12 A m 2 On the other hand, the σs of ε-iron oxide powder can be 40 A m 2 / kg or less, and 35A·m 2 / kg or less is more preferable.

[0058] In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powders is a value measured using a transmission electron microscope by the following method: The average primary particle size of carbide abrasives is determined by the method described above. The powder is photographed using a transmission electron microscope at a magnification of 100,000x, and the photograph of the particles that make up the powder is obtained by printing it on photographic paper or displaying it on a display so that the total magnification is 500,000x. From the obtained particle photograph, the target particle is selected and the particle outline is traced with a digitizer to measure the particle (primary particle) size. As mentioned above, primary particles are independent particles with no agglomerations. The above measurements are performed on 500 randomly selected particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained is the average particle size of the powder. The transmission electron microscope may be, for example, a Hitachi H-9000 transmission electron microscope. Furthermore, particle size measurements can be performed using known image analysis software, such as Carl Zeiss KS-400 image analysis software. Unless otherwise specified, the average particle sizes shown in the examples below are values ​​measured using a Hitachi H-9000 transmission electron microscope and Carl Zeiss KS-400 image analysis software. In this invention and this specification, "powder" refers to a collection of multiple particles. For example, "ferromagnetic powder" refers to a collection of multiple ferromagnetic particles. Furthermore, a collection of multiple particles is not limited to a configuration in which the particles constituting the collection are in direct contact with each other, but also includes a configuration in which binders, additives, etc., as described below, are interposed between the particles. The term "particle" is sometimes used to refer to powder. As mentioned above, the present inventors speculate that amorphous carbon may exist between primary particles in the aggregates of carbide abrasives, but this is merely speculation and does not limit the present invention.

[0059] 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 JP-A No. 2011-048878 can be used.

[0060] In the present invention and this specification, unless otherwise specified, the size of particles constituting the powder (particle size) is determined by the shape of the particles observed in the particle photograph. (1) In the case of needle-shaped, spindle-shaped, columnar (where the height is greater than the maximum diameter of the base), etc., the particle size is expressed by the length of the major axis that constitutes the particle, i.e., the major axis length. (2) In the case of a plate or columnar shape (where the thickness or height is smaller than the maximum major axis of the plate surface or base), it is expressed by the maximum major axis of the plate surface or base, (3) When the particle is spherical, polyhedral, irregular, etc., and the long axis of the particle cannot be identified from its shape, it is expressed as the equivalent circle diameter, which is determined by the circle projection method.

[0061] The acicular ratio of a powder is determined by measuring the minor axis length of the particles in the above measurement, i.e., the minor axis length, and calculating the arithmetic mean of the major axis lengths (average major axis length) and the minor axis lengths (average minor axis length) obtained for the 500 particles as "average major axis length / average minor axis length." Here, unless otherwise specified, the minor axis length refers to the length of the minor axis constituting the particle in the above definition of particle size (1), and to the thickness or height in the above definition of particle size (2). In the above definition of particle size (3), since there is no distinction between the major axis and the minor axis, (average major axis length / average minor axis length) is considered to be 1 for convenience. Unless otherwise specified, when the particle shape is specific, for example, in the case of the above definition of particle size (1), the average particle size is the average major axis length, in the case of definition (2), the average particle size is the average plate diameter, and in the case of definition (3), the average particle size is the average diameter (also called the average particle diameter or average particle size).

[0062] The content (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90 mass %, and more preferably in the range of 60 to 90 mass %, relative to the total mass of the magnetic layer.

[0063] (binder) The magnetic recording medium may be a coating-type magnetic recording medium, and the magnetic layer may contain a binder. The binder is one or more resins. Various resins commonly used as binders for coating-type magnetic recording media can be used as binders. For example, binders may be selected from polyurethane resins, polyester resins, polyamide resins, vinyl chloride resins, acrylic resins copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resins such as nitrocellulose, epoxy resins, phenoxy resins, polyvinyl acetal, polyvinyl butyral, etc., and may be used alone or in combination. Among these, polyurethane resins, acrylic resins, cellulose resins, and vinyl chloride resins are preferred. These resins may be homopolymers or copolymers. These resins may also be used as binders in the nonmagnetic layer and / or backcoat layer, which will be described later. For details of the binders described above, see paragraphs 0028 to 0031 of JP 2010-24113 A. The average molecular weight of the resin used as the binder can be, for example, 10,000 to 200,000 in weight-average molecular weight. The weight-average molecular weight of the binder in this invention and this specification is a value determined by converting a value measured by gel permeation chromatography (GPC) into polystyrene equivalent. The weight-average molecular weight of the binder shown in the examples described below is a value determined by converting a value measured under the following measurement conditions into polystyrene equivalent. 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 the ferromagnetic powder. GPC equipment: HLC-8120 (Tosoh Corporation) Column: TSK gel Multipore HXL-M (Tosoh Corporation, 7.8 mm ID (inner diameter) x 30.0 cm) Eluent: tetrahydrofuran (THF)

[0064] (hardening agent) A curing agent can also be used with a resin usable as a binder. In one form, the curing agent can be a thermosetting compound, which undergoes a curing reaction (crosslinking reaction) upon heating. In another form, the curing agent can be a photocurable compound, which undergoes a curing reaction (crosslinking reaction) upon irradiation with light. As the curing reaction progresses during the magnetic layer formation process, at least a portion of the curing agent can be included in the magnetic layer in a state of reaction (crosslinking) with other components, such as the binder. This also applies to layers formed using compositions containing a curing agent when the composition used to form other layers contains a curing agent. A preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. For details on polyisocyanates, see paragraphs 0124-0125 of JP 2011-216149 A. The curing agent can be used in an amount of, for example, 0 to 80.0 parts by weight, preferably 50.0 to 80.0 parts by weight, per 100.0 parts by weight of the binder, to prepare the magnetic layer-forming composition.

[0065] (additives)

[0066] (additives) The magnetic layer may contain one or more additives as needed. Additives can be selected from commercially available products or prepared by known methods according to the desired properties and used in any amount. Examples of additives include the curing agents mentioned above. Examples of additives contained in the magnetic layer include nonmagnetic powders, lubricants, dispersants, dispersion aids, antifungal agents, antistatic agents, and antioxidants. For information on lubricants, see paragraphs

[0030] to

[0033] ,

[0035] , and

[0036] of JP 2016-126817 A. The nonmagnetic layer described below may contain a lubricant. For information on lubricants that may be contained in the nonmagnetic layer, see paragraphs

[0030] ,

[0031] , and

[0034] to

[0036] of JP 2016-126817 A. For information on dispersants, see paragraphs

[0061] and

[0071] of JP 2012-133837 A. A dispersant may be added to the nonmagnetic layer-forming composition. For dispersants that can be added to the composition for forming the nonmagnetic layer, reference can be made to paragraph 0061 of JP-A No. 2012-133837.

[0067] Non-magnetic powders that can be contained in the magnetic layer include non-magnetic powders (e.g., non-magnetic colloidal particles, carbon black, etc.) that function as protrusion-forming agents that form moderately protruding protrusions on the surface of the magnetic layer. For example, protrusion-forming agents with an average particle size of 5 to 300 nm can be used. The average particle size of colloidal silica (silica colloidal particles) shown in the examples below is a value determined by the method described as a method for measuring average particle size in paragraph 0015 of JP 2011-048878 A. The content of the protrusion-forming agent in the magnetic layer is preferably 0.1 to 3.5 parts by weight, more preferably 0.1 to 3.0 parts by weight, per 100.0 parts by weight of ferromagnetic powder.

[0068] The magnetic layer described above can be provided directly on the surface of the non-magnetic support, or indirectly via a non-magnetic layer.

[0069] <Nonmagnetic layer> Next, the non-magnetic layer will be described. The magnetic recording medium may have a magnetic layer directly on the surface of a non-magnetic support, or may have a magnetic layer on the surface of a non-magnetic support via one or more non-magnetic layers containing non-magnetic powder.

[0070] In order to improve the surface smoothness of the magnetic layer, it is preferable to improve the surface smoothness of the non-magnetic layer on which the magnetic layer will be formed. From this perspective, it is preferable to use a non-magnetic powder with a small average particle size as the non-magnetic powder contained in the non-magnetic layer. The average particle size of the non-magnetic powder is preferably in the range of 500 nm or less, more preferably 200 nm or less, even more preferably 100 nm or less, and even more preferably 50 nm or less. Furthermore, from the viewpoint of ease of improving the dispersibility of the non-magnetic powder, the average particle size of the non-magnetic powder is preferably 5 nm or more, more preferably 7 nm or more, and even more preferably 10 nm or more.

[0071] The non-magnetic powder used in the non-magnetic layer may be either an inorganic powder or an organic powder, and carbon black or the like may also be used.

[0072] For information on carbon black that can be used in the nonmagnetic layer, see, for example, paragraphs 0040 to 0041 of Japanese Patent Laid-Open Publication No. 2010-24113. Carbon black generally tends to have a large particle size distribution and poor dispersibility. Therefore, nonmagnetic layers containing carbon black tend to have low surface smoothness. In one embodiment, therefore, it is preferable to provide a nonmagnetic layer containing a nonmagnetic powder other than carbon black as the nonmagnetic layer adjacent to the magnetic layer. It is also preferable to provide multiple nonmagnetic layers, with the nonmagnetic layer closest to the magnetic layer being a nonmagnetic layer containing a nonmagnetic powder other than carbon black. For example, it is preferable to provide two nonmagnetic layers between the nonmagnetic support and the magnetic layer, with the nonmagnetic layer on the nonmagnetic support side (also referred to as the "lower nonmagnetic layer") containing carbon black and the nonmagnetic layer on the magnetic layer side (also referred to as the "upper nonmagnetic layer") containing a nonmagnetic powder other than carbon black. Furthermore, in a non-magnetic layer-forming composition containing multiple types of non-magnetic powder, the dispersibility of the non-magnetic powder tends to be lower than in a non-magnetic layer-forming composition containing only one type of non-magnetic powder. From this perspective, it is preferable to provide multiple non-magnetic layers and reduce the number of types of non-magnetic powder contained in each non-magnetic layer. In one embodiment, it is preferable to use a dispersant to improve the dispersibility of the non-magnetic powder in a non-magnetic layer-forming composition containing multiple types of non-magnetic powder. Such dispersants will be described later.

[0073] Examples of inorganic powders include powders of metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These non-magnetic powders are commercially available or can be produced by known methods. For details, see paragraphs 0146 to 0150 of JP 2011-216149 A.

[0074] One form of non-magnetic powder is non-magnetic iron oxide powder. From the viewpoint of improving the surface smoothness of the non-magnetic layer on which the magnetic layer is formed, it is preferable to use non-magnetic iron oxide powder with a small particle size. From this viewpoint, it is preferable to use non-magnetic iron oxide powder with an average particle size within the range described above. Note that when the non-magnetic iron oxide powder has the particle shape described above in (1), the average particle size refers to the average major axis length. The acicular ratio (average major axis length / average minor axis length) of the non-magnetic iron oxide powder can be greater than 1.0. From the viewpoint of improving the surface smoothness of the non-magnetic layer, it is preferable to use non-magnetic iron oxide powder with a small acicular ratio. The acicular ratio (average major axis length / average minor axis length) of the non-magnetic iron oxide powder can be, for example, 7.0 or less, preferably 3.0 or less, and more preferably 1.5 or less. In one form, α-iron oxide powder is preferable as the non-magnetic iron oxide powder. α-iron oxide is iron oxide whose main phase is the α phase.

[0075] The non-magnetic powder content (filling rate) in the non-magnetic layer is preferably in the range of 50 to 90 mass %, more preferably 60 to 90 mass %, relative to the total mass of the non-magnetic layer. When multiple non-magnetic layers are provided, it is preferable that the non-magnetic powder content in at least one non-magnetic layer be in the above range, and it is even more preferable that the non-magnetic powder content in more non-magnetic layers be in the above range.

[0076] The non-magnetic layer contains a non-magnetic powder and may also contain a binder together with the non-magnetic powder. Other details of the binder, additives, etc. of the non-magnetic layer can be determined by known techniques related to non-magnetic layers. Furthermore, known techniques related to magnetic layers can also be applied to determine, for example, the type and content of the binder and the type and content of the additives.

[0077] Additives that can be included in the nonmagnetic layer include dispersants that contribute to improving the dispersibility of nonmagnetic powders. Examples of such dispersants include fatty acids represented by the formula RCOOH (R is an alkyl or alkenyl group) (e.g., caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid, etc.); alkali metal salts or alkaline earth metal salts of the above fatty acids; esters of the above fatty acids; fluorine-containing compounds of the above fatty acid esters; amides of the above fatty acids; polyalkylene oxide alkyl phosphate esters; lecithin; trialkyl polyolefinoxy quaternary ammonium salts (containing alkyl groups with 1 to 5 carbon atoms and olefins such as ethylene and propylene); phenylphosphonic acid; and copper phthalocyanine. These may be used alone or in combination. The content of the dispersant is preferably 0.2 to 5.0 parts by mass per 100.0 parts by mass of the nonmagnetic powder.

[0078] Further, an example of an additive is an organic tertiary amine. For details of organic tertiary amines, see paragraphs 0011 to 0018 and 0021 of JP 2013-049832 A. The organic tertiary amine can contribute to improving the dispersibility of carbon black. For details of the formulation of a composition for enhancing the dispersibility of carbon black using an organic tertiary amine, see paragraphs 0022 to 0024 and 0027 of the same publication.

[0079] The amine is more preferably a trialkylamine. The alkyl group in the trialkylamine is preferably an alkyl group having 1 to 18 carbon atoms. The three alkyl groups in the trialkylamine may be the same or different. For details about the alkyl groups, see paragraphs 0015 to 0016 of JP 2013-049832 A. As the trialkylamine, trioctylamine is particularly preferred.

[0080] In the present invention and this specification, the term "nonmagnetic layer" also includes a substantially nonmagnetic layer that contains a small amount of ferromagnetic powder, for example as an impurity or intentionally, along with a nonmagnetic powder. Here, a substantially nonmagnetic layer refers to a layer having a remanence of 10 mT or less, a coercivity of 7.96 kA / m (100 Oe) or less, or a remanence of 10 mT or less and a coercivity of 7.96 kA / m (100 Oe) or less. It is preferable that the nonmagnetic layer have no remanence or coercivity.

[0081] <Nonmagnetic support> Next, the non-magnetic support will be described. Examples of the non-magnetic support (hereinafter also simply referred to as "support") include known biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, aromatic polyamide, etc. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These supports may be previously subjected to corona discharge, plasma treatment, easy-adhesion treatment, heat treatment, etc.

[0082] <Backcoat layer> The magnetic recording medium may or may not have a backcoat layer containing nonmagnetic powder on the surface of the nonmagnetic support opposite the surface having the magnetic layer. The backcoat layer preferably contains either carbon black or inorganic powder, or both. The backcoat layer may contain a binder and / or additives. Known techniques related to backcoat layers can be applied to the binder and additives of the backcoat layer, and known techniques related to the formulation of magnetic and / or nonmagnetic layers can also be applied. For example, see paragraphs

[0018] to

[0020] of Japanese Patent Laid-Open No. 2006-331625 and U.S. Patent No. 7,029,774, column 4, line 65 to column 5, line 38, for information regarding the backcoat layer.

[0083] <Various thicknesses> With regard to the thickness (total thickness) of magnetic recording media, the enormous increase in the amount of information in recent years has led to a demand for increased recording capacity (higher capacity) for magnetic recording media. One way to achieve higher capacity is to reduce the thickness of the magnetic recording media (hereinafter also referred to as "thinning") and increase the length of magnetic tape housed in one magnetic tape cartridge. From this perspective, the thickness (total thickness) of the magnetic recording media is preferably 5.6 μm or less, more preferably 5.5 μm or less, even more preferably 5.4 μm or less, even more preferably 5.3 μm or less, and even more preferably 5.2 μm or less. Furthermore, from the perspective 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.

[0084] For example, the thickness (total thickness) of the magnetic tape can be measured by the following method. Ten tape samples (e.g., 5 to 10 cm long) are cut from any portion of the magnetic tape, and these tape samples are stacked and measured for thickness. The measured thickness is divided by 10 to obtain the value (thickness per tape sample), which is taken as the tape thickness. The thickness measurement can be performed using a known measuring device capable of measuring thickness to the order of 0.1 μm.

[0085] The thickness of the non-magnetic support is preferably 3.0 to 5.0 μm.

[0086] The thickness of the magnetic layer can be optimized depending on 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. From the viewpoint of high-density recording, it is preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.1 μm. At least one magnetic layer is sufficient, and the magnetic layer may be separated into two or more layers with different magnetic properties, and known configurations related to multilayer magnetic layers can be applied. When the magnetic layer is separated into two or more layers, the thickness of the magnetic layer refers to the total thickness of these layers. This also applies to the thickness of the nonmagnetic layer in a magnetic recording medium having multiple nonmagnetic layers.

[0087] Regarding the thickness of the nonmagnetic layer, the thicker the nonmagnetic layer, the more likely it is that the nonmagnetic powder particles will be unevenly distributed during the coating and drying processes of the nonmagnetic layer-forming composition, resulting in greater thickness variations at various locations and a rougher surface for the nonmagnetic layer. From the perspective of improving the smoothness of the magnetic layer surface, a high level of surface smoothness is desirable. From this perspective, the thickness of the nonmagnetic layer is preferably less than 1.0 μm, more preferably 0.9 μm or less, and even more preferably 0.8 μm or less. Furthermore, from the perspective of improving the uniformity of the coating of the nonmagnetic layer-forming composition, the thickness of the nonmagnetic layer is preferably 0.05 μm or more, and more preferably 0.1 μm or more. From the perspective of further improving the durability of the magnetic recording medium, the thickness of the nonmagnetic layer is preferably more than 0.5 μm, and more preferably 0.6 μm or more.

[0088] The thickness of the backcoat layer is preferably 0.9 μm or less, and more preferably 0.1 μm or more and 0.7 μm or less.

[0089] The thicknesses of the above-mentioned various layers and the non-magnetic support can be determined by the following method. A cross section of the magnetic recording medium in the thickness direction is exposed by an ion beam, and then the exposed cross section is observed using a scanning electron microscope or a transmission electron microscope. The thicknesses can be calculated as the arithmetic mean of the thicknesses measured at any two locations during cross-sectional observation. Alternatively, the thicknesses can be calculated as design thicknesses calculated from manufacturing conditions, etc. The thicknesses of the various layers shown in the Examples section below are design thicknesses calculated from manufacturing conditions.

[0090] <Manufacturing process> (Preparation of compositions for forming each layer) The process for preparing a composition for forming a magnetic layer, nonmagnetic layer, or backcoat layer typically includes at least a kneading step, a dispersing step, and optional mixing steps before or after these steps. Each step may be divided into two or more stages. The components used to prepare each layer-forming composition may be added at the beginning or during any step. Solvents may include one or more of the various solvents typically used in the manufacture of particulate magnetic recording media. For details about solvents, see, for example, paragraph 0153 of JP 2011-216149 A. Alternatively, individual components may be added in separate steps in two or more steps. For example, the binder may be added in separate steps in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. Known manufacturing techniques can be used in the various steps to produce the magnetic recording medium. For the kneading step, it is preferable to use a device with strong kneading power, such as an open kneader, continuous kneader, pressure kneader, or extruder. For details of the kneading treatment, reference can be made to Japanese Patent Application Laid-Open Nos. 1-106338 and 1-79274. Known dispersers can be used. Specific examples of means for controlling the abrasive aggregate ratio to 50% or more are as described above. Filtration may be carried out by known methods at any stage in the preparation of each layer-forming composition. Filtration can be carried out, for example, by filter filtration. Filters used for filtration include those with a pore size of 0.01 to 3 μm (e.g., glass fiber filters, polypropylene filters, etc.).

[0091] (Coating process) The magnetic layer can be formed by applying the magnetic layer-forming composition directly to the surface of the non-magnetic support, or by sequentially or simultaneously applying the magnetic layer-forming composition and the non-magnetic layer-forming composition in a multilayer. The backcoat layer can be formed by applying the backcoat layer-forming composition to the surface of the non-magnetic support opposite to the surface having the non-magnetic layer and / or magnetic layer (or on which the non-magnetic layer and / or magnetic layer will be subsequently formed). For details on the coating for forming each layer, see paragraph 0066 of JP 2010-231843 A.

[0092] (Other processes) After the coating process, various treatments can be performed, such as drying, magnetic layer orientation, and surface smoothing (calendering). For details of these processes, see known techniques, such as paragraphs 0052 to 0057 of JP 2010-24113 A. For example, the coating layer of the magnetic layer-forming composition can be subjected to orientation treatment while the coating layer is still wet. For orientation treatment, various known techniques, including those described in paragraph 0067 of JP 2010-231843 A, can be applied. For example, vertical orientation treatment can be performed by known methods, such as using magnets with opposite poles facing each other. In the orientation zone, the drying rate of the coating layer can be controlled by the temperature and volume of the drying air and / or the transport speed of the non-magnetic support bearing the coating layer. The coating layer may also be pre-dried before being transported to the orientation zone. Regarding calendering, strengthening the calendering conditions tends to improve the smoothness of the magnetic layer surface. Calendering conditions include the number of calendering passes (hereinafter also referred to as "calendering passes"), calendering pressure, calendering temperature (calender roll surface temperature), calendering speed, and calender roll hardness. The more the calendering passes, the stronger the calendering. The higher the calendering pressure, calendering temperature, and calender roll hardness, the stronger the calendering, and the slower the calendering speed. For example, the calendering pressure (linear pressure) can be 200 to 500 kg / cm, and preferably 250 to 350 kg / cm. The calendering temperature (calender roll surface temperature) can be, for example, 85 to 120°C, and preferably 90 to 110°C, and the calendering speed can be, for example, 50 to 300 m / min, and preferably 50 to 200 m / min. A long magnetic tape roll can be obtained through various processes. The obtained magnetic tape roll is cut (slit) using a known cutting machine to the width of the magnetic tape to be wound into a magnetic tape cartridge, for example. The width is determined according to a standard, and is, for example, 1 / 2 inch. 1 / 2 inch = 12.65 mm. A servo pattern is usually formed on the magnetic tape obtained by slitting, as will be described in detail later.

[0093] (Heat treatment) In one embodiment, the magnetic recording medium can be a magnetic tape manufactured through the following heat treatment: In another embodiment, the magnetic recording medium can be a magnetic tape manufactured without the following heat treatment.

[0094] The heat treatment can be carried out by winding the magnetic tape, which has been slit and cut to a width determined in accordance with a standard, around a core member and carrying out the heat treatment in the wound state.

[0095] In one embodiment, the above-mentioned heat treatment is performed with the magnetic tape wound around a core-shaped member for heat treatment (hereinafter referred to as the "heat treatment core"), and the magnetic tape after the heat treatment is wound onto a reel of a magnetic tape cartridge, thereby producing a magnetic tape cartridge with the magnetic tape wound onto a reel. The heat treatment core can be made of metal, resin, paper, or the like. The material of the heat treatment core is preferably a highly rigid material from the viewpoint of suppressing winding defects such as spalling. From this viewpoint, the heat treatment core is preferably made of metal or resin. Furthermore, as an index of rigidity, the flexural modulus of the material of the heat treatment core is preferably 0.2 GPa (gigapascal) or more, more preferably 0.3 GPa or more. On the other hand, since highly rigid materials are generally expensive, using a heat treatment core made of a material with a rigidity exceeding the rigidity required to suppress winding defects leads to increased costs. In consideration of the above, the flexural modulus of the material of the heat treatment core is preferably 250 GPa or less. The flexural modulus is a value measured in accordance with ISO (International Organization for Standardization) 178, and the flexural moduli of various materials are known. Furthermore, the heat treatment core can be a solid or hollow core-shaped member. If the core is hollow, the wall thickness is preferably 2 mm or more from the viewpoint of maintaining rigidity. The core for heat treatment may or may not have a flange. It is preferable to prepare a magnetic tape having a length equal to or greater than the length to be ultimately accommodated in a magnetic tape cartridge (hereinafter referred to as the "final product length") as the magnetic tape to be wound around the heat treatment core, and to perform heat treatment by placing this magnetic tape wound around the heat treatment core in a heat treatment environment. The length of the magnetic tape to be wound around the heat treatment core is equal to or greater than the final product length, and from the viewpoint of ease of winding onto the heat treatment core, it is preferable that it be "final product length + α". From the viewpoint of ease of winding, this α is preferably 5 m or more. The tension during winding onto the heat treatment core is preferably 0.1 N (Newton) or more. Furthermore, from the viewpoint of preventing excessive deformation, the tension during winding onto the heat treatment core is preferably 1.5 N or less, more preferably 1.0 N or less. The outer diameter of the heat treatment core is preferably 20 mm or more, more preferably 40 mm or more, from the viewpoints of ease of winding and prevention of coiling (longitudinal curl). The outer diameter of the heat treatment core is preferably 100 mm or less, more preferably 90 mm or less. The width of the heat treatment core need only be equal to or greater than the width of the magnetic tape wound around the core. After the heat treatment, when removing the magnetic tape from the heat treatment core, it is preferable to remove the magnetic tape from the heat treatment core after the magnetic tape and the heat treatment core have cooled sufficiently to prevent unintended deformation of the tape during the removal operation. The removed magnetic tape is preferably first wound onto another core (referred to as a "temporary take-up core"), and then wound from the temporary take-up core onto a reel of a magnetic tape cartridge (typically with an outer diameter of approximately 40 to 50 mm). This allows the magnetic tape to be wound onto the reel of a magnetic tape cartridge while maintaining the inner and outer positions of the magnetic tape relative to the heat treatment core during the heat treatment. For details about the temporary take-up core and the tension when winding the magnetic tape onto this core, please refer to the previous description of the heat treatment core. In a form in which the above-mentioned heat treatment is performed on a magnetic tape having a length of "final product length + α", the length of "+ α" can be cut off at any stage. For example, in one form, the magnetic tape of the final product length can be wound from the temporary winding core onto the reel of the magnetic tape cartridge, and the remaining length of "+ α" can be cut off.From the viewpoint of reducing the portion that is cut off and discarded, it is preferable that the above-mentioned α be 20 m or less.

[0096] A specific example of the heat treatment carried out in the state where the core member is wound as described above will be described below. The atmospheric temperature at which the heat treatment is performed (hereinafter referred to as "heat treatment temperature") is preferably 40° C. or higher, and more preferably 50° C. or higher. On the other hand, from the viewpoint of suppressing excessive deformation, the heat treatment temperature is preferably 75° C. or lower, more preferably 70° C. or lower, and even more preferably 65° C. or lower. The absolute humidity by weight of the atmosphere in which the heat treatment is carried out is preferably 0.1 g / kg dry air or more, more preferably 1 g / kg dry air or more. An atmosphere with an absolute humidity by weight in the above range is preferred because it can be prepared without using special equipment for reducing moisture. On the other hand, from the viewpoint of preventing condensation from forming and reducing workability, the absolute humidity by weight is preferably 70 g / kg dry air or less, more preferably 66 g / kg dry air or less. The heat treatment time is preferably 0.3 hours or more, more preferably 0.5 hours or more. Furthermore, from the viewpoint of production efficiency, the heat treatment time is preferably 48 hours or less.

[0097] (Servo pattern formation) The magnetic recording medium can be a tape-shaped magnetic recording medium (i.e., magnetic tape) or a disk-shaped magnetic recording medium (i.e., magnetic disk). In either form, the magnetic layer can have a servo pattern. "Forming a servo pattern" can also be called "recording a servo signal." Hereinafter, the formation of a servo pattern will be explained using magnetic tape as an example.

[0098] The servo pattern is usually formed along the length of the magnetic tape. Control methods that use servo signals (servo control) include timing-based servo (TBS), amplitude servo, and frequency servo.

[0099] As specified 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, a servo pattern is formed by a pair of non-parallel magnetic stripes (also called "servo stripes") arranged continuously along the longitudinal direction of the magnetic tape. In this invention and this specification, the term "timing-based servo pattern" refers to a servo pattern that enables head tracking in a timing-based servo system. The reason why the servo pattern is formed by a pair of non-parallel magnetic stripes as described above is to inform a servo signal reading element passing over the servo pattern of its passing position. Specifically, the spacing between the pair of magnetic stripes is formed so that it continuously changes along the width direction of the magnetic tape. By reading this spacing, the servo signal reading element can determine the relative position between the servo pattern and the servo signal reading element. This relative position information enables tracking of data tracks. For this reason, a plurality of servo tracks are usually set on the servo pattern along the width direction of the magnetic tape.

[0100] A servo band is made up of a continuous servo pattern along the length of the magnetic tape. Typically, multiple servo bands are provided on a magnetic tape. For example, there are five servo bands on an LTO tape. The area between two adjacent servo bands is the data band. A data band is made up of multiple data tracks, and each data track corresponds to one of the servo tracks.

[0101] Also, in one embodiment, as disclosed in Japanese Patent Application Laid-Open No. 2004-318983, information indicating the servo band number (also called "servo band ID (identification)" or "UDIM (Unique Data Band Identification Method) information") is embedded in each servo band. This servo band ID is recorded by shifting a specific one of a plurality of pairs of servo stripes in the servo band so that its position is displaced relative to the longitudinal direction of the magnetic tape. Specifically, the way in which a specific one of a plurality of pairs of servo stripes is shifted varies for each servo band. As a result, the recorded servo band ID is unique for each servo band, and therefore, simply by reading one servo band with a servo signal reading element, that servo band can be uniquely identified.

[0102] One method for uniquely identifying servo bands is the staggered method described in ECMA-319 (June 2001). In this staggered method, pairs of non-parallel magnetic stripes (servo stripes) are continuously arranged along the length of the magnetic tape, and are recorded so that each servo band is offset along the length of the magnetic tape. The combination of this offset between adjacent servo bands is unique across the entire magnetic tape, making it possible to uniquely identify servo bands when reading the servo pattern with two servo signal reading elements.

[0103] As specified in ECMA-319 (June 2001), each servo band also typically contains information indicating the longitudinal position of the magnetic tape (also known as "LPOS (Longitudinal Position) information"). Like UDIM information, this LPOS information is recorded by shifting the positions of a pair of servo stripes along the longitudinal direction of the magnetic tape. However, unlike UDIM information, the same signal is recorded in each servo band with this LPOS information.

[0104] It is also possible to embed information other than the UDIM information and LPOS information described above in the servo bands. In this case, the embedded information may be different for each servo band, such as UDIM information, or it may be common to all servo bands, such as LPOS information. Furthermore, methods other than those described above can be used to embed information in the servo bands. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of pairs of servo stripes.

[0105] The head for forming a servo pattern is called a servo write head. A servo write head typically has a pair of gaps corresponding to the pair of magnetic stripes, the number of which is equal to the number of servo bands. Typically, a core and a coil are connected to each pair of gaps. By supplying a current pulse to the coil, the magnetic field generated in the core can generate a leakage magnetic field in the pair of gaps. To form a servo pattern, a current pulse is input while running a magnetic tape over the servo write head, thereby transferring the magnetic pattern corresponding to the pair of gaps onto the magnetic tape, thereby forming the servo pattern. The width of each gap can be appropriately set depending on the density of the servo pattern to be formed. The width of each gap can be set, for example, to 1 μm or less, 1 to 10 μm, or 10 μm or more.

[0106] Before forming a servo pattern on a magnetic tape, the magnetic tape is usually subjected to a demagnetization (erase) process. This erase process can be performed by applying a uniform magnetic field to the magnetic tape using a direct current magnet or an alternating current magnet. There are two types of erase processes: direct current (DC) erase and alternating current (AC) erase. AC erase is performed by gradually reducing the strength of the magnetic field applied to the magnetic tape while reversing the direction of the magnetic field. DC erase, on the other hand, is performed by applying a unidirectional magnetic field to the magnetic tape. There are two other DC erase methods. The first method is horizontal DC erase, in which a unidirectional magnetic field is applied along the length of the magnetic tape. The second method is vertical DC erase, in which a unidirectional magnetic field is applied along the thickness of the magnetic tape. The erase process can be performed on the entire magnetic tape or on each servo band of the magnetic tape.

[0107] The direction of the magnetic field of the formed servo pattern is determined by the erase direction. For example, when a magnetic tape is subjected to horizontal DC erasure, the servo pattern is formed so that the direction of the magnetic field is opposite to the erase direction. This increases the output of the servo signal obtained by reading the servo pattern. As shown in Japanese Patent Application Laid-Open No. 2012-53940, when a magnetic pattern is transferred to a magnetic tape that has been vertically DC erased using the gap, the servo signal obtained by reading the formed servo pattern has a unipolar pulse shape. On the other hand, when a magnetic pattern is transferred to a magnetic tape that has been horizontally DC erased using the gap, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

[0108] In one embodiment, the width of the magnetic tape can be controlled by acquiring width dimensional information of the magnetic tape while it is running using a servo signal and adjusting and changing the tension applied to the magnetic tape in the longitudinal direction in accordance with the acquired dimensional information. Adjusting the tension in this manner can contribute to preventing the magnetic head for recording or reproducing data from being displaced from the target track position due to width deformation of the magnetic tape during recording or reproduction.

[0109] [Magnetic tape cartridge] In one embodiment, the magnetic recording medium may be a magnetic tape. Another aspect of the present invention relates to a magnetic tape cartridge including the magnetic tape.

[0110] The details of the magnetic tape contained in the tape cartridge are as described above.

[0111] A magnetic tape cartridge generally contains a magnetic tape wound on a reel within the cartridge body. The reel is rotatably mounted within the cartridge body. Widely used magnetic tape cartridges include single-reel magnetic tape cartridges with one reel within the cartridge body and dual-reel magnetic tape cartridges with two reels within the cartridge body. When a single-reel magnetic tape cartridge is loaded into a magnetic tape device for recording and / or reproducing data on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and rewound onto a reel on the magnetic tape device. A magnetic head is located 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 (supply reel) on the magnetic tape cartridge and the reel (take-up reel) on the magnetic tape device. For example, data is recorded and / or reproduced by contact and sliding between the magnetic head and the magnetic layer surface of the magnetic tape during this process. In contrast, a dual-reel magnetic tape cartridge is provided with both a supply reel and a take-up reel inside the magnetic tape cartridge.

[0112] [Magnetic recording and playback device] One aspect of the present invention relates to a magnetic recording and reproducing device including a magnetic recording medium. In one embodiment, in the magnetic recording and reproducing device, data can be recorded on the magnetic recording medium and / or data recorded on the magnetic recording medium can be reproduced by bringing a magnetic head into contact with the magnetic layer surface of the magnetic recording medium and sliding the magnetic head. This type of magnetic recording and reproducing device is generally called a sliding drive or a contact sliding drive.

[0113] In this invention and this specification, the term "magnetic recording and reproducing device" refers to a device capable of at least one of recording data to a magnetic recording medium and reproducing data recorded on the magnetic recording medium. Such a device is generally called a drive. The magnetic head included in the magnetic recording and reproducing device can be a recording head capable of recording data to a magnetic recording medium, or a reproducing head capable of reproducing data recorded on the magnetic recording medium. In one embodiment, the magnetic recording and reproducing device can include both a recording head and a reproducing head as separate magnetic heads. In another embodiment, the magnetic head included in the magnetic tape drive can have both a recording element and a reproducing element in a single magnetic head. The reproducing head is preferably a magnetic head (MR head) that includes a magnetoresistive (MR) element as a reproducing element, which can sensitively read information recorded on a magnetic recording medium. Various known MR heads (e.g., GMR (Giant Magnetoresistive) heads, TMR (Tunnel Magnetoresistive) heads, etc.) can be used as the MR head. The magnetic head that records and / or reproduces data may also include a servo signal reading element. Alternatively, the magnetic tape device may include a magnetic head (servo head) equipped with a servo signal read element as a separate head from the magnetic head that records and / or reproduces data. For example, a magnetic head that records and / or reproduces recorded data (hereinafter also referred to as a "recording / reproducing head") may include two servo signal read elements, each of which can simultaneously read two adjacent servo bands sandwiching a data band. One or more data elements may be disposed between the two servo signal read elements. The element for recording data (recording element) and the element for reproducing data (reproducing element) are collectively referred to as the "data element."

[0114] When recording and / or reproducing data, tracking using servo signals can be performed first. That is, by making the servo signal reading element follow a predetermined servo track, the data element can be controlled to pass over the target data track. The data track is moved by changing the servo track read by the servo signal reading element in the tape width direction. The read / write head can also record and / or read data from other data bands by using the UDIM information described above to move the servo signal read element to a specific servo band and start tracking that servo band.

[0115] FIG. 1 shows an example of the arrangement of data bands and servo bands. In FIG. 1, multiple servo bands 1 are sandwiched between guide bands 3 on the magnetic layer of a magnetic tape MT. Multiple regions 2 sandwiched between two servo bands form data bands. Servo patterns are magnetized regions formed by magnetizing specific regions of the magnetic layer with a servo write head. The regions magnetized by the servo write head (the positions where servo patterns are formed) are determined by standards. For example, in the industry-standard LTO Ultrium format tape, multiple servo patterns inclined with respect to the tape width direction are formed on the servo bands during magnetic tape manufacturing, as shown in FIG. 2. Specifically, in FIG. 2, a servo frame SF on servo band 1 is composed of a servo subframe 1 (SSF1) and a servo subframe 2 (SSF2). Servo subframe 1 is composed of an A burst (labeled A in FIG. 2) and a B burst (labeled B in FIG. 2). The A burst is composed of servo patterns A1 to A5, and the B burst is composed of servo patterns B1 to B5. On the other hand, servo subframe 2 is composed of a C burst (labeled C in FIG. 2) and a D burst (labeled D in FIG. 2). The C burst is composed of servo patterns C1 through C4, and the D burst is composed of servo patterns D1 through D4. These 18 servo patterns are arranged in sets of 5 and 4 in a 5, 5, 4, 4 arrangement in a subframe, and are used to identify servo frames. For illustrative purposes, FIG. 2 shows one servo frame. However, in reality, on the magnetic layer of a magnetic tape where head tracking is performed using a timing-based servo system, multiple servo frames are arranged in each servo band in the running direction. In FIG. 2, the arrow indicates the running direction. For example, an LTO Ultrium format tape typically has more than 5,000 servo frames per meter of tape length in each servo band of the magnetic layer.

[0116] In one embodiment of the magnetic recording and reproducing device, the magnetic recording medium is treated as a removable medium (so-called exchangeable medium), for example, a magnetic tape cartridge containing a magnetic tape is inserted into and removed from the magnetic recording and reproducing device. In another embodiment, the magnetic recording medium is not treated as an exchangeable medium, for example, the magnetic tape is wound around a reel of a magnetic recording and reproducing device equipped with a magnetic head, and the magnetic tape is housed in the magnetic recording and reproducing device. In one embodiment, in such a magnetic recording and reproducing device, the magnetic tape and the magnetic head can be housed in an enclosed space within the magnetic tape device. In the present invention and this specification, the term "enclosed space" refers to a space whose airtightness is evaluated by an immersion method (bombing method) using helium (He) as specified in JIS Z 2331:2006 Helium Leak Test Method of 10×10 -8 Pa·m 3 / sec or less. The airtightness of an enclosed space is, for example, 5 x 10 ―9 Pa·m 3 / sec or more 10 x 10 -8 Pa·m 3 / sec or less, or may be below the above range. In one embodiment, the entire space in the housing can be the sealed space, and in another embodiment, a portion of the space in the housing can be the sealed space. The sealed space can be the internal space of a housing that covers all or part of the magnetic tape device. The material and shape of the housing are not particularly limited, and can be, for example, the same as the material and shape of the housing of a typical magnetic tape device. Examples of materials for the housing include metal, resin, etc. [Example]

[0117] An embodiment of the present invention will be described below based on an example. However, the present invention is not limited to the embodiment shown in the example. The indications of "parts" and "%" below mean "parts by mass" and "% by mass" unless otherwise specified. "eq" is an equivalent, and is a unit that cannot be converted to SI units. Unless otherwise specified, the following steps and operations were carried out in an environment with a temperature of 20 to 25°C and a relative humidity of 40 to 60%.

[0118] [Abrasive] The average primary particle diameters of the various abrasives in Table 1 were determined by the method described above, using a Hitachi H-9000 transmission electron microscope at a magnification of approximately 50,000 to 100,000 times, and Carl Zeiss KS-400 image analysis software, with scale correction performed using a circle with a diameter of 1 cm when capturing images from a scanner and analyzing the images to calculate the equivalent circle diameter.

[0119] [Ferromagnetic powder] In Table 1, "BaFe" represents hexagonal barium ferrite powder with an average particle size (average plate diameter) of 21 nm.

[0120] In Table 1, "SrFe" represents hexagonal strontium ferrite powder prepared by the method described below, and "ε-iron oxide" represents ε-iron oxide powder prepared by the method described below. The average particle volumes of the various ferromagnetic powders described below are values ​​determined by the method described above. The various values ​​relating to the particle sizes of the various powders described below are also values ​​determined by the method described above. The anisotropy constant Ku is a value determined for each ferromagnetic powder by the method described above using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.). The mass magnetization σs is a value measured at a magnetic field strength of 15 kOe using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).

[0121] [Method for producing ferromagnetic powder] <Method for producing hexagonal strontium ferrite powder> 1707 g of SrCO3, 687 g of H3BO3, 1120 g of Fe2O3, 45 g of Al(OH)3, 24 g of BaCO3, 13 g of CaCO3, and 235 g of Nd2O3 were weighed and mixed in a mixer to obtain a raw material mixture. The resulting raw material mixture was melted in a platinum crucible at a melting temperature of 1390°C, and the melt was stirred while heating the tapping hole at the bottom of the platinum crucible, causing the melt to be poured into a rod shape at a rate of approximately 6 g / sec. The tapped liquid was rolled and quenched using a water-cooled twin roller to produce an amorphous body. 280 g of the produced amorphous body was placed in an electric furnace, heated to 635°C (crystallization temperature) at a rate of 3.5°C / min, and held at that temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles. The crystallized material obtained above, containing hexagonal strontium ferrite particles, was then coarsely crushed in a mortar. 1,000 g of 1 mm zirconia beads and 800 ml of 1% acetic acid solution were added to a glass bottle and dispersed for 3 hours using a paint shaker. The resulting dispersion was then separated from the beads and placed in a stainless steel beaker. The dispersion was left to stand at 100°C for 3 hours to dissolve the glass components, after which it was precipitated in a centrifuge and washed by repeated decantation. It was then dried for 6 hours in a heating furnace at 110°C to obtain hexagonal strontium ferrite powder. The average particle volume of the hexagonal strontium ferrite powder obtained above ("SrFe" in Table 1 below) was 900 nm 3 , the anisotropy constant Ku is 2.2×10 5 J / m 3 , mass magnetization σs is 49A m 2 / kg. A 12 mg sample powder was taken from the hexagonal strontium ferrite powder obtained above, and this sample powder was partially dissolved under the dissolution conditions exemplified above. The filtrate was subjected to elemental analysis using an ICP analyzer to determine the neodymium atom content in the surface layer. Separately, 12 mg of sample powder was collected from the hexagonal strontium ferrite powder obtained above, and this sample powder was completely dissolved under the dissolution conditions exemplified above. The filtrate thus obtained was subjected to elemental analysis using an ICP analyzer to determine the bulk content of neodymium atoms. The neodymium atom content (bulk content) of the hexagonal strontium ferrite powder obtained above relative to 100 atomic percent of iron atoms was 2.9 atomic percent. The neodymium atom content in the surface layer was 8.0 atomic percent. The ratio of the surface layer content to the bulk content, "surface layer content / bulk content," was 2.8, confirming that neodymium atoms were unevenly distributed in the surface layers of the particles.

[0122] The powder obtained above was confirmed to have a hexagonal ferrite crystal structure by scanning with CuKα radiation at a voltage of 45 kV and an intensity of 40 mA and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). The powder obtained above exhibited a magnetoplumbite (M-type) hexagonal ferrite crystal structure. Furthermore, the crystalline phase detected by X-ray diffraction analysis was a single magnetoplumbite phase. PANalytical X'Pert Pro diffractometer, PIXcel detector Soller slits for incident and diffracted beams: 0.017 radians Dispersion slit fixed angle: 1 / 4 degree Mask: 10mm Anti-scatter slit: 1 / 4 degree Measurement mode: Continuous Measurement time per step: 3 seconds Measurement speed: 0.017 degrees per second Measurement step: 0.05 degrees

[0123] <Method for producing ε-iron oxide powder> 8.3 g of iron(III) nitrate nonahydrate, 1.3 g of gallium(III) nitrate octahydrate, 190 mg of cobalt(II) nitrate hexahydrate, 150 mg of titanium(IV) sulfate, and 1.5 g of polyvinylpyrrolidone (PVP) were dissolved in 90 g of pure water. While stirring using a magnetic stirrer, 4.0 g of 25% aqueous ammonia was added in air at an ambient temperature of 25°C. The mixture was stirred for 2 hours at 25°C. A citric acid solution prepared by dissolving 1 g of citric acid in 9 g of pure water was added to the resulting solution and stirred for 1 hour. The precipitated powder was collected by centrifugation, washed with pure water, and dried in a heating oven at 80°C. 800g of pure water was added to the dried powder, and the powder was dispersed in water again to obtain a dispersion. The resulting dispersion was heated to 50°C, and 40g of a 25% aqueous ammonia solution was added dropwise while stirring. After stirring for 1 hour while maintaining the temperature at 50°C, 14mL of tetraethoxysilane (TEOS) was added dropwise and stirred for 24 hours. 50g of ammonium sulfate was added to the resulting reaction solution, and the precipitated powder was collected by centrifugation, washed with pure water, and dried for 24 hours in a heating furnace at 80°C to obtain a precursor of the ferromagnetic powder. The obtained precursor of the ferromagnetic powder was placed in a heating furnace at an internal temperature of 1000° C. in an air atmosphere and subjected to heat treatment for 4 hours. The heat-treated ferromagnetic powder precursor was placed in a 4 mol / L aqueous solution of sodium hydroxide (NaOH), and the liquid temperature was maintained at 70°C while stirring for 24 hours, thereby removing the impurity silicate compound from the heat-treated ferromagnetic powder precursor. Thereafter, the silicate compound was removed by centrifugation, and the ferromagnetic powder was collected and washed with pure water to obtain a ferromagnetic powder. The composition of the obtained ferromagnetic powder was confirmed by inductively coupled plasma optical emission spectrometry (ICP-OES). It was found that the powder consisted of Ga, Co, and Ti substituted ε-iron oxide (ε-Ga 0.28 Co 0.05 Ti 0.05 Fe 1.62O3). Furthermore, X-ray diffraction analysis was performed under the same conditions as those described above for the preparation of hexagonal strontium ferrite powder, and it was confirmed from the peaks in the X-ray diffraction pattern that the obtained ferromagnetic powder had a single-phase ε-phase crystal structure (ε-iron oxide crystal structure) that did not contain α-phase or γ-phase crystal structures. The average particle volume of the obtained ε-iron oxide powder (referred to as "ε-iron oxide" in Table 1 below) was 750 nm 3 , the anisotropy constant Ku is 1.2×10 5 J / m 3 , mass magnetization σs is 16A m 2 / kg.

[0124] [Example 1] (1) Preparation of abrasive dispersion 100.0 parts of the abrasive shown in Table 1 were mixed with 3.0 parts of 2,3-dihydroxynaphthalene (Tokyo Chemical Industry Co., Ltd.), 31.3 parts of a 32% solution of polyester polyurethane resin (UR-4800 (polar group amount: 80 meq / kg) manufactured by Toyobo Co., Ltd.) having SO3Na groups as polar groups (solvent: a mixed solvent of methyl ethyl ketone and toluene), and 570.0 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone at a 1:1 (mass ratio) and dispersed for 5 hours on a paint shaker in the presence of zirconia beads. After dispersion, the dispersion and the beads were separated using a mesh to obtain an abrasive dispersion. The beaker containing the abrasive dispersion was placed in an oven with an internal atmosphere temperature of 60°C and heated to volatilize the solvent in the abrasive dispersion, thereby concentrating the abrasive dispersion. In Example 1, heating was carried out until the mass of the abrasive dispersion became 30% of the mass before heating ("concentration rate" in Table 1). In this way, an abrasive dispersion liquid to be used in preparing the magnetic layer-forming composition was obtained.

[0125] (2) Magnetic Layer Formulation (Magnetic liquid) Ferromagnetic powder (type: see Table 1) 100.0 parts SO3Na group-containing polyurethane resin 14.0 parts Weight average molecular weight: 70,000, SO3Na group: 0.2meq / g Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (abrasive liquid) 6.0 parts of the abrasive dispersion prepared in (1) above (Protrusion forming agent liquid) Protrusion forming agent 2.0 parts Type: Colloidal silica (average particle size 120 nm) Methyl ethyl ketone 1.4 parts (Other ingredients) Stearic acid 2.0 parts Stearic acid amide 0.2 parts Butyl stearate 2.0 parts Polyisocyanate (Tosoh Corporation, Coronate (registered trademark) L) 2.5 parts (Finishing additive solvent) Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

[0126] (3) Nonmagnetic Layer Formulation Non-magnetic inorganic powder α-iron oxide 100.0 parts Average particle size (average major axis length): 0.15μm Acicular ratio: 7.0 BET (Brunauer-Emmett-Teller) specific surface area: 52m 2 / g Carbon black 20.0 parts Average particle size: 20nm SO3Na group-containing polyurethane resin 18.0 parts Weight average molecular weight: 70,000, SO3Na group: 0.2meq / g Stearic acid 2.0 parts Stearic acid amide 0.2 parts Butyl stearate 2.0 parts Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0 parts

[0127] (4) Formulation of composition for forming backcoat layer Carbon black 100.0 parts DBP (Dibutyl phthalate) oil absorption: 74cm 3 / 100g Nitrocellulose 27.0 parts 62.0 parts polyester polyurethane resin containing sulfonic acid groups and / or their salts Polyester resin 4.0 parts Alumina powder (BET specific surface area: 17 m 2 / g) 0.6 parts Methyl ethyl ketone 600.0 parts Toluene 600.0 parts Polyisocyanate (Tosoh Corporation, Coronate (registered trademark) L) 15.0 parts

[0128] (5) Preparation of compositions for forming each layer A magnetic layer-forming composition was prepared by the following method. The magnetic liquid was prepared by dispersing the above components for 24 hours (bead dispersion) using a batch-type vertical sand mill. Zirconia beads with a bead diameter of 0.5 mm were used as the dispersion beads. Using the sand mill, the prepared magnetic liquid, the abrasive liquid, and other components (protrusion-forming agent liquid, other components, and finishing additive solvent) were mixed and bead-dispersed for 5 minutes, and then treated with a batch-type ultrasonic device (20 kHz, 300 W) for 0.5 minutes (ultrasonic dispersion). The mixture was then filtered using a filter with a pore size of 0.5 μm to prepare the magnetic layer-forming composition. The nonmagnetic layer-forming composition was prepared by the following method. The above components, excluding the lubricants (stearic acid, stearic acid amide, and butyl stearate), were kneaded and diluted using an open kneader, and then dispersed using a horizontal bead mill disperser. The lubricants (stearic acid, stearic acid amide, and butyl stearate) were then added, and the mixture was stirred and mixed using a dissolver stirrer to prepare the nonmagnetic layer-forming composition. The backcoat layer-forming composition was prepared by the following method. The above components, excluding the polyisocyanate, were introduced into a dissolver mixer and stirred at a peripheral speed of 10 m / s for 30 minutes, and then dispersed using a horizontal bead mill disperser. The polyisocyanate was then added, and the mixture was stirred and mixed using the dissolver mixer to prepare the backcoat layer-forming composition.

[0129] (6) Manufacturing of magnetic tapes and magnetic tape cartridges The nonmagnetic layer-forming composition prepared in (5) above was applied and dried on the surface of a 4.1 μm thick biaxially oriented polyethylene terephthalate support to a thickness shown in Table 1, forming a nonmagnetic layer. The magnetic layer-forming composition prepared in (5) above was then applied to the nonmagnetic layer to a dried thickness of 0.1 μm, forming a coating layer. While the coated layer of the magnetic layer-forming composition was still wet, a magnetic field with a strength of 0.3 T was applied perpendicular to the surface of the coated layer to perform a vertical orientation treatment, followed by drying to form a magnetic layer. The backcoat layer-forming composition prepared in (5) above was then applied to the surface of the support opposite the surface on which the nonmagnetic and magnetic layers were formed, and dried to a dried thickness of 0.3 μm, forming a backcoat layer. Thereafter, a surface smoothing treatment (calendering treatment) was carried out using a calender roll consisting only of a metal roll at a speed of 100 m / min, a linear pressure of 300 kg / cm, and a calender temperature (surface temperature of the calender roll) of 90°C (calendering number of times: 2). The long magnetic tape was then heat-treated by storing it in a heat treatment furnace at an ambient temperature of 70°C (heat treatment time: 36 hours). After heat treatment, the tape was slit into 1 / 2-inch widths to obtain magnetic tape. Servo signals were recorded on the magnetic layer of the obtained magnetic tape using a commercially available servo writer, resulting in a magnetic tape with data bands, servo bands, and guide bands arranged in accordance with the LTO (Linear Tape-Open) Ultrium format, and with servo patterns (timing-based servo patterns) on the servo bands arranged and shaped in accordance with the LTO Ultrium format. The servo patterns thus formed conform to the specifications of JIS (Japanese Industrial Standards) X6175:2006 and Standard ECMA-319 (June 2001). The total number of servo bands was five, and the total number of data bands was four. The magnetic tape (length 970 m) after the servo pattern formation was taken up onto a core for heat treatment, and was heat treated while still wound on this core. A solid core-shaped member (outer diameter: 50 mm) made of resin with a flexural modulus of elasticity of 0.8 GPa was used as the core for heat treatment, and the tension during winding was 0.6 N. The heat treatment was carried out at a heat treatment temperature of 50°C for 5 hours. The weight absolute humidity of the atmosphere in which the heat treatment was carried out was 10 g / kg dry air. After the above heat treatment, once the magnetic tape and heat treatment core had sufficiently cooled, the magnetic tape was removed from the heat treatment core and wound onto a temporary take-up core. Thereafter, the final product length (960 m) of magnetic tape was wound from the temporary take-up core onto the reel (reel outer diameter: 44 mm) of a magnetic tape cartridge (LTO Ultrium 7 data cartridge). The remaining 10 m was cut off, and a leader tape in accordance with item 9 of Section 3 of Standard ECMA (European Computer Manufacturers Association)-319 (June 2001) was spliced ​​to the end of the cut-off side using commercially available splicing tape. The temporary take-up core was a solid core-shaped member made of the same material and with the same outer diameter as the heat treatment core, and the tension during winding was 0.6 N. In this manner, a single-reel magnetic tape cartridge of Example 1 was produced, in which a magnetic tape having a length of 960 m was wound around a reel.

[0130] [Examples 2, 3, 6 to 10, Comparative Examples 2 to 4] A magnetic tape cartridge was produced by the method described in Example 1, except that the abrasives shown in Table 1 were used as the abrasives.

[0131] [Examples 4 and 5] A magnetic tape cartridge was produced in the same manner as in Example 1, except that the abrasive dispersion was heated and concentrated to the concentration ratio shown in Table 1.

[0132] [Example 11] Two non-magnetic layers were formed as described below, and a magnetic layer was formed by applying a magnetic layer-forming composition to the upper non-magnetic layer as described in Example 1, and a magnetic tape cartridge was produced by the same method as described in Example 1, except that the number of calendering passes was one.

[0133] <Formulation of composition for forming lower nonmagnetic layer> Carbon black (average particle size: 20 nm) 100.0 parts Trioctylamine 4.0 parts Vinyl chloride resin 12.0 parts 1.5 parts stearic acid Stearic acid amide 0.3 parts Butyl stearate 1.5 parts Cyclohexanone 200.0 parts Methyl ethyl ketone 510.0 parts

[0134] <Formulation of composition for forming upper nonmagnetic layer> Non-magnetic inorganic powder α-iron oxide 100.0 parts Average particle size (average major axis length): 30nm Average short axis length: 15nm Acicular ratio: 2.0 SO3Na group-containing polyurethane resin 18.0 parts Weight average molecular weight: 70,000, SO3Na group: 0.2meq / g Stearic acid 1.0 parts Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0 parts

[0135] The components of the lower nonmagnetic layer composition and the upper nonmagnetic layer composition were kneaded in an open kneader for 240 minutes, and then dispersed in a sand mill. The dispersion conditions for each nonmagnetic layer composition were a 24-hour dispersion time and zirconia beads with a diameter of 0.1 mm. 4.0 parts of polyisocyanate (Tosoh Coronate 3041) were added to the dispersion liquid obtained in this way, and the mixture was stirred and mixed for another 20 minutes, after which it was filtered using a filter with a pore size of 0.5 μm. In this manner, a composition for forming a lower nonmagnetic layer and a composition for forming an upper nonmagnetic layer were prepared. The composition for forming a lower nonmagnetic layer was applied to one surface of a 4.1 μm thick biaxially oriented polyethylene terephthalate support to a dry thickness of 0.25 μm, and then dried in an ambient temperature of 100°C to form a lower nonmagnetic layer. The composition for forming an upper nonmagnetic layer was applied to the lower nonmagnetic layer to a dry thickness of 0.25 μm, and then dried in an ambient temperature of 100°C to form an upper nonmagnetic layer. In this manner, nonmagnetic layers (total number of layers: 2) with a total thickness of 0.5 μm were formed.

[0136] [Examples 12 and 13] A magnetic tape cartridge was produced by the method described for Example 11, except that the ferromagnetic powder shown in the "Ferromagnetic Powder" column in Table 1 was used as the ferromagnetic powder.

[0137] [Comparative Example 1] A magnetic tape cartridge was prepared by the method described in Example 1, except that the abrasive dispersion was not concentrated by heating.

[0138] For each of the examples and comparative examples, two magnetic tape cartridges were prepared, one of which was used to determine the abrasive aggregate ratio described below, and the other was used to evaluate head wear and durability, which will be described later.

[0139] [Evaluation method] <Abrasive aggregate ratio> The FE-SEM used was a Hitachi High-Technologies S-4800, and the free software ImageJ was used as image analysis software. The abrasive agglomerate ratio was determined by the method described above. For Example 1, the abrasive agglomerate ratio was determined using ImageJ under the procedures and conditions described above. For the other Examples and Comparative Examples, the threshold setting for the binarization conditions was adjusted depending on the type of abrasive.

[0140] <Wear evaluation (AlFeSil wear)> The magnetic tape removed from each magnetic tape cartridge was run using a reel tester, and the wear width of the AlFeSil rectangular pillars was measured after running. The AlFeSil rectangular pillars are made of AlFeSil, a sendust-based alloy. For the evaluation, AlFeSil rectangular pillars specified in ECMA (European Computer Manufacturers Association)-288 / Annex H / H2 were used. The wear width of the AlFeSil rectangular pillars was determined by observing the edge of the AlFeSil rectangular pillar from above using an optical microscope, as described in paragraph 0015 of Japanese Patent Laid-Open Publication No. 2007-026564 based on Figure 1 of the same publication. The running was performed under the following running conditions. In an environment with a temperature of 23°C and a relative humidity of 50%, the magnetic layer surface of the magnetic tape was brought into contact with one edge of the AlFeSil prism, perpendicular to the longitudinal direction of the prism, at a wrap angle of 12°, and with a tension of 100 gf applied in the longitudinal direction of the magnetic tape. Under this condition, a 50 m long section of the magnetic tape was run back and forth 50 times at a speed of 3 m / s. Note that "gf" stands for gram force, and 1 N (Newton) is approximately 102 gf. Head wear was evaluated based on the measured wear width of the AlFeSil prism according to the following evaluation criteria. (Evaluation criteria) A: AlFeSil wear width is 10 μm or less B: AlFeSil wear width is over 10 μm and 12 μm or less C: AlFeSil wear width is over 12 μm and 15 μm or less D: AlFeSil wear width exceeds 15 μm

[0141] <Durability (tape scraping)> After measuring the wear width of the AlFeSil square pillars, the magnetic layer surface of each magnetic tape was observed under an optical microscope, and the durability (tape abrasion) of the magnetic tape was evaluated based on the observation results according to the following evaluation criteria. (Evaluation criteria) A: No scratches or tape shavings were found on the surface of the magnetic layer. B: Slight scratches were observed on the surface of the magnetic layer. No tape shavings were observed on the surface of the magnetic layer. C: Slight scratches were observed on the surface of the magnetic layer, and slight tape shavings were observed on the surface of the magnetic layer. D: Scratches on the magnetic layer surface are more severe than those observed in B and C. Furthermore, a large amount of tape shavings are found adhering to the magnetic layer surface.

[0142] The results are shown in Table 1.

[0143] [Table 1]

[0144] The results shown in Table 1 confirm that the magnetic tapes of Examples 1 to 13, which have magnetic layers in which carbide abrasives with average primary particle diameters in the ranges described above exist at abrasive aggregation rates of 50% or more, were able to achieve both excellent durability and reduced wear of the AlFeSil rectangular columns. The inventors speculate that this is because, as described above, the presence of the carbide abrasives in the magnetic layer in the above-described state contributes to mitigating the impact that the magnetic layer surface receives when sliding against the AlFeSil rectangular columns. Such magnetic tapes can exhibit excellent durability and reduce head wear. [Industrial Applicability]

[0145] One aspect of the present invention is useful in the technical field of magnetic recording media for data storage.

Claims

1. A magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder, the magnetic layer contains an abrasive; the abrasive is a carbide; The average primary particle size of the abrasive is 10 nm or more and 100 nm or less, and A magnetic recording medium in which, in an electron microscope image of the surface of the magnetic layer, the area occupied by the abrasive in an aggregated state with a maximum Feret diameter of 0.2 μm or more accounts for 50% or more of the total area occupied by the abrasive, with the total area occupied by the abrasive being 100%.

2. 2. The magnetic recording medium according to claim 1, further comprising one or more non-magnetic layers containing non-magnetic powder between the non-magnetic support and the magnetic layer.

3. When the total number of the non-magnetic layers is one, the thickness of the single non-magnetic layer is less than 1.0 μm; 3. The magnetic recording medium according to claim 2, wherein when the total number of said non-magnetic layers is two or more, the total thickness of said two or more non-magnetic layers is less than 1.0 [mu]m.

4. 4. The magnetic recording medium according to claim 1, wherein the carbide is at least one selected from the group consisting of titanium carbide, tungsten carbide, zirconium carbide, silicon carbide, boron carbide, and vanadium carbide.

5. 5. The magnetic recording medium according to claim 1, wherein the abrasive particles existing in an agglomerated state with a maximum Feret diameter of 0.2 μm or more account for 50% to 95% of the surface area.

6. 6. The magnetic recording medium according to claim 1, wherein the abrasive particles existing in an agglomerated state with a maximum Feret diameter of 0.2 μm or more account for 60% to 95% of the surface area.

7. 7. The magnetic recording medium according to claim 1, wherein the abrasive particles existing in an agglomerated state with a maximum Feret diameter of 0.2 μm or more account for 80% to 95% of the surface area.

8. 8. The magnetic recording medium according to claim 1, further comprising a backcoat layer containing nonmagnetic powder on the surface of said nonmagnetic support opposite to the surface on which said magnetic layer is formed.

9. 9. The magnetic recording medium according to claim 1, which is a magnetic tape.

10. A magnetic tape cartridge comprising the magnetic tape of claim 9.

11. A magnetic recording and reproducing device comprising the magnetic recording medium according to any one of claims 1 to 9.

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