JP6858905B2 - Magnetic recording medium and magnetic recording / playback device - Google Patents

Description

The present invention relates to a magnetic recording medium and a magnetic recording / playback device.

In recent years, a magnetic recording medium has been widely used as a data storage recording medium for recording and storing various types of data (see, for example, Patent Document 1).

Patent No. 6378166

To reproduce the data recorded on the magnetic recording medium, the data recorded on the magnetic layer is usually read by sliding the magnetic head in contact with the surface of the magnetic layer while running the magnetic recording medium in the magnetic recording / reproducing device. It is done by. However, if the magnetic recording medium is inferior in running stability, the reproduction output is lowered due to off-track. Therefore, it is desired that the magnetic recording medium has excellent running stability.

Data recorded on various recording media such as magnetic recording media are called hot data, warm data, and cold data according to the access frequency (reproduction frequency). The access frequency decreases in the order of hot data, warm data, and cold data, and recording and storing data with low access frequency (for example, cold data) for a long period of time is called an archive. With the dramatic increase in the amount of information in recent years and the digitization of various types of information, the amount of data recorded and stored on recording media for archiving is increasing, so attention is increasing to recording and playback systems suitable for archiving. It's getting better.

A magnetic recording medium capable of exhibiting excellent running stability when reproducing data after long-term storage as described above is suitable as a recording medium for archiving.

In view of the above, one aspect of the present invention is to provide a magnetic recording medium having excellent running stability after long-term storage.

One aspect of the present invention is
A magnetic recording medium having a magnetic layer containing ferromagnetic powder on a non-magnetic support.
The portion on the non-magnetic support on the magnetic layer side contains one or more components selected from the group consisting of fatty acids and fatty acid amides.
After pressing the magnetic layer with a pressure of 70 atm, CH calculated from the CH peak area ratio in the C1s spectrum obtained by X-ray photoelectron spectroscopy performed at a photoelectron extraction angle of 10 degrees on the surface of the magnetic layer. A magnetic recording medium having a derived C concentration (hereinafter, also referred to as “CH-derived C concentration after pressing” or “CH-derived C concentration”) of 45 atomic% or more.
Regarding. Regarding the unit, 1 atm = 101325 Pa (Pascal) = 101325 N (Newton) / m ² .

In one form, the C-H-derived C concentration after pressing can be 45 atomic% or more and 80 atomic% or less.

In one form, the magnetic layer can contain inorganic oxide particles.

In one form, the inorganic oxide-based particles can be composite particles of an inorganic oxide and a polymer.

In one form, the magnetic recording medium can have a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

In one form, the magnetic recording medium may have a backcoat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer.

In one form, the magnetic recording medium can be a magnetic tape.

One aspect of the present invention relates to a magnetic recording / reproducing device including the magnetic recording medium and a magnetic head.

According to one aspect of the present invention, it is possible to provide a magnetic recording medium having excellent running stability after long-term storage. Further, according to one aspect of the present invention, it is possible to provide a magnetic recording / reproducing device including the above magnetic recording medium.

An example of a manufacturing process of a magnetic recording medium (schematic schematic diagram) is shown.

[Magnetic recording medium]
One aspect of the present invention is a magnetic recording medium having a magnetic layer containing a ferromagnetic powder on a non-magnetic support, in which a portion of the non-magnetic support on the magnetic layer side is composed of a fatty acid and a fatty acid amide. CH in the C1s spectrum obtained by X-ray photoelectron spectroscopic analysis performed on the surface of the magnetic layer at a photoelectron extraction angle of 10 degrees after pressing the magnetic layer with a pressure of 70 atm, which contains one or more of the components selected from The present invention relates to a magnetic recording medium in which the CH-derived C concentration calculated from the peak area ratio (CH-derived C concentration after pressing) is 45 atomic% or more.

The pressure of 70 atm for pressing the magnetic layer is a surface pressure applied to the surface of the magnetic layer by pressing. A surface pressure of 70 atm is applied to the surface of the magnetic layer by passing between the two rolls while running the magnetic recording medium at a speed of 20 m / min. A tension of 0.5 N / m is applied to the traveling magnetic recording medium in the traveling direction. For example, for a tape-shaped magnetic recording medium (that is, a magnetic tape), a tension of 0.5 N / m is applied in the longitudinal direction of the running magnetic tape. The pressing is performed by passing the magnetic recording medium between the two rolls a total of 6 times, and applying a surface pressure of 70 atm when passing between the rolls. A metal roll is used as the roll, and the roll is not heated. The pressing environment is an environment having an ambient temperature of 20 to 25 ° C. and a relative humidity of 40 to 60%. The magnetic recording medium to which the above pressing is performed is subjected to long-term storage for 10 years or more in a room temperature environment of 40 to 60% relative humidity, storage corresponding to such long-term storage, or accelerated test corresponding to such long-term storage. Use a non-magnetic recording medium. Unless otherwise specified, the same applies to various physical characteristics of the magnetic recording medium described in the present invention and the present specification.
The above pressing can be performed by using, for example, a calendar processing machine used for manufacturing a magnetic recording medium. For example, the magnetic tape can be pressed at a pressure of 70 atm by taking out the magnetic tape contained in the magnetic tape cartridge and passing it between the calendar rolls in the calendar processing machine.

The present inventor has been diligently studying to provide a magnetic recording medium having excellent running stability after long-term storage, and as an accelerated test corresponding to an example of an archive, the magnetic layer may be pressed with a pressure of 70 atm. It was concluded that it was appropriate. This point will be further described below.
For example, a magnetic tape is usually housed in a magnetic tape cartridge in a reeled state. Therefore, long-term storage of the magnetic tape after recording infrequently accessed data is also performed in a state of being housed in the magnetic tape cartridge. The magnetic tape wound around the reel has a magnetic layer surface and a backcoat layer (when it has a backcoat layer) or a surface opposite to the magnetic layer side of the non-magnetic support (when it does not have a backcoat layer). The magnetic layer is in a pressed state in the magnetic tape cartridge because it is in contact with. As a result of various simulations, the present inventor performed an accelerated test in which the magnetic layer was subjected to a pressure of 70 atm as an accelerated test corresponding to long-term storage (an example of archiving) for about 10 years in a room temperature environment of 40 to 60% relative humidity. We have come to the conclusion that it is appropriate to press. In the present invention and the present specification, room temperature means a temperature in the range of 20 to 25 ° C. Therefore, the present inventor conducted a running stability test after pressing the magnetic layer at 70 atm, and as a result of diligent studies based on the results of this test, a magnetic recording in which the C concentration derived from CH after pressing was 45 atomic% or more. It was found that the medium was excellent in running stability after pressing the magnetic layer at 70 atm, that is, running stability in a state corresponding to the long-term storage. This point is a new finding that has not been known in the past and is not described in Japanese Patent No. 6378166 (Patent Document 1) shown above.

The method for measuring the C-H-derived C concentration after pressing will be described below. In the present invention and the present specification, the “surface of the magnetic layer” is synonymous with the surface of the magnetic recording medium on the magnetic layer side.
"X-ray photoelectron spectroscopy" is an analysis method generally also called ESCA (Electron Spectroscopy for Chemical Analysis) or XPS (X-ray Photoelectron Spectroscopy). In the following, X-ray photoelectron spectroscopy will also be referred to as ESCA. ESCA is an analysis method that utilizes the emission of photoelectrons when the surface of a sample to be measured is irradiated with X-rays, and is widely used as an analysis method for the surface layer of the sample to be measured. According to ESCA, qualitative analysis and quantitative analysis can be performed using the X-ray photoelectron spectroscopic spectrum obtained by analysis on the surface of the sample to be measured. Between the depth from the sample surface to the analysis position (hereinafter, also referred to as "detection depth") and the photoelectron extraction angle (take-off angle), the following formula is generally used: detection depth ≒ mean of electrons. Free path x 3 x sin θ, is established. In the formula, the detection depth is the depth at which 95% of the photoelectrons constituting the X-ray photoelectron spectroscopic spectrum are generated, and θ is the photoelectron extraction angle. From the above equation, it can be seen that the smaller the photoelectron extraction angle is, the shallower the depth from the sample surface can be analyzed, and the larger the photoelectron extraction angle is, the deeper the part can be analyzed. In the analysis performed by ESCA at a photoelectron extraction angle of 10 degrees, the analysis position is usually a very surface layer portion having a depth of about several nm from the sample surface. Therefore, according to the analysis performed by ESCA at a photoelectron extraction angle of 10 degrees on the surface of the magnetic layer of the magnetic recording medium, it is possible to analyze the composition of a very surface layer portion having a depth of about several nm from the surface of the magnetic layer.
The CH-derived C concentration is the ratio of carbon atoms C constituting the CH bond to 100 atomic% of the total (atomic standard) of all elements detected by the qualitative analysis performed by ESCA. Is. The area to be analyzed is an area of 300 μm × 700 μm at an arbitrary position on the surface of the magnetic layer of the magnetic recording medium. A qualitative analysis is performed by wide scan measurements (path energy: 160 eV, scan range: 0-1200 eV, energy resolution: 1 eV / step) performed by ESCA. Next, the spectra of all the elements detected by the qualitative analysis are obtained by narrow scan measurement (path energy: 80 eV, energy resolution: 0.1 eV, scan range: set for each element so that the entire spectrum to be measured is included). From the peak area in each spectrum thus obtained, the atomic concentration (atomic concentration, unit: atomic%) of each element is calculated. Here, the atomic concentration (C concentration) of the carbon atom is also calculated from the peak area of the C1s spectrum.
Further, the C1s spectrum is acquired (path energy: 10 eV, scan range: 276 to 296 eV, energy resolution: 0.1 eV / step). The acquired C1s spectrum was fitted by a nonlinear least squares method using a Gauss-Lorentz composite function (Gaussian component 70%, Lorentz component 30%), and the peak of the CH bond in the C1s spectrum was peak-separated and separated. The ratio (peak area ratio) of the CH peak to the C1s spectrum is calculated. The C-H-derived C concentration is calculated by multiplying the calculated C-H peak area ratio by the above-mentioned C concentration.
The arithmetic mean of the values obtained by performing the above processing three times at different positions on the surface of the magnetic layer of the magnetic recording medium after pressing is taken as the C concentration derived from CH after pressing. Further, a specific embodiment of the above processing will be shown in Examples described later.

The magnetic recording medium contains one or more components selected from the group consisting of fatty acids and fatty acid amides in a portion on the non-magnetic support on the magnetic layer side. In the present invention and the present specification, the "part on the magnetic layer side on the non-magnetic support" is a magnetic layer for a magnetic recording medium having a magnetic layer directly on the non-magnetic support, and is referred to as a non-magnetic support. A magnetic recording medium having a non-magnetic layer, which will be described in detail later, between the magnetic layer and the magnetic layer is a magnetic layer and / or a non-magnetic layer. In the following, the "part on the non-magnetic support on the magnetic layer side" is also simply referred to as the "part on the magnetic layer side".
The fatty acid and fatty acid amide contained in the portion of the magnetic recording medium on the magnetic layer side are components that can each function as a lubricant in the magnetic recording medium. On the surface of the magnetic layer of a magnetic recording medium containing one or more of these components in the portion on the magnetic layer side of the non-magnetic support, the C-H-derived C concentration obtained by analysis performed by ESCA at a photoelectron extraction angle of 10 degrees is , It is considered to be an index of the abundance of the above-mentioned components (one or more of the components selected from the group consisting of fatty acids and fatty acid amides) in the very surface layer portion of the magnetic layer. The details are as follows.
In the X-ray photoelectron spectrum (horizontal axis: binding energy, vertical axis: intensity) obtained by the analysis performed by ESCA, the C1s spectrum contains information on the energy peak of the 1s orbit of the carbon atom C. In such a C1s spectrum, the peak located near the binding energy of 284.6 eV is the CH peak. This CH peak is a peak derived from the binding energy of the CH bond of the organic compound. A magnetic recording medium containing one or more components selected from the group consisting of fatty acids and fatty acid amides in a portion on the non-magnetic support on the magnetic layer side (in other words, one or more components selected from the group consisting of fatty acids and fatty acid amides). In the magnetic recording medium detected from the portion on the non-magnetic support on the magnetic layer side), in the very surface layer portion of the magnetic layer, the main constituent component of the CH peak is a component selected from the group consisting of fatty acid and fatty acid amide. It is presumed that there is. Therefore, it is considered that the C-H-derived C concentration can be used as an index of the abundance of the component as described above.
Then, after the pressing, the C-H-derived C concentration is 45 atomic% or more, that is, a large amount of one or more components selected from the group consisting of fatty acids and fatty acid amides is present on the very surface layer of the magnetic layer after the pressing. When the data recorded on the magnetic recording medium is reproduced after long-term storage, it contributes to promoting smooth sliding between the magnetic head and the surface of the magnetic layer (improving slidability). Conceivable. It is presumed that this improvement in slidability can improve running stability after long-term storage.
However, the above is a guess, and the present invention is not limited to such a guess. Further, the present invention is not limited to other inferences described in the present specification.
Hereinafter, the magnetic recording medium will be described in more detail.

<C concentration derived from CH after pressing>
The C-H-derived C concentration after pressing of the magnetic recording medium is 45 atomic% or more, and is preferably 48 atomic% or more, preferably 50 atomic% or more, from the viewpoint of further improving the running stability after long-term storage. The above is more preferable. Further, according to the study of the present inventor, from the viewpoint of easy formation of a magnetic layer having high surface smoothness, the C concentration derived from CH is, for example, 95 atomic% or less, 90 atomic% or less, 85 atomic% or less. It is preferably 80 atomic% or less, 75 atomic% or less, or 70 atomic% or less.

The C-H-derived C concentration after pressing described above can be controlled by, for example, the type of non-magnetic filler used for the magnetic layer and the manufacturing process of the magnetic recording medium. Details will be described later.

<Fatty acid, fatty acid amide>
The magnetic recording medium contains one or more components selected from the group consisting of fatty acids and fatty acid amides in a portion on the non-magnetic support on the magnetic layer side. The portion on the magnetic layer side may contain only one of the fatty acid and the fatty acid amide, or may contain both.

Examples of the fatty acid include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, bechenic acid, erucic acid, ellagic acid and the like, and stearic acid, myristic acid, palmitic acid and the like. Is preferable, and stearic acid is more preferable. The fatty acid may be contained in the magnetic layer in the form of a salt such as a metal salt.
Examples of the fatty acid amide include amides of the above-mentioned various fatty acids exemplified above, specifically, for example, lauric acid amide, myristic acid amide, palmitate amide, stearic acid amide and the like.
For fatty acids and fatty acid derivatives (amides, esters described below, etc.), the fatty acid-derived sites of the fatty acid derivatives preferably have the same or similar structure as the fatty acids used in combination. For example, when stearic acid is used as the fatty acid, it is preferable to use stearic acid amide and / or stearic acid ester in combination.

A magnetic recording medium containing at least one component selected from the group consisting of fatty acids and fatty acid amides in a portion on the magnetic layer side forms a magnetic layer containing at least one component selected from the group consisting of fatty acids and fatty acid amides. It can be produced by forming a magnetic layer using a composition for use. In one form, the non-magnetic layer is formed by using a composition for forming a non-magnetic layer containing one or more of the components selected from the group consisting of fatty acids and fatty acid amides, thereby selecting from the group consisting of fatty acids and fatty acid amides. It is possible to manufacture a magnetic recording medium containing one or more of these components in the portion on the magnetic layer side. Further, in one form, a non-magnetic layer is formed by using a composition for forming a non-magnetic layer containing one or more components selected from the group consisting of fatty acids and fatty acid amides, and the non-magnetic layer is formed and selected from the group consisting of fatty acids and fatty acid amides. By forming a magnetic layer using a composition for forming a magnetic layer containing one or more of the components, a magnetic recording medium containing at least one of the components selected from the group consisting of fatty acids and fatty acid amides in the portion on the magnetic layer side is produced. can do. The non-magnetic layer can play a role of holding a lubricant such as fatty acid and fatty acid amide and supplying it to the magnetic layer. Lubricants such as fatty acids and fatty acid amides contained in the non-magnetic layer can migrate to the magnetic layer and exist in the magnetic layer.

Regarding the fatty acid content, the fatty acid content of the magnetic layer (or the composition for forming the magnetic layer; the same applies hereinafter) is, for example, 0.1 to 10.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder, preferably 0.1 to 10.0 parts by mass. It is 1.0 to 7.0 parts by mass. When two or more different fatty acids are added to the composition for forming a magnetic layer, the content means the total content of the two or more different fatty acids. This point is the same for other components. Further, in the present invention and the present specification, unless otherwise specified, a certain component may be used alone or in combination of two or more.

The fatty acid amide content of the magnetic layer is, for example, 0.1 to 3.0 parts by mass, preferably 0.1 to 1.0 parts by mass, per 100.0 parts by mass of the ferromagnetic powder.

On the other hand, the fatty acid content of the non-magnetic layer (or the composition for forming the non-magnetic layer; the same applies hereinafter) is, for example, 1.0 to 10.0 parts by mass per 100.0 parts by mass of the non-magnetic powder, preferably 1. .0 to 7.0 parts by mass. The fatty acid amide content of the non-magnetic layer is, for example, 0.1 to 3.0 parts by mass, preferably 0.1 to 1.0 parts by mass, per 100.0 parts by mass of the non-magnetic powder.

Next, the magnetic layer and the like included in the magnetic recording medium will be described in more detail.

<Magnetic layer>
(Ferromagnetic powder)
As the ferromagnetic powder contained in the magnetic layer, one or a combination of two or more types of ferromagnetic powder known as the ferromagnetic powder used in the magnetic layer of various magnetic recording media can be used. It is preferable to use a ferromagnetic powder having a small average particle size from the viewpoint of improving the recording density. From this point, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, further preferably 40 nm or less, further preferably 35 nm or less, and more preferably 30 nm or less. It is 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, further preferably 10 nm or more, and further preferably 15 nm or more. Is even more preferable, and 20 nm or more is even more preferable.

Hexagonal ferrite powder As a preferable specific example of the ferromagnetic powder, hexagonal ferrite powder can be mentioned. For details of the hexagonal ferrite powder, for example, paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 of JP2012-204726 and the like. References can be made to paragraphs 0029 to 0084 of JP-A-2015-127985.

In the present invention and the present specification, the "hexagonal ferrite powder" refers to a ferromagnetic powder in which a hexagonal ferrite type crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to a structure to which the highest intensity diffraction peak belongs in the X-ray diffraction spectrum obtained by X-ray diffraction analysis. For example, when the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis belongs to the hexagonal ferrite type crystal structure, it is determined that the hexagonal ferrite type crystal structure is detected as the main phase. It shall be. When only a single structure is detected by X-ray diffraction analysis, this detected structure is used as the main phase. The hexagonal ferrite type crystal structure contains at least iron atoms, divalent metal atoms and oxygen atoms as constituent atoms. The divalent metal atom is a metal atom that can be a divalent cation as an ion, and examples thereof include an alkaline earth metal atom such as a strontium atom, a barium atom, and a calcium atom, and a lead atom. In the present invention and the present specification, the hexagonal strontium ferrite powder means that the main divalent metal atom contained in this powder is a strontium atom, and the hexagonal barium ferrite powder is the main contained in this powder. A divalent metal atom is a barium atom. The main divalent metal atom is a divalent metal atom that occupies the largest amount on an atomic% basis among the divalent metal atoms contained in this powder. However, rare earth atoms are not included in the above divalent metal atoms. The "rare earth atom" in the present invention and the present specification is selected from the group consisting of a scandium atom (Sc), a yttrium atom (Y), and a lanthanoid atom. The lanthanoid atom is a lanthanum atom (La), a cerium atom (Ce), a placeodim atom (Pr), a neodymium atom (Nd), a promethium atom (Pm), a samarium atom (Sm), a gadolinium atom (Eu), and a gadolinium atom (Gd). ), Terbium atom (Tb), dysprosium atom (Dy), formium atom (Ho), erbium atom (Er), samarium atom (Tm), ytterbium atom (Yb), and lutetium atom (Lu). To.

Hereinafter, the hexagonal strontium ferrite powder, which is a form of the hexagonal ferrite powder, will be described in more detail.

The activated volume of the hexagonal strontium ferrite powder is preferably in the range of ^{800 to 1600 nm 3.} The finely divided hexagonal strontium ferrite powder exhibiting an activated volume in the above range is suitable for producing a magnetic recording medium exhibiting excellent electromagnetic conversion characteristics. The activated volume of the hexagonal strontium ferrite powder is preferably 800 nm ³ or more, and can be, for example, 850 nm ³ or more. Further, from the viewpoint of further improvement of the electromagnetic conversion characteristics, activation volume of hexagonal strontium ferrite powder is more preferably 1500 nm ³ or less, further preferably 1400 nm ³ or less, and 1300 nm ³ or less Is even more preferably 1200 nm ³ or less, and even more preferably 1100 nm ³ or less. The same applies to the activated volume of the hexagonal barium ferrite powder.

The "activated volume" is a unit of magnetization reversal and is an index indicating the magnetic size of a particle. The activated volume described in the present invention and the present specification and the anisotropic constant Ku described later are measured using a vibrating sample magnetometer at magnetic field sweep speeds of 3 minutes and 30 minutes in the coercive force Hc measuring unit (measurement). Temperature: 23 ° C ± 1 ° C), which is a value obtained from the following relational expression between Hc and activated volume V. Regarding the unit of the anisotropy constant Ku, 1 erg / cc = 1.0 × 10 ^-1 J / m ³ .
Hc = 2Ku / Ms {1-[(kT / KuV) ln (At / 0.693)] ^1/2 }
[In the above formula, Ku: anisotropic constant (unit: J / m ³ ), Ms: saturation magnetization (unit: kA / m), k: Boltzmann constant, T: absolute temperature (unit: K), V: activity. Volume (unit: cm ³ ), A: spin lag frequency (unit: s ^-1 ), t: magnetic field reversal time (unit: s)]

Anisotropy constant Ku can be mentioned as an index for reducing thermal fluctuation, in other words, improving thermal stability. The hexagonal strontium ferrite powder can preferably have ^{a Ku of 1.8 × 10 5} J / m ³ or more, and more preferably a Ku of 2.0 × 10 ⁵ J / m ³ or more. Also, Ku of hexagonal strontium ferrite powder can be, for example, not 2.5 × ¹⁰ 5 J / ^{m 3} or less. However, the higher the Ku, the higher the thermal stability, which is preferable, and therefore, the value is not limited to the above-exemplified value.

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 hexagonal strontium ferrite powder contains rare earth atoms at a content of 0.5 to 5.0 atomic% (bulk content) with respect to 100 atomic% of iron atoms. In one form, the hexagonal strontium ferrite powder containing rare earth atoms can have uneven distribution on the surface layer of rare earth atoms. "Rare earth atom surface layer uneven distribution" in the present invention and the present specification refers to the rare earth atom content with respect to 100 atomic% of iron atoms in the solution obtained by partially dissolving hexagonal strontium ferrite powder with an acid (hereinafter referred to as "rare earth atom content"). “Rare earth atom surface layer content” or simply “surface layer content” for rare earth atoms) is 100 atomic% of iron atoms in the solution obtained by completely dissolving hexagonal strontium ferrite powder with an acid. Rare earth atom content (hereinafter referred to as "rare earth atom bulk content" or simply referred to as "bulk content" for rare earth atoms).
Rare earth atom surface layer content / Rare earth atom bulk content> 1.0
Means that the ratio of The rare earth atom content of the hexagonal strontium ferrite powder described later is synonymous with the rare earth atom bulk content. On the other hand, partial dissolution using an acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder. Therefore, the rare earth atom content in the solution obtained by partial dissolution is the composition of the hexagonal strontium ferrite powder. It is the rare earth atom content in the surface layer of the particles. The fact that the rare earth atom surface layer content satisfies the ratio of "rare earth atom surface layer content / rare earth atom bulk content>1.0" means that the rare earth atom is present in the surface layer of the particles constituting the hexagonal strontium ferrite powder. It means that it is unevenly distributed (that is, it exists more than inside). The surface layer portion in the present invention and the present specification means a partial region from the surface to the inside of the particles constituting the hexagonal strontium ferrite powder.

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 atom% with respect to 100 atom% of iron atoms. The fact that the rare earth atoms are contained in the bulk content in the above range and the rare earth atoms are unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder contributes to suppressing the decrease in the regeneration output in the repeated regeneration. Conceivable. This is because the hexagonal strontium ferrite powder contains rare earth atoms at a bulk content in the above range, and the rare earth atoms are unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder. It is presumed that this is because it can be enhanced. The higher the value of the anisotropy constant Ku, the more the occurrence of a phenomenon called thermal fluctuation can be suppressed (in other words, the thermal stability can be improved). By suppressing the occurrence of thermal fluctuation, it is possible to suppress a decrease in the reproduction output during repeated reproduction. The uneven distribution of rare earth atoms on the surface layer of the hexagonal strontium ferrite powder contributes to stabilizing the spin of iron (Fe) sites in the crystal lattice of the surface layer, which results in anisotropy constant Ku. It is speculated that it will increase.
In addition, it is presumed that the use of hexagonal strontium ferrite powder, which has uneven distribution on the surface layer of rare earth atoms, as the ferromagnetic powder of the magnetic layer also contributes to suppressing the surface of the magnetic layer from being scraped by sliding with the magnetic head. To. That is, it is presumed that the hexagonal strontium ferrite powder having uneven distribution of the rare earth atomic surface layer can also contribute to the improvement of the running durability of the magnetic recording medium. This is because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder improves the interaction between the particle surface and organic substances (for example, binders and / or additives) contained in the magnetic layer. As a result, it is presumed that the strength of the magnetic layer is improved.
The rare earth atom content (bulk content) is in the range of 0.5 to 4.5 atomic% from the viewpoint of further suppressing the decrease in the reproduction output in the repeated regeneration and / or further improving the running durability. It is more preferably in the range of 1.0 to 4.5 atomic%, further preferably in the range of 1.5 to 4.5 atomic%.

The bulk content is a content obtained by completely dissolving the hexagonal strontium ferrite powder. Unless otherwise specified, in the present invention and the present specification, the content of atoms means the bulk content obtained by completely dissolving hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing a rare earth atom may contain only one kind of rare earth atom as a rare earth atom, or may contain two or more kinds of rare earth atoms. The bulk content when two or more kinds of rare earth atoms are contained is determined for the total of two or more kinds of rare earth atoms. This point is the same for the present invention and other components in the present specification. That is, unless otherwise specified, a certain component may be used alone or in combination of two or more. The content or content rate when two or more types are used shall mean the total of two or more types.

When the hexagonal strontium ferrite powder contains a rare earth atom, the rare earth atom contained may be any one or more of the rare earth atoms. Examples of the rare earth atom preferable from the viewpoint of further suppressing the decrease in the reproduction output in the repeated regeneration include a neodymium atom, a samarium atom, an ythrium atom and a disprosium atom, and a neodymium atom, a samarium atom and an yttrium atom are more preferable, and neodymium atom Atoms are more preferred.

In the hexagonal strontium ferrite powder having uneven distribution on the surface layer of rare earth atoms, the rare earth atoms may be unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of uneven distribution is not limited. For example, a hexagonal strontium ferrite powder having uneven distribution on the surface layer of a rare earth atom is partially dissolved under the dissolution conditions described later, and the content of the surface layer of the rare earth atom is completely dissolved under the dissolution conditions described later. The ratio of the atom to the bulk content, "surface layer content / bulk content" is more than 1.0, and can be 1.5 or more. When the "surface layer content / bulk content" is larger than 1.0, it means that the rare earth atoms are unevenly distributed (that is, more than the inside) in the particles constituting the hexagonal strontium ferrite powder. To do. In addition, the ratio of the surface layer content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content of rare earth atoms obtained by total dissolution under the dissolution conditions described later, "Surface layer content / The "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 the hexagonal strontium ferrite powder having uneven distribution on the surface layer of rare earth atoms, the rare earth atoms need only be unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder. The "rate" is not limited to the upper or lower limit illustrated.

The partial dissolution and total dissolution of the hexagonal strontium ferrite powder will be described below. For the hexagonal strontium ferrite powder that exists as a powder, the sample powder that is partially or completely dissolved is collected from the same lot of powder. On the other hand, regarding the hexagonal strontium ferrite powder contained in the magnetic layer of the magnetic recording medium, a part of the hexagonal strontium ferrite powder taken out from the magnetic layer is subjected to partial dissolution, and the other part is subjected to total dissolution. .. The hexagonal strontium ferrite powder can be taken out from the magnetic layer by, for example, the method described in paragraph 0032 of JP2015-91747A.
The above-mentioned partial dissolution means that the hexagonal strontium ferrite powder is dissolved in the liquid to the extent that the residue can be visually confirmed at the end of the dissolution. For example, by partial dissolution, 10 to 20% by mass of the particles constituting the hexagonal strontium ferrite powder can be dissolved with the whole particles as 100% by mass. On the other hand, the above-mentioned total dissolution means that the hexagonal strontium ferrite powder is dissolved in the liquid until the residue is not visually confirmed at the end of the dissolution.
The partial dissolution and the measurement of the surface layer content are carried out by, for example, the following methods. However, the following dissolution conditions such as the amount of sample powder are examples, and dissolution conditions capable of partial dissolution and total dissolution can be arbitrarily adopted.
A container (for example, a beaker) containing 12 mg of sample powder and 10 mL of 1 mol / L hydrochloric acid is held on a hot plate at a set temperature of 70 ° C. for 1 hour. The obtained solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the filtrate thus obtained is performed by an inductively coupled plasma (ICP) analyzer. In this way, the surface layer content of rare earth atoms with respect to 100 atomic% of iron atoms can be determined. When a plurality of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is defined as the surface layer content. This point is the same in the measurement of bulk content.
On the other hand, the total dissolution and the measurement of the bulk content are performed by, for example, the following methods.
A container (for example, a beaker) containing 12 mg of sample powder and 10 mL of 4 mol / L hydrochloric acid is held on a hot plate at a set temperature of 80 ° C. for 3 hours. After that, the same procedure as the above-mentioned partial dissolution and measurement of the surface layer content can be performed to determine the bulk content with respect to 100 atomic% of iron atoms.

From the viewpoint of increasing the reproduction output when reproducing the 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, the hexagonal strontium ferrite powder containing rare earth atoms but not having uneven distribution on the surface layer of rare earth atoms tended to have a significantly lower σs than the hexagonal strontium ferrite powder containing no rare earth atoms. On the other hand, hexagonal strontium ferrite powder having uneven distribution on the surface layer of rare earth atoms is considered to be preferable in order to suppress such a large decrease in σs. In one form, the σs of the hexagonal strontium ferrite powder ^{can be 45 A · m 2} / kg or more, and can also be 47 A · m ^{2 / kg or more.} Meanwhile, [sigma] s from the viewpoint of noise reduction, is preferably not more than 80A ^· m 2 / kg, more preferably not more than 60A ^· m 2 / kg. σs can be measured using a known measuring device capable of measuring magnetic characteristics such as a vibrating sample magnetometer. Unless otherwise specified, in the present invention and the present specification, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe. 1 [koe] = 10 ⁶ / 4π [A / m].

Regarding the content of constituent atoms (bulk content) of the hexagonal strontium ferrite powder, the strontium atom content can be in the range of, for example, 2.0 to 15.0 atom% with respect to 100 atom% of iron atoms. .. In one form, the hexagonal strontium ferrite powder can contain only strontium atoms as divalent metal atoms. In another embodiment, the hexagonal strontium ferrite powder can also contain one or more other divalent metal atoms in addition to the strontium atom. For example, it can contain barium and / or calcium atoms. When a divalent metal atom other than the strontium atom is contained, the barium atom content and the calcium atom content in the hexagonal strontium ferrite powder are, for example, 0.05 to 5 with respect to 100 atomic% of iron atoms, respectively. It can be in the range of 0.0 atomic%.

As the crystal structure of hexagonal ferrite, magnetoplumbite type (also referred to as "M type"), W type, Y type and Z type are known. The hexagonal strontium ferrite powder may have any crystal structure. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder can be one in which a single crystal structure or two or more kinds of crystal structures are detected by X-ray diffraction analysis. For example, in one form, the hexagonal strontium ferrite powder can be such that only the M-type crystal structure is detected by X-ray diffraction analysis. For example, M-type hexagonal ferrite is represented by the composition formula of _{AFe 12} O _19. Here, A represents a divalent metal atom, and when the hexagonal strontium ferrite powder is M-type, A is only a strontium atom (Sr), or when A contains a plurality of divalent metal atoms. As mentioned above, the strontium atom (Sr) occupies the largest amount on the basis of atomic%. The divalent metal atom content of the hexagonal strontium ferrite powder is usually determined by the type of crystal structure of the hexagonal ferrite, and is not particularly limited. The same applies to the iron atom content and the oxygen atom content. The hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms and oxygen atoms, and can also contain rare earth atoms. Further, 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 an aluminum atom (Al). The content of aluminum atoms can be, for example, 0.5 to 10.0 atomic% with respect to 100 atomic% of iron atoms. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms and rare earth atoms, and the content of atoms other than these atoms is 100 iron atoms. % Is preferably 10.0 atomic% or less, more preferably in the range of 0 to 5.0 atomic%, and may be 0 atomic%. That is, in one form, the hexagonal strontium ferrite powder does not have to contain atoms other than iron atoms, strontium atoms, oxygen atoms and rare earth atoms. The content expressed in atomic% above is the content (unit: mass%) of each atom obtained by completely dissolving the hexagonal strontium ferrite powder, and is converted to the value expressed in atomic% using the atomic weight of each atom. Calculated by conversion. Further, in the present invention and the present specification, "not contained" for a certain atom means that the content is completely dissolved and the content measured by an ICP analyzer is 0% by mass. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The above-mentioned "not included" is used in the sense of including the inclusion in an amount less than the detection limit of the ICP analyzer. The hexagonal strontium ferrite powder can, in one form, be free of bismuth atoms (Bi).

Metal powder A preferred specific example of the ferromagnetic powder may be a ferromagnetic metal powder. For details of the ferromagnetic metal powder, for example, paragraphs 0137 to 0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351 can be referred to.

ε-Iron oxide powder A preferable specific example of the ferromagnetic powder is ε-iron oxide powder. In the present invention and the present specification, "ε-iron oxide powder" refers to a ferromagnetic powder in which an ε-iron oxide type crystal structure is detected as a main phase by X-ray diffraction analysis. For example, when the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is assigned to the ε-iron oxide type crystal structure, the ε-iron oxide type crystal structure is detected as the main phase. Judgment shall be made. As a method for producing ε-iron oxide powder, a method for producing ε-iron oxide powder, a reverse micelle method, and the like are known. All of the above manufacturing methods are known. Regarding the method for producing ε-iron oxide powder in which a part of Fe is substituted with a substituted atom such as Ga, Co, Ti, Al, Rh, for example, J.I. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mol. Mater. Chem. C, 2013, 1, pp. 5200-5206 and the like can be referred to. However, the method for producing 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 methods described here.

The activated volume of the ε-iron oxide powder is preferably in the range of ^{300 to 1500 nm 3.} The finely divided ε-iron oxide powder exhibiting an activated volume in the above range is suitable for producing a magnetic recording medium exhibiting excellent electromagnetic conversion characteristics. The activated volume of the ε-iron oxide powder is preferably 300 nm ³ or more, and can be, for example, 500 nm ³ or more. Further, from the viewpoint further improvement of the electromagnetic conversion characteristics, .epsilon. activation volume of the iron oxide powder is more preferably 1400 nm ³ or less, further preferably 1300 nm ³ or less, and 1200 nm ³ or less Is even more preferable, and 1100 nm ³ or less is even more preferable.

Anisotropy constant Ku can be mentioned as an index for reducing thermal fluctuation, in other words, improving thermal stability. The ε-iron oxide powder can preferably have ^{a Ku of 3.0 × 10 4} J / m ³ or more, and more preferably 8.0 × 10 ⁴ J / m ³ or more. Further, .epsilon. Ku iron oxide powder can be, for example, not 3.0 × ¹⁰ 5 J / ^{m 3} or less. However, the higher the Ku, the higher the thermal stability, which is preferable, and therefore, the value is not limited to the above-exemplified value.

From the viewpoint of increasing the reproduction output when reproducing the 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 form, the σs of the ε-iron oxide powder ^{can be 8 A · m 2} / kg or more, and can also be 12 A · m ^{2 / kg or more.} On the other hand, the σs of the ε-iron oxide powder ^{is preferably 40 A · m 2} / kg or less, and more preferably 35 A · m ² / kg or less, from the viewpoint of noise reduction.

Unless otherwise specified in the present invention and the present specification, the average particle size of various powders such as ferromagnetic powders is a value measured by the following method using a transmission electron microscope.
The powder is photographed using a transmission electron microscope at an imaging magnification of 100,000 times, and printed on photographic paper so as to have a total magnification of 500,000 times to obtain a photograph of the particles constituting the powder. Select the target particle from the obtained photograph of the particle, trace the outline of the particle with a digitizer, and measure the size of the particle (primary particle). Primary particles are independent particles without agglomeration.
The above measurements are performed on 500 randomly sampled particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained is taken as the average particle size of the powder. As the transmission electron microscope, for example, Hitachi's transmission electron microscope H-9000 can be used. Further, the particle size can be measured by using a known image analysis software, for example, an image analysis software KS-400 manufactured by Carl Zeiss. Unless otherwise specified, the average particle size shown in the examples described later was measured using a transmission electron microscope H-9000 manufactured by Hitachi as a transmission electron microscope and a Carl Zeiss image analysis software KS-400 as an image analysis software. The value. In the present invention and the present specification, the powder means an aggregate of a plurality of particles. For example, a ferromagnetic powder means a collection of a plurality of ferromagnetic particles. Further, the set of a plurality of particles is not limited to a form in which the particles constituting the set are in direct contact with each other, and also includes a form in which a binder, an additive, etc., which will be described later, are interposed between the particles. To. The term particle is sometimes used to describe powder.

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 JP2011-048878A can be adopted.

Unless otherwise specified in the present invention and the present specification, the size (particle size) of the particles constituting the powder is the shape of the particles observed in the above particle photograph.
(1) In the case of needle-shaped, spindle-shaped, columnar (however, the height is larger than the maximum major axis of the bottom surface), it is represented by the length of the major axis constituting the particle, that is, the major axis length.
(2) If it is plate-shaped or columnar (however, the thickness or height is smaller than the maximum major axis of the plate surface or bottom surface), it is represented by the maximum major axis of the plate surface or bottom surface.
(3) If the particle is spherical, polyhedral, amorphous, etc., and the long axis constituting the particle cannot be specified from the shape, it is represented by the diameter equivalent to a circle. The equivalent diameter of a circle is what is obtained by the circular projection method.

Further, for the average needle-like ratio of the powder, the length of the minor axis of the particles, that is, the minor axis length is measured in the above measurement, and the value of (major axis length / minor axis length) of each particle is obtained. Refers to the arithmetic mean of the values obtained for a particle. Here, unless otherwise specified, the minor axis length is the length of the minor axis constituting the particle in the case of (1) in the above definition of the particle size, and the thickness or height in the case of the same (2). In the case of (3), there is no distinction between the major axis and the minor axis, so (major axis length / minor axis length) is regarded as 1 for convenience.
Unless otherwise specified, when the shape of the particles 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, and in the case of the same definition (2), the average particle size is Average plate diameter. In the case of the same definition (3), the average particle size is an average diameter (also referred to as an average particle size or an average particle size).

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

(Binder)
The magnetic recording medium can be a coating type magnetic recording medium, and the magnetic layer can contain a binder. A binder is one or more resins. As the binder, various resins usually used as a binder for a coating type magnetic recording medium can be used. For example, as the binder, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, styrene, acrylonitrile, acrylic resin obtained by copolymerizing methyl methacrylate and the like, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, etc. A resin selected from a polyvinyl alkyral resin such as polyvinyl butyral can be used alone, or a plurality of resins can be mixed and used. Of these, polyurethane resins, acrylic resins, cellulose resins, and vinyl chloride resins are preferred. These resins may be homopolymers or copolymers. These resins can also be used as binders in the non-magnetic layer and / or the backcoat layer described later.
For the above binder, paragraphs 0028 to 0031 of JP-A-2010-24113 can be referred to. The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less as the weight average molecular weight. The weight average molecular weight in the present invention and the present specification is a value obtained by converting a value measured by gel permeation chromatography (GPC) under the following measurement conditions into polystyrene. The weight average molecular weight of the binder shown in Examples described later is a value obtained by converting a value measured under the following measurement conditions into polystyrene. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder.
GPC device: HLC-8120 (manufactured by Tosoh)
Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8 mm ID (Inner Diameter) x 30.0 cm)
Eluent: tetrahydrofuran (THF)

Further, a curing agent can be used together with a resin that can be used as a binder. The curing agent can be a thermosetting compound, which is a compound in which a curing reaction (crosslinking reaction) proceeds by heating in one form, and a photocuring agent in which a curing reaction (crosslinking reaction) proceeds by light irradiation in another form. It can be a sex compound. As the curing reaction proceeds in the process of forming the magnetic layer, at least a part of the curing agent can be contained in the magnetic layer in a state of reacting (crosslinking) with other components such as a binder. This point is the same for the layer formed by using this composition when the composition used for forming another layer contains a curing agent. Preferred curing agents are thermosetting compounds, with polyisocyanates being preferred. For details of the polyisocyanate, refer to paragraphs 0124 to 0125 of JP2011-216149A. The curing agent is, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder in the composition for forming the magnetic layer, preferably 50.0 to 80.0 from the viewpoint of improving the strength of the magnetic layer. It can be used in the amount of parts by mass.

The above description of the binder and the curing agent can also be applied to the non-magnetic layer and / or the backcoat layer. In that case, the above description regarding the content can be applied by replacing the ferromagnetic powder with a non-magnetic powder.

(Additive)
The magnetic layer may contain one or more additives, if necessary, in addition to the above-mentioned various components. As the additive, a commercially available product can be appropriately selected and used according to the desired properties. Alternatively, a compound synthesized by a known method can also be used as an additive. An example of the additive is the above-mentioned curing agent. Examples of additives that can be contained in the magnetic layer include non-magnetic fillers, lubricants, dispersants, dispersion aids, fungicides, antistatic agents, antioxidants and the like. Non-magnetic filler is synonymous with non-magnetic particles or non-magnetic powder. Examples of the non-magnetic filler include a non-magnetic filler capable of functioning as a protrusion forming agent and a non-magnetic filler capable of functioning as an abrasive. Further, as the additive, known additives such as various polymers described in paragraphs 0030 to 0080 of JP-A-2016-051493 can also be used.

Protrusion-forming agent As the protrusion-forming agent, which is a form of non-magnetic filler, particles of an inorganic substance can be used, particles of an organic substance can be used, and composite particles of an inorganic substance and an organic substance can be used. it can. Examples of the inorganic substance include inorganic oxides such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides and the like, and inorganic oxides are preferable. In one form, the protrusion-forming agent can be inorganic oxide-based particles. Here, "system" is used to mean "including". One form of inorganic oxide-based particles is particles composed of inorganic oxides. Further, another form of the inorganic oxide-based particles is a composite particle of an inorganic oxide and an organic substance, and specific examples thereof include a composite particle of an inorganic oxide and a polymer. Examples of such particles include particles in which a polymer is bonded to the surface of particles of an inorganic oxide.

The average particle size of the protrusion forming agent is, for example, 30 to 300 nm, preferably 40 to 200 nm. The closer the particle shape is to a true sphere, the smaller the pushing resistance that acts when a large pressure is applied, so that the particles are more likely to be pushed into the magnetic layer. On the other hand, if the shape of the particles is distant from the true sphere, for example, a so-called irregular shape, a large pushing resistance is likely to act when a large pressure is applied, so that the particles are difficult to be pushed into the magnetic layer. Further, even particles having an inhomogeneous particle surface and low surface smoothness are less likely to be pushed into the magnetic layer because a large pushing resistance tends to work when a large pressure is applied. When the magnetic layer contains particles that are easily pushed into the magnetic layer, the components selected from the group consisting of fatty acids and fatty acid amides are magnetic before being pressed due to the particles being pushed into the magnetic layer by pressing. Even if it is localized on the very surface layer of the layer, it is considered that the localized amount decreases after pressing. On the other hand, if the particles of the protrusion forming agent are difficult to be pushed into the magnetic layer by pressing, it is presumed that the decrease in the localized amount after pressing can be suppressed. That is, the use of a protrusion forming agent that is difficult to be pushed into the magnetic layer by pressing contributes to controlling the CH-derived C concentration measured after pressing at the above pressure of 70 atm to 45 atomic% or more. Inferred.

Abrasive The abrasive, which is another form of the non-magnetic filler, is preferably a non-magnetic powder having a Mohs hardness of more than 8, and more preferably a non-magnetic powder having a Mohs hardness of 9 or more. On the other hand, the Mohs hardness of the protrusion forming agent can be, for example, 8 or less or 7 or less. The maximum value of Mohs hardness is 10 for diamond. Specifically, alumina (Al ₂ O ₃ ), silicon carbide, boron carbide (B ₄ C), SiO ₂ , TiC, chromium oxide (Cr ₂ O ₃ ), cerium oxide, zirconium oxide (ZrO ₂ ), iron oxide. , Diamond and the like, and among them, alumina powder such as α-alumina and silicon carbide powder are preferable. The average particle size of the abrasive is, for example, in the range of 30 to 300 nm, preferably in the range of 50 to 200 nm.

Further, from the viewpoint that the protrusion-forming agent and the abrasive can exert their functions better, the content of the protrusion-forming agent in the magnetic layer is preferably 100.0 parts by mass of the ferromagnetic powder. , 1.0 to 4.0 parts by mass, more preferably 1.2 to 3.5 parts by mass. On the other hand, with respect to the abrasive, the content in the magnetic layer is preferably 1.0 to 20.0 parts by mass, more preferably 3.0 to 15.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder. Parts, more preferably 4.0 to 10.0 parts by mass.

As an example of an additive that can be used for a magnetic layer containing an abrasive, the dispersant described in paragraphs 0012 to 0022 of JP2013-131285 can be used to improve the dispersibility of the abrasive in the composition for forming a magnetic layer. It can be mentioned as a dispersant for making it. Further, regarding the dispersant, paragraphs 0061 and 0071 of JP2012-133387A can be referred to. The dispersant may be contained in the non-magnetic layer. For the dispersant that can be contained in the non-magnetic layer, paragraph 0061 of JP2012-133387A can be referred to.

Fatty acid ester One or both of the magnetic layer and the non-magnetic layer described in detail later may or may not contain the fatty acid ester.
Fatty acid esters, fatty acids and fatty acid amides are all components that can function as lubricants. Lubricants are generally classified into fluid lubricants and boundary lubricants. And while fatty acid ester is said to be a component that can function as a fluid lubricant, fatty acid and fatty acid amide are said to be components that can function as a boundary lubricant. The boundary lubricant is considered to be a lubricant capable of reducing contact friction by adsorbing to the surface of powder (for example, ferromagnetic powder) and forming a strong lubricating film. On the other hand, the fluid lubricant itself is considered to be a lubricant that can form a liquid film on the surface of the magnetic layer and reduce friction by the flow of the liquid film. As described above, the fatty acid ester is considered to have a different action as a lubricant from the fatty acid and the fatty acid amide. Then, the present inventor uses the CH-derived C concentration, which is considered to be an index of the abundance of one or more components selected from the group consisting of fatty acids and fatty acid amides in the very surface layer of the magnetic layer, as a value after pressing 45 atomic%. It is presumed that the above will contribute to the improvement of running stability after long-term storage.

Examples of the fatty acid ester include esters of the above-mentioned various fatty acids exemplified for fatty acids. Specific examples include, for example, butyl myristate, butyl palmitate, butyl stearate (butyl stearate), neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, Examples thereof include isocetyl stearate, isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate, butoxyethyl stearate and the like.

Regarding the fatty acid ester content, the fatty acid ester content of the magnetic layer is, for example, 0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the ferromagnetic powder.
The fatty acid ester content of the non-magnetic layer is, for example, 0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the non-magnetic powder.

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

<Non-magnetic layer>
Next, the non-magnetic layer will be described. The magnetic recording medium may have a magnetic layer directly on the non-magnetic support, or may have a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. The non-magnetic powder used for the non-magnetic layer may be an inorganic substance powder or an organic substance powder. In addition, carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides and the like. These non-magnetic powders are commercially available and can also be produced by known methods. For details thereof, refer to paragraphs 0146 to 0150 of JP2011-216149A. For carbon black that can be used for the non-magnetic layer, paragraphs 0040 to 0041 of JP2010-24113A can also be referred to. The content (filling rate) of the non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass.

The non-magnetic layer can contain a binder and can also contain an additive. For other details such as binders and additives for the non-magnetic layer, known techniques relating to the non-magnetic layer can be applied. Further, for example, with respect to the type and content of the binder, the type and content of the additive, and the like, known techniques relating to the magnetic layer can also be applied.

In the present invention and the present specification, the non-magnetic layer includes not only the non-magnetic powder but also a substantially non-magnetic layer containing a small amount of ferromagnetic powder, for example, as an impurity or intentionally. Here, the substantially non-magnetic layer means that the residual magnetic flux density of this layer is 10 mT or less, the coercive force is 100 Oe or less, or the residual magnetic flux density is 10 mT or less and the coercive force is 100 Oe. It refers to the following layers. The non-magnetic layer preferably has no residual magnetic flux density and coercive force.

<Non-magnetic 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 terephthalates, polyethylene naphthalates, polyamides, polyamideimides, aromatic polyamides and the like. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable. These supports may be subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like in advance.

<Back coat layer>
The magnetic recording medium may or may not have a backcoat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support. The backcoat layer preferably contains one or both of carbon black and inorganic powder. The backcoat layer can contain binders and can also contain additives. For binders and additives in the backcoat layer, known techniques relating to the backcoat layer can be applied, and known techniques relating to the formulation of magnetic and / or non-magnetic layers can also be applied. For example, paragraphs 0018 to 0020 of JP-A-2006-331625 and the description of US Pat. No. 7,029,774, column 4, line 65 to column 5, line 38 can be referred to for the backcoat layer. ..

<Various thickness>
The thickness of the non-magnetic support is preferably 3.0 to 6.0 μm.
The thickness of the magnetic layer is preferably 0.15 μm or less, and more preferably 0.1 μm or less, from the viewpoint of high-density recording that has been demanded in recent years. The thickness of the magnetic layer is more preferably in the range of 0.01 to 0.1 μm. The magnetic layer may be at least one layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a known configuration relating to a multi-layer magnetic layer can be applied. The thickness of the magnetic layer when separated into two or more layers is the total thickness of these layers.

The thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm, preferably 0.1 to 1.0 μm.

The thickness of the backcoat layer is preferably 0.9 μm or less, more preferably 0.1 to 0.7 μm.

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

<Manufacturing process>
(Preparation of composition for forming each layer)
The step of preparing the composition for forming the magnetic layer, the non-magnetic layer or the backcoat layer usually includes at least a kneading step, a dispersion step, and a mixing step provided before and after these steps as necessary. Can be done. Each process may be divided into two or more stages. The components used in the preparation of each layer-forming composition may be added at the beginning or in the middle of any step. As the solvent, one or more of various solvents usually used for producing a coating type magnetic recording medium can be used. For the solvent, for example, paragraph 0153 of JP2011-216149A can be referred to. In addition, individual components can be added separately in two or more steps. In order to manufacture the magnetic recording medium, conventionally known manufacturing techniques can be used in various steps. In the kneading step, it is preferable to use an open kneader, a continuous kneader, a pressurized kneader, an extruder or the like having a strong kneading force. For details of these kneading treatments, Japanese Patent Application Laid-Open No. 1-106338 and Japanese Patent Application Laid-Open No. 1-79274 can be referred to. A known disperser can be used. Each layer-forming composition may be filtered by a known method before being subjected to the coating step. Filtration can be performed, for example, by filter filtration. As the filter used for filtration, for example, a filter having a pore size of 0.01 to 3 μm (for example, a glass fiber filter, a polypropylene filter, etc.) can be used.

In one aspect, in the step of preparing the composition for forming a magnetic layer, after preparing a dispersion liquid containing a protrusion-forming agent (hereinafter, referred to as “projection-forming agent liquid”), the protrusion-forming agent liquid is magnetically applied. It can be mixed with one or more of the other components of the layering composition. For example, a protrusion-forming agent liquid, a dispersion liquid containing an abrasive (hereinafter, referred to as “abrasive liquid”), and a dispersion liquid containing a ferromagnetic powder (hereinafter, referred to as “magnetic liquid”) are separately prepared. After that, the composition can be mixed and dispersed to prepare a composition for forming a magnetic layer. It is preferable to prepare various dispersions separately in this way in order to improve the dispersibility of the ferromagnetic powder, the protrusion forming agent and the abrasive in the composition for forming a magnetic layer. For example, the protrusion forming agent liquid can be prepared by a known dispersion treatment such as ultrasonic treatment. The ultrasonic treatment can be performed for about 1 to 300 minutes with an ultrasonic output of about 10 to 2000 watts per 200 cc (1 cc = 1 cm ^{3), for example.} Further, filtration may be performed after the dispersion treatment. The above description can be referred to for the filter used for filtration.

(Coating process, cooling process, heating and drying process)
The magnetic layer can be formed by directly applying the composition for forming a magnetic layer onto a non-magnetic support, or by applying multiple layers sequentially or simultaneously with the composition for forming a non-magnetic layer. For details of the coating for forming each layer, refer to paragraph 0066 of Japanese Patent Application Laid-Open No. 2010-231843.

As described above, in one form, the magnetic recording medium may have a non-magnetic layer between the non-magnetic support and the magnetic layer. Such a magnetic recording medium can preferably be produced by sequential layer coating. The manufacturing process of sequentially applying multiple layers can be preferably carried out as follows. The non-magnetic layer is formed through a coating step of forming a coating layer by coating a composition for forming a non-magnetic layer on a non-magnetic support, and a heat-drying step of drying the formed coating layer by heat treatment. Then, the magnetic layer is formed through a coating step of forming a coating layer by applying the composition for forming a magnetic layer on the formed non-magnetic layer, and a heat-drying step of drying the formed coating layer by heat treatment.

In the non-magnetic layer forming step of the manufacturing method for performing the sequential layer coating, the coating step is performed using a non-magnetic layer forming composition containing at least one component selected from the group consisting of fatty acids and fatty acid amides, and the coating step is performed. Performing a cooling step of cooling the coating layer between the process and the heat-drying step means that the portion on the non-magnetic support on the magnetic layer side contains one or more components selected from the group consisting of fatty acids and fatty acid amides. In the recording medium, it is preferable to adjust the C concentration derived from CH to 45 atomic% or more. Although the reason is not clear, the above components (fatty acids and / or fatty acid amides) are not removed when the solvent is volatilized in the heat drying step by cooling the coating layer of the composition for forming a non-magnetic layer before the heating and drying step. It is presumed that this is because it is easy to move to the surface of the magnetic layer. Further, the use of the protrusion forming agent described above as the protrusion forming agent of the magnetic layer suppresses the localization amount of the above-mentioned component localized on the very surface layer portion of the magnetic layer before pressing from decreasing after pressing. It is considered preferable to do so.

Further, in one form, in the magnetic layer forming step, a coating for forming a coating layer is formed by coating a composition for forming a magnetic layer containing one or more of components selected from the group consisting of fatty acids and fatty acid amides on the non-magnetic layer. A heat-drying step can be performed in which the step is performed and the formed coating layer is dried by heat treatment.

Hereinafter, an example of the manufacturing process of the magnetic recording medium will be described with reference to FIG. However, the present invention is not limited to the following examples.

FIG. 1 is a process schematic diagram showing an example of a process of manufacturing a magnetic recording medium having a non-magnetic layer and a magnetic layer on one surface of a non-magnetic support in this order and a back coat layer on the other surface. is there. In the example shown in FIG. 1, the non-magnetic support (long film) is continuously wound from the feeding portion by the feeding winding portion, and is applied in each portion or each zone shown in FIG. By performing various treatments such as drying and orientation, a non-magnetic layer and a magnetic layer can be formed on one surface of the traveling non-magnetic support by successive layer coating, and a back coat layer can be formed on the other surface. it can. The example shown in FIG. 1 can be the same as the manufacturing process usually performed for manufacturing a coating type magnetic recording medium except that a cooling zone is included.

The non-magnetic layer forming composition is applied on the non-magnetic support sent out from the feeding portion at the first coating portion (coating step of the non-magnetic layer forming composition).

After the coating step, the coating layer of the non-magnetic layer forming composition formed in the coating step is cooled in the cooling zone (cooling step). For example, the cooling step can be performed by passing the non-magnetic support on which the coating layer is formed through the cooling atmosphere. The atmospheric temperature of the cooling atmosphere can be preferably in the range of −10 ° C. to 0 ° C., and more preferably in the range of −5 ° C. to 0 ° C. The time for performing the cooling step (for example, the time from when an arbitrary portion of the coating layer is carried into the cooling zone until it is carried out (hereinafter, also referred to as “stay time”)) is not particularly limited. Since the CH-derived C concentration tends to increase as the staying time is lengthened, adjustments are made by conducting preliminary experiments as necessary so that a CH-derived C concentration of 45 atomic% or more can be realized. Is preferable. In the cooling step, the cooled gas may be sprayed on the surface of the coating layer.

After the cooling zone, in the first heat treatment zone, the coating layer is dried by heating the coating layer after the cooling step (heat drying step). The heat-drying treatment can be performed by passing a non-magnetic support having a coating layer after the cooling step into the heating atmosphere. The ambient temperature of the heating atmosphere here is, for example, about 60 to 140 ° C. However, the temperature may be set so that the solvent can be volatilized to dry the coating layer, and the temperature is not limited to the above range. Alternatively, a heated gas may be sprayed onto the surface of the coating layer. The above points are the same for the heat drying step in the second heat treatment zone and the heat drying step in the third heat treatment zone, which will be described later.

Next, in the second coating portion, the magnetic layer forming composition is coated on the non-magnetic layer formed by performing the heat drying step in the first heat treatment zone (magnetic layer forming composition). Coating process).

After that, in the form of performing the alignment treatment, the orientation treatment of the ferromagnetic powder in the coating layer is performed in the alignment zone while the coating layer of the composition for forming the magnetic layer is in a wet state. For the orientation treatment, various known techniques such as the description in paragraph 0067 of JP-A-2010-231843 can be applied. For example, the vertical alignment treatment can be performed by a known method such as a method using a magnet opposite to the opposite pole. In the alignment zone, the drying rate of the coating layer can be controlled by the temperature of the drying air, the air volume, and / or the transport rate of the magnetic tape in the alignment zone. Alternatively, the coating layer may be pre-dried before being transported to the alignment zone.

The coating layer after the orientation treatment is subjected to a heat drying step in the second heat treatment zone.

Next, in the third coating portion, the backcoat layer forming composition is applied to the surface of the non-magnetic support opposite to the surface on which the non-magnetic layer and the magnetic layer are formed to form the coating layer. (Applying step of the composition for forming a back coat layer). Then, in the third heat treatment zone, the coating layer is heat-treated and dried.

Through the above steps, a magnetic recording medium having a non-magnetic layer and a magnetic layer on one surface of the non-magnetic support in this order and a back coat layer on the other surface can be obtained.

In order to manufacture the magnetic recording medium, various known processes for manufacturing the coating type magnetic recording medium can be performed. For various treatments, for example, paragraphs 0067 to 0069 of JP2010-231843A can be referred to.

From the above, the magnetic recording medium can be obtained. However, the above-mentioned production method is an example, and the C-H-derived C concentration after pressing can be controlled to 45 atomic% or more by any means capable of adjusting the C-H-derived C concentration after pressing. Also included in the present invention.

In the magnetic recording medium manufactured as described above, a servo pattern is formed by a known method in order to enable tracking control of the magnetic head in the magnetic recording / playback device, control of the traveling speed of the magnetic recording medium, and the like. Can be done. "Formation of servo pattern" can also be referred to as "recording of servo signal". The magnetic recording medium can be a tape-shaped magnetic recording medium (magnetic tape) in one form, and can be a disk-shaped magnetic recording medium (magnetic disk) in another form. In the following, the formation of a servo pattern will be described using a magnetic tape as an example.

The servo pattern is usually formed along the longitudinal direction of the magnetic tape. Examples of the control (servo control) method using the servo signal include timing-based servo (TBS), amplifier servo, frequency servo, and the like.

As shown in ECMA (European Computer Manufacturers Association) -319, a timing-based servo system is adopted in a magnetic tape (generally called "LTO tape") conforming to the LTO (Linear Tape-Open) standard. In this timing-based servo system, the servo pattern is composed of a pair of magnetic stripes (also referred to as "servo stripes") that are non-parallel to each other and are continuously arranged in the longitudinal direction of the magnetic tape. As described above, the reason why the servo pattern is composed of a pair of magnetic stripes that are non-parallel to each other is to teach the passing position to the servo signal reading element passing on the servo pattern. Specifically, the pair of magnetic stripes are formed so that their intervals change continuously along the width direction of the magnetic tape, and the servo signal reading element reads the intervals to obtain a servo pattern. And the relative position of the servo signal reading element can be known. This relative position information allows tracking of the data track. Therefore, a plurality of servo tracks are usually set on the servo pattern along the width direction of the magnetic tape.

The servo band is composed of servo signals continuous in the longitudinal direction of the magnetic tape. A plurality of these servo bands are usually provided on the magnetic tape. For example, in LTO tape, the number is five. The area sandwiched between two adjacent servo bands is called a data band. The data band is composed of a plurality of data tracks, and each data track corresponds to each servo track.

Further, in one form, as shown in Japanese Patent Application Laid-Open No. 2004-318983, each servo band has information indicating a servo band number (“servo band ID (identification)” or “UDIM (Unique DataBand Identification)”. Method) information ”) is embedded. The servo band ID is recorded by shifting a specific one of a plurality of pairs of servo stripes in the servo band so that the position thereof is displaced relative to the longitudinal direction of the magnetic tape. Specifically, the method of shifting a specific one of a plurality of pairs of servo stripes is changed for each servo band. As a result, the recorded servo band ID becomes unique for each servo band, so that the servo band can be uniquely identified by simply reading one servo band with the servo signal reading element.

As a method for uniquely specifying the servo band, there is also a method using a staggered method as shown in ECMA-319. In this staggered method, a group of a pair of magnetic stripes (servo stripes) that are continuously arranged in the longitudinal direction of the magnetic tape and are not parallel to each other are recorded so as to be shifted in the longitudinal direction of the magnetic tape for each servo band. To do. Since this combination of shifting methods between adjacent servo bands is unique to the entire magnetic tape, it is possible to uniquely identify the servo band when reading the servo pattern by the two servo signal reading elements. It is possible.

Further, as shown in ECMA-319, information indicating the position of the magnetic tape in the longitudinal direction (also referred to as "LPOS (Longitudinal Position) information") is usually embedded in each servo band. This LPOS information, like the UDIM information, is also recorded by shifting the positions of the pair of servo stripes in the longitudinal direction of the magnetic tape. However, unlike the UDIM information, in this LPOS information, the same signal is recorded in each servo band.

It is also possible to embed other information different from the above UDIM information and LPOS information in the servo band. In this case, the embedded information may be different for each servo band such as UDIM information, or may be common to all servo bands such as LPOS information.
Further, as a method of embedding information in the servo band, a method other than the above can be adopted. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of a pair of servo stripes.

The servo pattern forming head is called a servo light head. The servo light head has a pair of gaps corresponding to the pair of magnetic stripes as many as the number of servo bands. Normally, a core and a coil are connected to each pair of gaps, and by supplying a current pulse to the coil, a magnetic field generated in the core can generate a leakage magnetic field in the pair of gaps. When forming the servo pattern, the magnetic pattern corresponding to the pair of gaps is transferred to the magnetic tape by inputting a current pulse while running the magnetic tape on the servo light head to form the servo pattern. Can be done. The width of each gap can be appropriately set according to the density of the formed servo pattern. The width of each gap can be set to, for example, 1 μm or less, 1 to 10 μm, 10 μm or more, and the like.

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

The direction of the magnetic field of the formed servo pattern is determined by the direction of erase. For example, when the magnetic tape is horizontally DC erased, the servo pattern is formed so that the direction of the magnetic field is opposite to the direction of the erase. As a result, the output of the servo signal obtained by reading the servo pattern can be increased. As shown in Japanese Patent Application Laid-Open No. 2012-53940, when the magnetic pattern is transferred to the vertically DC-erased magnetic tape using the gap, the formed servo pattern is read and obtained. The servo signal has a unipolar pulse shape. On the other hand, when the magnetic pattern is transferred to the horizontally DC-erased magnetic tape using the gap, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

The magnetic tape is usually housed in a magnetic tape cartridge, and the magnetic tape cartridge is mounted in a magnetic recording / playback device.

In a magnetic tape cartridge, generally, the magnetic tape is housed inside the cartridge body in a state of being wound on a reel. The reel is rotatably provided inside the cartridge body. As the magnetic tape cartridge, a single reel type magnetic tape cartridge having one reel inside the cartridge main body and a twin reel type magnetic tape cartridge having two reels inside the cartridge main body are widely used. When the single reel type magnetic tape cartridge is attached to the magnetic recording / playback device for recording and / or playing back data on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and the reel on the magnetic recording / playback device side. It is taken up by. A magnetic head is arranged in the magnetic tape transport path from the magnetic tape cartridge to the take-up reel. The magnetic tape is sent out and wound between the reel (supply reel) on the magnetic tape cartridge side and the reel (winding reel) on the magnetic recording / playback device side. During this time, the magnetic head and the surface of the magnetic layer of the magnetic tape come into contact with each other and slide to record and / or reproduce the data. On the other hand, in the twin reel type magnetic tape cartridge, both a supply reel and a take-up reel are provided inside the magnetic tape cartridge. The magnetic tape cartridge may be either a single reel type or a double reel type magnetic tape cartridge. Known techniques can be applied to other details of magnetic tape cartridges.

[Magnetic recording / playback device]
One aspect of the present invention relates to a magnetic recording / reproducing device including the magnetic recording medium and a magnetic head.

In the present invention and the present specification, the "magnetic recording / reproducing device" means an apparatus capable of recording data on a magnetic recording medium and reproducing data recorded on the magnetic recording medium. To do. Such a device is commonly referred to as a drive. The magnetic recording / reproducing device can be a sliding type magnetic recording / reproducing device. The sliding type magnetic recording / reproducing device means a device in which the surface of the magnetic layer and the magnetic head slide in contact with each other when recording data on a magnetic recording medium and / or reproducing the recorded data.

The magnetic head included in the magnetic recording / reproducing device can be a recording head capable of recording data on a magnetic recording medium, and can reproduce data recorded on the magnetic recording medium. Can also be. Further, in one form, the magnetic recording / 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 recording / reproducing device includes both an element for recording data (recording element) and an element for reproducing data (reproduction element) in one magnetic head. It is also possible to have a configuration. Hereinafter, the element for recording data and the element for reproducing data are collectively referred to as "data element". As the reproduction head, a magnetic head (MR head) including a magnetoresistive (MR) element capable of reading data recorded on a magnetic tape with high sensitivity as a reproduction element is preferable. As the MR head, various known MR heads such as an AMR (Anisotropic Magnetoresistive) head, a GMR (Giant Magnetoresistive) head, and a TMR (Tunnel Magnetoresistive) head can be used. Further, the magnetic head that records data and / or reproduces data may include a servo signal reading element. Alternatively, the magnetic recording / playback device may include a magnetic head (servo head) provided with a servo signal reading element as a head separate from the magnetic head that records data and / or reproduces data. For example, a magnetic head that records data and / or reproduces recorded data (hereinafter, also referred to as “recording / reproducing head”) can include two servo signal reading elements, and two servo signal reading elements. Each of the two adjacent servo bands can be read at the same time. One or more data elements can be arranged between the two servo signal reading elements.

In the magnetic recording / reproducing device, recording of data on a magnetic recording medium and / or reproduction of data recorded on a magnetic recording medium is performed by bringing the surface of the magnetic layer of the magnetic recording medium and the magnetic head into contact with each other and sliding them. It can be carried out. The magnetic recording / reproducing device may include any magnetic recording medium according to one aspect of the present invention, and known techniques can be applied to others.

For example, when recording data on a magnetic recording medium on which a servo pattern is formed and / or reproducing the recorded data, first, tracking is performed using a servo signal obtained by reading the servo pattern. That is, by making the servo signal reading element follow a predetermined servo track, the data element is controlled to pass on the target data track. The movement of the data track is performed by changing the servo track read by the servo signal reading element in the tape width direction.
The recording / playback head can also record and / or play back to other data bands. In that case, the servo signal reading element may be moved to a predetermined servo band by using the UDIM information described above, and tracking for the servo band may be started.

Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiments shown in the examples. Unless otherwise specified, the indications of "part" and "%" described below indicate "parts by mass" and "% by mass". eq is an equivalent and is a unit that cannot be converted into SI units. Further, unless otherwise specified, the steps and evaluations described below were carried out in an environment with an ambient temperature of 23 ° C. ± 1 ° C.

[Example 1]
The formulation of each layer-forming composition is shown below.

<Prescription of composition for forming magnetic layer>
(Magnetic liquid)
Ferromagnetic powder (see Table 5): 10.0 parts Oleic acid: 2.0 parts Vinyl chloride copolymer (MR-104 manufactured by Kaneka): 10.0 parts SO ₃ Na group-containing polyurethane resin: 4.0 parts (Weight average molecular weight 70000, SO ₃ Na group: 0.07 meq / g)
Amine-based polymer (DISPERBYK-102 manufactured by Big Chemie): 6.0 parts Methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts (abrasive solution)
α-Alumina: 6.0 parts (BET (Brunauer-Emmett-Teller) specific surface area 19 m ² / g, Mohs hardness 9)
SO ₃ Na group-containing polyurethane resin: 0.6 parts (weight average molecular weight 70,000, SO ₃ Na group: 0.1 meq / g)
2,3-Dihydroxynaphthalene: 0.6 parts Cyclohexanone: 23.0 parts (protrusion forming agent solution)
Protrusion forming agent (see Table 5): 1.3 parts Methyl ethyl ketone: 9.0 parts Cyclohexanone: 6.0 parts (lubricant and curing agent solution)
Stearic acid: 3.0 parts Stearic acid amide: 0.3 parts Butyl stearate: 6.0 parts Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate (Tosoh Coronate (registered trademark) L): 3 .0 copies

<Prescription of non-magnetic layer forming composition>
Non-magnetic inorganic powder α-iron oxide: 100.0 parts (average particle size 10 nm, BET specific surface area 75 m ² / g)
Carbon black: 25.0 parts (average particle size 20 nm)
SO ₃ Na group-containing polyurethane resin: 18.0 parts (weight average molecular weight 70,000, SO ₃ Na group: 0.2 meq / g)
Stearic acid: see Table 5 Cyclohexanone: 300.0 parts Methyl ethyl ketone: 300.0 parts

<Prescription of composition for forming backcoat layer>
Non-magnetic inorganic powder α-iron oxide: 80.0 parts (average particle size 0.15 μm, BET specific surface area 52 m ² / g)
Carbon black: 20.0 parts (average particle size 20 nm)
Vinyl chloride copolymer: 13.0 parts Sulfonic acid base-containing polyurethane resin: 6.0 parts Phenylphosphonic acid: 3.0 parts Cyclohexanone: 155.0 parts Methyl ethyl ketone: 155.0 parts Stearic acid: 3.0 parts Stearic acid Butyl: 3.0 parts Polyisocyanate: 5.0 parts Cyclohexanone: 200.0 parts

<Preparation of composition for forming magnetic layer>
The composition for forming a magnetic layer was prepared by the following method.
The magnetic liquid was prepared by dispersing various components of the above magnetic liquid for 24 hours (bead dispersion) using a batch type vertical sand mill. As the dispersed beads, zirconia beads having a bead diameter of 0.5 mm were used.
Various components of the above abrasive liquid are mixed and placed in a horizontal bead mill disperser together with zirconia beads having a bead diameter of 0.3 mm so that the ratio of the bead volume to the total of the abrasive liquid volume and the bead volume is 80%. After adjustment, the bead mill dispersion treatment was performed for 120 minutes, the treated liquid was taken out, and the ultrasonic dispersion filtration treatment was performed using a flow-type ultrasonic dispersion filtration device. In this way, the abrasive solution was prepared.
The protrusion-forming agent liquid is a dispersion obtained by mixing the components of the protrusion-forming agent liquid and then ultrasonically treating (dispersing) the protrusion-forming agent liquid with an ultrasonic output of 500 watts per 200 cc for 60 minutes using a horn-type ultrasonic disperser. Was prepared by filtering with a filter having a pore size of 0.5 μm.
The magnetic liquid, the polishing agent liquid, the protrusion forming agent liquid and the remaining components (lubricant and curing agent liquid) are introduced into a dissolver stirrer, stirred at a peripheral speed of 10 m / sec for 30 minutes, and then flow-type ultrasonic waves. A composition for forming a magnetic layer was prepared by treating with a disperser at a flow rate of 7.5 kg / min for 3 passes and then filtering with a filter having a pore size of 1 μm.

<Preparation of composition for forming non-magnetic layer>
Various components of the above non-magnetic layer forming composition were dispersed by a batch type vertical sand mill using zirconia beads having a bead diameter of 0.1 mm for 24 hours, and then using a filter having a pore size of 0.5 μm. A composition for forming a non-magnetic layer was prepared by filtration.

<Preparation of composition for backcoat layer formation>
Of the various components of the backcoat layer forming composition described above, the components excluding the lubricant (stearic acid and butyl stearate), polyisocyanate and 200.0 parts of cyclohexanone are kneaded and diluted with an open kneader, and then dispersed in a horizontal bead mill. Using a zirconia bead having a bead diameter of 1 mm by a machine, the bead filling rate was 80% by volume, the rotor tip peripheral speed was 10 m / sec, the residence time per pass was set to 2 minutes, and 12 passes were subjected to the dispersion treatment. Then, the remaining components described above were added and stirred with a dissolver, and the obtained dispersion was filtered using a filter having a pore size of 1 μm to prepare a composition for forming a backcoat layer.

<Making magnetic tape>
A magnetic tape was produced as shown in FIG. The details are as follows.
A polyethylene naphthalate support having a thickness of 5.0 μm is sent out from a feeding portion, and a composition for forming a non-magnetic layer is applied to one surface of the first coating portion so that the thickness after drying becomes 0.1 μm. To form a coating layer. While the formed coating layer is in a wet state, it is passed through a cooling zone adjusted to an atmospheric temperature of 0 ° C. for a residence time shown in Table 5 to perform a cooling step, and then a first heat treatment zone having an atmospheric temperature of 100 ° C. is passed. A non-magnetic layer was formed by passing through and performing a heating and drying step.
Then, the composition for forming a magnetic layer prepared above was applied onto the non-magnetic layer so that the thickness after drying was 0.1 μm in the second coating portion to form a coating layer. While the coating layer was in a wet state (undried state), a magnetic field with a magnetic field strength of 0.3T was applied in the orientation zone in a direction perpendicular to the surface of the coating layer of the composition for forming a magnetic layer to perform a vertical alignment treatment. After that, it was dried in the second heat treatment zone (atmospheric temperature 100 ° C.).
Then, in the third coating portion, the bag prepared above so that the thickness after drying is 0.5 μm on the surface opposite to the surface on which the non-magnetic layer and the magnetic layer of the polyethylene naphthalate support are formed. The coating layer forming composition was applied to the surface of the non-magnetic support to form a coating layer, and the formed coating layer was dried in a third heat treatment zone (atmosphere temperature 100 ° C.).
Then, using a calendar roll composed only of a metal roll, a calendar treatment (surface smoothing) is performed at a speed of 80 m / min, a linear pressure of 294 kN / m (300 kg / cm), and a calendar temperature (surface temperature of the calendar roll) of 90 ° C. Processing) was performed.
Then, the heat treatment was performed for 36 hours in an environment having an ambient temperature of 70 ° C. After the heat treatment, a magnetic tape was prepared by slitting it to a width of 1/2 inch (0.0127 m).
In a state where the magnetic layer of the produced magnetic tape was demagnetized, a servo pattern having an arrangement and shape according to the LTO Ultra format was formed on the magnetic layer by a servo light head mounted on a servo writer. As a result, a magnetic tape having a data band, a servo band, and a guide band in an arrangement according to the LTO Ultra format on the magnetic layer and a servo pattern having an arrangement and a shape according to the LTO Ultra format on the servo band was obtained. ..

[Examples 2 to 18, Comparative Examples 1 to 23]
A magnetic tape was obtained in the same manner as in Example 1 except that the various items shown in Table 5 were changed as shown in Table 5.
In the comparative example in which "not performed" is described in the column of the cooling zone staying time in Table 5, the magnetic tape was produced by a manufacturing process in which the cooling zone was not included in the non-magnetic layer forming step.

[Protrusion forming agent]
The protrusion forming agents used for producing the magnetic tapes of Examples or Comparative Examples are as follows. The protrusion forming agent 1 and the protrusion forming agent 3 are particles having low surface smoothness on the particle surface. The particle shape of the protrusion forming agent 2 is a cocoon-like shape. The particle shape of the protrusion forming agent 4 is a so-called amorphous shape. The particle shape of the protrusion forming agent 5 is close to a true sphere.
Protrusion forming agent 1: ATLAS (composite particle of silica and polymer) manufactured by Cabot Corporation, average particle size 100 nm
Protrusion forming agent 2: TGC6020N (silica particles) manufactured by Cabot Corporation, average particle size 140 nm
Protrusion forming agent 3: Cataloid manufactured by JGC Catalysts and Chemicals Co., Ltd. (Aqueous dispersion sol of silica particles; a dry solid obtained by heating the above water dispersion sol to remove a solvent as a protrusion forming agent for preparing a protrusion forming agent liquid. (Uses material), average particle size 120 nm
Protrusion forming agent 4: Asahi # 50 (carbon black) manufactured by Asahi Carbon Co., Ltd., average particle size 300 nm
Protrusion forming agent 5: Quartron PL-10L manufactured by Fuso Chemical Industry Co., Ltd. (Aqueous dispersion sol of silica particles; obtained by heating the above water dispersion sol as a protrusion forming agent for preparing a protrusion forming agent liquid to remove a solvent. Uses dry material), average particle size 130 nm

[Ferromagnetic powder]
In Table 5, "BaFe" indicates a hexagonal barium ferrite powder having an average particle size (average plate diameter) of 21 nm. “SrFe1” and “SrFe2” indicate hexagonal strontium ferrite powder, and “ε-iron oxide” indicates ε-iron oxide powder.
The activated volume and anisotropy constant Ku of the various ferromagnetic powders described below can be determined for each ferromagnetic powder by the method described above using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.). Value.
The mass magnetization σs is a value measured with a magnetic field strength of 15 kOe using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).

<Method 1 for producing hexagonal strontium ferrite powder>
“SrFe1” shown in Table 5 is a hexagonal strontium ferrite powder produced by the following method.
The SrCO _{3 1707g,} H ₃ BO ₃ and 687 g, _Fe 2 _{O 3} to 1120g, Al _{(OH) 3} to 45 g, the BaCO ₃ 24 g, 13 g of CaCO _3, and _Nd 2 _{O 3} and 235g weighed, with a mixer The mixture was mixed to obtain a raw material mixture.
The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1390 ° C., and the hot water outlet provided at the bottom of the platinum crucible was heated while stirring the melt, and the melt was discharged into a rod shape at about 6 g / sec. .. The hot water was rolled and rapidly cooled with a water-cooled twin roller to prepare an amorphous body.
280 g of the produced amorphous body was charged into an electric furnace, the temperature was raised to 635 ° C (crystallization temperature) at a heating rate of 3.5 ° C / min, and the temperature was maintained at the same temperature for 5 hours to obtain hexagonal strontium ferrite particles. It was precipitated (crystallized).
Next, the crystallized product containing hexagonal strontium ferrite particles was roughly pulverized in a dairy pot, 1000 g of zirconia beads having a particle size of 1 mm and 800 mL of an aqueous acetic acid solution having a concentration of 1% were added to a glass bottle, and dispersion treatment was performed for 3 hours with a paint shaker. Was done. Then, the obtained dispersion was separated from the beads and placed in a stainless beaker. The dispersion is allowed to stand at a liquid temperature of 100 ° C. for 3 hours to dissolve the glass components, then precipitated by a centrifuge and repeatedly decanted for cleaning, and then in a heating furnace having a furnace temperature of 110 ° C. 6 It was dried for a time to obtain a hexagonal strontium ferrite powder.
The hexagonal strontium ferrite powder (“SrFe1” in Table 5) obtained above has an average particle size of 18 nm, an activated volume of 902 nm ³ , and an anisotropy constant Ku of 2.2 × 10 ⁵ J / m ³ . The mass magnetization σs was 49 A · m ² / kg.
12 mg of a sample powder was collected from the hexagonal strontium ferrite powder obtained above, and the sample powder was partially dissolved under the dissolution conditions exemplified above, and the elemental analysis of the obtained filtrate was performed by an ICP analyzer to obtain neodymium atoms. The content of the surface layer was determined.
Separately, 12 mg of a sample powder was collected from the hexagonal strontium ferrite powder obtained above, and the sample powder was completely dissolved under the dissolution conditions exemplified above to perform elemental analysis of the filtrate obtained by using an ICP analyzer. The bulk content of atoms was determined.
The content of neodymium atoms (bulk content) with respect to 100 atomic% of iron atoms of the hexagonal strontium ferrite powder obtained above was 2.9 atomic%. The surface layer content of neodymium atoms was 8.0 atomic%. The ratio of the surface layer content to the bulk content, "surface layer content / bulk content" was 2.8, and it was confirmed that the neodymium atoms were unevenly distributed on the surface layer of the particles.

To show the crystal structure of hexagonal ferrite in the powder obtained above, the CuKα ray is scanned under the conditions of a voltage of 45 kV and an intensity of 40 mA, and the X-ray diffraction pattern is measured under the following conditions (X-ray diffraction analysis). confirmed. The powder obtained above showed a magnetoplumbite-type (M-type) hexagonal ferrite crystal structure. The crystal phase detected by X-ray diffraction analysis was a magnetoplumbite-type single phase.
PANalytical X'Pert Pro Diffractometer, PIXcel Detector Singler slit of incident beam and diffracted beam: 0.017 Radian dispersion slit fixed angle: 1/4 degree Mask: 10 mm
Anti-scattering 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

<Method 2 for producing hexagonal strontium ferrite powder>
“SrFe2” shown in Table 5 is a hexagonal strontium ferrite powder produced by the following method.
The SrCO ₃ 1725 _g, 666 g of H ₃ BO 3, 1332g of _{Fe 2 O 3, Al (OH} ) 3 to 52 g, the CaCO ₃ 34g, the BaCO ₃ was 141g weighed to give a mixing in a mixer starting mixture.
The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1380 ° C., and the hot water outlet provided at the bottom of the platinum crucible was heated while stirring the melt, and the melt was discharged in a rod shape at about 6 g / sec. .. The hot water was rapidly cooled and rolled with a water-cooled twin roll to prepare an amorphous body.
280 g of the obtained amorphous material was charged into an electric furnace, heated to 645 ° C. (crystallization temperature), and kept at the same temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles.
Next, the crystallized product obtained above containing hexagonal strontium ferrite particles was roughly pulverized in a dairy pot, 1000 g of zirconia beads having a particle size of 1 mm and 800 mL of an aqueous acetic acid solution having a concentration of 1% were added to a glass bottle, and dispersion treatment was performed for 3 hours with a paint shaker. Was done. Then, the obtained dispersion was separated from the beads and placed in a stainless beaker. The dispersion is allowed to stand at a liquid temperature of 100 ° C. for 3 hours to dissolve the glass components, then precipitated by a centrifuge and repeatedly decanted for cleaning, and then in a heating furnace having a furnace temperature of 110 ° C. 6 It was dried for a time to obtain a hexagonal strontium ferrite powder.
(In Table 5, "SrFe2") resulting hexagonal strontium ferrite powder having an average particle size of 19 nm, activation volume 1102Nm ^3, the anisotropy constant Ku is ^{2.0 × 10 5 J / m 3} , the mass magnetization σs was 50 A · m ² / kg.

<Method of producing ε-iron oxide powder>
“Ε-Iron oxide” shown in Table 5 is an ε-iron oxide powder produced by the following method.
In 90 g of pure water, 8.3 g of iron (III) nitrate 9 hydrate, 1.3 g of gallium nitrate (III) octahydrate, 190 mg of cobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and While stirring 1.5 g of polyvinylpyrrolidone (PVP) using a magnetic stirrer, 4.0 g of an aqueous ammonia solution having a concentration of 25% was added in an atmospheric atmosphere under the condition of an atmospheric temperature of 25 ° C. The mixture was stirred for 2 hours under the temperature condition of an atmospheric temperature of 25 ° C. To the obtained solution, an aqueous citric acid solution obtained by dissolving 1 g of citric acid in 9 g of pure water was added, and the mixture was stirred for 1 hour. The powder precipitated after stirring was collected by centrifugation, washed with pure water, and dried in a heating furnace having a furnace temperature of 80 ° C.
800 g of pure water was added to the dried powder, and the powder was dispersed again in water to obtain a dispersion liquid. The obtained dispersion was heated to a liquid temperature of 50 ° C., and 40 g of a 25% aqueous ammonia solution was added dropwise with stirring. After stirring for 1 hour while maintaining the temperature of 50 ° C., 14 mL of tetraethoxysilane (TEOS) was added dropwise, and the mixture was stirred for 24 hours. 50 g of ammonium sulfate was added to the obtained reaction solution, and the precipitated powder was collected by centrifugation, washed with pure water, and dried in a heating furnace at a temperature of 80 ° C. for 24 hours to prepare a precursor of the ferromagnetic powder. Obtained.
The obtained precursor of the ferromagnetic powder was loaded into a heating furnace having a furnace temperature of 1000 ° C. under an air atmosphere, and heat-treated for 4 hours.
The precursor of the heat-treated ferromagnetic powder was put into a 4 mol / L aqueous solution of sodium hydroxide (NaOH), and the liquid temperature was maintained at 70 ° C. and stirred for 24 hours to obtain the heat-treated ferromagnetic powder. The silicate compound, which is an impurity, was removed from the precursor.
Then, the ferromagnetic powder from which the silicic acid compound was removed was collected by centrifugation and washed with pure water to obtain a ferromagnetic powder.
The composition of the obtained ferromagnetic powder was confirmed by high frequency inductively coupled plasma emission spectroscopy (ICP-OES; Inductively Coupled Plasma-Optical Mission Spectrometry) and found to be Ga, Co and Ti-substituted ε-iron oxide (ε-Ga _{0). It was .28} Co _0.05 Ti _0.05 Fe _1.62 O ₃ ). Further, X-ray diffraction analysis was performed under the same conditions as those described for the method 1 for producing hexagonal strontium ferrite powder, and the ferromagnetic powder obtained from the peak of the X-ray diffraction pattern was the α phase and the γ phase. It was confirmed that it had a ε-phase single-phase crystal structure (ε-iron oxide type crystal structure) that did not include the crystal structure of.
(In Table 5, "ε- iron oxide") obtained ε- iron oxide powder having an average particle size of 12 nm, activation volume 746 nm ^3, the anisotropy constant Ku is 1.2 × ¹⁰ 5 J / ^{m 3} The mass magnetization σs was 16 A · m ² / kg.

[Evaluation method]
(1) C concentration derived from CH after pressing For each of the magnetic tapes of Examples and Comparative Examples, a seven-stage structure composed of only metal rolls under an environment of an ambient temperature of 20 to 25 ° C. and a relative humidity of 40 to 60%. Using a calendering machine equipped with a calender roll, while running the magnetic tape at a speed of 20 m / min with a tension of 0.5 N / m in the longitudinal direction, between the two rolls (without heating the rolls). A total of 6 times was passed, and when passing between the rolls, a surface pressure of 70 atm was applied to the surface of each magnetic layer and pressed.
X-ray photoelectron spectroscopic analysis was performed on the surface of the magnetic layer (measurement area: 300 μm × 700 μm) of the measurement sample cut out from the magnetic tape after pressing by the following method using an ESCA device, and the analysis result was derived from CH. The C concentration was calculated.

(Analysis and calculation method)
The following measurements (i) to (iii) were all carried out under the measurement conditions shown in Table 1.

(I) Wide scan measurement Wide scan measurement (measurement conditions: see Table 2) was performed on the surface of the magnetic layer of the magnetic tape with an ESCA device, and the types of detected elements were investigated (qualitative analysis).

(Ii) Narrow scan measurement Narrow scan measurement (measurement conditions: see Table 3) was performed on all the elements detected in (i) above. Using the data processing software (Vision 2.2.6) attached to the device, the atomic concentration (unit: atomic%) of each element detected from the peak area of each element was calculated. Here, the C concentration was also calculated.

(Iii) Acquisition of C1s spectrum A C1s spectrum was acquired under the measurement conditions shown in Table 4. The acquired C1s spectrum is corrected for the shift (physical shift) caused by sample charging using the data processing software (Vision 2.2.6) attached to the device, and then the C1s spectrum is calculated using the same software. A fitting process (peak separation) was performed. A Gauss-Lorentz composite function (Gaussian component 70%, Lorenz component 30%) is used for peak separation, and the C1s spectrum is fitted by the nonlinear least squares method, and the ratio of the CH peak to the C1s spectrum (peak area ratio). Was calculated. The CH-derived C concentration was calculated by multiplying the calculated CH peak area ratio by the C concentration obtained in (ii) above.

The above treatment was performed three times at different positions on the surface of the magnetic layer of the measurement sample, and the arithmetic mean of the obtained values was taken as the C concentration derived from CH.

(2) Evaluation of running stability after pressing at a pressure of 70 atm For each of the magnetic tapes of Examples and Comparative Examples, PES (Position Error Signal) was determined by the following method after pressing in (1) above.
The servo pattern was read by the verify head on the servo writer used to form the servo pattern. The verify head is a reading magnetic head for confirming the quality of the servo pattern formed on the magnetic tape, and like the magnetic head of a known magnetic tape device (drive), the position of the servo pattern (width of the magnetic tape). The reading element is arranged at a position corresponding to the position in the direction).
A known PES calculation circuit that calculates the head positioning accuracy in the servo system as PES from the electric signal obtained by reading the servo pattern with the verify head is connected to the verify head. The PES calculation circuit calculates the displacement of the magnetic tape in the width direction from the input electric signal (pulse signal) at any time, and applies a high-pass filter (cutoff: 500 cycles / m) to the temporal change information (signal) of this displacement. ) Was applied, and the value was calculated as PES. The PES can be used as an index of running stability, and if the PES calculated above is 18 nm or less, it can be evaluated that the running stability is excellent.

The above results are shown in Table 5 (Tables 5-1 to 5-7).

From the results shown in Table 5, it can be confirmed that all of the magnetic tapes of the examples showed excellent running stability after being pressed at a pressure of 70 atm, that is, in a state corresponding to after long-term storage. With such a magnetic tape, stable running is possible in the magnetic recording / playback device even after the information with low access frequency is recorded and then stored in the magnetic tape cartridge in a state of being wound on a reel for a long period of time. Yes, it is suitable as a recording medium for archiving.

One aspect of the present invention is useful in data storage applications.

Claims (15)

A magnetic recording medium having a magnetic layer containing ferromagnetic powder on a non-magnetic support.
A non-magnetic layer containing non-magnetic powder is provided between the non-magnetic support and the magnetic layer.
A backcoat layer containing non-magnetic powder is provided on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer.
The ferromagnetic powder is a ferromagnetic powder selected from the group consisting of hexagonal ferrite powder and ε-iron oxide powder.
The portion on the non-magnetic support on the magnetic layer side contains one or more components selected from the group consisting of fatty acids and fatty acid amides.
Derived from CH calculated from the CH peak area ratio in the C1s spectrum obtained by X-ray photoelectron spectroscopy performed on the surface of the magnetic layer at a photoelectron extraction angle of 10 degrees after pressing the magnetic layer with a pressure of 70 atm. A magnetic recording medium having a C concentration of 45 atomic% or more. The magnetic recording medium according to claim 1, wherein the CH-derived C concentration is 45 atomic% or more and 95 atomic% or less. The magnetic recording medium according to claim 1 or 2 , wherein the C-H-derived C concentration is 45 atomic% or more and 80 atomic% or less. The magnetic recording medium according to any one of claims 1 to 3, wherein the magnetic layer contains inorganic oxide-based particles. The magnetic recording medium according to claim 4 , wherein the inorganic oxide-based particles are composite particles of an inorganic oxide and a polymer. The magnetic recording medium according to claim 4 or 5, wherein the average particle size of the inorganic oxide-based particles is in the range of 30 to 300 nm. The magnetic recording medium according to any one of claims 1 to 6, wherein one or both of the magnetic layer and the non-magnetic layer contains a fatty acid ester. The magnetic recording medium according to any one of claims 1 to 7, wherein the average particle size of the ferromagnetic powder is 25 nm or less. The magnetic recording medium according to any one of claims 1 to 8, wherein the average particle size of the ferromagnetic powder is 20 nm or less. The magnetic recording medium according to any one of claims 1 to 9, wherein the ferromagnetic powder is a hexagonal barium ferrite powder or a hexagonal strontium ferrite powder. The magnetic recording medium according to any one of claims 1 to 9, wherein the ferromagnetic powder is ε-iron oxide powder. The magnetic recording medium according to any one of claims 1 to 11, wherein the thickness of the non-magnetic support is in the range of 3.0 to 5.0 μm. The magnetic recording medium according to any one of claims 1 to 12, wherein the thickness of the backcoat layer is in the range of 0.1 to 0.5 μm. The magnetic recording medium according to any one of claims 1 to 13 , which is a magnetic tape. The magnetic recording medium according to any one of claims 1 to 14,
With a magnetic head
Magnetic recording / playback device including.

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