JP7299205B2 - Magnetic recording medium and magnetic recording/reproducing device - Google Patents

Description

The present invention relates to a magnetic recording medium and a magnetic recording/reproducing apparatus.

2. Description of the Related Art In recent years, magnetic recording media have been widely used as data storage recording media for recording and storing various data (see, for example, Patent Document 1).

Patent No. 6378166

To reproduce data recorded on a magnetic recording medium, the data recorded on the magnetic layer is read by sliding the magnetic head in contact with the surface of the magnetic layer while the magnetic recording medium is running in a magnetic recording/reproducing apparatus. It is done by However, if the magnetic recording medium is inferior in running stability, off-track will result in a decrease in reproduction output. Therefore, magnetic recording media are desired to have excellent running stability.

Data recorded on various recording media such as magnetic recording media are called hot data, warm data, or cold data, depending on the access frequency (reproduction frequency). The access frequency decreases in the order of hot data, warm data, and cold data. Recording and long-term storage of data with low access frequency (for example, cold data) is called an archive. With the dramatic increase in the amount of information and the digitization of various types of information in recent years, the amount of data that is recorded and stored on recording media for archiving is increasing. It's getting

A magnetic recording medium that can exhibit 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, an object of one aspect of the present invention is to provide a magnetic recording medium that is excellent in 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 nonmagnetic support,
containing at least one component selected from the group consisting of fatty acids and fatty acid amides in the magnetic layer-side portion of the non-magnetic support;
After pressing the magnetic layer at a pressure of 70 atm, the C—H calculated from the C—H peak area ratio in the C1s spectrum obtained by X-ray photoelectron spectroscopy performed on the surface of the magnetic layer at a photoelectron take-off angle of 10 degrees. A magnetic recording medium having a concentration of C derived from C (hereinafter also referred to as “C concentration derived from C—H after pressing” or “C concentration derived from C—H”) of 45 atomic % or more;
Regarding. In terms of units, 1 atm = 101325 Pa (Pascal) = 101325 N (Newton)/ ^m2 .

In one embodiment, the post-pressing CH-derived C concentration may 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 can have a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support.

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 above magnetic recording medium and a magnetic head.

According to one aspect of the present invention, it is possible to provide a magnetic recording medium with 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 apparatus including the above magnetic recording medium.

1 shows an example (process schematic diagram) of a manufacturing process of a magnetic recording medium.

[Magnetic recording medium]
One aspect of the present invention is a magnetic recording medium having a magnetic layer containing a ferromagnetic powder on a nonmagnetic support, wherein a group consisting of a fatty acid and a fatty acid amide is formed on the magnetic layer side of the nonmagnetic support. C—H in the C1s spectrum obtained by X-ray photoelectron spectroscopy performed on the surface of the magnetic layer at a photoelectron take-off angle of 10 degrees after pressing the magnetic layer at a pressure of 70 atm. The present invention relates to a magnetic recording medium having a C—H derived C concentration (C—H derived C concentration after pressing) calculated from a peak area ratio of 45 atomic % or more.

The pressure of 70 atm pressing the magnetic layer is the 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 the magnetic recording medium between two rolls while running at a speed of 20 m/min. A tension of 0.5 N/m is applied to the running magnetic recording medium in the running 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 two rolls six times in total and applying a surface pressure of 70 atm each time it passes between the rolls. A metal roll is used as the roll, and the roll is not heated. The environment for pressing is an environment with an ambient temperature of 20 to 25° C. and a relative humidity of 40 to 60%. The magnetic recording medium subjected to the above pressing has been subjected to long-term storage for 10 years or more in a room temperature environment with a relative humidity of 40 to 60%, storage corresponding to such long-term storage, or accelerated testing corresponding to such long-term storage. A magnetic recording medium that is not Unless otherwise specified, this point also applies to various physical properties of the magnetic recording medium described in the present invention and this specification.
The pressing described above can be performed using, for example, a calendering machine used for manufacturing magnetic recording media. For example, a magnetic tape contained in a magnetic tape cartridge can be taken out and passed between calender rolls in a calendering machine to press the magnetic tape with a pressure of 70 atm.

The inventor of the present invention has made intensive studies to provide a magnetic recording medium that is excellent in running stability after long-term storage. It was concluded that it is appropriate. This point will be further described below.
For example, a magnetic tape is normally housed in a magnetic tape cartridge in a reeled state. Therefore, long-term storage of the magnetic tape after recording data with low access frequency is also performed in a state of being housed in the magnetic tape cartridge. A magnetic tape wound on a reel is composed of a magnetic layer surface and a backcoat layer (in the case of having a backcoat layer) or the surface of the non-magnetic support opposite to the magnetic layer side (in the case of no backcoat layer). are in contact with each other, the magnetic layer is pressed in the magnetic tape cartridge. As a result of conducting various simulations, the present inventor found that as an accelerated test equivalent to long-term storage (an example of archiving) of about 10 years in a room temperature environment with a relative humidity of 40 to 60%, the magnetic layer was subjected to a pressure of 70 atm. I came to judge that it is appropriate to press. In the present invention and this specification, room temperature means a temperature in the range of 20 to 25°C. Therefore, the present inventors conducted a running stability test after pressing the magnetic layer at 70 atm, and as a result of extensive studies based on the results of this test, magnetic recording with a CH-derived C concentration of 45 atomic % or more after pressing was found. It was found that the medium has excellent running stability after the magnetic layer is pressed at 70 atm, that is, excellent running stability under conditions corresponding to the long-term storage described above. This point is a new finding that has not been known in the past and is not described in the above-mentioned Japanese Patent No. 6378166 (Patent Document 1).

The method for measuring the C concentration derived from CH after pressing will be described below. In the present invention and this specification, the term "(the) surface of the magnetic layer" is synonymous with the magnetic layer side surface of the magnetic recording medium.
"X-ray photoelectron spectroscopy" is an analysis method commonly also called ESCA (Electron Spectroscopy for Chemical Analysis) or XPS (X-ray Photoelectron Spectroscopy). In the following, X-ray photoelectron spectroscopy is also referred to as ESCA. ESCA is an analysis method that utilizes the fact that photoelectrons are emitted when the surface of a sample to be measured is irradiated with X-rays, and is widely used as a method for analyzing the surface layer of the sample to be measured. According to ESCA, qualitative analysis and quantitative analysis can be performed using an X-ray photoelectron spectroscopy spectrum obtained by analysis on the surface of a 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 take-off angle, the following formula is generally used: detection depth ≈ electron average Free path×3×sin θ is established. In the formula, the detection depth is the depth at which 95% of the photoelectrons forming the X-ray photoelectron spectroscopy spectrum are generated, and θ is the photoelectron extraction angle. From the above formula, it can be seen that the smaller the photoelectron take-off angle, the shallower the sample surface can be analyzed, and the larger the photoelectron take-off angle, the deeper the sample can be analyzed. In the analysis performed by ESCA at a photoelectron take-off angle of 10 degrees, the analysis position is usually a very superficial layer at a depth of several nanometers from the sample surface. Therefore, according to the analysis performed by ESCA on the surface of the magnetic layer of the magnetic recording medium at a photoelectron take-off angle of 10 degrees, it is possible to analyze the composition of the superficial layer at a depth of several nanometers from the surface of the magnetic layer.
The above C-H derived C concentration is the ratio of carbon atoms C constituting C-H bonds to 100 atomic% of the total (atomic basis) of all elements detected by qualitative analysis performed by ESCA. is. The area to be analyzed is an arbitrary position on the surface of the magnetic layer of the magnetic recording medium and has an area of 300 μm×700 μm. Qualitative analysis is performed by wide scan measurements (pass 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 (pass energy: 80 eV, energy resolution: 0.1 eV, scan range: set for each element so that the entire spectrum to be measured is included). The atomic concentration (atomic concentration, unit: atomic %) of each element is calculated from the peak area in each spectrum thus obtained. Here, the atomic concentration of carbon atoms (C concentration) is also calculated from the peak area of the C1s spectrum.
Furthermore, a C1s spectrum is acquired (pass energy: 10 eV, scan range: 276-296 eV, energy resolution: 0.1 eV/step). The acquired C1s spectrum was subjected to fitting processing by a nonlinear least squares method using a Gaussian-Lorentzian composite function (Gaussian component 70%, Lorentzian component 30%), and the C—H bond peak in the C1s spectrum was peak-separated and separated. The ratio of the CH peak to the C1s spectrum (peak area ratio) is calculated. The C concentration derived from C—H is calculated by multiplying the above C concentration by the calculated C—H peak area ratio.
The arithmetic average of the values obtained by performing the above process three times at different positions on the surface of the magnetic layer of the magnetic recording medium after pressing is defined as the CH-derived C concentration after pressing. Further, a specific form 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 the magnetic layer-side portion of the non-magnetic support. In the present invention and this specification, the term "portion of the nonmagnetic support on the side of the magnetic layer" means the magnetic layer in the case of a magnetic recording medium having the magnetic layer directly on the nonmagnetic support. A magnetic recording medium having a non-magnetic layer, which will be described later in detail, between the magnetic layer is a magnetic layer and/or a non-magnetic layer. Hereinafter, "the portion on the non-magnetic support on the side of the magnetic layer" is also simply referred to as the "portion on the side of the magnetic layer".
The fatty acid and fatty acid amide contained in the magnetic layer side portion of the magnetic recording medium are components capable of functioning as lubricants 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 take-off angle of 10 degrees is , is considered to be an index of the abundance of the above components (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. Details are as follows.
Among the X-ray photoelectron spectroscopy spectra (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 C1s orbital of carbon atoms. In this C1s spectrum, the peak located near the binding energy of 284.6 eV is the CH peak. This C—H peak is a peak derived from the bond energy of the C—H bond of the organic compound. A magnetic recording medium containing at least one component selected from the group consisting of fatty acids and fatty acid amides in a magnetic layer-side portion of a non-magnetic support (in other words, one or more components selected from the group consisting of fatty acids and fatty acid amides). magnetic recording medium detected from the magnetic layer side of the non-magnetic support), in the very surface layer of the magnetic layer, the main component of the CH peak is a component selected from the group consisting of fatty acids and fatty acid amides. It is assumed that there is. Therefore, it is considered that the above C—H derived C concentration can be used as an indicator of the abundance of the above components as described above.
After the pressing, a large amount of one or more components selected from the group consisting of fatty acids and fatty acid amides is present in the state where the C—H derived C concentration is 45 atomic % or more, that is, in the very surface layer portion of the magnetic layer after the pressing. This state contributes to promoting smooth sliding (improving slidability) between the magnetic head and the surface of the magnetic layer when reproducing data recorded on the magnetic recording medium after long-term storage. Conceivable. It is speculated that this improvement in slidability can improve running stability after long-term storage.
However, the above is speculation, and the present invention is not limited to such speculation. Also, the invention is not limited in any way to other conjectures described herein.
The magnetic recording medium will be described in more detail below.

<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 from the viewpoint of further improving running stability after long-term storage, it is preferably 48 atomic % or more, and 50 atomic %. It is more preferable that it is above. Further, according to the studies of the present inventors, from the viewpoint of ease of forming a magnetic layer with high surface smoothness, the C--H derived C concentration 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 in 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 the magnetic layer-side portion of the non-magnetic support. The portion on the magnetic layer side may contain only one of a fatty acid and a fatty acid amide, or may contain both.

Examples of fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid. is preferred, and stearic acid is more preferred. The fatty acid may be contained in the magnetic layer in the form of a salt such as a metal salt.
Examples of fatty acid amides include amides of the various fatty acids exemplified above, specifically, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, and the like.
With respect to fatty acids and fatty acid derivatives (such as amides and esters described below), the fatty acid-derived moiety of the fatty acid derivative preferably has the same or similar structure as the fatty acid used in combination. For example, when using stearic acid as a 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 the portion on the magnetic layer side has, in one form, a magnetic layer containing one or more components selected from the group consisting of fatty acids and fatty acid amides. It can be manufactured by forming a magnetic layer using a composition for. In one embodiment, a non-magnetic layer is formed using a non-magnetic layer-forming composition containing one or more components selected 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 the components in the portion on the magnetic layer side. In one embodiment, the non-magnetic layer is formed using a non-magnetic layer-forming composition containing one or more components selected from the group consisting of fatty acids and fatty acid amides, and the composition is selected from the group consisting of fatty acids and fatty acid amides. Manufacture of a magnetic recording medium containing at least one component selected from the group consisting of fatty acids and fatty acid amides in the portion on the magnetic layer side by forming a magnetic layer using a composition for forming a magnetic layer containing at least one component. can do. The non-magnetic layer can play a role of retaining a lubricant such as fatty acid or 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 migrate to the magnetic layer and remain 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 shall apply hereinafter) is, for example, 0.1 to 10.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder, preferably 1.0 to 7.0 parts by mass. When two or more different fatty acids are added to the composition for forming the magnetic layer, the content means the total content of the two or more different fatty acids. This point also applies to other components. In addition, in the present invention and this specification, unless otherwise specified, a certain component may be used singly 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 weight, preferably 0.1 to 1.0 parts by weight, per 100.0 parts by weight 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; hereinafter the same) is, for example, 1.0 to 10.0 parts by mass, preferably 1 part by mass, per 100.0 parts by mass of the non-magnetic powder. .0 to 7.0 parts by mass. The fatty acid amide content of the nonmagnetic layer is, for example, 0.1 to 3.0 parts by weight, preferably 0.1 to 1.0 parts by weight, per 100.0 parts by weight of the nonmagnetic 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 ferromagnetic powders known as ferromagnetic powders used in the magnetic layers of various magnetic recording media can be used. From the viewpoint of improving the recording density, it is preferable to use ferromagnetic powder having a small average particle size. From this point of view, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, even more preferably 40 nm or less, even more preferably 35 nm or less, and 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, still more preferably 10 nm or more, and 15 nm or more. is more preferable, and 20 nm or more is even more preferable.

Hexagonal Ferrite Powder A preferred specific example of the ferromagnetic powder is hexagonal ferrite powder. For details of the hexagonal ferrite powder, for example, paragraphs 0012 to 0030 of JP-A-2011-225417, paragraphs 0134-0136 of JP-A-2011-216149, paragraphs 0013-0030 of JP-A-2012-204726 and Paragraphs 0029 to 0084 of JP-A-2015-127985 can be referred to.

In the present invention and the specification, "hexagonal ferrite powder" refers to 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 the structure to which the highest intensity diffraction peak is attributed 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 is attributed to the hexagonal ferrite crystal structure, it is determined that the hexagonal ferrite crystal structure has been detected as the main phase. shall be When only a single structure is detected by X-ray diffraction analysis, this detected structure is taken as the main phase. The hexagonal ferrite type crystal structure contains at least an iron atom, a divalent metal atom and an oxygen atom as constituent atoms. A divalent metal atom is a metal atom that can become a divalent cation as an ion, and examples thereof include alkaline earth metal atoms such as strontium, barium, and calcium atoms, and lead atoms. In the present invention and the specification, hexagonal strontium ferrite powder means that the main divalent metal atoms contained in this powder are strontium atoms, and hexagonal barium ferrite powder means that the main divalent metal atoms contained in this powder are a barium atom as a divalent metal atom. The main divalent metal atom means the divalent metal atom that accounts for the largest amount on an atomic % basis among the divalent metal atoms contained in the powder. However, the above divalent metal atoms do not include rare earth atoms. "Rare earth atoms" in the present invention and herein are selected from the group consisting of scandium atoms (Sc), yttrium atoms (Y), and lanthanide atoms. Lanthanide atoms include lanthanum atom (La), cerium atom (Ce), praseodymium atom (Pr), neodymium atom (Nd), promethium atom (Pm), samarium atom (Sm), europium atom (Eu), gadolinium atom (Gd ), terbium atom (Tb), dysprosium atom (Dy), holmium atom (Ho), erbium atom (Er), thulium atom (Tm), ytterbium atom (Yb), and lutetium atom (Lu) be.

The hexagonal strontium ferrite powder, which is one form of the hexagonal ferrite powder, will be described in more detail below.

The activated volume of the hexagonal strontium ferrite powder is preferably in the range of 800-1600 nm ³ . A finely divided hexagonal strontium ferrite powder exhibiting an activation volume within 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 greater than or equal to 800 nm ³ , for example it may be greater than or equal to 850 nm ³ . Further, from the viewpoint of further improving electromagnetic conversion characteristics, the activated volume of the 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 more preferable, 1200 nm ³ or less is even more preferable, and 1100 nm ³ or less is even more preferable. The same is true for the activation volume of hexagonal barium ferrite powder.

The "activation volume" is a unit of magnetization reversal, and is an index indicating the magnetic size of a particle. The activation volume and the anisotropy constant Ku described in the present invention and this specification were measured using a vibrating sample magnetometer at magnetic field sweep speeds of 3 minutes and 30 minutes at the coercive force Hc measurement unit (measurement Temperature: 23° C.±1° C.), which is a value obtained from the following relational expression between Hc and activation volume V. Note that the unit of the anisotropy constant Ku is 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: anisotropy 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 precession frequency (unit: s ⁻¹ ), t: magnetic field reversal time (unit: s)]

An anisotropic constant Ku can be cited 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, more preferably 2.0×10 ⁵ J/m ³ or more. Also, Ku of the hexagonal strontium ferrite powder can be, for example, 2.5×10 ⁵ J/m ³ or less. However, the higher the Ku value, the higher the thermal stability, which is preferable.

The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, it preferably contains 0.5 to 5.0 atomic % of rare earth atoms (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 of rare earth atoms on the surface layer. In the present invention and in this specification, the term "rare earth atom surface uneven distribution" refers to the rare earth atom content ratio (hereinafter referred to as "Rare earth atom surface layer content" or simply "surface layer content" with respect to rare earth atoms.) is obtained by completely dissolving hexagonal strontium ferrite powder with acid. (hereinafter referred to as "rare earth atom bulk content" or simply "bulk content" with respect to rare earth atoms), and
Rare earth atom surface layer content/rare earth atom bulk content>1.0
means that the ratio of The rare earth atom content rate of the hexagonal strontium ferrite powder described later is synonymous with the rare earth atom bulk content rate. On the other hand, since partial dissolution using an acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder, the content of rare earth atoms in the solution obtained by partial dissolution is It is the rare earth atom content rate in the surface layer of the particles. The rare earth atom surface layer portion content ratio satisfies the ratio of "rare earth atom surface layer portion content/rare earth atom bulk content ratio >1.0" means that the rare earth atoms are present in the surface layer portion of the particles constituting the hexagonal strontium ferrite powder. It means that it is unevenly distributed (that is, it exists more than inside). In the present invention and in this specification, the term "surface layer portion" means a partial region extending from the surface toward the inside of a particle that constitutes 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 atomic % with respect to 100 atomic % of iron atoms. The fact that the rare earth atoms are contained in the bulk content in the above range and that the rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder contributes to suppressing the decrease in reproduction output during repeated reproduction. Conceivable. This is because the hexagonal strontium ferrite powder contains rare earth atoms with a bulk content within the above range, and the rare earth atoms are unevenly distributed in the surface layers of the particles constituting the hexagonal strontium ferrite powder. This is presumed to be due to the fact that The higher 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 reproduction output in repeated reproduction. The uneven distribution of rare earth atoms in the particle surface layer of the hexagonal strontium ferrite powder contributes to stabilizing the spin of the iron (Fe) site in the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. It is speculated that it will increase.
In addition, it is speculated that the use of hexagonal strontium ferrite powder, which has rare earth atoms unevenly distributed in the surface layer, as the ferromagnetic powder for the magnetic layer contributes to suppressing abrasion of the magnetic layer surface due to sliding against the magnetic head. be. That is, it is presumed that the hexagonal strontium ferrite powder having rare earth atoms unevenly distributed on the surface layer can 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 surfaces of the particles that make up the hexagonal strontium ferrite powder improves the interaction between the particle surfaces and organic substances (e.g., binders and/or additives) contained in the magnetic layer. and as a result, the strength of the magnetic layer is improved.
From the viewpoint of further suppressing the decrease in reproduction output in repeated reproduction and/or from the viewpoint of further improving running durability, the rare earth atom content (bulk content) is in the range of 0.5 to 4.5 atomic %. is more preferable, the range of 1.0 to 4.5 atomic % is more preferable, and the range of 1.5 to 4.5 atomic % is even more preferable.

The above bulk content is a content obtained by completely dissolving the hexagonal strontium ferrite powder. In the present invention and this specification, unless otherwise specified, the atomic content refers to the bulk content obtained by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one kind of rare earth atoms as rare earth atoms, or may contain two or more kinds of rare earth atoms. When two or more kinds of rare earth atoms are contained, the above-mentioned bulk content is obtained for the total of two or more kinds of rare earth atoms. This point also applies to the present invention and other components in this specification. That is, unless otherwise specified, one component may be used alone, or two or more may be used. When two or more types are used, the content or content rate refers to the total of two or more types.

When the hexagonal strontium ferrite powder contains rare earth atoms, the contained rare earth atoms may be one or more rare earth atoms. Preferred rare earth atoms from the viewpoint of further suppressing a decrease in reproduction output in repeated reproduction include neodymium atoms, samarium atoms, yttrium atoms and dysprosium atoms, with neodymium atoms, samarium atoms and yttrium atoms being more preferred, and neodymium atoms. Atoms are more preferred.

In the hexagonal strontium ferrite powder having rare earth atoms unevenly distributed on the surface layer, 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, for a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, the surface layer content of rare earth atoms obtained by partially dissolving under the dissolving conditions described later and the rare earth elements obtained by completely dissolving under the dissolving conditions described later The ratio of atoms to the bulk content, "surface layer content/bulk content", is greater than 1.0 and can be 1.5 or more. When the "surface layer content/bulk content" is greater than 1.0, it means that the rare earth atoms are unevenly distributed in the surface layer (ie, more present than in the interior) in the particles constituting the hexagonal strontium ferrite powder. do. In addition, the ratio between the surface layer content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later and the bulk content of rare earth atoms obtained by complete 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 rare earth atoms unevenly distributed in the surface layer portion, the rare earth atoms should be unevenly distributed in the surface layer portion of the particles constituting the hexagonal strontium ferrite powder. "Ratio" is not limited to the exemplified upper or lower limits.

Partial dissolution and total dissolution of hexagonal strontium ferrite powder are described below. For hexagonal strontium ferrite powders present as powders, sample powders for partial dissolution and total dissolution are taken from the same lot of powder. On the other hand, for the hexagonal strontium ferrite powder contained in the magnetic layer of the magnetic recording medium, 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 complete dissolution. . The hexagonal strontium ferrite powder can be extracted from the magnetic layer, for example, by the method described in paragraph 0032 of JP-A-2015-91747.
The partial dissolution means dissolution to such an extent that residual hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. For example, by partial dissolution, a region of 10 to 20% by mass of the particles constituting the hexagonal strontium ferrite powder can be dissolved out of 100% by mass of the entire particles. On the other hand, the above-mentioned complete dissolution means that the hexagonal strontium ferrite powder is dissolved to the point where no residue of the hexagonal strontium ferrite powder remains in the liquid at the end of dissolution.
The partial dissolution and the measurement of the surface layer content are performed, for example, by the following methods. However, the dissolution conditions such as the amount of sample powder described below are examples, and dissolution conditions that allow partial dissolution and complete 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 with a set temperature of 70° C. for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the filtrate thus obtained is performed by an inductively coupled plasma (ICP) analyzer. In this way, the surface layer portion content of rare earth atoms relative to 100 atomic % of iron atoms can be obtained. When multiple types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer portion content. This point also applies to the measurement of the bulk content.
On the other hand, the measurement of the total dissolution and bulk content is carried out, for example, by the following method.
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 with a set temperature of 80° C. for 3 hours. After that, the partial dissolution and the measurement of the surface layer portion content are carried out in the same manner as described above, and the bulk content with respect to 100 atom % of iron atoms can be obtained.

From the viewpoint of increasing the reproduction output when reproducing data recorded on a magnetic recording medium, it is desirable that the ferromagnetic powder contained in the magnetic recording medium has a high mass magnetization σs. In this regard, hexagonal strontium ferrite powder containing rare earth atoms but not unevenly distributed in the surface layer of rare earth atoms tends to have a significantly lower σs than hexagonal strontium ferrite powder containing no rare earth atoms. On the other hand, hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer is considered 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 greater, and can also be 47 A·m ² /kg or greater. On the other hand, from the viewpoint of noise reduction, σs is preferably 80 A·m ² /kg or less, more preferably 60 A·m ² /kg or less. σs can be measured using a known measuring device capable of measuring magnetic properties, such as a vibrating sample magnetometer. In the present invention and this specification, unless otherwise specified, mass magnetization σs is a value measured at a magnetic field strength of 15 kOe. 1 [kOe]=10 ⁶ /4π [A/m].

With respect to the content of constituent atoms (bulk content) of the hexagonal strontium ferrite powder, the strontium atom content can be, for example, in the range of 2.0 to 15.0 atomic % with respect to 100 atomic % of iron atoms. . In one form, the hexagonal strontium ferrite powder can have strontium atoms as the only divalent metal atoms contained in the powder. In yet another form, the hexagonal strontium ferrite powder can also contain one or more other divalent metal atoms in addition to the strontium atoms. For example, it can contain barium atoms and/or calcium atoms. When other divalent metal atoms other than strontium atoms are contained, the barium atom content and calcium atom content in the hexagonal strontium ferrite powder are, for example, 0.05 to 5 atoms per 100 atomic percent of iron atoms. can be in the range of .0 atomic %.

As crystal structures of hexagonal ferrite, magnetoplumbite type (also called “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 have a single crystal structure or two or more crystal structures detected by X-ray diffraction analysis. For example, in one form, a hexagonal strontium ferrite powder can be one in which only the M-type crystal structure is detected by X-ray diffraction analysis. For example, M-type hexagonal ferrite is represented by a composition formula of AFe ₁₂ O ₁₉ . Here, A represents a divalent metal atom, and if the hexagonal strontium ferrite powder is M-type, A is only a strontium atom (Sr), or if A contains a plurality of divalent metal atoms, , as described above, strontium atoms (Sr) account for the largest amount on an atomic % basis. 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 may also contain rare earth atoms. Furthermore, the hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may contain aluminum atoms (Al). The content of aluminum atoms can be, for example, 0.5 to 10.0 atomic % with respect to 100 atomic % of iron atoms. From the viewpoint of further suppressing the decrease in reproduction output in repeated reproduction, 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. %, 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 may contain no atoms other than iron atoms, strontium atoms, oxygen atoms and rare earth atoms. The content expressed in atomic % above is the content of each atom (unit: mass %) obtained by completely dissolving the hexagonal strontium ferrite powder, and converted to the value expressed in atomic % using the atomic weight of each atom. It is required by conversion. Moreover, in the present invention and this specification, the phrase "not containing" an atom means that the content of the atom is 0% by mass as measured by an ICP analyzer after being completely dissolved. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The above-mentioned "does not contain" shall be used in the sense of containing in an amount below the detection limit of the ICP analyzer. The hexagonal strontium ferrite powder, in one form, can be free of bismuth atoms (Bi).

Metal powder Ferromagnetic metal powder is also a preferred specific example of the ferromagnetic powder. For details of the ferromagnetic metal powder, for example, paragraphs 0137 to 0141 of JP-A-2011-216149 and paragraphs 0009-0023 of JP-A-2005-251351 can be referred to.

ε-iron oxide powder A preferred specific example of the ferromagnetic powder is ε-iron oxide powder. In the present invention and the specification, the term "ε-iron oxide powder" refers to a ferromagnetic powder in which an ε-iron oxide type crystal structure is detected as the main phase by X-ray diffraction analysis. For example, when the highest intensity diffraction peak in an X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the ε-iron oxide type crystal structure, the ε-iron oxide type crystal structure is detected as the main phase. shall judge. As a method for producing ε-iron oxide powder, a method of producing from goethite, a reverse micelle method, and the like are known. All of the above manufacturing methods are known. Also, a method for producing ε-iron oxide powder in which a part of Fe is substituted with substitution atoms such as Ga, Co, Ti, Al, and Rh is described in J. Am. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J.P. Mater. Chem. C, 2013, 1, pp. 5200-5206 and the like. However, the method for producing the ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer of the magnetic recording medium is not limited to the methods mentioned here.

The activated volume of the ε-iron oxide powder is preferably in the range of 300-1500 nm ³ . Micronized ε-iron oxide powder exhibiting an activation volume within the above range is suitable for producing magnetic recording media exhibiting excellent electromagnetic conversion characteristics. The activated volume of the ε-iron oxide powder is preferably greater than or equal to 300 nm ³ and may eg be greater than or equal to 500 nm ³ . Further, from the viewpoint of further improving the electromagnetic conversion characteristics, the activated volume of the ε-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 more preferable, and 1100 nm ³ or less is even more preferable.

An anisotropic constant Ku can be cited 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 higher, more preferably 8.0×10 ⁴ J/m ³ or higher. Also, Ku of the ε-iron oxide powder can be, for example, 3.0×10 ⁵ J/m ³ or less. However, the higher the Ku, the higher the thermal stability, which is preferable, and is not limited to the values exemplified above.

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

In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powder is a value measured by the following method using a transmission electron microscope.
The powder is photographed with a transmission electron microscope at a magnification of 100,000 times and printed on photographic paper at a total magnification of 500,000 times to obtain a photograph of the particles constituting the powder. The particles of interest are selected from the photograph of the particles obtained, and the contours of the particles are traced with a digitizer to measure the size of the particles (primary particles). Primary particles refer to individual particles without agglomeration.
The above measurements are performed on 500 randomly selected 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 H-9000 transmission electron microscope can be used. Further, the particle size can be measured using known image analysis software such as Carl Zeiss image analysis software KS-400. Unless otherwise specified, the average particle size shown in the examples below was measured using a transmission electron microscope H-9000 manufactured by Hitachi, and image analysis software KS-400 manufactured by Carl Zeiss as image analysis software. value. In the present invention and herein, powder means a collection of particles. For example, ferromagnetic powder means an aggregate of ferromagnetic particles. In addition, the aggregation of a plurality of particles is not limited to the form in which the particles constituting the aggregation are in direct contact, but also includes the form in which a binder, an additive, etc., which will be described later, is interposed between the particles. be. The term particles is sometimes used to describe powders.

As a method for collecting a sample powder from a magnetic recording medium for particle size measurement, for example, the method described in paragraph 0015 of JP-A-2011-048878 can be employed.

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

In addition, the average acicular ratio of the powder is obtained by measuring the length of the minor axis of the particles in the above measurement, that is, the minor axis length, and obtaining the value of (long axis length / minor axis length) of each particle. It refers to the arithmetic mean of the values obtained for the particles. 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 definition of the particle size, and the thickness or height in the case of (2). In the case of (3), since there is no distinction between the major axis and the minor axis, (long axis length/short axis length) is regarded as 1 for convenience.
Unless otherwise specified, when the particle shape is specific, for example, in the case of the definition (1) of the particle size, the average particle size is the average major axis length, and in the case of the definition (2), the average particle size is Average plate diameter. In the case of the same definition (3), the average particle size is the average diameter (also referred to as average particle size or average particle size).

The ferromagnetic powder content (filling rate) in the magnetic layer is preferably in the range of 50 to 90 mass %, more preferably in the range of 60 to 90 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 can contain a binder in the magnetic layer. A binder is one or more resins. As the binder, various resins commonly used as binders for coating-type magnetic recording media can be used. Examples of binders include polyurethane resins, polyester resins, polyamide resins, vinyl chloride resins, acrylic resins obtained by copolymerizing styrene, acrylonitrile, methyl methacrylate, etc., cellulose resins such as nitrocellulose, epoxy resins, phenoxy resins, polyvinyl acetal, A resin selected from polyvinyl alkylal resins such as polyvinyl butyral can be used singly, or a plurality of resins can be mixed and used. Preferred among these are polyurethane resins, acrylic resins, cellulose resins, and vinyl chloride resins. These resins may be homopolymers or copolymers. These resins can also be used as binders in the non-magnetic layer and/or backcoat layer, which will be described later.
Paragraphs 0028 to 0031 of JP-A-2010-24113 can be referred to for the above binders. The weight-average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less. The weight average molecular weight in the present invention and the 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 the examples below is a value obtained by converting the 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 Corporation)
Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8 mmID (Inner Diameter) × 30.0 cm)
Eluent: Tetrahydrofuran (THF)

Curing agents can also be used with resins that can be used as binders. The curing agent can be, in one form, a thermosetting compound which is a compound in which a curing reaction (crosslinking reaction) proceeds by heating, and in another form, a photocuring compound in which a curing reaction (crosslinking reaction) proceeds by light irradiation. can be a chemical compound. The curing agent can be contained in the magnetic layer in a state where at least a portion of it reacts (crosslinks) with other components such as a binder as the curing reaction progresses during the process of forming the magnetic layer. In this respect, when the composition used for forming other layers contains a curing agent, the same applies to layers formed using this composition. Preferred curing agents are thermosetting compounds, preferably polyisocyanates. For details of the polyisocyanate, paragraphs 0124 to 0125 of JP-A-2011-216149 can be referred to. The curing agent is contained in the composition for forming the magnetic layer in an amount of, for example, 0 to 80.0 parts by weight per 100.0 parts by weight of the binder, and preferably 50.0 to 80.0 parts by weight from the viewpoint of improving the strength of the magnetic layer. Parts by weight amounts can be used.

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

(Additive)
The magnetic layer may contain one or more additives as necessary in addition to the various components described above. Commercially available additives can be appropriately selected and used according to desired properties. Alternatively, a compound synthesized by a known method can be used as an additive. Examples of additives include the curing agents described above. Additives that can be contained in the magnetic layer include nonmagnetic fillers, lubricants, dispersants, dispersing aids, antifungal agents, antistatic agents, antioxidants, and the like. Non-magnetic filler is synonymous with non-magnetic particles or non-magnetic powder. Non-magnetic fillers can include non-magnetic fillers that can function as protrusion-forming agents and non-magnetic fillers that can function as abrasives. Further, as additives, 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 one form of the 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 also be used. can. Examples of inorganic substances include inorganic oxides such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides, and inorganic oxides are preferred. In one form, the protrusion-forming agent can be an inorganic oxide-based particle. Here, the term "system" is used in the sense of "including". One form of inorganic oxide particles is particles made of inorganic oxides. Another form of inorganic oxide particles is composite particles of an inorganic oxide and an organic substance, and specific examples thereof include composite particles of an inorganic oxide and a polymer. Examples of such particles include particles in which a polymer is bonded to the surface of inorganic oxide particles.

The average particle size of the projection-forming agent is, for example, 30-300 nm, preferably 40-200 nm. Particles with a shape closer to a true sphere have a lower pushing resistance when a large pressure is applied, and are more likely to be pushed into the magnetic layer. On the other hand, if the shape of the particles is far from a true sphere, for example, a so-called deformed shape, a large indentation resistance is likely to act when a large pressure is applied, making it difficult for the particles to be pushed into the magnetic layer. In addition, particles with non-homogeneous particle surfaces and low surface smoothness tend to exert a large indentation resistance when a large pressure is applied, so that they are less likely to be indented into the magnetic layer. If the magnetic layer contains particles that are likely to be pushed into the magnetic layer, such particles will be pushed into the magnetic layer by pressing. Even if it is localized in the very surface layer of the layer, it is considered that the localized amount is reduced after pressing. On the other hand, it is presumed that if the particles of the protrusion-forming agent are less likely to be pushed into the magnetic layer by pressing, 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 C—H derived C concentration measured after pressing at a pressure of 70 atm to 45 atomic % or more. guessed.

Abrasive Abrasive, which is another form of non-magnetic filler, is preferably a non-magnetic powder with a Mohs hardness of more than 8, more preferably a non-magnetic powder with a Mohs hardness of 9 or more. In contrast, the Mohs hardness of the protrusion-forming agent can be, for example, 8 or less, or 7 or less. The maximum Mohs hardness is 10 for diamond. Specifically, alumina ( _Al2O3 ) _, silicon carbide, boron carbide ( _B4C ) _{, SiO2} , TiC, chromium oxide ( _Cr2O3 ), cerium oxide, zirconium oxide ( _ZrO2 ), iron oxide , diamond and the like, among which alumina powder such as α-alumina and silicon carbide powder are preferred. Also, 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.

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

Examples of additives that can be used in a magnetic layer containing an abrasive include dispersants described in paragraphs 0012 to 0022 of JP-A-2013-131285, which improve the dispersibility of the abrasive in the composition for forming the magnetic layer. It can be mentioned as a dispersing agent for Further, regarding the dispersant, paragraphs 0061 and 0071 of JP-A-2012-133837 can be referred to. A dispersant may be contained in the non-magnetic layer. For the dispersant that can be contained in the non-magnetic layer, see paragraph 0061 of JP-A-2012-133837.

Fatty Acid Ester One or both of the magnetic layer and the non-magnetic layer, which will be detailed later, may or may not contain a fatty acid ester.
Fatty acid esters, fatty acids and fatty acid amides are all ingredients that can function as lubricants. Lubricants are generally classified into fluid lubricants and boundary lubricants. Fatty acid esters are said to be components that can function as fluid lubricants, while fatty acids and fatty acid amides are said to be components that can function as boundary lubricants. A 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, a fluid lubricant is considered to be a lubricant which itself forms a liquid film on the surface of the magnetic layer and can reduce friction due to the flow of this liquid film. Thus, fatty acid esters are considered to act differently as lubricants than fatty acids and fatty acid amides. The inventors of the present invention found that the C—H-derived C concentration, which is considered to be an indicator 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, was 45 atomic percent after pressing. It is speculated that the above will contribute to the improvement of running stability after long-term storage.

Examples of fatty acid esters include esters of various fatty acids described above as examples of fatty acids. Specific examples include butyl myristate, butyl palmitate, butyl stearate (butyl stearate), neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, Examples include isocetyl stearate, isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate, and butoxyethyl stearate.

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

<Nonmagnetic layer>
Next, the nonmagnetic layer will be explained. The magnetic recording medium may have a magnetic layer directly on a 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 in the non-magnetic layer may be inorganic powder or organic powder. Carbon black or the like can also be used. Examples of inorganic substances include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These non-magnetic powders are commercially available and can be produced by known methods. For details, paragraphs 0146 to 0150 of Japanese Patent Application Laid-Open No. 2011-216149 can be referred to. For carbon black that can be used in the non-magnetic layer, see paragraphs 0040 to 0041 of JP-A-2010-24113. The content (filling rate) of the non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90 mass %, more preferably in the range of 60 to 90 mass %.

The non-magnetic layer may contain a binder and may also contain additives. Known techniques for nonmagnetic layers can be applied to other details such as binders and additives for the nonmagnetic layer. Also, for example, the type and content of the binder, the type and content of the additive, etc., can be applied to known techniques relating to the magnetic layer.

In the present invention and herein, non-magnetic layers are intended to include non-magnetic powders as well as substantially non-magnetic layers containing small amounts of ferromagnetic powders, for example as impurities or intentionally. Here, the substantially non-magnetic layer means that the layer has a residual magnetic flux density of 10 mT or less, a coercive force of 100 Oe or less, or a residual magnetic flux density of 10 mT or less and a coercive force of 100 Oe. shall refer to a layer that is: The non-magnetic layer preferably has no residual magnetic flux density and no coercive force.

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

<Back coat layer>
The magnetic recording medium may or may not have a backcoat layer containing nonmagnetic powder on the surface of the nonmagnetic support opposite to the surface having the magnetic layer. The backcoat layer preferably contains one or both of carbon black and inorganic powder. The backcoat layer may contain a binder and may also contain additives. As for binders and additives for the backcoat layer, known techniques for the backcoat layer can be applied, and known techniques for the formulation of the magnetic layer and/or the non-magnetic layer can also be applied. For example, paragraphs 0018 to 0020 of JP-A-2006-331625 and US Pat. .

<Various thicknesses>
The thickness of the nonmagnetic support is preferably 3.0 to 6.0 μm.
The thickness of the magnetic layer is preferably 0.15 μm or less, more preferably 0.1 μm or less, from the viewpoint of high-density recording, which 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. At least one magnetic layer is required, and the magnetic layer may be separated into two or more layers having different magnetic properties, and a configuration relating to a known multi-layered 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 nonmagnetic 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 in the range of 0.1 to 0.7 μm.

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

<Manufacturing process>
(Preparation of each layer-forming composition)
The process of preparing a composition for forming a magnetic layer, non-magnetic layer or backcoat layer usually includes at least a kneading process, a dispersing process, and a mixing process provided before or after these processes as required. can be done. Each step may be divided into two or more stages. The components used for preparing 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 commonly used in the production of coating type magnetic recording media can be used. Regarding the solvent, for example, paragraph 0153 of JP-A-2011-216149 can be referred to. It is also possible to divide the addition of the individual components in two or more steps. In order to manufacture the above magnetic recording medium, conventional known manufacturing techniques can be used in various steps. In the kneading step, it is preferable to use a kneader having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader or an extruder. For details of these kneading processes, reference can be made to Japanese Patent Application Laid-Open Nos. 1-106338 and 1-79274. A known disperser can be used. Each layer-forming composition may be filtered by a known method before being applied to the coating step. Filtration can be performed, for example, by filter filtration. As a filter used for filtration, for example, a filter having a pore size of 0.01 to 3 μm (eg, glass fiber filter, polypropylene filter, etc.) can be used.

In one aspect, in the step of preparing the composition for forming the magnetic layer, after preparing a dispersion containing a protrusion-forming agent (hereinafter referred to as "protrusion-forming agent liquid"), this protrusion-forming agent liquid is added to the magnetic It can be mixed with one or more other components of the layer-forming composition. For example, a protrusion-forming agent liquid, a dispersion containing an abrasive (hereinafter referred to as "abrasive liquid"), and a dispersion containing ferromagnetic powder (hereinafter referred to as "magnetic liquid") are separately prepared. After mixing and dispersing, the composition for forming the magnetic layer can be prepared. It is preferable to separately prepare various dispersions in this manner in order to improve the dispersibility of the ferromagnetic powder, protrusion-forming agent and abrasive in the composition for forming the 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 at an ultrasonic output of about 10 to 2000 watts per 200 cc (1 cc=1 cm ³ ), for example. Moreover, you may filter after a dispersion|distribution process. The above description can be referred to for the filter used for filtration.

(Coating process, cooling process, heat drying process)
The magnetic layer can be formed by directly coating the magnetic layer-forming composition on the non-magnetic support, or by sequentially or simultaneously coating the magnetic layer-forming composition with the non-magnetic layer-forming composition. For details of coating for forming each layer, paragraph 0066 of JP-A-2010-231843 can be referred to.

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

In the nonmagnetic layer forming step of the manufacturing method in which such successive multilayer coating is performed, the coating step is performed using a nonmagnetic layer forming composition containing one or more components selected from the group consisting of fatty acids and fatty acid amides. and the heating and drying step, the cooling step of cooling the coating layer is carried out. It is preferable for adjusting the C—H derived C concentration to 45 atomic % or more in the recording medium. Although the reason for this is not clear, by cooling the coated layer of the composition for forming the non-magnetic layer before the heat drying process, the components (fatty acid and/or fatty acid amide) become non-magnetic when the solvent is volatilized in the heat drying process. It is presumed that this is because it becomes easier to migrate to the surface of the magnetic layer. Furthermore, the use of the protrusion-forming agent described above as the protrusion-forming agent for the magnetic layer suppresses the localized amount of the above-mentioned component localized in the very surface layer of the magnetic layer before pressing from decreasing after pressing. It is considered preferable to do so.

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

An example of the manufacturing process of the magnetic recording medium will be described below 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 the process of manufacturing a magnetic recording medium having a nonmagnetic layer and a magnetic layer on one side of a nonmagnetic support in this order and a backcoat layer on the other side. be. In the example shown in FIG. 1, the non-magnetic support (long film) is continuously fed from the feed section and wound up by the take-up section. By performing various treatments such as drying and orientation, a non-magnetic layer and a magnetic layer can be sequentially formed on one side of a running non-magnetic support by multilayer coating, and a back coat layer can be formed on the other side. can. The example shown in FIG. 1 can be similar to the manufacturing process normally performed for the manufacture of coated magnetic recording media, except that it includes a cooling zone.

On the non-magnetic support delivered from the delivery section, a non-magnetic layer-forming composition is applied in the first coating section (non-magnetic layer-forming composition coating step).

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 having the coating layer formed thereon through a cooling atmosphere. The ambient temperature of the cooling atmosphere is preferably in the range of -10°C to 0°C, 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 part of the coating layer is carried into the cooling zone to when it is carried out (hereinafter also referred to as "residence time")) is not particularly limited. Since the C concentration derived from C—H tends to increase as the residence time is lengthened, adjustments are made, such as by performing preliminary experiments, as necessary, so that a C concentration derived from C—H of 45 atomic % or more can be achieved. is preferred. In the cooling step, cooled gas may be sprayed onto the surface of the coating layer.

After the cooling zone, in the first heat treatment zone, the coating layer after the cooling step is heated to dry the coating layer (heat drying step). The heat drying treatment can be carried out by passing the non-magnetic support having the coated layer after the cooling step through a heated atmosphere. The ambient temperature of the heating atmosphere here is, for example, about 60 to 140.degree. However, the ambient temperature is not limited to the above range, as long as the temperature is sufficient to volatilize the solvent and dry the coating layer. Optionally, heated gas may also be blown onto the coating layer surface. The above points also apply to 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 section, a magnetic layer-forming composition is coated on the non-magnetic layer formed by the heating and drying process in the first heat treatment zone. coating process).

After that, in the form in which the orientation treatment is performed, the orientation treatment of the ferromagnetic powder in the coating layer is performed in the orientation zone while the coating layer of the composition for forming the magnetic layer is in a wet state. Various known techniques including those described in paragraph 0067 of JP-A-2010-231843 can be applied to the alignment treatment. For example, the vertical alignment treatment can be performed by a known method such as a method using opposed magnets with different polarities. In the orientation zone, the drying speed of the coating layer can be controlled by the temperature and air volume of the drying air and/or the transport speed of the magnetic tape in the orientation zone. Also, the coated layer may be pre-dried before being conveyed to the orientation zone.

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

Next, in the third coating portion, a coating layer is formed by coating a composition for forming a backcoat layer on the surface of the nonmagnetic support opposite to the surface on which the nonmagnetic layer and the magnetic layer are formed. (Step of applying composition for forming backcoat layer). After that, in the third heat treatment zone, the coating layer is heat-treated and dried.

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

In order to manufacture the above magnetic recording medium, various known treatments for manufacturing a coating type magnetic recording medium can be performed. For various types of processing, for example, paragraphs 0067 to 0069 of JP-A-2010-231843 can be referred to.

Through the above steps, the magnetic recording medium can be obtained. However, the above production method is an example, and the C concentration derived from C after pressing can be controlled to 45 atomic % or more by any means capable of adjusting the C concentration derived from C after pressing. forms are also included in the present invention.

A servo pattern is formed on the magnetic recording medium manufactured as described above by a known method in order to enable tracking control of a magnetic head in a magnetic recording/reproducing apparatus, control of the traveling speed of the magnetic recording medium, and the like. can be done. "Formation of servo patterns" can also be called "recording of servo signals." 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. The formation of servo patterns will be described below using a magnetic tape as an example.

A servo pattern is usually formed along the longitudinal direction of the magnetic tape. Methods of control using servo signals (servo control) include timing-based servo (TBS), amplitude servo, frequency servo, and the like.

As indicated in ECMA (European Computer Manufacturers Association)-319, a magnetic tape conforming to the LTO (Linear Tape-Open) standard (generally called "LTO tape") employs a timing-based servo system. In this timing-based servo system, a servo pattern is composed of a plurality of non-parallel pairs of magnetic stripes (also called "servo stripes") arranged continuously in the longitudinal direction of the magnetic tape. The reason why the servo pattern is composed of a pair of non-parallel magnetic stripes is to inform the servo signal reading element passing over the servo pattern of its passing position. Specifically, the pair of magnetic stripes are formed so that the interval between them changes continuously along the width direction of the magnetic tape. and the relative position of the servo signal reading element. This relative position information enables tracking of the data tracks. For this reason, a plurality of servo tracks are usually set on the servo pattern along the width direction of the magnetic tape.

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

In one form, as disclosed in JP-A-2004-318983, each servo band includes information indicating the number of the servo band (“servo band ID (identification)” or “UDIM (Unique Data Band Identification)”). Method (also called information) is embedded. This servo band ID is recorded by shifting a specific one of a plurality of pairs of servo stripes in the servo band so that the position thereof is relatively displaced in 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 is unique for each servo band, so that one servo band can be uniquely specified only by reading one servo band with a servo signal reading element.

As a method for uniquely specifying a servo band, there is also a method using a staggered method as indicated in ECMA-319. In this staggered method, groups of non-parallel pairs of magnetic stripes (servo stripes) arranged continuously in the longitudinal direction of the magnetic tape are recorded so as to be shifted in the longitudinal direction of the magnetic tape for each servo band. do. Since this combination of shifts between adjacent servo bands is unique for the entire magnetic tape, the servo band can be uniquely identified when reading the servo pattern with two servo signal reading elements. It is possible.

Each servo band also normally has embedded therein information indicating the longitudinal position of the magnetic tape (also called "LPOS (Longitudinal Position) information"), as specified in ECMA-319. Like the UDIM information, this LPOS information is also recorded by shifting the positions of a pair of servo stripes in the longitudinal direction of the magnetic tape. However, unlike the UDIM information, the same signal is recorded in each servo band in this LPOS information.

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

The servo pattern forming head is called a servo write head. The servo write 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 current pulses to the coils, 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 onto the magnetic tape by inputting a current pulse while the magnetic tape is running over the servo write head, thereby forming the servo pattern. can be done. The width of each gap can be appropriately set according to the density of the servo pattern to be formed. The width of each gap can be set to, for example, 1 μm or less, 1 to 10 μm, or 10 μm or more.

Before forming servo patterns on a magnetic tape, the magnetic tape is usually subjected to demagnetization (erase) processing. 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 erase is performed by gradually decreasing the strength of the magnetic field while reversing the direction of the magnetic field applied to the magnetic tape. DC erase, on the other hand, is performed by applying a unidirectional magnetic field to the magnetic tape. There are two methods of DC erase. The first method is a horizontal DC erase that applies a unidirectional magnetic field along the length of the magnetic tape. The second method is perpendicular DC erase, in which a unidirectional magnetic field is applied along the thickness of the magnetic tape. The erase 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 according to the erase direction. For example, when horizontal DC erasing is performed on a magnetic tape, the servo pattern is formed so that the direction of the magnetic field is opposite to the direction of erasing. As a result, the output of the servo signal obtained by reading the servo pattern can be increased. Incidentally, as disclosed in Japanese Patent Application Laid-Open No. 2012-53940, when a magnetic pattern is transferred to a perpendicular 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 a magnetic pattern is transferred to a magnetic tape that has been horizontally DC-erased using the gap, a servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

A magnetic tape is usually housed in a magnetic tape cartridge, and the magnetic tape cartridge is loaded into a magnetic recording/reproducing apparatus.

A magnetic tape cartridge generally contains a magnetic tape wound on a reel inside a cartridge body. The reel is rotatably provided inside the cartridge body. As magnetic tape cartridges, a single reel type magnetic tape cartridge having one reel inside the cartridge body and a dual reel type magnetic tape cartridge having two reels inside the cartridge body are widely used. When a single-reel type magnetic tape cartridge is mounted on a magnetic recording/reproducing apparatus for recording and/or reproducing data on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and placed on the reel of the magnetic recording/reproducing apparatus. be wound up. 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 fed and wound between the reel (supply reel) of the magnetic tape cartridge and the reel (take-up reel) of the magnetic recording/reproducing device. During this time, data is recorded and/or reproduced by contact and sliding between the magnetic head and the surface of the magnetic layer of the magnetic tape. On the other hand, a twin-reel magnetic tape cartridge has both a supply reel and a take-up reel inside the magnetic tape cartridge. The magnetic tape cartridge may be either a single reel type magnetic tape cartridge or a twin reel type magnetic tape cartridge. For other details of the magnetic tape cartridge, known techniques can be applied.

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

In the present invention and in this specification, the term "magnetic recording/reproducing apparatus" means a device capable of at least one of recording data on a magnetic recording medium and reproducing data recorded on the magnetic recording medium. do. Such devices are commonly called drives. The magnetic recording/reproducing device may be a sliding type magnetic recording/reproducing device. A sliding type magnetic recording/reproducing apparatus is an apparatus in which a magnetic layer surface and a magnetic head are in contact with each other and slide when data is recorded on a magnetic recording medium and/or the recorded data is reproduced.

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 a reproducing head capable of reproducing data recorded on the magnetic recording medium. can also be In one form, the magnetic recording/reproducing apparatus can include both a recording head and a reproducing head as separate magnetic heads. In another aspect, 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 (reproducing element) in one magnetic head. It can also have a configuration Hereinafter, elements for recording data and elements for reproducing data are collectively referred to as "data elements". As the reproducing 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 reproducing 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. A magnetic head for recording and/or reproducing data may also include a servo signal reading element. Alternatively, the magnetic recording/reproducing apparatus may include a magnetic head (servo head) having a servo signal reading element as a separate head from the magnetic head that records and/or reproduces data. For example, a magnetic head for recording data and/or reproducing recorded data (hereinafter also referred to as a "recording/reproducing head") may include two servo signal reading elements. can read two adjacent servo bands simultaneously. One or more data elements can be positioned between the two servo signal read elements.

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

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

The present invention will be described below based on examples. However, the present invention is not limited to the embodiments shown in the examples. "Parts" and "%" described below indicate "mass parts" and "mass%" unless otherwise specified. eq is equivalent and is a unit that cannot be converted to SI units. In addition, the processes and evaluations described below were performed in an environment with an ambient temperature of 23° C.±1° C. unless otherwise specified.

[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): 100.0 parts Oleic acid: 2.0 parts Vinyl chloride copolymer (MR-104 manufactured by Kaneka Corporation): 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 polymer (DISPERBYK-102 manufactured by BYK-Chemie): 6.0 parts Methyl ethyl ketone: 150.0 parts Cyclohexanone: 150.0 parts (abrasive liquid)
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 70000, SO ₃ Na group: 0.1 meq/g)
2,3-dihydroxynaphthalene: 0.6 parts Cyclohexanone: 23.0 parts (projection forming agent liquid)
Projection forming agent (see Table 5): 1.3 parts
Methyl ethyl ketone: 9.0 parts Cyclohexanone: 6.0 parts (lubricant and hardener liquid)
Stearic acid: 3.0 parts Stearamide: 0.3 parts Butyl stearate: 6.0 parts Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate (Coronate (registered trademark) L manufactured by Tosoh Corporation): 3 .0 copy

<Prescription of composition for forming non-magnetic layer>
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 70000, 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 group-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>
A composition for forming a magnetic layer was prepared by the following method.
A magnetic liquid was prepared by dispersing (bead dispersion) the various components of the magnetic liquid described above for 24 hours using a vertical batch sand mill. As dispersion beads, zirconia beads with a bead diameter of 0.5 mm were used.
Various components of the abrasive liquid were mixed and put into a horizontal bead mill dispersing machine together with zirconia beads with 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 was 80%. After adjustment, a bead mill dispersion treatment was performed for 120 minutes, and the treated liquid was taken out and subjected to ultrasonic dispersion filtration treatment using a flow-type ultrasonic dispersion filtration device. Thus, an abrasive liquid was prepared.
The projection-forming agent liquid is a dispersion liquid obtained by mixing the components of the projection-forming agent liquid and then performing ultrasonic treatment (dispersion treatment) for 60 minutes at an ultrasonic output of 500 watts per 200 cc using a horn-type ultrasonic disperser. was filtered through a filter with a pore size of 0.5 μm.
The magnetic liquid, the abrasive liquid, the protrusion-forming agent liquid, and the remaining components (lubricant and curing agent liquid) were introduced into a dissolver stirrer, stirred at a peripheral speed of 10 m/sec for 30 minutes, and then flow-type ultrasonic wave was applied. After three-pass treatment with a disperser at a flow rate of 7.5 kg/min, the mixture was filtered through a filter with a pore size of 1 μm to prepare a composition for forming a magnetic layer.

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

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

<Production of magnetic tape>
A magnetic tape was produced as shown in FIG. The details are as follows.
A support made of polyethylene naphthalate having a thickness of 5.0 μm was delivered from a delivery section, and a composition for forming a non-magnetic layer was applied to one surface of the support in a first coating section so that the thickness after drying was 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 the residence time shown in Table 5 to perform a cooling step, and then a first heat treatment zone with an atmospheric temperature of 100 ° C. A non-magnetic layer was formed by passing through and drying by heating.
After that, the composition for forming the magnetic layer prepared above was coated on the non-magnetic layer so that the thickness after drying was 0.1 μm on the second coated portion to form a coated layer. While this coating layer was in a wet state (undried state), a magnetic field with a magnetic field strength of 0.3 T was applied in the orientation zone in the vertical direction to the surface of the coating layer of the composition for forming the magnetic layer to perform vertical orientation treatment. After that, it was dried in the second heat treatment zone (ambient temperature 100°C).
After that, in the third coating portion, the above-prepared backing was applied to the surface of the polyethylene naphthalate support opposite to the surface on which the non-magnetic layer and the magnetic layer were formed so that the thickness after drying was 0.5 μm. The composition for forming a coat layer was applied to the surface of the non-magnetic support to form a coating layer, and the formed coating layer was dried in the third heat treatment zone (atmospheric temperature 100°C).
After that, using a calender roll composed only of metal rolls, calendering (surface smoothing processing) was performed.
After that, heat treatment was performed for 36 hours in an environment with an ambient temperature of 70°C. A magnetic tape was produced by slitting to a width of 1/2 inch (0.0127 m) after heat treatment.
With the magnetic layer of the manufactured magnetic tape demagnetized, a servo pattern having an arrangement and shape conforming to the LTO Ultrium format was formed on the magnetic layer by a servo write head mounted on a servo writer. As a result, a magnetic tape having a data band, a servo band, and a guide band arranged in accordance with the LTO Ultrium format on the magnetic layer and having a servo pattern arranged and shaped in accordance with the LTO Ultrium 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 various items shown in Table 5 were changed as shown in Table 5.
In Table 5, the magnetic tapes were produced by a manufacturing process that does not include a cooling zone in the non-magnetic layer forming process in the comparative examples described as "unimplemented" in the cooling zone staying time column.

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

[Ferromagnetic powder]
In Table 5, "BaFe" indicates hexagonal barium ferrite powder with 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 activation volume and anisotropy constant Ku of various ferromagnetic powders described below are obtained by the method described above using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) for each ferromagnetic powder. value.
Also, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe using a vibrating sample magnetometer (manufactured by Toei Industry 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.
1707 _g of SrCO3, 687 _g of _H3BO3 , 1120 g of _Fe2O3 , 45 g of Al(OH) ₃ , 24 g of _BaCO3 , 13 g of _CaCO3 , and 235 g _{of Nd2O3} were weighed and mixed in _a mixer. A raw material mixture was obtained by mixing.
The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1390° C., and while the melt was being stirred, a tap hole provided at the bottom of the platinum crucible was heated, and the melt was tapped in a rod shape at a rate of about 6 g/sec. . The tapped liquid was rolled and quenched with a water-cooled twin roller to prepare an amorphous body.
280 g of the produced amorphous material was placed in an electric furnace, heated to 635° C. (crystallization temperature) at a heating rate of 3.5° C./min, and held at the same temperature for 5 hours to produce hexagonal strontium ferrite particles. Precipitated (crystallized).
Next, the crystallized product obtained above containing hexagonal strontium ferrite particles was coarsely pulverized in a mortar, and 1000 g of zirconia beads having a particle size of 1 mm and 800 mL of 1% concentration of acetic acid aqueous solution were added to a glass bottle and dispersed for 3 hours using a paint shaker. did After that, the resulting dispersion was separated from the beads and placed in a stainless steel beaker. After the dispersion liquid was allowed to stand at a liquid temperature of 100°C for 3 hours to dissolve the glass component, it was precipitated in a centrifugal separator, washed by repeating decantation, and placed in a heating furnace at a temperature of 110°C for 6 hours. After drying for a few hours, hexagonal strontium ferrite powder was obtained.
The hexagonal strontium ferrite powder (“SrFe1” in Table 5) obtained above had an average particle size of 18 nm, an activated volume of 902 nm ³ , an anisotropic constant Ku of 2.2×10 ⁵ J/m ³ , The mass magnetization σs was 49 A·m ² /kg.
12 mg of sample powder was taken from the hexagonal strontium ferrite powder obtained above, and the sample powder was partially dissolved under the dissolution conditions exemplified above. The surface layer content was determined.
Separately, 12 mg of sample powder was taken from the hexagonal strontium ferrite powder obtained above, and the sample powder was completely dissolved under the dissolution conditions exemplified above. Atomic bulk content was determined.
The content of neodymium atoms (bulk content) with respect to 100 atomic % of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic %. The content of neodymium atoms in the surface layer was 8.0 atomic %. The ratio of the surface layer portion content rate to the bulk content rate, "surface layer portion content rate/bulk content rate", was 2.8, confirming that neodymium atoms were unevenly distributed in the surface layer of the particles.

The fact that the powder obtained above exhibits the crystal structure of hexagonal ferrite is confirmed by scanning CuKα rays under the conditions of a voltage of 45 kV and an intensity of 40 mA and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). confirmed. The powder obtained above exhibited a crystal structure of magnetoplumbite-type (M-type) hexagonal ferrite. The crystal phase detected by X-ray diffraction analysis was a magnetoplumbite single phase.
PANalytical X'Pert Pro diffractometer, PIXcel detector Soller slits for incident and diffracted beams: 0.017 radians Fixed divergence slit angle: ¼ degree Mask: 10 mm
Anti-scattering slit: 1/4 degree Measurement mode: continuous Measurement time per step: 3 seconds Measurement speed: 0.017 degree per second Measurement step: 0.05 degree

<Method 2 for producing hexagonal strontium ferrite powder>
"SrFe2" shown in Table 5 is a hexagonal strontium ferrite powder produced by the following method.
1725 _g of SrCO3, 666 _g of _H3BO3 , 1332 g of _Fe2O3 , 52 g of Al(OH) ₃ , 34 g of _CaCO3 and 141 _g of _BaCO3 were weighed and mixed in a mixer to obtain a raw material mixture.
The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1380° C., and the melt was stirred while heating the outlet provided at the bottom of the platinum crucible to dispense the melt in a rod shape at a rate of about 6 g/sec. . The tapped liquid was quench-rolled with water-cooled twin rolls to prepare an amorphous body.
280 g of the obtained amorphous material was placed in an electric furnace, heated to 645° C. (crystallization temperature), and held at the same temperature for 5 hours to precipitate (crystallize) hexagonal strontium ferrite particles.
Next, the crystallized product obtained above containing hexagonal strontium ferrite particles was coarsely pulverized in a mortar, and 1000 g of zirconia beads having a particle size of 1 mm and 800 mL of 1% concentration of acetic acid aqueous solution were added to a glass bottle and dispersed for 3 hours using a paint shaker. did After that, the resulting dispersion was separated from the beads and placed in a stainless steel beaker. After the dispersion liquid was allowed to stand at a liquid temperature of 100°C for 3 hours to dissolve the glass component, it was precipitated in a centrifugal separator, washed by repeating decantation, and placed in a heating furnace at a temperature of 110°C for 6 hours. After drying for a few hours, hexagonal strontium ferrite powder was obtained.
The obtained hexagonal strontium ferrite powder (“SrFe2” in Table 5) had an average particle size of 19 nm, an activated volume of 1102 nm ³ , an anisotropy constant Ku of 2.0×10 5 J/m 3 , and a mass magnetization of 2.0×10 ⁵ J/m ³ . σs was 50 A·m ² /kg.

<Method for producing ε-iron oxide powder>
“ε-iron oxide” shown in Table 5 is ε-iron oxide powder produced by the following method.
8.3 g of iron (III) nitrate nonahydrate, 1.3 g of gallium (III) nitrate octahydrate, 190 mg of cobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and 4.0 g of an aqueous ammonia solution having a concentration of 25% was added to a solution of 1.5 g of polyvinylpyrrolidone (PVP) in an air atmosphere at an ambient temperature of 25° C. while stirring using a magnetic stirrer. , and the mixture was stirred for 2 hours while maintaining the ambient temperature of 25°C. An aqueous citric acid solution obtained by dissolving 1 g of citric acid in 9 g of pure water was added to the obtained solution, 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 with an internal 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 an ammonia aqueous solution having a concentration of 25% was added dropwise while stirring. After stirring for 1 hour while maintaining the temperature at 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 an internal temperature of 80°C for 24 hours to obtain a ferromagnetic powder precursor. Obtained.
The obtained ferromagnetic powder precursor was placed in a heating furnace with an internal temperature of 1000° C. in an air atmosphere, and heat-treated for 4 hours.
The heat-treated ferromagnetic powder precursor was put into a 4 mol/L sodium hydroxide (NaOH) aqueous solution, and the liquid temperature was maintained at 70° C. and stirred for 24 hours to obtain the heat-treated ferromagnetic powder. A silicic acid compound as an impurity was removed from the precursor.
After that, the ferromagnetic powder from which the silicic acid compound was removed was collected by centrifugal separation and washed with pure water to obtain the ferromagnetic powder.
When the composition of the obtained ferromagnetic powder was confirmed by high-frequency inductively coupled plasma-optical emission spectrometry (ICP-OES), Ga, Co and Ti-substituted ε-iron oxide (ε-Ga _{0 .28} Co _0.05 Ti _0.05 Fe _1.62 O ₃ ). In addition, X-ray diffraction analysis was performed under the same conditions as described in the method 1 for producing hexagonal strontium ferrite powder, and from the peaks of the X-ray diffraction pattern, the ferromagnetic powder obtained was found to be in the α phase and the γ phase. It was confirmed that it has a single-phase ε-phase crystal structure (ε-iron oxide type crystal structure) that does not contain a crystal structure of
The obtained ε-iron oxide powder (“ε-iron oxide” in Table 5) had an average particle size of 12 nm, an activated volume of 746 nm ³ , and an anisotropic constant Ku of 1.2×10 ⁵ J/m ^{3 .} , and the mass magnetization σs was 16 A·m ² /kg.

[Evaluation method]
(1) C concentration derived from CH after pressing For each magnetic tape of Examples and Comparative Examples, under an atmosphere temperature of 20 to 25 ° C. and a relative humidity of 40 to 60%, a 7-step structure composed only of metal rolls was used. Using a calendering machine equipped with calender rolls, the magnetic tape was run at a speed of 20 m/min in the longitudinal direction with a tension of 0.5 N/m between the two rolls (without heating the rolls). was passed six times in total, so that the surface of the magnetic layer was pressed with a surface pressure of 70 atm when passing between the rolls.
X-ray photoelectron spectroscopy analysis was performed using an ESCA device on the magnetic layer surface (measurement area: 300 μm × 700 μm) of the magnetic layer of the measurement sample cut out from the magnetic tape after pressing by the following method. C concentration was calculated.

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

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

(ii) Narrow scan measurement All the elements detected in (i) above were subjected to narrow scan measurement (measurement conditions: see Table 3). Using data processing software (Vision 2.2.6) attached to the apparatus, the atomic concentration (unit: atomic %) of each element detected from the peak area of each element was calculated. The C concentration was also calculated here.

(iii) Acquisition of C1s spectrum A C1s spectrum was acquired under the measurement conditions described in Table 4. After correcting the shift (physical shift) due to the charging of the sample using the data processing software (Vision 2.2.6) attached to the acquired C1s spectrum, the C1s spectrum was corrected using the same software. A fitting process (peak separation) was performed. Gauss-Lorentz composite function (Gaussian component 70%, Lorentzian component 30%) is used for peak separation, C1s spectrum fitting is performed by the nonlinear least squares method, and the ratio of C-H peaks in the C1s spectrum (peak area ratio) was calculated. The C concentration derived from C—H was calculated by multiplying the C concentration obtained in (ii) above by the calculated C—H peak area ratio.

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

(2) Evaluation of running stability after pressing at a pressure of 70 atm For each of the magnetic tapes of Examples and Comparative Examples, after pressing in (1) above, PES (Position Error Signal) was obtained by the following method.
The servo pattern was read with a verify head on the servo writer used to form the servo pattern. The verify head is a reading magnetic head for checking the quality of the servo pattern formed on the magnetic tape. A reading element is arranged at a position corresponding to the direction position).
The verify head is connected to a known PES calculation circuit that calculates the head positioning accuracy in the servo system as a PES from an electrical signal obtained by reading a servo pattern with the verify head. The PES arithmetic circuit calculates the displacement in the width direction of the magnetic tape from the input electric signal (pulse signal) at any time, and applies a high-pass filter (cutoff: 500 cycles/m ) was calculated as the PES. 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 the magnetic tapes of Examples exhibited excellent running stability after pressing at a pressure of 70 atm, that is, after long-term storage. Such a magnetic tape can stably run in a magnetic recording/reproducing apparatus even after it is stored on a reel in a magnetic tape cartridge for a long period of time after infrequently accessed information has been recorded. There is, and it is suitable as a recording medium for archiving.

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

Claims (8)

A magnetic recording medium having a magnetic layer containing ferromagnetic powder on a nonmagnetic support,
a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer;
The non-magnetic layer has a thickness of 0.1 μm or more and 1.5 μm or less,
containing at least one component selected from the group consisting of fatty acids and fatty acid amides in the portion on the magnetic layer side of the non-magnetic support;
C—H origin calculated from the C—H peak area ratio in the C1s spectrum obtained by X-ray photoelectron spectroscopy performed at a photoelectron take-off angle of 10 degrees on the surface of the magnetic layer after pressing the magnetic layer at a pressure of 70 atm A magnetic recording medium having a C concentration of 45 atomic % or more. 2. The magnetic recording medium according to claim 1, wherein the C--H derived C concentration is 45 atomic % or more and 80 atomic % or less. 3. The magnetic recording medium according to claim 1, wherein said magnetic layer contains inorganic oxide particles. 4. The magnetic recording medium according to claim 3, wherein said inorganic oxide particles are composite particles of an inorganic oxide and a polymer. 5. The magnetic recording medium according to claim 1, wherein the non- magnetic layer has a thickness of 0.1 μm or more and 1.0 μm or less . 6. The magnetic recording medium according to any one of claims 1 to 5, further comprising a backcoat layer containing a nonmagnetic powder on the surface of the nonmagnetic support opposite to the surface having the magnetic layer. 7. The magnetic recording medium according to claim 1, which is a magnetic tape. a magnetic recording medium according to any one of claims 1 to 7;
a magnetic head;
A magnetic recording and reproducing device including

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