JP2020140757A - Magnetic tape, magnetic tape cartridge, and magnetic record reproducer - Google Patents

Abstract

To provide a coated magnetic tape including a magnetic layer containing ferromagnetic powder selected from a group of hexagonal crystal strontium ferrite powder and ε-iron oxide powder and a back coat layer, and capable of suppressing output deterioration of a servo signal.SOLUTION: The magnetic tape comprises: a magnetic layer including ferromagnetic powder and binder on one surface side of a nonmagnetic support; and a back coat layer including the nonmagnetic powder and the binder on the other surface side. The ferromagnetic powder is selected from a group of hexagonal crystal strontium ferrite powder and ε-iron oxide powder. The magnetic layer has a servo pattern. The number of protrusions with height of 50 nm or more and less than 75 nm on the surface of the back coat layer is in the range of 800-1500 pieces/6400 μm2. A magnetic tape cartridge and a magnetic record reproducer including the magnetic tape are also provided.SELECTED DRAWING: None

Description

The present invention relates to magnetic tapes, magnetic tape cartridges and magnetic recording / playback devices.

There are tape-shaped and disk-shaped magnetic recording media, and tape-shaped magnetic recording media, that is, magnetic tapes are mainly used for data storage applications such as data backup and archiving.

With the enormous increase in the amount of information (data) in recent years, magnetic tapes are required to have a higher recording capacity (higher capacity). As a means for increasing the capacity, it is possible to increase the recording density by arranging more data tracks on the magnetic layer by narrowing the width of the data tracks.

However, if the width of the data track is narrowed, it becomes difficult for the magnetic head to accurately follow the data track when the magnetic tape is run in the magnetic recording / playback device to record and / or reproduce the data, and the recording and / or recording and / or Or, it becomes easy to cause an error during playback. Therefore, in recent years, as a means for reducing the occurrence of such an error, a system that performs head tracking using a servo signal (hereinafter, referred to as a "servo system") has been proposed and put into practical use (for example). See Patent Document 1).

U.S. Pat. No. 5,689,384

Among the servo systems, in the magnetic servo system, the servo light head (servo pattern forming head) and the surface of the magnetic layer are brought into contact with each other and slid to form a servo pattern on the magnetic layer, and this servo pattern is magnetically formed. Head tracking is performed by the servo signal obtained by reading the system. More details are as follows.
First, the servo signal reading element reads the servo pattern formed on the magnetic layer to obtain a servo signal. Next, the position of the magnetic head in the magnetic recording / playback device is controlled according to the obtained servo signal to make the magnetic head follow the data track. As a result, when the magnetic tape is run in the magnetic recording / playback device in order to record data on the magnetic tape or reproduce the recorded data, even if the position of the magnetic tape fluctuates with respect to the magnetic head, the magnetic head is moved. It can be made to follow the data track.

By the way, magnetic recording media are roughly classified into two types, a coating type and a metal thin film type. The coating type magnetic tape has a non-magnetic support and a magnetic layer containing a ferromagnetic powder and a binder. Further, a coating type magnetic tape having a backcoat layer containing a non-magnetic powder and a binder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support is also known.

Various ferromagnetic powders have been proposed as ferromagnetic powders used for the magnetic layer of a coating type magnetic recording medium. In recent years, hexagonal strontium ferrite and ε-iron oxide powder have been used from the viewpoint of high-density recording suitability. It is attracting attention.

In view of the above points, the present inventor has provided a coating type magnetic tape having a magnetic layer containing a ferromagnetic powder selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder and a backcoat layer. We considered applying it to. However, as a result of examination, when head tracking is continued while the magnetic tape is running in the servo system, the output of the servo signal obtained by reading the servo pattern by the servo signal reading element is reduced compared to the initial stage of running (hereinafter, the phenomenon). It has been clarified that "decrease in servo signal output") occurs. The decrease in the output of the servo signal causes a decrease in the accuracy of making the magnetic head follow the data track in the servo system. Therefore, in order for the servo system to more accurately record data on the magnetic tape and / or to reproduce the data recorded on the magnetic tape more accurately, it is desirable to suppress a decrease in the output of the servo signal.

One aspect of the present invention has a magnetic layer and a backcoat layer containing a ferromagnetic powder selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder, and can suppress a decrease in the output of a servo signal. It is an object of the present invention to provide a possible coating type magnetic tape.

One aspect of the present invention is
A magnetic tape having a magnetic layer containing a ferromagnetic powder and a binder on one surface side of a non-magnetic support and a backcoat layer containing a non-magnetic powder and a binder on the other surface side.
The above-mentioned ferromagnetic powder is a ferromagnetic powder selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder.
The magnetic layer has a servo pattern and has a servo pattern.
A magnetic tape, wherein the number of protrusions having a height of 50 nm or more and less than 75 nm on the surface of the backcoat layer is in the range of 800 to 1500 pieces / 6400 μm ² .
Regarding.

In one aspect, the number of protrusions having a height of 75 nm or more on the surface of the backcoat layer can be 750/6400 μm ² or less.

In one aspect, the difference between the spacing Safter measured by optical interferometry on the surface of the magnetic layer _after washing with methyl ethyl ketone and the spacing S _before measured by optical interferometry on the surface of the magnetic layer before cleaning with methyl ethyl ketone. _(S after _{-S before)} may be equal to or less than 0nm super 15.0 nm. In the following, the above difference will also be referred to as "spacing difference _{before and after} washing with methyl ethyl ketone ( _After- S _before )" or simply "difference ( _After- S _before )". )

In one aspect, the magnetic tape can have a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

One aspect of the present invention relates to a magnetic tape cartridge containing the above magnetic tape.

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

According to one aspect of the present invention, it has a magnetic layer and a backcoat layer containing a ferromagnetic powder selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder, and suppresses a decrease in the output of a servo signal. It is possible to provide a coating type magnetic tape capable of this. Further, according to one aspect of the present invention, it is possible to provide a magnetic recording / reproducing device including such a magnetic tape.

An example of arranging the data band and the servo band is shown. An example of arranging the servo pattern of the LTO (Linear Tape-Open) Ultram format tape is shown.

[Magnetic tape]
One aspect of the present invention is magnetic having a magnetic layer containing a ferromagnetic powder and a binder on one surface side of a non-magnetic support and a backcoat layer containing a non-magnetic powder and a binder on the other surface side. In the tape, the ferromagnetic powder is a ferromagnetic powder selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder, and the magnetic layer has a servo pattern and is the backcoat layer. The present invention relates to a magnetic tape in which the number of protrusions having a height of 50 nm or more and less than 75 nm on the surface is in the range of 800 to 1500 pieces / 6400 μm ² .

In the formation of the servo pattern on the magnetic tape, usually, the magnetization region (that is, the servo pattern) is sequentially formed in the longitudinal direction of the magnetic layer while the magnetic tape is run to bring the surface of the magnetic layer into contact with the servo light head and slide it. It is done by doing. The inventor of the present invention sequentially forms the servo light head because the spacing between the magnetic layer surface and the servo light head fluctuates when the servo pattern is formed by the servo light head, which is the main cause of the decrease in the output of the servo signal described above. It is presumed that the magnetic force of the servo pattern to be used gradually decreases. In the magnetic layer having the servo pattern formed in this way, it is considered that the output of the servo signal decreases while the servo signal reading element continues to read the servo pattern (continues to reproduce the servo signal) in the servo system. .. The reason why such a phenomenon is likely to occur in a magnetic layer containing a ferromagnetic powder selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder is that it is conventionally used as a ferromagnetic powder for a coating type magnetic recording medium. The magnetic layer containing the ferromagnetic powder selected from the group consisting of the hexagonal strontium ferrite powder and the ε-iron oxide powder is generally different from the magnetic layer containing the ferromagnetic powder (for example, hexagonal barium ferrite powder). Since the square magnetic field Hk is high, it is presumed that it is easily affected by the spacing fluctuation between the magnetic layer surface and the servo light head.
On the other hand, on the surface of the backcoat layer of the magnetic tape, the number of protrusions having a height of 50 nm or more and less than 75 nm is in the range of 800 to 1500 pieces / 6400 μm ² , which means that the magnetic tape is used for forming a servo pattern. It is presumed that it contributes to improving the running stability when running. Further, when the magnetic tape is run for forming the servo pattern, the magnetic tape is usually sent out from the sending portion and wound up by the winding portion. On the surface of the backcoat layer of the magnetic tape, the number of protrusions having a height of 50 nm or more and less than 75 nm is in the range of 800 to 1500 pieces / 6400 μm ² , in order to improve the winding stability at the winding portion. Is also presumed to contribute. As a result, it is considered that the above results in suppressing the spacing fluctuation between the magnetic layer surface and the servo light head. This can suppress a decrease in the output of the servo signal in the magnetic tape having a magnetic layer containing a ferromagnetic powder selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder and a backcoat layer. The present inventor considers the reason.
However, the above includes the inventor's inference, and the present invention is not limited to such inference. Further, the present invention is not limited to other inferences described in the present specification.
Hereinafter, the magnetic tape will be described in more detail. In the present invention and the present specification, the "surface of the backcoat layer" of the magnetic tape is synonymous with the surface of the magnetic tape on the backcoat layer side, and the "surface of the magnetic layer" is the surface of the magnetic tape. It is synonymous with the surface on the magnetic layer side.

<Back coat layer>
(Number of protrusions)
The magnetic tape has a backcoat layer containing a non-magnetic powder and a binder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support. The number of protrusions having a height of 50 nm or more and less than 75 nm on the surface of the backcoat layer is in the range of 800 to 1500 pieces / 6400 μm ² . From the viewpoint of suppressing the output decrease of the servo signal, the number of the protrusions is 800 pieces / 6400 μm ² or more, more preferably 900 pieces / 6400 μm ² or more, and further preferably 950 pieces / 6400 μm ² or more. preferable. From the same viewpoint, the number of the protrusions is 1500 pieces / 6400 μm ² or less, more preferably 1450 pieces / 6400 μm ² or less, and further preferably 1400 pieces / 6400 μm ² or less.
Further, from the viewpoint of further suppressing the decrease in the output of the servo signal, the number of protrusions having a height of 75 nm or more on the surface of the backcoat layer is preferably 750/6400 μm ² or less, and 700/6400 μm ^2. It is more preferably 650 pieces / 6400 μm ² or less, further preferably 600 pieces / 6400 μm ² or less, and even more preferably 500 pieces / 6400 μm ² or less. The number of protrusions having a height of 75 nm or more on the surface of the backcoat layer is, for example, 0 pieces / 6400 μm ² or more, 50 pieces / 6400 μm ² or more, 100 pieces / 6400 μm ² or more, or 150 pieces / 6400 μm ² or more. Can be done.

The number of protrusions having a height of 50 nm or more and less than 75 nm and the number of protrusions having a height of 75 nm or more on the surface of the backcoat layer are determined by an atomic force microscope (AFM) in a region having an area of 80 μm × 80 μm on the surface of the backcoat layer. The value to be measured. The number of various protrusions is calculated as the arithmetic mean of the values obtained in the three different measurement regions on the surface of the backcoat layer. The following measurement conditions can be mentioned as an example of the measurement conditions. The number of protrusions shown in the examples described later is a value obtained by measurement under the following measurement conditions.

(Non-magnetic powder of back coat layer)
The backcoat layer is a layer containing a non-magnetic powder and a binder. The non-magnetic powder of the backcoat layer can be either one or both of carbon black and inorganic powder. For example, the number of protrusions can be controlled by using non-magnetic powders having different particle sizes as the non-magnetic powder of the back coat layer. For example, carbon black having an average particle size of 17 to 50 nm (hereinafter referred to as “fine particle carbon black”) and carbon black having an average particle size of 75 to 300 nm (hereinafter referred to as “coarse particle carbon black”) are described. ) In combination and adjusting the mixing ratio of both carbon blacks, the number of the above-mentioned protrusions can be controlled. In the backcoat layer, the mixing ratio of the fine particle carbon black having an average particle size of 17 to 50 nm and the coarse particle carbon black having an average particle size of 75 to 300 nm shall be in the range of the former: the latter = 98: 2 to 75:25. Is preferable, and the range is more preferably in the range of 97: 3 to 85:15. Regarding the content of carbon black in the backcoat layer, the total amount of carbon black can be in the range of, for example, 30 to 70% by mass with respect to the total solid content of the backcoat layer, and is 40 to 60% by mass. It is preferably in the range of%.

The backcoat layer can preferably contain one or more inorganic powders along with carbon black. Examples of the inorganic powder include an inorganic powder having an average particle size of 80 to 250 nm and a Mohs hardness of 5 to 9. Examples of the inorganic powder include non-magnetic powder generally used for the non-magnetic layer and non-magnetic powder generally used as an abrasive for the magnetic layer, and among them, α-iron oxide, α-alumina and the like are preferable. The content of the inorganic powder in the backcoat layer is preferably in the range of 3.0 to 40.0 parts by mass, and more preferably in the range of 5.0 to 30.0 with respect to 100.0 parts by mass of the binder. Is.

For binders contained in the backcoat layer and various additives that may be optionally contained, known techniques relating to the backcoat layer can be applied, and known techniques relating to the formulation of magnetic and / or non-magnetic layers shall be applied. You can also. For example, paragraphs 0018 to 0020 of JP-A-2006-331625 and the description of US Pat. No. 7,029,774, column 4, lines 65 to 5, line 38 can be referred to for the backcoat layer. .. Further, as a dispersant for the backcoat layer, for example, fatty acids having 8 to 18 carbon atoms such as caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, and linoleic acid, copper oleate, and copper. Phthalocyanin, barium sulfate, basic organic dye compounds and the like can be used. These may be used alone or in combination of two or more. The content of the dispersant in the backcoat layer can be, for example, 0.5 to 20.0 parts by mass with respect to 100.0 parts by mass of the binder.

<Magnetic layer>

(Ferromagnetic powder)
The magnetic layer of the magnetic tape contains a ferromagnetic powder selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder. It is preferable to use a ferromagnetic powder having a small average particle size from the viewpoint of improving the recording density. From this point, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, further preferably 40 nm or less, further preferably 35 nm or less, and more preferably 30 nm or less. It is even more preferably 25 nm or less, and even more preferably 20 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 8 nm or more, further preferably 10 nm or more, and further preferably 15 nm or more. Is more preferable, and 20 nm or more is even more preferable.

The magnetic layer of the magnetic tape may contain only hexagonal strontium ferrite powder as the ferromagnetic powder, may contain only ε-iron oxide powder, and may contain only hexagonal strontium ferrite powder and ε-. Iron oxide powder may be contained. Hereinafter, the hexagonal strontium ferrite powder and the ε-iron oxide powder will be further described.

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

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

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

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

The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the hexagonal strontium ferrite powder contains rare earth atoms at a content of 0.5 to 5.0 atomic% (bulk content) with respect to 100 atomic% of iron atoms. In one aspect, the hexagonal strontium ferrite powder containing rare earth atoms can have uneven distribution on the surface layer of rare earth atoms. The "uneven distribution of the surface layer of rare earth atoms" in the present invention and the present specification refers to the rare earth atom content with respect to 100 atomic% of iron atoms in the solution obtained by partially dissolving hexagonal strontium ferrite powder with an acid. “Rare earth atom surface layer content” or simply “surface layer content” for rare earth atoms) is 100 atomic% of iron atoms in the solution obtained by completely dissolving hexagonal strontium ferrite powder with an acid. Rare earth atom content (hereinafter referred to as "rare earth atom bulk content" or simply referred to as "bulk content" for rare earth atoms).
Rare earth atom surface layer content / Rare earth atom bulk content> 1.0
Means that the ratio of The rare earth atom content of the hexagonal strontium ferrite powder described later is synonymous with the rare earth atom bulk content. On the other hand, partial dissolution using an acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder. Therefore, the rare earth atom content in the solution obtained by partial dissolution is the composition of the hexagonal strontium ferrite powder. It is the rare earth atom content in the surface layer of the particles. The fact that the rare earth atom surface layer content satisfies the ratio of "rare earth atom surface layer content / rare earth atom bulk content>1.0" means that the rare earth atom is present in the surface layer of the particles constituting the hexagonal strontium ferrite powder. It means that it is unevenly distributed (that is, it exists more than inside). The surface layer portion in the present invention and the present specification means a partial region from the surface to the inside of the particles constituting the hexagonal strontium ferrite powder.

When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 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 the rare earth atoms are unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder contributes to suppressing the decrease in the regeneration output in the repeated regeneration. Conceivable. This is because the hexagonal strontium ferrite powder contains rare earth atoms at a bulk content in the above range, and the rare earth atoms are unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder. It is presumed that this is because it can be enhanced. The higher the value of the anisotropy constant Ku, the more the occurrence of a phenomenon called thermal fluctuation can be suppressed (in other words, the thermal stability can be improved). By suppressing the occurrence of thermal fluctuation, it is possible to suppress a decrease in the reproduction output during repeated reproduction. The uneven distribution of rare earth atoms on the surface layer of the hexagonal strontium ferrite powder contributes to stabilizing the spin of iron (Fe) sites in the crystal lattice of the surface layer, which results in anisotropy constant Ku. It is speculated that it will increase.
In addition, it is presumed that the use of hexagonal strontium ferrite powder, which has uneven distribution on the surface layer of rare earth atoms, as the ferromagnetic powder of the magnetic layer also contributes to suppressing the surface of the magnetic layer from being scraped by sliding with the magnetic head. To. That is, it is presumed that the hexagonal strontium ferrite powder having uneven distribution on the surface layer of rare earth atoms may contribute to the improvement of the running durability of the magnetic tape. This is because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder improves the interaction between the particle surface and the organic substances (for example, binder and / or additive) contained in the magnetic layer. As a result, it is presumed that the strength of the magnetic layer is improved.
The rare earth atom content (bulk content) is in the range of 0.5 to 4.5 atomic% from the viewpoint of further suppressing the decrease in the reproduction output in the repeated reproduction and / or further improving the running durability. It is more preferably in the range of 1.0 to 4.5 atomic%, further preferably in the range of 1.5 to 4.5 atomic%.

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

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

In the hexagonal strontium ferrite powder having uneven distribution on the surface layer of rare earth atoms, the rare earth atoms may be unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of uneven distribution is not limited. For example, a hexagonal strontium ferrite powder having an uneven distribution on the surface layer of a rare earth atom is partially dissolved under the dissolution conditions described later, and the content of the surface layer of the rare earth atom is completely dissolved under the dissolution conditions described later. The ratio of the atom to the bulk content, "surface layer content / bulk content" is more than 1.0, and can be 1.5 or more. When the "surface layer content / bulk content" is larger than 1.0, it means that rare earth atoms are unevenly distributed in the surface layer (that is, more than the inside) in the particles constituting the hexagonal strontium ferrite powder. To do. In addition, the ratio of the surface layer content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later to the bulk content of rare earth atoms obtained by total dissolution under the dissolution conditions described later, "Surface layer content / The "bulk content" can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in the hexagonal strontium ferrite powder having uneven distribution on the surface layer of rare earth atoms, the rare earth atoms need only be unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the above-mentioned "surface layer content / bulk content". The "rate" is not limited to the upper or lower limit illustrated.

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

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

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

As the crystal structure of hexagonal ferrite, magnetoplumbite type (also referred to as "M type"), W type, Y type and Z type are known. The hexagonal strontium ferrite powder may have any crystal structure. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder can be one in which a single crystal structure or two or more kinds of crystal structures are detected by X-ray diffraction analysis. For example, in one aspect, the hexagonal strontium ferrite powder can have only an M-type crystal structure detected by X-ray diffraction analysis. For example, M-type hexagonal ferrite is represented by the composition formula of AFe ₁₂ O ₁₉ . Here, A represents a divalent metal atom, and when the hexagonal strontium ferrite powder is M-type, A is only a strontium atom (Sr), or when A contains a plurality of divalent metal atoms. As mentioned above, the strontium atom (Sr) occupies the largest amount on the basis of atomic%. The divalent metal atom content of the hexagonal strontium ferrite powder is usually determined by the type of crystal structure of the hexagonal ferrite, and is not particularly limited. The same applies to the iron atom content and the oxygen atom content. The hexagonal strontium ferrite powder contains at least an iron atom, a strontium atom and an oxygen atom, and may further contain a rare earth atom. Further, the hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may contain an aluminum atom (Al). The content of aluminum atoms can be, for example, 0.5 to 10.0 atomic% with respect to 100 atomic% of iron atoms. From the viewpoint of further suppressing the decrease in regeneration output during repeated regeneration, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms and rare earth atoms, and the content of atoms other than these atoms is 100 iron atoms. It is preferably 10.0 atomic% or less, more preferably 0 to 5.0 atomic%, and may be 0 atomic%. That is, in one aspect, the hexagonal strontium ferrite powder does not have to contain atoms other than iron atoms, strontium atoms, oxygen atoms and rare earth atoms. The content expressed in atomic% above is the content (unit: mass%) of each atom obtained by completely dissolving the hexagonal strontium ferrite powder, and is converted to the value expressed in atomic% using the atomic weight of each atom. Calculated by conversion. Further, in the present invention and the present specification, "not contained" with respect to a certain atom means that the content is completely dissolved and the content measured by an ICP analyzer is 0% by mass. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The above-mentioned "not included" is used in the sense of including the inclusion in an amount less than the detection limit of the ICP analyzer. In one aspect, the hexagonal strontium ferrite powder can be free of bismuth atoms (Bi).

When the magnetic tape contains hexagonal strontium ferrite powder in the magnetic layer, the anisotropic magnetic field Hk of the magnetic layer is preferably 14 kOe or more, more preferably 16 kOe or more, and further preferably 18 kOe or more. preferable. Further, the anisotropic magnetic field Hk of the magnetic layer is preferably 90 kOe or less, more preferably 80 kOe or less, and further preferably 70 kOe or less.
The anisotropy magnetic field Hk in the present invention and the present specification means a magnetic field in which magnetization is saturated when a magnetic field is applied in the direction in which magnetization is difficult. The anisotropic magnetic field Hk can be measured using a known measuring device capable of measuring magnetic characteristics such as a vibrating sample magnetometer. In the magnetic layer containing the hexagonal strontium ferrite powder, the axial direction in which the magnetic layer is difficult to magnetize is the in-plane direction.

ε-Iron oxide powder In the present invention and the present specification, "ε-iron oxide powder" refers to a ferromagnetic powder in which an ε-iron oxide type crystal structure is detected as the main phase by X-ray diffraction analysis. And. For example, when the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is assigned to the ε-iron oxide type crystal structure, the ε-iron oxide type crystal structure is detected as the main phase. Judgment shall be made. As a method for producing ε-iron oxide powder, a method for producing ε-iron oxide powder, a reverse micelle method, and the like are known. All of the above manufacturing methods are known. Regarding the method for producing ε-iron oxide powder in which a part of Fe is substituted with a substituted atom such as Ga, Co, Ti, Al, Rh, for example, J.I. Jpn. Soc. Power Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mol. Mater. Chem. C, 2013, 1, pp. 5200-5206 and the like can be referred to. However, the method for producing ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer of the magnetic tape is not limited to the methods listed here.

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

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

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

When the magnetic tape contains ε-iron oxide powder in the magnetic layer, the anisotropic magnetic field Hk of the magnetic layer is preferably 18 kOe or more, more preferably 30 kOe or more, and further preferably 38 kOe or more. preferable. Further, the anisotropic magnetic field Hk of the magnetic layer is preferably 100 kOe or less, more preferably 90 kOe or less, and further preferably 75 kOe or less. In the magnetic layer containing ε-iron oxide powder, the axial direction in which the magnetic layer is difficult to magnetize is the in-plane direction.

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

As a method for collecting the sample powder from the magnetic tape for measuring the particle size, for example, the method described in paragraph 0015 of JP2011-048878A can be adopted.

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

Further, for the average needle-like ratio of the powder, the length of the minor axis of the particles, that is, the minor axis length is measured in the above measurement, and the value of (major axis length / minor axis length) of each particle is obtained, and the above 500 particles are obtained. Refers to the arithmetic average of the values obtained for a particle. Here, unless otherwise specified, the minor axis length is the length of the minor axis constituting the particle in the case of (1) in the above definition of the particle size, and the thickness or height in the case of the same (2). In the case of (3), there is no distinction between the major axis and the minor axis, so (major axis length / minor axis length) is regarded as 1 for convenience.
Unless otherwise specified, when the shape of the particles is specific, for example, in the case of the above definition of particle size (1), the average particle size is the average major axis length, and in the case of the same definition (2), the average particle size is Average plate diameter. In the case of the same definition (3), the average particle size is an average diameter (also referred to as an average particle size or an average particle size).

The content (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass. The components of the magnetic layer other than the ferromagnetic powder are at least a binder and may optionally include one or more additional additives. A high filling rate of the ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving the recording density.

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

In one aspect, a binder containing an active hydrogen-containing group can be used as the binder. The "active hydrogen-containing group" in the present invention and the present specification refers to a functional group capable of forming a crosslinked structure by causing a curing reaction of this group with a curable functional group and desorption of hydrogen atoms contained in this group. Say. Examples of the active hydrogen-containing group include a hydroxy group, an amino group (preferably a primary amino group or a secondary amino group), a mercapto group, a carboxy group and the like, and a hydroxy group, an amino group and a mercapto group are preferable. Is more preferable. In the binder containing an active hydrogen-containing group, the concentration of the active hydrogen-containing group is preferably in the range of 0.10 meq / g to 2.00 meq / g. “Eq” is an equivalent and is a unit that cannot be converted into SI units. The active hydrogen-containing group concentration can also be expressed in units of "mgKOH / g". In one aspect, in the resin containing active hydrogen-containing groups, the concentration of active hydrogen-containing groups is preferably in the range of 1 to 20 mgKOH / g.

In one aspect, a binder containing an acidic group can be used as the binder. The term "acidic group" as used in the present invention and the present specification is used to include the form of a group capable of releasing H ⁺ into an anion and a salt thereof by releasing H ⁺ in water or a solvent containing water (aqueous solvent). And. Specific examples of the acidic group include a sulfonic acid group _(-SO 3 H), sulfuric acid group (-OSO ₃ H), carboxyl group, phosphoric acid group, can be exemplified embodiment thereof and the like salts. For example, the salt form of a sulfonic acid group (-SO ₃ H) is a group represented by -SO ₃ M, where M represents an atom (eg, an alkali metal atom) that can be a cation in water or an aqueous solvent. means. This point is the same for the salt forms of the various groups described above. As an example of the binder containing an acidic group, for example, a resin containing at least one acidic group selected from the group consisting of a sulfonic acid group and a salt thereof (for example, polyurethane resin, vinyl chloride resin, etc.) can be mentioned. However, the resin contained in the magnetic layer is not limited to these resins. Further, in the binder containing an acidic group, the acidic group content can be in the range of, for example, 0.03 to 0.50 meq / g. The content of various functional groups such as acidic groups contained in the resin can be determined by a known method depending on the type of functional group. The binder can be used in the composition for forming a magnetic layer 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.

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

(Additive)
The magnetic layer contains a ferromagnetic powder and a binder, and may contain one or more additives, if necessary. As an example, the above-mentioned curing agent can be mentioned as an additive. Examples of the additive contained in the magnetic layer include non-magnetic powder (for example, inorganic powder, carbon black, etc.), lubricant, dispersant, dispersion aid, fungicide, antistatic agent, antioxidant, and the like. Can be done. For example, for lubricants, paragraphs 0030 to 0033, 0035 and 0036 of JP2016-126817A can be referred to. A lubricant may be contained in the non-magnetic layer described later. For the lubricant that can be contained in the non-magnetic layer, reference can be made to paragraphs 0030 to 0031, 0034, 0035 and 0036 of JP2016-126817A. For the dispersant, paragraphs 0061 and 0071 of JP2012-133387A can be referred to. Further, regarding the additive of the magnetic layer, paragraphs 0035 to 0077 of JP-A-2016-51493 can also be referred to. A dispersant may be added to the non-magnetic layer forming composition. For the dispersant that can be added to the composition for forming a non-magnetic layer, paragraph 0061 of JP2012-133837A can be referred to. Further, as the non-magnetic powder that can be contained in the magnetic layer, a non-magnetic powder that can function as a polishing agent and a non-magnetic powder that can function as a protrusion forming agent that forms protrusions that appropriately protrude on the surface of the magnetic layer. (For example, non-magnetic colloidal particles, etc.) and the like. The average particle size of colloidal silica (silica colloidal particles) shown in Examples described later is a value obtained by the method described as a method for measuring the average particle size in paragraph 0015 of JP2011-048878A. .. As the additive, a commercially available product can be appropriately selected according to the desired properties, or can be produced by a known method and used in an arbitrary amount. As an example of the additive that can be used to improve the dispersibility of the abrasive in the magnetic layer containing the abrasive, the dispersant described in paragraphs 0012 to 0022 of JP2013-131285A can be mentioned.

(Spacing difference _{before and after} washing with methyl ethyl ketone ( _After- S _before ))
In one aspect, the magnetic tape has a difference (S) between the spacing S _after measured by the optical interferometry _{after the} methyl ethyl ketone cleaning and the spacing S _before measured by the optical interferometry before the methyl ethyl ketone cleaning on the surface of the magnetic layer. _After- S _before ) can be more than 0 nm and 15.0 nm or less.

In the present invention and the present specification, "methyl ethyl ketone cleaning" means that a sample piece cut out from a magnetic tape is immersed in methyl ethyl ketone (200 g) having a liquid temperature of 20 to 25 ° C. and ultrasonically cleaned for 100 seconds (ultrasonic output: 40 kHz). It shall mean to do. A sample piece having a length of 5 cm is cut out from the magnetic tape to be cleaned and subjected to methyl ethyl ketone cleaning. The width of the magnetic tape and the width of the sample piece cut out from the magnetic tape are usually 1/2 inch (1 inch is 0.0254 meters). For magnetic tapes other than 1/2 inch width, a sample piece having a length of 5 cm may be cut out and subjected to methyl ethyl ketone washing. The measurement of spacing after washing with methyl ethyl ketone, which will be described in detail below, shall be performed after the sample piece after washing with methyl ethyl ketone is left to stand in an environment of a temperature of 23 ° C. and a relative humidity of 50% for 24 hours.

In the present invention and the present specification, the spacing measured by the optical interferometry on the surface of the magnetic layer of the magnetic tape is a value measured by the following method.
A state in which a magnetic tape (specifically, the above sample piece; the same applies hereinafter) and a transparent plate-shaped member (for example, a glass plate) are overlapped so that the magnetic layer surface of the magnetic tape faces the transparent plate-shaped member. , The pressing member is pressed with a pressure of 0.5 atm (1 atm is 101325 Pa (Pascal)) from the side opposite to the magnetic layer side of the magnetic tape. In this state, the surface of the magnetic layer of the magnetic tape is irradiated with light via the transparent plate-shaped member (irradiation area: 150,000 to 200,000 μm ² ), and the reflected light from the surface of the magnetic layer of the magnetic tape and the transparent plate-shaped member Between the magnetic layer surface of the magnetic tape and the magnetic tape side surface of the transparent plate-like member, based on the intensity of the interference light generated by the optical path difference from the reflected light from the magnetic tape side surface (for example, the contrast of the interference fringe image). Spacing (distance) of. The light emitted here is not particularly limited. When the emitted light is light having an emission wavelength over a relatively wide wavelength range, such as white light including light having a plurality of wavelengths, the transparent plate-shaped member and the light receiving portion that receives the reflected light are used. A member having a function of selectively cutting light of a specific wavelength or light other than the specific wavelength region such as an interference filter is arranged between them, and the light of a part of the reflected light or the light of a part of the wavelength region is arranged. Light is selectively incident on the light receiving part. When the light to be irradiated is light having a single emission peak (so-called monochromatic light), the above member may not be used. As an example, the wavelength of the light incident on the light receiving portion can be in the range of, for example, 500 to 700 nm. However, the wavelength of the light incident on the light receiving portion is not limited to the above range. Further, the transparent plate-shaped member may be a member having transparency that transmits the irradiated light to the extent that the magnetic tape is irradiated with light through this member to obtain interference light.
The interference fringe image obtained by the measurement of the spacing is divided into 300,000 points, and the spacing of each point (distance between the surface of the magnetic layer of the magnetic tape and the surface of the transparent plate-like member on the magnetic tape side) is obtained. This is a histogram, and the mode in this histogram is the spacing. The difference ( _After- S _before ) is defined as a value obtained by subtracting the mode value before the methyl ethyl ketone washing from the mode value after the methyl ethyl ketone washing at the above 300,000 points.
Two sample pieces are cut out from the same magnetic tape, one is subjected to the above-mentioned spacing value S _before without methyl ethyl ketone washing, and the other is subjected to the methyl ethyl ketone washing, and then the above-mentioned spacing value S _after is obtained. _After- S _before ) may be obtained. Alternatively, the difference ( _After- S _before ) may be obtained by obtaining the spacing value after subjecting the sample piece to which the above-mentioned spacing value has been obtained before the methyl ethyl ketone washing and then subjecting it to the methyl ethyl ketone washing.
The above measurement can be performed using, for example, a commercially available tape spacing analyzer (TSA) such as Tape Spacing Analyzer manufactured by Micro Physics. Spacing measurements in the examples were performed using a Tape Spacing Analyzer manufactured by Micro Physics.

On the surface of the magnetic layer, a portion (projection) that mainly contacts the servo light head (so-called true contact) when the surface of the magnetic layer and the servo light head slide, and a portion lower than this portion (hereinafter, "" It is described as "base part"). The above spacing is considered to be a value that serves as an index of the distance between the servo light head and the substrate portion when the surface of the magnetic layer and the servo light head slide. However, if some component is present on the surface of the magnetic layer, it is considered that the spacing becomes narrower as the amount of the above component interposed between the substrate portion and the servo light head increases. On the other hand, when this component is removed by washing with methyl ethyl ketone, the spacing spreads, so that the value of the spacing S _{after after} washing with methyl ethyl ketone becomes larger than the value of the spacing S _{before after} washing with methyl ethyl ketone. Therefore, it is considered that the difference in spacing ( _After- S _before ) _{before and after} washing with methyl ethyl ketone can be used as an index of the amount of the above-mentioned components intervening between the substrate portion and the servo light head.
Regarding the above points, the present inventor may also contribute to the fluctuation of the spacing between the magnetic layer surface and the servo light head when the servo pattern is formed by the servo light head, even if the component is removed by the methyl ethyl ketone cleaning. I believe. Therefore, reducing the difference in spacing ( _Safter- S _Before ) _{before and after} washing with methyl ethyl ketone, that is, reducing the amount of the components, is to reduce the amount of the components between the magnetic layer surface and the servo light when the servo pattern is formed by the servo light head. It is presumed that it contributes to further suppressing fluctuations in the spacing with the head. Therefore, it is considered that reducing the difference ( _After- S _before ) further suppresses the decrease in the output of the servo signal. In this regard, according to the study by the present inventors, the value of the spacing difference before and after washing using an organic solvent other than methyl ethyl ketone, for example, n-hexane, and the spacing difference _{before and after} washing with methyl ethyl ketone ( _After- S _before). ), No correlation was found. It is presumed that this is because the above-mentioned components cannot be removed or sufficiently removed with a solvent other than methyl ethyl ketone.
The details of the above components are not clear. As a speculation, the present inventor thinks that the above-mentioned component may have a higher molecular weight than the organic compound usually added as an additive to the magnetic layer. The present inventors infer one aspect of this component as follows. In one aspect, the magnetic layer is cured by applying a composition for forming a magnetic layer containing a curing agent in addition to a ferromagnetic powder and a binder directly or via another layer on a non-magnetic support. It is formed. By the curing treatment here, the binder and the curing agent can be subjected to a curing reaction (crosslinking reaction). However, it is considered that the binder that did not undergo a curing reaction with the curing agent or the binder that did not have a sufficient curing reaction with the curing agent is easily released from the magnetic layer and may be present on the surface of the magnetic layer. The present invention states that the presence of such a binder on the surface of the magnetic layer may also contribute to fluctuations in the spacing between the surface of the magnetic layer and the servo light head when the servo pattern is formed by the servo light head. Is guessing.
However, the above is the inventor's guess, and does not limit the present invention in any way.

The above difference ( _After- S _before ) is preferably more than 0 nm and 15.0 nm or less from the viewpoint of further suppressing the decrease in the output of the servo signal. From the viewpoint of further suppressing the decrease in the output of the servo signal, the difference ( _After- S _before ) is preferably 14.0 nm or less, more preferably 13.0 nm or less, and 12.0 nm or less. It is more preferable to have. As will be described in detail later, the difference ( _After- S _before ) can be controlled by the surface treatment of the magnetic layer in the process of manufacturing the magnetic tape. When the surface treatment of the magnetic layer is performed so that the difference ( _After- S _before ) _{before and after} washing with methyl ethyl ketone becomes 0 nm, a large amount of additives (for example, lubricant) of the magnetic layer are removed from the magnetic layer of the magnetic tape. It is thought that it will end up. In consideration of this point, the difference ( _After- S _before ) is preferably more than 0 nm, more preferably 1.0 nm or more, further preferably 2.0 nm or more, and more preferably 3.0 nm or more. Is even more preferable, and 4.0 nm or more is even more preferable.

In one aspect, in the above magnetic tape, the difference (P _{1 −} P ₀ ) between the maximum convex amount (P ₁ ) on the surface of the magnetic layer and the average value (P ₀ ) of the unevenness is set to 30 nm or less, and the maximum convex amount (P ₁ ) is set. ₁₎ and the 20-th protruding amount _(difference between _{P 20) (P} 1 _{-P 20)} can be 5nm or less. As a result, the spacing loss can be reduced, and the error rate characteristic and the off-track characteristic can be improved. A method for measuring the amount of convexity is disclosed in paragraph 0067 of JP-A-2002-203308.

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

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

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

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

<Non-magnetic support>
Examples of the non-magnetic support (hereinafter, also simply referred to as “support”) include known biaxially stretched polyethylene terephthalates, polyethylene naphthalates, polyamides, polyamideimides, aromatic polyamides and the like. Of these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable. These supports may be subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like in advance. For example, when protrusions are formed on the surface of the support by the non-magnetic powder contained in the support, the thicker the backcoat layer, the more the influence of the protrusions on the non-magnetic support is suppressed and the backcoat layer is formed. The number of protrusions on the surface can be reduced. Further, when the support is manufactured by a known method, the presence state of the protrusions on the surface of the support can be adjusted by adjusting the size and content of the non-magnetic powder contained in the support.

<Various thickness>
The thickness of the non-magnetic support is, for example, 3.0 to 80.0 μm, preferably in the range of 3.0 to 50.0 μm, and more preferably in the range of 3.0 to 10.0 μm.
The thickness of the magnetic layer can be optimized depending on the saturation magnetization amount of the magnetic head used, the head gap length, and the band of the recording signal. For example, it is 10 nm to 100 nm, and is preferably 20 to 90 nm from the viewpoint of high-density recording. The range is more preferably 30 to 70 nm. The magnetic layer may be at least one layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a known configuration relating to a multi-layer magnetic layer can be applied. The thickness of the magnetic layer when separated into two or more layers is the total thickness of these layers.
The thickness of the non-magnetic layer is, for example, 50 nm or more, preferably 70 nm or more, and more preferably 100 nm or more. On the other hand, the thickness of the non-magnetic layer is preferably 800 nm or less, more preferably 500 nm or less.
The thickness of the backcoat layer is preferably 0.9 μm or less, and more preferably 0.1 to 0.7 μm.
The thickness of each layer of the magnetic tape and the non-magnetic support can be determined by a known film thickness measuring method. As an example, for example, a cross section in the thickness direction of a magnetic tape is exposed by a known method such as an ion beam or a microtome, and then the cross section is observed using a scanning electron microscope in the exposed cross section. Various thicknesses can be obtained as the arithmetic mean of the thickness obtained at one location in the cross-sectional observation or at two or more randomly selected locations, for example, two locations. Alternatively, the thickness of each layer may be obtained as a design thickness calculated from the manufacturing conditions.

<Manufacturing process>
(Manufacturing process of magnetic tape on which a servo pattern is formed)
The composition for forming the magnetic layer, the non-magnetic layer and the backcoat layer usually contains a solvent together with the various components described above. As the solvent, various organic solvents generally used for producing a coating type magnetic recording medium can be used. The amount of the solvent in each layer-forming composition is not particularly limited, and can be the same as that of each layer-forming composition of a normal coating type magnetic recording medium. The step of preparing each layer-forming composition can usually include at least a kneading step, a dispersion step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. The various components used in the preparation of each layer-forming composition may be added at the beginning or in the middle of any step. In addition, individual components may be added separately in two or more steps.

Known techniques can be used to prepare the composition for forming each layer. 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 pressurized kneader, and an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, in order to disperse each layer-forming composition, one or more dispersed beads selected from the group consisting of glass beads and other dispersed beads can be used as the dispersion medium. As such dispersed beads, zirconia beads, titania beads, and steel beads, which are dispersed beads having a high specific density, are suitable. The particle size (bead diameter) and filling rate of these dispersed beads can be optimized and used. A known disperser can be used. Regarding the number of protrusions on the surface of the backcoat layer, the smaller the size of the non-magnetic powder used for forming the backcoat layer, the lower the dispersibility of the composition for forming the backcoat layer, and the more protrusions are formed on the surface of the backcoat layer. It tends to be easy to do. Since the dispersibility of the backcoat layer forming composition can be changed by the combination of the non-magnetic powder and the binder mixed for preparing the backcoat layer forming composition, the combination of the non-magnetic powder and the binder can be used. It is also possible to control the number of protrusions on the surface of the backcoat layer. Regarding the kneading of the composition for forming the backcoat layer, the smaller the amount of the solvent, the lower the dispersibility of the kneaded product and the more the number of protrusions on the surface of the backcoat layer tends to increase. Further, if it is directly dispersed without kneading, the number of protrusions on the surface of the backcoat layer tends to decrease. Regarding the dispersion conditions, in general, when the dispersion time at the time of preparing the composition for forming the backcoat layer is lengthened, the number of protrusions on the surface of the backcoat layer tends to decrease. Each layer-forming composition, such as the backcoat layer-forming composition, may be filtered by a known method before being subjected to the coating step. Filtration can be performed, for example, by filter filtration. As the filter used for filtration, for example, a filter having a pore size of 0.01 to 3 μm (for example, a glass fiber filter, a polypropylene filter, etc.) can be used.

The magnetic layer can be formed by, for example, applying the composition for forming a magnetic layer directly on a non-magnetic support, or applying multiple layers sequentially or simultaneously with the composition for forming a non-magnetic layer. The backcoat layer can be formed by applying the backcoat layer forming composition to the side opposite to the side having the magnetic layer of the non-magnetic support (or the magnetic layer is provided later). For details of the coating for forming each layer, refer to paragraph 0051 of JP-A-2010-24113.

After the coating step, various treatments such as a drying treatment, a magnetic layer orientation treatment, and a surface smoothing treatment (calendar treatment) can be performed. For various steps, for example, known techniques such as paragraphs 0052 to 0057 of JP-A-2010-24113 can be referred to. For example, it is preferable that the coating layer of the composition for forming a magnetic layer is subjected to an orientation treatment while the coating layer is in a wet (undried) state. For the orientation treatment, various known techniques can be applied, including the description in paragraph 0067 of JP2010-231843A. For example, the vertical alignment treatment can be performed by a known method such as a method using a magnet opposite to the opposite pole. In the alignment zone, the drying rate of the coating layer can be controlled by the temperature of the drying air, the air volume, and / or the transport rate of the magnetic tape in the alignment zone. Alternatively, the coating layer may be pre-dried before being transported to the alignment zone. Further, regarding the calendar treatment, when the calendar conditions are strengthened, the protrusions of the back coat layer tend to decrease. The calendar conditions include calendar pressure, calendar temperature (surface temperature of calendar roll), calendar speed, hardness of calendar roll, etc. The larger these values are, the more calendar pressure, calendar temperature, and hardness of calendar roll are. The processing is strengthened, and the slower the calendar speed, the stronger the calendar processing.

It is preferable to heat-treat the coating layer formed by coating the composition for forming the magnetic layer at an arbitrary stage after the coating step of the composition for forming the magnetic layer. This heat treatment can be carried out, for example, before and / or after the calendar treatment. The heat treatment can be carried out, for example, by placing a support on which a coating layer of the composition for forming a magnetic layer is formed in a heating atmosphere. The heating atmosphere can be an atmosphere having an atmospheric temperature of 65 to 90 ° C., and an atmosphere having an atmospheric temperature of 65 to 75 ° C. is preferable. This atmosphere can be, for example, an atmospheric atmosphere. The heat treatment in a heating atmosphere can be carried out, for example, for 20 to 50 hours. In one aspect, this heat treatment can allow the curing reaction of the curable functional groups of the curing agent to proceed.

One aspect of the method for producing a magnetic tape includes wiping the surface of the magnetic layer with a wiping material impregnated with methyl ethyl ketone (hereinafter, also referred to as “methyl ethyl ketone wiping treatment”), preferably after the heat treatment. The manufacturing method can be mentioned. By the methyl ethyl ketone wiping treatment, the value of the difference ( _After- S _before ) described above can be reduced. The presence of components that can be removed by the methyl ethyl ketone wiping process on the surface of the magnetic layer also contributes to the fluctuation in the spacing between the surface of the magnetic layer and the servo light head when the servo pattern is formed by the servo light head. It is thought to get.

The methyl ethyl ketone wiping treatment may be carried out by using a wiping material impregnated with methyl ethyl ketone in place of the wiping material used in the dry wiping treatment, in accordance with the dry wiping treatment generally performed in the manufacturing process of the magnetic recording medium. it can. For example, after slitting the magnetic tape to the width to be accommodated in the magnetic tape cartridge or before slitting, the magnetic tape is run between the feeding roller and the take-up roller, and methyl ethyl ketone is applied to the surface of the magnetic layer of the running magnetic tape. By pressing the infiltrated wiping material (for example, cloth (for example, non-woven fabric) or paper (for example, tissue paper)), the surface of the magnetic layer can be wiped off with methyl ethyl ketone. The traveling speed of the magnetic tape and the tension applied in the longitudinal direction of the surface of the magnetic layer in the above traveling (hereinafter, simply referred to as "tension") are generally adopted in the dry wiping process generally performed in the manufacturing process of the magnetic recording medium. It can be the same as the processing conditions that have been set. For example, the traveling speed of the magnetic tape in the methyl ethyl ketone wiping process can be about 60 to 600 m / min, and the tension can be about 0.196 to 3.920 N (Newton). The methyl ethyl ketone wiping treatment can be performed at least once.

Further, the surface of the magnetic layer may be subjected to polishing treatment and / or dry wiping treatment (hereinafter, these are referred to as “dry surface treatment”) generally performed in the manufacturing process of the coating type magnetic recording medium at least once. it can. According to the dry surface treatment, it is possible to remove foreign substances generated in the manufacturing process such as chips generated by slits and adhering to the surface of the magnetic layer. When the methyl ethyl ketone wiping treatment is performed, the dry surface treatment can be carried out before and / or after the methyl ethyl ketone wiping treatment. Further, the backcoat layer can be polished by pressing a polishing means such as a polishing tape or a diamond wheel against the surface of the backcoat layer. The number of protrusions on the surface of the backcoat layer can also be controlled by the type of polishing means used here, the pressing pressure for pressing the polishing means against the surface of the backcoat layer during polishing, and the like.

(Formation of servo pattern)
A servo pattern can be formed on the magnetic tape manufactured as described above by a known method in order to enable tracking control of the magnetic head in the magnetic recording / playback device, control of the traveling speed of the magnetic tape, and the like. .. "Formation of servo pattern" can also be referred to as "recording of servo signal". The formation of the servo pattern will be described below.

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

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

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

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

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

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

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

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

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

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

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

[Magnetic tape cartridge]
One aspect of the present invention relates to a magnetic tape cartridge containing the above magnetic tape.

The details of the magnetic tape included in the magnetic tape cartridge are as described above.

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

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

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

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

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

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

For example, in a magnetic tape applied to a linear scan method widely used as a recording method of a magnetic recording / playback device, a region (servo band) in which a servo pattern is formed on a magnetic layer is usually formed in the longitudinal direction of the magnetic tape. There are multiple along. The area sandwiched between two adjacent servo bands is called a data band. Data recording is performed on the data bands, and a plurality of data tracks are formed along the longitudinal direction in each data band. FIG. 1 shows an example of arranging the data band and the servo band. In FIG. 1, a plurality of servo bands 1 are arranged on the magnetic layer of the magnetic tape MT so as to be sandwiched between the guide bands 3. A plurality of regions 2 sandwiched between the two servo bands are data bands. The servo pattern is a magnetized region, which is formed by magnetizing a specific region of the magnetic layer with a servo light head. The region magnetized by the servo light head (the position where the servo pattern is formed) is defined by the standard. For example, in the LTO Ultra format tape, which is an industry standard, a plurality of servo patterns inclined with respect to the tape width direction are formed on the servo band at the time of manufacturing the magnetic tape. Specifically, in FIG. 2, the servo frame SF on the servo band 1 is composed of the servo subframe 1 (SSF1) and the servo subframe 2 (SSF2). The servo subframe 1 is composed of an A burst (reference numeral A in FIG. 2) and a B burst (reference numeral B in FIG. 2). The A burst is composed of servo patterns A1 to A5, and the B burst is composed of servo patterns B1 to B5. On the other hand, the servo subframe 2 is composed of a C burst (reference numeral C in FIG. 2) and a D burst (reference numeral D in FIG. 2). The C burst is composed of servo patterns C1 to C4, and the D burst is composed of servo patterns D1 to D4. Such 18 servo patterns are arranged in a set of 5 and 4 in subframes arranged in an array of 5, 5, 4, 4, and are used to identify the servo frames. FIG. 2 shows one servo frame for the sake of explanation. However, in reality, in the magnetic layer of the magnetic tape on which the head tracking of the timing-based servo method is performed, a plurality of servo frames are arranged in the traveling direction in each servo band. In FIG. 2, the arrow indicates the traveling direction. For example, an LTO Ultra format tape usually has 5000 or more servo frames per 1 m of tape length in each servo band of the magnetic layer. As described above, when a plurality of servo patterns are sequentially formed in the longitudinal direction of the magnetic layer while the magnetic tape is run so that the surface of the magnetic layer and the servo light head are brought into contact with each other and slid, the surface of the magnetic layer is formed. It is considered that the fluctuation of the spacing between the servo light head and the servo light head causes a decrease in the output of the servo signal. On the other hand, the servo signal reading element sequentially reads the servo pattern in the longitudinal direction in a plurality of servo frames while contacting and sliding on the surface of the magnetic layer of the magnetic tape traveling in the magnetic recording / reproducing device. However, if the output of the servo signal obtained by reading the servo pattern by the servo signal reading element decreases compared to the initial stage of travel (that is, when the output of the servo signal decreases), the servo system magnetically records according to the servo signal. The accuracy of controlling the position of the magnetic head in the playback device to make the magnetic head follow the data track is reduced. Therefore, in order to use the servo system to more accurately record the data on the magnetic tape and / or to reproduce the data recorded on the magnetic tape more accurately, it is possible to suppress a decrease in the output of the servo signal. Is desirable. According to the magnetic tape according to one aspect of the present invention, it is possible to suppress a decrease in the output of the servo signal.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the embodiments shown in the examples. Unless otherwise specified, "parts" and "%" described below indicate "parts by mass" and "% by mass". Unless otherwise specified, the following steps and evaluations were performed in the air at 23 ° C. ± 1 ° C.

In Table 1 described later, "SrFe1" and "SrFe2" indicate hexagonal strontium ferrite powder, "ε-iron oxide" indicates ε-iron oxide powder, and "BaFe" indicates hexagonal barium ferrite having an average particle size of 21 nm. Indicates powder.
The activated volume and anisotropic constant Ku of the various ferromagnetic powders described below can be determined for each ferromagnetic powder by the method described above using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.). Value.
The mass magnetization σs is a value measured with a magnetic field strength of 15 kOe using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).
The anisotropic magnetic field Hk of the magnetic layer described below is a value measured using a vibrating sample magnetometer TM-VSM5050-SMS type (manufactured by Tamagawa Seisakusho).

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

The powder obtained above exhibits a hexagonal ferrite crystal structure by scanning CuKα rays under the conditions of a voltage of 45 kV and an intensity of 40 mA, and measuring an X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). confirmed. The powder obtained above showed a magnetoplumbite-type (M-type) hexagonal ferrite crystal structure. The crystal phase detected by X-ray diffraction analysis was a magnetoplumbite-type single phase.
PANalytical X'Pert Pro Diffractometer, PIXcel Detector Singler slit of incident beam and diffracted beam: 0.017 Radian dispersion slit fixed angle: 1/4 degree Mask: 10 mm
Anti-scattering slit: 1/4 degree Measurement mode: Continuous Measurement time per step: 3 seconds Measurement speed: 0.017 degrees per second Measurement step: 0.05 degrees

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

<Method of producing ε-iron oxide powder>
In 90 g of pure water, 8.3 g of iron (III) nitrate 9 hydrate, 1.3 g of gallium nitrate (III) octahydrate, 190 mg of cobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and While stirring 1.5 g of polyvinylpyrrolidone (PVP) using a magnetic stirrer, 4.0 g of an aqueous ammonia solution having a concentration of 25% was added in an atmospheric atmosphere under the condition of an atmospheric temperature of 25 ° C. The mixture was stirred for 2 hours under the temperature condition of 25 ° C. To the obtained solution, a citric acid solution obtained by dissolving 1 g of citric acid in 9 g of pure water was added, and the mixture was stirred for 1 hour. The powder precipitated after stirring was collected by centrifugation, washed with pure water, and dried in a heating furnace having a furnace temperature of 80 ° C.
800 g of pure water was added to the dried powder, and the powder was dispersed again in water to obtain a dispersion liquid. The temperature of the obtained dispersion was raised to 50 ° C., and 40 g of a 25% aqueous ammonia solution was added dropwise with stirring. After stirring for 1 hour while maintaining the temperature of 50 ° C., 14 mL of tetraethoxysilane (TEOS) was added dropwise, and the mixture was stirred for 24 hours. 50 g of ammonium sulfate was added to the obtained reaction solution, and the precipitated powder was collected by centrifugation, washed with pure water, and dried in a heating furnace at a furnace temperature of 80 ° C. for 24 hours to prepare a precursor of the ferromagnetic powder. Obtained.
The obtained precursor of the ferromagnetic powder was loaded into a heating furnace having a furnace temperature of 1000 ° C. under an air atmosphere, and heat-treated for 4 hours.
The precursor of the heat-treated ferromagnetic powder was put into a 4 mol / L aqueous solution of sodium hydroxide (NaOH), and the liquid temperature was maintained at 70 ° C. and stirred for 24 hours to obtain the heat-treated ferromagnetic powder. The impurity silicate compound was removed from the precursor.
Then, the ferromagnetic powder from which the silicic acid compound was removed was collected by centrifugation and washed with pure water to obtain a ferromagnetic powder.
The composition of the obtained ferromagnetic powder was confirmed by high frequency inductively coupled plasma emission spectrometry (ICP-OES; Inductively Coupled Plasma-Optical Emission Spectrum) and found to be Ga, Co and Ti substituted ε-iron oxide (ε-Ga _{0). It was .58} Fe _1.42 O ₃ ). Further, X-ray diffraction analysis was performed under the same conditions as those described for the method 1 for producing hexagonal strontium ferrite powder, and the ferromagnetic powder obtained from the peak of the X-ray diffraction pattern was α phase and γ phase. It was confirmed that it had a ε-phase single-phase crystal structure (ε-iron oxide type crystal structure) that did not include the crystal structure of.
(In Table 1, "ε- iron oxide") obtained ε- iron oxide powder having an average particle size of 12 nm, activation volume 746 nm ^3, the anisotropy constant Ku is 1.2 × ¹⁰ 5 J / ^{m 3} The mass magnetization σs was 16 A · m ² / kg.

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

<Prescription of composition for forming magnetic layer>
(Magnetic liquid)
Hydroxy powder (type: see Table 1): 100.0 parts oleic acid: 2.0 parts Vinyl chloride copolymer (MR-104 manufactured by Kaneka): 10.0 parts (weight average molecular weight: 55,000, containing active hydrogen) group (hydroxy _{group): 0.33meq / g, OSO 3} K group (potassium salt of sulfate group): 0.09meq / g)
SO ₃ Na group-containing polyurethane resin: 4.0 parts
(Weight average molecular weight: 70,000, active hydrogen-containing group (hydroxy group): 4 to 6 mgKOH / g, SO ₃ Na group (sodium salt of sulfonic acid group): 0.07 meq / g)
Polyalkyleneimine-based polymer (synthetic product obtained by the method described in paragraphs 0115 to 0123 of JP-A-2016-51493): 6.0 parts Methyl ethyl ketone: 150.0 parts Cyclohexanone: 15.0 parts (abrasive solution) )
α-Alumina (BET (Brunauer-Emmett-Teller) specific surface area 19 m ^{2 /} g): 6.0 parts 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 (protrusion forming agent solution)
Colloidal silica (average particle size 120 nm): 2.0 parts Methyl ethyl ketone: 8.0 parts (other components)
Stearic acid: 3.0 parts Stearic acid amide: 0.3 parts Butyl stearate: 6.0 parts Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate (Tosoh Coronate (registered trademark) L): 3 Department

<Prescription of non-magnetic layer forming composition>
Non-magnetic inorganic powder α-iron oxide (average particle size 10 nm, BET specific surface area 75 m ^{2 /} g): 100.0 parts carbon black (average particle size: 20 nm): 25.0 parts SO ₃ Na group-containing polyurethane resin (weight) Average molecular weight 70,000, SO ₃ Na group content 0.2 meq / g): 18.0 parts Stealic acid: 1.0 parts Cyclohexanone: 300.0 parts Methyl ethyl ketone: 300.0 parts

<Prescription of composition for forming backcoat layer>
Fine particle carbon black (average particle size: see Table 1): 100.0 parts Coarse particle carbon black (average particle size: see Table 1): See Table 1 α-iron oxide (average particle size: 0.11 μm): 20. 0 parts α-alumina (average particle size: 0.20 μm): 5.0 parts Nitrocellulose resin: 55.0 parts Polyurethane resin: 40.0 parts Copper oleate: 0.1 parts Copper phthalocyanine: 0.2 parts

<Preparation of composition for forming magnetic layer>
The composition for forming a magnetic layer was prepared by the following method.
A magnetic liquid was prepared by dispersing various components of the magnetic liquid for 24 hours (bead dispersion) using a batch type vertical sand mill. As the dispersed beads, zirconia beads having a bead diameter of 0.5 mm were used.
The abrasive liquid is a mixture of various components of the above abrasive liquid and placed in a horizontal bead mill disperser together with zirconia beads having a bead diameter of 0.3 mm, so that the bead volume / (abrasive liquid volume + bead volume) becomes 80%. The bead mill dispersion treatment was performed for 120 minutes, the liquid after the treatment was taken out, and the ultrasonic dispersion filtration treatment was performed using a flow-type ultrasonic dispersion filtration device. In this way, the abrasive solution was prepared.
The prepared magnetic liquid and abrasive liquid, as well as the above-mentioned protrusion forming agent liquid and other components were introduced into a dissolver stirrer, stirred at a peripheral speed of 10 m / sec for 30 minutes, and then flown by a flow type ultrasonic disperser. After 3 passes treatment at 5 kg / min, a composition for forming a magnetic layer was prepared by filtering with a filter having a pore size of 1 μm.

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

<Preparation of composition for backcoat layer formation>
After dispersing various components of the above composition for forming a backcoat layer with a sand mill for 120 minutes, 15.0 parts of polyisocyanate is added and filtered using a filter having a pore size of 1 μm to form a backcoat layer. The composition was prepared.

<Making magnetic tape>
On the surface of a biaxially stretched polyethylene naphthalate support having a thickness of 5.0 μm, the composition for forming a non-magnetic layer prepared above so as to have a thickness of 400 nm after drying is applied and dried to form a non-magnetic layer. After the formation, the composition for forming a magnetic layer prepared above was applied onto the surface of the non-magnetic layer so that the thickness after drying was 70 nm to form a coating layer. While the coating layer of the composition for forming a magnetic layer was in a wet (undried) state, a magnetic field having a magnetic field strength of 0.3T was applied in a direction perpendicular to the surface of the coating layer, and the coating layer was dried. .. Then, the composition for forming a backcoat layer prepared above was applied to the opposite surface of the support so that the thickness after drying was 0.4 μm, and the mixture was dried. In this way, a magnetic tape raw fabric was produced.
With respect to the produced magnetic tape raw fabric, a calendar composed of only metal rolls has a speed of 100 m / min, a linear pressure of 294 kN / m (1 kg / cm is 0.98 kN / m), and a surface temperature of the calendar roll of 100 ° C. The calendar treatment (surface smoothing treatment) was performed, and then the heat treatment was performed in the environment of the atmospheric temperature shown in Table 1 for the time shown in Table 1. After the heat treatment, the original magnetic tape was slit by a cutting machine to obtain a 1/2 inch wide magnetic tape. While the magnetic tape was run between the feeding roller and the take-up roller (running speed 120 m / min, tension: see Table 1), blade polishing and dry wiping treatment on the surface of the magnetic layer were carried out in this order. Specifically, a sapphire blade and a dry wiping material (Toray Industries, Inc. Toraysee (registered trademark)) are placed between the two rollers, and are placed on the surface of the magnetic layer of the magnetic tape running between the two rollers. The sapphire blade was pressed against the blade to polish the blade, and then the surface of the magnetic layer was wiped dry with the above-mentioned dry wiping material. As described above, the blade polishing and the dry wiping treatment were performed once on the surface of the magnetic layer.
In a state where the magnetic layer of the magnetic tape obtained above was demagnetized, a servo pattern having an arrangement and shape according to the LTO Ultra format was formed on the magnetic layer by a servo light head mounted on a servo tester. As a result, the magnetic layer has a data band, a servo band, and a guide band arranged according to the LTO Ultra format, and a servo pattern (timing-based servo pattern) having an arrangement and shape according to the LTO Ultra format is provided on the servo band. Obtained a magnetic tape to have. A total of 5,000,000 servo frames having A burst, B burst, C burst, and D burst are formed on this magnetic tape in the arrangement shown in FIG. The servo tester includes a servo light head and a servo head. This servo tester was also used in the evaluation described later.
Through the above steps, the magnetic tape of Example 1 in which the timing-based servo pattern was formed on the magnetic layer was produced.

[Examples 2-9, Comparative Examples 1-6, Reference Examples 1 and 2]
A magnetic tape was produced in the same manner as in Example 1 except that various conditions were changed as shown in Table 1.
In Examples 8 and 9, the magnetic tape raw fabric produced by the same method as in Example 1 was subjected to a calendar consisting of only metal rolls, a speed of 100 m / min, a linear pressure of 294 kN / m, and a calendar roll. The calendar treatment (surface smoothing treatment) was carried out at a surface temperature of 100 ° C., and then the heat treatment was carried out in the environment of the atmospheric temperature shown in Table 1 for the time shown in Table 1. After the heat treatment, the original magnetic tape was slit by a cutting machine to obtain a 1/2 inch wide magnetic tape. While running this magnetic tape between the feeding roller and the winding roller (running speed 120 m / min, tension: see Table 1), blade polishing of the magnetic layer surface, dry wiping treatment, and methyl ethyl ketone wiping treatment are performed in this order. did. Specifically, a sapphire blade, a dry wiping material (Toray's Toraysee (registered trademark)) and a wiping material impregnated with methyl ethyl ketone (Toray's Toraysee (registered trademark)) are placed between the above two rollers. The sapphire blade is pressed against the surface of the magnetic layer of the magnetic tape running between the two rollers to polish the blade, and then the surface of the magnetic layer is dry-wiped with the above-mentioned dry wiping material, and then the above-mentioned The surface of the magnetic layer was wiped off with a wiping material impregnated with the methyl ethyl ketone. As described above, the blade polishing, the dry wiping treatment, and the methyl ethyl ketone wiping treatment were performed once on the surface of the magnetic layer.

[Evaluation method]
(1) Number of protrusions on the backcoat layer For each magnetic tape, the number of protrusions having a height of 50 nm or more and less than 75 nm and the number of protrusions having a height of 75 nm or more were determined by the following methods.

(2) Spacing difference _{before and after} washing with methyl ethyl ketone ( _After- S _before )
Using TSA (Tape Spacing Analyzer (manufactured by Micro Physics)), the spacing difference ( _After- S _before ) _{before and after} washing with methyl ethyl ketone was determined by the following method.
Two sample pieces having a length of 5 cm were cut out from each magnetic tape, and the spacing ( _Sbefore ) of one sample piece was determined by the following method without washing with methyl ethyl ketone. After about the other sample piece was methylethylketone washing by the method described above, was determined spacing (S _after) by the following method.
A glass plate provided for TSA (Thorlabs, Inc. glass plate (model number: WG10530)) is provided on the surface of the magnetic layer of the magnetic tape (specifically, the above sample piece) and prepared for TSA as a pressing member. The hemisphere made of urethane was pressed against the surface of the backcoat layer of the magnetic tape at a pressure of 0.5 atm. In this state, white light is irradiated from the stroboscope provided in the TSA to a certain region (150,000 to 200,000 μm ² ) on the surface of the magnetic layer of the magnetic tape through a glass plate, and the obtained reflected light is applied to an interference filter (wavelength 633 nm). By receiving light with a CCD (Charge-Coupled Device) through a filter that selectively transmits the light of the above, an interference fringe image generated by the unevenness of this region was obtained.
This image is divided into 300,000 points, the distance (spacing) from the surface of the glass plate on the magnetic tape side to the surface of the magnetic layer of the magnetic tape at each point is obtained, and this is used as a histogram to obtain a sample piece after washing with methyl ethyl ketone. The mode (S _After − S _before ) was obtained by subtracting the mode S _{Before of} the histogram obtained for the sample piece without methyl ethyl ketone washing from the mode S _{After of} the histogram.

(3) Spacing difference before and after washing with n-hexane (S _reference- S _before ) (reference value)
One more sample piece with a length of 5 cm was cut out from each magnetic tape, washed in the same manner as above except that n-hexane was used instead of methyl ethyl ketone, and then the spacing after n-hexane washing was obtained in the same manner as above. It was. As a reference value, the difference (S _reference- S _before ) between the spacing S _reference obtained here and the spacing S _before obtained for the unwashed sample piece obtained in (2) above was obtained.

(4) Decrease in servo signal output A magnetic tape on which the above timing-based servo pattern was formed was attached to the servo tester. In the servo tester, while the surface of the magnetic layer of the traveling magnetic tape and the servo head are brought into contact with each other and slid, the servo pattern of the first servo frame formed on the magnetic tape by the servo head is the final 5, The servo patterns were sequentially read (reproduction of the servo signal) up to the servo pattern of the ,000,000th servo frame. Let A be the arithmetic mean of the signal outputs obtained in the 1st to 100th servo frames, and B be the arithmetic mean of the signal outputs obtained in the 4,999,900th to 5,000,000th servo frames. The output decrease (unit:%) of the servo signal was calculated as "[(BA) / A] x 100".

The above results are shown in Table 1 (Table 1-1 and Table 1-2).

From the comparison between Reference Examples 1 and 2 shown in Table 1 and Comparative Examples 1 to 6, a magnetic layer and a bag containing a ferromagnetic powder selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder. It can be confirmed that the output of the servo signal is significantly reduced in the magnetic tape having the coat layer.
Further, from the comparison between Examples 1 to 6 and Comparative Examples 1 to 6, it can be confirmed that such a decrease in the output of the servo signal is suppressed in Examples 1 to 6.
Incidentally, as shown in Table 1, between the value of n- hexane wash before and after the spacing difference _{(S reference} -S _before) values and methyl ethyl ketone before and after washing of the spacing difference _{(S after -S before)} No correlation was found.

One aspect of the present invention is useful in the art of high-density recording magnetic tapes.

Claims (6)

A magnetic tape having a magnetic layer containing a ferromagnetic powder and a binder on one surface side of a non-magnetic support and a backcoat layer containing a non-magnetic powder and a binder on the other surface side.
The ferromagnetic powder is a ferromagnetic powder selected from the group consisting of hexagonal strontium ferrite powder and ε-iron oxide powder.
The magnetic layer has a servo pattern and has a servo pattern.
A magnetic tape in which the number of protrusions having a height of 50 nm or more and less than 75 nm on the surface of the backcoat layer is in the range of 800 to 1500 pieces / 6400 μm ² . The magnetic tape according to claim 1, wherein the number of protrusions having a height of 75 nm or more on the surface of the backcoat layer is 750 pieces / 6400 μm ² or less. The difference between the spacing S _after being measured by an optical interference method after methylethylketone washing the surface of the magnetic layer, the spacing S _before being measured by an optical interference method before methylethylketone washing the surface of the magnetic layer, S _after - The magnetic tape according to claim 1 or 2, wherein S _before is more than 0 nm and 15.0 nm or less. The magnetic tape according to any one of claims 1 to 3, further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. A magnetic tape cartridge including the magnetic tape according to any one of claims 1 to 4. The magnetic tape according to any one of claims 1 to 4,
With a magnetic head
Magnetic recording / playback device including.