WO2022025154A1

WO2022025154A1 - Magnetic recording medium, magnetic tape cartridge, and magnetic recording playback device

Info

Publication number: WO2022025154A1
Application number: PCT/JP2021/028012
Authority: WO
Inventors: 典子小柳; 佑介和多田
Original assignee: 富士フイルム株式会社
Priority date: 2020-07-31
Filing date: 2021-07-29
Publication date: 2022-02-03
Also published as: JP2022027074A

Abstract

Provided are a magnetic recording medium having a non-magnetic support and a magnetic layer that includes a ferromagnetic powder, and a magnetic tape cartridge and magnetic recording playback device that include said magnetic recording medium. Half-Rq derived in the surface of the magnetic layer is 3.0 nm or less. The Half-Rq is the root mean square roughness derived for only the positive section of surface profile data obtained by inverse Fourier transformation of components having a frequency of 25 Hz or less in a power spectrum density on the surface of the magnetic layer.

Description

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

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

A magnetic recording medium is widely used as a recording medium for recording various data (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2004-103137

The magnetic recording medium is required to exhibit excellent electromagnetic conversion characteristics, and further improvement of the electromagnetic conversion characteristics is desired.

The magnetic recording medium usually has a magnetic layer containing a ferromagnetic powder on a non-magnetic support, and the surface shape of the magnetic layer may affect the performance of the magnetic recording medium. Regarding the surface shape of the magnetic layer, Patent Document 1 (Japanese Unexamined Patent Publication No. 2004-103137) described above proposes to control the surface shape of the magnetic layer based on the power spectrum density. On the other hand, the present inventor has aimed to provide a magnetic recording medium having further excellent electromagnetic conversion characteristics than the electromagnetic conversion characteristics that can be achieved by controlling the surface shape of the magnetic layer, which has been conventionally proposed.

That is, one aspect of the present invention is to provide a magnetic recording medium capable of exhibiting excellent electromagnetic conversion characteristics.

One aspect of the present invention is
A magnetic recording medium having a non-magnetic support and a magnetic layer containing a ferromagnetic powder.
A magnetic recording medium having a Half-Rq of 3.0 nm or less required on the surface of the magnetic layer.
Regarding. The above-mentioned Half-Rq is the root mean square roughness obtained only for the positive part of the surface profile data obtained by inverse Fourier transforming the components having a frequency of 25 Hz (hertz) or less with respect to the power spectrum density of the surface of the magnetic layer. That's right.

In one form, the Half-Rq can be 0.5 nm or more and 3.0 nm or less.

In one form, the Half-Rq can be 2.0 nm or less.

In one form, the Half-Rq can be 0.5 nm or more and 2.0 nm or less.

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

In one form, the magnetic recording medium can have two non-magnetic layers.

In one form, the magnetic recording medium can contain non-magnetic iron oxide powder in the non-magnetic layer on the magnetic layer side of the two non-magnetic layers, and carbon black in the non-magnetic layer on the non-magnetic support side. Can be included.

In one form, the non-magnetic iron oxide powder can be α-iron oxide powder.

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

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

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

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

According to one aspect of the present invention, it is possible to provide a magnetic recording medium capable of exhibiting excellent electromagnetic conversion characteristics. Further, according to one aspect of the present invention, it is possible to provide a magnetic tape cartridge and a magnetic recording / reproducing device including the magnetic recording medium.

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) Ultrium format tape is shown.

[Magnetic recording medium]
One aspect of the present invention relates to a magnetic recording medium having a non-magnetic support and a magnetic layer containing a ferromagnetic powder. In the magnetic recording medium, Half-Rq required on the surface of the magnetic layer is 3.0 nm or less. The Half-Rq is the root mean square roughness obtained only for the positive part of the surface profile data obtained by inverse Fourier transforming the components having a frequency of 25 Hz or less with respect to the power spectrum density of the surface of the magnetic layer. ..

<Half-Rq>
The above-mentioned "Half-Rq" in the present invention and the present specification is, in detail, a value obtained by the following method.

(AFM measurement)
On the surface of the magnetic layer of the magnetic recording medium to be measured, an atomic force microscope (AFM) is used for measurement, and an AFM image is acquired. In the present invention and the present specification, the "surface of the magnetic layer" is synonymous with the surface of the magnetic recording medium on the magnetic layer side. In the AFM measurement, the measurement area is a 40 μm square (40 μm × 40 μm) area. Measurements are made at three randomly selected different measurement points on the surface of the magnetic layer (n = 3). The resolution is 512pixel × 512pixel. The following measurement conditions can be mentioned as an example of the AFM measurement conditions.
AFM (Nanoscope 4 manufactured by Veeco) is used in a tapping mode to measure a region having an area of 40 μm × 40 μm on the surface of the magnetic layer of the magnetic recording medium. As the probe, RTESS-300 manufactured by BRUKER is used, the resolution is 512pixel × 512pixel, and the scanning speed is the speed at which one screen (512pixel × 512pixel) is measured in 341 seconds.

(Acquisition of PSD)
"PSD" is used as an abbreviation for Power Spectrum Density. In the AFM image acquired by AFM measurement, one side of the measurement area of 40 μm × 40 μm is divided into 512, the sampling ratio is set to 40/512 μm in profiling, two-dimensional Fourier transform is performed on the surface roughness curved surface, and the maximum wavelength is 40 μm. A total of 256 wavelength component PSDs up to the shortest wavelength of 0.15625 μm are obtained. The above-mentioned sampling ratio means the frequency of setting the sample points.

(Calculation of Half-Rq)
With respect to the PSD obtained above, in the surface profile data obtained by inverse Fourier transforming the components having a frequency of 25 Hz or less, only the positive part is calculated by the following formula to obtain Half-Rq. The positive portion corresponds to the height value of the portion (convex portion) having a convex shape with respect to the reference plane. The reference plane is a plane (height zero) in which the volumes of the convex portion and the concave portion are equal to each other. Half-Rq includes the data of the positive part (positive value data) corresponding to the height value of the convex portion and the data of the negative part (negative value data) corresponding to the depth value of the concave portion. Unlike the value calculated from those absolute values, it is a value obtained by calculating only the positive part. Therefore, "Half" is added and it is expressed as Half-Rq. In the following formula, the "average height" is the arithmetic mean of the height values, and the "sample point height" is the height value at the sample points. The arithmetic mean of the values calculated for each of the three different measurement points is defined as Half-Rq obtained on the surface of the magnetic layer of the magnetic recording medium to be measured.

The following examples can be given as specific flow examples.
An AFM image (512pixel × 512pixel) is acquired, and the surface roughness curve of this AFM image is Fourier transformed to obtain a frequency component image (512pixel × 512pixel). In the obtained frequency component image, if the central part is not a low frequency component and the peripheral part is not a high frequency component, a shift operation is performed so that the central part is a low frequency component and the peripheral part is a high frequency component. .. Substitute 0 (zero) for the component in the circle corresponding to the radius of 25pixel at the center. At this time, a sigmoid function may be used in order to make the boundary between the inside and the outside of the circle smooth. After that, if the shift operation has been performed in the above, the shift operation is performed again. In this way, a low frequency image having a frequency of 25 Hz or less is obtained. For the obtained low frequency image, Half-Rq is obtained as described above.

In the magnetic recording medium, the fact that Half-Rq obtained by the method described above is 3.0 nm or less can contribute to the improvement of electromagnetic conversion characteristics. Hereinafter, this point will be further described.
Regarding the surface shape of the magnetic layer, it is considered that the shape of the waviness existing on the surface of the magnetic layer may affect the electromagnetic conversion characteristics. The present inventor can obtain a value that can be an index of a swell having a longer wavelength than the swell conventionally evaluated by the PSD by performing an inverse Fourier transform on a component having a frequency of 25 Hz or less in the PSD as described above. I think I can do it. The period of such long-wavelength swell is the period of unevenness that may exist on the sliding surface of the magnetic head that is normally used for recording data on the magnetic layer and / or reproducing the data recorded on the magnetic layer. The present inventor speculates that the cycle is close to that of. The present inventor thinks that this is the reason why controlling Half-Rq obtained by the method described above may contribute to the improvement of electromagnetic conversion characteristics. In addition, the Half-Rq is a value obtained only for the positive part of the surface profile data, that is, only for the convex part of the surface of the magnetic layer. Regarding the spacing between the magnetic layer surface and the magnetic head, if the spacing is wide, the electromagnetic conversion characteristics tend to deteriorate due to the spacing loss. Since the convex portion in the unevenness of the magnetic layer surface affects this spacing, Half-Rq, which is obtained only for the positive portion as described above, is a value that can be well correlated with the electromagnetic conversion characteristics. The present inventor believes that setting this value to 3.0 nm or less leads to improvement in electromagnetic conversion characteristics.
However, the above includes speculation. The inferences described herein are not limited to the present invention.

From the viewpoint of improving the electromagnetic conversion characteristics, the Half-Rq required on the surface of the magnetic layer of the magnetic recording medium is 3.0 nm or less, preferably 2.8 nm or less, and more preferably 2.6 nm or less. It is preferably 2.4 nm or less, more preferably 2.2 nm or less, further preferably 2.0 nm or less, still more preferably 1.8 nm or less. The Half-Rq required on the surface of the magnetic layer of the magnetic recording medium can be, for example, 0.5 nm or more, 0.7 nm or more, or 1.0 nm or more, and can be lower than the values exemplified here. It is preferable that the value of Half-Rq is small from the viewpoint of improving the electromagnetic conversion characteristics.

The control of Half-Rq required on the surface of the magnetic layer of the magnetic recording medium will be described later.

Hereinafter, the above magnetic recording medium will be described in more detail.

<Magnetic layer>
(Ferromagnetic powder)
As the ferromagnetic powder contained in the magnetic layer, one or a combination of two or more kinds of ferromagnetic powder known as the ferromagnetic powder used in the magnetic layer of various magnetic recording media can be used. It is preferable to use a ferromagnetic powder having a small average particle size from the viewpoint of improving the recording density. From this point, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, further preferably 40 nm or less, further preferably 35 nm or less, and more preferably 30 nm or less. It is even more preferably 25 nm or less, and even more preferably 20 nm or less. On the other hand, from the viewpoint of the stability of magnetization, 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.

Regarding the particle size of the ferromagnetic powder, the average particle volume can also be mentioned as an index of the particle size. From the viewpoint of improving the recording density, the average particle volume is preferably 2500 nm ³ or less, more preferably 2300 nm ³ or less, further preferably 2000 nm ³ or less, and even more preferably 1500 nm ³ or less. .. From the viewpoint of magnetization stability, the average particle volume of the ferromagnetic powder is preferably 500 nm ³ or more, more preferably 600 nm ³ or more, further preferably 650 nm ³ or more, and 700 nm ³ or more. Is more preferable. The above average particle volume is a value obtained as a sphere-equivalent volume from the average particle size obtained by the method described later.

Hexagonal ferrite powder As a preferable specific example of the ferromagnetic powder, hexagonal ferrite powder can be mentioned. For details of the hexagonal ferrite powder, for example, paragraphs 0012 to 0030 of JP 2011-225417, paragraphs 0134 to 0136 of JP 2011-216149, paragraphs 0013 to 0030 of JP 2012-204726 and References can be made to paragraphs 0029 to 0084 of JP-A-2015-127985.

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

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

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

The "activated volume" is a unit of magnetization reversal and is an index showing 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. With respect to 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 old 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 2.0 × ¹⁰⁵ J / m ³ or more. Further, the Ku of the hexagonal strontium ferrite powder can be, for example, ^2.5 × 105 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 values.

The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, it is preferable that the hexagonal strontium ferrite powder contains rare earth atoms at a content of 0.5 to 5.0 atomic% (bulk content) with respect to 100 atomic% of iron atoms. In one form, the hexagonal strontium ferrite powder containing a rare earth atom can have uneven distribution on the surface layer of the rare earth atom. The term "unevenly distributed on the surface of rare earth atoms" as used in the present invention and the present specification refers to the rare earth atom content with respect to 100 atomic% of iron atoms in the solution obtained by partially dissolving hexagonal strontium ferrite powder with an acid (hereinafter referred to as "rare earth atom content"). “Rare earth atom surface layer content” or simply “surface layer content” for rare earth atoms) is 100 atomic% of iron atoms in the solution obtained by completely dissolving hexagonal strontium ferrite powder with an acid. Rare earth atom content (hereinafter referred to as "rare earth atom bulk content" or simply referred to as "bulk content" for rare earth atoms).
Rare earth atom surface layer content / Rare earth atom bulk content> 1.0
Means to meet 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, so 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 on the surface layer in the particles constituting the hexagonal strontium ferrite powder. It means that they are unevenly distributed (that is, they exist more than inside). The surface layer portion in the present invention and the present specification means a partial region from the surface of the particles constituting the hexagonal strontium ferrite powder toward the inside.

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 it is possible to increase. The higher the value of the anisotropy constant Ku, the more the occurrence of the so-called thermal fluctuation phenomenon 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 in 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 may increase.
In addition, it is speculated that the use of hexagonal strontium ferrite powder, which has uneven distribution on the surface of rare earth atoms, as a ferromagnetic powder for the magnetic layer also contributes to suppressing the surface of the magnetic layer from being scraped by sliding with the magnetic head. Ru. That is, it is presumed that the hexagonal strontium ferrite powder having uneven distribution of the rare earth atomic surface layer can also contribute to the improvement of the running durability of the magnetic recording medium. This is because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder improves the interaction between the particle surface and 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. Preferred rare earth atoms from the viewpoint of further suppressing the decrease in regeneration output in 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 more 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 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 and the rare earths obtained by completely dissolving under the dissolution conditions described later. The ratio of the atom to the bulk content, "surface layer content / bulk content" is more than 1.0, and can be 1.5 or more. When the "surface layer content / bulk content" is larger than 1.0, it means that the rare earth atoms are unevenly distributed (that is, more present than the inside) in the particles constituting the hexagonal strontium ferrite powder. do. Further, the ratio of the surface layer content of the rare earth atom obtained by partial melting under the dissolution conditions described later and the bulk content of the rare earth atom 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 may be unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder. The "rate" is not limited to the upper and lower limits exemplified.

Partial and total melting of hexagonal strontium ferrite powder will be described below. For the hexagonal strontium ferrite powder that exists as a powder, the sample powder that is partially or completely dissolved is collected from the same lot of powder. On the other hand, regarding the hexagonal strontium ferrite powder contained in the magnetic layer of the magnetic recording medium, a part of the hexagonal strontium ferrite powder taken out from the magnetic layer is subjected to partial dissolution, and the other part is subjected to total dissolution. .. The hexagonal strontium ferrite powder can be taken out from the magnetic layer by, for example, the method described in paragraph 0032 of Japanese Patent Application Laid-Open No. 2015-91747.
The above partial dissolution means that the hexagonal strontium ferrite powder is dissolved in the liquid to the extent that the residue of the hexagonal strontium ferrite powder can be visually confirmed at the end of the dissolution. For example, by partial dissolution, a region of 10 to 20% by mass can be dissolved with respect to the particles constituting the hexagonal strontium ferrite powder, with the entire 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 above partial melting and 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 content of the rare earth atom in the surface layer with respect to 100 atom% of the iron atom can be obtained. 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 same procedure as the above-mentioned partial melting and measurement of the surface layer content can be performed to determine the bulk content with respect to 100 atomic% of iron atoms.

From the viewpoint of increasing the reproduction output when reproducing the data recorded on the magnetic recording medium, it is desirable that the mass magnetization σs of the ferromagnetic powder contained in the magnetic recording medium is high. In this regard, the hexagonal strontium ferrite powder containing rare earth atoms but not having uneven distribution on the surface layer of rare earth atoms tended to have a significantly lower σs than the hexagonal strontium ferrite powder containing no rare earth atoms. On the other hand, hexagonal strontium ferrite powder having uneven distribution on the surface layer of rare earth atoms is considered to be preferable in order to suppress such a large decrease in σs. In one embodiment, 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. On the other hand, σs is preferably 80 A · m ² / kg or less, and more preferably 60 A · m ² / kg or less, from the viewpoint of noise reduction. σs can be measured using a known measuring device capable of measuring magnetic characteristics such as a vibration 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 (bulk content) of the constituent atoms of the hexagonal strontium ferrite powder, the strontium atom content can be in the range of, for example, 2.0 to 15.0 atom% with respect to 100 atom% of iron atoms. .. In one form, the hexagonal strontium ferrite powder can contain only strontium atoms as divalent metal atoms contained in the powder. In another embodiment, the hexagonal strontium ferrite powder may 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 the iron atom, respectively. It can be in the range of 0.0 atomic%.

As the crystal structure of hexagonal ferrite, a magnetoplumbite type (also referred to as "M type"), a W type, a Y type, and a 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. Hexagonal strontium ferrite powder can be one in which a single crystal structure or two or more kinds of crystal structures are detected by X-ray diffraction analysis. For example, in one form, the hexagonal strontium ferrite powder can be such that only the M-type crystal structure is detected by X-ray diffraction analysis. For example, M-type hexagonal ferrite is represented by the composition formula of AFe ₁₂ O ₁₉ . Here, A represents a divalent metal atom, and when the hexagonal strontium ferrite powder is M-type, A is only a strontium atom (Sr), or when A contains a plurality of divalent metal atoms. As mentioned above, the strontium atom (Sr) occupies the largest amount on the basis of atomic%. The divalent metal atom content of the hexagonal strontium ferrite powder is usually determined by the type of the 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 in repeated regeneration, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms and rare earth atoms, and the content of atoms other than these atoms is 100 iron atoms. % Is preferably 10.0 atomic% or less, more preferably in the range of 0 to 5.0 atomic%, and may be 0 atomic%. That is, in one form, the hexagonal strontium ferrite powder does not have to contain atoms other than iron atoms, strontium atoms, oxygen atoms and rare earth atoms. The content expressed in atomic% above is the content of each atom (unit: mass%) obtained by completely dissolving the hexagonal strontium ferrite powder, and is 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 the ICP analyzer is 0% by mass. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The above-mentioned "not included" is used in the sense of including the inclusion in an amount less than the detection limit of the ICP analyzer. The hexagonal strontium ferrite powder can, in one form, be free of bismuth atoms (Bi).

Metallic powder Ferromagnetic metal powder can also be mentioned as a preferable specific example of the ferromagnetic powder. For details of the ferromagnetic metal powder, for example, paragraphs 0137 to 0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351 can be referred to.

ε-Iron oxide powder As a preferable specific example of the ferromagnetic powder, ε-iron oxide powder can also be mentioned. In the present invention and the present specification, "ε-iron oxide powder" refers to a ferromagnetic powder in which an ε-iron oxide type crystal structure is detected as a main phase by X-ray diffraction analysis. For example, when the highest intensity diffraction peak is attributed to the ε-iron oxide type crystal structure in the X-ray diffraction spectrum obtained by X-ray diffraction analysis, the ε-iron oxide type crystal structure is detected as the main phase. It shall be judged. As a method for producing ε-iron oxide powder, a method for producing goethite, a reverse micelle method, and the like are known. All of the above manufacturing methods are known. Further, regarding a method for producing an 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. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mol. Mater. Chem. C, 2013, 1, pp. 5200-5206 and the like can be referred to. However, the method for producing ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer of the magnetic recording medium is not limited to the method described here.

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

Anisotropy constant Ku can be mentioned as an index for reducing thermal fluctuation, in other words, improving thermal stability. The ε-iron oxide powder can preferably have a Ku of 3.0 × 10 ⁴ J / m ³ or more, and more preferably 8.0 × 10 ⁴ J / m ³ or more. Further, the Ku of the ε-iron oxide powder can be, for example, 3.0 × ^{105 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 values.

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

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

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

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

Further, the needle-like ratio of the powder is shorter than the arithmetic average (average major axis length) of the major axis length obtained for the above 500 particles by measuring the minor axis length of the particles in the above measurement, that is, the minor axis length. It is obtained as "average major axis length / average minor axis length" from the arithmetic average (average minor axis length) of the axis length. 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 (average major axis length / average 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 The 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 and an average particle size).

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

(Binder)
The magnetic recording medium can be a coating type magnetic recording medium, and the magnetic layer can contain a binder. A binder is one or more resins. As the binder, various resins usually used as a binder for a coated 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 resin, acrylic resin, cellulose resin, and vinyl chloride resin are preferable. 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 binder, paragraphs 0028 to 0031 of JP-A-2010-24113 can be referred to. The average molecular weight of the resin used as a binder can be, for example, 10,000 or more and 200,000 or less as a weight average molecular weight. The weight average molecular weight in the present invention and the present specification is a value obtained by converting a value measured under the following measurement conditions by gel permeation chromatography (GPC) into polystyrene. The weight average molecular weight of the binder shown in Examples described later is a value obtained by converting a value measured under the following measurement conditions into polystyrene. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder.
GPC device: HLC-8120 (manufactured by Tosoh)
Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8 mm ID (Inner Diameter) x 30.0 cm)
Eluent: Tetrahydrofuran (THF)

(Hardener)
A curing agent can also be used 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 embodiment, and in another embodiment, a photocuring compound in which a curing reaction (crosslinking reaction) proceeds by light irradiation. It can be a sex compound. The curing agent can be contained in the magnetic layer in a state of reacting (crosslinking) with other components such as a binder, at least in part, as the curing reaction proceeds in the process of forming the magnetic layer. 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. The preferred curing agent is a thermosetting compound, and polyisocyanate is preferable. 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 may contain one or more additives, if necessary. The additive can be used in any amount by appropriately selecting a commercially available product according to desired properties or by producing it by a known method. Examples of the additive include the above-mentioned curing agent. Examples of the additive contained in the magnetic layer include non-magnetic powders, lubricants, dispersants, dispersion aids, fungicides, antistatic agents, antioxidants and the like. For example, for the lubricant, paragraphs 0030 to 0033, 0035 and 0036 of JP-A-2016-126817 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, 0031, 0034 to 0036 of JP-A-2016-126817. For the dispersant, paragraphs 0061 and 0071 of JP2012-133387A can be referred to. A dispersant may be added to the composition for forming a non-magnetic layer. For the dispersant that can be added to the composition for forming a non-magnetic layer, paragraph 0061 of Japanese Patent Application Laid-Open No. 2012-1333837 can be referred to.

Examples of the non-magnetic powder that can be contained in the magnetic layer include non-magnetic powder that can function as an abrasive. 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.

Examples of the non-magnetic powder that can be contained in the magnetic layer include non-magnetic powder (for example, non-magnetic colloid particles, carbon black, etc.) that can function as a protrusion forming agent that forms protrusions that appropriately project on the surface of the magnetic layer. Be done. As the protrusion forming agent, for example, one having an average particle size of 5 to 300 nm can be used. The average particle size of colloidal silica (silica colloidal particles) shown in Examples described later is a value obtained by the method described in paragraph 0015 of JP-A-2011-048878 as a method for measuring the average particle size. be. The content of the protrusion-forming agent in the magnetic layer is preferably 0.1 to 3.5 parts by mass, more preferably 0.1 to 3.0 parts by mass, for example, per 100.0 parts by mass of the ferromagnetic powder. preferable. When the amount of the protrusion forming agent in the magnetic layer is reduced, the value of Half-Rq tends to decrease.

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

<Non-magnetic layer>
Next, the non-magnetic layer will be described. The magnetic recording medium may have a magnetic layer directly on the surface of the non-magnetic support, and the magnetic layer is formed on the surface of the non-magnetic support via one layer or a plurality of non-magnetic layers containing the non-magnetic powder. You may have.

In order to reduce the value of Half-Rq on the surface of the magnetic layer, it is preferable to increase the surface smoothness of the non-magnetic layer, which is the surface on which the magnetic layer is formed. From this point of view, it is preferable to use a non-magnetic powder having a small average particle size as the non-magnetic powder contained in the non-magnetic layer. The average particle size of the non-magnetic powder is preferably in the range of 500 nm or less, more preferably 200 nm or less, further preferably 100 nm or less, still more preferably 50 nm or less. Further, from the viewpoint of easiness of improving the dispersibility of the non-magnetic powder, the average particle size of the non-magnetic powder is preferably 5 nm or more, more preferably 7 nm or more, and further preferably 10 nm or more. preferable.

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.

For carbon black that can be used for the non-magnetic layer, for example, paragraphs 0040 to 0041 of JP2010-24113A can be referred to. Carbon black generally tends to have a large particle size distribution and tends to have poor dispersibility. Therefore, the non-magnetic layer containing carbon black tends to have low surface smoothness. From this point of view, in one embodiment, it is preferable to provide a non-magnetic layer containing a non-magnetic powder other than carbon black as the non-magnetic layer adjacent to the magnetic layer. Further, it is preferable to provide a plurality of non-magnetic layers and to use the non-magnetic layer located closest to the magnetic layer as a non-magnetic layer containing non-magnetic powder other than carbon black. For example, two non-magnetic layers are provided between the non-magnetic support and the magnetic layer, and the non-magnetic layer on the non-magnetic support side (also referred to as “lower non-magnetic layer”) is a non-magnetic layer containing carbon black. It is preferable that the non-magnetic layer on the magnetic layer side (also referred to as "upper non-magnetic layer") is a non-magnetic layer containing a non-magnetic powder other than carbon black. Further, in the composition for forming a non-magnetic layer containing a plurality of types of non-magnetic powder, the dispersibility of the non-magnetic powder tends to be lower than that in the composition for forming a non-magnetic layer containing one kind of non-magnetic powder. From this point of view, it is preferable to provide a plurality of non-magnetic layers and reduce the types of non-magnetic powder contained in each non-magnetic layer. Further, in one form, it is preferable to use a dispersant in order to enhance the dispersibility of the non-magnetic powder in the composition for forming a non-magnetic layer containing a plurality of types of non-magnetic powder. The dispersant will be described later.

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 thereof, refer to paragraphs 0146 to 0150 of JP2011-216149A.

As one form of non-magnetic powder, non-magnetic iron oxide powder can be mentioned. From the viewpoint of reducing the value of Half-Rq on the surface of the magnetic layer by increasing the surface smoothness of the non-magnetic layer on which the magnetic layer is formed, a non-magnetic iron oxide powder having a small particle size is used. That is preferable. From this point, it is preferable to use a non-magnetic iron oxide powder having an average particle size in the range described above, and it is more preferable to use a non-magnetic iron oxide powder having an average particle size of 50 nm or less. When the non-magnetic iron oxide powder has the particle shape of (1) described above, the average particle size is the average major axis length. The needle-like ratio (average major axis length / average minor axis length) of the non-magnetic iron oxide powder can be more than 1.0. It is preferable to use a non-magnetic iron oxide powder having a small needle-like ratio from the viewpoint of improving the surface smoothness of the non-magnetic layer. From this point, the needle-like ratio (average major axis length / average minor axis length) of the non-magnetic iron oxide powder is preferably 3.0 or less, and more preferably 1.5 or less. As the non-magnetic iron oxide powder, α-iron oxide powder is preferable in one form. The α-iron oxide is iron oxide whose main phase is the α phase.

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. When a plurality of non-magnetic layers are provided, the content of the non-magnetic powder in at least one non-magnetic layer is preferably in the above range, and the content of the non-magnetic powder in more non-magnetic layers is described above. It is more preferably in the range.

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

Examples of the additive that can be contained in the non-magnetic layer include a dispersant that can contribute to improving the dispersibility of the non-magnetic powder. Examples of such dispersants include fatty acids represented by RCOOH (where R is an alkyl group or an alkenyl group) (eg, capric acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, and eridine). Acid, linoleic acid, linolenic acid, etc.); Alkali metal salt or alkaline earth metal salt of the above fatty acid; Ester of the above fatty acid; Fluorine-containing compound of the ester of the above fatty acid; Amid of the above fatty acid; Polyalkylene oxide alkyl phosphate Ester; Recitin; Trialkyl polyolefin oxyquaternary ammonium salt (alkyl group contained is an alkyl group having 1 to 5 carbon atoms, olefin contained is ethylene, propylene, etc.); phenylphosphonic acid; copper phthalocyanine, etc. is used. can do. These may be used alone or in combination of two or more. The content of the dispersant is preferably 0.2 to 5.0 parts by mass with respect to 100.0 parts by mass of the non-magnetic powder.

Further, as an example of the additive, an organic tertiary amine can be mentioned. For the organic tertiary amine, paragraphs 0011 to 0018 and 0021 of JP2013-049832A can be referred to. Organic tertiary amines can contribute to improving the dispersibility of carbon black. For the formulation of a composition for enhancing the dispersibility of carbon black with an organic tertiary amine, refer to paragraphs 0022 to 0024 and 0027 of the same publication.

The amine is more preferably a trialkylamine. The alkyl group contained in the trialkylamine is preferably an alkyl group having 1 to 18 carbon atoms. The three alkyl groups of the trialkylamine may be the same or different. For details of the alkyl group, refer to paragraphs 0015 to 0016 of JP2013-049832A. As the trialkylamine, trioctylamine is particularly preferable.

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 7.96 kA / m (100 Oe) or less, or the residual magnetic flux density is 10 mT or less. It refers to a layer having a coercive force of 7.96 kA / m (100 Oe) or less. The non-magnetic layer preferably has no residual magnetic flux density and coercive force.

<Non-magnetic support>
Next, the non-magnetic support will be described. Examples of the non-magnetic support (hereinafter, also simply referred to as “support”) include known biaxially stretched polyethylene terephthalates, polyethylene naphthalates, polyamides, polyamideimides, aromatic polyamides and the like. Among these, polyethylene terephthalate, polyethylene naphthalate and polyamide are preferable. These supports may be subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like in advance.

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

<Various thickness>
With regard to the thickness (total thickness) of the magnetic recording medium, with the enormous increase in the amount of information in recent years, the magnetic recording medium is required to have an increased recording capacity (higher capacity). As a means for increasing the capacity, the thickness of the magnetic recording medium may be reduced (hereinafter, also referred to as “thinning”), and the length of the magnetic tape accommodated in one magnetic tape cartridge may be increased. .. From this point, the thickness (total thickness) of the magnetic recording medium is preferably 5.6 μm or less, more preferably 5.5 μm or less, and even more preferably 5.4 μm or less. It is more preferably 3 μm or less, and even more preferably 5.2 μm or less. Further, from the viewpoint of ease of handling, the thickness of the magnetic recording medium is preferably 3.0 μm or more, and more preferably 3.5 μm or more.

For example, the thickness (total thickness) of the magnetic tape can be measured by the following method.
Ten tape samples (for example, 5 to 10 cm in length) are cut out from an arbitrary part of the magnetic tape, and these tape samples are stacked and the thickness is measured. The value obtained by dividing the measured thickness by 1/10 (thickness per tape sample) is defined as the tape thickness. The thickness measurement can be performed using a known measuring instrument capable of measuring the thickness on the order of 0.1 μm.

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

The thickness of the magnetic layer can be optimized by the saturation magnetization amount of the magnetic head used, the head gap length, the band of the recording signal, etc., and is generally 0.01 μm to 0.15 μm, from the viewpoint of high-density recording. It is preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.1 μm. The magnetic layer may be at least one layer, and the magnetic layer may be separated into two or more layers having different magnetic properties, 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. This point also applies to the thickness of the non-magnetic layer in the magnetic recording medium having the plurality of non-magnetic layers.

Regarding the thickness of the non-magnetic layer, the thicker the non-magnetic layer is formed, the more likely the non-magnetic powder particles are present to be non-uniform in the coating step and the drying step of the composition for forming the non-magnetic layer, and the presence state of the particles of the non-magnetic powder tends to be non-uniform at each position. The difference in thickness tends to increase and the surface of the non-magnetic layer tends to become rough. In order to reduce the value of Half-Rq on the surface of the magnetic layer, it tends to be preferable that the surface smoothness of the non-magnetic layer is high, and from this viewpoint, the thickness of the non-magnetic layer is 1.5 μm or less. It is preferably 1.0 μm or less, and more preferably 1.0 μm or less. Further, the thickness of the non-magnetic layer is preferably 0.05 μm or more, more preferably 0.1 μm or more, from the viewpoint of improving the uniformity of coating of the composition for forming the non-magnetic layer.

The thickness of the backcoat layer is preferably 0.9 μm or less, more preferably 0.1 to 0.7 μm.
Various thicknesses such as the thickness of the magnetic layer can be obtained by the following methods.
After exposing the cross section of the magnetic recording medium in the thickness direction with an ion beam, the cross section of the exposed cross section is observed with a scanning electron microscope. Various thicknesses can be obtained as the arithmetic mean of the thicknesses obtained at any two points in the cross-sectional observation. Alternatively, various thicknesses can be obtained as design thicknesses calculated from manufacturing conditions and the like.

<Manufacturing process>
(Preparation of composition for forming each layer)
The step of preparing the composition for forming the magnetic layer, the non-magnetic layer or the backcoat layer usually includes at least a kneading step, a dispersion step, and a mixing step provided before and after these steps as necessary. Can be done. Each process may be divided into two or more stages. The components used in the preparation of each layer-forming composition may be added at the beginning or in the middle of any step. As the solvent, one kind or two or more kinds of various solvents usually used for producing a coating type magnetic recording medium can be used. For the solvent, for example, paragraph 0153 of JP-A-2011-216149 can be referred to. Further, the individual components may be added separately in two or more steps. For example, the binder may be divided and added in a kneading step, a dispersion step and a mixing step for adjusting the viscosity after dispersion. In order to manufacture the magnetic recording medium, known manufacturing techniques can be used in various steps. In the kneading step, it is preferable to use an open kneader, a continuous kneader, a pressurized kneader, an extruder or the like having a strong kneading force. For details of the kneading process, Japanese Patent Application Laid-Open No. 1-106338 and Japanese Patent Application Laid-Open No. 1-79274 can be referred to. A known disperser can be used. Filtration may be performed by a known method at any stage of preparing each layer-forming composition. 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.

(Applying process)
The magnetic layer can be formed by directly applying the composition for forming a magnetic layer on the surface of a non-magnetic support, or by applying multiple layers sequentially or simultaneously with the composition for forming a non-magnetic layer. In the backcoat layer, the composition for forming the backcoat layer is placed on the opposite side of the surface having the non-magnetic layer and / or the magnetic layer of the non-magnetic support (or the non-magnetic layer and / or the magnetic layer is additionally provided). It can be formed by applying it to the surface. For details of the coating for forming each layer, refer to paragraph 0066 of Japanese Patent Application Laid-Open No. 2010-231843.

(Other processes)
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, the coating layer of the composition for forming a magnetic layer can be subjected to an orientation treatment while the coating layer is in a wet state. Various known techniques such as the description in paragraph 0067 of JP-A-2010-231843 can be applied to the alignment treatment. For example, the vertical alignment treatment can be performed by a known method such as a method using a magnet opposite to the opposite pole. In the alignment zone, the drying rate of the coating layer can be controlled by the temperature and air volume of the drying air and / or the transport speed of the non-magnetic support forming the coating layer in the alignment zone. In addition, 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 value of Half-Rq on the surface of the magnetic layer tends to decrease. Examples of the calendar conditions include the number of times the calendar treatment is performed (hereinafter, also referred to as “number of calendars”), the calendar pressure, the calendar temperature (surface temperature of the calendar roll), the calendar speed, the hardness of the calendar roll, and the like. The more calendars you have, the stronger the calendaring process. As for the calendar pressure, the calendar temperature, and the hardness of the calendar roll, the larger these values are, the stronger the calendar treatment is, and the slower the calendar speed is, the stronger the calendar treatment is. For example, the calendar pressure (linear pressure) can be 200 to 500 kg / cm, preferably 250 to 350 kg / cm. The calendar temperature (surface temperature of the calendar roll) can be, for example, 85-120 ° C, preferably 90-110 ° C, and the calendar speed can be, for example, 50-300 m / min, 50-. It is preferably 200 m / min.
By going through various steps, a long magnetic recording medium raw fabric can be obtained. The obtained magnetic recording medium raw material is cut (slit) by a known cutting machine to, for example, the width of the magnetic tape to be wound around the magnetic tape cartridge. The above width is determined according to the standard and is usually 1/2 inch. 1/2 inch = 12.65 mm.
A servo pattern is usually formed on the magnetic recording medium obtained by slitting. The details of the servo pattern will be described later.

(Heat treatment)
In one form, the magnetic recording medium can be a magnetic tape manufactured through the following heat treatment. Further, in another embodiment, the magnetic recording medium can be a magnetic tape manufactured without undergoing the following heat treatment.

As the heat treatment, a magnetic tape that has been slit and cut to a width determined according to the standard can be wound around a core-shaped member, and the heat treatment can be performed in the wound state.

In one form, the heat treatment is performed with the magnetic tape wound around a core-shaped member for heat treatment (hereinafter referred to as “heat treatment winding core”), and the heat-treated magnetic tape is wound around a reel of a magnetic tape cartridge. , A magnetic tape cartridge in which a magnetic tape is wound on a reel can be manufactured.
The heat treatment core can be made of metal, resin, paper, or the like. The material of the core for heat treatment is preferably a material having high rigidity from the viewpoint of suppressing the occurrence of winding failure such as spoking. From this point, the heat treatment core is preferably made of metal or resin. Further, as an index of rigidity, the flexural modulus of the material of the heat treatment core is preferably 0.2 GPa (gigapascal) or more, and more preferably 0.3 GPa or more. On the other hand, since a high-rigidity material is generally expensive, using a heat-treating winding core of a material having a rigidity exceeding the rigidity capable of suppressing the occurrence of winding failure leads to an increase in cost. Considering the above points, the flexural modulus of the material of the heat treatment core is preferably 250 GPa or less. The flexural modulus is a value measured according to ISO (International Organization for Standardization) 178, and the flexural modulus of various materials is known. Further, the heat treatment winding core can be a solid or hollow core-shaped member. In the case of a hollow shape, the wall thickness is preferably 2 mm or more from the viewpoint of maintaining rigidity. Further, the heat treatment core may or may not have a flange.
As a magnetic tape to be wound around the heat treatment core, prepare a magnetic tape having a length longer than the length finally accommodated in the magnetic tape cartridge (hereinafter referred to as "final product length"), and wind this magnetic tape around the heat treatment core. It is preferable to perform the heat treatment by placing the magnet in a heat treatment environment. The length of the magnetic tape wound around the heat treatment core is longer than the final product length, and from the viewpoint of ease of winding around the heat treatment core or the like, it is preferably "final product length + α". This α is preferably 5 m or more from the viewpoint of ease of winding. The tension at the time of winding to the heat treatment core is preferably 0.1 N (Newton) or more. Further, from the viewpoint of suppressing the occurrence of excessive deformation, the tension at the time of winding to the heat treatment winding core is preferably 1.5 N or less, more preferably 1.0 N or less. The outer diameter of the heat treatment core is preferably 20 mm or more, more preferably 40 mm or more, from the viewpoint of ease of winding and suppression of coiling (curl in the longitudinal direction). The outer diameter of the heat treatment core is preferably 100 mm or less, more preferably 90 mm or less. The width of the heat treatment core may be equal to or larger than the width of the magnetic tape wound around the core. Further, when the magnetic tape is removed from the heat treatment core after the heat treatment, the magnetic tape and the heat treatment core are sufficiently cooled before the magnetic tape is sufficiently cooled in order to prevent unintended tape deformation during the removal operation. Is preferably removed from the heat treatment core. The removed magnetic tape is once wound on another winding core (referred to as "temporary winding core"), and then from the temporary winding core to the reel of the magnetic tape cartridge (generally, the outer diameter is 40 to 50 mm). It is preferable to wind the magnetic tape around. As a result, the magnetic tape can be wound around the reel of the magnetic tape cartridge while maintaining the relationship between the inside and the outside of the magnetic tape with respect to the heat treatment core during the heat treatment. For details of the temporary winding core and the tension when winding the magnetic tape around this winding core, refer to the previous description regarding the heat treatment winding core. In the form in which the above heat treatment is applied to a magnetic tape having a length of "final product length + α", the length of "+ α" may be cut off at an arbitrary stage. For example, in one form, the magnetic tape for the final product length may be wound from the temporary winding core to the reel of the magnetic tape cartridge, and the remaining “+ α” length may be cut off. From the viewpoint of reducing the portion to be cut and discarded, the α is preferably 20 m or less.

The specific form of the heat treatment performed in the state of being wound around the core-shaped member as described above will be described below.
The atmospheric temperature at which the heat treatment is performed (hereinafter, referred to as “heat treatment temperature”) is preferably 40 ° C. or higher, more preferably 50 ° C. or higher. On the other hand, from the viewpoint of suppressing excessive deformation, the heat treatment temperature is preferably 75 ° C. or lower, more preferably 70 ° C. or lower, and even more preferably 65 ° C. or lower.
The weight absolute humidity of the atmosphere in which the heat treatment is performed is preferably 0.1 g / kg Dry air or more, and more preferably 1 g / kg Dry air or more. Atmospheres with a weight absolute humidity in the above range are preferable because they can be prepared without using a special device for reducing moisture. On the other hand, the weight absolute humidity is preferably 70 g / kg Dry air or less, and more preferably 66 g / kg Dry air or less, from the viewpoint of suppressing the occurrence of dew condensation and deterioration of workability. The heat treatment time is preferably 0.3 hours or more, more preferably 0.5 hours or more. The heat treatment time is preferably 48 hours or less from the viewpoint of production efficiency.

(Formation of servo pattern)
The magnetic recording medium can be a tape-shaped magnetic recording medium (that is, a magnetic tape) or a disk-shaped magnetic recording medium (that is, a magnetic disk). In any form, the magnetic layer can have a servo pattern. "Formation of servo pattern" can also be referred to as "recording of servo signal". Hereinafter, the formation of the servo pattern will be described using a magnetic tape as an example.

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

As shown in ECMA (European Computer Manufacturers Association) -319 (June 2001), the timing-based servo method is adopted in the magnetic tape (generally called "LTO tape") compliant with the LTO (Linear Tape-Open) standard. ing. 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 a plurality 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 to the servo signal reading element passing on the servo pattern. Specifically, the pair of magnetic stripes described above are formed so that their spacing changes continuously along the width direction of the magnetic tape, and the servo signal reading element reads the spacing 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 a servo pattern that is 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 the data band. The data band is composed of a plurality of data tracks, and each data track corresponds to each servo track.

Further, in one form, as shown in Japanese Patent Application Laid-Open No. 2004-318983, each servo band has information indicating a servo band number (“servo band ID (identification)” or “UDIM (Unique DataBand Identification)”. It is also called "Servo) information".) Is embedded. The servo band ID is recorded by shifting a specific pair of servo stripes in the servo band so that their positions are relatively displaced in the longitudinal direction of the magnetic tape. Specifically, the method of shifting a specific pair of servo stripes is changed for each servo band. As a result, the recorded servo band ID becomes unique for each servo band, so that the servo band can be uniquely identified by simply reading one servo band with the servo signal reading element.

As a method for uniquely specifying the servo band, there is also a method using a staggered method as shown in ECMA-319 (June 2001). 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 non-parallel to each other are recorded so as to be shifted in the longitudinal direction of the magnetic tape for each servo band. do. Since this combination of shifting methods between adjacent servo bands is unique in 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 (June 2001), information indicating the position of the magnetic tape in the longitudinal direction (also referred to as "LPOS (Longitorial Position) information") is usually embedded in each servo band. ing. This LPOS information, like the UDIM information, is also recorded by shifting the position 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 usually 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 a servo pattern, the magnetic pattern corresponding to a 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 erase 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 erase 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 subjected to horizontal DC erase, 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 a magnetic pattern using the above gap is transferred to a vertically DC-erased magnetic tape, 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.

Further, in one form, dimensional information in the width direction of the traveling magnetic tape is acquired by using a servo signal, and the tension applied in the longitudinal direction of the magnetic tape is adjusted and changed according to the acquired dimensional information. Allows you to control the widthwise dimensions of the magnetic tape. Performing such tension adjustment prevents the magnetic head for recording or reproducing data from being displaced from the target track position during recording or reproduction due to the width deformation of the magnetic tape, and recording or reproducing the data. Can contribute to suppression.

[Magnetic tape cartridge]
In one form, the magnetic recording medium can be a magnetic tape. One aspect of the present invention relates to a magnetic tape cartridge containing the magnetic tape.

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

In a magnetic tape cartridge, the magnetic tape is generally housed inside the cartridge body in a state of being wound on a reel. The reel is rotatably provided inside the cartridge body. As the magnetic tape cartridge, a single reel type magnetic tape cartridge having one reel inside the cartridge main body and a twin reel type magnetic tape cartridge having two reels inside the cartridge main body are widely used. When the single reel type magnetic tape cartridge is attached to the magnetic tape device for recording and / or playing back data on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and wound on the reel on the magnetic tape device side. Taken. 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 tape 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, so that data can be recorded and / or reproduced. On the other hand, in the twin reel type magnetic tape cartridge, both the supply reel and the take-up reel are provided inside the magnetic tape cartridge.

[Magnetic recording / playback device]
One aspect of the present invention relates to a magnetic recording / reproducing device including a magnetic recording medium. In one embodiment, in the magnetic recording / reproducing device, the recording of data on the magnetic recording medium and / or the reproduction of the data recorded on the magnetic recording medium are performed by bringing the surface of the magnetic layer of the magnetic recording medium into contact with the magnetic head. It can be done by moving it. Such a form of magnetic recording / reproduction device is generally called a sliding drive or a contact sliding drive. In another embodiment, the magnetic head records data on a magnetic recording medium and / or data recorded on a magnetic recording medium in a non-contact state, except in the case of random contact with the surface of the magnetic layer. Play back. Such a form of magnetic recording / reproduction device is generally called a levitation type drive. For example, in a form in which the magnetic recording medium is a magnetic tape, the magnetic recording / reproducing device can be a sliding drive in one form and a floating drive in another form.

In the present invention and the present specification, the "magnetic recording / reproduction device" means an apparatus capable of recording data on a magnetic recording medium and reproducing data recorded on the magnetic recording medium. do. Such a device is commonly referred to as a drive. The magnetic head included in the magnetic recording / reproducing device can be a recording head capable of recording data on a magnetic recording medium, and can reproduce data recorded on the magnetic recording medium. Can also be. Further, in one form, the magnetic recording / reproducing device may include both a recording head and a reproducing head as separate magnetic heads. In another embodiment, the magnetic head included in the magnetic tape device may have a configuration in which both a recording element and a reproducing element are provided in one magnetic head. As the reproduction head, a magnetic head (MR head) including a magnetoresistive (MR; Magnetoresistive) element capable of reading information recorded on a magnetic recording medium with high sensitivity is preferable. As the MR head, various known MR heads (for example, GMR (Giant Magnetoresistive) head, TMR (Tunnel Magnetorestive) head, etc.) can be used. Further, the magnetic head that records data and / or reproduces data may include a servo signal reading element. Alternatively, the magnetic tape device may include a magnetic head (servohead) provided with a servo signal reading element as a head separate from the magnetic head that records and / or reproduces data. For example, a magnetic head that records data and / or reproduces recorded data (hereinafter, also referred to as “recording / reproducing head”) can include two servo signal reading elements, and two servo signal reading elements. Each of the two servo bands adjacent to each other with the data band in between can be read at the same time. One or more data elements can be arranged between the two servo signal reading elements. Elements for recording data (recording elements) and elements for reproducing data (reproduction elements) are collectively referred to as "data elements".

When recording data and / or reproducing recorded data, tracking using a servo signal can be performed first. That is, by making the servo signal reading element follow a predetermined servo track, the data element can be controlled to pass 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.

FIG. 1 shows an example of arrangement of a data band and a 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 magnetization 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 a 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 a subframe arranged in an array of 5, 5, 4, 4, and used to identify the servo frame. FIG. 2 shows one servo frame for illustration. However, in reality, a plurality of servo frames are arranged in the traveling direction in each servo band on the magnetic layer of the magnetic tape on which the head tracking of the timing-based servo method is performed. In FIG. 2, the arrow indicates the traveling direction. For example, an LTO Ultra format tape usually has a servo frame of 5000 or more per 1 m of tape length in each servo band of the magnetic layer.

In the above magnetic recording / playback device, in one form, the magnetic recording medium is treated as a removable medium (so-called replaceable medium), and for example, a magnetic tape cartridge containing a magnetic tape is inserted into the magnetic recording / playback device and taken out. .. In another embodiment, the magnetic recording medium is not treated as a convertible medium, for example, the magnetic tape is wound around a reel of a magnetic recording / playback device provided with a magnetic head, and the magnetic tape is housed in the magnetic recording / playback device. ..

Hereinafter, one aspect of the present invention will be described based on examples. However, the present invention is not limited to the embodiments shown in the examples. The indications of "part" and "%" described below indicate "parts by mass" and "% by mass" unless otherwise specified. “Eq” is an equivalent and is a unit that cannot be converted into SI units.
Unless otherwise specified, the following various steps and operations were performed in an environment with a temperature of 20 to 25 ° C. and a relative humidity of 40 to 60%.

The ferromagnetic powder described as "metal" in Table 1 described later is similar to the ferromagnetic powder used in Example 1 of Patent Document 1 (Japanese Unexamined Patent Publication No. 2004-103137) shown above. As a material, an iron-cobalt alloy-based ferromagnetic powder was used.

In Table 1 below, "BaFe" indicates a hexagonal barium ferrite powder having an average particle size (average plate diameter) of 21 nm.

In Table 1 below, "SrFe" indicates a hexagonal strontium ferrite powder prepared by the method described below, and "ε-iron oxide" indicates an ε-iron oxide powder prepared by the method described below. ..
The average particle volume of the various ferromagnetic powders described below is a value obtained by the method described above. The various values related to the particle size of the various powders described below are also the values obtained by the method described above.
The anisotropy constant Ku is a value obtained for each ferromagnetic powder by the method described above using a vibration sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).
The mass magnetization σs is a value measured at a magnetic field strength of 15 kOe using a vibration sample magnetometer (manufactured by Toei Kogyo Co., Ltd.).

[Method for producing ferromagnetic powder]
<Method for producing hexagonal strontium ferrite powder>
Weigh 1707 g of SrCO ₃ , 687 g of H ₃ BO ₃ , 1120 g of Fe ₂ O ₃ , 45 g of Al (OH) ₃ , 24 g of BaCO ₃ , 13 g of CaCO ₃ , and 235 g of Nd ₂ O ₃ 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, so that the melt was discharged into a rod shape at about 6 g / sec. .. The hot water was rolled and rapidly cooled with a water-cooled twin roller to prepare an amorphous body.
280 g of the prepared 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 obtained above containing hexagonal strontium ferrite particles was coarsely 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 steel beaker. The dispersion is allowed to stand at a liquid temperature of 100 ° C. for 3 hours to dissolve the glass components, then settled in a centrifuge and decanted repeatedly for cleaning. It was dried for a time to obtain a hexagonal strontium ferrite powder.
The hexagonal strontium ferrite powder (“SrFe” in Table 1 below) obtained above has an average particle volume of 900 nm ³ , anisotropy constant Ku of 2.2 × ^{105 J / m 3} ^, and mass magnetization σs. It 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 to perform elemental analysis of the filtrate obtained by using an ICP analyzer. 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 atom (bulk content) with respect to 100 atomic% of iron atom of the hexagonal strontium ferrite powder obtained above was 2.9 atomic%. The content of the neodymium atom in the surface layer was 8.0 atom%. The ratio of the surface layer content to the bulk content, "surface layer content / bulk content" was 2.8, and it was confirmed that the neodymium atoms were unevenly distributed on the surface layer of the particles.

To show the crystal structure of hexagonal ferrite in the powder obtained above, CuKα rays are scanned under the conditions of a voltage of 45 kV and an intensity of 40 mA, and the X-ray diffraction pattern is measured under the following conditions (X-ray diffraction analysis). confirmed. The powder obtained above showed a crystal structure of a magnetoplumbite type (M type) hexagonal ferrite. Moreover, the crystal phase detected by the X-ray diffraction analysis was a single phase of the magnetoplumbite type.
PANalitic X'Pert Pro Diffractometer, PIXcel Detector Soller slit of incident beam and diffracted beam: 0.017 Fixed angle of radian dispersion slit: 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 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) dissolved in it 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 in water again 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 temperature of 80 ° C. for 24 hours to obtain 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 atmospheric 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 prepare the precursor of the heat-treated ferromagnetic powder. The caustic compound, which is an impurity, was removed from the material.
Then, the ferromagnetic powder from which the silicic acid compound was removed was collected by centrifugation and washed with pure water to obtain a ferromagnetic powder.
The composition of the obtained ferromagnetic powder was confirmed by high frequency inductively coupled plasma emission spectroscopy (ICP-OES; Inductively Coupled Plasma-Optical Operation Spectroscopy) and found to be Ga, Co and Ti substituted ε-iron oxide (ε-Ga ₀ ). It was _.28 Co _0.05 Ti _0.05 Fe _1.62 O ₃ ). Further, X-ray diffraction analysis was performed under the same conditions as those described above for the method for producing hexagonal strontium ferrite powder, and the ferromagnetic powder obtained from the peak of the X-ray diffraction pattern was of 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 contain a crystal structure.
The average particle volume of the obtained ε-iron oxide powder (“ε-iron oxide” in Table 1 below) is 750 nm ³ , the anisotropic constant Ku is 1.2 × ^{105 J / m 3} ^, and the mass magnetization σs. Was 16 A · m ² / kg.

[Example 1]
(1) Preparation of alumina dispersion 3. For 100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) having an pregelatinization rate of about 65% and a BET (Brunauer-Emmett-Teller) specific surface area of 20 m ² / g. A 32% solution of 0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo Kasei Co., Ltd.) and a polyester polyurethane resin having an SO ₃ Na group as a polar group (UR-4800 manufactured by Toyo Boseki Co., Ltd. (polar group amount: 80 meq / kg)) ( 31.3 parts of a mixed solvent of methyl ethyl ketone and toluene) was mixed as a solvent, and 570.0 parts of a mixed solution of methyl ethyl ketone and cyclohexanone 1: 1 (mass ratio) was mixed as a solvent, and dispersed for 5 hours with a paint shaker in the presence of zirconia beads. I let you. After the dispersion, the dispersion liquid and the beads were separated by a mesh to obtain an alumina dispersion.

(2) Formulation of composition for forming a magnetic layer (magnetic liquid)
Ferromagnetic powder (type: see Table 1) 100.0 parts SO ₃ Na group-containing polyurethane resin 14.0 parts Weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g
Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (abrasive solution)
6.0 parts of alumina dispersion prepared in (1) above (projection forming agent solution)
Protrusion forming agent See Table 1 Type: Colloidal silica (average particle size 120 nm)
Methyl ethyl ketone 1.4 parts (other ingredients)
Stearic acid 2.0 parts Stearic acid amide 0.2 parts Butyl stearate 2.0 parts Polyisocyanate (Tosoh Coronate (registered trademark) L) 2.5 parts (finishing additive solvent)
Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

(3) Formulation of composition for forming a non-magnetic layer Non-magnetic inorganic powder: α-iron oxide 100.0 parts Average particle size (average major axis length): 0.15 μm
Needle ratio: 7
BET specific surface area: 52m ² / g
Carbon black 20.0 parts Average particle size: 20nm
SO ₃ Na group-containing polyurethane resin 18.0 parts Weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g
Stearic acid 2.0 parts Stearic acid amide 0.2 parts Butyl stearate 2.0 parts Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0 parts

(4) Composition for backcoat layer formation Formulation Carbon black 100.0 parts DBP (Dibutyl phthalate) Oil absorption: 74 cm ^3/100 g
27.0 parts of nitrocellulose Polyester polyurethane resin containing a sulfonic acid group and / or a salt thereof 62.0 parts Polyester resin 4.0 parts Alumina powder (BET specific surface area: 17 m ² / g) 0.6 parts Methyl ethyl ketone 600.0 parts 600.0 parts Polyisocyanate (Coronate (registered trademark) L manufactured by Toso Co., Ltd.) 15.0 parts

(5) Preparation of composition for forming each layer A composition for forming a magnetic layer was prepared by the following method. The above magnetic liquid was prepared by dispersing each component 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. Using the above sand mill, the prepared magnetic solution, the above abrasive solution and other components (silica sol, other components and finish addition solvent) are mixed and bead-dispersed for 5 minutes, and then a batch type ultrasonic device (20 kHz, 300 W). The treatment (ultrasonic dispersion) was carried out for 0.5 minutes. Then, filtration was performed using a filter having a pore size of 0.5 μm to prepare a composition for forming a magnetic layer.
A composition for forming a non-magnetic layer was prepared by the following method. The above components excluding the lubricants (stearic acid, stearic acid amide and butyl stearate) were kneaded and diluted with an open kneader, and then dispersed with a horizontal bead mill disperser. Then, a lubricant (stearic acid, stearic acid amide and butyl stearate) was added, and the mixture was stirred and mixed with a dissolver stirrer to prepare a composition for forming a non-magnetic layer.
The composition for forming the back coat layer was prepared by the following method. The above components excluding polyisocyanate were introduced into a dissolver stirrer, stirred at a peripheral speed of 10 m / sec for 30 minutes, and then dispersed by a horizontal bead mill disperser. Then, polyisocyanate was added, and the mixture was stirred and mixed with a dissolver stirrer to prepare a composition for forming a backcoat layer.

(6) Preparation of Magnetic Tape and Magnetic Tape Cartridge Prepared in (5) above on the surface of a biaxially stretched polyethylene terephthalate support having a thickness of 4.1 μm so that the thickness after drying is 0.7 μm. The non-magnetic layer forming composition was applied and dried to form a non-magnetic layer. Next, the composition for forming a magnetic layer prepared in (5) above was applied onto the non-magnetic layer so that the thickness after drying was 0.1 μm to form a coated layer. After that, while the coated layer of the composition for forming a magnetic layer is in an undried state, a magnetic field having a magnetic field strength of 0.3 T is applied in the direction perpendicular to the surface of the coated layer to perform a vertical alignment treatment, and then drying. And formed a magnetic layer. Then, on the surface of the support opposite to the surface on which the non-magnetic layer and the magnetic layer were formed, the composition for forming the back coat layer prepared in (5) above so that the thickness after drying is 0.3 μm is applied. It was applied and dried to form a backcoat layer.
Then, using a calendar roll composed of only metal rolls, a surface smoothing treatment (calender treatment) is performed at a speed of 100 m / min, a linear pressure of 300 kg / cm, and a calendar temperature of 90 ° C. (the surface temperature of the calendar roll). (Number of calendars: see Table 1).
Then, the raw magnetic tape was stored in a heat treatment furnace having an atmospheric temperature of 70 ° C. for heat treatment (heat treatment time: 36 hours). After the heat treatment, slits were made to a width of 1/2 inch to obtain a magnetic tape. By recording a servo signal on the magnetic layer of the obtained magnetic tape with a commercially available servo writer, it has a data band, a servo band, and a guide band in an arrangement according to the LTO (Linear Tape-Open) Ultra format, and has a servo. A magnetic tape having a servo pattern (timing-based servo pattern) arranged and shaped according to the LTO Ultra format on the band was obtained. The servo pattern thus formed is a servo pattern according to JIS (Japanese Industrial Standards) X6175: 2006 and Standard ECMA-319 (June 2001). The total number of servo bands is 5, and the total number of data bands is 4.
The magnetic tape (length 970 m) after forming the servo pattern was wound around a core for heat treatment, and the heat treatment was performed in a state of being wound around the core. As the core for heat treatment, a resin-made solid core member (outer diameter: 50 mm) having a flexural modulus of 0.8 GPa was used, and the tension at the time of winding was 0.6 N. The heat treatment was performed at a heat treatment temperature of 50 ° C. for 5 hours. The weight absolute humidity of the heat-treated atmosphere was 10 g / kg Dry air.
After the above heat treatment, after the magnetic tape and the heat treatment core have been sufficiently cooled, the magnetic tape is removed from the heat treatment core, wound around the temporary winding core, and then the magnetic tape cartridge (from the temporary winding core). Wind the magnetic tape for the final product length (960 m) on the reel (reel outer diameter: 44 mm) of the LTO Ultra7 data cartridge, cut off the remaining 10 m, and use a commercially available splicing tape at the end of the cut side to standard ECMA ( European Computer Manufacturers Association)-319 (June 2001) Leader tapes were bonded according to Item 9 of Section 3. As the winding core for temporary winding, a solid core-shaped member made of the same material as the winding core for heat treatment and having the same outer diameter was used, and the tension at the time of winding was 0.6N.
As described above, a single reel type magnetic tape cartridge of Example 1 in which a magnetic tape having a length of 960 m was wound on a reel was produced.

[Example 2]
A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 1 except that the calendar temperature was set to the temperature shown in Table 1.

[Example 3]
A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 1 except that the amount of carbon black (average particle size: 20 nm) shown in Table 1 was used as the protrusion forming agent.

[Example 4]
Two non-magnetic layers are formed as shown below, and the magnetic layer forming composition is applied onto the formed upper non-magnetic layer in the same manner as in Example 1 to form the magnetic layer and the number of calendars is once. A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 1.

<Prescription of composition for forming lower non-magnetic layer>
Carbon black (average particle size: 20 nm) 100.0 parts Trioctylamine 4.0 parts Vinyl chloride resin 12.0 parts Stearic acid 1.5 parts Stearic acid amide 0.3 parts Butyl stearate 1.5 parts Cyclohexanone 200. 0 parts Methyl ethyl ketone 510.0 parts

<Prescription of composition for forming upper non-magnetic layer>
Non-magnetic inorganic powder α-iron oxide 100.0 parts Average particle size (average major axis length): 30 nm
Average minor axis length: 15 nm
Needle ratio: 2.0
SO ₃ Na group-containing polyurethane resin 18.0 parts Weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g
Stearic acid 1.0 part Cyclohexanone 300.0 part Methyl ethyl ketone 300.0 part

For each of the above composition for forming a lower non-magnetic layer and the composition for forming an upper non-magnetic layer, each component was kneaded with an open kneader for 240 minutes and then dispersed with a sand mill. As the dispersion conditions of each non-magnetic layer forming composition, the dispersion time was 24 hours, and zirconia beads having a bead diameter of 0.1 mm were used as the dispersed beads. 4.0 parts each of polyisocyanate (Coronate 3041 manufactured by Tosoh Corporation) was added to the dispersion obtained in this manner, and the mixture was further stirred and mixed for 20 minutes, and then filtered using a filter having a pore size of 0.5 μm.

Based on the above, a composition for forming a lower non-magnetic layer and a composition for forming an upper non-magnetic layer were prepared. The composition for forming the lower non-magnetic layer was applied onto one surface of the same support as in Example 1 so that the thickness after drying was 0.25 μm, and dried in an environment with an ambient temperature of 100 ° C. A lower non-magnetic layer was formed. A composition for forming an upper non-magnetic layer was applied onto the lower non-magnetic layer so that the thickness after drying was 0.25 μm, and the composition was dried in an environment with an atmospheric temperature of 100 ° C. to form an upper non-magnetic layer.

[Example 5]
A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 4, except that the calendar temperature was set to the temperature shown in Table 1.

[Example 6]
As the ferromagnetic powder, a hexagonal strontium ferrite powder (“SrFe” in Table 1) prepared by the method described above was used, and two non-magnetic layers were formed by the same method as in Example 4. A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 3, except that the points and the number of calendars were set to 1.

[Example 7]
As the ferromagnetic powder, ε-iron oxide powder (“ε-iron oxide” in Table 1) produced by the method described above was used, and two non-magnetic layers were used in the same manner as in Example 4. The magnetic tape and the magnetic tape cartridge were produced in the same manner as in Example 3 except that the points where the above was formed and the number of times of calendering was set to 1.

[Comparative Example 1]
A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 1 except that the amount of colloidal silica added as a component of the composition for forming a magnetic layer was set to the amount shown in Table 1 and the number of calendars was set to 1.

[Comparative Example 2]
A magnetic tape and a magnetic tape cartridge were produced in the same manner as in Example 3 except that the number of calendars was one.

[Comparative Example 3]
In order to prepare a magnetic tape similar to Example 1 of Patent Document 1 (Japanese Unexamined Patent Publication No. 2004-103137) shown above, the magnetic tape shown in Table 1 was used as the ferromagnetic powder, and no protrusion forming agent was added. The same as in Example 1 except that a magnetic layer is formed on the surface, a composition for forming a non-magnetic layer is applied so that the thickness of the non-magnetic layer after drying is 1.3 μm, and the number of calenders is one. A magnetic tape and a magnetic tape cartridge were manufactured in.

For Examples and Comparative Examples, two magnetic tape cartridges were made, one for the following Half-Rq measurements and the other for the evaluation of the following electromagnetic conversion characteristics. ..

[Measurement of Half-Rq]
The AFM measurement conditions were as follows, and Half-Rq on the surface of the magnetic layer of each magnetic tape of Examples and Comparative Examples was determined according to the example shown above as a specific flow example.
AFM (Nanoscope 4 manufactured by Veeco) is used in a tapping mode to measure a region having an area of 40 μm × 40 μm on the surface of the magnetic layer of the magnetic recording medium. As the probe, RTESS-300 manufactured by BRUKER is used, the resolution is 512pixel × 512pixel, and the scanning speed is the speed at which one screen (512pixel × 512pixel) is measured in 341 seconds.

[Evaluation of electromagnetic conversion characteristics]
Each of the magnetic tape cartridges of Examples and Comparative Examples is attached to a magnetic recording / playback device, the magnetic tape is run under the following running conditions, and a magnetic signal is recorded in the longitudinal direction of the magnetic tape under the following recording / playback conditions and played back. It was reproduced by a head (MR head). The reproduced signal was frequency-analyzed using a spectrum analyzer manufactured by Shibasoku, and the ratio of the output of 300 kfci to the noise integrated in the range of 0 kfci to 600 kfci was defined as SNR (Signal-to-Noise-ratio). The unit kfci is a unit of line recording density (cannot be converted into the SI unit system). When determining the SNR, a sufficiently stable signal was used after the running of the magnetic tape was started. Table 1 below shows SNR as a relative value with the value of Comparative Example 3 as zero. If the SNR value is 2.0 dB or more, it can be determined that the electromagnetic conversion characteristics are excellent.
-Driving conditions-
Transport speed (head / tape relative speed): 5.5 m / sec-Recording / playback conditions-
(record)
Recording track width: 5.0 μm
Recording gap: 0.17 μm
Magnetic flux density of magnetic head (Bs): 1.8T
(reproduction)
Playback track width: 0.4 μm
Distance between shields: 0.08 μm
Line recording density: 300 kfci

The above results are shown in Table 1.

From the results shown in Table 1, it can be confirmed that the magnetic tape of the example is superior in electromagnetic conversion characteristics to the magnetic tape of the comparative example.
As a reference value, the root mean square roughness Rq, which is a value calculated including the negative part in addition to the positive part, was obtained according to JIS B 0601: 2013. As a result, Rq was obtained in Example 1: 2. It is 0.7 nm, Comparative Example 2: 2.5 nm, and the evaluation result of the electromagnetic conversion characteristics shown in Table 1 is inferior to that of Example 1. The Rq of Comparative Example 2 is smaller than the Rq of Example 1. there were. From the comparison between this result and the result shown in Table 1, it can be confirmed that controlling the value of Half-Rq obtained only from the positive part leads to improvement of the electromagnetic conversion characteristic.

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

Claims

A magnetic recording medium having a non-magnetic support and a magnetic layer containing a ferromagnetic powder.
The Half-Rq required on the surface of the magnetic layer is 3.0 nm or less, and is
The Half-Rq is the root mean square roughness obtained only for the positive part of the surface profile data obtained by inverse Fourier transforming the components having a frequency of 25 Hz or less with respect to the power spectrum density of the surface of the magnetic layer. , Magnetic recording medium.
The magnetic recording medium according to claim 1, wherein the Half-Rq is 0.5 nm or more and 3.0 nm or less.
The magnetic recording medium according to claim 1, wherein the Half-Rq is 2.0 nm or less.
The magnetic recording medium according to claim 3, wherein the Half-Rq is 0.5 nm or more and 2.0 nm or less.
The magnetic recording medium according to any one of claims 1 to 4, further comprising at least one non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.
The magnetic recording medium according to claim 5, which has two non-magnetic layers.
The magnetic recording medium according to claim 6, wherein the non-magnetic layer on the magnetic layer side of the two non-magnetic layers contains non-magnetic iron oxide powder, and the non-magnetic layer on the non-magnetic support side contains carbon black.
The magnetic recording medium according to claim 7, wherein the non-magnetic iron oxide powder is α-iron oxide powder.
The magnetic recording medium according to any one of claims 1 to 8, further comprising a backcoat layer containing a non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer.
The magnetic recording medium according to any one of claims 1 to 9, which is a magnetic tape.
A magnetic tape cartridge comprising the magnetic recording medium according to claim 10.
A magnetic recording / reproducing device including the magnetic recording medium according to any one of claims 1 to 10 and a magnetic head.