阅读说明：本技术 磁记录介质以及磁记录再生装置 (Magnetic recording medium and magnetic recording/reproducing apparatus ) 是由 笠田成人 于 2020-04-24 设计创作，主要内容包括：本发明提供一种磁记录介质以及包含该磁记录介质的磁记录再生装置。本发明在包含芳香族聚酰胺支撑体的磁记录介质中,抑制在高湿下从低温至高温的温度变化后进一步保存于高温高湿环境下之后的行进稳定性的降低。所述磁记录介质在非磁性支撑体的一个表面侧具有包含强磁性粉末的磁性层,在另一个表面侧具有包含非磁性粉末的背涂层,在所述磁记录介质中,在上述背涂层的表面上进行甲基乙基酮清洗后通过光学干涉法测定的间距S<Sub>after</Sub>与在上述背涂层的表面上进行甲基乙基酮清洗前通过光学干涉法测定的间距S<Sub>before</Sub>的差分(S<Sub>after</Sub>-S<Sub>before</Sub>)超过0nm且为30.0nm以下,并且上述非磁性支撑体是吸湿率为2.2％以下的芳香族聚酰胺支撑体。(The invention provides a magnetic recording medium and a magnetic recording and reproducing apparatus including the same. The present invention provides a magnetic recording medium comprising an aromatic polyamide support, which suppresses a decrease in running stability after the magnetic recording medium is further stored in a high-temperature and high-humidity environment after a temperature change from a low temperature to a high temperature under high humidity. The magnetic recording medium has a magnetic layer containing ferromagnetic powder on one surface side of a nonmagnetic support and a back coat layer containing nonmagnetic powder on the other surface side, and the magnetic recording medium has a pitch S measured by optical interferometry after methyl ethyl ketone cleaning on the surface of the back coat layer after And the spacing S as measured by optical interferometry before the cleaning with methyl ethyl ketone on the surface of the above-mentioned back coating before Difference (S) of after ‑S before ) The non-magnetic support is an aromatic polyamide support having a moisture absorption rate of 2.2% or less and having a thickness of more than 0nm and 30.0nm or less.)

1. A magnetic recording medium having a magnetic layer containing ferromagnetic powder on one surface side of a nonmagnetic support and a back coat layer containing nonmagnetic powder on the other surface side,

spacing S measured by optical interferometry after methyl ethyl ketone cleaning on the surface of the back coating_afterAnd the spacing S as determined by optical interferometry before the methyl ethyl ketone cleaning on the surface of the back coating_beforeDifference of (2), namely S_after－S_beforeMore than 0nm and not more than 30.0nm, and,

the non-magnetic support is an aromatic polyamide support having a moisture absorption rate of 2.2% or less.

2. The magnetic recording medium according to claim 1,

the difference is S_after－S_beforeIs 4.0nm or more and 28.0nm or less.

3. The magnetic recording medium according to claim 1 or 2,

the aromatic polyamide support has a moisture absorption rate of 2.0% or less.

4. The magnetic recording medium according to claim 1 or 2,

the aromatic polyamide support has a moisture absorption rate of 1.0% or more and 2.0% or less.

5. The magnetic recording medium according to claim 1 or 2,

a nonmagnetic layer containing nonmagnetic powder is provided between the nonmagnetic support and the magnetic layer.

6. The magnetic recording medium according to claim 1 or 2,

the magnetic recording medium is a magnetic tape.

7. A magnetic recording and reproducing apparatus, comprising:

a magnetic recording medium according to any one of claims 1 to 6; and

a magnetic head is provided.

Technical Field

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

Background

Magnetic recording media (for example, refer to patent document 1) are recording media useful as data storage media for storing large-capacity data (information) for a long time.

Patent document 1: japanese laid-open patent publication No. 9-227883

Recording of data in a magnetic recording medium and reproduction of recorded data are generally performed by mounting the magnetic recording medium in a magnetic recording and reproducing apparatus (referred to as a drive) and running the magnetic recording medium in the drive. In order to suppress the occurrence of errors in recording and reproduction, it is desirable to stabilize the running of the magnetic recording medium in the drive (to improve the running stability).

On the other hand, magnetic recording media used for data storage are sometimes used in data centers that manage temperature and humidity. On the other hand, in a data center, power saving is required to reduce costs. In order to save power, it is desirable to be able to relax the management conditions of the temperature and humidity in the data center or to eliminate the need for management. However, if the temperature and humidity control conditions are relaxed or not controlled, it is assumed that the magnetic recording medium is exposed to environmental changes due to climate changes, seasonal changes, and the like, and is stored in various temperature and humidity environments. An example of the environmental change is a temperature change from a low temperature to a high temperature under high humidity. Further, as an example of the temperature and humidity environment, a high temperature and high humidity environment can be given. Therefore, it is desirable to stabilize the progress of the magnetic recording medium in the drive even after such an environment change and after the magnetic recording medium is stored in such a temperature and humidity environment.

The magnetic recording medium generally has a structure including a nonmagnetic support and a magnetic layer containing ferromagnetic powder. As described in claim 2 of japanese patent application laid-open No. 9-227883 (patent document 1), a back coat layer is provided on the surface side of the nonmagnetic support of the magnetic recording medium opposite to the surface side having the magnetic layer. As the nonmagnetic support, various thin films that can be used as a nonmagnetic support are exemplified in, for example, paragraph 0062 of japanese patent application laid-open No. 9-227883 (patent document 1).

As described above, the present inventors have studied and found that a magnetic recording medium including an aromatic polyamide support as a nonmagnetic support has a phenomenon in which the running stability is lowered when the magnetic recording medium is stored in a high-temperature and high-humidity environment after a temperature change from a low temperature to a high temperature occurs under high humidity.

Disclosure of Invention

An object of one embodiment of the present invention is to suppress a decrease in running stability after storage in a high-temperature and high-humidity environment after a temperature change from a low temperature to a high temperature under high humidity in a magnetic recording medium including an aromatic polyamide support.

In one aspect of the present invention, there is provided a magnetic recording medium having a magnetic layer containing ferromagnetic powder on one surface side of a nonmagnetic support and a back coat layer containing nonmagnetic powder on the other surface side, wherein in the magnetic recording medium,

The distance S measured by optical interferometry after cleaning with methyl ethyl ketone on the surface of the above-mentioned back coating_afterAnd the spacing S as measured by optical interferometry before the cleaning with methyl ethyl ketone on the surface of the above-mentioned back coating_beforeDifference (S) of_after-S_before) (hereinafter, the term "difference in pitch between before and after methyl ethyl ketone washing" (S)_after-S_before) "or simply" difference (S)_after-S_before)". ) More than 0nm and not more than 30.0nm, and,

the non-magnetic support is an aromatic polyamide support having a moisture absorption rate of 2.2% or less.

In one aspect, the difference (S) is_after-S_before) Can be 4.0nm or more and 28.0nm or less.

In one aspect, the aromatic polyamide support may have a moisture absorption rate of 2.0% or less.

In one aspect, the aromatic polyamide support may have a moisture absorption rate of 1.0% or more and 2.0% or less.

In one aspect, the magnetic recording medium may have a nonmagnetic layer containing nonmagnetic powder between the nonmagnetic support and the magnetic layer.

In one aspect, the magnetic recording medium may be a magnetic tape.

An aspect of the present invention relates to a magnetic recording and reproducing apparatus including the magnetic recording medium and the magnetic head.

Effects of the invention

According to an aspect of the present invention, it is possible to provide a magnetic recording medium including an aramid support and having little deterioration in running stability even when stored in a high-temperature and high-humidity environment after a temperature change from a low temperature to a high temperature under high humidity, and a magnetic recording and reproducing apparatus including the magnetic recording medium.

Detailed Description

[ magnetic recording Medium ]

One aspect of the present invention relates to a magnetic recording medium having a magnetic layer containing ferromagnetic powder on one surface side of a nonmagnetic support and a back coat layer containing nonmagnetic powder on the other surface side, wherein the magnetic recording medium has a pitch S measured by optical interferometry after methyl ethyl ketone cleaning on the surface of the back coat layer_afterAnd the spacing S as measured by optical interferometry before the cleaning with methyl ethyl ketone on the surface of the above-mentioned back coating_beforeDifference (S) of_after-S_before) The non-magnetic support is an aromatic polyamide support having a moisture absorption rate of 2.2% or less and is more than 0nm and 30.0nm or less.

In the present invention and the present specification, "methyl ethyl ketone cleaning" refers to a process of immersing a sample piece cut out from a magnetic recording medium in methyl ethyl ketone (200g) having a liquid temperature of 20 to 25 ℃ and performing ultrasonic cleaning (ultrasonic output: 40kHz) for 100 seconds. When the magnetic recording medium to be cleaned was a magnetic tape, a 5cm long piece was cut out and subjected to methyl ethyl ketone cleaning. The width of the magnetic tape and the width of the test pieces cut from the tape are typically 1/2 inches. 1 inch to 0.0254 meters. A magnetic tape having a width other than 1/2 inches was cut out into a 5cm long piece and washed with methyl ethyl ketone. When the magnetic recording medium to be cleaned is a magnetic disk, a sample piece of 5cm × 1.27cm in size is cut out and subjected to methyl ethyl ketone cleaning. The measurement of the pitch after methyl ethyl ketone washing, which will be described in detail below, is performed after a test piece after methyl ethyl ketone washing is left for 24 hours in an environment of 23 ℃ and 50% relative humidity.

In the present invention and in the present specification, the "back coat side surface" of the magnetic recording medium has the same meaning as the back coat side surface of the magnetic recording medium.

In the present invention and the present specification, the pitch measured by optical interference on the surface of the back coat layer of the magnetic recording medium is a value measured by the following method.

Magnetic recording medium (detailed content is the above sample sheet). The same applies hereinafter. ) The pressing member is pressed against a transparent plate-like member (e.g., a glass plate) from the side opposite to the back coat layer side of the magnetic recording medium with a pressure of 0.5atm (lam is 101325 Pa) in a state where the back coat layer surface of the magnetic recording medium and the transparent plate-like member are superposed so as to face each other. In this state, light is irradiated to the back coat layer surface of the magnetic recording medium through the transparent plate-like member (irradiation region: 150000 to 200000 μm)²) The distance (distance) between the surface of the back coating layer of the magnetic recording medium and the surface of the transparent plate-like member on the magnetic recording medium side is determined from the intensity of interference light (for example, the contrast of an interference fringe image) generated by the optical path difference between the reflected light from the surface of the back coating layer of the magnetic recording medium and the reflected light from the surface of the transparent plate-like member on the magnetic recording medium side. Here, the light to be irradiated is not particularly limited. When the light to be irradiated is light having an emission wavelength over a relatively wide wavelength range, such as white light including light of a plurality of wavelengths, a member having a function of selectively cutting light of a specific wavelength or light other than the specific wavelength range, such as an interference filter, is disposed between the transparent plate-like member and the light receiving unit that receives the reflected light, and light of a part of the wavelengths or light of a part of the wavelength range in the reflected light is selectively made incident on the light receiving unit. When the light to be irradiated is light having a single light emission peak (so-called monochromatic light), the above-described member may not be used. The wavelength of the light incident on the light receiving unit may be, for example, in the range of 500 to 700 nm. However, the wavelength of the light incident on the light receiving unit is not limited to the above range. The transparent plate-like member may be a member having transparency such that light irradiated through the member is transmitted to the magnetic recording medium to the extent that the light is irradiated to the magnetic recording medium through the member to obtain interference light.

The interference fringe image obtained by the above-described measurement of the pitch was divided into 300000 dots, and the pitch of each dot (the distance between the surface of the back coating layer of the magnetic recording medium and the magnetic recording medium side surface of the transparent plate-like member) was obtained as a histogram (histogram), and the mode in the histogram was used as the pitch. Difference (S)_after-S_before) The value is obtained by subtracting the mode before washing of methyl ethyl ketone from the mode after washing of methyl ethyl ketone at the above 300000 points.

Similarly, 2 pieces of the magnetic recording medium were cut out, and one piece was not cleaned with methyl ethyl ketone to obtain the value S of the above-mentioned pitch_beforeAnd the other is subjected to methyl ethyl ketone cleaning to obtain the value S of the spacing_afterThereby obtaining a difference (S)_after-S_before). Alternatively, the difference (S) may be obtained by washing a sample piece, which was obtained before washing with methyl ethyl ketone, with methyl ethyl ketone and then obtaining the value of the pitch_after-S_before)。

The measurement can be carried out using, for example, a commercially available band gap Analyzer (TSA) such as a Tape Spacing Analyzer manufactured by Micro Physics. The pitch measurement in the examples was carried out using a tape pitch analyzer manufactured by MicroPhysics.

In the present invention and the present specification, "aromatic polyamide" refers to a polyamide containing an aromatic skeleton, and "aromatic polyamide support" refers to a support containing an aromatic polyamide film. The aromatic polyamide support may be a single-layer aromatic polyamide film, or may be a laminated film of 2 or more layers of aromatic polyamide films having the same composition, or a laminated film of 2 or more layers of aromatic polyamide films having different compositions. The "aromatic polyamide film" refers to a film in which the most component of the components constituting the film is aromatic polyamide on a mass basis. An adhesive layer or the like may be optionally included between the adjacent 2 layers in the laminated film.

In the present invention and the present specification, the moisture absorption rate of the aromatic polyamide support is a value obtained by the following method.

A sample piece cut out from an aromatic polyamide support body to be measured for moisture absorption rate (for example, a sample piece having a mass of several grams) is dried in a vacuum dryer at a temperature of 180 ℃ and a pressure of 100Pa or less until the temperature becomes constant. The mass of the thus-dried sample piece was W1. W1 is a value measured in a measurement environment at a temperature of 23 ℃ and a relative humidity of 50% within 30 seconds after being taken out from the vacuum dryer. Then, the mass of the sample piece left standing at 25 ℃ and 75% relative humidity for 48 hours was designated as W2. W2 is a value measured in a measurement environment at a temperature of 23 ℃ and a relative humidity of 50% within 30 seconds after being taken out from the above environment. The moisture absorption rate is calculated by the following formula.

Moisture absorption rate (%) [ (W2-W1)/W1] × 100

For example, the moisture absorption rate of the aromatic polyamide support can be determined by a known method (for example, stripping using an organic solvent) after removing a portion other than the aromatic polyamide support, such as the magnetic layer, from the magnetic recording medium.

The inventors of the present invention have concluded that the magnetic recording medium described above can suppress a decrease in the running stability after the magnetic recording medium is stored in a high-temperature and high-humidity environment after a temperature change from a low temperature to a high temperature under high humidity (hereinafter, simply referred to as "a decrease in the running stability").

Recording of data in a magnetic recording medium and reproduction of the recorded data are generally performed by running the magnetic recording medium in a drive. Typically, the back-coated surface contacts the actuator structural components within the actuator while making the relevant travel. Examples of the drive component include a roll for feeding and/or winding a tape-shaped magnetic recording medium (magnetic tape). If the contact state of such a drive component with the back coat surface becomes unstable, it is considered that the traveling stability of the magnetic recording medium in the drive is lowered.

On the other hand, when a temperature change from a low temperature to a high temperature occurs under high humidity, dew condensation (adhesion of moisture) is considered to occur on the surface of the back coating layer of the magnetic recording medium. The presence of this moisture increases the friction coefficient when the back coat surface comes into contact with the actuator structural member, and this is presumed to be one of the causes of the reduction in the running stability. Therefore, if the amount of moisture adhering to the surface of the back coat layer can be reduced when a temperature change from low temperature to high temperature occurs under high humidity, it is considered that an increase in the friction coefficient is suppressed, and as a result, a decrease in the running stability can be suppressed.

In addition, on the back coat surface, there are usually a portion (protrusion) mainly in contact with the actuator structural member (so-called actual contact) and a portion (hereinafter referred to as "base portion") lower than the portion when the back coat surface is in contact with the actuator structural member. The pitch described above is considered to be a value that serves as an index of the distance between the actuator structural member and the base portion when the back coating surface is in contact with the actuator structural member. It is inferred that if any component is present on the surface of the back coat layer, the larger the amount of the above component interposed between the base body portion and the driver structural member, the narrower the pitch becomes. On the other hand, if this component is removed by methyl ethyl ketone cleaning, the pitch S after methyl ethyl ketone cleaning becomes wider, and therefore _afterBecomes larger than the space S before the methyl ethyl ketone cleaning_beforeThe value of (c). Therefore, the difference (S) between the above-mentioned distances before and after the methyl ethyl ketone washing is considered_after-S_before) The amount of the above-described component interposed between the base portion and the actuator structural member can be an index.

With respect to the above points, the present inventors concluded that components removed by methyl ethyl ketone cleaning are present on the back coat surface, which promotes adhesion of moisture on the back coat surface when a temperature change from low temperature to high temperature occurs under high humidity. Therefore, it is considered that the difference (S) between the above pitches before and after the methyl ethyl ketone cleaning is reduced_after-S_before) That is, the reduction of the amount of the component contributes to the suppression of the adhesion of moisture, and as a result, the increase of the friction coefficient is suppressed. The present inventors believe that this contributes to suppressing a decrease in the running stability caused by a temperature change from low temperature to high temperature under high humidity. In contrast, according to the study by the present inventors, no correlation was found between the value of the difference in pitch before and after washing with a solvent other than methyl ethyl ketone, for example, n-hexane, and the value of the difference in pitch before and after methyl ethyl ketone washing. This is presumably because the above components cannot be removed or cannot be sufficiently removed in n-hexane cleaning.

The details of the above components are unclear. As a conclusion, the inventors have concluded that the above-mentioned components may have a molecular weight larger than that of the organic compound which is usually added as an additive to the back coat layer. The present inventors inferred an aspect of the component as follows. In one embodiment, the back coat layer is formed by applying a back coat layer-forming composition containing a binder and a curing agent to a non-magnetic support and then curing the composition, in addition to the non-magnetic powder. By the curing treatment, the binder and the curing agent can be subjected to a curing reaction (crosslinking reaction). Among them, it is considered that a binder which does not undergo a curing reaction with a curing agent or a binder which does not undergo a curing reaction with a curing agent is easily separated from the back coat layer and may be present on the surface of the back coat layer. The present inventors concluded that such a binder (e.g., having a functional group of the binder) readily adsorbs moisture, which is likely to be a cause of promoting adhesion of moisture on the surface of the back coating layer when a temperature change from low temperature to high temperature is generated under high humidity.

Further, it is considered that when the nonmagnetic support absorbs excessive moisture during storage in a high-temperature and high-humidity environment, the friction coefficient increases when the back coat surface of the magnetic recording medium including the nonmagnetic support comes into contact with the actuator component. This is considered to be one of the causes of the deterioration of the running stability after further storage in a high-temperature and high-humidity environment after a temperature change from low temperature to high temperature under high humidity. It is estimated that the aromatic polyamide support tends to absorb moisture in general, and therefore such an increase in the friction coefficient is likely to occur. In contrast, in the magnetic recording medium, the moisture absorption rate of the aramid support is 2.2% or less, and therefore the amount of moisture absorbed by the aramid support during storage in a high-temperature and high-humidity environment is considered to be small. It is inferred that this also contributes to suppression of reduction in running stability.

However, the above is an inference and does not limit the present invention in any way. The recording medium will be described in more detail below.

< non-magnetic support >

The magnetic recording medium contains a non-magnetic support having a moisture absorption rate of 2.2% or lessThe aromatic polyamide support of (3). From the viewpoint of suppressing the decrease in the running stability, the moisture absorption rate of the aromatic polyamide support is 2.2% or less, preferably 2.1% or less, more preferably 2.0% or less, further preferably 1.9% or less, further preferably 1.8% or less, further preferably 1.7% or less, further preferably 1.6% or less, further more preferably 1.5% or less. The moisture absorption rate of the aromatic polyamide support may be, for example, 0% or more, more than 0%, 0.1% or more, 0.3% or more, 0.5% or more, 0.7% or more, 1.0% or more, or 1.2% or more. From the viewpoint of suppressing the reduction in the running stability, the moisture absorption rate of the aromatic polyamide support is preferably low, and therefore the moisture absorption rate may be 0%. In addition, it is also preferable to use an aramid support having a low moisture absorption rate as the nonmagnetic support of the magnetic recording medium, from the viewpoint of suppressing deformation of the magnetic recording medium after long-term storage. For example, a tape-shaped magnetic recording medium (magnetic tape) is preferably used from the viewpoint of suppressing deformation of the magnetic tape in the tape width direction after long-term storage, since it contains an aramid support having a low moisture absorption rate. Further, in the magnetic tape, the Young's modulus of the aromatic polyamide support is preferably 3000N/mm in the longitudinal direction ²As above, 4000N/mm is preferable in the width direction²The above. From the viewpoint of increasing the capacity of the magnetic recording medium, the surface roughness of one or both surfaces of the aramid support is preferably 10nm or less as the center line average roughness Ra.

The aromatic ring included in the aromatic skeleton of the aromatic polyamide is not particularly limited, and specific examples of the aromatic ring include benzene ring, naphthalene ring, and the like. The moisture absorption rate of the aromatic polyamide support can be controlled by the kind, ratio, and the like of the constituent units constituting the aromatic polyamide. For details of the aramid support usable as the nonmagnetic support for the magnetic recording medium, a known technique can be referred to, and for example, the descriptions of paragraphs 0007 to 0054 of japanese patent application laid-open No. 9-176306 and practical examples of the same can be referred to. The nonmagnetic support may be a biaxially stretched film, or a film subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, or the like.

<Difference in distance between before and after methyl ethyl ketone cleaning (S)_after-S_before)>

The difference in the pitch between before and after cleaning of methyl ethyl ketone, measured by optical interferometry, on the surface of the back coating layer of the magnetic recording medium (S) _after-S_before) Is more than 0nm and not more than 30.0 nm. Difference (S)_after-S_before) 30.0nm or less, which can contribute to suppression of a decrease in the running stability in the above magnetic recording medium. According to this, difference (S)_after-S_before) Is 30.0nm or less, preferably 29.0nm or less, more preferably 28.0nm or less, still more preferably 27.0nm or less, yet more preferably 26.0nm or less, and yet more preferably 25.0nm or less. The difference (S) will be described in detail later_after-S_before) Can be controlled by surface treatment of the back coat layer in the production process of the magnetic recording medium.

Then, the difference in the distance between the surface treatment of the back coating and the cleaning with methyl ethyl ketone (S) was estimated_after-S_before) When the thickness is 0nm, a large amount of a component (e.g., lubricant) contributing to improvement in the running stability is removed from the magnetic recording medium. This is not intended to be construed in any way as limiting the invention. From this point of view, the difference (S) of the magnetic recording medium described above_after-S_before) Above 0nm, it is preferably 1.0nm or more, more preferably 2.0nm or more, still more preferably 3.0nm or more, and still more preferably 4.0nm or more.

Next, the magnetic layer, the back coat layer, the nonmagnetic support, and the optionally included nonmagnetic layer of the magnetic recording medium will be further described.

< magnetic layer >

(ferromagnetic powder)

As the ferromagnetic powder contained in the magnetic layer, one kind or a combination of two or more kinds of ferromagnetic powders known as ferromagnetic powders used in magnetic layers of various magnetic recording media can be used. As the ferromagnetic powder, a powder having a small average particle size is preferable from the viewpoint of improving the recording density. From this point of view, the average particle size of the ferromagnetic powder is preferably 50nm or less, more preferably 45nm or less, further preferably 40nm or less, further preferably 35nm or less, further preferably 30nm or less, further preferably 25nm or less, and further more preferably 20nm or less. On the other hand, from the viewpoint of the stability of magnetization, the average particle size of the ferromagnetic powder is preferably 5nm or more, more preferably 8nm or more, further preferably 10nm or more, further preferably 15nm or more, and further preferably 20nm or more.

Hexagonal ferrite powder

A preferred specific example of the ferromagnetic powder is hexagonal ferrite powder. For details of the hexagonal ferrite powder, for example, refer to paragraphs 0012 to 0030 of Japanese patent application laid-open No. 2011-225417, paragraphs 0134 to 0136 of Japanese patent application laid-open No. 2011-216149, paragraphs 0013 to 0030 of Japanese patent application laid-open No. 2012-204726, and paragraphs 0029 to 0084 of Japanese patent application laid-open No. 2015-127985.

In the present invention and the present specification, "hexagonal ferrite powder" refers to a ferromagnetic powder in which a hexagonal ferrite-type crystal structure is detected as a main phase by X-ray diffraction analysis. The main phase refers to a structure to which a diffraction peak having the highest intensity belongs in an X-ray diffraction spectrum obtained by X-ray diffraction analysis. For example, when a diffraction peak of the highest intensity in an X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to a hexagonal ferrite type crystal structure, it is determined that the hexagonal ferrite type crystal structure is detected as a main phase. When only a single structure is detected by X-ray diffraction analysis, the detected structure is regarded as a main phase. The hexagonal ferrite type crystal structure contains at least an iron atom, a divalent metal atom, and an oxygen atom as constituent atoms. The divalent metal atom is a metal atom capable of forming 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, a lead atom and the like. In the present invention and the present specification, the hexagonal strontium ferrite powder means that the main divalent metal atom contained in the powder is a strontium atom, and the hexagonal barium ferrite powder means that the main divalent metal atom contained in the powder is a barium atom. The main divalent metal atom means the divalent metal atom that accounts for the most in terms of atomic% among the divalent metal atoms contained in the powder. Wherein the divalent metal atom does not contain a rare earth atom. The "rare earth atom" in the present invention and the present specification is selected from the group consisting of scandium atom (Sc), yttrium atom (Y), and lanthanoid atom. The lanthanoid atom is selected from the group consisting of a lanthanum atom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymium atom (Nd), a promethium atom (Pm), a samarium atom (Sm), an europium atom (Eu), a gadolinium atom (Gd), a terbium atom (Tb), a dysprosium atom (Dy), a holmium atom (Ho), an erbium atom (Er), a thulium atom (Tm), an ytterbium atom (Yb), and a lutetium atom (Lu).

Hereinafter, hexagonal strontium ferrite powder, which is one embodiment of hexagonal ferrite powder, will be described in further detail.

The preferred activation volume of the hexagonal strontium ferrite powder is 800-1600 nm³The range of (1). The micronized hexagonal strontium ferrite powder exhibiting an activation volume in the above range is suitable for use in the production of magnetic recording media exhibiting excellent electromagnetic conversion characteristics. The preferred activation volume of the hexagonal strontium ferrite powder is 800nm³The wavelength can be, for example, 850nm³The above. Further, from the viewpoint of further improving the electromagnetic conversion characteristics, it is more preferable that the activation volume of the hexagonal strontium ferrite powder is 1500nm³Hereinafter, 1400nm is more preferable³Hereinafter, 1300nm is more preferable³Hereinafter, more preferably 1200nm³Hereinafter, 1100nm is more preferable³The following. The same applies to the activated volume of the hexagonal barium ferrite powder.

The "activation volume" is a unit of magnetization reversal and is an index indicating the magnetic size of the particle. The activation volume and the anisotropy constant Ku described later in the present invention and the present specification are the magnetic field scanning speed of the coercive force Hc measurement unit for 3 minutes using the vibration sample type magnetometer, and The measurement was carried out for 30 minutes (measurement temperature: 23 ℃ C. + -1 ℃ C.), and the value was determined from the following equation of Hc vs. activation volume V. In addition, regarding the unit of the anisotropy constant Ku, lerg/cc is 1.0 × 10^-1J/m³。

Hc＝2Ku/Ms{1-[(kT/KuV)ln(At/0.693)]^1/2}

[ in the above formula, Ku: anisotropy constant (unit: J/m)³) Ms: saturation magnetization (unit: kA/m), k: boltzmann constant, T: absolute temperature (unit: K), V: activation volume (unit: cm)³) And A: spin precession frequency (unit: s)^-1) T: magnetic field reversal time (unit: s)]

As an index of the reduction of thermal fluctuation, in other words, the improvement of thermal stability, the anisotropy constant Ku can be cited. The hexagonal strontium ferrite powder can preferably have a size of 1.8 × 10⁵J/m³The Ku may have a value of 2.0 × 10⁵J/m³Ku above. The Ku of the hexagonal strontium ferrite powder may be, for example, 2.5 × 10⁵J/m³The following. However, the higher Ku is preferable because the higher Ku is the higher thermal stability, and therefore the value is not limited to the values shown in the above examples.

The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms are preferably contained in a content of 0.5 to 5.0 atomic% (bulk) with respect to 100 atomic% of iron atoms. In one embodiment, the hexagonal strontium ferrite powder containing rare earth atoms can have a surface layer portion containing rare earth atoms. The term "partial surface layer portion of rare earth atoms" in the present invention and the present specification means that the content of rare earth atoms per 100 atomic% of iron atoms in a solution obtained by partially dissolving hexagonal strontium ferrite powder with an acid (hereinafter, the "content of the surface layer portion of rare earth atoms" or rare earth atoms is simply referred to as "content of the surface layer portion") and the content of rare earth atoms per 100 atomic% of iron atoms in a solution obtained by completely dissolving hexagonal strontium ferrite powder with an acid (hereinafter, the "content of bulk of rare earth atoms" or rare earth atoms is simply referred to as "content of bulk") satisfy the ratio of the content of the surface layer portion of rare earth atoms/the content of bulk of rare earth atoms > 1.0. The rare earth element content of the hexagonal strontium ferrite powder described later is the same as the rare earth element bulk content. On the other hand, since the surface layer portion of the particles constituting the hexagonal strontium ferrite powder is dissolved by the partial dissolution with the acid, the rare earth atom content in the solution obtained by the partial dissolution is the rare earth atom content in the surface layer portion of the particles constituting the hexagonal strontium ferrite powder. The content ratio of the rare earth atoms at the surface layer portion satisfying the "content ratio of the rare earth atoms at the surface layer portion/content ratio of the rare earth atoms in the bulk state > 1.0" indicates that the rare earth atoms are localized at the surface layer portion (i.e., more than the inside) in the particles constituting the hexagonal strontium ferrite powder. The surface layer portion in the present invention and the present specification indicates a partial region of the particles constituting the hexagonal strontium ferrite powder from the surface toward the inside.

When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atom content (block content) is preferably in the range of 0.5 to 5.0 atomic% with respect to 100 atomic% of iron atoms. It is considered that the rare earth atoms are contained in the bulk content in the above range and are localized in the surface layer portion of the particles constituting the hexagonal strontium ferrite powder, which contributes to suppressing the reduction of the reproduction output during the repeated reproduction. This is presumed to be because the hexagonal strontium ferrite powder contains rare earth atoms in the above-described bulk content ratio and the rare earth atoms are localized in the surface layer portion of the particles constituting the hexagonal strontium ferrite powder, whereby the anisotropy constant Ku can be increased. The higher the value of the anisotropy constant Ku is, the more the occurrence of a phenomenon called thermal fluctuation can be suppressed (in other words, thermal stability is improved). By suppressing the occurrence of thermal fluctuation, it is possible to suppress a decrease in the regeneration output during repeated regeneration. It is estimated that the rare earth atoms are biased in the surface layer portion of the hexagonal strontium ferrite powder particles to contribute to stabilization of the spins of iron (Fe) bits in the crystal lattice of the surface layer portion, thereby improving the anisotropy constant Ku.

Further, it is estimated that the use of hexagonal strontium ferrite powder having a property of containing rare earth atoms localized in the surface layer portion as ferromagnetic powder of the magnetic layer also contributes to suppression of scratching of the surface of the magnetic layer due to sliding with the magnetic head. That is, it is estimated that the hexagonal strontium ferrite powder having the property of containing the rare earth atoms in the surface layer portion contributes to the improvement of the running durability of the magnetic recording medium. It is presumed that this is probably due to the fact that rare earth atoms are localized on the surface of the particles constituting the hexagonal strontium ferrite powder, which contributes to the improvement of the interaction between the surface of the particles and the organic substances (e.g., binder and/or additive) contained in the magnetic layer, resulting in the improvement of the strength of the magnetic layer.

From the viewpoint of further suppressing a decrease in regeneration output during repeated regeneration and/or from the viewpoint of further improving the running durability, the rare earth element atom content (block content) is more preferably in the range of 0.5 to 4.5 atomic%, still more preferably in the range of 1.0 to 4.5 atomic%, and still more preferably in the range of 1.5 to 4.5 atomic%.

The above-mentioned bulk content is a content obtained by completely dissolving the hexagonal strontium ferrite powder. In the present invention and the present specification, unless otherwise specified, the atomic content means a bulk content obtained by completely dissolving the hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing rare earth atoms may contain only one rare earth atom as a rare earth atom, or may contain two or more rare earth atoms. The block content when two or more rare earth atoms are contained is determined by the total of two or more rare earth atoms. This is also true for the present invention and other components in this specification. That is, unless otherwise specified, one or two or more of the components may be used. The content or content ratio when two or more kinds are used means the total of two or more kinds.

When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atoms contained may be any one or more of rare earth atoms. As preferable rare earth atoms from the viewpoint of further suppressing a decrease in the regeneration output during repeated regeneration, neodymium atoms, samarium atoms, yttrium atoms, and dysprosium atoms are mentioned, neodymium atoms, samarium atoms, and yttrium atoms are more preferable, and neodymium atoms are even more preferable.

In the hexagonal strontium ferrite powder having the property of containing a rare earth atom in the surface layer portion, the degree of the rare earth atom may be contained in any amount as long as the rare earth atom is contained in the surface layer portion of the particles constituting the hexagonal strontium ferrite powder. For example, regarding the hexagonal strontium ferrite powder having a property of localized surface layer portions of rare earth atoms, "surface layer portion content/bulk content", which is the ratio of the content of the surface layer portions of rare earth atoms obtained by partial dissolution under the dissolution conditions described below to the content of the bulk of rare earth atoms obtained by complete dissolution under the dissolution conditions described below, may be more than 1.0 and 1.5 or more. The "surface portion content/bulk content" of more than 1.0 means that rare earth atoms are localized in the surface portion (i.e., more than the inside) of the particles constituting the hexagonal strontium ferrite powder. The "surface portion content/bulk content" which is the ratio of the surface portion content of the rare earth atoms obtained by partial dissolution under the dissolution conditions described below to the bulk content of the rare earth atoms obtained by complete dissolution under the dissolution conditions described below may 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. In the hexagonal strontium ferrite powder having a property of containing a localized surface layer portion of rare earth atoms, the rare earth atoms may be localized in the surface layer portion of the particles constituting the hexagonal strontium ferrite powder, and the "surface layer portion content/bulk content" is not limited to the upper limit or the lower limit of the examples.

As for the partial dissolution as well as the complete dissolution of the hexagonal strontium ferrite powder, the following description will be made. As for the hexagonal strontium ferrite powder existing as the powder, the partially dissolved and completely dissolved sample powders were collected from the same batch of powders. 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 partially dissolved, and the other part is completely dissolved. The extraction of the hexagonal strontium ferrite powder from the magnetic layer can be performed by, for example, the method described in paragraph 0032 of japanese patent application laid-open No. 2015-091747.

The local dissolution is a dissolution to such an extent that the hexagonal strontium ferrite powder can be visually confirmed to remain in the solution after the dissolution is completed. For example, by local dissolution, a region of 10 to 20 mass% can be dissolved with respect to the entire particles constituting the hexagonal strontium ferrite powder as 100 mass%. On the other hand, the complete dissolution means a state in which the hexagonal ferrite powder is dissolved so that the residual hexagonal ferrite powder cannot be visually observed in the solution at the end of the dissolution.

The local dissolution and the measurement of the content of the surface layer portion are performed by the following methods, for example. However, the following dissolution conditions such as the amount of sample powder are exemplified, and the dissolution conditions capable of partial dissolution and complete dissolution can be adopted.

A container (for example, a beaker) containing 12mg of the sample powder and 10mL of 1mol/L hydrochloric acid was held on a hot plate at a set temperature of 70 ℃ for 1 hour. The resulting solution was filtered through a 0.1 μm membrane filter. Elemental analysis of the filtrate thus obtained was carried out by an Inductively Coupled Plasma (ICP; Inductively Coupled Plasma) analysis apparatus. In this way, the content of the surface portion of the rare earth atoms can be determined with respect to 100 atomic% of the iron atoms. When a plurality of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is defined as the content of the surface layer portion. This also applies to the measurement of the block content.

On the other hand, the complete dissolution and the block content are measured by the following methods, for example.

A container (for example, a beaker) containing 12mg of the sample powder and 10mL of 4mol/L hydrochloric acid was held on a hot plate at a set temperature of 80 ℃ for 3 hours. Then, the bulk content of 100 atomic% with respect to the iron atom can be obtained by the same method as the above-described local dissolution and measurement of the content of the surface layer portion.

From the viewpoint of improving the reproduction output when reproducing data recorded on a magnetic recording medium, it is desirable that the mass magnetization σ s of the ferromagnetic powder contained in the magnetic recording medium is high. In this connection, it was found that a hexagonal strontium ferrite powder containing rare earth atoms but having no surface layer localization of rare earth atoms and a hexagonal strontium ferrite powder containing no rare earth atomsHexagonal strontium ferrite powder containing rare earth atoms tends to have a significantly lower σ s than hexagonal strontium ferrite powder containing rare earth atoms. In view of suppressing such a large reduction in σ s, it is considered that hexagonal strontium ferrite powder having a property of localized surface layer portions of rare earth atoms is also preferable. In one aspect, the σ s of the hexagonal strontium ferrite powder can be 45A · m²/kg or more, and may be 47A · m²More than kg. On the other hand, σ s is preferably 80A · m from the viewpoint of noise reduction²Is less than or equal to kg, more preferably 60 A.m²Is less than/kg. σ s can be measured using a known measuring device capable of measuring magnetic characteristics, such as a vibration sample type magnetometer. In the present invention and the present specification, unless otherwise specified, the mass magnetization σ s is a value measured at a magnetic field strength of 15 kOe. 1kOe ═ 10⁶/4π)A/m。

The content of the constituent atoms (bulk content) of the hexagonal strontium ferrite powder can be, for example, 2.0 to 15.0 atomic% with respect to 100 atomic% of iron atoms. In one aspect, in the hexagonal strontium ferrite powder, the divalent metal atoms contained in the powder can be only strontium atoms. In another embodiment, the hexagonal strontium ferrite powder may contain one or more kinds of other divalent metal atoms in addition to the strontium atom. For example, barium atoms and/or calcium atoms can be included. When a divalent metal atom other than a strontium atom is contained, the barium atom content and the calcium atom content in the hexagonal strontium ferrite powder can be, for example, in the range of 0.05 to 5.0 atomic% with respect to 100 atomic% of an iron atom.

As the crystal structure of hexagonal ferrite, magnetoplumbite type (also referred to as "M type"), W type, Y type, and Z type are known. The hexagonal strontium ferrite powder can take any crystal structure. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder can be a powder in which a single crystal structure or two or more crystal structures are detected by X-ray diffraction analysis. For example, in one mode, the hexagonal strontium ferrite powder can be a powder in which only the M-type crystal structure is detected by X-ray diffraction analysis. E.g. hexagonal ferrite of M typeBody made of AFe₁₂O₁₉The compositional formula (2) of (a). Here, a represents a divalent metal atom, and when a is only a strontium atom (Sr) or contains a plurality of divalent metal atoms as a in the case where the hexagonal strontium ferrite powder is M-type, the strontium atom (Sr) occupies the most amount on an atomic% basis as described above. The content of the divalent metal atom in the hexagonal strontium ferrite powder is generally determined by the kind of crystal structure of the hexagonal ferrite, but is not particularly limited. The same applies to the content of iron atoms and the content of oxygen atoms. The hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms, and oxygen atoms, and may further contain rare earth atoms. The hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may include aluminum atoms (a 1). 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 reduction in the reproduction output during repeated reproduction, the hexagonal strontium ferrite powder preferably contains iron atoms, strontium atoms, oxygen atoms, and rare earth atoms, and the content of atoms other than these atoms is 10.0 atomic% or less, more preferably in the range of 0 to 5.0 atomic%, and may be 0 atomic% with respect to 100 atomic% of iron atoms. That is, in one aspect, the hexagonal strontium ferrite powder may not contain atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The content expressed by atomic% is determined by converting the content (unit: mass%) of each atom obtained by completely dissolving the hexagonal strontium ferrite powder into a value expressed by atomic% using the atomic weight of each atom. In the present invention and the present specification, the phrase "not including" with respect to a certain atom means that the content of the atom is 0% by mass as measured by an ICP analyzer because the atom is completely dissolved. The detection limit of the ICP analyzer is usually 0.01ppm (parts per million) or less on a mass basis. The above "not included" is used in a meaning including an amount smaller than the detection limit of the ICP analytical apparatus. In one aspect, the hexagonal strontium ferrite powder may be a powder that does not contain bismuth atoms (Bi).

Metal powder

As a preferred specific example of the ferromagnetic powder, a ferromagnetic metal powder can be also cited. For details of the ferromagnetic metal powder, for example, reference can be made to paragraphs 0137 to 0141 of Japanese patent application laid-open No. 2011-216149 and paragraphs 0009 to 0023 of Japanese patent application laid-open No. 2005-251351.

-iron oxide powder

As a preferred specific example of the ferromagnetic powder, an iron oxide powder can be cited. In the present invention and the present specification, "-iron oxide powder" means a ferromagnetic powder in which an iron oxide type crystal structure is detected as a main phase by X-ray diffraction analysis. For example, when a diffraction peak of the highest intensity in an X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the crystal structure of the-iron oxide type, a powder in which the crystal structure of the-iron oxide type is detected as a main phase is judged. As a method for producing the iron oxide powder, a method of producing from goethite, a reverse micelle method, and the like are known. The above-described production methods are all known methods. Further, as a method for producing an iron oxide powder in which a part of Fe is substituted with a substitution atom of Ga, Co, Ti, Al, Rh, or the like, for example, j.pn.soc.powder metallic vol.61 Supplement, No. S1, pp.s280-S284, j.mater.chem.c, 2013, 1, pp.5200-5206, or the like can be referred to. However, the method for producing the iron oxide powder that can be used as a ferromagnetic powder in the magnetic layer of the magnetic recording medium is not limited to the method mentioned here.

The activation volume of the iron oxide powder is preferably 300 to 1500nm³The range of (1). The micronized iron oxide powder having an activation volume in the above range is suitable for use in the production of magnetic recording media exhibiting excellent electromagnetic conversion characteristics. The activation volume of the iron oxide powder is preferably 300nm³The above can be 500nm, for example³The above. Further, from the viewpoint of further improving the electromagnetic conversion characteristics, it is more preferable that the activation volume of the iron oxide powder is 1400nm³Hereinafter, 1300nm is more preferable³Hereinafter, 1200nm is more preferable³Hereinafter, 1100nm is more preferable³The following.

As an index of the reduction of thermal fluctuation, in other words, the improvement of thermal stability, the anisotropy constant Ku can be cited. The iron oxide powder can preferably have a size of 3.0X 10⁴J/m³The Ku may have a value of 8.0 × 10 more preferably⁴J/m³Ku above. Ku of the iron oxide powder may be, for example, 3.0X 10⁵J/m³The following. However, the higher Ku is preferable because the higher Ku is more stable against heat, and thus the value is not limited to the above exemplified values.

From the viewpoint of improving the reproduction output when reproducing data recorded on a magnetic recording medium, it is desirable that the mass magnetization σ s of the ferromagnetic powder contained in the magnetic recording medium is high. In this regard, in one aspect, σ s of the-iron oxide powder can be 8A · m ²Is not less than kg, and can be 12 A.m²More than kg. On the other hand, σ s of the-iron oxide powder is preferably 40A · m from the viewpoint of reducing noise²Less than kg, more preferably 35 A.m²Is less than/kg.

In the present invention and the present specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powder is measured by the following method using a transmission electron microscope.

The powder was photographed at a magnification of 100000 times by using a transmission electron microscope, and a photograph of particles constituting the powder was obtained by printing a photographic paper or displaying it on a display or the like so as to be a magnification of 500000 times as a total magnification. The target particle is selected from the obtained image of the particle, and the particle profile is followed by a digitizer to measure the size of the particle (primary particle). Primary particles refer to individual particles that do not agglomerate.

The above measurement was performed on 500 randomly extracted particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained was taken as the average particle size of the powder. As the transmission electron microscope, for example, a transmission electron microscope H-9000 model manufactured by Hitachi, ltd. The particle size can be measured using known image analysis software, for example, image analysis software KS-400 manufactured by Carl Zeiss. The average particle size shown in the examples described below is a value measured by using a transmission electron microscope model H-9000 manufactured by Hitachi, Ltd and an image analysis software using an image analysis software KS-400 manufactured by Carl Zeiss company, unless otherwise specified. In the present invention and the present specification, the powder represents an aggregate of a plurality of particles. For example, a ferromagnetic powder represents an aggregate of a plurality of ferromagnetic particles. The aggregate of the plurality of types of particles is not limited to a mode in which the particles constituting the aggregate are in direct contact with each other, and includes a mode in which a binder, an additive, and the like, which will be described later, are interposed between the particles. The term particle is sometimes also used to refer to powders.

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 japanese patent application laid-open publication No. 2011-048878 can be used.

In the present invention and the present specification, as far as no particular description is given, regarding the size (particle size) of the particles constituting the powder, the shape of the particles observed in the above-mentioned particle photograph is

(1) Needle-like, spindle-like, columnar (wherein the height is larger than the maximum major axis of the bottom surface), etc., the length of the major axis constituting the particle, i.e., the major axis length;

(2) a plate-like or columnar shape (wherein, the thickness or height is smaller than the maximum major axis of the plate surface or the bottom surface), expressed by the maximum major axis of the plate surface or the bottom surface;

(3) spherical, polyhedral, and unspecified shapes, and the major axis of the constituent particles cannot be determined depending on the shape, they are expressed by the circle-equivalent diameter. The circle-equivalent diameter is a diameter obtained by a circle projection method.

The average acicular ratio of the powder is an arithmetic average of values obtained by measuring the length of the short axis of the particles, that is, the short axis length, and obtaining the value (long axis length/short axis length) of each particle in the above measurement, and the values obtained for the above 500 particles. Unless otherwise specified, in the definition of the particle size, (1) the minor axis length is the length of the minor axis constituting the particle, similarly, (2) the thickness or the height, respectively, and (3) the major axis and the minor axis are not divided, and therefore (major axis length/minor axis length) is regarded as 1 for convenience.

Further, unless otherwise specified, when the particle shape is determined, for example, in the case of the above definition (1) of the particle size, the average particle size is the average long axis length, and in the case of the definition (2) of the particle size, the average particle size is the average plate diameter. In the case of the definition (3) of the particle size, the average particle size is an average diameter (also referred to as an average particle diameter and an average particle diameter).

The content (filling ratio) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90 mass%, and more preferably in the range of 60 to 90 mass%. From the viewpoint of improving the recording density, the magnetic layer preferably has a high filling ratio of the ferromagnetic powder.

(Binder and curing agent)

The magnetic recording medium may be a coating-type magnetic recording medium, and the magnetic layer may contain a binder. The binder is more than one resin. As the binder, various resins generally used as binders for coating-type magnetic recording media can be used. For example, as the binder, a resin selected from a polyurethane resin, a polyester resin, a polyamide resin, a vinyl chloride resin, styrene, acrylonitrile, an acrylic resin obtained by copolymerizing methyl methacrylate or the like, a cellulose resin such as nitrocellulose, an epoxy resin, a phenoxy resin, polyvinyl acetal, a polyvinyl alkyl aldehyde resin such as polyvinyl butyral, or the like can be used alone, or a plurality of resins can be used in combination. Among these, polyurethane resins, acrylic resins, cellulose resins, and vinyl chloride resins are preferable. These resins may be homopolymers or copolymers (copolymers). These resins can also be used as binders in the back coat layer and/or the nonmagnetic layer described later.

As for the above binder, reference can be made to paragraphs 0028 to 0031 of Japanese patent application laid-open No. 2010-024113. The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less as a weight average molecular weight. The weight average molecular weight in the present invention and the present specification is a value obtained by polystyrene conversion of a value measured by Gel Permeation Chromatography (GPC) under the following measurement conditions. The weight average molecular weight of the binder shown in the examples described later is a value obtained by converting a value measured under the following measurement conditions into polystyrene.

GPC apparatus: HLC-8120 (manufactured by Tosoh Corporation)

Pipe column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mm ID (InnerDeiameter, inner diameter). times.30.0 cm)

Eluent: tetrahydrofuran (THF)

In one aspect, a binder containing an active hydrogen-containing group can be used as the binder. The "active hydrogen-containing group" in the present invention and the present specification means a functional group which can undergo a curing reaction with a curable functional group and in which a hydrogen atom contained in the group is detached to form a crosslinked structure. Examples of the active hydrogen-containing group include a hydroxyl group, an amino group (preferably a primary amino group or a secondary amino group), a mercapto group, and a carboxyl group, and a hydroxyl group, an amino group, and a mercapto group are preferable, and a hydroxyl group is more preferable. In the binder containing active hydrogen-containing groups, the active hydrogen-containing group concentration is preferably in the range of 0.10meq/g to 2.00 meq/g. Eq is an equivalent (equivalent) and is a unit that cannot be converted to SI units. The concentration of the active hydrogen-containing group can also be expressed by the unit "mgKOH/g". In one aspect, in the resin containing an active hydrogen-containing group, the concentration of the active hydrogen-containing group is preferably in the range of 1 to 20 mgKOH/g.

In one embodiment, as the binder, a binder containing an acidic group can be used. The term "acidic group" as used herein and in the present specification means a group capable of releasing H when contained in water or a solvent containing water (aqueous solvent)⁺And a group dissociating into anions, and a salt form thereof. Specific examples of the acidic group include a sulfonic acid group (-SO)₃H) Sulfuric acid radical (-OSO)₃H) Carboxyl group, phosphate group, and salt forms thereof. For example, sulfonic acid groups (-SO)₃H) The salt form is defined as-SO₃M represents a group of atoms (for example, alkali metal atoms) which can be converted into cations in water or an aqueous solvent. This is relevant for the various radicals mentioned aboveThe salt morphology of the clusters is also the same. Examples of the binder containing an acidic group include resins (e.g., urethane resins, vinyl chloride resins, etc.) containing at least one acidic group selected from a sulfonic acid group and salts thereof. However, the resin contained in the magnetic layer is not limited to these resins. The content of the acidic group in the binder containing the acidic group may be, for example, in the range of 0.03 to 0.50 meq/g. The content of various functional groups such as an acidic group contained in the resin can be determined by a known method depending on the type of the functional group. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass per 100.0 parts by mass of the ferromagnetic powder in the composition for forming a magnetic layer.

Also, a curing agent can be used together with a resin that can be used as a binder. In one embodiment, the curing agent may be a thermosetting compound that is a compound that undergoes a curing reaction (crosslinking reaction) by heating, and in another embodiment, the curing agent may be a photocurable compound that undergoes a curing reaction (crosslinking reaction) by light irradiation. By performing the curing reaction in the magnetic layer forming step, at least a part of the curing agent can be contained in the magnetic layer in a state of being reacted (crosslinked) with other components such as a binder. This also applies to a layer formed using the composition for forming other layers when the composition contains a curing agent. Preferred curing agents are thermosetting compounds, preferably polyisocyanates. For the details of the polyisocyanate, refer to paragraphs 0124 to 0125 of Japanese patent application laid-open No. 2011-216149. The curing agent can be used, for example, in an amount of 0 to 80.0 parts by mass per 100.0 parts by mass of the binder in the composition for forming a magnetic layer, and is preferably used in an amount of 50.0 to 80.0 parts by mass from the viewpoint of improving the strength of the magnetic layer.

The above description relating to the binder and the curing agent can also be applied to the back coat layer and/or the nonmagnetic layer. In this case, the ferromagnetic powder can be used in place of the nonmagnetic powder in the description of the content.

(additives)

The magnetic layer may contain one or more additives as needed. Examples of the additive include the above-mentioned curing agent. Examples of the additive to be contained in the magnetic layer include a non-magnetic powder (for example, inorganic powder, carbon black, and the like), a lubricant, a dispersant, a dispersion aid, a fungicide, an antistatic agent, and an antioxidant. Examples of the nonmagnetic powder include a nonmagnetic powder capable of functioning as a polishing agent, and a nonmagnetic powder (for example, nonmagnetic colloidal particles) capable of functioning as a protrusion forming agent for forming a proper protrusion on the surface of the magnetic layer. The average particle size of colloidal silica (silica colloidal particles) shown in examples described later is a value obtained by a method described in paragraph 0015 of Japanese patent application laid-open No. 2011-048878 as a method for measuring an average particle size. The additives can be used in any amount by suitably selecting commercially available products or producing them by a known method according to the desired properties. Examples of additives that can be used in a magnetic layer containing a polishing agent include dispersants described in paragraphs 0012 to 0022 of Japanese patent application laid-open No. 2013-131285 as dispersants for improving dispersibility of the polishing agent. For example, as for the lubricant, refer to paragraphs 0030 to 0033, 0035, and 0036 of Japanese patent laid-open No. 2016 and 126817. A lubricant may also be included in the nonmagnetic layer. As for the lubricant that can be contained in the nonmagnetic layer, paragraphs 0030, 0031, 0034, 0035, and 0036 of japanese patent laid-open No. 2016-. As the dispersant, refer to paragraphs 0061 and 0071 of japanese patent application laid-open No. 2012-133837. Further, as the dispersant, it is also possible to refer to paragraphs 0061 and 0071 of japanese patent application laid-open No. 2012 and 133837 and paragraph 0035 of japanese patent application laid-open No. 2017 and 016721. Regarding the additive of the magnetic layer, reference can also be made to paragraphs 0035 to 0077 of Japanese patent laid-open publication No. 2016-051493.

A dispersant may also be included in the nonmagnetic layer. As for the dispersant that can be contained in the nonmagnetic layer, refer to paragraph 0061 of japanese patent laid-open No. 2012-133837.

The various additives can be used in any amount by suitably selecting commercially available products or producing them by a known method according to the desired properties.

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

< nonmagnetic layer >

Next, the nonmagnetic layer will be described. The magnetic recording medium may have the magnetic layer directly on the nonmagnetic support, or may have a nonmagnetic layer containing nonmagnetic powder between the nonmagnetic support and the magnetic layer. The nonmagnetic powder used in the nonmagnetic layer may be either a powder of an inorganic substance or a powder of an organic substance. Further, carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These nonmagnetic powders are commercially available products, and can be produced by a known method. For details, reference can be made to paragraphs 0146 to 0150 of Japanese patent application laid-open No. 2011-216149. Regarding carbon black that can be used for the nonmagnetic layer, reference can also be made to paragraphs 0040 to 0041 of jp 2010-024113 a. The content (filling ratio) of the nonmagnetic powder in the nonmagnetic layer is preferably in the range of 50 to 90 mass%, and more preferably in the range of 60 to 90 mass%.

The nonmagnetic layer can contain a binder and can also contain additives. As for details of the binder, the additive, and the like of the nonmagnetic layer, known techniques related to the nonmagnetic layer can be applied. For example, the type and content of the binder, and the type and content of the additive, and the like, known techniques related to the magnetic layer can be applied.

In the present invention and in the present specification, the non-magnetic layer also includes a substantially non-magnetic layer containing a non-magnetic powder and containing, for example, as an impurity or intentionally containing a small amount of a ferromagnetic powder. Here, the substantially nonmagnetic layer means a layer having a remanent magnetic flux density of 10mT or less or a coercivity of 100Oe or a layer having a remanent magnetic flux density of 10mT or less and a coercivity of 100Oe or less. The nonmagnetic layer preferably has no residual magnetic flux density and no coercive force.

< Back coating layer >

The magnetic recording medium has magnetism in the non-magnetic supportThe surface side opposite to the surface side of the layer has a back coating layer containing a nonmagnetic powder. As for the kind of the nonmagnetic powder contained in the back coat layer, reference can be made to the description relating to the nonmagnetic powder contained in the nonmagnetic layer. The nonmagnetic powder contained in the back coat layer may preferably be one or more nonmagnetic powders selected from the group consisting of inorganic powders and carbon black. In the magnetic recording medium, for example, the main powder of the nonmagnetic powder (the nonmagnetic powder contained most on a mass basis among the nonmagnetic powders) as the back coat layer may contain an inorganic powder. When the nonmagnetic powder contained in the back coat layer is one or more nonmagnetic powders selected from the group consisting of inorganic powders and carbon black, the ratio of the inorganic powder to the total amount of the nonmagnetic powder of 100.0 parts by mass may be, for example, in the range of more than 50.0 parts by mass and 100.0 parts by mass or less, and preferably in the range of 60.0 parts by mass and 100.0 parts by mass. When the proportion of the inorganic powder in the nonmagnetic powder is increased, a difference (S) may be observed _after-S_before) The value of (c) has a tendency to decrease.

The average particle size of the nonmagnetic powder may be, for example, in the range of 10 to 200 nm. The average particle size of the inorganic powder is preferably in the range of 50 to 200nm, more preferably in the range of 80 to 150 nm. On the other hand, the average particle size of the carbon black is preferably in the range of 10 to 50nm, more preferably in the range of 15 to 30 nm.

The back coating can comprise a binder and can also comprise additives. As an example of the additive, a known dispersant that can contribute to the improvement of the dispersibility of the nonmagnetic powder can be cited.

Further, as an example of the additive, a lubricant can be cited.

For example, the lubricant may be a fatty acid, a fatty acid ester, or a fatty acid amide, and the magnetic layer may be formed using one or more selected from the group consisting of a fatty acid, a fatty acid ester, and a fatty acid amide.

Examples of the fatty acid include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, elaidic acid, and the like, with stearic acid, myristic acid, palmitic acid being preferred, and stearic acid being more preferred. The fatty acid may be contained in the magnetic layer in the form of a salt such as a metal salt.

Examples of the fatty acid ester include esters such as dodecanoic acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid. Specific examples thereof include butyl myristate, butyl palmitate, butyl stearate, neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl stearate, isotridecyl stearate, octyl stearate, isooctyl stearate, pentyl stearate, butoxyethyl stearate, and the like.

Examples of the fatty acid amide include amides of the above various fatty acids, such as lauric acid amide, myristic acid amide, palmitic acid amide, and stearic acid amide.

The fatty acid content of the back coat layer is, for example, 0 to 10.0 parts by mass, preferably 0.1 to 10.0 parts by mass, and more preferably 1.0 to 7.0 parts by mass per 100.0 parts by mass of the nonmagnetic powder contained in the back coat layer. The content of the fatty acid ester in the back coat layer is, for example, 0.1 to 10.0 parts by mass, preferably 1.0 to 5.0 parts by mass, per 100.0 parts by mass of the nonmagnetic powder contained in the back coat layer. The content of the fatty acid amide in the back coat layer is, for example, 0 to 3.0 parts by mass, preferably 0 to 2.0 parts by mass, and more preferably 0 to 1.0 part by mass per 100.0 parts by mass of the nonmagnetic powder contained in the back coat layer.

In the present invention and the present specification, one kind of a certain component may be used alone or two or more kinds may be used unless otherwise specified. The content when two or more kinds of a certain component are used means the total content of the two or more kinds.

As for the binder, additive, and the like of the back coat layer, known techniques related to the back coat layer can be applied, and known techniques related to the prescription of the magnetic layer and/or the nonmagnetic layer can be applied. For example, as for the back coating layer, reference can be made to the descriptions in paragraphs 0018 to 0020 of Japanese patent application laid-open No. 2006-331625 and in column 4, line 65 to column 5, line 38 of the specification of U.S. Pat. No. 7029774.

< various thicknesses >

The thickness of the nonmagnetic support of the magnetic recording medium is, for example, 3.0 to 80.0. mu.m, preferably 3.0 to 50.0. mu.m, and more preferably 3.0 to 10.0. mu.m. When the nonmagnetic support is a laminated film of 2 or more thin films, the thickness of the nonmagnetic support means the total thickness of the laminated film.

The thickness of the magnetic layer can be optimized in accordance with the saturation magnetization amount of the magnetic head to be used, the head gap length, and the bandwidth of a recording signal, and is, for example, 10nm to 100nm, preferably 20 to 90nm, and more preferably 30 to 70nm from the viewpoint of high-density recording. The magnetic layer may be at least one layer, or the magnetic layer may be separated into 2 or more layers having different magnetic properties, and a known structure of a multilayer magnetic layer may be applied. The thickness of the magnetic layer when the magnetic layer is separated into 2 or more layers is the total thickness of these layers.

The thickness of the nonmagnetic layer is, for example, 50nm or more, preferably 70nm or more, and more preferably 100nm or more. On the other hand, the thickness of the nonmagnetic layer is preferably 800nm or less, and more preferably 500nm or less.

The thickness of the back coat layer is preferably 0.9 μm or less, and more preferably in the range of 0.1 to 0.7. mu.m.

The thickness of each layer of the magnetic recording medium and the thickness of the nonmagnetic support can be determined by a known film thickness measurement method. For example, a cross section of the magnetic recording medium in the thickness direction is exposed by a known method such as an ion beam or a microtome, and then the exposed cross section is observed by a scanning electron microscope. In the cross-sectional observation, various thicknesses can be obtained as an arithmetic average of the thickness obtained at an arbitrary position or the thicknesses obtained at 2 or more positions extracted at random, for example, 2 positions. Alternatively, the thickness of each layer may be determined as a design thickness calculated from the manufacturing conditions.

< production method >

(preparation of composition for Forming Each layer)

The composition for forming the magnetic layer, the back coat layer, and the nonmagnetic layer contains the various components described above, and generally contains a solvent. As the solvent, various organic solvents generally used for the production of a coating-type magnetic recording medium can be used. The amount of the solvent in the composition for forming each layer is not particularly limited, and can be the same as that of the composition for forming each layer of a general coating-type magnetic recording medium. The step of preparing the composition for forming each layer usually includes at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each process may be divided into 2 or more stages. All the raw materials used in the present invention may be added at the beginning or in the middle of any step. Further, each raw material may be added separately in two or more steps.

For preparing the composition for forming each layer, a known technique can be used. In the kneading step, a kneader having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder is preferably used. Details of these kneading processes are described in Japanese patent application laid-open Nos. H1-106338 and H1-079274. In order to disperse the composition for forming each layer, one or more kinds of dispersion beads selected from the group consisting of glass beads and other dispersion beads can be used as a dispersion medium. As such dispersed beads, zirconia beads, titania beads, and steel beads are preferable as dispersed beads of high specific gravity. The particle diameter (bead diameter) and the filling ratio of these dispersed beads can be optimized and used. The dispersing machine may be a known dispersing machine. The composition for forming each layer may be filtered by a known method before the coating step. The filtration can be performed by, for example, 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 filter made of glass fiber, a filter made of polypropylene, etc.) can be used.

(coating Process)

The magnetic layer can be formed by, for example, directly applying the composition for forming a magnetic layer to the nonmagnetic support or by sequentially or simultaneously applying the composition for forming a magnetic layer and the composition for forming a nonmagnetic layer in a multilayer manner. The back coat layer can be formed by applying the back coat layer-forming composition to the side of the non-magnetic support opposite to the side having the magnetic layer (or additionally provided with the magnetic layer). For details of the coating for forming each layer, reference can be made to paragraph 0051 of japanese patent application laid-open No. 2010-024113.

(other steps)

After the coating step, various treatments such as drying treatment, orientation treatment of the magnetic layer, and surface smoothing treatment (rolling treatment) can be performed. For various steps, refer to paragraphs 0052 to 0057 of jp 2010-024113 a. For example, the vertical alignment treatment can be performed by a known method such as a method using a heteropolar opposed magnet. In the orientation zone, the drying speed of the coating layer can be controlled by the temperature of the drying air, the air volume, and/or the carrying speed in the orientation zone. Also, the coated layer may be pre-dried before being carried to the orientation zone.

The heat treatment of the coating layer formed by coating the back coat layer-forming composition is preferably performed at an arbitrary stage after the coating step of the back coat layer-forming composition. For example, the heating treatment may be performed before and/or after the rolling treatment. The heat treatment can be performed, for example, by placing the support on which the coating layer of the composition for forming a back coating layer is formed in a heated atmosphere. The heating environment can be an environment with an ambient temperature of 65-90 ℃, and is more preferably an environment with an ambient temperature of 65-75 ℃. The environment can be, for example, an atmospheric environment. The heat treatment in the heating environment can be performed, for example, for 20 to 50 hours. In one embodiment, the heat treatment can cause a curing reaction of the curable functional group of the curing agent.

(one mode of production method)

As one mode of the method for producing the magnetic recording medium, there can be mentioned a production method including wiping the surface of the back coat layer with a wiping material impregnated with methyl ethyl ketone after the heat treatment (hereinafter, also referred to as "methyl ethyl ketone wiping treatment"). It is considered that the components capable of being removed by the methyl ethyl ketone wiping treatment are present on the surface of the back coating layer as beforeIt is described that adhesion of moisture on the surface of the back coating layer is promoted when a temperature change from low temperature to high temperature occurs under high humidity. The methyl ethyl ketone wiping treatment can be performed by using a wiping material impregnated with methyl ethyl ketone instead of the wiping material used in the dry wiping treatment in accordance with the dry wiping treatment generally performed in the production process of the magnetic recording medium. For example, in the case of a tape-shaped magnetic recording medium (magnetic tape), after the magnetic tape is cut to a width to be stored in a tape cassette or before the cutting, the magnetic tape is fed and run between a roller and a winding roller, and a wiping material (for example, cloth (for example, nonwoven fabric) or paper (for example, facial tissue)) impregnated with methyl ethyl ketone is pressed against the back coat surface of the running magnetic tape, whereby the methyl ethyl ketone wiping treatment of the back coat surface can be performed. The running speed of the running magnetic tape and the tension applied to the surface of the back coat layer in the longitudinal direction (hereinafter simply referred to as "tension") can be set to the same conditions as those generally used in the dry wiping process generally performed in the manufacturing process of the magnetic recording medium. For example, the tape running speed in the methyl ethyl ketone wiping treatment can be about 60 to 600 m/min, and the tension can be about 0.196 to 3.920N (Newton). Also, the methyl ethyl ketone wiping treatment can be performed at least 1 time. Preferably, the difference (S) between the distances between before and after the washing with methyl ethyl ketone _after-S_before) The treatment conditions and the number of times of the methyl ethyl ketone wiping treatment are set so as to be more than 0nm and 30.0nm or less.

Before and/or after the methyl ethyl ketone wiping treatment, the surface of the back coat layer may be subjected to a polishing treatment and/or a dry wiping treatment (hereinafter, these are referred to as "dry surface treatment") which are generally performed in the production process of a coating-type magnetic recording medium, 1 or more times. By the dry surface treatment, foreign substances such as chips generated by cutting and the like generated in the manufacturing process and adhering to the surface of the back coat layer can be removed.

The description above has been made taking a tape-shaped magnetic recording medium (magnetic tape) as an example. The disk-shaped magnetic recording medium (magnetic disk) can also be subjected to various processes with reference to the above description.

The magnetic recording medium according to one aspect of the present invention described above can be a magnetic recording medium including an aramid support, and the running stability of the magnetic recording medium is less degraded even when the magnetic recording medium is stored in a high-temperature and high-humidity environment after undergoing a temperature change from low temperature to high temperature under high humidity. The temperature change from low temperature to high temperature under high humidity can be, for example, a temperature change of about 15 to 50 ℃ exceeding 0 ℃ to 15 ℃ to 30 to 50 ℃ in an environment with a relative humidity of about 70 to 100%. The storage under a high-temperature and high-humidity environment can be performed, for example, under an environment having a temperature of 30 to 50 ℃ and a relative humidity of 70 to 100%.

The magnetic recording medium may be, for example, a tape-shaped magnetic recording medium (magnetic tape). Magnetic tape is typically circulated and used in a tape cartridge. A magnetic tape cassette is mounted on a magnetic recording/reproducing apparatus, and data can be recorded and reproduced on and from the magnetic tape by sliding the surface of the magnetic tape (magnetic layer surface) in contact with a magnetic head while the magnetic tape is being run in the magnetic recording/reproducing apparatus. However, the magnetic recording medium according to one aspect of the present invention is not limited to a magnetic tape. The magnetic recording medium according to one embodiment of the present invention is suitable for various magnetic recording media (magnetic tapes, disk-shaped magnetic recording media (magnetic disks), and the like) used in a sliding-type magnetic recording and reproducing apparatus. The sliding type device is a device in which a surface of a magnetic layer slides in contact with a head when recording data in a magnetic recording medium and/or reproducing recorded data.

The servo pattern can be formed by a known method so that the magnetic recording medium manufactured as described above can be subjected to tracking control of a magnetic head in a magnetic recording/reproducing apparatus, control of the traveling speed of the magnetic recording medium, and the like. The "formation of servo patterns" can also be referred to as "recording of servo signals". The magnetic recording medium may be a tape-shaped magnetic recording medium (magnetic tape) or a disk-shaped magnetic recording medium (magnetic disk). The following describes the formation of servo patterns by taking a magnetic tape as an example.

The servo patterns are typically formed along the length of the tape. Examples of the control (servo control) using the servo signal include timing-based servo (TBS), amplitude servo, and frequency servo.

As shown in ECMA (European Computer Manufacturers Association ) -319, in a Tape (generally referred to as "LTO Tape") conforming to the LTO (Linear-Tape-Open) standard, a timing-based servo scheme is employed. In this timing-based servo system, a plurality of servo patterns are formed by arranging a pair of magnetic stripes (also referred to as "servo stripes") that are not parallel to each other continuously in the longitudinal direction of the magnetic tape. As described above, the reason why the servo pattern is formed of a pair of magnetic stripes which are not parallel to each other is to notify the passing position to the servo signal reading element passing through the servo pattern. Specifically, the pair of magnetic stripes are formed such that the interval therebetween continuously changes in the width direction of the magnetic tape, and the servo signal reading element reads the interval, whereby the relative position between the servo pattern and the servo signal reading element can be known. The relative position information enables tracking of the data tracks. Therefore, a plurality of servo tracks are generally set in the servo pattern along the width direction of the magnetic tape.

The servo band is composed of a servo signal that continues in the longitudinal direction of the magnetic tape. The servo band is typically provided in a plurality of strips on the tape. For example, the number of which is 5 on LTO tape. The area sandwiched by the adjacent 2 servo bands is called a data band. The data band is composed of a plurality of data tracks, each corresponding to each servo track.

In one aspect, as shown in japanese patent application laid-open No. 2004-318983, information indicating the number of a servo band (also referred to as "servo band ID (Identification)" or "UDIM (unique data band Identification) information") is embedded in each servo band. The servo band ID is recorded by shifting the position of a specific servo band out of a pair of servo bands among a plurality of servo bands so as to be relatively displaced along the longitudinal direction of the magnetic tape. Specifically, the method of changing the offset of a specific pair of servo stripes among a plurality of pairs of servo stripes is performed for each servo stripe. Thus, the recorded servo band ID becomes a unique servo band for each servo band, and the servo band can be uniquely (uniquely) specified only by reading one servo band with the servo signal reading element.

In addition, in the method of uniquely determining the servo band, an interleaved (steady) system as shown in ECMA-319 is also used. In the interleave method, a plurality of sets of a pair of magnetic stripes (servo stripes) which are not parallel to each other are continuously arranged in the longitudinal direction of the magnetic tape and are recorded so as to be shifted in the longitudinal direction of the magnetic tape for each servo stripe. Since the combination of the offset methods between adjacent servo bands is unique throughout the entire magnetic tape, the servo bands can be uniquely identified even when the servo patterns are read by the 2 servo signal reading elements.

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

Other information than the UDIM information and LPOS information can be embedded in the servo band. In this case, the embedded information may be different for each servo band, as in the case of the UDIM information, or may be shared by all servo bands, as in the case of the LPOS information.

As a method of embedding information in the servo band, a method other than the above-described method can be adopted. For example, a predetermined code may be recorded by dividing a predetermined pair from a group of a pair of servo stripes.

The magnetic head for servo pattern formation is called a servo write head. The servo write head has a pair of gaps corresponding to the pair of magnetic stripes for the number of servo bands. In general, each pair of gaps is connected to the core and the coil, and a magnetic field generated in the core can generate a leakage magnetic field in the pair of gaps by supplying a current pulse to the coil. When forming the servo pattern, the magnetic pattern corresponding to the pair of gaps can be transferred to the magnetic tape by inputting a current pulse while the magnetic tape is being advanced on the servo write head, thereby forming the servo pattern. 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 1 μm or less, 1 to 10 μm, 10 μm or more, and the like, for example.

Prior to forming the servo patterns on the magnetic tape, the magnetic tape is typically demagnetized (demagnetized). This demagnetization can be performed by applying the same magnetic field to the magnetic tape using a dc magnet or an ac magnet. The demagnetization process includes DC (direct Current) demagnetization and AC (Alternating Current) demagnetization. AC demagnetization can be performed by gradually decreasing the magnetic field strength while reversing the direction of the magnetic field applied to the magnetic tape. DC demagnetization, on the other hand, is performed by applying a unidirectional magnetic field to the tape. DC demagnetization further includes 2 methods. The first method is horizontal DC demagnetization with unidirectional magnetic field applied along the length of the tape. The second method is perpendicular DC demagnetization with application of a unidirectional magnetic field in the thickness direction of the tape. The demagnetization process may be performed for the entire tape or for each servo band of the tape.

The magnetic field orientation of the formed servo pattern is determined by the demagnetization orientation. For example, when horizontal DC demagnetization is performed on a magnetic tape, the servo pattern is formed such that the direction of the magnetic field is opposite to the direction of demagnetization. This can increase the output of the servo signal obtained by reading the servo pattern. Further, as shown in japanese patent laid-open No. 2012-053940, when a magnetic pattern using the above-described gap is transferred onto a magnetic tape which is demagnetized by a vertical DC, a servo signal obtained by reading the formed servo pattern has a unipolar pulse shape. On the other hand, when the magnetic pattern using the gap is transferred onto the magnetic tape demagnetized with the horizontal DC, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

[ magnetic recording/reproducing apparatus ]

An aspect of the present invention relates to a magnetic recording and reproducing apparatus including the magnetic recording medium and the magnetic head.

In the present invention and the present specification, the "magnetic recording/reproducing device" refers to a device capable of at least one of recording data in a magnetic recording medium and reproducing data recorded in the magnetic recording medium. The associated device is commonly referred to as a drive. The magnetic recording and reproducing device may be a slide type magnetic recording and reproducing device. The magnetic head included in the magnetic recording and reproducing device may be a recording head capable of recording data on the magnetic recording medium, or a reproducing head capable of reproducing data recorded on the magnetic recording medium. In one aspect, the magnetic recording and reproducing apparatus may include both a recording head and a reproducing head as individual magnetic heads. In another aspect, the magnetic head included in the magnetic recording/reproducing device may have a structure in which 1 magnetic head includes both a recording element and a reproducing element. As the reproducing head, a magnetic head (MR head) including a Magnetoresistive (MR) element as a reproducing element, which can read data recorded in a magnetic recording medium with good sensitivity, is preferable. As the MR head, various known MR heads can be used. The magnetic head for recording and/or reproducing data may include a servo pattern reading element. Alternatively, a magnetic head (servo head) provided with a servo pattern read element may be included in the magnetic recording/reproducing device as a head independent from the magnetic head for performing data recording and/or data reproduction.

In the magnetic recording and reproducing device, recording of data in the magnetic recording medium and reproduction of data recorded in the magnetic recording medium can be performed by sliding a surface of the magnetic layer of the magnetic recording medium in contact with the magnetic head. The magnetic recording/reproducing device described above may include the magnetic recording medium according to one embodiment of the present invention, and known techniques may be applied to other portions.