JP2023099751A - Magnetic recording medium and magnetic recording and reproducing device - Google Patents

Abstract

To prevent a deterioration in running stability of a magnetic recording medium including an aromatic polyester support after a temperature change from a high temperature to a low temperature at a low humidity and further after being stored in a low-temperature and low-humidity environment.SOLUTION: The magnetic recording medium has a magnetic layer including a ferromagnetic powder on one surface of a non-magnetic support, and has a back coating layer including a non-magnetic powder on the other surface, in which a difference (Safter-Sbefore) between a spacing Safter measured by optical interferometry regarding a surface of the back coating layer after ethanol cleaning and a spacing Sbefore measured by the optical interferometry before the ethanol cleaning is greater than 0 nm and equal to or less than 15.0 nm, and the non-magnetic support is an aromatic polyester support having a moisture absorption of 0.3% or less. A magnetic recording and reproducing device comprises the magnetic recording medium.SELECTED DRAWING: None

Description

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

A magnetic recording medium (see, for example, Patent Document 1) is a recording medium useful as a data storage medium for storing large amounts of data (information) for a long period of time.

JP-A-9-227883

Recording of data on a magnetic recording medium and reproduction of recorded data are generally performed by mounting the magnetic recording medium in a magnetic recording/reproducing device (called 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 (improve the running stability).

On the other hand, magnetic recording media used for data storage are sometimes used in data centers where temperature and humidity are controlled. On the other hand, data centers are required to save power in order to reduce costs. In order to save power, it is desirable that the temperature and humidity management conditions in data centers can be relaxed more than at present, or management can be made unnecessary. However, if the temperature and humidity control conditions are relaxed or not controlled, the magnetic recording media will be exposed to environmental changes caused by changes in the weather and seasons, or stored under various temperature and humidity environments. It is assumed that An example of an environmental change is a temperature change from high temperature to low temperature under low humidity. An example of a temperature and humidity environment is a low temperature and low humidity environment. Therefore, it is desirable to be able to stabilize the running of the magnetic recording medium in the drive even after such environmental changes and storage in such temperature and humidity environments.

By the way, a magnetic recording medium generally has a structure having a non-magnetic support and a magnetic layer containing ferromagnetic powder. Further, as described in claim 2 of Japanese Patent Application Laid-Open No. 9-227883 (Patent Document 1), a back coating is applied to the surface of the magnetic recording medium opposite to the surface having the magnetic layer of the non-magnetic support. Layering is also practiced. Regarding the non-magnetic support, for example, paragraph 0062 of JP-A-9-227883 (Patent Document 1) lists various films that can be used as the non-magnetic support.

With respect to the above points, the present inventors have investigated and found that a magnetic recording medium containing an aromatic polyester support as a non-magnetic support can be stored in a low-temperature, low-humidity environment after a temperature change from high to low under low humidity. Then, it became clear that the phenomenon that running stability deteriorates occurs.

One aspect of the present invention is a reduction in running stability after temperature change from high temperature to low temperature under low humidity and storage in a low temperature and low humidity environment in a magnetic recording medium containing an aromatic polyester support. The purpose is to suppress

One aspect of the present invention is
A magnetic recording medium having a magnetic layer containing a ferromagnetic powder on one surface of a nonmagnetic support and a backcoat layer containing a nonmagnetic powder on the other surface,
_The difference ₍ S _after −S _before ) (hereinafter also referred to as “spacing difference before and after ethanol washing (S _after −S _before )” or simply “difference (S _after −S _before )”) is greater than 0 nm and 15.0 nm or less; and the magnetic recording medium, wherein the non-magnetic support is an aromatic polyester support having a moisture absorption of 0.3% or less;
Regarding.

In one aspect, the difference (S _after −S _before ) can be 1.0 nm or more and 15.0 nm or less.

In one aspect, the difference (S _after −S _before ) can be 2.0 nm or more and 13.0 nm or less.

In one aspect, the aromatic polyester support may have a moisture absorption rate of 0.1% or more and 0.3% or less.

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

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

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

According to one aspect of the present invention, a magnetic recording medium comprising an aromatic polyester support, which shows little decrease in running stability even when stored in a low-temperature and low-humidity environment after temperature change from high temperature to low temperature under low humidity, and A magnetic recording/reproducing apparatus including this magnetic recording medium can be provided.

One aspect of the present invention is a magnetic recording medium having a magnetic layer containing a ferromagnetic powder on one surface side of a nonmagnetic support and a backcoat layer containing a nonmagnetic powder on the other surface side, _The difference ₍ S _after −S _before ) is more than 0 nm and 15.0 nm or less, and the non-magnetic support is an aromatic polyester support having a moisture absorption of 0.3% or less.

In the present invention and the specification, "ethanol cleaning" means that a sample piece cut out from a magnetic recording medium is immersed in ethanol (200 g) at a liquid temperature of 20 to 25 ° C. and ultrasonically cleaned for 100 seconds (ultrasonic output: 40 kHz ). When the magnetic recording medium to be washed is a magnetic tape, a 5 cm long sample piece is cut out and washed with ethanol. The width of the magnetic tape and the width of the sample piece cut from the magnetic tape is typically 1/2 inch. 1 inch = 0.0254 meters. For magnetic tapes other than 1/2 inch wide, a 5 cm long sample piece may be cut and washed with ethanol. When the magnetic recording medium to be cleaned is a magnetic disk, a sample piece having a size of 5 cm×1.27 cm is cut out and washed with ethanol. The measurement of the spacing after washing with ethanol, which will be described in detail below, is performed after leaving the specimen after washing with ethanol in an environment with a temperature of 23° C. and a relative humidity of 50% for 24 hours.

In the present invention and this specification, the term "(the) surface of the backcoat layer" of the magnetic recording medium is synonymous with the backcoat layer side surface of the magnetic recording medium.

In the present invention and this specification, the spacing measured by the optical interferometry on the surface of the backcoat layer of the magnetic recording medium is the value measured by the following method.
A magnetic recording medium (specifically, the sample piece described above; the same shall apply hereinafter) and a transparent plate-like member (for example, a glass plate) are superposed so that the surface of the back coat layer of the magnetic recording medium faces the transparent plate-like member. In this state, a pressing member is pressed with a pressure of 0.5 atm (1 atm=101325 Pa (pascal)) from the side of the magnetic recording medium opposite to the back coat layer side. In this state, the surface of the backcoat layer of the magnetic recording medium was irradiated with light through a transparent plate-like member (irradiation area: 150,000 to 200,000 μm ² ). Based on the intensity of interference light (for example, the contrast of the interference fringe image) generated by the optical path difference between the reflected light from the magnetic recording medium side surface of the plate-shaped member and the surface of the back coat layer of the magnetic recording medium and the transparent plate-shaped member. Find the spacing (distance) with the magnetic recording medium side surface. The light irradiated here is not particularly limited. When the light to be irradiated is light having emission wavelengths over a relatively wide range of wavelengths, such as white light containing light of multiple wavelengths, a transparent plate-like member and a light receiving portion that receives reflected light are required. A member having a function to selectively cut light of a specific wavelength or light other than a specific wavelength range, such as an interference filter, is placed between them, and light of a part of the wavelength or a part of the wavelength range in the reflected light is placed. Light is selectively made incident on the light receiving section. When the light to be irradiated is light having a single emission peak (so-called monochromatic light), the above members may not be used. For example, the wavelength of the light incident on the light receiving section can be in the range of 500 to 700 nm. However, the wavelength of light incident on the light receiving section is not limited to the above range. Further, the transparent plate-shaped member may be a member having such transparency that the irradiated light can be transmitted through the member so that the magnetic recording medium can be irradiated with the light and interference light can be obtained.
The interference fringe image obtained by the spacing measurement was divided into 300,000 points, and the spacing of each point (the distance between the backcoat layer surface of the magnetic recording medium and the magnetic recording medium side surface of the transparent plate member) was calculated. is obtained, this is taken as a histogram, and the mode in this histogram is taken as the spacing. The difference (S _after -S _before ) refers to a value obtained by subtracting the mode value before ethanol washing from the mode value after ethanol washing at the above 300,000 points.
Two sample pieces are cut out from the same magnetic recording medium, one of which is not washed with ethanol to obtain the spacing value S _before , and the other of which is subjected to ethanol washing to obtain the spacing value S _after , thereby obtaining the difference ( S _after -S _before ) may be determined. Alternatively, the difference (S _after -S _before ) may be obtained by obtaining the spacing value after subjecting the sample piece for which the spacing value is obtained before washing with ethanol to ethanol washing.
The above measurements can be performed using a commercially available Tape Spacing Analyzer (TSA) such as Tape Spacing Analyzer manufactured by Micro Physics. Spacing measurements in the examples were performed using a Tape Spacing Analyzer manufactured by Micro Physics.

In the present invention and herein, "aromatic polyester" means a resin containing an aromatic skeleton and a plurality of ester bonds, and "aromatic polyester support" means at least one layer of aromatic polyester film. means a support comprising The term "aromatic polyester film" refers to a film in which an aromatic polyester is the most abundant component on a mass basis among the components constituting this film. The "aromatic polyester support" in the present invention and the specification includes those in which the resin films contained in the support are all aromatic polyester films, and those in which the aromatic polyester film and other resin films are included. is included. Specific embodiments of the aromatic polyester support include a single-layer aromatic polyester film, a laminate film of two or more layers of aromatic polyester films having the same constituent components, and a laminate of two or more layers of aromatic polyester films having different constituent components. Examples include films, laminated films containing one or more layers of aromatic polyester films and one or more layers of resin films other than aromatic polyester films. An adhesive layer or the like may optionally be included between two adjacent layers in the laminated film. The aromatic polyester support may also optionally include a metal film and/or a metal oxide film formed by vapor deposition or the like on one or both surfaces.

In the present invention and this specification, the moisture absorption rate of the aromatic polyester support is a value determined by the following method.
A sample piece (for example, a sample piece having a mass of several grams) cut from an aromatic polyester support to be measured for moisture absorption is dried in a vacuum dryer at a temperature of 180° C. and a pressure of 100 Pa or less until the weight becomes constant. Let W1 be the mass of the sample piece thus dried. W1 is a value measured within 30 seconds after being removed from the vacuum dryer in a measurement environment of temperature 23° C. and relative humidity 50%. Next, let W2 be the mass of this sample piece after it has been placed in an environment with a temperature of 25° C. and a relative humidity of 75% for 48 hours. W2 is a value measured in a measurement environment with a temperature of 23° C. and a relative humidity of 50% within 30 seconds after being removed from the above environment. The moisture absorption rate is calculated by the following formula.
Moisture absorption rate (%) = [(W2-W1)/W1] x 100
For example, after removing portions other than the aromatic polyester support such as the magnetic layer from the magnetic recording medium by a known method (e.g., film removal using an organic solvent, etc.), the moisture absorption of the aromatic polyester support is measured by the above method. You can also ask.

Hereinafter, deterioration in running stability after temperature change from high temperature to low temperature under low humidity and storage in a low temperature and low humidity environment (hereinafter also simply referred to as "decrease in running stability"). The conjecture of the present inventors will be described as to the fact that the above magnetic recording medium enables suppression.

Recording of data on a magnetic tape and reproduction of recorded data are generally performed by running a magnetic recording medium in a drive. During such travel, the backcoat layer surface normally contacts drive components within the drive. If the contact state between the surface of the back coat layer and the drive components becomes unstable, it is considered that the running stability of the magnetic recording medium in the drive will deteriorate.
On the other hand, under low humidity and high temperature conditions, it is believed that organic components tend to seep out onto the surface of the backcoat layer. It is presumed that when the temperature changes from high to low under low humidity, the organic component that has permeated the surface of the backcoat layer solidifies or becomes highly viscous. It is presumed that such a solidified or highly viscous organic component destabilizes the contact state between the surface of the backcoat layer and the drive component. Therefore, if it is possible to reduce the amount of the organic component that solidifies or becomes highly viscous when the temperature changes from high to low under low humidity, it is thought that this will lead to a reduction in running stability.
By the way, the surface of the back coat layer usually has a portion (protrusion) that mainly contacts the drive component when the back coat layer surface and the drive component come into contact (so-called true contact), and a portion that is lower than this portion (protrusion). Hereinafter, it will be described as a “base portion”). Spacing, as previously described, is considered a value that is indicative of the distance between the drive component and the substrate when the backcoat layer surface and the drive component are in contact. However, if any component is present on the backcoat layer surface, it is believed that the greater the amount of such component interposed between the substrate and the drive component, the narrower the spacing. On the other hand, when this component is removed by ethanol cleaning, the spacing is widened, so the value of spacing S _after after ethanol cleaning becomes larger than the value of spacing S _before before ethanol cleaning. Therefore, it is believed that the difference in spacing before and after ethanol cleaning (S _after −S _before ) can be an indicator of the amount of the component interposed between the substrate and the drive component.
Regarding the above point, the present inventor believes that the component removed by ethanol washing is an organic component that solidifies or becomes highly viscous on the surface of the backcoat layer due to the temperature change from high temperature to low temperature under low humidity as described above. thinking. Therefore, reducing the difference (S _after -S _before ) in the spacing before and after washing with ethanol, that is, reducing the amount of the component, will improve the running stability caused by the temperature change from high temperature to low temperature under low humidity. It is thought that it will lead to suppressing the decrease. On the other hand, according to the study of the present inventors, there is a no correlation was found. This is presumed to be due to the fact that the above components cannot be removed or sufficiently removed by n-hexane washing.
The details of the above ingredients are not clear. Merely speculating, the present inventors believe that the above components may be derived from organic components and/or binders that are commonly added to the backcoat layer as additives (eg, lubricants). Regarding components derived from binders, relatively low-molecular-weight components among the resins used as binders (usually having a molecular weight distribution) tend to seep out onto the surface of the backcoat layer under low-humidity and high-temperature conditions. The inventor of the present invention speculates that this is the case.

In addition, if the aromatic polyester support absorbs a large amount of water during storage in a low-temperature, low-humidity environment after the temperature change, the surface of the backcoat layer of the magnetic recording medium containing this support and the drive components may become damaged. It is thought that the friction coefficient at the time of contact of This is considered to be one of the reasons why the running stability is lowered after being stored in a low-temperature, low-humidity environment after the temperature change. On the other hand, in the above magnetic recording medium, since the moisture absorption rate of the aromatic polyester support is 0.3% or less, the amount of water absorbed by the aromatic polyester support during storage is considered to be small. It is presumed that this also contributes to suppressing deterioration in running stability.

However, the above is just speculation and does not limit the present invention. The magnetic recording medium will be described in more detail below.

<Nonmagnetic support>
The magnetic recording medium includes an aromatic polyester support having a moisture absorption of 0.3% or less as a non-magnetic support. From the viewpoint of suppressing a decrease in running stability, the moisture absorption of the aromatic polyester support is 0.3% or less, preferably 0.2% or less, more preferably 0.1% or less. preferable. The moisture absorption of the aromatic polyester support may be, for example, 0% or more, 0% or more, or 0.1% or more. From the viewpoint of suppressing deterioration in running stability, it is preferable that the aromatic polyester support has a low moisture absorption rate, so the moisture absorption rate can be 0%. In addition, it is preferable to use an aromatic polyester support having a low moisture absorption rate as a non-magnetic support of a magnetic recording medium from the viewpoint of suppressing deformation of the magnetic recording medium after long-term storage. For example, it is preferable for a tape-shaped magnetic recording medium (magnetic tape) to contain an aromatic polyester support with a low moisture absorption rate from the viewpoint of suppressing deformation in the tape width direction of the magnetic tape after long-term storage. In the magnetic tape, the Young's modulus of the aromatic polyester support is preferably 3000 N/mm ² or more in the longitudinal direction and 4000 N/mm ² or more in the width direction. From the viewpoint of increasing the capacity of the magnetic recording medium, the surface roughness of one or both surfaces of the aromatic polyester support is preferably 10 nm or less in terms of center line average roughness Ra.

The aromatic ring contained in the aromatic skeleton of the aromatic polyester is not particularly limited. Specific examples of the aromatic ring include benzene ring, naphthalene ring, and the like.
For example, polyethylene terephthalate (PET) is a polyester containing benzene rings, and is a resin obtained by polycondensation of ethylene glycol with terephthalic acid and/or dimethyl terephthalate. The term "polyethylene terephthalate" in the present invention and the specification includes structures having one or more other components (e.g., copolymer components, components introduced into terminals or side chains, etc.) in addition to the above components. be done. Hereinafter, an aromatic polyester film containing polyethylene terephthalate as aromatic polyester may be referred to as a polyethylene terephthalate film.
Polyethylene naphthalate (PEN) is a polyester containing a naphthalene ring, and is obtained by performing an esterification reaction between dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol, followed by transesterification and polycondensation reactions. Resin. "Polyethylene naphthalate" in the present invention and the specification includes those having a structure having one or more other components (e.g., copolymer components, components introduced into terminals or side chains, etc.) in addition to the above components. subsumed. Hereinafter, an aromatic polyester film containing polyethylene naphthalate as the aromatic polyester may be referred to as a polyethylene naphthalate film.
The hygroscopicity of the aromatic polyester support can be controlled by, for example, the types and proportions of the components constituting the aromatic polyester. For example, aromatic polyesters such as polyethylene terephthalate and polyethylene naphthalate can be resins synthesized using a hydrophobic component as a copolymerization component, and a hydrophobic component is introduced into the side chain and/or terminal. can also be Examples of hydrophobic components include long-chain alkyl group-containing components and fluorine-containing components. By including a hydrophobic component in the aromatic polyester, the hygroscopicity of the aromatic polyester film can be reduced, and by increasing the proportion of the hydrophobic component, the hygroscopicity can be further reduced. As a means for reducing the moisture absorption of the aromatic polyester support, it is possible to reduce the moisture absorption of the aromatic polyester film. Further, when the aromatic polyester support is a laminated film of one or more layers of the aromatic polyester film and one or more layers of other resin film, by using a resin film having a low moisture absorption rate as the other resin film, Moisture absorption of the aromatic polyester support can also be reduced. Examples of such aromatic polyester supports include laminated films described in JP-A-2011-84036. For details of such a laminated film, reference can be made to paragraphs 0014 to 0061 of the same publication and the description of Examples of the same publication. Further, the aromatic polyester support may be a biaxially stretched film, or may be a film subjected to corona discharge, plasma treatment, adhesion-facilitating treatment, heat treatment, or the like.

<Magnetic layer>
(Spacing difference before and after ethanol washing (S _after -S _before ))
The spacing difference (S _after -S _before ) before and after washing with ethanol on the surface of the backcoat layer of the magnetic recording medium measured by optical interferometry is more than 0 nm and 15.0 nm or less. The difference (S _after −S _before ) being 15.0 nm or less can contribute to suppressing deterioration in running stability of the magnetic recording medium. From this point, the difference (S _after −S _before ) is 15.0 nm or less, preferably 14.0 nm or less, more preferably 13.0 nm or less, and further preferably 12.0 nm or less. It is preferably 11.0 nm or less, more preferably 10.0 nm or less. As will be described later in detail, the difference (S _after -S _before ) can be controlled by surface treatment of the backcoat layer in the manufacturing process of the magnetic recording medium.
Further, if the surface treatment of the backcoat layer is carried out to such an extent that the spacing difference (S _after −S _before ) before and after washing with ethanol becomes 0 nm, a component (for example, a lubricant) that contributes to the improvement of running stability will be lost to magnetic recording. It is presumed that a large amount is removed from the medium. However, this is a guess and does not limit the present invention. From this point of view, the spacing difference (S _after -S _before ) of the magnetic recording medium before and after washing with ethanol is more than 0 nm, preferably 1.0 nm or more, more preferably 2.0 nm or more.

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

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

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

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

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

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

An anisotropic constant Ku can be cited as an index for reducing thermal fluctuation, in other words, improving thermal stability. The hexagonal strontium ferrite powder can preferably have a Ku of 1.8×10 ⁵ J/m ³ or more, more preferably 2.0×10 ⁵ J/m ³ or more. Also, Ku of the hexagonal strontium ferrite powder can be, for example, 2.5×10 ⁵ J/m ³ or less. However, the higher the Ku value, the higher the thermal stability, which is preferable.

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

When the hexagonal strontium ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 atomic % with respect to 100 atomic % of iron atoms. The fact that the rare earth atoms are contained in the bulk content in the above range and that the rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder contributes to suppressing the decrease in reproduction output during repeated reproduction. Conceivable. This is because the hexagonal strontium ferrite powder contains rare earth atoms with a bulk content within the above range, and the rare earth atoms are unevenly distributed in the surface layers of the particles constituting the hexagonal strontium ferrite powder. This is presumed to be due to the fact that The higher the anisotropy constant Ku, the more the occurrence of a phenomenon called thermal fluctuation can be suppressed (in other words, the thermal stability can be improved). By suppressing the occurrence of thermal fluctuation, it is possible to suppress a decrease in reproduction output in repeated reproduction. The uneven distribution of rare earth atoms in the particle surface layer of the hexagonal strontium ferrite powder contributes to stabilizing the spin of the iron (Fe) site in the crystal lattice of the surface layer, thereby increasing the anisotropy constant Ku. It is speculated that it will increase.
In addition, it is speculated that the use of hexagonal strontium ferrite powder, which has rare earth atoms unevenly distributed in the surface layer, as the ferromagnetic powder for the magnetic layer contributes to suppressing abrasion of the magnetic layer surface due to sliding against the magnetic head. be. That is, it is presumed that the hexagonal strontium ferrite powder having rare earth atoms unevenly distributed on the surface layer can contribute to the improvement of the running durability of the magnetic recording medium. This is because the uneven distribution of rare earth atoms on the surfaces of the particles that make up the hexagonal strontium ferrite powder improves the interaction between the particle surfaces and organic substances (e.g., binders and/or additives) contained in the magnetic layer. and as a result, the strength of the magnetic layer is improved.
From the viewpoint of further suppressing the decrease in reproduction output in repeated reproduction and/or from the viewpoint of further improving running durability, the rare earth atom content (bulk content) is in the range of 0.5 to 4.5 atomic %. is more preferable, the range of 1.0 to 4.5 atomic % is more preferable, and the range of 1.5 to 4.5 atomic % is even more preferable.

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

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

In the hexagonal strontium ferrite powder having rare earth atoms unevenly distributed on the surface layer, the rare earth atoms may be unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder, and the degree of uneven distribution is not limited. For example, for a hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer, the surface layer content of rare earth atoms obtained by partially dissolving under the dissolving conditions described later and the rare earth elements obtained by completely dissolving under the dissolving conditions described later The ratio of atoms to the bulk content, "surface layer content/bulk content", is greater than 1.0 and can be 1.5 or more. When the "surface layer content/bulk content" is greater than 1.0, it means that the rare earth atoms are unevenly distributed in the surface layer (ie, more present than in the interior) in the particles constituting the hexagonal strontium ferrite powder. do. In addition, the ratio between the surface layer content of rare earth atoms obtained by partial dissolution under the dissolution conditions described later and the bulk content of rare earth atoms obtained by complete dissolution under the dissolution conditions described later, "surface layer content/ The "bulk content" can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in the hexagonal strontium ferrite powder having rare earth atoms unevenly distributed in the surface layer portion, the rare earth atoms should be unevenly distributed in the surface layer portion of the particles constituting the hexagonal strontium ferrite powder. "Ratio" is not limited to the exemplified upper or lower limits.

Partial dissolution and total dissolution of hexagonal strontium ferrite powder are described below. For hexagonal strontium ferrite powders present as powders, sample powders for partial dissolution and total dissolution are taken from the same lot of powder. On the other hand, for the hexagonal strontium ferrite powder contained in the magnetic layer of the magnetic recording medium, part of the hexagonal strontium ferrite powder taken out from the magnetic layer is subjected to partial dissolution and the other part is subjected to complete dissolution. . The hexagonal strontium ferrite powder can be extracted from the magnetic layer, for example, by the method described in paragraph 0032 of JP-A-2015-91747.
The partial dissolution means dissolution to such an extent that residual hexagonal strontium ferrite powder can be visually confirmed in the liquid at the end of dissolution. For example, by partial dissolution, a region of 10 to 20% by mass of the particles constituting the hexagonal strontium ferrite powder can be dissolved out of 100% by mass of the entire particles. On the other hand, the above-mentioned complete dissolution means that the hexagonal strontium ferrite powder is dissolved to the point where no residue of the hexagonal strontium ferrite powder remains in the liquid at the end of dissolution.
The partial dissolution and the measurement of the surface layer content are performed, for example, by the following methods. However, the dissolution conditions such as the amount of sample powder described below are examples, and dissolution conditions that allow partial dissolution and complete dissolution can be arbitrarily adopted.
A container (for example, a beaker) containing 12 mg of sample powder and 10 mL of 1 mol/L hydrochloric acid is held on a hot plate with a set temperature of 70° C. for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the filtrate thus obtained is performed by an inductively coupled plasma (ICP) analyzer. In this way, the surface layer portion content of rare earth atoms relative to 100 atomic % of iron atoms can be obtained. When multiple types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is taken as the surface layer portion content. This point also applies to the measurement of the bulk content.
On the other hand, the measurement of the total dissolution and bulk content is carried out, for example, by the following method.
A container (for example, a beaker) containing 12 mg of sample powder and 10 mL of 4 mol/L hydrochloric acid is held on a hot plate with a set temperature of 80° C. for 3 hours. After that, the partial dissolution and the measurement of the surface layer portion content are carried out in the same manner as described above, and the bulk content with respect to 100 atom % of iron atoms can be obtained.

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

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

As crystal structures of hexagonal ferrite, magnetoplumbite type (also called “M type”), W type, Y type and Z type are known. The hexagonal strontium ferrite powder may have any crystal structure. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder can have a single crystal structure or two or more crystal structures detected by X-ray diffraction analysis. For example, in one aspect, the hexagonal strontium ferrite powder can be one in which only the M-type crystal structure is detected by X-ray diffraction analysis. For example, M-type hexagonal ferrite is represented by a composition formula of AFe ₁₂ O ₁₉ . Here, A represents a divalent metal atom, and if the hexagonal strontium ferrite powder is M-type, A is only a strontium atom (Sr), or if A contains a plurality of divalent metal atoms, , as described above, strontium atoms (Sr) account for the largest amount on an atomic % basis. The divalent metal atom content of the hexagonal strontium ferrite powder is usually determined by the type of crystal structure of the hexagonal ferrite, and is not particularly limited. The same applies to the iron atom content and the oxygen atom content. The hexagonal strontium ferrite powder contains at least iron atoms, strontium atoms and oxygen atoms, and may also contain rare earth atoms. Furthermore, the hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may contain aluminum atoms (Al). The content of aluminum atoms can be, for example, 0.5 to 10.0 atomic % with respect to 100 atomic % of iron atoms. From the viewpoint of further suppressing the decrease in reproduction output in repeated reproduction, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms and rare earth atoms, and the content of atoms other than these atoms is 100 iron atoms. %, preferably 10.0 atomic % or less, more preferably in the range of 0 to 5.0 atomic %, and may be 0 atomic %. That is, in one aspect, the hexagonal strontium ferrite powder may contain no atoms other than iron atoms, strontium atoms, oxygen atoms and rare earth atoms. The content expressed in atomic % above is the content of each atom (unit: mass %) obtained by completely dissolving the hexagonal strontium ferrite powder, and converted to the value expressed in atomic % using the atomic weight of each atom. It is required by conversion. Moreover, in the present invention and this specification, the phrase "not containing" an atom means that the content of the atom is 0% by mass as measured by an ICP analyzer after being completely dissolved. The detection limit of an ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The above-mentioned "does not contain" shall be used in the sense of containing in an amount below the detection limit of the ICP analyzer. The hexagonal strontium ferrite powder, in one aspect, can be free of bismuth atoms (Bi).

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

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

The activated volume of the ε-iron oxide powder is preferably in the range of 300-1500 nm ³ . Micronized ε-iron oxide powder exhibiting an activation volume within the above range is suitable for producing magnetic recording media exhibiting excellent electromagnetic conversion characteristics. The activated volume of the ε-iron oxide powder is preferably greater than or equal to 300 nm ³ and may eg be greater than or equal to 500 nm ³ . Further, from the viewpoint of further improving the electromagnetic conversion characteristics, the activated volume of the ε-iron oxide powder is more preferably 1400 nm ³ or less, further preferably 1300 nm ³ or less, and 1200 nm ³ or less. is more preferable, and 1100 nm ³ or less is even more preferable.

An anisotropic constant Ku can be cited as an index for reducing thermal fluctuation, in other words, improving thermal stability. The ε-iron oxide powder can preferably have a Ku of 3.0×10 ⁴ J/m ³ or higher, more preferably 8.0×10 ⁴ J/m ³ or higher. Also, Ku of the ε-iron oxide powder can be, for example, 3.0×10 ⁵ J/m ³ or less. However, the higher the Ku, the higher the thermal stability, which is preferable, and is not limited to the values exemplified above.

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

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

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

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

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

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

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

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

The above descriptions of binders and hardeners can also be applied to the backcoat layer and/or the non-magnetic layer. In that case, the above description regarding the content can be applied by replacing ferromagnetic powder with non-magnetic powder. From the viewpoint of reducing the spacing difference (S _after -S _before ) before and after washing with ethanol, it is preferable to reduce the amount of components derived from the binder that ooze out to the surface of the backcoat layer under low humidity and high temperature conditions. From this point of view, reducing the amount of the binder used in forming the backcoat layer can be cited as one means of reducing the spacing difference (S _after -S _before ) before and after washing with ethanol.

(Additive)
The magnetic layer may contain one or more additives as required. Examples of additives include the curing agents described above. Additives contained in the magnetic layer include nonmagnetic powders (e.g., inorganic powders, carbon black, etc.), lubricants, dispersants, dispersing aids, antifungal agents, antistatic agents, antioxidants, and the like. can be done. Examples of the non-magnetic powder include a non-magnetic powder that can function as an abrasive, and a non-magnetic powder that can function as a protrusion-forming agent that forms moderately protruding protrusions on the surface of the magnetic layer (e.g., non-magnetic colloidal particles). etc.). The average particle size of colloidal silica (silica colloidal particles) shown in the examples below is a value obtained by the method described as a method for measuring the average particle size in paragraph 0015 of JP-A-2011-048878. . Additives can be appropriately selected from commercial products according to desired properties, or can be produced by known methods and used in any amount. Examples of additives that can be used in a magnetic layer containing an abrasive include dispersants described in paragraphs 0012 to 0022 of JP-A-2013-131285 as dispersants for improving the dispersibility of the abrasive. be able to. For example, regarding lubricants, paragraphs 0030 to 0033, 0035 and 0036 of JP-A-2016-126817 can be referred to. The non-magnetic layer may contain a lubricant. Paragraphs 0030, 0031, 0034, 0035 and 0036 of JP-A-2016-126817 can be referred to for lubricants that can be contained in the non-magnetic layer. Regarding the dispersant, paragraphs 0061 and 0071 of JP-A-2012-133837 can be referred to. In addition, regarding the dispersant, paragraphs 0061 and 0071 of JP-A-2012-133837 and paragraph 0035 of JP-A-2017-016721 can also be referred to. Regarding additives for the magnetic layer, paragraphs 0035 to 0077 of JP-A-2016-51493 can also be referred to.
A dispersant may be contained in the non-magnetic layer. For the dispersant that can be contained in the non-magnetic layer, see paragraph 0061 of JP-A-2012-133837.
Various additives can be appropriately selected from commercial products according to desired properties, or can be produced by known methods and used in arbitrary amounts.

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

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

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

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

<Back coat layer>
The magnetic recording medium has a back coat layer containing non-magnetic powder on the surface of the non-magnetic support opposite to the surface having the magnetic layer. For the type of non-magnetic powder contained in the backcoat layer, reference can be made to the description of the non-magnetic powder contained in the non-magnetic layer. The non-magnetic powder contained in the backcoat layer is preferably one or more non-magnetic powders selected from the group consisting of inorganic powders and carbon black. The magnetic recording medium can contain, for example, an inorganic powder as the main powder of the non-magnetic powder in the backcoat layer (the non-magnetic powder contained in the largest amount on a mass basis among the non-magnetic powders). When the non-magnetic powder contained in the back coat layer is one or more types of non-magnetic powder selected from the group consisting of inorganic powder and carbon black, the ratio of the inorganic powder to the total amount of 100.0 parts by mass of the non-magnetic powder is For example, it can be in the range of more than 50.0 parts by mass to 100.0 parts by mass, preferably in the range of 60.0 parts by mass to 100.0 parts by mass. In some cases, the value of the difference ( _after -S _before ) tends to decrease when the proportion of the inorganic powder in the non-magnetic powder is increased.

The average particle size of the non-magnetic powder can range, for example, from 10 to 200 nm. The average particle size of the inorganic powder is preferably in the range of 50-200 nm, more preferably in the range of 80-150 nm. On the other hand, the average particle size of carbon black is preferably in the range of 10-50 nm, more preferably in the range of 15-30 nm.

The backcoat layer may contain a binder and may also contain additives. An example of the additive is a known dispersant that can contribute to improving the dispersibility of the non-magnetic powder.

An example of an additive also includes a lubricant.
For example, lubricants include fatty acids, fatty acid esters and fatty acid amides, and the magnetic layer can be formed using one or more selected from the group consisting of fatty acids, fatty acid esters and fatty acid amides.
Examples of fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, and elaidic acid. is preferred, and stearic acid is more preferred. The fatty acid may be contained in the magnetic layer in the form of a salt such as a metal salt.
Examples of fatty acid esters include esters of lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid and elaidic acid. Specific examples include butyl myristate, butyl palmitate, butyl stearate, neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, isocetyl stearate, and stearin. Examples include isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate, butoxyethyl stearate and the like.
Examples of fatty acid amides include amides of the various fatty acids described above, such as lauric acid amide, myristic acid amide, palmitic acid amide, and stearic acid amide.
The fatty acid content of the backcoat layer is, for example, 0 to 10.0 parts by mass, preferably 0.1 to 10.0 parts by mass, per 100.0 parts by mass of the non-magnetic powder contained in the backcoat layer, More preferably, it is 1.0 to 7.0 parts by mass. The content of fatty acid ester in the backcoat layer is, for example, 0.1 to 10.0 parts by weight, preferably 1.0 to 5.0 parts by weight, per 100.0 parts by weight of the non-magnetic powder contained in the backcoat layer. is. The fatty acid amide content of the backcoat layer is, for example, 0 to 3.0 parts by mass, preferably 0 to 2.0 parts by mass, per 100.0 parts by mass of the non-magnetic powder contained in the backcoat layer. It is preferably 0 to 1.0 parts by mass.
In the present invention and this specification, unless otherwise specified, one component or two or more components may be used. When two or more kinds of certain components are used, the content means the total content of these two or more kinds.

As for binders, additives, etc. for the backcoat layer, known techniques for the backcoat layer can be applied, and known techniques for the formulation of the magnetic layer and/or the non-magnetic layer can also be applied. For example, paragraphs 0018 to 0020 of JP-A-2006-331625 and US Pat. No. 7,029,774 from column 4, line 65 to column 5, line 38 can be referred to for the back coat layer.

<Various thicknesses>
The thickness of the non-magnetic support of the magnetic recording medium is, for example, 3.0 to 80.0 μm, preferably 3.0 to 50.0 μm, more preferably 3.0 to 10.0 μm. is. The thickness of the non-magnetic support is the thickness of the film when the non-magnetic support consists of only a single-layer aromatic polyester film, or the total thickness of the non-magnetic support in other cases.

The thickness of the magnetic layer can be optimized depending on the saturation magnetization amount and head gap length of the magnetic head to be used, and the band of the recording signal. and more preferably from 30 to 70 nm. At least one magnetic layer is sufficient, and the magnetic layer may be separated into two or more layers having different magnetic properties, and a configuration relating to a known multi-layered magnetic layer can be applied. The thickness of the magnetic layer when separated into two or more layers is the total thickness of these layers.

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

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

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

<Manufacturing method>
(Preparation of each layer-forming composition)
Compositions for forming the magnetic layer, backcoat layer and non-magnetic layer usually contain a solvent as well as the various components described above. As the solvent, various organic solvents generally used for producing coating type magnetic recording media can be used. The amount of solvent in each layer-forming composition is not particularly limited, and can be the same as in each layer-forming composition for a conventional coating type magnetic recording medium. The step of preparing a composition for forming each layer usually includes at least a kneading step, a dispersing step, and a mixing step provided before or after these steps as required. Each step may be divided into two or more stages. Various components used for forming each layer may be added at the beginning or during any step. Alternatively, individual components may be added in portions in two or more steps.

A known technique can be used to prepare each layer-forming composition. In the kneading step, it is preferable to use a kneader having a strong kneading force such as an open kneader, continuous kneader, pressure kneader, extruder or the like. Details of these kneading processes are described in Japanese Patent Application Laid-Open Nos. 1-106338 and 1-79274. Moreover, in order to disperse each layer-forming composition, one or more kinds of dispersing beads selected from the group consisting of glass beads and other dispersing beads can be used as dispersing media. As such dispersing beads, zirconia beads, titania beads, and steel beads, which are high specific gravity dispersing beads, are suitable. The particle size (bead diameter) and filling rate of these dispersed beads can be optimized for use. A known disperser can be used. Each layer-forming composition may be filtered by a known method before being applied to the coating step. Filtration can be performed, for example, by filter filtration. As a filter used for filtration, for example, a filter having a pore size of 0.01 to 3 μm (eg, glass fiber filter, polypropylene filter, etc.) can be used.

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

(Other processes)
After the coating step, various treatments such as drying treatment, magnetic layer orientation treatment, and surface smoothing treatment (calender treatment) can be performed. For various steps, paragraphs 0052 to 0057 of JP-A-2010-24113 can be referred to. For example, the vertical alignment treatment can be performed by a known method such as a method using opposed magnets with different polarities. In the orientation zone, the drying speed of the coating layer can be controlled by the temperature and air volume of the drying air and/or the conveying speed in the orientation zone. Also, the coated layer may be pre-dried before being conveyed to the orientation zone.

It is preferable to heat-treat the coating layer formed by applying the backcoat layer-forming composition at any stage after the step of applying the backcoat layer-forming composition. This heat treatment can be performed before and/or after calendering, as an example. The heat treatment can be carried out, for example, by placing the support on which the coated layer of the backcoat layer-forming composition is formed in a heated atmosphere. The heating atmosphere can be an atmosphere with an ambient temperature of 65 to 90°C, more preferably an atmosphere with an ambient temperature of 65 to 75°C. This atmosphere can be, for example, an atmospheric atmosphere. The heat treatment in a heating atmosphere can be carried out for 20 to 50 hours, for example. In one aspect, this heat treatment can promote the curing reaction of the curable functional groups of the curing agent.

(One mode of manufacturing method)
In one aspect of the method for manufacturing the magnetic recording medium, the surface of the backcoat layer is wiped with a wiping material impregnated with alcohol, preferably after the heat treatment (hereinafter also referred to as "alcohol wiping treatment"). A manufacturing method including As described above, the components that can be removed by this alcohol wiping treatment ooze out onto the surface of the backcoat layer under low humidity and high temperature conditions, and solidify or increase in viscosity on the surface of the backcoat layer as the temperature changes from high to low. Thus, it is considered to be the cause of the decrease in running stability due to the temperature change from high temperature to low temperature under low humidity. The alcohol used for the alcohol wiping treatment is preferably an alcohol having 2 to 4 carbon atoms, more preferably ethanol, 1-propanol and 2-propanol, and still more preferably ethanol. The alcohol wiping process can be performed using a wiping material soaked with alcohol in place of the wiping material used in the dry wiping process, according to the dry wiping process generally performed in the manufacturing process of the magnetic recording medium. can. For example, for a tape-shaped magnetic recording medium (magnetic tape), after or before slitting the magnetic tape to the width to be accommodated in the magnetic tape cartridge, the magnetic tape is run between the feed roller and the take-up roller. A wiping material (e.g., cloth (e.g., non-woven fabric) or paper (e.g., tissue paper)) impregnated with alcohol is pressed against the back-coat layer surface of the running magnetic tape to wipe off the back-coat layer surface with alcohol. can be done. The running speed of the magnetic tape during running and the tension applied in the longitudinal direction of the backcoat layer surface (hereinafter simply referred to as "tension") are generally determined in the dry wiping treatment generally performed in the manufacturing process of the magnetic recording medium. It can be similar to the processing conditions employed. For example, the running speed of the magnetic tape in the alcohol wiping process can be about 60 to 600 m/min, and the tension can be about 0.196 to 3.920 N (Newton). Also, the alcohol wiping treatment can be performed at least once. It is preferable to set the treatment conditions and the number of treatments for the alcohol wiping treatment so that the spacing difference (S _after −S _before ) before and after ethanol washing is more than 0 nm and 15.0 nm or less.
Before and/or after the alcohol wiping treatment, the surface of the backcoat layer is subjected to a polishing treatment and/or a dry wiping treatment (hereinafter referred to as "dry surface treatment") which is generally performed in the manufacturing process of a coating type magnetic recording medium. described.) can be performed one or more times. According to the dry surface treatment, it is possible to remove foreign matters such as shavings generated by slitting and adhering to the surface of the backcoat layer during the manufacturing process.
A tape-shaped magnetic recording medium (magnetic tape) has been described above as an example. Various types of processing can also be performed on disk-shaped magnetic recording media (magnetic disks) by referring to the above description.

The magnetic recording medium according to one aspect of the present invention described above is a magnetic recording medium containing an aromatic polyester support, and is stored in a low-temperature and low-humidity environment after a temperature change from high temperature to low temperature under low humidity. It can be a magnetic recording medium with little decrease in running stability. A temperature change from a high temperature to a low temperature under low humidity is, for example, a temperature change from a high temperature of 30°C to 50°C to a low temperature of over 0°C to 15°C in an environment with a relative humidity of 0% to 30%. can be done. In addition, storage under a low temperature and low humidity environment can be storage under an environment with a temperature of over 0° C. to 15° C. and a relative humidity of 0 to 30%, for example.

The magnetic recording medium can be, for example, a tape-shaped magnetic recording medium (magnetic tape). Magnetic tapes are usually housed in magnetic tape cartridges for distribution and use. A magnetic tape cartridge is loaded into a magnetic recording/reproducing device, and the magnetic tape is run in the magnetic recording/reproducing device. can be recorded and played back. However, the magnetic recording medium according to one aspect of the present invention is not limited to magnetic tapes. The magnetic recording medium according to one aspect of the present invention is suitable as various magnetic recording media (magnetic tapes, disc-shaped magnetic recording media (magnetic discs), etc.) used in sliding-type magnetic recording/reproducing devices. The sliding type device is a device in which the surface of the magnetic layer and the head slide in contact with each other when data is recorded on the magnetic recording medium and/or the recorded data is reproduced.

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

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

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

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

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

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

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

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

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

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

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

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

In the present invention and in this specification, the term "magnetic recording/reproducing apparatus" means a device capable of at least one of recording data on a magnetic recording medium and reproducing data recorded on the magnetic recording medium. do. Such devices are commonly called drives. The magnetic recording/reproducing device may be a sliding type magnetic recording/reproducing device. The magnetic head included in the magnetic recording/reproducing device can be a recording head capable of recording data on a magnetic recording medium, and a reproducing head capable of reproducing data recorded on the magnetic recording medium. can also be In one aspect, the magnetic recording/reproducing apparatus can include both a recording head and a reproducing head as separate magnetic heads. In another aspect, the magnetic head included in the magnetic recording/reproducing device may have a configuration in which both the recording element and the reproducing element are provided in one magnetic head. As the reproducing head, a magnetic head (MR head) including a magnetoresistive (MR) element as a reproducing element capable of reading data recorded on a magnetic recording medium with high sensitivity is preferable. Various known MR heads can be used as the MR head. A magnetic head for recording and/or reproducing data may also include a servo pattern reading element. Alternatively, the magnetic recording/reproducing apparatus may include a magnetic head (servo head) having a servo pattern reading element as a separate head from the magnetic head that records and/or reproduces data.

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

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

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

<Prescription of composition for forming magnetic layer>
(Magnetic liquid)
Ferromagnetic powder (see Table 1): 100.0 parts Oleic acid: 2.0 parts Vinyl chloride copolymer (MR-104 manufactured by Kaneka Corporation): 10.0 parts SO ₃ Na group-containing polyurethane resin: 4.0 parts (Weight average molecular weight: 70000, SO ₃ Na group: 0.07 meq/g)
Polyalkyleneimine polymer (synthetic product obtained by the method described in paragraphs 0115 to 0123 of JP-A-2016-51493): 6.0 parts methyl ethyl ketone: 150.0 parts cyclohexanone: 150.0 parts (abrasive liquid )
α-alumina (BET (Brunauer-Emmett-Teller) specific surface area 19 m ² /g): 6.0 parts SO ₃ Na group-containing polyurethane resin: 0.6 parts (weight average molecular weight: 70000, SO ₃ Na group: 0. 1 meq/g)
2,3-dihydroxynaphthalene: 0.6 parts Cyclohexanone: 23.0 parts (projection forming agent liquid)
Colloidal silica (average particle size: 120 nm): 2.0 parts Methyl ethyl ketone: 8.0 parts (other components)
Stearic acid: 3.0 parts Stearamide: 0.3 parts Butyl stearate: 6.0 parts Methyl ethyl ketone: 110.0 parts Cyclohexanone: 110.0 parts Polyisocyanate (Coronate (registered trademark) L manufactured by Tosoh Corporation): 3 .0 copy

<Prescription of composition for forming non-magnetic layer>
Non-magnetic inorganic powder (kind: α-iron oxide, average particle size: 10 nm, BET specific surface area: 75 m ² /g): 100.0 parts Carbon black (average particle size: 20 nm): 25.0 parts SO ₃ Na group Containing polyurethane resin (weight average molecular weight: 70000, SO ₃ Na group: 0.2 meq/g): 18.0 parts stearic acid: 1.0 parts cyclohexanone: 300.0 parts methyl ethyl ketone: 300.0 parts

<Prescription of Composition for Forming Backcoat Layer>
Non-magnetic powder: 100.0 parts α-iron oxide: See Table 1 for mixing ratio (mass ratio)
Average particle size (average major axis length): 150 nm
Average acicular ratio: 7
BET specific surface area: 52 m ² /g
Carbon black: See Table 1 for mixing ratio (mass ratio)
Average particle size: 20 nm
Vinyl chloride copolymer (MR-104 manufactured by Kaneka Corporation): see Table 1 SO ₃ Na group-containing polyurethane resin: 6.0 parts Phenylphosphonic acid: 3.0 parts Cyclohexanone: 155.0 parts Methyl ethyl ketone: 155.0 parts Stearin Acid: 3.0 parts Butyl stearate: 3.0 parts Polyisocyanate: 5.0 parts Cyclohexanone: 200.0 parts

<Preparation of Composition for Forming Magnetic Layer>
A composition for forming a magnetic layer was prepared by the following method.
A magnetic liquid was prepared by dispersing (bead dispersion) various components of the above magnetic liquid for 24 hours using a batch-type vertical sand mill. As dispersion beads, zirconia beads with a bead diameter of 0.5 mm were used.
The abrasive liquid is prepared by mixing various components of the above abrasive liquid and putting them in a horizontal bead mill disperser together with zirconia beads with a bead diameter of 0.3 mm. The content was adjusted to 80%, and the bead mill dispersion treatment was performed for 120 minutes. Thus, an abrasive liquid was prepared.
The prepared magnetic liquid and abrasive liquid, as well as the protrusion-forming agent liquid and other components were introduced into a dissolver stirrer, stirred at a peripheral speed of 10 m/sec for 30 minutes, and then adjusted to a flow rate of 7.0 by a flow-type ultrasonic disperser. After three passes at 5 kg/min, it was filtered through a filter with a pore size of 1 μm to prepare a composition for forming a magnetic layer.

<Preparation of composition for forming non-magnetic layer>
Various components of the above composition for forming a non-magnetic layer were dispersed in a batch-type vertical sand mill using zirconia beads with a bead diameter of 0.1 mm for 24 hours. A composition for forming a magnetic layer was prepared.

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

<Production of magnetic tape>
On the surface of an aromatic polyester support (see Table 1), the non-magnetic layer-forming composition prepared above was coated and dried to a thickness of 400 nm after drying to form a non-magnetic layer. A coating layer was formed by coating the magnetic layer-forming composition prepared above on the surface of the non-magnetic layer so that the thickness after drying was 70 nm. While the coated layer of the magnetic layer-forming composition was in a wet (undried) state, it was subjected to a vertical alignment treatment in which a magnetic field with a magnetic field strength of 0.3 T was applied in a direction perpendicular to the surface of the coated layer, and dried. . Thereafter, the composition for forming a backcoat layer prepared above was coated on the opposite side of the support so that the thickness after drying was 0.4 μm, and dried. Thus, a magnetic tape stock was produced.
The produced magnetic tape raw material is calendered (surface smoothed) by a calender consisting only of metal rolls at a speed of 100 m/min, a linear pressure of 294 kN/m, and a calender roll surface temperature of 100°C. , and the heat treatment was performed for 36 hours in an environment with an ambient temperature of 70°C. After the heat treatment, the original magnetic tape was slit by a cutter to obtain a magnetic tape having a width of 1/2 inch. While the magnetic tape was run between the delivery roller and the take-up roller (running speed: 120 m/min, tension: see Table 1), the surface of the back coat layer was polished with a blade, dry wiped, and alcohol wiped with ethanol. were performed in this order. Specifically, a sapphire blade, a dry wiping material (Toraysee (registered trademark) manufactured by Toray Industries, Inc.), and a wiping material (Toraysee (registered trademark) manufactured by Toray Industries, Inc.) impregnated with ethanol are placed between the two rollers. A sapphire blade is pressed against the backcoat layer surface of the magnetic tape running between the two rollers to grind the backcoat layer, and then the backcoat layer surface is dry-wiped with the dry wiping material. Then, the surface of the backcoat layer was wiped with ethanol using the above-mentioned wiping material impregnated with ethanol. As described above, the surface of the backcoat layer was subjected to blade polishing, dry wiping treatment and ethanol wiping treatment once each.
With the magnetic layer of the manufactured magnetic tape demagnetized, a servo pattern having an arrangement and shape conforming to the LTO (Linear Tape-Open) Ultrium format was formed on the magnetic layer by a servo write head mounted on a servo writer. In this way, a magnetic tape having a data band, a servo band, and a guide band arranged in accordance with the LTO Ultrium format on the magnetic layer and having a servo pattern arranged and shaped in accordance with the LTO Ultrium format on the servo band was obtained.
Thus, the magnetic tape of Example 1 was obtained.

[Examples 2 to 11, Comparative Examples 1 to 9]
A magnetic tape was produced in the same manner as in Example 1, except that various conditions were changed as shown in Table 1.
Regarding the surface treatment of the backcoat layer surface after slitting, the following surface treatments were carried out in Examples 2 to 11 and Comparative Examples 1 to 9, respectively.
In Examples 2 to 4, 7, 9 to 11 and Comparative Examples 4 and 5, blade polishing, dry wiping treatment and ethanol wiping treatment were carried out in the same manner as in Example 1.
In Examples 5, 6, 8, and Comparative Examples 6 and 9, blade polishing, dry wiping treatment and ethanol wiping treatment were performed in the same manner as in Example 1, except that the tension was changed.
In Comparative Examples 1-3, 7 and 8, the blade polishing and dry wiping treatments were performed in the same manner as in Example 1, and the ethanol wiping treatment was not performed.

In Table 1, "BaFe" is hexagonal barium ferrite powder with an average particle size (average plate diameter) of 21 nm.

In Table 1, "SrFe1" is hexagonal strontium ferrite powder produced by the following method.
1707 _g of SrCO3, 687 _g of _H3BO3 , 1120 g of _Fe2O3 , 45 g of Al(OH) ₃ , 24 g of _BaCO3 , 13 g of _CaCO3 , and 235 g _{of Nd2O3} were weighed and mixed in _a mixer. A raw material mixture was obtained by mixing.
The obtained raw material mixture was melted in a platinum crucible at a melting temperature of 1390° C., and while the melt was being stirred, a tap hole provided at the bottom of the platinum crucible was heated, and the melt was tapped in a rod shape at a rate of about 6 g/sec. . The tapped liquid was rolled and quenched with a water-cooled twin roller to prepare an amorphous body.
280 g of the produced amorphous material was placed in an electric furnace, heated to 635° C. (crystallization temperature) at a heating rate of 3.5° C./min, and held at the same temperature for 5 hours to produce hexagonal strontium ferrite particles. Precipitated (crystallized).
Next, the crystallized product obtained above containing hexagonal strontium ferrite particles was coarsely pulverized in a mortar, and 1000 g of zirconia beads having a particle size of 1 mm and 800 ml of a 1% concentration aqueous solution of acetic acid were added to a glass bottle and dispersed for 3 hours using a paint shaker. did After that, the resulting dispersion was separated from the beads and placed in a stainless steel beaker. After the dispersion liquid was allowed to stand at a liquid temperature of 100°C for 3 hours to dissolve the glass component, it was precipitated in a centrifugal separator, washed by repeating decantation, and placed in a heating furnace at a temperature of 110°C for 6 hours. After drying for a few hours, hexagonal strontium ferrite powder was obtained.
The average particle size of the hexagonal strontium ferrite powder obtained above is 18 nm, the activation volume is 902 nm ³ , the anisotropy constant Ku is 2.2×10 ⁵ J/m ³ , and the mass magnetization σs is 49 A·m ² /. kg.
12 mg of sample powder was taken from the hexagonal strontium ferrite powder obtained above, and the sample powder was partially dissolved under the dissolution conditions exemplified above. The surface layer content was determined.
Separately, 12 mg of sample powder was taken from the hexagonal strontium ferrite powder obtained above, and the sample powder was completely dissolved under the dissolution conditions exemplified above. Atomic bulk content was determined.
The content of neodymium atoms (bulk content) with respect to 100 atomic % of iron atoms in the hexagonal strontium ferrite powder obtained above was 2.9 atomic %. The content of neodymium atoms in the surface layer was 8.0 atomic %. The ratio of the surface layer portion content rate to the bulk content rate, "surface layer portion content rate/bulk content rate", was 2.8, confirming that neodymium atoms were unevenly distributed in the surface layer of the particles.
The fact that the powder obtained above exhibits the crystal structure of hexagonal ferrite is confirmed by scanning CuKα rays under the conditions of a voltage of 45 kV and an intensity of 40 mA and measuring the X-ray diffraction pattern under the following conditions (X-ray diffraction analysis). confirmed. The powder obtained above exhibited a crystal structure of magnetoplumbite-type (M-type) hexagonal ferrite. The crystal phase detected by X-ray diffraction analysis was a magnetoplumbite single phase.
PANalytical X'Pert Pro diffractometer, PIXcel detector Soller slits for incident and diffracted beams: 0.017 radians Fixed divergence slit angle: ¼ degree Mask: 10 mm
Anti-scattering slit: 1/4 degree Measurement mode: continuous Measurement time per step: 3 seconds Measurement speed: 0.017 degree per second Measurement step: 0.05 degree

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

In Table 1, "ε-iron oxide" is ε-iron oxide powder prepared by the following method.
8.3 g of iron (III) nitrate nonahydrate, 1.3 g of gallium (III) nitrate octahydrate, 190 mg of cobalt (II) nitrate hexahydrate, 150 mg of titanium (IV) sulfate, and 4.0 g of an aqueous ammonia solution having a concentration of 25% was added to a solution of 1.5 g of polyvinylpyrrolidone (PVP) in an air atmosphere at an ambient temperature of 25° C. while stirring using a magnetic stirrer. , and the mixture was stirred for 2 hours while maintaining the ambient temperature of 25°C. A citric acid solution obtained by dissolving 1 g of citric acid in 9 g of pure water was added to the obtained solution, and the mixture was stirred for 1 hour. The powder precipitated after stirring was collected by centrifugation, washed with pure water, and dried in a heating furnace with an internal furnace temperature of 80°C.
800 g of pure water was added to the dried powder, and the powder was dispersed again in water to obtain a dispersion liquid. The obtained dispersion was heated to a liquid temperature of 50° C., and 40 g of an ammonia aqueous solution having a concentration of 25% was added dropwise while stirring. After stirring for 1 hour while maintaining the temperature at 50° C., 14 mL of tetraethoxysilane (TEOS) was added dropwise and the mixture was stirred for 24 hours. 50 g of ammonium sulfate was added to the obtained reaction solution, and the precipitated powder was collected by centrifugation, washed with pure water, and dried in a heating furnace at an internal temperature of 80°C for 24 hours to obtain a ferromagnetic powder precursor. Obtained.
The obtained ferromagnetic powder precursor was placed in a heating furnace with an internal temperature of 1000° C. in an air atmosphere, and heat-treated for 4 hours.
The heat-treated ferromagnetic powder precursor was put into a 4 mol/L sodium hydroxide (NaOH) aqueous solution, and the liquid temperature was maintained at 70° C. and stirred for 24 hours to obtain the heat-treated ferromagnetic powder. A silicic acid compound as an impurity was removed from the precursor.
After that, the ferromagnetic powder from which the silicic acid compound was removed was collected by centrifugal separation and washed with pure water to obtain the ferromagnetic powder.
When the composition of the obtained ferromagnetic powder was confirmed by high-frequency inductively coupled plasma-optical emission spectrometry (ICP-OES), Ga, Co and Ti-substituted ε-iron oxide (ε-Ga _{0 .28} Co _0.05 Ti _0.05 Fe _1.62 O ₃ ). In addition, X-ray diffraction analysis was performed under the same conditions as those described above for SrFe1, and from the peaks of the X-ray diffraction pattern, it was confirmed that the obtained ferromagnetic powder did not contain the crystal structure of α phase and γ phase, ε It was confirmed to have a single-phase crystal structure (ε-iron oxide type crystal structure).
The resulting ε-iron oxide powder had an average particle size of 12 nm, an activated volume of 746 nm ³ , an anisotropy constant Ku of 1.2×10 ⁵ J/m ³ and a mass magnetization σs of 16 A·m ² /kg. there were.

The activation volume and anisotropy constant Ku of the above hexagonal strontium ferrite powder and ε-iron oxide powder were obtained using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) for each ferromagnetic powder, as previously described. It is a value obtained by the method of
Also, the mass magnetization σs is a value measured at a magnetic field strength of 15 kOe using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.).

In Table 1, "Support 1" is an aromatic polyester film produced by the method described in Example 2 of JP-A-2011-84036. Support 1 is a laminated film containing a polyethylene naphthalate film, and the thickness of the support is 4.2 μm.
“Support 2” is an aromatic polyester film produced by the method described in Example 1 of JP-A-2011-84036. The support 2 is a laminated film containing a polyethylene terephthalate film and has a thickness of 5.0 μm.
“Support 3” is an aromatic polyester film produced by the method described in Example 6 of JP-A-2011-84036. The support 3 is a laminated film containing a polyethylene naphthalate film and has a thickness of 4.2 μm.
"Support 4" is a laminated film containing a polyethylene naphthalate film, and the thickness of the support is 4.2 µm.
"Support 5" is a laminated film containing a polyethylene terephthalate film, and the thickness of the support is 4.2 µm.
A sample piece of several grams was cut out from each aromatic polyester support, and the moisture absorption was determined by the method described above.

[Evaluation method]
(1) Spacing difference before and after ethanol washing (S _after -S _before )
Using TSA (Tape Spacing Analyzer (manufactured by Micro Physics)), the spacing difference (S _after -S _before ) before and after ethanol washing was determined by the following method.
Two sample pieces each having a length of 5 cm were cut out from each of the magnetic tapes of Examples and Comparative Examples, and the spacing (S _before ) of one of the sample pieces was determined by the following method without washing with ethanol. After the other sample piece was washed with ethanol by the method described above, the spacing (S _after ) was determined by the following method.
A glass plate provided in the TSA (Thorlabs, Inc. glass plate (model number: WG10530)) was placed on the surface of the back coat layer of the magnetic tape (more specifically, the sample piece), and the TSA was used as a pressing member. Using a provided urethane hemisphere, this hemisphere was pressed against the magnetic layer surface of the magnetic tape with a pressure of 0.5 atm. In this state, a stroboscope provided in the TSA irradiates a certain area (150,000 to 200,000 μm ² ) on the surface of the back coat layer of the magnetic tape with white light through the glass plate, and the resulting reflected light is passed through an interference filter (wavelength By receiving light with a CCD (Charge-Coupled Device) through a filter that selectively transmits light of 633 nm, an interference fringe image generated by the unevenness of this region was obtained.
This image was divided into 300,000 points, and the distance (spacing) from the surface of the magnetic tape side of the glass plate to the surface of the back coat layer of the magnetic tape at each point was determined and used as a histogram. The difference (S _after −S _before ) was obtained by subtracting the mode S _before of the histogram obtained for the sample piece without ethanol washing from the mode S _after of the obtained histogram.

(2) Spacing difference before and after n-hexane washing (S _reference -S _before ) (reference value)
One more sample piece with a length of 5 cm was cut out from each of the magnetic tapes of Examples and Comparative Examples, washed in the same manner as described above except that n-hexane was used instead of ethanol, and then washed with n-hexane in the same manner as described above. Asked for later spacing. As a reference value, the difference (S _reference -S _before ) between the spacing S _reference obtained here and the spacing S _before obtained for the unwashed sample piece obtained in (1) above was obtained.

(3) Evaluation of Decrease in Running Stability The magnetic tapes of Examples and Comparative Examples were stored for 3 hours in a thermobox whose interior was kept at a temperature of 32° C. and a relative humidity of 20%. Thereafter, the magnetic tape was taken out from the thermobox (outside air temperature: 23°C, relative humidity: 50%), transferred within 1 minute to a thermoroom kept at a temperature of 10°C, relative humidity: 20%, and stored for a week. PES (Position Error Signal) was determined in a thermo room by the following method.
Servo patterns of the magnetic tapes of Examples and Comparative Examples were read with a verify head on the servo writer used for forming the servo patterns. The verify head is a reading magnetic head for checking the quality of the servo pattern formed on the magnetic tape. A reading element is arranged at a position corresponding to the direction position).
The verify head is connected to a known PES calculation circuit that calculates the head positioning accuracy in the servo system as a PES from an electrical signal obtained by reading a servo pattern with the verify head. The PES arithmetic circuit calculates the displacement in the width direction of the magnetic tape from the input electric signal (pulse signal) at any time, and applies a high-pass filter (cutoff: 500 cycles/m ) was calculated as the PES. PES can be used as an indicator of running stability, and if the value of PES calculated above is 15 nm or less, it is stored in a low-temperature and low-humidity environment after a temperature change from high temperature to low temperature under low humidity. It can be evaluated that deterioration in running stability is suppressed.

The above results are shown in Table 1 (Tables 1-1 to 1-4).

Example magnetic tapes are magnetic tapes having an aromatic polyester support. From the PES values in Table 1, it can be seen that the magnetic tapes of the examples are less likely to deteriorate in running stability after being stored in a low-temperature, low-humidity environment after a temperature change from high to low under low humidity. I can confirm.
As shown in Table 1, there is a correlation between the value of the spacing difference before and after n-hexane washing (S _reference −S _before ) and the value of the spacing difference before and after ethanol washing (S _after −S _before ). was not seen.

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

Claims (15)

A magnetic recording medium having a magnetic layer containing a ferromagnetic powder on one surface of a nonmagnetic support and a backcoat layer containing a nonmagnetic powder on the other surface,
a non-magnetic layer containing a non-magnetic powder between the non-magnetic support and the magnetic layer;
the non-magnetic layer has a thickness of 800 nm or less,
The difference between the spacing S _after measured by optical interferometry on the surface of the backcoat layer after washing with ethanol and the spacing S _before measured by optical interferometry on the surface of the backcoat layer before washing with ethanol, S _after - S _before is more than 0 nm and less than or equal to 15.0 nm, and the non-magnetic support is an aromatic polyester support having a moisture absorption of 0.3% or less. 2. The magnetic recording medium according to claim 1, wherein said non-magnetic layer has a thickness of 500 nm or less. 3. The magnetic recording medium according to claim 1, wherein the difference S _after -S _before is 1.0 nm or more and 15.0 nm or less. 4. The magnetic recording medium according to claim 1, wherein the difference S _after -S _before is 2.0 nm or more and 13.0 nm or less. 5. The magnetic recording medium according to claim 1, wherein the aromatic polyester support has a moisture absorption rate of 0.1% or more and 0.3% or less. The magnetic recording medium of any one of claims 1-5, wherein the aromatic polyester support comprises polyethylene naphthalate. The magnetic recording medium of any one of claims 1-5, wherein the aromatic polyester support comprises polyethylene terephthalate. 8. The magnetic recording medium according to claim 1, wherein the aromatic polyester support has a Young's modulus of 3000 N/mm ² or more in the longitudinal direction. 9. The magnetic recording medium according to claim 1, wherein the aromatic polyester support has a Young's modulus of 4000 N/mm ² or more in the width direction. The magnetic recording medium according to any one of claims 1 to 9, wherein said ferromagnetic powder has an average particle size of 25 nm or less. 11. The magnetic recording medium according to claim 1, wherein said ferromagnetic powder has an average particle size of 20 nm or less. The magnetic recording medium according to any one of claims 1 to 11, wherein the thickness of said nonmagnetic support is in the range of 3.0 to 4.2 µm. The magnetic recording medium according to any one of claims 1 to 12, wherein the magnetic layer has a thickness in the range of 30 to 70 nm. 14. The magnetic recording medium according to any one of claims 1 to 13, which is a magnetic tape. a magnetic recording medium according to any one of claims 1 to 14;
a magnetic head;
A magnetic recording and reproducing device including