Magnetic recording medium, magnetic tape cartridge, and magnetic recording and reproducing apparatus

Abstract

To provide a magnetic recording medium having a magnetic layer that contains ε-iron oxide powder, with which it is possible to exhibit excellent electromagnetic conversion characteristics when reproducing data having been recorded using an in-plane recording scheme.SOLUTION: Provided is a magnetic recording medium having a magnetic layer that contains ferromagnetic powder. The ferromagnetic powder is ε-iron oxide powder, a ratio (Hr(45°) / Hr(0°)) of Hr(0°) to Hr(45°) being 0.50 or less. The Hr(0°) is a residual coercive force Hr obtained by applying a pulse magnetic field with a pulse width of 0.76 ms in an in-plane direction of the magnetic recording medium, and the Hr(45°) is a residual coercive force Hr obtained by applying a pulse magnetic field with a pulse width of 0.76 ms to the magnetic recording medium, causing it to enter from a direction which is inclined 45° from the in-plane direction toward a vertical direction, with an angle in the in-plane direction of the magnetic recording medium defined as 0° and an angle in the vertical direction defined as 90°. Also provided are a magnetic tape cartridge and a magnetic recording-reproduction device that include the magnetic recording medium.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a magnetic recording medium, a magnetic tape cartridge, and a magnetic recording and reproducing apparatus.

Background Art

[0002] As a recording medium for data storage for recording and storing various data, a magnetic recording medium is widely used (see, for example, paragraph 0089 of Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a magnetic recording medium, a magnetic layer containing ferromagnetic powder is usually provided on a nonmagnetic support. Regarding the ferromagnetic powder, ε-iron oxide powder has attracted attention in recent years as described in, for example, Patent Document 1.

[0005] Magnetic recording methods include an in-plane recording method and a perpendicular recording method. For example, in a magnetic recording medium such as a magnetic tape, the in-plane recording method is the mainstream. Therefore, a magnetic recording medium having a magnetic layer containing ε-iron oxide powder and excellent in-plane recording suitability is desirable. For example, a magnetic recording medium capable of exhibiting excellent electromagnetic conversion characteristics when reproducing data recorded by the in-plane recording method can be said to be a magnetic recording medium with excellent in-plane recording suitability.

[0006] In view of the above, an aspect of the present invention is to provide a magnetic recording medium having a magnetic layer containing ε-iron oxide powder and capable of exhibiting excellent electromagnetic conversion characteristics when reproducing data recorded by the in-plane recording method.

Means for Solving the Problem

[0007] One aspect of the present invention is a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the ferromagnetic powder is ε-iron oxide powder, a magnetic tape having a ratio (Hr(45°) / Hr(0°)) of Hr(0°) to Hr(45°) of 0.50 or less, relates to wherein the Hr(0°) is the residual coercive force Hr obtained by applying a pulse magnetic field with a pulse width of 0.76 ms in the in-plane direction of the magnetic recording medium, the Hr(45°) is the residual coercive force Hr obtained by applying a pulse magnetic field with a pulse width of 0.76 ms to the magnetic recording medium by making the angle in the in-plane direction of the magnetic recording medium 0° and the angle in the perpendicular direction of the magnetic recording medium 90°, and making the pulse magnetic field incident from a direction inclined 45° from the in-plane direction toward the perpendicular direction.

[0008] In one form, the ratio (Hr(45°) / Hr(0°)) can be 0.45 or less.

[0009] In one form, the ratio (Hr(45°) / Hr(0°)) can be 0.40 or less.

[0010] In one form, the ratio (Hr(45°) / Hr(0°)) can be 0.35 or less.

[0011] In one form, the ratio (Hr(45°) / Hr(0°)) can be 0.10 or more and 0.35 or less.

[0012] In one form, the ε-iron oxide powder can contain a cobalt element, an element selected from the group consisting of a gallium element and an aluminum element, and a titanium element.

[0013] In one embodiment, the magnetic recording medium can further include a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

[0014] In one embodiment, the magnetic recording medium can further include a backcoat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer.

[0015] In one embodiment, the magnetic recording medium can be a magnetic tape.

[0016] One aspect of the present invention relates to a magnetic tape cartridge including the magnetic tape.

[0017] One aspect of the present invention relates to a magnetic recording and reproducing apparatus including the magnetic recording medium.

Effects of the Invention

[0018] According to one aspect of the present invention, there can be provided a magnetic recording medium having a magnetic layer containing ε-iron oxide powder, which exhibits excellent electromagnetic conversion characteristics when reproducing data recorded in an in-plane recording mode. Further, according to one aspect of the present invention, there can be provided a magnetic tape cartridge and a magnetic recording and reproducing apparatus including such a magnetic recording medium.

Embodiments for Carrying out the Invention

[0019] [Magnetic Tape] One aspect of the present invention relates to a magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder. The ferromagnetic powder is ε-iron oxide powder, and in the magnetic recording medium, the ratio of Hr(0°) to Hr(45°) (Hr(45°) / Hr(0°)) is 0.50 or less. In the present invention and this specification, the above Hr(0°) is the residual coercive force Hr obtained by applying a pulse magnetic field with a pulse width of 0.76 ms in the in-plane direction of the magnetic recording medium. The above Hr(45°) is obtained by setting the angle in the in-plane direction of the magnetic recording medium to 0° and the angle in the vertical direction of the magnetic recording medium to 90°, and applying a pulse magnetic field with a pulse width of 0.76 ms to the magnetic recording medium by making it incident from a direction inclined 45° from the in-plane direction toward the vertical direction (the direction opposite to the saturation magnetization direction described later). The unit "ms" is milliseconds. Also, in the present invention and this specification, the "in-plane direction of the magnetic recording medium" means the longitudinal direction for a tape-shaped magnetic recording medium, i.e., a magnetic tape, and the radial direction for a disk-shaped magnetic recording medium, i.e., a magnetic disk. The "vertical direction of the magnetic recording medium" is the direction orthogonal to the in-plane direction of the magnetic recording medium in the thickness direction of the magnetic recording medium. The "surface of the magnetic layer" is synonymous with the side surface of the magnetic layer of the magnetic recording medium.

[0020] The above Hr(0°) and Hr(45°) are obtained by the following method. Two sample pieces are cut out from the magnetic recording medium to be measured. One is used for the measurement of Hr(0°), and the other is used for the measurement of Hr(45°). The size of the sample piece may be any size that can be introduced into the vibrating sample type fluxmeter used for the measurement. The in-plane direction and vertical direction of the following sample piece refer to the directions that were the in-plane direction and vertical direction when the sample piece was contained in the magnetic recording medium. The following pulse magnetic field is a single-shot pulse magnetic field. Also, the measurement of the following residual magnetization amount is performed at a measurement temperature of 23°C. Such a measurement temperature is the temperature of the sample piece. By setting the ambient temperature around the sample piece to the measurement temperature (23°C), the temperature of the sample piece can be made the measurement temperature due to the establishment of temperature equilibrium.

[0021] For the sample piece for Hr(0°) measurement, Hr(0°) is measured by the following method. (1) First, using a pulse magnetic field generator, a DC magnetic field of 40 kOe is applied in the vertical direction of the sample piece for 10 seconds to saturate the ferromagnetic powder contained in the magnetic layer of the sample piece, and then the applied magnetic field is removed. Here, the DC magnetic field applied in the vertical direction may be incident from the surface side of the magnetic layer of the sample piece or from the other surface side. Regarding the unit, 1 [kOe] = 10 6 / 4π [A / m]. As the pulse magnetic field generator, for example, MPM-04 manufactured by Toei Industry Co., Ltd. can be used, and MPM-04 manufactured by Toei Industry Co., Ltd. was used in the examples described later. This also applies to the measurement of Hr(45°). (2) Within 20 seconds from the above-mentioned saturation magnetization, using the same pulse magnetic field generator, a pulse magnetic field with a pulse width of 0.76 ms is applied to the sample piece in the in-plane direction (either the front or back direction in the in-plane direction is acceptable) at an arbitrary magnetic field strength. (3) Within 20 seconds from the end of the application of the above-mentioned pulse magnetic field, the residual magnetization of the sample piece is measured using a vibrating sample magnetometer. As the vibrating sample magnetometer, for example, P2SH manufactured by Toei Industry Co., Ltd. can be used, and P2SH manufactured by Toei Industry Co., Ltd. was used in the examples described later. This also applies to the measurement of Hr(45°). (4) The processes of (1) to (3) above are repeated at various pulse magnetic field strengths, and the value of the pulse magnetic field when the residual magnetization becomes 0 Am 2 / kg is obtained, and this is defined as Hr(0°).

[0022] For the sample piece for Hr(45°) measurement, Hr(45°) is measured by the following method. (1) First, using a pulse magnetic field generator, a DC magnetic field of 40 kOe is applied in the vertical direction of the sample piece for 10 seconds to saturate the ferromagnetic powder contained in the magnetic layer of the sample piece, and then the applied magnetic field is removed. Here, the DC magnetic field applied in the vertical direction may be incident from the surface side of the magnetic layer of the sample piece or from the other surface side. (2) Within 20 seconds from the above saturation magnetization, using the same pulse magnetic field generator, set the in-plane angle of the sample piece to 0°, and set the angle in the vertical direction opposite to the above saturation magnetization direction of the sample piece to 90°. Then, apply a pulse magnetic field with a pulse width of 0.76 ms at an arbitrary magnetic field strength to the sample piece by making it incident from a direction inclined 45° from the in-plane direction to the vertical direction (opposite to the above saturation magnetization direction), that is, from a direction with an angle of 45° (it doesn't matter which direction, front or back, as long as it is the direction of angle 45°). (3) Within 20 seconds from the end of the application of the above pulse magnetic field, measure the residual magnetization of the sample piece using a vibration sample type magnetometer. (4) Repeat the above processes (1) to (3) at various pulse magnetic field strengths. When the residual magnetization becomes 0 Am 2 / kg, determine the value of the pulse magnetic field at this time and denote it as Hr(45°).

[0023] Calculate the ratio (Hr(45°) / Hr(0°)) as the value obtained by dividing Hr(45°) by Hr(0°) determined by the above method.

[0024] In the above magnetic recording medium, the ratio (Hr(45°) / Hr(0°)) obtained as described above is 0.50 or less. Thereby, the above magnetic recording medium can exhibit excellent electromagnetic conversion characteristics when reproducing data recorded in the in-plane recording method. Regarding this point, the present inventor speculates as follows. However, the present invention is not limited by the speculations described in this specification including the following speculation. Recording of data on the magnetic layer of a magnetic recording medium is performed by applying a magnetic field (hereinafter also referred to as "recording magnetic field") from a magnetic head to reverse the magnetization of the particles of ferromagnetic powder in the magnetic layer. When applying the recording magnetic field from the magnetic head, by causing the recording magnetic field to enter the magnetic layer from a direction inclined with respect to the in-plane direction (oblique direction), the recording magnetic field that has entered the magnetic layer follows a path that becomes horizontal with respect to the in-plane direction within the magnetic layer and then exits the magnetic layer in an oblique direction and is collected by the recording head. A recording method that controls the direction of the recording magnetic field applied to the recording layer for magnetization reversal to be horizontal with respect to the in-plane direction is the in-plane recording method. The in-plane recording method is generally also called the horizontal recording method, the longitudinal recording method, etc. Note that a recording method that controls the direction of the recording magnetic field applied to the magnetic layer for magnetization reversal to be perpendicular to the magnetic layer surface is the perpendicular recording method. Here, regarding the direction of the recording magnetic field, "perpendicular" does not necessarily mean only strictly perpendicular, but includes the range of error allowed in the technical field to which the present invention belongs. The range of error can mean, for example, a range of strictly perpendicular ± less than 10°. The same applies to "horizontal" in this regard. In in-plane recording type magnetic recording, a recording magnetic field is made incident on the magnetic layer from an oblique direction as described above. In examining the improvement of the in-plane recording suitability of a magnetic recording medium having a magnetic layer containing ε-iron oxide powder, the present inventors considered that in a magnetic recording medium having a magnetic layer containing ε-iron oxide powder, making it easier for the magnetization reversal of the particles of the ε-iron oxide powder to occur with respect to a magnetic field incident on the magnetic layer from an oblique direction could contribute to the improvement of the electromagnetic conversion characteristics when reproducing data recorded by the in-plane recording method. Then, through further repeated examinations, the present inventors considered that the above ratio (Hr(45°) / Hr(0°)) could be an index for the ease of occurrence of the above magnetization reversal, and conducted intensive examinations. As a result, it was newly found that a magnetic recording medium having a magnetic layer containing ε-iron oxide powder, in which the above ratio (Hr(45°) / Hr(0°)) is 0.50 or less, exhibits excellent electromagnetic conversion characteristics when reproducing data recorded by the in-plane recording method, specifically, it is possible to exhibit a high SNR (Signal-to-Noise Ratio). In obtaining the above ratio (Hr(45°) / Hr(0°)), the reason for adopting the angle of 45° is that it was adopted as an example of the incident angle of the recording magnetic field incident on the magnetic layer from an oblique direction, and the incident angle of the recording magnetic field applied for recording data on the magnetic layer of the above magnetic recording medium is not limited to 45°. Also, regarding the pulse width, only 0.76 ms was adopted in consideration of general recording conditions in recent magnetic recording, and the recording conditions when recording data on the magnetic layer of the above magnetic recording medium are not particularly limited. Hereinafter, the above magnetic recording medium will be described in more detail.

[0025] <Ratio (Hr(45°) / Hr(0°))> In the above magnetic recording medium, the ratio (Hr(45°) / Hr(0°)) is 0.50 or less from the viewpoint of improving the electromagnetic conversion characteristics when reproducing data recorded by the in-plane recording method. The present inventor believes that the smaller the value of the ratio (Hr(45°) / Hr(0°)), the easier it is for the particles of ε-iron oxide powder to reverse magnetization with respect to the magnetic field incident on the magnetic layer from an oblique direction. From the viewpoint of further improving the above electromagnetic conversion characteristics, the ratio (Hr(45°) / Hr(0°)) is preferably 0.48 or less, more preferably 0.45 or less, still more preferably 0.43 or less, even more preferably 0.40 or less, yet even more preferably 0.38 or less, and still even more preferably 0.35 or less. The ratio (Hr(45°) / Hr(0°)) can be, for example, 0.10 or more or 0.20 or more, or can be less than the values exemplified herein. A method for controlling the ratio (Hr(45°) / Hr(0°)) will be described later.

[0026] Regarding Hr(45°) and Hr(0°), it is only necessary that the ratio (Hr(45°) / Hr(0°)) is 0.50 or less, and it is not particularly limited. In one form, Hr(45°) can be, for example, 3000 Oe or more or 3500 Oe or more, and can be, for example, 8000 Oe or less or 7000 Oe or less. Also, in one form, Hr(0°) can be, for example, 8000 Oe or more or 10000 Oe or more, and can be, for example, 20000 Oe or less or 15000 Oe or less.

[0027] <Magnetic layer> <<ε-iron oxide powder>> The above magnetic recording medium contains ε-iron oxide powder as the ferromagnetic powder in the magnetic layer. In the present invention and this specification, the "ε-iron oxide powder" refers to a ferromagnetic powder in which the crystal structure (ε-phase) of ε-iron oxide is detected as the main phase by X-ray diffraction analysis. For example, in the X-ray diffraction spectrum obtained by X-ray diffraction analysis, when the diffraction peak with the highest intensity is attributed to the crystal structure (ε-phase) of ε-iron oxide, it is determined that the crystal structure of ε-iron oxide has been detected as the main phase. In addition to the ε-phase of the main phase, an α-phase and / or a γ-phase may or may not be included. The ε-iron oxide powder in the present invention and this specification includes a so-called unsubstituted type of ε-iron oxide powder composed of iron and oxygen, and a so-called substituted type of ε-iron oxide powder containing one or more substitution elements substituting for iron.

[0028] (Method for producing ε-iron oxide powder) As methods for producing ε-iron oxide powder, a method of producing from goethite, an inverse micelle method, etc. are known. The above production methods are all publicly known. Also, for methods of producing ε-iron oxide powder in which a part of iron is substituted by a substitution element, for example, reference can be made to J. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280 - S284, J. Mater. Chem. C, 2013, 1, pp.5200 - 5206, etc.

[0029] As an example, for instance, the ε-iron oxide powder contained in the magnetic layer of the above magnetic recording medium preparing a precursor of ε-iron oxide (hereinafter, also referred to as the "precursor preparation step"), subjecting the above precursor to a film formation treatment (hereinafter, also referred to as the "film formation step"), converting the above precursor to ε-iron oxide by subjecting the precursor after the above film formation treatment to a heat treatment (hereinafter, also referred to as the "heat treatment step"), and subjecting the above ε-iron oxide to a film removal treatment (hereinafter, also referred to as the "film removal step"), It can be obtained by a production method for obtaining ε-iron oxide powder. The following further describes such a production method. However, the production method described below is an example, and the above ε-iron oxide powder is not limited to those produced by the production methods exemplified below.

[0030] Precursor preparation step The precursor of ε-iron oxide refers to a substance that, when heated, contains the crystal structure of ε-iron oxide as the main phase. The precursor can be, for example, a hydroxide, oxyhydroxide (oxided hydroxide), etc. containing iron and an element capable of substituting a part of iron in the crystal structure. The precursor preparation step can be carried out using the coprecipitation method, reverse micelle method, etc. The preparation method of such a precursor is known, and the precursor preparation step in the above production method can be carried out by a known method. For example, for the preparation method of the precursor, reference can be made to known techniques such as paragraphs 0017 to 0021 and the examples of JP-A-2008-174405, paragraphs 0025 to 0046 and the examples of WO2016 / 047559A1, paragraphs 0038 to 0040, 0042, 0044, 0045 and the examples of WO2008 / 149785A1.

[0031] ε-Iron oxide that does not contain a substitution element that substitutes a part of iron (Fe) has the compositional formula: Fe 2 O 3 It can be represented by. On the other hand, ε-iron oxide in which a part of iron is substituted by, for example, one or more elements has the compositional formula: A 1 x A 2 y A 3 z Fe (2-x-y-z) O 3 It can be represented by. A 1 、 A 2 And A 3 ​each independently represents one or more substitution elements that replace iron, x, y, and z are each independently greater than or equal to 0 and less than 2, provided that at least one is greater than 0, and x + y + z is less than 2. The above ε-iron oxide powder may or may not contain a substitution element that replaces iron, and it is preferable to contain it. The type of substitution element can be one or more, and can also be 1 to 3 types, 1 to 5 types, or 1 to 6 types. The magnetic properties of the ε-iron oxide powder can be adjusted by the type and substitution amount of the substitution element. For example, by adjusting the magnetic properties of the ε-iron oxide powder in this way, the value of Hr(0°) can be adjusted. When a substitution element is contained, examples of the substitution element include one or more of Ga, Al, In, Rh, Mn, Co, Ni, Zn, Ti, Sn, etc. For example, in the above composition formula, A 1 can be one or more selected from the group consisting of Ga, Al, In, and Rh, and A 2 can be one or more selected from the group consisting of Co, Mn, Ni, and Zn, and A 3 can be one or more selected from the group consisting of Ti and Sn. As the ε-iron oxide powder, those containing cobalt element (Co) are preferable, those containing cobalt element and one or more selected from the group consisting of gallium element (Ga), aluminum element (Al), indium element (In), and rhodium element (Rh), and one or more selected from the group consisting of titanium element (Ti) and tin element (Sn) are more preferable, those containing cobalt element, gallium element and / or aluminum element, titanium element and / or tin element are further preferable, and those containing cobalt element, gallium element and / or aluminum element, and titanium element are even more preferable. When producing an ε-iron oxide powder containing a substitution element that replaces iron, a part of the compound serving as a source of iron in ε-iron oxide may be replaced with a compound of the substitution element. The composition of the obtained ε-iron oxide powder can be controlled by the substitution amount. Examples of the compounds serving as sources of iron and various substitution elements include inorganic salts such as nitrates, sulfates, chlorides (which may be hydrates), organic salts such as pentakis (hydrogen oxalate) salts (which may be hydrates), hydroxides, oxyhydroxides, etc.

[0032] Film-forming step When the precursor is heated after the film-forming treatment, the reaction in which the precursor is converted to ε-iron oxide can proceed under the film. Also, the film is considered to be able to play a role in preventing sintering from occurring during heating. From the viewpoint of ease of film formation, the film-forming treatment is preferably carried out in a solution, and more preferably carried out by adding a film-forming agent (a compound for film formation) to a solution containing the precursor. For example, when performing the film-forming treatment in the same solution following precursor preparation, a film can be formed on the precursor by adding a film-forming agent to the solution after precursor preparation and stirring. A preferable film in terms of ease of forming a film on the precursor in a solution can be a silicon-containing film. Examples of the film-forming agent for forming a silicon-containing film include silane compounds such as alkoxysilane. By hydrolysis of the silane compound, preferably using the sol-gel method, a silicon-containing film can be formed on the precursor. Specific examples of the silane compound can include tetraethoxysilane (TEOS: Tetraethyl orthosilicate), tetramethoxysilane, and various silane coupling agents. Regarding the film-forming treatment, reference can be made to known techniques such as paragraph 0022 of JP-A-2008-174405 and the examples of that publication, paragraphs 0047 to 0049 of WO2016 / 047559A1 and the examples of that publication, paragraphs 0041 and 0043 of WO2008 / 149785A1 and the examples of that publication. For example, the film-forming treatment can be carried out by stirring a solution having a liquid temperature of 50 to 90°C containing the precursor and the film-forming agent. The stirring time can be, for example, 5 to 36 hours. Note that the film may cover the entire surface of the precursor, or there may be a portion on the surface of the precursor that is not covered by the film.

[0033] Heat treatment step By subjecting the precursor after the above-mentioned film formation treatment to heat treatment, the precursor can be converted into ε-iron oxide. The heat treatment can be performed, for example, on the powder collected from the solution on which the film formation treatment has been performed (powder of the precursor having a film). Regarding the heat treatment step, for example, reference can be made to the known techniques such as paragraph 0023 of JP-A-2008-174405 and the examples of the publication, paragraph 0050 of WO2016 / 047559A1 and the examples of the publication, and paragraphs 0041 and 0043 of WO2008 / 149785A1 and the examples of the publication. The heat treatment step can be performed, for example, in a heating furnace with an internal temperature of 900 to 1200°C for about 3 to 6 hours. The higher the heat treatment step is performed at a higher temperature and / or the longer the heat treatment time, the larger the size of the particles of the obtained ε-iron oxide powder tends to be.

[0034] Film removal step By performing the above heat treatment step, the precursor having a film can be converted into ε-iron oxide. Since a film remains in the ε-iron oxide thus obtained, preferably, a film removal treatment is performed. Regarding the film removal treatment, for example, reference can be made to the known techniques such as paragraph 0025 of JP-A-2008-174405 and the examples of the publication, and paragraph 0053 of WO2008 / 149785A1 and the examples of the publication. The film removal treatment can be performed, for example, by stirring the ε-iron oxide having a film in an aqueous sodium hydroxide solution with a concentration of about 1 to 5 mol / L and a liquid temperature of about 60 to 90°C for about 5 to 36 hours. However, the ε-iron oxide powder contained in the magnetic layer of the magnetic recording medium may be manufactured without undergoing the film removal treatment, or the film may not be completely removed in the film removal treatment and a part of the film may remain.

[0035] Before and / or after each of the various steps described above, known steps can also be arbitrarily implemented. Examples of such steps include various known steps such as classification, centrifugation, filtration, washing, and drying.

[0036] (Average particle size) From the viewpoint of magnetization stability, the average particle size of the ε-iron oxide powder contained in the magnetic layer of the magnetic recording medium is preferably 5.0 nm or more, more preferably 6.0 nm or more, still more preferably 7.0 nm or more, even more preferably 8.0 nm or more, and yet even more preferably 9.0 nm or more. From the viewpoint of high-density recording, the average particle size of the ε-iron oxide powder is preferably 20.0 nm or less, more preferably 19.0 nm or less, still more preferably 18.0 nm or less, even more preferably 17.0 nm or less, yet even more preferably 16.0 nm or less, and still even more preferably 15.0 nm or less. A magnetic recording medium having a magnetic layer containing ε-iron oxide powder with a small average particle size tends to have a small value of Hr(0°).

[0037] In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ε-iron oxide powder is the value measured by the following method using a transmission electron microscope. The powder is photographed at a magnification of 100,000 times using a transmission electron microscope, and printed on photographic paper or displayed on a display so that the total magnification becomes 500,000 times to obtain a photograph of the particles constituting the powder. From the obtained photograph of the particles, the target particles are selected, and the contour of the particles is traced with a digitizer to measure the size of the particles (primary particles). The primary particles refer to independent particles without aggregation. The above measurement is performed on 500 particles randomly extracted. 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, the Hitachi transmission electron microscope model H-9000 can be used. Further, the measurement of the particle size can be carried out using known image analysis software, for example, the image analysis software KS-400 manufactured by Carl Zeiss. The average particle size shown in the examples described later is a value measured using the Hitachi transmission electron microscope model H-9000 as the transmission electron microscope and the Carl Zeiss image analysis software KS-400 as the image analysis software unless otherwise specified. In the present invention and this specification, powder means a collection of a plurality of particles. For example, ferromagnetic powder means a collection of a plurality of ferromagnetic particles. Further, the collection of a plurality of particles is not limited to the form in which the particles constituting the collection are in direct contact, and forms in which binders, additives, etc. described later are interposed between the particles are also included. The term "particle" may also be used to represent powder.

[0038] As a method for collecting a sample powder from the magnetic recording medium for particle size measurement, for example, the method described in paragraph 0015 of JP-A-2011-048878 can be adopted.

[0039] In the present invention and this specification, unless otherwise specified, the size of the particles (particle size) constituting the powder is such that the shape of the particles observed in the above particle photograph is (1) In the case of acicular, spindle-shaped, columnar (however, the height is greater than the maximum major axis length of the bottom surface), etc., it is represented by the length of the major axis constituting the particle, that is, the major axis length, (2) In the case of plate-like or columnar (however, the thickness or height is smaller than the maximum major axis length of the plate surface or the bottom surface), it is represented by the maximum major axis length of the plate surface or the bottom surface, (3) In the case of spherical, polyhedral, amorphous, etc., and the major axis constituting the particle cannot be specified from the shape, it is represented by the equivalent circle diameter. The equivalent circle diameter means that obtained by the circle projection method.

[0040] The average aspect ratio of the powder refers to the length of the minor axis of the particle, i.e., the minor axis length, measured in the above measurement, and the value of (major axis length / minor axis length) for each particle is obtained, and the arithmetic mean of the values obtained for the above 500 particles is referred to. Here, unless otherwise specified, the minor axis length refers to the length of the minor axis constituting the particle in the case of (1) in the above definition of particle size, the thickness or height in the case of (2), respectively. In the case of (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience. And unless otherwise specified, when the shape of the particle is specific, for example, in the case of the above definition (1) of particle size, the average particle size is the average major axis length, and in the case of the above definition (2), the average particle size is the average plate diameter. In the case of the above definition (3), the average particle size is the average diameter (also referred to as the average particle diameter or average particle size).

[0041] The content rate (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass, based on the total mass of the magnetic layer. A high filling rate of the ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving the recording density.

[0042] <<Binder>> The above magnetic recording medium can be a coating-type magnetic recording medium and can contain a binder in the magnetic layer. The binder is one or more resins. As the binder, various resins usually used as the binder for coating-type magnetic recording media can be used. For example, as the binder, a polyurethane resin, a polyester resin, a polyamide resin, a vinyl chloride resin, an acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., a cellulose resin such as nitrocellulose, an epoxy resin, a phenoxy resin, a polyvinyl acetal, a polyvinyl butyral, etc., a polyvinyl alkylal resin, etc. can be used alone or a plurality of resins can be mixed and used. Among these, preferred are a polyurethane resin, an acrylic resin, a cellulose resin, and a vinyl chloride resin. These resins may be homopolymers or copolymers. These resins can also be used as the binder in the non-magnetic layer and / or backcoat layer described later. Regarding the above binders, paragraphs 0028 to 0031 of JP-A-2010-24113 can be referred to. Further, the binder may be a radiation-curable resin such as an electron beam-curable resin. Regarding the radiation-curable resin, paragraphs 0044 to 0045 of JP-A-2011-048878 can be referred to. The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less in terms of weight average molecular weight. The weight average molecular weight in the present invention and this specification is a value obtained by converting the value measured under the following measurement conditions by gel permeation chromatography (GPC) into polystyrene conversion. The weight average molecular weight of the binder shown in the examples described later is a value obtained by converting the value measured under the following measurement conditions into polystyrene conversion. The binder can be used in an amount of, for example, 1.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder. GPC apparatus: 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)

[0043] A curing agent can also be used together with a resin that can be used as a binder. The curing agent can be a thermosetting compound, which is a compound in which a curing reaction (crosslinking reaction) proceeds by heating in one form, and can be a photocurable compound in which a curing reaction (crosslinking reaction) proceeds by light irradiation in another form. The curing agent can be included in the magnetic layer at least partially in a state of reacting (crosslinking) with other components such as a binder by the progress of the curing reaction during the magnetic layer forming step. This also applies to the layer formed using this composition when the composition used to form other layers contains a curing agent. A preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. For details of polyisocyanate, reference can be made to paragraphs 0124 to 0125 of JP-A-2011-216149. The curing agent can be used in the magnetic layer forming composition in an amount of, for example, 0 to 80.0 parts by mass, preferably 10.0 to 80.0 parts by mass, more preferably 50.0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder from the viewpoint of improving the strength of the magnetic layer.

[0044] The above description regarding the binder and the curing agent can also be applied to the non-magnetic layer and / or the backcoat layer. In that case, the above description regarding the content can be applied by replacing the ferromagnetic powder with the non-magnetic powder.

[0045] <<Additive>> The magnetic layer may contain one or more additives as necessary. Examples of the additives include the above-mentioned curing agent. In addition, examples of the additives contained in the magnetic layer include non-magnetic powders (e.g., inorganic powders, carbon black, etc.), lubricants, dispersants, dispersion aids, fungicides, antistatic agents, antioxidants, and the like. For example, for lubricants, reference can be made to paragraphs 0030 to 0033, 0035, and 0036 of JP-A-2016-126817. The non-magnetic layer described later may contain a lubricant. For the lubricants that can be contained in the non-magnetic layer, reference can be made to paragraphs 0030 to 0031, 0034, 0035, and 0036 of JP-A-2016-126817. For dispersants, reference can be made to paragraphs 0061 and 0071 of JP-A-2012-133837. A dispersant may be added to the composition for forming the non-magnetic layer. For the dispersants that can be added to the composition for forming the non-magnetic layer, reference can be made to paragraph 0061 of JP-A-2012-133837. In addition, examples of the non-magnetic powders that can be contained in the magnetic layer include non-magnetic powders that can function as abrasives, and non-magnetic powders that can function as projection-forming agents for forming projections that moderately protrude from the surface of the magnetic layer (e.g., non-magnetic colloidal particles, etc.). The average particle size of the colloidal silica (silica colloidal particles) shown in the examples described later was determined by the method described in paragraph 0015 of JP-A-2011-048878 as the method for measuring the average particle diameter. The additives can be appropriately selected from commercially available products according to the desired properties, or can be produced by known methods and used in any amount. As an example of the additives that can be used to improve the dispersibility of the abrasive in the magnetic layer containing an abrasive, the dispersants described in paragraphs 0012 to 0022 of JP-A-2013-131285 can be mentioned.

[0046] The magnetic layer described above can be provided directly on the surface of the non-magnetic support or indirectly via the non-magnetic layer.

[0047] <Non-magnetic layer> The non-magnetic powder used for the non-magnetic layer may be a powder of an inorganic substance or an organic substance. Also, carbon black or the like can be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, etc. These non-magnetic powders are available as commercial products and can also be manufactured by known methods. For details thereof, reference can be made to paragraphs 0146 to 0150 of Japanese Patent Application Laid-Open No. 2011-216149. For carbon black that can be used for the non-magnetic layer, reference can also be made to paragraphs 0040 to 0041 of Japanese Patent Application Laid-Open No. 2010-24113. The content rate (filling rate) of the non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass, based on the total mass of the non-magnetic layer.

[0048] The non-magnetic layer can contain a binder and can also contain additives. For other details such as the binder and additives of the non-magnetic layer, known techniques related to the non-magnetic layer can be applied. Also, for example, regarding the type and content of the binder, the type and content of the additives, etc., known techniques related to the magnetic layer can also be applied.

[0049] In the present invention and this specification, the non-magnetic layer shall also include a substantially non-magnetic layer containing, for example, as impurities or intentionally, a small amount of ferromagnetic powder together with the non-magnetic powder. Here, the substantially non-magnetic layer refers to a layer having a residual magnetic flux density of 10 mT or less, a coercive force of 7.96 kA / m (100 Oe) or less, or a layer having a residual magnetic flux density of 10 mT or less and a coercive force of 7.96 kA / m (100 Oe) or less. The non-magnetic layer preferably has no residual magnetic flux density and coercive force.

[0050] <Non-magnetic support> Next, the non-magnetic support will be described. Examples of the non-magnetic support (hereinafter also simply referred to as "support") include known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamides such as aromatic polyamides, and polyamideimides. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferred. These supports may be subjected to corona discharge, plasma treatment, adhesion-promoting treatment, heat treatment, etc. in advance.

[0051] <Back coat layer> In one form, the above magnetic recording medium can have a back coat layer containing non-magnetic powder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support, and in another form, it can be one that does not have a back coat layer. Preferably, the back coat layer contains one or both of carbon black and inorganic powder. The back coat layer can contain a binder and can also contain additives. Regarding the binder and additives of the back coat layer, known technologies related to the back coat layer can be applied, and known technologies related to the formulation of the magnetic layer and / or non-magnetic layer can also be applied. For example, the descriptions in paragraphs 0018 to 0020 of JP-A-2006-331625 and lines 65 to 38 in column 5 of US Patent No. 7,029,774 can be referred to for the back coat layer.

[0052] <Various thicknesses> The thickness of the non-magnetic support is preferably 3.0 to 6.0 μm.

[0053] From the perspective of high-density recording required in recent years, the thickness of the magnetic layer is preferably 200 nm or less, more preferably in the range of 8 to 200 nm, and even more preferably in the range of 10 to 200 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 the known configurations related to multi-layer magnetic layers can be applied. The thickness of the magnetic layer when separated into two or more layers is the total thickness of these layers.

[0054] The thickness of the non-magnetic layer is, for example, 0.1 to 1.5 μm, preferably 0.1 to 1.0 μm.

[0055] The thickness of the backcoat layer is preferably 0.9 μm or less, more preferably 0.1 to 0.7 μm.

[0056] The thicknesses of the layers of the magnetic recording medium and the non-magnetic support can be determined by known film thickness measurement methods. As an example, for instance, after exposing a cross-section in the thickness direction of the magnetic recording medium by a known method such as an ion beam or a microtome, cross-section observation is performed using a transmission electron microscope or a scanning electron microscope on the exposed cross-section. The various thicknesses can be determined as the thickness obtained at one location in the cross-section observation or the arithmetic mean of the thicknesses obtained at two or more locations randomly selected. Alternatively, the thickness of each layer may be determined as the designed thickness calculated from the manufacturing conditions.

[0057] <Manufacturing Process> The process of preparing a composition for forming a magnetic layer, a non-magnetic layer, or a backcoat layer can usually include at least a kneading process, a dispersion process, and a mixing process that may be provided as necessary before and after these processes. Each individual process may be divided into two or more steps. The components used in the preparation of each layer-forming composition may be added at the beginning or during any process. As the solvent, one or more of various solvents commonly used in the manufacture of coating-type magnetic recording media can be used. For the solvent, reference can be made to, for example, paragraph 0153 of JP-A-2011-216149. Also, the individual components can be added in two or more divided steps. To manufacture the above magnetic recording media, conventional known manufacturing techniques can be used in various processes. In the kneading process, it is preferable to use those having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader, an extruder, etc. For details of these kneading treatments, reference can be made to JP-A-1-106338 and JP-A-1-79274. Known dispersers can be used. Each layer-forming composition may be filtered by a known method before being subjected to the coating process. Filtration can be performed, for example, by filter filtration. As the filter used for filtration, for example, a filter having a pore size of 0.01 to 3 μm (such as a glass fiber filter, a polypropylene filter, etc.) can be used.

[0058] The magnetic layer can be formed by directly coating a magnetic layer-forming composition on a non-magnetic support, or by applying a multilayer coating successively or simultaneously with a non-magnetic layer-forming composition. For details of the coating for each layer formation, reference can be made to paragraph 0066 of JP-A-2010-231843.

[0059] After the coating process, various processes such as a drying process, an orientation process of the magnetic layer, and a surface smoothing process (calendering process) can be performed. Regarding the various processes, reference can be made to known techniques such as those described in paragraphs 0052 to 0057 of Japanese Patent Application Laid-Open No. 2010-24113. For example, an orientation process can be performed on the coating layer of the composition for forming a magnetic layer while this coating layer is in a wet state. Regarding the orientation process, various known techniques including the description in paragraph 0067 of Japanese Patent Application Laid-Open No. 2010-231843 can be applied. For example, the vertical orientation process can be performed by a known method such as a method using a magnet with opposite poles facing each other. In the orientation zone, the drying rate of the coating layer can be controlled by the temperature and the air volume of the drying air and / or the conveyance speed of the nonmagnetic support on which the above coating layer is formed in the orientation zone. Also, the coating layer may be pre-dried before being conveyed to the orientation zone.

[0060] Regarding the control of the ratio (Hr(45°) / Hr(0°)), performing an alternating magnetic field application process while the coating layer of the composition for forming a magnetic layer is in a wet state after the vertical orientation process can be cited as an example of a method for controlling the ratio (Hr(45°) / Hr(0°)). The application of the alternating magnetic field is preferably applied to the coating layer of the composition for forming a magnetic layer in a direction that becomes the in-plane direction in the finally formed magnetic layer. The reason why the ratio (Hr(45°) / Hr(0°)) can be controlled by performing the alternating magnetic field application process after the vertical orientation process is conjectured by the present inventor as follows. Regarding the orientation direction described below, "vertical" does not necessarily mean only strictly vertical, but includes the range of errors acceptable in the technical field to which the present invention belongs. The range of errors can mean, for example, a range of strictly vertical ± less than 10°. This also applies to "horizontal". By performing perpendicular alignment treatment, in the coating layer of the composition for forming a magnetic layer (hereinafter, also simply referred to as "coating layer"), particles of various sizes constituting the ε-iron oxide powder can be aligned in a direction perpendicular to the surface of the coating layer. Then, when an alternating magnetic field is applied in the in-plane direction in the finally formed magnetic layer, among the particles of various sizes of the ε-iron oxide powder contained in the coating layer, it is presumed that particles having a relatively small size can be selectively aligned in a horizontal direction (the direction that becomes the in-plane direction in the finally formed magnetic layer) with respect to the surface of the coating layer. The reason for such presumption is that particles with a small size are low-Hk particles with a low anisotropy magnetic field Hk and are thus easily magnetically reversed by the application of an alternating magnetic field, while particles with a large size are high-Hk particles with a high anisotropy magnetic field Hk and are thus difficult to magnetically reverse. Therefore, in the magnetic layer formed by drying the coating layer subjected to perpendicular alignment treatment and alternating magnetic field application treatment, among the particles of various sizes of the ε-iron oxide powder, the high-Hk particles mainly involved in data recording are in a vertically aligned state, and the low-Hk particles are in an in-plane aligned state. When a recording magnetic field is applied to the magnetic layer containing the ε-iron oxide powder in such a state for data recording in an in-plane recording method, the low-Hk particles aligned in the in-plane direction can play a role in assisting the magnetic reversal of the high-Hk particles aligned in the vertical direction. As a result, it is considered that the magnetic reversal of the high-Hk particles mainly involved in data recording can be easily caused. It is presumed that the reason why the low-Hk particles can assist the magnetic reversal of the high-Hk particles is that the low-Hk particles are aligned in a direction inclined with respect to the incident direction of the recording magnetic field incident on the magnetic layer from an oblique direction for data recording in the in-plane recording method. And it is considered that the more strongly the magnetic reversal of the high-Hk particles is assisted by the low-Hk particles, the smaller the value of the ratio (Hr(45°) / Hr(0°)) becomes. For example, the higher the magnetic field strength of the applied alternating magnetic field, the smaller the value of Hr(45°) can be, and as a result, the value of the ratio (Hr(45°) / Hr(0°)) can be made smaller. The magnetic field strength of the alternating magnetic field can be, for example, in the range of 150 Oe or more and 700 Oe or less. Also, the frequency of the alternating magnetic field can be, for example, 20 Hz or more and 200 Hz or less.

[0061] A magnetic recording medium according to an aspect of the present invention can be a tape-shaped magnetic recording medium (magnetic tape), or can also be a disk-shaped magnetic recording medium (magnetic disk). For example, a magnetic tape is usually housed in a magnetic tape cartridge, and the magnetic tape cartridge is mounted on a magnetic recording and reproducing device. A servo pattern can be formed on the magnetic recording medium by a known method in order to enable head tracking in the magnetic recording and reproducing device. "Formation of a servo pattern" can also be referred to as "recording of a servo signal". Hereinafter, with a magnetic tape as an example, the formation of a servo pattern will be described.

[0062] The servo pattern is usually formed along the longitudinal direction of the magnetic tape. Examples of the method of control using a servo signal (servo control) include timing-based servo (TBS), amplitude servo, frequency servo, and the like.

[0063] As shown in ECMA (European Computer Manufacturers Association)-319 (June 2001), in a magnetic tape compliant with the LTO (Linear Tape-Open) standard (commonly referred to as an "LTO tape"), a timing-based servo system is adopted. In this timing-based servo system, the servo pattern is constituted by arranging a plurality of pairs of magnetic stripes (also referred to as "servo stripes") that are non-parallel to each other continuously in the longitudinal direction of the magnetic tape. As described above, the reason why the servo pattern is constituted by 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 such that their interval changes continuously along the width direction of the magnetic tape, and by the servo signal reading element reading this interval, the relative position between the servo pattern and the servo signal reading element can be known. This relative position information enables the tracking of data tracks. For this purpose, usually, a plurality of servo tracks are set along the width direction of the magnetic tape on the servo pattern.

[0064] A servo band is constituted by servo signals continuous in the longitudinal direction of the magnetic tape. Usually, a plurality of such servo bands are provided on the magnetic tape. For example, in an LTO tape, the number is five. The region sandwiched between two adjacent servo bands is called a data band. A data band is constituted by a plurality of data tracks, and each data track corresponds to each servo track.

[0065] Also, in one form, as disclosed in Japanese Unexamined Patent Application Publication No. 2004-318983, information indicating the number of each servo band (also referred to as "servo band ID (identification)" or "UDIM (Unique DataBand Identification Method) information") is embedded in each servo band. 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 its position is relatively displaced in the longitudinal direction of the magnetic tape. Specifically, the shifting method of 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 becomes unique for each servo band, so that by simply reading one servo band with a servo signal reading element, that servo band can be uniquely identified.

[0066] In addition, there is also a method of uniquely identifying a servo band that uses a staggered method as disclosed in ECMA-319 (June 2001). In this staggered method, a group of a pair of magnetic stripes (servo stripes) that are arranged continuously in the longitudinal direction of the magnetic tape and are non-parallel to each other is recorded so as to be shifted in the longitudinal direction of the magnetic tape for each servo band. Since the combination of this shifting method between adjacent servo bands is unique throughout the magnetic tape, it is also possible to uniquely identify a servo band when reading a servo pattern by two servo signal reading elements.

[0067] Also, as disclosed in ECMA-319 (June 2001), information indicating the position in the longitudinal direction of the magnetic tape (also referred to as "LPOS (Longitudinal Position) information") is usually embedded in each servo band. This LPOS information is also recorded by shifting the position 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 for this LPOS information.

[0068] It is also possible to embed other information different from the above UDIM information and LPOS information in the servo band. In this case, the information to be embedded may be different for each servo band like the UDIM information, or it may be common to all servo bands like the 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 a pair of servo stripes.

[0069] The head for forming the servo pattern is called a servo write head. The servo write head has a pair of gaps corresponding to the above pair of magnetic stripes, the number of which is equal to the number of servo bands. Usually, a core and a coil are connected to each pair of gaps, and by supplying a current pulse to the coil, the magnetic field generated in the core can cause a leakage magnetic field in the pair of gaps. When forming the servo pattern, a magnetic pattern corresponding to the pair of gaps can be transferred to the magnetic tape by inputting a current pulse while running the magnetic tape on the servo write head, thereby forming the servo pattern. The width of each gap can be appropriately set according to the density of the servo pattern to be formed. The width of each gap can be set, for example, to 1 μm or less, 1 to 10 μm, 10 μm or more, etc.

[0070] Before forming a servo pattern on a magnetic tape, the magnetic tape is usually subjected to a demagnetization (erase) process. This erase process can be performed by applying a uniform magnetic field to the magnetic tape using a DC magnet or an AC magnet. There are two types of erase processes: DC (Direct Current) erase and AC (Alternating Current) erase. The AC erase is performed by gradually decreasing the intensity of the magnetic field while reversing the direction of the magnetic field applied to the magnetic tape. On the other hand, the DC erase is performed by applying a magnetic field in one direction to the magnetic tape. There are further two methods for DC erase. The first method is a horizontal DC erase in which a magnetic field in one direction is applied along the longitudinal direction of the magnetic tape. The second method is a vertical DC erase in which a magnetic field in one direction is applied along the thickness direction of the magnetic tape. The erase process may be performed on the entire magnetic tape or on each servo band of the magnetic tape.

[0071] The direction of the magnetic field of the formed servo pattern is determined according to the direction of the erase. For example, when a horizontal DC erase is performed on the magnetic tape, the servo pattern is formed such that the direction of the magnetic field is opposite to the direction of the erase. Thereby, the output of the servo signal obtained by reading the servo pattern can be increased. As shown in Japanese Patent Application Laid-Open No. 2012-53940, when a magnetic pattern is transferred using the above-described gap onto a vertically DC-erased magnetic tape, the servo signal obtained by reading the formed servo pattern has a monopolar pulse shape. On the other hand, when a magnetic pattern is transferred using the above-described gap onto a horizontally DC-erased magnetic tape, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

[0072] The magnetic tape is accommodated in, for example, a magnetic tape cartridge, and the magnetic tape cartridge is mounted on a magnetic recording and reproducing apparatus.

[0073] Since the magnetic recording medium can exhibit excellent electromagnetic conversion characteristics when reproducing data recorded by an in-plane recording method, it is suitable as an in-plane recording magnetic recording medium. However, it is not excluded that magnetic recording is performed on the magnetic recording medium by a perpendicular recording method.

[0074] [Magnetic tape cartridge] One aspect of the present invention relates to a magnetic tape cartridge including the above-described tape-shaped magnetic recording medium (i.e., magnetic tape).

[0075] Details of the magnetic tape included in the magnetic tape cartridge are as described above.

[0076] In a magnetic tape cartridge, generally, a magnetic tape is housed in a state of being wound around a reel inside the cartridge body. The reel is rotatably provided inside the cartridge body. As magnetic tape cartridges, a single-reel type magnetic tape cartridge having one reel inside the cartridge body and a dual-reel type magnetic tape cartridge having two reels inside the cartridge body are widely used. When the single-reel type magnetic tape cartridge is mounted on a magnetic recording and / or reproducing apparatus for recording and / or reproducing data on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge and wound around the reel on the magnetic recording and reproducing apparatus side. A magnetic head is disposed in the magnetic tape conveyance path from the magnetic tape cartridge to the take-up reel. The feeding and take-up of the magnetic tape are performed between the reel on the magnetic tape cartridge side (supply reel) and the reel on the magnetic recording and reproducing apparatus side (take-up reel). During this period, data recording and / or reproducing is performed by the contact and sliding between the magnetic head and the surface of the magnetic layer side of the magnetic tape. On the other hand, in the dual-reel type magnetic tape cartridge, both the supply reel and the take-up reel are provided inside the magnetic tape cartridge. The magnetic tape cartridge may be either a single-reel type or a dual-reel type magnetic tape cartridge. The magnetic tape cartridge may include a magnetic tape according to an aspect of the present invention, and known techniques can be applied to other aspects. The total length of the magnetic tape housed in the magnetic tape cartridge can be, for example, 800 m or more, and can also be in the range of about 800 m to 2000 m. The longer total length of the tape housed in the magnetic tape cartridge is preferable from the viewpoint of increasing the capacity of the magnetic tape cartridge.

[0077] [Magnetic recording and reproducing apparatus] One aspect of the present invention relates to a magnetic recording and reproducing apparatus including the above magnetic recording medium.

[0078] In the present invention and this specification, the "magnetic recording and reproducing apparatus" means an apparatus that can perform at least one of recording data on a magnetic recording medium and reproducing data recorded on the magnetic recording medium. Such an apparatus is generally called a drive. The magnetic recording and reproducing apparatus can be, for example, a sliding type magnetic recording and reproducing apparatus. The sliding type magnetic recording and reproducing apparatus refers to an apparatus in which the surface on the magnetic layer side and the magnetic head come into contact and slide when recording data on the magnetic recording medium and / or reproducing the recorded data. For example, the magnetic recording and reproducing apparatus can detachably include the magnetic tape cartridge.

[0079] The magnetic recording and reproducing apparatus can include a magnetic head. The magnetic head can be a recording head that can record data on a magnetic tape, or can also be a reproducing head that can reproduce data recorded on the magnetic tape. Further, in one form, the magnetic recording and reproducing apparatus can include both a recording head and a reproducing head as separate magnetic heads. In another form, the magnetic head included in the magnetic recording and reproducing apparatus can have a configuration in which both an element for data recording (recording element) and an element for data reproduction (reproducing element) are provided in one magnetic head. The recording head can be an in-plane recording magnetic head or a perpendicular recording magnetic head. For the in-plane recording magnetic head and the perpendicular recording magnetic head, known techniques related to those heads can be applied. When reproducing data recorded in the in-plane recording method, the magnetic recording medium can exhibit excellent electromagnetic conversion characteristics. Therefore, the recording head included in the magnetic recording and reproducing apparatus is preferably an in-plane recording magnetic head. As the reproducing head, a magnetic head (MR head) including a magnetoresistive (MR) element capable of sensitively reading data recorded on a magnetic tape as a reproducing element is preferable. As the MR head, various known MR heads such as an AMR (Anisotropic Magnetoresistive) head, a GMR (Giant Magnetoresistive) head, and a TMR (Tunnel Magnetoresistive) head can be used. Further, the magnetic head for recording and / or reproducing data may include a servo signal reading element. Alternatively, as a head separate from the magnetic head for recording and / or reproducing data, a magnetic head (servo head) equipped with a servo signal reading element may be included in the magnetic recording and reproducing apparatus. For example, a magnetic head for recording and / or reproducing recorded data (hereinafter, also referred to as a "recording and reproducing head") can include two servo signal reading elements, and each of the two servo signal reading elements can simultaneously read two adjacent servo bands. One or more data elements can be arranged between the two servo signal reading elements. The elements for data recording and the elements for reproduction are collectively referred to as "data elements".

[0080] In the above magnetic recording and reproducing apparatus, recording of data on the magnetic recording medium and / or reproduction of data recorded on the magnetic recording medium can be performed, for example, by bringing the surface of the magnetic layer of the magnetic recording medium into contact with the magnetic head and sliding them. The magnetic recording and reproducing apparatus only needs to include a magnetic recording medium according to one aspect of the present invention, and known techniques can be applied to other aspects.

[0081] For example, when recording data and / or playing back the recorded data, first, tracking using a servo signal is performed. That is, by causing the servo signal reading element to follow a predetermined servo track, the data element is controlled to pass over the target data track. The movement of the data track is performed by changing the servo track read by the servo signal reading element in the tape width direction. Also, the recording and reproducing head can record and / or play back other data bands. In that case, the servo signal reading element may be moved to a predetermined servo band using the UDIM information described above, and tracking for that servo band may be started.

Embodiment

[0082] Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiments shown in the examples. "Parts" and "%" described below indicate "parts by mass" and "% by mass" unless otherwise specified. "eq" is equivalent, which is a unit that cannot be converted into SI units. Also, the processes and evaluations described below were performed in an environment with an ambient temperature of 23°C ± 1°C unless otherwise specified.

[0083] [Preparation of ε-Iron Oxide Powders No. 1 to No. 6] Dissolve 90 g of pure water, iron(III) nitrate nonahydrate (addition amount: "amount of iron nitrate" in Table 1), gallium(III) nitrate octahydrate (addition amount: "amount of gallium nitrate" in Table 1) or aluminum(III) nitrate nonahydrate (addition amount: "amount of aluminum nitrate" in Table 1), cobalt(II) nitrate hexahydrate (addition amount: "amount of cobalt nitrate" in Table 1), titanium(IV) sulfate (addition amount: "amount of titanium sulfate" in Table 1), and 16.7 g of polyvinylpyrrolidone (PVP). While stirring using a magnetic stirrer, under the conditions of an air atmosphere and an ambient temperature of 25°C, add 44.0 g of an aqueous ammonia solution with a concentration of 25%, and stir for 2 hours while maintaining the temperature condition of the ambient temperature at 25°C. To the obtained solution, add an aqueous citric acid solution obtained by dissolving 11 g of citric acid in 100 g of pure water, and stir for 1 hour. Collect the precipitated powder after stirring by centrifugation, wash it with pure water, and dry it in a heating furnace with an internal temperature of 80°C. Add 8900 g of pure water to the dried powder and disperse the powder in water again to obtain a dispersion. Heat the obtained dispersion to a liquid temperature of 50°C, and while stirring, dropwise add 440 g of an aqueous ammonia solution with a concentration of 25%. After stirring for 1 hour while maintaining the temperature at 50°C, dropwise add 160 mL of tetraethoxysilane (TEOS), and stir for 24 hours. Add 500 g of ammonium sulfate to the obtained reaction solution, collect the precipitated powder by centrifugation, wash it with pure water, and dry it in a heating furnace with an internal temperature of 80°C for 24 hours to obtain a precursor of the ferromagnetic powder. Load the obtained precursor of the ferromagnetic powder into a heating furnace with the internal temperature described in Table 1 ( "heat treatment temperature" in Table 1) under an air atmosphere, and perform heat treatment for 4 hours. Put the powder after heat treatment into a 4 mol / L aqueous sodium hydroxide (NaOH) solution, maintain the liquid temperature at 75°C, and stir for 24 hours to perform a film removal process. Thereafter, collect the ferromagnetic powder subjected to the film removal treatment by centrifugation, wash it with pure water, and dry it in a heating furnace with an internal temperature of 95°C. Regarding the ferromagnetic powder obtained after the above drying, high-frequency inductively coupled plasma optical emission spectrometry (ICP-OES: Inductively Coupled Plasma-Optical Emission Spectrometry) was performed to confirm the composition, and it was confirmed that it is a substituted ε-iron oxide having the composition shown in Table 1. The values described in Table 1 for the composition are the numbers of each element (x, y, z, (2 - x - y - z)) in the composition formula: A 1 x A 2 y A 3 z Fe (2-x-y-z) O 3 It is the number of each element in. Also, the CuKα ray was scanned under the conditions of a voltage of 45 kV and an intensity of 40 mA, and the X-ray diffraction pattern was measured under the following conditions (X-ray diffraction analysis). From the peaks of the X-ray diffraction pattern, it was confirmed that the obtained ferromagnetic powder all has a single crystal structure of the ε-phase (crystal structure of ε-iron oxide) that does not contain the crystal structures of the α-phase and γ-phase. PANalytical X’Pert Pro diffractometer, PIXcel detector Soller slits for incident beam and diffracted beam: 0.017 radians Fixed angle of dispersion slit: 1 / 4 degree Mask: 10 mm Anti-scattering slit: 1 / 4 degree Measurement mode: continuous Measurement time per step: 3 seconds Measurement speed: 0.017 degrees per second Measurement step: 0.05 degrees

[0084] The average particle size of the above ferromagnetic powder was determined by the method described above using a Hitachi transmission electron microscope H-9000 type as a transmission electron microscope and Carl Zeiss image analysis software KS-400 as image analysis software. The obtained average particle size is shown in Table 1.

[0085] [Example 1] [Composition for forming magnetic layer] (Magnetic liquid) ε-iron oxide powder (refer to Table 1): 100.0 parts Sulfonic acid group-containing polyurethane resin: 15.0 parts Cyclohexanone: 150.0 parts Methyl ethyl ketone: 150.0 parts (Abrasive liquid) α-alumina (average particle size: 110 nm): 9.0 parts Vinyl chloride copolymer (MR110 manufactured by Kaneka Corporation): 0.7 part Cyclohexanone: 20.0 parts (Projection forming agent liquid) Colloidal silica (average particle size 100 nm): 1.3 parts Methyl ethyl ketone: 9.0 parts Cyclohexanone: 6.0 parts (Other components) Butyl stearate: 1.0 part Stearic acid: 1.0 part Polyisocyanate (Coronate manufactured by Tosoh Corporation): 2.5 parts (Finishing additive solvent) Cyclohexanone: 180.0 parts Methyl ethyl ketone: 180.0 parts

[0086] <Composition for forming non-magnetic layer> Non-magnetic inorganic powder (α-iron oxide): 80.0 parts (Average particle size: 0.15 μm, average aspect ratio: 7, BET (Brunauer-Emmett-Teller) specific surface area: 52 m 2 / g) Carbon black (average particle size: 20 nm): 20.0 parts Electron beam curable vinyl chloride copolymer: 13.0 parts Electron beam curable polyurethane resin: 6.0 parts Phenylphosphonic acid: 3.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Butyl stearate: 4.0 parts Stearic acid: 1.0 part

[0087] <Composition for forming back coat layer> Non-magnetic inorganic powder (α-iron oxide): 80.0 parts (Average particle size: 0.15 μm, average aspect ratio: 7, BET specific surface area: 52 m 2 / g) Carbon black (average particle size: 20 nm): 20.0 parts Carbon black (average particle size: 100 nm): 3.0 parts Vinyl chloride copolymer: 13.0 parts Sulfonic acid group-containing polyurethane resin: 6.0 parts Phenylphosphonic acid: 3.0 parts Cyclohexanone: 140.0 parts Methyl ethyl ketone: 170.0 parts Stearic acid: 3.0 parts Polyisocyanate (Coronate manufactured by Tosoh Corporation): 5.0 parts Methyl ethyl ketone: 400.0 parts

[0088] <Preparation of Composition for Each Layer Formation> The composition for magnetic layer formation was prepared by the following method. The various components of the above magnetic liquid were dispersed to prepare a magnetic liquid. For the dispersion treatment, a batch-type vertical sand mill was used, and zirconia beads were used as the dispersion beads. After mixing the various components of the above abrasive liquid, it was put into a vertical sand mill disperser together with zirconia beads having a bead diameter of 1 mm, and adjusted so that the ratio of the bead volume to the total of the abrasive liquid volume and the bead volume was 60%, and sand mill dispersion treatment was performed for 180 minutes. The liquid after the sand mill dispersion treatment was taken out and subjected to ultrasonic dispersion filtration treatment using a flow-type ultrasonic dispersion filtration device to prepare an abrasive liquid. The magnetic liquid, the projection forming agent liquid, the abrasive liquid, other components and the finishing additive solvent were introduced into a dissolver stirrer and stirred at a peripheral speed of 10 m / sec for 30 minutes. Then, after performing the treatment at a flow rate of 7.5 kg / min with a flow-type ultrasonic disperser for 2 passes, filtration was performed once with a filter having a pore size of 1.0 μm to prepare a composition for magnetic layer formation.

[0089] The composition for non-magnetic layer formation was prepared by the following method. After kneading and diluting the above components except for the lubricants (butyl stearate and stearic acid) with an open kneader, a dispersion treatment was carried out using a horizontal bead mill disperser. Thereafter, the lubricants (butyl stearate and stearic acid) were added, and stirring and mixing treatments were performed with a dissolver stirrer to prepare a composition for forming a non-magnetic layer.

[0090] A composition for forming a backcoat layer was prepared by the following method. After kneading and diluting the above components except for the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts) with an open kneader, a dispersion treatment was carried out using a horizontal bead mill disperser. Thereafter, the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts) were added, and stirring and mixing treatments were performed with a dissolver stirrer to prepare a composition for forming a backcoat layer.

[0091] <Fabrication of Magnetic Tape> On the surface of a biaxially stretched polyethylene naphthalate support with a thickness of 5.0 μm, the composition for forming a non-magnetic layer was applied so that the thickness after drying would be 1.0 μm, and after drying, an electron beam was irradiated at an acceleration voltage of 125 kV to obtain an energy of 40 kGy to form a non-magnetic layer. On the formed non-magnetic layer, the composition for forming a magnetic layer was applied so that the thickness after drying would be 50 nm to form a coating layer. While this coating layer was in a wet state, a magnetic field with a magnetic field strength of 0.6 T was applied in a direction perpendicular to the surface of the above coating layer using a permanent magnet in an alignment zone to perform a perpendicular alignment treatment. Immediately thereafter, an alternating magnetic field with a magnetic field strength described in Table 1 and a frequency of 50 Hz was applied in the longitudinal direction of the above coating layer (specifically, the direction that will be the longitudinal direction in the finally formed magnetic tape) using an alternating magnetic field application device, and then dried to form a magnetic layer. Thereafter, the composition for forming a backcoat layer was applied to the surface of the support opposite to the surface on which the non-magnetic layer and the magnetic layer were formed so that the thickness after drying would be 0.5 μm, and dried to form a backcoat layer. Subsequently, a calendaring process (surface smoothing process) was performed using a calendar roll composed only of metal rolls at a calendaring speed of 80 m / min, a line pressure of 300 kg / cm (294 kN / m), and a surface temperature of the calendar roll of 110°C. Subsequently, heat treatment was performed for 36 hours in an environment with an ambient temperature of 70°C. After the heat treatment, it was slit into a width of 1 / 2 inch (0.0127 meters), and the cleaning of the surface of the magnetic layer was performed using a tape cleaning device equipped with a nonwoven fabric and a razor blade attached so as to press against the surface of the magnetic layer in a device having a feeding and winding device for the slit product. After that, in a state where the magnetic layer of the magnetic tape was 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. Thus, a magnetic tape having a data band, a servo band, and a guide band in an arrangement conforming to the LTO Ultrium format in the magnetic layer and having a servo pattern with an arrangement and shape conforming to the LTO Ultrium format on the servo band was obtained.

[0092] [Examples 2 - 9, Comparative Examples 1, 2] Magnetic tapes were produced by the method described for Example 1 except that the items shown in Table 1 were changed as described in Table 1. For Comparative Example 1, since the AC magnetic field application process after the vertical alignment process was not performed, a "-" was indicated in the column for the magnetic field strength of the AC magnetic field.

[0093] For each of the above Examples and Comparative Examples, two magnetic tapes were produced, one was used for evaluation regarding SNR (Signal - to - Noise Ratio), and the other was used for other evaluations.

[0094] [Physical Property Evaluation Method] <Ratio (Hr(45°) / Hr(0°))> Sample pieces for measuring Hr(0°) and sample pieces for measuring Hr(45°) were cut out from each of the magnetic tapes of the examples and comparative examples. Using the cut-out sample pieces, Hr(0°) and Hr(45°) were measured by the method described above. The ratio (Hr(45°) / Hr(0°)) was calculated by dividing Hr(45°) obtained by the measurement by Hr(0°).

[0095] [Performance Evaluation Method] <In-plane Recording Suitability (SNR)> In an environment with an ambient temperature of 23°C ± 1°C and a relative humidity of 50%, a recording head (MIG (Metal-in-gap) head, gap length 0.15 μm, 1.8 T) and a reproducing GMR (Giant Magnetoresistive) head (reproducing track width 1 μm) were attached to a loop tester, and a signal with a linear recording density of 325 kfci was recorded by an in-plane recording method (a recording method in which the direction of the recording magnetic field applied to the recording layer for magnetization reversal is controlled to be horizontal with respect to the in-plane direction as described above), and then the reproduced signal was measured with a spectrum analyzer manufactured by Advantest Corporation. The unit kfci is a unit of linear recording density (not convertible to the SI unit system). The ratio of the output value of the carrier signal to the integrated noise in the entire spectrum band was defined as SNR. For the SNR measurement, the signal in the portion where the signal was sufficiently stable after starting the running of the magnetic tape was used. The SNR thus obtained is shown in Table 1 as a relative value with respect to the value of Comparative Example 1.

[0096] The above results are shown in Table 1 (Tables 1-1 to 1-3).

[0097]

Table 1-1

[0098]

Table 1-2

[0099]

Table 1-3

[0100] From the results shown in Table 1, it can be confirmed that the magnetic tape of the example is a magnetic tape having a magnetic layer containing ε-iron oxide powder and exhibits excellent electromagnetic conversion characteristics (high SNR) when reproducing data recorded by an in-plane recording method.

Industrial Applicability

[0101] One aspect of the present invention is useful in data storage applications.

Claims

1. A magnetic recording medium having a non-magnetic support and a magnetic layer containing ferromagnetic powder, wherein the ferromagnetic powder is ε-iron oxide powder, and the ratio of Hr(0°) to Hr(45°), Hr(45°) / Hr(0°), is 0.50 or less, wherein the Hr(0°) is the residual coercive force Hr obtained by applying a pulse magnetic field with a pulse width of 0.76 ms in the in-plane direction of the magnetic recording medium, and the Hr(45°) is the residual coercive force Hr obtained by applying a pulse magnetic field with a pulse width of 0.76 ms to the magnetic recording medium by making the angle in the in-plane direction of the magnetic recording medium 0° and the angle in the perpendicular direction of the magnetic recording medium 90°, and making the magnetic field incident from a direction inclined 45° from the in-plane direction toward the perpendicular direction,

2. The magnetic recording medium according to claim 1, wherein the ratio, Hr(45°) / Hr(0°), is 0.45 or less.

3. The magnetic recording medium according to claim 1 or 2, wherein the ratio, Hr(45°) / Hr(0°), is 0.40 or less.

4. The magnetic recording medium according to any one of claims 1 to 3, wherein the ratio, Hr(45°) / Hr(0°), is 0.35 or less.

5. The magnetic recording medium according to any one of claims 1 to 4, wherein the ratio, Hr(45°) / Hr(0°), is 0.10 or more and 0.35 or less.

6. The magnetic recording medium according to any one of claims 1 to 5, wherein the ε-iron oxide powder contains cobalt element, an element selected from the group consisting of gallium element and aluminum element, and titanium element.

7. The magnetic recording medium according to any one of claims 1 to 6, further having a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

8. The magnetic recording medium according to any one of claims 1 to 7, further having a back coat layer containing non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer.

9. The magnetic recording medium according to any one of claims 1 to 8, which is a magnetic tape.

10. A magnetic tape cartridge containing the magnetic tape according to claim 9.

11. A magnetic recording and reproducing apparatus containing the magnetic recording medium according to any one of claims 1 to 9.

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