JP2019169229A - Magnetic tape and magnetic recording and reproducing device - Google Patents

Abstract

To provide a magnetic tape in which frequency of occurrence of a missing pulse under a low-temperature and high-humid environment is reduced.SOLUTION: There is provided a magnetic tape having a magnetic layer containing ferromagnetic powder and binding agent on a non-magnetic substrate. In the magnetic tape, the magnetic layer includes one or more kinds of components selected from a group consisting of fatty acid and fatty acid amide, a C-H-originating C concentration calculated from a C-H peak area ratio in a C1s spectrum obtained by an X-ray photoelectron spectroscopy analysis conducted at 10 degrees of a photoelectron take-off angle on the surface of the magnetic layer is 45 atom% or more, and an absolute value ΔN of a difference between a refractive index Nxy measured with respect to an in-plane direction of the magnetic layer and a refractive index Nz measured with respect to a thickness direction of the magnetic layer is 0.25 or more and 0.40 or less. There is also provided a magnetic recording and reproducing device including the magnetic tape.SELECTED DRAWING: None

Description

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

  There are two types of magnetic recording media, tape-shaped and disk-shaped. For data storage applications, tape-shaped magnetic recording media, ie magnetic tape, are mainly used. Recording and / or reproducing information on a magnetic tape is usually performed by bringing the surface of the magnetic tape (the surface of the magnetic layer) and a magnetic head (hereinafter also simply referred to as “head”) into contact and sliding. . As a magnetic tape, one having a configuration in which a magnetic layer containing a ferromagnetic powder and a binder is provided on a nonmagnetic support is widely used (see, for example, Patent Document 1).

JP-A-2005-243162

  When the information recorded on the magnetic tape is reproduced, the error rate increases as the frequency of partial reduction of the reproduction signal amplitude (referred to as “missing pulse”) increases. Reliability is reduced. Therefore, in order to provide a magnetic tape that can be used with high reliability, it is desirable to reduce the frequency of occurrence of missing pulses.

  Incidentally, in recent years, magnetic tapes used for data storage are sometimes used in data centers in which 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 the data center can be relaxed from the current level or management can be made unnecessary. However, if the temperature and humidity control conditions are relaxed or not managed, the magnetic tape is assumed to be used in various environments, and is also assumed to be used in a low temperature and high humidity environment. However, as a result of studies by the present inventors, it has been found that the frequency of occurrence of missing pulses tends to increase in a low temperature and high humidity environment.

  Therefore, an object of the present invention is to provide a magnetic tape in which the frequency of occurrence of missing pulses in a low temperature and high humidity environment is reduced.

One embodiment of the present invention provides:
A magnetic tape having a magnetic layer comprising a ferromagnetic powder and a binder on a non-magnetic support,
The magnetic layer contains one or more components selected from the group consisting of fatty acids and fatty acid amides,
The C—H-derived C concentration calculated from the C—H peak area ratio in the C1s spectrum obtained by X-ray photoelectron spectroscopic analysis performed at a photoelectron extraction angle of 10 degrees on the surface of the magnetic layer (hereinafter referred to as “C— H-derived C concentration "or simply" CH-derived C concentration ") is 45 atomic% or more, and the refractive index Nxy measured in the in-plane direction of the magnetic layer and the thickness direction of the magnetic layer The absolute value ΔN of the difference from the refractive index Nz measured for the magnetic tape is 0.25 or more and 0.40 or less,
About.

  In one aspect, the difference (Nxy−Nz) between the refractive index Nxy and the refractive index Nz can be 0.25 or more and 0.40 or less.

  In one embodiment, the C—H-derived C concentration can be 45 atom% or more and 80 atom% or less.

  In one embodiment, the C—H-derived C concentration can be 45 atomic% or more and 70 atomic% or less.

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

  In one aspect, the magnetic tape may have a backcoat layer containing a nonmagnetic powder and a binder on the surface side of the nonmagnetic support opposite to the surface side having the magnetic layer.

  A further aspect of the present invention relates to a magnetic recording / reproducing apparatus including the magnetic tape and a magnetic head.

  According to one embodiment of the present invention, a magnetic tape capable of reducing the frequency of occurrence of missing pulses in a low temperature and high humidity environment can be provided. According to one embodiment of the present invention, a magnetic recording / reproducing apparatus including the magnetic tape can be provided.

An example (process schematic diagram) of the specific aspect of a magnetic tape manufacturing process is shown.

[Magnetic tape]
One aspect of the present invention is a magnetic tape having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support, wherein the magnetic layer contains one or more components selected from the group consisting of fatty acids and fatty acid amides. In addition, the C—H-derived C concentration calculated from the C—H peak area ratio in the C1s spectrum obtained by X-ray photoelectron spectroscopic analysis performed at a photoelectron extraction angle of 10 degrees on the surface of the magnetic layer is 45 atomic% or more. The absolute value ΔN of the difference between the refractive index Nxy measured in the in-plane direction of the magnetic layer and the refractive index Nz measured in the thickness direction of the magnetic layer is 0.25 or more and 0.40 or less. About.

  In the present invention and the present specification, “the surface of the magnetic layer” is synonymous with the magnetic layer side surface of the magnetic tape. Further, in the present invention and the present specification, “ferromagnetic powder” means a set of a plurality of ferromagnetic particles. The term “aggregation” is not limited to an aspect in which particles constituting the aggregation are in direct contact with each other, and an aspect in which a binder, an additive, and the like are interposed between particles is also included. The same applies to various powders such as the non-magnetic powder in the present invention and the present specification.

  Below, the measuring method of (DELTA) N and C-H origin C density | concentration is demonstrated.

In the present invention and this specification, the absolute value ΔN of the difference between the refractive index Nxy measured in the in-plane direction of the magnetic layer and the refractive index Nz measured in the thickness direction of the magnetic layer is a value obtained by the following method. And
The refractive index in each direction of the magnetic layer is determined by spectroscopic ellipsometry using a two-layer model. In order to obtain the refractive index of the magnetic layer using the two-layer model by spectroscopic ellipsometry, the value of the refractive index of the portion adjacent to the magnetic layer is used. In the following, a case where the refractive indexes Nxy and Nz of the magnetic layer are obtained will be described as an example for a magnetic tape having a layer structure in which a nonmagnetic layer and a magnetic layer are laminated in this order on a nonmagnetic support. However, the magnetic tape according to one embodiment of the present invention can also be a magnetic tape having a layer structure in which a magnetic layer is directly laminated on a nonmagnetic support without using a nonmagnetic layer. For the magnetic tape having such a configuration, the refractive index in each direction of the magnetic layer is obtained using the two-layer model of the magnetic layer and the nonmagnetic support in the same manner as described below. In addition, the incident angles described below are incident angles when the incident angle in the case of vertical incidence is 0 °.
(1) Preparation of measurement sample For magnetic tapes having a backcoat layer on the surface opposite to the surface having the magnetic layer of the nonmagnetic support, the backcoat layer of the measurement sample cut out from the magnetic tape is removed. Make measurements after The backcoat layer can be removed by a known method such as dissolving the backcoat layer using a solvent. As the solvent, for example, methyl ethyl ketone can be used. However, any solvent that can remove the backcoat layer may be used. The surface of the non-magnetic support after the backcoat layer is removed is roughened by a known method so that reflected light on the surface is not detected in the measurement with an ellipsometer. The roughening can be performed by, for example, a method of polishing the surface of the nonmagnetic support after removing the backcoat layer using sandpaper. For the measurement sample cut out from the magnetic tape having no back coat layer, the surface of the nonmagnetic support opposite to the surface having the magnetic layer is roughened.
Further, in order to measure the refractive index of the following nonmagnetic layer, the magnetic layer is further removed to expose the surface of the nonmagnetic layer. In order to measure the refractive index of the nonmagnetic support described below, the nonmagnetic layer is also removed to expose the surface of the nonmagnetic support on the magnetic layer side. The removal of each layer can be performed by a known method as described for the removal of the backcoat layer. The longitudinal direction described below refers to the direction that was the longitudinal direction of the magnetic tape when it was included in the magnetic tape before the measurement sample was cut out. This also applies to the other directions described below.
(2) Refractive Index Measurement of Magnetic Layer Using an ellipsometer, the incident angles are 65 °, 70 ° and 75 °, and the surface of the magnetic layer is irradiated with incident light having a beam diameter of 300 μm from the longitudinal direction to obtain Δ (s The phase difference between polarized light and p-polarized light) and ψ (amplitude ratio between s-polarized light and p-polarized light) are measured. The measurement is performed by changing the wavelength of the incident light in the range of 400 to 700 nm in increments of 1.5 nm, and the measurement value is obtained for each wavelength.
Using the measured values of Δ and Ψ of the magnetic layer at each wavelength, the refractive index of the nonmagnetic layer in each direction determined by the following method, and the thickness of the magnetic layer, the magnetic layer at each wavelength according to the two-layer model as follows: Find the refractive index of.
The 0th layer, which is a two-layer model substrate, is a nonmagnetic layer, and the first layer is a magnetic layer. Considering only the reflection at the interface between the air / magnetic layer and the magnetic layer / nonmagnetic layer, the two-layer model is created assuming that there is no influence of the back surface reflection of the nonmagnetic layer. The refractive index of the first layer that most closely matches the obtained measured value is obtained by fitting by the least square method. As the value at a wavelength of 600nm obtained from the result of the fitting, obtaining the refractive index Nz ₁ in the thickness direction of the longitudinal refractive index of the magnetic layer in the direction Nx, and the magnetic layer as measured by the incidence of the incident light from the longitudinal direction.
Similar to the above except that the direction in which the incident light is incident is the width direction of the magnetic tape, the refractive index Ny of the magnetic layer in the width direction and the incident from the width direction as the value at the wavelength of 600 nm obtained from the fitting result determining the refractive index Nz ₂ in the thickness direction of the magnetic layer was measured by entering the light.
The fitting is performed by the following method.
Generally, “complex refractive index n = η + iκ”. Where η is the real part of the refractive index, κ is the extinction coefficient, and i is the imaginary number. Complex permittivity ε = ε1 + iε2 (ε1 and ε2 satisfy the Kramers-Kronig relationship) and ε1 = η ² −κ ² , ε2 = 2ηκ, and when calculating Nx and Nz ₁ , Nx complex _{Let the} dielectric constant be ε _x = ε _x 1 + iε _x 2 and the complex dielectric constant of Nz _{1 be} ε _z1 = ε _z1 1 + iε _z1 2.
ε _x 2 is one Gaussian, the peak position is 5.8 to 5.1 eV, σ is 4 to 3.5 eV, and the starting point is the dielectric constant outside the measurement wavelength range (400 to 700 nm) Nx is obtained by placing a parameter to be an offset in and fitting the measured value to the least squares. Similarly, ε _z1 2 is obtained by setting an offset parameter and fitting a measured value to the least squares with an arbitrary point having a peak position of 3.2 to 2.9 eV and σ of 1.5 to 1.2 eV. Nz ₁ is obtained. Ny and Nz ₂ are obtained in the same manner. The refractive index Nxy measured in the in-plane direction of the magnetic layer is obtained as “Nxy = (Nx + Ny) / 2”. The refractive index Nz measured in the thickness direction of the magnetic layer is obtained as “Nz = (Nz ₁ + Nz ₂ ) / 2”. An absolute value ΔN of these differences is obtained from the obtained Nxy and Nz.
(3) Refractive index measurement of non-magnetic layer The refractive index at a wavelength of 600 nm of the non-magnetic layer (refractive index in the longitudinal direction, refractive index in the width direction, incident light from the longitudinal direction is incident as in the above method, except for the following points. And the refractive index in the thickness direction measured and the refractive index in the thickness direction measured by making incident light incident from the width direction).
The wavelength of the incident light is changed in increments of 1.5 nm in the range of 250 to 700 nm.
Using a two-layer model of a nonmagnetic layer and a nonmagnetic support, the zeroth layer, which is a substrate of the two-layer model, is a nonmagnetic support, and the first layer is a nonmagnetic layer. Considering only the reflection at the interface between the air / nonmagnetic layer and the nonmagnetic layer / nonmagnetic support, it is assumed that there is no influence of the back surface reflection of the nonmagnetic support, and a two-layer model is created.
In the fitting, 7 peaks (0.6 eV, 2.3 eV, 2.9 eV, 3.6 eV, 4.6 eV, 5.0 eV, 6.0 eV) are assumed in the imaginary part (ε2) of the complex dielectric constant. Then, a parameter that is offset in the dielectric constant is placed outside the measurement wavelength range (250 to 700 nm).
(4) Refractive index measurement of nonmagnetic support The refractive index at a wavelength of 600 nm of the nonmagnetic support used for obtaining the refractive index of the nonmagnetic layer by a two-layer model (refractive index in the longitudinal direction, refractive index in the width direction, The refractive index in the thickness direction measured by entering incident light from the longitudinal direction and the refractive index in the thickness direction measured by entering incident light from the width direction are the refractive indices of the magnetic layer except for the following points. Determined in the same manner as the above method for measurement.
A one-layer model with only surface reflection is used without using a two-layer model.
The fitting is performed by a Cauchy model (n = A + B / λ ² , n is a refractive index, A and B are constants determined by fitting, and λ is a wavelength).

Next, the C—H-derived C concentration calculated from the C—H peak area ratio in the C1s spectrum obtained by X-ray photoelectron spectroscopic analysis performed at a photoelectron extraction angle of 10 degrees on the surface of the magnetic layer will be described.
“X-ray photoelectron spectroscopic analysis” is an analytical method generally called ESCA (Electron Spectroscopic for Chemical Analysis) or XPS (X-ray Photoelectron Spectroscopy). Hereinafter, the X-ray photoelectron spectroscopic analysis is also referred to as ESCA. ESCA is an analysis method that utilizes the fact that photoelectrons are emitted when a sample surface to be measured is irradiated with X-rays, and is widely used as an analysis method for the surface layer portion of a sample to be measured. According to ESCA, qualitative analysis and quantitative analysis can be performed using an X-ray photoelectron spectrum obtained by analysis on the surface of a sample to be measured. Between the depth from the sample surface to the analysis position (hereinafter also referred to as “detection depth”) and the photo-electron take-off angle (take-off angle), in general, the following equation: detection depth≈electron average The free stroke × 3 × sin θ is established. In the formula, the detection depth is a depth at which 95% of the photoelectrons constituting the X-ray photoelectron spectrum is generated, and θ is a photoelectron extraction angle. From the above formula, it can be seen that the smaller the photoelectron take-off angle is, the smaller the depth from the sample surface can be analyzed, and the greater the photoelectron take-out angle is, the deeper the portion can be analyzed. In the analysis performed by ESCA at a photoelectron take-off angle of 10 degrees, a very surface layer portion with a depth of about several nm from the sample surface is usually the analysis position. Therefore, according to the analysis performed by ESCA on the surface of the magnetic layer of the magnetic tape with a photoelectron extraction angle of 10 degrees, it is possible to perform a composition analysis of a very surface layer portion about several nanometers deep from the surface of the magnetic layer.
The C—H-derived C concentration is the ratio of carbon atoms C constituting the C—H bond to 100 atomic% of the total (atomic basis) of all elements detected by qualitative analysis performed by ESCA. It is. The region to be analyzed is a region having an area of 300 μm × 700 μm at an arbitrary position on the surface of the magnetic layer of the magnetic tape. Qualitative analysis is performed by wide scan measurement (path energy: 160 eV, scan range: 0 to 1200 eV, energy resolution: 1 eV / step) performed by ESCA. Next, the spectra of all elements detected by qualitative analysis are obtained by narrow scan measurement (path energy: 80 eV, energy resolution: 0.1 eV, scan range: set for each element so that the entire spectrum to be measured is included). From the peak area in each spectrum thus obtained, the atomic concentration (atomic concentration, unit: atomic%) of each element is calculated. Here, the atomic concentration of carbon atoms (C concentration) is also calculated from the peak area of the C1s spectrum.
Furthermore, a C1s spectrum is acquired (path energy: 10 eV, scan range: 276 to 296 eV, energy resolution: 0.1 eV / step). The obtained C1s spectrum was subjected to fitting processing by a non-linear least square method using a Gauss-Lorentz composite function (Gauss component 70%, Lorentz component 30%), and the peak of the C—H bond in the C1s spectrum was separated into peaks. The ratio (peak area ratio) in the C1s spectrum of the C—H peak is calculated. The C—H-derived C concentration is calculated by multiplying the calculated C—H peak area ratio by the above C concentration.
The arithmetic average of the values obtained by performing the above treatment three times at different positions on the magnetic layer surface of the magnetic tape is defined as the C-H-derived C concentration. Moreover, the specific aspect of the above process is shown in the below-mentioned Example.

The present inventor infers the reason why the occurrence frequency of missing pulses in a low temperature and high humidity environment can be reduced in the magnetic tape as follows.
When information recorded on the magnetic tape is reproduced, if the magnetic layer surface is scraped by sliding between the magnetic layer surface and the head, the generated shavings may adhere to the head and become a head deposit. The present inventor has found that the cause of the occurrence of missing pulses in a low temperature and high humidity environment is that the friction coefficient during sliding between the magnetic layer surface and the head tends to increase in the low temperature and high humidity environment. It is presumed that the contact state at the time of sliding is likely to be unstable, and the cause of the unstable contact state is the occurrence of deposits on the head.
With regard to the above points, the present inventor considers that ΔN obtained by the above method is a value that can be an indicator of the presence state of the ferromagnetic powder in the surface layer region of the magnetic layer. This ΔN is assumed to be a value affected by various factors such as the presence state of the binder and the density distribution of the ferromagnetic powder in addition to the orientation state of the ferromagnetic powder in the magnetic layer. And it is considered that the magnetic layer having ΔN of 0.25 or more and 0.40 or less by controlling various factors has high strength on the surface of the magnetic layer and is not easily scraped by sliding with the head. This contributes to suppressing the occurrence of head deposits due to the surface of the magnetic layer being scraped when sliding with the head in a low-temperature and high-humidity environment, resulting in a missing pulse in a low-temperature and high-humidity environment. The present inventors infer that it will lead to a reduction in the occurrence frequency.
Furthermore, regarding the C—H-derived C concentration, the present inventors infer as follows.
The magnetic tape contains at least one component selected from the group consisting of fatty acids and fatty acid amides in at least the magnetic layer. Fatty acids and fatty acid amides are components that can each function as a lubricant in the magnetic tape. At the surface of the magnetic layer of the magnetic tape containing at least one of these components in the magnetic layer, the C—H-derived C concentration obtained by the analysis performed by ESCA at a photoelectron take-off angle of 10 degrees is the above-mentioned in the very surface layer portion of the magnetic layer. It is considered to be an indicator of the abundance of components (one or more components selected from the group consisting of fatty acids and fatty acid amides). Details are as follows.
In the X-ray photoelectron spectroscopy spectrum (horizontal axis: binding energy, vertical axis: intensity) obtained by the analysis performed by ESCA, the C1s spectrum includes information on the energy peak of the 1s orbit of carbon atom C. In such a C1s spectrum, a peak located near the binding energy of 284.6 eV is a C—H peak. This C—H peak is a peak derived from the binding energy of the C—H bond of the organic compound. In the very surface layer portion of the magnetic layer containing one or more components selected from the group consisting of fatty acids and fatty acid amides, it is presumed that the main component of the CH peak is a component selected from the group consisting of fatty acids and fatty acid amides. . Therefore, it is considered that the C—H-derived C concentration can be used as an index of the abundance of the components as described above.
And the above-mentioned C-H origin C density | concentration is a state which is 45 atomic% or more, ie, the state in which 1 or more types of the component chosen from the group which consists of a fatty acid and fatty acid amide exists in the very surface layer part of a magnetic layer in large quantities. However, the present inventor believes that it contributes to promoting smooth sliding (improving slidability) between the magnetic layer surface and the head in a low temperature and high humidity environment. If the slidability can be improved, it is considered that the head deposit can be prevented from being generated when the magnetic layer surface slides between the magnetic layer surface and the head due to damage. The present inventors speculate that this also contributes to reducing the frequency of occurrence of missing pulses in a low temperature and high humidity environment.
However, the above is an assumption and does not limit the present invention.

  Hereinafter, the magnetic tape will be described in more detail. Hereinafter, the frequency of occurrence of missing pulses in a low temperature and high humidity environment is also simply referred to as “frequency of occurrence of missing pulses”.

<Magnetic layer>
(ΔN of magnetic layer)
ΔN of the magnetic layer of the magnetic tape is 0.25 or more and 0.40 or less. As described above, it is surmised that the magnetic layer having ΔN of 0.25 or more and 0.40 or less has high strength on the surface of the magnetic layer and is difficult to be scraped by sliding with the head in a low temperature and high humidity environment. . For this reason, it is considered that the magnetic layer having ΔN in the above range is less likely to be scraped on the surface of the magnetic layer during sliding between the magnetic layer surface and the head when reproducing information recorded on the magnetic layer in a low temperature and high humidity environment. It is done. This is presumed to contribute to reducing the occurrence frequency of missing pulses in a low temperature and high humidity environment. From the viewpoint of further reducing the occurrence frequency of missing pulses, ΔN is preferably 0.25 or more and 0.35 or less. A specific mode of means for adjusting ΔN will be described later.

  ΔN is the absolute value of the difference between Nxy and Nz. Nxy is a refractive index measured in the in-plane direction of the magnetic layer, and Nz is a refractive index measured in the thickness direction of the magnetic layer. In one aspect, Nxy> Nz can be satisfied, and in another aspect, Nxy <Nz can be satisfied. From the viewpoint of the electromagnetic conversion characteristics of the magnetic tape, it is preferable that Nxy> Nz. Therefore, the difference between Nxy and Nz (Nxy−Nz) is preferably 0.25 or more and 0.40 or less, and 0.25. More preferably, it is 0.35 or less.

  Various means for adjusting ΔN described above will be described later.

(C-H-derived C concentration)
The C—H-derived C concentration of the magnetic tape is 45 atomic% or more from the viewpoint of reducing the frequency of occurrence of missing pulses in a low temperature and high humidity environment. From the viewpoint of further reducing the frequency of occurrence of missing pulses, the C—H-derived C concentration is preferably 48 atomic% or more, and more preferably 50 atomic% or more. Further, according to the study of the present inventors, from the viewpoint of easy formation of a magnetic layer having high surface smoothness, the C—H-derived C concentration is, for example, 95 atomic% or less, 90 atomic% or less, 85 atomic% or less, It is preferable that they are 80 atomic% or less, 75 atomic% or less, 70 atomic% or less, or 65 atomic% or less.

  As a preferable means for adjusting the C—H-derived C concentration described above, a cooling step can be performed in the nonmagnetic layer forming step as will be described in detail later. However, the magnetic tape is not limited to those manufactured through the cooling process.

(Ferromagnetic powder)
As the ferromagnetic powder contained in the magnetic layer, a ferromagnetic powder usually used in the magnetic layer of various magnetic recording media can be used. It is preferable to use a ferromagnetic powder having a small average particle size from the viewpoint of improving the recording density of the magnetic recording medium. From this point, it is preferable to use a ferromagnetic powder having an average particle size of 50 nm or less as the ferromagnetic powder. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, and more preferably 10 nm or more.

  Preferable specific examples of the ferromagnetic powder include ferromagnetic hexagonal ferrite powder. The ferromagnetic hexagonal ferrite powder can be a ferromagnetic hexagonal barium ferrite powder, a ferromagnetic hexagonal strontium ferrite powder, or the like. The average particle size of the ferromagnetic hexagonal ferrite powder is preferably 10 nm or more and 50 nm or less, and more preferably 20 nm or more and 50 nm or less, from the viewpoint of improvement in recording density and magnetization stability. Details of the ferromagnetic hexagonal ferrite powder include, for example, paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, and paragraph 0013 of JP2012-204726A. ˜0030 can be referred to.

  Preferable specific examples of the ferromagnetic powder include a ferromagnetic metal powder. The average particle size of the ferromagnetic metal powder is preferably 10 nm or more and 50 nm or less, and more preferably 20 nm or more and 50 nm or less, from the viewpoint of improvement in recording density and magnetization stability. For details of the ferromagnetic metal powder, reference can be made to, for example, paragraphs 0137 to 0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A.

  Preferable specific examples of the ferromagnetic powder include ε-iron oxide powder. 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 production methods are known. For a method for producing ε-iron oxide powder in which a part of Fe is substituted by a substitution atom such as Ga, Co, Ti, Al, Rh, etc., see, for example, J. Org. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. 61; S1, pp. S280-S284, J.M. Mater. Chem. C, 2013, 1, pp. Reference may be made to 5200-5206. However, the manufacturing method of the ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer is not limited.

In the present invention and the present specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powders is a value measured by the following method using a transmission electron microscope.
The powder is photographed at a photographing magnification of 100,000 using a transmission electron microscope, and printed on photographic paper so that the total magnification is 500,000 times to obtain a photograph of particles constituting the powder. The target particle is selected from the photograph of the obtained particle, the outline of the particle is traced with a digitizer, and the size of the particle (primary particle) is measured. Primary particles refer to independent particles without agglomeration.
The above measurements are performed on 500 randomly extracted particles. The arithmetic average 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 transmission electron microscope H-9000 type can be used. The particle size can be measured using known image analysis software, for example, image analysis software KS-400 manufactured by Carl Zeiss. Unless otherwise specified, values relating to the size of the powder, such as average particle size, shown in the examples described later are as follows: Hitachi transmission electron microscope H-9000 type as a transmission electron microscope, and Carl Zeiss image analysis software KS- as image analysis software. This is a value measured using 400.

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

In the present invention and the present 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 photograph,
(1) In the case of needle shape, spindle shape, columnar shape (however, the height is larger than the maximum major axis of the bottom surface), it is represented by the length of the major axis constituting the particle, that is, the major axis length,
(2) In the case of plate shape or columnar shape (thickness or height is smaller than the maximum major axis of the plate surface or bottom surface), it is represented by the maximum major axis of the plate surface or bottom surface,
(3) In the case of a spherical shape, a polyhedral shape, an unspecified shape, etc., and the major axis constituting the particle cannot be specified from the shape, it is represented by an equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.

The average acicular ratio of the powder is determined by measuring the length of the minor axis of the particle, that is, the minor axis length in the above measurement, and obtaining the value of (major axis length / minor axis length) of each particle. Refers to the arithmetic average of the values obtained for the particles. Here, unless otherwise specified, the minor axis length is the definition of the particle size in the case of (1), the length of the minor axis constituting the particle, and in the case of (2), the thickness or height. 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.
Unless otherwise specified, when the shape of the particle is specific, for example, in the case of definition (1) of the particle size, the average particle size is the average major axis length, and in the case of definition (2), the average particle size is Average plate diameter. In the case of the same definition (3), the average particle size is an average diameter (also referred to as an average particle diameter or an average particle diameter).

  In one embodiment, the shape of the ferromagnetic particles constituting the ferromagnetic powder contained in the magnetic layer can be a plate shape. Hereinafter, a ferromagnetic powder composed of plate-like ferromagnetic particles is referred to as a plate-like ferromagnetic powder. The average plate ratio of the plate-like ferromagnetic powder can preferably be in the range of 2.5 to 5.0. The average plate ratio is an arithmetic average of (maximum major axis / thickness or height) in the case of the above definition (2). As the average plate ratio is larger, the orientation treatment tends to increase the uniformity of the orientation state of the ferromagnetic particles constituting the plate-like ferromagnetic powder, and the value of ΔN tends to increase.

In addition, an activated volume can be used as an index of the particle size of the ferromagnetic powder. “Activation volume” is a unit of magnetization reversal. The activation volume described in the present invention and this specification is measured in an environment having an ambient temperature of 23 ° C. ± 1 ° C. using a vibrating sample magnetometer at a magnetic field sweep rate of 3 minutes and 30 minutes of the coercive force Hc measurement unit. And a value obtained from the following relational expression between Hc and activation volume V. The activation volume shown in the examples described later is a value obtained by performing measurement using a vibrating sample magnetometer manufactured by Toei Kogyo Co., Ltd.
Hc = 2Ku / Ms {1-[(kT / KuV) ln (At / 0.693)] ^1/2 }
[In the above formula, Ku: anisotropy constant, Ms: saturation magnetization, k: Boltzmann constant, T: absolute temperature, V: activation volume, A: spin precession frequency, t: magnetic field inversion time]
From the viewpoint of recording density, the activation volume of the ferromagnetic powder is preferably 2500 nm ³ or less, more preferably 2300 nm ³ or less, and further preferably 2000 nm ³ or less. On the other hand, from the viewpoint of magnetization stability, the activation volume of the ferromagnetic powder is preferably, for example, 800 nm ³ or more, more preferably 1000 nm ³ or more, and further preferably 1200 nm ³ or more.

  The content (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. Components other than the ferromagnetic powder of the magnetic layer are at least one or more components selected from the group consisting of fatty acids and fatty acid amides and binders, and may optionally include one or more additional additives. A high filling rate of the ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving the recording density.

(Binder, curing agent)
The magnetic tape is a coating type magnetic tape and includes a binder in the magnetic layer. A binder is one or more resins. The resin may be a homopolymer or a copolymer. As binders contained in the magnetic layer, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, styrene, acrylonitrile, acrylic resin copolymerized with methyl methacrylate, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, Those selected from polyvinyl alkylal resins such as polyvinyl acetal and polyvinyl butyral can be used alone, or a plurality of resins can be mixed and used. Among these, preferred are polyurethane resin, acrylic resin, cellulose resin and vinyl chloride resin. These resins can also be used as a binder in the nonmagnetic layer and / or backcoat layer described below. As for the above binder, paragraphs 0029 to 0031 of JP2010-24113A can be referred to. The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less as the weight average molecular weight. The weight average molecular weight in the present invention and the present specification is a value obtained by converting a value measured by gel permeation chromatography (GPC) into polystyrene. The following conditions can be mentioned as measurement conditions. The weight average molecular weight shown in the Examples described later is a value obtained by converting a value measured under the following measurement conditions into polystyrene.
GPC device: HLC-8120 (manufactured by Tosoh Corporation)
Column: TSK gel Multipore HXL-M (Tosoh Corporation, 7.8 mm ID (Inner Diameter) × 30.0 cm)
Eluent: Tetrahydrofuran (THF)

In one embodiment, a binder containing an acidic group can be used as the binder. The term “acidic group” in the present invention and the present specification is intended to include a group capable of releasing H ⁺ in water or a solvent containing water (aqueous solvent) to dissociate into an anion and a salt form thereof. . Specific examples of the acidic group include a sulfonic acid group, a sulfuric acid group, a carboxy group, a phosphoric acid group, and a salt form thereof. For example, the salt form of a sulfonic acid group (—SO ₃ H) is a group represented by —SO ₃ M, in which M represents an atom (for example, an alkali metal atom) that can be a cation in water or an aqueous solvent. means. This also applies to the salt forms of the various groups described above. As an example of the binder containing an acidic group, for example, a resin containing at least one acidic group selected from the group consisting of a sulfonic acid group and a salt thereof (for example, polyurethane resin, vinyl chloride resin, etc.) can be mentioned. However, the resin contained in the magnetic layer is not limited to these resins. Moreover, in the binder containing an acidic group, the amount of acidic groups can be in the range of 20 to 500 eq / ton, for example. In addition, eq is an equivalent and is a unit that cannot be converted into SI units. Content of various functional groups, such as an acidic group contained in resin, can be calculated | required by a well-known method according to the kind of functional group. As the binder having a larger amount of acidic groups is used, the value of ΔN tends to increase. The binder can be used in the magnetic layer forming composition in an amount of, for example, 1.0 to 30.0 parts by mass, preferably 1.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder. It can be used in an amount of 20.0 parts by weight. The value of ΔN tends to increase as the amount of binder used for the ferromagnetic powder increases.

  Moreover, a hardening | curing agent can also be used with resin which can be used as a binder. In one aspect, the curing agent can be a thermosetting compound that is a compound that undergoes a curing reaction (crosslinking reaction) by heating, and in another aspect, photocuring in which a curing reaction (crosslinking reaction) proceeds by light irradiation. It can be a sex compound. The curing agent may be included in the magnetic layer in a state of being reacted (crosslinked) with other components such as a binder as the curing reaction proceeds in the magnetic layer forming step. This applies to the layer formed using this composition when the composition used to form the other layer contains a curing agent. A preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. JP, 2011-216149, A paragraphs 0124-0125 can be referred to for the details of polyisocyanate. The curing agent is, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder in the composition for forming a magnetic layer, and preferably 50.0 to 80.0 from the viewpoint of improving the strength of the magnetic layer. It can be used in an amount of parts by mass.

(Fatty acid, fatty acid amide)
The magnetic tape contains at least one component selected from the group consisting of fatty acids and fatty acid amides in at least the magnetic layer. The magnetic layer may contain only one of fatty acid and fatty acid amide, or may contain both. The presence of these components in the very surface layer of the magnetic layer in an amount such that the C—H-derived C concentration is 45 atomic% or more contributes to reducing the frequency of occurrence of missing pulses in a low temperature and high humidity environment. The inventor thinks. In the magnetic tape having a nonmagnetic layer, the details of which will be described later, between the nonmagnetic support and the magnetic layer, one or more components selected from the group consisting of fatty acids and fatty acid amides are contained in the nonmagnetic layer. Also good. The nonmagnetic layer can serve to hold a lubricant such as fatty acid and fatty acid amide and supply it to the magnetic layer. Lubricants such as fatty acids and fatty acid amides contained in the nonmagnetic layer may migrate to the magnetic layer and be present in the magnetic layer.

Examples of fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, elaidic acid, and the like. Stearic acid, myristic acid, palmitic 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 amides include the amides of the above-mentioned various fatty acids, and specific examples include lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, and the like.
For fatty acids and fatty acid derivatives (amides and esters described below), the fatty acid-derived site of the fatty acid derivative preferably has the same or similar structure as the fatty acid used in combination. For example, as an example, when stearic acid is used as the fatty acid, it is preferable to use stearic acid amide and / or stearic acid ester in combination.

  The fatty acid content is, for example, 0.1 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the ferromagnetic powder, as the content in the composition for forming a magnetic layer. It is. When two or more different fatty acids are added to the magnetic layer forming composition, the content refers to the total content of the two or more different fatty acids. This is the same for the other components. In the present invention and the present specification, unless otherwise specified, a certain component may be used alone or in combination of two or more.

  The fatty acid amide content in the composition for forming a magnetic layer is, for example, 0.1 to 3.0 parts by mass, preferably 0.1 to 1.0 parts by mass, per 100.0 parts by mass of the ferromagnetic powder. .

  On the other hand, the fatty acid content in the composition for forming a nonmagnetic layer is, for example, 1.0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the nonmagnetic powder. It is. The fatty acid amide content in the composition for forming a nonmagnetic layer is, for example, 0.1 to 3.0 parts by weight, preferably 0.1 to 1.0 parts by weight, per 100.0 parts by weight of the nonmagnetic powder. Part.

(Additive)
The magnetic layer contains the various components described above, and may contain one or more additives as necessary. Examples of the additive include the above-described curing agent. Examples of the additive contained in the magnetic layer include non-magnetic powders (for example, inorganic powder, carbon black, etc.), lubricants, dispersants, dispersion aids, antifungal agents, antistatic agents, antioxidants, and the like. Can do. Further, as the non-magnetic powder, non-magnetic powder that can function as an abrasive, non-magnetic powder that can function as a protrusion-forming agent that forms protrusions that protrude moderately on the surface of the magnetic layer (for example, non-magnetic colloid particles) Etc.). In addition, the average particle size of colloidal silica (silica colloidal particles) shown in Examples described later is a value obtained by the method described in paragraph 0015 of JP2011-048878A as an average particle size measurement method. . As the additive, a commercially available product can be appropriately selected according to the desired properties, or it can be produced by a known method and used in any amount. As an example of an additive that can be used in a magnetic layer containing an abrasive, the dispersant described in paragraphs 0012 to 0022 of JP2013-131285A is exemplified as a dispersant for improving the dispersibility of the abrasive. be able to. For example, as for the lubricant, reference can be made to paragraphs 0030 to 0033, 0035 and 0036 of JP-A-2006-126817. A lubricant may be contained in the nonmagnetic layer. Regarding the lubricant that can be contained in the nonmagnetic layer, reference can be made to paragraphs 0030, 0031, 0034, 0035 and 0036 of JP-A-2006-126817. As for the dispersant, reference can be made to paragraphs 0061 and 0071 of JP2012-133737A. The dispersant may be contained in the nonmagnetic layer. Regarding the dispersant that can be contained in the nonmagnetic layer, reference can be made to paragraph 0061 of JP2012-133737A.

In addition, one or both of the magnetic layer and the nonmagnetic layer whose details will be described later may or may not contain a fatty acid ester.
Fatty acid esters, fatty acids, and fatty acid amides are all components that can function as a lubricant. Lubricants are generally roughly classified into fluid lubricants and boundary lubricants. Fatty acid esters are said to be components that can function as fluid lubricants, whereas fatty acids and fatty acid amides are said to be components that can function as boundary lubricants. The boundary lubricant is considered to be a lubricant that can reduce the contact friction by adsorbing to the surface of a powder (for example, ferromagnetic powder) to form a strong lubricant film. On the other hand, the fluid lubricant is considered to be a lubricant that itself forms a liquid film on the surface of the magnetic layer and can reduce friction by the flow of the liquid film. Thus, it is considered that the fatty acid ester is different in the action as a lubricant from the fatty acid and the fatty acid amide. And this inventor makes the C-H origin C density | concentration considered to be a parameter | index of 1 or more types of a component selected from the group which consists of a fatty acid and fatty acid amide in the very surface layer part of a magnetic layer to 45 atomic% or more. It is speculated that it contributes to reducing the frequency of missing pulses in a low temperature and high humidity environment.

  Examples of the fatty acid ester include esters of the above-mentioned various fatty acids exemplified for the fatty acid. Specific examples include, for example, butyl myristate, butyl palmitate, butyl stearate (butyl stearate), neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tristearate, oleyl oleate, Examples include isocetyl stearate, isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate, butoxyethyl stearate, and the like.

The fatty acid ester content is, for example, 0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the ferromagnetic powder, as the content in the composition for forming a magnetic layer. is there.
The fatty acid ester content in the composition for forming a nonmagnetic layer is, for example, 0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the nonmagnetic powder. is there.

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

<Nonmagnetic layer>
Next, the nonmagnetic layer will be described.
The magnetic tape may have a magnetic layer directly on the surface of the nonmagnetic support, and a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. Also good. The nonmagnetic powder contained in the nonmagnetic layer may be an inorganic powder or an organic powder. Carbon black or the like can also be used. Examples of the inorganic powder include powders of metal, metal oxide, metal carbonate, metal sulfate, metal nitride, metal carbide, metal sulfide, and the like. These nonmagnetic powders are available as commercial products, and can also be produced by a known method. Details thereof can be referred to paragraphs 0036 to 0039 of JP 2010-24113 A. The content (filling rate) of the nonmagnetic powder in the nonmagnetic layer is preferably in the range of 50 to 90 mass%, more preferably in the range of 60 to 90 mass%.

  For other details such as binders and additives for the nonmagnetic layer, known techniques relating to the nonmagnetic layer can be applied. Further, for example, with respect to the type and content of the binder, the type and content of the additive, etc., known techniques relating to the magnetic layer can also be applied.

  The nonmagnetic layer of the present invention and the present specification shall include a substantially nonmagnetic layer containing a small amount of ferromagnetic powder together with the nonmagnetic powder, for example, as an impurity or intentionally. Here, the substantially non-magnetic layer means that the residual magnetic flux density of this layer is 10 mT or less, the coercive force is 7.96 kA / m (100 Oe) or less, or the residual magnetic flux density is 10 mT or less. And a layer having a coercive force of 7.96 kA / m (100 Oe) or less. The nonmagnetic layer preferably has no residual magnetic flux density and no coercive force.

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

<Back coat layer>
The magnetic tape may have a backcoat layer containing a nonmagnetic powder and a binder on the surface side opposite to the surface side having the magnetic layer of the nonmagnetic support. The back coat layer preferably contains one or both of carbon black and inorganic powder. Regarding the binder contained in the backcoat layer and various additives that can optionally be contained, a known technique relating to the backcoat layer can be applied, and a known technique relating to the formulation of the magnetic layer and / or the nonmagnetic layer should be applied. You can also. For example, the description in paragraphs 0018 to 0020 of JP-A-2006-331625 and the description in column 4, line 65 to column 5, line 38 of US Pat. No. 7,029,774 can be referred to for the backcoat layer. .

<Various thicknesses>
The nonmagnetic support and the thickness of each layer in the magnetic tape will be described below.
The thickness of the nonmagnetic support is, for example, 3.0 to 80.0 μm, preferably 3.0 to 50.0 μm, and more preferably 3.0 to 10.0 μm.

  The thickness of the magnetic layer can be optimized according to the saturation magnetization of the magnetic head used, the head gap length, the band of the recording signal, and the like. The thickness of the magnetic layer is generally 10 nm to 100 nm, preferably 20 to 90 nm, more preferably 30 to 70 nm from the viewpoint of high density recording. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied. The thickness of the magnetic layer when separating into two or more layers is the total thickness of these layers.

  The thickness of the nonmagnetic layer is, for example, 0.1 to 1.5 μm, and preferably 0.1 to 1.0 μm.

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

  The thickness of each layer and the non-magnetic support is determined by exposing a cross section in the thickness direction of the magnetic tape by a known method such as ion beam or microtome, and then using a scanning transmission electron microscope (STEM) in the exposed cross section. ) By cross-sectional observation. For specific examples of the method for measuring the thickness, the description regarding the method for measuring the thickness in Examples described later can be referred to.

<Manufacturing process>
(Preparation of each layer forming composition)
The step of preparing a composition for forming a magnetic layer, a nonmagnetic layer, or a backcoat layer usually includes at least a kneading step, a dispersing step, and a mixing step provided before and after these steps. Each process may be divided into two or more stages. The components used for the preparation of each layer forming composition may be added at the beginning or during any step. As the solvent, one kind or two or more kinds of various solvents usually used for the production of a coating type magnetic recording medium can be used. Regarding the solvent, for example, paragraph 0153 of JP2011-216149A can be referred to. Individual components may be divided and added in two or more steps. For example, the binder may be divided and added in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion. In order to manufacture the magnetic tape, conventional known manufacturing techniques can be used in various steps. In the kneading step, it is preferable to use a material having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. JP-A-1-106338 and JP-A-1-79274 can be referred to for details of these kneading treatments. A well-known thing can be used for a disperser. Further, the ferromagnetic powder and the abrasive can be separately dispersed. More specifically, the different dispersion means a step of mixing an abrasive liquid containing an abrasive and a solvent (substantially free of ferromagnetic powder) with a magnetic liquid containing ferromagnetic powder, a solvent and a binder. This is a method for preparing a composition for forming a magnetic layer. The phrase “substantially free of ferromagnetic powder” means that no ferromagnetic powder is added as a constituent of the abrasive liquid, and a trace amount of ferromagnetic powder is added as an unintentionally mixed impurity. It is allowed to exist. Regarding ΔN, the value of ΔN tends to increase as the dispersion time of the magnetic liquid is increased. The longer the dispersion time of the magnetic liquid, the higher the dispersion of the ferromagnetic powder in the coating layer of the composition for forming the magnetic layer, and the uniformity of the orientation state of the ferromagnetic particles constituting the ferromagnetic powder by the orientation treatment. This is considered to be due to a tendency to increase. In addition, the value of ΔN tends to increase as the dispersion time for mixing and dispersing the various components of the composition for forming a nonmagnetic layer increases. The dispersion time of the magnetic liquid and the dispersion time of the composition for forming a nonmagnetic layer may be set so that ΔN of 0.25 or more and 0.40 or less can be realized.
In any stage of preparing each layer forming composition, filtration may be performed by a known method. Filtration can be performed by, for example, filter filtration. As a filter used for filtration, for example, a filter having a pore diameter of 0.01 to 3 μm (for example, a glass fiber filter, a polypropylene filter, or the like) can be used.

(Coating process)
The nonmagnetic layer and the magnetic layer can be formed by sequentially or simultaneously coating the nonmagnetic layer forming composition and the magnetic layer forming composition. The back coat layer has a composition for forming the back coat layer on the surface opposite to the surface having the nonmagnetic layer and the magnetic layer of the nonmagnetic support (or the nonmagnetic layer and / or the magnetic layer are provided later). It can be formed by coating. Moreover, the coating process for forming each layer can also be divided into two or more steps. For example, in one embodiment, the magnetic layer forming composition can be applied in two or more steps. In this case, the drying process may or may not be performed between the two stages of the coating process. Further, the alignment treatment may or may not be performed between the two stages of the coating process. For details of the coating for forming each layer, reference can also be made to paragraph 0066 of JP2010-231843A. Moreover, a well-known technique can be applied about the drying process after apply | coating each composition for layer formation. With regard to the magnetic layer forming composition, a coating layer formed by applying the magnetic layer forming composition (hereinafter also referred to as “coating layer of the magnetic layer forming composition” or simply “coating layer”). The value of ΔN tends to increase as the drying temperature is lowered. The drying temperature can be, for example, the atmospheric temperature at which the drying process is performed, and may be set so that ΔN of 0.25 or more and 0.40 or less can be realized.

(Other processes)
Known techniques can be applied to other various processes for manufacturing the magnetic tape. For various steps, reference can be made, for example, to paragraphs 0067 to 0070 of JP-A-2010-231843.
For example, the coating layer of the magnetic layer forming composition is preferably subjected to an orientation treatment while the coating layer is in a wet state. From the viewpoint of ease of realizing ΔN of 0.25 or more and 0.40 or less, the orientation treatment is performed by arranging a magnet so that a magnetic field is applied perpendicularly to the surface of the coating layer of the magnetic layer forming composition. (That is, vertical alignment treatment) is preferable. What is necessary is just to set the intensity | strength of the magnetic field at the time of an orientation process so that (DELTA) N of 0.25 or more and 0.40 or less is realizable. Moreover, when performing the application | coating process of the composition for magnetic layer formation by a 2 or more steps application process, it is preferable to perform an orientation process at least after the last application process, and it is more preferable to perform a vertical orientation process. For example, when a magnetic layer is formed by a two-step coating process, a drying process is performed without performing an orientation process after the first-stage coating process, and then the coating layer formed in the second-stage coating process is applied. Orientation treatment can be performed.
Moreover, it is preferable to perform a calendar process in the arbitrary steps after drying the application layer of the composition for magnetic layer formation. Regarding the conditions for the calendar processing, reference can be made to paragraph 0026 of JP 2010-231843 A, for example. As the calendar temperature (the surface temperature of the calendar roll) is increased, the value of ΔN tends to increase. The calendar temperature may be set so that ΔN of 0.25 or more and 0.40 or less can be realized.

(One aspect of preferred production method)
As described above, in one embodiment, the magnetic tape has a nonmagnetic layer between the nonmagnetic support and the magnetic layer. Such a magnetic tape can be preferably manufactured by sequential multilayer coating. The manufacturing process for performing sequential multilayer coating can be preferably carried out as follows. The nonmagnetic layer is formed through a coating process for forming a coating layer by coating a composition for forming a nonmagnetic layer on a nonmagnetic support, and a heat drying process for drying the formed coating layer by heat treatment. Then, the magnetic layer is formed through an application step of forming a coating layer by applying a composition for forming a magnetic layer on the formed nonmagnetic layer, and a heating and drying step of drying the formed coating layer by heat treatment.

  In the nonmagnetic layer forming step of the production method for performing such sequential multilayer coating, the coating step is performed using a nonmagnetic layer forming composition containing one or more components selected from the group consisting of fatty acids and fatty acid amides, and the coating step The cooling step of cooling the coating layer between the step of heating and drying is performed in a magnetic recording medium containing at least one component selected from the group consisting of fatty acids and fatty acid amides in a magnetic layer, derived from C—H. It is preferable for adjusting the C concentration to 45 atomic% or more. Although the reason for this is not clear, by cooling the coating layer of the composition for forming a nonmagnetic layer before the heat drying step, the above components (fatty acid and / or fatty acid amide) are reduced when the solvent volatilizes in the heat drying step. It is presumed that it is likely to move to the surface of the magnetic layer. However, this is merely a guess and does not limit the present invention.

  Further, in the magnetic layer forming step, the coating layer is formed by coating a composition for forming a magnetic layer containing a ferromagnetic powder, a binder, a component selected from the group consisting of a fatty acid and a fatty acid amide, and a solvent on the nonmagnetic layer. It is possible to perform a heating and drying process in which a coating process to be formed is performed and the formed coating layer is dried by heat treatment. The magnetic tape contains one or more components selected from the group consisting of fatty acids and fatty acid amides in the magnetic layer. When the magnetic tape has a nonmagnetic layer between the nonmagnetic support and the magnetic layer, the magnetic layer forming composition is a component selected from the group consisting of fatty acids and fatty acid amides in order to produce such a magnetic tape. It is preferable that one or more of these are included. However, it is not essential that the magnetic layer forming composition contains one or more components selected from the group consisting of fatty acids and fatty acid amides. After these components contained in the composition for forming a nonmagnetic layer have migrated to the surface of the nonmagnetic layer, the composition for forming a magnetic layer is applied onto the nonmagnetic layer to form a magnetic layer. This is because it is considered that a magnetic layer containing at least one component selected from the group consisting of fatty acid amides can be formed.

  Hereinafter, a specific aspect of the method for producing the magnetic tape will be described with reference to FIG. However, the present invention is not limited to the following specific embodiments.

  FIG. 1 is a process schematic diagram showing a specific embodiment of a process for producing a magnetic tape having a nonmagnetic layer and a magnetic layer in this order on one side of a nonmagnetic support and a backcoat layer on the other side. It is. In the embodiment shown in FIG. 1, the operation of continuously winding the nonmagnetic support (long film) from the sending-out part at the sending-out winding part is performed, and coating is performed in each part or each zone shown in FIG. 1. By performing various treatments such as drying and orientation, a nonmagnetic layer and a magnetic layer can be successively formed on one surface of a traveling nonmagnetic support by multilayer coating, and a backcoat layer can be formed on the other surface. it can. The embodiment shown in FIG. 1 can be the same as the manufacturing process normally performed for manufacturing a coating type magnetic tape except that it includes a cooling zone.

  On the nonmagnetic support sent out from the delivery part, the nonmagnetic layer forming composition is applied in the first application part (application process of the nonmagnetic layer forming composition).

  After the coating step, the coating layer of the nonmagnetic layer forming composition formed in the coating step is cooled in the cooling zone (cooling step). For example, the cooling step can be performed by passing a nonmagnetic support on which the coating layer is formed in a cooling atmosphere. The atmospheric temperature of the cooling atmosphere can be preferably in the range of −10 ° C. to 0 ° C., more preferably in the range of −5 ° C. to 0 ° C. The time for performing the cooling step (for example, the time from when an arbitrary part of the coating layer is carried into the cooling zone until it is carried out (hereinafter also referred to as “stay time”)) is not particularly limited. Since the C-H-derived C concentration tends to increase as the length increases, it is preferable to adjust by performing preliminary experiments as necessary so that a C-H-derived C concentration of 45 atomic% or more can be realized. In the cooling step, the cooled gas may be sprayed onto the coating layer surface.

  After the cooling zone, in the first heat treatment zone, the coating layer after the cooling step is heated to dry the coating layer (heat drying step). The heat drying treatment can be performed by passing a nonmagnetic support having a coating layer after the cooling step into a heated atmosphere. The atmospheric temperature of the heating atmosphere here is, for example, about 40 to 140 ° C. However, the temperature may be a temperature at which the solvent can be volatilized and the coating layer can be dried, and is not limited to the atmospheric temperature in the above range. Moreover, you may spray the heated gas on the coating layer surface arbitrarily. The same applies to the heat drying step in the second heat treatment zone and the heat drying step in the third heat treatment zone described later.

  Next, in the second application part, the magnetic layer forming composition is applied onto the nonmagnetic layer formed by performing the heat drying step in the first heat treatment zone (of the magnetic layer forming composition). Application process).

  Thereafter, in the embodiment in which the orientation treatment is performed, the orientation treatment of the ferromagnetic powder in the coating layer is performed in the orientation zone while the coating layer of the magnetic layer forming composition is in a wet state. Regarding the orientation treatment, the above description can also be referred to.

  The coating layer after the orientation treatment is subjected to a heat drying step in the second heat treatment zone.

  Next, in the third application part, the composition for forming the backcoat layer is applied to the surface of the nonmagnetic support opposite to the surface on which the nonmagnetic layer and the magnetic layer are formed to form a coating layer. (Application | coating process of the composition for backcoat layer formation). Thereafter, in the third heat treatment zone, the coating layer is heat treated and dried.

  Through the above steps, a magnetic tape having a nonmagnetic layer and a magnetic layer in this order on one surface of the nonmagnetic support and a backcoat layer on the other surface can be obtained.

  Through the above, a magnetic tape according to one embodiment of the present invention can be obtained. However, the above-mentioned production method is an exemplification, and those values can be controlled within the above ranges by any means capable of adjusting the ΔN and C—H-derived C concentrations, and such an embodiment is also included in the present invention. Is included. The magnetic tape is usually accommodated in a magnetic tape cartridge, and the magnetic tape cartridge is attached to the magnetic recording / reproducing apparatus. When reproducing information recorded on a magnetic tape in a magnetic recording / reproducing apparatus in a low-temperature and high-humidity environment, the occurrence frequency of missing pulses can be reduced with the magnetic tape according to one embodiment of the present invention.

  In the magnetic tape manufactured as described above, a servo pattern can be formed by a known method in order to enable tracking control of the magnetic head in the magnetic recording / reproducing apparatus, control of the traveling speed of the magnetic tape, and the like. . “Servo pattern formation” can also be referred to as “servo signal recording”. Hereinafter, the formation of the servo pattern will be described.

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

  As shown in ECMA (European Computer Manufacturers Association) -319, a magnetic tape (generally referred to as “LTO tape”) compliant with the LTO (Linear Tape-Open) standard employs a timing-based servo system. In this timing-based servo system, the servo pattern is configured by continuously arranging a plurality of non-parallel pairs of magnetic stripes (also referred to as “servo stripes”) in the longitudinal direction of the magnetic tape. As described above, the reason why the servo pattern is composed of a pair of non-parallel magnetic stripes is to teach the servo signal reading element passing over the servo pattern the passing position. Specifically, the pair of magnetic stripes is formed so that the interval thereof continuously changes along the width direction of the magnetic tape, and the servo signal reading element reads the interval to thereby generate a servo pattern. And the relative position of the servo signal reading element. This relative position information enables tracking of the data track. Therefore, a plurality of servo tracks are usually set on the servo pattern along the width direction of the magnetic tape.

  The servo band is composed of servo signals continuous in the longitudinal direction of the magnetic tape. A plurality of servo bands are usually provided on the magnetic tape. For example, in an 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, and each data track corresponds to each servo track.

  In one aspect, as shown in Japanese Patent Application Laid-Open No. 2004-318983, each servo band includes information indicating a servo band number ("servo band ID (identification)" or "UDIM (Unique DataBand Identification)". (Method) Information ") is embedded. The servo band ID is recorded by shifting a specific one of a plurality of servo stripes in the servo band so that the position thereof is relatively displaced in the longitudinal direction of the magnetic tape. Specifically, the shifting method of a specific one of a plurality of servo stripes is changed for each servo band. Thus, since the recorded servo band ID is unique for each servo band, the servo band can be uniquely specified only by reading one servo band with the servo signal reading element.

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

  Also, as shown in ECMA-319, 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 the pair of servo stripes in the longitudinal direction of the magnetic tape, as with the UDIM information. However, unlike UDIM information, in this LPOS information, the same signal is recorded in each servo band.

Other information different from the above UDIM information and LPOS information can be embedded in the servo band. In this case, the information to be embedded may be different for each servo band like UDIM information, or may be common to all servo bands like LPOS information.
In addition, as a method for embedding information in the servo band, methods other than those described above can be adopted. For example, a predetermined code may be recorded by thinning out a predetermined pair from a pair of 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 by the number of servo bands. Usually, a core and a coil are connected to each pair of gaps, and a magnetic field generated in the core can generate a leakage magnetic field in the pair of gaps by supplying a current pulse to the coils. When forming a servo pattern, by inputting a current pulse while running the magnetic tape on the servo write head, the magnetic pattern corresponding to the pair of gaps is transferred to the magnetic tape to form the servo pattern. Can do. 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 1 μm or less, 1 to 10 μm, 10 μm or more, for example.

  Before the servo pattern is formed on the magnetic tape, the magnetic tape is usually subjected to a demagnetization (erase) process. 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 process includes a DC (Direct Current) erase and an 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. On the other hand, DC erase is performed by applying a unidirectional magnetic field to the magnetic tape. There are two additional methods for DC erase. The first method is a horizontal DC erase that applies a magnetic field in one direction along the longitudinal direction of the magnetic tape. The second method is vertical DC erase, which applies a magnetic field in one direction along the thickness direction of the magnetic tape. The erase process may be performed on the entire magnetic tape or may be performed for each servo band of the magnetic tape.

  The direction of the magnetic field of the servo pattern to be formed is determined according to the direction of the erase. For example, when the horizontal DC erase is applied to the magnetic tape, the servo pattern is formed so 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 using the gap is transferred to a magnetic tape that has been vertically DC erased, the formed servo pattern is read and obtained. The servo signal has a monopolar pulse shape. On the other hand, when a magnetic pattern using the gap is transferred to a magnetic tape subjected to horizontal DC erase, a servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

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

  In the present invention and the present specification, the “magnetic recording / reproducing apparatus” means an apparatus capable of performing at least one of recording information on the magnetic tape and reproducing information recorded on the magnetic tape. Such a device is generally called a drive. The magnetic head included in the magnetic recording / reproducing apparatus can be a recording head capable of recording information on a magnetic tape, and is a reproducing head capable of reproducing information recorded on the magnetic tape. You can also. In one embodiment, 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 apparatus 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 capable of reading information recorded on the magnetic tape with high sensitivity is preferable. Various known MR heads can be used as the MR head. The magnetic head for recording information and / or reproducing information may include a servo pattern reading element. Alternatively, a magnetic head (servo head) including a servo pattern reading element may be included in the magnetic recording / reproducing apparatus as a head different from the magnetic head that records information and / or reproduces information.

  In the magnetic recording / reproducing apparatus, recording of information on the magnetic tape and reproduction of information recorded on the magnetic tape can be performed by sliding the magnetic layer surface of the magnetic tape and the magnetic head in contact with each other. The magnetic recording / reproducing apparatus only needs to include the magnetic tape according to one embodiment of the present invention, and publicly known techniques can be applied to the others.

  The magnetic recording / reproducing apparatus includes a magnetic tape according to one embodiment of the present invention. Therefore, when reproducing information recorded on the magnetic tape in a low temperature and high humidity environment, the frequency of occurrence of missing pulses can be reduced. In addition, even when the magnetic layer surface and the head slide for recording information on the magnetic tape in a low temperature and high humidity environment, the magnetic layer surface and the head are caused by head deposits resulting from the abrasion of the magnetic layer surface. It is also possible to suppress the unstable contact state with.

  Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiment shown in the examples. The “parts” and “%” described below are based on mass.

[Example 1]
<Preparation of abrasive liquid>
2,3-dihydroxynaphthalene (Tokyo Kasei Co., Ltd.) with respect to 100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) having an alpha conversion rate of about 65% and a BET (Brunauer-Emmett-Teller) specific surface area of 20 m ² / g 3.0 parts of SO ₃ Na group-containing polyester polyurethane resin (Toyobo UR-4800 (SO ₃ Na group: 0.08 meq / g)) solution (solvent is a mixed solvent of methyl ethyl ketone and toluene) Was mixed with 570.0 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone 1: 1 (mass ratio) as a solvent, and dispersed in a paint shaker for 5 hours in the presence of zirconia beads. After dispersion, the dispersion and beads were separated with a mesh to obtain an alumina dispersion.

<Preparation of magnetic layer forming composition>
(Magnetic liquid)
Plate-like ferromagnetic hexagonal barium ferrite powder 100.0 parts (activation volume: 1600 nm ³ , average plate ratio: 3.5)
SO ₃ Na group-containing polyurethane resin See Table 5 (weight average molecular weight: 70,000, SO ₃ Na group amount: see Table 5)
Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (Abrasive liquid)
6.0 parts of the alumina dispersion prepared above (silica sol (protrusion forming agent liquid))
Colloidal silica (average particle size: 100 nm) 2.0 parts methyl ethyl ketone 1.4 parts (other components)
Stearic acid 2.0 parts Butyl stearate 2.0 parts Polyisocyanate (Tosoh Coronate (registered trademark)) 2.5 parts (finishing additive solvent)
Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

(Preparation method)
The magnetic liquid was prepared by dispersing the various components of the magnetic liquid using beads as a dispersion medium in a batch type vertical sand mill. As beads, zirconia beads (bead diameter: see Table 5) were used, and the beads were dispersed for the time shown in Table 5 (magnetic liquid bead dispersion time).
The magnetic liquid thus obtained, the above-mentioned abrasive liquid, silica sol, other components and finishing additive solvent were mixed and the beads were dispersed for 5 minutes, followed by treatment with a batch type ultrasonic apparatus (20 kHz, 300 W) for 0.5 minutes (ultrasound Dispersion). Then, it filtered using the filter which has a 0.5 micrometer hole diameter, and prepared the composition for magnetic layer formation.

<Preparation of nonmagnetic layer forming composition>
Among the various components of the composition for forming a nonmagnetic layer described below, components other than stearic acid, cyclohexanone and methyl ethyl ketone were dispersed using a batch type vertical sand mill (dispersion media: zirconia beads (bead diameter: 0.1 mm ), Dispersion time: see Table 5) to obtain a dispersion. Thereafter, the remaining components were added to the obtained dispersion and stirred with a dissolver stirrer. Next, the obtained dispersion was filtered using a filter (pore size: 0.5 μm) to prepare a composition for forming a nonmagnetic layer.

Nonmagnetic inorganic powder α-iron oxide: 100.0 parts (average particle size 10 nm, BET specific surface area 75 m ² / g)
Carbon black: 25.0 parts (average particle size 20 nm)
SO ₃ Na group-containing polyurethane resin: 18.0 parts (weight average molecular weight 70,000, SO ₃ Na group content 0.2 meq / g)
Stearic acid: 1.0 part Cyclohexanone: 300.0 parts Methyl ethyl ketone: 300.0 parts

<Preparation of composition for forming backcoat layer>
Among the various components of the composition for forming a backcoat layer described below, components other than stearic acid, butyl stearate, polyisocyanate and cyclohexanone were kneaded and diluted with an open kneader to obtain a mixed solution. Thereafter, the obtained mixed solution was mixed with a horizontal bead mill using zirconia beads having a bead diameter of 1.0 mm, and the residence time per pass was 2 minutes at a bead filling rate of 80 vol% and a rotor tip peripheral speed of 10 m / sec. And 12-pass distributed processing. Thereafter, the remaining components were added to the obtained dispersion and stirred with a dissolver stirrer. Subsequently, the obtained dispersion was filtered using a filter (pore diameter: 1.0 μm) to prepare a composition for forming a backcoat layer.

Nonmagnetic inorganic powder: α-iron oxide 80.0 parts Average particle size (average major axis length): 0.15 μm
Average needle ratio: 7
BET specific surface area: 52 m ² / g
Carbon black 20.0 parts Average particle size: 20 nm
Vinyl chloride copolymer 13.0 parts Polysulfonate resin containing sulfonate group 6.0 parts Phenylphosphonic acid 3.0 parts Methyl ethyl ketone 155.0 parts Stearic acid 3.0 parts Butyl stearate 3.0 parts Polyisocyanate 5.0 parts Cyclohexanone 355.0 parts

<Preparation of magnetic tape>
A magnetic tape was produced according to the specific embodiment shown in FIG. The details are as follows.
A support made of polyethylene naphthalate having a thickness of 5.0 μm is sent out from the delivery part, and a composition for forming a nonmagnetic layer is applied to one surface so that the thickness after drying in the first application part is 0.7 μm. Thus, a coating layer was formed. While the formed coating layer is in a wet state, it is passed through a cooling zone adjusted to an atmospheric temperature of 0 ° C. for the residence time shown in Table 5 to perform a cooling step, and then a first heat treatment zone having an atmospheric temperature of 100 ° C. A non-magnetic layer was formed by passing through a heat drying process.
Thereafter, the magnetic layer forming composition prepared above was applied onto the nonmagnetic layer so that the thickness after drying in the second application portion was 50 nm, thereby forming an application layer. While this coating layer was in a wet state (undried state), a magnetic field having a strength shown in Table 5 was applied in the orientation zone in a direction perpendicular to the surface of the coating layer of the composition for forming a magnetic layer to perform a vertical orientation treatment. Then, it was dried in a second heat treatment zone (atmosphere temperature: magnetic layer drying temperature in Table 5).
Thereafter, in the third coating portion, the back prepared above so that the thickness after drying is 0.5 μm on the surface opposite to the surface on which the nonmagnetic layer and magnetic layer of the support made of polyethylene naphthalate are formed. The coating layer forming composition was applied to the surface of the nonmagnetic support to form a coating layer, and the formed coating layer was dried in a third heat treatment zone (atmosphere temperature 100 ° C.).
Thereafter, using a calender roll composed only of a metal roll, calendering (surface) at a speed of 80 m / min, a linear pressure of 294 kN / m (300 kg / cm), and a calender temperature (calendar roll surface temperature) shown in Table 5 Smoothing treatment).
Thereafter, heat treatment was performed for 36 hours in an environment with an atmospheric temperature of 70 ° C. After heat treatment and slitting to a width of 1/2 inch (0.0127 meter), a servo pattern was formed on the magnetic layer by a commercially available servo writer.
Thus, a magnetic tape of Example 1 was obtained.

[Example 4, Comparative Examples 1-6]
A magnetic tape was produced in the same manner as in Example 1 except that various items shown in Table 5 were changed as shown in Table 5.
In Table 5, in the comparative example described as “No orientation treatment” in the “Formation and orientation of magnetic layer” column, a magnetic tape was prepared without performing orientation treatment on the coating layer of the magnetic layer forming composition.
In Table 5, in the comparative example described as “Not implemented” in the column of the cooling zone residence time, a magnetic tape was manufactured by a manufacturing process that does not include a cooling zone in the nonmagnetic layer forming process.

[Example 2]
After the formation of the nonmagnetic layer, the magnetic layer forming composition was applied onto the surface of the nonmagnetic layer so that the thickness after drying was 25 nm, thereby forming a first coating layer. This first coating layer was passed through an atmosphere having an atmospheric temperature (magnetic layer drying temperature) shown in Table 5 without applying a magnetic field to form a first magnetic layer (without orientation treatment).
Then, the composition for magnetic layer formation was apply | coated so that the thickness after drying might be set to 25 nm on the surface of a 1st magnetic layer, and the 2nd application layer was formed. While the second coating layer is in a wet state, a magnetic field having the strength shown in Table 5 is applied to the surface of the second coating layer using an opposing magnet in an atmosphere at the atmospheric temperature (magnetic layer drying temperature) shown in Table 5. A second magnetic layer was formed by applying a vertical orientation treatment and a drying treatment with respect to the film.
A magnetic tape was produced in the same manner as in Example 1 except that the multilayer magnetic layer was formed as described above.

[Example 3]
A magnetic tape was produced in the same manner as in Example 2 except that the cooling zone residence time was changed as shown in Table 5.

[Comparative Example 7]
After the formation of the nonmagnetic layer, the magnetic layer forming composition was applied onto the surface of the nonmagnetic layer so that the thickness after drying was 25 nm, thereby forming a first coating layer. While the first coating layer is in a wet state, a magnetic field having the strength shown in Table 5 is applied to the surface of the first coating layer using an opposing magnet in an atmosphere at the atmospheric temperature (magnetic layer drying temperature) shown in Table 5. The first magnetic layer was formed by applying the film perpendicularly to the film, performing vertical alignment treatment and drying treatment.
Then, the composition for magnetic layer formation was apply | coated so that the thickness after drying might be set to 25 nm on the surface of a 1st magnetic layer, and the 2nd application layer was formed. This second coating layer was passed through an atmosphere having an atmospheric temperature (magnetic layer drying temperature) shown in Table 5 without applying a magnetic field to form a second magnetic layer (without orientation treatment).
A magnetic tape was produced in the same manner as in Comparative Example 2 except that the multilayer magnetic layer was formed as described above.

[Comparative Example 8]
After the formation of the nonmagnetic layer, the magnetic layer forming composition was applied onto the surface of the nonmagnetic layer so that the thickness after drying was 25 nm, thereby forming a first coating layer. While the first coating layer is in a wet state, a magnetic field having the strength shown in Table 5 is applied to the surface of the first coating layer using an opposing magnet in an atmosphere at the atmospheric temperature (magnetic layer drying temperature) shown in Table 5. The first magnetic layer was formed by applying the film perpendicularly to the film, performing vertical alignment treatment and drying treatment.
Then, the composition for magnetic layer formation was apply | coated so that the thickness after drying might be set to 25 nm on the surface of a 1st magnetic layer, and the 2nd application layer was formed. This second coating layer was passed through an atmosphere having an atmospheric temperature (magnetic layer drying temperature) shown in Table 5 without applying a magnetic field to form a second magnetic layer (without orientation treatment).
A magnetic tape was produced in the same manner as in Comparative Example 6 except that the magnetic layer was produced by a production process in which the multilayer magnetic layer was formed as described above and the nonmagnetic layer formation process did not include a cooling zone.

[Comparative Example 9]
After the formation of the nonmagnetic layer, the magnetic layer forming composition was applied onto the surface of the nonmagnetic layer so that the thickness after drying was 25 nm, thereby forming a first coating layer. This first coating layer was passed through an atmosphere having an ambient temperature (magnetic layer drying temperature) shown in Table 5 without applying a magnetic field to form a first magnetic layer (without orientation treatment).
Then, the composition for magnetic layer formation was apply | coated so that the thickness after drying might be set to 25 nm on the surface of a 1st magnetic layer, and the 2nd application layer was formed. While the second coating layer is in a wet state, a magnetic field having the strength shown in Table 5 is applied to the surface of the second coating layer using an opposing magnet in an atmosphere at the atmospheric temperature (magnetic layer drying temperature) shown in Table 5. A second magnetic layer was formed by applying a vertical orientation treatment and a drying treatment with respect to the film.
A magnetic tape was produced in the same manner as in Comparative Example 3 except that the multilayer magnetic layer was formed as described above.

[Evaluation of physical properties of magnetic tape]
(1) C—H-derived C concentration X-ray photoelectron spectroscopic analysis was performed using the ESCA apparatus on the magnetic layer surface (measurement region: 300 μm × 700 μm) of the magnetic tape by the following method. Concentration was calculated.

(Analysis and calculation method)
The following measurements (i) to (iii) were all performed under the measurement conditions shown in Table 1.

(I) Wide scan measurement Wide scan measurement (measurement conditions: see Table 2) was performed on the magnetic layer surface of the magnetic tape using an ESCA apparatus, and the types of detected elements were examined (qualitative analysis).

(Ii) Narrow scan measurement For all the elements detected in (i) above, narrow scan measurement (measurement conditions: see Table 3) was performed. The atomic concentration (unit: atomic%) of each element detected from the peak area of each element was calculated using data processing software (Vision 2.2.6) attached to the apparatus. Here, the C concentration was also calculated.

(Iii) Acquisition of C1s spectrum A C1s spectrum was acquired under the measurement conditions described in Table 4. The acquired C1s spectrum is corrected for shift (physical shift) caused by sample charging using the data processing software (Vision 2.2.6) attached to the apparatus, and then the C1s spectrum of the acquired C1s spectrum is corrected using the software. A fitting process (peak separation) was performed. For the peak separation, a Gauss-Lorentz compound function (Gauss component 70%, Lorentz component 30%) is used, C1s spectrum fitting is performed by nonlinear least square method, and the proportion of C—H peaks in the C1s spectrum (peak area ratio) Was calculated. The C—H-derived C concentration was calculated by multiplying the calculated C—H peak area ratio by the C concentration obtained in (ii) above.

  The above treatment was performed three times at different positions on the magnetic layer surface of the magnetic tape, and the arithmetic average of the obtained values was defined as the C—H-derived C concentration.

(2) Nonmagnetic support and thickness of each layer The thicknesses of the magnetic layer, nonmagnetic layer, nonmagnetic support and backcoat layer of each magnetic tape produced were measured by the following method. As a result of the measurement, in any magnetic tape, the thickness of the magnetic layer was 50 nm, the thickness of the nonmagnetic layer was 0.7 μm, the thickness of the nonmagnetic support was 5.0 μm, and the thickness of the backcoat layer was 0.5 μm. It was.
The thicknesses of the magnetic layer, the nonmagnetic layer, and the nonmagnetic support measured here were used for the following refractive index calculation.
(I) Preparation of cross-sectional observation sample In accordance with the method described in paragraphs 0193 to 0194 of JP-A No. 2006-177851, the entire region in the thickness direction from the magnetic layer side surface of the magnetic tape to the backcoat layer side surface is included. A sample for cross-sectional observation was prepared.
(Ii) Thickness measurement The prepared sample was observed with a STEM, and a STEM image was taken. This STEM image is a STEM-HAADF (High-Angle Angular Dark Field) image imaged at an acceleration voltage of 300 kV and an imaging magnification of 450,000 times. One image is formed from the magnetic layer side surface of the magnetic tape to the backcoat layer side surface. Images were taken so that the entire region in the thickness direction was included. In the STEM image thus obtained, a straight line connecting both ends of a line segment representing the magnetic layer surface was determined as a reference line representing the magnetic layer side surface of the magnetic tape. The straight line connecting both ends of the above-mentioned line segment is, for example, a STEM image when the STEM image is imaged so that the magnetic layer side of the sample for cross-sectional observation is positioned above the image and the back coat layer side is positioned below. Is a straight line connecting the intersection of the left side of the image (the shape is rectangular or square) and the line segment, and the intersection of the right side of the STEM image and the line segment. Similarly, a reference line representing the interface between the magnetic layer and the nonmagnetic layer, a reference line representing the interface between the nonmagnetic layer and the nonmagnetic support, a reference line representing the interface between the nonmagnetic support and the backcoat layer, and magnetic tape A reference line representing the backcoat layer side surface of was determined.
The thickness of the magnetic layer was determined as the shortest distance from one randomly selected point on the reference line representing the magnetic layer side surface of the magnetic tape to the reference line representing the interface between the magnetic layer and the nonmagnetic layer. Similarly, the thickness of the nonmagnetic layer, the nonmagnetic support and the backcoat layer was determined.

(3) ΔN of magnetic layer
Below, M-2000U made from Woollam Co. was used as an ellipsometer. Creation and fitting of a two-layer model or a one-layer model was performed using WVASE32 manufactured by Woollam as analysis software.
(I) Refractive index measurement of nonmagnetic support A sample for measurement is cut out from each magnetic tape, and the backcoat layer of the measurement sample is wiped off using a cloth soaked with methyl ethyl ketone to expose the surface of the nonmagnetic support. After that, the surface was roughened with sandpaper so that the reflected light of the exposed surface was not detected in the subsequent ellipsometer measurement.
Then, after wiping and removing the magnetic layer and nonmagnetic layer of the measurement sample using a cloth soaked with methyl ethyl ketone, the surface of the silicon wafer and the roughened surface are pasted using static electricity for measurement. The sample was placed on a silicon wafer with the surface of the nonmagnetic support exposed by removing the magnetic layer and the nonmagnetic layer (hereinafter referred to as “the magnetic layer side surface of the nonmagnetic support”) facing upward. .
Using an ellipsometer, incident light was made incident on the surface of the nonmagnetic support of the measurement sample on the silicon wafer as described above, and Δ and Ψ were measured. Using the obtained measured value and the thickness of the nonmagnetic support obtained in (2) above, the refractive index of the nonmagnetic support (refractive index in the longitudinal direction, refractive index in the width direction, longitudinal direction) by the method described above. The refractive index in the thickness direction measured by making incident light incident from the direction and the refractive index in the thickness direction measured by making incident light incident from the width direction were determined.
(Ii) Refractive index measurement of nonmagnetic layer A sample for measurement was cut out from each magnetic tape, and the backcoat layer of the sample for measurement was wiped off using a cloth soaked with methyl ethyl ketone to expose the surface of the nonmagnetic support. The surface was then roughened with sandpaper so that reflected light from the exposed surface was not detected in subsequent spectroscopic ellipsometer measurements.
Thereafter, the surface of the magnetic layer of the sample for measurement is wiped lightly with a cloth soaked with methyl ethyl ketone to remove the magnetic layer and expose the surface of the nonmagnetic layer, and then the measurement is performed on the silicon wafer in the same manner as in (i) above. A sample was placed.
The surface of the nonmagnetic layer of the measurement sample on the silicon wafer is measured using an ellipsometer, and the refractive index of the nonmagnetic layer (refractive index in the longitudinal direction, width direction) is determined by spectroscopic ellipsometry by the method described above. , The refractive index in the thickness direction measured by making incident light incident from the longitudinal direction, and the refractive index in the thickness direction measured by making incident light incident from the width direction).
(Iii) Refractive index measurement of magnetic layer After cutting out a measurement sample from each magnetic tape and using a cloth soaked with methyl ethyl ketone, the back coat layer of the measurement sample was wiped off to expose the surface of the nonmagnetic support. The surface was roughened with sandpaper so that the reflected light of the exposed surface was not detected in the subsequent spectroscopic ellipsometer measurement.
Thereafter, the measurement sample was placed on the silicon wafer in the same manner as in the above (i).
The surface of the magnetic layer of the measurement sample on the silicon wafer is measured using an ellipsometer, and the refractive index of the magnetic layer (the refractive index Nx in the longitudinal direction and the refractive index in the width direction is measured by spectroscopic ellipsometry by the method described above. The refractive index Ny, the refractive index Nz ₁ in the thickness direction measured by making incident light incident from the longitudinal direction, and the refractive index Nz ₂ in the thickness direction measured by making incident light incident from the width direction were determined. Nxy and Nz were obtained from the obtained values, and the absolute value ΔN of these differences was obtained. For any of the magnetic tapes of Examples and Comparative Examples, the obtained Nxy was a value larger than Nz (that is, Nxy> Nz).

(4) Vertical squareness ratio (SQ; Squareness Ratio)
The perpendicular squareness ratio of the magnetic tape is a squareness ratio measured in the perpendicular direction of the magnetic tape. The “vertical direction” described with respect to the squareness ratio refers to a direction orthogonal to the magnetic layer surface. About each magnetic tape of an Example and a comparative example, using a vibration sample type magnetometer (manufactured by Toei Kogyo Co., Ltd.), at a measurement temperature of 23 ° C. ± 1 ° C., an external magnetic field was applied to the magnetic tape at a maximum external magnetic field of 1194 kA / m ( 15 kOe) and a scanning speed of 4.8 kA / m / sec (60 Oe / sec), the vertical squareness ratio was obtained. The measured value is a value after demagnetizing field correction, and is obtained as a value obtained by subtracting the magnetization of the sample probe of the vibrating sample type magnetometer as background noise. In one aspect, the perpendicular squareness ratio of the magnetic tape is preferably 0.60 or more and 1.00 or less, and more preferably 0.65 or more and 1.00 or less. Moreover, in one aspect, the perpendicular squareness ratio of the magnetic tape can be, for example, 0.90 or less, 0.85 or less, or 0.80 or less, and can exceed these values.

[Missing pulse frequency in low temperature and high humidity environment]
The following measurements were performed in a low temperature and high humidity environment at a temperature of 13 ° C. and a relative humidity of 80%.
The magnetic tape cartridges containing the magnetic tapes of the examples and comparative examples (total length of magnetic tape 500 m) were set in an LTO-G6 (Linear Tape-Open Generation 6) drive manufactured by IBM, and the magnetic tape was loaded with a tension of 0.6 N. And 1500 reciprocations at a traveling speed of 8 m / sec.
The magnetic tape cartridge after running was set in a reference drive (IBM LTO-G6 drive), and the magnetic tape was run to perform recording and reproduction. The reproduction signal during driving is taken into an external AD (Analog / Digital) converter, and a signal whose reproduction signal amplitude is reduced by 70% or more with respect to the average (average of measured values in all tracks) is used as a missing pulse, and its frequency of occurrence. The (number of occurrences) was divided by the total length of the magnetic tape, and was determined as the frequency of occurrence of missing pulses per unit length (per meter) of the magnetic tape (unit: times / m). If the missing pulse generation frequency is 5 times / m or less, it can be determined that the magnetic tape is practically highly reliable.

  The above results are shown in Table 5 (Tables 5-1 to 5-4).

From the results shown in Table 5, the magnetic tapes of Examples 1 to 4 in which the ΔN and C—H-derived C concentrations of the magnetic layer are in the ranges described above are lower in temperature than the magnetic tapes of Comparative Examples 1 to 9, respectively. It can be confirmed that the frequency of occurrence of missing pulses in a high humidity environment is reduced.
In general, the squareness ratio is known as an index of the existence state of the ferromagnetic powder in the magnetic layer. However, as shown in Table 5, ΔN is different even for magnetic tapes having the same vertical squareness ratio (for example, Example 1 and Comparative Example 8). The inventor believes that this indicates that ΔN is a value that is influenced by other factors in addition to the presence of the ferromagnetic powder in the magnetic layer.

  One embodiment of the present invention is useful in the technical field of various magnetic recording media such as magnetic tapes for data storage.

Claims (7)

A magnetic tape having a magnetic layer comprising a ferromagnetic powder and a binder on a non-magnetic support,
The magnetic layer contains one or more components selected from the group consisting of fatty acids and fatty acid amides,
The C—H-derived C concentration calculated from the C—H peak area ratio in the C1s spectrum obtained by X-ray photoelectron spectroscopy performed at a photoelectron extraction angle of 10 degrees on the surface of the magnetic layer is 45 atomic% or more, and The absolute value ΔN of the difference between the refractive index Nxy measured in the in-plane direction of the magnetic layer and the refractive index Nz measured in the thickness direction of the magnetic layer is 0.25 to 0.40. 2. The magnetic tape according to claim 1, wherein a difference between the refractive index Nxy and the refractive index Nz, Nxy−Nz, is not less than 0.25 and not more than 0.40. The magnetic tape according to claim 1, wherein the C—H-derived C concentration is 45 atomic% or more and 80 atomic% or less. The magnetic tape according to claim 1, wherein the C—H-derived C concentration is 45 atomic% or more and 70 atomic% or less. The magnetic tape of any one of Claims 1-4 which has a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. The magnetic tape according to any one of claims 1 to 5, further comprising a backcoat layer containing a nonmagnetic powder and a binder on the surface side opposite to the surface side having the magnetic layer of the nonmagnetic support. . The magnetic tape according to any one of claims 1 to 6,
A magnetic head;
A magnetic recording / reproducing apparatus.