JP2023054373A - Magnetic tape and magnetic recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: 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, 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 and logarithmic decrement calculated by a pendulum viscoelasticity test on the surface of the magnetic layer is 0.050 or less. There is also provided a magnetic recording and reproducing device including the magnetic tape.

SELECTED DRAWING: None

COPYRIGHT: (C)2023,JPO&INPIT

Description

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

Magnetic recording media include tape-shaped and disk-shaped magnetic recording media, and tape-shaped magnetic recording media, ie, magnetic tapes, are mainly used for data storage applications. Recording and/or reproduction of information on a magnetic tape is usually carried out by contacting and sliding the surface of the magnetic tape (surface of the magnetic layer) and a magnetic head (hereinafter also simply referred to as "head"). . As a magnetic tape, one having a structure in which a magnetic layer containing ferromagnetic powder and a binder is provided on a non-magnetic support is widely used (see, for example, Patent Document 1).

JP 2005-243162 A

When reproducing information recorded on a magnetic tape, the higher the frequency of occurrence of a partial drop in the reproduced signal amplitude (called a "missing pulse"), the greater the error rate. Reliability goes down. 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.

By the way, in recent years, magnetic tapes used for data storage are sometimes used in data centers where temperature and humidity are controlled. On the other hand, data centers are required to save power in order to reduce costs. In order to save power, it is desirable that the temperature and humidity management conditions in data centers can be relaxed more than at present, or management can be made unnecessary. However, if the temperature and humidity control conditions are relaxed or not controlled, magnetic tapes are expected to be used in various environments, including low temperature and high humidity environments. However, as a result of investigation by the present inventor, it has been found that the frequency of occurrence of missing pulses tends to increase in a low-temperature, high-humidity environment.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a magnetic tape in which the frequency of occurrence of missing pulses is reduced in a low-temperature, high-humidity environment.

One aspect of the present invention is
A magnetic tape having a magnetic layer comprising a ferromagnetic powder and a binder on a non-magnetic support,
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, and a magnetic tape having a logarithmic decrement of 0.050 or less on the surface of the layer determined by a pendulum viscoelasticity test (hereinafter also referred to as "logarithmic decrement of the magnetic layer" or simply "logarithmic decrement");
Regarding.

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 aspect, the logarithmic decrement can be 0.010 or more and 0.050 or less.

In one aspect, the magnetic tape can have a non-magnetic layer containing non-magnetic powder and a binder between the non-magnetic support and the magnetic layer.

In one aspect, the magnetic tape can have a back coat layer containing non-magnetic powder and a binder on the surface of the non-magnetic support opposite to the surface having the magnetic layer.

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

According to one aspect of the present invention, it is possible to provide a magnetic tape capable of reducing the frequency of occurrence of missing pulses in a low-temperature, high-humidity environment. Further, according to one aspect of the present invention, it is possible to provide a magnetic recording/reproducing apparatus including the above magnetic tape.

FIG. 4 is an explanatory diagram of a method of measuring a logarithmic decrement; FIG. 4 is an explanatory diagram of a method of measuring a logarithmic decrement; FIG. 4 is an explanatory diagram of a method of measuring a logarithmic decrement; An example of a specific embodiment of a magnetic tape manufacturing process (process schematic diagram) 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 refractive index Nxy measured in the in-plane direction of the magnetic layer and the magnetic layer The absolute value ΔN of the difference from the refractive index Nz measured in the thickness direction is 0.25 or more and 0.40 or less, and the logarithmic decrement obtained by the pendulum viscoelasticity test on the surface of the magnetic layer is 0.050 or less. for magnetic tapes.

In the present invention and this specification, the term "(the) surface of the magnetic layer" has the same meaning as the magnetic layer side surface of the magnetic tape. In addition, in the present invention and this specification, "ferromagnetic powder" means an aggregate of a plurality of ferromagnetic particles. The term “aggregation” is not limited to the aspect in which the particles constituting the aggregation are in direct contact, but also includes the aspect in which a binder, an additive, or the like is interposed between the particles. The above points also apply to various powders such as non-magnetic powders in the present invention and this specification.

The method for measuring ΔN and the logarithmic decrement will be described below.

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 determined by the following method. and
The refractive index in each direction of the magnetic layer is obtained by spectroscopic ellipsometry using a two-layer model. In order to determine the refractive index of the magnetic layer by spectroscopic ellipsometry using the two-layer model, the refractive index value of the portion adjacent to the magnetic layer is used. An example of determining the refractive indices Nxy and Nz of the magnetic layer of 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 will be described below. However, the magnetic tape according to one aspect of the present invention can also be a magnetic tape having a layer structure in which a magnetic layer is directly laminated on a non-magnetic support without interposing a non-magnetic layer. For a magnetic tape having such a structure, a two-layer model of a magnetic layer and a non-magnetic support is used to determine the refractive index in each direction of the magnetic layer in the same manner as described below. Also, the incident angle described below is the incident angle when the incident angle in the case of vertical incidence is assumed to be 0°.
(1) Preparation of sample for measurement For a magnetic tape having a backcoat layer on the surface opposite to the surface having the magnetic layer of the non-magnetic support, the backcoat layer of the sample for measurement cut out from the magnetic tape is removed. After that, take measurements. The backcoat layer can be removed by a known method such as dissolving the backcoat layer using a solvent. As a solvent, for example, methyl ethyl ketone can be used. However, any solvent may be used as long as it can remove the back coat layer. After removing the backcoat layer, the surface of the non-magnetic support is roughened by a known method so that light reflected from this surface is not detected during measurement with an ellipsometer. The roughening can be carried out, for example, by polishing the surface of the non-magnetic support with sandpaper after removing the back coat layer. For the measurement sample cut out from the magnetic tape having no back coat layer, the surface of the non-magnetic support opposite to the surface having the magnetic layer is roughened.
Further, the magnetic layer is further removed to expose the surface of the nonmagnetic layer for the following refractive index measurement of the nonmagnetic layer. For the following refractive index measurement of the non-magnetic support, the non-magnetic layer is also removed to expose the surface of the non-magnetic support on the magnetic layer side. Each layer can be removed by known methods as described for the removal of the backcoat layer. The longitudinal direction described below refers to the longitudinal direction of the magnetic tape when the sample for measurement was included in the magnetic tape before it was cut out. This point also applies to other directions described below.
(2) Measurement of Refractive Index of Magnetic Layer Using an ellipsometer, incident light with a beam diameter of 300 μm was irradiated onto the surface of the magnetic layer from the longitudinal direction at incident angles of 65°, 70° and 75°. (phase difference between s-polarized and p-polarized light) and Ψ (amplitude ratio between s-polarized and p-polarized light) are measured. The measurement is performed by changing the wavelength of incident light in the range of 400 to 700 nm in increments of 1.5 nm, and the measured 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 non-magnetic layer in each direction determined by the method described below, and the thickness of the magnetic layer, the magnetic layer at each wavelength is calculated by the two-layer model as follows: Find the refractive index of
The 0th layer, which is the substrate of the two-layer model, is a non-magnetic layer, and the first layer is a magnetic layer. A two-layer model is created by considering only the reflection at the interface between the air/magnetic layer and the magnetic layer/non-magnetic layer and assuming that the back reflection of the non-magnetic layer has no effect. The refractive index of the first layer that best matches the obtained measured value is obtained by fitting using the least squares method. As values at a wavelength of 600 nm obtained from the fitting results, the refractive index Nx of the magnetic layer in the longitudinal direction and the refractive index Nz ₁ in the thickness direction of the magnetic layer measured by incident light from the longitudinal direction are obtained.
The same as above except that the direction in which the incident light is incident is the width direction of the magnetic tape. A refractive index _Nz2 in the thickness direction of the magnetic layer measured by incident light is obtained.
Fitting is performed by the following method.
Generally, it is "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. The complex dielectric constant ε=ε1+iε2 (ε1 and ε2 satisfy the Kramers-Kronig relationship) and ε1=η ² −κ ² and ε2= _2ηκ . 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.
Let ε _x 2 be one Gaussian, take an arbitrary point with a peak position of 5.8 to 5.1 eV and σ of 4 to 3.5 eV as a starting point, and set the dielectric constant outside the measurement wavelength range (400 to 700 nm). Nx is obtained by putting an offset parameter in and performing least-squares fitting of the measured values. Similarly, ε _z1 2 is obtained by starting from an arbitrary point with a peak position of 3.2 to 2.9 eV and σ of 1.5 to 1.2 eV, placing an offset parameter, and performing least-squares fitting of the measured values. Find Nz ₁ . Ny and _Nz2 are determined similarly. 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". From the obtained Nxy and Nz, the absolute value ΔN of the difference between them is obtained.
(3) Refractive index measurement of non-magnetic layer Except for the following points, the refractive index of the non-magnetic layer at a wavelength of 600 nm (refractive index in the longitudinal direction, refractive index in the width direction, incident light from the longitudinal direction) and the refractive index in the thickness direction measured by making incident light enter from the width direction).
The wavelength of the incident light is changed in increments of 1.5 nm within the range of 250 to 700 nm.
Using a two-layer model of a non-magnetic layer and a non-magnetic support, the 0th layer, which is the substrate of the two-layer model, is the non-magnetic support and the first layer is the non-magnetic layer. A two-layer model is created by considering only the reflection at the interface between the air/non-magnetic layer and the non-magnetic layer/non-magnetic support, and assuming that there is no influence of the back surface reflection of the non-magnetic support.
In 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 permittivity Then, a parameter that offsets the dielectric constant is placed outside the measurement wavelength range (250 to 700 nm).
(4) Measurement of refractive index of non-magnetic support The refractive index of the non-magnetic support at a wavelength of 600 nm (refractive index in the longitudinal direction, refractive index in the width direction, refractive index in the width direction, The refractive index in the thickness direction measured with incident light incident from the longitudinal direction, and the refractive index in the thickness direction measured with incident light incident from the width direction) are the refractive indices of the magnetic layers, except for the following points. Determined similarly to the above method for measurement.
Instead of using a two-layer model, a one-layer model with only surface reflection is used.
The fitting is performed by a Cauchy model (n=A+B/λ ² , n is the refractive index, A and B are constants determined by fitting, and λ is the wavelength).

Next, the logarithmic decrement of the magnetic layer will be explained.
In the present invention and this specification, the logarithmic decrement of the magnetic layer is a value obtained by the following method.
1 to 3 are explanatory diagrams of the method of measuring the logarithmic decrement. The method of measuring the logarithmic decrement will be described below with reference to these drawings. However, the illustrated embodiment is an example and does not limit the present invention.
A measurement sample 100 is cut out from a magnetic tape to be measured. A cut-out measurement sample 100 is placed on a substrate 103 on a sample stage 101 in a pendulum viscoelasticity tester, with the surface to be measured (magnetic layer surface) facing upward, and no wrinkles that can be visually confirmed. Then, it is fixed with a fixing tape 105 or the like.
A cylindrical cylinder edge 104 with a pendulum (4 mm in diameter) having a mass of 13 g is placed on the measurement surface of the measurement sample 100 so that the longitudinal direction of the cylinder edge is parallel to the longitudinal direction of the measurement sample 100 . FIG. 1 shows an example of a state in which the cylindrical edge 104 with a pendulum is placed on the measurement surface of the measurement sample 100 (viewed from above). In the embodiment shown in FIG. 1, a holder/temperature sensor 102 is installed so that the surface temperature of the substrate 103 can be monitored. However, this configuration is not required. In the embodiment shown in FIG. 1, the longitudinal direction of the measurement sample 100 is the direction indicated by the arrow in the figure, which is the same direction as the longitudinal direction of the magnetic tape cut out from the measurement sample. As the pendulum 107 (see FIG. 2), a pendulum made of a material (for example, metal, alloy, etc.) having a property of being attracted to a magnet is used.
The surface temperature of the substrate 103 on which the measurement sample 100 is placed is raised to 80° C. at a temperature elevation rate of 5° C./min or less (any temperature elevation rate of 5° C./min or less is acceptable), The pendulum motion is started (initial vibration is induced) by releasing the attraction between the pendulum 107 and the magnet 106 . FIG. 2 shows an example of the pendulum 107 in pendulum motion (as seen from the side). In the embodiment shown in FIG. 2, in the pendulum viscoelasticity tester, the magnet (electromagnet) 106 placed below the sample stage is deenergized (turned off) to release the adsorption, thereby starting the pendulum motion. Then, the energization of the electromagnet is resumed (the switch is turned on), and the pendulum motion is stopped by attracting the pendulum 107 to the magnet 106 . During pendulum motion, pendulum 107 repeats its amplitude, as shown in FIG. From the results obtained by monitoring the displacement of the pendulum by the displacement sensor 108 while the pendulum repeats its amplitude, a displacement-time curve is obtained with displacement on the vertical axis and elapsed time on the horizontal axis. An example of a displacement-time curve is shown in FIG. FIG. 3 schematically shows the correspondence between the state of the pendulum 107 and the displacement-time curve. At a certain measurement interval, static (adsorption) and pendulum motion are repeated, and the displacement-time curve obtained at the measurement interval after 10 minutes or more (any time is acceptable as long as it is 10 minutes or more) is used. Then, the logarithmic decrement Δ (unitless) is obtained from the following formula, and this value is defined as the logarithmic decrement of the surface of the magnetic layer of the magnetic tape. The adsorption time for one adsorption is set to 1 second or more (arbitrary time as long as it is 1 second or longer), and the interval from the end of adsorption to the start of the next adsorption is 6 seconds or longer (any time if 6 seconds or longer). time is fine.). A measurement interval is a time interval from the start of adsorption to the start of the next adsorption. Moreover, the humidity of the environment in which the pendulum motion is performed may be any relative humidity within the range of 40 to 70% relative humidity.

In the displacement-time curve, the interval from the minimum displacement to the minimum again is defined as one period of the wave. Let n be the number of waves included in the displacement-time curve during the measurement interval and An be the difference between the minimum and maximum displacements at the nth wave. In FIG. 3, the interval from the minimum to the minimum displacement of the nth wave is denoted by Pn (eg P ₁ for the first wave, P ₂ for the second wave, P ₃ for the third wave). are doing. In calculating the logarithmic decrement, the difference between the minimum displacement and the maximum displacement that appears next to the n-th wave (A _n+1 in the above formula, and A ₄ in the displacement-time curve shown in FIG. 3) is also used. After that, the part where the pendulum 107 is stationary (attracted) is not used for counting the number of waves. Also, the part where the pendulum 107 is stationary (attracted) before the maximum displacement is not used for counting the number of waves. Therefore, in the displacement-time curve shown in FIG. 3, the number of waves is three (n=3).

The present inventor speculates as follows about the reason why the magnetic tape described above can reduce the frequency of occurrence of missing pulses in a low-temperature, high-humidity environment.
When reproducing information recorded on a magnetic tape, if the surface of the magnetic layer is scraped due to sliding between the surface of the magnetic layer and the head, the resulting scrapings may adhere to the head and become deposits on the head. The present inventor believes that the cause of the occurrence of missing pulses in a low temperature and high humidity environment is that the coefficient of friction between the magnetic layer surface and the head tends to increase when the magnetic layer surface slides against the head in a low temperature and high humidity environment. This is because the contact state tends to be unstable when sliding, and it is surmised that the cause of the unstable contact state is the generation of head deposits.
With respect to the above points, the present inventor believes that ΔN obtained by the above method can be a value that can serve as an indicator of the state of existence of ferromagnetic powder in the surface region of the magnetic layer. This ΔN is presumed to be affected by various factors such as the orientation of the ferromagnetic powder in the magnetic layer, the presence of the binder, and the density distribution of the ferromagnetic powder. A magnetic layer having a ΔN of 0.25 or more and 0.40 or less by controlling various factors is considered to have a high strength on the surface of the magnetic layer and is difficult to be scraped by sliding with the head. This contributes to suppressing the magnetic layer surface from being scraped off and deposits on the head when sliding against the head in a low temperature and high humidity environment, resulting in missing pulses in a low temperature and high humidity environment. The present inventor presumes that this leads to a reduction in the frequency of occurrence of
Furthermore, the present inventor conjectures as follows regarding the logarithmic decrement.
The logarithmic decrement obtained by the above method is an index of the amount of adhesive components separated from the magnetic layer surface and interposed between the magnetic layer surface and the head when the head and the magnetic layer surface contact and slide. value. It is thought that the greater the presence of such tacky components, the higher the adhesion between the surface of the magnetic layer and the head, and the more unstable the contact state when the surface of the magnetic layer and the head slide. On the other hand, in the magnetic tape, the logarithmic decrement of the magnetic layer is 0.050 or less, that is, the adhesive component is reduced, so that the surface of the magnetic layer and the head slide smoothly. It is thought that it will contribute to making The present inventor believes that this contributes to the stabilization of the contact state when the magnetic layer surface and the head slide, and as a result, leads to a reduction in the frequency of occurrence of missing pulses in a low-temperature, high-humidity environment. speculates.
Details of the adhesive component are not clear. The present inventor speculates that the adhesive component may be derived from the resin used as the binder. Details are as follows. As the binder, various resins can be used as described later in detail. A resin is a polymer (including homopolymers and copolymers) of two or more polymerizable compounds, and a component having a molecular weight lower than the average molecular weight (hereinafter referred to as a "low molecular weight binder component"). usually included. The present inventor believes that such a low-molecular-weight binder component is released from the magnetic layer surface and intervenes between the magnetic layer surface and the head when the head slides over the magnetic layer surface. The low-molecular-weight binder component is considered to have stickiness, and the logarithmic decrement determined by the pendulum viscoelasticity test is the low-molecular-weight binder released from the magnetic layer surface when the magnetic layer surface and the head slide. The present inventors speculate that it may serve as an indicator of the amount of ingredients. In one embodiment, the magnetic layer is formed by applying a magnetic layer-forming composition containing a curing agent in addition to a ferromagnetic powder and a binder onto a non-magnetic support directly or via another layer, followed by curing. It is formed by applying By the curing treatment here, a curing reaction (crosslinking reaction) can be caused between the binder and the curing agent. However, the present inventor believes that the low-molecular-weight binder component has poor reactivity in the curing reaction, although the reason is not clear. For this reason, the low-molecular-weight binder component is difficult to stay in the magnetic layer and is likely to be released from the magnetic layer. The inventor of the present invention speculates that this is one of the reasons why the
However, the above is just speculation and does not limit the present invention.

The magnetic tape will be described in more detail below. In the following, the frequency of occurrence of missing pulses in a low-temperature and high-humidity environment is also simply referred to as "the 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, a magnetic layer having a ΔN of 0.25 or more and 0.40 or less is presumed to have a high strength on the surface of the magnetic layer and to be less likely to be scraped by sliding against the head in a low-temperature, high-humidity environment. . For this reason, it is believed that the magnetic layer having a ΔN within the above range is unlikely to be scraped off due to sliding between the magnetic layer surface and the head when reproducing information recorded on the magnetic layer in a low-temperature, high-humidity environment. be done. It is presumed that this contributes to reducing the frequency of occurrence of missing pulses in a low-temperature, high-humidity environment. From the viewpoint of further reducing the frequency of occurrence of missing pulses, ΔN is preferably 0.25 or more and 0.35 or less. Specific aspects of means for adjusting ΔN will be described later.

ΔN is the absolute value of the difference between Nxy and Nz. Nxy is the refractive index measured in the in-plane direction of the magnetic layer, and Nz is the refractive index measured in the thickness direction of the magnetic layer. In one aspect, Nxy>Nz, and in another aspect, Nxy<Nz. From the viewpoint of the electromagnetic conversion characteristics of the magnetic tape, it is preferable that Nxy>Nz. It is more preferable to be 0.35 or less.

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

(logarithmic decay rate)
The logarithmic decrement obtained by a pendulum viscoelasticity test on the surface of the magnetic layer of the magnetic tape is 0.050 or less from the viewpoint of reducing the frequency of occurrence of missing pulses under a low-temperature, high-humidity environment. From the viewpoint of further reducing the frequency of occurrence of missing pulses, the logarithmic decrement is preferably 0.048 or less, more preferably 0.045 or less, and even more preferably 0.040 or less. On the other hand, from the viewpoint of reducing the frequency of occurrence of missing pulses, the lower the logarithmic decrement, the better, so the lower limit is not particularly limited. As an example, the logarithmic decrement can be, for example, 0.010 or greater, or 0.015 or greater. However, the logarithmic decay rate may be less than the values exemplified above. Specific aspects of the means for adjusting the logarithmic decrement will be described later.

(ferromagnetic powder)
Ferromagnetic powders commonly used in the magnetic layers of various magnetic recording media can be used as the ferromagnetic powder contained in the magnetic layer. It is preferable to use ferromagnetic powder having a small average particle size from the viewpoint of improving the recording density of the magnetic recording medium. From this point of view, ferromagnetic powder having an average particle size of 50 nm or less is preferably used 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, more preferably 10 nm or more.

Ferromagnetic hexagonal ferrite powder can be cited as a preferred specific example of the ferromagnetic powder. The ferromagnetic hexagonal ferrite powder can be ferromagnetic hexagonal barium ferrite powder, ferromagnetic hexagonal strontium ferrite powder, and the like. The average particle size of the ferromagnetic hexagonal ferrite powder is preferably 10 nm or more and 50 nm or less, more preferably 20 nm or more and 50 nm or less, from the viewpoints of recording density improvement and magnetization stability. For details of the ferromagnetic hexagonal ferrite powder, see, for example, paragraphs 0012 to 0030 of JP-A-2011-225417, paragraphs 0134-0136 of JP-A-2011-216149, and paragraph 0013 of JP-A-2012-204726. . . . 0030 can be referenced.

Ferromagnetic metal powder can also be given as a preferred specific example of the ferromagnetic powder. The average particle size of the ferromagnetic metal powder is preferably 10 nm or more and 50 nm or less, more preferably 20 nm or more and 50 nm or less, from the viewpoints of recording density improvement and magnetization stability. For details of the ferromagnetic metal powder, for example, paragraphs 0137 to 0141 of JP-A-2011-216149 and paragraphs 0009-0023 of JP-A-2005-251351 can be referred to.

A preferred specific example of the ferromagnetic powder is 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 manufacturing methods are known. Also, a method for producing ε-iron oxide powder in which a part of Fe is substituted with substitution atoms such as Ga, Co, Ti, Al, and Rh is described in J. Am. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J.P. Mater. Chem. C, 2013, 1, pp. 5200-5206 and the like. However, the method for producing the ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer is not limited.

In the present invention and this specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powder is a value measured by the following method using a transmission electron microscope.
The powder is photographed with a transmission electron microscope at a magnification of 100,000 times and printed on photographic paper at a total magnification of 500,000 times to obtain a photograph of the particles constituting the powder. The particles of interest are selected from the photograph of the particles obtained, and the contours of the particles are traced with a digitizer to measure the size of the particles (primary particles). Primary particles refer to individual particles without agglomeration.
The above measurements are performed on 500 randomly selected particles. The arithmetic mean of the particle sizes of the 500 particles thus obtained is taken as the average particle size of the powder. As the transmission electron microscope, for example, Hitachi's H-9000 transmission electron microscope can be used. Further, the particle size can be measured using known image analysis software such as Carl Zeiss image analysis software KS-400. Unless otherwise specified, the values related to the size of the powder such as the average particle size shown in the examples below are obtained using a Hitachi transmission electron microscope H-9000 as a transmission electron microscope, and Carl Zeiss image analysis software KS- as image analysis software. 400 is the value measured.

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

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

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

In one aspect, the ferromagnetic particles constituting the ferromagnetic powder contained in the magnetic layer can have a plate-like shape. Ferromagnetic powder composed of plate-like ferromagnetic particles is hereinafter referred to as plate-like ferromagnetic powder. The average platelet ratio of the platelet-like ferromagnetic powder can preferably range from 2.5 to 5.0. The average tabular ratio is the arithmetic mean of (maximum length/thickness or height) in the definition (2) above. As the average tabular ratio increases, the orientation treatment tends to increase the uniformity of the orientation state of the ferromagnetic particles constituting the tabular ferromagnetic powder, and the value of ΔN tends to increase.

Also, the activation volume can be used as an index of the particle size of the ferromagnetic powder. An "activation volume" is a unit of magnetization reversal. The activation volume described in the present invention and this specification is measured using a vibrating sample magnetometer at a magnetic field sweep speed of 3 minutes and 30 minutes at the coercive force Hc measurement part in an environment of an ambient temperature of 23 ° C. ± 1 ° C. , and is a value obtained from the following relational expression between Hc and activation volume V. The activation volume shown in the examples below 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 reversal time]
From the viewpoint of improving the recording density, the activated volume of the ferromagnetic powder is preferably 2500 nm ³ or less, more preferably 2300 nm ³ or less, and even more preferably 2000 nm ³ or less. On the other hand, from the viewpoint of magnetization stability, the activated volume of the ferromagnetic powder is preferably, for example, 800 nm ³ or more, more preferably 1000 nm ³ or more, and even more preferably 1200 nm ³ or more.

The ferromagnetic powder content (filling rate) in the magnetic layer is preferably in the range of 50 to 90 mass %, more preferably in the range of 60 to 90 mass %. Components of the magnetic layer other than the ferromagnetic powder are at least one or more components selected from the group consisting of fatty acids and fatty acid amides, a binder, and optionally 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 coated magnetic tape, and contains a binder in the magnetic layer. A binder is one or more resins. Resins may be homopolymers or copolymers. Binders contained in the magnetic layer include polyurethane resins, polyester resins, polyamide resins, vinyl chloride resins, acrylic resins obtained by copolymerizing styrene, acrylonitrile, methyl methacrylate, etc., cellulose resins such as nitrocellulose, epoxy resins, phenoxy resins, A resin selected from polyvinyl acetal, polyvinyl butyral, and other polyvinyl alkylal resins can be used alone, or a plurality of resins can be mixed and used. Preferred among these are polyurethane resins, acrylic resins, cellulose resins and vinyl chloride resins. These resins can also be used as binders in the non-magnetic layer and/or backcoat layer, which will be described later. Paragraphs 0029 to 0031 of JP-A-2010-24113 can be referred to for the above binders. The weight-average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less. The weight average molecular weight in the present invention and the specification is a value obtained by converting a value measured by gel permeation chromatography (GPC) into polystyrene. The following conditions can be mentioned as measurement conditions. The weight average molecular weight shown in the examples below is a value obtained by converting the value measured under the following measurement conditions into polystyrene.
GPC device: HLC-8120 (manufactured by Tosoh Corporation)
Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8 mmID (Inner Diameter) × 30.0 cm)
Eluent: Tetrahydrofuran (THF)

In one aspect, a binder containing an acidic group can be used as the binder. The term "acidic group" as used in the present invention and the specification includes a group capable of dissociating into an anion by releasing H ⁺ in water or a solvent containing water (aqueous solvent) and a salt form thereof. . Specific examples of the acidic group include, for example, a sulfonic acid group, a sulfate group, a carboxyl group, a phosphoric acid group, and salt forms thereof. For example, the salt form of a sulfonic acid group (—SO ₃ H) is a group represented by —SO ₃ M, where M is an atom that can become a cation in water or an aqueous solvent (for example, an alkali metal atom, etc.). means. This point also applies to the salt forms of the various groups described above. Examples of binders containing acidic groups include resins containing at least one acid group selected from the group consisting of sulfonic acid groups and salts thereof (eg, polyurethane resins, vinyl chloride resins, etc.). However, the resin contained in the magnetic layer is not limited to these resins. In addition, in the binder containing acidic groups, the amount of acidic groups can be, for example, in the range of 20 to 500 eq/ton. Note that eq is equivalent and is a unit that cannot be converted into SI units. The content of various functional groups such as acidic groups contained in the resin can be obtained by a known method according to the type of functional group. The value of ΔN tends to increase with the use of a binder having a large amount of acidic groups. 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, per 100.0 parts by mass of the ferromagnetic powder. An amount of 20.0 parts by weight can be used. The value of ΔN tends to increase as the amount of binder used relative to the ferromagnetic powder increases.

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

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

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

<Nonmagnetic layer>
Next, the nonmagnetic layer will be explained.
The magnetic tape may have a magnetic layer directly on the surface of the non-magnetic support, or have a non-magnetic layer containing non-magnetic powder and a binder between the non-magnetic support and the magnetic layer. good too. The non-magnetic powder contained in the non-magnetic layer may be inorganic powder or organic powder. Carbon black or the like can also be used. Examples of inorganic powders include powders of metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. These non-magnetic powders are commercially available and can be produced by known methods. For details, paragraphs 0036 to 0039 of JP-A-2010-24113 can be referred to. The content (filling rate) of the non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90 mass %, more preferably in the range of 60 to 90 mass %.

Other details such as binders and additives for the non-magnetic layer can be applied to known techniques for non-magnetic layers. In addition, for example, the type and content of the binder, the type and content of the additive, and the like can be applied to known techniques related to magnetic layers.

Non-magnetic layers in the present invention and herein are intended to include non-magnetic powders as well as substantially non-magnetic layers containing small amounts of ferromagnetic powders, for example as impurities or intentionally. Here, the substantially non-magnetic layer means that the 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 coercive force of 7.96 kA/m (100 Oe) or less. The non-magnetic layer preferably has no residual magnetic flux density and no coercive force.

<Nonmagnetic support>
Next, the non-magnetic support (hereinafter also simply referred to as "support") will be described.
Examples of the non-magnetic 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 preferred. These supports may be previously subjected to corona discharge, plasma treatment, adhesion-enhancing treatment, heat treatment, or the like.

<Back coat layer>
The magnetic tape can also have a back coat layer containing non-magnetic powder and a binder on the surface of the non-magnetic support opposite to the surface having the magnetic layer. The backcoat layer preferably contains one or both of carbon black and inorganic powder. The binder contained in the backcoat layer and the various additives that can be optionally contained can be applied to the known techniques relating to the backcoat layer, and the known techniques relating to the formulation of the magnetic layer and/or the non-magnetic layer can be applied. can also For example, paragraphs 0018 to 0020 of JP-A-2006-331625 and US Pat. .

<Various thicknesses>
The non-magnetic support and the thickness of each layer in the magnetic tape are described below.
The thickness of the nonmagnetic support is, for example, 3.0 to 80.0 μm, preferably 3.0 to 50.0 μm, 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 recording signal band, 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. At least one magnetic layer is required, and the magnetic layer may be separated into two or more layers having different magnetic properties, and a configuration relating to a known multi-layered magnetic layer can be applied. The thickness of the magnetic layer when separated into two or more layers is the total thickness of these layers.

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

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

The thickness of each layer and the non-magnetic support can be determined by exposing a section in the thickness direction of the magnetic tape by a known technique such as an ion beam or a microtome, and then examining the exposed section with a scanning transmission electron microscope (STEM). ) shall be obtained by observing the cross section. For a specific example of the method for measuring the thickness, it is possible to refer to the description of the method for measuring the thickness in Examples described later.

<Manufacturing process>
(Preparation of each layer-forming composition)
The process of preparing a composition for forming a magnetic layer, a non-magnetic layer or a backcoat layer usually includes at least a kneading process, a dispersing process, and a mixing process provided before or after these processes as required. Each step may be divided into two or more stages. The components used for preparing each layer-forming composition may be added at the beginning or in the middle of any step. As the solvent, one or more of various solvents commonly used in the production of coating type magnetic recording media can be used. Regarding the solvent, for example, paragraph 0153 of JP-A-2011-216149 can be referred to. Alternatively, individual components may be added in two or more steps. For example, the binder may be dividedly added in the kneading step, the dispersing step, and the mixing step for viscosity adjustment after dispersion. Conventionally known manufacturing techniques can be used in various steps to manufacture the magnetic tape. In the kneading step, it is preferable to use a kneader having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader or an extruder. For details of these kneading processes, reference can be made to Japanese Patent Application Laid-Open Nos. 1-106338 and 1-79274. A known disperser can be used. Alternatively, the ferromagnetic powder and the abrasive can be dispersed separately. More specifically, separate dispersion is a step of mixing an abrasive liquid containing an abrasive and a solvent (but substantially free of ferromagnetic powder) with a magnetic liquid containing ferromagnetic powder, a solvent and a binder. This is a method of preparing a composition for forming a magnetic layer through The above-mentioned "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 unintentionally mixed as an impurity. shall be allowed to exist. Regarding ΔN, there is a tendency that the longer the dispersion time of the magnetic liquid, the larger the value of ΔN. This is because the longer the dispersion time of the magnetic liquid, the higher the dispersibility 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 thought to be because there is a tendency for the Also, the value of ΔN tends to increase as the dispersion time for mixing and dispersing the various components of the composition for forming a non-magnetic layer increases. The dispersion time of the magnetic liquid and the dispersion time of the composition for forming the non-magnetic layer may be set so as to achieve a ΔN of 0.25 or more and 0.40 or less.
Filtration may be performed by a known method at any stage of preparing each layer-forming composition. Filtration can be performed, for example, by filter filtration. As a filter used for filtration, for example, a filter having a pore size of 0.01 to 3 μm (eg, glass fiber filter, polypropylene filter, etc.) can be used.

(Coating process)
The non-magnetic layer and the magnetic layer can be formed by sequentially or simultaneously coating the composition for forming the non-magnetic layer and the composition for forming the magnetic layer. The backcoat layer is formed by applying a backcoat layer-forming composition to the surface opposite to the surface of the nonmagnetic support having the nonmagnetic layer and the magnetic layer (or the nonmagnetic layer and/or the magnetic layer is subsequently provided). It can be formed by coating. Also, the coating process for forming each layer can be divided into two or more steps. For example, in one aspect, the composition for forming the magnetic layer can be applied in two or more steps. In this case, the drying treatment may or may not be performed between the two stages of the coating process. Also, the orientation treatment may or may not be performed between the two stages of the coating process. For details of coating for forming each layer, paragraph 0066 of JP-A-2010-231843 can also be referred to. In addition, a known technique can be applied to the drying process after applying each layer-forming composition. As for the composition for forming the magnetic layer, a coating layer formed by applying the composition for forming the magnetic layer (hereinafter also referred to as "coating layer of the composition for forming the magnetic layer" or simply "coating layer"). The value of ΔN tends to increase as the drying temperature decreases. The drying temperature can be, for example, the ambient temperature at which the drying process is performed, and may be set so as to achieve a ΔN of 0.25 or more and 0.40 or less.

(Other processes)
Known techniques can be applied to other various steps for manufacturing the magnetic tape. For various steps, for example, paragraphs 0067 to 0070 of JP-A-2010-231843 can be referred to.
For example, the coating layer of the composition for forming the magnetic layer is preferably subjected to orientation treatment while the coating layer is in a wet state. From the viewpoint of the ease of achieving a ΔN of 0.25 or more and 0.40 or less, the orientation treatment involves arranging a magnet so that a magnetic field is applied perpendicularly to the surface of the coating layer of the composition for forming the magnetic layer. It is preferable to carry out by (that is, vertical alignment treatment). The strength of the magnetic field during the orientation treatment may be set so as to achieve a ΔN of 0.25 or more and 0.40 or less. When the magnetic layer-forming composition is coated in two or more steps, it is preferable to perform the orientation treatment at least after the final coating step, and more preferably to perform the vertical orientation treatment. For example, when a magnetic layer is formed by a two-step coating process, after the first coating process, a drying process is performed without performing an orientation treatment, and then the coating layer formed in the second coating process is orientation treatment can be applied.
It is also preferable to carry out calendering at any stage after drying the coated layer of the composition for forming the magnetic layer. For conditions of calendar processing, for example, paragraph 0026 of Japanese Patent Application Laid-Open No. 2010-231843 can be referred to. The value of ΔN tends to increase as the calender temperature (the surface temperature of the calender rolls) increases. The calendar temperature may be set so as to achieve a ΔN of 0.25 or more and 0.40 or less.

(One embodiment of preferred production method)
In a preferred embodiment, a coating step of forming a coating layer by coating a magnetic layer-forming composition containing a ferromagnetic powder, a binder, a curing agent, and a solvent on a non-magnetic support directly or via a non-magnetic layer. The magnetic layer can be formed through a magnetic layer forming step including a heat drying step of drying the coating layer by heat treatment and a curing step of curing the coating layer. The magnetic layer forming step preferably includes a cooling step for cooling the coating layer between the coating step and the heat drying step. burnish) preferably includes a varnish treatment step.

Carrying out the cooling step and the varnishing step in the above magnetic layer forming step is considered to be a preferable means for keeping the logarithmic decrement to 0.050 or less. Details are as follows.
Performing a cooling step of cooling the coating layer between the coating step and the heat drying step localizes the adhesive component described above on the surface and/or the surface layer portion near the surface of the coating layer. It is presumed that it contributes to This is not because cooling the coating layer of the composition for forming the magnetic layer before the heat-drying process makes it easier for the adhesive component to migrate to the coating layer surface and/or surface layer portion during the solvent volatilization in the heat-drying process. It is thought that However, the reason is not clear. Then, it is considered that the adhesive component can be removed by varnishing the surface of the coating layer in which the adhesive component is localized on the surface and/or the surface layer portion. It is presumed that performing the curing step after removing the tacky component in this way leads to a logarithmic decay rate of 0.050 or less. However, the above is only a guess, and does not limit the present invention in any way.

As described above, the composition for forming the magnetic layer and the composition for forming the non-magnetic layer can be coated sequentially or simultaneously. In a preferred embodiment, the magnetic tape can be produced by sequential multilayer coating. A manufacturing process involving sequential multi-layer coating can preferably be carried out as follows. A non-magnetic layer is formed through a coating step of forming a coating layer by coating a non-magnetic layer-forming composition on a non-magnetic support and a heat drying step of drying the formed coating layer by heat treatment. Then, a magnetic layer is formed through a coating step of forming a coating layer by applying a composition for forming a magnetic layer on the formed non-magnetic layer, and a heat drying step of drying the formed coating layer by heat treatment. .

A specific embodiment of the above manufacturing method will be described below with reference to FIG. However, the present invention is not limited to the following specific embodiments. Hereinafter, the coating layer of the composition for forming a magnetic layer before the curing treatment is sometimes referred to as the magnetic layer. This point is the same for other layers.

FIG. 4 is a schematic process diagram showing specific steps of manufacturing a magnetic tape having a nonmagnetic layer and a magnetic layer on one side of a nonmagnetic support in this order and a backcoat layer on the other side. is. In the embodiment shown in FIG. 4, the non-magnetic support (long film) is continuously fed from the feeding section and wound up by the winding section, and coating is performed in each section or zone shown in FIG. By performing various treatments such as drying and orientation, a non-magnetic layer and a magnetic layer can be sequentially formed on one side of a running non-magnetic support by multilayer coating, and a back coat layer can be formed on the other side. can. This manufacturing method can be the same as the manufacturing method commonly used for manufacturing coated magnetic tapes, except that a cooling zone is included in the magnetic layer forming step and a varnishing step is included before the hardening treatment. can.

On the non-magnetic support delivered from the delivery section, a non-magnetic layer-forming composition is applied in the first coating section (non-magnetic layer-forming composition coating step).

After the coating step, in the first heat treatment zone, the coating layer of the composition for forming a non-magnetic layer formed in the coating step is heated to dry the coating layer (heat drying step). The heat-drying step can be carried out by passing the non-magnetic support having the coating layer of the non-magnetic layer-forming composition through a heated atmosphere. The ambient temperature of the heating atmosphere here can be, for example, about 40 to 140.degree. However, the temperature is not limited to the above range, as long as the temperature is such that the solvent can be volatilized and the coating layer can be dried. Optionally, heated gas may also be blown onto the coating layer surface. The above points also apply to the heat drying step in the second heat treatment zone and the heat drying step in the third heat treatment zone, which will be described later.

Next, in the second coating section, a magnetic layer-forming composition is coated on the non-magnetic layer formed by the heating and drying process in the first heat treatment zone. coating process).

After the coating step, the coating layer of the composition for forming the magnetic layer formed in the coating step is cooled in the cooling zone (cooling step). For example, the cooling step can be performed by passing the non-magnetic support having the coating layer formed on the non-magnetic layer through a cooling atmosphere. The ambient temperature of the cooling atmosphere is 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 to when it is carried out (hereinafter also referred to as "residence time")) is not particularly limited. Since the value of the logarithmic decrement tends to decrease as the residence time is lengthened, it is preferable to perform preliminary experiments and the like to make adjustments as necessary so that a logarithmic decrement of 0.050 or less can be achieved. In the cooling step, cooled gas may be blown onto the surface of the coating layer.

After that, 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 composition for forming the magnetic layer is in a wet state. Regarding the alignment treatment, the above description can also be referred to.

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

Next, in the third coating portion, a coating layer is formed by coating a composition for forming a backcoat layer on the surface of the nonmagnetic support opposite to the surface on which the nonmagnetic layer and the magnetic layer are formed. (Step of applying composition for forming backcoat layer). After that, in the third heat treatment zone, the coating layer is heat-treated and dried.

Thus, a magnetic tape having a magnetic layer on a nonmagnetic layer on one side of a nonmagnetic support and a backcoat layer on the other side can be obtained. The magnetic tape obtained here is subjected to various treatments described later, and then becomes a product magnetic tape.

The obtained magnetic tape is wound by the winding unit and then cut (slit) into the size of the product magnetic tape. Slitting can be performed using a known cutting machine.

Before the slit magnetic tape is subjected to a curing treatment (heating, light irradiation, etc.) according to the type of curing agent contained in the magnetic layer, the surface of the magnetic layer is varnished (heat drying and curing). varnishing process between processes). It is presumed that this varnishing can remove the sticky components that are cooled in the cooling zone and migrate to the surface and/or surface layer of the magnetic layer, leading to the logarithmic decrement of 0.050 or less. However, this is only a guess and does not limit the present invention.

The burnishing treatment is a treatment of rubbing the surface of the object to be treated with a member (for example, an abrasive tape, or a grinding tool such as a grinding blade or a grinding wheel). You can do the same. However, after the cooling process and the heat-drying process, the varnishing process has not been performed before the curing process. On the other hand, the logarithmic decrement can be reduced to 0.050 or less by performing burnishing at the above stage.

Burnishing is preferably performed by rubbing (polishing) the surface of the layer to be treated with an abrasive tape and/or rubbing (grinding) the surface of the layer to be treated with a grinding tool. can be implemented. As the polishing tape, a commercially available product may be used, or a polishing tape produced by a known method may be used. As the grinding tool, known grinding blades such as fixed blades, diamond wheels and rotary blades, grinding wheels and the like can be used. Also, a wiping treatment may be performed in which the surface of the layer rubbed by the abrasive tape and/or the grinding tool is wiped off with a wiping material. For details of preferred polishing tapes, grinding tools, varnishing treatment and wiping treatment, reference can be made to paragraphs 0034 to 0048, FIG. The value of the logarithmic decay rate tends to decrease as the varnish treatment is strengthened. The burnishing treatment can be strengthened by using a high-hardness abrasive as the abrasive contained in the polishing tape, and can be strengthened by increasing the amount of abrasive in the polishing tape. In addition, it can be strengthened by using a grinding tool having a high hardness as the grinding tool. As for the burnishing conditions, the faster the sliding speed between the surface of the layer to be processed and the member (for example, the polishing tape or the grinding tool), the stronger the burnishing can be. The sliding speed can be increased by increasing one or both of the speed of moving the member and the speed of moving the magnetic tape to be processed.

After the burnishing treatment (burnishing process), the magnetic layer is subjected to a hardening treatment. In the embodiment shown in FIG. 4, the magnetic layer is subjected to surface smoothing treatment after burnishing treatment and before hardening treatment. The surface smoothing treatment is preferably performed by calendering.

Thereafter, the magnetic layer is subjected to a curing treatment according to the type of curing agent contained in this layer (curing step). The curing treatment can be performed by a treatment such as heat treatment or light irradiation depending on the type of curing agent contained in the coating layer. Curing conditions are not particularly limited, and may be appropriately set according to the formulation of the composition for forming the magnetic layer, the type of curing agent, the thickness of the magnetic layer, and the like. For example, when the magnetic layer is formed using a magnetic layer-forming composition containing polyisocyanate as a curing agent, the curing treatment is preferably heat treatment. When a layer other than the magnetic layer contains a curing agent, the curing reaction of that layer can also proceed by the curing treatment here. Alternatively, a curing step may be provided separately. In addition, you may perform a burnishing process after a hardening process.

As described above, the magnetic tape according to one aspect of the present invention can be obtained. However, the above manufacturing method is only an example, and any means capable of adjusting ΔN and the logarithmic decay rate can be used to control these values within the above ranges, and such embodiments are also included in the present invention. . A magnetic tape is usually housed in a magnetic tape cartridge, and the magnetic tape cartridge is loaded into a magnetic recording/reproducing apparatus. When information recorded on a magnetic tape is reproduced in a magnetic recording/reproducing apparatus in a low-temperature and high-humidity environment, the magnetic tape according to one aspect of the present invention can reduce the frequency of occurrence of missing pulses.

A servo pattern can be formed on the magnetic tape manufactured as described above by a known method in order to enable tracking control of a magnetic head in a magnetic recording/reproducing apparatus, control of the traveling speed of the magnetic tape, and the like. . "Formation of servo patterns" can also be called "recording of servo signals." Formation of the servo pattern will be described below.

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

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

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

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

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

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

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

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

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

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

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

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

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

The magnetic recording/reproducing device includes the magnetic tape according to one aspect of the present invention. Therefore, when reproducing information recorded on a magnetic tape in a low temperature and high humidity environment, the frequency of occurrence of missing pulses can be reduced. Also, when the magnetic layer surface slides against the head to record information on the magnetic tape in a low-temperature, high-humidity environment, the magnetic layer surface and the head may be damaged by deposits on the head caused by scraping of the magnetic layer surface. It is also possible to suppress the contact state from becoming unstable.

The present invention will be described below based on examples. However, the present invention is not limited to the modes shown in the examples. "Parts" and "%" described below are based on mass.

[Example 1]
<Preparation of abrasive liquid>
2,3-Dihydroxynaphthalene (Tokyo Chemical Industry Co., Ltd.) is added to 100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) having a gelatinization rate of about 65% and a BET (Brunauer-Emmett-Teller) specific surface area of 20 m ² /g. 3.0 parts of SO Na group-containing polyester polyurethane resin (UR-4800 manufactured by Toyobo Co., Ltd. ( _SO Na group: 0.08 meq/g) ₎ 32% 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 by weight) as a solvent, and dispersed for 5 hours with a paint shaker in the presence of zirconia beads. After dispersion, the dispersion liquid and the beads were separated by a mesh to obtain an alumina dispersion.

<Preparation of Composition for Forming Magnetic Layer>
(Magnetic liquid)
Plate-shaped 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 1 (weight average molecular weight: 70,000, SO ₃ Na group content: see Table 1)
Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (abrasive liquid)
6.0 parts of 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 (Coronate (registered trademark) manufactured by Tosoh Corporation) 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 above magnetic liquid in a batch-type vertical sand mill using beads as a dispersing medium. Zirconia beads (bead diameter: see Table 1) were used as the beads, and the beads were dispersed for the time shown in Table 1 (magnetic fluid bead dispersion time).
The magnetic liquid thus obtained, the above-mentioned abrasive liquid, silica sol, other components, and finishing additive solvent are mixed and dispersed in beads for 5 minutes, and then treated with a batch type ultrasonic device (20 kHz, 300 W) for 0.5 minutes (ultrasonic dispersion) was performed. Thereafter, filtration was performed using a filter having a pore size of 0.5 μm to prepare a composition for forming a magnetic layer.

<Preparation of composition for forming non-magnetic layer>
Of the various components of the composition for forming a non-magnetic layer below, components other than stearic acid, cyclohexanone and methyl ethyl ketone were dispersed in beads using a batch-type vertical sand mill (dispersion media: zirconia beads (bead diameter: 0.1 mm). ), dispersion time: see Table 1) to obtain a dispersion. The remaining ingredients were then added to the resulting dispersion and stirred with a dissolver stirrer. Next, the resulting dispersion was filtered using a filter (pore size 0.5 μm) to prepare a composition for forming a non-magnetic layer.

Non-magnetic 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 parts Cyclohexanone: 300.0 parts Methyl ethyl ketone: 300.0 parts

<Preparation of Composition for Forming Backcoat Layer>
Of 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 in an open kneader to obtain a mixture. After that, the resulting mixed solution is subjected to a horizontal bead mill, using zirconia beads with a bead diameter of 1.0 mm, at a bead filling rate of 80% by volume and a rotor tip peripheral speed of 10 m / sec, with a residence time of 2 minutes per pass. , and 12 passes of distributed processing were performed. The remaining ingredients were then added to the resulting dispersion and stirred with a dissolver stirrer. Next, the resulting dispersion was filtered using a filter (pore size: 1.0 μm) to prepare a composition for forming a backcoat layer.

Non-magnetic inorganic powder: α-iron oxide 80.0 parts Average particle size (average major axis length): 0.15 μm
Average acicular 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 Sulfonic acid group-containing polyurethane resin 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

<Production 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 was delivered from a delivery section, and a composition for forming a non-magnetic layer was applied to one surface of the support in a first coating section so that the thickness after drying was 0.7 μm. , and dried in the first heat treatment zone (atmospheric temperature 100° C.) to form a non-magnetic layer.
After that, the composition for forming the magnetic layer was coated on the non-magnetic layer so that the thickness after drying was 50 nm in the second coated portion to form a coated layer. While the formed coating layer was in a wet state, it was passed through a cooling zone adjusted to an ambient temperature of 0° C. for a residence time shown in Table 1 to carry out a cooling step. After that, in the orientation zone, a magnetic field having a strength shown in Table 1 was applied in a direction perpendicular to the surface of the coating layer of the composition for forming the magnetic layer to perform a vertical orientation treatment. A magnetic layer was formed by drying at ambient temperature: magnetic layer drying temperature in Table 1).
After that, in the third coated portion, a back coat layer was applied to the surface of the polyethylene naphthalate support opposite to the surface on which the non-magnetic layer and the magnetic layer were formed so that the thickness after drying was 0.5 μm. The forming composition was applied to form a coating layer, and the formed coating layer was dried in a third heat treatment zone (atmospheric temperature 100° C.) to form a backcoat layer.
After slitting the magnetic tape thus obtained to a width of 1/2 inch (0.0127 m), the surface of the magnetic layer was varnished and wiped. Burnishing treatment and wiping treatment were carried out using a commercially available polishing tape (trade name: MA22000 manufactured by Fuji Film Co., Ltd., polishing agent: diamond/Cr ₂ A commercially available sapphire blade (manufactured by Kyocera Corporation, width 5 mm, length 35 mm, tip angle 60 degrees) is used as a grinding blade, and a commercially available wiping material (manufactured by Kuraray Co. _, Ltd.) is used as a wiping material. was performed using the name WRP736). As the processing conditions, the processing conditions in Example 12 of JP-A-6-52544 were adopted.
After the varnishing and wiping treatments, a calender roll composed only of metal rolls was used at a speed of 80 m/min, a linear pressure of 300 kg/cm (294 kN/m), and a calender temperature shown in Table 1 (surface temperature of the calender roll). Calendering treatment (surface smoothing treatment) was performed.
After that, heat treatment (curing treatment) was performed for 36 hours in an environment with an ambient temperature of 70° C., and then a servo pattern was formed on the magnetic layer using a commercially available servo writer.
As described above, the magnetic tape of Example 1 was obtained.

[Example 4, Comparative Examples 1 to 6]
A magnetic tape was produced in the same manner as in Example 1, except that various items shown in Table 1 were changed as shown in Table 1.
In Table 1, the magnetic tapes were produced without performing orientation treatment on the coating layer of the composition for forming the magnetic layer in the comparative examples described as "no orientation treatment" in the "formation and orientation of magnetic layer" column.
In Table 1, the cooling zone stay time column and the varnish treatment before hardening column indicate "unperformed". A magnetic tape was produced by a manufacturing process without nishing and wiping.

[Example 2]
After forming the non-magnetic layer, a first coating layer was formed by coating the composition for forming the magnetic layer on the surface of the non-magnetic layer so that the thickness after drying was 25 nm. This first coating layer was passed through an atmosphere at the ambient temperature (magnetic layer drying temperature) shown in Table 1 without application of a magnetic field to form a first magnetic layer (without orientation treatment).
Thereafter, a second coating layer was formed by coating the composition for forming a magnetic layer on the surface of the first magnetic layer so that the thickness after drying was 25 nm. While the formed second coating layer was in a wet state, it was passed through a cooling zone adjusted to an ambient temperature of 0° C. for a residence time shown in Table 1 to perform a cooling step. After that, in the orientation zone, a magnetic field having an intensity shown in Table 1 was applied in a direction perpendicular to the surface of the second coating layer to perform vertical orientation treatment, and then a second heat treatment zone (ambient temperature: magnetic field in Table 1 layer drying temperature) to form a second magnetic layer.
A magnetic tape was produced in the same manner as in Example 1, except that the multi-layered 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 residence time in the cooling zone was changed as shown in Table 1.

[Comparative Example 7]
After forming the non-magnetic layer, a first coating layer was formed by coating the composition for forming the magnetic layer on the surface of the non-magnetic layer so that the thickness after drying was 25 nm. While the first coating layer was in a wet state, a magnetic field having a strength shown in Table 1 was applied to the surface of the first coating layer using opposing magnets in an atmosphere at an ambient temperature (magnetic layer drying temperature) shown in Table 1. A vertical orientation treatment and a drying treatment were performed by applying voltage in a direction perpendicular to the magnetic field to form a first magnetic layer.
Thereafter, a second coating layer was formed by coating the composition for forming a magnetic layer on the surface of the first magnetic layer so that the thickness after drying was 25 nm. This second coating layer was passed through an atmosphere at the ambient temperature (magnetic layer drying temperature) shown in Table 1 without application of 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 multi-layered magnetic layer was formed as described above.

[Comparative Example 8]
After forming the non-magnetic layer, a first coating layer was formed by coating the composition for forming the magnetic layer on the surface of the non-magnetic layer so that the thickness after drying was 25 nm. While the first coating layer was in a wet state, a magnetic field having a strength shown in Table 1 was applied to the surface of the first coating layer using opposing magnets in an atmosphere at an ambient temperature (magnetic layer drying temperature) shown in Table 1. A vertical orientation treatment and a drying treatment were performed by applying voltage in a direction perpendicular to the magnetic field to form a first magnetic layer.
Thereafter, a second coating layer was formed by coating the composition for forming a magnetic layer on the surface of the first magnetic layer so that the thickness after drying was 25 nm. This second coating layer was passed through an atmosphere at the ambient temperature (magnetic layer drying temperature) shown in Table 1 without application of a magnetic field to form a second magnetic layer (without orientation treatment).
Except for the fact that the multilayer magnetic layer was formed as described above, and that the magnetic tape was produced by a manufacturing process that did not include a cooling zone in the magnetic layer formation process and did not perform varnishing and wiping treatments before hardening treatment, comparison was made. A magnetic tape was produced in the same manner as in Example 6.

[Comparative Example 9]
After forming the non-magnetic layer, a first coating layer was formed by coating the composition for forming the magnetic layer on the surface of the non-magnetic layer so that the thickness after drying was 25 nm. This first coating layer was passed through an atmosphere at an ambient temperature (magnetic layer drying temperature) shown in Table 1 without application of a magnetic field to form a first magnetic layer (without orientation treatment).
Thereafter, a second coating layer was formed by coating the composition for forming a magnetic layer on the surface of the first magnetic layer so that the thickness after drying was 25 nm. While the second coating layer is in a wet state, a magnetic field having a strength shown in Table 1 is applied to the surface of the second coating layer using opposing magnets in an atmosphere at an ambient temperature (magnetic layer drying temperature) shown in Table 1. A vertical orientation treatment and a drying treatment were performed by applying a voltage in a direction perpendicular to the magnetic field to form a second magnetic layer.
A magnetic tape was produced in the same manner as in Comparative Example 3, except that the multi-layered magnetic layer was formed as described above.

[Evaluation of physical properties of magnetic tape]
(1) Measurement of Logarithmic Decay Rate of Magnetic Layer As a measuring device, a rigid pendulum physical property tester RPT-3000W manufactured by A&D Co., Ltd. (pendulum: made of brass, substrate: glass substrate, substrate temperature rise rate: 5° C./ min) was used to determine the logarithmic decrement of the magnetic layer of the magnetic tape by the method described above. A sample for measurement cut out from the magnetic tape was placed on a glass substrate having a size of about 3 cm×about 5 cm, with a fixing tape (Kapton tape manufactured by Toray DuPont) fixed at four locations as shown in FIG. An adsorption time of 1 second and a measurement interval of 7 to 10 seconds was used to create a displacement-time curve for the 86th measurement interval, and this curve was used to determine the logarithmic decay rate. Measurement was performed in an environment with a relative humidity of about 50%.

(2) Thickness of Non-Magnetic Support and Each Layer The thicknesses of the magnetic layer, non-magnetic layer, non-magnetic support and back coat layer of each magnetic tape produced were measured by the following methods. As a result of measurement, the thickness of the magnetic layer was 50 nm, the thickness of the non-magnetic layer was 0.7 μm, the thickness of the non-magnetic support was 5.0 μm, and the thickness of the backcoat layer was 0.5 μm. rice field.
The thicknesses of the magnetic layer, non-magnetic layer and non-magnetic support measured here were used to calculate the refractive index below.
(i) Preparation of sample for cross-sectional observation According to the method described in paragraphs 0193 to 0194 of JP-A-2016-177851, including the entire region in the thickness direction from the magnetic layer side surface to the backcoat layer side surface of the magnetic tape. A sample for cross-sectional observation was prepared.
(ii) Thickness measurement The produced sample was observed by STEM, and an STEM image was taken. This STEM image is a STEM-HAADF (High-Angle Annular Dark Field) image taken at an acceleration voltage of 300 kV and an imaging magnification of 450,000 times. The image was taken so as to include the entire area in the thickness direction. In the STEM image thus obtained, a straight line connecting both ends of a line representing the surface of the magnetic layer was determined as a reference line representing the surface of the magnetic layer on the side of the magnetic layer. The straight line connecting the two ends of the line segment is, for example, an STEM image when an STEM image is taken such that the magnetic layer side of the sample for cross-sectional observation is positioned above the image and the backcoat layer side is positioned below the image. is a straight line connecting the intersection of the left side of the image (having a rectangular or square shape) and the line segment and the intersection of the right side of the STEM image and the line segment. Similarly, the reference line representing the interface between the magnetic layer and the non-magnetic layer, the reference line representing the interface between the non-magnetic layer and the non-magnetic support, the reference line representing the interface between the non-magnetic support and the back coat layer, the 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 a 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 non-magnetic layer. Similarly, the thicknesses of the non-magnetic layer, the non-magnetic support and the back coat layer were determined.

(3) ΔN of the magnetic layer
In the following, M-2000U manufactured by Woollam was used as an ellipsometer. The creation and fitting of the two-layer model or the one-layer model were performed using WVASE32 manufactured by Woollam as analysis software.
(i) Measurement of refractive index of non-magnetic support A sample for measurement was cut out from each magnetic tape, and the back coat layer of the sample for measurement was wiped off with a cloth impregnated with methyl ethyl ketone to expose the surface of the non-magnetic support. The surface was then roughened with sandpaper so that reflected light from the exposed surface would not be detected in subsequent ellipsometer measurements.
Then, after wiping off the magnetic layer and non-magnetic layer of the measurement sample with a cloth impregnated with methyl ethyl ketone, the surface of the silicon wafer and the roughened surface are adhered using static electricity to obtain a sample for measurement. The sample was placed on a silicon wafer with the surface of the non-magnetic support exposed by removing the magnetic layer and the non-magnetic layer (hereinafter referred to as "magnetic layer side surface of the non-magnetic support") facing upward. .
Using an ellipsometer, incident light was incident on the surface of the magnetic layer side of the non-magnetic support of the measurement sample on the silicon wafer, and Δ and ψ were measured as described above. Using the obtained measured value and the thickness of the non-magnetic support obtained in (2) above, the refractive index of the non-magnetic support (refractive index in the longitudinal direction, refractive index in the width direction, refractive index in the longitudinal direction, refractive index in the The refractive index in the thickness direction measured by incident light from the direction and the refractive index in the thickness direction measured by incident light incident from the width direction) were obtained.
(ii) Measurement of refractive index of non-magnetic layer A sample for measurement was cut out from each magnetic tape, and the back coat layer of the sample for measurement was wiped off with a cloth impregnated with methyl ethyl ketone to expose the surface of the non-magnetic support. Afterwards, this surface was roughened with sandpaper so that the reflected light of the exposed surface was not detected in subsequent spectroscopic ellipsometer measurements.
Thereafter, the surface of the magnetic layer of the sample for measurement was lightly wiped with a cloth impregnated with methyl ethyl ketone to remove the magnetic layer to expose the surface of the non-magnetic layer. A sample was placed.
The non-magnetic layer surface of the measurement sample on this silicon wafer is measured using an ellipsometer, and the refractive index of the non-magnetic layer (refractive index in the longitudinal direction, refractive index in the width direction, , the refractive index in the thickness direction measured with incident light incident from the longitudinal direction, and the refractive index in the thickness direction measured with incident light incident from the width direction) were determined.
(iii) Refractive index measurement of magnetic layer After cutting out a measurement sample from each magnetic tape and wiping off the back coat layer of the measurement sample with a cloth impregnated with methyl ethyl ketone to expose the surface of the non-magnetic support. This surface was roughened with sandpaper so that reflected light from the exposed surface would not be detected in subsequent spectroscopic ellipsometer measurements.
Thereafter, a measurement sample was placed on a silicon wafer in the same manner as in (i) above.
The magnetic layer surface of the measurement sample on this silicon wafer was measured using an ellipsometer, and spectroscopic ellipsometry was used to determine the refractive index of the magnetic layer (refractive index Nx in the longitudinal direction, refractive index Nx in the width direction, Refractive index Ny, refractive index Nz ₁ in the thickness direction measured by incident light from the longitudinal direction, and refractive index Nz ₂ in the thickness direction measured by incident light incident from the width direction were determined. Nxy and Nz were obtained from the obtained values, and the absolute value ΔN of the difference between them was obtained. For both 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)
The vertical squareness ratio of the magnetic tape is the squareness ratio measured in the vertical direction of the magnetic tape. The "perpendicular direction" described in relation to the squareness ratio means the direction perpendicular to the surface of the magnetic layer. For each magnetic tape of Examples and Comparative Examples, 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) to obtain the vertical squareness ratio. The measured value is a value after demagnetization correction, and is obtained by subtracting the magnetization of the sample probe of the vibrating sample magnetometer as background noise. In one aspect, the vertical squareness ratio of the magnetic tape is preferably 0.60 or more and 1.00 or less, more preferably 0.65 or more and 1.00 or less. Also, in one aspect, the perpendicular squareness ratio of the magnetic tape can be, for example, less than or equal to 0.90, less than or equal to 0.85, or less than or equal to 0.80, or even greater than these values.

[Frequency of missing pulses under low temperature and high humidity environment]
The following measurements were performed under a low temperature and high humidity environment with a temperature of 13° C. and a relative humidity of 80%.
A magnetic tape cartridge containing each magnetic tape (total length of magnetic tape: 500 m) of Examples and Comparative Examples was set in an IBM LTO-G6 (Linear Tape-Open Generation 6) drive, and the magnetic tape was applied with a tension of 0.6 N. , 1500 reciprocations at a running speed of 8 m/sec.
The magnetic tape cartridge after running was set in a reference drive (LTO-G6 drive manufactured by IBM), and the magnetic tape was run to perform recording and reproduction. A reproduced signal during running is taken into an external AD (Analog/Digital) converter, and a signal whose reproduced signal amplitude has decreased by 70% or more relative to the average (average of measured values for all tracks) is regarded as a missing pulse, and its occurrence frequency. (number of occurrences) was divided by the total length of the magnetic tape to obtain the frequency of occurrence of missing pulses per unit length (per 1 m) of the magnetic tape (unit: times/m). If the frequency of occurrence of missing pulses is 5 times/m or less, it can be judged that the magnetic tape has high practical reliability.

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

From the results shown in Table 1, the magnetic tapes of Examples 1 to 4, in which the ΔN and the logarithmic decrement of the magnetic layer are within the ranges described above, are superior to the magnetic tapes of Comparative Examples 1 to 9 in a low-temperature, high-humidity environment. It can be confirmed that the frequency of occurrence of missing pulses is reduced.
The squareness ratio is generally known as an index of the state of existence of ferromagnetic powder in the magnetic layer. However, as shown in Table 1, even magnetic tapes having the same vertical squareness ratio have different ΔN values (for example, Example 1 and Comparative Example 8). The present inventor believes that this indicates that ΔN is a value affected by other factors in addition to the state of existence of the ferromagnetic powder in the magnetic layer.

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

Claims (6)

A magnetic tape having a magnetic layer containing ferromagnetic powder on a non-magnetic support,
The non-magnetic support contains one or more selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide and aromatic polyamide,
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, and A magnetic tape whose surface has a logarithmic decrement of 0.050 or less as determined by a pendulum viscoelasticity test. 2. The magnetic tape according to claim 1, wherein a difference between said refractive index Nxy and said refractive index Nz, Nxy-Nz, is 0.25 or more and 0.40 or less. 3. The magnetic tape according to claim 1, wherein said logarithmic decrement is 0.010 or more and 0.050 or less. 4. The magnetic tape according to claim 1, further comprising a non-magnetic layer containing non-magnetic powder between said non-magnetic support and said magnetic layer. 5. The magnetic tape according to any one of claims 1 to 4, further comprising a backcoat layer containing a nonmagnetic powder on the surface of the nonmagnetic support opposite to the surface having the magnetic layer. A magnetic tape according to any one of claims 1 to 5;
a magnetic head;
A magnetic recording and reproducing device including

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