JP2021007065A - Magnetic tape, magnetic tape cartridge, and magnetic tape device - Google Patents

Abstract

To provide a magnetic tape having a total thickness of a non-magnetic layer and a magnetic layer of 0.60 μm or less, with little deterioration in electromagnetic conversion characteristics during repeated reproduction under low temperature and high humidity environment.SOLUTION: Provided is a magnetic tape having a non-magnetic layer containing a non-magnetic powder and a binder on a non-magnetic support medium, and having a magnetic layer containing a ferromagnetic powder and the binder on the non-magnetic layer, wherein a total thickness of the non-magnetic layer and the magnetic layer is 0.60 μm or less, and an isoelectric point of a surface zeta potential of the magnetic layer is 5.5 or more, the magnetic layer contains an oxide abrasive, and an average particle diameter of the oxide abrasive obtained from a secondary ion image obtained by irradiating the surface of the magnetic layer with a focused ion beam is 0.04 μm or more and 0.08 μm or less. Also provided are a magnetic tape cartridge including the magnetic tape and a magnetic tape device including the magnetic tape and a magnetic head.SELECTED DRAWING: None

Description

The present invention relates to magnetic tapes, magnetic tape cartridges and magnetic tape devices.

There are tape-shaped and disk-shaped magnetic recording media, and tape-shaped magnetic recording media, that is, magnetic tapes are mainly used for data storage applications such as data backup. For recording and / or reproduction of information on a magnetic tape, a magnetic tape cartridge containing the magnetic tape is usually mounted on the drive, and the magnetic tape is run in the drive to run the magnetic tape on the magnetic tape surface (magnetic layer surface) and the magnetic head. (Hereinafter, also simply referred to as "head") is brought into contact with and slid. As the magnetic tape, a tape having a structure in which a magnetic layer containing an abrasive in addition to a ferromagnetic powder and a binder is provided on a non-magnetic layer is widely used (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-243162

One of the desired performances of the magnetic tape is that it can exhibit excellent electromagnetic conversion characteristics when reproducing the information recorded on the magnetic tape. However, if the magnetic layer surface and / or the head is scraped while the magnetic layer surface and the head are repeatedly slid, a phenomenon (so-called spacing loss) occurs in which the distance between the magnetic layer surface and the regenerating element of the head increases. Resulting in. In this regard, for example, as described in Patent Document 1, the inclusion of an abrasive in the magnetic layer can contribute to providing head cleaning property on the surface of the magnetic layer by the abrasive. By providing the head cleaning property on the surface of the magnetic layer, it is possible to prevent foreign matter generated by scraping the surface of the magnetic layer from intervening between the surface of the magnetic layer and the head to cause a spacing loss. However, on the other hand, the higher the head cleaning property of the magnetic layer surface, the easier it is for the head to be scraped due to sliding with the magnetic layer surface, which also causes a spacing loss. Such a spacing loss causes a phenomenon in which the electromagnetic conversion characteristic deteriorates as the information recorded on the magnetic tape is repeatedly reproduced (hereinafter, also referred to as “decrease in the electromagnetic conversion characteristic in repeated reproduction”).

By the way, the magnetic tape is usually housed in a magnetic tape cartridge, distributed, and used. In order to increase the recording capacity per roll of the magnetic tape cartridge, it is desirable to increase the total length of the magnetic tape contained in one roll of the magnetic tape cartridge. For that purpose, it is required to make the magnetic tape thinner (hereinafter, referred to as "thinner"). As one of the means for reducing the thickness of the magnetic tape, for the magnetic tape having the non-magnetic layer and the magnetic layer in this order on the non-magnetic support, the total thickness of the non-magnetic layer and the magnetic layer should be reduced. Can be mentioned. However, as a result of examination by the present inventors, in a magnetic tape in which the total thickness of the non-magnetic layer and the magnetic layer is reduced to 0.60 μm or less, the total thickness of the non-magnetic layer and the magnetic layer exceeds 0.60 μm. It was found that the electromagnetic conversion characteristics in repeated reproduction are more likely to be deteriorated in a low temperature and high humidity environment than the tape. Since the magnetic tape can be used in a low temperature and high humidity environment, it is desirable to be able to suppress a decrease in electromagnetic conversion characteristics during repeated reproduction in such an environment.

One aspect of the present invention provides a magnetic tape in which the total thickness of the non-magnetic layer and the magnetic layer is 0.60 μm or less, and the electromagnetic conversion characteristics are less deteriorated in repeated reproduction in a low temperature and high humidity environment. The purpose is to do.

One aspect of the present invention is
Having a non-magnetic layer containing non-magnetic powder and binder on a non-magnetic support,
Having a magnetic layer containing a ferromagnetic powder and a binder on the non-magnetic layer,
The total thickness of the non-magnetic layer and the magnetic layer is 0.60 μm or less.
The isoelectric point of the surface zeta potential of the magnetic layer is 5.5 or more.
The magnetic layer contains an oxide polishing agent, and the average particles of the oxide polishing agent obtained from a secondary ion image obtained by irradiating the surface of the magnetic layer with a focused ion beam (FIB). A magnetic tape having a diameter (hereinafter, also referred to as “FIB abrasive diameter”) of 0.04 μm or more and 0.08 μm or less.
Regarding.

In one aspect, the isoelectric point can be 5.5 or more and 7.0 or less.

In one aspect, the magnetic layer can contain a binder having an acidic group.

In one aspect, the acidic group can be at least one acidic group selected from the group consisting of sulfonic acid groups and salts thereof.

In one aspect, the oxide abrasive can be an alumina powder.

In one aspect, the total thickness of the non-magnetic layer and the magnetic layer can be 0.15 μm or more and 0.60 μm or less.

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

One aspect of the present invention relates to a magnetic tape cartridge containing the above magnetic tape.

One aspect of the present invention relates to a magnetic tape device including the magnetic tape and a magnetic head.

According to one aspect of the present invention, a magnetic tape having a total thickness of a non-magnetic layer and a magnetic layer of 0.60 μm or less and capable of suppressing a decrease in electromagnetic conversion characteristics during repeated reproduction in a low temperature and high humidity environment. Can be provided. Further, according to one aspect of the present invention, it is possible to provide a magnetic tape cartridge and a magnetic tape device including the above magnetic tape.

[Magnetic tape]
One aspect of the present invention has a non-magnetic layer containing a non-magnetic powder and a binder on a non-magnetic support, a magnetic layer containing a ferromagnetic powder and a binder on the non-magnetic layer, and the non-magnetic layer. The total thickness of the magnetic layer and the magnetic layer is 0.60 μm or less, the isoelectric point of the surface zeta potential of the magnetic layer is 5.5 or more, the magnetic layer contains an oxide polishing agent, and the above. The average particle diameter (FIB polishing agent diameter) of the oxide polishing agent obtained from the secondary ion image obtained by irradiating the surface of the magnetic layer with a focused ion beam is 0.04 μm or more and 0.08 μm or less. Regarding.

In the present invention and the present specification, "the surface of the magnetic layer" is synonymous with the surface of the magnetic tape on the magnetic layer side.

In the present invention and the present specification, the isoelectric point of the surface zeta potential of the magnetic layer is the pH at which the surface zeta potential of the magnetic layer measured by the flow potential method (also referred to as the flow current method) becomes zero. The value. A sample is cut out from the magnetic tape to be measured, and the sample is placed in the measurement cell so that the surface of the magnetic layer, which is the target surface for which the surface zeta potential is obtained, is in contact with the electrolytic solution. The surface zeta potential is calculated by the following formula after changing the pressure in the measurement cell to flow an electrolytic solution and measuring the flow potential at each pressure.

[Ζ: Surface zeta potential, p: Pressure, I: Flow potential, η: Electrolyte solution viscosity, ε: Electrolytic solution relative permittivity, ε- ₀ : Vacuum dielectric constant, L: Channel (between two electrodes) Flow path) length, A: channel cross-sectional area]

The pressure is varied in the range of 0 to 400,000 Pa (0 to 400 mbar). The flow potential is measured by flowing the electrolytic solution through the measurement cell, and the surface zeta potential is calculated using electrolytic solutions having different pH (from pH 9 to pH 3 in steps of about 0.5). The measurement points are a total of 13 points starting from the measurement point of pH 9 and ending with the 13th measurement point of pH 3. In this way, the surface zeta potential is obtained for each pH measurement point. Since the value of the surface zeta potential decreases as the pH decreases, two measurement points appear in which the polarity of the surface zeta potential changes (changes from a positive value to a negative value) as the pH decreases from 9 to 3. In some cases. When such two measurement points appear, the pH at zero surface zeta potential is obtained by interpolation using a straight line (linear function) showing the relationship between the surface zeta potential and pH of those two measurement points. .. On the other hand, when the surface zeta potentials obtained while the pH drops from 9 to 3 are all positive values, the surfaces of the 13th measurement point (pH 3) and the 12th measurement point, which are the final measurement points. Using a straight line (linear function) showing the relationship between the zeta potential and pH, the pH at zero surface zeta potential is obtained by extrapolation. On the other hand, when the surface zeta potentials obtained while the pH drops from 9 to 3 are all negative values, the surfaces of the first measurement point (pH 9) and the twelfth measurement point, which are the first measurement points. The pH at zero surface zeta potential is extrapolated using a straight line (linear function) showing the relationship between the zeta potential and pH. In this way, the value of pH when the surface zeta potential of the magnetic layer measured by the flow potential method becomes zero is obtained.
The above measurement is performed three times in total at room temperature using different samples cut out from the same magnetic tape (magnetic tape to be measured), and the pH at which the surface zeta potential becomes zero is determined for each sample. As the viscosity and relative permittivity of the electrolytic solution, the measured values at room temperature are used. Room temperature is in the range of 20 to 27 ° C. The arithmetic mean of the three pH values thus obtained is set as the isoelectric point of the surface zeta potential of the magnetic layer of the magnetic tape to be measured. Further, as the electrolytic solution having pH 9, a 1 mmol / L KCl aqueous solution adjusted to pH 9 with a 0.1 mol / L KOH aqueous solution is used. As the electrolytic solution having another pH, the electrolytic solution having a pH of 9 adjusted in this way is adjusted in pH with a 0.1 mol / L HCl aqueous solution.

In the present invention and the present specification, the "oxide abrasive" means a non-magnetic oxide powder having a Mohs hardness of more than 8.

In the present invention and the present specification, the FIB abrasive diameter is a value obtained by the following method.
(1) Acquisition of secondary ion image A focused ion beam device is used to acquire a secondary ion image in a region of 25 μm square (25 μm × 25 μm) on the surface of the magnetic layer of the target magnetic tape for which the diameter of the FIB abrasive is to be determined. As the focused ion beam device, MI4050 manufactured by Hitachi High-Technologies Corporation can be used.
The beam irradiation conditions of the focused ion beam device when acquiring the secondary ion image are set to an acceleration voltage of 30 kV, a current value of 133 pA (picoampere), a BeamSize of 30 nm, and a Voltage of 50%. No coating treatment is performed on the surface of the magnetic layer before imaging. A secondary ion detector detects a secondary ion (SI; secondary ion) signal and images a secondary ion image. The imaging conditions for the secondary ion image are determined by the following method. ACB (Auto Control Brightness) is performed (that is, ACB is performed three times) at three non-imaging regions on the surface of the magnetic layer to stabilize the color of the image and determine the contrast reference value and the brightness reference value. .. The contrast value 1% lower than the contrast reference value determined by the ACB and the above-mentioned brightness reference value are used as imaging conditions. An unimaging region on the surface of the magnetic layer is selected, and a secondary ion image is imaged under the imaging conditions determined above. The part displaying the size and the like (micron bar, cross mark, etc.) is erased from the captured image, and a secondary ion image having a pixel number of 2000pixel × 2000pixel is acquired. For specific examples of imaging conditions, the examples described later can be referred to.
(2) Calculation of FIB Abrasive Diameter The secondary ion image obtained in (1) above is taken into image processing software and binarized according to the following procedure. As the image analysis software, for example, the free software ImageJ can be used.
The color tone of the secondary ion image acquired in (1) above is changed to 8 bits. The threshold value for the binarization process is 250 tones for the lower limit and 255 tones for the upper limit, and the binarization process is executed according to these two thresholds. After the binarization process, the noise component removal process is performed by image analysis software. The noise component removing process can be performed by, for example, the following method. In the image analysis software ImageJ, the noise cut processing Despeckle is selected, and the Size 4.0-Infinity is set in the Analyze Party to remove the noise component.
In the binarized image thus obtained, each part that shines white is determined to be an oxide abrasive, and the number of parts that shine white is determined by image analysis software, and the area of each part that shines white is determined. From the area of each part that glows white, the diameter equivalent to the circle of each part is obtained. Specifically, the circle equivalent diameter L is calculated from the obtained area A by (A / π) ^ (1/2) × 2 = L.
The above steps were carried out four times at different locations (25 μm square) on the surface of the magnetic layer of the magnetic tape for which the FIB abrasive diameter was to be determined, and from the results obtained, the FIB abrasive diameter was determined to be the FIB abrasive diameter = Σ. Calculated by (Li) / Σi. Σi is the total number of white glowing portions observed in the binarized image obtained by the four times. Σ (Li) is the total of the equivalent circle diameters L obtained for each portion that glows white observed in the binarized image obtained by the four times. Regarding the portion that glows white, it is possible that only a part of the portion is included in the binarized image. In such a case, Σi and Σ (Li) are obtained without including that part.

Although the magnetic tape has a total thickness of 0.60 μm or less between the non-magnetic layer and the magnetic layer, the present inventors suppress a decrease in electromagnetic conversion characteristics during repeated reproduction in a low temperature and high humidity environment. The reason why it can be done is inferred as follows.

As described above, the magnetic tape in which the total thickness of the non-magnetic layer and the magnetic layer is reduced to 0.60 μm or less is compared with the magnetic tape in which the total thickness of the non-magnetic layer and the magnetic layer is more than 0.60 μm. It was found that in a low temperature and high humidity environment, deterioration of the electromagnetic conversion characteristics in repeated regeneration is likely to occur. The reason is considered to be that the contact state between the magnetic layer surface and the head changes as the total thickness of the non-magnetic layer and the magnetic layer decreases. The present inventors speculate that one of the causes of the spacing loss is that the head is easily partially scraped by the oxide abrasive present in the magnetic layer due to this change in the contact state.
On the other hand, the FIB abrasive diameter is a value that can be used as an index of the presence state of the oxide abrasive in the magnetic layer, and is obtained by irradiating the surface of the magnetic layer with a focused ion beam (FIB). Obtained from the statue. This secondary ion image is generated by capturing the secondary ions generated from the surface of the magnetic layer irradiated with FIB. On the other hand, as a method of observing the presence state of the abrasive in the magnetic layer, as described in paragraph 0109 of JP-A-2005-243162 (Patent Document 1), for example, a scanning electron microscope (SEM) is used. A method using a Scanning Electron Microscope) has been proposed. In SEM, the surface of the magnetic layer is irradiated with an electron beam, and secondary electrons emitted from the surface of the magnetic layer are captured to generate an image (SEM image). Due to such a difference in the image generation principle, even if the same magnetic layer is observed, the size of the oxide abrasive obtained from the secondary ion image and the size of the oxide abrasive obtained from the SEM image are different. It becomes. As a result of diligent studies, the present inventors have set the FIB abrasive diameter obtained by the method described above from the above secondary ion image as a new index of the presence state of the oxide abrasive in the magnetic layer, and used the FIB abrasive. It has been decided to control the presence state of the oxide abrasive in the magnetic layer so that the diameter is 0.04 μm or more and 0.08 μm or less. By controlling the presence state of the oxide abrasive in the magnetic layer in this way, in a magnetic tape having a total thickness of the non-magnetic layer and the magnetic layer of 0.60 μm or less, electromagnetic waves in repeated regeneration in a low temperature and high humidity environment The present inventors consider that it contributes to suppressing the deterioration of the conversion characteristics. Specifically, the FIB abrasive diameter of 0.08 μm or less contributes to the suppression of head scraping, and the FIB abrasive diameter of 0.04 μm or more suppresses head scraping in a low temperature and high humidity environment. The present inventors speculate that it contributes to imparting head cleaning property to the surface of the magnetic layer.
On the other hand, the magnetic layer in which the oxide abrasive is present so that the FIB abrasive diameter is 0.04 μm or more and 0.08 μm or less is head-cleaned as compared with the magnetic layer in which the FIB abrasive diameter exceeds the above range. The sex is considered to be low. Therefore, if no measures are taken, it is presumed that the foreign matter adhering to the head is not sufficiently removed and spacing loss occurs, and even if the head scraping can be suppressed, the electromagnetic conversion characteristics are deteriorated. On the other hand, as a result of diligent studies, the present inventors have found that the total thickness of the non-magnetic layer and the magnetic layer is 0.60 μm or less, and the diameter of the FIB abrasive is 0.04 μm or more and 0.08 μm or less. In a magnetic tape having a magnetic layer in which an oxide polishing agent is present, the isoelectric point of the surface zeta potential of the magnetic layer is set to 5.5 or more so that it can be repeatedly regenerated in a low temperature and high humidity environment. We have newly found that the deterioration of electromagnetic conversion characteristics can be suppressed. The reason for this is that the present inventors have found that a magnetic tape having an isoelectric point of the surface zeta potential of the magnetic layer of 5.5 or more, that is, in the pH range from near neutral to basic, can be scraped even if the surface of the magnetic layer is scraped. It is inferred that the foreign matter generated by the above is difficult to stick to the head.
As described above, as a result of reducing the spacing loss by suppressing the scraping of the head and suppressing the adhesion of foreign matter to the head, the total thickness of the non-magnetic layer and the magnetic layer is reduced to 0.60 μm or less. In the present invention, the present inventors presume that it is possible to suppress a decrease in electromagnetic conversion characteristics during repeated regeneration in a low temperature and high humidity environment. However, the present invention is not limited to the above inference.

Hereinafter, the magnetic tape will be described in more detail.

<Magnetic layer>
(Isoelectric point of the surface zeta potential of the magnetic layer)
The method for measuring the isoelectric point of the surface zeta potential of the magnetic layer is as described above. The isoelectric point of the surface zeta potential obtained by such a measuring method is the isoelectric point obtained for the surface of the magnetic layer. In the above magnetic tape having a total thickness of the non-magnetic layer and the magnetic layer of 0.60 μm or less, the surface zeta potential of the magnetic layer is determined from the viewpoint of suppressing deterioration of electromagnetic conversion characteristics during repeated reproduction in a low temperature and high humidity environment. The isoelectric point is 5.5 or more, preferably 5.7 or more, and more preferably 6.0 or more. The isoelectric point of the surface zeta potential of the magnetic layer can be controlled by the type of the component used for forming the magnetic layer, the process of forming the magnetic layer, and the like, as will be described in detail later. From the viewpoint of ease of control and the like, the isoelectric point of the surface zeta potential of the magnetic layer is preferably 7.0 or less, more preferably 6.7 or less, and 6.5 or less. Is more preferable.

(FIB Abrasive Diameter)
The FIB abrasive diameter obtained from the secondary ion image obtained by irradiating the surface of the magnetic layer of the magnetic tape with FIB is 0.04 μm or more and 0.08 μm or less. In the above magnetic tape having a total thickness of the non-magnetic layer and the magnetic layer of 0.60 μm or less, the FIB abrasive diameter is set from the viewpoint of further suppressing the deterioration of the electromagnetic conversion characteristics during repeated reproduction in a low temperature and high humidity environment. It is preferably 0.05 μm or more, and more preferably 0.06 μm or more. From the same viewpoint, the FIB abrasive diameter is preferably 0.07 μm or less. Specific aspects of the means for adjusting the diameter of the FIB abrasive will be described later.

(Ferromagnetic powder)
As the ferromagnetic powder contained in the magnetic layer, a ferromagnetic powder usually used in the magnetic layer of various magnetic recording media can be used. It is preferable to use a ferromagnetic powder having a small average particle size from the viewpoint of improving the recording density of the magnetic tape. From this point of view, as the ferromagnetic powder, it is preferable to use a ferromagnetic powder having an average particle size of 50 nm or less, and more preferably to use a ferromagnetic powder having an average particle size of 40 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 10 nm or more, further preferably 15 nm or more, and more preferably 20 nm or more. Is more preferable.

A preferred specific example of the ferromagnetic powder is a hexagonal ferrite powder. For details of the hexagonal ferrite powder, for example, paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 of JP2012-204726 and the like. References can be made to paragraphs 0029 to 0084 of JP-A-2015-127985.

A metal powder can also be mentioned as a preferable specific example of the ferromagnetic powder. For details of the metal powder, for example, paragraphs 0137 to 0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351 can be referred to.

As a preferable specific example of the ferromagnetic powder, ε-iron oxide powder can also be mentioned. As a method for producing ε-iron oxide powder, a method for producing from goethite, a reverse micelle method, and the like are known. All of the above manufacturing methods are known. Regarding the method for producing ε-iron oxide powder in which a part of Fe is substituted with a substituent such as Ga, Co, Ti, Al, Rh, for example, J.I. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J. Mol. Mater. Chem. C, 2013, 1, pp. 5200-5206 and the like can be referred to. However, the method for producing ε-iron oxide powder that can be used as the ferromagnetic powder in the magnetic layer is not limited.

Unless otherwise specified in the present invention and the present specification, the average particle size of various powders such as ferromagnetic powders is a value measured by the following method using a transmission electron microscope.
The powder is photographed using a transmission electron microscope at an imaging magnification of 100,000 times, and printed on photographic paper so as to have a total magnification of 500,000 times to obtain a photograph of the particles constituting the powder. Select the target particle from the obtained photograph of the particle, trace the outline of the particle with a digitizer, and measure the size of the particle (primary particle). Primary particles are independent 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 transmission electron microscope H-9000 can be used. Further, the particle size can be measured by using known image analysis software, for example, image analysis software KS-400 manufactured by Carl Zeiss. Unless otherwise specified, the average particle size shown in the examples described later was measured using a transmission electron microscope H-9000 manufactured by Hitachi as a transmission electron microscope and a Carl Zeiss image analysis software KS-400 as an image analysis software. The value. In the present invention and the present specification, the powder means an aggregate of a plurality of particles. For example, a ferromagnetic powder means a collection of a plurality of ferromagnetic particles. Further, the set of a plurality of particles is not limited to a mode in which the particles constituting the set are in direct contact with each other, and also includes a mode in which a binder, an additive, etc., which will be described later, are interposed between the particles. To. The term particle is sometimes used to describe powder.

As a method for collecting the sample powder from the magnetic tape for measuring the particle size, for example, the method described in paragraph 0015 of JP2011-048878A can be adopted.

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

For the average needle-like ratio of the powder, the length of the minor axis of the particles, that is, the minor axis length is measured in the above measurement, and the value of (major axis length / minor axis length) of each particle is obtained. Refers to the arithmetic mean of the values obtained for a particle. 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 above definition of the particle size, and the thickness or height in the case of the same (2). In the case of (3), there is no distinction between the major axis and the minor axis, so (major axis length / minor axis length) is regarded as 1 for convenience.
Unless otherwise specified, when the shape of the particles is specific, for example, in the case of the above definition of particle size (1), the average particle size is the average major axis length, and in the case of the same definition (2), the average particle size is Average plate diameter. In the case of the same definition (3), the average particle size is an average diameter (also referred to as an average particle size or an average particle size).

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

(Binder, hardener)
The magnetic tape is a coating type magnetic tape and contains a binder in the magnetic layer. A binder is one or more resins. As the binder, various resins usually used as a binder for a coating type magnetic recording medium can be used. For example, as the binder, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, styrene, acrylonitrile, acrylic resin obtained by copolymerizing methyl methacrylate and the like, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, etc. A resin selected from a polyvinyl alkyral resin such as polyvinyl butyral can be used alone, or a plurality of resins can be mixed and used. Of these, polyurethane resins, acrylic resins, cellulose resins, and vinyl chloride resins are preferred. These resins may be homopolymers or copolymers. These resins can also be used as binders in the non-magnetic layer and / or the backcoat layer described later.
For the above binder, paragraphs 0028 to 0031 of JP-A-2010-24113 can be referred to. The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less as the weight average molecular weight. The weight average molecular weight in the present invention and the present specification is a value obtained by converting a value measured by gel permeation chromatography (GPC) under the following measurement conditions into polystyrene. The weight average molecular weight of the binder shown in Examples described later is a value obtained by converting a value measured under the following measurement conditions into polystyrene.
GPC device: HLC-8120 (manufactured by Tosoh)
Column: TSK gel Multipore HXL-M (manufactured by Tosoh, 7.8 mm ID (Inner Diameter) x 30.0 cm)
Eluent: tetrahydrofuran (THF)

In one aspect, a binder having an acidic group can be used as the binder. The term "acidic group" in the present invention and the present specification is used to include the form of a group capable of releasing H ⁺ and dissociating into an anion in water or a solvent containing water (aqueous solvent) and a salt thereof. .. Specific examples of the acidic group include a sulfonic acid group, a sulfate group, a carboxy group, a phosphoric acid group, and a salt form thereof. For example, the salt form of a sulfonic acid group (-SO ₃ H) is a group represented by -SO ₃ M, which represents an atom (eg, an alkali metal atom) in which M can be a cation in water or an aqueous solvent. means. This point is the same for the salt forms of the various groups described above. As an example of the binder having an acidic group, for example, a resin containing at least one acidic group selected from the group consisting of a sulfonic acid group and a salt thereof (for example, polyurethane resin, vinyl chloride resin, etc.) can be mentioned. However, the resin contained in the magnetic layer is not limited to these resins. Further, in the binder having an acidic group, the acidic group content can be in the range of, for example, 0.03 to 0.50 meq / g. “Eq” is an 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 determined by a known method depending on the type of functional group. The binder can be used in the composition for forming a magnetic layer in an amount of, for example, 1.0 to 30.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder.

Regarding the control of the isoelectric point of the surface zeta potential of the magnetic layer, forming the magnetic layer so as to reduce the abundance of the acidic component in the surface layer portion of the magnetic layer contributes to increasing the value of the isoelectric point. Then it is inferred. Further, it is presumed that increasing the abundance of the basic component in the surface layer portion of the magnetic layer also contributes to increasing the value of the isoelectric point. The acidic component is used in the sense of including a component capable of releasing H ⁺ in water or an aqueous solvent and dissociating into an anion and a salt thereof. The basic component is used in the sense of including a component capable of releasing OH ⁻ in water or an aqueous solvent and dissociating into a cation, and a salt thereof. For example, when an acidic component is used, it is possible to first perform a treatment for unevenly distributing the acidic component on the surface layer portion of the coating layer of the composition for forming a magnetic layer, and then perform a treatment for reducing the amount of the acidic component on the surface layer portion. It is considered that the value of the isoelectric point of the surface zeta potential of the magnetic layer is increased to control it to 5.5 or more. For example, in the step of applying the composition for forming a magnetic layer onto a non-magnetic support via a non-magnetic layer, applying an alternating magnetic field and applying the composition in the alternating magnetic field is a method of applying the composition for forming a magnetic layer. It is considered that this leads to uneven distribution of acidic components on the surface layer of the layer. Further, it is presumed that the subsequent burnish treatment contributes to the removal of at least a part of the unevenly distributed acidic components. The burnish treatment is a treatment of rubbing the surface to be treated with a member (for example, a polishing tape or a grinding tool such as a grinding blade or a grinding wheel). The details of the magnetic layer forming step including the burnish treatment will be described later. Examples of the acidic component include a binder having an acidic group.

Further, a curing agent can be used together with a resin that can be used as a binder. The curing agent can be a thermosetting compound which is a compound in which a curing reaction (crosslinking reaction) proceeds by heating in one aspect, and a photocuring agent in which a curing reaction (crosslinking reaction) proceeds by light irradiation in another aspect. It can be a sex compound. As the curing reaction proceeds in the process of forming the magnetic layer, at least a part of the curing agent can be contained in the magnetic layer in a state of reacting (crosslinking) with other components such as a binder. This point is the same for the layer formed by using this composition when the composition used for forming another layer contains a curing agent. Preferred curing agents are thermosetting compounds, with polyisocyanates being preferred. For details of the polyisocyanate, refer to paragraphs 0124 to 0125 of JP2011-216149A. The curing agent is, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder in the composition for forming the magnetic layer, preferably 50.0 to 80.0 from the viewpoint of improving the strength of the magnetic layer. It can be used in the amount of parts by mass.

(Oxide abrasive)
The magnetic tape contains an oxide abrasive in a magnetic layer. The oxide abrasive is a non-magnetic oxide powder having a Mohs hardness of more than 8, and is preferably a non-magnetic oxide powder having a Mohs hardness of 9 or more. The maximum value of Mohs hardness is 10. The oxide abrasive may be an inorganic oxide powder or an organic oxide powder, and is preferably an inorganic oxide powder. Specifically, examples of the abrasive include powders of alumina (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), cerium oxide (CeO ₂ ), zirconium oxide (ZrO ₂ ), and the like, and among them, alumina powder. Is preferable. The Mohs hardness of alumina is about 9. Regarding the alumina powder, paragraph 0021 of JP2013-229090A can also be referred to. Further, the specific surface area can be used as an index of the particle size of the oxide abrasive. It can be considered that the larger the specific surface area, the smaller the particle size of the primary particles of the particles constituting the oxide abrasive. As the oxide abrasive, an oxide abrasive having a specific surface area (hereinafter referred to as “BET specific surface area”) measured by the BET (Brunauer-Emmett-Teller) method of 14 m ² / g or more shall be used. Is preferable. From the viewpoint of dispersibility, it is preferable to use an oxide polishing agent having a BET specific surface area of 40 m ² / g or less. The content of the oxide abrasive in the magnetic layer is preferably 1.0 to 20.0 parts by mass, preferably 1.0 to 10.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder. Is more preferable.

(Additive)
The magnetic layer contains a ferromagnetic powder, a binder and an oxide abrasive, and may further contain one or more additives, if desired. As an example, the above-mentioned curing agent can be mentioned as an additive. Examples of additives that can be contained in the magnetic layer include non-magnetic powders other than oxide abrasives, lubricants, dispersants, dispersion aids, fungicides, antistatic agents, antioxidants, and the like. .. As the additive, a commercially available product can be appropriately selected according to the desired properties, or can be produced by a known method and used in an arbitrary amount. For example, for lubricants, paragraphs 0030 to 0033, 0035 and 0036 of JP2016-126817A can be referred to. The non-magnetic layer may contain a lubricant. For the lubricant that can be contained in the non-magnetic layer, reference can be made to paragraphs 0030 to 0031, 0034, 0035 and 0036 of JP2016-126817A. For the dispersant, paragraphs 0061 and 0071 of JP2012-133387A can be referred to. The dispersant may be contained in the non-magnetic layer. For the dispersant that can be contained in the non-magnetic layer, paragraph 0061 of JP2012-133387A can be referred to.

Further, as the dispersant, a dispersant for enhancing the dispersibility of the oxide abrasive can be mentioned. Examples of the compound that can function as such a dispersant include aromatic hydrocarbon compounds having a phenolic hydroxy group. The "phenolic hydroxy group" refers to a hydroxy group directly bonded to an aromatic ring. The aromatic ring contained in the aromatic hydrocarbon compound may be a monocyclic ring, a polycyclic ring structure, or a condensed ring. From the viewpoint of improving the dispersibility of the oxide abrasive, an aromatic hydrocarbon compound containing a benzene ring and / or a naphthalene ring is preferable. In addition, the aromatic hydrocarbon compound may have a substituent other than the phenolic hydroxy group. Examples of the substituent other than the phenolic hydroxy group include a halogen atom, an alkyl group, an alkoxy group, an amino group, an acyl group, a nitro group, a nitroso group, a hydroxyalkyl group and the like, and include a halogen atom, an alkyl group and the like. An alkoxy group, an amino group and a hydroxyalkyl group are preferable. The number of phenolic hydroxy groups contained in one molecule of the aromatic hydrocarbon compound may be one, two, three, or more.

As a preferred embodiment of the aromatic hydrocarbon compound having a phenolic hydroxy group, a compound represented by the following general formula 100 can be mentioned.

[In the general formula 100, two of X ^{101 to} X ¹⁰⁸ are hydroxy groups, and the other six independently represent a hydrogen atom or a substituent. ]

In the compound represented by the general formula 100, the substitution positions of the two hydroxy groups (phenolic hydroxy groups) are not particularly limited.

In the compound represented by the general formula 100, two of X ^{101 to} X ¹⁰⁸ are hydroxy groups (phenolic hydroxy groups), and the other six independently represent hydrogen atoms or substituents. Further, all of X ^{101 to} X ¹⁰⁸ other than the two hydroxy groups may be hydrogen atoms, and some or all of them may be substituents. As the substituent, the above-mentioned substituent can be exemplified. One or more phenolic hydroxy groups may be contained as a substituent other than the two hydroxy groups. From the viewpoint of improving the dispersibility of the oxide polishing agent, it is preferable that there are no phenolic hydroxy groups other than the two hydroxy groups of X ^{101 to} X ¹⁰⁸ . That is, the compound represented by the general formula 100 is preferably dihydroxynaphthalene or a derivative thereof, and more preferably 2,3-dihydroxynaphthalene or a derivative thereof. Preferred substituents represented by X ^{101 to} X ¹⁰⁸ are halogen atoms (for example, chlorine atom and bromine atom), amino groups, alkyl groups having 1 to 6 carbon atoms (preferably 1 to 4), and methoxy groups. And ethoxy group, acyl group, nitro group and nitroso group, and -CH ₂ OH group can be mentioned.

Further, for the dispersant for enhancing the dispersibility of the oxide polishing agent, also refer to paragraphs 0024 to 0028 of JP2014-179149A.

The dispersant for enhancing the dispersibility of the oxide abrasive is applied to 100.0 parts by mass of the abrasive at the time of preparing the composition for forming a magnetic layer (preferably at the time of preparing the abrasive liquid as described later). For example, it can be used in a proportion of 0.5 to 20.0 parts by mass, and preferably used in a proportion of 1.0 to 10.0 parts by mass.

As the non-magnetic powder other than the oxide abrasive that can be contained in the magnetic layer, the non-magnetic powder that can contribute to the control of friction characteristics by forming protrusions on the surface of the magnetic layer (hereinafter, also referred to as “protrusion forming agent”). Can be mentioned. As the protrusion forming agent, various non-magnetic powders generally used as the protrusion forming agent in the magnetic layer can be used. These may be inorganic substance powder (inorganic powder) or organic substance powder (organic powder). In one aspect, from the viewpoint of uniform friction characteristics, the particle size distribution of the protrusion forming agent is preferably a monodisperse showing a single peak rather than a polydisperse having a plurality of peaks in the distribution. From the viewpoint of availability of monodisperse particles, the protrusion forming agent is preferably an inorganic powder. Examples of the inorganic powder include powders of metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides and the like. The particles constituting the protrusion forming agent are preferably colloidal particles, and more preferably inorganic oxide colloidal particles. Further, from the viewpoint of availability of monodisperse particles, it is preferable that the inorganic oxide constituting the inorganic oxide colloidal particles is silicon dioxide (silica). The inorganic oxide colloidal particles are more preferably colloidal silica (silica colloidal particles). In the present invention and the present specification, "colloidal particles" are added in an amount of 1 g per 100 mL of at least one organic solvent containing methyl ethyl ketone, cyclohexanone, toluene or ethyl acetate, or two or more of the above solvents in an arbitrary mixing ratio. It refers to particles that can disperse without settling and provide a colloidal dispersion. In another aspect, the protrusion forming agent is also preferably carbon black. The average particle size of the protrusion forming agent can be, for example, 30 to 300 nm, preferably 40 to 200 nm. Further, from the viewpoint that the protrusion forming agent can exert its function better, the content of the protrusion forming agent in the magnetic layer is 1.0 to 4.0 mass with respect to 100.0 parts by mass of the ferromagnetic powder. It is preferably parts, and more preferably 1.5 to 3.5 parts by mass.

The magnetic layer described above is provided on the surface of the non-magnetic support via the non-magnetic layer.

<Non-magnetic layer>
Next, the non-magnetic layer will be described. The magnetic tape has a non-magnetic layer on the surface of the non-magnetic support and a magnetic layer on the non-magnetic layer. The non-magnetic layer contains at least a non-magnetic powder and a binder. The non-magnetic powder used for the non-magnetic layer may be an inorganic powder or an organic powder. In addition, carbon black or the like can also be used. Examples of the inorganic powder 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 also be produced by known methods. For details thereof, refer to paragraphs 0146 to 0150 of JP2011-216149A. For carbon black that can be used for the non-magnetic layer, paragraphs 0040 to 0041 of JP2010-24113A can also 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% by mass, and more preferably in the range of 60 to 90% by mass.

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

In the present invention and the present specification, the non-magnetic layer includes not only the non-magnetic powder but also a substantially non-magnetic layer containing a small amount of ferromagnetic powder, for example as an impurity or intentionally. Here, the substantially non-magnetic layer means that the residual magnetic flux density of this layer is 10 mT or less, the coercive force is 7.96 kA / m (100 Oe) or less, or the residual magnetic flux density is 10 mT or less. It means a layer having a coercive force of 7.96 kA / m (100 Oe) or less. The non-magnetic layer preferably has no residual magnetic flux density and coercive force.

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

<Back coat layer>
The magnetic tape may or may not have a backcoat layer containing a non-magnetic powder and a binder on the surface side opposite to the surface side having the magnetic layer of the non-magnetic support. The backcoat layer preferably contains one or both of carbon black and inorganic powder. For the binder contained in the backcoat layer and various additives that may be optionally contained, the known technique relating to the backcoat layer can be applied, and the known technique relating to the formulation of the magnetic layer and / or the non-magnetic layer shall be applied. You can also. For example, paragraphs 0018 to 0020 of JP-A-2006-331625 and the description of US Pat. No. 7,029,774, column 4, lines 65 to 5, line 38 can be referred to for the backcoat layer. ..

<Various thickness>
The total thickness of the non-magnetic layer and the magnetic layer of the magnetic tape is 0.60 μm or less, preferably 0.50 μm or less, from the viewpoint of thinning the magnetic tape. The total thickness of the non-magnetic layer and the magnetic layer can be, for example, 0.10 μm or more, 0.15 μm or more, or 0.20 μm or more.
The thickness of the non-magnetic support of the magnetic tape is preferably 3.00 to 5.50 μm.
The thickness of the magnetic layer can be optimized according to the saturation magnetization amount of the magnetic head used, the head gap length, the band of the recording signal, and the like. The thickness of the magnetic layer is generally 0.01 μm to 0.15 μm, preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.10 μm from the viewpoint of high-density recording. .. The magnetic layer may be at least one layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a known configuration relating to a multi-layer 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 non-magnetic layer is, for example, 0.10 to 0.55 μm, preferably 0.10 to 0.50 μm.
The thickness of the backcoat layer is preferably 0.90 μm or less, more preferably 0.10 to 0.70 μm.
The total thickness of the magnetic tape is preferably 7,000 μm or less, more preferably 6.00 μm or less, and more preferably 5.50 μm or less, from the viewpoint of improving the recording capacity per winding of the magnetic tape cartridge. Is even more preferable. On the other hand, from the viewpoint of ease of handling (handleability) of the magnetic tape, the total thickness of the magnetic tape is preferably 3.00 μm or more.

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

<Manufacturing process>
The step of preparing the composition for forming the magnetic layer, the non-magnetic layer or the backcoat layer usually includes at least a kneading step, a dispersion step, and a mixing step provided before and after these steps as necessary. Can be done. Each process may be divided into two or more stages. The components used in the preparation of 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 usually used for producing a coating type magnetic recording medium can be used. For the solvent, for example, paragraph 0153 of JP2011-216149A can be referred to. Further, each component may be added separately in two or more steps. For example, the binder may be divided and added in a kneading step, a dispersion step, and a mixing step for adjusting the viscosity after dispersion. In order to manufacture the magnetic tape, conventionally known manufacturing techniques can be used in various steps. In the kneading step, it is preferable to use an open kneader, a continuous kneader, a pressurized kneader, an extruder or the like having a strong kneading force. For details of these kneading treatments, JP-A-1-106338 and JP-A-1-79274 can be referred to. A known disperser can be used. 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 the filter used for filtration, for example, a filter having a pore size of 0.01 to 3 μm (for example, a glass fiber filter, a polypropylene filter, etc.) can be used.

The FIB abrasive diameter tends to be smaller due to the presence of the oxide abrasive in a finer state in the magnetic layer. As one of the means for allowing the oxide abrasive to exist in a finer state in the magnetic layer, the use of a dispersant capable of enhancing the dispersibility of the oxide abrasive as described above can be mentioned. it can. Further, in order to allow the oxide abrasive to exist in a finer state in the magnetic layer, an oxide abrasive having a small particle size is used to suppress aggregation of the oxide abrasive and uniformly to suppress uneven distribution. It is preferable to disperse it in a magnetic layer. One of the means for that purpose is to strengthen the dispersion conditions of the oxide abrasive at the time of preparing the composition for forming the magnetic layer. For example, dispersing the oxide abrasive separately from the ferromagnetic powder is one aspect of strengthening the dispersion conditions. More specifically, the separate dispersion is a step of mixing an abrasive liquid containing an oxide abrasive and a solvent (however, substantially free of ferromagnetic powder) with a magnetic liquid containing a ferromagnetic powder, a solvent and a binder. This is a method for preparing a composition for forming a magnetic layer. By separately dispersing the oxide abrasive and the ferromagnetic powder and then mixing them in this way, the dispersibility of the oxide abrasive in the composition for forming a magnetic layer can be enhanced. The above-mentioned "substantially free of ferromagnetic powder" means that ferromagnetic powder is not added as a constituent component of the abrasive liquid, and a small amount of ferromagnetic powder is added as an unintentionally mixed impurity. It is permissible for the existence of. In addition to or in combination with separate dispersion, means such as long-term dispersion processing, use of small-sized dispersed media (for example, smaller diameter of dispersed beads in bead dispersion), and higher filling of dispersed media in a disperser. The dispersion conditions can be strengthened by arbitrarily combining. Commercially available dispersers and dispersive media can be used. In addition, the centrifugal separation treatment of the abrasive liquid removes particles larger than the average particle size and / or agglomerated particles among the particles constituting the oxide abrasive, thereby forming an oxide in the magnetic layer. It can contribute to the presence of the abrasive in a finer state. The centrifugation can be performed using a commercially available centrifuge. Further, it is preferable to filter the abrasive liquid by filter filtration or the like in order to remove coarse aggregates in which particles constituting the oxide abrasive are aggregated. Removing such coarse aggregates can also contribute to the presence of the oxide abrasive in a finer state in the magnetic layer. For example, filtering using a filter having a smaller pore size can contribute to the presence of the oxide abrasive in a finer state in the magnetic layer. Further, by adjusting various treatment conditions (for example, stirring conditions, dispersion treatment conditions, filtration conditions, etc.) after mixing the abrasive liquid with components for preparing a composition for forming a magnetic layer such as a ferromagnetic powder, The dispersibility of the oxide abrasive in the composition for forming a magnetic layer can be enhanced. This can also contribute to the presence of the oxide abrasive in a finer state in the magnetic layer. However, if the oxide abrasive is present in the magnetic layer in an extremely fine state, the diameter of the FIB abrasive will be less than 0.04 μm. Therefore, various conditions for preparing the abrasive solution are 0.04 μm or more and 0.08 μm. It is preferable to adjust so that the following FIB abrasive diameter can be realized.

The magnetic layer can be formed by coating the composition for forming the magnetic layer on the surface of the non-magnetic support sequentially or simultaneously with the composition for forming the non-magnetic layer and drying it. For details of the coating for forming each layer, refer to paragraph 0066 of JP-A-2010-231843. Further, applying the composition for forming a magnetic layer in an alternating magnetic field can contribute to controlling the isoelectric point of the surface zeta potential of the magnetic layer to 5.5 or more. This is because when an AC magnetic field is applied, acidic components (for example, a binder having an acidic group) tend to be unevenly distributed on the surface layer portion of the coating layer of the composition for forming a magnetic layer, so that the coating layer is dried. Therefore, it is presumed that a magnetic layer in which acidic components are unevenly distributed on the surface layer can be obtained. Further, it is presumed that the subsequent burnish treatment contributes to removing at least a part of the unevenly distributed acidic components and controlling the isoelectric point of the surface zeta potential of the magnetic layer to 5.5 or more. .. However, the above is just a guess. The application of the alternating magnetic field can be performed by arranging a magnet in the coating device so that the alternating magnetic field is applied perpendicularly to the surface of the coating layer of the composition for forming the magnetic layer. The magnetic field strength of the alternating magnetic field can be, for example, about 0.05 to 3.00 T. However, it is not limited to this range. Note that "vertical" in the present invention and the present specification does not necessarily mean only vertical in a strict sense, but includes a range of errors allowed in the technical field to which the present invention belongs. The range of error can mean, for example, a range of less than the exact vertical ± 10 °.

The burnish treatment is a treatment of rubbing the surface to be treated with a member (for example, a polishing tape or a grinding tool such as a grinding blade or a grinding wheel), and is a burnish treatment known for manufacturing a coating type magnetic recording medium. It can be done in the same way. The burnishing treatment may be carried out, preferably by rubbing (polishing) the surface of the object to be treated with a polishing tape, rubbing (grinding) the surface of the object to be treated with a grinding tool, or both. it can. As the polishing tape, a commercially available product may be used, or a polishing tape produced by a known method may be used. Further, as the grinding tool, known grinding blades such as fixed blades, diamond wheels, and rotary blades, grinding wheels, and the like can be used. Further, a wiping treatment may be performed in which the surface rubbed by the polishing tape and / or the grinding tool is wiped off with a wiping material. For details of preferable polishing tapes, grinding tools, burnishing treatments and wiping treatments, reference can be made to paragraphs 0034 to 0048 of JP-A-6-52544, FIG. 1 and examples of the same publication. It is considered that the stronger the burnish treatment, the more acidic components unevenly distributed on the surface layer portion of the coating layer of the composition for forming a magnetic layer can be removed by coating in an alternating magnetic field. The burnish 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 the abrasive in the polishing tape. Further, the more a high hardness grinding tool is used as the grinding tool, the stronger the burnishing process can be. Regarding the burnish treatment conditions, the faster the sliding speed between the surface to be treated and the member (for example, a polishing tape or a grinding tool), the stronger the burnish treatment can be. The sliding speed can be increased by increasing one or both of the speed at which the member is moved and the speed at which the magnetic tape to be processed is moved. Although the reason is not clear, the larger the amount of the binder having an acidic group in the coating layer of the composition for forming a magnetic layer, the higher the isoelectric point of the surface zeta potential of the magnetic layer tends to be after the burnish treatment. May be seen.

When the composition for forming a magnetic layer contains a curing agent, it is preferable to perform the curing treatment at any stage of the step for forming the magnetic layer. The burnish treatment is preferably performed at least before the curing treatment. After the curing treatment, a further burnish treatment may be performed. In order to increase the removal efficiency of removing the acidic component from the surface layer portion of the coating layer of the composition for forming a magnetic layer, it is considered preferable to perform a burnish treatment before the curing treatment. The curing treatment can be performed by a treatment such as heat treatment or light irradiation, depending on the type of the curing agent contained in the composition for forming a magnetic layer. The curing treatment conditions are not particularly limited, and may be appropriately set according to the formulation of the composition for forming a magnetic layer, the type of curing agent, the thickness of the coating layer, and the like. For example, when the coating layer is formed by using a composition for forming a magnetic layer containing polyisocyanate as a curing agent, the curing treatment is preferably heat treatment. When a curing agent is contained in a layer other than the coating layer of the composition for forming a magnetic layer, the curing reaction of that layer can also proceed. Alternatively, a curing process can be performed separately.

Preferably, a surface smoothing treatment can be performed before the curing treatment. The surface smoothing treatment is a treatment performed to improve the smoothness of the magnetic layer surface and / or the backcoat layer surface, and is preferably performed by a calendar treatment. For details of the calendar processing, for example, paragraph 0026 of Japanese Patent Application Laid-Open No. 2010-231843 can be referred to.

Known techniques can be applied to various other steps for the production of magnetic tapes. For various steps, for example, paragraphs 0067 to 0070 of JP-A-2010-231843 can be referred to. In one aspect, the coating layer of the composition for forming a magnetic layer can be oriented while the coating layer is in a wet (undried) state. For the orientation treatment, various known techniques can be applied, including the description in paragraph 0067 of JP2010-231843A. For example, the vertical alignment treatment can be performed by a known method such as a method using a magnet opposite to the opposite pole. In the alignment zone, the drying rate of the coating layer can be controlled by the temperature of the drying air, the air volume, and / or the transport rate of the magnetic tape in the alignment zone. The coating layer may also be pre-dried before being transported to the alignment zone. When the alignment treatment is performed, it is preferable to apply a magnetic field (for example, a DC magnetic field) for aligning the ferromagnetic powder to the coating layer of the composition for forming a magnetic layer applied in an alternating magnetic field.

From the above, the magnetic tape according to one aspect of the present invention can be obtained. The magnetic tape is usually housed in a magnetic tape cartridge, and the magnetic tape cartridge is mounted on the magnetic tape device. A servo pattern can also be formed on the magnetic layer of the magnetic tape by a known method in order to enable head tracking servo to be performed in the magnetic tape device.

Although the total thickness of the non-magnetic layer and the magnetic layer of the magnetic tape is 0.60 μm or less, it is possible to suppress a decrease in electromagnetic conversion characteristics during repeated reproduction in a low temperature and high humidity environment. In one aspect, the low temperature and high humidity environment can be, for example, an environment having an ambient temperature of 10 to 20 ° C. and a relative humidity of 70 to 90%.

[Magnetic tape cartridge]
One aspect of the present invention relates to a magnetic tape cartridge containing the above magnetic tape.

In a magnetic tape cartridge, generally, the magnetic tape is housed inside the cartridge body in a state of being wound on a reel. The reel is rotatably provided inside the cartridge body. As the magnetic tape cartridge, a single reel type magnetic tape cartridge having one reel inside the cartridge main body and a twin reel type magnetic tape cartridge having two reels inside the cartridge main body are widely used. When a single reel type magnetic tape cartridge is attached to a magnetic tape device (drive) for recording and / or reproducing information (magnetic signal) on the magnetic tape, the magnetic tape is pulled out from the magnetic tape cartridge to drive the drive. It is wound on the side reel. A magnetic head is arranged in the magnetic tape transport path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed and wound between the reel (supply reel) on the magnetic tape cartridge side and the reel (winding reel) on the drive side. During this time, the magnetic head and the surface of the magnetic layer of the magnetic tape come into contact with each other and slide to record and / or reproduce information. On the other hand, in the twin reel type magnetic tape cartridge, both a supply reel and a take-up reel are provided inside the magnetic tape cartridge. The magnetic tape cartridge may be either a single reel type or a double reel type magnetic tape cartridge. The magnetic tape cartridge may be any one containing the magnetic tape according to one aspect of the present invention, and known techniques can be applied to others.

[Magnetic tape device]
One aspect of the present invention relates to a magnetic tape device including the magnetic tape and a magnetic head.

In the present invention and the present specification, the "magnetic tape device" means a device capable of recording information on a magnetic tape and reproducing the information recorded on the magnetic tape. Such a device is commonly referred to as a drive. The magnetic tape device can be a sliding magnetic tape device. The sliding type device refers to a device in which the surface of the magnetic layer and the magnetic head slide in contact with each other when recording information on a magnetic tape and / or reproducing the recorded information.

The magnetic head included in the magnetic tape device can be a recording head capable of recording information on the magnetic tape, and can be a reproduction head capable of reproducing the information recorded on the magnetic tape. You can also. Further, in one aspect, the magnetic tape device can include both a recording head and a reproducing head as separate magnetic heads. In another aspect, the magnetic head included in the magnetic tape may have a configuration in which both a recording element and a reproducing element are provided in one magnetic head. As the reproduction head, a magnetic head (MR head) including a magnetoresistive (MR) element capable of reading information recorded on a magnetic tape with high sensitivity is preferable. As the MR head, various known MR heads can be used. Further, the magnetic head that records information and / or reproduces information may include a servo pattern reading element. Alternatively, the magnetic tape device may include a magnetic head (servo head) provided with a servo pattern reading element as a head separate from the magnetic head that records and / or reproduces information.

In the magnetic tape device, the recording of information on the magnetic tape and / or the reproduction of the 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 tape device may include any magnetic tape according to one aspect of the present invention, and known techniques can be applied to others.

Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiments shown in the examples. The indications of "part" and "%" described below indicate "parts by mass" and "% by mass" unless otherwise specified. Further, unless otherwise specified, the steps and evaluations described below were carried out in an environment with an ambient temperature of 23 ° C. ± 1 ° C.

The "binder A" described below is an SO ₃ Na group-containing polyurethane resin (weight average molecular weight: 70,000, SO ₃ Na group: 0.20 meq / g).
The "binder B" described below is a vinyl chloride copolymer manufactured by Kaneka Corporation (trade name: MR110, SO ₃ K group-containing vinyl chloride copolymer, SO ₃ K group: 0.07 meq / g).

[Making magnetic tape]
<Example 1>
(1) Preparation of alumina dispersion With respect to 100.0 parts of the oxide abrasive (alumina powder) shown in Table 1, the amount of 2,3-dihydroxynaphthalene (manufactured by Tokyo Kasei Co., Ltd.) shown in Table 1 and SO as a polar group ₃ A 32% solution of a polyester polyurethane resin having a Na group (UR-4800 manufactured by Toyo Boseki Co., Ltd. (polar group amount: 80 meq / kg)) (solve is a mixed solvent of methyl ethyl ketone and toluene) 31.3 parts, methyl ethyl ketone and cyclohexanone 1 as a solvent 570.0 parts of a 1: 1 (mass ratio) mixture was mixed and dispersed with a paint shaker in the presence of zirconia beads (bead diameter: 0.1 mm) for the time shown in Table 1 (bead dispersion time). After the dispersion, the dispersion liquid and the beads were separated by a mesh, and the obtained dispersion liquid was centrifuged. For the centrifuge treatment, CS150GXL manufactured by Hitachi Koki Co., Ltd. (the rotor used is S100AT6 manufactured by the same company) is used as the centrifuge, and the rotation speed (rpm; rotation per minute) shown in Table 1 is the time shown in Table 1 (centrifugation time). ),Carried out. Then, filtration was performed with a filter having a pore size shown in Table 1 to obtain an alumina dispersion (abrasive solution).

(2) Formulation of composition for forming a magnetic layer (magnetic liquid)
Ferromagnetic powder 100.0 parts Average particle size (average plate diameter) 21 nm hexagonal barium ferrite powder Binder A and / or Binder B (see Table 1) See Table 1 Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (see Table 1) Abrasive liquid)
6.0 parts of alumina dispersion prepared in (1) above (silica sol (projection forming agent solution))
Colloidal silica (average particle size: 120 nm) 2.0 parts methyl ethyl ketone 1.4 parts (other components)
Stearic acid 2.0 parts Stearic acid amide 0.2 parts Butyl stearate 2.0 parts
Polyisocyanate (Tosoh Coronate (registered trademark)) 2.5 parts (finishing additive solvent)
Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

(3) Composition for forming a non-magnetic layer Non-magnetic inorganic powder: α-iron oxide 100.0 parts Average particle size (average major axis length): 0.15 μm
Average needle-like ratio: 7
BET specific surface area: 52m ² / g
Carbon black 20.0 parts Average particle size: 20 nm
Binder A 18.0 parts Stearic acid 2.0 parts Stearic acid amide 0.2 parts Butyl stearate 2.0 parts
Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0 parts

(4) Composition for backcoat layer formation Non-magnetic inorganic powder: α-iron oxide 80.0 parts Average particle size (average major axis length): 0.15 μm
Average needle-like ratio: 7
BET specific surface area: 52m ² / g
Carbon black 20.0 parts Average particle size: 20 nm
Vinyl chloride copolymer 13.0 parts Sulfonic acid base-containing polyurethane resin 6.0 parts Phosphonate 3.0 parts Methyl ethyl ketone 155.0 parts Polyisocyanate 5.0 parts Cyclohexanone 355.0 parts

(5) Preparation of composition for forming each layer A composition for forming a magnetic layer was prepared by the following method.
A magnetic liquid was prepared by dispersing various components of the magnetic liquid for 24 hours (bead dispersion) using a batch type vertical sand mill. As the dispersed beads, zirconia beads having a bead diameter of 0.5 mm were used.
The magnetic liquid thus obtained, the above-mentioned abrasive liquid, silica sol, other components and a finishing addition solvent were introduced into a dissolver stirrer and stirred at a peripheral speed of 10 m / sec for the time shown in Table 1 (stirring time). After that, the time shown in Table 1 (ultrasonic processing time) and the ultrasonic dispersion treatment were performed with a flow type ultrasonic disperser at a flow rate of 7.5 kg / min, and then the number of times shown in Table 1 with a filter having a pore size shown in Table 1. A composition for forming a magnetic layer was prepared by filtration.
A composition for forming a non-magnetic layer was prepared by the following method.
Each component except for the lubricant (stearic acid, stearic acid amide and butyl stearate), cyclohexanone and methyl ethyl ketone was dispersed for 24 hours using a batch vertical sand mill to obtain a dispersion. As the dispersed beads, zirconia beads having a bead diameter of 0.5 mm were used. Then, the remaining components were added to the obtained dispersion, and the mixture was stirred with a dissolver stirrer. The dispersion thus obtained was filtered using a filter having a pore size of 0.5 μm to prepare a composition for forming a non-magnetic layer.
A composition for forming a backcoat layer was prepared by the following method.
After kneading and diluting each component except polyisocyanate and cyclohexanone with an open kneader, zirconia beads with a bead diameter of 1 mm were used by a horizontal bead mill disperser at a bead filling rate of 80% by volume and a rotor tip peripheral speed of 10 m / sec. The 1-pass residence time was set to 2 minutes, and 12-pass dispersion processing was performed. Then, the remaining components were added to the obtained dispersion, and the mixture was stirred with a dissolver stirrer. The dispersion thus obtained was filtered using a filter having a pore size of 1 μm to prepare a composition for forming a backcoat layer.

(6) Method for producing magnetic tape For forming a non-magnetic layer prepared in (5) above on the surface of a polyethylene naphthalate support having a thickness of 5.00 μm so that the thickness after drying becomes the thickness shown in Table 1. The composition was applied and dried to form a non-magnetic layer.
Next, in a coating device in which a magnet for applying an alternating magnetic field is arranged, the composition for forming a magnetic layer prepared in (5) above is applied onto the surface of the non-magnetic layer so that the thickness after drying becomes the thickness shown in Table 1. , The coating layer was formed by coating while applying an alternating magnetic field (magnetic field strength: 0.15T). The alternating magnetic field was applied so that the alternating magnetic field was applied perpendicularly to the surface of the coating layer. Then, while the coating layer of the composition for forming a magnetic layer was in a wet (undried) state, a DC magnetic field having a magnetic field strength of 0.30T was applied perpendicularly to the surface of the coating layer to perform a vertical alignment treatment. Then, it was dried to form a magnetic layer.
Then, on the surface of the polyethylene naphthalate support opposite to the surface on which the non-magnetic layer and the magnetic layer were formed, the back coat prepared in (5) above was prepared so that the thickness after drying would be 0.50 μm. The layer-forming composition was applied and dried to form a backcoat layer.
The magnetic tape thus obtained was slit to a width of 1/2 inch (0.0127 m), and then the surface of the magnetic layer was burnished and wiped. The burnish treatment and the wiping treatment are performed as a commercially available polishing tape (trade name MA22000 manufactured by FUJIFILM Corporation, abrasive: diamond / Cr _{2) in} the processing apparatus having the configuration shown in FIG. 1 of JP-A-6-52544. O ₃ / Bengala) is used, and a commercially available sapphire blade (Kyocera, width 5 mm, length 35 mm, tip angle 60 degrees) is used as a grinding blade, and a commercially available wiping material (Kurare product) is used as a wiping material. The name WRP736) was used. As the processing conditions, the processing conditions in Example 12 of JP-A-6-52544 were adopted.
After the above burnish treatment and wiping treatment, the calendar roll is composed of only metal rolls, and is calendared at a speed of 80 m / min, a linear pressure of 300 kg / cm (294 kN / m), and a calendar temperature (surface temperature of the calendar roll) of 100 ° C. Treatment (surface smoothing treatment) was performed.
Then, after performing heat treatment (curing treatment) for 36 hours in an environment having an ambient temperature of 70 ° C., a servo pattern was formed on the magnetic layer by a commercially available servo lighter.
From the above, the magnetic tape of Example 1 was obtained.

<Examples 2 to 6, Comparative Examples 1 to 7, Reference Examples 1 and 2>
A magnetic tape was produced in the same manner as in Example 1 except that various conditions were changed as shown in Table 1.
In Examples 2 to 6, Comparative Example 3 and Comparative Example 5 in which "Yes" is described in the column of applying an AC magnetic field during coating and the column of burnish treatment in Table 1, the same method as in Example 1 is used. The steps after the coating step of the composition for forming the magnetic layer were carried out. That is, as in Example 1, an alternating magnetic field was applied during the application of the composition for forming a magnetic layer, and the magnetic layer was subjected to a burnish treatment and a wiping treatment.
On the other hand, in Comparative Example 7 in which "None" is described in the column of burnish treatment, the magnetic layer is magnetic by the same method as in Example 1 except that the burnish treatment and the wiping treatment are not performed. The steps after the coating step of the layer-forming composition were carried out.
In Comparative Example 6 in which "None" is described in the column of applying an AC magnetic field during coating, the process of applying the composition for forming a magnetic layer is performed by the same method as in Example 1 except that the AC magnetic field is not applied. The process of was carried out.
In Comparative Example 1, Comparative Example 2, Comparative Example 4, Reference Example 1 and Reference Example 2 in which "None" is described in the AC magnetic field application column and the burnish treatment column during coating, an AC magnetic field is applied. The steps after the application step of the composition for forming the magnetic layer were carried out by the same method as in Example 1 except that the magnetic layer was not burnished or wiped.

The thickness of each layer and the thickness of the non-magnetic support of each magnetic tape of Examples, Comparative Examples and Reference Examples are determined by the following methods, and the thickness of the non-magnetic layer and the thickness of the magnetic layer are the thicknesses shown in Table 1. It was also confirmed that the thickness of the back coat layer and the non-magnetic support was the above thickness.
After exposing the cross section of the magnetic tape in the thickness direction with an ion beam, the cross section of the exposed cross section was observed with a scanning electron microscope. Various thicknesses were calculated as the arithmetic mean of the thicknesses obtained at the two randomly selected locations in the cross-sectional observation.

[Evaluation of physical properties of magnetic tape]
(1) Isoelectric point of surface zeta potential of magnetic layer Six samples for isoelectric point measurement are cut out from each magnetic tape of Examples, Comparative Examples and Reference Examples, and two samples are taken in the measurement cell in one measurement. Placed in. In the measurement cell, the sample installation surface and the backcoat layer surface of the sample were bonded to the sample tables above and below the measurement cell (the size of each sample installation surface was 1 cm × 2 cm) with double-sided tape. As a result, when the electrolytic solution is passed through the measurement cell, the surface of the magnetic layer of the sample comes into contact with the electrolytic solution, so that the surface zeta potential of the magnetic layer can be measured. Two samples were used in each measurement, and measurements were performed a total of three times to determine the isoelectric point of the surface zeta potential of the magnetic layer. The arithmetic mean of the three values obtained is shown in Table 1 as the isoelectric point of the surface zeta potential of the magnetic layer of each magnetic tape. As the surface zeta potential measuring device, SurPASS manufactured by Antonio Par was used. The measurement conditions were as follows. Other details of the method for determining the isoelectric point are as described above.
Measurement cell: Variable gap cell (20 mm x 10 mm)
Measurement mode: Streaming Current
Gap: Approximately 200 μm
Measurement temperature: Room temperature Ramp Target Pressure / Time: 400,000 Pa (400 mbar) / 60 seconds Electrolyte: 1 mmol / L KCl aqueous solution (adjusted to pH 9)
pH adjustment solution: 0.1 mol / L HCl aqueous solution or 0.1 mol / L KOH aqueous solution Measurement pH: pH 9 → pH 3 (measured at a total of 13 measurement points in steps of about 0.5)

(2) FIB Abrasive Diameter The FIB abrasive diameter of each magnetic tape of Examples, Comparative Examples and Reference Examples was determined by the following method. MI4050 manufactured by Hitachi High-Technologies Corporation was used as the focused ion beam device, and ImageJ, a free software, was used as the image analysis software.
(I) Acquisition of secondary ion image The surface of the backcoat layer of the measurement sample cut out from each magnetic tape is a commercially available carbon double-sided tape for SEM measurement (double-sided tape in which a carbon film is formed on an aluminum base material). It was attached to the adhesive layer. The adhesive layer on the back coat layer surface of the double-sided tape and the surface opposite to the pasted surface was attached to the sample table of the focused ion beam device. In this way, the measurement sample was placed on the sample table of the focused ion beam device with the magnetic layer surface facing upward.
The beam setting of the focused ion beam device was set to an acceleration voltage of 30 kV, a current value of 133 pA, a beam size of 30 nm and a voltage of 50% without performing the pre-imaging coating process, and the SI signal was detected by the secondary ion detector. By performing ACB at three unimaging regions on the surface of the magnetic layer, the tint of the image was stabilized, and the contrast reference value and the brightness reference value were determined. The contrast value 1% lower than the contrast reference value determined by the ACB and the above-mentioned brightness reference value were determined as imaging conditions. An unimaging region on the surface of the magnetic layer was selected, and imaging was performed at Pixel distance = 25.0 (nm / pixel) under the imaging conditions determined above. The image capture method was PhotoScan Dot × 4_Dwell Time 15 μsec (capture time: 1 minute), and the capture size was 25 μm square. In this way, a secondary ion image of a 25 μm square region on the surface of the magnetic layer was obtained. After the scanning of the obtained secondary ion image was completed, the mouse was right-clicked on the capture screen, and the file format was saved as JPEG by ExportImage. It was confirmed that the number of pixels of the image was 2000pixel × 2100pixel, and the cross marks and micron bars of the captured image were erased to obtain a 2000pixel × 2000pixel image.
(Ii) Calculation of FIB Abrasive Diameter The image data of the secondary ion image acquired in (i) above was dragged and dropped into the image analysis software ImageJ.
The color tone of the image data was changed to 8 bits using image analysis software. Specifically, I pressed Image in the operation menu of the image analysis software and selected 8 bits of Type.
In order to perform binarization processing, a lower limit value of 250 gradations and an upper limit value of 255 gradations were selected, and binarization processing was performed using these two threshold values. Specifically, on the operation menu of the image analysis software, Image was pressed, Trend of Adjust was selected, the lower limit value 250 and the upper limit value 255 were selected, and then application was selected. For the obtained image, the process of the operation menu of the image analysis software was pressed, Despekle was selected from Noise, and Size 4.0-Infinity was set in the Analyze Particle to remove the noise component.
For the binarized image thus obtained, AnalizeParticle was selected from the operation menu of the image analysis software, and the number of white shining portions on the image and Area (unit: Pixel) were obtained. The area was obtained by converting Area (unit: Pixel) into an area for each part that glows white on the screen by image analysis software. Specifically, in the image obtained under the above imaging conditions, 1 pixel corresponds to 0.0125 μm, so the area A [μm ² ] was calculated by the area A = Area pixel × 0.0125 ^ 2. Using the area calculated in this way, the equivalent circle diameter L was obtained for each portion shining white by the equivalent circle diameter L = (A / π) ^ (1/2) × 2 = L.
The above steps were carried out four times at different locations (25 μm square) on the surface of the magnetic layer of the measurement sample, and the FIB abrasive diameter was calculated by FIB abrasive diameter = Σ (Li) / Σi from the obtained results. did.

[Changes in electromagnetic conversion characteristics (SNR; Signal-to-Noise-Ratio) after repeated regeneration in a low-temperature and high-humidity environment (SNR reduction amount)]
The signal-to-noise ratio (SNR) was measured by the following method using a 1/2 inch (0.0127 m) reel tester with a fixed head.
For recording, the relative head / tape speed is 5.5 m / sec, a MIG (Metal-In-Gap) head (gap length 0.15 μm, track width 1.0 μm) is used, and the recording current is optimally recorded for each magnetic tape. It was set to the current.
A GMR (Giant-Magnetoresisive) head having an element thickness of 15 nm, a shield spacing of 0.1 μm, and a lead width of 0.5 μm was used as the reproduction head. The signal was recorded at a line recording density of 270 kfci, and the reproduced signal was measured with a spectrum analyzer manufactured by ShibaSoku Co., Ltd. The unit kfci is a unit of line recording density (cannot be converted into the SI unit system). As the signal, the part where the signal was sufficiently stable after the start of running of the magnetic tape was used. The ratio of the output value of the carrier signal to the integrated noise in the entire spectrum was defined as SNR.
Under the above conditions, the tape length per pass is set to 1,000 m, and 8,000 passes are reciprocated in an environment with an ambient temperature of 13 ° C. and a relative humidity of 80% for reproduction (head / tape relative speed: 8.0 m / sec). Was performed and the SNR was measured. The difference between the SNR of the first pass and the SNR of the 8,000th pass (SNR of the 8,000th pass and the SNR of the first pass) was obtained. If the difference is less than −2.0 dB, it can be determined that the magnetic tape exhibits excellent electromagnetic conversion characteristics desired for a data backup tape.

The above results are shown in Table 1 (Table 1-1 and Table 1-2).

By comparing the reference example and the comparative example, the total thickness of the non-magnetic layer and the magnetic layer is larger than that of the case where the total thickness of the non-magnetic layer and the magnetic layer exceeds 0.60 μm (Reference Example 1 and Reference Example 2). In the case of 0.60 μm or less (Comparative Examples 1 to 7), it was confirmed that the electromagnetic conversion characteristics were significantly reduced in the repeated reproduction in a low temperature and high humidity environment.
On the other hand, from the results shown in Table 1, according to the magnetic tapes of Examples 1 to 6, the total thickness of the non-magnetic layer and the magnetic layer is 0.60 μm or less, but Comparative Examples 1 to 7 It can be confirmed that the deterioration of the electromagnetic conversion characteristics during repeated reproduction in a low temperature and high humidity environment could be suppressed as compared with the magnetic tape of.

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 (9)

Having a non-magnetic layer containing non-magnetic powder on a non-magnetic support,
A magnetic tape having a magnetic layer containing ferromagnetic powder on the non-magnetic layer.
The total thickness of the non-magnetic layer and the magnetic layer is 0.60 μm or less.
The total thickness of the magnetic tape is 5.50 μm or less.
The isoelectric point of the surface zeta potential of the magnetic layer is 5.5 or more.
The magnetic layer contains an oxide polishing agent, and the average particle diameter of the oxide polishing agent obtained from the secondary ion image obtained by irradiating the surface of the magnetic layer with a focused ion beam is 0.04 μm or more and 0. A magnetic tape that is .08 μm or less. The magnetic tape according to claim 1, wherein the isoelectric point is 5.5 or more and 7.0 or less. The magnetic tape according to claim 1 or 2, wherein the magnetic layer contains a binder having an acidic group. The magnetic tape according to claim 3, wherein the acidic group is at least one acidic group selected from the group consisting of a sulfonic acid group and a salt thereof. The magnetic tape according to any one of claims 1 to 4, wherein the oxide abrasive is an alumina powder. The magnetic tape according to any one of claims 1 to 5, wherein the total thickness of the non-magnetic layer and the magnetic layer is 0.15 μm or more and 0.60 μm or less. The magnetic tape according to any one of claims 1 to 6, which has a backcoat layer containing a non-magnetic powder on the surface side of the non-magnetic support opposite to the surface side having the magnetic layer. A magnetic tape cartridge including the magnetic tape according to any one of claims 1 to 7. A magnetic tape device including the magnetic tape according to any one of claims 1 to 7 and a magnetic head.