JP2019169228A - Magnetic tape and magnetic tape device - Google Patents

Abstract

To improve both of surface smoothness of a magnetic layer in a magnetic tape and head positioning accuracy in a timing base servo system.SOLUTION: There is provided a magnetic tape having a magnetic layer including ferromagnetic powder and binding agent on a non-magnetic support. The magnetic layer has a timing base servo pattern, center line average surface roughness Ra measured on the surface of the magnetic layer is 1.8 nm or less and an isoelectric point of surface zeta potential of the magnetic layer is 5.5 or more. There is also provided a magnetic tape device including the magnetic tape.SELECTED DRAWING: None

Description

  The present invention relates to a magnetic tape and a magnetic tape device.

  There are two types of magnetic recording media: tape-shaped and disk-shaped, and tape-shaped magnetic recording media, ie magnetic tape, are mainly used for data storage applications such as data backup and archive. Information recording on a magnetic tape is usually performed by recording a magnetic signal on a data band of the magnetic tape. As a result, a data track is formed in the data band.

  With the enormous increase in information volume in recent years, magnetic tapes are required to increase recording capacity (higher capacity). As a means for increasing the capacity, it is possible to increase the recording density by forming more data tracks in the width direction of the magnetic tape by narrowing the width of the data tracks.

  However, when the width of the data track is reduced, when the magnetic tape is run in a magnetic tape device (generally referred to as a “drive”) to record and / or reproduce information, the magnetic head is affected by the position variation of the magnetic tape. However, it is difficult to accurately follow the data track, and errors are likely to occur during recording and / or reproduction. Therefore, in recent years, a system using a head tracking servo using a servo signal (hereinafter referred to as “servo system”) has been proposed and put into practical use as a means for reducing the occurrence of such errors ( For example, see Patent Document 1).

US Pat. No. 5,689,384

In the servo system of the servo system, a servo signal (servo pattern) is formed on the magnetic layer of the magnetic tape, and the servo pattern is magnetically read to perform head tracking. More details are as follows.
First, the servo head reads the servo pattern formed on the magnetic layer (that is, reproduces the servo signal). The position of the magnetic head is controlled in the magnetic tape device according to the value obtained by reading the servo pattern. Thus, when the magnetic tape is transported in the magnetic tape device for recording and / or reproducing information, the accuracy of the magnetic head following the data track can be improved even if the position of the magnetic tape fluctuates. For example, when recording and / or reproducing information by transporting a magnetic tape in a magnetic tape device, even if the position of the magnetic tape fluctuates in the width direction with respect to the magnetic head, by performing head tracking servo, The position of the magnetic head in the width direction of the magnetic tape can be controlled in the magnetic tape device. In this way, it is possible to accurately record information on the magnetic tape and / or accurately reproduce information recorded on the magnetic tape in the magnetic tape device.

  In recent years, a timing-based servo system has been widely used as the above-described magnetic servo system servo system. In a timing-based servo system servo system (hereinafter referred to as a “timing-based servo system”), a plurality of servo patterns having two or more different shapes are formed on a magnetic layer, and a servo head has two different shapes. The position of the servo head is recognized by the time interval at which the servo pattern is reproduced (read) and the time interval at which two servo patterns having the same shape are reproduced. Based on the recognized position of the servo head, the position of the magnetic head in the width direction of the magnetic tape is controlled.

  Incidentally, in recent years, magnetic tapes are required to improve the surface smoothness of the magnetic layer. This is because increasing the surface smoothness of the magnetic layer leads to an improvement in electromagnetic conversion characteristics. However, as the present inventors repeatedly investigate, when the surface smoothness of the magnetic layer of the magnetic tape becomes high, the accuracy of causing the magnetic head to follow the data track in the timing-based servo system (hereinafter referred to as “head positioning accuracy”). It has become clear that a phenomenon that has not been known in the past occurs, such as a decrease.

  Accordingly, an object of the present invention is to achieve both improvement in surface smoothness of a magnetic layer in a magnetic tape and improvement in head positioning accuracy in a timing-based servo system.

One embodiment of the present invention provides:
A magnetic tape having a magnetic layer comprising a ferromagnetic powder and a binder on a non-magnetic support,
The magnetic layer has a timing-based servo pattern,
The center line average surface roughness Ra (hereinafter also referred to as “magnetic layer surface roughness Ra”) measured on the surface of the magnetic layer is 1.8 nm or less, and the surface zeta potential of the magnetic layer is Isoelectric point is 5.5 or more, magnetic tape,
About.

  In one embodiment, the isoelectric point may be 5.5 or more and 7.0 or less.

  In one aspect, the binder can be a binder that includes an acidic group.

  In one aspect | mode, the said acidic group can contain at least 1 type of acidic group chosen from the group which consists of a sulfonic acid group and its salt.

  In one aspect, the center line average surface roughness Ra measured on the surface of the magnetic layer may be 1.2 nm or more and 1.8 nm or less.

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

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

  The further aspect of this invention is related with the magnetic tape apparatus containing the said magnetic tape, a magnetic head, and a servo head.

  According to one aspect of the present invention, a magnetic tape having a timing base servo pattern in a magnetic layer having high surface smoothness, the magnetic tape having improved head positioning accuracy in the timing base servo system, and the magnetic tape A magnetic tape device for recording and / or reproducing signals can be provided.

An arrangement example of data bands and servo bands is shown. An example of servo pattern arrangement on an LTO (Linear-Tape-Open) Ultrium format tape will be described.

[Magnetic tape]
A magnetic tape according to an aspect of the present invention is a magnetic tape having a magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support, the magnetic layer having a timing-based servo pattern, and the magnetic layer The center line average surface roughness Ra measured on the surface of the magnetic layer is 1.8 nm or less, and the isoelectric point of the surface zeta potential of the magnetic layer is 5.5 or more.
Hereinafter, the magnetic tape will be described in more detail. The following description includes the inventor's inference. The present invention is not limited by such inference. Moreover, below, it may explain by example based on drawing. However, the present invention is not limited to the illustrated embodiment.

<Magnetic layer>
(Timing-based servo pattern)
The magnetic tape has a timing-based servo pattern in the magnetic layer. The “timing-based servo pattern” in the present invention and this specification refers to a servo pattern capable of head tracking in a timing-based servo system. The timing-based servo system is as described above. Servo patterns that can be head-tracked in a timing-based servo system are servo pattern recording heads (also referred to as “servo write heads”) that are used as a plurality of servo patterns of two or more different shapes on the magnetic layer. It is formed. In one example, a plurality of servo patterns having two or more different shapes are continuously arranged at a constant interval for each servo pattern having the same shape. In another example, different types of servo patterns are alternately arranged. Note that the servo pattern having the same shape does not mean that the servo pattern is completely the same shape, and a shape error that may occur due to a device such as a servo write head is allowed. . The shape of the servo pattern capable of head tracking and the arrangement in the magnetic layer in the timing-based servo system are known, and a specific mode will be described later. Hereinafter, the timing-based servo pattern is also simply referred to as a servo pattern. In this specification, “servo write head”, “servo head”, and “magnetic head” are described as heads. The servo write head is a head that records servo signals (that is, forms a servo pattern) as described above. The servo head is a head that reproduces a servo signal (that is, reads a servo pattern), and the magnetic head is a head that records and / or reproduces information unless otherwise specified.

  For example, in a magnetic tape applied to a linear recording method widely used as a recording method of a magnetic tape device, a region (called a “servo band”) in which a servo pattern is formed on a magnetic layer is usually a magnetic tape. There exist a plurality along the longitudinal direction. A region sandwiched between two servo bands is called a data band. Information (magnetic signal) recording is performed on data bands, and a plurality of data tracks are formed along the longitudinal direction in each data band.

  FIG. 1 shows an arrangement example of data bands and servo bands. In FIG. 1, a plurality of servo bands 10 are sandwiched between guide bands 12 in the magnetic layer of the magnetic tape 1. A plurality of regions 11 sandwiched between two servo bands are data bands. The servo pattern is a magnetization region, and is formed by magnetizing a specific region of the magnetic layer with a servo write head. The region magnetized by the servo write head (position where the servo pattern is formed) is determined by the standard. For example, on an LTO Ultrium format tape that is an industry standard, a plurality of servo patterns inclined with respect to the tape width direction are formed on a servo band as shown in FIG. Specifically, in FIG. 2, the servo frame SF on the servo band 10 is composed of a servo subframe 1 (SSF1) and a servo subframe 2 (SSF2). The servo subframe 1 is composed of A burst (symbol A in FIG. 2) and B burst (symbol B in FIG. 2). The A burst is composed of servo patterns A1 to A5, and the B burst is composed of servo patterns B1 to B5. On the other hand, the servo subframe 2 is composed of a C burst (reference symbol C in FIG. 2) and a D burst (reference symbol D in FIG. 2). The C burst is composed of servo patterns C1 to C4, and the D burst is composed of servo patterns D1 to D4. Such 18 servo patterns are arranged in a sub-frame with a set of 5 and 4 in an array of 5, 5, 4, 4 and used to identify the servo frame. Although one servo frame is shown in FIG. 2, a plurality of servo frames are arranged in the traveling direction in each servo band. In FIG. 2, the arrow indicates the traveling direction.

  In the timing-based servo system, the position of the servo head is recognized by the time interval at which the servo head reproduces (reads) two servo patterns of different shapes and the time interval at which two servo patterns of the same shape are reproduced. . The time interval is usually obtained as the time interval of the peak of the reproduced waveform of the servo signal. For example, in the embodiment shown in FIG. 2, the servo pattern of the A burst and the servo pattern of the C burst are servo patterns of the same type, and the servo pattern of the B burst and the servo pattern of the D burst are servo patterns of the same type. . The servo pattern of the A burst and the servo pattern of the C burst are servo patterns having different shapes from the servo pattern of the B burst and the servo pattern of the D burst. The time interval when the servo head reproduces two servo patterns having different shapes is, for example, the interval between the time when any servo pattern of A burst is reproduced and the time when any servo pattern of B burst is reproduced. . The time interval at which the servo head reproduces two servo patterns of the same shape is, for example, the interval between the time at which any servo pattern of A burst is reproduced and the time at which any servo pattern of C burst is reproduced. is there.

  The timing-based servo system is a system based on the premise that when the above time interval deviates from a set value, the time interval shift is caused by a positional variation in the width direction of the magnetic tape. The set value is a time interval when the magnetic tape travels without causing position fluctuation in the width direction. In the timing-based servo system, the magnetic head is moved in the width direction in accordance with the degree of deviation from the set value of the obtained time interval. Specifically, the larger the deviation from the set value of the time interval, the larger the magnetic head is moved in the width direction. This point is not limited to the embodiment shown in FIGS. 1 and 2 and applies to the entire timing-based servo system.

With respect to the above points, the present inventor presumes the magnetic tape as follows.
In magnetic tapes with improved surface smoothness of the magnetic layer, the head positioning accuracy in the timing-based servo system is reduced because the deviation from the set value of the above time interval is due to positional fluctuations in the width direction of the magnetic tape. Other factors (hereinafter referred to as “other factors”). The timing-based servo system recognizes the displacement caused by other factors as the displacement caused by the position variation in the width direction of the magnetic tape. As a result, the movement required to make the magnetic head follow the position variation in the width direction of the magnetic tape. It can be inferred that moving more than the distance is a cause of deterioration in head positioning accuracy in the timing-based servo system.
The present inventor considers that the fluctuation in the traveling speed of the servo head occurs as another factor for the other factors described above (that is, causes a deviation from the set value of the time interval), Further studies were made. As a result, by setting the isoelectric point of the surface zeta potential of the magnetic layer to 5.5 or more, the head positioning accuracy in the timing-based servo system is improved in the magnetic tape having the magnetic layer surface roughness Ra of 1.8 nm or less. I found out that it would be possible. This point will be further described.
In a magnetic tape having a magnetic layer surface roughness Ra of 1.8 nm or less, the servo head is more sensitive when the servo head travels on the surface of the magnetic layer to read servo signals than a magnetic tape with a rough magnetic layer surface. It is thought that it is easy to stick to the magnetic layer surface. This sticking hinders smooth sliding between the servo head and the magnetic layer surface (that is, the slidability is lowered) and the running stability of the servo head is lowered. The inventor has inferred that this will result.
On the other hand, the present inventor believes that setting the isoelectric point of the surface zeta potential of the magnetic layer to 5.5 or more contributes to promoting smooth sliding between the servo head and the magnetic layer surface. . This point will be further described later.

(Magnetic layer surface roughness Ra)
The centerline average surface roughness Ra (magnetic layer surface roughness Ra) measured on the magnetic layer surface of the magnetic tape is 1.8 nm or less. A magnetic tape having a magnetic layer surface roughness Ra of 1.8 nm or less will cause a phenomenon that the head positioning accuracy decreases in the timing-based servo system unless any countermeasure is taken. On the other hand, the magnetic tape having an isoelectric point of the surface zeta potential of the magnetic layer of 5.5 or more is a head in a timing-based servo system even though the magnetic layer surface roughness Ra is 1.8 nm or less. A decrease in positioning accuracy can be suppressed. The magnetic tape having a magnetic layer surface roughness Ra of 1.8 nm or less can exhibit excellent electromagnetic conversion characteristics. From the viewpoint of further improving the electromagnetic conversion characteristics, the magnetic layer surface roughness Ra is preferably 1.7 nm or less, and more preferably 1.6 nm or less. Further, the magnetic layer surface roughness Ra can be, for example, 1.2 nm or more or 1.3 nm or more. However, from the viewpoint of improving electromagnetic conversion characteristics, the lower the magnetic layer surface roughness Ra, the better. In the present invention and the present specification, the “magnetic layer surface” of the magnetic tape has the same meaning as the magnetic layer side surface of the magnetic tape.

The center line average surface roughness Ra measured on the surface of the magnetic layer of the present invention and the magnetic tape in the present specification is measured in an area of 40 μm × 40 μm in the area of the magnetic layer surface by an atomic force microscope (AFM). The value to be measured. Examples of the measurement conditions include the following measurement conditions. The magnetic layer surface roughness Ra shown in the examples described later is a value obtained by measurement under the following measurement conditions.
An area of 40 μm × 40 μm on the surface of the magnetic layer of the magnetic tape is measured using AFM (Nanoscope 4 manufactured by Veeco) in a tapping mode. As the probe, RTESP-300 manufactured by BRUKER is used, the scanning speed (probe moving speed) is 40 μm / second, and the resolution is 512 pixels × 512 pixels.

  The magnetic layer surface roughness Ra can be controlled by a known method. For example, the surface roughness Ra of the magnetic layer can vary depending on the size of various powders contained in the magnetic layer (eg, ferromagnetic powder, optional nonmagnetic powder, etc.), the manufacturing conditions of the magnetic tape, and the like. Therefore, by adjusting these, a magnetic tape having a magnetic layer surface roughness Ra of 1.8 nm or less can be obtained.

(Isoelectric point of surface zeta potential of magnetic layer)
In the magnetic tape, the isoelectric point of the surface zeta potential of the magnetic layer is 5.5 or more. 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 streaming potential method (also called the streaming current method) becomes zero. 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 can be obtained from the following calculation formula after changing the pressure to the measurement cell and flowing the electrolyte solution and measuring the flow potential at each pressure.

The pressure is changed in the range of 0 to 400000 Pa (0 to 400 mbar). The surface zeta potential is calculated by flowing the electrolytic solution through the measurement cell and measuring the streaming potential using electrolytic solutions having different pH (from pH 9 to pH 3 in steps of about 0.5). The measurement points start from the measurement point at pH 9 and reach a total of 13 points up to the 13th measurement point at pH 3. Thus, the surface zeta potential is determined for each pH measurement point. As the value of the surface zeta potential decreases as the pH decreases, two measurement points appear where 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. There is a case. When such two measurement points appear, the pH at which the surface zeta potential is zero is obtained by interpolation using a straight line (linear function) indicating the relationship between the surface zeta potential and the pH at the two measurement points. . On the other hand, when the surface zeta potential obtained while the pH is lowered from 9 to 3 is a positive value, the surfaces of the 13th measurement point (pH3) and the 12th measurement point are the final measurement points. Using a straight line (linear function) indicating the relationship between zeta potential and pH, the pH at a surface zeta potential of zero is obtained by extrapolation. On the other hand, when the surface zeta potential obtained while the pH is lowered from 9 to 3 is all negative, the surface of the first measurement point (pH 9) and the 12th measurement point is the first measurement point. Using a straight line (linear function) indicating the relationship between zeta potential and pH, the pH at a surface zeta potential of zero is obtained by extrapolation. Thus, the value of pH when the surface zeta potential of the magnetic layer measured by the streaming potential method becomes zero is obtained.
The above measurement is performed three times 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 obtained for each sample. The measured value at room temperature is used as the viscosity and relative dielectric constant of the electrolytic solution. The room temperature is in the range of 20-27 ° C. The arithmetic average of the three pH values thus obtained is taken as the isoelectric point of the surface zeta potential of the magnetic layer of the magnetic tape to be measured. Moreover, the electrolyte solution of pH9 uses what adjusted 1 pH of KCl aqueous solution of 1 mmol / L to pH9 using 0.1 mol / L KOH aqueous solution. For the other pH electrolyte, an electrolyte having a pH of 9 adjusted by using a 0.1 mol / L HCl aqueous solution is used.

The isoelectric point of the surface zeta potential measured by the above method is the isoelectric point required for the surface of the magnetic layer. As a result of intensive studies, the present inventor has made a magnetic tape having a magnetic layer surface roughness Ra of 1.8 nm or less to a timing-based servo by setting the isoelectric point of the surface zeta potential of the magnetic layer to 5.5 or more. It has been newly found that it is possible to suppress a decrease in head positioning accuracy when applied to a system. For this reason, the present inventor has found that the magnetic layer surface and the servo head are less likely to react electrochemically with a magnetic tape whose isoelectric point of the surface zeta potential of the magnetic layer is in the vicinity of neutral to basic pH range. It is considered that this may contribute to lowering the coefficient of friction when sliding between the servo head and the magnetic layer surface. As a result, since the sticking between the servo head and the surface of the magnetic layer is less likely to occur, the present inventor has inferred that the decrease in slidability can be suppressed. It is just a guess. Therefore, the present invention is not limited to the above estimation.
The isoelectric point of the surface zeta potential of the magnetic layer can be controlled by the type of components used for forming the magnetic layer, the formation process of the magnetic layer, etc., 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. The isoelectric point of the surface zeta potential of the magnetic layer is 5.5 or more, preferably 5.7 or more, and more preferably 6.0 or more.

  Next, details of the magnetic layer will be further described.

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

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

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

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

In the present invention and the present specification, unless otherwise specified, the average particle size of various powders such as ferromagnetic powders is a value measured by the following method using a transmission electron microscope.
The powder is photographed at a photographing magnification of 100,000 using a transmission electron microscope, and printed on photographic paper so that the total magnification is 500,000 times to obtain a photograph of particles constituting the powder. The target particle is selected from the photograph of the obtained particle, the outline of the particle is traced with a digitizer, and the size of the particle (primary particle) is measured. Primary particles refer to independent particles without agglomeration.
The above measurements are performed on 500 randomly extracted particles. The arithmetic average of the particle sizes of the 500 particles thus obtained is taken as the average particle size of the powder. As the transmission electron microscope, for example, Hitachi transmission electron microscope H-9000 type can be used. The particle size can be measured using known image analysis software, for example, image analysis software KS-400 manufactured by Carl Zeiss. Unless otherwise specified, the average particle size shown in the examples described below was measured using a Hitachi transmission electron microscope H-9000 type as a transmission electron microscope, and Carl Zeiss image analysis software KS-400 as image analysis software. Value. In the present invention and the present specification, the powder means an aggregate of a plurality of particles. For example, the ferromagnetic powder means an aggregate of a plurality of ferromagnetic particles. The aggregate of a plurality of particles is not limited to an embodiment in which the particles constituting the assembly are in direct contact with each other, and an embodiment in which a binder, an additive, and the like described later are interposed between the particles is also included. The The term particle is sometimes used to describe a powder.

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

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

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

  The content (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass. Ingredients other than the ferromagnetic powder of the magnetic layer are at least a binder and may optionally include one or more additional additives. A high filling rate of the ferromagnetic powder in the magnetic layer is preferable from the viewpoint of improving the recording density.

(Binder, curing agent)
The magnetic recording medium is a coating type magnetic recording medium, and includes 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 a binder, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, styrene, acrylonitrile, acrylic resin copolymerized with methyl methacrylate, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, A resin selected from polyvinyl alkylal resins such as polyvinyl butyral can be used alone, or a plurality of resins can be mixed and used. Among these, polyurethane resins, acrylic resins, cellulose resins, and vinyl chloride resins are preferable. These resins may be homopolymers or copolymers (copolymers). These resins can also be used as a binder in the nonmagnetic layer and / or backcoat layer described below.
As for the above binder, paragraphs 0028 to 0031 of JP 2010-24113 A 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 the below-mentioned Examples is a value obtained by converting a value measured under the following measurement conditions into polystyrene.
GPC device: HLC-8120 (manufactured by Tosoh Corporation)
Column: TSK gel Multipore HXL-M (Tosoh Corporation, 7.8 mm ID (Inner Diameter) × 30.0 cm)
Eluent: Tetrahydrofuran (THF)

In one embodiment, a binder containing an acidic group can be used as the binder. The term “acidic group” in the present invention and the present specification is intended to include a group capable of releasing H ⁺ in water or a solvent containing water (aqueous solvent) to dissociate into an anion and a salt form thereof. . Specific examples of the acidic group include a sulfonic acid group, a sulfuric acid group, a carboxy group, a phosphoric acid group, and a salt form thereof. For example, the salt form of a sulfonic acid group (—SO ₃ H) is a group represented by —SO ₃ M, in which M represents an atom (for example, an alkali metal atom) that can be a cation in water or an aqueous solvent. means. This also applies to the salt forms of the various groups described above. As an example of the binder containing an acidic group, for example, a resin containing at least one acidic group selected from the group consisting of a sulfonic acid group and a salt thereof (for example, polyurethane resin, vinyl chloride resin, etc.) can be mentioned. However, the resin contained in the magnetic layer is not limited to these resins. Moreover, in the binder containing an acidic group, the acidic group content can be, for example, in the range of 0.03 to 0.50 meq / g. In addition, eq is an equivalent and is a unit that cannot be converted into SI units. Content of various functional groups, such as an acidic group contained in resin, can be calculated | required by a well-known method according to the kind of functional group. 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, the present inventor has determined that the value of the isoelectric point is to form the magnetic layer so as to reduce the abundance of acidic components in the surface layer portion of the magnetic layer. I guess it will contribute to enlargement. In addition, the present inventors speculate that increasing the amount of the basic component in the surface layer portion of the magnetic layer also contributes to increasing the value of the isoelectric point. The term “acidic component” is intended to include a component capable of releasing H ⁺ in water or an aqueous solvent to dissociate into an anion and a salt form thereof. The basic component is used in the meaning including a component capable of releasing OH ⁻ and dissociating into a cation in water or an aqueous solvent and a salt form thereof. For example, when an acidic component is used, first, after performing the treatment of unevenly distributing the acidic component in the surface layer portion of the coating layer of the composition for forming a magnetic layer, performing the treatment for reducing the amount of the acidic component in the surface layer portion, It is thought that the value of the isoelectric point of the surface zeta potential of the magnetic layer is increased to be controlled to 5.5 or more. For example, in the step of coating the magnetic layer forming composition directly on the nonmagnetic support or via the nonmagnetic layer, applying an alternating magnetic field and applying in an alternating magnetic field is a composition for forming the magnetic layer. The present inventor believes that the acidic component is unevenly distributed in the surface layer portion of the coating layer. Furthermore, the present inventor has inferred that performing a burnish treatment after that contributes to removing at least a part of the unevenly distributed acidic components. The burnishing process is a process of rubbing the surface to be processed with a member (for example, a polishing tape or a grinding tool such as a grinding blade or a grinding wheel). Details of the magnetic layer forming step including burnishing will be described later. As an acidic component, the binder containing an acidic group can be mentioned, for example.

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

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

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

<Nonmagnetic layer>
Next, the nonmagnetic layer will be described. The magnetic tape may have a magnetic layer directly on the nonmagnetic support, or may have a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. Good. The nonmagnetic powder used for the nonmagnetic layer may be an inorganic powder or an organic powder. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. These nonmagnetic powders are available as commercial products, and can also be produced by a known method. Details thereof can be referred to paragraphs 0146 to 0150 of JP2011-216149A. Regarding the carbon black that can be used in the nonmagnetic layer, paragraphs 0040 to 0041 of JP2010-24113A can also be referred to. The content (filling rate) of the nonmagnetic powder in the nonmagnetic layer is preferably in the range of 50 to 90 mass%, more preferably in the range of 60 to 90 mass%.

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

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

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

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

<Nonmagnetic support and thickness of each layer>
The thickness of the nonmagnetic support is preferably 3.00 to 4.50 μm. The thickness of the magnetic layer is preferably 0.15 μm or less, and more preferably 0.10 μm or less, from the viewpoint of high density recording that has been demanded in recent years. The thickness of the magnetic layer is more preferably in the range of 0.01 to 0.10 μm. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied. The thickness of the magnetic layer when separating into two or more layers is the total thickness of these layers.

  The thickness of the nonmagnetic layer is, for example, 0.10 to 1.50 μm, and preferably 0.10 to 1.00 μm.

  The thickness of the backcoat layer is preferably 0.90 μm or less, and more preferably in the range of 0.10 to 0.70 μm.

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

<Manufacturing method>
(Manufacture of magnetic tape on which timing-based servo patterns are formed)
The composition for forming the magnetic layer and the optionally provided nonmagnetic layer and backcoat layer usually contains a solvent together with the various components described above. As the solvent, various organic solvents generally used for producing a coating type magnetic recording medium can be used. The amount of solvent in each layer-forming composition is not particularly limited, and can be the same as that of each layer-forming composition of a normal coating type magnetic recording medium. The step of preparing a composition for forming each layer usually includes at least a kneading step, a dispersing step, and a mixing step provided as necessary before and after these steps. Each process may be divided into two or more stages. All the raw materials used in the present invention may be added at the beginning or during any step. In addition, individual raw materials may be added in two or more steps.

  In order to prepare each layer forming composition, a known technique can be used. In the kneading step, it is preferable to use a kneader having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading processes are described in JP-A-1-106338 and JP-A-1-79274. Moreover, in order to disperse each layer forming composition, one or more kinds of dispersed beads selected from the group consisting of glass beads and other dispersed beads can be used as a dispersion medium. As such dispersed beads, zirconia beads, titania beads, and steel beads which are dispersed beads having a high specific gravity are suitable. The particle diameter (bead diameter) and filling rate of these dispersed beads can be optimized and used. A well-known thing can be used for a disperser. You may filter each layer forming composition by a well-known method, before attaching | subjecting to an application | coating process. Filtration can be performed by, for example, filter filtration. As a filter used for filtration, for example, a filter having a pore diameter of 0.01 to 3 μm (for example, a glass fiber filter, a polypropylene filter, or the like) can be used.

  The magnetic layer is formed by directly applying the composition for forming the magnetic layer onto the surface of the nonmagnetic support and drying it, or by applying it successively or simultaneously with the composition for forming the nonmagnetic layer and drying it. Can do. For details of coating for forming each layer, reference can be made to paragraph 0066 of JP2010-231843A. Also, applying the magnetic layer forming composition 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 higher. This is because when an alternating magnetic field is applied, an acidic component (for example, a binder containing an acidic group) tends to be unevenly distributed in the surface layer portion of the coating layer of the magnetic layer forming composition. Thus, the present inventor presumes that a magnetic layer in which acidic components are unevenly distributed in the surface layer portion is obtained. Further, the subsequent burnish treatment contributes to removing at least a part of the unevenly distributed acidic component and controlling the isoelectric point of the surface zeta potential of the magnetic layer to 5.5 or more. I guess. However, the above is only a guess. The application of the alternating magnetic field can be performed by arranging a magnet in the coating apparatus so that the alternating magnetic field is applied perpendicularly to the surface of the coating layer of the magnetic layer forming composition. The magnetic field strength of the alternating magnetic field can be set to, for example, about 0.05 to 3.00 T. However, it is not limited to this range. The term “vertical” in the present invention and the present specification does not necessarily mean only the strict meaning of vertical, but includes a range of errors allowed in the technical field to which the present invention belongs. The error range can mean, for example, a strictly vertical range of less than ± 10 °.

  The burnishing process is a process of rubbing the surface to be processed with a member (for example, a polishing tape or a grinding tool such as a grinding blade or a grinding wheel), and is a known burnishing process for producing a coating type magnetic recording medium. The same can be done. The burnish treatment is preferably performed by performing one or both of rubbing (polishing) the coating layer surface to be treated with an abrasive tape and rubbing (grinding) the coating layer surface to be treated with a grinding tool, Can be implemented. As a polishing tape, a commercial item may be used and the polishing tape produced by the well-known method may be used. As the grinding tool, a known grinding blade such as a fixed blade, a diamond wheel, or a rotary blade, a grinding wheel, or the like can be used. Moreover, you may perform the wiping process which wipes off the coating layer surface rubbed with the polishing tape and / or the grinding tool with the wiping material. For details of the preferred polishing tape, grinding tool, burnishing and wiping, reference can be made to paragraphs 0034 to 0048 of JP-A-6-52544, FIG. 1 and the examples of the publication. It is considered that as the varnish treatment is strengthened, more acidic components unevenly distributed in the surface layer portion of the coating layer of the magnetic layer forming composition can be removed by coating in an alternating magnetic field. The burnish treatment can be strengthened as a hard abrasive is used as the abrasive contained in the abrasive tape, and can be enhanced as the amount of the abrasive in the abrasive tape is increased. Moreover, the burnishing can be strengthened as the grinding tool having higher hardness is used as the grinding tool. Regarding the burnishing conditions, the burnishing can be enhanced as the sliding speed between the surface of the coating layer to be processed and the member (for example, a polishing tape or a grinding tool) is increased. The sliding speed can be increased by increasing one or both of the speed of moving the member and the speed of moving the magnetic tape to be processed. Although the reason is not clear, the isoelectric point of the surface zeta potential of the magnetic layer tends to increase after the burnishing process, as the amount of the binder containing an acidic group in the coating layer of the composition for forming a magnetic layer increases. May be seen.

  When the composition for forming a magnetic layer contains a curing agent, it is preferable to perform a curing treatment at any stage of the process for forming the magnetic layer. The burnish treatment is preferably performed at least before the curing treatment. A burnishing treatment may be further performed after the curing treatment. The present inventor believes that it is preferable to perform a burnish treatment before the curing treatment in order to increase the removal efficiency for removing acidic components from the surface layer portion of the coating layer of the magnetic layer forming composition. The curing treatment can be performed by a treatment such as heat treatment or light irradiation according to the kind of the curing agent contained in the magnetic layer forming composition. The curing treatment conditions are not particularly limited, and may be appropriately set according to the formulation of the magnetic layer forming composition, the type of curing agent, the thickness of the coating layer, and the like. For example, when the coating layer is formed using a magnetic layer forming composition containing polyisocyanate as a curing agent, the curing treatment is preferably a heat treatment. In addition, when a hardening | curing agent is contained in layers other than the application layer of the composition for magnetic layer formation, the hardening reaction of the layer can also be advanced. Alternatively, a curing process can be performed separately.

  Preferably, a surface smoothing treatment can be performed before the curing treatment. The surface smoothing process is a process performed to improve the smoothness of the magnetic layer surface and / or the backcoat layer surface, and is preferably performed by a calendar process. For details of the calendar process, reference can be made to paragraph 0026 of JP 2010-231843 A, for example.

  Known techniques can be applied to various other processes for manufacturing the magnetic tape on which the timing-based servo pattern is formed. For various steps, reference can be made, for example, to paragraphs 0067 to 0070 of JP-A-2010-231843.

(Formation of timing-based servo pattern)
The magnetic tape has a timing-based servo pattern in the magnetic layer. An arrangement example of a region (servo band) where a timing base servo pattern is formed and a region (data band) sandwiched between two servo bands is shown in FIG. An arrangement example of the timing base servo pattern is shown in FIG. However, the arrangement examples shown in the drawings are merely examples, and the servo patterns, servo bands, and data bands may be arranged in accordance with the arrangement of the magnetic tape device (drive). For the shape and arrangement of the timing base servo pattern, see FIG. 5 of US Pat. No. 5,689,384. 4, FIG. 5, FIG. 6, FIG. 9, FIG. 17, FIG. A publicly known technique such as the arrangement example illustrated in No. 20 can be applied without any limitation.

  The servo pattern can be formed by magnetizing a specific area of the magnetic layer with a servo write head mounted on a servo writer. In a timing-based servo system, for example, a servo signal is read by a pair of non-parallel servo patterns (also referred to as “servo stripes”) continuously arranged in the longitudinal direction of a magnetic tape. Is obtained.

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

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

  Also, as shown in ECMA-319, information indicating the position in the longitudinal direction of the magnetic tape (also referred to as “LPOS (Longitudinal Position) information”) is usually embedded in each servo band. This LPOS information is also recorded by shifting the positions of the pair of servo patterns in the longitudinal direction of the magnetic tape, as with the UDIM information. However, unlike UDIM information, in this LPOS information, the same signal is recorded in each servo band.

Other information different from the above UDIM information and LPOS information can be embedded in the servo band. In this case, the information to be embedded may be different for each servo band like UDIM information, or may be common to all servo bands like LPOS information.
In addition, as a method for embedding information in the servo band, methods other than those described above can be adopted. For example, a predetermined code may be recorded by thinning out a predetermined pair from a pair of servo patterns.

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

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

  The direction of the magnetic field of the servo pattern to be formed is determined according to the direction of the erase. For example, when the horizontal DC erase is applied to the magnetic tape, the servo pattern is formed so that the direction of the magnetic field is opposite to the direction of the erase. Thereby, the output of the servo signal obtained by reading the servo pattern can be increased. As shown in Japanese Patent Laid-Open No. 2012-53940, when a pattern using the gap is transferred to a perpendicular DC erased magnetic tape, the servo pattern obtained by reading the formed servo pattern is obtained. The signal has a monopolar pulse shape. On the other hand, when the pattern using the gap is transferred to a magnetic tape that has been subjected to horizontal DC erase, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

  The magnetic tape is usually accommodated in a magnetic tape cartridge, and the magnetic tape cartridge is mounted on the magnetic tape device. In a magnetic tape cartridge, generally, a magnetic tape is accommodated inside a cartridge body in a state of being wound around 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 body and a dual reel type magnetic tape cartridge having two reels inside the cartridge body are widely used. When a single reel type magnetic tape cartridge is mounted on a magnetic tape device (drive) for recording and / or reproducing information (magnetic signal) on the magnetic tape, the magnetic tape is pulled out of the magnetic tape cartridge and the drive is driven. It is wound on the side reel. A magnetic head is disposed in the magnetic tape conveyance path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed and taken up between the reel (supply reel) on the magnetic tape cartridge side and the reel (winding reel) on the drive side. During this period, the magnetic head and the magnetic layer surface of the magnetic tape come into contact with each other and slide, whereby magnetic signals are recorded and / or reproduced. On the other hand, in the dual reel type magnetic tape cartridge, both the supply reel and the take-up reel are provided inside the magnetic tape cartridge. The magnetic tape according to one embodiment of the present invention may be accommodated in either a single reel type or a dual reel type magnetic tape cartridge. The configuration of the magnetic tape cartridge is known.

  The magnetic tape according to one embodiment of the present invention described above has high surface smoothness with a magnetic layer surface roughness Ra of 1.8 nm or less, and can improve the head positioning accuracy in the timing-based servo system.

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

  Details of the magnetic tape mounted on the magnetic tape device are as described above. Such magnetic tape has a timing-based servo pattern. Therefore, when recording a magnetic signal on the data band by the magnetic head to form a data track and / or reproducing the recorded signal, timing is based on the servo pattern read while reading the servo pattern by the servo head. By performing base servo head tracking, the magnetic head can follow the data track with high accuracy. As an index of the head positioning accuracy, PES (Position Error Signal) obtained by a method shown in an example described later can be cited. The PES is an indicator that the magnetic head has traveled out of the position where the magnetic head should travel, even if the head tracking is performed by the servo system when the magnetic tape travels in the magnetic tape device. Means that the head positioning accuracy in the servo system is low. The magnetic tape according to one embodiment of the present invention can achieve a PES of, for example, 9.0 nm or less (for example, in the range of 7.0 to 9.0 nm).

  As the magnetic head mounted on the magnetic tape device, a known magnetic head capable of recording and / or reproducing magnetic signals on the magnetic tape can be used. The recording head and the reproducing head may be a single magnetic head or separate magnetic heads. As the servo head, a known servo head capable of reading the timing base servo pattern of the magnetic tape can be used. At least one servo head may be included in the magnetic tape device, and two or more servo heads may be included. A servo pattern reading element may be included in a magnetic head including an element for recording a magnetic signal and / or an element for reproducing. That is, the magnetic head and the servo head may be a single head.

  For details of the timing-based servo head tracking servo, known techniques such as those described in US Pat. No. 5,689,384, US Pat. No. 6,542,325, and US Pat. No. 7,876,521 can be applied.

  Commercially available magnetic tape devices are usually provided with a magnetic head and a servo head according to the standard. In addition, a commercially available magnetic tape apparatus is usually provided with a servo control mechanism for enabling head tracking in a servo system according to the standard. The magnetic tape device according to one embodiment of the present invention can be configured, for example, by incorporating the magnetic tape according to one embodiment of the present invention into a commercially available magnetic tape device.

Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiment shown in the examples. Unless otherwise specified, “parts” and “%” described below are based on mass.
“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).
“Binder B” described below is a vinyl chloride copolymer (trade name: MR110, SO ₃ K group-containing vinyl chloride copolymer, SO ₃ K group: 0.07 meq / g) manufactured by Kaneka Corporation.

[Production of magnetic tape]
<Example 1>
(1) Preparation of Alumina Dispersion Alumina powder having a pregelatinization rate of about 65% and a BET (Brunauer-Emmett-Teller) specific surface area of 20 m ² / g, 100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.) 3.0 parts of 3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd.), 32% solution (solvent) of SO ₃ Na group-containing polyester polyurethane resin (UR-4800 (SO ₃ Na group: 0.08 meq / g) manufactured by Toyobo Co., Ltd.) 31.3 parts of a mixed solvent of methyl ethyl ketone and toluene) and 570.0 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone 1: 1 (mass ratio) as a solvent are mixed and dispersed in a paint shaker for 5 hours in the presence of zirconia beads. I let you. After dispersion, the dispersion and beads were separated with a mesh to obtain an alumina dispersion.

(2) Composition formulation for magnetic layer formation (magnetic liquid)
Ferromagnetic powder 100.0 parts Ferromagnetic hexagonal barium ferrite powder binder having an average particle size (average plate diameter) of 21 nm (see Table 1) Table 1 reference Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (Abrasive liquid)
6.0 parts of alumina dispersion prepared in (1) above (silica sol (protrusion forming agent liquid))
Colloidal silica (average particle size: 120 nm) 2.0 parts methyl ethyl ketone 1.4 parts (other components)
Stearic acid 2.0 parts stearamide 0.2 parts butyl stearate 2.0 parts
Polyisocyanate (Tosoh Corp. Coronate (registered trademark)) 2.5 parts (finishing addition solvent)
Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

(3) Nonmagnetic layer forming composition formulation Nonmagnetic inorganic powder: α-iron oxide 100.0 parts Average particle size (average major axis length): 0.15 μm
Average needle ratio: 7
BET specific surface area: 52 m ² / g
Carbon black 20.0 parts Average particle size: 20 nm
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 forming back coat layer Nonmagnetic inorganic powder: α-iron oxide 80.0 parts Average particle size (average major axis length): 0.15 μm
Average needle ratio: 7
BET specific surface area: 52 m ² / g
Carbon black 20.0 parts Average particle size: 20 nm
Vinyl chloride copolymer 13.0 parts Polysulfonate resin containing sulfonate group 6.0 parts Phenylphosphonic acid 3.0 parts Methyl ethyl ketone 155.0 parts 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.
The magnetic liquid was prepared by dispersing each component for 24 hours (bead dispersion) using a batch type vertical sand mill. As dispersion beads, zirconia beads having a bead diameter of 0.5 mm were used.
Using the sand mill, the prepared magnetic liquid, the abrasive liquid, and other components (silica sol, other components and finishing additive solvent) are mixed and dispersed for 5 minutes, and then a batch type ultrasonic device (20 kHz, 300 W). For 0.5 minute (ultrasonic dispersion). Then, it filtered using the filter which has a 0.5 micrometer hole diameter, and prepared the composition for magnetic layer formation.
A composition for forming a nonmagnetic layer was prepared by the following method.
Each component excluding the lubricant (stearic acid, stearic acid amide and butyl stearate), cyclohexanone and methyl ethyl ketone was dispersed for 24 hours using a batch type vertical sand mill to obtain a dispersion. As dispersion beads, zirconia beads having a bead diameter of 0.5 mm were used. Thereafter, the remaining components were added to the obtained dispersion and stirred with a dissolver. The dispersion thus obtained was filtered using a filter having a pore size of 0.5 μm to prepare a composition for forming a nonmagnetic layer.
A composition for forming a backcoat layer was prepared by the following method.
After kneading and diluting each component excluding polyisocyanate and cyclohexanone with an open kneader, using a zirconia bead with a bead diameter of 1 mm by a horizontal bead mill disperser, with a bead filling rate of 80% by volume and a rotor tip peripheral speed of 10 m / sec. The 1-pass residence time was 2 minutes, and 12-pass dispersion treatment was performed. Thereafter, the remaining components were added to the obtained dispersion and stirred with a dissolver. 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 A composition for forming a nonmagnetic layer prepared in (5) above on the surface of a 4.30 μm thick polyethylene naphthalate support so that the thickness after drying is 1.00 μm. Was applied and dried to form a nonmagnetic layer.
Next, in the coating apparatus in which the magnet for applying the alternating magnetic field is arranged, the magnetic layer forming composition prepared in the above (5) is applied to the surface of the nonmagnetic layer so that the thickness after drying becomes 0.10 μm. Coating was performed while applying a magnetic field (magnetic field strength: 0.15 T) to form a coating layer. The alternating magnetic field was applied so that the alternating magnetic field was applied perpendicularly to the surface of the coating layer. Thereafter, while the coating layer of the magnetic layer forming composition was in a wet (undried) state, a vertical magnetic field treatment was performed by applying a DC magnetic field having a magnetic field strength of 0.30 T in a direction perpendicular to the surface of the coating layer. . Thereafter, it was dried to form a magnetic layer.
Thereafter, the backcoat prepared in the above (5) so that the thickness after drying becomes 0.60 μm on the surface opposite to the surface on which the nonmagnetic layer and magnetic layer of the polyethylene naphthalate support are formed. The composition for layer formation was applied and dried to form a backcoat layer.
After slitting the magnetic tape thus obtained to a width of ½ inch (0.0127 meter), burnishing and wiping treatments were performed on the surface of the coating layer of the magnetic layer forming composition. The burnishing and wiping treatments were performed using a commercially available polishing tape (trade name MA22000, manufactured by Fuji Film Co., Ltd., abrasive: diamond / Cr ₂₎ as the polishing tape in the processing apparatus having the configuration shown in FIG. 1 of JP-A-6-52544. O ₃ / Bengara), a commercially available sapphire blade (made by Kyocera, width 5 mm, length 35 mm, tip angle 60 degrees) as a grinding blade, and a commercially available wiping material (Kuraray product) 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, a calender roll composed only of a metal roll, with a speed of 80 m / min, a linear pressure of 300 kg / cm (294 kN / m), and a calender temperature (calendar roll surface temperature) shown in Table 1 And calendaring (surface smoothing).
Then, after performing a heat treatment (curing treatment) for 36 hours in an environment with an atmospheric temperature of 70 ° C., slitting to a width of ½ inch (0.0127 meter) was performed to produce a magnetic tape. With the magnetic layer of the produced magnetic tape demagnetized, a servo pattern having an arrangement and shape according to the LTO Ultrium format was formed on the magnetic layer by a servo write head mounted on the servo writer. As a result, the magnetic layer has a data band, a servo band, and a guide band in an arrangement according to the LTO Ultrium format, and a servo pattern (timing-based servo pattern) having an arrangement and shape in accordance with the LTO Ultium format on the servo band. A magnetic tape of Example 1 was obtained.

<Examples 2-6, Comparative Examples 1-11>
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 Table 1, in Examples 2 to 6 where “Yes” is described in the column of alternating magnetic field application during application and the column of burnish treatment, the magnetic layer forming composition was applied by the same method as in Example 1. The process after the process was implemented. That is, as in Example 1, an alternating magnetic field was applied during application of the magnetic layer forming composition, and burnishing and wiping were performed on the magnetic layer forming composition.
On the other hand, in Comparative Example 10 in which “None” is described in the column of the burnishing process, the burnishing process and the wiping process were not performed on the coating layer of the magnetic layer forming composition. 1 and the subsequent steps of applying the magnetic layer forming composition were performed.
In Comparative Example 11 in which “None” is described in the column of alternating magnetic field application during coating, the magnetic layer forming composition and the subsequent steps are applied in the same manner as in Example 1 except that no alternating magnetic field is applied. The process of was implemented.
In Comparative Examples 1 to 9 described as “None” in the column of alternating magnetic field application during coating and the column of burnish treatment, no alternating magnetic field was applied and the coating layer of the composition for forming a magnetic layer was not used. The steps after the coating step of the composition for forming a magnetic layer were carried out in the same manner as in Example 1 except that the burnishing and wiping treatments were not performed.

The thickness of each layer and the thickness of the nonmagnetic support of each magnetic tape of Examples and Comparative Examples were determined by the following method and confirmed to be the above thickness.
After the cross section in the thickness direction of the magnetic tape was exposed with an ion beam, the exposed cross section was observed with a scanning electron microscope. Various thicknesses were obtained as an arithmetic average of thicknesses obtained at two locations randomly extracted in cross-sectional observation.

[Evaluation of magnetic tape]
(1) Isoelectric point of surface zeta potential of magnetic layer Six samples for isoelectric point measurement were cut out from each magnetic tape of Examples and Comparative Examples, and two samples were arranged in a measurement cell in one measurement. . In the measurement cell, the sample mounting surface and the sample backcoat layer surface were bonded to a sample table above and below the measurement cell (each sample mounting surface size was 1 cm × 2 cm) with double-sided tape. As a result, when the electrolyte is passed through the measurement cell, the surface of the magnetic layer of the sample comes into contact with the electrolyte, so that the surface zeta potential of the magnetic layer can be measured. In each measurement, two samples were used and the measurement was performed three times in total to obtain the isoelectric point of the surface zeta potential of the magnetic layer. The arithmetic average 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 a surface zeta potential measuring device, SurPASS manufactured by Anton Paar was used. The measurement conditions were as follows. Other details of the method for obtaining the isoelectric point are as described above.
Measurement cell: Variable gap cell (20mm x 10mm)
Measurement mode: Streaming Current
Gap: about 200μm
Measurement temperature: room temperature Ramp Target Pressure / Time: 400000 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 about 0.5 increments)

(2) Centerline average surface roughness Ra measured on the surface of the magnetic layer
Using an atomic force microscope (AFM, Nanoscope 4 manufactured by Veeco) in tapping mode, a measurement area of 40 μm × 40 μm was measured on the surface of the magnetic layer of the magnetic tape to determine the centerline average surface roughness Ra. The probe used was RTESP-300 manufactured by BRUKER, the scan speed (probe moving speed) was 40 μm / second, and the resolution was 512 pixels × 512 pixels.

(3) PES
For the magnetic tape on which the timing base servo pattern was formed, the servo pattern was read with a verify head on the servo writer used for forming the servo pattern. The verify head is a read magnetic head for confirming the quality of the servo pattern formed on the magnetic tape. Like the magnetic head of a known magnetic tape device (drive), the position of the servo pattern (the width of the magnetic tape). A reading element is arranged at a position corresponding to the direction position.
A known PES arithmetic circuit is connected to the verify head for calculating the head positioning accuracy in the servo system as PES from the electric signal obtained by reading the servo pattern with the verify head. The PES arithmetic circuit calculates the displacement in the width direction of the magnetic tape from time to time based on the input electric signal (pulse signal), and a high-pass filter (cutoff: 500 cycles / m) with respect to the temporal change information (signal) of this displacement. ) Was calculated as PES.

(4) Electromagnetic conversion characteristics (SNR (Signal-to-Noise-Ratio))
With respect to each of the magnetic tapes of the example and the comparative example in an environment having an ambient temperature of 23 ° C. ± 1 ° C. and a relative humidity of 50%, a recording magnetic head (MIG (Metal-in-gap) head, gap length 0.15 μm, 1.8T) and a magnetic head for reproduction (GMR (Giant Magnetosensitive) head, reproduction track width 1 μm) are attached to a loop tester, and a signal with a linear recording density of 325 kfci is recorded. Then, the reproduction output is measured, SNR was determined as a ratio to noise. The unit kfci is a unit of linear recording density (cannot be converted into SI unit system). If the SNR of Comparative Example 1 is 0 dB and the SNR is 2.0 dB or more, it can be evaluated that the performance can meet future severe needs associated with high density recording.

  The above results are shown in Table 1 (Table 1-1 to Table 1-3).

That the PES calculated | required by the said method is 9.0 nm or less means that a magnetic head can be positioned with high precision by the head tracking in a timing base servo system.
By comparison between Comparative Examples 1 to 3 and Comparative Examples 4 and 6 to 11, in the magnetic tape (Comparative Examples 4 and 6 to 11) having a magnetic layer surface roughness Ra of 1.8 nm or less, the PES is significantly larger than 9.0 nm. It was confirmed that a phenomenon exceeding that (decrease in head positioning accuracy) occurred.
In the magnetic tape of Comparative Example 5, the slidability between the servo head and the surface of the magnetic layer was extremely low, and sticking to the surface of the magnetic layer occurred, and the servo head could not be run. Therefore, PES could not be measured for Comparative Example 5.
On the other hand, the magnetic tapes of Examples 1 to 6 achieve a PES of 9.0 nm or less although the surface roughness Ra of the magnetic layer is 1.8 nm or less, that is, improve the head positioning accuracy in the timing-based servo system. Was possible. Furthermore, from the value of SNR, it can be confirmed that the magnetic tapes of Examples 1 to 6 are excellent in electromagnetic conversion characteristics.

  One embodiment of the present invention is useful in the technical field of magnetic tapes for high-density recording.

Claims (8)

A magnetic tape having a magnetic layer comprising a ferromagnetic powder and a binder on a non-magnetic support,
The magnetic layer has a timing-based servo pattern;
The magnetic tape has a centerline average surface roughness Ra measured on the surface of the magnetic layer of 1.8 nm or less, and an isoelectric point of the surface zeta potential of the magnetic layer is 5.5 or more. 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, wherein the binder is a binder containing an acidic group. The magnetic tape according to claim 3, wherein the acidic group includes at least one acidic group selected from the group consisting of a sulfonic acid group and a salt thereof. 5. The magnetic tape according to claim 1, wherein the center line average surface roughness Ra measured on the surface of the magnetic layer is 1.2 nm or more and 1.8 nm or less. The magnetic tape according to claim 1, further comprising a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. The magnetic tape according to any one of claims 1 to 6, further comprising a backcoat layer containing a nonmagnetic powder and a binder on the surface side opposite to the surface side having the magnetic layer of the nonmagnetic support. . A magnetic tape device comprising the magnetic tape according to claim 1, a magnetic head, and a servo head.