JP2019169227A - Magnetic tape and magnetic tape device - Google Patents

Abstract

An object of the present invention is to suppress a decrease in output of a servo signal in a servo system in a magnetic tape having a total thickness of a nonmagnetic layer and a magnetic layer of 0.60 μm or less. The magnetic tape has a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and a magnetic layer containing a ferromagnetic powder and a binder on the nonmagnetic layer. A magnetic tape wherein the total thickness of the non-magnetic layer and the magnetic layer is 0.60 μm or less, the magnetic layer has a servo pattern, and the isoelectric point of the surface zeta potential of the magnetic layer is 5.5 or more. . A magnetic tape device including the magnetic tape. [Selection diagram] 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. For data storage applications such as data backup and archive, a tape-shaped magnetic recording medium, that is, a magnetic tape (hereinafter also simply referred to as “tape”). ) Is mainly used. Information recording on a magnetic tape is usually performed by recording a magnetic signal in 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 arranging 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 means for suppressing the occurrence of such an error ( 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.

  By the way, the magnetic tape is usually accommodated and used in a magnetic tape cartridge. In order to increase the recording capacity per volume of the magnetic tape cartridge, it is desirable to increase the total length of the magnetic tape stored in one volume of the magnetic tape cartridge. For this purpose, it is required to make the magnetic tape thinner (hereinafter referred to as “thinning”). As one means for reducing the thickness of a magnetic tape, for a magnetic tape having a nonmagnetic layer and a magnetic layer in this order on a nonmagnetic support, the total thickness of the nonmagnetic layer and the magnetic layer should be reduced. Is mentioned.

  In view of the above points, the present inventor studied the application of a magnetic tape having a reduced total thickness of the nonmagnetic layer and the magnetic layer to the timing-based servo system. However, in such a study, with a magnetic tape whose total thickness of the nonmagnetic layer and the magnetic layer is 0.60 μm or less, if the head tracking is continued while the magnetic tape is running in the timing-based servo system, the servo head It has become clear that a phenomenon that has not been known in the past occurs that the output of the servo signal reproduced by the above decreases compared to the initial stage of travel (hereinafter also referred to as “servo signal output decrease”). The decrease in the output of the servo signal causes a decrease in the accuracy (hereinafter referred to as “head positioning accuracy”) for causing the magnetic head to follow the data track in the servo system. Therefore, in order to record the information on the magnetic tape more accurately and / or to reproduce the information recorded on the magnetic tape more accurately by using the servo system, the output reduction of the servo signal is suppressed. Is required.

  Accordingly, an object of the present invention is to suppress a decrease in output of a servo signal in a servo system in a magnetic tape having a total thickness of a nonmagnetic layer and a magnetic layer of 0.60 μm or less.

One embodiment of the present invention provides:
A magnetic tape having a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and having a magnetic layer containing a ferromagnetic powder and a binder on the nonmagnetic layer,
The total thickness of the nonmagnetic layer and the magnetic layer is 0.60 μm or less,
The magnetic layer has a servo pattern, and the isoelectric point of the surface zeta potential of the magnetic layer is 5.5 or more, a 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 embodiment, the total thickness of the nonmagnetic layer and the magnetic layer may be 0.20 μm or more and 0.60 μm or less.

  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.

  In this specification, “servo write head”, “servo head”, and “magnetic head” are described as heads. The servo write head (servo write head) is a head that performs recording of a servo signal (that is, formation of a servo pattern). 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.

  According to one aspect of the present invention, there is provided a magnetic tape having a total thickness of a nonmagnetic layer and a magnetic layer of 0.60 μm or less and having a servo pattern formed on the magnetic layer, and outputting servo signals in the servo system It is possible to provide a magnetic tape in which the decrease is suppressed, and a magnetic tape device that records and / or reproduces a magnetic signal on the magnetic tape.

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 one embodiment of the present invention has a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and has a magnetic layer containing a ferromagnetic powder and a binder on the nonmagnetic layer. The total thickness of the nonmagnetic layer and the magnetic layer is 0.60 μm or less, the magnetic layer has a servo pattern, 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>
(Servo pattern)
The magnetic tape has a servo pattern in the magnetic layer. The servo pattern is formed on the magnetic layer by magnetizing a specific position of the magnetic layer with a servo write head. The shape of the servo pattern and the arrangement in the magnetic layer for enabling the head tracking servo are known. A known technique can be applied to the servo pattern of the magnetic layer of the magnetic tape. For example, a timing-based servo system and an amplitude-based servo system are known as head tracking servo systems. The servo pattern of the magnetic layer of the magnetic tape may be a servo pattern that enables any type of head tracking servo. A servo pattern that enables head tracking servo by the timing-based servo system and a servo pattern that enables head tracking servo by the amplitude-based servo system may be formed on the magnetic layer.

  Hereinafter, a head tracking servo of a timing-based servo system will be described as one specific aspect of the head tracking servo. However, the head tracking servo in the present invention is not limited to the following specific mode.

  In the timing-based servo head tracking servo (hereinafter referred to as “timing-based servo”), a plurality of servo patterns having two or more different shapes are formed on the magnetic layer, and the servo head is divided into two different shapes. The position of the servo head is recognized based on the time interval at which the servo pattern is read and the time interval at which two servo patterns having the same shape are read. 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. The magnetic head whose position is controlled is a magnetic head (reproducing head) that reproduces information recorded on the magnetic tape in one aspect, and a magnetic head (recording head) that records information on the magnetic tape in another aspect. ).

  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. FIG. 2 shows one servo frame for explanation. However, actually, in the magnetic layer of the magnetic tape on which the timing tracking servo head tracking servo is performed, a plurality of servo frames are arranged in the running direction in each servo band. In FIG. 2, the arrow indicates the traveling direction. For example, an LTO Ultrium format tape usually has 5000 or more servo frames per 1 m of tape length in each servo band of the magnetic layer. The servo head sequentially reads servo patterns in a plurality of servo frames while sliding in contact with the magnetic layer surface of the magnetic tape conveyed in the magnetic tape device.

  In the timing-based servo head tracking servo, the time interval when the servo head read two servo patterns of different shapes (reproducing the servo signal) and the time interval of reading two servo patterns of the same shape are Recognize the position of the servo head. 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 reads two servo patterns having different shapes is, for example, the interval between the time when one servo pattern of A burst is read and the time when any servo pattern of B burst is read. . The time interval when the servo head reads two servo patterns of the same type is, for example, the interval between the time when one servo pattern of A burst is read and the time when one servo pattern of C burst is read. is there. The timing tracking servo head tracking servo is a system on the premise that when the above time interval deviates from a set value, the time interval misalignment occurs due to a position 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.

For example, when a magnetic tape is run in a magnetic tape apparatus using a timing-based servo system and a magnetic signal (information) is recorded or reproduced by the magnetic head, the servo pattern is continuously read by the servo head (servo signal is continuously reproduced). If the output of the servo signal is lowered, the measurement accuracy of the time interval is lowered. As a result, the head positioning accuracy decreases as the running continues. If the output of the servo signal is lowered while the servo pattern is continuously read by the servo head in a magnetic tape apparatus using the servo system, not only the timing-based servo system, the head positioning accuracy is lowered while the running is continued.
With regard to the above points, it has been found by the present inventors that the servo signal output is significantly reduced in a magnetic tape having a total thickness of the nonmagnetic layer and the magnetic layer of 0.60 μm or less. The main cause of the decrease in the output of the servo signal is that the servo write head is formed by sequentially forming a plurality of servo patterns on the magnetic layer while sliding in contact with the magnetic layer surface of the magnetic tape. It is thought that foreign matter adheres to the servo light head. As a result of the servo pattern forming ability of the servo write head being reduced due to the influence of the adhered foreign matter, it is presumed that the magnetic force of the formed servo pattern gradually decreases as the servo pattern is continuously formed. In the magnetic layer having the servo pattern formed as described above, it is considered that the output of the servo signal decreases while the servo pattern is continuously read by the servo head (the servo signal is continuously reproduced). The reason why such a phenomenon occurs in a magnetic tape having a total thickness of the nonmagnetic layer and the magnetic layer of 0.60 μm or less is that, in such a magnetic tape, the total thickness of the nonmagnetic layer and the magnetic layer exceeds 0.60 μm. The present inventor has inferred that the contact state between the servo write head and the magnetic layer surface is different from the magnetic tape. However, it is only a guess. On the other hand, a decrease in servo signal output in a magnetic tape having a total thickness of the nonmagnetic layer and the magnetic layer of 0.60 μm or less is suppressed by setting the isoelectric point of the surface zeta potential of the magnetic layer to 5.5 or more. As a result of intensive studies by the present inventor, it has been clarified. The inventors' inference regarding this point will be described later.

(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 inventors have determined that the magnetic layer has a surface zeta potential isoelectric point of 5.5 or more in a magnetic tape having a total thickness of the nonmagnetic layer and the magnetic layer of 0.60 μm or less. It was newly found that the output reduction of the servo signal can be suppressed. As described above, while the servo write head is in contact with the magnetic layer surface of the magnetic tape and sliding while forming multiple servo patterns on the magnetic layer, foreign matter may adhere to the servo write head. As a result, it is considered that the output of the servo signal is reduced while the servo pattern is continuously read by the servo head (the servo signal is continuously reproduced). In contrast, a magnetic tape whose surface zeta potential isoelectric point of the magnetic layer is in the neutral to basic pH range is free of foreign matter due to the difficulty of electrochemical reaction between the magnetic layer surface and the servo write head. It is considered that it is difficult to generate, and / or shavings generated when the magnetic layer surface and the servo write head come into contact with each other and the magnetic layer surface is scraped are difficult to adhere to the servo write head. From the above, the present inventor has inferred that adhesion of foreign matter to the servo write head 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.

<Various thicknesses>
The total thickness of the nonmagnetic 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 reducing the thickness of the magnetic tape. The total thickness of the nonmagnetic layer and the magnetic layer can be, for example, 0.10 μm or more, or 0.20 μm or more.
The thickness of the nonmagnetic support of the magnetic tape is preferably 3.00 to 4.50 μm.
The thickness of the magnetic layer can be optimized according to the saturation magnetization of the magnetic head used, the head gap length, the band of the recording signal, and the like. The thickness of the magnetic layer is generally 0.01 μm to 0.15 μm, preferably 0.02 μm to 0.12 μm, more preferably 0.03 μm to 0.10 μm from the viewpoint of high density recording. . There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied. The thickness of the magnetic layer when separating into two or more layers is the total thickness of these layers.
The thickness of the nonmagnetic layer is, for example, 0.10 to 0.55 μm, and preferably 0.10 to 0.50 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.
Further, the total thickness of the magnetic tape is preferably 6.00 μm or less, more preferably 5.70 μm or less, and more preferably 5.50 μm or less, from the viewpoint of improving the recording capacity per magnetic tape cartridge. More preferably. On the other hand, from the viewpoint of easy handling (handling properties) of the magnetic tape, the total thickness of the magnetic tape is preferably 1.00 μm or more.

  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 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 a magnetic tape on which a servo pattern is formed. For various steps, reference can be made, for example, to paragraphs 0067 to 0070 of JP-A-2010-231843.

(Servo pattern formation)
The magnetic tape has a servo pattern in the magnetic layer. The details of the servo pattern are as described above. For example, FIG. 1 shows 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. 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. Known techniques such as the arrangement example illustrated in 20 can be applied.

  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 is a magnetic tape in which the total thickness of the nonmagnetic layer and the magnetic layer is 0.60 μm or less, and a servo pattern is formed on the magnetic layer, and the servo system It is possible to suppress a decrease in servo signal output at.

[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 a magnetic tape has a servo pattern. Therefore, when a magnetic signal is recorded on the data band by the magnetic head to form a data track and / or when the recorded signal is reproduced, the head is based on the servo pattern read while reading the servo pattern by the servo head. By performing tracking, the magnetic head can be made to follow the data track with high accuracy.

  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. For details of the amplitude-based servo head tracking servo, for example, known techniques such as US Pat. No. 5,426,543 and US Pat. No. 5,898,533 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 On the surface of a 4.30 μm thick polyethylene naphthalate support, for forming the nonmagnetic layer prepared in (5) above so that the thickness after drying is as shown in Table 1. The composition 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) so that the thickness after drying becomes the thickness shown in Table 1 on the surface of the nonmagnetic layer. The coating layer was formed by applying an alternating magnetic field (magnetic field strength: 0.15 T) while applying. 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 burnishing and wiping, the calender roll is composed of only a metal roll, and the calender is at a speed of 80 m / min, a linear pressure of 300 kg / cm (294 kN / m), and a calender temperature (calendar roll surface temperature) of 95 ° C. Treatment (surface smoothing treatment) was performed.
Then, after performing a heat treatment (curing treatment) for 36 hours in an environment with an atmospheric temperature of 70 ° C., a servo pattern (timing base servo pattern) was formed on the magnetic layer by a commercially available servo writer.
Thus, a magnetic tape of Example 1 was obtained.

<Examples 2 to 6, Comparative Examples 1 to 6, 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 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 5 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 6 in which “None” is described in the column of application of alternating magnetic field during coating, the application of the composition for forming a magnetic layer is performed 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 4, Reference Example 1 and Reference Example 2 in which “None” is described in the column of alternating magnetic field application during coating and the column of burnish treatment, no alternating magnetic field is applied and magnetic layer formation is performed. The process after the application | coating process of the composition for magnetic layer formation was implemented by the method similar to Example 1 except the point which did not perform a varnish process and a wiping process with respect to the application layer of the composition for magnetic layers.

The thickness of each layer and the thickness of the nonmagnetic support of each of the magnetic tapes of Examples, Comparative Examples and Reference Examples were determined by the following method, and confirmed to be the thicknesses described in Table 1 or above.
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, Comparative Examples and Reference Examples, and two samples were measured in one measurement cell in one measurement. Arranged. 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) Reduced output of servo signal The magnetic tape on which the servo pattern was formed was attached to a servo testing machine. In the servo testing machine, the surface of the magnetic layer of the traveling magnetic tape and the servo head are brought into contact with each other and slid while the servo pattern of the first servo frame formed on the magnetic tape by the servo head is changed to the final 5, Servo patterns were read in sequence (servo signal reproduction) up to the servo pattern of the 000,000th servo frame. Let A be the arithmetic average of the signal outputs obtained in the first to 100th servo frames, and B be the arithmetic average of the signal outputs obtained in the 4,999,900th to 5,000,000th servo frames. The servo signal output decrease (unit:%) was calculated as “[(B−A) / A] × 100”.

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

By comparison between the reference example and the comparative example, the total thickness of the nonmagnetic layer and the magnetic layer is 0. 0 compared to the case where the total thickness of the nonmagnetic layer and the magnetic layer exceeds 0.60 μm (Reference Examples 1 and 2). In the case of 60 μm or less (Comparative Examples 1 to 6), it was confirmed that the output of the servo signal was significantly reduced.
On the other hand, although the magnetic tapes of Examples 1 to 6 have a total thickness of the nonmagnetic layer and the magnetic layer of 0.60 μm or less, the output decrease of the servo signal is suppressed as compared with the magnetic tapes of Comparative Examples 1 to 6. It was done.

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

Claims (7)

A magnetic tape having a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and having a magnetic layer containing a ferromagnetic powder and a binder on the nonmagnetic layer,
The total thickness of the nonmagnetic layer and the magnetic layer is 0.60 μm or less,
The magnetic layer has a servo pattern, and the 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. The total thickness of the said nonmagnetic layer and the said magnetic layer is a magnetic tape of any one of Claims 1-4 which are 0.20 micrometer or more and 0.60 micrometer or less. The magnetic tape according to any one of claims 1 to 5, further comprising a backcoat layer containing a nonmagnetic powder and a binder on the surface side opposite to the surface side having the magnetic layer of the nonmagnetic support. . A magnetic tape device comprising the magnetic tape according to claim 1, a magnetic head, and a servo head.