JP2020009522A - Magnetic tape device - Google Patents

Abstract

To provide a magnetic tape device that can improve reproduction quality.SOLUTION: In a magnetic tape device, a magnetic tape has a servo pattern in a magnetic layer; in the longitudinal direction of the magnetic tape, ΔSFD is 0.50 or less; a reading element unit has a plurality of reading elements that each read data in a linear scanning system from a specific track area including a track to be read among track areas included in the magnetic tape; an extraction section extracts data derived from the track to be read from results of reading by executing waveform equalization processing according to the amount of shift in position between the magnetic tape and reading element units for each of the results of reading performed by the reading elements; the amount of shift is defined according to a result obtained by a servo element reading the servo pattern included in the magnetic layer of the magnetic tape.SELECTED DRAWING: None

Description

  The present invention relates to a magnetic tape device.

  A magnetic recording / reproducing apparatus that records data on a magnetic recording medium and / or reads (reproduces) the recorded data is roughly classified into a magnetic disk device and a magnetic tape device. A typical example of the magnetic disk device is an HDD (Hard Disk Drive). In a magnetic disk device, a magnetic disk is used as a magnetic recording medium. On the other hand, in a magnetic tape device, a magnetic tape is used as a magnetic recording medium.

  In any of the magnetic disk device and the magnetic tape device, it is preferable to reduce the recording track width in order to increase the recording capacity (increase the capacity). On the other hand, as the recording track width becomes narrower, the signal of the adjacent track is more likely to be mixed with the signal of the track to be read at the time of reproduction. Therefore, it is difficult to maintain reproduction quality such as SNR (Signal-to-Noise Ratio). Become. In this regard, in recent years, it has been proposed to improve the reproduction quality by reading a signal of a recording track two-dimensionally by a plurality of reading elements (also referred to as “reproducing elements”) (for example, Patent Document 1). 3). If the reproduction quality can be improved in this way, the reproduction quality can be maintained even if the recording track width is narrowed, so that the recording capacity can be increased by narrowing the recording track width.

JP 2016-110680 A JP 2011-134372 A U.S. Pat. No. 7,755,863

  Patent Literatures 1 and 2 discuss a magnetic disk drive. On the other hand, magnetic tapes have recently attracted attention as data storage media for storing large volumes of data for long periods of time. However, a magnetic tape device is generally a sliding-type device in which data reading (reproduction) is performed by a magnetic tape and a reading element coming into contact and sliding. Therefore, the relative position between the read element and the track to be read tends to fluctuate during reproduction, and improvement in reproduction quality tends to be more difficult than in a magnetic disk device. Patent Document 3 describes a magnetic tape device (tape drive), but does not show specific means for improving reproduction quality in the magnetic tape device.

  One embodiment of the present invention provides a magnetic tape device capable of improving reproduction quality.

One embodiment of the present invention provides:
Magnetic tape,
A reading element unit;
An extraction unit;
Including
The magnetic tape has a magnetic layer containing a ferromagnetic powder and a binder on a non-magnetic support,
The magnetic layer has a servo pattern,
In the longitudinal direction of the magnetic tape, the following formula 1:
ΔSFD = SFD _{25 ° C.−} SFD _{−190 ° C.} Formula 1
(Hereinafter, also simply referred to as “ΔSFD”) is 0.50 or less. In the equation 1, SFD _{25 ° C.} is measured in the longitudinal direction of the magnetic tape at a temperature of 25 ° C. The switching field distribution SFD is as follows: SFD _{−190 ° C.} is a switching field distribution SFD measured in the longitudinal direction of the magnetic tape under an environment of a temperature of −190 ° C.
The reading element unit has a plurality of reading elements that respectively read data from a specific track area including a track to be read among track areas included in the magnetic tape by a linear scan method,
The extraction unit performs, on each of the read results for each of the read elements, a waveform equalization process in accordance with a positional shift amount between the magnetic tape and the read element unit, thereby obtaining the read result from the read result. Extract data from the track to be read,
The deviation amount is determined according to the result obtained by reading the servo pattern of the magnetic layer of the magnetic tape by the servo element, a magnetic tape device,
About. The SFD means a switching field distribution.

  In one aspect, a part of each of the plurality of reading elements may overlap in a running direction of the magnetic tape.

  In one aspect, the specific track area may be an area including the track to be read and an adjacent track adjacent to the track to be read, and each of the plurality of read elements may When the positional relationship changes, both the track to be read and the adjacent track can be straddled together.

  In one aspect, the plurality of reading elements may be arranged side by side in a width direction of the magnetic tape.

  In one aspect, in the width direction of the magnetic tape, the plurality of reading elements can be contained within the read target track.

  In one aspect, the waveform equalization process may be performed using a tap coefficient determined according to the shift amount.

  In one aspect, for each of the plurality of read elements, the ratio of the overlap area with the track to be read and the overlap area with the adjacent track adjacent to the track to be read can be specified from the deviation amount, The tap coefficient may be determined according to the specified ratio.

  In one aspect, the reading operation of the reading element unit may be performed in synchronization with the reading operation performed by the servo element.

  In one aspect, the extraction unit can include a two-dimensional FIR (Finite Impulse Response) filter, and the two-dimensional FIR filter performs the waveform equalization process on each of the reading results for each of the reading elements. By combining the results obtained as described above, data derived from the read target track can be extracted from the read result.

  In one aspect, the plurality of reading elements can be a pair of reading elements.

  In one aspect, the coercive force measured in the longitudinal direction of the magnetic tape can be 167 kA / m or less.

  In one aspect, ΔSFD can be 0.03 or more and 0.50 or less.

  According to one embodiment of the present invention, a magnetic tape device capable of reproducing data recorded on a magnetic tape with high reproduction quality can be provided.

FIG. 1 is a schematic configuration diagram illustrating an example of an overall configuration of a magnetic tape device. FIG. 2 is a schematic plan view illustrating an example of a schematic configuration of a read head and a magnetic tape included in the magnetic tape device in plan view. FIG. 3 is a schematic plan view illustrating an example of a schematic configuration of a reading element unit and a magnetic tape in plan view. FIG. 3 is a schematic plan view illustrating an example of a schematic configuration of a track area and a reading element pair in a plan view. 9 is a graph illustrating an example of a correlation between an SNR and a track offset for each of the single read element data and the first combined data under the first condition. 9 is a graph illustrating an example of a correlation between an SNR and a track offset for each of the single read element data and the second combined data under the second condition. FIG. 3 is a block diagram illustrating an example of a main configuration of electric hardware of the magnetic tape device. It is a conceptual diagram provided for explanation of the calculation method of the amount of shift. It is a flowchart which shows an example of the flow of a magnetic tape reading process. FIG. 7 is a conceptual diagram serving to explain a process performed by a two-dimensional FIR filter of an extraction unit. FIG. 9 is a schematic plan view showing an example of a state in which a reading element unit straddles a reading target track and a second noise mixing source track. FIG. 9 is a schematic plan view showing a first modification of the reading element unit. FIG. 13 is a schematic plan view illustrating a second modification of the reading element unit. FIG. 4 shows an example of a servo pattern arrangement on an LTO (Linear-Tape-Open) Ultra format tape. FIG. 4 is an explanatory diagram of an angle α related to an edge shape of a servo pattern. FIG. 4 is an explanatory diagram of an angle α related to an edge shape of a servo pattern. 4 shows an example of an edge shape of a servo pattern. 4 shows an example of a servo pattern. 4 shows an example of a servo pattern. 4 shows an example of a servo pattern. It is a conceptual diagram provided for explanation of the first conventional example. It is a conceptual diagram provided for explanation of the second conventional example. FIG. 4 is a diagram illustrating an example of a two-dimensional image of a reproduction signal obtained from a single reading element.

  A magnetic tape device according to one aspect of the present invention includes a magnetic tape, a reading element unit, and an extraction unit.

  Regarding reading of data from a magnetic tape, in the conventional example shown in FIG. 21, a long read head 200 includes a plurality of read elements 202 along a longitudinal direction. A plurality of tracks 206 are formed on the magnetic tape 204. The read head 200 is arranged so that its longitudinal direction matches the width direction of the magnetic tape 204. Further, each of the plurality of reading elements 202 is assigned to each of the plurality of tracks 206 in a one-to-one relationship, and reads data from the track 206 at an opposing position.

  However, the magnetic tape 204 normally expands and contracts due to fluctuations in time, environment, tension, and the like. When the magnetic tape expands and contracts in the width direction of the magnetic tape 204, the center of the read elements 202 arranged at both ends in the longitudinal direction of the read head 200 is shifted from the center of the track 206. When the magnetic tape 204 deforms due to expansion and contraction in the width direction, the read elements 202 closer to both ends of the read head 200 among the plurality of read elements 202 are greatly affected by off-track. In order to reduce the influence of off-track, for example, a method of giving a margin to the width of the track 206 can be considered. However, as the width of the track 206 increases, the recording capacity of the magnetic tape 204 decreases.

  Also, as in the conventional example shown in FIG. 22, the read head 200 is usually provided with a servo element 208. A servo pattern previously applied to the magnetic tape 204 along the running direction of the magnetic tape 204 is read by a servo element 208. Then, from a servo signal obtained by reading the servo pattern by the servo element 208, the controller (not shown) moves the reading element 202 at any position on the magnetic tape 204 at a fixed time interval, for example. Is specified. Thus, the PES (Position Error Signal) in the width direction of the magnetic tape 204 is detected by the control device.

  As described above, when the control device specifies the traveling position of the reading element 202, the control device performs feedback control on the read head actuator (not shown) based on the specified traveling position. Accordingly, tracking in the width direction of the magnetic tape 204 is realized.

However, even if tracking is performed, steep vibrations and high frequency components of jitter and the like may cause an increase in PES, leading to a decrease in reproduction quality of data read from a track to be read.
On the other hand, in the magnetic tape device according to one aspect of the present invention, the read element unit reads a plurality of data from a specific track area including a track to be read among the track areas included in the magnetic tape by a linear scan method. Having a reading element, the extracting unit performs a waveform equalization process on each of the reading results for each of the reading elements in accordance with a shift amount of the position between the magnetic tape and the reading element unit, Data derived from the read target track is extracted from the read result. Thus, according to the magnetic tape device, it is possible to improve the reproduction quality of the data read from the read target track, as compared with the case where the data is read from the read target track by only a single read element by the linear scan method. As a result, it is possible to increase the allowable amount of a shift amount (track offset amount) that can ensure good reproduction quality.
Further, the above-mentioned shift amount is detected by reading the servo pattern. However, if there is a large error between the amount of deviation detected by reading the servo pattern and the amount of deviation actually occurring, the read result read at each location on the magnetic tape may have a waveform corresponding to the amount of deviation described above. The equalization process may not always be the optimal waveform equalization process. On the other hand, if the error between the amount of deviation detected by reading the servo pattern and the amount of deviation actually occurring can be reduced, waveform equalization more suitable for the read result read at each location Processing can be performed. As a result, it is possible to increase the allowable amount of the shift amount that can ensure good reproduction quality by the above-described waveform equalization processing.
As described above, increasing the allowable amount of the shift amount that can ensure good reproduction quality means that even if the track margin (recording track width-reproduction element width) is reduced, high reproduction quality (for example, high SNR, low error rate, etc.) ) Can be played back. Reducing the track margin can contribute to increasing the number of recording tracks that can be arranged in the width direction of the magnetic tape by reducing the recording track width, that is, increasing the capacity.
Regarding the above points, it is considered that the ΔSFD of the magnetic tape from which data is read in the magnetic tape device is 0.50 or less contributes to increasing the accuracy of reading the servo pattern and specifying the position of the reading element. Can be It is presumed that this leads to a reduction in the error between the deviation detected by reading the servo pattern and the deviation actually occurring. This point will be further described later.

  Hereinafter, the magnetic tape device will be described in more detail. Hereinafter, the magnetic tape device may be described with reference to the drawings. However, the magnetic tape device is not limited to the embodiment shown in the drawings.

[Configuration of Magnetic Tape Device and Magnetic Tape Reading Process]
As an example, as shown in FIG. 1, the magnetic tape device 10 includes a magnetic tape cartridge 12, a transport device 14, a read head 16, and a control device 18.

  The magnetic tape device 10 is a device that pulls out a magnetic tape MT from a magnetic tape cartridge 12 and reads data from the pulled-out magnetic tape MT using a read head 16 in a linear scan system. Reading data can also be referred to as reproducing data.

  The control device 18 controls the entire magnetic tape device 10. In one aspect, the control performed by the control device 18 may be realized by an ASIC (Application Specific Integrated Circuit). In one embodiment, the control performed by the control device 18 can be realized by an FPGA (Field-Programmable Gate Array). Further, the control performed by the control device 18 may be realized by a computer including a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). Further, the above control may be realized by a combination of two or more of the AISC, the FPGA, and the computer.

  The transport device 14 is a device that selectively transports the magnetic tape MT in the forward direction and the reverse direction, and includes a delivery motor 20, a take-up reel 22, a take-up motor 24, a plurality of guide rollers GR, and a control device 18. ing.

  In the magnetic tape cartridge 12, a cartridge reel CR is provided. A magnetic tape MT is wound around the cartridge reel CR. The delivery motor 20 drives the cartridge reel CR in the magnetic tape cartridge 12 to rotate under the control of the controller 18. The control device 18 controls the rotation direction, the rotation speed, the rotation torque, and the like of the cartridge reel CR by controlling the sending motor 20.

  When the magnetic tape MT is taken up by the take-up reel 22, the controller 18 rotates the delivery motor 20 so that the magnetic tape MT runs in the forward direction. The rotation speed and the rotation torque of the delivery motor 20 are adjusted according to the speed of the magnetic tape MT wound by the winding reel 22.

  The take-up motor 24 drives the take-up reel 22 to rotate under the control of the control device 18. The control device 18 controls the rotation direction, the rotation speed, the rotation torque, and the like of the winding reel 22 by controlling the winding motor 24.

  When the magnetic tape MT is taken up by the take-up reel 22, the control device 18 rotates the take-up motor 24 so that the magnetic tape MT runs in the forward direction. The rotation speed and rotation torque of the winding motor 24 are adjusted according to the speed of the magnetic tape MT wound by the winding reel 22.

  By adjusting the rotation speed, the rotation torque, and the like of each of the delivery motor 20 and the winding motor 24 in this manner, a tension within a predetermined range is applied to the magnetic tape MT. Here, “within the predetermined range” indicates, for example, a range of tension obtained by computer simulation and / or actual machine test as a range of tension in which data can be read from the magnetic tape MT by the read head 16.

  When rewinding the magnetic tape MT to the cartridge reel CR, the controller 18 rotates the sending motor 20 and the winding motor 24 so that the magnetic tape MT runs in the reverse direction.

  In one embodiment, the tension of the magnetic tape MT is controlled by controlling the rotation speed and the rotation torque of the delivery motor 20 and the winding motor 24. Further, in one embodiment, the tension of the magnetic tape MT may be controlled using a dancer roller, or may be controlled by drawing the magnetic tape MT into a vacuum chamber.

  Each of the plurality of guide rollers GR is a roller that guides the magnetic tape MT. The traveling path of the magnetic tape MT is determined by arranging a plurality of guide rollers GR at positions between the magnetic tape cartridge 12 and the take-up reel 22 across the read head 16.

  The reading head 16 includes a reading unit 26 and a holder 28. The reading section 26 is held by a holder 28 so as to contact the running magnetic tape MT.

  As an example, as shown in FIG. 2, the magnetic tape MT includes a track area 30 and a servo pattern 32. The servo pattern 32 is a pattern used for detecting the position of the read head 16 with respect to the magnetic tape MT. The servo pattern 32 includes a first oblique line 32A at a first predetermined angle (for example, 95 degrees) and a second oblique line 32B at a second predetermined angle (for example, 85 degrees) at both ends in the tape width direction. Is a pattern arranged alternately at a constant pitch (period) along the traveling direction. Here, the “tape width direction” refers to the width direction of the magnetic tape MT.

  The track area 30 is an area where data to be read is written, and is formed at the center of the magnetic tape MT in the tape width direction. Here, the “central portion in the tape width direction” refers to, for example, a region between the servo pattern 32 at one end and the servo pattern 32 at the other end in the tape width direction of the magnetic tape MT. Hereinafter, for convenience of description, the “running direction of the magnetic tape MT” is simply referred to as the “running direction”.

  The reading section 26 includes a servo element pair 36 and a plurality of reading element units 38. The holder 28 is formed to be long in the tape width direction, and the entire length of the holder 28 in the longitudinal direction is longer than the width of the magnetic tape MT. The servo element pairs 36 are arranged at both ends of the holder 28 in the longitudinal direction, and the plurality of reading element units 38 are arranged at the central part of the holder 28 in the longitudinal direction.

  The servo element pair 36 includes servo elements 36A and 36B. The servo element 36A is disposed at a position facing the servo pattern 32 at one end in the tape width direction of the magnetic tape MT, and the servo element 36B is connected to the servo pattern 32 at the other end in the tape width direction of the magnetic tape MT. They are arranged at opposing positions.

  In the holder 28, a plurality of reading element units 38 are arranged along the tape width direction between the servo elements 36A and 36B. The track area 30 includes a plurality of tracks at equal intervals in the tape width direction. When the magnetic tape device 10 is in a default state, each of the plurality of reading element units 38 faces each track in the track area 30. Are located.

  Therefore, when the reading unit 26 and the magnetic tape MT relatively linearly move along the longitudinal direction of the magnetic tape MT, the data of each track in the track area 30 is stored in the position of the plurality of reading element units 38. Are read by each of the corresponding reading element units 38 in a linear scan system. In the linear scan method, the servo pattern 32 is read by the servo element pair 36 in synchronization with the reading operation of the reading element unit 38. That is, in one mode of the linear scan system, reading from the magnetic tape MT is performed in parallel by the plurality of reading element units 38 and the servo element pairs 36.

  Here, the "each track in the track area 30" refers to a track included in "each of a plurality of specific track areas each including a read target track among the track areas included in the magnetic tape".

  The above-described “state in which the magnetic tape device 10 is in a default state” refers to a state in which the magnetic tape MT is not deformed and the positional relationship between the magnetic tape MT and the read head 16 is correct. Here, the “correct positional relationship” indicates, for example, a positional relationship in which the center of the magnetic tape MT in the tape width direction coincides with the center of the read head 16 in the longitudinal direction.

  In one aspect, each of the plurality of reading element units 38 has the same configuration. Hereinafter, one of the plurality of reading element units 38 will be described as an example for convenience of description. As an example, as shown in FIG. 3, the reading element unit 38 includes a pair of reading elements. In the example illustrated in FIG. 3, “a pair of reading elements” indicates the first reading element 40 and the second reading element 42. Each of the first reading element 40 and the second reading element 42 reads data from the specific track area 31 including the read target track 30A in the track area 30.

  In the example shown in FIG. 3, one specific track area 31 is shown for convenience of explanation. In practice, usually, a plurality of specific track areas 31 exist in the track area 30, and each specific track area 31 includes a read target track 30A. One reading element unit 38 is assigned to each of the plurality of specific track areas 31. Specifically, one read element unit 38 is assigned to each read target track 30 </ b> A of the plurality of specific track areas 31.

  The specific track area 31 indicates three adjacent tracks. The first track of the three adjacent tracks is the read target track 30 </ b> A in the track area 30. The second track of the three adjacent tracks is a first noise mixing source track 30B which is one of the adjacent tracks adjacent to the read target track 30A. The third track of the three adjacent tracks is a second noise mixing source track 30C which is one of the adjacent tracks adjacent to the read target track 30A. The read target track 30 </ b> A is a track at a position facing the read element unit 38 in the track area 30. In other words, the read target track 30A refers to a track from which data of the read element unit 38 is to be read.

  The first noise mixing source track 30B is a track adjacent to the reading target track 30A on one side in the tape width direction and serving as a mixing source of noise mixed in data read from the reading target track 30A. is there. The second noise mixing source track 30C is adjacent to the reading target track 30A on the other side in the tape width direction, and is a track serving as a mixing source of noise mixed in data read from the reading target track 30A. is there. In the following, for convenience of explanation, when it is not necessary to distinguish and describe the first noise mixing source track 30B and the second noise mixing source track 30C, they are referred to as “adjacent tracks” without reference numerals.

  In one aspect, a plurality of specific track areas 31 are arranged at regular intervals in the tape width direction in the track area 30. For example, in the track area 30, 32 specific track areas 31 are arranged at regular intervals in the tape width direction, and one reading element unit 38 is assigned to each specific track area 31.

  The first reading element 40 and the second reading element 42 are arranged in a state where they are close to each other in the traveling direction and partially overlap in the traveling direction. In the default state of the magnetic tape device 10, the first reading element 40 is arranged at a position across the read target track 30A and the first noise mixing source track 30B. In the default state of the magnetic tape device 10, the second reading element 42 is arranged at a position straddling the read target track 30A and the first noise mixing source track 30B.

  In the default state of the magnetic tape device 10, the area of the portion of the first reading element 40 facing the read target track 30 </ b> A in plan view is the first noise mixing source of the first reading element 40. It is larger than the area of the portion facing the track 30B. On the other hand, in the default state of the magnetic tape device 10, the area of the portion of the second reading element 42 facing the first noise mixing source track 30B in plan view is equal to the area of the first reading element 40. It is larger than the area of the portion facing the read target track 30A.

  The data read by the first reading element 40 is subjected to a waveform equalization process by a first equalizer 70 (see FIG. 7) described later. The data read by the second reading element 42 is subjected to a waveform equalization process by a second equalizer 72 (see FIG. 7) described later. Each data obtained by performing the waveform equalization processing by each of the first equalizer 70 and the second equalizer 72 is synthesized by being added by the adder 44.

  FIG. 3 illustrates an example in which the reading element unit 38 includes the first reading element 40 and the second reading element 42. However, for example, even if only one of the pair of reading elements (hereinafter, also referred to as a single reading element) is used, a signal corresponding to the reproduction signal obtained from the reading element unit 38 can be obtained.

  In this case, for example, as shown in FIG. 8 as an example, a reproduction signal obtained from a single reading element is converted into a plane position on a track calculated from a servo signal obtained by a servo element pair 36 in synchronization with the reproduction signal. Assign to By repeating this while moving the single reading element in the tape width direction, a two-dimensional image of a reproduction signal (hereinafter, simply referred to as “two-dimensional image”) is obtained. Here, a reproduction signal (for example, a reproduction signal corresponding to a position of a plurality of tracks) constituting a two-dimensional image or a part of the two-dimensional image is a signal corresponding to a reproduction signal obtained from the reading element unit 38. is there.

  FIG. 23 shows an example of a two-dimensional image of a reproduced signal obtained by using a loop tester on a magnetic tape MT (hereinafter, also referred to as a “loop tape”) in a loop shape. Here, the loop tester refers to, for example, an apparatus that transports a loop tape in a state of repeatedly contacting a single reading element. In order to obtain a two-dimensional image similarly to the loop tester, a reel tester may be used, or an actual tape drive may be used. Here, the “reel tester” refers to, for example, a device for transporting the magnetic tape MT in a reel form.

  As described above, even when a conventional magnetic tape head having no read element unit having a plurality of read elements mounted in close proximity is used, the effect according to the technology described in this specification is quantitatively evaluated. be able to. An example of an index for quantitatively evaluating an effect according to the technology described in this specification includes an SNR, an error rate, and the like.

  4 to 6 show the results obtained by experiments by the present inventors. As an example, as shown in FIG. 4, a reading element pair 50 is arranged on the track area 49. The track area 49 includes a first track 49A, a second track 49B, and a third track 49C adjacent in the tape width direction. The reading element pair 50 includes a first reading element 50A and a second reading element 50B. The first reading element 50A and the second reading element 50B are arranged at positions close to each other in the tape width direction. The first reading element 50A is arranged so as to face the second track 49B, which is the track to be read, and to fit in the second track 49B. The second reading element 50B is arranged so as to face the first track 49A adjacent to one side of the second track 49B and to fit in the first track 49A.

  FIG. 5 shows an example of the correlation between the SNR and the track offset for each of the single read element data and the first combined data under the first condition. FIG. 6 shows an example of the correlation between the SNR and the track offset for each of the single read element data and the second combined data under the second condition.

  Here, the single reading element data refers to data obtained by performing a waveform equalization process on the data read by the first reading element 50A, similarly to the first reading element 40 shown in FIG. Point. The first condition refers to a condition where the read element pitch is 700 nm (nanometer). The second condition refers to a condition where the read element pitch is 500 nm. The read element pitch refers to a pitch in the tape width direction between the first read element 50A and the second read element 50B as shown in FIG. 4 as an example. As shown in FIG. 4 as an example, the track offset indicates a shift amount between the center of the second track 49B in the tape width direction and the center of the first reading element 50A in the track width direction.

  The first combined data refers to data combined by adding the first waveform equalized data and the second waveform equalized data obtained under the first condition, respectively. The first waveform equalized data is data obtained by performing a waveform equalization process on data read by the first reading element 50A, similarly to the first reading element 40 shown in FIG. Point. The second waveform equalization-processed data is data obtained by performing a waveform equalization process on data read by the second reading element 50B, similarly to the second reading element 42 illustrated in FIG. Point. The second combined data refers to data combined by adding the first waveform equalized data and the second waveform equalized data obtained under the second condition.

  Comparing the SNR of the first combined data shown in FIG. 5 with the SNR of the second combined data shown in FIG. 6, the SNR of the first combined data has a track offset around −0.4 μm (micrometer) to 0.2 μm. , And a groove is formed in the middle of the graph, whereas the SNR of the second combined data does not suddenly decrease in the middle as in the SNR graph of the first combined data. Each of the SNR of the first combined data and the SNR of the second combined data is higher than the SNR of the single read element data, and in particular, the SNR of the second combined data is higher than the single read element data over the entire range of the track offset. Higher than the SNR.

  From the experimental results shown in FIGS. 5 and 6, the present inventors have found that the first reading element 50A and the second reading element 50B are different from each other in the case where data is read only by the first reading element 50A in the tape width direction. It has been found that it is preferable to read data in a state where the data is brought close to. Here, the “closed state” means, for example, that the first reading element 50A and the second reading element 50B do not come into contact with each other, and the SNR is smaller than the SNR of the single reading element data in the entire range of the track offset. In the tape width direction so as to be higher.

  In one embodiment, as shown in FIG. 3 as an example, in the reading element unit 38, the first reading element 40 and the second reading element 42 partially overlap each other in the running direction, so that the magnetic tape MT The density of the tracks included in the data is realized.

  As an example, as shown in FIG. 7, the magnetic tape device 10 includes an actuator 60, an extraction unit 62, A / D (Analog / Digital) converters 64, 66, 68, a decoding unit 69, and a computer 73.

  The control device 18 is connected to the servo element pair 36 via an A / D (Analog-to-digital) converter 68. The A / D converter 68 sends the servo signal obtained by converting the analog signal obtained by reading the servo pattern 32 by the servo elements 36A and 36B included in the servo element pair 36 into a digital signal to the control device 18. Output.

  The control device 18 is connected to the actuator 60. The actuator 60 is attached to the read head 16 and changes the read head 16 in the tape width direction by applying power to the read head 16 under the control of the controller 18. The actuator 60 includes, for example, a voice coil motor, and the power applied to the read head 16 is obtained by converting electric energy based on current flowing through the coil into kinetic energy using the energy of a magnet as a medium. Power.

  Here, an embodiment in which a voice coil motor is mounted on the actuator 60 is described. However, the magnetic tape device is not limited to such an embodiment. For example, a piezoelectric element may be used instead of the voice coil motor. It is also possible to use a voice coil motor and a piezoelectric element together.

  The amount of displacement between the magnetic tape MT and the read element unit 38 is determined according to a servo signal obtained as a result of reading the servo pattern 32 by the servo element pair 36. The control device 18 controls the actuator 60 to apply a power to the read head 16 in accordance with the amount of displacement between the magnetic tape MT and the read element unit 38, thereby causing the read head 16 to fluctuate in the tape width direction. Then, the position of the reading head 16 is adjusted to a normal position. Here, the normal position indicates, for example, the position of the read head 16 when the magnetic tape device 10 is in a default state as shown in FIG.

  In the following, for the sake of convenience of description, the amount of displacement between the position of the magnetic tape MT and the reading element unit 38 is simply referred to as “the amount of displacement”. The shift amount is calculated based on the ratio of the distance A to the distance B, for example, as shown in FIG. The distance A indicates a distance calculated from a result obtained by reading the adjacent first oblique line 32A and second oblique line 32B by the servo element 36A. The distance B indicates a distance calculated from a result obtained by reading two adjacent first oblique lines 32A by the servo element 36A.

  The extraction unit 62 includes the control device 18 and a two-dimensional FIR filter 71. The two-dimensional FIR filter 71 includes an adder 44, a first equalizer 70, and a second equalizer 72.

  The first equalizer 70 is connected to the first reading element 40 via the A / D converter 64. The first equalizer 70 is connected to each of the control device 18 and the adder 44. The data read from the specific track area 31 by the first reading element 40 is an analog signal, and the A / D converter 64 converts the data read from the specific track area 31 by the first reading element 40 into a digital signal. The first read signal thus obtained is output to the first equalizer 70.

  The second equalizer 72 is connected to the second reading element 42 via the A / D converter 66. Further, the second equalizer 72 is connected to each of the control device 18 and the adder 44. The data read from the specific track area 31 by the second reading element 42 is an analog signal, and the A / D converter 66 converts the data read from the specific track area 31 by the second reading element 42 into a digital signal. The second read signal obtained in this way is output to the second equalizer 72. Note that the first read signal and the second read signal are examples of “read result for each read element”.

  The first equalizer 70 performs a waveform equalization process on the input first read signal. For example, the first equalizer 70 performs a convolution operation on a tap coefficient with respect to the input first read signal, and outputs a first operation-processed signal that is a signal after the operation process.

  The second equalizer 72 performs a waveform equalization process on the input second read signal. For example, the second equalizer 72 performs a convolution operation on a tap coefficient with respect to the input second read signal, and outputs a second operation-processed signal that is a signal after the operation process.

  Each of the first equalizer 70 and the second equalizer 72 outputs the first processed signal and the second processed signal to the adder 44. The adder 44 adds the first operation-processed signal input from the first equalizer 70 and the second operation-processed signal input from the second equalizer 72 to synthesize the signal, The combined data obtained by combining is output to the decoding unit 69.

  Each of the first equalizer 70 and the second equalizer 72 is a one-dimensional FIR filter.

  In one aspect, the FIR filter itself is a sequence of real values including positive and negative, the number of rows in the sequence is called the number of taps, and the value itself is called the tap coefficient. In one aspect, waveform equalization refers to a process of convoluting (accumulating and multiplying) a series of real numbers, that is, tap coefficients, on a read signal. Here, the “read signal” is a general term for the first read signal and the second read signal. In one embodiment, the equalizer refers to a circuit that performs a convolution operation on a read signal or another input signal with a tap coefficient and outputs a signal after the operation processing. In one embodiment, an adder refers to a circuit that simply adds two streams. The weights of the two sequences are reflected in the numerical values of the FIR filters used in the first equalizer 70 and the second equalizer 72, that is, the tap coefficients.

  The control device 18 sets a tap coefficient in accordance with the amount of deviation for each of the FIR filters of the first equalizer 70 and the second equalizer 72, so that the first equalizer 70 and the second equalizer 72 are set. For each of the equalizers 72, a waveform equalization process corresponding to the shift amount is performed.

  The control device 18 includes a correspondence table 18A. In the correspondence table 18A, the tap coefficient and the shift amount are associated with each other for each of the first equalizer 70 and the second equalizer 72. The combination of the tap coefficient and the shift amount is, for example, a combination of the tap coefficient and the shift amount at which the best combined data is obtained by the adder 44 based on the result of at least one of the test and the simulation of the actual device. Is a combination obtained in advance. The “best combined data” here refers to data corresponding to the read target track data.

  Here, “read target track data” refers to “data derived from the read target track 30A”. The “data derived from the read target track 30A” refers to data corresponding to the data written in the read target track 30A. An example of the data corresponding to the data written to the read target track 30A is data read from the read target track 30A and data in which a noise component from an adjacent track is not mixed.

  In the above, the correspondence table 18A is illustrated. In another embodiment, an arithmetic expression may be used instead of the correspondence table 18A. The “calculation formula” here refers to, for example, a calculation formula in which an independent variable is a shift amount and a dependent variable is a tap coefficient.

  In the above description, an example is given in which the tap coefficients are derived from the correspondence table 18A in which the combinations of the tap coefficients and the shift amounts are defined. In another aspect, for example, a tap coefficient may be derived from a correspondence table or an arithmetic expression that defines a combination of a tap coefficient and a ratio. Here, the “ratio” refers to the ratio of the overlapping area of the track 30A to be read and the overlapping area of the adjacent track for each of the first reading element 40 and the second reading element 42. The ratio is specified by the control device 18 by being calculated from the deviation amount, and the tap coefficient is determined according to the specified ratio.

  The decoding unit 69 decodes the combined data input from the adder 44, and outputs a decoded signal obtained by decoding to the computer 73. The computer 73 performs various processes on the decoded signal input from the decoding unit 69.

  Next, a magnetic tape reading process performed by the extracting unit 62 will be described with reference to FIG. In the following, for convenience of explanation, the description will be made on the assumption that a servo signal is input to the control device 18 when the sampling time comes. Here, the sampling means not only the sampling of the servo signal but also the sampling of the read signal. That is, in one embodiment, since the track area 30 is formed in parallel with the servo pattern 32 along the running direction, the reading operation of the reading element unit 38 is performed in synchronization with the reading operation of the servo element pair 36.

  In the process shown in FIG. 9, first, at step 100, the control device 18 determines whether or not the sampling time has come. If it is determined in step 100 that the sampling time has come, the determination is affirmative, and the magnetic tape reading process proceeds to step 102. If it is determined in step 100 that the sampling time has not come, the determination is negative and the determination in step 100 is performed again.

  In step 102, the first equalizer 70 acquires the first read signal, the second equalizer 72 acquires the second read signal, and the magnetic tape reading process proceeds to step 104.

  In step 104, the control device 18 acquires a servo signal, calculates a deviation amount from the acquired servo signal, and thereafter, the magnetic tape reading process proceeds to step 106.

  In step 106, the control device 18 calculates a tap coefficient corresponding to the shift amount calculated in the processing of step 104 for each of the first to third taps of the first equalizer 70 and the second equalizer 72. Derived from 18A. That is, by executing the processing of step 106, an optimal combination as a combination of a one-dimensional FIR filter as an example of the first equalizer 70 and a one-dimensional filter as an example of the second equalizer 72 is determined. Determined. Here, the “optimal combination” refers to, for example, a combination that converts the synthesized data output by performing the processing of step 112 described below into data corresponding to the read target track data.

  In the next step 108, the control device 18 sets the tap coefficients derived in the processing of step 106 for each of the first equalizer 70 and the second equalizer 72, and thereafter, the magnetic tape reading processing proceeds to step 106. Move to 110.

  In step 110, the first equalizer 70 performs a waveform equalization process on the first read signal acquired in the process in step 102, thereby generating a first operation-processed signal. The first equalizer 70 outputs the generated first processed signal to the adder 44. The second equalizer 72 performs a waveform equalization process on the second read signal acquired in the process of step 102 to generate a second arithmetically processed signal. The second equalizer 72 outputs the generated second processed signal to the adder 44.

  In the next step 112, the adder 44, as shown in FIG. 10 by way of example, outputs the first operation-processed signal input from the first equalizer 70 and the second signal processed from the second equalizer 72. The signal is synthesized by adding the two processed signals. Then, the adder 44 outputs the synthesized data obtained by the synthesis to the decoding unit 69.

  When the reading element unit 38 is arranged on the specific track area 31 as in the example shown in FIG. 3, the processing of the step 112 is executed, so that the first noise mixing source track 30B is output as synthesized data. The data corresponding to the read target track data from which the noise component has been removed is output. That is, by executing the processing of steps 102 to 112, the extraction unit 62 extracts only data derived from the read target track 30A.

  When the tape width direction of the magnetic tape MT expands or contracts, or when at least one of the magnetic tape MT and the read head 16 is vibrated, the read element unit 38 is moved from the position shown in FIG. It may be displaced to the position shown in. In the example shown in FIG. 11, the first reading element 40 and the second reading element 42 are arranged at positions that both straddle both the read target track 30A and the second noise mixing source track 30C. In this case, by executing the processing of Steps 102 to 112, data corresponding to the read target track data from which the noise component from the second noise mixing source track 30C has been removed is output to the decoding unit 69 as synthesized data. Is done.

  In the next step 114, the control device 18 determines whether or not a condition for ending the magnetic tape reading process (hereinafter, referred to as an “end condition”) is satisfied. The termination condition refers to, for example, a condition that the entire magnetic tape MT has been wound by the take-up reel 22, a condition that an instruction to forcibly terminate the magnetic tape reading process has been given from the outside, and the like.

  If the end condition is not satisfied in step 114, the determination is negative and the magnetic tape reading process proceeds to step 100. In step 114, if the termination condition is satisfied, the determination is affirmative, and the magnetic tape reading process ends.

  As described above, in one embodiment of the magnetic tape device 10, data is read from the specific track area 31 by the first reading element 40 and the second reading element 42 arranged close to each other. Then, the extraction unit 62 performs a waveform equalization process on each of the first reading element 40 and the second reading element 42 in accordance with the amount of deviation, thereby obtaining the first reading signal and the second reading signal. , Data derived from the read target track 30A is extracted. Therefore, the magnetic tape device 10 reduces the reproduction quality of the data read from the read target track 30A by the linear scan method as compared with the case where the data is read from the read target track 30A by the single read element only in the linear scan method. Can be suppressed.

  In one embodiment of the magnetic tape device 10, the first reading element 40 and the second reading element 42 partially overlap each other in the running direction. Therefore, the magnetic tape device 10 can improve the reproduction quality of data read by the linear scan method from the read target track 30A, as compared with the case where the entirety of the plurality of read elements overlap in the running direction.

  Further, in one embodiment of the magnetic tape device 10, the specific track area 31 includes the read target track 30A, the first noise mixing source track 30B, and the second noise mixing source track 30C, and includes the first read element 40 and the second noise mixing source track 30C. When the positional relationship with the magnetic tape MT changes, each of the two reading elements 42 straddles both the read target track 30A and the adjacent track. Therefore, the magnetic tape device 10 performs the first reading by entering the adjacent track from the read target track 30A in the tape width direction as compared with the case where data is read from the read target track 30A by only a single read element by the linear scan method. A noise component generated by one of the element 40 and the second reading element 42 is reduced by using the reading result of the other reading element that enters the adjacent track from the read target track 30A in the tape width direction. Can be.

  Further, in one aspect of the magnetic tape device 10, the tap coefficient used in the waveform equalization processing is determined according to the shift amount. Therefore, the magnetic tape device 10 can reduce the noise component generated by entering the read target track 30A from the adjacent track in the tape width direction, as compared with the case where the tap coefficient is determined according to a parameter that is not related to the deviation amount. It can be reduced immediately by following the change in the positional relationship between the tape MT and the reading element unit 38.

  Further, in one embodiment of the magnetic tape device 10, for each of the first read element 40 and the second read element 42, the ratio between the overlapping area of the track 30A to be read and the overlapping area of the adjacent track is specified from the deviation amount. The tap coefficient is determined according to the specified ratio. Thereby, in the magnetic tape device 10, the tap coefficient is determined according to a parameter that is not related to the ratio of the overlapping area with the track 30A to be read and the overlapping area with the adjacent track for each of the plurality of read elements. As compared with the case, even if the positional relationship between the magnetic tape MT and the reading element unit 38 changes, the noise component can be accurately reduced.

  Further, in one embodiment of the magnetic tape device 10, the amount of deviation is determined according to the result obtained by reading the servo pattern 32 by the servo element pair 36. Thus, the magnetic tape device 10 can easily determine the amount of displacement as compared with the case where the servo pattern 32 is not provided on the magnetic tape MT.

  In one embodiment of the magnetic tape device 10, the reading operation of the reading element unit 38 is performed in synchronization with the reading operation of the servo element pair 36. As a result, the magnetic tape device 10 can enter the track to be read from the adjacent track in the width direction of the magnetic tape as compared with a magnetic disk and a helical scan type magnetic tape which cannot read the servo pattern and data in synchronization. The generated noise component can be immediately reduced.

  In one aspect of the magnetic tape device 10, the extracting unit 62 has a two-dimensional FIR filter 71. The two-dimensional FIR filter 71 combines the results obtained by performing the waveform equalization processing on each of the first read signal and the second read signal, thereby combining the first read signal and the second read signal. (2) Data derived from the read target track 30A is extracted from the read signal. Thereby, the magnetic tape device 10 can quickly extract data derived from the read target track 30A from the first read signal and the second read signal as compared with the case where only the one-dimensional FIR filter is used. Further, the magnetic tape device 10 can realize an operation with a smaller amount of operation than in the case of performing a matrix operation.

  In one embodiment of the magnetic tape device 10, a first reading element 40 and a second reading element 42 are employed as a pair of reading elements. Thereby, the magnetic tape device 10 can contribute to downsizing of the reading element unit 38 as compared with the case where three or more reading elements are used. By reducing the size of the reading element unit 38, the reading unit 26 and the reading head 16 can also be reduced in size. In addition, the magnetic tape device 10 can also suppress occurrence of a situation in which adjacent read element units 38 come into contact with each other.

  Further, in one embodiment of the magnetic tape device 10, data is read by each of the plurality of read element units 38 from the corresponding read target track 30A included in each of the plurality of specific track areas 31 by the linear scan method. As a result, the magnetic tape device 10 completes reading data from the plurality of read target tracks 30A more quickly than when data is read from each of the plurality of read target tracks 30A by only the single read element unit 38. can do.

  In the above embodiment, when the magnetic tape device 10 is in the default state, the first reading element 40 and the second reading element 42 are both The magnetic tape device is provided so as to straddle, but is not limited to such an embodiment. In the example shown in FIG. 12, a reading element unit 138 is employed instead of the reading element unit 38 described above. The reading element unit 138 includes a first reading element 140 and a second reading element 142. When the magnetic tape device 10 is in a default state, the center of the first reading element 140 in the tape width direction coincides with the center CL of the track 30A to be read in the tape width direction. When the magnetic tape device 10 is in the default state, the first read element 140 and the second read element 142 read without protruding into the first noise mixing source track 30B and the second noise mixing source track 30C. It is contained in the target track 30A. Further, when the magnetic tape device 10 is in the default state, each of the first reading element 140 and the second reading element 142 is moved in the running direction similarly to the first reading element 40 and the second reading element 42 described in the above embodiment. Are provided so as to partially overlap each other.

  As an example, as shown in FIG. 12, even when the first read element 140 and the second read element 142 face the read target track 30A without protruding from the read target track 30A, the read element unit 138 and The positional relationship with the magnetic tape MT may change. That is, the read element unit 138 may straddle the read target track 30A and the first noise mixing source track 30B, and the read element unit 138 may cross the read target track 30A and the second noise mixing source track 30C. . Even in these cases, by performing the processing of steps 102 to 112 described above, the reading from which the noise component from the first noise mixing source track 30B or the second noise mixing source track 30C has been removed is performed. Data corresponding to the target track data can be obtained.

  In addition, since the first reading element 140 and the second reading element 142 are arranged at positions where a part of each of them overlaps in the traveling direction, a portion of the reading target track 30A that cannot be read by the first reading element 140 is used. The second reading element 142 can read data. As a result, the reliability of the track data to be read can be improved as compared with the case where the first reading element 140 reads data from the track 30A to be read alone.

  As an example, as shown in FIG. 11, when the magnetic tape device 10 is in a default state, each of the first read element 40 and the second read element 42 is connected to the read target track 30A and the second noise mixing source track 30C. You may be arrange | positioned at the position which straddles both with respect to both.

  In the above, the reading element unit 38 including the first reading element 40 and the second reading element 42 has been exemplified. However, the magnetic tape device is not limited to such an embodiment. In the example shown in FIG. 13, a reading element unit 238 is used instead of the reading element unit 38. The reading element unit 238 is different from the reading element unit 38 in that it has a third reading element 244. When the magnetic tape device 10 is in a default state, the third reading element 244 is disposed at a position where the third reading element 244 partially overlaps with the first reading element 40 in the running direction. When the magnetic tape device 10 is in a default state, the third reading element 244 is arranged at a position straddling the read target track 30A and the second noise mixing source track 30C.

  In this case, similar to the case where the first equalizer 70 is assigned to the first reading element 40 and the second equalizer 72 is assigned to the second reading element 42, the third equalizing element 72 is also assigned to the third reading element 244. Three equalizers (not shown) are assigned. The third equalizer also has a function similar to that of the first and second equalizers described above, and performs a third read signal read by the third read element 244 to obtain a third read signal. To perform waveform equalization processing. Then, the third equalizer performs, for example, a convolution operation on the third read signal with a tap coefficient, and outputs a third operation-processed signal that is a signal after the operation processing. The adder 44 includes a first processed signal corresponding to the first read signal, a second processed signal corresponding to the second read signal, and a third processed signal corresponding to the third read signal. The signals are combined by adding the signals, and the combined data obtained by combining is output to the decoding unit 69.

  In the example illustrated in FIG. 13, the third reading element 244 is arranged at a position straddling the read target track 30 </ b> A and the second noise mixing source track 30 </ b> C in the default state of the magnetic tape device 10. Is not limited to this. When the magnetic tape device 10 is in a default state, the third reading element 244 may be arranged at a position facing the read target track 30A without protruding from the read target track 30A.

  In the above, the reading element unit 38 has been exemplified. However, the magnetic tape device is not limited to such an embodiment. For example, instead of the reading element unit 38, a reading element pair 50 shown in FIG. In this case, the first reading element 50A and the second reading element 50B are arranged at positions close to each other in the tape width direction. In addition, the first reading element 50A and the second reading element 50B do not come into contact with each other, and the SNR is higher than the SNR of the single reading element data in the entire range of the track offset as shown in FIG. 6 as an example. So that they are arranged side by side in the tape width direction.

  In the example shown in FIG. 4, for example, the first reading element 50A is accommodated in the second track 49B in plan view, and the second reading element 50B is contained in the first track 49A in plan view.

  In the above, the servo element pair 36 has been illustrated. However, the magnetic tape device is not limited to such an embodiment. For example, instead of the servo element pair 36, one of the servo elements 36A and 36B may be employed.

  Further, in the above description, the aspect has been described in which a plurality of specific track areas 31 are arranged at regular intervals in the tape width direction in the track area 30. However, the magnetic tape device is not limited to such an embodiment. For example, in two adjacent specific track areas 31 among a plurality of specific track areas 31, the tape width is set such that one specific track area 31 and the other specific track area 31 overlap by one track in the tape width direction. It may be arranged in the direction. In this case, one adjacent track (for example, the first noise mixing track 30B) included in one specific track area 31 becomes a read target track 30A in the other specific track area 31. The read target track 30A included in one specific track area 31 becomes an adjacent track area (for example, the second noise mixing source track 30C) in the other specific track area 31.

The configuration of the magnetic tape device and the magnetic tape reading process described above are merely examples. Therefore, needless to say, unnecessary steps can be deleted, new steps can be added, and the processing order can be changed without departing from the spirit of the invention.
Further, the magnetic tape device can read (reproduce) data recorded on the magnetic tape, and can further have a configuration for recording data on the magnetic tape.

[Magnetic tape]
Next, details of a magnetic tape from which data is read in the magnetic tape device will be described.

<ΔSFD>
ΔSFD of the magnetic tape is 0.50 or less. ΔSFD is a value indicating the temperature dependence of the switching field distribution SFD measured in the longitudinal direction of the magnetic tape. The smaller the value, the smaller the change in SFD due to temperature, and the larger the value, the larger the change in SFD due to temperature. Means The SFD in the longitudinal direction of the magnetic tape can be obtained by a known magnetic property measuring device such as a vibrating sample magnetometer. The same applies to the SFD measurement of the ferromagnetic powder described later. The temperature at the time of SFD measurement can be adjusted by setting the measurement device.

By setting ΔSFD to 0.50 or less, it is considered that it is possible to suppress unintended portions on the magnetic layer from being magnetized when magnetized (servo pattern is formed) by the servo write head. As a result, the accuracy of specifying the position of the reading element by reading the servo pattern can be increased, and as a result, the error between the amount of deviation detected by reading the servo pattern and the amount of deviation actually occurring can be reduced. It is presumed that it becomes possible. This is considered to contribute to enabling more appropriate waveform equalization processing to be performed on the reading result read at each location. ΔSFD is preferably at most 0.45, more preferably at most 0.40, even more preferably at most 0.35, even more preferably at most 0.30. ΔSFD can be, for example, 0.03 or more, 0.05 or more, or 0.10 or more.

ΔSFD calculated by Expression 1 can be controlled by the method of preparing a magnetic tape, and the following trends are mainly observed.
(A) The value decreases as the dispersibility of the ferromagnetic powder in the magnetic layer increases.
(B) The value decreases as the temperature dependence of SFD is smaller as the ferromagnetic powder.
(C) The value decreases as the particles of the ferromagnetic powder are aligned in the longitudinal direction of the magnetic layer (as the orientation in the longitudinal direction is increased), and increases as the orientation in the longitudinal direction decreases.

  For example, with respect to (A), the dispersion conditions may be strengthened (longer dispersion time, smaller diameter and / or higher filling of the dispersion beads used for dispersion, etc.), use of a dispersant, and the like. As the dispersant, a known dispersant, a commercially available dispersant, and the like can be used.

On the other hand, with respect to (B), for example, as an example, the difference ΔSFD _powder between the SFD measured at a temperature of 100 ° C. and the SFD measured at a temperature of 25 ° C. of the ferromagnetic _powder is 0 Ferromagnetic powder in the range of 0.05 to 1.50 can be used. However, even if it is out of the above range, ΔSFD calculated by Expression 1 for the magnetic tape can be controlled to a range of 0.50 or less by other control.
ΔSFD _powder = SFD _{powder 100 ° C.} −SFD _{powder 25 ° C.} Formula 2
(In Equation 2, SFD powder 100 ° _C. is the _switching field distribution SFD of the ferromagnetic powder measured at a temperature of 100 ° C., and SFD powder 25 ° _C. is the _switching field distribution SFD of the ferromagnetic powder measured at a temperature of 25 ° C. .)

  Regarding the above (C), ΔSFD tends to be reduced by setting the orientation treatment of the magnetic layer to longitudinal orientation. ΔSFD tends to increase when the orientation treatment of the magnetic layer is made to be vertical orientation or non-oriented without the orientation treatment.

  Therefore, for example, by controlling one or a combination of two or more of the above means (A) to (C), it is possible to obtain a magnetic tape having a ΔSFD calculated by Expression 1 of 0.50 or less. it can.

  Next, the magnetic layer and the like included in the magnetic tape will be described in more detail.

<Magnetic layer>
(Ferromagnetic powder)
As the ferromagnetic powder contained in the magnetic layer, ferromagnetic powder generally used in magnetic layers of various magnetic recording media can be used. It is preferable to use a ferromagnetic powder having a small average particle size from the viewpoint of improving the recording density of the magnetic tape. In this respect, the average particle size of the ferromagnetic powder is preferably 50 nm or less, more preferably 45 nm or less, still more preferably 40 nm or less, still more preferably 35 nm or less, and more preferably 30 nm or less. More preferably, it is even more preferably 25 nm or less, and even more preferably 20 nm or less. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 5 nm or more, more preferably 8 nm or more, still more preferably 10 nm or more, and more preferably 15 nm or more. Is more preferable, and more preferably 20 nm or more.

In one embodiment, it is possible to use a ferromagnetic powder having a difference ΔSFD _powder between the SFD measured at a temperature of 100 ° C. and the SFD measured at a temperature of 25 ° C., which is calculated by the above equation 2, within the range described above. preferable.

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

  In the present invention and the present specification, “hexagonal ferrite powder” refers to a ferromagnetic powder in which a hexagonal ferrite type crystal structure is detected as a main phase by X-ray diffraction analysis. The main phase refers to a structure to which the highest intensity diffraction peak belongs in an X-ray diffraction spectrum obtained by X-ray diffraction analysis. For example, when the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by the X-ray diffraction analysis is attributed to the hexagonal ferrite type crystal structure, it is determined that the hexagonal ferrite type crystal structure has been detected as the main phase. Shall be. When only a single structure is detected by the X-ray diffraction analysis, the detected structure is used as a main phase. The hexagonal ferrite crystal structure contains at least an iron atom, a divalent metal atom, and an oxygen atom as constituent atoms. The divalent metal atom is a metal atom that can be a divalent cation as an ion, and examples thereof include a strontium atom, a barium atom, an alkaline earth metal atom such as a calcium atom, and a lead atom. In the present invention and the present specification, the hexagonal strontium ferrite powder refers to a powder in which the main divalent metal atom contained in the powder is a strontium atom, and the hexagonal barium ferrite powder refers to a powder contained in the powder. A divalent metal atom is a barium atom. The main divalent metal atom means the divalent metal atom that accounts for the largest part of the divalent metal atoms contained in the powder on an atomic percent basis. However, the above-mentioned divalent metal atoms do not include rare earth atoms. In the present invention and in the present specification, the “rare earth atom” is selected from the group consisting of a scandium atom (Sc), an yttrium atom (Y), and a lanthanoid atom. The lanthanoid atom includes a lanthanum atom (La), a cerium atom (Ce), a praseodymium atom (Pr), a neodymium atom (Nd), a promethium atom (Pm), a samarium atom (Sm), a europium atom (Eu), and a gadolinium atom (Gd ), Terbium atom (Tb), dysprosium atom (Dy), holmium atom (Ho), erbium atom (Er), thulium atom (Tm), ytterbium atom (Yb), and lutetium atom (Lu). You.

  Hereinafter, the hexagonal strontium ferrite powder, which is one embodiment of the hexagonal ferrite powder, will be described in more detail.

Activation volume of hexagonal strontium ferrite powder is preferably in the range of 800~1600nm ^3. The finely divided hexagonal strontium ferrite powder having an activation volume within the above range is suitable for producing a magnetic tape exhibiting excellent electromagnetic conversion characteristics. The activation volume of the hexagonal strontium ferrite powder is preferably 800 nm ³ or more, for example, 850 nm ³ or more. Further, from the viewpoint of further improvement of the electromagnetic conversion characteristics, activation volume of hexagonal strontium ferrite powder is more preferably 1500 nm ³ or less, further preferably 1400 nm ³ or less, and 1300 nm ³ or less Is more preferably 1,200 nm ³ or less, still more preferably 1,100 nm ³ or less. The same applies to the activation volume of the hexagonal barium ferrite powder.

The “activation volume” is a unit of magnetization reversal and is an index indicating the magnetic magnitude of a particle. The activation volume and the anisotropy constant Ku described later in the present invention and the present specification are measured at a magnetic field sweep speed of 3 minutes and 30 minutes of a coercive force Hc measuring unit using a vibrating sample magnetometer (measurement). (Temperature: 23 ° C. ± 1 ° C.), which is a value obtained from the following relational expression between Hc and activation volume V. The unit of the anisotropy constant Ku is ¹ erg / cc = 1.0 × 10 ⁻¹ J / m ³ .
Hc = 2Ku / Ms {1-[(kT / KuV) ln (At / 0.693)] ^1/2 }
[In the above formula, Ku: anisotropy constant (unit: J / m ³ ), Ms: saturation magnetization (unit: kA / m), k: Boltzmann constant, T: absolute temperature (unit: K), V: activity Volume (unit: cm ³ ), A: spin precession frequency (unit: s ⁻¹ ), t: magnetic field inversion time (unit: s)]

An index for reducing thermal fluctuation, in other words, improving thermal stability includes an anisotropic constant Ku. The hexagonal strontium ferrite powder can preferably have a Ku of 1.8 × 10 ⁵ J / m ³ or more, and more preferably have a Ku of 2.0 × 10 ⁵ J / m ³ or more. Further, the Ku of the hexagonal strontium ferrite powder can be, for example, 2.5 × 10 ⁵ J / m ³ or less. However, the higher the value of Ku, the higher the thermal stability, which is preferable. Therefore, the value is not limited to the above values.

The hexagonal strontium ferrite powder may or may not contain rare earth atoms. When the hexagonal strontium ferrite powder contains a rare earth atom, it is preferable to contain the rare earth atom at a content (bulk content) of 0.5 to 5.0 atom% with respect to 100 atom% of the iron atom. In one embodiment, the hexagonal strontium ferrite powder containing a rare earth atom can have a localized distribution of a rare earth atom surface layer portion. In the present invention and in the present specification, the term “rare earth atom surface layer uneven distribution” refers to a rare earth atom content rate (hereinafter, referred to as a 100% by atom) in a solution obtained by partially dissolving hexagonal strontium ferrite powder with an acid. “Rare earth atom surface layer content” or “Rare earth atom simply referred to as“ surface layer content ”) is 100 atomic% of iron atoms in a solution obtained by completely dissolving hexagonal strontium ferrite powder with an acid. (Hereinafter referred to as "bulk content of rare earth atoms" or simply "bulk content" with respect to rare earth atoms).
Rare earth atomic surface layer content / rare earth atomic bulk content> 1.0
It means satisfying the ratio of The rare earth atom content of the hexagonal ferrite powder described later is synonymous with the rare earth atom bulk content. On the other hand, the partial dissolution using an acid dissolves the surface layer of the particles constituting the hexagonal strontium ferrite powder.Therefore, the rare earth atom content in the solution obtained by partial dissolution is equivalent to the hexagonal strontium ferrite powder. Is the rare earth atom content in the surface layer of the particles. The rare earth atom surface layer content satisfying the ratio of “rare earth atom surface portion content / rare earth atom bulk content> 1.0” means that the rare earth atom is contained in the surface portion of the particles constituting the hexagonal strontium ferrite powder. It means that it is unevenly distributed (that is, present more than inside). In the present invention and in the present specification, the surface layer means a partial region extending from the surface to the inside of the particles constituting the hexagonal strontium ferrite powder.

When the hexagonal ferrite powder contains rare earth atoms, the rare earth atom content (bulk content) is preferably in the range of 0.5 to 5.0 atom% with respect to 100 atom% of iron atoms. Containing rare earth atoms in the bulk content of the above range, and that the rare earth atoms are unevenly distributed in the surface layer portion of the particles constituting the hexagonal strontium ferrite powder, which contributes to suppressing a decrease in reproduction output in repeated reproduction. Conceivable. This is because the hexagonal strontium ferrite powder contains rare earth atoms at a bulk content in the above range, and the rare earth atoms are unevenly distributed on the surface layer of the particles constituting the hexagonal strontium ferrite powder. It can be inferred that the As the value of the anisotropy constant Ku increases, the occurrence of a phenomenon called thermal fluctuation can be suppressed (in other words, the thermal stability can be improved). By suppressing the occurrence of thermal fluctuation, it is possible to suppress a decrease in reproduction output in repeated reproduction. The uneven distribution of rare earth atoms in the surface layer portion of the hexagonal strontium ferrite powder contributes to stabilizing the spin of iron (Fe) sites in the crystal lattice of the surface layer portion. It is presumed that it will increase.
It is also assumed that the use of hexagonal strontium ferrite powder having a localized distribution of the rare earth atoms as the ferromagnetic powder for the magnetic layer also contributes to suppressing the surface of the magnetic layer from being scraped by sliding with the magnetic head. You. That is, it is presumed that the hexagonal strontium ferrite powder having the uneven distribution of the rare earth atom surface layer can contribute to the improvement of the running durability of the magnetic tape. This is because the uneven distribution of rare earth atoms on the surface of the particles constituting the hexagonal strontium ferrite powder improves the interaction between the particle surface and an organic substance (for example, a binder and / or an additive) contained in the magnetic layer. It is presumed that the strength of the magnetic layer is improved as a result.
From the viewpoint of further suppressing the decrease in the reproduction output in repeated reproduction and / or further improving the running durability, the rare earth atom content (bulk content) is in the range of 0.5 to 4.5 atom%. Is more preferably, in the range of 1.0 to 4.5 atomic%, and still more preferably in the range of 1.5 to 4.5 atomic%.

  The bulk content is a content determined by completely dissolving hexagonal strontium ferrite powder. In the present invention and the present specification, unless otherwise specified, the content of atoms refers to a bulk content obtained by completely dissolving hexagonal strontium ferrite powder. The hexagonal strontium ferrite powder containing a rare earth atom may contain only one kind of rare earth atom as a rare earth atom, or may contain two or more kinds of rare earth atoms. The above-mentioned bulk content when two or more kinds of rare earth atoms are contained is obtained for a total of two or more kinds of rare earth atoms. This applies to the present invention and the other components in the present specification. That is, unless otherwise specified, one component may be used alone, or two or more components may be used. When two or more types are used, the content or content refers to the total of two or more types.

  When the hexagonal strontium ferrite powder contains a rare earth atom, the contained rare earth atom may be any one or more of the rare earth atoms. From the viewpoint of further suppressing the decrease in the reproduction output in repeated reproduction, preferred rare earth atoms include a neodymium atom, a samarium atom, a yttrium atom and a dysprosium atom, and a neodymium atom, a samarium atom and a yttrium atom are more preferable. Atoms are more preferred.

  In the hexagonal strontium ferrite powder having a rare earth atom surface layer uneven distribution property, the rare earth atoms only need to be unevenly distributed in the surface layer portion of the particles constituting the hexagonal strontium ferrite powder, and the degree of uneven distribution is not limited. For example, for a hexagonal strontium ferrite powder having a rare earth atom surface layer portion uneven distribution, a rare earth atom surface layer content determined by partially dissolving under a dissolving condition described below and a rare earth obtained by completely dissolving under a dissolving condition described below. The ratio of the atomic content to the bulk content, “surface layer content / bulk content” is more than 1.0 and can be 1.5 or more. When the ratio of “surface layer portion content / bulk content ratio” is greater than 1.0, it means that in the particles constituting the hexagonal strontium ferrite powder, rare earth atoms are unevenly distributed in the surface layer portion (that is, present more than inside). I do. Further, the ratio of the surface layer content of rare earth atoms determined by partial dissolution under the dissolution conditions described below to the bulk content of rare earth atoms determined by total dissolution under the dissolution conditions described below, “surface layer content / The "bulk content" can be, for example, 10.0 or less, 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, or 4.0 or less. However, in the hexagonal strontium ferrite powder having a rare earth atom surface layer uneven distribution property, it is sufficient that the rare earth atoms are unevenly distributed in the surface layer of the particles constituting the hexagonal strontium ferrite powder. The “rate” is not limited to the upper limit or the lower limit illustrated.

The partial and total dissolution of the hexagonal strontium ferrite powder will be described below. For hexagonal strontium ferrite powder present as powder, the partially and totally dissolved sample powders are collected from the same lot of powder. On the other hand, as for the hexagonal strontium ferrite powder contained in the magnetic layer of the magnetic tape, a part of the hexagonal strontium ferrite powder taken out of the magnetic layer is subjected to partial melting, and the other part is subjected to total melting. The removal of the hexagonal strontium ferrite powder from the magnetic layer can be performed, for example, by the method described in paragraph 0032 of JP-A-2015-91747.
The above-mentioned partial dissolution means that the hexagonal strontium ferrite powder is dissolved in the solution to the extent that the powder can be visually confirmed at the end of the dissolution. For example, with respect to the particles constituting the hexagonal strontium ferrite powder, the region of 10 to 20% by mass can be dissolved with respect to the whole particles as 100% by mass by partial dissolution. On the other hand, the above-mentioned total dissolution refers to dissolution until the residual hexagonal strontium ferrite powder is not visually confirmed at the end of the dissolution.
The partial dissolution and measurement of the surface layer content are performed, for example, by the following methods. However, the following dissolution conditions, such as the amount of sample powder, are merely examples, and any dissolution conditions that allow partial dissolution and total dissolution can be adopted.
A container (eg, a beaker) containing 12 mg of the sample powder and 10 ml of 1 mol / L hydrochloric acid is held on a hot plate at a set temperature of 70 ° C. for 1 hour. The resulting solution is filtered through a 0.1 μm membrane filter. Elemental analysis of the filtrate thus obtained is performed by an inductively coupled plasma (ICP) analyzer. In this way, the content of the rare earth element in the surface layer relative to 100 atomic% of the iron atom can be determined. When a plurality of types of rare earth atoms are detected by elemental analysis, the total content of all rare earth atoms is defined as the surface layer content. The same applies to the measurement of the bulk content.
On the other hand, the total dissolution and the measurement of the bulk content are performed, for example, by the following methods.
A container (for example, a beaker) containing 12 mg of the sample powder and 10 ml of 4 mol / L hydrochloric acid is held on a hot plate at a set temperature of 80 ° C. for 3 hours. Thereafter, the measurement is performed in the same manner as the above-described partial dissolution and surface layer content measurement, and the bulk content with respect to 100 atom% of iron atoms can be obtained.

From the viewpoint of increasing the reproduction output when reproducing the information recorded on the magnetic tape, it is desirable that the ferromagnetic powder contained in the magnetic tape has a high mass magnetization σs. In this regard, the hexagonal strontium ferrite powder containing rare earth atoms but not having the localized distribution of the rare earth atom surface layer tended to have a large decrease in σs as compared with the hexagonal strontium ferrite powder containing no rare earth atoms. On the other hand, it is considered that the hexagonal strontium ferrite powder having a rare earth atom surface layer localization is also preferable in suppressing such a large decrease in σs. In one embodiment, the s of the hexagonal strontium ferrite powder can be greater than or equal to 45 Am · m ² / kg, and can be greater than or equal to 47 Am · m ² / kg. Meanwhile, [sigma] s from the viewpoint of noise reduction, is preferably not more than 80A ^· m 2 / kg, more preferably not more than 60A ^· m 2 / kg. σs can be measured using a known measuring device capable of measuring magnetic properties such as a vibrating sample magnetometer. In the present invention and the present specification, unless otherwise specified, the mass magnetization s is a value measured at a magnetic field strength of 1194 kA / m (15 kOe).

  Regarding the content (bulk content) of the constituent atoms of the hexagonal ferrite powder, the strontium atom content can be, for example, in the range of 2.0 to 15.0 atom% with respect to 100 atom% of iron atoms. In one embodiment, the hexagonal strontium ferrite powder can have only divalent metal atoms in the powder as strontium atoms. In yet another aspect, the hexagonal strontium ferrite powder can include one or more other divalent metal atoms in addition to the strontium atoms. For example, it can contain barium and / or calcium atoms. When a divalent metal atom other than strontium atoms is contained, the barium atom content and the calcium atom content in the hexagonal strontium ferrite powder are, for example, 0.05 to 5 with respect to 100 atom% of iron atoms, respectively. It can be in the range of 0.0 atomic%.

As the crystal structure of the hexagonal ferrite, magnetoplumbite type (also called “M type”), W type, Y type and Z type are known. The hexagonal strontium ferrite powder may have any crystal structure. The crystal structure can be confirmed by X-ray diffraction analysis. The hexagonal strontium ferrite powder may have a single crystal structure or two or more crystal structures detected by X-ray diffraction analysis. For example, in one embodiment, the hexagonal strontium ferrite powder can be one in which only an M-type crystal structure is detected by X-ray diffraction analysis. For example, M-type hexagonal ferrite is represented by a composition formula of AFe ₁₂ O ₁₉ . Here, A represents a divalent metal atom, and when the hexagonal strontium ferrite powder is of M type, A is only a strontium atom (Sr), or when A contains a plurality of divalent metal atoms, As described above, strontium atoms (Sr) occupy the largest amount on an atomic% basis. The content of divalent metal atoms in the hexagonal strontium ferrite powder is usually determined by the type of the crystal structure of the hexagonal ferrite, and is not particularly limited. The same applies to the iron atom content and the oxygen atom content. The hexagonal strontium ferrite powder contains at least an iron atom, a strontium atom, and an oxygen atom, and may further contain a rare earth atom. Further, the hexagonal strontium ferrite powder may or may not contain atoms other than these atoms. As an example, the hexagonal strontium ferrite powder may contain aluminum atoms (Al). The content of aluminum atoms can be, for example, 0.5 to 10.0 atom% with respect to 100 atom% of iron atoms. From the viewpoint of further suppressing the decrease in the reproduction output in the repeated reproduction, the hexagonal strontium ferrite powder contains iron atoms, strontium atoms, oxygen atoms, and rare earth atoms, and the content of atoms other than these atoms is 100 atoms of iron atoms. %, Preferably at most 10.0 atomic%, more preferably in the range of 0 to 5.0 atomic%, and may be 0 atomic%. That is, in one embodiment, the hexagonal strontium ferrite powder may not include atoms other than iron atoms, strontium atoms, oxygen atoms, and rare earth atoms. The content expressed in atomic% above is obtained by dissolving the hexagonal strontium ferrite powder in total and converting the content (unit: mass%) of each atom to a value expressed in atomic% using the atomic weight of each atom. It is obtained by conversion. Further, in the present invention and the present specification, “not including” for a certain atom means that the content is 0 mass% as measured by an ICP analyzer after being completely dissolved. The detection limit of the ICP analyzer is usually 0.01 ppm (parts per million) or less on a mass basis. The term “not included” is used to mean that it is contained in an amount less than the detection limit of the ICP analyzer. In one aspect, the hexagonal strontium ferrite powder can be free of bismuth atoms (Bi).

−Metal powder−
Preferred specific examples of the ferromagnetic powder include a ferromagnetic metal powder. For details of the ferromagnetic metal powder, for example, paragraphs 0137 to 0141 of JP-A-2011-216149 and paragraphs 0009 to 0023 of JP-A-2005-251351 can be referred to.

-Ε-iron oxide powder-
Preferred specific examples of the ferromagnetic powder include ε-iron oxide powder. In the present invention and the present specification, the term “ε-iron oxide powder” refers to a ferromagnetic powder in which an ε-iron oxide type crystal structure is detected as a main phase by X-ray diffraction analysis. For example, when the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis is attributed to the ε-iron oxide type crystal structure, the ε-iron oxide type crystal structure was detected as the main phase. Judge. As a method for producing the ε-iron oxide powder, a method of preparing from a goethite, a reverse micelle method, and the like are known. All of the above production methods are known. Further, a method for producing an ε-iron oxide powder in which a part of Fe is substituted by a substitution atom such as Ga, Co, Ti, Al, and Rh is described, for example, in J. Am. Jpn. Soc. Powder Metallurgy Vol. 61 Supplement, No. S1, pp. S280-S284, J.I. Mater. Chem. C, 2013, 1 pp. 5200-5206 and the like. However, the method for producing ε-iron oxide powder that can be used as a ferromagnetic powder in the magnetic layer of the magnetic tape is not limited to the method described here.

ε- activation volume of the iron oxide powder is preferably in the range of 300 to 1500 nm ^3. The finely divided ε-iron oxide powder having an activation volume in the above range is suitable for producing a magnetic tape exhibiting excellent electromagnetic conversion characteristics. The activation volume of the ε-iron oxide powder is preferably 300 nm ³ or more, for example, 500 nm ³ or more. Further, from the viewpoint further improvement of the electromagnetic conversion characteristics, .epsilon. activation volume of the iron oxide powder is more preferably 1400 nm ³ or less, further preferably 1300 nm ³ or less, and 1200 nm ³ or less Is more preferably 1100 nm ³ or less.

An index for reducing thermal fluctuation, in other words, improving thermal stability includes an anisotropic constant Ku. The ε-iron oxide powder can preferably have a Ku of 3.0 × 10 ⁴ J / m ³ or more, and more preferably have a Ku of 8.0 × 10 ⁴ J / m ³ or more. The Ku of the ε-iron oxide powder can be, for example, 3.0 × 10 ⁵ J / m ³ or less. However, the higher the Ku, the higher the thermal stability, which is preferable, and is not limited to the above exemplified values.

From the viewpoint of increasing the reproduction output when reproducing the information recorded on the magnetic tape, it is desirable that the ferromagnetic powder contained in the magnetic tape has a high mass magnetization σs. In this regard, in one aspect, the σs of ε- iron oxide powder can be 8A ^· m 2 / kg or more may also be at 12A ^· m 2 / kg or more. On the other hand, .epsilon. [sigma] s of the iron oxide powder, from the viewpoint of noise reduction, is preferably not more than 40A ^· m 2 / kg, more preferably not more than 35A ^· m 2 / kg.

In the present invention and the present specification, “ferromagnetic powder” means an aggregate of a plurality of ferromagnetic particles. The term “aggregate” is not limited to an embodiment in which particles constituting the aggregate are in direct contact, but also includes an embodiment in which a binder, an additive, and the like are interposed between particles. The same applies to the present invention and various powders such as the non-magnetic powder in the present specification. In the present invention and the present specification, unless otherwise specified, the average particle size of various powders such as a ferromagnetic powder is a value measured by the following method using a transmission electron microscope.
The powder is photographed with a transmission electron microscope at a magnification of 100,000, and printed on photographic paper so as to have a total magnification of 500,000, or displayed on a display to obtain a photograph of the particles constituting the powder. The target particles are selected from the photograph of the obtained particles, and the outline of the particles is traced by a digitizer to measure the size of the particles (primary particles). Primary particles refer to independent particles without aggregation.
The above measurement is performed on 500 randomly extracted particles. The arithmetic average of the particle sizes of the 500 particles thus obtained is defined as the average particle size of the powder. As the transmission electron microscope, for example, a transmission electron microscope H-9000 manufactured by Hitachi 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 Examples described below was measured using a transmission electron microscope H-9000 manufactured by Hitachi as a transmission electron microscope, and image analysis software KS-400 manufactured by Carl Zeiss as image analysis software. Value.

  As a method of collecting the sample powder from the magnetic tape for measuring the particle size, for example, a method described in paragraph 0015 of JP-A-2011-048878 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-like, spindle-like, column-like (however, the height is larger than the maximum major axis of the bottom), it is expressed by the length of the major axis constituting the particle, that is, the major axis length,
(2) In the case of plate shape or column shape (thickness or height is smaller than the maximum major axis of the plate surface or bottom surface), it is expressed by the maximum major axis of the plate surface or bottom surface,
(3) If the particle is spherical, polyhedral, unspecified, or the like, and the major axis of the particle cannot be specified from the shape, the particle is represented by an equivalent circle diameter. The equivalent circle diameter is determined by a circular projection method.

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

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

(Binder)
The magnetic tape is a coating type magnetic tape and includes a binder in a magnetic layer. A binder is one or more resins. The resin may be a homopolymer or a copolymer (copolymer). As the binder contained in the magnetic layer, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, styrene, acrylonitrile, acrylic resin copolymerized with methyl methacrylate, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, Those selected from polyvinyl alkylal resins such as polyvinyl acetal and polyvinyl butyral can be used alone, or a plurality of resins can be mixed and used. Preferred among these are polyurethane resins, acrylic resins, cellulose resins and vinyl chloride resins. These resins can be used as a binder also in a nonmagnetic layer and / or a back coat layer described later. With respect to the above binder, paragraphs 0029 to 0031 of JP-A-2010-24113 can be referred to. The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less as a weight average molecular weight. In the present invention and the present specification, the weight average molecular weight is a value obtained by converting a value measured by gel permeation chromatography (GPC) into polystyrene. The following conditions can be mentioned as measurement conditions. The weight average molecular weight shown in the examples described below 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 (manufactured by Tosoh Corporation, 7.8 mm ID (Inner Diameter (inner diameter)) x 30.0 cm)
Eluent: tetrahydrofuran (THF)

  Further, a curing agent can be used together with a resin usable as a binder. In one embodiment, the curing agent can be a thermosetting compound that is a compound in which a curing reaction (crosslinking reaction) proceeds by heating, and in another embodiment, a photocuring in which a curing reaction (crosslinking reaction) proceeds by light irradiation. Compounds. The curing agent may be included in the magnetic layer in a state where at least a part thereof has reacted (cross-linked) with other components such as a binder as the curing reaction proceeds in the process of manufacturing the magnetic tape. Preferred curing agents are thermosetting compounds, with polyisocyanates being preferred. For details of the polyisocyanate, refer to paragraphs 0124 to 0125 of JP-A-2011-216149. In the composition for forming a magnetic layer, the hardener is preferably, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder, and preferably 50.0 to 80.0 parts from the viewpoint of improving the strength of the magnetic layer. It can be used in parts by weight.

(Additive)
The magnetic layer contains a ferromagnetic powder and a binder, and may optionally contain one or more additives. As an example of the additive, the above-mentioned curing agent can be used. Examples of the additives contained in the magnetic layer include nonmagnetic powders (eg, inorganic powders, carbon black, etc.), lubricants, dispersants, dispersing aids, fungicides, antistatic agents, antioxidants, and the like. Can be. The non-magnetic powder includes a non-magnetic powder that can function as an abrasive, and a non-magnetic powder (for example, non-magnetic colloid particles) that can function as a projection-forming agent that forms projections that appropriately project on the surface of the magnetic layer. Etc.). The average particle size of colloidal silica (silica colloid particles) shown in Examples described later is a value determined by a method described as a method for measuring an average particle diameter in paragraph 0015 of JP-A-2011-048878. . The additive can be used in an arbitrary amount by appropriately selecting a commercially available product depending on desired properties or by manufacturing by a known method. As an example of an additive that can be used in a magnetic layer containing an abrasive, the dispersants described in paragraphs 0012 to 0022 of JP-A-2013-131285 are cited as dispersants for improving the dispersibility of the abrasive. be able to. For example, for lubricants, reference can be made to paragraphs 0030 to 0033, 0035 and 0036 of JP-A-2006-126817. The nonmagnetic layer may contain a lubricant. As for the lubricant that can be contained in the nonmagnetic layer, paragraphs 0030, 0031, 0034, 0035 and 0036 of JP-A-2006-126817 can be referred to. For the dispersant, reference can be made to paragraphs 0061 and 0071 of JP-A-2012-133837. The dispersant may be contained in the non-magnetic layer. For the dispersant that can be contained in the non-magnetic layer, see paragraph 0061 of JP-A-2012-133837.

  The magnetic layer described above can be provided directly on the surface of the nonmagnetic support or indirectly via 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 non-magnetic powder used for the non-magnetic layer may be an inorganic substance powder or an organic substance powder. Further, carbon black or the like can 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 manufactured by a known method. For details, refer to paragraphs 0146 to 0150 of JP-A-2011-216149. For carbon black that can be used for the non-magnetic layer, reference can also be made to paragraphs 0040 to 0041 of JP-A-2010-24113. The content (filling rate) of the nonmagnetic powder in the nonmagnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass.

  For other details such as a binder and an additive of the non-magnetic layer, a known technique regarding the non-magnetic layer can be applied. Further, for example, with respect to the type and content of the binder, the type and content of the additive, and the like, a known technique for the magnetic layer can be applied.

  The non-magnetic layer of the magnetic tape also includes a substantially non-magnetic layer containing a small amount of ferromagnetic powder together with the non-magnetic powder, for example, as an impurity or intentionally. Here, the substantially non-magnetic layer means that the layer has a residual magnetic flux density of 10 mT or less, a coercive force of 7.96 kA / m (100 Oe) or less, or a residual magnetic flux density of 10 mT or less. A layer having a coercive force of 7.96 kA / m (100 Oe) or less. The nonmagnetic layer preferably does not have a residual magnetic flux density and a coercive force.

<Non-magnetic support>
Next, the non-magnetic support will be described. Examples of the nonmagnetic support (hereinafter, also simply referred to as “support”) include known materials such as polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide that have been biaxially stretched. Among these, polyethylene terephthalate, polyethylene naphthalate and polyamide are preferred. These supports may be previously subjected 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 of the nonmagnetic support opposite to the surface having the magnetic layer. The back coat layer preferably contains one or both of carbon black and inorganic powder. As for the binder contained in the back coat layer and various additives that can be optionally contained, a known technique relating to the back coat layer can be applied, and a known technique relating to the formulation of the magnetic layer and / or the non-magnetic layer can be applied. Can also. For example, JP-A-2006-331625, paragraphs 0018 to 0020 and U.S. Patent No. 7,029,774, column 4, line 65 to column 5, line 38 can be referred to for the backcoat layer. .

<Various thickness>
The thickness of the non-magnetic support is preferably from 3.0 to 6.0 μm.
The thickness of the magnetic layer is preferably 0.15 μm or less, and more preferably 0.1 μm or less, from the viewpoint of high-density recording, which has recently been required. The thickness of the magnetic layer is more preferably in the range of 0.01 to 0.1 μm. The number of the magnetic layers may be at least one. The magnetic layer may be divided into two or more layers having different magnetic properties, and a known configuration relating to a multilayer magnetic layer can be applied. The thickness of the magnetic layer when it is separated into two or more layers is the total thickness of these layers.

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

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

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

<Manufacturing process>
The step of preparing a composition for forming a magnetic layer, a non-magnetic layer, or a back coat layer usually includes at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. The components used for preparing each layer forming composition may be added at the beginning or during any step. As the solvent, one kind or two or more kinds of various kinds of solvents usually used for producing a coating type magnetic recording medium can be used. For the solvent, for example, paragraph 0153 of JP-A-2011-216149 can be referred to. In addition, individual components may be added in two or more steps in a divided manner. For example, the binder may be added separately in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. In order to manufacture the magnetic tape, a conventionally known manufacturing technique can be used in various steps. In the kneading step, it is preferable to use one having a strong kneading force, such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. For details of these kneading processes, reference can be made to JP-A-1-106338 and JP-A-1-79274. A well-known disperser can be used. Further, as described above, as one of means for obtaining a magnetic tape having a ΔSFD calculated by the expression 1 of 0.50 or less, the dispersion conditions are strengthened (dispersion time is increased, dispersion beads used for dispersion are used). It is also preferable to reduce the diameter and / or increase the packing. Each layer forming composition may be filtered by a known method before being subjected to the coating step. Filtration can be performed, for example, by filter filtration. As a filter used for filtration, for example, a filter having a pore size of 0.01 to 3 μm (for example, a glass fiber filter, a polypropylene filter, or the like) can be used. For details of the method for manufacturing a magnetic tape, for example, paragraphs 0051 to 0057 of JP-A-2010-24113 can also be referred to. For the alignment treatment, various known techniques including the description in paragraph 0052 of JP-A-2010-24113 can be applied. In the orientation zone, the drying speed of the coating layer can be controlled by the temperature and amount of the drying air and / or the transport speed of the magnetic tape in the orientation zone. Further, the coating layer may be pre-dried before being transported to the orientation zone.

  A servo pattern is formed on the magnetic layer of the magnetic tape. The formation of the servo pattern on the magnetic layer is performed by magnetizing a specific position of the magnetic layer with a servo pattern recording head (also referred to as “servo write head”). The shape of the servo pattern and the arrangement in the magnetic layer for enabling tracking are known, and the area magnetized by the servo write head (the position where the servo pattern is formed) is determined by standards. Known techniques 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 tracking systems. The servo pattern that can be formed on the magnetic layer of the magnetic tape may be a servo pattern that enables any type of tracking. Further, a servo pattern that enables tracking by the timing-based servo method and a servo pattern that enables tracking by the amplitude-based servo method may be formed on the magnetic layer.

  In a magnetic tape, data is usually recorded on a data band of the magnetic tape. As a result, a track is formed in the data band. More specifically, a magnetic tape usually has a plurality of regions having a servo pattern (called “servo bands”) along the longitudinal direction. The data band is an area between two servo bands. For example, the track area 30 in FIG. 2 is a data band. Data recording is performed on a data band, and a plurality of tracks are formed in the data band along the longitudinal direction. As an example, for example, a servo pattern that can be tracked by a timing-based servo method is formed on an LTO Ultra format tape that is an industry standard. For tracking by the timing-based servo method, a plurality of servo patterns of two or more different shapes are formed on the magnetic layer. The time interval at which the servo head reproduces (reads) two servo patterns of different shapes and the time interval at which the servo head reproduces two servo patterns of the same shape recognize the position of the servo head. Tracking is performed based on the position of the servo head thus recognized. More specifically, at the time of manufacturing an LTO Ultra format tape, a plurality of servo patterns inclined with respect to the tape width direction are formed on the servo band as shown in FIG. In FIG. 14, the servo frame SF on the servo band includes a servo subframe 1 (SSF1) and a servo subframe 2 (SSF2). The servo subframe 1 is composed of an A burst (reference A in FIG. 14) and a B burst (reference B in FIG. 14). A burst is composed of servo patterns A1 to A5, and B burst is composed of servo patterns B1 to B5. On the other hand, the servo sub-frame 2 is composed of a C burst (reference C in FIG. 14) and a D burst (reference D in FIG. 14). The C burst includes servo patterns C1 to C4, and the D burst includes servo patterns D1 to D4. Such 18 servo patterns are arranged in sub-frames arranged in an arrangement of 5, 5, 4, and 4 in sets of 5 and 4 and used to identify servo frames. FIG. 14 shows one servo frame for explanation. However, in practice, in the magnetic layer of the magnetic tape on which the tracking based on the timing-based servo method is performed, a plurality of servo frames are arranged in the running direction in each servo band. In FIG. 14, the arrows indicate the traveling directions. For example, an LTO Ultra format tape usually has more than 5000 servo frames per meter of tape length in each servo band of the magnetic layer. The servo element sequentially reads a servo pattern 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. Hereinafter, a servo pattern that can be tracked by the timing-based servo method is referred to as a “timing-based servo pattern”.

  For example, in a timing-based servo system servo system (timing-based servo system), for example, a plurality of non-parallel servo patterns (also referred to as “servo stripes”) arranged continuously in a plurality in the longitudinal direction of a magnetic tape. Is read by the servo element to obtain a servo signal.

  In one embodiment, as described in Japanese Patent Application Laid-Open No. 2004-318983, each servo band includes information indicating a servo band number (“servo band ID (identification)” or “UDIM (Unique DataBand Identification Method)”). Information) is embedded. The servo band ID is recorded by shifting a specific one of a plurality of servo patterns in the servo band such that its position is relatively displaced in the longitudinal direction of the magnetic tape. Specifically, the way of shifting a specific one of a plurality of pairs of servo patterns is changed for each servo band. As a result, the recorded servo band ID becomes unique for each servo band. Therefore, by simply reading one servo band with a servo element, the servo band can be uniquely specified.

  As a method of 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 plurality 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. I do. Since this combination of shifting methods between adjacent servo bands is unique for the entire magnetic tape, it is possible to uniquely specify a servo band when reading a servo pattern by two servo elements. Has become.

  Further, as shown in ECMA-319, information indicating the longitudinal position of the magnetic tape (also referred to as “LPOS (Longitudinal Position) information”) is usually embedded in each servo band. Like the UDIM information, the LPOS information is also recorded by shifting the position of the pair of servo patterns in the longitudinal direction of the magnetic tape. However, unlike the UDIM information, in the 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.
Further, as a method of embedding information in the servo band, a method other than the above method can be adopted. For example, a predetermined code may be recorded by thinning out a predetermined pair from a group of a pair of servo patterns.

  The servo write head has a pair of gaps corresponding to the pair of servo patterns by the number of servo bands. Normally, 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 coil. When forming a servo pattern, a magnetic pulse corresponding to a pair of gaps is transferred to the magnetic tape by inputting a current pulse while running the magnetic tape on the servo write head to form a servo pattern. Can be. The width of each gap can be appropriately set according to the density of the formed servo pattern. The width of each gap can be set to, for example, 1 μm or less, 1 to 10 μm, 10 μm or more.

  Before forming a servo pattern on a magnetic tape, the magnetic tape is usually subjected to a degaussing (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 erasing processing includes a DC (Direct Current) erase and an AC (Alternating Current) erase. AC erasing is performed by reversing the direction of the magnetic field applied to the magnetic tape and gradually reducing the intensity of the magnetic field. On the other hand, DC erase is performed by applying a magnetic field in one direction to the magnetic tape. There are two more methods for DC erase. The first is horizontal DC erase, which applies a magnetic field in one direction along the length of the magnetic tape. The second method is a vertical DC erase in which a magnetic field is applied in one direction along the thickness direction of the magnetic tape. The erasing process may be performed on the entire magnetic tape, or may be performed on each servo band of the magnetic tape.

  The direction of the magnetic field of the formed servo pattern is determined according to the direction of the erase. For example, when a horizontal DC erase is applied to the magnetic tape, the servo pattern is formed such 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 described in Japanese Patent Application Laid-Open No. 2012-53940, when a pattern is transferred using the above-described gap to a magnetic tape that has been subjected to vertical DC erase, a servo pattern formed by reading the formed servo pattern is obtained. The signal has a unipolar pulse shape. On the other hand, when the pattern using the gap is transferred to the magnetic tape erased in the horizontal DC direction, the servo signal obtained by reading the formed servo pattern has a bipolar pulse shape.

The fact that unintended portions on the magnetic layer are also prevented from being magnetized when magnetized (servo pattern is formed) by the servo write head is, for example, an edge specified by a magnetic force microscope observation of the timing-based servo pattern. the difference between the positional deviation cumulative distribution function 99.9% of the values _{L 99.9} and the cumulative distribution function of 0.1% of the values _{L 0.1} width from the ideal shape in the longitudinal direction of the magnetic tape shape _{(L 99 .9-} L _0.1 ) (hereinafter also simply referred to as "difference (L _99.9- L _0.1 )"). The timing-based servo pattern is formed as a plurality of servo patterns of two or more different shapes on the magnetic layer. In one example, a plurality of servo patterns of two or more different shapes are continuously arranged at a constant interval for each of a plurality of servo patterns of the same shape. In another example, different types of servo patterns are alternately arranged. Regarding that the servo patterns have the same shape, the positional deviation of the edge shape of the servo pattern is irrelevant. The shape of a servo pattern that can be tracked by the timing-based servo method and the arrangement on a servo band are known, and the servo pattern shown in FIG. 14 is a specific example. In the present invention and the present specification, the edge shape specified by observing a timing-based servo pattern by a magnetic force microscope is referred to as a running direction of a magnetic tape when recording a magnetic signal (data) (hereinafter, also simply referred to as a “running direction”). )) On the downstream side (end side). For example, in FIG. 14, the direction of the arrow is the upstream side, and the opposite side is the downstream side.

The following is the value L _{99.9 of the} edge shape specified by the magnetic force microscope observation of the timing-based servo pattern and the cumulative distribution function 99.9% of the positional deviation width of the edge shape from the ideal shape in the longitudinal direction of the magnetic tape. a difference _(L 99.9 _{-L 0.1)} between the cumulative distribution function of 0.1% of the values _{L 0.1,} and the ideal shape will be described.
In the following description, a linear servo pattern extending continuously from one side to the other in the width direction of the magnetic tape and inclined at an angle α with respect to the width direction of the magnetic tape will be mainly described as an example. The angle α is defined as a line segment connecting two end portions in the tape width direction of the edge of the servo pattern positioned downstream with respect to the running direction of the magnetic tape when recording a magnetic signal (data). Angle with the width direction. This point will be further described below.

15 and 16 are explanatory diagrams of the angle α. In the servo pattern shown in FIG. 14, the servo pattern A1 to A5, for servo pattern which is inclined toward the upstream side in the running direction as C1 -C4, connecting the ends two locations on the downstream side of the edge E _L The angle between the line segment (dashed line L1 in FIG. 15) and the tape width direction (dashed line L2 in FIG. 15) is defined as an angle α. On the other hand, the servo pattern B1 to B5, the servo pattern which is inclined toward the downstream side in the traveling direction as shown in D1 to D4, the line segment connecting the ends two locations on the downstream side of the edge E _L (in FIG. 16 , The dashed line L1) and the tape width direction (dashed line L2 in FIG. 16) make an angle α. This angle α is generally called an azimuth angle, and is determined by setting a servo write head when forming a magnetized region (servo pattern) on a servo band.

When forming a magnetized region (servo pattern) on the servo band, if the servo pattern is ideally formed, the edge shape of the servo pattern inclined at an angle α with respect to the width direction of the magnetic tape is as described above. 15 (FIG. 15 and FIG. 16, broken line L1). That is, it becomes a straight line. Therefore, at each location on the edge, the positional deviation width from the ideal shape in the longitudinal direction of the magnetic tape (hereinafter, also simply referred to as “positional deviation width”) becomes zero. However, as shown in an example in FIG. 17, the edge shape of the servo pattern deviates from the ideal shape, and this positional deviation width is large and the deviation of the value of the positional deviation width at each position of the edge is large. This is considered to be a factor that lowers the accuracy of reading and reading the position of the reading element. On the other hand, the difference (L _99.9 -L _0.1 ) indicates that the position deviation width from the ideal shape is small at each position of the edge of the servo pattern, and the value of the position deviation width at each position of the edge is small. Is a value that can be an index of being small.

The difference (L _99.9 -L _0.1 ) is a value obtained by the following method.
The surface of the magnetic layer of the magnetic tape on which the servo pattern is formed is observed with a magnetic force microscope (MFM; Magnetic Force Microscope). The measurement range is a range including five servo patterns. For example, with an LTO Ultra format tape, five servo patterns of A burst or B burst can be observed by setting the measurement range to 90 μm × 90 μm. A servo pattern (magnetized region) is extracted by measuring the measurement range at a pitch of 100 nm (coarse measurement).
Thereafter, in order to detect the boundary between the magnetized region and the non-magnetized region at the edge of the servo pattern located downstream with respect to the running direction, measurement is performed at a pitch of 5 nm near the boundary to obtain a magnetic profile. If the obtained magnetic profile is inclined at an angle α with respect to the width direction of the magnetic tape, the rotation is corrected by analysis software so that α = 0 ° along the magnetic tape width direction. After that, the position coordinates of the peak value of each profile measured at a 5 nm pitch are calculated by the analysis software. The position coordinates of this peak value indicate the position of the boundary between the magnetized region and the non-magnetized region. The position coordinates are specified by, for example, an xy coordinate system in which the traveling direction is the x coordinate and the width direction is the y coordinate.
Taking the case where the ideal shape is a straight line and the position coordinates of a certain position on the straight line are (x, y) = (a, b) as an example, the actually obtained edge shape (the position coordinates of the above boundary) Is coincident with the ideal shape, the calculated position coordinates are (x, y) = (a, b). In this case, the displacement width is zero. On the other hand, if the actually obtained edge shape deviates from the ideal shape, the x coordinate of the boundary at the position of y = b is x = a + c or x = ac. x = a + c is, for example, a case where the width c is shifted to the upstream side with respect to the traveling direction. Then, -c) is a case where it is shifted. Here, c is the displacement width. That is, the absolute value of the positional deviation width of the x coordinate from the ideal shape is the positional deviation width in the longitudinal direction of the magnetic tape from the ideal shape. In this way, the displacement width at each point on the downstream edge in the running direction obtained by the measurement at the pitch of 5 nm is obtained.
From the values obtained for each servo pattern, a cumulative distribution function is obtained by analysis software. From the obtained cumulative distribution function, a value L _{99.9 of} 99.9% of the cumulative distribution function and a value L _{0.1 of} 0.1% are obtained, and a difference (L _90.9) for each servo pattern is obtained from the obtained value _{. 9} −L _0.1 ).
The above measurement is performed in three different measurement ranges (the number of measurements N = 3).
The arithmetic average of the difference (L _99.9 -L _0.1 ) obtained for each servo pattern is defined as the above difference (L _99.9 -L _0.1 ) for the magnetic tape.

The “ideal shape” of the edge shape of the servo pattern in this specification refers to the edge shape when the servo pattern is formed without any positional displacement. For example, in one aspect, the servo pattern is a linear servo pattern extending continuously or discontinuously from one side to the other in the width direction of the magnetic tape. The “linear shape” of the servo pattern means that the pattern shape does not include a curved portion, regardless of the positional deviation of the edge shape. “Continuous” means that the tape extends from one side in the tape width direction to the other side without any inflection point of the inclination angle and without interruption. An example of a servo pattern extending continuously from one side to the other in the width direction of the magnetic tape is the servo pattern shown in FIG. On the other hand, “discontinuous” means that there is at least one inflection point of the inclination angle and / or that the inflection point extends at one or more points. A shape that has an inflection point of the inclination angle but extends without interruption is a so-called polygonal line shape. An example of a discontinuous servo pattern having one inflection point of the inclination angle and extending from one side to the other side in the tape width direction without interruption is the servo pattern shown in FIG. On the other hand, an example of a discontinuous servo pattern that is interrupted at one location without an inflection point of the tilt angle and extends from one side to the other in the tape width direction is the servo pattern shown in FIG. Further, an example of a discontinuous servo pattern which has one inflection point of the inclination angle and is interrupted at one position and extends from one side to the other in the tape width direction is the servo pattern shown in FIG.
For a linear servo pattern that extends continuously from one side to the other in the tape width direction, the “ideal shape” of the edge shape connects two end portions of the downstream edge in the running direction of the linear servo pattern. It is the shape of a line segment (linear shape). For example, the linear servo pattern shown in FIG. 14 has a linear shape indicated by L1 in FIG. 15 or FIG. On the other hand, for a linear servo pattern that extends discontinuously, the ideal shape is defined as the shape of a line segment connecting one end to the other end of a portion having the same inclination angle (linear shape). It is. In addition, the shape extending discontinuously at one or more locations is a shape of a line segment (linear shape) connecting one end to the other end of each continuously extending portion. For example, the servo pattern shown in FIG. 18 is a line segment connecting e1 and e2 and a line segment connecting e2 and e3. The servo pattern shown in FIG. 19 is a line segment connecting e4 and e5, and a line segment connecting e6 and e7. The servo pattern shown in FIG. 20 is a line segment connecting e8 and e9 and a line segment connecting e10 and e11.

In the above, the linear servo pattern has been described as an example. However, the servo pattern may be a servo pattern in which the ideal shape of the edge shape is a curved shape. For example, for a servo pattern in which the edge shape on the downstream side with respect to the traveling direction is ideally a partial arc shape, with respect to the position coordinates of the partial arc, a magnetic force microscope with the edge shape on the downstream side with respect to the traveling direction is used. The difference (L _99.9- L _0.1 ) can be obtained from the positional deviation width obtained from the obtained position coordinates.

As the magnetic force microscope used in the above measurement, a commercially available or known magnetic force microscope is used in a frequency modulation (FM) mode. As a probe of the magnetic force microscope, for example, SSS-MFMR (nominal radius of curvature 15 nm) manufactured by Nanoworld can be used. The distance between the surface of the magnetic layer and the tip of the probe during observation with a magnetic force microscope is in the range of 20 to 50 nm.
As the analysis software, commercially available analysis software or analysis software incorporating a known arithmetic expression can be used.

The difference (L _99.9 -L _0.1 ) can be 180 nm or less, and is 170 nm or less, 160 nm or less, 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, or 100 nm or less. be able to. The difference (L _99.9 -L _0.1 ) can be, for example, 50 nm or more, 60 nm or more, or 70 nm or more. The difference (L _99.9 -L _0.1 ) can be controlled by the type (specifically, leakage magnetic field) of the servo write head used to form the servo pattern. As the servo write head, for example, a servo write head having a leakage magnetic field in the range of 150 to 400 kA / m, preferably 200 to 400 kA / m can be used. However, as the coercive force of the magnetic tape decreases, it is not easy to reduce the difference (L _99.9 -L _0.1 ) by simply increasing the capability of the servo write head. This is presumed to be because the coercive force is low and the magnetization is easily reversed. In contrast, a magnetic tape having a ΔSFD of 0.50 or less can easily reduce the difference (L _99.9 -L _0.1 ), for example, to 180 nm or less, even if the coercive force is small. It is. This point can be applied to servo patterns other than the timing-based servo pattern. That is, ΔSFD of 0.50 or less can contribute to suppressing unintended portions on the magnetic layer from being magnetized when magnetized (servo pattern is formed) by the servo write head.

  The coercive force measured in the longitudinal direction of the magnetic tape is, for example, 167 kA / m or less (2100 Oe or less), and may be 160 kA / m or less, 155 kA / m or less, or 150 kA / m or less. Further, the coercive force of the magnetic tape can be, for example, 119 kA / m or more, 120 kA / m or more, or 130 kA / m or more from the viewpoint of the retention of information recorded on the magnetic tape. Generally, the coercive force measured in the longitudinal direction of the magnetic tape can be controlled by the coercive force of the ferromagnetic powder contained in the magnetic layer. The coercive force is converted into a unit by a conversion formula of 1 Oe (1 Oe) = 79.6 A / m. The coercive force can be obtained by a known magnetic property measuring device such as a vibrating sample magnetometer.

  The magnetic tape described above is usually housed in a magnetic tape cartridge, and the magnetic tape cartridge is mounted on a magnetic tape device. The configuration of a magnetic tape cartridge is known. For the embodiment of the magnetic tape cartridge, the above description of the magnetic tape cartridge 12 in FIG. 1 can be referred to.

According to one aspect, the following magnetic tape is also provided.
Having a magnetic layer containing a ferromagnetic powder and a binder on a non-magnetic support,
The magnetic layer has a servo pattern,
ΔSFD calculated by Expression 1 in the longitudinal direction of the magnetic tape is 0.50 or less.

According to one aspect, the following magnetic tape is also provided.
A magnetic tape used for recording data and reading the recorded data,
Having a magnetic layer containing a ferromagnetic powder and a binder on a non-magnetic support,
The magnetic layer has a servo pattern,
ΔSFD calculated by Expression 1 in the longitudinal direction of the magnetic tape is 0.50 or less.
In one aspect, the reading of the data may be performed by a reading element unit.
In one aspect, the reading element unit may include a plurality of reading elements that respectively read data from a specific track area including a track to be read among the track areas included in the magnetic tape by a linear scan method.
In one aspect, the reading result of each reading element can be extracted by the extracting unit.
In one aspect, the extraction unit can extract data derived from the read target track from the read result of each of the read elements.
In one aspect, the extraction unit performs a waveform equalization process on each of the read results for each of the read elements in accordance with a positional shift amount between the magnetic tape and the read element unit, thereby performing the read operation. From the result, data derived from the track to be read can be extracted.

  The above description can be referred to for specific modes that can be taken by the magnetic tape, the reading element unit, and the extracting unit.

  Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiments shown in the examples. The indication of “parts” and “%” described below indicates “parts by mass” and “% by mass” unless otherwise specified. “Eq” described below is an equivalent and is a unit that cannot be converted to SI unit. Further, the steps and evaluations described below were performed in an environment at an ambient temperature of 23 ° C. ± 1 ° C. unless otherwise specified.

[Example 1]
1. Preparation of Alumina Dispersion (Abrasive Solution) 100.0 parts of alumina powder (HIT-70 manufactured by Sumitomo Chemical Co., Ltd.) having a pregelatinization rate of about 65% and a BET (Brunauer-Emmett-Teller) specific surface area of 30 m ² / g was used. A 32% solution of 3.0 parts of 2,3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry) and a polyester polyurethane resin having a SO ₃ Na group as a polar group (UR-4800 manufactured by Toyobo Co., Ltd. (polar group amount: 80 meq / kg)) 31.3 parts of a solvent (a mixed solvent of methyl ethyl ketone and toluene) and 570.0 parts of a mixed solution of methyl ethyl ketone and cyclohexanone 1: 1 (mass ratio) as a solvent were mixed, and the mixture was mixed with a paint shaker for 5 hours in the presence of zirconia beads. Dispersed. After the dispersion, the dispersion and the beads were separated by a mesh to obtain an alumina dispersion.

2. Composition formulation for magnetic layer formation (magnetic liquid)
Ferromagnetic powder (hexagonal barium ferrite powder; see Table 1) 100.0 parts SO ₃ Na group-containing polyurethane resin 14.0 parts (weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g)
Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (polishing liquid)
The above 1. 6.0 parts (silica sol) of alumina dispersion prepared in
Colloidal silica (average particle size 100 nm) 2.0 parts Methyl ethyl ketone 1.4 parts (other components)
2.0 parts of stearic acid 6.0 parts of butyl stearate 6.0 parts of polyisocyanate (Coronate (registered trademark) manufactured by Tosoh Corporation) 2.5 parts (finishing additive solvent)
Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

3. Formulation of composition for forming nonmagnetic layer Nonmagnetic inorganic powder: α-iron oxide 100.0 parts Average particle size (average long axis length): 10 nm
Average needle ratio: 1.9
BET specific surface area: 75 m ² / g
Carbon black 20.0 parts Average particle size 20nm
18.0 parts of SO ₃ Na group-containing polyurethane resin (weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g)
Stearic acid 1.0 part 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 20nm
Vinyl chloride copolymer 13.0 parts Sulfonate group-containing polyurethane resin 6.0 parts Phenylphosphonic acid 3.0 parts Cyclohexanone 155.0 parts Methyl ethyl ketone 155.0 parts Stearic acid 3.0 parts Butyl stearate 3.0 parts Poly Isocyanate 5.0 parts Cyclohexanone 200.0 parts

5. Preparation of Composition for Forming Each Layer A composition for forming a magnetic layer was prepared by the following method.
A magnetic liquid was prepared by dispersing (bead dispersion) various components of the above magnetic liquid using a batch type vertical sand mill for the dispersion times shown in Table 1. Zirconia beads having a bead diameter of 0.5 mm were used as the dispersed beads. Using the above-mentioned sand mill, the prepared magnetic liquid and the above-mentioned abrasive liquid are mixed with other components (silica sol, other components and finishing additive solvent) and dispersed for 5 minutes, and then a batch type ultrasonic device (20 kHz, 300 W) For 0.5 minutes (ultrasonic dispersion). Thereafter, the mixture was filtered using a filter having a pore size of 0.5 μm to prepare a composition for forming a magnetic layer. A part of the prepared composition for forming a magnetic layer was sampled, and the dispersed particle size, which is an index of the dispersibility of the ferromagnetic powder, was measured by the method described below. Table 1 shows the measured values.
A composition for forming a nonmagnetic layer was prepared by the following method.
The above various components except for stearic acid, cyclohexanone and methyl ethyl ketone were dispersed for 24 hours using a batch type vertical sand mill to obtain a dispersion. As the dispersed beads, zirconia beads having a bead diameter of 0.1 mm were used. Thereafter, the remaining components were added to the obtained dispersion, and the mixture was 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 back coat layer was prepared by the following method.
After kneading and diluting the above various components except for the lubricant (stearic acid and butyl stearate), polyisocyanate and cyclohexanone with an open kneader, using a zirconia bead having a bead diameter of 1 mm with a horizontal bead mill disperser, the bead filling rate is determined. At 80% by volume, the peripheral speed of the rotor tip was 10 m / sec, the residence time per pass was 2 minutes, and dispersion treatment of 12 passes was performed. Thereafter, the remaining components were added to the obtained dispersion, and the mixture was 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 back coat layer.

6. Preparation of Magnetic Tape The above-mentioned item 5 was applied onto a surface of a 5.0 μm-thick polyethylene naphthalate support so that the thickness after drying was 1.0 μm. After applying and drying the composition for forming a non-magnetic layer prepared in the above, the thickness of the dried composition is adjusted so as to be 0.1 μm. The composition for forming a magnetic layer prepared in the above was applied. The composition for forming a magnetic layer was dried without an alignment treatment (non-alignment). Thereafter, the polyethylene naphthalate support is dried on the surface opposite to the surface on which the nonmagnetic layer and the magnetic layer are formed so that the thickness after drying becomes 0.5 μm. Was applied and dried.
Thereafter, a calender roll composed only of a metal roll is used. The surface is smoothed at a speed of 100 m / min, a linear pressure of 300 kg / cm (294 kN / m), and a calender temperature (calender roll surface temperature) of 100 ° C. (calender treatment). After that, heat treatment was performed for 36 hours in an environment at an ambient temperature of 70 ° C. After the heat treatment, the tape was slit to a width of 1/2 inch (0.0127 meters) to obtain a magnetic tape.
With the magnetic layer of the produced magnetic tape demagnetized, a servo write head (leakage magnetic field: see Table 1) was used to form a servo pattern on the magnetic layer in an arrangement and shape according to the LTO Ultrium format. Accordingly, 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 a shape according to the LTO Ultra format on the servo band. Magnetic tape was obtained.

[Examples 2 to 4, Comparative Examples 1 to 5]
Ferromagnetic powder (hexagonal barium ferrite powder) used for producing each of the magnetic tapes of Examples 2 to 4 and Comparative Examples 1 to 5, beads dispersion time when preparing a composition for forming a magnetic layer, presence or absence of an orientation treatment Table 1 shows the leakage magnetic field of the servo write head. It can be said that the servo write head has a higher ability to record a servo pattern as the value of the leakage magnetic field is larger. In Examples and Comparative Examples, two types of servo write heads having different leakage magnetic fields were used.
In addition, what is described as “absent” in the column of orientation is a non-oriented one without performing the orientation treatment. What is described as "longitudinal" means that a magnetic field having a magnetic field strength of 0.3 T is applied in the longitudinal direction to the surface of the coating layer while the coating layer of the applied magnetic layer forming composition is in an undried state. This is a result of a hand alignment treatment.
Magnetic tapes of Examples 2 to 4 and Comparative Examples 1 to 5 were produced in the same manner as in Example 1, except that the various items shown in Table 1 were changed as shown in Table 1.

[Evaluation method]
(1) Dispersion particle size of magnetic layer forming composition A sample obtained by partially collecting the magnetic layer forming composition prepared above and diluting it to 1/50 by mass with the organic solvent used for preparing this composition. A solution was prepared. For the prepared sample solution, the arithmetic average particle size measured using a light scattering type particle size distribution meter (LB500 manufactured by HORIBA) was defined as the dispersed particle size.

(2) Average particle size of ferromagnetic powder The average particle size of the ferromagnetic powder was determined by the method described above.

(3) ΔSFD _powder and coercive force Hc of ferromagnetic powder
The SFD of the ferromagnetic powder was measured at a temperature of 100 ° C. and a temperature of 25 ° C. using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.) with an applied magnetic field of 796 kA / m (10 kOe). From the SFD measurement results, ΔSFD _powder was calculated by the above equation (2).
The coercive force Hc of the ferromagnetic powder was measured at a temperature of 25 ° C. using a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.) with an applied magnetic field of 796 kA / m (10 kOe).

(4) Measurement of ΔSFD and coercive force Hc in the longitudinal direction of the magnetic tape Using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) at a temperature of 25 ° C. and a temperature of −190 ° C., applying an applied magnetic field of 796 kA / m (10 kOe). Was measured in the longitudinal direction. From the measurement results, ΔSFD in the longitudinal direction of the magnetic tape was calculated by the above equation (1).
The coercive force Hc in the longitudinal direction of the magnetic tape was measured using a vibrating sample magnetometer (manufactured by Toei Kogyo KK) with an applied magnetic field of 796 kA / m (10 kOe).

(5) For each of the magnetic tapes of the measurement and calculation examples and comparative examples of the difference _(L 99.9 _{-L 0.1),} was determined difference _(L 99.9 _{-L 0.1)} by the following method.
Using a Bruker Dimension 3100 as a magnetic force microscope in a frequency modulation mode, and using a Nanoworld SSS-MFMR (nominal radius of curvature 15 nm) as a probe, 90 μm × 90 μm of the magnetic layer surface of the magnetic tape on which the servo pattern was formed. , A rough measurement was performed at a pitch of 100 nm to extract a servo pattern (magnetized region). The distance between the surface of the magnetic layer and the tip of the probe during observation with a magnetic force microscope was 20 nm. Since the above measurement range includes five servo patterns of the A burst formed according to the LTO Ultra format, these five servo patterns were extracted.
Using the above-described magnetic force microscope and the probe, the vicinity of the boundary between the magnetized region and the non-magnetized region was measured at a pitch of 5 nm for the edge on the downstream side in the running direction of each servo pattern to obtain a magnetic profile. Since the obtained magnetic profile was inclined at the angle α = 12 °, the rotation was corrected by analysis software so that the angle α = 0 °.
The measurement was performed at three different locations on the surface of the magnetic layer. Each measurement range included five servo patterns of the A burst.
Then, to determine the difference _(L 99.9 _{-L 0.1)} by the method described above with reference to analysis software. As the analysis software, MATLAB used by MathWorks was used. Table 1 shows the difference (L _99.9 -L _0.1 ) thus obtained.

(6) Performance evaluation (i) Line recording at a speed of 6 m / s using a recording / reproducing head mounted on an IBM TS1155 tape drive with respect to the magnetic layer of each magnetic tape of Examples and Comparative Examples. Data recording was performed under the recording conditions of density: 600 kbpi (255 bit PRBS) and track pitch: 2 μm. The unit kbpi is a unit of linear recording density (not convertible to SI unit system). The PRBS is an abbreviation for Pseudo Random Bit Sequence.
By the above recording, a specific track area in which the track to be read is located is located in the magnetic layer of each magnetic tape between two adjacent tracks, that is, between the first noise mixing source track and the second noise mixing source track. It is formed.
(Ii) The following data reading was performed as a model experiment in which data reading was performed using a reading element unit having two reading elements arranged in close proximity. In the following model experiments, data reading was performed by the contact and sliding of the magnetic layer surface and the reading element.
Reading is started with a magnetic head having a single reading element arranged so that the center of the reading target track in the tape width direction coincides with the center of the reading element in the track width direction, and the first data reading is performed. went. During the first data reading, a servo pattern was read by a servo element, and tracking by a timing-based servo system was also performed. Further, a data reading operation was performed by the reading element in synchronization with the servo pattern reading operation.
Next, the same magnetic head was shifted by 500 nm in the tape width direction (one adjacent track side), and the second data reading was performed in the same manner as the first data reading. The above two data readings were performed under reading conditions of a reproducing element width: 0.2 μm, a speed: 4 m / s, and a sampling rate: 1.25 times the bit rate.
A read signal obtained in the first data reading is input to the equalizer, and a waveform equalization process is performed in accordance with a displacement amount between the magnetic tape and the magnetic head (reading element) in the first data reading. . This waveform equalization process is a process performed as follows. The ratio of the overlap area between the read element and the track to be read and the overlap area between the read element and the adjacent track is calculated based on the amount of positional deviation obtained by reading the servo pattern formed at a constant period by the servo element. Identify. By performing a convolution operation on the read signal with a tap coefficient derived from the specified ratio using an arithmetic expression, a waveform equalization process is performed. The above arithmetic expression is an arithmetic expression using EPR4 (Extended Partial Response class 4) as a basic waveform (target). The read signal obtained in the second data read was also subjected to the waveform equalization process.
By performing the phase matching processing (hereinafter, referred to as “two-dimensional signal processing”) of the two read signals subjected to the above-described waveform equalization processing, two reading elements (reading elements) arranged close to each other are read. A read signal that would be obtained by a read element unit having an element pitch of 500 nm was obtained. With respect to the read signal thus obtained, the SNR at the signal detection point was calculated.
(Iii) As described in (ii) above, the position of the read element at the start of the first data reading is set at a distance of 0.1 μm from the center of the track to be read in the tape width direction and on the first noise mixing source track side and the second position. This is repeated while the track is offset to the noise mixing source track side, thereby obtaining an SNR envelope with respect to the track position.
In Table 1, in Examples and Comparative Examples in which “Yes” is described in the column of “Two-dimensional signal processing”, envelopes of SNR were obtained by the above method.
In Table 1, in the comparative example in which "None" is described in the column of "two-dimensional signal processing", the result of the first data reading (that is, only the single element is used) without performing the second data reading described above. The data reading result of (1) obtained an SNR envelope.
(Iv) The SNR envelope of Comparative Example 1 was set as a reference envelope, and a point where the SNR was reduced by -3 dB from the SNR of the track center in the reference envelope was set as the SNR lower limit value. In each envelope, the maximum track offset amount equal to or larger than the lower limit value is defined as an allowable track offset amount. For each of the example and the comparative example, the increase rate of the allowable track offset amount with respect to the allowable track offset amount of Comparative Example 1 was determined as “acceptable track offset amount increase rate”.

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

As shown in Table 1, according to the example, an allowable track offset amount increase rate of 20% or more was realized.
The fact that the allowable track offset amount obtained by the above method is large is advantageous in enabling reproduction with high reproduction quality even if the track margin is reduced. From this point, it is preferable that the allowable track offset amount increase rate is 20% or more.

  One embodiment of the present invention is useful in magnetic recording applications where it is desired to reproduce data recorded at high density with high reproduction quality.

Claims (12)

Magnetic tape,
A reading element unit;
An extraction unit;
Including
The magnetic tape has a magnetic layer containing a ferromagnetic powder and a binder on a non-magnetic support,
The magnetic layer has a servo pattern,
In the longitudinal direction of the magnetic tape, the following formula 1:
ΔSFD = SFD _{25 ° C.−} SFD _{−190 ° C.} Formula 1
Is equal to or less than 0.50, and in Equation 1, SFD _{25 ° C.} is a reversal magnetic field distribution SFD measured in the longitudinal direction of the magnetic tape under an environment of temperature 25 ° C., and SFD _{−190 ° C.} , A switching field distribution SFD measured in the longitudinal direction of the magnetic tape under an environment of a temperature of -190 ° C,
The reading element unit has a plurality of reading elements that respectively read data in a linear scan manner from a specific track area including a read target track among track areas included in the magnetic tape,
The extraction unit performs, on each of the read results for each of the read elements, a waveform equalization process in accordance with a shift amount of a position between the magnetic tape and the read element unit, thereby obtaining the read result from the read result. Extract data from the track to be read,
The magnetic tape device, wherein the shift amount is determined according to a result obtained by a servo element reading a servo pattern included in a magnetic layer of the magnetic tape. 2. The magnetic tape device according to claim 1, wherein a part of each of the plurality of reading elements overlaps in a running direction of the magnetic tape. The specific track area is an area including the read target track and an adjacent track adjacent to the read target track,
3. The magnetic tape device according to claim 2, wherein each of the plurality of read elements straddles both the read target track and the adjacent track when the positional relationship with the magnetic tape changes. . 2. The magnetic tape device according to claim 1, wherein the plurality of reading elements are arranged side by side in a state of being close to each other in a width direction of the magnetic tape. 5. The magnetic tape device according to claim 1, wherein the plurality of reading elements are accommodated in the read target track in a width direction of the magnetic tape. 6. The magnetic tape device according to any one of claims 1 to 5, wherein the waveform equalization processing is performed using a tap coefficient determined according to the shift amount. For each of the plurality of read elements, a ratio of an overlapping area with the track to be read and an overlapping area with an adjacent track adjacent to the track to be read is specified from the deviation amount, and the ratio is determined by the specified ratio. The magnetic tape device according to claim 6, wherein the tap coefficient is determined according to the value. The magnetic tape device according to claim 1, wherein a reading operation of the reading element unit is performed in synchronization with a reading operation performed by the servo element. The extraction unit has a two-dimensional FIR filter,
The two-dimensional FIR filter derives the read target track from the read result by synthesizing each result obtained by performing the waveform equalization process on each of the read results for each of the read elements. The magnetic tape device according to claim 1, wherein data is extracted. The magnetic tape device according to claim 1, wherein the plurality of reading elements are a pair of reading elements. The magnetic tape device according to any one of claims 1 to 10, wherein a coercive force measured in a longitudinal direction of the magnetic tape is 167 kA / m or less. The magnetic tape device according to claim 1, wherein the ΔSFD is 0.03 or more and 0.50 or less.