Magnetic tapes, cassette tapes and magnetic tape devices

Abstract

A magnetic tape having a time base servo pattern is provided for use in a magnetic tape device with a total data track count of 8705 or more when converted to a 1 / 2-inch wide magnetic tape, wherein the ΔPNL of the time base servo pattern is 10.0% or less of the track pitch. A magnetic tape device is also provided, comprising a tape cassette and a magnetic tape, the tape cassette including the aforementioned magnetic tape, the magnetic tape device having a total data track count of 8705 or more when converted to a 1 / 2-inch wide magnetic tape, the magnetic tape having a time base servo pattern, wherein the ΔPNL of the time base servo pattern is 10.0% or less of the track pitch. The ΔPNL represents the amount by which the time base servo pattern deviates from linearity.

Description

Technical Field

[0001] This invention relates to a magnetic tape, a magnetic tape cassette, and a magnetic tape device. Background Technology

[0002] In recent years, magnetic recording media (i.e., magnetic tape) have been primarily used for data storage purposes such as backup and archiving. With the tremendous increase in information volume, there is a demand to increase the recording capacity of magnetic tape (high capacity). One solution for achieving this high capacity is to increase the recording density by reducing the width of the data tracks and then configuring more data tracks on the magnetic layer.

[0003] However, if the width of the data track is reduced and more data tracks are arranged on the magnetic layer, the magnetic head will have difficulty accurately tracking the data tracks when the magnetic tape travels within the tape drive for data recording and / or playback, leading to errors during recording and playback. Therefore, as a solution to reduce such errors, a system for magnetic head tracking using servo signals (hereinafter referred to as a "servo system") has been proposed and put into practical use in recent years (for example, see Patent Document 1).

[0004] Previous technical documents

[0005] Patent documents

[0006] Patent Document 1: US Patent No. 10366716 Summary of the Invention

[0007] The technical problem to be solved by the invention

[0008] In a magnetic servo system, a servo pattern is formed on the magnetic layer of the magnetic tape, and the head tracks the data by magnetically reading this pattern. More specifically, as follows.

[0009] First, a servo pattern reading element mounted on the magnetic head is used to read the servo pattern formed on the magnetic layer. Next, based on the servo pattern reading result, the position of the magnetic head in the width direction of the magnetic tape is controlled so that the magnetic head tracks the data track. Therefore, when the magnetic tape travels within the magnetic tape device to record or reproduce data on the tape, even if the position of the tape relative to the magnetic head changes in the width direction, the accuracy of the magnetic head tracking the data track can be improved. Thus, data can be accurately recorded onto the magnetic tape and / or accurately reproduced.

[0010] As a type of servo system using magnetic servo technology, time-based servo technology has become widely used in recent years. In a time-based servo system (hereinafter also referred to as a "time-based servo system"), multiple servo patterns of two or more different shapes are formed on the servo tape. The position of the magnetic head is identified based on the time interval between the readings of two servo patterns of different shapes by the servo pattern reading element and the time interval between the readings of two servo patterns of the same shape by the servo pattern reading element. The position of the magnetic head in the width direction of the magnetic tape is controlled based on this identified position.

[0011] Regarding time-based servo systems, Patent Document 1 (US Patent No. 10,366,716) discloses a method for evaluating the nonlinearity of the servo pattern of a timing-based servo (see claim 1 of Patent Document 1, etc.).

[0012] In a time-based servo system, the servo pattern formed on the magnetic layer is intended to achieve perfect linearity for head tracking. However, in reality, forming a perfectly linear servo pattern on the magnetic layer is not easy. Patent Document 1 (US Patent No. 10,366,716) only describes the evaluation of the nonlinearity of the servo pattern. However, if a nonlinear servo pattern is actually formed on the magnetic layer, but head tracking is performed with the assumption of perfect linearity, the accuracy of head tracking will decrease. As a result, errors are more likely to occur during recording and reproduction, reducing the quality of recording and reproduction. Furthermore, unless otherwise specified, "recording and reproduction" in this specification means "recording only," "reproducing only," or "recording and reproduction."

[0013] In view of the above, one aspect of the present invention aims to improve the recording and reproduction quality in a magnetic tape device utilizing a time-base servo system.

[0014] means for solving technical problems

[0015] One aspect of the present invention relates to a magnetic tape,

[0016] It features a time-based servo pattern.

[0017] Used in magnetic tape devices with a total data track count of 8705 or more when converted to 1 / 2-inch width magnetic tape.

[0018] The ΔPNL of the aforementioned time-base servo pattern is less than 10.0% of the track pitch.

[0019] The above ΔPNL represents the amount by which the above time base servo pattern deviates from linearity.

[0020] One aspect of the present invention relates to a magnetic tape device comprising a magnetic tape,

[0021] The total number of data tracks for the 1 / 2-inch wide magnetic tape of the magnetic tape device is over 8705.

[0022] The aforementioned magnetic tape has a time-base servo pattern.

[0023] The ΔPNL of the aforementioned time-base servo pattern is less than 10.0% of the track pitch.

[0024] The above ΔPNL represents the amount by which the above time base servo pattern deviates from linearity.

[0025] In one approach, the total number of data tracks can be 8960 or more.

[0026] In one embodiment, the ΔPNL of the aforementioned time base servo pattern can be more than 0.5% and less than 10.0% of the track pitch.

[0027] In one embodiment, the magnetic tape may have a non-magnetic support and a magnetic layer containing strongly magnetic powder.

[0028] In one embodiment, the magnetic tape may further have a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

[0029] In one embodiment, the magnetic tape may further have a back coating containing non-magnetic powder on the surface of the non-magnetic support opposite to the surface having the magnetic layer.

[0030] One aspect of the present invention relates to a magnetic tape cassette comprising the aforementioned magnetic tape.

[0031] Invention Effects

[0032] According to one aspect of the present invention, the recording and reproduction quality in a magnetic tape device utilizing a time-base servo system can be improved. Attached Figure Description

[0033] Figure 1 This shows an example of the configuration of the data tape and servo tape in a magnetic tape.

[0034] Figure 2 This is an example of a servo pattern configuration for an LTO (Linear Tape-Open) Ultrium format magnetic tape.

[0035] Figure 3 This is an explanatory diagram of the azimuth angle α.

[0036] Figure 4 This is an explanatory diagram of the azimuth angle α.

[0037] Figure 5 This is an illustration of a method for measuring values ​​related to the shape of a servo pattern.

[0038] Figure 6A This is an explanatory diagram of the method for determining ΔPNL.

[0039] Figure 6B This is an explanatory diagram of the method for determining ΔPNL.

[0040] Figure 7 This is a configuration example showing the write gap of the servo write head.

[0041] Figure 8 This is a 3D diagram illustrating an example of a servo write head.

[0042] Figure 9 yes Figure 8 The servo write head 20 shown is a cross-sectional view.

[0043] Figure 10 yes Figure 9 A partially enlarged cross-sectional view of the servo write head 20 shown.

[0044] Figure 11 This is a schematic diagram showing the structure of the servo writer. Detailed Implementation

[0045] [Magnetic tape, magnetic tape device]

[0046] One aspect of the present invention relates to a magnetic tape having a time base servo pattern, used in a magnetic tape device with a total data track count of 8705 or more in a 1 / 2-inch width magnetic tape conversion, wherein the ΔPNL of the time base servo pattern is less than 10.0% of the track pitch. The ΔPNL represents the amount by which the time base servo pattern deviates from linearity.

[0047] Furthermore, one aspect of the present invention relates to a magnetic tape device comprising a magnetic tape, wherein the total number of data tracks in the form of a 1 / 2-inch wide magnetic tape is 8705 or more, the magnetic tape having a time base servo pattern, wherein the ΔPNL of the time base servo pattern is less than 10.0% of the track pitch.

[0048] The magnetic tape and magnetic tape device described above will now be described in more detail.

[0049] <Total number of data tracks>

[0050] When recording data on the aforementioned magnetic tape, the total number of data tracks, calculated using a 1 / 2-inch width magnetic tape, is 8705 or more. Through in-depth research, the inventors discovered that even with a large number of data tracks (8705 or more) on the magnetic tape through narrowing, setting ΔPNL to 10.0% or less of the track pitch can improve recording and reproduction quality. This is a new discovery by the inventors, as it was not mentioned in Patent Document 1 (US Patent No. 10366716), which simply disclosed the nonlinearity of the servo pattern used to evaluate time-base servoing.

[0051] In this invention and this specification, "total number of data tracks" is a value calculated by the following formula.

[0052] Total number of data tracks = Number of data tapes × Number of loops within one data tape × Number of recording elements

[0053] The term "number of recording elements" refers to the number of recording elements possessed by the magnetic head used for data recording. In a typical magnetic head, a pair of recording elements and a playback element is called a channel, and the number of recording elements is the same as the number of channels. Furthermore, the term "number of wraps in a data band" refers to the number of track groups read in a single, one-way, end-to-end pass. In industry standards, the number of data bands is typically labeled "number of databand," the number of wraps in a data band is labeled "number of wraps in 1DB (data band)," and the number of channels is labeled "number of channels." These values ​​are defined for each magnetic tape system according to industry standards, and are naturally determined to be inherent values ​​of that magnetic tape system once the applicable tape system is determined.

[0054] In this invention and specification, "total number of data tracks" refers to a value converted to a 1 / 2-inch wide magnetic tape. The width of the magnetic tape can be a value defined according to standards such as LTO (Linear Tape-Open). For example, a standard 1 / 2-inch width magnetic tape can be used as the width value. For magnetic tapes wider than 1 / 2 inch, the total number of data tracks is calculated by dividing the total number of data tracks by the tape's bandwidth (in inches) multiplied by 2. Additionally, 1 / 2 inch = 12.65 mm.

[0055] When recording data on the aforementioned magnetic tape, the total number of data tracks is 8705 or more, preferably 8960 or more. Furthermore, the total number of data tracks can be, for example, 35840 or less. From the viewpoint of high capacity, a higher total number of data tracks is preferred; therefore, the total number of data tracks on the aforementioned magnetic tape can also exceed the value shown in this example.

[0056] <Time-Based Servo Pattern>

[0057] The aforementioned magnetic tape has a time-based servo pattern. Specifically, the magnetic tape may have a magnetic layer from which the time-based servo pattern is formed. As described above, in a time-based servo system, multiple servo patterns of two or more different shapes are formed on the magnetic layer. The position of the magnetic head is identified based on the time interval between the servo pattern reading element located on the magnetic head reading two servo patterns of different shapes and the time interval between the servo pattern reading element reading two servo patterns of the same shape. In this invention and specification, "time-based servo pattern" refers to a servo pattern capable of head tracking in a time-based servo system. A servo pattern capable of head tracking in a time-based servo system can be formed on the magnetic layer in the form of multiple servo patterns of two or more different shapes using a servo write head, which serves as the head for forming the servo pattern. In one example, multiple servo patterns of two or more different shapes are arranged consecutively at predetermined intervals for each of multiple servo patterns of the same shape. In another example, different types of servo patterns are arranged alternately. Regarding servo patterns of the same shape, the degree of shape difference that is typically possible during the formation of the servo pattern is ignored. The shape of the servo pattern that enables head tracking in a time-based servo system and its configuration on the servo tape are well known, and the specific form will be described later. Hereinafter, the "time-based servo pattern" will be referred to simply as the "servo pattern".

[0058] For example, in currently widely used linear recording methods, a time-based servo system is typically employed. In magnetic tapes suitable for this system, multiple regions with servo patterns (called "servo tapes") are usually present along the length of the magnetic layer. The region sandwiched between two servo tapes is called the data tape. Data (magnetic signals) is recorded on the data tapes, each with multiple data tracks formed along its length. Figure 1 The diagram shows an example of the configuration of the data band and the servo band. Figure 1In this design, multiple servo bands 10 are arranged on the magnetic layer of magnetic tape 1, sandwiched between guard bands 12. Multiple regions 11 sandwiched between two servo bands are data bands. The servo pattern is a magnetized region, formed by magnetizing specific areas of the magnetic layer using a servo writing head. The region magnetized by the servo writing head (the location where the servo pattern is formed) is determined according to a standard. For example, for LTO (Linear Tape-Open) Ultrium format magnetic tape, which is an industry standard, during tape manufacturing, such as... Figure 2 As shown, multiple servo patterns are formed on the servo tape, tilted relative to the tape width direction. More specifically, Figure 2 In the context of servo frame SF on servo band 10, it consists of servo subframe 1 (SSF1) and servo subframe 2 (SSF2). Servo subframe 1 is composed of A burst (...). Figure 2 Symbols A and B in the middle) sudden ( Figure 2 The A burst consists of servo patterns A1 to A5, and the B burst consists of servo patterns B1 to B5. On the other hand, servo subframe 2 consists of the C burst (… Figure 2 The symbols C and D bursts (in the text) Figure 2 The symbols in the diagram are D). The C burst consists of servo patterns C1 to C4, and the D burst consists of servo patterns D1 to D4. These 18 servo patterns are configured in combinations of 5 and 4 on servo subframes arranged in an array of 5, 5, 4, 4, and are used to identify servo frames. Figure 2 The image shows a single servo frame. However, multiple servo frames are configured along the conveyor belt direction on each servo belt. Figure 2 In the image, the arrow indicates the direction of tape travel. The arrow indicates the direction of tape travel (the direction of travel indicated by the arrow). Figure 2 The right side of the middle is the downstream side, and the opposite side is the opposite side. Figure 2 The left side of the middle section is the upstream side.

[0059] Figure 3 and Figure 4 This is a diagram illustrating the azimuth angle α. In Figure 2 In the servo patterns shown, for servo patterns such as servo patterns A1~A5 and C1~C4 that are inclined towards the downstream side in the belt conveyor direction, the edge E connecting the upstream side... L The line segments at both ends ( Figure 3 The dashed line L1 in the middle is perpendicular to the width direction of the magnetic tape. Figure 3 The angle formed by the dashed line L2 in the diagram is the azimuth angle α. On the other hand, for servo patterns like servo patterns B1~B5 and D1~D4 that are tilted towards the upstream side in the belt conveyor direction, the edge E connecting the upstream side... L The line segments at both ends ( Figure 4 The dashed line L1 in the middle is perpendicular to the width direction of the magnetic tape. Figure 4The angle formed by the dashed line L2 in the figure is the azimuth angle α.

[0060] The azimuth angle α of the time base servo pattern of the aforementioned magnetic tape can be, for example, 37° or less, 30° or less, or 25° or less. Furthermore, the azimuth angle α can be, for example, 5° or more, or 10° or more. If more data tracks are to be arranged on the magnetic layer to increase recording density, a larger azimuth angle α is preferred from the perspective of head tracking in the time base servo system.

[0061] In addition to the azimuth angle, other values ​​related to the shape of the servo pattern include "pattern height," "midpoint distance," and "subframe length." The meaning of "pattern height" is the same as the meaning of the servo pattern length in the width direction of the tape. "Midpoint distance" refers to the distance (in the length direction) at the midpoint of the pattern height between adjacent bursts within a servo frame. It can be the distance (in the length direction) from the upstream edge of the upstream servo pattern of the upstream burst within the upstream servo subframe to the upstream edge of the upstream servo pattern in the adjacent burst at the midpoint of the pattern height. For example, in... Figure 2 In the servo frame SF shown, the distance (distance along the length of the magnetic tape) at the midpoint of the pattern height of the upstream edge of servo pattern A1 and the upstream edge of servo pattern B1 can be used as the midpoint distance. In the embodiments described later, this distance is used as the midpoint distance. "Subframe length" refers to the distance (distance along the length) between the upper or lower ends of the upstream edges of adjacent servo subframes within a servo frame. This can be the distance (distance along the length) between the upper or lower ends of the upstream edge of the upstream servo pattern of the upstreammost servo subframe and the upstream edge of the upstreammost servo pattern of the adjacent servo subframe. For example, in... Figure 2 In the servo frame SF shown, the distance (distance in the length direction) between the upper or lower ends of the upstream edge of servo pattern A1 and the upstream edge of servo pattern C1 can be used as the subframe length. In the embodiments described later, this distance is used as the subframe length. The pattern height can be, for example, 40 μm or more or 45 μm or more, and can be 120 μm or less or 100 μm or less. The midpoint distance can be, for example, 20 μm or more or 25 μm or more, and can be 45 μm or less or 40 μm or less. The subframe length can be, for example, 45 μm or more or 50 μm or more, and can be 85 μm or less or 80 μm or less.

[0062] Regarding the servo pattern of the magnetic tape, the determination of the various values ​​related to the shape of the servo pattern is performed on a servo frame randomly selected from among multiple servo frames of the magnetic tape to be measured. The randomly selected servo frame is then magnetically developed within the magnetic tape to be measured. Magnetic development can be performed, for example, using a magnetic pattern observation colloidal solution (e.g., Sigmarker Q manufactured by SIGMA HI-CHEMICAL INC.). The various values ​​related to the shape of the magnetically developed servo pattern can be determined by measuring the length using a microscope with X / Y direction length measurement capabilities (e.g., MM-800 manufactured by Nikon Corporation). Here, the minimum resolution for length measurement is preferably 1 μm or less. The number of measurements used to obtain each value is set to 5, and the values ​​are calculated as the arithmetic mean of the values ​​obtained from the 5 measurements.

[0063] Figure 5 The diagram illustrates the method for measuring values ​​related to the shape of the servo pattern. Figure 5 As shown in Figure 2 The image shows a servo frame configured with a servo pattern.

[0064] Regarding "azimuth angle α", if we take it as... Figure 3 Taking servo pattern A1, which is tilted towards the downstream side in the tape transport direction, as an example, the azimuth angle α can be calculated as follows: Measure the xy coordinates of the lower left and upper left edges (or lower right and upper right edges) of the servo pattern, using the tape edge as the reference point (0°), and apply the arctangent. For example... Figure 4 The azimuth angle α can also be obtained from the servo pattern tilted towards the upstream side in the direction of the conveyor belt.

[0065] The “pattern height” can be calculated by taking the difference between the y coordinates of the lower left and upper left edges (or the lower right and upper right edges) of the servo pattern obtained above.

[0066] The "subframe length" can be calculated by taking the difference between the x-coordinate of the lower left (or upper left, lower right, or upper right) part of the first servo pattern A1 of burst A and the x-coordinate of the first lower left part of burst C (same as above).

[0067] The "midpoint distance" can be calculated as the difference between the x-coordinate of the midpoint of the pattern height of the upstream side edge of the first servo pattern A1 in burst A and the x-coordinate of the midpoint of the pattern height of the upstream side edge of the first servo pattern B1 in burst B.

[0068] <track spacing>

[0069] Track spacing refers to the physical distance along the width of the magnetic tape between adjacent data tracks. Assuming we calculate the track spacing for the data tracks formed by records passing through the aforementioned total number of data tracks, the track spacing is determined using the following method.

[0070] On the surface of the magnetic layer of the magnetic tape to be measured, a randomly selected area (size: 90μm × 90μm) is observed using a magnetic force microscope (MFM). At a randomly selected location within this area, the track distance in the width direction of the magnetic tape is measured between adjacent data tracks. The track distance between adjacent data tracks can be determined, for example, as the distance between the lower ends of one data track and the lower ends of another data track, or the distance between the upper ends of one data track and the upper ends of another data track in the width direction of the magnetic tape. "Lower" and "upper" are relative terms used here; any direction can be defined as "lower," and the opposite direction as "upper." A commercially available or known magnetic force microscope can be used. The magnetic force microscope is used in frequency modulation (FM) mode. For example, a Nanoworld SSS-MFMR probe (nominal radius of curvature 15nm) can be used as the probe for the magnetic force microscope. The measurement interval during magnetic force microscopy observation is in the range of 10–100 nm, and the distance between the magnetic layer surface and the probe tip is in the range of 20–50 nm.

[0071] Perform the above operation on 5 randomly selected regions respectively, and take the arithmetic mean of the obtained values ​​as the track spacing.

[0072] As mentioned above, the total number of data tracks is a value calculated based on the number of data tapes, the number of loops within a data tape, and the number of recording elements defined for each magnetic tape system according to industry standards, etc. If the magnetic tape system to which the tape is applicable is determined, it will be calculated as a value inherent to that magnetic tape system. Furthermore, the standard name given to the commercially available tape serves as the standard for the magnetic tape system to which it is applicable. Magnetic tapes are typically sold in the form of tape cartridges (also called data cartridges). For example, when sold as an "LTOUltrium 8 data cartridge," the tape inside is compatible with the "LTO Ultrium 8" magnetic tape system, which is one of the industry standards.

[0073] The track pitch can be, for example, 0.10 μm or more or 0.15 μm or more, and can be 2.00 μm or less, 1.50 μm or less, or 1.20 μm or less. However, as mentioned above, the track pitch is a value determined according to the standard of the magnetic tape system and is not limited to the range exemplified above.

[0074] <ΔPNL>

[0075] In a time-based servo system, multiple servo patterns of two or more different shapes are formed on a magnetic layer. The position of the magnetic head equipped with the servo pattern reading element is identified based on the time interval between the readings of two servo patterns of different shapes and the time interval between the readings of two servo patterns of the same shape by the servo pattern reading element. Figure 2 In the example shown, A1-A5 and C1-C4 are servo patterns of the same shape, B1-B5 and D1-D4 are servo patterns of the same shape, and the preceding and following servo patterns are servo patterns of different shapes. In a time-based servo system, the distance between two servo patterns is not based on physical measurement, but rather on the time interval between reading one servo pattern and reading another. If a perfectly linear servo pattern is formed, then, as described above, the track spacing, which is the physical distance, will be proportional to the aforementioned time interval. However, in reality, servo patterns are usually nonlinear. As an example of a nonlinear servo pattern, a servo pattern with curved edges can be illustrated in FIG. 10A and FIG. 10B of Patent Document 1 (US Patent No. 10366716). If the position of the read head is identified based on the reading result of a nonlinear servo pattern, then head tracking based on this identified position information will reduce the accuracy of the head tracking the data tracks. This is considered to be a reason for the reduced recording reproduction quality. In contrast, the inventors have conducted in-depth research and discovered that in magnetic tape devices with a total data track count of 8705 or more when the tape width is converted to 1 / 2-inch tape, the value of ΔPNL, an index that is a nonlinearity of the servo pattern relative to track pitch control, is reduced to less than 10.0% of the track pitch, which helps to improve the recording and reproduction quality.

[0076] A time-base servo pattern is typically a linear servo pattern tilted at an angle α (where α is the azimuth angle) relative to the width direction of the magnetic tape. It can be a servo pattern that extends continuously from one side of the magnetic tape to the other. Furthermore, "linear" in the context of a linear servo pattern means that the pattern shape does not include curved portions, ignoring whether it exhibits non-linearity that can be used as an indicator (ΔPNL). "Continuous" means that it extends uninterruptedly from one side of the magnetic tape to the other without any inflection points in the tilt angle. An example of a servo pattern that extends continuously from one side of the magnetic tape to the other is... Figure 2 The servo pattern shown.

[0077] In this invention and specification, "PNL" is used as an abbreviation for pattern nonlinearity. "ΔPNL" represents the amount by which the servo pattern deviates from linearity; it is a value that can be considered an indicator of the degree of deviation from linearity. Therefore, PNL is marked with the symbol delta (Δ) to indicate the deviation and is labeled "ΔPNL". ΔPNL is a value obtained by the following method.

[0078] Figure 6A and Figure 6B This is an explanatory diagram of the method for determining ΔPNL. The following will... Figure 6A and Figure 6B Collectively referred to as Figure 6. In Figure 6, R represents the read head, R1 is the first read element, and R2 is the second read element. The servo pattern in Figure 6 is... Figure 2 The example shown is a servo pattern. Furthermore, the parts in Figure 6 are shown as examples, and their dimensions are not limited to the illustrated form. This also applies to the other figures. The two read elements R1 and R2 of the read head R can be commercially available or known read elements capable of reading servo patterns. Preferably, GMR (Giant Magnetoresistive) elements or TMR (Tunnel Magnetoresistive) elements are used, with TMR elements being more preferred. Furthermore, the element width is preferably 2 μm or less. The element width is a physical dimension that can be measured using an optical microscope, scanning electron microscope, or the like.

[0079] In the read head R, two read elements R1 and R2 are positioned a distance d apart in the width direction of the magnetic tape. During the read operation described below, R1 and R2 perform read operations while maintaining the distance d. The distance d is set to the same value as the track pitch. The track pitch is as described above.

[0080] The first reading element starts reading from position y0 in the width direction, and the second reading element starts reading from position y1. Figure 6A The read head R is used in all servo tapes of the tape for which ΔPNL is to be determined. The first read element R1 reads the servo pattern at position y0, and the second read element R2 reads the servo pattern at position y1. Through this reading, the time intervals for servo patterns of different shapes and the time intervals for servo patterns of the same shape are determined. Figure 2 In the example shown, the time intervals for different servo patterns are the time intervals for A1 and B1, A2 and B2, A3 and B3, A4 and B4, A5 and B5, C1 and D1, C2 and D2, C3 and D3, and C4 and D4. Figure 2In the example shown, the time intervals for servo patterns of the same shape are the time intervals for A1 and C1, A2 and C2, A3 and C3, A4 and C4, B1 and D1, B2 and D2, B3 and D3, and B4 and D4. Furthermore, as another example, sometimes a servo frame includes bursts A through F. Bursts A, C, D, and F include servo patterns of the same shape, while bursts B and E include servo patterns of the same shape. The former is a servo pattern tilted towards the downstream side in the conveyor direction, and the latter is a servo pattern tilted towards the upstream side in the conveyor direction. There are 27 servo patterns arranged from the upstream side to the downstream side in a sequence of 5 (A1–A5), 5 (B1–B5), 5 (C1–C5), 4 (D1–D4), 4 (E1–E4), and 4 (F1–F4). In this case, bursts A and B constitute a subframe, and adjacent subframes are composed of bursts C through F. In this example, the time intervals for servo patterns of different shapes are the time intervals for A1 and B1, A2 and B2, A3 and B3, A4 and B4, A5 and B5, D1 and E1, D2 and E2, D3 and E3, and D4 and E4. The time intervals for servo patterns of the same shape are the time intervals for A1 and C1, A2 and C2, A3 and C3, A4 and C4, A5 and C5, D1 and F1, D2 and F2, D3 and F3, and D4 and F4.

[0081] The arithmetic mean of all measured values ​​of time intervals obtained for servo patterns of different shapes is labeled as Td, and the arithmetic mean of all measured values ​​of time intervals obtained for servo patterns of the same shape is labeled as Ts. Furthermore, the value obtained by reading from the first reading element at position y0 is labeled "(1)0". For example, Td obtained by reading from the first reading element at position y0 is labeled "Td(1)0", and Ts obtained by reading from the first reading element at position y0 is labeled "Ts(1)0". Td obtained by reading from the second reading element at position y1 is labeled "Td(2)1", and Ts obtained by reading from the second reading element at position y1 is labeled "Ts(2)1". Furthermore, the measured value of the y position obtained from the result obtained by reading from the first reading element R1 at position y0 is labeled "Y(1)0", and the measured value of the y position obtained from the result obtained by reading from the second reading element R2 at position y1 is labeled "Y(2)1". The readings at each subsequent measurement location were also marked in the same way.

[0082] The measured value Y(1)0 at position y is calculated by the following formula. The methods for determining the subframe length and azimuth angle α are as described above.

[0083] Y(1)0=Subframe length×{1-(Td(1)0 / Ts(1)0)} / 2tanα

[0084] The measured value Y(2)1 at position y is calculated by the following formula.

[0085] Y(2)1=Subframe length×{1-(Td(2)1 / Ts(2)1)} / 2tanα

[0086] After reading by positioning the first reading element R1 at position y0 and the second reading element R2 at position y1, the same process is repeated, positioning the first reading element R1 at position y1 and the second reading element R2 at position y2. Figure 6B The y2 position is a distance d from the y1 position. This process is repeated, with the second reading element R2 determining the final y2 position. E The reading at the position. The final reading position of the first reading element becomes y. (E-1) Position. E is preferably the same value as the number of loops within a data band, for example, it can be in the range of 32 to 102.

[0087] If the position number of y is labeled n, then position y0 is n=0, position y1 is n=1, and position y2 is n=2. If the servo pattern is formed on the magnetic tape with perfect linearity, then the y... n The measured value of the location "Y(2)" n "and the y obtained from the reading result of the first reading element R1" (n-1) The measured value of the location "Y(1)" (n-1) The difference between "Y(2)" and "Y(2)" n -Y(1) (n-1) "It should be the same value as the distance d (i.e., the track spacing). Furthermore, y is obtained based on the reading result from the second reading element R2." (n-1) The measured value of the location "Y(2)" (n-1) "and the y obtained from the reading result of the first reading element R1" (n-2) The measured value of the location "Y(1)" (n-2) The difference between "Y(2)" and "Y(2)" (n-1) -Y(1) (n-2) "It should also be the same value as the distance d (i.e., track spacing). However, in reality, servo patterns are usually non-linear. Using d with "Y(2)" n -Y(1) (n-1) The difference between "d-(Y(2)" and "d-(Y(2)") n -Y(1) (n - 1) The mark "e" is used to indicate the correct usage. (n-1) Furthermore, d is compared with "Y(2)". (n-1) -Y(1) (n-2) The difference between "d-(Y(2)" and "d-(Y(2)") (n-1) -Y(1)(n-2) The mark "e" is used to indicate the correct usage. (n-2) As a nonlinear indicator, the difference "e" is calculated. (n-2) -e (n-1) The absolute value of " is calculated. A total of "n-1" absolute values ​​are obtained, and their arithmetic mean is taken as ΔPNL. Here, n = the aforementioned E.

[0088] In the aforementioned magnetic tape, the ΔPNL calculated by the above method is 10.0% or less of the track pitch. That is, if the track pitch is set to "C", the value calculated by "(ΔPNL / C)×100" is 10.0% or less. A ΔPNL of 10.0% or less of the track pitch helps improve the recording reproduction quality when the total number of data tracks is within the aforementioned range. From the viewpoint of further improving this recording reproduction quality, ΔPNL is preferably 9.5% or less of the track pitch, more preferably 9.0% or less, and even more preferably 8.5% or less, 8.0% or less, 7.5% or less, 7.0% or less, 6.5% or less, 6.0% or less, 5.5% or less, and 5.0% or less. Furthermore, ΔPNL can, for example, be 0.5% or more, 1.0% or more, 1.5% or more, or 2.0% or more of the track pitch. As long as ΔPNL is 10.0% or less of the track pitch, its value is not limited. As an example, ΔPNL can be in the range of 0.005 to 0.300 μm. The method for controlling ΔPNL will be described later.

[0089] <Forming of Servo Patterns>

[0090] A recording head that forms a servo pattern on the magnetic layer of a magnetic tape is called a servo write head. A servo write head typically has a magnetic film including a write gap. The magnetic film can be a strongly magnetic film, preferably a softly magnetic film. The "write gap" included in the magnetic film of the servo write head is a magnetic spacing, which is a spacing that generates a leakage magnetic field for forming the servo pattern as a magnetized region. To form a servo pattern with a ΔPNL of less than 10.0% of the track pitch, it is preferable to form the write gap on the magnetic film by ion beam processing. In this invention and specification, "ion beam processing" refers to a process of forming an opening by irradiating an ion beam. Ion beam processing, for example, can form an opening extending from the recording surface side of the magnetic film to the back surface side. Furthermore, "recording surface side" refers to the servo write head surface side that faces the magnetic layer surface of the magnetic tape in a contact or non-contact state during servo pattern formation; the surface side opposite to this surface is called the "back surface side." The meaning of "magnetic layer (surface)" is the same as the meaning of the magnetic layer side surface of the magnetic tape.

[0091] The configuration of the write gap of the servo write head used to form the time-base servo pattern is illustrated in... Figure 7 . Figure 7 This is a schematic top view of the magnetic film observed from the recording surface side of the servo write head. Five pairs of " / " shaped write gaps are arranged along the length direction L. Therefore, a total of 10 write gaps WG (white portion in the figure) are provided on the magnetic film M of the servo write head. Each write gap is inclined relative to the length direction at the same azimuth angle α as the servo pattern to be formed on the magnetic layer of the magnetic tape. During servo pattern formation, a pulsed current is applied to the servo write head, which is in a contact or non-contact state opposite to the magnetic layer surface of the magnetic tape, generating a leakage magnetic field between the write gaps at the location where the specified servo pattern is to be formed. This allows for the formation of a leakage magnetic field on each of the five servo tapes, for example... Figure 2 The configuration shown forms a servo pattern. For example, by applying a pulsed current, a pair of servo patterns (servo pattern A1 and servo pattern B1) can be formed using a pair of write gaps " / \", and servo patterns A2 and B2, A3 and B3, A4 and B4, A5 and B5, C1 and D1, C2 and D2, C3 and D3, and C4 and D4 can be formed sequentially. By repeatedly forming servo pattern pairs in this way, multiple servo frames SF can be formed sequentially along the length of the servo tape in the magnetic layer of the magnetic tape.

[0092] (Example of a servo write head structure)

[0093] Hereinafter, an example of the structure of the servo write head will be described with reference to the accompanying drawings. However, the form shown in the drawings is illustrative, and the present invention is not limited to this form.

[0094] Servo writing heads can be either ring-shaped recording heads or inductive heads. Inductive heads are also commonly referred to as electromagnetic induction heads or magnetic induction heads. Inductive heads generate a leakage magnetic field from the writing gap of the head core by allowing current to flow through the coil, and use this leakage magnetic field to form a magnetized region on the magnetic layer of the magnetic tape.

[0095] Figure 8 This is a 3D diagram illustrating an example of a servo write head. Figure 8 This is a three-dimensional view of the state of the servo writing head when viewed from the recording surface side. Figure 8 The servo write head 20 shown has a head block 21, a shield 22, and a coil 25 (reference). Figure 9 ).

[0096] The shielding shell 22 is used to shield the coil 25 (reference) of the servo write head 20. Figure 9 The shielding shell 22 is a housing that generates magnetic fields and / or shields magnetic fields from other external components. The shielding shell 22 may be a rectangular shell with a hollow interior, formed of a known material that can shield magnetic fields.

[0097] The upper part of the shielding shell 22 is provided with an opening 24 for the magnetic head block 21 to be exposed from the shielding shell 22. Furthermore, the lower part of the shielding shell 22 is provided with an opening for pulling the wire 23 connected to the coil 25 to the outside of the shielding shell 22.

[0098] Figure 9 yes Figure 8 The servo write head 20 shown is a cross-sectional view. Figure 9 The sectional view shown is a sectional view in the width direction W, which is orthogonal to the length direction L of the servo write head 20.

[0099] The magnetic head block 21 has a core 201 and a substrate 202 on which a magnetic film M is formed. When the core 201 is excited by the coil 25, the write gap of the magnetic film blocks the magnetic flux that is about to pass through the magnetic film. As a result, a leakage magnetic field is generated at the location of the write gap. Using this leakage magnetic field, a magnetized region (i.e., recording) can be formed on the magnetic layer of the magnetic tape.

[0100] As the material constituting the core 201, a magnetic material commonly used for the core of a toroidal recording head can be used. Examples of magnetic materials include single-crystal ferrite, polycrystalline ferrite, and manganese-zinc ferrite. An opening 203 extending vertically along the length direction is formed near the center in the width direction of the upper portion of the core 201. The substrate 202 is disposed within the opening 203 in such a way that it is embedded in the opening 203.

[0101] Examples of materials that can be used as substrate 202 include non-magnetic materials (e.g., various glass materials, various ceramic materials).

[0102] Figure 10 yes Figure 9 This is a partially enlarged cross-sectional view of the servo write head 20 shown. A write gap WG is provided on the magnetic film M disposed on the substrate 202.

[0103] The magnetic film M can be a metal film. Here, "metal film" includes alloy film. The metal film can be a deposited film formed by depositing one or more metal materials selected from the group consisting of one or more pure metals and one or more alloys, and may contain one or more additives and / or may contain one or more impurities that are inevitably mixed in. The magnetic film M can be an iron-based alloy film. Here, "based" means "including". The iron-based alloy film is preferably an iron nitride alloy film. As an iron nitride alloy, examples include iron nitride alloys that contain one or more constituent elements selected from the group consisting of Al, Ta, etc., together with Fe and N. The magnetic film can be a deposited film formed by depositing metal materials on a substrate by known film formation methods such as sputtering, vacuum evaporation, physical vapor deposition (PVD), chemical vapor deposition (CVD), etc.

[0104] Ion beam processing for forming openings in magnetic films can be performed using known ion beam processing methods that form openings by irradiating the workpiece with an ion beam. Ion beam processing can be performed using a process commonly known as ion milling, but from the viewpoint of processing accuracy, focused ion beam (FIB) processing is preferred. An ion beam is a beam of ions accelerated by an electric field, and a focused ion beam is an ion beam focused using a lens or the like. Focused ion beam processing is also commonly referred to as FIB processing. Focused ion beam processing can be performed using commercially available or known focused ion beam apparatus. The processing conditions can be set according to the type of material to be processed, the film thickness, etc. For example, the smaller the beam diameter set in focused ion beam processing, the smaller the value of ΔPNL can be.

[0105] The servo pattern of the aforementioned magnetic tape is a time-based servo pattern. As shown in ECMA (European Computer Manufacturers Association) 319 (June 2001), time-based servoing is used in magnetic tapes conforming to the LTO (Linear Tape-Open) standard (commonly referred to as "LTO tapes"). In this time-based servoing method, the servo pattern is constructed by continuously arranging multiple pairs of non-parallel magnetic strips (also called "servo strips") along the length of the tape. As mentioned above, the reason for using a pair of non-parallel magnetic strips to form the servo pattern is to inform the servo pattern reading element passing over the servo pattern of its position. Specifically, the pair of magnetic strips is formed such that the interval changes continuously along the width of the tape, and the servo pattern reading element can determine the relative position of the servo pattern and the servo pattern reading element by reading this interval. This relative position information makes data track tracking possible. Therefore, multiple servo tracks are typically arranged along the width of the tape on the servo pattern.

[0106] The servo tape consists of a continuous servo pattern along the length of the magnetic tape. Multiple servo tapes are typically present on the tape. For example, in an LTO tape, there are five. The area between two adjacent servo tapes is the data tape. The data tape consists of multiple data tracks, each corresponding to a servo track.

[0107] Furthermore, in one approach, as shown in Japanese Patent Application Publication No. 2004-318983, each servo tape contains embedded information indicating the servo tape's number (also referred to as "servo tape ID (identification)" or "UDIM (Unique Data Band Identification Method) information"). This servo tape ID is recorded by moving a specific pair of servo magnetic strips from a pair of servo magnetic strips present in the servo tape, causing their positions to shift relative to each other along the length of the magnetic tape. Specifically, the movement of a specific pair of servo magnetic strips from a pair of servo magnetic strips is changed for each servo tape. Therefore, the recorded servo tape ID is unique for each servo tape, and thus, by reading a servo tape using a servo pattern reading element, the servo tape can be uniquely identified.

[0108] Another method for uniquely identifying servo tapes is the interleaving method shown in ECMA-319 (June 2001). In this interleaving method, each servo tape is recorded by moving a group of multiple pairs of non-parallel magnetic strips arranged consecutively along the length of the magnetic tape. Since this combination of movement patterns between adjacent servo tapes is unique throughout the entire magnetic tape, the servo tape can also be uniquely identified when reading the servo pattern using two servo pattern reading elements.

[0109] Furthermore, as shown in ECMA-319 (June 2001), information indicating the position of the magnetic tape along its length (also known as "LPOS (Longitudinal Position) information") is typically embedded in each servo tape. Similar to UDIM information, this LPOS information is recorded by shifting the position of a pair of servo strips along the length of the tape. However, unlike UDIM information, the same signal is recorded in each servo tape in this LPOS information.

[0110] Other information, different from the UDIM and LPOS information mentioned above, can also be embedded into the server tape. In this case, the embedded information can vary depending on the server tape, like the UDIM information, or it can be universal across all server tapes, like the LPOS information.

[0111] Furthermore, other methods besides those mentioned above can also be used as a way to embed information in the servo strip. For example, a specified code can be recorded by pulling a specified pair from the middle of a pair of servo magnetic strips.

[0112] Before forming servo patterns on the magnetic tape, the tape is typically demagnetized (erased). This erasure process can be performed by applying a uniform magnetic field to the tape using a DC or AC magnet. Erasure processes include DC (Direct Current) erasure and AC (Alternating Current) erasure. AC erasure is performed by gradually reducing the strength of the magnetic field while reversing the direction applied to the tape. On the other hand, DC erasure is performed by applying a unidirectional magnetic field to the tape. DC erasure includes two methods. The first method is horizontal DC erasure, which applies a unidirectional magnetic field along the length of the tape. The second method is vertical DC erasure, which applies a unidirectional magnetic field along the thickness of the tape. Erasure processes can be performed on the entire tape or on each servo section of the tape.

[0113] The orientation of the magnetic field in the formed servo pattern depends on the erasure orientation. For example, when performing horizontal DC erasure on a magnetic tape, the servo pattern is formed in such a way that the magnetic field orientation is opposite to the erasure orientation. This increases the output of the servo signal obtained by reading the servo pattern. Furthermore, as shown in Japanese Patent Application Publication No. 2012-53940, when a servo pattern is formed using a write gap (also referred to as the formation of a magnetized region or the transfer of a magnetic pattern) on a magnetic tape that has been vertically DC erased, the servo signal obtained by reading the formed servo pattern is a monopole pulse shape. On the other hand, when a servo pattern is formed using a write gap on a magnetic tape that has been horizontally DC erased, the servo signal obtained by reading the formed servo pattern is a bipole pulse shape.

[0114] (Magnetic tape used to form the servo pattern)

[0115] Magnetic tapes are generally classified into coated type and metal film type. The magnetic tape forming the above-mentioned servo pattern can be either a coated type or a metal film type. Magnetic tapes typically have a non-magnetic support and a magnetic layer containing strongly magnetic powder, and a non-magnetic layer containing non-magnetic powder is present between the non-magnetic support and the magnetic layer. A back coating containing non-magnetic powder may also be present on the surface of the non-magnetic support opposite to the surface containing the magnetic layer. In coated type magnetic tapes, the magnetic layer, non-magnetic layer, and back coating may contain a binder and may contain one or more additives. Metal film type magnetic recording media may, for example, have a magnetic layer formed by sputtering. Details regarding magnetic tapes can be found in known technologies, such as paragraphs 0135 to 0201 of Japanese Patent Application Publication No. 2020-126704 and the embodiments described in that publication. However, this is not a limitation; details regarding the components, layer structure, etc., contained in the magnetic tape can be found in known technologies.

[0116] Examples of strongly magnetic powders contained in the magnetic layer of magnetic tape include hexagonal ferrite powder and ε-iron oxide powder.

[0117] In this invention and specification, "hexagonal ferrite powder" refers to a strongly magnetic powder in which the hexagonal ferrite crystal structure is detected as the main phase by X-ray diffraction analysis. The main phase refers to the structure to which the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis belongs. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis belongs to a hexagonal ferrite crystal structure, then the hexagonal ferrite crystal structure is determined to be the main phase. If only a single structure is detected by X-ray diffraction analysis, that detected structure is considered the main phase. As constituent atoms, the hexagonal ferrite crystal structure contains at least iron atoms, divalent metal atoms, and oxygen atoms. Divalent metal atoms refer to metal atoms that can become divalent cations as ions; examples include strontium atoms, barium atoms, calcium atoms, and lead atoms. In this invention and specification, "hexagonal strontium ferrite powder" refers to a hexagonal ferrite in which the predominant divalent metal atom is strontium, and "hexagonal barium ferrite powder" refers to a hexagonal ferrite in which the predominant divalent metal atom is barium. The predominant divalent metal atom refers to the divalent metal atom with the highest atomic percentage among the divalent metal atoms contained in the powder. However, the aforementioned divalent metal atoms do not include rare earth atoms. In this invention and specification, "rare earth atoms" are selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanides. The lanthanide atoms are selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and argonium (Lu).

[0118] In this invention and specification, "ε-iron oxide powder" refers to a strongly magnetic powder in which an ε-iron oxide crystal structure is detected as the main phase by X-ray diffraction analysis. For example, if the highest intensity diffraction peak in the X-ray diffraction spectrum obtained by X-ray diffraction analysis belongs to an ε-iron oxide crystal structure, then the ε-iron oxide crystal structure is determined to be the main phase. ε-iron oxide powder includes substituted ε-iron oxide powder in which a portion of Fe is replaced by substituted atoms such as Ga, Co, Ti, Al, and Rh, and unsubstituted ε-iron oxide powder that does not contain these substituted atoms.

[0119] (Example of a servo writer's structure)

[0120] A magnetic recording device that has a servo writing head and uses the servo writing head to form a servo pattern on the magnetic layer of the magnetic tape is called a servo writer. Figure 11 This is a schematic diagram showing the structure of the servo writer. Figure 11 The servo writer 30 shown has a reel 31 for dispensing the magnetic tape 1 before servo pattern formation and a reel 32 for rewinding the magnetic tape 1 with the servo pattern formed. Figure 11 The arrows in the diagram indicate the direction of tape 1's transport. Multiple guides 33 and a tension adjustment device T for adjusting the tension of the transported tape 1 are arranged along the transport path of tape 1. The servo writing head 20 forms a servo pattern on the magnetic layer of the transported tape 1. The write signal generation circuit 34 sends pulse signals to the servo writing head 20 for forming the servo pattern. Thus, a leakage magnetic field can be generated from the write gap WG of the servo writing head 20, and this leakage magnetic field is used to form a magnetized region (servo pattern) on the magnetic layer of the tape.

[0121] <Magnetic Tape Device>

[0122] In this invention and specification, a "magnetic tape device" is at least a device capable of recording data on a magnetic tape, and can also be a device capable of reproducing data recorded on a magnetic tape. A device capable of recording data on a magnetic tape and / or reproducing the recorded data is generally called a drive.

[0123] The aforementioned magnetic tape apparatus includes the aforementioned magnetic tape, and typically also includes a magnetic head. In the aforementioned magnetic tape apparatus, data recording to the magnetic tape and / or reproduction of data recorded on the magnetic tape can be performed, for example, by contacting and sliding the magnetic head with the surface of the magnetic layer of the magnetic tape.

[0124] Data recording in the aforementioned magnetic tape apparatus is performed according to the total number of data tracks mentioned above. The aforementioned magnetic tape apparatus may have a magnetic head including a recording element capable of recording data on the magnetic tape, and may include a reproduction element capable of reproducing the data recorded on the magnetic tape, either the same as or different from this magnetic head. In recent years, commonly used magnetic heads typically have a structure in which both a recording element and a reproduction element are disposed within a single magnetic head. Examples of recording elements include MIG (Metal-In-Gap) elements. As a reproduction element, a magnetoresistive (MR) element capable of sensitively reading data recorded on the magnetic tape is preferred. Examples of MR elements include various known MR elements (e.g., GMR (Giant Magnetoresistive) elements, TMR (Tunnel Magnetoresistive) elements, etc.). Furthermore, the magnetic head including the recording element and / or reproduction element may include a servo pattern readout element (generally also referred to as a "servo signal readout element"). Alternatively, the aforementioned magnetic tape apparatus may include a magnetic head equipped with a servo pattern readout element in a form different from a magnetic head including a recording element and / or reproduction element. A magnetic head equipped with servo pattern reading elements is often referred to as a "servo head." For example, a magnetic head including recording and / or playback elements (hereinafter also referred to as a "recording / playback head") may include two servo pattern reading elements, each capable of simultaneously reading two adjacent servo tapes while holding a data tape. One or more data elements may be configured between the two servo pattern reading elements. The elements used for recording data (recording elements) and the elements used for playing back data (playback elements) are collectively referred to as "data elements."

[0125] When recording and / or reproducing recorded data, firstly, head tracking can be performed using the reading results of the servo pattern. For example, by making the servo pattern reading element track a specified servo track, it is possible to control the data element to pass on the target data track. Movement of the data track can be achieved by changing the servo track read by the servo pattern reading element in the width direction of the magnetic tape.

[0126] Furthermore, the recording and playback head can also record and / or reproduce data for other data bands. In this case, simply use the aforementioned UDIM information to move the servo pattern reading element to the specified servo band to begin tracking that servo band.

[0127] Regarding the recording and reproduction of data on the aforementioned magnetic tape, reference can be made to paragraphs 0033 to 0134 of Japanese Patent Application Publication No. 2020-126704 and the embodiments described therein. However, this is not a limitation. For data recording on the magnetic tape in the aforementioned magnetic tape apparatus, in addition to recording data for the total number of data tracks, known techniques related to data recording on the magnetic tape can also be applied. Furthermore, for data reproduction, known techniques related to the reproduction of data recorded on the magnetic tape can be applied.

[0128] [Cassette Tape Case]

[0129] One aspect of the present invention relates to a magnetic tape cassette comprising the aforementioned magnetic tape.

[0130] The details of the magnetic tapes included in the aforementioned cassette are as described above.

[0131] In a magnetic tape cassette, the magnetic tape is typically housed inside the cassette body while being wound onto a reel. The reel is configured to rotate within the cassette body. Single-reel cassettes, with one reel inside the cassette body, and double-reel cassettes, with two reels inside the cassette body, are widely used. When a single-reel cassette is installed on a tape drive for recording and / or reproducing data on the magnetic tape, the magnetic tape is pulled out of the cassette and wound onto a reel on the tape drive side. A magnetic head is positioned along the magnetic tape transport path from the cassette to the take-up reel. Magnetic tape feeding and winding occur between the reel on the cassette side (feed reel) and the reel on the tape drive side (take-up reel). During this process, the magnetic head contacts and slides against the magnetic layer surface of the magnetic tape, thereby recording and / or reproducing data. In contrast, a double-reel cassette has both a feed reel and a take-up reel inside the cassette.

[0132] Example

[0133] The present invention will now be described with reference to embodiments. However, the present invention is not limited to the embodiments shown. Unless otherwise specified, “parts” and “%” as used below refer to mass. Furthermore, unless otherwise specified, the processes and evaluations described below were performed at an ambient temperature of 23°C ± 1°C. “eq” as used below refers to equivalent, a unit that cannot be converted to SI units. The various physical property values ​​of the various components described below are values ​​measured using the method described in Japanese Patent Application Publication No. 2020-126704. Furthermore, the recording element width and reproducing element width in Table 1 are the physical dimensions of the element width, values ​​measured by observation using an optical microscope, scanning electron microscope, etc.

[0134] [Example 1]

[0135] <The Making of Cassette Tapes>

[0136] <<Composition for Forming Magnetic Layers>>

[0137] (Magnetic fluid)

[0138] Strong magnetic powder (type: hexagonal barium ferrite powder, activation volume: 1600nm) 3 ): 100.0 copies

[0139] Oleic acid: 2.0 parts

[0140] Vinyl chloride copolymer (KANEKA CORPORATION MR-104): 10.0 parts

[0141] Polyurethane resin containing SO3Na groups: 4.0 parts

[0142] (Weight-average molecular weight 70,000, SO3Na group: 0.07 meq / g)

[0143] Additive A: 10.0 parts

[0144] Methyl ethyl ketone: 150.0 parts

[0145] Cyclohexanone: 150.0 parts

[0146] (Abrasive solution)

[0147] α-Alumina (average particle size: 110 nm): 6.0 parts

[0148] Vinyl chloride copolymer (KANEKA CORPORATION MR110): 0.7 parts

[0149] Cyclohexanone: 20.0 parts

[0150] (Protrusion-forming agent solution)

[0151] Protrusion forming agent: 1.3 parts

[0152] Methyl ethyl ketone: 9.0 parts

[0153] Cyclohexanone: 6.0 parts

[0154] (Lubricant and curing agent liquid)

[0155] Stearic acid: 3.0 parts

[0156] Stearamide: 0.3 parts

[0157] Butyl stearate: 6.0 parts

[0158] Methyl ethyl ketone: 110.0 parts

[0159] Cyclohexanone: 110.0 parts

[0160] Polyisocyanate (TOSOH CORPORATION CORONATE (registered trademark) L): 3.0 parts

[0161] The additive A mentioned above is a polymer synthesized by the method described in paragraphs 0115 to 0123 of Japanese Patent Application Publication No. 2016-051493.

[0162] The aforementioned protrusion forming agent is ATLAS (a composite particle of silica and polymer, with an average particle size of 100 nm) manufactured by Cabot Corporation.

[0163] <<Composition for Non-Magnetic Layer Formation>>

[0164] Non-magnetic inorganic powder (α-iron oxide): 80.0 parts

[0165] (Average particle size: 0.15 μm, average needle ratio: 7, BET (Brunauer-Emmett-Teller) specific surface area: 52 m²) 2 / g)

[0166] Carbon black (average particle size: 20 nm): 20.0 parts

[0167] Electron beam cured vinyl chloride copolymer: 13.0 parts

[0168] Electron beam cured polyurethane resin: 6.0 parts

[0169] Phenylated phosphonic acid: 3.0 parts

[0170] Cyclohexanone: 140.0 parts

[0171] Methyl ethyl ketone: 170.0 parts

[0172] Butyl stearate: 2.0 parts

[0173] Stearic acid: 1.0 part

[0174] <<Composition for Back Coating Forming>>

[0175] Non-magnetic inorganic powder (α-iron oxide): 80.0 parts

[0176] (Average particle size: 0.15μm, average needle ratio: 7, BET specific surface area: 52m²) 2 / g)

[0177] Carbon black (average particle size: 20 nm): 20.0 parts

[0178] Carbon black (average particle size: 100 nm): 3.0 parts

[0179] Vinyl chloride copolymer: 13.0 parts

[0180] Polyurethane resin containing sulfonic acid groups: 6.0 parts

[0181] Phenylated phosphonic acid: 3.0 parts

[0182] Cyclohexanone: 140.0 parts

[0183] Methyl ethyl ketone: 170.0 parts

[0184] Stearic acid: 3.0 parts

[0185] Polyisocyanate (TOSOH CORPORATION CORONATE (registered trademark)): 5.0 parts

[0186] Methyl ethyl ketone: 400.0 parts

[0187] <<Preparation of the Composition for Forming Each Layer>>

[0188] The composition for forming a magnetic layer is prepared by the following method.

[0189] After mixing and diluting the components of the above magnetic liquid using an open kneader, a horizontal bead mill disperser was used to disperse the liquid 12 times using 0.5 mm zirconia (ZrO2) beads (hereinafter referred to as "Zr beads") with a bead filling rate of 80% by volume and a rotor front end circumferential speed of 10 m / s. The residence time for each dispersion was set to 2 minutes.

[0190] After mixing the components of the above-mentioned grinding agent solution, it was placed together with Zr beads with a particle size of 1 mm into a vertical sand mill disperser. The ratio of bead volume to the sum of the grinding agent solution volume and bead volume was adjusted to 60%, and the sand mill dispersion treatment was carried out for 180 minutes. The liquid after sand mill dispersion treatment was taken out and subjected to ultrasonic dispersion filtration using a flow ultrasonic dispersion filtration device, thereby preparing the grinding agent solution.

[0191] The magnetic fluid, abrasive fluid, protrusion forming agent fluid, lubricant and curing agent fluid were introduced into a dissolving mixer and stirred at a circumferential speed of 10 m / s for 30 minutes. After being processed three times using a flow ultrasonic disperser at a flow rate of 7.5 kg / min, the mixture was filtered through a filter with a pore size of 1 μm to prepare a composition for forming a magnetic layer.

[0192] The composition for forming a nonmagnetic layer is prepared by the following method.

[0193] After mixing and diluting the above-mentioned components (excluding lubricants (butyl stearate and stearic acid)) using an open kneader, dispersion was carried out using a horizontal bead mill disperser. Then, lubricants (butyl stearate and stearic acid) were added, and the mixture was stirred using a dissolving mixer to prepare a composition for forming a non-magnetic layer.

[0194] The composition for forming the back coating is prepared by the following method.

[0195] After mixing and diluting the above-mentioned components, excluding the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts), using an open kneader, dispersion was carried out using a horizontal bead mill disperser. Then, the lubricant (stearic acid), polyisocyanate, and methyl ethyl ketone (400.0 parts) were added, and the mixture was stirred using a dissolving mixer to prepare a composition for forming a back coating.

[0196] <<Magnetic tape manufacturing and servo pattern formation>>

[0197] A non-magnetic layer forming composition was coated onto a biaxially stretched polyethylene naphthalate support with a thickness of 6.0 μm after drying to a thickness of 1.0 μm. After drying, the support was irradiated with an electron beam at an accelerating voltage of 125 kV to achieve an energy of 40 kGy. A magnetic layer forming composition was then coated onto the support with a thickness of 50 nm after drying and dried. Finally, a back coating forming composition was coated onto the surface of the support opposite to the surfaces where the non-magnetic and magnetic layers were formed with a thickness of 0.5 μm after drying and dried.

[0198] Then, calendering was performed using a seven-stage calendering roll system consisting only of metal rolls at a calendering speed of 80 m / min, a linear pressure of 294 kN / m, and a calendering temperature of 80°C (the surface temperature of the calendering rolls). Following this, a heat treatment was performed for 36 hours at an ambient temperature of 70°C. After the heat treatment, the rolls were cut into 1 / 2-inch widths and fed out. The cut pieces were then cleaned using a magnetic tape cleaning device mounted on a winding device with a non-woven fabric and a scraper against the magnetic layer surface to obtain the magnetic tape.

[0199] With the magnetic layer of the obtained magnetic tape demagnetized, a servo writing head mounted on a servo writer forms a compliant shape on the magnetic layer. Figure 2The example shown is a servo pattern (time base servo pattern) with an LTO Ultrium format configuration and shape. Thus, a magnetic tape of Embodiment 1 is obtained, having a data tape, a servo tape, and a guard tape configured according to the LTO Ultrium format on the magnetic layer, and a servo pattern with an LTO Ultrium format configuration and shape on the servo tape. As a servo writer, a servo pattern is used... Figure 11 The servo writer with the structure shown is equipped with a servo write head that has a write gap with an opening formed by FIB processing under the processing conditions described below, and the shape of the write gap corresponds to the servo pattern with azimuth angle, pattern height, midpoint distance and subframe length shown in Table 1.

[0200] (Processing conditions)

[0201] Focused ion beam device: Hitachi High-Tech Corporation FB-2200

[0202] Accelerating voltage: 30kV

[0203] Focusing lens: Yes

[0204] Pore ​​size: 80μm

[0205] Dwell Time (irradiation time per pixel): 5μsec

[0206] The processing setting is for a beam diameter of 1.0 μm.

[0207] For Example 1, two magnetic tapes were produced using the same method, one of which was used to record the reproduction test, and the other was used for other determinations.

[0208] <Record Reproduction Experiment>

[0209] The electromagnetic upstream characteristics of magnetic tape were measured using a 1 / 2-inch reel tester with a magnetic head tracking control mechanism as described in Japanese Patent Application Publication No. 2020-126704, paragraphs 0080 to 0086, by the following method.

[0210] The tape feed speed (relative speed between the magnetic head and the tape) was set to 2 m / s. Signal recording was performed at a line recording density of 325 kfci. kfci is the unit of line recording density (cannot be converted to SI units). The "Number of Recording and Reproduction Elements" in Table 1 refers to the number of channels with one recording element and one reproduction element. MIG (Metal-In-Gap) elements (gap length 0.15 μm, recording element width: refer to Table 1) were used as recording elements, and the recording current was set to the optimal recording current for each tape. Shingled magnetic recording was used as the recording method. Shingled magnetic recording is also called "wa" recording in Japanese. It is a method of recording data by forming data tracks with a track spacing narrower than the recording element width and by overlapping adjacent tracks. TMR (Tunnel Magneto-Resistive) elements with a thickness of 15 nm, a shielding spacing of 0.1 μm, and the reproduction element width listed in Table 1 were used as reproduction elements. The reproduced signal was measured using a spectrum analyzer manufactured by Shibasoku Co., Ltd. The ratio of the carrier signal output value to the cumulative noise across the entire spectrum was defined as the SNR (Signal-to-Noise Ratio). Regarding SNR, the SNR during simultaneous recording and reproduction (recorded by the recording element as the downstream module and immediately reproduced by the reproduction element as the upstream module) performed before shingled magnetic recording was set to 0 dB. If the SNR during reproduction of a track after narrowing it using shingled magnetic recording is within -3.00 dB of the SNR during simultaneous recording and reproduction, a good reproduced signal can be determined (i.e., improved recording and reproduction quality).

[0211] The total number of data tracks in the above-mentioned shingled magnetic recording is calculated using the following formula. The value of "number of recording elements" in Table 1 is used as "number of recording and reproduction elements" in the formula.

[0212] Total number of data tracks = Number of data tapes × Number of loops within one data tape × Number of recording elements

[0213] The track spacing of the magnetic tape after shingled magnetic recording was determined using the method described above. A Bruker Dimension 3100 magnetic force microscope was used in frequency modulation mode, and a Nanoworld SSS-MFMR probe (nominal radius of curvature 15 nm) was used as the probe. During observation with the magnetic force microscope, the track spacing was set to 100 nm, and the distance between the magnetic layer surface and the probe tip was set to 20 nm.

[0214] <Determination of azimuth angle, pattern height, midpoint distance, and subframe length of the servo pattern>

[0215] The above method was used to determine various values ​​related to the shape of the servo pattern from a randomly selected servo frame among multiple servo frames in the magnetic tape of Example 1. Specifically, in the magnetic tape of Example 1, a randomly selected servo frame was magnetically developed. Magnetic development was performed using a magnetic pattern observation colloidal solution (Sigmaker Q manufactured by SI GMA HI-CHEMICAL INC.). Various values ​​related to the shape of the magnetically developed servo pattern were determined by measuring the length using a microscope with X / Y direction length measurement capabilities (Nikon Corporation MM-800; minimum resolution for length measurement is 1 μm or less). The number of measurements used to obtain each value was set to 5, and the values ​​shown in Table 1 were obtained as the arithmetic mean of the values ​​obtained from the 5 measurements.

[0216] <ΔPNL>

[0217] refer to Figure 6A and Figure 6B ΔPNL was calculated using the method described above. Here, d = track pitch. Table 1 shows the measured values ​​and their values ​​relative to the track pitch for ΔPNL. TMR elements with a width of less than 2 μm were used as readout elements R1 and R2.

[0218] [Example 2]

[0219] The processing setting beam diameter in the FIB processing conditions for manufacturing servo write heads was reduced. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 1.

[0220] [Comparative Example 1]

[0221] As a servo write head, a servo write head with an opening formed by a write gap through MEMS (Micro Electro Mechanical Systems) processing was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 1.

[0222] [Comparative Example 2]

[0223] As a servo write head, a servo write head with an opening formed by MEMS processing under different processing conditions than Comparative Example 1 was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 1.

[0224] [Example 3]

[0225] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Example 1.

[0226] [Example 4]

[0227] The processing setting beam diameter in the FIB processing conditions for manufacturing servo write heads was reduced. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 3.

[0228] [Example 5]

[0229] The processing setting beam diameter in the FIB processing conditions for manufacturing servo write heads was reduced. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 3.

[0230] [Comparative Example 3]

[0231] As a servo write head, a servo write head with an opening formed by MEMS processing was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 3.

[0232] [Example 6]

[0233] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Example 1.

[0234] [Example 7]

[0235] The processing setting beam diameter in the FIB processing conditions for manufacturing the servo write head was reduced. Apart from that, the magnetic tape was manufactured, the recording and reproduction test was conducted, and various measurements were performed in the same manner as in Example 6.

[0236] [Example 8]

[0237] The processing setting beam diameter in the FIB processing conditions for manufacturing the servo write head was reduced. Apart from that, the magnetic tape was manufactured, the recording and reproduction test was conducted, and various measurements were performed in the same manner as in Example 6.

[0238] [Comparative Example 4]

[0239] As a servo write head, a servo write head with an opening formed by MEMS processing was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 6.

[0240] [Example 9]

[0241] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Example 1.

[0242] [Example 10]

[0243] The processing setting beam diameter in the FIB processing conditions for manufacturing the servo write head was reduced. Apart from that, the magnetic tape was manufactured, the recording and reproduction test was conducted, and various measurements were performed in the same manner as in Example 9.

[0244] [Comparative Example 5]

[0245] As a servo write head, a servo write head with an opening formed by MEMS processing was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 9.

[0246] [Example 11]

[0247] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Example 1.

[0248] [Example 12]

[0249] The processing setting beam diameter in the FIB processing conditions for manufacturing servo write heads was reduced. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 11.

[0250] [Comparative Example 6]

[0251] As a servo write head, a servo write head with an opening formed by MEMS processing was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 11.

[0252] [Example 13]

[0253] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Example 1.

[0254] [Example 14]

[0255] The processing setting beam diameter in the FIB processing conditions for manufacturing servo write heads was reduced. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 13.

[0256] [Comparative Example 7]

[0257] As a servo write head, a servo write head with an opening formed by MEMS processing was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 13.

[0258] [Example 15]

[0259] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Example 1.

[0260] [Comparative Example 8]

[0261] As a servo write head, a servo write head with an opening formed by MEMS processing was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 15.

[0262] [Example 16]

[0263] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Example 1.

[0264] [Example 17]

[0265] The processing setting beam diameter in the FIB processing conditions for manufacturing the servo write head was reduced. Otherwise, the magnetic tape was manufactured, the recording and reproduction test was conducted, and various measurements were performed in the same manner as in Example 16.

[0266] [Comparative Example 9]

[0267] As a servo write head, a servo write head with an opening formed by MEMS processing was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 16.

[0268] [Example 18]

[0269] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Example 1.

[0270] [Example 19]

[0271] The processing setting beam diameter in the FIB processing conditions for manufacturing the servo write head was reduced. Otherwise, the magnetic tape was manufactured, recording and reproduction tests and various measurements were performed in the same manner as in Example 18.

[0272] [Comparative Example 10]

[0273] As a servo write head, a servo write head with an opening formed by MEMS processing was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Example 18.

[0274] [Reference Example 1]

[0275] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Example 1.

[0276] [Reference Example 2]

[0277] As a servo write head, a servo write head with an opening formed by MEMS processing was used. Otherwise, magnetic tape manufacturing, recording and reproduction tests and various measurements were performed in the same manner as in Reference Example 1.

[0278] [Reference Example 3]

[0279] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Reference Example 2.

[0280] [Refer to Example 4, Refer to Example 6]

[0281] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Example 1.

[0282] [Reference Example 5]

[0283] As shown in Table 1, the items listed in Table 1 were changed. Otherwise, the magnetic tape was made, the recording and reproduction tests were conducted, and various measurements were performed in the same manner as in Reference Example 4.

[0284] The results are shown in Table 1 (Table 1-1 to Table 1-4).

[0285]

[0286]

[0287]

[0288] [Table 1-4]

[0289]

[0290] The results of the embodiments, comparative examples and reference examples shown in Table 1 confirm that when the total number of data tracks is 8705 or more (converted to 1 / 2-inch wide magnetic tape), setting the ΔPNL of the time base servo pattern to 10.0% or less of the track pitch (reference to Examples 1 to 19) helps to improve the recording and reproduction quality.

[0291] Industrial availability

[0292] One aspect of the present invention is useful in various data storage applications.

Claims

1. A magnetic tape having a time base servo pattern, This magnetic tape is used in magnetic tape devices with a total data track count of 8705 or more when converted to a 1 / 2-inch width magnetic tape. The ΔPNL of the time base servo pattern is less than 10.0% of the track pitch. ΔPNL represents the deviation of the time-base servo pattern from linearity. The ΔPNL is the arithmetic mean of the difference between the track spacing and the measured values ​​of two positions obtained by reading through two reading elements, wherein the two reading elements perform the reading along the width direction of the magnetic tape while maintaining the track spacing.

2. The magnetic tape according to claim 1, wherein, The total number of data tracks is 8960 or more.

3. The magnetic tape according to claim 1 or 2, wherein, The ΔPNL of the time base servo pattern is greater than 0.5% and less than 10.0% of the track pitch.

4. The magnetic tape according to claim 1 or 2, wherein, The magnetic tape has a non-magnetic support and a magnetic layer containing strongly magnetic powder.

5. The magnetic tape according to claim 4, wherein, Between the non-magnetic support and the magnetic layer, there is also a non-magnetic layer containing non-magnetic powder.

6. The magnetic tape according to claim 4, wherein, The non-magnetic support also has a back coating containing non-magnetic powder on the side opposite to the side with the magnetic layer.

7. A magnetic tape cassette comprising the magnetic tape according to any one of claims 1 to 6.

8. A magnetic tape device comprising a magnetic tape, The total number of data tracks for the 1 / 2-inch wide magnetic tape of the magnetic tape device is over 8705. The magnetic tape has a time-base servo pattern. The ΔPNL of the time base servo pattern is less than 10.0% of the track pitch. ΔPNL represents the deviation of the time-base servo pattern from linearity. The ΔPNL is the arithmetic mean of the difference between the track spacing and the measured values ​​of two positions obtained by reading through two reading elements, wherein the two reading elements perform the reading along the width direction of the magnetic tape while maintaining the track spacing.

9. The magnetic tape device according to claim 8, wherein, The total number of data tracks is 8960 or more.

10. The magnetic tape device according to claim 8 or 9, wherein, The ΔPNL of the time base servo pattern is greater than 0.5% and less than 10.0% of the track pitch.

11. The magnetic tape device according to claim 8 or 9, wherein, The magnetic tape has a non-magnetic support and a magnetic layer containing strongly magnetic powder.

12. The magnetic tape device according to claim 11, wherein, The magnetic tape also has a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer.

13. The magnetic tape device according to claim 11, wherein, The magnetic tape also has a back coating containing non-magnetic powder on the side of the non-magnetic support opposite to the side with the magnetic layer.

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