WO2024162018A1 - 磁気記録媒体 - Google Patents

磁気記録媒体 Download PDF

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Publication number
WO2024162018A1
WO2024162018A1 PCT/JP2024/001207 JP2024001207W WO2024162018A1 WO 2024162018 A1 WO2024162018 A1 WO 2024162018A1 JP 2024001207 W JP2024001207 W JP 2024001207W WO 2024162018 A1 WO2024162018 A1 WO 2024162018A1
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WO
WIPO (PCT)
Prior art keywords
magnetic
recording medium
magnetic recording
less
chlorine
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/JP2024/001207
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English (en)
French (fr)
Japanese (ja)
Inventor
実 山鹿
貴広 高山
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Sony Group Corp
Original Assignee
Sony Group Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sony Group Corp filed Critical Sony Group Corp
Priority to JP2024574424A priority Critical patent/JPWO2024162018A1/ja
Publication of WO2024162018A1 publication Critical patent/WO2024162018A1/ja
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B23/00—Record carriers not specific to the method of recording or reproducing; Accessories, e.g. containers, specially adapted for co-operation with the recording or reproducing apparatus ; Intermediate mediums; Apparatus or processes specially adapted for their manufacture
    • G11B23/02—Containers; Storing means both adapted to cooperate with the recording or reproducing means
    • G11B23/04—Magazines; Cassettes for webs or filaments
    • G11B23/08—Magazines; Cassettes for webs or filaments for housing webs or filaments having two distinct ends
    • G11B23/107—Magazines; Cassettes for webs or filaments for housing webs or filaments having two distinct ends using one reel or core, one end of the record carrier coming out of the magazine or cassette
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
    • G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
    • G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
    • G11B5/706—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
    • G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
    • G11B5/71—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the lubricant
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/74—Record carriers characterised by the form, e.g. sheet shaped to wrap around a drum
    • G11B5/78—Tape carriers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers

Definitions

  • This technology relates to magnetic recording media.
  • Magnetic recording media are often used as a medium for recording large amounts of data.
  • Patent Document 1 discloses a magnetic recording medium having a magnetic layer with a thickness of 0.3 ⁇ m or less that contains at least iron-atom-containing magnetic powder and a binder on one or both sides of a non-magnetic support, and that is characterized in that, when the average iron element content of the surface layer from the center of the magnetic layer is S(Fe) and the average iron element content of the layer deeper than the center of the magnetic layer is D(Fe), S(Fe)/D(Fe) ⁇ 1.1 is satisfied.
  • Patent Document 2 discloses a magnetic recording medium that has excellent electromagnetic conversion characteristics in high-temperature environments.
  • the aim of this technology is to provide a magnetic recording tape that has shape stability and running stability even when subjected to wide changes in temperature and humidity environments, ensuring overall reliability.
  • a magnetic recording medium including a magnetic layer, an underlayer, and a base layer in this order, the undercoat layer comprises a chlorine-containing binder;
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less,
  • the present invention also provides a magnetic recording medium in which the following first index Q is not less than ⁇ 250 ppm and not more than 250 ppm.
  • the present invention also provides a magnetic recording medium in which the second index R below is ⁇ 750 ppm or more and 750 ppm or less.
  • [Threshold] [average chlorine count in the undercoat layer] + 6 ⁇ [standard deviation obtained when calculating the average chlorine count]
  • R 70[%RH] ⁇ (CHH-CHR) (wherein CHH is the humidity expansion coefficient of the magnetic head [ppm/% RH], and CHR is the humidity expansion coefficient of the magnetic recording medium in a temperature environment of 10° C. or higher and 60° C. or lower that is the humidity expansion coefficient that is the most deviated from the humidity expansion coefficient of the magnetic head [ppm/% RH])
  • the total thickness of the magnetic layer and the underlayer may be 1000 nm or less.
  • the magnetic layer may have a thickness of 80 nm or less.
  • the underlayer may contain non-magnetic powder.
  • the underlayer may include a lubricant.
  • the magnetic recording medium may have an average thickness tT of 5.3 ⁇ m or less.
  • the magnetic layer may include magnetic powder.
  • the magnetic powder may include hexagonal ferrite, ⁇ iron oxide, or Co-containing spinel ferrite.
  • this technology includes a magnetic layer, an underlayer, and a base layer, in that order.
  • the undercoat layer comprises a chlorine-containing binder; the thickness of a portion of the undercoat layer where the chlorine count is equal to or greater than the threshold value is 13% or less of the thickness of the undercoat layer,
  • the present invention also provides a magnetic recording medium in which the first index Q below is ⁇ 250 ppm or more and 250 ppm or less.
  • the magnetic layer includes a magnetic layer, an underlayer, and a base layer, in that order.
  • the undercoat layer comprises a chlorine-containing binder; the thickness of a portion of the undercoat layer where the chlorine count is equal to or greater than the threshold value is 13% or less of the thickness of the undercoat layer,
  • the present invention also provides a magnetic recording medium in which the second index R below is ⁇ 750 ppm or more and 750 ppm or less.
  • the base layer may have an average thickness of 4.4 ⁇ m or less.
  • a magnetic recording medium including a magnetic layer, an underlayer, and a base layer in this order, the undercoat layer comprises a chlorine-containing binder;
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less.
  • the present invention also provides a magnetic recording medium having an environmental relative humidity between 10% RH and 80% RH, at which the temperature expansion coefficient of the magnetic recording medium is 6.0 ppm/° C. or more and 8.0 ppm/° C. or less.
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less.
  • the present invention also provides a magnetic recording medium, in which the humidity expansion coefficient of the magnetic recording medium is ⁇ 4.0 ppm/° C. or more and 4.0 ppm/° C. or less at an environmental temperature between 10° C. and 60° C.
  • a spindle on which a magnetic recording medium can be mounted A drive device that drives the spindle; a magnetic head for recording and reproducing information on the magnetic recording medium;
  • the magnetic recording medium is A magnetic layer, an underlayer, and a base layer in this order; the undercoat layer comprises a chlorine-containing binder;
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less,
  • the environmental relative humidity is between 10% RH and 80% RH, such that the temperature expansion coefficient of the magnetic recording medium is 6.0 ppm/° C.
  • this technology a spindle on which a magnetic recording medium can be mounted; A drive device that drives the spindle; a magnetic head for recording and reproducing information on the magnetic recording medium;
  • the magnetic recording medium is A magnetic layer, an underlayer, and a base layer in this order; the undercoat layer comprises a chlorine-containing binder;
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less,
  • a recording/reproducing device in which the environmental temperature is between 10° C.
  • the base layer may comprise a polyester based material or a polyetheretherketone based material.
  • FIG. 1 is a cross-sectional view showing a configuration of a magnetic recording medium according to a first embodiment.
  • FIG. 2 is a diagram showing an example of the shape of a particle of a magnetic powder.
  • 1 is an example of a TEM photograph of a cross section of a sample.
  • 13 is another example of a TEM photograph of a cross section of a sample.
  • FIG. 13 shows an example of a HAADF STEM image. This is a diagram to explain the Cl K ⁇ line extraction region set for a HAADF STEM image.
  • FIG. 13 is a diagram showing an example of plot data in which net counts are plotted against pixel position in the thickness direction.
  • FIG. 1 is a diagram for explaining the net count number, in particular, a diagram for explaining an example of a line where K ⁇ rays are counted.
  • FIG. 13 is a diagram showing an example of plot data in which the chlorine count number after normalization is plotted against the position in the thickness direction.
  • FIG. 2 is a schematic diagram showing the appearance of a measuring device used to measure the width of a magnetic recording medium.
  • FIG. 1 is a schematic diagram showing a configuration of a recording and reproducing device.
  • FIG. 2 is an exploded perspective view showing an example of the configuration of a magnetic recording cartridge.
  • FIG. 2 is a block diagram showing an example of a configuration of a cartridge memory.
  • FIG. 13 is an exploded perspective view showing an example of the configuration of a modified example of the magnetic recording cartridge.
  • the measurements are performed in an environment of 25°C ⁇ 2°C and 50% RH ⁇ 5% RH.
  • a coating material for forming a primer layer is applied onto a base layer to form a primer layer, and then a coating material for forming a magnetic layer is applied onto the primer layer to form a magnetic layer. It has been found that the application of the coating material for forming a magnetic layer results in uneven distribution of the binder contained in the primer layer in the thickness direction. It was also found that uneven distribution of the binder in the underlayer affects the reliability of the magnetic recording tape. Due to uneven distribution of the binder, the ratio of the inorganic material and the binder in the underlayer becomes non-uniform across the thickness direction.
  • the reliability of the magnetic recording tape decreases, and for example, the possibility of defects occurring that require rewriting during recording processing increases.
  • the inventors have discovered that by controlling the distribution of the binder in the underlayer, the reliability of the magnetic recording tape can be improved.
  • the magnetic recording medium of the present technology includes a magnetic layer, an underlayer, and a base layer in this order.
  • the underlayer includes a chlorine-containing binder
  • the underlayer includes a portion having a chlorine count equal to or greater than the following threshold value.
  • [Threshold] [average chlorine count in the undercoat layer] + 6 ⁇ [standard deviation obtained when calculating the average chlorine count]
  • the chlorine count corresponds to the amount of chlorine-containing binder.
  • the portion where the chlorine count is equal to or greater than the threshold has a higher chlorine count than the other portions of the undercoat layer, and contains more chlorine-containing binder than the other portions. In other words, the portion where the chlorine count is equal to or greater than the threshold is a portion where the chlorine-containing binder is unevenly distributed.
  • the width in the thickness direction of the portion that is equal to or greater than the threshold i.e., the uneven distribution width
  • the width in the thickness direction of the portion that is equal to or greater than the threshold is controlled, thereby improving the reliability of the magnetic recording medium, for example, the reliability during running for performing recording processing.
  • the thickness of the portion of the underlayer where the chlorine count is equal to or greater than the following threshold value may be, for example, 130 nm or less, preferably 125 nm or less, and more preferably 120 nm or less, 115 nm or less, 110 nm or less, 105 nm or less, 100 nm or less, 95 nm or less, or 90 nm or less.
  • the thickness of the portion where the thickness is equal to or greater than the threshold value means the length of the portion where the thickness is equal to or greater than the threshold value in the thickness direction of the magnetic recording medium.
  • the thickness of the portion may be, for example, 30 nm or more, 40 nm or more, or 50 nm or more.
  • the thickness of the portion that is equal to or greater than the threshold value fall within the above-mentioned numerical range, i.e., by having such a small uneven distribution width, the reliability of the magnetic recording medium can be improved, and for example, the occurrence of rewrite during recording processing can be prevented.
  • the thickness of the portion of the underlayer where the chlorine count is equal to or greater than the threshold may be, for example, preferably 13% or less of the thickness of the underlayer, more preferably 12% or less, 11% or less, and even more preferably 10% or less, 9.5% or less, or 9% or less.
  • the thickness of the portion where the chlorine count is equal to or greater than the threshold means the length of the portion where the chlorine count is equal to or greater than the threshold in the thickness direction of the magnetic recording medium.
  • the thickness of the portion may be, for example, 4% or more or 5% or more.
  • the thickness of the portion that is equal to or greater than the threshold value fall within the above-mentioned numerical range, i.e., by having such a small uneven distribution width, the reliability of the magnetic recording medium can be improved, and for example, the occurrence of rewrite during recording processing can be prevented.
  • the portion having a value equal to or greater than the threshold value is present on the base layer side of the underlayer.
  • the portion having a value equal to or greater than the threshold value may be present in the base layer side region.
  • the portion of the underlayer that is equal to or greater than the threshold value may be present within 200 nm, preferably within 150 nm, and particularly preferably within 130 nm, 120 nm, 110 nm, or 100 nm of the interface between the underlayer and the base layer.
  • the portion that is equal to or greater than the threshold value may be present so as to be in contact with the interface between the underlayer and the base layer. Controlling the positions of the portions where the concentration is above the threshold, that is, the positions of the portions where the chlorine-containing binder is unevenly distributed, also contributes to improving the reliability of the magnetic recording medium.
  • Some of the chlorine-containing binder is adsorbed to the inorganic material contained in the underlayer, while some is present without being adsorbed to the inorganic material.
  • the uneven distribution of the chlorine-containing binder described above is believed to be mainly due to the chlorine-containing binder not being adsorbed to the inorganic material. It is believed that the reliability of the magnetic recording medium can be improved by controlling the uneven distribution of the chlorine-containing binder. This will be described in more detail below.
  • the solvent in the paint affects the distribution state of the binder contained in the already formed undercoat layer, and in particular affects the distribution state of the binder that is present without being adsorbed to the inorganic material.
  • the possibility of powder falling off may increase in the early stages of use of the magnetic recording medium, which may reduce the reliability of the magnetic recording medium. For example, when a large number of reels of magnetic recording tape are run in one round trip or when full-surface recording is performed on a large number of reels of magnetic recording tape, the reliability of the magnetic recording tape may be adversely affected.
  • the reliability of the magnetic recording medium can be improved. For example, the possibility of defects that require rewriting during recording processing can be reduced.
  • the reliability is improved because the lubricant contained in the underlayer is appropriately supplied to the surface of the magnetic recording medium by controlling the uneven distribution.
  • the uneven distribution is caused by the chlorine-containing binder that is not adsorbed to the inorganic material as described above.
  • the chlorine-containing binder that is not adsorbed to the inorganic material can block the pores that supply the lubricant to the surface, and prevent the lubricant from being supplied to the surface of the magnetic recording medium. It is believed that by reducing the width of the uneven distribution, the range in which the chlorine-containing binder that is not adsorbed to the inorganic material is present is narrowed, thereby making it possible to appropriately supply the lubricant to the surface of the magnetic recording medium.
  • the width of the uneven distribution smaller and having the uneven distribution exist in the base layer, it is possible to more effectively prevent the supply of lubricant from being hindered due to the chlorine-containing binder blocking pores.
  • the chlorine-containing binder that is not adsorbed to the inorganic material may be present in a certain amount on the interface side between the magnetic layer and the undercoat layer. In this case, the chlorine-containing binder that is not adsorbed to the inorganic material may be likely to block the pores. Therefore, the thickness of the above-mentioned part is preferably 1/25 or more of the thickness of the undercoat layer, more preferably 1/20 or more.
  • the off-track phenomenon refers to the absence of the target track at the track position where the magnetic head should read, or the magnetic head reading information at the wrong track position, or the state in which information is read across two tracks and thus the correct information is not obtained. Reliability can be improved by controlling the uneven distribution of the chlorine-containing binder so that excess chlorine-containing binder does not remain on the magnetic layer side.
  • the inventors discovered that the parameters Q and R, which are related to the amount of variation in the dimension of the magnetic recording medium in the track width direction relative to the magnetic head due to changes in the temperature and humidity environment, i.e., the amount of variation in the width of the magnetic recording medium when the position of the magnetic head is used as the reference, affect the amount of variation in the track width, and found that in addition to ensuring reliability by controlling the uneven distribution of the chlorine-containing binder, it is possible to ensure overall reliability, combining shape stability and running stability, by adjusting the indicators Q and R within specific ranges.
  • the magnetic recording cartridge may be driven in an environment where the temperature is kept constant but the humidity is not regulated, or the temperature is kept constant but the humidity is not regulated, thereby reducing the cost of environmental management. Therefore, even in such an environment, it is required that the deformation amount of the magnetic recording medium with respect to temperature and humidity is small. Under such circumstances, the inventor has found that the humidity expansion coefficient of the magnetic recording medium when the environmental temperature is kept constant and the temperature expansion coefficient of the magnetic recording medium when the environmental humidity is kept constant differ depending on the environmental temperature and environmental humidity that are kept constant.
  • the present technology provides a magnetic recording medium that can reduce the fluctuation in the deformation amount even in an environment where the temperature and humidity change or in an environment where either is constant, by optimizing the temperature expansion coefficient and humidity expansion coefficient of the magnetic recording medium, and can ensure overall reliability by combining shape stability and running stability.
  • the inventors have discovered that by setting the first index Q and the second index R, which are parameters relating to the amount of variation in the dimension of the magnetic recording medium in the track width direction relative to the magnetic head accompanying changes in the temperature and humidity environment, i.e., the amount of variation in the width of the magnetic recording medium when the position of the magnetic head is used as the reference, to appropriate values, it is possible to reduce the variation in the amount of deformation even in environments where temperature and humidity change, and ensure overall reliability that combines shape stability and running stability. Note that the smaller the values of the first index Q and the second index R, the smaller the amount of variation in width.
  • the magnetic recording medium according to the present technology has a first index Q of ⁇ 250 ppm or more and 250 ppm or less.
  • Q 50[°C] ⁇ (CTH-CTQ)
  • CTH represents the temperature expansion coefficient [ppm/°C] of the magnetic head that performs recording and reproduction of the magnetic recording medium
  • CTQ represents the temperature expansion coefficient [ppm/°C] of the magnetic recording medium that is the most deviated from the temperature expansion coefficient of the magnetic head in a relative humidity environment of 10% RH to 80% RH.
  • the magnetic head refers to the magnetic head used in a recording and reproduction device (drive) that corresponds to the standard, in the case of a magnetic recording medium that corresponds to a standard such as LTO.
  • the temperature expansion coefficient of the magnetic head is preferably 6.0 ppm/°C to 8.0 ppm/°C, for example, 7.0 ppm/°C, in a relative humidity environment of 10% RH to 80% RH.
  • the measurement method of CTH and CTQ will be described in 2. (3) below. Therefore, for example, when the magnetic recording medium 10 is run in the recording and reproducing device 30, the temperature expansion coefficient of the magnetic recording medium 10 and the temperature expansion coefficient of the magnetic head can be made close to each other by adjusting the first index Q to an appropriate value. Therefore, even if the environmental temperature changes, the deformation amount of the magnetic recording medium 10 and the deformation amount of the magnetic head become approximately the same, and the relative positional relationship between the magnetic recording medium 10 and the magnetic head is maintained.
  • the deviation between the deformation amount of the magnetic recording medium 10 in the track width direction and the deformation amount of the magnetic head in the track width direction can be made smaller than the off-track margin. Therefore, the recording density of the magnetic recording medium 10 can be improved.
  • the drive's tape width adjustment mechanism e.g., tension control or head tilt mechanism
  • the drive's tape width adjustment mechanism can be adjusted to accommodate variations in the width of the magnetic recording medium.
  • the magnetic recording medium of the present technology has a second index R of ⁇ 750 ppm or more and 750 ppm or less.
  • R 70[%RH] ⁇ (CHH-CHR)
  • CHH represents the humidity expansion coefficient [ppm/% RH] of the magnetic head that performs recording and reproduction on this magnetic recording medium
  • CHR represents the humidity expansion coefficient [ppm/% RH] that is the most deviated from the humidity expansion coefficient of the magnetic head among the humidity expansion coefficients of the magnetic recording medium in a temperature environment of 10° C. to 60° C.
  • the humidity expansion coefficient of the magnetic head is preferably ⁇ 0.5 ppm/° C.
  • the humidity expansion coefficient of the magnetic recording medium 10 and the humidity expansion coefficient of the magnetic head can be made close to each other by adjusting the second index R to an appropriate value. Therefore, even if a change in environmental humidity occurs, the deformation amount of the magnetic recording medium 10 and the deformation amount of the magnetic head become approximately the same, and the relative positional relationship between the magnetic recording medium 10 and the magnetic head is maintained.
  • the deviation between the deformation amount of the magnetic recording medium 10 in the track width direction and the deformation amount of the magnetic head in the track width direction can be made smaller than the off-track margin. Therefore, the recording density of the magnetic recording medium 10 can be improved.
  • the index R is within the above range, variations in the width of the magnetic recording medium can be accommodated by adjusting the drive's tape width adjustment mechanism (e.g., tension control or head tilt mechanism).
  • the magnetic recording medium of the present technology preferably has an environmental relative humidity between 10% RH and 80% RH such that the temperature expansion coefficient ⁇ of the magnetic recording medium 10 is 6.0 ppm/°C or more and 8.0 ppm/°C or less. If these conditions are met, for example, when the magnetic recording medium 10 is run in a recording and reproducing device 30 described later, the temperature expansion coefficient of the magnetic recording medium 10 and the temperature expansion coefficient of the magnetic head can be made closer to each other by adjusting the surrounding environmental relative humidity to an appropriate relative humidity between 10% RH and 80% RH.
  • the deformation amount of the magnetic recording medium and the deformation amount of the magnetic head become approximately the same, and the relative positional relationship between the magnetic recording medium and the magnetic head is maintained. Therefore, for example, when recording and reproducing the magnetic recording medium 10 while running the magnetic recording medium 10 in the recording and reproducing device 30, the deviation between the deformation amount of the magnetic recording medium 10 in the track width direction and the deformation amount of the magnetic head in the track width direction can be made smaller than the off-track margin.
  • any one of the temperature expansion coefficient ⁇ in a relative humidity environment of 10% RH, the temperature expansion coefficient ⁇ in a relative humidity environment of 40% RH, and the temperature expansion coefficient ⁇ in a relative humidity environment of 80% RH should be 4.5 ppm/°C or more and 9.5 ppm/°C or less, or even better, all of them should be 4.5 ppm/°C or more and 9.5 ppm/°C or less.
  • the temperature expansion coefficient of the magnetic recording medium 10 and the temperature expansion coefficient of the magnetic head can be made close to each other even if the surrounding environment is adjusted to a relative humidity between 10% RH and 80% RH. Therefore, even if a change in the environmental temperature occurs, the deformation amount of the magnetic recording medium and the deformation amount of the magnetic head become approximately the same, and the relative positional relationship between the magnetic recording medium and the magnetic head is maintained.
  • the deviation between the deformation amount in the track width direction of the magnetic recording medium 10 and the deformation amount in the track width direction of the magnetic head can be made smaller than the off-track margin.
  • the humidity expansion coefficient ⁇ of the magnetic recording medium 10 is ⁇ It is preferable that the environmental temperature is 4.0 ppm/°C or more and 4.0 ppm/°C or less. If these conditions are satisfied, for example, when the magnetic recording medium 10 is run in the recording and reproducing device 30, the humidity expansion coefficient of the magnetic recording medium 10 and the humidity expansion coefficient of the magnetic head can be made close to each other by adjusting the surrounding environment to an appropriate temperature between 10°C and 60°C. Therefore, even if a change in the environmental humidity occurs, the deformation amount of the magnetic recording medium and the deformation amount of the magnetic head become approximately the same, and the relative positional relationship between the magnetic recording medium and the magnetic head is maintained.
  • the deviation between the deformation amount of the magnetic recording medium 10 in the track width direction and the deformation amount of the magnetic head in the track width direction can be made smaller than the off-track margin.
  • the magnetic recording medium according to the present technology may preferably be a long magnetic recording medium, for example, a magnetic recording tape (particularly a long magnetic recording tape).
  • the magnetic recording medium according to the present technology may have a magnetic layer, a non-magnetic layer (underlayer), a base layer, and a back layer in this order, and may include other layers in addition to these layers.
  • the other layers may be appropriately selected depending on the type of magnetic recording medium.
  • the magnetic recording medium may be a coating-type magnetic recording medium, that is, a magnetic recording medium manufactured by coating a base layer with a material (particularly a paint) that forms other layers and then drying it.
  • the average thickness (average total thickness) tT of the magnetic recording medium according to the present technology may be, for example, 5.3 ⁇ m or less, 5.2 ⁇ m or less, 5.1 ⁇ m or less, preferably 5.0 ⁇ m or less, 4.9 ⁇ m or less, more preferably 4.8 ⁇ m or less, and even more preferably 4.6 ⁇ m or less or 4.4 ⁇ m or less. Since the magnetic recording medium is thus thin, for example, the length of the tape wound into one magnetic recording cartridge can be made longer, thereby increasing the recording capacity per one magnetic recording cartridge.
  • the lower limit of the average thickness (average total thickness) tT of the magnetic recording medium is not particularly limited, but is, for example, 3.5 ⁇ m ⁇ tT .
  • the method for measuring the average thickness of the magnetic recording medium will be described in 2. (3) below.
  • the average thickness tm of the magnetic layer of the magnetic recording medium according to the present technology may be preferably 80 nm or less, more preferably 70 nm or less, even more preferably 60 nm or less, 50 nm or less, and even more preferably 40 nm or less.
  • the lower limit of the average thickness tm of the magnetic layer is not particularly limited, but is preferably 30 nm or more. The method for measuring the average thickness of the magnetic layer will be described in 2.(3) below.
  • the average thickness of the underlayer (also called the non-magnetic layer) of the magnetic recording medium according to the present technology can be 1100 nm or less, preferably 1050 nm or less, 1000 nm or less, 950 nm or less, more preferably 900 nm or less, 850 nm or less, or 800 nm or less, or 700 nm or less, and even more preferably 600 nm or less.
  • the lower limit of the average thickness of the underlayer is not particularly limited, but is preferably 200 nm or more, and more preferably 300 nm or more. The method for measuring the average thickness of the underlayer is explained in 2. (3) below.
  • the average thickness of the base layer (also referred to as the substrate layer) of the magnetic recording medium according to the present technology may be preferably 4.4 ⁇ m or less, more preferably 4.2 ⁇ m or less, 4.0 ⁇ m or less, 3.8 ⁇ m or less, or 3.6 ⁇ m or less, and even more preferably 3.4 ⁇ m or less, 3.2 ⁇ m or less, or 3.0 ⁇ m or less.
  • the lower limit of the average thickness of the base layer is not particularly limited, but may be, for example, preferably 2.0 ⁇ m or more, 2.2 ⁇ m or more, 2.4 ⁇ m or more, and more preferably 2.5 ⁇ m or more.
  • the method for measuring the average thickness of the base layer is described below in 2. (3).
  • the average thickness of the back layer of the magnetic recording medium according to the present technology may be preferably 0.6 ⁇ m or less, more preferably 0.5 ⁇ m or less, even more preferably 0.4 ⁇ m or less, 0.3 ⁇ m or less, 0.25 ⁇ m or less, or 0.2 ⁇ m or less.
  • the lower limit of the average thickness of the back layer is not particularly limited, but may be, for example, preferably 0.1 ⁇ m or more, more preferably 0.15 ⁇ m or more.
  • the method for measuring the average thickness of the back layer is described below in 2. (3).
  • the total thickness of the magnetic layer and the underlayer of the magnetic recording medium according to the present technology is preferably 1000 nm or less, and may be, for example, 950 nm or less, 900 nm or less, or 800 nm or less.
  • the total may be, for example, 300 nm or more, particularly 400 nm or more.
  • the magnetic recording medium according to the present technology may have, for example, at least one data band and at least two servo bands.
  • the number of data bands may be, for example, 2 to 10, particularly 3 to 6, and more particularly 4 or 5.
  • the number of servo bands may be, for example, 3 to 11, particularly 4 to 7, and more particularly 5 or 6.
  • These servo bands and data bands may be arranged, for example, so as to extend in the longitudinal direction of a long magnetic recording medium (particularly a magnetic recording tape), particularly so as to be substantially parallel.
  • the data band and the servo band may be provided on the magnetic layer.
  • An example of a magnetic recording medium having such a data band and a servo band is a magnetic recording tape conforming to the LTO (Linear Tape-Open) standard.
  • the magnetic recording medium according to the present technology may be a magnetic recording tape conforming to the LTO standard.
  • the magnetic recording medium according to the present technology may be a magnetic recording tape conforming to the LTO8 standard or a later standard (e.g., LTO9, LTO10, LTO11, or LTO12, etc.).
  • the width of the long magnetic recording medium (particularly the magnetic recording tape) according to the present technology may be, for example, 5 mm to 30 mm, particularly 7 mm to 25 mm, more particularly 10 mm to 20 mm, and even more particularly 11 mm to 19 mm.
  • the length of the long magnetic recording medium (particularly the magnetic recording tape) may be, for example, 500 m to 1500 m.
  • the tape width according to the LTO8 standard is 12.65 mm and the length is 960 m.
  • the magnetic recording medium 10 is, for example, a magnetic recording medium that has been subjected to a vertical orientation treatment.
  • the magnetic recording medium 10 includes a long base layer (also called a substrate) 11, an underlayer 12 provided on one main surface of the base layer 11, a magnetic layer (also called a recording layer) 13 provided on the underlayer 12, and a back layer 14 provided on the other main surface of the base layer 11.
  • the surface on which the magnetic layer 13 is provided is referred to as the magnetic surface
  • the surface opposite to the magnetic surface (the surface on which the back layer 14 is provided) is referred to as the back surface.
  • the magnetic recording medium 10 has an elongated shape, and runs in the longitudinal direction during recording and playback.
  • the magnetic recording medium 10 may be configured to be capable of recording signals at a shortest recording wavelength of preferably 60 nm or less, more preferably 50 nm or less, even more preferably 45 nm or less, and particularly preferably 40 nm or less, and may be used, for example, in a recording and playback device whose shortest recording wavelength is within the above range.
  • This recording and playback device may be equipped with a ring-type head as a recording head.
  • the recording track width is, for example, 2 ⁇ m or less.
  • the base layer 11 can function as a support for the magnetic recording medium 10 and can be, for example, a flexible, long, non-magnetic substrate, particularly a non-magnetic film.
  • the base layer 11 can contain, for example, at least one of polyester resins, polyolefin resins, cellulose derivatives, vinyl resins, aromatic polyether ketone resins, and other polymer resins. When the base layer 11 contains two or more of the above materials, the two or more materials can be mixed, copolymerized, or laminated.
  • the polyester-based resin may be, for example, one or a mixture of two or more of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PBT (polybutylene terephthalate), PBN (polybutylene naphthalate), PCT (polycyclohexylene dimethylene terephthalate), PEB (polyethylene-p-oxybenzoate), and polyethylene bisphenoxycarboxylate.
  • the base layer 11 may be formed from PET or PEN.
  • the polyolefin resin may be, for example, one or a mixture of two or more of PE (polyethylene) and PP (polypropylene).
  • the cellulose derivative may be, for example, one or a mixture of two or more of cellulose diacetate, cellulose triacetate, CAB (cellulose acetate butyrate), and CAP (cellulose acetate propionate).
  • the vinyl resin may be, for example, one or a mixture of two or more of PVC (polyvinyl chloride) and PVDC (polyvinylidene chloride).
  • the aromatic polyetherketone resin may be, for example, one or a mixture of two or more of PEK (polyetherketone), PEEK (polyetheretherketone), PEKK (polyetherketoneketone), and PEEKK (polyetheretherketoneketone).
  • the base layer 11 may be formed from PEEK.
  • the other polymer resin may be, for example, one or a mixture of two or more of PA (polyamide, nylon), aromatic PA (aromatic polyamide, aramid), PI (polyimide), aromatic PI (aromatic polyimide), PAI (polyamideimide), aromatic PAI (aromatic polyamideimide), PBO (polybenzoxazole, e.g. Zylon (registered trademark), polyether, polyetherester, PES (polyethersulfone), PEI (polyetherimide), PSF (polysulfone), PPS (polyphenylene sulfide), PC (polycarbonate), PAR (polyarylate), and PU (polyurethane).
  • PA polyamide, nylon
  • aromatic PA aromatic polyamide, aramid
  • PI polyimide
  • PAI polyamideimide
  • PAI aromatic PAI
  • PBO polybenzoxazole, e.g. Zylon (registered trademark)
  • polyether polyetherester
  • the base layer may be formed from a resin that does not contain chlorine, and in particular from a polyester-based resin that does not contain chlorine.
  • the base layer may also be formed from a resin that contains chlorine.
  • the magnetic layer 13 may be, for example, a perpendicular recording layer.
  • the magnetic layer 13 includes magnetic powder.
  • the magnetic layer 13 may further include a binder.
  • the magnetic layer 13 may further include non-magnetic particles.
  • the magnetic layer 13 may further include additives such as a lubricant and an anti-rust agent, as necessary.
  • the magnetic layer 13 is preferably a magnetic layer that is vertically oriented.
  • vertical orientation means that the squareness ratio S1 measured in the longitudinal direction (travel direction) of the magnetic recording medium 10 is 35% or less.
  • the magnetic particles constituting the magnetic powder contained in the magnetic layer 13 may include, but are not limited to, hexagonal ferrite, epsilon iron oxide ( ⁇ iron oxide), Co-containing spinel ferrite, gamma hematite, magnetite, chromium dioxide, cobalt-coated iron oxide, and metal.
  • the magnetic powder may be one of these, or a combination of two or more.
  • the magnetic powder may include hexagonal ferrite, ⁇ iron oxide, or Co-containing spinel ferrite.
  • the magnetic powder is hexagonal ferrite.
  • the hexagonal ferrite may particularly preferably include at least one of Ba and Sr.
  • the ⁇ iron oxide may particularly preferably include at least one of Al and Ga.
  • the shape of the magnetic particles depends on the crystal structure of the magnetic particles.
  • barium ferrite (BaFe) and strontium ferrite can be hexagonal plate-shaped.
  • ⁇ -iron oxide can be spherical.
  • Cobalt ferrite can be cubic.
  • Metal can be spindle-shaped.
  • the hexagonal ferrite particles contain Fe and a metal M1 other than Fe.
  • the metal M1 contains an alkaline earth metal.
  • the alkaline earth metal may contain at least one or more of Sr, Ba, and Ca, and among these metals, it is preferable to contain Sr.
  • the metal M1 may contain Pb in addition to the alkaline earth metal.
  • the hexagonal ferrite particles may further contain a metal M2 in addition to Fe and the metal M1.
  • the metal M2 includes, for example, one selected from the group consisting of rare earth elements, transition metal elements other than Fe, and metal elements of Group 13 of the periodic table, and among these, at least one selected from the group consisting of Ti, Al, and Nd is preferable.
  • the hexagonal ferrite particles may be barium ferrite particles or strontium ferrite particles.
  • the strontium ferrite particles refer to hexagonal ferrite particles in which the atomic ratio of Sr to metal M1 is 50 atomic % or more. Therefore, the hexagonal ferrite particles containing Sr and metal M1 other than Sr are included in the strontium ferrite particles when the atomic ratio of Sr to metal M1 is 50 atomic % or more.
  • metal M1 contains Sr and Ba
  • the hexagonal ferrite particles in which the atomic ratio of Sr to the total amount of Sr and Ba is 50 atomic % or more are called strontium ferrite particles.
  • the hexagonal ferrite may have an average composition represented by the following general formula (1): Sr(1-x) ⁇ xFe(12-y) ⁇ yO 19 ...(1)
  • ⁇ represents at least one element selected from the group consisting of Ba, Ca, and Pb
  • ⁇ represents at least one element selected from the group consisting of rare earth elements, transition metal elements other than Fe, and metal elements of Group 13 of the periodic table
  • x is within the range of 0 ⁇ x ⁇ 0.9, preferably 0 ⁇ x ⁇ 0.7, and more preferably 0.3 ⁇ x ⁇ 0.7
  • y represents 0 ⁇ y ⁇ 0.80, preferably 0.22 ⁇ y ⁇ 0.80, and more preferably 0.26 ⁇ y ⁇ 0.80.
  • the average particle size of the magnetic powder may be preferably 30 nm or less, more preferably 25 nm or less, even more preferably 20 nm or less, 18 nm or less, 16 nm or less, 14 nm or less, or 12 nm or less.
  • the average particle size may be, for example, 8 nm or more, preferably 9 nm or more, more preferably 10 nm or more.
  • the average particle size of the magnetic powder may be 8 nm or more and 30 nm or less, 8 nm or more and 25 nm or less, 9 nm or more and 20 nm or less, 9 nm or more and 16 nm or less, or 9 nm or more and 14 nm or less.
  • the average particle size of the magnetic powder is the upper limit value or less (for example, 50 nm or less, particularly 30 nm or less)
  • good electromagnetic conversion characteristics for example, SNR
  • the average particle size of the magnetic powder is the lower limit value or more (for example, 10 nm or more, preferably 12 nm or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (for example, SNR) can be obtained.
  • the average aspect ratio of the magnetic powder may be preferably 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.8 or less, and even more preferably 1.5 or more and 2.5 or less.
  • the average particle size and average aspect ratio of the magnetic powder can be determined as follows.
  • the magnetic recording medium (hereinafter also referred to as "magnetic tape") contained in the magnetic recording cartridge is unwound, and the magnetic tape to be measured is cut out to about 50 mm.
  • the cut-out position may be 30 m in the longitudinal direction from the connection part 221 between the magnetic tape T and the leader tape LT.
  • the magnetic tape to be measured is processed by the FIB method or the like to be thinned.
  • a carbon layer and a tungsten layer are formed as protective films as a pretreatment for observing the TEM image of the cross section described later.
  • the carbon layer is formed on the surface of the magnetic layer side and the surface of the back layer side of the magnetic tape by the vapor deposition method, and the tungsten layer is further formed on the surface of the magnetic layer side by the vapor deposition method or the sputtering method.
  • the thinning is performed along the length direction (longitudinal direction) of the magnetic tape. In other words, this slicing creates a cross section that is parallel to both the length and thickness of the magnetic tape.
  • the cross section of the obtained thin sample is observed using a transmission electron microscope (Hitachi High-Technologies Corporation H-9500) at an acceleration voltage of 200 kV and a total magnification of 500,000 times to ensure that the entire magnetic layer is included in the thickness direction of the magnetic layer, and a TEM photograph is taken.
  • TEM photographs are prepared in sufficient numbers to extract 50 particles for which the plate diameter DB and plate thickness DA (see Figure 2A) shown below can be measured.
  • the size of the hexagonal ferrite particles (hereinafter referred to as "particle size") is defined as the plate diameter DB, which is the long diameter of the plate surface or base, when the shape of the particle observed in the above TEM photograph is plate-like or columnar (however, the thickness or height is smaller than the long diameter of the plate surface or base) as shown in Figure 2A.
  • the thickness or height of the particle observed in the above TEM photograph is defined as the plate thickness DA.
  • the long diameter means the longest diagonal distance.
  • the thickness or height of a particle is not constant within a single particle, the thickness or height of the maximum particle is defined as the plate thickness DA.
  • 50 particles are selected from the TEM photograph based on the following criteria. Particles that are partially outside the field of view of the TEM photograph are not measured, and only particles that have a clear outline and exist in isolation are measured. If there are overlapping particles, those with a clear boundary between them and whose overall shape can be determined are measured as individual particles, but particles with unclear boundaries and whose overall shape cannot be determined are not measured as their shape cannot be determined.
  • 2B and 2C show examples of TEM photographs.
  • the particles indicated by the arrows a and d are selected because the plate thickness (thickness or height) DA of the particle can be clearly confirmed.
  • the plate thickness DA of each of the selected 50 particles is measured.
  • the plate thickness DA thus obtained is simply averaged (arithmetic mean) to obtain the average plate thickness DA ave .
  • the average plate thickness DA ave is the average particle plate thickness.
  • the plate diameter DB of each magnetic powder is measured.
  • 50 particles whose plate diameter DB of the particle can be clearly confirmed are selected from the TEM photograph taken.
  • the particles indicated by the arrows b and c are selected because the plate diameter DB can be clearly confirmed.
  • the plate diameter DB of each of the selected 50 particles is measured.
  • the plate diameter DB thus obtained is simply averaged (arithmetic mean) to obtain the average plate diameter DB ave .
  • the average plate diameter DB ave is the average particle size.
  • the average particle volume of the magnetic powder is preferably 1800 nm3 or less, more preferably 1600 nm3 or less, more preferably 1400 nm3 or less, even more preferably 1200 nm3 or less, 1000 nm3 or less, or even 900 nm3 or less.
  • the average particle volume of the magnetic powder may be preferably 500 nm3 or more, more preferably 700 nm3 or more.
  • the average particle volume of the magnetic powder is equal to or less than the upper limit (e.g., 2000 nm3 or less), good electromagnetic conversion characteristics (e.g., SNR) can be obtained in the high recording density magnetic recording medium 10.
  • the average particle volume of the magnetic powder is equal to or more than the lower limit (e.g., 500 nm3 or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (e.g., SNR) can be obtained.
  • the average particle volume of the magnetic powder is calculated as follows. First, the average plate thickness DA ave and the average plate diameter DB ave are calculated as described above in relation to the method for calculating the average particle size of the magnetic powder. Next, the average particle volume V of the magnetic powder is calculated using the following formula.
  • the magnetic powder may be barium ferrite magnetic powder or strontium ferrite magnetic powder, and more preferably barium ferrite magnetic powder.
  • Barium ferrite magnetic powder includes magnetic particles of iron oxide with barium ferrite as the main phase (hereinafter referred to as "barium ferrite particles").
  • Barium ferrite magnetic powder has high reliability in data recording, for example, its coercive force does not decrease even in a high temperature and high humidity environment. From this viewpoint, barium ferrite magnetic powder is preferred as the magnetic powder.
  • the average particle size of the barium ferrite magnetic powder may preferably be 30 nm or less, more preferably 25 nm or less, even more preferably 20 nm or less, 18 nm or less, 16 nm or less, 14 nm or less, or 12 nm or less.
  • the average particle size may be, for example, 8 nm or more, preferably 9 nm or more, more preferably 10 nm or more.
  • the average particle size of the magnetic powder may be 8 nm or more and 30 nm or less, 8 nm or more and 25 nm or less, 9 nm or more and 20 nm or less, 9 nm or more and 16 nm or less, or 9 nm or more and 14 nm or less.
  • the coercive force Hc1 measured in the thickness direction (perpendicular direction) of the magnetic recording medium 10 is preferably 2010 [Oe] or more and 3520 [Oe] or less, more preferably 2070 [Oe] or more and 3460 [Oe] or less, and even more preferably 2140 [Oe] or more and 3390 [Oe] or less.
  • the magnetic powder may preferably include a powder of nanoparticles containing ⁇ -iron oxide (hereinafter referred to as " ⁇ -iron oxide particles"). Even fine particles of ⁇ -iron oxide particles can achieve high coercivity. It is preferable that the ⁇ -iron oxide contained in the ⁇ -iron oxide particles has a preferential crystal orientation in the thickness direction (perpendicular direction) of the magnetic recording medium 10.
  • the ⁇ -iron oxide particles may have a composite particle structure. More specifically, the ⁇ -iron oxide particles include an ⁇ -iron oxide portion and a portion having soft magnetism or a portion having a higher saturation magnetization ⁇ s and a smaller coercive force Hc than ⁇ -iron oxide (hereinafter referred to as the "soft magnetic portion, etc.”).
  • the ⁇ -iron oxide portion contains ⁇ -iron oxide.
  • the ⁇ -iron oxide contained in the ⁇ -iron oxide portion preferably has ⁇ -Fe 2 O 3 crystals as a main phase, and more preferably is made of single-phase ⁇ -Fe 2 O 3 .
  • the soft magnetic portion is in contact with at least a portion of the ⁇ -iron oxide portion. Specifically, the soft magnetic portion may partially cover the ⁇ -iron oxide portion, or may cover the entire periphery of the ⁇ -iron oxide portion.
  • the soft magnetic portion (the magnetic portion having a higher saturation magnetization ⁇ s and a smaller coercive force Hc than ⁇ -iron oxide) includes, for example, a soft magnetic material such as ⁇ -Fe, a Ni-Fe alloy, or an Fe-Si-Al alloy.
  • ⁇ -Fe may be obtained by reducing the ⁇ -iron oxide contained in the ⁇ -iron oxide portion.
  • the portion having soft magnetic properties may contain, for example, Fe 3 O 4 , ⁇ -Fe 2 O 3 , or spinel ferrite.
  • the coercive force Hc of the ⁇ -iron oxide portion alone can be kept high to ensure thermal stability, while the coercive force Hc of the ⁇ -iron oxide particle (composite particle) as a whole can be adjusted to a coercive force Hc suitable for recording.
  • the ⁇ iron oxide particles may contain an additive instead of the structure of the composite particles, or may have the structure of the composite particles and contain an additive. In this case, part of the Fe in the ⁇ iron oxide particles is replaced with the additive.
  • the additive is a metal element other than iron, preferably a trivalent metal element, more preferably at least one selected from the group consisting of Al, Ga and In, and even more preferably at least one selected from the group consisting of Al and Ga.
  • the ⁇ -iron oxide containing the additive is an ⁇ -Fe2 - xMxO3 crystal (wherein M is a metal element other than iron, preferably a trivalent metal element, more preferably one or more selected from the group consisting of Al, Ga, and In; x is, for example, 0 ⁇ x ⁇ 1).
  • the average particle size (average maximum particle size) of the magnetic powder is preferably 22 nm or less, more preferably 8 nm to 22 nm, and even more preferably 12 nm to 22 nm.
  • the area with a size of 1/2 the recording wavelength becomes the actual magnetization area. Therefore, by setting the average particle size of the magnetic powder to less than half the shortest recording wavelength, a good SNR can be obtained. Therefore, when the average particle size of the magnetic powder is 22 nm or less, good electromagnetic conversion characteristics (e.g., SNR) can be obtained in a high recording density magnetic recording medium 10 (e.g., a magnetic recording medium 10 configured to be able to record signals at the shortest recording wavelength of 44 nm or less).
  • the average particle size of the magnetic powder is 8 nm or more, the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (e.g., SNR) can be obtained.
  • the average aspect ratio of the magnetic powder is preferably 1.0 or more and 3.0 or less, more preferably 1.0 or more and 2.9 or less, and even more preferably 1.0 or more and 2.5 or less.
  • the average aspect ratio of the magnetic powder is within the above numerical range, aggregation of the magnetic powder can be suppressed, and the resistance applied to the magnetic powder when the magnetic powder is vertically oriented in the process of forming the magnetic layer 13 can be suppressed. Therefore, the vertical orientation of the magnetic powder can be improved.
  • the average particle size and average aspect ratio of the magnetic powder can be determined as follows. First, the magnetic recording medium to be measured is cut out as described above for the case where the magnetic powder contains hexagonal ferrite particles. The magnetic recording medium to be measured is processed and sliced by FIB (Focused Ion Beam) method or the like. When the FIB method is used, a carbon film and a tungsten thin film are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below.
  • FIB Flucused Ion Beam
  • the carbon film is formed on the magnetic layer side surface and back layer side surface of the magnetic recording medium by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer side surface by a vapor deposition method or a sputtering method.
  • the slicing is performed along the length direction (longitudinal direction) of the magnetic recording medium. In other words, the slicing forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium.
  • the cross section of the obtained thin sample is observed using a transmission electron microscope (Hitachi High-Technologies Corporation H-9500) at an acceleration voltage of 200 kV and a total magnification of 500,000 times, so that the entire magnetic layer 13 is included in the thickness direction of the magnetic layer 13, and a TEM photograph is taken.
  • a transmission electron microscope Hagachi High-Technologies Corporation H-9500
  • the long axis length DL refers to the maximum distance between two parallel lines drawn from any angle so as to be tangent to the contour of each particle (the so-called maximum Feret diameter).
  • the short axis length DS refers to the maximum length of the particle in the direction perpendicular to the long axis (DL) of the particle.
  • the long axis lengths DL of the 50 measured particles are simply averaged (arithmetic mean) to determine the average long axis length DL ave .
  • the average long axis length DL ave thus determined is the average particle size of the magnetic powder.
  • the short axis lengths DS of the 50 measured particles are also simply averaged (arithmetic mean) to determine the average short axis length DS ave .
  • the average aspect ratio of the particles (DL ave /DS ave ) is then calculated from the average long axis length DL ave and the average short axis length DS ave .
  • the average particle volume of the magnetic powder is preferably 1800 nm3 or less, more preferably 1600 nm3 or less, more preferably 1400 nm3 or less, even more preferably 1200 nm3 or less, 1100 nm3 or less, or even 1000 nm3 or less.
  • the average particle volume of the magnetic powder may be preferably 500 nm3 or more, more preferably 700 nm3 or more.
  • the average particle volume of the magnetic powder is equal to or less than the upper limit (e.g., 2000 nm3 or less), good electromagnetic conversion characteristics (e.g., SNR) can be obtained in the high recording density magnetic recording medium 10.
  • the average particle volume of the magnetic powder is equal to or more than the lower limit (e.g., 500 nm3 or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (e.g., SNR) can be obtained.
  • the average particle volume of the magnetic powder can be found as follows.
  • the magnetic recording medium 10 is processed and sliced by FIB (Focused Ion Beam) method or the like.
  • FIB Flucused Ion Beam
  • a carbon film and a tungsten thin film are formed as protective films as a pretreatment for observing the cross-sectional TEM image described below.
  • the carbon film is formed on the magnetic layer side surface and back layer side surface of the magnetic recording medium 10 by a vapor deposition method, and the tungsten thin film is further formed on the magnetic layer side surface by a vapor deposition method or a sputtering method.
  • the slices are formed along the length direction (longitudinal direction) of the magnetic recording medium 10. In other words, the slices form a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic recording medium 10.
  • the obtained thin-section sample is observed using a transmission electron microscope (Hitachi High-Technologies Corporation H-9500) at an acceleration voltage of 200 kV and a total magnification of 500,000 times to observe the cross section of the magnetic layer 13 in the thickness direction so as to include the entire magnetic layer 13, and a TEM photograph is obtained. Note that the magnification and acceleration voltage may be adjusted appropriately depending on the type of device.
  • V ave particle volume
  • the coercive force Hc of the ⁇ iron oxide particles is preferably 2500 Oe or more, and more preferably 2800 Oe or more and 4200 Oe or less.
  • the magnetic powder may include a powder of nanoparticles (hereinafter also referred to as "cobalt ferrite particles") containing Co-containing spinel ferrite. That is, the magnetic powder may be cobalt ferrite magnetic powder.
  • the cobalt ferrite particles preferably have uniaxial crystal anisotropy.
  • the cobalt ferrite magnetic particles have, for example, a cubic or nearly cubic shape.
  • the Co-containing spinel ferrite may further include one or more selected from the group consisting of Ni, Mn, Al, Cu, and Zn in addition to Co.
  • Cobalt ferrite has, for example, an average composition represented by the following formula: C x M y Fe 2 O z
  • M is, for example, one or more metals selected from the group consisting of Ni, Mn, Al, Cu, and Zn.
  • x is a value within the range of 0.4 ⁇ x ⁇ 1.0.
  • y is a value within the range of 0 ⁇ y ⁇ 0.3.
  • x and y satisfy the relationship of (x+y) ⁇ 1.0.
  • z is a value within the range of 3 ⁇ z ⁇ 4.
  • a part of Fe may be substituted with another metal element.
  • the average particle size of the cobalt ferrite magnetic powder is preferably 21 nm or less, more preferably 19 nm or less.
  • the coercive force Hc of the cobalt ferrite magnetic powder is preferably 2500 Oe or more, more preferably 2600 Oe or more and 3500 Oe or less.
  • the average particle size of the magnetic powder is preferably 25 nm or less, more preferably 10 nm or more and 19 nm or less. Such a small average particle size of the magnetic powder makes it possible to obtain good electromagnetic conversion characteristics (e.g., SNR) in a high recording density magnetic recording medium 10. On the other hand, when the average particle size of the magnetic powder is 10 nm or more, the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (e.g., SNR) can be obtained.
  • the average aspect ratio and average particle size of the magnetic powder are determined in the same manner as when the magnetic powder contains ⁇ iron oxide particles.
  • the average particle volume of the magnetic powder is preferably 2000 nm3 or less, more preferably 1900 nm3 or less, more preferably 1800 nm3 or less, even more preferably 1700 nm3 or less, 1600 nm3 or less, or even 1500 nm3 or less.
  • the average particle volume of the magnetic powder may be preferably 500 nm3 or more, more preferably 700 nm3 or more.
  • the average particle volume of the magnetic powder is equal to or less than the upper limit (e.g., 2000 nm3 or less), good electromagnetic conversion characteristics (e.g., SNR) can be obtained in the high recording density magnetic recording medium 10.
  • the average particle volume of the magnetic powder is equal to or more than the lower limit (e.g., 500 nm3 or more), the dispersibility of the magnetic powder is further improved, and better electromagnetic conversion characteristics (e.g., SNR) can be obtained.
  • a binder a resin having a structure in which a cross-linking reaction has been imparted to a polyurethane resin or a vinyl chloride resin is preferable.
  • the binder is not limited to these, and other resins may be appropriately blended depending on the physical properties required for the magnetic recording medium 10.
  • the resin to be blended so long as it is a resin that is generally used in coating-type magnetic recording media 10.
  • binder examples include polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-acrylonitrile copolymer, acrylate-vinyl chloride-vinylidene chloride copolymer, acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-vinyl chloride copolymer, methacrylate-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene-butad
  • the binder may be a thermosetting resin or a reactive resin, examples of which include phenolic resin, epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, polyamine resin, and urea formaldehyde resin.
  • examples of the polar functional group include side chain type groups having terminal groups of -NR1R2, -NR1R2R3 + X- , and main chain type groups of >NR1R2 + X- .
  • R1, R2, and R3 are hydrogen atoms or hydrocarbon groups
  • X- is a halogen element ion such as fluorine, chlorine, bromine, or iodine, or an inorganic or organic ion.
  • examples of the polar functional group include -OH, -SH, -CN, and an epoxy group.
  • the magnetic layer includes a chlorine-containing binder.
  • the chlorine-containing binder may be a chlorine-containing resin.
  • the chlorine-containing resin is a resin that includes a chlorine atom as at least one of the elements constituting the resin.
  • the chlorine-containing binder is, for example, a vinyl chloride resin.
  • chlorine-containing binder examples include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-vinyl chloride-vinylidene chloride copolymer, acrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer, and synthetic rubber.
  • the content of the chlorine-containing binder in the magnetic layer may be, for example, preferably 30 parts by mass or more, more preferably 35 parts by mass or more, and even more preferably 40 parts by mass or more, per 100 parts by mass of magnetic powder. Also, the content may be, for example, preferably 70 parts by mass or less, more preferably 65 parts by mass or less, and even more preferably 60 parts by mass or less, per 100 parts by mass of magnetic powder.
  • the magnetic layer may further contain a chlorine-free binder in addition to the chlorine-containing binder.
  • the chlorine-free binder may be a chlorine-free resin.
  • the chlorine-free resin may contain, for example, a polyurethane-based resin.
  • the polyurethane-based resin may be, for example, a urethane-modified copolymer polyester.
  • the urethane-modified copolymer polyester may be a urethane-modified copolymer polyester having an aromatic polyester as a basic skeleton and a urethane component in the side chain, or a urethane-modified copolymer polyester containing an ester repeat unit and a urethane repeat unit in the basic skeleton.
  • the content of the chlorine-free binder in the magnetic layer may be, for example, preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of magnetic powder. Also, the content may be, for example, preferably 10 parts by mass or less, more preferably 9 parts by mass or less, and even more preferably 8 parts by mass or less, per 100 parts by mass of magnetic powder.
  • the magnetic layer may contain a lubricant.
  • the lubricant may be, for example, one or more selected from fatty acids and/or fatty acid esters, and may preferably contain both fatty acids and fatty acid esters.
  • the fatty acid may preferably be a compound represented by the following general chemical formula (1) or general chemical formula (2).
  • the fatty acid may contain one or both of the compound represented by the following general chemical formula (1) and the compound represented by the general chemical formula (2).
  • the fatty acid ester may preferably be a compound represented by the following general chemical formula (3), (4), or (5).
  • the fatty acid ester may contain any one of the compounds represented by the following general chemical formula (3), (4), and (5), or may contain two or more selected from these.
  • the lubricant contains either one or both of the compound represented by general chemical formula (1) and the compound represented by general chemical formula (2), and either one or more of the compound represented by general chemical formula (3), the compound represented by general chemical formula (4), and the compound represented by general chemical formula (5), so that an increase in the dynamic friction coefficient of the magnetic recording medium due to repeated recording or reproduction can be suppressed.
  • the lubricant may be, for example, an ester of a monobasic fatty acid having 10 to 24 carbon atoms with any one of monohydric to hexahydric alcohols having 2 to 12 carbon atoms, a mixed ester thereof, a di-fatty acid ester, a tri-fatty acid ester, etc.
  • the lubricant include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, butyl stearate, pentyl stearate, heptyl stearate, octyl stearate, isooctyl stearate, octyl myristate, etc.
  • the magnetic layer may contain any one or more of these.
  • the amount of the lubricant may be, for example, preferably 1 part by mass or more, and more preferably 2 parts by mass or more, per 100 parts by mass of the magnetic powder. Also, the amount of the lubricant may be, for example, preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, per 100 parts by mass of the magnetic powder.
  • the magnetic layer 13 may further contain non-magnetic reinforcing particles such as aluminum oxide ( ⁇ , ⁇ , or ⁇ alumina), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile or anatase titanium oxide), etc.
  • non-magnetic reinforcing particles such as aluminum oxide ( ⁇ , ⁇ , or ⁇ alumina), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (rutile or anatase titanium oxide), etc.
  • the magnetic layer may contain first particles having electrical conductivity and second particles having a Mohs hardness of 7 or more.
  • the first particles and the second particles may form protrusions on the surface of the magnetic layer side.
  • the magnetic layer has an uneven shape formed by the protrusions on the surface of the magnetic layer side (hereinafter referred to as the "magnetic surface").
  • the first particles can prevent an increase in frictional force during the running of the magnetic recording tape, and function as, for example, a solid lubricant component.
  • the second particles can provide an abrasive effect (and an anchor effect) for magnetic head cleaning. It is considered that by including these two components in the magnetic layer of the magnetic recording tape, an increase in frictional force can be prevented and the magnetic head can be cleaned, thereby improving running performance.
  • the undercoat layer 12 is a non-magnetic layer containing non-magnetic powder and a binder as the main components. If necessary, the undercoat layer 12 may further contain at least one additive selected from the group consisting of other particles, lubricants, hardeners, and rust inhibitors.
  • the non-magnetic powder contained in the undercoat layer 12 includes, for example, at least one type selected from inorganic particles and organic particles, and particularly includes at least one type selected from inorganic particles.
  • One type of non-magnetic powder may be used alone, or two or more types of non-magnetic powder may be used in combination.
  • the non-magnetic inorganic particles may be, for example, one or a combination of two or more types selected from metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides.
  • the inorganic particles may be, for example, one or two or more types selected from iron oxide, aluminum oxide, carbon black, iron oxyhydroxide, hematite, titanium oxide, silicon oxide, titanium carbide, silicon carbide, diamond, and calcium carbonate.
  • the shape of the non-magnetic powder may be, for example, various shapes such as needle-like, spherical, cubic, and plate-like, but is not particularly limited to these.
  • the non-magnetic powder contains at least iron oxide, in particular acicular iron oxide.
  • the non-magnetic powder may further contain carbon black and/or aluminum oxide.
  • the average major axis length of the iron oxide may be, for example, preferably 0.01 ⁇ m or more, more preferably 0.04 ⁇ m or more, and even more preferably 0.07 ⁇ m or more.
  • the average major axis length may be, for example, preferably 0.5 ⁇ m or less, more preferably 0.4 ⁇ m or less, and even more preferably 0.3 ⁇ m or less.
  • the average particle size of the carbon black may be, for example, preferably 10 nm or more, more preferably 12 nm or more, and even more preferably 15 nm or more.
  • the average particle size of the carbon black may be, for example, preferably 250 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less.
  • the carbon black content may be, for example, preferably 15 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 25 parts by mass or more, per 100 parts by mass of the iron oxide.
  • the carbon black content may be, for example, preferably 45 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less, per 100 parts by mass of the iron oxide.
  • the average particle size of the aluminum oxide may be, for example, preferably 30 nm or more, more preferably 40 nm or more, and even more preferably 60 nm or more.
  • the average particle size of the aluminum oxide may be, for example, preferably 180 nm or less, more preferably 150 nm or less, and even more preferably 120 nm or less.
  • the content of aluminum oxide may be, for example, preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of the iron oxide.
  • the content of aluminum oxide may be, for example, preferably 10 parts by mass or less, more preferably 9 parts by mass or less, and even more preferably 8 parts by mass or less, per 100 parts by mass of the iron oxide.
  • the underlayer contains a binder.
  • the above description of the binder contained in the magnetic layer 13 also applies to the binder contained in the underlayer 12.
  • the undercoat layer includes at least a chlorine-containing binder.
  • the chlorine-containing binder may be a chlorine-containing resin.
  • the chlorine-containing resin is a resin that includes a chlorine atom as at least one of the elements constituting the resin.
  • the chlorine-containing binder is, for example, a vinyl chloride resin.
  • chlorine-containing binder examples include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic acid ester-vinyl chloride-vinylidene chloride copolymer, acrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer, and synthetic rubber.
  • the underlayer contains a chlorine-containing binder adsorbed to the non-magnetic powder and a chlorine-containing binder not adsorbed to the non-magnetic powder.
  • the distribution state of the chlorine-containing binder not adsorbed to the non-magnetic powder in the underlayer is affected by the solvent contained in the paint for forming the magnetic layer and the paint drying process during the magnetic layer formation process in the manufacturing process of the magnetic recording medium. By controlling the distribution state according to this technology, the reliability of the magnetic recording medium can be improved.
  • the content by volume of the chlorine-containing binder in the undercoat layer may be, for example, an amount equivalent to 20% by volume or more of the non-magnetic powder volume (particularly the total volume of the non-magnetic powder), preferably 30% by volume or more, more preferably 40% by volume or more.
  • the content by volume may be, for example, an amount equivalent to 180% by volume or less of the non-magnetic powder volume (particularly the total volume of the non-magnetic powder), preferably 170% by volume or less, more preferably 160% by volume or less.
  • the volume of the chlorine-containing binder in the underlayer may be, for example, preferably 20 to 180, more preferably 30 to 170, and even more preferably 40 to 160.
  • the undercoat layer contains iron oxide as a non-magnetic powder.
  • the content of the chlorine-containing binder in the undercoat layer may be, for example, preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the iron oxide.
  • the content may be, for example, preferably 70 parts by mass or less, more preferably 65 parts by mass or less, and even more preferably 60 parts by mass or less, per 100 parts by mass of the iron oxide.
  • the undercoat layer may further contain a chlorine-free binder in addition to the chlorine-containing binder.
  • the chlorine-free binder may be a chlorine-free resin.
  • the chlorine-free resin may contain, for example, a polyurethane-based resin.
  • the polyurethane-based resin may be, for example, a urethane-modified copolymer polyester.
  • the urethane-modified copolymer polyester may be a urethane-modified copolymer polyester having an aromatic polyester as a basic skeleton and a urethane component in the side chain, or a urethane-modified copolymer polyester containing an ester repeat unit and a urethane repeat unit in the basic skeleton.
  • the content by volume of the chlorine-free binder in the undercoat layer may be, for example, an amount equivalent to 0% or more of the volume of the non-magnetic powder (particularly the total volume of the non-magnetic powder), preferably 10% or more, more preferably 20% or more.
  • the content by volume may be, for example, an amount equivalent to 150% or less of the volume of the non-magnetic powder (particularly the total volume of the non-magnetic powder), preferably 140% or less, more preferably 130% or less.
  • the undercoat layer may not contain the chlorine-free binder.
  • the volume of the chlorine-containing binder in the underlayer may be, for example, preferably 0 to 150, more preferably 10 to 140, and even more preferably 200 to 130.
  • the undercoat layer contains iron oxide as a non-magnetic powder.
  • the content of the chlorine-free binder in the undercoat layer may be, for example, preferably 0 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 100 parts by mass of the iron oxide.
  • the content may be, for example, preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the iron oxide.
  • the underlayer may contain a lubricant.
  • the lubricant may be, for example, one or more selected from fatty acids and/or fatty acid esters, and the lubricant may preferably be a compound represented by general chemical formula (1) or general chemical formula (2), or general chemical formula (3) or general chemical formula (4) described above with respect to the magnetic layer. One or more of these compounds may be included.
  • the lubricant may be, for example, an ester of a monobasic fatty acid having 10 to 24 carbon atoms with any one of monohydric to hexahydric alcohols having 2 to 12 carbon atoms, a mixed ester thereof, a di-fatty acid ester, a tri-fatty acid ester, etc.
  • the lubricant include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, butyl stearate, pentyl stearate, heptyl stearate, octyl stearate, isooctyl stearate, octyl myristate, etc.
  • the magnetic layer may contain any one or more of these.
  • the content of the lubricant in the undercoat layer may be, for example, preferably 1 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2 parts by mass or more, per 100 parts by mass of non-magnetic powder (100 parts by mass of total amount of non-magnetic powder).
  • the content may be, for example, preferably 12 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 8 parts by mass or less, per 100 parts by mass of non-magnetic powder (100 parts by mass of total amount of non-magnetic powder).
  • the above numerical range may be applied, for example, when the non-magnetic powder contains iron oxide.
  • the undercoat layer contains iron oxide as a non-magnetic powder.
  • the content of the lubricant in the undercoat layer may be, for example, preferably 2 parts by mass or more, more preferably 2.5 parts by mass or more, and even more preferably 3 parts by mass or more, per 100 parts by mass of the iron oxide.
  • the content may be, for example, preferably 8 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 6 parts by mass or less, per 100 parts by mass of the iron oxide.
  • the back layer 14 may contain a binder and a non-magnetic powder.
  • the back layer 14 may contain various additives such as a lubricant, a hardener, and an antistatic agent as necessary.
  • a lubricant such as a lubricant, a hardener, and an antistatic agent as necessary.
  • the explanation given above regarding the binder and non-magnetic powder contained in the non-magnetic layer 12 also applies to the binder and non-magnetic powder contained in the back layer 14.
  • the average particle size of the inorganic particles contained in the back layer 14 is preferably 10 nm or more and 150 nm or less, more preferably 15 nm or more and 110 nm or less.
  • the average particle size of the inorganic particles is determined in the same manner as the average particle size D of the magnetic powder described above.
  • the thickness of the portion of the underlayer 12 of the magnetic recording medium 10 where the chlorine count is equal to or greater than the threshold value described below is, for example, 130 nm or less, as described above.
  • [Threshold] [average chlorine count in the undercoat layer] + 6 ⁇ [standard deviation obtained when calculating the average chlorine count]
  • the thickness of this portion is the thickness of a region where the chlorine count is equal to or greater than the threshold value, as determined by measuring the chlorine count across the thickness direction of the underlayer using a STEM (scanning transmission electron microscope).
  • the method for measuring the thickness of the portion is as follows.
  • sample Preparation Method To prepare a sample, a portion of the tape-shaped magnetic recording medium housed in a magnetic recording cartridge, which is about 20 m from the outermost portion in the tape longitudinal direction, is used.
  • the magnetic tape T housed in a cartridge such as the cartridge 10A described later is unwound, and a portion about 20 m from the connection portion 221 between the magnetic tape T and the leader tape LT in the longitudinal direction is used to prepare a sample.
  • a substantially central portion in the width direction of the magnetic tape T is cut out to a size appropriate for preparing a sample for STEM observation (e.g., a rectangle of about 1 mm x about 1 mm).
  • a carbon deposition process is applied to the surface of the cut sample, and a carbon deposition film is formed on the magnetic surface.
  • the sample that has been subjected to this process is introduced into a focused ion beam (FIB) processing device equipped with a scanning electron microscope (SEM). From the sample that has been subjected to this process, the processing device microsamples minute pieces having a size appropriate for STEM observation (e.g., a rectangle of 10 ⁇ m to 50 ⁇ m on a side). The minute piece is fixed to the sample stage of the processing device and thinned. The thinning is performed so that the thickness of the minute piece in the direction parallel to the magnetic surface is a thickness that allows the electron beam used in STEM observation to pass through.
  • FIB focused ion beam
  • SEM scanning electron microscope
  • STEM device FEI Talos F200X (Schottky-FEG)
  • EDX system FEI Super-X EDX detector: 4 windowless SDD detectors (30 mm 2 , objective lens built-in) manufactured by Bruker
  • Acceleration voltage 200 kV
  • Acquired image BF STEM image (Bright Field: BF)
  • HAADF STEM image High Angle Annular Dark Field:HAADF
  • Camera length 98mm
  • Display magnification 57,000x
  • Acceleration voltage 200 kV
  • Display magnification 57,000x
  • Surface analysis resolution 800 pixels x 700 pixels (1 pixel is equivalent to approximately 2.1 nm.)
  • Moving average filter 3 pixels
  • Data type Net count Cl K ⁇ ray extraction integrated width x thickness
  • the "length in the thickness direction" is the length of the side of a rectangle that defines the region in which Cl K ⁇ rays are extracted, the side being approximately parallel to the thickness direction of the magnetic recording medium.
  • the K ⁇ net count of Cl at a certain position in the thickness direction of the magnetic recording medium corresponds to the amount of Cl at that position. Therefore, the distribution state of the chlorine content can be grasped based on the K ⁇ net count of Cl. Note that the energy of the K ⁇ ray of the characteristic X-ray generated when irradiating Cl with an electron beam is 2.62 keV.
  • a HAADF STEM image of the STEM observation sample is obtained in a direction parallel to the magnetic surface.
  • An example of the obtained HAADF STEM image is shown in FIG. 3A.
  • the magnetic layer M and the underlayer U can be confirmed from the image.
  • the STEM cross-sectional photograph is checked to confirm that there are no parts in the cross section of the underlayer that are clearly different from the normal state of the underlayer, such as coarse inorganic particles, voids, or undispersed binder, and the analysis is performed on a cross section that does not contain such parts.
  • a K ⁇ ray extraction region A ex region surrounded by a white rectangle
  • the K ⁇ ray extraction region is a rectangle, particularly a rectangle.
  • the length of one side of the rectangle in the horizontal direction is 700 pixels, which is the above-mentioned "Cl K ⁇ ray extraction integrated width", that is, the length of the rectangular area in which Cl K ⁇ ray extraction is performed in a direction approximately horizontal to the magnetic surface of the magnetic recording medium.
  • the width indicated by the double-headed arrow L a is the Cl K ⁇ ray extraction integrated width.
  • the length of one vertical side of the rectangle is 650 pixels, which is the above-mentioned “length in the thickness direction.”
  • the length indicated by the double-headed arrow Lb is the length in the thickness direction.
  • the magnetic layer and the underlayer can be identified by visual observation of the HAADF image.
  • the rectangle set as the Cl K ⁇ ray extraction region is set so that the side corresponding to the Cl K ⁇ ray extraction integrated width is approximately parallel to the visually identified magnetic layer surface, and the rectangle covers the carbon deposition film, the magnetic layer, the underlayer, and the base layer. In actual setting, it is not necessary to draw the white lines shown in the figure.
  • (iv) Identification of the Magnetic Layer Surface The fact that the carbon deposition film does not contain chlorine is utilized to identify the magnetic layer surface in the chlorine count extraction region. To identify the magnetic layer surface, first, the carbon deposition film portion is identified. The carbon deposition film portion can be roughly identified from the plot. For example, since the peak on the left side of the plot in FIG. 3C corresponds to the magnetic layer portion, the portion with a low net count number on the left side of the magnetic layer portion is the carbon deposition film portion. Then, the average value (simple average value) of the net count number of the first 6 nm portion starting from the net count number of 0 is identified as the background value.
  • the position (pixel position in the thickness direction) where the net count number exceeding the background value is recorded in the plot generated in (ii) above is determined as the position of the magnetic layer surface.
  • the position of the magnetic layer surface For example, in FIG. 3C, moving to the right from the 0 nm point on the extraction position axis, there is an extraction position data point where the background value is recorded.
  • the extraction position of the data point immediately to the right of the extraction position data point is the position of the magnetic layer surface.
  • the first position within the 6 nm where the moving average value is equal to or greater than the threshold value is determined as the "start point on the magnetic surface side of the portion where the chlorine count is equal to or greater than the threshold value."
  • An example of the start point is shown in FIG. 3E.
  • the interface between the undercoat layer and the base layer is identified. As the chlorine counts move further from the starting point toward the base layer, they begin to decrease.
  • the first position at which the chlorine counts become lower than the "average chlorine counts in the undercoat layer” is determined as the "interface between the undercoat layer and the base layer.”
  • An example of the position of the interface is also shown in FIG. 3E.
  • the position of the interface may be identified as the first position where the chlorine count becomes lower than the average chlorine count in the underlayer, as described above.
  • the base layer is made of a material that contains chlorine. In this case, when the chlorine count of the base layer is different from the net chlorine K ⁇ count of the average part of the underlayer, the position of the interface may be identified based on the difference.
  • the length from the "start point on the magnetic surface side of the portion where the chlorine count is equal to or greater than the threshold value" to the "interface between the underlayer and the base layer” specified as above is defined as the "thickness of the portion of the underlayer where the chlorine count is equal to or greater than the threshold value.”
  • An example of this portion is also shown in FIG. 3E.
  • a peak portion corresponding to the magnetic layer can be seen on the left side of the plot.
  • the maximum value of the chlorine count number in this peak portion is the "peak chlorine count number in the magnetic layer.”
  • the average thickness tT of the magnetic recording medium 10 (hereinafter also referred to as magnetic tape T) is obtained as follows. First, the magnetic tape T housed in a cartridge such as the cartridge 10A described below is unwound, and the magnetic tape T is cut into a length of 250 mm at a position 30 m in the longitudinal direction from the joint 221 between the magnetic tape T and the leader tape LT to prepare a sample. Next, the thickness of the sample is measured at five positions using a Mitutoyo laser hologram (LGH-110C) as a measuring device, and the measured values are simply averaged (arithmetic average) to calculate the average thickness tT [ ⁇ m]. The five measurement positions are selected randomly from the sample so that they are different positions in the longitudinal direction of the magnetic tape T.
  • LGH-110C Mitutoyo laser hologram
  • the average thickness of the underlayer 12 is obtained as follows. First, the magnetic tape T housed in a cartridge such as the cartridge 10A described below is unwound, and the magnetic tape T is cut into three samples of 250 mm length at three positions, 10 m, 30 m, and 50 m from the connection 221 between the magnetic tape T and the leader tape LT in the longitudinal direction. Then, each sample is processed by FIB method or the like to be thinned. When the FIB method is used, a carbon layer and a tungsten layer are formed as a protective film as a pretreatment for observing the TEM image of the cross section described below.
  • the carbon layer is formed by deposition on the surface of the magnetic tape T on the magnetic layer 13 side and the surface on the back layer 14 side, and the tungsten layer is further formed on the surface on the magnetic layer 13 side by deposition or sputtering.
  • the thinning is performed along the longitudinal direction of the magnetic tape T. That is, the thinning forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape T.
  • TEM transmission electron microscope
  • Equipment TEM (H9000NAR manufactured by Hitachi) Acceleration voltage: 300 kV
  • Magnification 100,000x
  • the thickness of the underlayer 12 is measured at at least 10 or more points in the longitudinal direction of the magnetic tape T, and then the measured values are simply averaged (arithmetic averaged) to obtain the average thickness (nm) of the underlayer 12.
  • the average thickness of the base layer 11 is determined as follows. First, the magnetic tape T housed in a cartridge, such as the magnetic recording cartridge 10A described below, is unwound, and a sample is prepared by cutting the magnetic tape T to a length of 250 mm at a position 30 m in the longitudinal direction from the connection 221 between the magnetic tape T and the leader tape LT.
  • the "longitudinal direction" in the “longitudinal direction from the connection between the magnetic tape T and the leader tape LT” refers to the direction from one end on the leader tape LT side to the other end on the opposite side.
  • the non-magnetic layer (underlayer) 12, the magnetic layer 13, and the back layer 14 are removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid.
  • a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid.
  • the thickness of the sample (base layer 11) is measured at five positions, and the measured values are simply averaged (arithmetic mean) to calculate the average thickness of the base layer 11. Note that the five measurement positions are selected randomly from the sample so that they are each different positions in the longitudinal direction of the magnetic tape T.
  • the average thickness t b of the back layer 14 is obtained as follows. First, the average thickness (average total thickness) t T of the magnetic tape T is measured. The method for measuring the average thickness t T (average total thickness) is as described above. Next, the magnetic tape T housed in the cartridge 10A is unwound, and the magnetic tape T is cut into a length of 250 mm at a position 30 m in the longitudinal direction from the joint 221 between the magnetic tape T and the leader tape LT to prepare a sample. Next, the back layer 14 of the sample is removed with a solvent such as MEK (methyl ethyl ketone) or dilute hydrochloric acid.
  • MEK methyl ethyl ketone
  • the thickness of the sample is measured at five positions using a Mitutoyo laser hologram (LGH-110C), and the measured values are simply averaged (arithmetic average) to calculate the average value t B [ ⁇ m]. Then, the average thickness t b [ ⁇ m] of the back layer 14 is obtained from the following formula.
  • the average thickness t m of the magnetic layer 13 is obtained as follows. First, the magnetic tape T housed in the cartridge 10A is unwound, and the magnetic tape T is cut into three samples of 250 mm length at three positions, 10 m, 30 m, and 50 m from the connection 221 between the magnetic tape T and the leader tape LT in the longitudinal direction. Then, each sample is processed by FIB method or the like to be thinned. When the FIB method is used, a carbon layer and a tungsten layer are formed as a protective film as a pretreatment for observing a TEM image of a cross section, which will be described later.
  • the carbon layer is formed by a vapor deposition method on the surface of the magnetic tape T on the magnetic layer 13 side and the surface on the back layer 14 side, and the tungsten layer is further formed by a vapor deposition method or a sputtering method on the surface on the magnetic layer 13 side.
  • the thinning is performed along the longitudinal direction of the magnetic tape T. That is, the thinning forms a cross section parallel to both the longitudinal direction and the thickness direction of the magnetic tape T.
  • the cross section of each of the obtained sliced samples is observed under the following conditions using a transmission electron microscope (TEM) to obtain a TEM image of each of the sliced samples.
  • TEM transmission electron microscope
  • the magnification and acceleration voltage may be appropriately adjusted depending on the type of the apparatus.
  • the thickness of the magnetic layer 13 is measured at 10 positions of each sliced sample.
  • the 10 measurement positions of each sliced sample are randomly selected from the sample so that they are different positions in the longitudinal direction of the magnetic tape T.
  • the average value obtained by simply averaging (arithmetic mean) the measured values of each of the obtained sliced samples (a total of 30 thicknesses of the magnetic layer 13) is defined as the average thickness t m [nm] of the magnetic layer 13.
  • the temperature expansion coefficient ⁇ of the magnetic recording medium 10 is preferably 3 [ppm/°C] ⁇ 10 [ppm/°C].
  • the change in width of the magnetic recording medium 10 can be suppressed by adjusting the longitudinal tension of the magnetic recording medium 10 using the recording/reproducing device 30 described below.
  • the temperature expansion coefficient ⁇ is calculated as follows. First, a magnetic recording medium 10 with a width of 1/2 inch is prepared, and cut into a length of 250 mm to obtain a sample 10S. Then, when measuring the temperature expansion coefficient ⁇ under a relative humidity environment of 10% RH, for example, the measurement device with the sample 10S set therein is placed in a chamber controlled to a constant environment of 29°C temperature and 10% relative humidity. Next, a load of 0.2 N is applied to the length of the sample 10S, and the sample 10S is kept in the above environment for more than 2 hours to allow it to acclimate.
  • the temperature is changed in the order of 45°C, 29°C, and 10°C, and the width of the sample 10S at 45°C and 10°C is measured, and the temperature expansion coefficient ⁇ is calculated from the following formula. Note that the measurement of the width of the sample 10S at a temperature of 29°C is performed to check whether any abnormalities have occurred in the measurement (especially to check that the results of these three measurements are linear), and the measurement result is not used in the following formula.
  • FIG. 4 is a schematic diagram showing the appearance of a measuring device 510 used to measure the width of the magnetic recording medium 10.
  • the measuring device 510 includes a base 511, a support column 512, a light emitter 513, a light receiver 514, a support plate 515, five support members 516A to 516E, and a fixing portion 517.
  • the base 511 has a rectangular plate shape.
  • a light receiver 514 is provided in the center of the base 511.
  • the support pillar 512 is erected adjacent to the light receiver 514 at a position shifted from the center of the base 511 to one of the long sides.
  • a fixing part 517 is provided on one of the short sides of the base 511.
  • the light emitter 513 is supported at the tip of the support column 512.
  • the light emitter 513 and the light receiver 514 face each other.
  • the sample 10S supported by the support members 516A to 516E is placed between the opposing light emitter 513 and light receiver 514.
  • the light emitter 513 and the light receiver 514 are connected to a PC (personal computer) (not shown), and under the control of this PC, the width of the sample 10S supported by the support members 516A to 516E is measured and the measurement results are output to the PC.
  • PC personal computer
  • the light emitter 513 and the light receiver 514 incorporate a digital dimension measuring device LS-7000 manufactured by Keyence Corporation.
  • the light emitter 513 irradiates the sample 10S supported by the support members 516A to 516E with linear light parallel to the width direction of the sample 10S.
  • the light receiver 514 measures the width of the sample 10S by measuring the amount of light not blocked by the sample 10S.
  • a long, thin rectangular support plate 515 is fixed at approximately half the height of the support column 512.
  • the support plate 515 is supported so that its long side is parallel to the main surface of the base 511.
  • Five support members 516A-516E are supported on one main surface of the support plate 515.
  • the support members 516A-516E are cylindrical rod-shaped, and support the back surface of the sample 10S (magnetic recording medium 10). All five support members 516A-516E (particularly their surfaces) are made of stainless steel SUS304, and have a surface roughness Rz (maximum height) of 0.15 ⁇ m to 0.3 ⁇ m.
  • each of the five support members 516A to 516E is placed on the five support members 516A to 516E.
  • the diameter of each of the five support members 516A to 516E is, for example, 7 mm.
  • the distance d1 between support member 516A and support member 516B (particularly the distance between the central axes of these support members) is 20 mm.
  • the distance d2 between support member 516B and support member 516C is 30 mm.
  • the distance d3 between support member 516C and support member 516D is 30 mm.
  • the distance d4 between support member 516D and support member 516E is 20 mm.
  • the support member 516C which is located between the light emitter 513 and the light receiver 514 and is located approximately in the center between the fixed part 517 and the part where the load is applied, has a slit 516S.
  • Light L is irradiated from the light emitter 513 to the light receiver 514 through the slit 516S.
  • the slit width of the slit 516S is 1 mm, and the light L can pass through the slit 516S without being blocked by the frame of the slit 516S.
  • the sample 10S is set in the measuring device 510. Specifically, one end of the long sample 10S is fixed by the fixing part 517. Next, the sample 10S is placed on the five support members 516A to 516E. At this time, the back surface of the sample 10S is in contact with the five support members 516A to 516E.
  • the measuring device 510 is placed in a chamber controlled to a constant environment of 29°C temperature and 10% relative humidity, and then a weight for applying a 0.2N load is attached to the other end of the sample 10S, and the sample 10S is kept in the above environment for at least 2 hours to allow the sample 10S to acclimate to the above environment. Thereafter, while maintaining the relative humidity at 10%, the temperature is changed in the order of 45°C, 29°C, and 10°C, and the width of the sample 10S at 45°C and 10°C is measured.
  • CTH represents the temperature expansion coefficient [ppm/°C] of the magnetic head that records and reproduces on this magnetic recording medium.
  • CTH is measured using a measuring device similar to the above-mentioned temperature expansion coefficient ⁇ , and the magnetic head taken out by disassembling the recording and reproducing device is placed on the slit 516S where the light (laser) of the measuring device 510 hits, and the temperature of the thermostatic chamber is changed in the same manner as in the measurement of the temperature expansion coefficient ⁇ to measure the width of the magnetic head (the length of the magnetic head in the direction that coincides with the width direction of the magnetic tape in the arrangement in the recording and reproducing device).
  • CTQ represents the temperature expansion coefficient [ppm/°C] of the magnetic recording medium that is the most deviated from the temperature expansion coefficient of the magnetic head in a relative humidity environment of 10% RH or more and 80% RH or less.
  • nine samples are taken from a portion approximately 20 m in the longitudinal direction of the tape from the outermost portion of the tape-like magnetic recording medium housed in a magnetic recording cartridge.
  • the magnetic tape T housed in a cartridge such as cartridge 10A described below is unwound, and a portion approximately 20 m in the longitudinal direction from the connection 221 between the magnetic tape T and the leader tape LT is used to prepare the sample.
  • the humidity expansion coefficient ⁇ of the magnetic recording medium 10 is preferably ⁇ 5 [ppm/% RH].
  • the change in width of the magnetic recording medium 10 can be further suppressed by adjusting the longitudinal tension of the magnetic recording medium 10 using the recording/reproducing device 30.
  • the humidity expansion coefficient ⁇ is calculated as follows. First, the sample 10S is prepared in the same manner as in the measurement method of the temperature expansion coefficient ⁇ , and the sample 10S is set in the same measuring device 510 as in the measurement method of the temperature expansion coefficient ⁇ . Then, when measuring the humidity expansion coefficient ⁇ in a temperature environment of, for example, 10°C, the measuring device 510 in which the sample 10S is set is placed in a chamber controlled to a constant environment of 10°C temperature and 24% relative humidity. Next, a load of 0.2 N is applied to the longitudinal direction of the sample 10S, and the sample 10S is kept in the above environment for more than 2 hours to allow it to acclimate.
  • the relative humidity is changed in the order of 80%, 24%, and 10%, and the width of the sample 10S at 80% and 10% is measured, and the humidity expansion coefficient ⁇ is calculated from the following formula. Note that the measurement of the width of the sample 10S at a humidity of 24% is performed to check whether any abnormalities have occurred in the measurement (especially to check that these three measurement results are linear), and the measurement result is not used in the following formula.
  • CHH represents the humidity expansion coefficient [ppm/% RH] of the magnetic head that records and reproduces on this magnetic recording medium, using a measuring device similar to the humidity expansion coefficient ⁇ described above.
  • CHH is measured by disassembling the recording and reproducing device, placing the magnetic head removed, and changing the humidity of the thermostatic chamber in the same manner as in the measurement of the humidity expansion coefficient ⁇ , and measuring the width of the magnetic head (the length of the magnetic head in the direction that coincides with the width direction of the magnetic tape in the arrangement in the recording and reproducing device).
  • CHH is measured in a temperature environment of 35°C.
  • CHR represents the humidity expansion coefficient [ppm/% RH] of the humidity expansion coefficient of the magnetic recording medium that is the most deviated from the humidity expansion coefficient of the magnetic head in a temperature environment of 10°C to 60°C.
  • samples are collected in the same manner as in the CTQ measurement.
  • the arithmetic mean roughness Ra of the surface of the magnetic layer 13 is preferably 2.5 nm or less, more preferably 2.2 nm or less, and even more preferably 1.9 nm or less. When the arithmetic mean roughness Ra is 2.5 nm or less, excellent electromagnetic conversion characteristics can be obtained.
  • the lower limit of the arithmetic mean roughness Ra of the surface of the magnetic layer 13 is preferably 1.0 nm or more, more preferably 1.2 nm or more, and even more preferably 1.4 nm or more. When the lower limit of the arithmetic mean roughness Ra of the surface of the magnetic layer 13 is 1.0 nm or more, deterioration of running properties due to increased friction can be suppressed.
  • the arithmetic mean roughness Ra of the surface of the magnetic layer 13 is obtained as follows. First, the surface of the magnetic layer 13 is observed with an AFM (Atomic Force Microscope) to obtain an AFM image of 40 ⁇ m ⁇ 40 ⁇ m. A Nano Scope IIIa D3100 manufactured by Digital Instruments is used as the AFM, a single crystal silicon cantilever is used, and measurements are performed with a tapping frequency of 200 Hz to 400 Hz tuning.
  • the deviation Z"(i) (
  • the data used is filtered using Flatten order 2 and planefit order 3 XY as image processing.
  • the squareness ratio Rs1 measured in the longitudinal direction of the magnetic tape T is preferably 35% or less, more preferably 30% or less, even more preferably 25% or less, particularly preferably 20% or less, and most preferably 15% or less. If the squareness ratio Rs1 is 35% or less, the magnetic powder will have a sufficiently high vertical orientation, resulting in a better SNR. Therefore, better electromagnetic conversion characteristics can be obtained. In addition, the servo signal shape is improved, making it easier to control on the drive side.
  • the squareness ratio Rs1 in the longitudinal direction of the magnetic tape is obtained as follows. First, the magnetic tape contained in the cartridge is unwound, and six magnetic tapes are cut out at a position 30 to 40 m in the longitudinal direction from one end of the outer periphery of the magnetic tape. At this time, marking is performed with any non-magnetic ink so that the longitudinal direction (running direction) of the magnetic tape can be recognized. Next, the three cut-out magnetic tapes are superimposed with double-sided tape so that the longitudinal directions of the three cut-out magnetic tapes are the same, and then punched out with a ⁇ 6.39 mm punch to prepare a measurement sample.
  • the M-H loop of the measurement sample (whole magnetic tape) corresponding to the longitudinal direction of the magnetic tape (longitudinal direction of the magnetic tape) is measured using a vibrating sample magnetometer (VSM).
  • VSM vibrating sample magnetometer
  • the coatings (undercoat layer, magnetic layer, back layer, etc.) of the remaining three cut-out magnetic tapes are wiped off with acetone or ethanol, etc., leaving only the base layer.
  • Three of the obtained base layers are stacked with double-sided tape, and then punched out with a ⁇ 6.39 mm punch to prepare a sample for background correction (hereinafter, simply "correction sample").
  • the M-H loop of the correction sample (base layer) corresponding to the longitudinal direction of the base layer (longitudinal direction of the magnetic tape) is measured using a VSM.
  • the MH loop of the measurement sample (entire magnetic tape) and the MH loop of the correction sample (base layer) are measured using a high-sensitivity vibration sample magnetometer "VSM-P7-15 type" manufactured by Toei Industry Co., Ltd.
  • the measurement conditions are as follows: measurement mode: full loop, maximum magnetic field: 15 kOe, magnetic field step: 40 bits, time constant of locking amp: 0.3 sec, waiting time: 1 sec, number of MH averages: 20.
  • the M-H loop of the measurement sample (whole magnetic tape) and the M-H loop of the correction sample (base layer) are obtained, the M-H loop of the correction sample (base layer) is subtracted from the M-H loop of the measurement sample (whole magnetic tape) to perform background correction and obtain the M-H loop after background correction.
  • the measurement and analysis program attached to the "VSM-P7-15 type" is used for the calculation of this background correction. Note that all of the above M-H loop measurements are performed at 25°C ⁇ 2°C and 50% RH ⁇ 5% RH. Also, when measuring the M-H loop in the longitudinal direction of the magnetic tape, "demagnetization field correction" is not performed.
  • the M-H loop may be measured by stacking multiple samples to be measured according to the sensitivity of the VSM used.
  • a method for manufacturing the magnetic recording medium 10 having the above-mentioned configuration will be described.
  • a paint for forming the base layer is prepared by kneading and/or dispersing non-magnetic powder, binder, etc. in a solvent.
  • a paint for forming the magnetic layer is prepared by kneading and/or dispersing magnetic powder, non-magnetic particles, binder, etc. in a solvent.
  • the following solvents, dispersing devices, and kneading devices can be used, for example, to prepare the paint for forming the magnetic layer and the paint for forming the base layer (non-magnetic layer).
  • Solvents used in the preparation of the above-mentioned paints include, for example, ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol-based solvents such as methanol, ethanol, and propanol; ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate, and ethylene glycol acetate; ether-based solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, and dioxane; aromatic hydrocarbon-based solvents such as benzene, toluene, and xylene; and halogenated hydrocarbon-based solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, and chlorobenzene.
  • the kneading device used in the above-mentioned paint preparation may be, for example, a continuous twin-screw kneader, a continuous twin-screw kneader capable of dilution in multiple stages, a kneader, a pressure kneader, a roll kneader, or the like, but is not limited to these devices.
  • the dispersing device used in the above-mentioned paint preparation may be, for example, a bead mill, a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, a pearl mill (such as the "DCP Mill” manufactured by Eirich), a homogenizer, or an ultrasonic dispersing machine, but is not limited to these devices.
  • a paint for forming the undercoat layer is applied to one main surface of the base layer 11 and dried to form the undercoat layer 12.
  • a paint for forming the magnetic layer is applied onto this undercoat layer 12 and dried to form the magnetic layer 13 on the non-magnetic layer 12.
  • the thickness and/or position of the portion where the chlorine count is equal to or greater than the threshold value described below can be adjusted by adjusting the method of forming the magnetic layer and/or the base layer and/or the composition of the paint for forming the magnetic layer and/or the paint for forming the base layer.
  • the thickness and/or the position of the portion where the chlorine count is equal to or greater than the following threshold value can be adjusted, for example, by adjusting the drying temperature of the paint for forming the magnetic layer and/or the paint for forming the undercoat layer. For example, lowering the drying temperature makes the thickness wider, and conversely, increasing the drying temperature makes the thickness narrower on the base layer side.
  • the thickness and/or the position of the portion can be adjusted by modifying the non-magnetic powder contained in the undercoat layer coating material with a surface modifier.
  • the amount of binder adsorbed to the non-magnetic powder can be adjusted by modifying the surface with a surface modifier.
  • An example of the modifier is a polycarboxylic acid.
  • the thickness and/or the position of the part can be adjusted. For example, if the time is longer, the binder is less likely to move in the undercoat layer when the magnetic layer paint is applied, and the thickness becomes wider.
  • the binder is more likely to move in the undercoat layer when the magnetic layer paint is applied, and the thickness can be made narrower by being present on the base layer side.
  • the thickness of the portion can also be adjusted by the solids concentration of the paint for forming the magnetic layer and/or the paint for forming the undercoat layer. For example, if the solids concentration of the paint for forming the magnetic layer is high, the amount of solvent that seeps into the undercoat layer when the paint for forming the magnetic layer is applied is reduced, and the thickness of the portion becomes wider. Conversely, if the solids concentration is low, the thickness of the portion becomes smaller.
  • the thickness of the portion can also be adjusted by changing the ratio of the non-magnetic powder to the binder in the coating material for forming the undercoat layer. For example, by increasing the amount of binder, the amount of binder that does not adhere to the non-magnetic powder increases, and the thickness of the portion becomes thicker. Conversely, by decreasing the amount of binder, the thickness of the portion can be made thinner.
  • the magnetic powder When drying, the magnetic powder is magnetically oriented in the thickness direction of the base layer 11, for example, by a solenoid coil. Also, when drying, the magnetic powder may be magnetically oriented in the longitudinal direction (running direction) of the base layer 11, for example, by a solenoid coil, and then magnetically oriented in the thickness direction of the base layer 11.
  • a solenoid coil By performing such a magnetic field orientation process, it is possible to reduce the ratio Hc2/Hc1 of the coercive force in the vertical direction "Hc1" to the coercive force in the longitudinal direction "Hc2", and to improve the degree of vertical orientation of the magnetic powder.
  • a back layer 14 is formed on the other main surface of the base layer 11. This results in a magnetic recording medium 10.
  • the ratio Hc2/Hc1 is set to a desired value by, for example, adjusting the strength of the magnetic field applied to the coating of the magnetic layer-forming paint, the concentration of the solids in the magnetic layer-forming paint, and the drying conditions (drying temperature and drying time) of the coating of the magnetic layer-forming paint.
  • the strength of the magnetic field applied to the coating is preferably two to three times the holding power of the magnetic powder.
  • the methods for adjusting the ratio Hc2/Hc1 may be used alone or in combination of two or more.
  • the obtained magnetic recording medium 10 is rewound on a large diameter core and subjected to a hardening process. Finally, the magnetic recording medium 10 is subjected to a calendar process and then cut to a predetermined width (e.g., 1/2 inch width). In this manner, the desired long and thin magnetic recording medium 10 is obtained.
  • a predetermined width e.g., 1/2 inch width
  • the recording and reproducing device 30 may be configured to be able to adjust the tension applied in the longitudinal direction of the magnetic recording medium 10.
  • the recording and reproducing device 30 is also configured to be able to load a magnetic recording cartridge 10A.
  • the recording and reproducing device 30 is preferably a timing servo type magnetic recording and reproducing device.
  • the magnetic recording medium of the present technology is suitable for use in a timing servo type magnetic recording and reproducing device.
  • the recording and reproducing device 30 is connected to information processing devices such as a server 41 and a personal computer (hereinafter referred to as "PC") 42 via a network 43, and is configured to be able to record data supplied from these information processing devices onto the magnetic recording cartridge 10A.
  • the shortest recording wavelength of the recording and reproducing device 30 is preferably 100 nm or less, more preferably 75 nm or less, even more preferably 60 nm or less, and particularly preferably 50 nm or less.
  • the recording/playback device includes a spindle 31, a reel 32 on the recording/playback device side, a spindle drive unit 33, a reel drive unit 34, a number of guide rollers 35, a head unit 36, a communication interface (hereinafter, I/F) 37, and a control device 38.
  • I/F communication interface
  • the spindle 31 is configured to be able to mount the magnetic recording cartridge 10A.
  • the magnetic recording cartridge 10A is compliant with the LTO (Linear Tape Open) standard, and a single reel 10C around which the magnetic recording medium 10 is wound is rotatably housed in a cartridge case 10B.
  • a V-shaped servo pattern is recorded in advance as a servo signal on the magnetic recording medium 10.
  • the reel 32 is configured to be able to fix the tip of the magnetic recording medium 10 pulled out from the magnetic recording cartridge 10A.
  • the present technology also provides a magnetic recording cartridge including a magnetic recording medium according to the present technology.
  • the magnetic recording medium may be wound on a reel, for example, and may be housed in a case while being wound on the reel.
  • the spindle drive device 33 is a device that rotates the spindle 31.
  • the reel drive device 34 is a device that rotates the reel 32. When recording or reproducing data on the magnetic recording medium 10, the spindle drive device 33 and the reel drive device 34 rotate the spindle 31 and the reel 32, thereby running the magnetic recording medium 10.
  • the guide roller 35 is a roller that guides the running of the magnetic recording medium 10.
  • the head unit 36 includes a plurality of recording heads for recording data signals on the magnetic recording medium 10, a plurality of reproducing heads for reproducing the data signals recorded on the magnetic recording medium 10, and a plurality of servo heads for reproducing the servo signals recorded on the magnetic recording medium 10.
  • a ring-type head can be used as the recording head, for example, but the type of recording head is not limited to this.
  • the communication I/F 37 is for communicating with information processing devices such as the server 41 and the PC 42, and is connected to the network 43.
  • the control device 38 controls the entire recording/playback device 30.
  • the control device 38 records data signals supplied from information processing devices such as the server 41 and the PC 42 on the magnetic recording medium 10 using the head unit 36 in response to requests from the information processing devices.
  • the control device 38 also reproduces data signals recorded on the magnetic recording medium 10 using the head unit 36 in response to requests from the information processing devices such as the server 41 and the PC 42, and supplies the reproduced data signals to the information processing devices.
  • the magnetic recording cartridge 10A is loaded into the recording and reproducing device 30, the tip of the magnetic recording medium 10 is pulled out and transported to the reel 32 via multiple guide rollers 35 and the head unit 36, and the tip of the magnetic recording medium 10 is attached to the reel 32.
  • the spindle drive device 33 and the reel drive device 34 are driven under the control of the control device 38, and the spindle 31 and the reel 32 are rotated in the same direction so that the magnetic recording medium 10 runs from the reel 10C to the reel 32.
  • the head unit 36 records information onto the magnetic recording medium 10 or reproduces information recorded on the magnetic recording medium 10.
  • the spindle 31 and reel 32 are rotated in the opposite direction to that described above, causing the magnetic recording medium 10 to run from the reel 32 to the reel 10C.
  • the head unit 36 also records information onto the magnetic recording medium 10 or reproduces information recorded on the magnetic recording medium 10.
  • the magnetic recording medium 10 may be incorporated into a library device.
  • the present technology also provides a library device equipped with at least one magnetic recording medium 10.
  • the library device has a configuration that allows adjustment of the tension applied to the magnetic recording medium 10 in the longitudinal direction, and may be equipped with multiple recording/reproducing devices 30 described above.
  • Second embodiment One embodiment of a magnetic recording cartridge
  • the present technology also provides a magnetic recording cartridge (also called a tape cartridge) including a magnetic recording medium according to the present technology.
  • the magnetic recording medium may be wound around a reel, for example.
  • the magnetic recording cartridge may include, for example, a communication unit that communicates with a recording and playback device, a storage unit, and a control unit that stores information received from the recording and playback device via the communication unit in the storage unit, and reads information from the storage unit and transmits it to the recording and playback device via the communication unit in response to a request from the recording and playback device.
  • the information may include adjustment information for adjusting the tension applied to the magnetic recording medium in the longitudinal direction.
  • the magnetic recording cartridge 10A is a magnetic recording cartridge that conforms to the LTO (Linear Tape-Open) standard, and is equipped with a reel 10C on which a magnetic tape (tape-like magnetic recording medium) T is wound inside a cartridge case 10B consisting of a lower shell 212A and an upper shell 212B, a reel lock 214 and a reel spring 215 for locking the rotation of the reel 10C, a spider 216 for unlocking the reel 10C, a sliding door 217 that straddles the lower shell 212A and the upper shell 212B and opens and closes a tape outlet 212C provided in the cartridge case 10B, a door spring 218 that biases the sliding door 217 to a closed position of the tape outlet 212C, a write protector 219 for preventing accidental erasure, and a cartridge memory 211.
  • LTO Linear Tape-Open
  • the reel 10C is generally disk-shaped with an opening in the center, and is composed of a reel hub 213A and a flange 213B made of a hard material such as plastic.
  • a leader tape LT is connected to one end of the magnetic tape T.
  • a leader pin 220 is provided at the tip of the leader tape LT.
  • the cartridge memory 211 is provided near one corner of the magnetic recording cartridge 10A.
  • the cartridge memory 211 faces a reader/writer (not shown) of the recording and reproducing device 80.
  • the cartridge memory 211 communicates with the recording and reproducing device 30, specifically the reader/writer (not shown), using a wireless communication standard that complies with the LTO standard.
  • FIG. 7 is a block diagram showing an example of the configuration of the cartridge memory 211.
  • the cartridge memory 211 includes an antenna coil (communication unit) 331 that communicates with a reader/writer (not shown) using a specified communication standard, a rectification/power circuit 332 that generates power from radio waves received by the antenna coil 331 using induced electromotive force and rectifies it to generate power, a clock circuit 333 that generates a clock from the radio waves received by the antenna coil 331 using induced electromotive force, a detection/modulation circuit 334 that detects the radio waves received by the antenna coil 331 and modulates the signal to be transmitted by the antenna coil 331, a controller (control unit) 335 consisting of logic circuits and the like for determining commands and data from the digital signal extracted from the detection/modulation circuit 334 and processing them, and a memory (storage unit) 336 that stores information.
  • the cartridge memory 211 also includes a capacitor 337 connected in parallel to the antenna coil 331, and the antenna coil 331 and the capacitor 3
  • Memory 336 stores information related to magnetic recording cartridge 10A.
  • Memory 336 is non-volatile memory (NVM).
  • the storage capacity of memory 336 is preferably approximately 32 KB or more.
  • the memory 336 has a first memory area 336A and a second memory area 336B.
  • the first memory area 336A is an area for storing information that complies with the LTO standard prior to LTO8.
  • Information that complies with the LTO standard prior to LTO8 is, for example, manufacturing information (such as a unique number for the magnetic recording cartridge 10A), usage history (such as the number of times the tape has been pulled out (Thread Count)), etc.
  • the second memory area 336B is an area for storing additional information.
  • additional information means information related to the magnetic recording cartridge 10A that is not specified in the LTO standard prior to LTO8. Examples of additional information include tension adjustment information, management ledger data, index information, or thumbnail information of videos stored on the magnetic tape T, but are not limited to these data.
  • Memory 336 may have multiple banks. In this case, some of the multiple banks may form a first memory area 336A, and the remaining banks may form a second memory area 336B.
  • the antenna coil 331 induces an induced voltage by electromagnetic induction.
  • the controller 335 communicates with the recording/playback device 80 via the antenna coil 331 in accordance with a prescribed communication standard. Specifically, for example, mutual authentication, sending and receiving commands, and data exchange are performed.
  • the controller 335 stores information received from the recording and playback device 80 via the antenna coil 331 in the memory 336. In response to a request from the recording and playback device 80, the controller 335 reads information from the memory 336 and transmits it to the recording and playback device 80 via the antenna coil 331.
  • the magnetic tape cartridge is described as a one-reel type cartridge, but the magnetic recording cartridge of the present technology may be a two-reel type cartridge.
  • the magnetic recording cartridge of the present technology may have one or more (e.g., two) reels on which the magnetic tape is wound.
  • FIG 8 is an exploded perspective view showing an example of the configuration of a two-reel type cartridge 421.
  • the cartridge 421 includes an upper half 402 made of synthetic resin, a transparent window member 423 that fits into and is fixed to a window portion 402a opened on the upper surface of the upper half 402, a reel holder 422 that is fixed to the inside of the upper half 402 and prevents the reels 406 and 407 from floating up, a lower half 405 that corresponds to the upper half 402, the reels 406 and 407 that are stored in the space formed by combining the upper half 402 and the lower half 405, the magnetic tape MT1 wound on the reels 406 and 407, a front lid 409 that closes the front opening formed by combining the upper half 402 and the lower half 405, and a back lid 409A that protects the magnetic tape MT1 exposed at this front opening.
  • the reel 406 comprises a lower flange 406b having a cylindrical hub portion 406a in the center around which the magnetic tape MT1 is wound, an upper flange 406c having approximately the same size as the lower flange 406b, and a reel plate 411 sandwiched between the hub portion 406a and the upper flange 406c.
  • the reel 407 has a similar configuration to the reel 406.
  • the window member 423 has mounting holes 423a at positions corresponding to the reels 406 and 407 for attaching reel holders 422, which are reel holding means for preventing the reels from floating up.
  • the magnetic tape MT1 is the same as the magnetic tape T in the first embodiment.
  • a magnetic recording medium including a magnetic layer, an underlayer, and a base layer in this order, the undercoat layer comprises a chlorine-containing binder;
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less,
  • the magnetic recording medium has a first index Q of -250 ppm or more and 250 ppm or less.
  • [Threshold] [average chlorine count in the undercoat layer] + 6 ⁇ [standard deviation obtained when calculating the average chlorine count]
  • R 70[%RH] ⁇ (CHH-CHR) (wherein CHH is the humidity expansion coefficient of the magnetic head [ppm/% RH], and CHR is the humidity expansion coefficient of the magnetic recording medium in a temperature environment of 10° C. or higher and 60° C. or lower that is the humidity expansion coefficient that is the most deviated from the humidity expansion coefficient of the magnetic head [ppm/% RH])
  • the magnetic recording medium according to [1] or [2], wherein the total thickness of the magnetic layer and the underlayer is 1000 nm or less.
  • the magnetic layer contains magnetic powder.
  • the magnetic recording medium includes a magnetic layer, an underlayer, and a base layer, in that order.
  • the undercoat layer comprises a chlorine-containing binder; the thickness of a portion of the undercoat layer where the chlorine count is equal to or greater than the threshold value is 13% or less of the thickness of the undercoat layer,
  • the magnetic recording medium has a first index Q of -250 ppm or more and 250 ppm or less.
  • the magnetic layer includes a magnetic layer, an underlayer, and a base layer, in that order.
  • the undercoat layer comprises a chlorine-containing binder; the thickness of a portion of the undercoat layer where the chlorine count is equal to or greater than the threshold value is 13% or less of the thickness of the undercoat layer,
  • the magnetic recording medium has a second index R of -750 ppm or more and 750 ppm or less.
  • a magnetic recording medium including a magnetic layer, an underlayer, and a base layer in this order, the undercoat layer comprises a chlorine-containing binder;
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less, and an environmental relative humidity in which the temperature expansion coefficient of the magnetic recording medium is 6.0 ppm/° C. or more and 8.0 ppm/° C. or less is between 10% RH and 80% RH.
  • a magnetic recording medium including a magnetic layer, an underlayer, and a base layer in this order, the undercoat layer comprises a chlorine-containing binder; The thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less, The magnetic recording medium has an environmental temperature between 10° C. and 60° C. at which the humidity expansion coefficient of the magnetic recording medium is ⁇ 4.0 ppm/° C. or more and 4.0 ppm/° C. or less.
  • [Threshold] [average chlorine count in the undercoat layer] + 6 ⁇ [standard deviation obtained when calculating the average chlorine count] [16] Case and a reel housed in the case and around which a magnetic recording medium is wound;
  • the magnetic recording medium is A magnetic layer, an underlayer, and a base layer in this order; the undercoat layer comprises a chlorine-containing binder;
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less,
  • [Threshold] [average chlorine count in the undercoat layer] + 6 ⁇ [standard deviation obtained when calculating the average chlorine count] [17] Case and a reel housed in the case and around which a magnetic recording medium is wound;
  • the magnetic recording medium is A magnetic layer, an underlayer, and a base layer in this order; the undercoat layer comprises a chlorine-containing binder;
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less,
  • [Threshold] [average chlorine count in the undercoat layer] + 6 ⁇ [standard deviation obtained when calculating the average chlorine count] [18] a spindle on which a magnetic recording medium can be mounted; A drive device that drives the spindle; a magnetic head for recording and reproducing information on the magnetic recording medium;
  • the magnetic recording medium is A magnetic layer, an underlayer, and a base layer in this order; the undercoat layer comprises a chlorine-containing binder;
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less,
  • a recording and reproducing apparatus wherein the environmental relative humidity is between 10% RH and 80% RH, such that the temperature expansion coefficient of the magnetic recording medium is 6.0 ppm/° C.
  • [Threshold] [average chlorine count in the undercoat layer] + 6 ⁇ [standard deviation obtained when calculating the average chlorine count] [19] a spindle on which a magnetic recording medium can be mounted; A drive device that drives the spindle; a magnetic head for recording and reproducing information on the magnetic recording medium;
  • the magnetic recording medium is A magnetic layer, an underlayer, and a base layer in this order; the undercoat layer comprises a chlorine-containing binder;
  • the thickness of a portion of the underlayer where the chlorine count is equal to or greater than the following threshold value is 130 nm or less, A recording and reproducing apparatus, wherein the environmental temperature is between 10° C.
  • the magnetic layer coating material was prepared as follows. First, the first composition having the following composition was mixed with an extruder. Next, the mixed first composition and the second composition having the following composition were added to a stirring tank equipped with a disperser and premixed. Then, further mixing was performed with a dyno mill and filtering was performed to prepare the magnetic layer coating material.
  • Aluminum oxide powder 5 parts by mass ( ⁇ -Al 2 O 3 , average particle size 0.1 ⁇ m)
  • a third composition having the following composition was kneaded with an extruder.
  • the kneaded third composition and a fourth composition having the following composition were added to a stirring tank equipped with a disperser and premixed.
  • mixing was further carried out using a bead mill ECM-PRO (Shinmaru Enterprises Co., Ltd.) at a circulation flow rate of 500 L/h to 2000 L/h for a processing time in the bead mill of 30 to 150 minutes, followed by filtering to prepare a coating material for forming an undercoat layer.
  • Carbon black 30 parts by mass (average particle size 20 nm)
  • Polyurethane resin UR4800 manufactured by Toyobo
  • 44.0 parts by mass resin solution: resin 30% by mass, methyl ethyl ketone 35% by mass, toluene 35% by mass
  • n-Butyl stearate 2 parts by weight Methyl ethyl ketone: 188.0 parts by weight
  • Toluene 188.0 parts by weight
  • Cyclohexanone 119.6 parts by weight
  • the coating material for forming the back layer was prepared as follows: The following raw materials were mixed in a stirring tank equipped with a disperser, and the mixture was filtered to prepare the coating material for forming the back layer.
  • Carbon black manufactured by Asahi Carbon Co., Ltd., product name: #80
  • Polyester polyurethane 150 parts by mass
  • refsin solution polyurethane resin blend amount 30% by mass, cyclohexanone blend amount 70% by mass
  • Methyl ethyl ketone 500 parts by weight
  • Toluene 400 parts by weight
  • Cyclohexanone 100 parts by weight
  • Polyisocyanate product name: Coronate L, manufactured by Tosoh Corporation
  • a long PEN film (base film) with an average thickness of 4.00 ⁇ m was prepared as a support that would serve as the base layer of the magnetic tape.
  • a base layer was formed on one main surface of the PEN film by applying a paint for forming a base layer and drying it, so that the base layer would have an average thickness of 840 nm when made into a final product.
  • a magnetic layer was formed on the base layer by applying a paint for forming a magnetic layer and drying it, so that the magnetic layer would have an average thickness of 60 nm when made into a final product. The magnetic layer was then subjected to a vertical orientation process using a solenoid coil.
  • a paint for forming a back layer was applied to the other main surface of the PEN film on which the undercoat layer and magnetic layer were formed, and then dried to form a back layer so that the average thickness of the final product would be 0.30 ⁇ m.
  • the magnetic tape was wound into a roll, and then heated in this state at 65° C. for 48 hours to harden the underlayer and the magnetic layer.
  • the magnetic tape obtained as described above was cut into a width of 1/2 inch (12.65 mm), thereby obtaining a long magnetic tape.
  • the 1/2 inch wide magnetic tape was wound around a reel provided inside a cartridge case to obtain a multi-wrap magnetic recording cartridge.
  • a servo signal was recorded on the magnetic tape by a servo track writer.
  • the servo signal consisted of a series of V-shaped magnetic patterns, and the magnetic patterns were pre-recorded in two or more series parallel to the longitudinal direction at known intervals (hereinafter referred to as "the known intervals of the pre-recorded magnetic patterns").
  • the magnetic recording cartridge was measured for various values related to chlorine distribution, such as the chlorine count in the underlayer and the thickness of the portion where the chlorine count is equal to or greater than the threshold value.
  • Table 1 the average chlorine count C ave in the underlayer was 1.01.
  • the standard deviation ⁇ was 0.070. Therefore, the threshold value (C ave +6 ⁇ ) was 1.41.
  • the thickness of the portion of the underlayer that was equal to or greater than the threshold was 154 nm.
  • the portion that was equal to or greater than the threshold was in contact with the interface between the underlayer and the base layer, that is, was within 200 nm of the interface.
  • the ratio of the "thickness of the portion equal to or greater than the threshold value" to the "thickness of the underlayer” was 18%.
  • the same undercoat layer forming paint as in Comparative Example 1 was used, a PEN film having an average thickness of 4.0 ⁇ m was used as the base layer, the undercoat layer was formed to have an average thickness of 1120 nm, a back layer was formed to have an average thickness of 0.3 ⁇ m, the average thickness of the magnetic tape was set to 5.5 ⁇ m, and a magnetic tape was obtained in the same manner as in Comparative Example 1. Also, a magnetic recording cartridge containing the magnetic tape was obtained in the same manner as in Comparative Example 1.
  • the drying temperature after coating the magnetic layer was higher than that of Comparative Example 1, and the solvent volatilization rate from the magnetic layer surface was increased, so that the chlorine-containing binder that had once moved to the base layer side was moved to the surface side together with the volatilized solvent, and the amount of chlorine-containing binder (binder) remaining on the base layer side was reduced.
  • a PEN film with an average thickness of 4.0 ⁇ m was used as the base layer.An undercoat layer was formed so that the average thickness was 880 nm, and a back layer was formed so that the average thickness was 0.30 ⁇ m, and a magnetic tape with an average thickness of 5.25 ⁇ m was obtained.Furthermore, a magnetic recording cartridge containing the magnetic tape was obtained in the same manner as in Comparative Example 1.
  • the processing time in the bead mill in the preparation process of the coating material for forming the undercoat layer was extended by 1.2 times compared to that in Comparative Example 1, and the dispersion was increased, thereby increasing the amount of adsorption of the chlorine-containing binder in the undercoat layer, which was moved to the interface side of the undercoat layer and the base layer by the solvent that seeped in during the application of the magnetic layer, and the amount of the chlorine-containing binder (binder) in the undercoat layer that moves to the interface side of the undercoat layer and the base layer due to the solvent that seeped in during the application of the magnetic layer was reduced.
  • a PEN film with an average thickness of 4.0 ⁇ m was used as the base layer, and the magnetic powder was magnetically oriented in the thickness direction of the film by a solenoid coil.
  • the squareness ratio in the tape running direction (longitudinal direction) of the magnetic recording medium was set to 32%.
  • a calendaring process was performed to smooth the magnetic layer surface. At this time, since the calendaring efficiency changes due to the large amount of adsorbed chlorine-containing binder (binder), the conditions (temperature) of the calendaring process were adjusted to obtain the same surface properties as in Comparative Example 1, and then a re-hardening process was performed to obtain a magnetic tape with an average thickness of 5.25 ⁇ m.
  • a magnetic recording cartridge containing the magnetic tape was obtained in the same manner as in Comparative Example 1.
  • various values related to chlorine distribution, the temperature expansion coefficient ⁇ , the humidity expansion coefficient ⁇ , the average thickness of the base layer, the average thickness of the magnetic recording medium, the average thickness of the underlayer, the average thickness of the back layer, and the arithmetic mean roughness Ra of the surface of the magnetic layer were measured in the same manner as in Comparative Example 1. The measurement results are shown in Table 1 below.
  • the drying temperature after the magnetic layer was applied was higher than that in Example 1, and the solvent volatilization rate from the magnetic layer surface was increased, so that the chlorine-containing binder that had once migrated to the base layer side was migrated to the magnetic layer surface side together with the volatilized solvent, and the amount of chlorine-containing binder (binder) remaining on the base layer side was reduced.
  • a reinforced PET film with an average thickness of 4.0 ⁇ m was used as the base layer, and a re-hardening process was performed after calendaring, and the roll was rewound, and then a strain relaxation process (similar to the hardening conditions) was additionally performed.
  • the processing time in the bead mill in the preparation process of the coating material for forming the undercoat layer is extended by 1.1 times compared to the case of Comparative Example 1, and the amount of the chlorine-containing binder adsorbed is increased by increasing the dispersion, and the amount of the chlorine-containing binder that moves to the interface side of the undercoat layer and the base layer by the solvent that permeates during the application of the magnetic layer is reduced.
  • a reinforced PET film with an average thickness of 4.0 ⁇ m is used, and after calendaring, a re-hardening process is performed, and after rewinding the roll, a strain relaxation process (same as the hardening conditions) is additionally performed, to obtain a magnetic tape with an average thickness of 5.28 ⁇ m.
  • a magnetic recording cartridge containing the magnetic tape is obtained.
  • various values related to chlorine distribution, the temperature expansion coefficient ⁇ , the humidity expansion coefficient ⁇ , the average thickness of the base layer, the average thickness of the magnetic recording medium, the average thickness of the underlayer, the average thickness of the back layer, and the arithmetic mean roughness Ra of the surface of the magnetic layer were measured in the same manner as in Comparative Example 1. The measurement results are shown in Table 1 below.
  • the reliability of the magnetic tape contained in each of the magnetic recording cartridges manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 was evaluated. The evaluation was performed as follows.
  • the magnetic recording cartridges of Examples 1 to 3 and Comparative Examples 1 to 4 were inserted into the LTO8 drive immediately after the cleaning tape had been run, and one round trip recording process was performed after the insertion. This operation was performed on the magnetic recording cartridges of Examples 1 to 3 and Comparative Examples 1 to 4, each having a large number of turns. The recording process was performed sequentially on 25 turns (25 round trips) of the magnetic recording cartridge, and when the cartridge ran without any problems in the recording process of any turn, the reliability was determined to be "good.” If rewrites occurred twice at any point before the recording process of 25 reels was completed, the reliability was determined to be "bad.” The number of reels on which rewrites occurred twice was also recorded. The evaluation results for each magnetic tape are shown in Table 1 below.
  • Table 1 show that reliability during running is improved by making the thickness of the portion of the underlayer where the chlorine count is equal to or greater than the threshold smaller.
  • the results shown in the same table suggest that reliability during running of the magnetic tape is improved by making the thickness of the portion where the chlorine count is equal to or greater than the threshold, for example, 130 nm or less, 125 nm or less, or 123 nm or less, and more preferably 120 nm or less, 110 nm or less, 100 nm or less, or 90 nm or less.
  • the results shown in Table 1 also show that reliability during running is improved by having a smaller proportion of the thickness of the underlayer where the chlorine count is equal to or greater than the threshold.
  • the results shown in the table suggest that reliability during running of the magnetic tape is improved by having the proportion of the thickness of the portion where the chlorine count is equal to or greater than the threshold preferably be 13% or less, more preferably be 12% or less or 11% or less, and even more preferably be 10% or less, 9.5% or less, or 9% or less.
  • the index Q is -250 ppm ⁇ Q ⁇ 250 PPM, so in a system such as LTO, it is possible to accommodate variations in the width of the magnetic recording medium by adjusting the drive's tape width adjustment mechanism (for example, tension control or head tilt mechanism) to ensure an off-track margin during recording and playback operations.
  • the drive's tape width adjustment mechanism for example, tension control or head tilt mechanism
  • the index R is -750 ppm ⁇ R ⁇ 750 PPM, so in a system such as LTO, it is possible to accommodate variations in the width of the magnetic recording medium by adjusting the drive's tape width adjustment mechanism (for example, tension control or head tilt mechanism) to ensure an off-track margin during recording and playback operations.
  • the drive's tape width adjustment mechanism for example, tension control or head tilt mechanism
  • the configurations, methods, steps, shapes, materials, and values given in the above-mentioned embodiments and examples are merely examples, and different configurations, methods, steps, shapes, materials, and values may be used as necessary.
  • the chemical formulas of compounds, etc. are representative, and are not limited to the valences, etc. given as long as they are general names of the same compounds.
  • a numerical range indicated using “ ⁇ ” indicates a range that includes the numerical values before and after " ⁇ " as the minimum and maximum values, respectively.
  • the upper or lower limit of a numerical range of a certain stage may be replaced with the upper or lower limit of a numerical range of another stage.
  • the materials exemplified in this specification may be used alone or in combination of two or more types.

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000090431A (ja) * 1998-09-10 2000-03-31 Fuji Photo Film Co Ltd 磁気テープ及びその製造方法
JP2000155935A (ja) * 1998-11-20 2000-06-06 Sony Corp 磁気記録媒体
JP2001273623A (ja) * 2000-01-18 2001-10-05 Toray Ind Inc 磁気記録媒体
JP2007265547A (ja) * 2006-03-29 2007-10-11 Fujifilm Corp 磁気記録媒体
WO2022097542A1 (ja) * 2020-11-09 2022-05-12 ソニーグループ株式会社 磁気記録媒体、磁気記録カートリッジおよび記録再生装置

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000090431A (ja) * 1998-09-10 2000-03-31 Fuji Photo Film Co Ltd 磁気テープ及びその製造方法
JP2000155935A (ja) * 1998-11-20 2000-06-06 Sony Corp 磁気記録媒体
JP2001273623A (ja) * 2000-01-18 2001-10-05 Toray Ind Inc 磁気記録媒体
JP2007265547A (ja) * 2006-03-29 2007-10-11 Fujifilm Corp 磁気記録媒体
WO2022097542A1 (ja) * 2020-11-09 2022-05-12 ソニーグループ株式会社 磁気記録媒体、磁気記録カートリッジおよび記録再生装置

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