Magnetic recording medium

A magnetic recording medium comprising:

• a magnetic layer;
• an underlayer;
• and a base layer in this order, wherein
• the underlayer contains a chlorine-containing binder, and
• in the underlayer, a part having a chlorine count equal to or more than a threshold described below has a thickness of 130 nm or less, and
• a second index R described below is −750 ppm or more and 750 ppm or less:
• [
• Threshold
• ]
• =
• [
• an
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ⁢
• in
• ⁢
• the
• ⁢
• underlayer
• ]
• +
• 6
• ×
• [
• a
• ⁢
• standard
• ⁢
• deviation
• ⁢
• determined
• ⁢
• in
• ⁢
• calculation
• ⁢
• of
• ⁢
• the
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ]
• ⁢
• R
• =
• 70
• [
• %
• ⁢
• RH
• ]
• ×
• (
• CTH
• -
• CTQ
• )
• where CHH is a humidity expansion coefficient [ppm/% RH] of a magnetic head, and CHR is a humidity expansion coefficient [ppm/% RH] of a value most deviated from the humidity expansion coefficient of the magnetic head among humidity expansion coefficients of the magnetic recording medium under a temperature environment of 10° C. or higher and 60° C. or lower.

A magnetic recording medium comprising:

• a magnetic layer;
• an underlayer;
• and a base layer in this order, wherein
• the underlayer contains a chlorine-containing binder, and
• in the underlayer, a part having a chlorine count equal to or more than a threshold described below has a thickness of 13% or less of a thickness of the underlayer, and
• a first index Q described below is −250 ppm or more and 250 ppm or less:
• [
• Threshold
• ]
• =
• [
• an
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ⁢
• in
• ⁢
• the
• ⁢
• underlayer
• ]
• +
• 6
• ×
• [
• a
• ⁢
• standard
• ⁢
• deviation
• ⁢
• determined
• ⁢
• in
• ⁢
• calculation
• ⁢
• of
• ⁢
• the
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ]
• ⁢
• Q
• =
• 50
• [
• °
• ⁢
• C
• .
• ]
• ×
• (
• CTH
• -
• CTQ
• )
• where CTH is a temperature expansion coefficient [ppm/° C.] of a magnetic head, and CTQ is a temperature expansion coefficient [ppm/° C.] of a value most deviated from the temperature expansion coefficient of the magnetic head among the temperature expansion coefficients of the magnetic recording medium under a relative humidity environment of 10% RH or more and 80% RH or less.

A magnetic recording medium comprising:

• a magnetic layer;
• an underlayer;
• and a base layer in this order, wherein
• the underlayer contains a chlorine-containing binder, and
• in the underlayer, a part having a chlorine count equal to or more than a threshold described below has a thickness of 13% or less of a thickness of the underlayer, and
• a second index R described below is −750 ppm or more and 750 ppm or less:
• [
• Threshold
• ]
• =
• [
• an
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ⁢
• in
• ⁢
• the
• ⁢
• underlayer
• ]
• +
• 6
• ×
• [
• a
• ⁢
• standard
• ⁢
• deviation
• ⁢
• determined
• ⁢
• in
• ⁢
• calculation
• ⁢
• of
• ⁢
• the
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ]
• ⁢
• R
• =
• 70
• [
• %
• ⁢
• RH
• ]
• ×
• (
• CTH
• -
• CTQ
• )
• where CHH is a humidity expansion coefficient [ppm/% RH] of a magnetic head, and CHR is a humidity expansion coefficient [ppm/% RH] of a value most deviated from the humidity expansion coefficient of the magnetic head among humidity expansion coefficients of the magnetic recording medium under a temperature environment of 10° C. or higher and 60° C. or lower.

A magnetic recording medium comprising:

• a magnetic layer;
• an underlayer;
• and a base layer in this order, wherein
• the underlayer contains a chlorine-containing binder, and
• in the underlayer, a part having a chlorine count equal to or more than a threshold described below has a thickness of 130 nm or less, and
• there is an environmental relative humidity between 10% RH and 80% RH at which a temperature expansion coefficient of the magnetic recording medium is 6.0 ppm/° C. or more and 8.0 ppm/° C. or less.
• [
• Threshold
• ]
• =
• [
• an
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ⁢
• in
• ⁢
• the
• ⁢
• underlayer
• ]
• +
• 6
• ×
• [
• a
• ⁢
• standard
• ⁢
• deviation
• ⁢
• determined
• ⁢
• in
• ⁢
• calculation
• ⁢
• of
• ⁢
• the
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ]

A magnetic recording medium comprising:

• a magnetic layer;
• an underlayer;
• and a base layer in this order, wherein
• the underlayer contains a chlorine-containing binder, and
• in the underlayer, a part having a chlorine count equal to or more than a threshold described below has a thickness of 130 nm or less, and
• there is an environmental temperature between 10° C. and 60° C. at which a humidity expansion coefficient of the magnetic recording medium is −4.0 ppm/° C. or more and 4.0 ppm/° C. or less.
• [
• Threshold
• ]
• =
• [
• an
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ⁢
• in
• ⁢
• the
• ⁢
• underlayer
• ]
• +
• 6
• ×
• [
• a
• ⁢
• standard
• ⁢
• deviation
• ⁢
• determined
• ⁢
• in
• ⁢
• calculation
• ⁢
• of
• ⁢
• the
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ]

A magnetic recording cartridge comprising:

• a case;
• and
• a reel which is accommodated in the case and around which a magnetic recording medium is wound, wherein
• the magnetic recording medium includes:
• a magnetic layer;
• an underlayer;
• and a base layer in this order,
• the underlayer contains a chlorine-containing binder,
• in the underlayer, a part having a chlorine count equal to or more than a threshold described below has a thickness of 130 nm or less, and
• there is an environmental relative humidity between 10% RH and 80% RH at which a temperature expansion coefficient of the magnetic recording medium is 6.0 ppm/° C. or more and 8.0 ppm/° C. or less.
• [
• Threshold
• ]
• =
• [
• an
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ⁢
• in
• ⁢
• the
• ⁢
• underlayer
• ]
• +
• 6
• ×
• [
• a
• ⁢
• standard
• ⁢
• deviation
• ⁢
• determined
• ⁢
• in
• ⁢
• calculation
• ⁢
• of
• ⁢
• the
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ]

A magnetic recording cartridge comprising:

• a case;
• and
• a reel which is accommodated in the case and around which a magnetic recording medium is wound, wherein
• the magnetic recording medium includes:
• a magnetic layer;
• an underlayer;
• and a base layer in this order,
• the underlayer contains a chlorine-containing binder,
• in the underlayer, a part having a chlorine count equal to or more than a threshold described below has a thickness of 130 nm or less, and
• there is an environmental temperature between 10° C. and 60° C. at which a humidity expansion coefficient of the magnetic recording medium is −4.0 ppm/° C. or more and 4.0 ppm/° C. or less.
• [
• Threshold
• ]
• =
• [
• an
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ⁢
• in
• ⁢
• the
• ⁢
• underlayer
• ]
• +
• 6
• ×
• [
• a
• ⁢
• standard
• ⁢
• deviation
• ⁢
• determined
• ⁢
• in
• ⁢
• calculation
• ⁢
• of
• ⁢
• the
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ]

A recording and reproducing apparatus comprising:

• a spindle to which a magnetic recording medium is mountable;
• a driver that drives the spindle;
• and
• a magnetic head that performs recording and reproducing of the magnetic recording medium, wherein
• the magnetic recording medium includes:
• a magnetic layer;
• an underlayer;
• and a base layer in this order,
• the underlayer contains a chlorine-containing binder,
• in the underlayer, a part having a chlorine count equal to or more than a threshold described below has a thickness of 130 nm or less, and
• there is an environmental relative humidity between 10% RH and 80% RH at which a temperature expansion coefficient of the magnetic recording medium is 6.0 ppm/° C. or more and 8.0 ppm/° C. or less.
• [
• Threshold
• ]
• =
• [
• an
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ⁢
• in
• ⁢
• the
• ⁢
• underlayer
• ]
• +
• 6
• ×
• [
• a
• ⁢
• standard
• ⁢
• deviation
• ⁢
• determined
• ⁢
• in
• ⁢
• calculation
• ⁢
• of
• ⁢
• the
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ]

A recording and reproducing apparatus comprising:

• a spindle to which a magnetic recording medium is mountable;
• a driver that drives the spindle;
• and
• a magnetic head that performs recording and reproducing of the magnetic recording medium, wherein
• the magnetic recording medium includes:
• a magnetic layer;
• an underlayer;
• and a base layer in this order,
• the underlayer contains a chlorine-containing binder,
• in the underlayer, a part having a chlorine count equal to or more than a threshold described below has a thickness of 130 nm or less, and
• there is an environmental temperature between 10° C. and 60° C. at which a humidity expansion coefficient of the magnetic recording medium is −4.0 ppm/° C. or more and 4.0 ppm/° C. or less.
• [
• Threshold
• ]
• =
• [
• an
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ⁢
• in
• ⁢
• the
• ⁢
• underlayer
• ]
• +
• 6
• ×
• [
• a
• ⁢
• standard
• ⁢
• deviation
• ⁢
• determined
• ⁢
• in
• ⁢
• calculation
• ⁢
• of
• ⁢
• the
• ⁢
• average
• ⁢
• chlorine
• ⁢
• count
• ]