The magnetic tape includes a non-magnetic support, and a magnetic layer including a ferromagnetic powder. The non-magnetic support is a polyethylene naphthalate support, and a deformation rate ratio of a deformation rate in a width direction to a deformation rate in a longitudinal direction of the magnetic tape, (the deformation rate in the width direction/the deformation rate in the longitudinal direction), is 0.42 or less, the deformation rates each being measured after a load is applied in the longitudinal direction of the magnetic tape for 96 hours.

The magnetic tape cartridge group includes a plurality of magnetic tape cartridges. Regarding 100 reels of magnetic tape cartridges, in a case where a maximum value of an absolute value of a difference between a servo band spacing obtained before predetermined storage and a servo band spacing obtained after the predetermined storage is defined as A, an arithmetic mean of medium lives calculated by a linear function derived from a value of A obtained for different N and a value of the logarithm of total storage time T of the storage of N cycles is 3 years or longer and 3σ is 1 year or shorter. Medium life: T in a case where A satisfies A=1.5−B. B: a value calculated by multiplying a difference between a maximum value and a minimum value of servo band spacings obtained in each of the five environments by ½.

A magnetic tape in which a minimum value of TDStens among five TDStens measured respectively at a temperature of 16° C. and a relative humidity of 20%, a temperature of 16° C. and a relative humidity of 80%, a temperature of 26° C. and a relative humidity of 80%, a temperature of 32° C. and a relative humidity of 20% and a temperature of 32° C. and a relative humidity of 55% is 1.43 μm/N or more, a ratio of a change of TDStens to a change of a relative humidity obtained from the five TDStens is 0.005 μm/N/% or less, and a ratio of a change of TDStens to a change of a temperature obtained from the five TDStens is 0.020 μm/N/° C. or less.

A method for making a magnetic recording tape, in accordance with one approach, includes coupling an underlayer to a substrate, the substrate comprising a poly ether ether ketone (PEEK). A method for making a magnetic recording tape in accordance with another approach includes coupling an underlayer to a substrate via radiation-induced grafting, the substrate comprising a poly ether ether ketone (PEEK). A recording layer may be coupled to the underlayer.

Provided is a magnetic tape cartridge of a single reel type in which a magnetic tape is wound around a reel, in which the magnetic tape includes a non-magnetic support and a magnetic layer containing a ferromagnetic powder, and has a tape thickness of 5.3 μm or less, the magnetic layer includes a plurality of servo bands, and a difference (G.sub.inner−G.sub.outer) between a servo band interval G.sub.inner in a range of 49 m to 51 m from a tape inner end and a servo band interval G.sub.outer in a range of 49 m to 51 m from a tape outer end is −3.9 μm to −1.1 μm as a value measured on 100th day from a date of magnetic tape cartridge manufacture.

A magnetic recording tape, in accordance with one approach, includes a substrate comprising a poly ether ether ketone (PEEK). An underlayer is positioned above the substrate. A recording layer is positioned above the underlayer. A tape cartridge, in accordance with one approach, includes a housing and a magnetic recording tape at least partially stored in the housing. The magnetic recording tape includes a substrate comprising a poly ether ether ketone (PEEK), an underlayer above the substrate, and a recording layer above the underlayer.

An object of the present invention is to more conveniently provide a copolyester for a polyester film which exhibits excellent dimensional stability and in particular excellent dimensional stability against environmental changes in, for example, temperature and humidity, and has a small film elongation percentage at 110° C. A copolyester of the present invention comprises: (A) an aromatic dicarboxylic acid component; (B) an alkylene glycol component; and (C1) a dimer acid component and/or (C2) a dimer diol component, wherein the copolyester contains, with reference to a molar number of a total dicarboxylic acid component, 0.5 to 3.5 mol % of the dimer acid component (C1) and/or 0.3 to 5.0 mol % of the dimer diol component (C2).

The present disclosure provides where a magnetic recording medium is provided and includes a base; an underlayer that is provided over the base and includes a non-magnetic powder; and a magnetic layer that is provided over the underlayer and includes a magnetic powder and a binder, wherein an average particle volume V of the magnetic powder is 1600 nm.sup.3 or less, an average thickness of the magnetic recording medium is 5.3 μm or less, a thermal stability K.sub.uV.sub.act/k.sub.BT of the magnetic recording medium is 63 or more, and a ratio Hrp/Hc1 of a residual coercive force Hrp of the magnetic recording medium measured using a pulsed magnetic field in a perpendicular direction to a coercive force Hc1 of the magnetic recording medium in the perpendicular direction is 1.98 or less.

A method for making a magnetic recording tape, in accordance with one approach, includes coupling an underlayer to a substrate, the substrate comprising a poly ether ether ketone (PEEK). A method for making a magnetic recording tape in accordance with another approach includes coupling an underlayer to a substrate via radiation-induced grafting, the substrate comprising a poly ether ether ketone (PEEK). A recording layer is coupled to the underlayer.

The magnetic tape satisfies TDSage+TDSenv−TC≤0.30 μm. TDSage is a maximum absolute value of a difference between the servo band interval obtained before a predetermined storage and the servo band interval obtained after the storage, TDSenv is a value calculated by multiplying a difference between a maximum value and a minimum value of the servo band interval respectively obtained under five predetermined environments by ½, TC is a value calculated by multiplying TDStens by 0.5 N, and TDStens is a ratio of a change in the servo band interval to a change in tension calculated from the servo band interval respectively obtained under five predetermined environments by applying a plurality of different tensions in the longitudinal direction of the magnetic tape.