The present technology provides a tape-shaped magnetic recording medium including: a magnetic layer; an underlayer; a base layer; and a back layer, in which the number of recesses having a depth of 20% or more of the thickness of the magnetic layer is 10 or more and 200 or less per surface area of 1600 μm.sup.2, the base layer includes a polyester as a main component, a surface on a side of the back layer has a kurtosis of 2.0 or more and 4.4 or less, the magnetic recording medium has an average thickness t.sub.T of 5.6 μm or less, the magnetic recording medium includes a lubricant, the magnetic recording medium has pores, and the pores have an average diameter of 6 nm or more and 11 nm or less when the diameters of the pores are measured in a state where the lubricant has been removed from the magnetic recording medium and the magnetic recording medium has been dried.

A biaxially orientated polyester film has a P.sub.L/V.sub.L ratio of 0.3 to 1.2, P.sub.L and V.sub.L representing the average diameter of the convex portions and the average diameter of the concave portions, respectively, that are defined on the basis of a slice level with a height of 0 nm (reference plane) in a roughness curve determined for at least one surface using a three dimensional surface roughness meter, and the convex portions accounting for an area ratio of 30% to 51% of the reference plane. The biaxially oriented polyester film is excellent in travelling property, slitting property, and dimensional stability, and serves, when used for magnetic recording medium production, to provide a high density magnetic recording medium having a smooth magnetic layer, suffering little dimensional change due to variations in environmental parameters such as temperature and humidity or due to storage, and having good electromagnetic conversion characteristics with little dropout.

A magnetic recording medium is a magnetic recording medium in the form of a tape and includes a substrate, a foundation layer provided on the substrate, and a magnetic layer provided on the foundation layer and containing a magnetic powder. The foundation layer and the magnetic layer each contain a lubricant. A squareness ratio of the magnetic layer in a perpendicular direction is equal to or higher than 65%, an average thickness of the magnetic recording medium is equal to or smaller than 5.6 μm, a plurality of recessed portions each having a depth corresponding to 20% or higher of the average thickness of the magnetic layer is provided on a surface of the magnetic layer, and the number of the recessed portions per unit area of 1,600 μm.sup.2 of the surface of the magnetic layer is equal to or greater than 20 and equal to or smaller than 200, and an amount of exudation of the lubricant per unit region of 12.5 μm×9.3 μm on the surface of the magnetic layer in a vacuum is equal to or greater than 3.0 μm.sup.2 and equal to or smaller than 6.5 μm.sup.2.

The magnetic recording medium includes a non-magnetic support; a magnetic layer including a ferromagnetic powder on one surface of the non-magnetic support; and a back coating layer including a non-magnetic powder on the other surface of the non-magnetic support, in which a difference (S.sub.after−S.sub.before) between a spacing S.sub.after measured by optical interferometry regarding a surface of the back coating layer after ethanol cleaning and a spacing S.sub.before measured by optical interferometry regarding the surface of the back coating layer before ethanol cleaning is greater than 0 nm and equal to or smaller than 15.0 nm, and the non-magnetic support is an aromatic polyester support having a moisture absorption of 0.3% or less.

An object is to provide a magnetic recording medium having excellent traveling stability and a thin total thickness.

The present technology provides a tape-shaped magnetic recording medium including: a magnetic layer; an underlayer; a base layer; and a back layer, in which the number of recesses having a depth of 20% or more of the thickness of the magnetic layer is 10 or more and 200 or less per surface area of 1600 μm.sup.2, the base layer includes a polyester as a main component, a surface on a side of the back layer has a kurtosis of 2.0 or more and 4.4 or less, the magnetic recording medium has an average thickness t.sub.T of 5.6 μm or less, the magnetic recording medium includes a lubricant, the magnetic recording medium has pores, and the pores have an average diameter of 6 nm or more and 11 nm or less when the diameters of the pores are measured in a state where the lubricant has been removed from the magnetic recording medium and the magnetic recording medium has been dried.

A magnetic recording medium that can exhibit good traveling performance during use is provided. This magnetic recording medium is a tape-shaped magnetic recording medium, and includes a substrate, a base layer disposed on the substrate, and a magnetic layer disposed on the base layer. On the surface of the magnetic layer, recesses having a depth of 20% or more of the average thickness of the magnetic layer are formed at a ratio of 20 or more and 200 or less per 1600 μm.sup.2. On the surface of the magnetic layer, a logarithmic decay rate determined by a pendulum viscoelasticity test at a temperature of 10° C. or higher and 45° C. or lower is 0.025 or more and 0.040 or less. A difference between a maximum value of the logarithmic decay rate and a minimum value of the logarithmic decay rate is 0 or more and 0.020 or less. The squareness ratio in the perpendicular direction is 65% or more. The average thickness of the magnetic layer is 80 nm or less. The average thickness of the magnetic recording medium is 5.6 μm or less.

A magnetic recording medium that can exhibit good traveling performance during use is provided. This magnetic recording medium is a tape-shaped magnetic recording medium, and includes a substrate, a base layer disposed on the substrate, and a magnetic layer disposed on the base layer. The substrate includes a polyester as a main component. The average thickness of the base layer is 0.9 μm or less. The base layer and the magnetic layer each include a lubricant. The magnetic layer has a surface having a large number of holes, and the arithmetic average roughness Ra of the surface is 2.5 nm or less. The BET specific surface area of the entire magnetic recording medium is 3.5 m.sup.2/g or more in a state where the lubricant has been removed from the magnetic recording medium and the magnetic recording medium has been dried. The squareness ratio in the perpendicular direction is 65% or more. The average thickness of the magnetic layer is 90 nm or less. The average thickness of the magnetic recording medium is 5.6 μm or less.

The magnetic recording medium includes: a non-magnetic support; and a magnetic layer including ferromagnetic powder, in which a difference S.sub.after−S.sub.before between a spacing S.sub.after measured on a surface of the magnetic layer by optical interferometry after ethanol cleaning and a spacing S.sub.before measured on the surface of the magnetic layer by optical interferometry before ethanol cleaning is more than 0 nm and 6.0 nm or less, and the non-magnetic support is an aromatic polyester support having a moisture absorption of 0.3% or less.

An object is to provide a magnetic recording medium having excellent traveling stability and a thin total thickness.

The present technology provides a tape-shaped magnetic recording medium including: a magnetic layer; an underlayer; a base layer; and a back layer, in which a surface on a side of the magnetic layer has a kurtosis of 3.0 or more, a surface on a side of the back layer has a kurtosis of 2.0 or more, the surface on the magnetic layer side has arithmetic average roughness R.sub.a of 2.5 nm or less, the base layer includes a polyester as a main component, the magnetic recording medium has an average thickness t.sub.T of 5.6 μm or less, the magnetic recording medium includes a lubricant, the lubricant includes a fatty acid and a fatty acid ester, and a mass ratio between the fatty acid and the fatty acid ester extracted with hexane satisfies fatty acid/fatty acid ester ≤0.6, and the magnetic recording medium has pores, and the pores have an average diameter of 6 nm or more and 11 nm or less when the diameters of the pores are measured in a state where the lubricant has been removed from the magnetic recording medium and the magnetic recording medium has been dried.

A magnetic recording medium is a magnetic recording medium in the form of a tape and includes a substrate, a foundation layer provided on the substrate, and a magnetic layer provided on the foundation layer and containing a magnetic powder. The foundation layer and the magnetic layer each contain a lubricant. A squareness ratio of the magnetic layer in a perpendicular direction is equal to or higher than 65%, an average thickness of the magnetic recording medium is equal to or smaller than 5.6 μm, a plurality of recessed portions each having a depth corresponding to 20% or higher of the average thickness of the magnetic layer is provided on a surface of the magnetic layer, and the number of the recessed portions per unit area of 1,600 μm.sup.2 of the surface of the magnetic layer is equal to or greater than 20 and equal to or smaller than 200, and an amount of exudation of the lubricant per unit region of 12.5 μm×9.3 μm on the surface of the magnetic layer in a vacuum is equal to or greater than 3.0 μm.sup.2 and equal to or smaller than 6.5 μm.sup.2.