JP2666498B2 - Metal thin film magnetic recording media - Google Patents

Description

The present invention relates to a metal thin-film magnetic recording medium.

[Prior Art] As a metal thin-film magnetic recording medium, a magnetic recording medium in which a metal thin-film magnetic layer is provided on a polyester film is known (for example, JP-A-58-68225).

[Problems to be Solved by the Invention] A metal thin film magnetic recording medium in which a metal thin film magnetic layer is provided on a base film by a method such as vapor deposition is a magnetic recording medium for high density recording due to its output characteristics and frequency characteristics. Is regarded as important. However, in the above-mentioned conventional metal thin film type magnetic recording medium, the durability (hereinafter referred to as durability) of the magnetic layer is insufficient, and the size of the particles contained in the base film is increased in order to improve the durability. Then, there was a problem that the output characteristics became poor.

It is an object of the present invention to improve such a problem and to provide a metal thin-film magnetic recording medium selected for the durability of a magnetic layer while maintaining the excellent output characteristics inherently provided by the metal thin-film magnetic recording medium. I do.

[Means for Solving the Problems] The present invention provides (1) a metal thin film magnetic recording medium in which a metal thin film magnetic layer is provided on at least one surface of a base film, wherein the base film is made of a thermoplastic resin. A biaxially oriented film in which a layer (B layer) made of thermoplastic resin B containing inert particles is laminated on at least one surface of a layer made of A (layer A), and the inert particles contained in layer B the average particle diameter d _B is 5 to 200 nm, the content of the particles of the layer B 1.5 of
40 wt%, 0.1 ratio t _B / d _B of the B layer and the thickness t _B average particle diameter d _B
(2) a thermoplastic resin containing inert particles on one surface of a layer (A layer) made of thermoplastic resin A, wherein A biaxially oriented film comprising a layer (B layer) made of B and a surface (C surface) made of a thermoplastic resin C containing inert particles on the other surface, wherein the layer B of the substrate film and metal thin film type magnetic layer is provided only on the side, the average particle diameter d _B of the inert particles contained in the B layer is 5 to 80 nm, the content of the particles of the layer B 1.5 to 40 wt%, the ratio t _B / d _B is from 0.1 to 3 in average particle diameter d _B and the thickness t _B of the B layer, the average particle diameter d _C of the inert particles contained in the C layer is 40 to 200 nm, the particles of C amount contained in the layer is 1.5 to 40 wt%, the metal thin film type magnetic recording medium, wherein the ratio t _C / d _C of the average particle diameter d _C the thickness t _C of the C layer is 0.1 to 3 thereof To the essence It is.

Thermoplastic resin A constituting the base film of the present invention,
B and C may be the same or different, and are not particularly limited, such as polyester, polyolefin, polyamide, and polyphenylene sulfide. In particular, polyester, especially ethylene terephthalate, ethylene α, β-bis (2- Chlorphenoxy) ethane-4,
When at least one structural unit selected from the group consisting of 4'-dicarboxylate and ethylene 2,6-naphthalate is used as a main component, the durability is further improved, which is desirable.

Here, in particular, the thermoplastic resin B and / or the thermoplastic resin constituting the present invention.
Or, C is very desirable because it has better durability when it is crystalline. The crystallinity here indicates that it is not so-called amorphous, and quantitatively, the cold crystallization temperature Tcc in the crystallinity parameter is detected, and the crystallization parameter ΔTcg is 150 ° C or less. . Further, when the heat of fusion (change in enthalpy of fusion) measured by a differential scanning calorimeter shows a crystallinity of 7.5 cal / g or more, the durability is further improved, which is extremely desirable.
In addition, in the case of a polyester containing ethylene terephthalate as a main component, the durability is further improved, which is particularly desirable.

As long as the present invention is not impaired, at least one of the thermoplastic resins A, B, and C may be mixed with another type of thermoplastic resin, or a copolymer may be used. In addition, organic additives such as an antioxidant, a heat stabilizer, a lubricant, and an ultraviolet absorber are usually added to at least one selected from the thermoplastic resins A, B, and C within a range that does not impair the object of the present invention. It may be added to some extent.

The average particle diameter d _B of the inert particles in the B layer of the base film constituting the metal thin film type magnetic recording medium of the present invention is required to be 5~200nm view of durability, further B layer The thickness is preferably 5 to 80 nm when a magnetic layer is provided, and 40 to 200 nm when no magnetic layer is provided.

The average particle size d _{C of the} inert particles in the C layer of the base film
The thickness is preferably from 40 to 200 nm in order to obtain a film handling property in a processing step such as vapor deposition and a good running property without back coating.

Further, the layer A of the base film does not particularly need to contain inert particles, but has an average particle size of 5 to 200 nm, particularly 10 to 200 nm.
0.001 to 0.15% by weight of inert particles of ~ 150 nm, especially 0.005%
It is desirable for the content to be 0.05% by weight, since the durability will be further improved.

The inert particles used in the present invention are desirably particles having a particle size ratio (particle major axis / minor axis) of 1.0 to 1.3, particularly spherical particles, because durability is further improved.

The inert particles used in the present invention are particularly desirable when the single particle index in the film is 0.7 or more, preferably 0.9 or more, because the durability is further improved.

The inert particles used in the present invention have a relative standard deviation of the particle size.
When the value is 0.6 or less, preferably 0.5 or less, it is desirable because the durability is further improved.

The type of the inert particles used in the present invention is not particularly limited, and examples thereof include substantially spherical silica particles caused by colloidal silica, particles made of a crosslinked polymer (for example, crosslinked polyethylene), and the like. Temperature (measured using a thermogravimetric analyzer Shimadzu TG-30M in nitrogen.
(0 ° C./min) is particularly desirable in the case of crosslinked polymer particles having a high degree of crosslinking until the temperature reaches 380 ° C. or higher, since the durability is further improved. In the case of spherical silica originating from colloidal silica, it is particularly desirable in the case of substantially spherical silica produced by the alkoxide method and having a low sodium content and substantially spherical, since the durability is further improved. However, other particles such as calcium carbonate, titanium dioxide, alumina and the like may be used to form the thermoplastic resin B layer having a thickness t _B.
Those literate enough by appropriate control of the ratio of the average particle diameter d _B as.

The content of the inert particles in the base film B layer of the present invention is
It is necessary to be 1.5 to 40% by weight, preferably 2 to 30% by weight, more preferably 3 to 20% by weight. If the content is less than the above range, the durability becomes poor, and if it is too high, the output characteristics become poor, which is not preferable.

The ratio t _B / d _B having an average particle diameter d _B of the inert particles contained in the thickness t _B and the B layer of the base film layer B of the present invention is 0.1 to 3, preferably 0.2 to 2.0, more preferably Must be in the range of 0.3 to 1.5. t _B / d _B is the range smaller than the durability of the bad, because a large output characteristic conversely becomes poor undesirably.

Further, the content of the inert particles contained in the C layer is 1.5 to 4
0% by weight, preferably 2-15% by weight,
It is necessary to obtain a magnetic recording medium having a good handling property of the film in a processing step such as vapor deposition and a good running property without a back coat treatment.

The thickness t _{C of the} C layer and the average particle size of the contained inert particles
that the ratio t _C / d _C of d _C in the range of 0.1 to 3 is to further improve the handling properties of the film in processing steps such as vapor deposition, even more more runnability when no back coat treatment It is necessary to make it good.

The base film constituting the present invention is a film obtained by biaxially orienting a laminated film made of the above composition, and a uniaxial or non-oriented film is not preferable because the winding appearance is poor. The degree of this orientation is not particularly limited, but the output characteristics and durability are further improved when the Young's modulus, which is a measure of the degree of molecular orientation of the polymer, is 350 kg / mm ² or more in both the longitudinal direction and the width direction. So highly desirable. The upper limit of the Young's modulus, which is a measure of the degree of molecular orientation, is not particularly limited, but usually about 1500 kg / mm ² is the manufacturing limit.

When the total reflection Raman crystallization index of the surface of the layer B of the base film constituting the present invention is 20 cm ^-1 or less, the durability is further improved, and the handling property is also improved.

Further, when the total reflection Raman crystallization index of the surface of the C layer of the base film constituting the present invention is 20 cm ^-1 or less, the durability is further improved, and the handling property is also improved.

The present invention is a magnetic recording medium in which a metal thin film type magnetic layer is provided on at least one surface of the above-mentioned biaxially oriented film. The type of the metal thin film type magnetic layer is not particularly limited, but a ferromagnetic thin film of iron, cobalt, nickel, chromium or an alloy thereof, a metal oxide thin film layer obtained by evaporating a metal in an oxygen atmosphere, or the like is preferably used.

The thickness t _M of the metal thin film type magnetic layer is not particularly limited, the ratio of the thickness t _B of the magnetic layer side of the layer B (more), t _B / t _M 0.02 to 1
When the ratio is 50, particularly 0.1 to 150, and more preferably 0.2 to 100, the output characteristics and durability are further improved, which is desirable. The value of t _M is 0.02 to
It is preferable to set the thickness in the range of 0.5 μm and in the case of perpendicular recording in the range of 0.2 to 1.5 μm, because the output characteristics and durability are further improved.

When the thickness unevenness in the width direction of the layer B of the base film constituting the present invention is 25% or less, more preferably 20% or less, it is particularly desirable because output characteristics and durability are further improved.

The thickness of the B layer of the base film constituting the present invention is 0.00
When the thickness is 5 to 0.6 μm, preferably 0.01 to 0.5 μm, durability and output characteristics are further improved, which is particularly desirable.

It is preferable that the protrusion height on the surface of the layer B of the base film constituting the present invention is 25 nm or more, preferably 30 nm or more, because durability and output characteristics are further improved. In addition, 100 or more protrusions more than double rings measured by the multiple interference method
0 cm ² or less is desirable.

The ratio of the center line average roughness Ra and the maximum height Rt of the surface of the B layer of the base film constituting the present invention, Rt / Ra is 9.0 or less, particularly
A value of 8.5 or less is particularly preferable because output characteristics and durability are further improved.

The surface layer particle concentration ratio measured by the secondary ion mass spectrum of the surface of the layer B of the base film constituting the present invention is not particularly limited, but the surface layer particle concentration ratio is 1/10 or less,
In particular, when the ratio is 1/50 or less, durability and output characteristics are further improved, which is particularly desirable.

Further, fine projections may be formed by applying a water-soluble polymer to at least one surface of the base film constituting the present invention. In this case, the magnetic layer may be on the side to which the water-soluble polymer is applied, or may be on the specific coating side.

Next, a method for manufacturing the magnetic recording medium of the present invention will be described.

First, as a method of incorporating the inert particles into the thermoplastic resin B, a method in which the inert particles are made into a slurry of ethylene glycol and kneaded into the thermoplastic resin using a vent-type biaxial kneading extruder without stretching and breaking. It is very effective for obtaining a base film having a relationship between the thickness and the average particle diameter and the content in the range of the present invention.

As a method of adjusting the content of the particles, a high-concentration master is prepared by the above method, and the content is adjusted by diluting the master with a thermoplastic resin substantially free of inert particles during film formation. The method is effective.

Next, the thermoplastic resin A and the pellets of the thermoplastic resin B containing a predetermined amount of inert particles are dried as necessary, and then supplied to a known extruder for melt lamination to form a sheet from a slit-shaped die. Extruded and cooled and solidified on a casting roll to make an unstretched film. That is, 2
Alternatively, thermoplastic resins A and B are laminated using three extruders, two or three layers of manifolds or merging blocks, and two or three layers of sheets are extruded from a die, cooled with a casting roll, and unstretched film. make. In this case, the method of installing a static mixer and a gear pump in the polymer passage of the thermoplastic resin B does not cause stretching and breaking, and the film having the relationship between the thickness and the average particle diameter within the range of the present invention, the content, and the surface layer particle concentration ratio within the desirable range. It is effective to get
Also, the use of a rectangular feed block as the merging block is extremely effective for obtaining the thickness unevenness in the range of the present invention. Further, the melting temperature of the extruder on the thermoplastic resin B side is higher by 10 to 40 ° C. than that on the thermoplastic resin A side, without stretching and breaking, the relationship between the thickness and the average particle diameter in the range of the present invention, the content, It is effective to obtain a film having a desired range of the thickness unevenness, the surface layer particle concentration ratio, and the total reflection Raman crystallization index. In the above description, A / B and B / A / B were described as configurations. In the case of the B / A / C configuration, a three-layer manifold or a merging block was similarly formed using three extruders. The thermoplastic resins B, A, and C are laminated, and a three-layer sheet is extruded from a die and cooled by a casting roll to form an unstretched film.

Next, the unstretched film is biaxially stretched and biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used. However, first use the sequential biaxial stretching method of stretching in the longitudinal direction, then in the width direction,
The longitudinal stretching is divided into three or more stages and the total longitudinal stretching ratio is
The method carried out at a ratio of 3.0 to 6.5 times is effective for obtaining a film having the relationship between the thickness and the average particle size in the range of the present invention and the content.
The longitudinal stretching temperature varies depending on the type of the thermoplastic resin and cannot be generally described, but usually, the first stage is set to 50 to 130 ° C., and it is preferable that the second and subsequent stages have a lamination thickness within a desirable range of the present invention. Irregularity, effective for obtaining a surface particle concentration ratio film. The longitudinal stretching speed is 5,000 to 50,000% /
A range of minutes is preferred. As a stretching method in the width direction, a method using a stenter is generally used. Stretch ratio is 3.0
A range of up to 5.0 times is appropriate. The stretching speed in the width direction is 100
The preferred range is 0 to 20000% / min and the temperature is in the range of 80 to 160 ° C. Next, this stretched film is heat-treated. The heat treatment temperature in this case is 170-200 ° C, especially 170-190 ° C, and the time is 0.5-6.
A range of 0 seconds is preferred.

Next, a metal thin film is formed on this film. The method of depositing the magnetic layer can be performed by a known method,
For example, it is preferable to form a metal thin film of iron, cobalt, nickel or an alloy thereof directly on a base film by vacuum deposition, ion plating, sputtering, or the like, or via a base thin film of aluminum, titanium, chromium, or the like. In this case, the direction of the axis of easy magnetization is not particularly limited, but perpendicular magnetization by oblique deposition is particularly preferable from the viewpoint of durability.

[Method for Measuring Physical Properties and Method for Evaluating Effect] The method for measuring characteristic values and the method for evaluating effect according to the present invention are as follows.

(1) Average particle size of particles The thermoplastic resin is removed from the film by a plasma low-temperature incineration method to expose the particles. Processing conditions are selected such that the thermoplastic resin is ashed but the particles are not damaged. This is observed with a scanning electron microscope (SEM), and the image of the particles is processed with an image analyzer. The following numerical processing is performed for the number of particles of 5,000 or more by changing the observation point, and the number average diameter D obtained by this is defined as the average particle diameter.

D = ΣD _i / N where, D _i is a circle equivalent diameter of the particles, N is the a number of particles.

(2) Particle size ratio In the measurement of the above (1), (average value of major axis) of particles
/ (Average value of minor axis). That is, it is obtained by the following equation.

Major axis = ΣD1i / N Minor axis = ΣD2i / N D1i and D2i are the major axis (maximum diameter) and the minor axis (shortest axis) of each particle, and N is the number of particles.

(3) Relative standard deviation of particle diameter Standard deviation σ [= ｛Σ (D _i −) calculated from individual particle diameter D _i , average diameter D, and number N of particles measured by the method (1).
D) ² / N｝ ^1/2 ] divided by the average diameter D (σ / D).

(4) Single Particle Index A cross section of the film is photographically observed with a transmission electron microscope (TEM) to detect particles. When the observation magnification is set to about 100,000, one particle that cannot be further divided can be observed. When the total area occupied by the particles is A, and the area occupied by the aggregate in which two or more particles are agglomerated is B,
Let (AB) / A be the single particle index. The TEM conditions are as follows. One visual field area: 2 μm ² , measurement was performed at 500 visual fields at different locations.

• Observation magnification: 100,000 times • Acceleration voltage: 100 kV • Section thickness: about 1,000 mm (5) Particle content Select a solvent that dissolves thermoplastic resin but does not dissolve particles, and centrifuge particles from thermoplastic resin. The ratio (% by weight) to the total weight of the particles is defined as the particle content.
In some cases, the combined use of infrared spectroscopy is also effective.

(6) Crystallization parameter ΔTcg, heat of fusion Measured using a differential scanning calorimeter (DSC). The measurement conditions for DSC are as follows. That is, 10 mg of a sample is set in a DSC apparatus, melted at a temperature of 300 ° C. for 5 minutes, and then rapidly cooled in liquid nitrogen. The quenched sample is heated at a rate of 10 ° C./min, and the glass transition point Tg is detected. The temperature is further increased and the cooling crystallization temperature Tc is determined by the peak temperature of the crystallization exotherm from the glassy state.
c. The temperature was further increased, and the heat of fusion was determined from the melting peak. Here, the difference between Tcc and Tg (Tcc−Tg) is defined as a crystallization parameter ΔTcg.

(7) Young's modulus According to the method specified in JIS-Z-1702, use an Instron type tensile tester at 25 ° C and 65%
Measured at RH.

(8) Total reflection Raman crystallization index The total reflection Raman crystallization index was measured, and the half reflection width of 1730 cm ⁻¹ , which is the stretching vibration of the carbonyl group, was taken as the total reflection Raman crystallization index of the surface. The measurement conditions are as follows.
The measurement depth is about 500 to 1000 mm from the surface.

Light source Argon ion laser (5145Å) Sample setting The film surface is pressed against a total reflection prism, and the angle of incidence of the laser on the prism (the angle with the film thickness direction) is 60
゜

Detector PM: RCA31034 / Photon Counting System (Hamamatu C123
0) (supply 1600V) Measurement conditions SLIT 1000μm LASER 100mW GATE TIME 1.0sec SCAN SPEED 12cm ^-1 / min SAMPLING INTERVAL 0.2cm ^-1 REPEAT TIME 6 (9) Intrinsic viscosity [η] (unit: dl / g) orthochlorophenol The value calculated by the following formula from the solution viscosity measured at 25 ° C. is used. That is, η _SP / C = [η] + K [η] ² · C where η _SP = (solution viscosity / solvent viscosity) −1, and C is the weight of dissolved polymer per 100 ml of solvent (g / 100 ml, usually 1.
2), K is the Haggins constant (0.343). Further, the dissolution viscosity and the solvent viscosity were measured using an Ostwald viscometer.

(10) Surface layer particle concentration ratio Using secondary ion mass spectrum (SIMS), the concentration ratio of the highest concentration element among the elements originating from the particles in the film to the carbon element of the thermoplastic resin is defined as the particle concentration, Perform a vertical analysis. The ratio A / B between the particle concentration A at the outermost layer particle concentration (point at depth 0) measured by SIMS and the maximum concentration B obtained by further analyzing the depth direction, A / B, was defined as the surface layer particle concentration ratio. The measuring device and conditions are as follows.

Primary ion species: O ₂ ⁺ Primary ion acceleration voltage: 12 KV Primary ion current: 200 nA Raster area: 400 μm □ Analysis area: Gate 30% Measurement vacuum degree: 6.0 × 10 ^-9 Torr E-GUN: 0.5 KV-3.0 A (11) Surface roughness parameter Ra (center line average roughness), Rt
(Maximum height) It measured using the surface roughness meter. The conditions were as follows, and the value was an average value of 20 measurements.

・ Stylus tip radius: 0.5μm ・ Stylus load: 5mg ・ Measurement length: 1mm ・ Cutoff value: 0.08mm (12) Durability Tape running test of film slit into a 1/2 inch wide tape Using a machine to run on guide pins (surface roughness: 100 nm in Ra) (running speed 1,000 m / mi
n, number of runs 10pass, winding angle: 60 °, running tension: 65
g). At this time, observe the wound in the film with a microscope,
Excellent if less than 2 scratches with a width of 2.5 μm or more per tape width
More than 10 and less than 10 were judged as good, and more than 10 were judged as bad. Although excellent is desirable, even good is practically usable.

[Examples] The present invention will be described based on examples.

Examples 1, 2, 5 and Comparative Examples 2, 3 An ethylene glycol slurry containing crosslinked polystyrene particles having different average particle diameters and silica particles derived from colloidal silica was prepared, and this ethylene glycol slurry was heat-treated at 190 ° C. for 1.5 hours. After that, transesterification with dimethyl terephthalate and polycondensation, the particles are 1 to 10
Polyethylene terephthalate (hereinafter referred to as PET)
Abbreviated). At this time, the intrinsic viscosity was adjusted to 0.70 by adjusting the polycondensation time (thermoplastic resin B). Also,
PET having an intrinsic viscosity of 0.62 was produced by a conventional method, and was designated as thermoplastic resin A.

Each of these polymers was dried under reduced pressure at 180 ° C for 6 hours (3
(Torr), the thermoplastic resin B is supplied to the extruder 1 and
C., and further, the thermoplastic resin A is supplied to the extruder 2 and melted at 280.degree. The film was wound around a casting drum at a temperature of 200 ° C. and solidified by cooling to form a laminated unstretched film. At this time, the discharge amount of the discharger of each extruder was adjusted to adjust the total thickness and the thickness of the thermoplastic resin B layer.

This unstretched film was stretched 4.5 times in the longitudinal direction at a temperature of 80 ° C. This stretching is performed at the peripheral speed difference between two sets of rolls,
Performed in stages. This uniaxially stretched film is stretched 4.0 times in the width direction at 100 ° C. at a stretching speed of 2,000% / min using a stenter, and is treated at 190 ° C. for 5 seconds under a constant length to obtain a total thickness of 15 μm.
m, a biaxially oriented laminated film having a thermoplastic resin B layer thickness of 0.07 to 0.9 μm.

On one side of this film, a cobalt-nickel alloy (Ni 20% by weight) was obliquely vapor-deposited by a high-frequency sputtering method in a vacuum vapor deposition machine in the presence of a trace amount of oxygen to form a ferromagnetic thin film layer having a thickness of 0.2 μm. Subsequently, slitting was performed to the tape width to obtain a metal thin film type magnetic recording medium.

Examples 3 and 4 and Comparative Examples 1 and 4 In the same manner as in the above Examples, in Example 3, a three-layer laminated unstretched film was produced by using three extruders.
In addition, a three-layer laminated unstretched film in which different polymers are laminated on both sides of the A layer, a normal single-layer film in Comparative Example 1, and a three-layer laminated film using three extruders in Comparative Example 4 An unstretched film was obtained.

These unstretched films in the longitudinal direction at a temperature of 80 ° C. 4.
It was stretched twice. This uniaxially stretched film was stretched 4.5 times in the width direction at 105 ° C. at a stretching speed of 2,000% / min using a stenter and heat-treated at 190 ° C. for 5 seconds under a constant length to obtain a biaxially oriented film.

On one side of this film, a 1.0 μm thick ferromagnetic thin film layer was formed by obliquely depositing a cobalt-nickel alloy (Ni 20 wt%) in a vacuum deposition machine in the presence of a small amount of oxygen by a high frequency sputtering method. Subsequently, slitting was performed to the tape width to obtain a metal thin film type magnetic recording medium.

The parameters of the present invention for these films are as shown in Table 1, and when the parameters of the present invention are within the range, the durability was excellent or good as shown in Table 1, but it was not. In this case, a film satisfying the durability was not obtained.

[Effects of the Invention] The present invention uses a thermoplastic resin containing inactive particles by means of a manufacturing method to make the relationship between the particle size and the film thickness and the content within a specific range, thereby providing excellent durability. Thus, a magnetic recording medium is obtained, which can cope with an increase in film processing speed in each application.

Claims (7)

(57) [Claims] A metal thin film magnetic recording medium comprising a base film and a metal thin film magnetic layer provided on at least one side of the base film, wherein the base film is made of a layer (A) made of thermoplastic resin A.
A biaxially oriented film obtained by laminating a layer (B layer) made of thermoplastic resin B containing inactive particles on at least one surface of the layer (B), and the average particle diameter d _{B of the} inactive particles contained in the B layer
But 5 to 200 nm, 1.5 to 40% by weight content in the particles of the layer B, a ratio t _B / d _B of the B layer and the thickness t _B average particle diameter d _B is in the range of 0.1 to 3 Characteristic metal thin film type magnetic recording medium. Wherein at least one of the metal thin film type magnetic layer is provided on the B layer side, the average particle diameter d _B is 5 to inert particles contained in the magnetic layer side of the B layer of the base film 2. The metal thin-film magnetic recording medium according to claim 1, wherein the thickness is 80 nm. 3. The base film is a biaxially oriented film in which a layer B is laminated only on one side of the layer A, and a metal thin film type magnetic layer is provided only on the side of the layer A. claim (1), wherein the metal thin film type magnetic recording medium having an average particle diameter d _B of the inert particles is characterized in that it is a 40~20nm being. 4. A substrate film comprising a layer (B layer) made of thermoplastic resin B containing inactive particles on one side of a layer (A layer) made of thermoplastic resin A and an inert layer on the other side. A biaxially oriented film obtained by laminating a layer (C layer) made of thermoplastic resin C containing particles, wherein a metal thin film type magnetic layer is provided only on layer B side of the base film; the average particle diameter d _B is 5~80nm inert particles contained in the B layer, said particles B
1.5 to 40% by weight content in the layer, the average particle diameter of the inert particles the ratio t _B / d _B having an average particle diameter d _B and the thickness t _B of the B layer is 0.1 to 3, it is contained in the C layer d _c is 40 to 200 nm, the content of the particles in the C layer is 1.5 to 40% by weight, the thickness t _c of the C layer and the average particle diameter d _c
Wherein the ratio t _c / d _c is 0.1-3. 5. The thermoplastic resin C is a crystalline polyester, and the total reflection Raman crystallization index on the surface of the C layer is 20 cm ^-1.
The metal thin-film magnetic recording medium according to claim 4, wherein: 6. The thermoplastic resin B is a crystalline polyester, and the surface of the layer B has a total reflection Raman crystallization index of 20 cm ^-1.
The metal thin-film magnetic recording medium according to any one of claims 1 to 5, wherein: 7. The thickness t _B of the B layer on the magnetic layer side and the thickness of the magnetic layer
The ratio of t _M, t _B / t _M is the metal thin film type magnetic recording medium according to any one of claims (1) to (6), characterized in that in the range of 0.02 to 150.