JPH0373409A - Metal thin film type magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent durability by using a thermoplastic resin containing inert particles and specifying the amt. of particles in the resin and the relation between the particle size and film thickness. CONSTITUTION:The substrate film consists of a thermoplastic resin layer (layer A) and a thermoplastic resin layer (layer B) containing inert particles formed on at least one side of the layer A. The inert particles contained in the layer B are specified to have the average particle size dB of 5 - 200 nm and incorpo rated by 1.5 - 40 wt.% into the layer B. The ratio of the thickness tB of the layer B to the average particle size dB, tB/dB, is specified to a range of 0.1 - 3. Thereby, the magnetic layer of the obtd. metal thin film type magnetic recording medium has excellent durability.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a metal thin film magnetic recording medium.

[Prior Art] As a metal thin film type magnetic recording medium, a magnetic recording medium in which a metal thin film type magnetic layer is provided on a polyester film is known (for example, Japanese Patent Laid-Open No. 58-68225).

[Problems to be Solved by the Invention L2] 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 has the following characteristics:
Because of its frequency characteristics, it is considered important as a magnetic recording medium for high-density recording. However, in the conventional metal thin film magnetic recording media mentioned above, the durability of the magnetic layer (hereinafter referred to as durability) is insufficient, and in order to improve the durability, the size of the particles contained in the base film is increased. Then, there was a problem that the output characteristics were poor.

An object of the present invention is to improve such problems and provide a metal thin film magnetic recording medium that maintains the excellent output characteristics originally possessed by the metal thin film magnetic recording medium and has a magnetic layer with excellent durability. .

[Means for Solving the Problems] The present invention provides (1) a metal thin model magnetic recording medium comprising a metal thin film type magnetic layer provided on at least one side of a base film, the base film being made of thermoplastic resin. A layer consisting of A (A
It is a biaxially oriented film formed by laminating a layer (B layer) made of thermoplastic resin B containing inert particles on at least one side of the layer), and the average particle diameter d of the inert particles contained in the B layer.
B is 5 to 200 nm, and the content of the particles in the B layer is 1
．． 5 to 40% by weight, and a metal thin film magnetic recording medium characterized in that the ratio ts, , /de of the thickness tB of the B layer to the average grain size da is in the range of 0.1 to 3, The material film is a layer made of thermoplastic resin A (layer A) and a layer made of thermoplastic resin B containing inert particles on one side (layer B).
A biaxially oriented film formed by laminating a layer (C layer) made of thermoplastic resin C containing inert particles on the other side, and a metal thin film type magnetic layer only on the B layer side of the base film. is provided, the average particle diameter dB of the inert particles contained in the B layer is 5 to 80 nrrx, the content of the particles in the B layer is 1-45 to 40% by weight, and the thickness of the B layer is tIl. The ratio ts/ds of the average particle diameter d6 is 0. 1 to 3, the average particle diameter dc of the inert particles contained in the 0 layer is 40 to 200n
m, the content of the particles in the 0 layer is 1.5 to 40% by weight
, the ratio tc between the thickness tC of the 0 layer and the average grain size dc, , /dB is 0. The gist of the present invention is a metal thin film type magnetic recording medium characterized by the following characteristics: 1 to 3.

Thermoplastic resins A, B constituting the base film of the present invention
, C may be the same or different types, and are not particularly limited to polyester, polyolefin, polyamide, polyphenylene sulfide, etc., but are particularly suitable for polyester, especially ethylene terephthalate, ethylene α, β-bis(2-chloro phenoxy)ethane-4,4
It is preferable to use at least one type of structural unit selected from '-dicarboxylate and ethylene 2,6-naphthalate units as the main constituent, since the durability will be even better.

Here, it is particularly desirable that the thermoplastic resins B and/or C constituting the present invention be crystalline, since the durability will be even better. Crystallinity here indicates that it is not so-called amorphous, and quantitatively, the cold crystallization temperature Tcc in the crystallization parameter is detected, and the crystallization parameter ΔTeg is 150°C or less. .

Furthermore, it is extremely desirable to exhibit crystallinity with a heat of fusion (change in enthalpy of fusion) of 7.5 cal/g or more as measured by a differential scanning calorimeter because durability is even better. Further, polyester containing ethylene terephthalate as a main component is particularly desirable because it has even better durability.

In addition, within the range that does not impede the present invention, thermoplastic resin A,
At least one selected from BSC may be mixed with other thermoplastic resins, or a copolymer may be used. Furthermore, within a range that does not impede the object of the present invention, at least one selected from thermoplastic resins A and BXC may contain an antioxidant,
Organic additives such as heat stabilizers, lubricants, and ultraviolet absorbers may be added to the extent that they are normally added.

The average particle diameter da of the inert particles in the eight layers of the base film constituting the metal thin film magnetic recording medium of the present invention must be 5 to 200 nm from the viewpoint of durability, and the When a magnetic layer is provided, 5 to 80 rirri,
When a magnetic layer is not provided, 40 to 200 nrn is preferable.

Also, the average particle diameter dB of the inert particles in the C layer of the base film
is preferably 40 to 200 nm in order to obtain good handling properties of the film in processing steps such as vapor deposition, and furthermore good runnability without back coating treatment.

Furthermore, the A layer of the base film does not particularly need to contain inert particles, but the inert particles with an average particle size of 5 to 200 nm, particularly 10 to 150 nm, are 0.001 to 0.1 nm.
It is desirable that the content be 5% by weight, especially 0.005 to 0.05% by weight, since the durability will be even better.

The durability of the inert particles used in the present invention is even better when the particle size ratio (major axis/minor axis) is 1.0 to 1.3, especially when the particles are spherical. Therefore, it is desirable.

The inert particles used in the present invention have a single particle index in the film of 0.7 or more, preferably 0.7 or more. A value of 9 or more is particularly desirable because the durability becomes even better.

The inert particles used in the present invention have a relative standard deviation of particle size of 0.
．． If it is 6 or less, preferably 0.5 or less, the durability will be better, so it is desirable.

The type of inert particles used in the present invention is not particularly limited, but includes substantially spherical silica particles derived from colloidal silica, particles made of crosslinked polymers (for example, crosslinked polyester), and in particular, In the case of crosslinked polymer particles whose degree of crosslinking is increased until the temperature at % weight loss (measured in nitrogen using a thermogravimetric analyzer Shimadzu TG-30M, continuous heating window 20°C 7/min) is 380°C or higher. Particularly desirable 1. since the durability is better. stomach. Note that in the case of spherical silica derived from colloidal silica, substantially spherical silica with a low sodium content produced by an alkoxide method is particularly desirable because the durability is even better. However, other particles, such as calcium carbonate, titanium dioxide, aluminum, etc., can also be used in the thermoplastic resin B [by appropriately controlling the ratio of the thickness tB to the average particle diameter dB].

The content of inert particles in the 8 layers of the base film of the present invention is 1
．． It is necessary that the amount is 5 to 40% by weight, preferably 2 to 30% by weight, and more preferably 3 to 20% by weight. If the content is less than the above range, the durability will be poor, and if it is too much, the output characteristics will be poor, which is not preferable.

The ratio 1°/dB of the thickness 18 of the 8 layers of the base film of the present invention to the average particle diameter dB of the inert particles contained in the 8 layers is 0.1
-3, preferably l;! It needs to be in the range of 0.2-2° ol, more preferably 0.3-1.5. j
If 8/dB is smaller than the above range, the durability will be poor, whereas if it is larger than the above range, the output characteristics will be poor, which is not preferable.

Furthermore, the content of inert particles contained in the 0 layer is 1.5~
The setting of 40% by weight, preferably 2 to 15% by weight, is necessary to obtain a magnetic recording medium that has good handling properties of the film in processing steps such as vapor deposition, and also has good running properties even without back coating treatment. necessary to obtain.

The thickness of this zero layer is t. By setting the ratio tC/dC of the average particle diameter dc of the contained inert particles to a range of 0.1 to 3, the handling properties of the film in processing steps such as vapor deposition are further improved, and furthermore, the back This is necessary to further improve the runnability when no coating treatment is applied.

The base film constituting the present invention is a film in which the laminated film 14 made of the above composition is biaxially oriented, and -
A shaft or non-oriented film is not preferred because the winding appearance will be poor. The degree of this orientation is not particularly limited, but if the Young's modulus, which is a measure of the degree of molecular orientation of the polymer, is 350 kg/mm2 or more in both the long and width directions, the output characteristics and durability will be improved. This is highly desirable as it gives good results. The upper limit of Young's modulus, which is a measure of the degree of molecular orientation, is not particularly limited, but is usually 1500 kg/rr.
About im2 is the manufacturing limit.

It is particularly desirable that the surface total reflection Raman crystallization index of the B layer of the base film constituting the present invention be 2 cm-' or less, since this results in even better durability and better handling properties.

Further, it is particularly desirable that the surface total reflection Raman crystallization index of the zero layer of the base film constituting the present invention is 20 cm<-1> or less, since this results in even better durability and better handling properties.

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

The thickness tM of the metal thin film type magnetic layer is not particularly limited, but the ratio to the thickness tB (-layer) of the B layer on the magnetic layer side, t n /
tM is 0.02 to 150, especially 0. 1-150,
More preferably, it is in the range of 0.2-100 because the output characteristics and durability are even better. In addition, the value of tM is 0.02 to 0.5 in the case of horizontal recording.
In the case of perpendicular recording of 1 .mu.m, it is desirable to keep the thickness in the range of 0.2 to 1.5 .mu.m since this will further improve the output characteristics and durability.

It is particularly desirable that the thickness unevenness in the width direction of the B layer 5 of the base film constituting the present invention be 25% or less, more preferably 20% or less, since the output characteristics and durability will be even better.

The thickness of the B layer of the base film constituting the present invention is 0.
005~0. 6 μm, preferably 0.01-0.5
In the case of μm, durability and output characteristics are even better, so it is particularly desirable.

It is preferable that the protrusion height on the surface of layer B of the base film constituting the present invention is 25 nm or more, preferably 30 nrn or more, since durability and output characteristics will be even better. Furthermore, the number of protrusions with double rings or more measured by multiple interferometry is 1.
00 pieces/100ci or less is desirable.

When the BJii (ratio of the center line average roughness Ra of the D surface to the maximum height R1, Rt/Ra, of the base film constituting the present invention is 9.0 or less, particularly 8.5 or less, the 84 force characteristics, This is particularly desirable since the durability is even better.

The surface layer particle concentration ratio measured by the secondary ion mass spectrum of the surface of the B layer of the base film constituting the present invention is not particularly limited, but when the surface layer particle concentration ratio is 1/10 or less, particularly 1150 or less This is particularly desirable since the durability and output characteristics are even better.

Furthermore, fine protrusions may be formed by applying a water-soluble polymer to at least one side of the base film constituting the present invention. In that case, the magnetic layer may be coated with the water-soluble polymer or may be coated with the water-soluble polymer.3 Next, a method for manufacturing the magnetic recording medium of the present invention will be described.

First, as a method for impregnating thermoplastic resin B with inert particles, there is a method in which the inert particles are made into an ethylene glycol slurry and kneaded into the thermoplastic resin using a vent type twin-screw kneading extruder. This is extremely effective for obtaining a base film having a relationship between thickness and average particle size and content within the range of the present invention.

A method for adjusting the particle content is to prepare a high-concentration master using the above method, and then dilute it with a thermoplastic resin that does not substantially contain inert particles during film formation to adjust the particle content. The method is valid.

Next, after drying the pellets of thermoplastic resin B containing a predetermined amount of inert particles of thermoplastic resin A1 as necessary,
It is supplied to a known extrusion device for melt lamination, extruded into a sheet through a slit-shaped die, and cooled and solidified on a casting roll to produce an unstretched film. That is, thermoplastic resins A and B are laminated using two or three extruders, a two or three-layer manifold or a merging block,
A 2 or 3R sheet is extruded from the die and cooled with a casting roll to form an unstretched film. In this case, the method of installing a static mixer and a gear pump in the polymer flow path of the thermoplastic resin R will prevent stretching and tearing, and the film will have a relationship between thickness and average particle size, a content within the range of the present invention, and a surface layer particle concentration ratio within the desired range. It is effective to obtain Further, it is extremely effective to use a rectangular feed block as the merging block to obtain the laminated thickness unevenness within the range of the present invention. In addition, setting the melting temperature of the extruder on the thermoplastic resin B side 10 to 40°C higher than that on the thermoplastic resin A side will prevent stretching breakage, and the relationship between the thickness and average particle size, the content, and the content within the range of the present invention. This is effective in obtaining a film with desired ranges of lamination thickness unevenness, surface layer particle concentration ratio, and total reflection Raman crystallization index. The above explanation describes the configurations A/B and B/A/B, but in the case of the B/A/C configuration, three extruders are used to create a three-layer manifold or confluence block. The three-layer sheet is extruded from a die and cooled with a casting roll to form an unstretched film.

Next, this 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, by using a sequential biaxial stretching method that first stretches in the longitudinal direction and then in the width direction, the longitudinal stretching is divided into three or more stages, and the total longitudinal stretching ratio is 3.
．． The method carried out at a magnification of 0 to 6.5 times is effective for obtaining a film having a relationship between thickness and average particle size and content within the range of the present invention.

Although the longitudinal stretching temperature varies depending on the type of thermoplastic resin and cannot be generalized, it is usually 50 to 130 ℃ in the first stage.
℃, and setting it higher in the second and subsequent stages is effective in obtaining a film with uneven lamination thickness and surface layer particle concentration ratio within the desired range of the present invention.

The longitudinal stretching speed is preferably in the range of 5,000 to 50,000%/min. A common method for stretching in the width direction is to use a stenter. Stretching ratio is 3.0 to 5.0
A double range is appropriate. The stretching speed in the width direction is 1000
-20000%/min, temperature is preferably 80-(60°C). Next, this stretched film is heat treated. In this case, the heat treatment temperature is 170-200°C, especially 170-19
A temperature of 0° C. and a time of 0.5 to 60 seconds are preferable.

Next, a metal thin film is formed on this film.

The magnetic layer can be deposited by any known method. For example, a thin metal film of iron, cobalt, nickel or an alloy thereof is deposited directly on the base film by vacuum deposition, ion blasting, sputtering, etc. It is preferable to form the layer through a base thin film of , 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 preferred from the viewpoint of durability.

[Method for Measuring Physical Properties and Evaluating Effects] The methods for measuring the characteristic values and evaluating the effects of the present invention are as follows.

(1) Average particle size of particles The thermoplastic resin is removed from the film by plasma low-temperature ashing treatment to expose the particles. The processing conditions are selected so that the thermoplastic resin is incinerated 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 when the number of particles is 5000 or more while changing the observation location, and the number average diameter obtained thereby is taken as the average particle diameter.

D=ΣD, /N Here, D is the equivalent circle diameter of the particles, and N is the number of particles.

0 Particle Size Ratio In the measurement of (1) above, the (average value of major axis)/
(average value of short axis). That is, in the following % formula, % D I I % D 2 + is the major axis (maximum diameter) and minor axis (shortest axis) of each individual particle, and N is the number of particles.

(3) Relative standard deviation of particle diameter Standard deviation calculated from individual particle diameter D11 mean diameter D1 particle number N measured by the method in (1) above σ[=(Σ(D+
D)'/N)I/2] divided by the average diameter (σ/D).

(4) A cross section of the single particle index film is photographed and observed using a transmission electron microscope (TEM) to detect particles. If the observation magnification is set to about 100,000 times, a single particle that cannot be separated any further can be observed. When the total area occupied by particles is A1, and the area occupied by aggregates in which two or more particles are aggregated is B, (
A-B)/A is the single particle index. The TEM conditions are as follows, and 500 visual fields are measured by changing the measurement location of 1 visual field area = 2 μm 2 .

・Observation magnification = 100,000 times ・Acceleration voltage + 100kV ・Section thickness: Approximately 1.0OOA (5) Particle content Select a solvent that dissolves the thermoplastic resin but does not dissolve the particles, and centrifuge the particles from the thermoplastic resin. The particle content is defined as the ratio (coulometric %) of the particles to the total weight. In some cases, infrared spectroscopy may also be effective.

(6) Crystallization parameter ΔTag, heat of fusion was measured using a differential scanning calorimeter (DSC).

The DSC measurement conditions are as follows. That is, sample 1
0+g is set in a DSC device, melted at a temperature of 300° C. for 5 minutes, and then rapidly cooled in liquid nitrogen.

This rapidly cooled sample was heated at a rate of 10°C/min, and the glass transition point Tg
Detect. The temperature was further increased, and the exothermic peak temperature of crystallization from the glass state was defined as the cold crystallization temperature Tcc.

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 25
Measured at 65% RH.

(8) Total reflection Raman crystallization index The total reflection Raman spectrum was measured, and the half width of 1 730 crm-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. Measurement depth is 500~100OA from the surface
That's about it.

■Light source Argon ion laser (5145A) ■Setting the sample The surface of the film is pressed against a total reflection prism, and the incident angle of the laser to the prism (angle with the film thickness direction) is 6
It was set to 01.

■Detector PM: RCA31034/Photon Coun
Nng System (tlan+amaju Cl2
30) (supply 1600V) ■Measurement conditions 5LIT 100hmL100h
100mWGATE TIME
1.0secSCAN 5PEED f2
cm-'/minSAMPLING INTERVAL
O, 2cm"'REPEAT TIME
6 (9) Intrinsic viscosity [η] (Units: cl/g) A value calculated by the following formula from the solution viscosity measured at 1.25°C in orthochlorophenol is used. That is, ηsr/C= [η+K[η] 2 ・Nico, η, P=(solution viscosity/solvent viscosity)-1, C is the weight of dissolved polymer per 100ml of solvent (g/l 00ml
．． Usually 1.2), K is Huggins constant (C, 343). In addition, solution viscosity and solvent viscosity were measured using an Ostwald viscometer.

■ Surface layer particle concentration ratio Using secondary ion mass spectrometry (SIMS), the particle concentration is defined as the concentration ratio of the element with the highest concentration among the elements caused by particles in the film and the carbon element of the thermoplastic resin, and We will conduct an analysis of The ratio of the particle concentration A at the outermost layer particle concentration (point at depth O) measured by SIMS to the maximum concentration B obtained by further analysis in 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: 02 Primary ion acceleration voltage: 12KV 1, Secondary ion current: 200nA Raster area: 400μm Mouth analysis area: Gate 30% Measurement vacuum degree: 6. OX 10-9 TorrE −
GUN: 0.5KV-3,0Aαυ Surface roughness parameters Ra (center line average roughness), Rt (maximum height) Measured using a surface roughness meter. The conditions were as follows, and the average value of 20 measurements was taken as the value.

・Stylus tip radius: 0.5μm ・Stylus load: 5mg ・Measurement length: 1mm ・Force/Soft-off value 20.08mm (Support) Durable film slit into 1/2 inch wide tape. Using a tape running tester, run on a guide pin (surface roughness: Ra, 10100n (running speed 1).
．． 000m/min, number of runs IQpais, wrapping angle: 60°, running tension +65g).

At this time, the scratches in the film were observed under a microscope, and the width was 2.
If there were less than two scratches per tape width of 5 μm or more, it was determined to be excellent, if there were 2 or more and less than 10 scratches, it was determined to be good, and if there were 10 or more scratches, it was determined to be poor. Excellent is desirable, but good is still usable for practical purposes.

[Example] The present invention will be explained based on examples.

Examples 1, 2.5, Comparative Example 2.3 Ethylene glycol slurry containing crosslinked polystyrene particles with different average particle sizes and silica particles derived from colloidal silica was prepared, and this ethylene glycol slurry was heated at 190°C to 1.5 After heat treatment for a period of time, transesterification reaction with dimethyl terephthalate and polycondensation were carried out, and the particles were
Pellets of polyethylene terephthalate (hereinafter abbreviated as TPET) containing ~10% by weight were made. At this time, the polycondensation time was adjusted to give an intrinsic viscosity of 0.70 (thermoplastic resin B). In addition, PET with an intrinsic viscosity of 0°62 was prepared using a conventional method.
was produced and designated as thermoplastic resin A.

These polymers were each dried under reduced pressure at 180°C for 6 hours (
3 Torr), thermoplastic resin B was supplied to extruder 1 and melted at 310°C, thermoplastic resin A was further supplied to extruder 2 and melted at 280°C, and these polymers were transferred to a confluence block (feed block). ) and then casted at a surface temperature of 30°C using the electrostatic casting method.
It was wound around a drum and cooled and solidified to produce a laminated unstretched film.

At this time, the total thickness and the thickness of the thermoplastic resin B layer were adjusted by adjusting the discharge amount of each extruder.

This unstretched film was heated to 4.5 mm in the longitudinal direction at a temperature of 80°C.
Stretched twice. This stretching is done by the difference in circumferential speed between the two sets of rolls.
It was done in 4 stages. This -axially stretched film was stretched 4.0 times in the width direction at 100°C at a stretching rate of 2.000%/min using a stenter, and then heat-treated at 190°C for 5 seconds under constant length to a total thickness of 15 μm. Thermoplastic resin B layer thickness 0607~
A biaxially oriented laminated film of 0.9 μm was obtained.

One side of this film was coated with a cobalt-nickel alloy (N i 20% by weight) in the presence of a trace amount of oxygen in a vacuum evaporator.
is obliquely deposited by high frequency sputtering method to a thickness of 0.
A ferromagnetic thin film layer of 2 μm was formed. Subsequently, slits were made to the width of the tape to obtain a metal thin film type magnetic recording medium.

Examples 3 and 4, Comparative Example 1.4 In the same manner as in the above examples, in Example 3, a three-layer laminated unstretched film was produced using three extruders, and in Example 4, a laminated unstretched film was produced using three extruders. A 3-layer laminated unstretched film with different polymers laminated on a tube, a normal single-layer film in Comparative Example 1, and a 3-layer unstretched laminated film in Comparative Example 4 using three extruders. Obtained.

These unstretched films were stretched 4 times in the longitudinal direction at a temperature of 80°C.
．． It was stretched 2 times. This -axially stretched film was stretched in the width direction at 105°C at a stretching rate of 2.000%/min using a stenter.
．． Stretched 5 times, heat treated at 190°C for 5 seconds under constant length,
A biaxially oriented film was obtained.

Cobalt-nickel alloy (N i 20w1%) was deposited on one side of this film in the presence of a trace amount of oxygen in a vacuum evaporator.
is obliquely deposited using high frequency sputtering method to a thickness of 0.1
A ferromagnetic thin film layer of μm was formed.

Subsequently, slits were made to the width of the tape 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 were within the range, the durability was excellent or good as shown in Table 1, but when it was not. In this case, a film with satisfactory durability could not be obtained.

[Effects of the invention] The present invention uses a thermoplastic resin containing inert particles by devising a manufacturing method, and the relationship between the particle size and film thickness and the content are set within a specific range, resulting in excellent durability. This results in a magnetic recording medium that can accommodate increased film processing speeds in various applications.

Claims (7)

[Claims] (1) A metal thin film type magnetic recording medium comprising a metal thin film type magnetic layer provided on at least one side of a base film, wherein the base film has a layer (A layer) made of thermoplastic resin A and a layer (A layer) that is not formed on at least one side of the base film. It is a biaxially oriented film formed by laminating a layer (B layer) made of thermoplastic resin B containing active particles, and the average particle diameter d_B of the inert particles contained in the B layer is 5 to 5.
200 nm, the content of the particles in the B layer is 1.5 to 4
0% by weight, ratio t_B of layer B thickness t_B to average particle diameter d_B
A metal thin film magnetic recording medium characterized in that B/d_B is in the range of 0.1 to 3. (2) A metal thin film type magnetic layer is provided on at least one B layer side of the base film, and the average particle diameter d_B of the inert particles contained in the B layer on the magnetic layer side is 5 to 80 nm. The metal thin film magnetic recording medium according to claim 1, characterized in that: (3) The base film is a biaxially oriented film in which the B layer is laminated only on one side of the A layer, and a metal thin film type magnetic layer is provided only on the A layer side, and the B layer contains 2. The metal thin film magnetic recording medium according to claim 1, wherein the inert particles have an average particle diameter d_B of 40 to 200 nm. (4) The base film is a layer made of thermoplastic resin A (A
thermoplastic resin B containing inert particles on one side of the layer)
A biaxially oriented film formed by laminating a layer (B layer) consisting of a thermoplastic resin C containing inert particles on the other side (C layer) on the B layer side of the base film. A metal thin film type magnetic layer is provided only in the B layer, 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 in the B layer is 1.5 to 40% by weight, The ratio t_B/d_B of the thickness t_B of the B layer and the average grain size d_B is 0.1 to
3. The average particle diameter d_C of the inert particles contained in the C layer is 40 to 200 nm, and the content of the particles in the C layer is 1.
5 to 40% by weight, and the ratio t_C/d_C of the thickness t_C of the C layer to the average grain size d_C is 0.1 to 3. (5) Thermoplastic resin C is crystalline polyester, and the total reflection Raman crystallization index of the C layer surface is 20 cm^-
5. The metal thin film magnetic recording medium according to claim 4, wherein the magnetic recording medium is ^1 or less. (6) Thermoplastic resin B is crystalline polyester, and the total reflection Raman crystallization index of the B layer surface is 20 cm^-
Claims (1) to (5) characterized in that ^1 or less
The metal thin film magnetic recording medium according to any one of the above. (7) Thickness t_B of layer B on the magnetic layer side and thickness t of the magnetic layer
7. The metal thin film magnetic recording medium according to claim 1, wherein the ratio of _M, t_B/t_M, is in the range of 0.02 to 150.