JP2546225B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly to a flexible magnetic disk.

[Prior art]

Due to the popularization of office computers and micro computers, flexible magnetic discs, commonly known as floppy discs, have come into wide use, but they are cheaper than conventional hard magnetic discs, and replacement is extremely easy. However, it has drawbacks such as a small recording capacity, and the base film being a plastic sheet, which is slightly unreliable in shape stability such as curling and bending.

The recording capacity of the floppy disk is the linear recording density and the track density (the number of tracks per unit length in the radial direction of the floppy disk, which is generally TPI = track) in a track (a thin annular recording area arranged concentrically). / Inches). The increase in the linear recording density is achieved by improving the magnetic layer and the magnetic recording method, and the increase in the track density is that the reversible and irreversible dimensional change of the disk due to the change of temperature and humidity is as small as possible. The point is that these dimensional changes occur in the same direction in each direction.

On the other hand, it goes without saying that the disk is completely flat and has excellent flatness.
If it is curled or has irregularities, the contact between the recording / reproducing head and the magnetic layer becomes unstable and the reliability of recording / reproducing is greatly reduced. The floppy disc itself is protected by a cover, which is generally called a "jacket" made of paper or plastic sheet. However, it is preferable that the curl is as small as possible, and this requirement is further strengthened especially when the recording density is increased or the size is reduced.

Conventionally, biaxially oriented polyethylene terephthalate film has been most widely used as the base film of the floppy disc, but this is largely due to its excellent mechanical properties and surface smoothness. However, as long as this base film is used, the humidity expansion coefficient is as large as about 10 × 10 ^-6 / RH%, so the humidity environment changes from 80 to 90 when the disk is used.
Since accurate track traceability over a wide range of RH% is required, the track density must automatically have a certain limit. For this reason, various measures have been taken to modify the polyethylene terephthalate, or to combine it with other low moisture absorption materials to reduce the substantial coefficient of hygroscopic expansion, but other thermal properties and mechanical properties deteriorate. Therefore, favorable results have not been obtained yet. Therefore, JP-A-55
-38613 has a possibility of high recording density in a floppy disc using a biaxially oriented poly-p-phenylene sulfide film as a base film, which is essentially excellent in humidity characteristics. , Conventional biaxially oriented poly-p
The disk made of Feniren Surufuido film included some problems from the viewpoint of making a flat shape such as the above-mentioned curl. Particularly when the ferromagnetic thin film layer is formed directly on the base film by vapor deposition or the like for higher density, the disk shape is often unsatisfactory.

In these vacuum thin film forming processes, it is generally difficult to maintain the shape of the magnetic disk to be formed into a sufficiently good flatness because the base film is subjected to many thermal and mechanical loads as follows. .

(1) Generation of cohesive force due to deposition of metal thin film (2) Transfer of energy possessed by metal atoms to the base film (3) Effect of axial heat of heat when melting metal or heat generated by plasma etc. ( 4) Bimetal effect due to the difference in thermal expansion coefficient between the film and metal thin film when they have the same dimensions at high temperature and then returns to normal temperature. Due to the many defects in the flatness, stable contact with the head during recording and reproduction, running, etc. are often hindered and unsatisfactory results are often obtained.

[Object of the Invention]

An object of the present invention is to enable stable recording at a high recording density by using a biaxially oriented polyphenylene sulfide film as a main component of a base film and using a floppy disc having excellent curl and substantially flatness. Magnetic recording medium,
Preferably, a magnetic disk (floppy disk) is provided.

[Structure of Invention]

In order to achieve the above object, the present invention provides a structural formula In a magnetic recording medium having a biaxially oriented p-phenylene polysulfide film containing 90 mol% or more of repeating units as the main constituent layer of the base film and having a ferromagnetic layer on at least one side of the base film, the characteristics of the base film Is characterized by a flexible magnetic recording medium satisfying the following characteristics in all in-plane directions.

2 × 10 ⁻⁷ A × C 5 × 10 ⁻⁵ where A: thermal expansion coefficient at 120 ° C. (° C. ⁻¹ ) C: thermal shrinkage ratio at 120 ° C. (%) Polypphenylene sulfide ( Below PP
(S) is a structural formula 90 mole% or more, preferably 95
It is necessary to contain more than mol%. The repeating unit
If it is less than 90 mol%, the crystallinity of the polymer will be deteriorated and the mechanical properties of the film will be poor, making it brittle as a base film for floppy discs, and in extreme cases even biaxial stretching to give biaxial orientation is impossible. However, the glass transition temperature is lowered to 65 ° C or lower, which causes a serious defect in the high temperature dimensional stability of the disk, which is not preferable. For the remaining 10 mol% or less of the repeating units of the polymer, metaphenylene sulfide ether Biphenyl Nuclear-substituted phenyl sulfide (Wherein R is selected from an alkyl group having 1 to 10 carbon atoms, an alkoxy group or a nitro group, a phenyl group, a sulfonic acid group), a trifunctional phenyl sulfide Etc., and these may be included in the form of block copolymer or may be included in the state of random copolymerization. It is the main constitutional unit of the polymer at or near the end of the polymer. The fact that the constituent units other than the above are connected does not change the essence of the present invention. Further, the PPS and other components, for example, a polymer mixed for another purpose, an inorganic filler and the like may coexist in the base film as long as they do not seriously affect the purpose of the present invention.

The melt viscosity of PPS used in the present invention is 200 to 20,000 poise at a temperature of 300 ° C. and an apparent shear rate of 200 sec ⁻¹ .
More preferably, it is from 500 to 12,000 poise from the viewpoint of film forming properties and mechanical properties of the film.

The PPS biaxially oriented film is a film obtained by melt-molding the above PPS into a sheet, biaxially stretching and heat treating, and its thickness is preferably in the range of 5 to 100 μm.

The base film is a flexible support on which a magnetic recording layer is provided, and at least 50% or more of the thickness of the base film is the PPS biaxially oriented film described above.

The thickness of the base film is preferably in the range of 10 to 100 μm (more preferably 20 to 80 μm) from the viewpoint of shape retention as a floppy disc and head touch.

Less than 50% of the thickness of the base film can be made of a flexible sheet other than the PPS biaxially oriented film.
Examples are polyethylene terephthalate film, polyethylene 2,6 naphthalate film, polyethylene α, β bis (2-chlorophenoxy) ethane 4,4 ′.
Examples thereof include, but are not limited to, dicarboxylate film, polypropylene film, aromatic polyamide film, aromatic polyimide film, and aluminum foil.

Further, in particular, a coating layer of an organic polymer may be provided in order to improve the surface smoothness of the PPS film. This is because a magnetic layer with a higher magnetic recording density tends to have a smaller thickness, and it is necessary to improve the surface roughness and surface protrusion of the base film, so an extremely thin surface smoothing layer is provided. The PPS film remains the main constituent layer of the base film. Here, the surface roughness requirement, especially the maximum allowable projection height varies depending on the type of magnetic layer, but is 0.1 to 2μ for general coating type and 0.01 to 0.2μ for thin film metal type for direct deposition of magnetic metal. The thickness of the smoothing layer is also slightly thicker than this.

The present invention is constructed by providing a magnetic layer on one side or both sides of the base film, and various treatments are applied to the base film in order to improve the adhesiveness between the magnetic layer and the base film. This is because if the adhesiveness is weak, the magnetic layer may be scratched by repeated contact with the head, or if it is significantly peeled off. The most typical treatment is corona treatment. This is generally processed by corona discharge in air or in an atmosphere of nitrogen or carbon dioxide gas, and the surface tension of the PPS film when untreated is about 32 dyn / cm and is 35 to 60 dy due to corona discharge treatment in air.
As can be inferred from the increase to n / cm, it is effective as a treatment for stably providing the magnetic layer. Further, as will be described later, glow discharge treatment (plasma discharge treatment) is effective as the easy adhesion treatment particularly when a ferromagnetic metal layer is provided. The glow discharge treatment is performed under a vacuum of about 10 ^-5 to 10 Torr for 0.1 to 100 seconds using a power supply with a wide range of frequencies from direct current to high frequency. Gases such as oxygen, nitrogen, hydrogen and argon are used. Helium, carbon dioxide, carbon monoxide, ammonia, sulfurous acid gas, hydrogen sulfide, and a mixed gas thereof are used.

The magnetic layer in the present invention is made of Fe ₂ O ₃ , Fe ₃ O ₄ , CrO ₂ , Fe, Co, N.
A so-called "coating type" in which a fine ferromagnetic powder such as i is applied on a base film together with an organic binder, and a so-called "coating type" in which a ferromagnetic metal is deposited on the base film by a method such as vacuum deposition, sputtering, and plating. It is called "metal thin film type".

The magnetic layer has a thickness in the range of 0.3 to 5 μm in the case of the coating type and 0.05 to 2 μm in the case of the metal thin film type, and the latter generally has a higher linear density in magnetic recording. In the case of a metal thin film, an extremely thin protective layer is often provided in order to prevent mechanical deterioration of the magnetic layer due to direct contact with the head. An example of the protective layer is a silicone-based organic ultra-thin layer (thickness of tens to hundreds of angstroms), but the present invention is not limited to this. Further, the magnetization forms of the magnetic layer include horizontal magnetization and vertical magnetization, and the present invention is applied to both of them.

The magnetic recording medium of the present invention can be applied to various applications such as a tape and a floppy disc, but it is particularly preferably used for a floppy disc (magnetic disc).

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

First, the PPS used in the present invention is basically composed of a dihalogenated aromatic compound represented by p-dichlorobenzene using N-methylpyrrolidone as a solvent and substantially the same moles of sodium sulfide or sodium hydrosulfide and caustic soda. It is obtained by a high temperature reaction of a sulfur-containing compound represented by a mixture. Before starting the polymerization reaction, first add sodium sulfide (or a compound capable of synthesizing sodium sulfide) into N-methylpyrrolidone, and then add 10% to sodium sulfide.
To 100 mol% of a polymerization aid, and heated to 100 ° C or higher for dehydration. As the polymerization aid, an alkali metal carboxylic acid salt such as lithium benzoate is used. Next, 98 to 105 mol% of dihalogenated aromatic compound (of which 90 mol% or more is p-dichlorobenzene) is added to sodium sulfide as a monomer, and after nitrogen sealing, the reaction system is hermetically sealed.
Polymerize at 280 ° C for about 2-6 hours. After completion of the reaction, the cooled system is diluted with a sufficient amount of water and washed. The polymer is obtained in the form of powder or granules, washed with water several times and then dried to be used as the polymer used in the present invention.

The polymer is formed into a biaxially oriented film by known methods. That is, the resin melted by the extruder is
Quantitatively cast on the cooling drum from the base,
A non-oriented, amorphous sheet is formed by rapid cooling. Next, this sheet is sequentially biaxially or simultaneously biaxially stretched. Generally, sequential biaxial stretching is performed in the longitudinal direction between rolls having different peripheral speeds, and then transverse stretching is performed in a tenter. . Then, the biaxially stretched oriented film thus obtained is subjected to a constant length heat treatment in the same tenter, and then relaxed if necessary. The relax is performed by reducing the rail spacing at the rear part of the tenter in the horizontal direction by a fixed ratio, and by decreasing the roll peripheral speed by a fixed ratio in the vertical direction after exiting the tenter. In each case this ratio is in the range of a few percent.

In order to produce the film used in the present invention in the process of producing such a biaxially oriented film, the longitudinal and transverse stretching conditions, heat treatment conditions and relax conditions are particularly important. That is, in the longitudinal stretching step, the conditions must be selected so that the optical orientation degree after stretching and immediately before transverse stretching is in the range of 0.135 to 0.165. The actual stretching temperature and stretching ratio differ depending on the polymer, but generally within the range of 95-105 ℃, 3.9-
It is within the range of 4.9 times. Next, in the transverse stretching process, the degree of optical orientation after stretching is 0.05 or less in the longitudinal direction or 0.05 in the transverse direction.
It is desirable to select the conditions as follows.

The actual conditions are a stretching temperature of 95 to 110 ° C and a stretching ratio of 3.5 to 4.0. Also, the heat treatment temperature is from 200 ℃ to 270 ℃
In general, the relax is 0 to 5% in both vertical and horizontal directions. The film of the present invention is produced by an appropriate combination of these conditions, but as described above, the difference due to the polymer is large, and the product of the thermal expansion coefficient and the thermal contraction rate of the present invention is within this range of conditions. Select the condition that has.

As described above, the present invention requires a process of forming a magnetic layer on the biaxially oriented PPS film obtained by the above process, which includes a coating type and a metal thin film type. It is the latter that the effects of the present invention are particularly remarkable, and the latter will be described here.

Ferromagnetic metals typified by Co, Ni, Fe, and Co-
Ni, Co-Cr, Co-Fe, Co-V, Co-Rh, Co-Ru, Co-W, Co-Sn,
Ferromagnetic metal alloys such as Ni-Fe and Co-Ni-Al, components such as iron oxide, Co-doped iron oxide, chromium oxide, and ferromagnetic metal oxides such as barium ferrite.
There are the following methods for forming a non-ferromagnetic metal, a low-melting point metal, or the like included in the following range as a metal thin film layer on the film.

That is, vacuum deposition methods such as resistance heating, electron beam heating, induction heating, laser beam heating, etc., and further sputtering methods such as direct current bipolar method, high frequency bipolar method, direct current magnetron, high frequency magnetron, opposed bipolar method, etc.
Moreover, the cathode heating method, the high frequency excitation method, the ion plating method by the cluster ion beam method, etc.

Next, the definition, measurement method, and evaluation method of the characteristic values of the polymer, film, and floppy disk used in the description of the present invention will be described.

(1) Characteristic Melt Viscosity (μ) The volumetric discharge rate when the polymer is extruded at pressure P under temperature T using a high-performance flotator having a capillary die of length L and radius R is Q Then, the apparent shear stress τ, the apparent shear rate, and the apparent viscosity μ are defined as follows.

γ = (RP) / (2L) = (4Q) / (πR ³ ) μ = τ / At this time, the curve μ = f () obtained by plotting μ at various times is = 200 Define the characteristic melt viscosity μ ₀ with the value at (sec) ⁻¹ .

In the present invention, a die of L = 10 mm and R = 0.5 mm is used,
The value measured at T = 300 ° C. was used.

(2) optical orientation degree (n _gamma -n _beta) polarizing microscope equipped with crossed Nicols, and excisional the sample film so that the film surface is perpendicular to the optical axis, further sample, 45 ° to the analyzer axis Insert to have azimuth. Then, the sample is rotated around the optical axis to the phase reduction in the plus or minus 45 ° direction from the extinction position (the position on the side where the phase difference caused by the sample decreases by the compensator). Then, the optical path difference Γ ₀ caused by the birefringence of the sample at this time is obtained from the compensation value of the compensator, and the optical orientation degree n _γ −n _β is defined with Γ ₀ / d ₀ (here, d ₀ Represents the thickness of the sample). At this time,
On the sample, the direction perpendicular to the rotation axis of the compensator is the sample's γ direction, and the parallel direction is the β direction.

In the present invention, a polarization microscope POH type Leitz universal stage made by Nippon Kogaku, a universal stage made by Leitz, and a compensator made by Leitz were used to measure with monochromatic light of sodium D line (wavelength 0.5893 μm).

(3) Density of film (ρ) It was measured at 20 ° C. using a density gradient tube with an aqueous solution of lithium bromide.

(4) was measured by the glass transition point of the polymer (T _g) · the thermal melting point (T _m) and the film after biaxial stretching melting point (T _mf) DSC method.

(5) Coefficient of thermal expansion (A) at 120 ° C A 30 mm long and 5 mm wide section was cut out from the base film, and a thermomechanical property analyzer: TMA (TM-300 manufactured by Vacuum Riko Co., Ltd.)
Set to 0) and record the expansion and contraction of the sample when the following thermal history is applied under a constant tensile stress of 10 g / mm ² .

a. Temperature increase from 25 ℃ to 120 ℃ at 1 ℃ / min b. Hold at 120 ℃ for 5 minutes c. Temperature increase to 130 ℃ at 1 ℃ / min d. Immediately decrease to 110 ℃ at 1 ℃ / min At this time, Let ΔL be the dimensional change in the process of d (falling temperature from 130 ° C to 110 ° C) and have A = (ΔL / (20 × L ₀ ) (where L ₀ is the length when the sample is set in TMA), The coefficient of thermal expansion A at 120 ° C. in the length direction of the sample is defined.

(6) Thermal shrinkage at 120 ° C (C) After placing the sample at 23 ° C and 50% RH for 24 hours, measure the distance between two pre-marked points in that atmosphere,
l ₀ .

Then, after placing in a hot air oven set at 120 ° C for 30 minutes and then again at 23 ° C / 50% RH for 24 hours, the distance between the two points previously measured under that atmosphere was measured again. ， L ₁
And

At this time, C = 100 × (l ₀ −l ₁ ) / l ₀ is defined and the heat shrinkage rate C at 120 ° C. is defined.

(7) Directionality of A × C The measurement of A and C described above is carried out in the plane of the base film.
8 directions at 22.5 ° intervals (0 ° to 157.5 °, remaining 180 ° to
The 8 directions of 337.5 ° can be regarded as the same as the previous 8 directions due to the symmetry of the circle), and A × for each direction.
Calculate C. When all the values of A × C in these 8 directions are in the range of 2 × 10 ^{-7 to} 5 × 10 ^-5 ,
It is considered that A × C is within the scope of the present invention in all directions in the plane, and is otherwise outside the scope of the present invention.

(8) Reproduction characteristics of floppy disk A commercially available 8-inch standard disk drive (manufactured by NEC Corporation) was used.

◎ Test A… Characteristics against changes in humidity After inserting the floppy disc to be tested into the drive placed in a thermo-hygrostat and leaving it for 24 hours, put it on the outermost track (Track 00) at 25 ℃ ・ 20% RH. The minimum signal amplitude when a 125 KHz sine wave signal is recorded and immediately reproduced is R ₀ . After that, the atmosphere was changed to 25 ° C and 70%, and the minimum signal amplitude when reproduced again after 24 hours was A _1, and A ₁ / A ₀ was obtained and used as an index of the humidity resistance change characteristics.

◎ Test B… Insert the floppy disk to be tested for permanent deformation under high temperature and high humidity into the drive, 2
Record a 125 KHz sine signal on the outermost track at 3 ° C and 50% RH, and let B ₀ be the minimum signal amplitude when it is immediately played back. Next, take out only the disk, and place it at 70 ° C / 90% RH for 2
After waiting for a period of time, insert it again into the drive at 23 ° C and 50% RH, and let it be S ₁ as the minimum signal amplitude when playing back 24 hours later. An indicator of the permanent deformation characteristics with B ₁ / B _0.

(9) After the step of forming the magnetic layer on the curl base film, the disk cut into a 5.25-inch disk shape is stored as it is on the horizontal and flat table with one surface thereof stored in a jacket. Place it face down on its own and measure the maximum height of the disc. Do this for the other surface as well, and set the curl (unit: mm) with the larger value.

〔The invention's effect〕

As described above, according to the present invention, since the biaxially oriented poly-p-phenylene sulfide film having specific characteristics is used as the main constituent layer, there is no curl, the flatness is excellent, and the magnetic recording density is high. It was possible to obtain a recording medium, especially a floppy disc.

〔Example〕

Next, the present invention will be described in more detail with reference to examples.

Example 1 (1) Preparation of PPS polymer In an autoclave, 32.6 kg of sodium sulfide (250 mol, containing 40 wt% of water of crystallization), 100 g of sodium hydroxide, 36.1 kg (250 mol) of sodium benzoate, and N-methyl-2. -Preparing 79.2 kg of pyrrolidone (hereinafter abbreviated as NMP) and gradually raising the temperature to 205 ° C with stirring to remove 7.0 l of distillate containing 6.9 kg of water. To the residual mixture, 37.5 kg (255 mol) of 1,4-dichlorobenzene (hereinafter referred to as DCB) and 20.0 kg of NMP were added, and the mixture was heated at 265 ° C for 4 hours. The reaction product was washed 8 times with boiling water and then dried at 80 ° C for 24 hours using a vacuum dryer.
After drying for an hour, μ ₀ 2900 poise, N1.17, T _g 91 ℃, T _m 285 ℃
21.1 kg (yield 78%) of PPS having a high degree of polymerization was obtained. (PPS
-U).

(2) Melt molding To the composition obtained in (1) above, 0.1 wt% of calcium stearate powder was added as a lubricant, and after stirring and mixing with a mixer, the mixture was put into a hopper of an extruder having a diameter of 40 mm and the inside of the hopper The air is replaced with nitrogen gas. The composition melted at 310 ° C was passed through a filter (using metal fiber material, maximum pore size 10 μmφ) attached to the tip of the extruder, and extruded from a T-die having a linear lip with a length of 250 mm and a gap of 0.8 mm, It was cast on a metal drum whose surface temperature was kept at 30 ° C. to be cooled and solidified. At this time, at a position about 5 mm away from the point where the extruded melt comes into contact with the drum in the radial direction of the drum, in parallel with the drum axis and with a thickness of 0.1 mmφ
The stainless steel wire of No. 3 was stretched, and cast (electrostatic cast) while applying a DC voltage of about 5 kv between the wire and the drum. The obtained film was an unstretched film having a width of 230 mm, a thickness of 800 μm and a density of 1.3201 (referred to as a film U).

(3) Biaxial stretching, heat treatment The film U is set by a longitudinal stretching device composed of rolls,
Stretching temperature 96 ℃, stretching speed 30,000% in the longitudinal direction of the film
The film was stretched 4.1 times at a speed of / min.

Then, the film was fed to a tenter and the stretching temperature was set to 99.
The film was stretched 3.75 times in the width direction at a stretching temperature of 1000% / min at ℃. At this time, the degree of optical orientation immediately before stretching was 0.155. In the subsequent heat treatment chamber in the same tenter, heat treatment was performed at 220 ° C for 10 seconds, and then 2% relax in the width direction while gradually cooling. Then, using a vertical relax device consisting of rolls, the film was subjected to 2% relax at 200 ° C in the longitudinal direction of the film,
A PPS biaxially stretched film having a thickness of 50 μm was obtained (referred to as base film U).

(4) Characteristics of base film When the characteristics of the base film thus obtained were measured, A × C was found to have a minimum value of 7.2 × 10 ^-6 (A = 6.5 × 10 ^-5 , C = 0.11) The value was 8.5 × 10 ⁻⁶ (A = 6.1 × 10 ⁻⁵ , C = 0.14), which satisfied the properties required for the base film used in the present invention.

(5) Formation of magnetic layer First, one surface of the base film was subjected to corona discharge treatment in air to increase the surface tension to 50 dyne / cm. Then, Co
A target consisting of 80% by weight and 20% by weight of Ni was prepared, and by this target, a Co-Ni magnetic thin film with a thickness of about 3000 Å was formed on the corona-treated surface of the base film by the RF sputtering method. .

At this time, the distance between the target and the film is 60mm,
Plate voltage 2kV, Plate current 150mA, Argon pressure 1.2 × 1
It was 0 ^-1 mmHg.

Next, this was punched into a disk having an outer diameter of the 5.25-inch mini Flotpie disk standard, and a central hole of the same standard was further punched to create a magnetic disk (referred to as disk U).

On the other hand, for comparison, on a polyethylene terephthalate film having a thickness of 50 μm, under the same conditions as above, about 3000 Å of Co-
A Ni magnetic layer was formed, and this was also used as a mini-floppy disk size magnetic disk (referred to as disk V).

(6) Evaluation Table 1 shows the results when the prepared disk was inserted into a commercially available mini floppy diskette and evaluated.

It can be seen from Table 1 that the magnetic disk of the present invention has excellent reproduction characteristics when the humidity changes and is exposed to high temperature and high humidity, and is suitable for high track density recording.

Example 2 (1) Preparation of PPS Polymer In the same manner as in Example 1, μ ₀ 3500 poise, N1.25, T _g 91
A high polymerization degree PPS having a temperature of ℃ and T _{m of} 285 ℃ was obtained (referred to as PPS-W).

(2) Melt molding In the same manner as in Example 1, an unstretched film having a width of 240 mm and a thickness of 1200 μm was obtained (referred to as film-W).

(3) Biaxial stretching, heat treatment In the same manner as in (3) of Example 1, the longitudinal and transverse stretching ratios, heat treatment temperatures, and relax rates were adjusted to obtain five types of two types of thermal expansion coefficients and heat fluxes at 120 ° C. Axial stretched PPS film (thickness: about 75 μm) was obtained (base film W-1 to W).
-5).

(4) Characteristics of base film Table 2 shows the characteristics of the obtained base film.

(5) Preparation of Floppy Disk A disk was prepared in exactly the same manner as in Example 1 (disk W-1).
~ W-5).

(6) Evaluation results Table 2 shows the evaluation results of the prepared disks.

From this result, even with the PPS biaxially stretched film, the product of the present invention has a small curl and stable recording can be expected, while the thermal expansion coefficient and heat yield of the base film are out of the range of the present invention. It can be seen that in the case of the object, the curl is large and the recording becomes unstable.

Claims (1)

(57) [Claims] 1. Structural formula In a magnetic recording medium having a biaxially oriented poly (p-phenylene sulfide film) containing 90 mol% or more of repeating units as a main constituent layer of the base film and having a ferromagnetic layer on at least one surface of the base film. A flexible magnetic recording medium whose characteristics satisfy the following expressions in all in-plane directions. 2 × 10 ^-7 A × C 5 × 10 ^-5 where A: thermal expansion coefficient at 120 ° C (° C ^-1 ) C: thermal shrinkage at 120 ° C (%)