JPH07101500B2 - Perpendicular magnetic recording medium - Google Patents

Description

The present invention relates to a perpendicular magnetic recording medium comprising a polymer film substrate and a Co—Cr based ferromagnetic alloy layer deposited on the polymer film substrate. In particular, the present invention relates to a perpendicular magnetic recording medium in which the occurrence of curls, wrinkles, etc., which adversely affect the magnetic head touch, running property, etc., is prevented.

(Prior Art) In recent years, a perpendicular magnetic recording method in which magnetic recording is performed by utilizing residual magnetization in a direction perpendicular to the medium surface of a magnetic recording medium has been drawing attention as a method suitable for high density recording in principle.

A typical perpendicular magnetic recording medium used for this perpendicular magnetic recording has an easy magnetization axis in a direction perpendicular to the film surface.
It is known that a Co—Cr ferromagnetic alloy layer is formed on a polymer film by sputtering or vapor deposition to form a magnetic layer.

Such a perpendicular magnetic recording medium, as shown in FIG.
A substrate 1 made of a heat-resistant polymer film such as polyimide, polyethylene terephthalate, or aromatic polyamide, and a ferromagnetic alloy layer 2 made of a Co-Cr alloy or the like are formed on at least one surface of the substrate 1, A protective film 3 and a lubricating layer 4 are provided in this order on the magnetic alloy layer 2,
It is considered to be used for magnetic tapes and floppy disks.

The Co-Cr type ferromagnetic alloy layer is generally formed by an ordinary conventional sputtering method or magnetron sputtering method in an argon atmosphere. The Co--Cr based ferromagnetic alloy layer thus formed is C
It has a columnar structure oriented to the axis, and its magnetic characteristics are mainly Co
In addition to the saturation magnetization Ms determined by the composition of the −Cr ferromagnetic alloy layer, the magnetic anisotropy energy Ku perpendicular to the film surface and the coercive force Hc _{1 in the} direction perpendicular to the film surface are large, respectively, and conditions under which high density recording is possible Is equipped with.

However, when the Co—Cr based ferromagnetic alloy layer having desired magnetic properties is formed by the above-mentioned manufacturing method, it is necessary to heat the polymer film as the substrate to 80 to 200 ° C. in a vacuum. As shown in FIGS. (A) and (b), curling occurs due to the difference in the coefficient of thermal expansion between the polymer film 5 and the ferromagnetic alloy layer 6, and wrinkles occur when the coefficient of thermal expansion is too different. . Such curls and wrinkles cause problems such as deterioration of magnetic head touch and runnability when used with a magnetic recording medium. In this curl phenomenon, a Co-Cr type ferromagnetic alloy layer with a film thickness of 5000 Å is
When a polymer film having a different linear expansion coefficient of 75 μm is formed, that is, when a magnetic layer is formed on only one side of the polymer film, a film having a larger linear expansion coefficient than the Co—Cr ferromagnetic alloy layer is stronger. An outer curl in which the magnetic alloy layer 6 is on the outer side occurs, and conversely, a heat-resistant film having a small linear expansion coefficient causes an inner curl in which the ferromagnetic alloy layer 6 is on the inner side. The Co-Cr ferromagnetic alloy layer is usually formed in consideration of mass productivity by using a roll-type continuous sputtering apparatus as shown in FIG. 3 to form a cylindrical roll 8a facing the Co-Cr targets 7a and 7b. The polymer film 12 is made to run along the peripheral side surface of 8b by using the front and rear supply rolls 9 and take-up rolls 10, and the polymer film temperature is controlled by the cylindrical rolls 8a and 8b. Reference numerals 13a, 13b and 13c in FIG. 3 are auxiliary rollers for film transfer. In this case, the amount of shrinkage of the Co-Cr alloy layer and the polymer film when the temperature changes from the high temperature at the time of film formation of the ferromagnetic alloy layer of 80 to 200 ° C to the room temperature after film formation is different from that of the one-sided medium. In the case of a polymer film having a larger linear expansion coefficient than the Co-Cr ferromagnetic alloy layer (coefficient of linear expansion of about 11 × 10 ^-6 / ° C), an outer curl occurs, and conversely, an inner curl of a film having a smaller linear expansion coefficient. Will occur.

Therefore, the following method can be considered as a method for producing a medium without curl.

A magnetic layer having the same thickness is formed on both sides of a polymer film (double-sided medium).

A polymer film having a linear expansion coefficient similar to that of the magnetic layer is used.

A nonmagnetic metal layer is formed on the surface of the polymer film opposite to the magnetic layer.

When considering a recording medium such as a floppy disk, it is desirable to form a magnetic layer on both sides in order to increase the recording capacity, but for this purpose, it is necessary to deposit a magnetic layer on each side, When the magnetic layer is attached, the linear expansion coefficient is compounded, and because the linear expansion coefficient of the polymer film itself differs due to problems such as thermal history of the polymer film and heat shrinkage, curl with the same film thickness. It is difficult to get rid of. Also, the method of using a polymer film having the same linear expansion coefficient as that of the magnetic layer is difficult because the thermal characteristics of the polymer film, such as thermal history and heat shrinkage, show non-linearity. In addition to the same problem as in the case of the above method, there is a problem in that the nonmagnetic layer deposited has no function other than curling prevention, so that the total cost considering the function becomes high.

Further, in JP-A-58-159243, the linear expansion coefficient of the substrate is 1.0
A method is disclosed in which the curl is prevented by setting the temperature of the peripheral side surface of the can (roll) to 150 to 300 ° C. at a temperature of × 10 ^{-5 to} 2.9 × 10 ^-5 / ° C. 9-26μ with this method
It has a magnetic layer formed on one side on a thin substrate with a curl value of 4m or less, and the curl value is 4% or less, which is a very large curl allowance value. For example, in case of 3.5 inch floppy disk. In addition, it is difficult to apply it to those that are 0.6% or less and also require its isotropy.

The linear expansion coefficient of the substrate film is 10 × 10 ^{-6 to} 29 × 10.
^-6 / ° C is shown, but this value shows an example when the roll temperature during vapor deposition is as high as 150 to 300 ° C and the film traveling speed is as high as 10 m / min, and the temperature range is 80-200
It is not the one of the substrate film used under the normal vapor deposition conditions of ° C.

In any case, in magnetic recording media, it is important to eliminate curl and wrinkles in the medium, but to prevent the occurrence of curls and wrinkles in composite films with substances having different linear expansion coefficients, the thermal behavior of the polymer film is It is very difficult because it easily changes depending on the heat treatment conditions before and after.

The present inventor has conducted research to solve such a conventional drawback, and on a substrate made of a polymer film, Co-
Cr-based ferromagnetic alloy layer under normal heating conditions, that is, temperature range
When the film is sputtered or vapor-deposited at a temperature of 80 to 200 ° C. and a roll traveling speed is slowed to 1 to 20 mm / min and the roll temperature and the film temperature are substantially the same, the linear expansion coefficient of the polymer film is 4.5 ×. When 10 ^{−6 to} 9.5 × 10 ⁻⁶ / ° C. is used and the linear expansion coefficient is substantially isotropic with respect to the plane of the substrate, the curl height when a disk-shaped medium having a diameter of 85 mm is used. 2 mm or less [0.6% or less for ((l ₀ −l) / l ₀ ).
However, l ₀ : medium diameter without curl (85 mm) (see FIG. 4 a), l: shortest medium diameter with curl (see FIG. 4 b). The same applies hereinafter], and it was found that curls and wrinkles were virtually eliminated.

The present invention has been made to solve such conventional problems, and an object of the present invention is to provide a perpendicular magnetic recording medium which is free from curling and wrinkling and has a good magnetic head touch and running property.

[Structure of the Invention] (Means for Solving Problems) A perpendicular magnetic recording medium of the present invention is a perpendicular magnetic recording medium in which a ferromagnetic alloy layer is adhered and formed on a substrate made of a polymer film. The linear expansion coefficient of the substrate is 4.5 × 10 ^-6
˜9.5 × 10 ⁻⁶ / ° C., and the linear expansion coefficient is isotropic with respect to the plane of the substrate.

As the polymer film used in the present invention, a heat resistant polymer film such as polyimide, polyethylene terephthalate or aromatic polyamide is suitable. And in the present invention, the linear expansion coefficient of these polymer films is 4.5 to 9.5.
Those of × 10 ^-6 / ° C are used. The polymer film having such a linear expansion coefficient can be obtained by adjusting the skeleton of the constituent polymer molecules, copolymerization and the ratio thereof, the reaction method at the time of synthesis, the adjustment of the molecular weight, the adjustment of the stretching ratio, the heat treatment and the like. It may be used in the form of a disk such as a floppy disk, and since it is desired that the curl state is not isotropic, the coefficient of linear expansion is isotropic in the plane of the substrate.

Further, as the ferromagnetic alloy used in the ferromagnetic alloy layer of the present invention, a Co-Cr type ferromagnetic alloy is suitable, and particularly a Co-Cr type ferromagnetic alloy having a Cr content of 10 to 30 atom% is used. Is suitable.
Even if the magnetic layer has a two-layer structure such as a Ni-Fe (atomic% about 80:20) soft magnetic layer and a Co-Cr ferromagnetic layer, the linear expansion coefficient of the underlayer is a Co-Cr ferromagnetic layer. (Ni-Fe (80:20) has a linear expansion coefficient of about 12 × 10 ^-6 /
C.), the present invention can be applied.

As a curl that can be satisfied, the height is 2 mm or less, and (l ₀ −l) / l ₀ corresponds to 0.6% or less.

Further, in the present invention, the coefficient of linear expansion is substantially isotropic with respect to the plane of the substrate means that the coefficient of linear expansion is equal with respect to the plane of the substrate, or the height of the curl is 2 mm or less at various places, or (l ₀ − l) / l ₀ means that it is set to 0.6% or less. The results shown in the above table were almost the same even when the thickness of the Co-Cr alloy layer was changed from 2000Å to 7500Å and the film thickness was changed from 30 µm to 100 µm. In this case, the roll temperature substantially coincides with the film temperature because the time during which the film is in contact with the roll and the roll running speed are as slow as 1 to 20 mm / min.

Further, the stability of curling can be further improved by subjecting the polymer film to heat treatment at a temperature of 100 to 300 ° C. for 5 minutes to 1 hour in a vacuum better than 10 ⁻⁵ torr before film formation. By this heat treatment, thermal history, thermal shrinkage, etc. are released, and the linear expansion characteristics when the heat is applied next become stable.

(Operation) Although the reason why the curling is eliminated by the present invention is not always clear, the thickness of the magnetic film and the polymer film, the difference in Young's modulus, the internal stress of the magnetic film, the thermal expansion characteristics of the polymer film, etc. Taking into account the effects of non-linearity, thermal deformability of polymer film, and difference in linear expansion coefficient with magnetic film, the temperature range of normal sputtering or vapor deposition conditions is 80-
When a magnetic film is formed at 200 ° C, it does not happen that curl occurs in this range [curl height is 2 mm or less [(l ₀ −
l) / l ₀ is 0.6% or less]. The stability of curl prevention can be further improved by subjecting the polymer film to a heat treatment for 5 minutes to 1 hour at a temperature of 100 to 300 ° C. in a vacuum of 10 ⁻⁵ torr or less before film formation. This is the effect of removing the heat history of the polymer film.

That is, when Co-Cr-based ferromagnetic layers are formed on both sides of the polymer film in a temperature range of 80 to 200 ° C., a polymer film having a linear expansion coefficient equal to or larger than that of the magnetic layer as in the conventional example is used. Instead of the above, a magnetic recording medium with curl suppressed can be obtained by using a polymer film having a linear expansion coefficient slightly smaller than that of the magnetic layer as in the present invention.

In the present invention, the same effect can be obtained even when the thickness of the Co-Cr alloy layer is changed from 2000Å to 7500Å and the film thickness is changed from 30 µm to 100 µm.

Further, in the present invention, since the coefficient of linear expansion is almost isotropic in the plane of the substrate, a slight curl hardly affects the characteristics of the magnetic recording medium, and particularly in a floppy disk. This is advantageous when used in the form of a disc.

(Example) [Experimental example] First, using a roll-type continuous sputtering apparatus shown in FIG. 3, a polymer film having a thickness of 75 μm was heated at a temperature of 100 to 300 ° C. for 5 minutes in a vacuum degree lower than 10 ⁻⁵ torr. After heat treatment for 1 minute to 1 hour, a Co-Cr ferromagnetic alloy layer was formed on both surfaces of the substrate to a thickness of 5000Å in an argon atmosphere. Then, the curled state was evaluated by punching out a 3.5-inch floppy disk with the warped side facing upward and placing it on a flat glass plate and measuring the height of the outermost peripheral portion away from the glass plate. The following table shows the results of applying the above method to polymer films having different linear expansion coefficients while changing the roll temperature.

The values of the coefficient of linear expansion in the above table indicate the average coefficient of linear expansion when the material is once heated to about 200 ° C, cooled to room temperature, and then heated again from room temperature to 200 ° C. This measurement was performed using a thermomechanical analyzer in a dry nitrogen atmosphere at a heating rate of 5 ° C / m.
This is the result of in.

In this experiment, the film temperature is almost the same as the roll temperature because the time of contact with the roll and the roll running speed are as slow as 1 to 20 mm / min.

From the results in the above table, the linear expansion coefficient of the polymer film is 4.5 to 9.5 × 10 ^-6 / in the magnetic layer forming temperature range of the roll temperature of 80 to 200 ° C required to secure the magnetic properties of the Co-Cr alloy layer.
It can be seen that a temperature of 0 ° C. results in a curl-free and wrinkle-free medium.

In this experiment, the thickness of the Co-Cr ferromagnetic alloy layer was set to 2000Å
To 7500Å and film thickness from 30μm to 100μm
The same effect was obtained even when changing to.

Also, the stability of curl prevention is better than 10 ^-5 torr once before forming a polymer film in a vacuum at a temperature of 100-300 ° C for 5 minutes-
The heat treatment for 1 hour makes it even better. This is because this heat treatment releases the thermal covering property, the heat shrinkage property, and the like, and the linear expansion characteristic is stabilized when the heat is applied next.

Example 1 A substrate having a linear expansion coefficient of 7.0 × 10 ⁻⁶ / ° C. and an isotropic thickness of 75
Heat treatment for about 40 minutes at 200 ℃ in a vacuum of 10 ^-7 torr before forming a Co-Cr ferromagnetic alloy layer with a roll type continuous sputtering device as shown in Fig. 3 using a μm polyimide film. The film was run at such a film running speed. After that, a Co-Cr type ferromagnetic alloy layer was formed on both sides by 5000 Å by the sputtering method in an argon atmosphere.
The roll temperature at this time was 150 ° C. The curl (height) of the magnetic recording medium of this example was 1 mm or less.

Example 2 A substrate having a linear expansion coefficient of 7.0 × 10 ⁻⁶ / ° C. and an isotropic thickness of 75
A magnetic recording medium was prepared in the same manner as in Example 1 except that the thickness of the Co—Cr ferromagnetic alloy layer was changed to 3000 Å by using a polyimide film of μm. The curl in this example is 1 m
It was less than m.

Example 3 A magnetic recording medium under the same conditions as in Example 1 except that a polyimide-based heat-resistant polymer film having a linear expansion coefficient of 6.8 × 10 ⁻⁶ / ° C. and an isotropic thickness of 45 μm was used as the substrate. It was created. The curl for the 3.5 inch media created in this example is 1 mm
It was below.

Comparative Example 1 A magnetic recording medium was prepared under the same conditions as in Example 1 by using a polyimide film having a linear expansion coefficient of 22 × 10 ⁻⁶ / ° C. and a thickness of 75 μm which was not isotropic as a substrate. The curl of this comparative example was 6 mm.

Comparative Example 2 A medium was prepared under the same conditions as in Example 1 by using a polyimide film having a linear expansion coefficient of 44 × 10 ⁻⁶ / ° C. and a non-isotropic thickness of 75 μm as a substrate. In this comparative example, a curl of 10 mm was generated and wrinkles were significantly generated.

Comparative Example 3 A medium was prepared under the same conditions as in Example 1 by using a polyester film having a coefficient of linear expansion of 15 × 10 ⁻⁶ / ° C. and a poor isotropic property and having a thickness of 75 μm as a substrate. The curl of this comparative example was 5 mm.

EFFECTS OF THE INVENTION As is clear from the above embodiments, according to the present invention,
Curling or wrinkling does not occur depending on the working conditions used for sputtering or vapor deposition of a normal Co—Cr type ferromagnetic alloy layer, and it is possible to obtain a perpendicular magnetic recording medium with good magnetic head touch and good running performance.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a perpendicular magnetic recording medium, and FIG.
The figure is a perspective view showing a curled state in the case of a single-sided magnetic layer,
FIG. 4 is a diagram schematically showing a continuous sputtering apparatus used for manufacturing a magnetic medium, and FIG. 4 is a diagram for explaining the curl value. 1, 5 ... Polymer film substrate 2, 6 ... Magnetic layer 3 ... Protective layer 4 ... Lubrication layer

Claims (3)

[Claims] 1. A Co—Cr film formed on a substrate made of a polymer film.
In a perpendicular magnetic recording medium having a system ferromagnetic alloy layer deposited thereon, the coefficient of linear expansion of the substrate is 4.5 × 10 ^{−6 to} 9.5 × 10 which is smaller than the coefficient of linear expansion of the Co—Cr system ferromagnetic alloy layer. A perpendicular magnetic recording medium at ⁻⁶ / ° C., wherein the coefficient of linear expansion is substantially isotropic with respect to the plane of the substrate. 2. The ferromagnetic alloy layer comprises a polymer film of 80 to 20.
The perpendicular magnetic recording medium according to claim 1, which is formed by sputtering while heating at 0 ° C. 3. A Co—Cr based ferromagnetic alloy having a Cr content of 10 to 10
The perpendicular magnetic recording medium according to claim 1 or 2, wherein the perpendicular magnetic recording medium is a Co-Cr type ferromagnetic alloy containing 30 atomic%.