JPS62202315A - Vertical magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a vertical magnetic recording medium which is free from curling and wrinkling and has good touch of a magnetic head and running property by forming a substrate which has the coefft. of linear expansion in a specific range and has the coefft. of linear expansion approximately isotropic with respect to the plane of the substrate. CONSTITUTION:The coefft. of linear expansion of the recording medium consisting of a high-polymer film is 4.5X10<-6>-9.5X10<-6>/ deg.C and the coefft. of linear expansion is approximately isotropic with respect to the plane of the substrate. The high-polymer film having such coefft. of linear expansion is obtd. by the adjustment of the skeleton of the constituting polymer particles, copolymn. thereof and the reaction method in the stage of adjusting the ratio thereof and synthesizing, the adjustment of the mol.wt., adjustment of the degree of stretching, a heat treatment, etc. Since the coefft. of linear expansion is made approximately isotropic within the plane of the substrate, the slightly generated curling does not affect the characteristics of the magnetic recording medium and such is advantageous in the case of using the medium in the form of a disk such as floppy disk in particular.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a perpendicular magnetic recording medium in which a Co-Cr based ferromagnetic alloy layer is deposited and formed on a polymer film substrate. ,
In particular, the present invention relates to a perpendicular magnetic recording medium that prevents the occurrence of curls, wrinkles, etc. that adversely affect magnetic head tack, runnability, etc.

(Prior Art) In recent years, the perpendicular magnetic recording method, which performs magnetic recording using residual magnetization perpendicular to the medium surface of a magnetic recording medium, has been attracting attention as a method suitable in principle for high-density recording.

As a typical perpendicular magnetic recording medium used for this perpendicular magnetic recording, a Go-Cr-based ferromagnetic alloy layer having an axis of easy magnetization perpendicular to the film surface is formed on a polymer film by sputtering or vapor deposition. The magnetic layer is made from a ceramic material.

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 this substrate 1. Magnetic alloy layer 2
A protective film 3 and a lubricating layer 48 are sequentially provided on the magnetic tape, and it is considered to be used for magnetic tapes and floppy disks.

The co-cr based ferromagnetic alloy layer is generally formed by conventional sputtering or magnetron sputtering in an argon atmosphere.

The Co-Cr ferromagnetic alloy layer thus formed has a columnar structure oriented along the C-axis, and its magnetic properties are determined mainly by the composition of the Co-Cr ferromagnetic alloy layer, as well as saturation magnetization MS. In addition, the magnetic anisotropy energy Ku perpendicular to the film surface and the retention quadrature lc+ perpendicular to the film surface each have conditions that enable extremely high-density recording.

However, when forming a Co-0r-based ferromagnetic alloy layer with desired magnetic properties by the above-mentioned method i, it is necessary to heat the polymer film covering the substrate to 80 to 200°C in vacuum. As shown in Figure 2 (a) and (b), curls occur due to the difference in thermal expansion coefficients between the polymer film 5 and the ferromagnetic alloy layer 6, and wrinkles occur especially when the thermal expansion coefficient is too high. I come to do it. Such curls and wrinkles cause problems such as poor magnetic head touch and running performance when used with magnetic recording media. In this curl phenomenon, Co-C with a film thickness of 5000
When the r-based ferromagnetic alloy layer is formed into a polymer film having a thickness of 75 μm and different coefficients of linear expansion, the ferromagnetic alloy layer 6 of the film having a larger coefficient of linear expansion than the Co-Cr-based ferromagnetic alloy layer is on the outside. An outer curl occurs, and conversely, a heat-resistant film with a small coefficient of linear expansion causes an inner curl with the ferromagnetic alloy layer 6 on the inside. The Co--Cr ferromagnetic alloy layer is usually formed by using a roll-type continuous sputtering apparatus as shown in FIG. 8b
The polymer film 12 is run while applying tension along the circumferential side of the cylindrical roll 9 using the supply port 9 and the spring removal roll 10, and the temperature of the polymer film is controlled by the cylindrical rolls 8a and 8b. be exposed. Code 13 in Figure 3
A, 13b, and 13c are auxiliary rollers for film transfer. In this case, the amount of shrinkage of the Co-Cr alloy layer and the polymer film is different when the temperature changes from 80 to 200°C, which is a high temperature during film formation of the ferromagnetic alloy layer, to room temperature after film formation. A polymer film with a larger coefficient of linear expansion than the Cr-based ferromagnetic alloy layer will cause outer curl, while a film with a smaller coefficient of linear expansion will cause inner curl.

Therefore, the following method can be considered as a method for producing a curl-free medium.

■ Forming magnetic layers of the same thickness on both sides of a polymer film (double-sided media).

■ Use a polymer film with a linear expansion coefficient similar to that of the magnetic layer.

■ Form a non-magnetic metal layer on the opposite side of the polymer film 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 of (2) in order to avoid increasing the recording capacity. When a magnetic layer is attached to a film, the coefficient of linear expansion becomes complex, and the coefficient of linear expansion of the polymer film itself differs due to issues such as thermal coverage and heat shrinkage of the polymer film. It is difficult to get rid of curls. In addition, there is a method using a polymer film with the same linear expansion coefficient as the magnetic layer in (■).
This is difficult because thermal properties such as heat shrinkability exhibit nonlinearity. Rarani method ■ has the same problems as ■, and
Since the deposited non-magnetic layer has no function other than preventing curling, there is a problem in that the 1-tal cost is high even when functions are taken into account.

Furthermore, in Japanese Patent Application Laid-Open No. 58-159243, the coefficient of linear expansion of the substrate is 1. Ox 10-5~2.5X10-5/°C
and set the temperature of the peripheral side of the can (roll) to 150 to 300.
A method is disclosed in which curling is prevented by setting the temperature at .degree. In this method, a magnetic layer is formed on one side on a substrate with a diameter of 9 to 26 μm, and the curl value is 64% or less, which is a very large curl tolerance value, for example, 3.5 μm. It is difficult to apply this to something that requires less than 0.6% and isotropy, such as inch floppy disks.

Also, the linear expansion coefficient of the substrate film is 10XIO-6~
29X10-6/℃, but this value shows an example when the roll temperature during vapor deposition is as high as 150 to 300℃ and the film running speed is as fast as 10m/min. This does not represent a substrate film used under normal vapor deposition conditions of 80 to 200°C.

In any case, it is important to eliminate curls and wrinkles in magnetic recording media, but prevention of curls and wrinkles in composite films made of substances with different coefficients of linear expansion depends on the thermal behavior of polymer films. This is extremely difficult because it tends to change depending on the heat treatment conditions before and after the heat treatment.

The present inventor carried out research to solve these conventional difficulties, and found that Co
-The Cr-based ferromagnetic alloy layer is heated under normal heating conditions, that is, at a temperature range of 80 to 200°C and a roll running speed of 1 to 20°C.
When performing sputtering or vapor deposition with the roll temperature and film temperature almost the same at a slow speed of mm/min, the linear expansion coefficient of the polymer film is 4.5X 10'.
~9.5X 10-6/℃ and the linear expansion coefficient is approximately isotropic with respect to the substrate plane, and when using a disk-shaped medium with a diameter of 85 mm, the curl height is 2.
■■ Below [(flo-λ)/flo is almost 0.
Less than 6%. However, β0: Medium diameter when there is no curl (85 I11> (see Figure 4 a), shortest medium diameter when fl2 curl occurs (see Figure 4); the same applies hereinafter), It has been found that curly wrinkles are virtually eliminated.

The present invention has been made to solve these conventional problems, and it is an object of the present invention to provide a perpendicular magnetic recording medium that is free from curls and wrinkles and has good magnetic rad touch and running properties.

[Structure of the Invention] (Means for Solving the Problems) The perpendicular magnetic recording medium of the present invention is a perpendicular magnetic recording medium in which a ferromagnetic alloy layer is deposited on a substrate made of a polymer film. The linear expansion coefficient of the substrate is 4.5X1
0' to 9.5 x 10-6/°C, and the coefficient of linear expansion is substantially isotropic with respect to the plane of the substrate.

As the polymer film used in the present invention, heat-resistant polymer films such as polyimide, polyethylene terephthalate, and aromatic polyamide are suitable. In the present invention, among these polymer films, linear expansion coefficients of 4.5 to 4.5 are used.
9.5X 10-6/°C is used. A polymer film having such a coefficient of linear expansion can be obtained by adjusting the skeleton of the constituent polymer molecules, copolymerization, adjusting the ratio, reaction method during synthesis, adjusting the molecular weight:A, adjusting the stretching ratio, heat treatment, etc. can. In some cases, the substrate is used in the form of a disk such as a floppy disk, and it is desired that the substrate is isotropically free from curling. Therefore, a coefficient of linear expansion that is approximately isotropic within the plane of the substrate is used.

Further, as the ferromagnetic alloy used in the ferromagnetic alloy layer of the present invention, a Co-Cr based ferromagnetic alloy is suitable, and in particular, a Co-Cr based ferromagnetic alloy is suitable.
A Co-Cr based ferromagnetic alloy having a content of 10 to 30 atomic % is suitable. Note that the magnetic layer is made of, for example, N1-Fe (atomic %
approximately 80:20) soft magnetic layer and C.

Even with a two-layer structure such as a -Cr ferromagnetic layer, if the linear expansion coefficient of the underlayer is not significantly different from that of the GO-Cr ferromagnetic layer, the linear expansion coefficient of (N i -Fe (80:20) (approximately 12×10 −6 /° C.), the present invention can be applied.

A satisfactory curl here is that the above height is 2 times or less, which corresponds to approximately 16% or less for (λo fl>/flo).The results shown in the table above show that the thickness of the Co-Cr alloy layer is 200 From 7,500 people to 3,000 people and film thickness 3
Even when the thickness was changed from 0 μm to 100 μm, it remained almost the same. In this case, the roll temperature is determined by the time d3 during which the film is in contact with the roll and the roll running speed of 1 to 20 mo/mi.
Since the temperature is slow (n), it almost matches the film temperature.

Also, before forming the polymer film, 10-” to
The stability of curl prevention can be further improved by heat treatment for 5 minutes to 1 hour at a temperature of 100 to 300" Cu) in a vacuum better than rr. This heat treatment improves heat coverage and heat shrinkability. etc. are removed, and the linear expansion characteristics become stable the next time heat is applied.

(Function) The reasons why the present invention eliminates curling are not necessarily clear, but include the difference in thickness and Young's modulus between the magnetic film and the polymer film, internal stress in the magnetic film, thermal expansion of the polymer film, etc. Nonlinearity of properties, thermal deformability of polymer films,
When considering the influence of the difference in linear expansion coefficient with the magnetic film, the temperature range is 80 to 20, which is the normal sputtering or vapor deposition condition.
When forming a magnetic film at 0°C, it happens that no curl occurs in this range [curl height is 21nT11 or less [(
J2. o - Q ) /, 9 o is considered to be approximately 0.6% or less. The stability of the roll prevention is determined by the stability of the polymer film before it is formed.
Rough improvement can be achieved by heat treatment at a temperature of 100 to 300''C for 5 minutes to 1 hour in a vacuum below r'r.

In addition, in the present invention, the thickness of the Co-Qr alloy layer is increased from 2000 to 7500 mm, and the thickness of the aluminum film is increased from 30 μm to 1 μm.
Even if the IJ changes up to 100A1, the effect of K can be obtained.

Furthermore, in the present invention, since the coefficient of linear expansion is almost isotropic within the plane of the M plate, even slight curling hardly affects the characteristics of the magnetic recording medium, especially )['' 1° which is advantageous when used in the disk shape of a tsupi disk (Example) [Experimental example] First, using the roll type continuous sputtering apparatus shown in Fig. 3, Polymer film of 10' to
Temperature [5 at 100-300°C] in a vacuum lower than rr
After heat treatment for minutes to 1 hour, Co
-Cr ferromagnetic alloy layers were formed on both sides of the substrate to a thickness of 5000 nm. Then, beat a 365-inch floppy disk and place it on top of a flat piece of glass with the curved side facing up. - Assessed the condition of the vehicle. The following table shows the results of applying the above method to polymer films having different coefficients of linear expansion and varying the roll temperature.

Table α 4,5~6°56.6~9.5 15~44 The values of linear expansion coefficient in the above table are after heating to about -H200℃,
It shows the average linear expansion coefficient when the sample was cooled to room temperature and then heated again from room temperature to 200°C. This measurement was performed using a thermomechanical analyzer at a heating rate of 5°C in a dry nitrogen atmosphere.
/min.

In this experiment, the contact time with the roll and the roll running speed were determined to be 1 to 20IIITll/I[li
Since the film temperature is slow as n, the film temperature almost matches the roll temperature.

From the results in the above table, the linear expansion coefficient of the polymer film was determined to be 4.5 in the magnetic layer forming temperature range of 80 to 200°C, which is the roll temperature necessary to ensure the magnetic properties of the Co-(:r alloy layer).
It can be seen that curl and wrinkle free media is obtained by ~9.5xlO'/°C.

In this experiment, the thickness of the Go-Cr ferromagnetic alloy layer was set to 2
From 000 to 7500 people, the film thickness is 3
Similar effects were obtained even when the thickness was changed from 0 μm to 100 μm.

In addition, the stability of preventing curling is determined by heating the polymer film once in a vacuum higher than 10' torr at a temperature of 100 to 300 torr before forming the film.
It is further improved by heat treatment at a temperature of 5 minutes to 1 hour. Due to this heat treatment, thermal hysteresis,
This is because the thermal shrinkage properties are removed and the linear expansion characteristics become stable when heat is next applied.

Example 1 The linear expansion coefficient of the substrate is 7. Ox 10', y"C
A polyimide film having a thickness of 75 μm and an approximately isotropic surface was used to form a Co-Cr based ferromagnetic alloy layer of 10-7 t using a continuous roll sputtering apparatus as shown in FIG.

The film was polished at a high speed of 10 lines to avoid running the film, which was subjected to heat treatment at 200° C. for 40 minutes in a vacuum of 100 mm. Thereafter, Go--Cr based ferromagnetic alloy layers were formed on both sides with a thickness of 5000 Å by sputtering 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 mTIf or less.

Example 2 Using a nearly isotropic polyimide film with a linear expansion coefficient of 7.0×10-6/°C and a thickness of 75 μm as a substrate, the thickness of the Co-Cr ferromagnetic alloy layer was changed to 3000 μm. A magnetic recording medium was produced in the same manner as in Example 1 except for the above. The curl in this example was 11 IITn or less.

Example 3 A magnetic recording medium was prepared under the same conditions as in Example 1, except that a polyimide-based heat-resistant polymer film with a linear expansion coefficient of 6.8xlO'/°C and an approximately isotropic thickness of 45 μm was used as the substrate. It was created. The curl of the 3.5-inch medium produced in this example was 1 mm or less.

Comparative Example 1 A magnetic recording medium was prepared under the same conditions as in Example 1 using a polyimide film having a linear expansion coefficient of 22×lO'/° C. and a slightly non-isotropic thickness of 75 μm as a substrate. The curl of this comparative example was 6 dragons.

Comparative Example 2 A medium was prepared under the same conditions as in Example 1, using a polyimide film having a linear expansion coefficient of 44 x 10-6/°C and a thickness of 75 μm, which was not slightly isotropic, as a substrate. In this comparative example, not only curls of 10+ nm occurred but also significant wrinkles occurred.

Comparative Example 3 A medium was prepared under the same conditions as in Example 1 using a 75 μm thick polyester film with a linear expansion coefficient of 15×10 −6 /°C and slightly poor isotropy as a substrate. The curl in this comparative example was 5 cm.

[Effect of the invention] As is clear from the above examples, according to the present invention,
Depending on the working conditions used for sputtering or vapor deposition of a typical Co--Cr based ferromagnetic alloy layer, it is possible to obtain a perpendicular magnetic recording medium that does not generate curls or wrinkles and has good magnetic rad touch and running properties.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view schematically showing a perpendicular magnetic recording medium, and FIG.
The figure is a perspective view showing the curled state in the case of a single-sided magnetic layer.
This figure schematically shows a continuous sputtering apparatus used for manufacturing magnetic media, and FIG. 4 is a diagram for explaining the curl value. 1.5... Polymer film substrate 2.6... Magnetic layer 3... Protective layer 4... Lubricating layer

Claims (3)

[Claims] (1) In a perpendicular magnetic recording medium in which a Co-Cr-based ferromagnetic alloy layer is deposited on a substrate made of a polymer film, the coefficient of linear expansion of the substrate is 4.5×10^-^6
˜9.5×10^-^6/°C, and the linear expansion coefficient is approximately isotropic with respect to the plane of the substrate. (2) The ferromagnetic alloy layer has a polymer film of 80 to 200
The perpendicular magnetic recording medium according to claim 1, which is formed by sputtering or vapor deposition while heating at .degree. (3) The Co-Cr-based ferromagnetic alloy has a Cr content of 10
3. The perpendicular magnetic recording medium according to claim 1 or 2, which is a Co-Cr based ferromagnetic alloy containing up to 30 atomic %.