JPH0754582B2 - Flexible magnetic disk - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thin film type flexible magnetic disk (flexible magnetic disk).

[Conventional technology]

In recent years, a flexible magnetic disk device using a flexible magnetic disk as a recording medium has been widely used as an external storage device of a small computer since it can exchange media, can be randomly accessed, and is inexpensive. Reliability is being promoted. Higher recording density in magnetic recording is realized mainly by increasing the coercive force and thinning of the magnetic layer of the magnetic recording medium, but a base material is one in which conventionally used magnetic fine particles are dispersed in a polymer binder. Compared to the so-called coating type magnetic recording medium with the structure coated above, a metal that uses a Co-Ni alloy vapor deposition film or sputtered film, or a Co-Pt alloy sputtered film that is easy to achieve high coercive force and suitable for thinning A thin film magnetic recording medium has been attracting attention. On the other hand, unlike the conventional longitudinal recording method of recording in the in-plane direction of such a magnetic recording medium, the perpendicular magnetic recording method of recording a signal by forming residual magnetization in the thickness direction of the magnetic recording medium is Attention has been paid to the fact that a high recording density can be obtained, and a vapor-deposited film or a sputtered film of a Co—Cr alloy is being researched as the recording medium.

Attempts have been made to use these high recording density thin film media as flexible magnetic disks. At this time, a flexible polymer film is used as a substrate, and the ferromagnetic thin film is formed on both surfaces thereof by a method such as vapor deposition sputtering to form a disk shape.

[Problems to be solved by the invention]

However, the conventional thin film type flexible magnetic disk has a problem that mechanical durability against sliding with a magnetic head is not practically sufficient.

In the flexible magnetic disk device, the medium is pressed against the magnetic head when recording / reproducing a signal. However, the flexibility of the medium deforms the medium so that it closely adheres to the surface of the magnetic head, and the contact magnetically slides as the disk rotates. Therefore, the gap between the medium and the magnetic head becomes small, and excellent recording / reproducing characteristics can be obtained. However, conversely, such deformation and contact sliding are repeated in the operating state of the apparatus, and therefore the medium is required to have excellent mechanical durability against sliding with the magnetic head.

In conventional coating media, the magnetic layer is as thick as several μm, and magnetic fine particles are dispersed in the polymer binder, so it is practically durable against repeated deformation and sliding. Was realized. On the other hand, in the thin-film medium, the thickness of the magnetic layer is as thin as 1 μm or less, and since it is a continuous thin film, it is difficult to realize the mechanical durability required for practical use.

It is known that the flexibility or rigidity of the entire material has a great influence on the durability of a flexible material such as a flexible magnetic disk (for example, "Lubrication", Volume 30 issued by the Japan Society of Lubrication). , No. 8, p. 554). However, the optimum value cannot be generally determined because it depends on each mechanical system.

In order to improve the mechanical durability of the thin film type flexible magnetic disk, the present inventor prototyped media having various bending rigidity, and for the sliding durability thereof, there was a certain optimum value for the bending rigidity. The present invention has been discovered and has led to the present invention.

[Means for solving problems]

The flexible magnetic disk of the present invention is a flexible magnetic disk in which ferromagnetic thin films are formed on both sides of a flexible substrate to form a magnetic recording layer, and the bending rigidity is 1 × 10 ⁻⁵ N · m or more. × 10 ^-4
It is characterized by being Nm or less.

〔Example〕

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

Flexible magnetic disks were manufactured by trial using substrates having different materials and thicknesses shown in Samples 1 to 12 in Table 1 below. The material of the substrate is polyimide (PI) and polyethylene terephthalate (PET).

The sample with a single magnetic layer structure has a CoCr thin film with a thickness of 3000 liters formed on both sides of the substrate by sputtering in a CoCr alloy targeting Ar gas. The sample with a two-layer magnetic layer was prepared by sputtering NiFe alloy on both sides of the substrate in Ar gas to a thickness of 5000Å.
A thin film is formed on top of which a CoCr alloy target Ar
A CoCr thin film with a thickness of 3000Å was formed by sputtering in gas. For both the single layer and the two layers, a SiO ₂ protective film having a thickness of 200 Å was further formed on these magnetic layers by sputtering in Ar gas with SiO ₂ as a target. After processing these into the shape of a 3.5 inch diameter micro floppy disk, perfluoroalkyl polyether (DuPont Co., trade name Crytox) was applied as a lubricant to form a lubricating layer, which was used as a flexible magnetic disk medium. .

In addition, the coating type medium (NEC Corporation, Micro Floppy Disk, product number PC-FD802-10) that has been conventionally used as Sample 13 was also evaluated.

In addition, the flexural rigidity of these samples was measured. FIG. 1 shows an outline of a bending stiffness measuring device. If the sample 1 to be measured is supported by a knife edge 2.2 'with a distance L and a load W is applied to the center of the sample 1 by the knife edge 3 and the center of the sample 1 is bent by a deflection y, the bending rigidity D of the sample 1 is
Is given by the first equation, where b is the width of the sample 1.

Here, E and I are the elastic modulus and the second moment of area of the sample 1, respectively.

The bending stiffness of each sample thus measured is summarized in Table 1.

After mounting these samples on a commercially available micro floppy disk drive and recording a signal of 15KFRPI, the signal was read in the head-loaded state, and the number of slides until the playback output dropped to 70% of the initial output Is the sliding durability,
The results are summarized in Fig. 2. The temperature is 25 ℃ and the relative humidity is 50.
% Environment.

As can be seen from FIG. 2, the sliding durability of the thin film type flexible magnetic disk does not depend on the material of the substrate and the structure of the magnetic layer but depends on the bending rigidity of the entire medium. According to JIS C 6291, if the practicable sliding durability of the flexible magnetic disk is set to 3 million times or more, the practicable thin film medium has a bending rigidity of 1 × 10 ⁻⁵ N · m or more and 1 × 10 ⁻⁴ N or more. -It can be seen that the range is m or less. The flexural rigidity of conventional coated media is greater than this range, which indicates that the thin film media cannot achieve sufficient durability at the same flexural rigidity as conventional coated media. There is.

The sliding durability of a thin film type flexible magnetic disk greatly depends on its bending rigidity, and the optimum range of the value is 1x.
The reason why it is 10 ⁻⁵ N · m or more and 1 × 10 ⁻⁴ N · m or less is not yet clear. However, when the bending rigidity is too high, the medium cannot be deformed well along the surface of the magnetic head, the contact area with the magnetic head becomes small, and as a result, the load per unit area becomes large and the durability is lowered. On the contrary, when the bending rigidity is too small, it is considered that the entire medium is largely deformed by the frictional force with the magnetic head, and the deformation limit of the thin film is exceeded.

The substrate of the flexible magnetic disk for carrying out the present invention is not limited to the above-mentioned polyimide or polyethylene terephthalate, but may be, for example, cellulose acetate, nitrocellulose, polyamide, polymethylmethacrylate, polytetrafluoroethylene, polytrifluoroethylene. Also usable are organic polymer films such as polymers or copolymers of α-olefins such as ethylene and propylene, polymers or copolymers of polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyethylene naphthalate.

Further, the ferromagnetic thin film is not limited to the above CoCr or NiFe,
For example, Fe, Co, Ni and other ferromagnetic metals or their oxides, or Fe-Co, Co-Ni, Fe-Ti, Fe-Cr, Fe
-Si, Co-V, Co-Sm, Co-Pt, Co-P, Co-Ni-P, Fe-Cr-Co and other ferromagnetic alloys or those with additives added are vacuum deposited and sputtered , Ion plating method,
It may be formed into a thin film by an electroplating method, an electroless plating method, or the like. The thickness of the ferromagnetic thin film is 0.01-2 μm
Is preferred.

Further, the above-mentioned SiO ₂ protective film is not always necessary. Also
In addition to the SiO ₂ protective film, for example, Ti, Cr, Mo, W, Al ₂ O ₃ , S
iO ₂ , TiO ₂ , ZrO ₂ , Cr ₂ O ₃ , B ₄ C, SiC, TiC, WC, BN, Si ₃
A protective film such as N ₄ may be provided.

Further, a lubricating layer is formed on the ferromagnetic thin film, or on the protective film when the protective cover is provided. As a lubricating layer, hydrocarbon-based lubricants such as fatty acids and metal soaps, lubricating oils such as silicone oils, fluorosilicone oils, perfluoroalkyl polyethers, low-polymer tetrafluoroethylene, carbon, solid lubricants such as molybdenum disulfide Agent, or a mixture of these directly or dissolved or dispersed in a suitable solvent on the ferromagnetic thin film or coating vacuum deposition method, immersion method spray method, vapor deposition method, roller coating method,
It is formed by coating by a coating method such as a spin coating method.

〔The invention's effect〕

As described above, according to the present invention, a flexible magnetic disk having a ferromagnetic thin film formed on a flexible substrate as a magnetic recording layer has excellent durability against sliding with a magnetic head. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing a method for measuring bending rigidity of a sample, and FIG. 2 is a graph showing a relationship between bending rigidity of a sample and sliding durability. 1 ... Sample, 2,2 ', 3 ... edge.

Claims (1)

[Claims] 1. A flexible magnetic disk in which ferromagnetic thin films are formed on both sides of a flexible substrate to form a magnetic recording layer, and the flexural rigidity is 1 × 10 ⁻⁵ N · m or more and 1 × 10 ⁻⁴ N. -A flexible magnetic disk characterized by being m or less.