JPH05314470A - Magnetic disk - Google Patents

Abstract

PURPOSE:To improve track density and storage capacity by providing many recessed areas which realizes random reflection of incident light at the surface of a magnetic layer to determine the layer to a particular thickness. CONSTITUTION:Many recessed areas 4 are provided with the predetermined interval along the tracks on which information signal is recorded at the surface 3 of a magnetic layer 2 of a magnetic disk 1. The surface 3 of the layer 2 is finished as a mirror surface and the incident light A is regularly reflected. On the other hand, the recessed area 4 has the bottom having the rough surface 5 to reflect the incident light at random. Thickness of the layer 2 is set to 5 times or less that of the wavelength of the incident light. It is desirable that the layer 2 has the thickness so that when the light is incident on the surface 3 between recessed regions 4 of the disk 1, the light B reflected regularly at the surface 3 and the light C reflected regularly at the interface 7 between the layer 2 and substrate 6 after passing the layer 2 are reinforced by the interface with each other. Such magnetic disk realizes good optical tracking servo and remarkably improves storing capacity through high track density and also improves the overwrite characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magnetic disk,
More specifically, the present invention relates to a magnetic disk having a high track density and a high storage capacity, which enables good optical tracking servo.

[0002]

2. Description of the Related Art Generally, a magnetic disk is formed by coating a base material such as a polyester film with a magnetic coating composed of magnetic powder, a binder resin, an organic solvent and other necessary components.
After it is dried, it is punched out into a disk shape, and it is possible to record new information signals, or to record additional information by erasing unnecessary information once recorded and recording new information in that part. Widely used as a thing. However, in this type of magnetic disk, if an information signal is recorded and reproduced, then once removed, reattached and additional recording is performed, the magnetic disk is deformed and eccentric, and the like, resulting in a track already formed. Abnormally approaching or crossing the track due to additional recording.

[0003]

Therefore, the track pitch is set large in consideration of the deformation distortion and eccentricity of the magnetic disk. However, if the track pitch of the magnetic disk is set large, the recording density is increased. Limited by the large track pitch, a sufficiently large storage capacity cannot be obtained.

[0004]

The present invention has been made as a result of various studies in order to overcome such problems, and an information signal can be recorded on the surface of a magnetic layer that reflects and reflects incident light of a magnetic disk. A large number of concave portions that diffusely reflect incident light are provided along a track at predetermined intervals, and when the thickness of the magnetic layer is 5 times or less the wavelength of the incident light and light is incident on the magnetic layer between the concave portions, By narrowing the track pitch, the reflected light that is regularly reflected on the surface of the layer and the reflected light that is transmitted through the magnetic layer and is regularly reflected at the interface between the magnetic layer and the substrate are strengthened by interference. However, the optical tracking servo can be performed well, the track density is increased, and the storage capacity is remarkably improved.

An example of the magnetic disk of the present invention will be described below with reference to the drawings. In FIGS. 1 and 2, reference numeral 1 denotes a magnetic disk, in which a large number of recesses 4 are provided on a surface 3 of a magnetic layer 2 at predetermined intervals along a track on which an information signal is recorded. The magnetic layer 2 has a surface 3
Has been mirror-finished so that light is regularly reflected when light is incident, and the bottom surface 5 of the concave portion 4 is roughened and diffusely reflected when light is incident.

FIG. 3 shows a part of the magnetic disk 1 in a sectional view along a track.
When incident on the surface 3 of the laser light, a part of the light is reflected and reflected as reflected light B, and the other part of the light is transmitted through the magnetic layer 2 to be reflected and reflected as reflected light C at the interface 7 between the magnetic layer 2 and the substrate 6. To be done. When the incident light A is incident on the bottom surface 5 of the recess 4, it is diffusely reflected.

In such a magnetic disk 1, FIG. 4 shows that the thickness of the magnetic layer 2 having the same composition is variously changed and the reflected light B which is regularly reflected on the surface 3 of the magnetic layer 2 and the magnetic layer 2 are transmitted. Then, the reflectance of the incident light A obtained by the reflected light C that is regularly reflected at the interface 7 between the magnetic layer 2 and the base body 4 interferes with each other, and the graph E of the calculated value is calculated based on the measured value. Is displayed, and as shown in this graph E, the incident light A
The reflectance of increases and decreases with the thickness of the magnetic layer 2, and converges to a certain value when the thickness of the magnetic layer 2 becomes infinite.

Therefore, in order to increase the reflectance of the incident light A, the thickness of the magnetic layer 2 is adjusted so that the light B reflected by the surface 3 of the magnetic layer 2 and the magnetic layer 2 are transmitted through the magnetic layer 2. It is necessary to make the thickness such that the reflected light C, which is regularly reflected at the interface 7 between the substrate and the substrate 6, is strengthened by interference.
m, 0.6 μm, 0.9 μm, 1.15 μm, 1.4 μm, ...
Need to be each thickness.

If the reflectance of the incident light A is required to be 8% or more in accordance with the capability of the photodetector, the thickness of the magnetic layer 2 should be 0.05 to 0.2 μm, 0.32 to 0.45 μm, 0.55
~ 0.72μm, 0.83 ~ 0.97μm, 1.08 ~ 1.24μm, 1.32 ~
It is necessary to make each thickness of 1.5 μm ...
If the thickness is out of these ranges, the reflected light of the incident light A cannot be detected.

Further, the magnetic layer 2 of the magnetic disk 1 contains magnetic powder, binder resin, filler, etc., and when the content ratio of the magnetic powder or the like is changed or the kind of binder resin is different, it becomes magnetic. The refractive index of the layer 2 changes, the relationship between the reflectance of the incident light A and the thickness of the magnetic layer 2 changes, and a deviation occurs in the graph E of the calculated values shown in FIG. Further, when the type of the incident light A, the incident angle, etc. are changed, the same is true, and the graph E is deviated.

Therefore, the thickness of the magnetic layer 2 needs to take into consideration changes in the refractive index of the magnetic layer 2 and changes in the type of incident light A, the incident angle, and the like. It is preferable to set the wavelength to 5 times or less, which is 5 times the wavelength of incident light A
If the thickness is thicker than twice, the degree of enhancement of reflected light due to interference becomes small, which is not preferable.

Therefore, when the thickness of the magnetic layer 2 of the magnetic disk 1 is 5 times or less of the wavelength of the incident light A and the light is incident on the magnetic layer surface 3 between the recesses 4 of the magnetic disk 1,
The thickness of the reflected light B that is regularly reflected on the surface 3 of the magnetic layer 2 and the reflected light C that is transmitted through the magnetic layer 2 and is regularly reflected at the interface 7 between the magnetic layer 2 and the substrate 6 are strengthened by interference. With such a thickness, the reflected light of the incident light A incident on the magnetic layer 2 is favorably detected by the photodetector.

On the other hand, since the incident light A is diffusely reflected from the bottom surface 5 of the recess 4 provided in the magnetic layer 2, the surface 3 of the magnetic layer 2 and the recess 4 are clearly recognized and compared with each other. Such a tracking servo can be performed satisfactorily, and even if the track pitch is narrowed, the already formed track can be accurately grasped, and the additional recording can be accurately performed. as a result,
The tracking density can be increased and the storage capacity can be significantly improved.

When additional recording of the information signal is performed,
Unnecessary information previously recorded must be sufficiently erased, and therefore, the overwrite characteristic of the magnetic disk 1 is preferably set to -26 dB or less.

Since such an overwrite characteristic is improved as the thickness of the magnetic layer 2 is made thinner and the coercive force is made lower, the magnetic disk 1 of the present invention has the thickness of the magnetic layer 2 as follows.
When light is incident on the surface 3 of the magnetic layer between the recesses 4 of the magnetic disk 1 at a wavelength 5 times or less of the wavelength of the incident light A, the reflected light B and the magnetic layer 2 which are regularly reflected by the surface 3 of the magnetic layer 2 are separated. The thickness is set so that the reflected light C which is transmitted and is regularly reflected at the interface 7 between the magnetic layer 2 and the substrate 6 is strengthened by interference, and the overwriting characteristic is -26 dB or less. Is preferred,
The coercive force is preferably 650 Oersted or more.

To manufacture the magnetic disk of the present invention,
On a substrate such as polyester film, magnetic powder, binder resin, an organic solvent and a magnetic coating material consisting of other necessary components are applied and dried to form a magnetic layer, which is then punched into a disk shape. It is manufactured by providing a large number of concave portions at predetermined intervals along the track on which the information signal is recorded by a method such as pressing on the surface of the magnetic layer.

The magnetic powder used in the magnetic layer is γ
-Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, Co-containing gamma-Fe
₂ O ₃ powder, Co-containing Fe ₃ O ₄ powder, CrO ₂ powder,
Fe powder, Fe-based powder in which Fe contains elements such as Al, Cr, Mn, Si and Zn, Co powder, F
Magnetic powders generally used in magnetic recording media such as e-Ni powder and barium ferrite powder are widely included.

Further, as the binder resin, vinyl chloride-
Generally used as a binder resin for magnetic recording media, such as vinyl acetate-based copolymers, fibrin-based resins, polyvinyl butyral-based resins, polyurethane-based resins, polyester-based resins, isocyanate compounds, and radiation-curable resins. Things are widely used.

As the organic solvent, commonly used organic solvents such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, ethyl acetate and toluene may be used alone or in admixture of two or more.

In the magnetic coating composition, various commonly used additives such as a dispersant, an abrasive and an antistatic agent may be optionally added and used.

[0021]

Next, examples of the present invention will be described. Example 1 Barium ferrite magnetic powder (coercive force 730 Oersted) 100 parts by weight VAGH (manufactured by UCC; vinyl chloride-vinyl acetate-vinyl 15 〃 alcohol copolymer) UR8310 (manufactured by Nippon Polyurethane Industry Co., Ltd .; urethane resin) 10 Coronet L (manufactured by Nippon Polyurethane Industry Co., Ltd .; trifunctional low content 10 〃 isocyanate compound) HS-500 (manufactured by Asahi Carbon Co., Ltd .; carbon black) 10 〃 Bengala 5〃 α-alumina 5 〃 Myristic acid 5 〃 Zinc stearate 2 〃 Stearic acid-n-butyl 5 〃 Cyclohexanone 117 〃 Toluene 117 〃 A magnetic paint was prepared by mixing and dispersing this composition. The magnetic layer is coated on both sides of the film in various thicknesses, dried, and calendered. Formed.

Then, after punching these into a disk shape,
By pressing with a pressing machine equipped with a die for marking the recesses, a large number of recesses 4 are formed on the surface of the magnetic layer at predetermined intervals along the tracks on which information signals are recorded, and a large number of magnetic disks are formed. I made it.

Example 2 In the composition of the magnetic paint in Example 1, the coercive force was 7
A barium ferrite magnetic powder having a coercive force of 760 oersted was used in place of the barium ferrite magnetic powder of 30 oersted to prepare a magnetic paint, and the magnetic paint prepared in Example 1 was used as the magnetic paint. A magnetic disk was prepared in the same manner as in Example 1 except that the both surfaces of the film were coated so that the dry thickness was 0.66 μm, dried, and calendered to form a magnetic layer.

Example 3 In the composition of the magnetic paint in Example 1, the coercive force was 7
A barium ferrite magnetic powder having a coercive force of 760 oersted was used in place of the barium ferrite magnetic powder of 30 oersted to prepare a magnetic paint, and the magnetic paint prepared in Example 1 was used as the magnetic paint. A magnetic disk was prepared in the same manner as in Example 1 except that the dry thickness was 0.82 μm on both surfaces of the film, the coating was dried, and calendering was performed to form a magnetic layer.

Example 4 In the composition of the magnetic paint in Example 1, the coercive force was 7
A barium ferrite magnetic powder having a coercive force of 760 oersted was used in place of the barium ferrite magnetic powder of 30 oersted to prepare a magnetic paint, and the magnetic paint prepared in Example 1 was used as the magnetic paint. A magnetic disk was produced in the same manner as in Example 1 except that the both surfaces of the film were coated so as to have a dry thickness of 0.88 μm, dried, and calendered to form a magnetic layer.

Example 5 In the composition of the magnetic coating material of Example 1, the coercive force is 7
A barium ferrite magnetic powder having a coercive force of 670 oersted was used in place of the barium ferrite magnetic powder of 30 oersted to prepare a magnetic paint, and the magnetic paint prepared in Example 1 was used instead of the magnetic paint to prepare a polyester having a thickness of 62 μm. A magnetic disk was produced in the same manner as in Example 1 except that the both surfaces of the film were coated to a dry thickness of 0.68 μm, dried, and calendered to form a magnetic layer.

Example 6 In the composition of the magnetic paint in Example 1, the coercive force was 7
A barium ferrite magnetic powder having a coercive force of 670 oersted was used in place of the barium ferrite magnetic powder of 30 oersted to prepare a magnetic paint, and the magnetic paint prepared in Example 1 was used instead of the magnetic paint to prepare a polyester having a thickness of 62 μm. A magnetic disk was produced in the same manner as in Example 1 except that the dried layer was coated on both surfaces of the film to a dry thickness of 0.90 μm, dried, and calendered to form a magnetic layer.

Comparative Example 1 In Example 1, the magnetic coating material prepared in Example 1 was applied to both sides of a polyester film having a thickness of 62 μm and the dry thickness was 0.8.
The magnetic disk was coated in the same manner as in Example 1 except that the magnetic layer was formed by coating and drying so as to have a thickness of .mu.m, a magnetic layer was formed, and the magnetic layer was punched out into a disk shape to form a magnetic disk. Made.

For each magnetic disk obtained in Example 1, light having a central wavelength of 880 nm was incident on the surface of the magnetic disk at an incident angle of 20 degrees, and reflected light was detected by a photodetector to determine the thickness of the magnetic layer. The relationship with the reflectance was investigated. FIG. 4 shows the measured values in the relationship between the thickness of the magnetic layer and the reflectance, and the calculated reflectance is represented by a graph E. The magnetic disk obtained in FIG. , The thickness of the magnetic layer
0.05-0.2 μm, 0.32-0.45 μm, 0.55-0.72 μm, 0.
83 to 0.97 μm, 1.08 to 1.24 μm, 1.32 to 1.5 μm, ...
It turns out that it is necessary to make each thickness of.

Further, with respect to the magnetic disks of Samples 1 to 4 each having a different magnetic layer thickness obtained in Example 1 and the magnetic disks obtained in Examples 2 to 6, the coercive force, the light reflectance and the on-off coefficient were set. -Burlite characteristics were investigated. Overwrite characteristics are such that a signal is written on the outermost track of 2 MB FDD at a writing frequency of 250 KHz, the signal level is 1 F, and the writing frequency is 500 KHz on it.
The intensity ratio (1F '/ 1F) with the remaining signal level 1F' when the signal was overwritten with was measured using a spectrum analyzer and examined. Table 1 below shows the results.

[0031]

FIG. 5 shows the results obtained in Table 1 as a relation between the thickness of the magnetic layer and the coercive force. From FIG. 5, the magnetic layer thickness is 0.40 μm and the coercive force is Is 780
Oersted and magnetic layer thickness is 0.65-0.85μ
In the range of m, the coercive force in the range of 700 to 830 oersted has good overwriting characteristics, and the magnetic layer has a thickness of 0.80 to 0.90 μm and the coercive force of 760 to 830.
It can be seen that those in the Oersted range cannot obtain good overwriting characteristics.

Further, the magnetic disks obtained in the respective examples can be optically provided with a tracking servo,
As a result of being able to accurately grasp the already formed tracks even if the track pitch was narrowed, the track density could be increased. However, the magnetic disk obtained in Comparative Example 1 had an optical tracking servo. Therefore, the track density cannot be increased.

[0034]

As described above, the magnetic disk obtained according to the present invention can favorably perform the optical tracking servo, the track density is increased, and the storage capacity is remarkably improved. Can be made Also, the over
The light characteristics can also be improved.

[Brief description of drawings]

FIG. 1 is a plan view showing an example of a magnetic disk of the present invention.

FIG. 2 is a partially enlarged sectional perspective view of the magnetic disk shown in FIG.

3 is a partially enlarged cross-sectional explanatory view of the magnetic disk shown in FIG.

FIG. 4 is a relationship diagram between the thickness of the magnetic layer of the magnetic disk obtained by the present invention and the light reflectance.

FIG. 5 is a relationship diagram between the thickness of the magnetic layer and the coercive force of the magnetic disk obtained by the present invention.

[Explanation of symbols]

 1 magnetic disk 2 magnetic layer 3 surface 4 concave portion 5 bottom surface 6 substrate 7 interface A incident light B, C reflected light

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kimihiko Kanno 1-88-1 Tora, Ibaraki-shi, Osaka Inside Hitachi Maxell Co., Ltd.

Claims (2)

[Claims] 1. A magnetic disk having a magnetic layer containing magnetic powder on a substrate, wherein the surface of a magnetic layer that reflects and reflects incident light is a concave portion that diffusely reflects incident light along a track where an information signal is recorded. Are provided at predetermined intervals, and the thickness of the magnetic layer is 5 times or less the wavelength of the incident light, and when light is incident on the magnetic layer between the recesses, the reflected light is regularly reflected on the surface of the magnetic layer. A magnetic disk having a thickness that enhances the interference of reflected light that is transmitted through the magnetic layer and is regularly reflected at the interface between the magnetic layer and the substrate. 2. The reflectance of incident light that is strengthened by interference between reflected light that is regularly reflected on the surface of the magnetic layer and reflected light that is transmitted through the magnetic layer and is regularly reflected at the interface between the magnetic layer and the substrate. The magnetic disk according to claim 1, wherein the content is 9% or more.