JPH09161341A - Production of disk-shaped recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to form a protective film at a specific thickness and film thickness error and to obtain a sufficient protective effect by supplying a UV curing resin to the side inner than the position half the innermost peripheral radius of a data region and applying the resin from this position by spin coating. SOLUTION: A disk 24 is rotated at 30rpm and the UV curing resin 21 is discharged from a nozzle 22 and is supplied circumferentially to the inner peripheral side. In succession, the rotating speed of the disk 24 is increased up to 3000rpm and is held at this speed for 8 sec. During this time, the UV curing resin 21 supplied on the disk 24 is spread to the outer peripheral side by centrifugal force, by which the coating film is formed over the entire surface. The coating film is thereafter irradiated with UV rays at irradiation power of about 500mj/cm<2> , by which the resin is cured and the protective film is formed. In such a case, the UV curing resin 21 is supplied to the side inner than half the innermost peripheral radius of the data region A and is applied by spin coating from this position, by which the protective film is formed on the data region A to >=5μm average thickness and <=2.0μm film thickness error. The sufficient protective effect is thus obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc-shaped recording medium and a method of manufacturing the same, and more particularly to improvement of a method of forming a protective layer.

[0002]

2. Description of the Related Art In a magneto-optical recording system, a magnetic thin film is partially heated above a Curie point or a temperature compensation point to eliminate the coercive force of this portion and magnetize in the direction of a recording magnetic field applied from the outside. The basic principle is to reverse the orientation of the above, and it is being put to practical use in an optical filing system, an external storage device of a computer, a recording device of audio and video information, and the like.

A magneto-optical disk for recording by the above-mentioned magneto-optical recording system has an easy axis of magnetization in a direction perpendicular to the film surface on one main surface of a transparent substrate made of plastic such as polycarbonate or glass. It is known that a recording portion is formed by laminating a magnetic thin film (recording magnetic film: for example, a rare earth-transition metal alloy amorphous thin film), a dielectric film, and a reflective film having a large magneto-optical effect. In such a magneto-optical disk, in addition to the above components, a protective film made of an ultraviolet curable resin or the like is provided on the reflective film, which is the uppermost layer of the recording section, for the purpose of preventing the recording magnetic film from being corroded or scratched. It is generally formed so as to cover the film.

Further, although this magneto-optical disk has a single plate structure, in addition to this, the recording portions of the two magneto-optical disks or the substrates of the two magneto-optical disks are made to face each other to be integrated.
A magneto-optical disk having a double plate structure has also been proposed. In the magneto-optical disk having the both-plate structure, recording and reproduction are independently performed in the two recording portions, so that at least twice the amount of recorded information can be obtained as compared with the magneto-optical disk having the single-plate structure. In addition, since it has a bilaterally symmetrical structure with the bonding surface sandwiched, there is also an advantage that the disk is less likely to warp with respect to changes in temperature and humidity of the external environment, as compared with a magneto-optical disk having a single plate structure.

By the way, the magneto-optical recording method is roughly classified into an optical modulation method and a magnetic field modulation method. Among them, the magnetic field modulation method is capable of overwriting and is suitable for high density recording and high access. Since it is also advantageous, it is being energetically studied.

In this magnetic field modulation method, an information signal is written in a magnetic thin film by reversing the applied magnetic field at high speed, and the magnetic field is normally applied by a magnetic head having magnetic field generating means.

A magnetic head that reverses the magnetic field at a high speed cannot generate a very strong magnetic field as compared with a magnetic head that does not reverse the magnetic field as used in the optical modulation method.

On the other hand, the strength of the magnetic field applied by the magnetic head is almost inversely proportional to the distance from the magnetic head,
The larger the distance, the weaker the magnetic field. Therefore, in the magnetic head that can generate only a relatively weak magnetic field as described above,
It is necessary to dispose as close to the recording magnetic film as possible.

Therefore, in the case of a magneto-optical disk having a single plate structure, an optical pickup device for irradiating a laser beam is arranged on the substrate side of the magneto-optical disk, and the magnetic head is arranged on the opposite side, that is, the recording section side. .

In the case of a double plate construction, Japanese Patent Laid-Open No. 2-31 is used.
As reported in Japanese Patent Application No. 0841 and Japanese Patent Application Laid-Open No. 3-241551, the recording sections are arranged on both sides of the disk. Then, the optical pickup device and the magnetic head are integrated and arranged on one side of the magneto-optical disk.

In the system using the integrated head as described above, the laser light from the optical pickup device is directly applied to the recording magnetic film without passing through the substrate. Therefore, the material of the substrate is not limited to the transparent material, and various opaque materials can be used. Therefore, as disclosed in JP-A-3-178062, it is possible to prevent the warp of the disk by using Al or the like as the material of the substrate.

[0012]

As described above, magneto-optical disks having various configurations have been proposed in the magneto-optical recording system. In any of the configurations, the protective film is usually formed by spin coating. To be done.

To form a protective film by this spin coating method, the disk on which the protective film is to be formed is placed on a turntable and first rotated at a low speed. Then, the ultraviolet curable resin is discharged from the nozzle, and the ultraviolet curable resin is supplied in a circumferential shape along the innermost circumference of the data area of the disc. Subsequently, the disk is rotated at a high speed, and the coating material supplied to the inner circumference is spread to the outer circumference by the centrifugal force to form a coating film of the ultraviolet curable resin on the entire surface of the disk. Then, the protective film is formed by irradiating this coating film with ultraviolet rays and curing it. The thickness of this protective film is set to approximately 15 μm from the viewpoint of obtaining a sufficient protective effect.

However, the protective film formed by the spin coating method as described above tends to be thicker on the outer peripheral side.

Further, the film thickness of the coating film varies depending on the conditions such as the viscosity of the resin, the number of revolutions of the disk, the rotation time, etc. There is a phenomenon in which the film thickness difference between the inner circumference and the outer circumference is caused by a fixed value no matter how much is changed.

That is, FIG. 6 shows a film thickness distribution when an ultraviolet curable resin film is formed on a disk having a diameter of 3.5 inches by a spin coating method. The horizontal axis represents the radial position on the disk, and the vertical axis represents the film thickness of the ultraviolet curable resin film (protective film) at the radial position.

The ultraviolet curable resin has a viscosity of 500c.
Three types of ps, 140 cps and 37 cps were used. In the figure, ◯ is the film thickness distribution when the 500 cps ultraviolet curing resin is applied, Δ is the film thickness distribution when the 140 cps ultraviolet curing resin is applied, and □ is the film thickness distribution when the 37 cps ultraviolet curing resin is applied. Is the measured value of. In all of these, when the disk is rotated at a low speed, the resin is circumferentially supplied from the radial position of 17 mm to the outer circumference, and the rotation speed is increased to 3000 rpm over 1 second. After holding for a second, a film was formed by irradiating with ultraviolet rays. The solid line drawn along each data is the calculated value of the film thickness distribution obtained from the equation of the balance between the viscous resistance force and the centrifugal force.

In general, it is known that the film thickness of a coating film when ultraviolet curable resins having different viscosities are applied under the same conditions is proportional to the square root of the viscosity. Are applied with different film thicknesses. Theoretically, the film thickness ratio between applying 500 cps UV curing resin and 140 cps UV curing resin is (500/140) ^1/2 = 1.9, and applying 500 cps UV curing resin. The film thickness ratio between the above case and the case where the 37 cps ultraviolet curable resin was applied is (500/37) ^1/2 = 3.7.

Here, when the UV curable resin having a viscosity of 140 cps is used and standardized by multiplying the film thickness when the UV curable resin having a viscosity of 37 cps is multiplied by 1.9 and 3.7, respectively, A film thickness distribution as shown in 7 is obtained.

Looking at FIG. 7, the three film thickness distributions are on the same curve. This means that in the ordinary spin coating method, no matter how the conditions are controlled, when trying to form a coating film with a certain specific film thickness, the film thickness error is always a value determined by the inner circumference and the outer circumference. Is generated.

For example, if the thickness of the protective film is set to be thin by using an ultraviolet curable resin having a viscosity of 37 cps or by increasing the spin coating rotation time, it is 24 mm.
Radius position (inner side) and 40 mm radius position (outer side)
The film thickness difference at 1 is suppressed to 1.5 μm. However, in order to sufficiently prevent the corrosion of the recording magnetic film, the film thickness of the protective film cannot be extremely thinned, and the film thickness of 15 μm on average is required as it is. However, if the average film thickness of the protective film is set to 15 μm by controlling the conditions, the film thickness difference between the inner peripheral side and the outer peripheral side is 5
It will reach μm.

Here, in the case of using an optical device in which the laser light emitted from the optical pickup device through the protective film is emitted to the recording magnetic film from the protective film side without passing through the substrate, If the film thickness error between the inner and outer circumferences of the protective film increases, the problem of destabilization due to wavefront aberration becomes a problem. The wavefront aberration W40d is quantified based on the following Expression 1.

W40d = (n ² −1) / 8n ³ · (NA) ⁴ · Δd Equation 1 n: Refractive index of protective film Δd: Thickness error of protective film NA: Numerical aperture of lens of optical system In the case of the current magneto-optical disk, the refractive index n of the protective film is 1.
58, the laser wavelength λ of the optical system is 780 nm, and the numerical aperture NA (Numerical Aperture) of the lens is
e) is 0.5. Under these conditions, if the thickness error Δd of the protective film is 50 μm, the wavefront aberration W40d is 0.19λ (= 0.148 μm) from the equation (1).

However, recently, in order to improve the recording density, the laser wavelength λ of the optical system is shortened and the numerical aperture NA of the lens is increased.

This is because the spot size of the laser light focused by the optical lens is proportional to the laser wavelength λ and inversely proportional to the numerical aperture NA of the lens. In the current optical system, the beam spot diameter is about 1.6 μm, but for example, the laser wavelength is 480 nm and the numerical aperture NA of the lens is as described above.
Is 0.9, the beam spot diameter is reduced to 0.5 μm, which is 1/3 of the current value, and the recording density per area is increased to about 9 times.

However, when the factor of the optical system is changed in such a direction and the film thickness error Δd at the inner and outer peripheries of the protective film remains 5 μm, the wavefront aberration W40d obtained by the above mathematical formula 1 is obtained. The value becomes extremely large, making stable recording and reproduction difficult. For example, if the laser wavelength is 48
When the wavelength numerical aperture NA is 0 nm and the lens numerical aperture is 0.9, in order to suppress the wavefront aberration W40d to at least the current 0.19λ, the film thickness error Δd at the inner and outer circumferences of the protective film is 2.9 μm.
It is necessary to keep it below.

Further, such a thickness error of the protective film affects not only the irradiation of the laser beam by the optical system but also the application of the magnetic field by the magnetic head. In the magnetic field modulation method, as a magnetic head, a magnetic field is applied while sliding on a levitation type magnetic head or a disk surface that applies a magnetic field while levitating while having a minute gap of several μm to several tens μm with respect to the disk surface. In some cases, a sliding magnetic head for applying voltage is used. When using these types of magnetic heads, if there is a film thickness error in the protective film, the distance between the recording magnetic film and the magnetic head becomes non-uniform reflecting this film thickness error. As a result, the strength of the magnetic field applied to the recording magnetic film varies. For example, in a system using a flying magnetic head with a flying height of 5 μm, if there is a film thickness difference of 5 μm between the inner and outer circumferences of the protective film, the strength of the magnetic field applied will differ by 15 Oe between the inner and outer circumferences.

Therefore, the present invention has been proposed in view of such a conventional situation, and 15 μ is added on the data area.
An object of the present invention is to provide a method for manufacturing a disc-shaped recording medium, which can form a protective film having an average film thickness of m or more with a small film thickness error.

[0029]

In order to achieve the above-mentioned object, a method for manufacturing a disc-shaped recording medium of the present invention is such that after at least a recording layer is formed on a disc-shaped substrate, the recording layer is formed on the recording layer. When forming a protective film by spin-coating a UV-curable resin, supply the UV-curable resin to the inner circumference side of the position of 1/2 of the innermost radius of the data area and spin coat from this position. It is characterized by.

When the UV curable resin is spin-coated under such conditions, a protective film having an average film thickness of 15 μm or more is formed on the data area with a film thickness error of 2.0 μm or less.
In the disc-shaped recording medium in which the protective film is formed under such a film thickness condition, the protective film provides a sufficient protective effect. Further, it is possible to stably irradiate the recording layer with laser light and apply a magnetic field.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments to which the present invention is applied will be described below with reference to the drawings. Here, a case of manufacturing a magneto-optical disk will be described as an example.

The magneto-optical disk manufactured here is applied to the magnetic field modulation method, and as shown in FIG. 1, the recording portion 2 is formed on the substrate 1, and the protective film 3 is formed on the recording portion 2. Are formed and configured.

In such a magneto-optical disk, as shown in FIG. 1, for example, an optical pickup device is arranged on the substrate 1 side, and the magnetic head 5 is arranged on the opposite side, that is, the recording section 2 side.
Is arranged. Alternatively, an integrated head in which the optical pickup device and the magnetic head are integrated is arranged on the recording unit 2 side. Then, an information signal is written by irradiating the laser light L with the optical pickup device and applying a magnetic field while reversing the recording head 2 at high speed by the magnetic head 5.

The substrate 1 is a disk-shaped transparent substrate having a thickness of about several mm, and its material is acrylic resin,
In addition to plastic materials such as polycarbonate resin, polyolefin resin and epoxy resin, glass and the like are also used.

The recording portion 2 is a region excluding the inner peripheral region of the substrate 1, that is, the distance from the center is 24 to 40 mm.
Is formed in an annular shape in the range (hereinafter, the annular area in which the recording portion is formed is referred to as a data area). The recording section 2 is composed of four layers of a recording magnetic film, a first dielectric film, a second dielectric film and a reflecting film. The first dielectric film, the recording magnetic film, the second dielectric film, The reflective films are laminated in this order.

The recording magnetic film is an amorphous magnetic thin film having a direction of easy magnetization in a direction perpendicular to the film surface, which is excellent in magneto-optical characteristics and has a large coercive force at room temperature. It is desirable to have a Curie point near 200 ° C. A recording material satisfying such conditions includes a rare earth-transition metal alloy amorphous thin film and the like.
A FeCo-based amorphous thin film is suitable. An additive element such as Cr may be added to the recording magnetic film for the purpose of improving corrosion resistance.

As the dielectric film, oxides, nitrides and the like can be used. However, nitride is more preferable because oxygen in the dielectric may adversely affect the recording magnetic film. Silicon nitride, aluminum nitride, or the like is suitable as a substance that does not transmit moisture and can sufficiently transmit the used laser beam.

The reflective film is preferably composed of a film having a high reflectance that reflects 70% or more of the laser light at the boundary with the second dielectric film, and a non-magnetic metal vapor deposition film is suitable. . Further, this reflective film is preferably a good thermal conductor, and aluminum is suitable in consideration of availability and film formation.

Each of these layers is formed by a so-called vapor phase plating technique such as vapor deposition or sputtering. At this time, the film thickness of each layer can be arbitrarily set, but usually several hundred to
It is set to about several thousand angstroms. These film thicknesses are preferably determined not only by considering the optical properties of each layer alone, but also by considering the effect of combination. This is because, for example, multiple interference occurs with light that has passed through the recording magnetic film and is reflected at each layer boundary, and the effective optical and magneto-optical characteristics of the recording magnetic layer 5 greatly vary depending on the combination of film thicknesses.

After forming the recording portion as described above, a protective film is formed on the recording portion by spin coating an ultraviolet curable resin. Hereinafter, the process of forming this protective film will be described in detail.

FIG. 2 shows a spin coater for forming a protective film.

This spin coater has a turntable for mounting and rotating a disk 24 on which a protective film is to be formed, and a nozzle 22 for supplying an ultraviolet curable resin to the disk 24. There is. The nozzle 2
2 is attached to one end of a resin supply pipe 23 connected to the resin supply unit, and the resin stored in the resin supply unit passes through the resin supply pipe 23 and is discharged from the nozzle 22. .

The protective film 3 is formed by such a spin coater as follows, for example.

First, the disk 24 having the recording portion 2 formed thereon is placed on a turntable with the surface on which the protective film is to be formed facing upward, and the disk 24 is rotated at a low speed of 30 rpm. Then, the viscosity is 500 cp from the nozzle 22.
The ultraviolet curable resin of s is discharged and is supplied to the inner peripheral side of the disk in a circular shape. As the ultraviolet curable resin, an acrylic ultraviolet curable resin or the like which is usually used as a protective film material for a magneto-optical disk can be used.

Subsequently, the rotation speed of the disk 24 is increased to 3000 rpm over 1 second, and the rotation speed is increased to 8 rpm.
Hold for seconds. During this rotation, the ultraviolet curable resin circumferentially supplied onto the disk 24 spreads to the outer peripheral side by centrifugal force, and a coating film of the ultraviolet curable resin is formed on the entire surface of the disk 37.

After forming a coating film of the ultraviolet curable resin on the disk in this way, 500 mJ / cm
Irradiate ultraviolet rays with irradiation power of about ² . As a result, the resin is cured and the protective film 3 is formed.

Here, in order to obtain a sufficient protective effect by the protective film, the average thickness of the protective film on the data area A is 15
It must be at least μm. Further, the magnetic film applied to the recording magnetic film is stabilized, or a protective film is provided by an optical pickup device designed for high density recording such that the laser wavelength λ is 480 nm and the numerical aperture NA of the lens is 0.9. When the laser beam is incident from the side, in order to suppress the wavefront aberration W40d to 0.19λ or less, the film thickness error Δd between the innermost circumference and the outermost circumference of the data area A is 2.0 μm.
It must be kept below.

In this manufacturing method, in order to form the protective film under such a film thickness condition, the ultraviolet curable resin is supplied to the inner peripheral side of the position of 1/2 of the innermost peripheral radius of the data area A. And spin coat from this position.

First, the relationship between the resin supply position and the film thickness error will be described.

FIG. 3 shows the film thickness distribution of the coating film in the radial direction of the disk when the supply position of the ultraviolet curable resin is changed within the range of 8 to 14 mm from the disk center. In addition, in the figure, ◯ is an actual measurement value measured by a contact type step meter, and a solid line is a calculated value obtained from the equation of the balance between the viscous resistance force and the centrifugal force. Further, the average film thickness of the protective film on the data area A was set to around 15 μm.

Here, the data area A of the disk is in the range of 24 to 40 mm from the center of the disk. Looking at the film thickness error between the innermost circumference R ₁ and the outermost circumference R ₂ in this area, the UV curable resin is supplied. You can see that it depends on the position. For example,
The supply position R ₀ of the ultraviolet curable resin is 14 mm or 17
On the relatively outer peripheral side of mm, the film thickness difference between the innermost circumference and the outermost circumference of the data area A becomes a value larger than 2 μm. On the other hand, the supply position R ₀ of the ultraviolet curable resin is 1
The innermost circumference R of the data area A when the inner circumference is more than 2 mm
The film thickness difference between ₁ and the outermost circumference R ₂ is surely suppressed to 2 μm or less.

Further, in FIG. 3, the data area A is 24 to
Regarding the case of a disc having a diameter of 3.5 mm and a diameter of 40 mm, the calculation result in consideration of the disc having a diameter of 5.25 inches is shown in FIG. The data area A of the current 5.25 inch diameter optical disc is 30 to 60 m from the center of the disc.
m. Therefore, when an optical disc having a diameter of 5.25 inches is included, it can be considered that the innermost circumference R ₁ of the data area A on the optical disc is in the range of 20 mm ≦ R ₁ ≦ 30 mm. In FIG. 4, the innermost circumference R ₁ of the data area A is 20 m.
For each of m, 25 mm, and 30 mm, the film thickness error between the innermost circumference R ₁ and the outermost circumference R ₂ of the data area A was examined when the supply position R ₀ of the ultraviolet curable resin was variously changed. It is a thing. The average thickness of the protective film on the data area A is 15 μm, and the outermost circumference R of the data area A is
₂ is set to 60 mm.

As can be seen from FIG. 4, the data area A
The difference in film thickness between the innermost circumference R ₁ and the outermost circumference R ₂ is 2 μm or less because the disk R having an innermost circumference R ₁ of 20 mm in the data area A has a supply position R ₀ of the UV curable resin of more than 10 mm. In the case of the disc having the innermost circumference R ₁ of 25 mm, when the supply position R ₀ of the UV curable resin is on the inner side of 12.5 mm, the UV cure of the disc having the innermost circumference R ₁ of 30 mm is performed. This is the case where the resin supply position R ₀ is on the inner peripheral side of 15 mm.

The supply position R ₀ of the ultraviolet curable resin whose film thickness error is suppressed to 2.0 μm or less is a position on the inner circumference side of the half of the innermost circumference R ₁ of the data area A. is there. That is, when the protective film is formed on the data area A by the spin coating method, the supply position R ₀ of the ultraviolet curable resin is set to the inner circumference side of the position 1/2 of the innermost circumference R ₁ of the data area A. By doing so, the protective film can be formed with an average film thickness of 15 μm or more and within an error range of 2.0 μm or less.

When the protective film having an average film thickness of 15 μm or more is formed on the data area as described above, corrosion of the recording magnetic film is sufficiently prevented by this protective film, and the warp due to the temperature change of the disk is surely suppressed.

When the thickness error of the protective film on the data area is 2 μm or less, the laser light is incident on the recording magnetic film from the protective film side without passing through the substrate, and the laser wavelength λ is 480 nm, lens numerical aperture NA
Even when the value of 0.9 is used, the wavefront aberration W40d can be suppressed to 0.19λ or less. That is, even when an optical system designed for high recording density is used, the recording / reproducing light can be stably applied to the recording magnetic film.

Further, if the thickness error of the protective film is 2 μm or less, the distance between the recording magnetic film and the magnetic head can be kept substantially constant even when a sliding magnetic head or a floating magnetic head is used. Therefore, for example, in the flying type magnetic head in which the flying height is set to 5 μm, the difference in the magnetic field applied to the recording magnetic film is suppressed to about 4 Oe on the inner and outer circumferences, and the recording pits are stably formed on the entire surface of the disk. become. In addition,
The relationship between the distance from the magnetic head of the disk and the applied magnetic field is
This is as shown in FIG.

Although the manufacturing method of the present invention has been described above by taking the case of manufacturing an optical disk having a single-plate structure as an example, the disk-shaped recording medium manufactured by the present invention is composed of magneto-optical disk substrates having a single-plate structure. It is also possible to use a magneto-optical disk having a two-plate structure in which the two are bonded together. In a magneto-optical disk with a double-plate structure, the recording part covered with a protective film faces both sides,
The magnetic field is applied while the laser light is irradiated from the one recording portion side. Also in this case, if the protective film having a small film thickness error on the inner and outer circumferences is formed with a relatively large film thickness,
This protective film exerts a sufficient protective effect, and irradiation of recording / reproducing light and application of a magnetic field to the recording magnetic film are stably performed.

Further, here, the description has been made focusing on the magneto-optical disk, but the disk-shaped recording medium manufactured by the present invention is not limited to the magneto-optical disk. Also in the case of manufacturing other disk-shaped recording media such as a hard disk, according to the present invention, similarly, a thick protective film can be formed with a small film thickness error, an excellent protective effect, and a magnetic field can be stably applied. A disc-shaped recording medium can be manufactured.

[0060]

As is apparent from the above description, in the manufacturing method of the present invention, at least the recording layer is formed on the disk-shaped substrate, and then the ultraviolet curable resin is spin-coated on the recording layer. When the protective film is formed with, the ultraviolet curable resin is supplied to the inner circumference side of the position of 1/2 of the innermost radius of the data area, and spin coating is performed from this position, so that the average film is formed on the data area. A protective film having a thickness of 15 μm or more can be formed with a film thickness error of 2.0 μm or less. In the disc-shaped recording medium in which the protective film is formed under such a film thickness condition, this protective film provides a sufficient protective effect. Further, it is possible to stably irradiate the recording layer with laser light and apply a magnetic field. Therefore, it is possible to obtain excellent recording and reproducing characteristics as well as excellent durability.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a disc-shaped recording medium manufactured by the present invention.

FIG. 2 is a schematic view showing a spin coater for forming a protective film.

FIG. 3 is a characteristic diagram showing a film thickness distribution of a protective film in a disc radial direction when a supply position of an ultraviolet curable resin is changed.

FIG. 4 is a characteristic diagram showing a relationship between a supply position of an ultraviolet curable resin and a film thickness error of a protective film on a data area.

FIG. 5 is a characteristic diagram showing the relationship between the distance from the magnetic head of the disk and the applied magnetic field.

FIG. 6 shows the case where UV curable resins having different viscosities are used,
FIG. 6 is a characteristic diagram showing a film thickness distribution of a protective film in a radial direction of a disc.

FIG. 7 is a characteristic diagram in which the film thickness distribution of FIG. 6 is standardized.

[Explanation of symbols]

 1 Substrate 2 Recording Part 3 Protective Film 5 Magnetic Head 21 Ultraviolet Curing Resin 22 Nozzle 23 Supply Pipe 24 Disk A Data Area L Laser Light

Claims (2)

[Claims] 1. When forming a protective film by forming at least a recording layer on a disk-shaped substrate and then spin-coating an ultraviolet-curing resin on the recording layer, the ultraviolet-curing resin is applied to the uppermost part of the data area. A method for manufacturing a disk-shaped recording medium, characterized in that the disk-shaped recording medium is supplied to the inner peripheral side with respect to a position of 1/2 of the inner peripheral radius, and spin-coated from this position. 2. The protective film to be formed has an average film thickness of 15 μm or more on the data area and a film thickness difference of 2 μm or less between the inner peripheral portion and the outer peripheral portion.
A method for producing the disk-shaped recording medium described in the above.