JPH10199056A - Protective film forming device and protective film forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective film forming device that forms a protective layer to have a prescribed film thickness, and forms this protective layer has a uniform film thickness over the entire part of the substrate, and a protective film forming method. SOLUTION: This protective film forming device 20 is a protective film forming device, which forms the protective film by applying a protective film material on a disk-shaped recording medium 1, then irradiating this disk-shaped recording medium 1 with light to cure the protective film material. The device has a light source 22 which irradiates the recording medium with UV rays and a shutter 23 which allows the transmission of UV rays by opening a diaphragm and shuts off the UV rays by closing the diaphragm. The center of the diaphragm of the shutter 23 is set right above the center of the disk-shaped recording medium 1 to be irradiated with the light. This protective film formation method has a stage for applying the protective film material on the disk-shaped recording medium 1 and a stage for curing the protective film material by photoirradiation. This protective film curing stage spreads the photoirradiated region successively toward the outer peripheral side of the disk-shaped recording medium 1 after the irradiation of the inner peripheral side of the disk-shaped recording medium 1 with the light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for forming a protective film on a disk-shaped recording medium for forming a protective film on the disk-shaped recording medium.

[0002]

2. Description of the Related Art In a magneto-optical recording system, a recording layer made of a magnetic material is partially heated to a temperature higher than a Curie point or a temperature compensation point to reduce a coercive force, and recording is performed by externally applying a recording magnetic field. In this method, information signals are recorded by changing the magnetization direction of the layer. This magneto-optical recording method is being put to practical use in an optical filing system, an external storage device of a computer, or a recording device for audio information, video information, and the like.

A magneto-optical disk on which recording is performed by the above-described magneto-optical recording method is, for example, a magneto-optical disk in which a recording layer made of a magnetic thin film is formed on a transparent substrate made of plastic such as polycarbonate or glass. . This recording layer includes a magnetic film on which an information signal is recorded,
A dielectric film and a reflection film are laminated. Here, examples of the magnetic film include a magnetic thin film made of, for example, a rare earth-transition metal alloy amorphous thin film having an easy axis of magnetization in a direction perpendicular to the film surface and having a large magneto-optical effect. In general, a protective film made of an ultraviolet curable resin or the like is formed on the reflective film laminated on the uppermost layer of the recording layer for the purpose of preventing corrosion and damage of the recording layer.

The magneto-optical disk is not limited to the single-plate configuration as described above, but is a two-plate configuration in which two magneto-optical disks are integrated by bonding together with the recording layer side or substrate side facing each other. Has been proposed. In the magneto-optical disk having the two-plate configuration, an independent signal is recorded on the recording layer of each magneto-optical disk.
Double. In addition, since the magneto-optical disk of this two-plate configuration has a symmetrical structure with respect to the bonding surface, it is more resistant to changes in the external environment such as temperature and humidity than a magneto-optical disk of a single-plate structure. Therefore, there is an advantage that deformation such as warpage of the substrate is unlikely to occur.

The magneto-optical recording system for recording on the magneto-optical disk is roughly classified into an optical modulation system in which a signal is recorded by modulating light and a magnetic field modulation system in which a signal is recorded by modulating a recording magnetic field. .

[0006] Of these methods, the magnetic field modulation method is a method of recording a signal on a magnetic layer by reversing a recording magnetic field at a high speed in a state of light irradiation when recording a signal. In order to achieve high recording density, high-speed access, and the like, research is being actively conducted.

In this magnetic field modulation system, a magnetic field is applied by a magnetic head that generates a magnetic field in a recording layer when recording and reproducing a signal. Since the magnetic head needs to be inverted at a high speed when recording a signal, it cannot generate a strong magnetic field as in the above-described optical modulation method.

Here, the magnitude of the magnetic field applied to the magneto-optical disk by the magnetic head is inversely proportional to the distance between the magneto-optical disk and the magnetic head. That is, the magnitude of the magnetic field applied to the magneto-optical disk decreases as the distance between the magneto-optical disk and the magnetic head increases. Therefore, in such a magnetic head, when recording a signal, the distance from the magneto-optical disk must be reduced.

Therefore, in a magneto-optical disk having a single-plate configuration, an optical pickup device for irradiating a laser beam on one surface of the magneto-optical disk is provided, and a magnetic head is provided on the other surface of the magneto-optical disk. doing.

On the other hand, in a magneto-optical disk having a two-plate configuration, the optical pickup device and the magnetic head are integrated, and the optical pickup device and the magnetic head integrated from both sides of the magneto-optical disk are provided. .

The integrated optical pickup device and magnetic head directly irradiate the recording layer with laser light without passing through the substrate. Therefore, the material of the substrate constituting the magneto-optical disk is not limited to a transparent material, and an opaque substrate can be used. Therefore, the magneto-optical disk having the two-plate structure has an advantage that, for example, Al can be used as the material of the substrate, and the warpage of the substrate can be prevented.

As described above, as the magneto-optical disk, a magneto-optical disk having a single-plate configuration and a double-plate configuration has been proposed. On these magneto-optical disks, a protective layer is formed to prevent corrosion of the recording layer and the like. This protective layer is usually formed by a spin coating method.

In forming this protective layer, first, a magneto-optical disk on which a protective layer is to be formed is placed on a turntable and rotated at a low speed by a spindle motor. Then, the ultraviolet curable resin is supplied circumferentially along the inner peripheral portion of the recording layer of the magneto-optical disk. Then, the ultraviolet curable resin is applied to the outer peripheral portion by the centrifugal force generated by rotating the magneto-optical disk at high speed, and the ultraviolet curable resin is applied to the entire surface of the magneto-optical disk. The thickness of the protective layer is about 15 μm in order to obtain a sufficient protective effect after being irradiated with ultraviolet rays in a later step.

Next, the magneto-optical disk coated with the ultraviolet curable resin is transported immediately below the ultraviolet lamp. The magneto-optical disk is irradiated with light from the ultraviolet lamp by opening a shutter disposed between the disk and the ultraviolet lamp. Here, the shutter is opened when the magneto-optical disk is conveyed directly below the ultraviolet lamp or immediately before being conveyed, by being slid in the horizontal direction. Then, the ultraviolet curable resin is cured by being irradiated with light from an ultraviolet lamp, and becomes a protective layer.

[0015]

However, the protective layer formed in the above-described process tends to be thicker toward the outer periphery of the magneto-optical disk.

As described above, the thickness of the protective layer formed by the spin coating method varies depending on conditions such as the viscosity of the ultraviolet curing resin, the rotation speed and the rotation time of the magneto-optical disk. However, as described above, even if the protective layer is applied from the inner peripheral portion of the magneto-optical disk, and the rotation speed and the rotation time are changed, the protective layer is applied to a uniform film thickness over the entire surface of the magneto-optical disk. The thickness of the outer peripheral portion of the magneto-optical disk is larger than that of the inner peripheral portion.

Here, the viscosity of the ultraviolet curable resin is set to 500
FIG. 6 shows the film thickness distribution when the protective layer was formed while changing the thickness to cps, 140 cps, and 37 cps. Here, FIG.
Is a diagram in which the vertical axis indicates the thickness of the protective layer and the horizontal axis indicates the radial position of the magneto-optical disk. Further, the characteristic A in FIG.
Shows the relationship between the thickness of the protective layer and the radial position of the magneto-optical disk when the protective layer is formed of an ultraviolet curable resin having a viscosity of 500 cps. The characteristic B in FIG.
FIG. 6 shows the relationship between the thickness of the protective layer and the radial position of the magneto-optical disk when the protective layer was formed of an ultraviolet curable resin of cps, and the characteristic C in FIG. It is an actually measured value showing the relationship between the thickness of the protective layer when formed and the radial position of the magneto-optical disk.

The measurement of the relationship between the thickness of the protective layer and the radial position of the magneto-optical disk shown in FIG. 6 was performed by rotating the magneto-optical disk at a low speed, and measuring a radius of about 17 mm from the center of the magneto-optical disk. At a position, the ultraviolet curable resin is supplied in an annular shape, the rotation speed is increased to about 3000 rpm over 1 second, and the rotation is maintained at about 3000 rpm for about 8 seconds, and then the protection formed by irradiating ultraviolet rays. The layer is to be measured. The solid line in FIG.
This is a calculated value of the film thickness distribution obtained from the equation of the balance between the viscous drag force and the centrifugal force.

Here, it is known that the thickness of a protective layer formed by applying UV curable resins having different viscosities under the same conditions is proportional to the square root of the viscosity. Therefore, for example, the film thickness ratio when the film thickness formed of an ultraviolet curable resin having a viscosity of 140 cps and the film thickness of a protective layer formed of an ultraviolet curable resin having a viscosity of 500 cps are applied under the same conditions is theoretically , (500/140) ^1/2 = 1.9.
Further, for example, when the thickness of a protective layer formed of an ultraviolet curable resin having a viscosity of 37 cps and the thickness of a protective layer formed of an ultraviolet curable resin having a viscosity of 500 cps are applied under the same conditions, the film thickness ratio is as follows: 500/37) ^1/2 = 3.7.

The first normalized film thickness distribution calculated by multiplying the film thickness distribution of the protective layer formed of an ultraviolet curable resin having a viscosity of 140 cps by 1.9 based on the above-mentioned film thickness ratio is obtained. A second normalized film thickness distribution calculated by multiplying the film thickness distribution of a protective layer formed of an ultraviolet curable resin having a viscosity of 37 cps by 3.7 times, and a viscosity of 500 cps.
FIG. 7 shows the thickness distribution of the protective layer formed of the ultraviolet curable resin of FIG. Note that, in FIG.
FIG. 4 is a diagram in which a film thickness distribution when a protective layer is formed at 0 cps is indicated by ○, a first normalized distribution is indicated by 、, and a second normalized film thickness distribution is indicated by □.

According to FIG. 7, the first normalized film thickness distribution, the second normalized film thickness distribution, and the film thickness distribution of the protective layer formed of an ultraviolet curable resin having a viscosity of 500 cps are substantially on the same curve. It is on. Therefore, it can be seen that the thickness of the protective layer is proportional to the square root of the viscosity when formed under the same conditions.

FIG. 7 shows that the spin coating method, which is usually performed as a method for forming the protective layer, has a rotational speed,
Even if the conditions such as the rotation time are changed, if the protective layer is formed with a predetermined thickness, the thickness formed on the inner peripheral portion of the magneto-optical disk and the thickness formed on the outer peripheral portion of the magneto-optical disk are: It can be seen that a film thickness error occurs by a certain fixed value.

Here, the difference in film thickness between the inner peripheral portion and the outer peripheral portion of the protective layer is determined by using a low-viscosity ultraviolet curable resin, increasing the rotation time of the magneto-optical disk, and applying a thickness of the ultraviolet curable resin to be applied. Can be reduced by reducing the thickness over the entire surface of the magneto-optical disk. For example, the protective layer is made of an ultraviolet curable resin having a viscosity of 37 cps, the rotation time is lengthened, and the film thickness of the entire protective layer is reduced, so that the position 24 mm from the center of the magneto-optical disk and 40 mm
And a film thickness difference of about 1.5 μm.

However, if the thickness of the protective layer is extremely small, it becomes impossible to prevent corrosion of the recording layer of the magneto-optical disk, so that the protective layer has an average thickness of about 15 μm over the entire surface of the magneto-optical disk. is necessary. As described above, the average thickness of the protective layer over the entire surface of the magneto-optical disk is 1
If the thickness is 5 μm, a film thickness difference of about 5 μm occurs between the inner peripheral portion and the outer peripheral portion even if the above-mentioned conditions are changed.

By the way, in an optical pickup device that performs recording and reproduction by irradiating a laser beam from the protective layer side, if the thickness of the protective layer is different between the inner and outer peripheral portions of the magneto-optical disk, the laser beam is removed. There is a problem that wavefront aberration of light occurs. As described above, in the optical pickup device, when the wavefront aberration occurs due to the difference in the thickness of the protective layer, the irradiated laser beam becomes unstable, and the recording and reproducing characteristics deteriorate. Here, the wavefront aberration W _40d is represented by the following equation 1 when n is the refractive index of the protective layer, _Δd is the film thickness distribution of the protective layer, and NA is the numerical aperture of the lens of the optical system. It becomes an expression.

[0026]

(Equation 1)

In the case of the current magneto-optical disk, the refractive index n of the protective layer is 1.58, the wavelength λ of the laser light of the optical system is 780 nm, and the numerical aperture NA of the lens is 0.5. Under such conditions, if the thickness error Δd of the protective layer is 5 μm, the wavefront aberration W _40d is 0.19λ (0.
148 μm).

In the optical system of a magneto-optical disk, the wavelength λ of the laser beam of the optical system has been increased with the recent increase in recording density.
And increasing the numerical aperture NA of the lens. This is because the spot diameter of the laser light condensed by the optical lens is proportional to the wavelength λ of the laser light and inversely proportional to the numerical aperture NA of the lens. Here, the current laser spot diameter is about 1.6 μm. For example, when the wavelength of the laser beam is 480 nm and the numerical aperture NA of the lens is 0.9, the laser spot diameter is 0.5 μm.
m, so that the laser spot diameter can be reduced to about 1/3 of the current laser spot diameter. Therefore, according to such an optical system, the surface recording density can be approximately nine times as high as the current surface recording density.

However, when the recording density is improved and the optical system is changed as described above, if the thickness error of about 5 μm occurs in the protective layer as described above, it is calculated from the above equation (1). The resulting wavefront aberration W _40d has a large value, making it difficult to perform stable recording and reproduction. For example, when the wavelength λ of the laser beam is set to 480 nm and the numerical aperture NA of the lens is set to 0.9, the wavefront aberration W _40d becomes very large, which causes a problem that stable recording and reproduction cannot be performed. In such an optical system of a magneto-optical disk, in order to suppress the wavefront aberration W _40d to at least about 0.19λ, which is the same as the current level, the thickness difference Δd between the inner and outer peripheral portions of the protective layer is set to 2.9 μm It is necessary to suppress the following.

The difference in the thickness of the protective layer as described above is as follows.
This affects not only the irradiation of the laser beam by the optical system described above but also the application of the magnetic field of the magnetic head. The magnetic head used in the above-described magnetic field modulation system includes a magnetic head for recording a signal from a protective layer of a magneto-optical disk through a minute interval of about several μm to several tens μm, and a protective layer for a magneto-optical disk. There is a magnetic head that records a signal while sliding. In a magnetic field modulation system using such a magnetic head, if there is a film thickness difference in the protective layer, the distance between the magnetic head and the magneto-optical disk changes. In the magnetic field modulation method, if there is a film thickness error in the protective layer, the distance between the recording layer and the magnetic head becomes non-uniform reflecting the film thickness difference. As a result, as shown in FIG. 8, the intensity of the magnetic field applied to the recording layer varies. The magnitude of the magnetic field applied to the recording layer changes, and the magnetic field applied over the entire surface of the magneto-optical disk becomes non-uniform. For example, when recording a signal, the flying height of the magnetic head is set to 5
When the thickness of the protective layer is 5 μm on the outer peripheral portion from the inner peripheral portion,
If the thickness is increased by μm, there arises a problem that the magnitude of the magnetic field applied to the recording layer differs by about 15 Oe between the inner peripheral portion and the outer peripheral portion.

Therefore, as a method for suppressing the above-mentioned difference in the thickness of the protective layer, a magneto-optical disk is used at 1000 rpm.
irradiating ultraviolet rays while rotating at a rotational speed of at least m
A method of forming a protective layer has been proposed. However, even with the protective layer formed by such a method, there is a problem that a difference in film thickness occurs between the inner peripheral portion and the outer peripheral portion, and the film thickness increases in the outer peripheral portion. The cause of the difference in film thickness is that the ultraviolet curable resin is applied with a centrifugal force and a viscous resistance force due to rotation of the magneto-optical disk during spin coating. When the ultraviolet curable resin is supplied to the inner peripheral portion of the magneto-optical disk, it moves to the outer peripheral portion. Here, when ultraviolet light is irradiated from the outer peripheral portion to the inner peripheral portion of the magneto-optical disk, the outer peripheral portion is cured, but in the inner peripheral portion where the ultraviolet light is not irradiated, the ultraviolet light moves to the outer peripheral portion by centrifugal force and gradually moves. become thinner. Then, the outer peripheral portion cured by being irradiated with ultraviolet rays is
Since the ultraviolet curing resin is supplied from the uncured inner peripheral portion, the thickness gradually increases. That is, the difference in film thickness between the inner peripheral portion and the outer peripheral portion increases as compared with the case where the magneto-optical disk is cured without rotating.

The present invention has been proposed in view of the above-described circumstances, and has a protective film having a predetermined thickness and a uniform thickness over the entire substrate. It is an object to propose a forming apparatus and a protective film forming method.

[0033]

A protective film forming apparatus according to the present invention for solving the above-mentioned problems applies a protective film material to a disk-shaped recording medium and then irradiates light while rotating the disk-shaped recording medium. In a protective film forming apparatus that cures the protective film material to form a protective film, a light source that irradiates the disc-shaped recording medium with light, a light from the light source is transmitted by opening the diaphragm, and the diaphragm is closed. A shutter for blocking light from the light source, wherein the center of the aperture of the shutter is located immediately above the center of the disk-shaped recording medium to be irradiated with light.

The protective film forming apparatus configured as above is
Since light is emitted from the inner peripheral portion of the disk-shaped recording medium by the shutter, the inner peripheral portion can be cured before the outer peripheral portion. Therefore, according to this protective film forming apparatus, the protective film on the inner peripheral portion does not move due to the centrifugal force caused by rotating to the outer peripheral portion, so that the outer peripheral portion does not become thicker than the inner peripheral portion. .

Further, the method for forming a protective film according to the present invention comprises:
The method includes a protective film applying step of applying a protective film material on a disc-shaped recording medium, and a protective film curing step of irradiating light to cure the protective film material. After irradiating the light on the peripheral side, the light irradiation area is expanded toward the outer peripheral side of the disc-shaped recording medium.

In such a protective film forming method, since the protective film is cured by irradiating light from the inner peripheral portion of the disc-shaped recording medium, the inner peripheral portion can be cured before the outer peripheral portion. Therefore, according to this protective film forming method,
The inner peripheral portion does not move due to centrifugal force generated by rotating the inner peripheral portion toward the outer peripheral portion, so that the outer peripheral portion does not become thicker than the inner peripheral portion.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a protective film forming apparatus and a protective film forming method according to the present invention will be described in detail with reference to the drawings. The protective film forming apparatus and the protective film forming method for the magneto-optical disk according to the present embodiment are suitable examples of the protective film forming apparatus and the protective film forming method according to the present invention. However, the present invention is not limited to this.

The magneto-optical disk 1 on which a protective layer is formed by the magneto-optical disk protective film forming apparatus according to the present embodiment is a magneto-optical disk on which recording and reproduction are performed by a so-called magnetic field modulation method, and is shown in FIG. As described above, the recording layer 3 is formed on the substrate 2, and the protective layer 4 is formed on the recording layer 3. In such a magneto-optical disk 1, an optical pickup device is provided on the substrate 2 side and a magnetic head 5 is provided on the protective layer 4 side during recording and reproduction. And
During recording, the magneto-optical disc 1 is irradiated with laser light L from the substrate 2 side by the optical pickup device, and a magnetic field is applied at a high frequency from the protective layer 4 side by the magnetic head 5 to record an information signal. Is done.

The magneto-optical disk 1 is, as described above,
A substrate 2 made of a synthetic resin material; a recording layer 3 laminated on the substrate 2 to record information signals;
And a protective layer 4 for protecting the.

The substrate 2 is a disk-shaped transparent substrate having a thickness of about several mm. Examples of the material of the substrate 2 include a plastic material such as an acrylic resin, a polycarbonate resin, a polyolefin resin, and an epoxy resin, and further, a glass material.

The recording layer 3 is formed on the substrate 2.
Is formed in an annular shape within a range of a radius of about 24 mm to 40 mm from the center of the circle. This recording layer 3 includes a first dielectric film,
A recording magnetic film on which an information signal is recorded, a second dielectric film, and a reflective film are laminated.

The recording magnetic film is composed of an amorphous magnetic thin film having an easy axis of magnetization perpendicular to the film surface. In addition, the recording magnetic film is excellent in magneto-optical characteristics,
At room temperature, it has a large coercive force and has a Curie point at about 200 ° C. In this embodiment, the recording magnetic film is made of a rare earth-transition metal amorphous thin film or the like, and is made of, for example, a TbFeCo-based amorphous thin film. An element such as Cr may be added to the recording magnetic film for the purpose of improving corrosion resistance.

As the first dielectric film and the second dielectric film, oxides and nitrides can be used. However, since oxygen in the dielectric film may adversely affect the recording magnetic film, A nitride is preferable, and silicon nitride or aluminum nitride is suitable as a substance which is advantageous for preventing oxygen and water molecules from permeating and which can sufficiently transmit laser light.

The reflection film is preferably made of a film having a high reflectivity that reflects laser light at 70% or more at the boundary with the second dielectric film, and is preferably a nonmagnetic metal deposited film. Further, it is desirable that the reflective film be a good conductor thermally, and aluminum is suitable in consideration of availability.

The recording magnetic film, the first dielectric film, and the second
Are formed by a so-called vapor phase plating method such as a vapor deposition method or a sputtering method. The thickness of each of the recording layers 3 is usually about several tens to several hundreds of nm, but it is desirable to determine the thickness in consideration of not only the optical properties of each layer alone but also the effects of the combination. This means that, for example, the light transmitted through the recording magnetic film and reflected at the interface of each layer causes multiple interference, and the combination of the respective film thicknesses allows
This is because the effective optical characteristics and magneto-optical characteristics of the recording magnetic film fluctuate.

The protective layer 4 is formed on the above-mentioned recording layer 3 and is made of, for example, an ultraviolet curable resin. This protective layer 4
It is formed by a spin coating method described later. The protective layer 4 is formed such that the average film thickness is about 15 μm or more over the entire surface of the magneto-optical disk 1, and the film thickness difference between the inner and outer peripheral parts of the magneto-optical disk 1 is about 2 μm or less. Has become. The protective layer 4 has an average thickness of about 15 μm.
By setting m or more, it is possible to sufficiently prevent corrosion of the recording layer 3 and prevent deformation of the magneto-optical disk 1 due to warpage or the like due to a temperature change.

The protective film forming apparatus for the magneto-optical disk for forming the protective layer 4 of the magneto-optical disk 1 having the above-described structure first emits ultraviolet light onto the magneto-optical disk 1 transported by a magneto-optical disk transport mechanism (not shown). A spin coater for supplying a curable resin and applying an ultraviolet curable resin to the entire surface of the magneto-optical disk 1; and irradiating the magneto-optical disk 1 conveyed from the spin coater with ultraviolet light to convert the ultraviolet curable resin. It consists of an ultraviolet irradiation device for curing.

As shown in FIG. 2, the spin coater 10 mounts the magneto-optical disk 1 and rotates the mounted magneto-optical disk 1 with a turntable. A nozzle 12 for supplying resin.

The turntable serves to transport and place the magneto-optical disk 1 and rotate the magneto-optical disk 1 during spin coating. The spin table rotates the magneto-optical disk 1 at a predetermined rotation speed by a rotation driving means such as a spindle motor during spin coating.

The nozzle 12 is attached to one end of a resin supply pipe 14 connected to the resin supply section 13. The nozzle 12 is disposed on the inner peripheral portion 1a of the magneto-optical disk 1 during spin coating, and emits ultraviolet curable resin to supply the inner peripheral portion 1a of the magneto-optical disk 1.

In the spin coating apparatus 10, when forming the spin coat, the ultraviolet curable resin in a fluid state is supplied from the resin supply section 13 to the resin supply pipe 14 and the nozzle 12 while the magneto-optical disk 1 is rotated at a low speed. To supply the ultraviolet curable resin to the inner peripheral portion 1a of the magneto-optical disk 1. Then, the spin coater 10 spreads and applies the ultraviolet curable resin supplied to the inner peripheral portion 1a of the magneto-optical disk 1 to the outer peripheral portion 1b while the magneto-optical disk 1 is rotated at a low speed. Then, the spin coater 10 forms the protective layer 4 uniformly on the entire surface of the magneto-optical disk 1 by increasing the rotation speed of the magneto-optical disk 1 by the above-mentioned rotation driving means. In this embodiment, the protective layer 4 is formed by rotating the magneto-optical disk 1 at a high speed so that the film thickness becomes about 15 μm.

As shown in FIG. 3, the ultraviolet irradiation device 20 includes a disk support 21 for mounting the magneto-optical disk 1 coated with the ultraviolet curing resin,
An ultraviolet lamp 22 that emits ultraviolet light to the magneto-optical disk 1 mounted on the optical disk 1, a light from the ultraviolet lamp 22 is transmitted by opening the aperture, and a light from the ultraviolet lamp 22 is blocked by closing the aperture. And a shutter 23.

The disk support 21 supports the magneto-optical disk 1 coated with the ultraviolet curable resin by the above-described spin coater 10 and, at the same time, rotates the magneto-optical disk 1 at a predetermined number of revolutions by, for example, a rotary driving means such as a spindle motor. Is driven to rotate. Also, this disk support 2
At the time of forming the protective layer, the magneto-optical disk 1 coated with the ultraviolet curable resin by the spin coater 10 is placed and moved on the transport path, and the magneto-optical disk 1 is disposed immediately below the ultraviolet lamp 22 when forming the protective layer. .

The ultraviolet lamp 22 is provided at a predetermined distance from the disk support 21. The ultraviolet lamp 22 is for curing the ultraviolet curing resin applied on the magneto-optical disk 1. That is, the ultraviolet lamp 22 irradiates the magneto-optical disk 1 with light in the ultraviolet wavelength region to cure the ultraviolet-curable resin. A mirror 24 that reflects light is provided around the ultraviolet lamp 22.
The mirror 24 is formed so as to condense the light other than the direction of the magneto-optical disk 1 out of the light emitted from the ultraviolet lamp 22 in the direction of the magneto-optical disk 1. The mirror 24 condenses the light from the ultraviolet lamp 22 on the entire surface of the magneto-optical disk 1. The mirror 24 condenses the light from the ultraviolet lamp 22 so that about 500 m
Irradiate with ultraviolet rays of J / cm ² or more.

The shutter 23 is disposed between the ultraviolet lamp 22 and the disk support 21 and transmits the light from the ultraviolet lamp 22 by opening the aperture, and transmits the light from the ultraviolet lamp 22 by closing the aperture. It blocks out light. 4 (a) and FIG.
As shown in (b), it is configured to have an aperture shape. The shutter 23 is configured to have an aperture shape so as to open from a central portion 23a.

When the protective layer is formed, the shutter 23 transmits the light from the ultraviolet lamp 22 by gradually opening as shown in FIGS. Irradiate 1 The shutter 23 can control the opening / closing speed, the opening radius, and the like by a shutter control unit (not shown) when the protective layer is formed.

In the protective film forming apparatus for the magneto-optical disk 1 configured as described above, when forming the protective layer, the magneto-optical disk 1 coated with the ultraviolet curable resin is placed and placed immediately below the ultraviolet lamp 22. And a diaphragm-shaped shutter 23 disposed directly above the disk support 21 so that the inner peripheral portion of the magneto-optical disk 1 can be exposed to ultraviolet light when forming the protective layer. 1
Light can be emitted from the a side. Therefore, according to the protective film forming apparatus for the magneto-optical disk 1,
After applying the ultraviolet curable resin to the magneto-optical disk 1 by the spin coater 10, the ultraviolet curable resin applied to the magneto-optical disk 1 can be cured from the inner peripheral portion 1a side. Therefore, according to the protective film forming apparatus for the magneto-optical disk 1, the ultraviolet-curable resin applied to the inner peripheral portion 1a is not moved to the outer peripheral portion 1b side by rotating the magneto-optical disk 1, and the The protective resin 4 can be formed by curing the cured resin. Further, according to the protective film forming apparatus for the magneto-optical disk 1, as described above, the ultraviolet curable resin of the inner peripheral portion 1a does not move to the outer peripheral portion 1b. The protective layer 4 having no thickness difference between the outer layer 1b and the outer layer 1b can be formed.

Next, a method of forming the protective layer 4 on the magneto-optical disk 1 by the above-described apparatus for forming a protective film on the magneto-optical disk 1 will be described.

The method for forming a protective film according to the present embodiment
It comprises a step of applying an ultraviolet curable resin on the magneto-optical disk 1 on which the recording layer is formed, and a step of irradiating the magneto-optical disk 1 coated with the ultraviolet curable resin with light to cure the ultraviolet curable resin. .

In the step of applying the ultraviolet curable resin on the magneto-optical disk 1, the ultraviolet curable resin is applied using the spin coater 10 described above. In the step of applying the ultraviolet curable resin on the magneto-optical disk 1, first, the magneto-optical disk 1 is placed on a turntable and the magneto-optical disk 1 is rotated at a rotation speed of about 30 rpm.

Then, a viscosity of about 500 c
ps ultraviolet curable resin is applied to the inner peripheral portion 1a of the magneto-optical disk 1.
To supply. Here, the magneto-optical disk 1 is set at about 30 rpm.
Therefore, the ultraviolet curable resin supplied to the inner peripheral portion 1a spreads to the outer peripheral portion 1b side by centrifugal force and is applied on the entire surface of the magneto-optical disk 1, that is, on the recording layer 3. In this embodiment, the magneto-optical disk 1
The ultraviolet curable resin is supplied at a position of about 17 mm from the center.

Next, the number of revolutions of the magneto-optical disk 1 is increased to about 3000 rpm for about 1 second, and about 3000 rpm.
Hold for about 8 seconds while rotating at pm. By rotating the magneto-optical disk 1 in this way, the entire surface of the magneto-optical disk 1 is coated with an ultraviolet curable resin.

Next, the magneto-optical disk 1 coated with the ultraviolet curable resin is placed on the disk support 21 and transported under the ultraviolet irradiation device 20. Here, the central portion of the magneto-optical disk 1 is disposed immediately below the ultraviolet irradiation device 20. Then, the magneto-optical disk 1 is fixed directly below the ultraviolet irradiation device 20.

Next, the magneto-optical disk 1 fixed immediately below the ultraviolet irradiation device 20 is first moved for about one second to about 30 seconds.
The rotation speed is increased to 00 rpm to rotate. Then, the magneto-optical disk 1 is held for about 6 seconds while being rotated at about 3000 rpm.

The ultraviolet irradiation device 20 rotates the magneto-optical disk 1 as described above, and opens the shutter 23 in synchronization with the rotation of the magneto-optical disk 1. That is, the shutter 23 is opened so that the light from the ultraviolet lamp 22 is irradiated from the center of the magneto-optical disk 1 to the inner peripheral portion 1a over about one second. Thereafter, the magneto-optical disk 1 is moved from the inner peripheral portion 1a by about 4 mm every about one second.
The ultraviolet curable resin is cured by controlling the opening speed of the shutter 23 so as to irradiate light to the outer peripheral portion 1b side of the ultraviolet curable resin. In the present embodiment, a position approximately 24 mm from the center of the magneto-optical disk 1 is defined as the inner peripheral portion 1 a, and the shutter 2 is irradiated with light from the ultraviolet lamp 22.
3 is opened.

The protective layer 4 formed by the method for forming a protective film on the magneto-optical disk 1 has a film thickness as shown in FIG. In FIG. 5, the horizontal axis indicates the radial position [mm] of the magneto-optical disk, and the vertical axis indicates the thickness [μm] of the protective layer at the radial position of the magneto-optical disk. Also,
In FIG. 5, the thickness of the protective layer formed by the above-described method for forming a protective film is indicated by ●, and the calculated value when the protective layer is formed without rotating the magneto-optical disk is shown by a solid line as Comparative Example b. ing. The range A of the recording layer formed on the magneto-optical disk is approximately 24
mm to about 40 mm. That is, the range A is a region where the protective layer is to be formed.

According to FIG. 5, the film thickness is approximately 16 μm when the radial position of the magneto-optical disk is within the range of approximately 24 mm to approximately 40 mm, and is substantially uniform.
In addition, this film thickness is such that the radial position is about 24 mm to about 40 mm.
Is within about 2 μm.

On the other hand, in Comparative Example b in FIG. 5, the film thickness tends to increase from the inner peripheral portion toward the outer peripheral portion over the entire radial position of the magneto-optical disk. Further, according to Comparative Example b, the radial position of the magneto-optical disk was approximately 24 mm to
Within the range of about 40 mm, the film thickness is thicker on the outer peripheral side.

Therefore, according to the above-described method for forming a protective film for a magneto-optical disk, as shown in FIG. 5, a protective layer having a thickness of about 15 μm or more is formed in the area A where the recording layer is formed. It is possible to form a protective layer in which the thickness error between the inner peripheral side and the outer peripheral side is suppressed to about 2 μm or less.

According to such a method for forming a protective film on a magneto-optical disk, since a protective layer having a thickness of 15 μm or more is formed on the entire surface of the magneto-optical disk, it is possible to sufficiently protect the recording layer from corrosion and the like. It is.

In this method of forming a protective film on a magneto-optical disk, since the thickness error of the protective layer is formed to be 2 μm or less over the entire surface of the magneto-optical disk, a laser beam is incident from the protective layer side. However, there is no portion where the wavefront aberration becomes large on the entire surface of the magneto-optical disk. That is, for example, when using an optical device that allows laser light to enter from the protective layer side, the protective layer is formed of a wavelength λ
Is 480 nm and the numerical aperture NA of the lens for condensing the laser beam on the magneto-optical disk is 0.9, which is the upper limit of the film thickness difference of 2.9 μm or less so that the wavefront aberration is 0.19λ or less. Is formed. Therefore, according to this magneto-optical disk, since the protective layer is formed with a small difference in film thickness between the inner peripheral portion and the outer peripheral portion, recording and reproduction are performed using an optical system designed for high recording density. However, it is possible to irradiate the recording layer with laser light stably without increasing the wavefront aberration due to the difference in the thickness of the protective layer.

According to such a method for forming a protective film on a magneto-optical disk, even if a magnetic head for recording a signal while sliding on the magneto-optical disk is used, the difference in film thickness of the protective layer causes It is possible to record signals without damaging the surface of the magneto-optical disk.
According to the method for forming a protective film on a magneto-optical disk,
Even if a signal is recorded using a magnetic head that flies over the surface of the magneto-optical disk via a minute interval, the magnetic head is maintained at a predetermined distance without coming into contact with the surface of the magneto-optical disk. The signal can be recorded. Here, for example, the interval between the magneto-optical disk and the magnetic head is 5 μm.
When a magnetic head set to m is used and the thickness difference of the protective layer over the entire surface of the magneto-optical disk is 2 μm or less, the variation caused by the thickness difference of the magnetic field applied by the magnetic head is ± 4 Oe. Can be suppressed within. Therefore, according to such a method for forming a protective film on a magneto-optical disk, a magnetic field can be stably applied, and recording pits can be stably formed on the entire surface of the magneto-optical disk.

In the present embodiment, if the ultraviolet-curable resin is used as a protective layer material for a magneto-optical disk, such as an acrylic ultraviolet-curable resin, the protection of the magneto-optical disk according to the present embodiment will be described. The present invention is applicable to a film forming apparatus and a protective film forming method. In addition, the viscosity of the ultraviolet curable resin is about 500 cps in this embodiment.
Although the ultraviolet curable resin is used to the extent, for example, even if the degree of polymerization or the like is controlled and changed, the apparatus and method for forming a protective film of a magneto-optical disk according to the present embodiment can be applied.

Further, as described in the present embodiment, the magneto-optical disk is not limited to a so-called single-plate structure in which the recording layer and the protective layer are formed only on one side of the substrate. That is, the magneto-optical disk may have a so-called double-plate configuration in which the substrates of a single-plate magneto-optical disk are opposed to each other and bonded together.

In the magneto-optical disk having the two-plate configuration, at the time of recording / reproducing, laser light is irradiated from both sides and a magnetic field is applied by a magnetic head. That is, the recording layer on which the protective layer is formed is formed on both sides. Even in such a magneto-optical disk having a two-plate configuration,
As described above, since there is no difference in film thickness between the inner and outer peripheral portions of the magneto-optical disk, it is possible to stably irradiate laser light and apply a magnetic field.

Further, the protective film forming apparatus and the protective film forming method according to the present invention are not limited to the magneto-optical disk as described above, and signals are recorded by, for example, forming physical irregularities on the surface. It is also applicable to a read-only optical disk or the like. Further, the protective film forming apparatus and the protective film forming method for a magneto-optical disk according to the present embodiment
Of course, the present invention can be applied to any recording medium, such as a magnetic disk, an optical disk, and a phase-change disk, which is formed by applying a protective film material by a spin coating method and irradiating light to form a protective layer. is there.

[0077]

As described in detail above, in the protective film forming apparatus according to the present invention, when forming the protective film, the disk-shaped recording medium is disposed immediately below the light source, and the light source and the disk-shaped recording medium are connected to each other. Between the inner peripheral portion and the outer peripheral portion of the disc-shaped recording medium, since a shutter that transmits light from the light source by opening the aperture and blocks light from the light source by closing the aperture is provided. Then, a protective film can be formed from the inner peripheral side of the disc-shaped recording medium. Therefore, according to the protective film forming apparatus, the protective film can be formed by rotating the disk-shaped recording medium without moving the protective film applied to the inner peripheral portion toward the outer peripheral portion. Further, according to the protective film forming apparatus, since the ultraviolet curable resin in the inner peripheral portion does not move to the outer peripheral portion,
It is possible to form a uniform protective film having no difference in the thickness of the protective film between the inner peripheral portion and the outer peripheral portion of the disk-shaped recording medium.

Further, according to the method for forming a protective film according to the present invention, a protective film is coated on a disk-shaped recording medium, and light is irradiated from the inner peripheral portion of the disk-shaped recording medium. Since the protective film is formed by spreading to the outer peripheral portion of the disk-shaped recording medium, there is no difference in film thickness between the inner peripheral portion and the outer peripheral portion of the disk-shaped recording medium. A protective film having a uniform thickness can be formed on the entire surface of the substrate.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a recording / reproducing apparatus for a magneto-optical disk.

FIG. 2 is a diagram showing an example of a spin coater constituting a protective film forming apparatus to which the present invention is applied.

FIG. 3 is a view showing an example of an ultraviolet irradiation device constituting the protective film forming device.

4 is a top view illustrating an example of a shutter included in the ultraviolet irradiation device illustrated in FIG.

FIG. 5 is a diagram showing a relationship between a radial position of a magneto-optical disk and a thickness of a protective layer.

FIG. 6 is a diagram showing the relationship between the radial position of the magneto-optical disk and the thickness of the protective layer when the viscosity is changed using a conventional magneto-optical disk protective film forming apparatus.

FIG. 7 is a diagram showing a relationship between a radial position of a first standardized magnetic disk and a thickness of a protective layer using a conventional magneto-optical disk protective film forming apparatus.

FIG. 8 is a diagram showing a relationship between a distance between a magnetic head and a magneto-optical disk and a magnetic field applied to the magneto-optical disk.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 magneto-optical disk, 2 substrate, 3 recording layer, 4 protective layer, 5 magnetic head, 10 spin coating device, 11
Turntable, 12 nozzles, 20 UV irradiation device, 21 Disk support, 22 UV lamp, 23
Shutter

Claims (2)

[Claims] 1. A protective film forming apparatus for applying a protective film material to a disk-shaped recording medium and then irradiating light while rotating the disk-shaped recording medium to cure the protective film material and form a protective film. A light source for irradiating the disc-shaped recording medium with light, and a shutter for transmitting light from the light source by opening the aperture and blocking light from the light source by closing the aperture, wherein the center of the aperture of the shutter is An apparatus for forming a protective film, wherein the apparatus is located immediately above the center of a disk-shaped recording medium to be irradiated with light. 2. A protective film applying step of applying a protective film material on a disk-shaped recording medium; and a protective film curing step of irradiating light to cure the protective film material. A method for forming a protective film, comprising: irradiating an inner peripheral side of a disc-shaped recording medium with light, and then expanding a light irradiation area toward an outer peripheral side of the disc-shaped recording medium.