JPH0544738B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical recording disk for recording, reproducing, or erasing signals such as video, audio, and digital data using a laser beam, and a method for manufacturing the same.

Conventional configuration and its problems By converging laser light using a lens system, it is possible to create a small light spot with a diameter on the order of the wavelength of the light. Therefore, it is possible to create a light spot with high energy density per unit area even from a light source with a small output. Record this information.
Optical recording disks were used for playback.

The basic structure of an optical recording disk is that a recording thin film whose state changes in some way by laser spot light irradiation is provided on a disk-shaped substrate with a flat surface. The following methods are used to record and reproduce signals. That is, the disk is rotated by a rotating means such as a motor, and laser light is focused and irradiated onto the recording thin film surface of the disk by a lens system. The recording thin film absorbs the laser light and increases its temperature. When the output of the laser beam is increased above a certain threshold, the state of the recording thin film changes and information is recorded. This threshold value is determined by the thermal characteristics of the substrate as well as the characteristics of the recording thin film itself.
This amount depends on the relative speed of the disk to the light spot, etc. The recorded information is obtained by irradiating the recording section with a laser beam spot with an output sufficiently lower than the threshold value, and some optical characteristics such as the transmitted light intensity, reflected light intensity, or their polarization direction are different between the recorded section and the unrecorded section. Detect and play. As recording thin films, Bi, Te, metal thin films containing these as main components, and compound thin films containing Te are known. These thin films are melted or evaporated by laser light irradiation, forming small holes and recording.
Reproduction is performed by detecting a change in the amount of reflected light from the recording section. In addition, amorphous ascalcogenide thin film, TeOxb consisting of Te and TeO ₂
There are oxide-based thin films whose main component is (O<x<2). These perform recording by changing at least one of the absorption coefficient or refractive index of the thin film by laser beam irradiation, and detect a change in transmittance or reflectance in this portion to detect a signal. Among them, a thin film mainly composed of TeOx is a material that has good sensitivity and variation, and is excellent in stability.

The substrate of optical recording disks is usually made of transparent materials such as glass, polymethyl methacrylate resin,
A disc made of resin such as polycarbonate resin is used, and for recording and reproduction on the disc, a laser beam is incident on the side of the transparent substrate opposite to the side on which the recording thin film is provided, and the laser beam is passed through the transparent substrate. Focus on the recording thin film. This is done so that the substrate itself has the function of protecting the recording thin film and prevents foreign matter such as dirt and dust present on the light incident side from entering the focal depth of the lens system (depending on the thickness of the transparent substrate). It is for the purpose of Even when such a configuration is adopted, the recording thin film on the substrate must be protected by some method from mechanical damage and physical/chemical deterioration caused by exposure to the outside air. When using a material that performs recording by forming small pores through melting and evaporation of the recording thin film, it is difficult to provide a protective layer directly on the recording thin film, and the protective plate is usually separated from the recording thin film by a certain distance via a spacer. A so-called air sanderch structure is used to protect the recording thin film from the outside air by providing a sealed space surrounded by the recording thin film on the substrate, this protection plate, and a spacer. It is complicated and the volume and weight of the entire disk is large, which puts a heavy burden on the rotation of the disk, and the manufacturing method is also complicated, making it unsuitable for practical use. On the other hand, when using a material that performs recording by changing the above-mentioned absorption coefficient, refractive index, or both (without changing the shape of the recording thin film), it is possible to directly cover the recording thin film with a protective layer. be. Next, a structure in which the direct protective layer is provided in close contact with each other (hereinafter referred to as a close contact protective structure) will be explained using the drawings. FIG. 1a is a partial sectional view of a disk having such a structure. 1 is a transparent substrate, 2 is a recording thin film, and 3 is an adhesion protective layer. Laser beams used for recording and reproducing information on such disks include Ar laser, He-Cd laser,
A He-Ne laser, a GaAlAs semiconductor laser, etc. are used. Therefore, the wavelength of normal light is 300nm to 1μm.
Use the range of The NA of the lens system is usually about 0.3 to 0.7. Although the thickness of the substrate 1 depends on the design values of the lens system, it is usually about 0.5 mm to 5 mm (and the diameter of the substrate is in the range of several cm to several 100 cm).
On the other hand, the thickness of the recording thin film is in the range of about 10 nm to 1 μm. Any material can be used as the protective layer 3 as long as it has the function of protecting the recording thin film, and its thickness is not particularly limited as long as it maintains the above-mentioned protective function. However, from the perspective of the volume and weight of the disk, it is preferable that the protective layer be as thin as possible, and from the viewpoint of the manufacturing method, it is a resin material that can be easily formed using a spinner coating method, spray coating method, etc., and the thickness is 500 nm to 200 μm. A range of degrees is preferred.

However, the above-mentioned amorphous chalcogen-based recording thin film and TeOx (O< _z <
Recording thin films such as oxide-based thin films mainly composed of 2) have a considerable transmittance (up to 5% depending on the film thickness).
~50%), of the irradiated laser light, the light that passes through the recording thin film is reflected back to the surface of the protective layer (the surface in contact with the outside air). Conventionally, this reflected light has caused noise during recording and reproduction. The details will be explained below using the drawings. In Fig. 2, 1 is a transparent substrate, 2 is a recording thin film, 3 is an adhesion protective layer,
4 is an aperture lens at the final stage of the lens system. The laser beam passes through the optical path 5 by the lens 4, passes through the transparent substrate 1, and is converged to a point 101 on the recording thin film 2. A portion of the laser beam is reflected, travels backward along the optical path 5, and passes through the lens 4 again to the laser beam detection system. (not shown). In addition, another part of the laser beam passes through the recording thin film 2,
It is reflected at the interface 201 between the adhesive protective layer 3 and the outside air.
This reflected light enters the lens along the optical path 5a as if it were emitted from a point 102 which is symmetrical with respect to the surface 201 of the point 101. The light reflected from the point 101 and the returning light emitted from the point 102 interfere with each other and their intensity changes.

It is difficult to control the thickness of a resin layer formed by the spinner method or spray method on the order of the wavelength of light;
The phase difference between the reflected light from point 101 and the returned light from point 102 varies depending on the position on the disk, and as a result, the intensity of light incident on the laser light detection system changes. Therefore, when a laser beam is irradiated while rotating the disk to continuously reproduce information at each position on the disk, the intensity of the reproduced light changes, which causes noise. Also, in the case of recording, the amount of laser light absorbed by the recording thin film differs depending on the position on the disk, and even if recorded with the same laser light output, the recorded state will be different, resulting in so-called uneven writing, which will cause noise during reproduction.

Conventionally, in order to avoid such a phenomenon, the thickness was sufficiently thick (0.5 mm to 5 mm, which is about the same as the thickness of the board), as shown in Figure 1b.
mm), and a structure was used in which the transmitted light is sufficiently spread on the surface of the adhesive protective layer and almost no reflected light enters the reproduction light detection system, but the overall volume and weight of the disk is large. It had the disadvantage of becoming. In addition, the adhesive protective layer with this structure required a complicated formation method, such as gluing a transparent plate similar to the substrate with transparent adhesive, and raw materials were also expensive, contributing to an increase in the cost of the disk. .

In addition, attempts have been made to provide an opaque protective layer as another method to avoid this phenomenon, but
A protective layer made of metal etc. has high thermal conductivity,
This was not practical in that it prevented the recording thin film from increasing in temperature due to laser beam irradiation. Attempts have also been made to mix pigments into the resin to make it opaque, but the optical and thermal properties of the area where the recording film and pigment contact at the interface between the recording thin film and the protective layer and the resin body contact Due to the difference in noise, noise occurred during recording and playback, making it impossible to put it into practical use.

Purpose of the invention In view of the above-mentioned problems, the purpose of the present invention is to
Low noise during playback, small volume and weight,
An object of the present invention is to provide an optical recording disk that is easy to manufacture and inexpensive, and a method for manufacturing the same.

Structure of the Invention In order to achieve the above-mentioned object, the optical recording disk of the present invention is provided with a recording thin film which is provided on a transparent substrate and whose state changes when irradiated with light such as a laser beam. A protective layer made of transparent resin is provided on top, and the surface of the protective layer made of transparent resin is used as a light scattering surface.By adopting such a structure, light can be transmitted through the recording thin film as detailed in the conventional example above. The emitted light is scattered on the surface of the protective layer and does not return to the reproduction light detection system, so that no noise is generated during reproduction.

Note that the scattering surface referred to herein refers to a surface that has a function of sufficiently scattering light within the area where the light transmitted through the recording thin film spreads on the surface of the protective layer, out of the laser light focused on the recording thin film. When converging a laser beam with a converging lens having an NA of about 0.3 to 0.7, this area corresponds to the area of a circle of about 0.6 to 1.4×t with respect to the thickness t of the protective layer. Therefore, it is necessary that portions having a light scattering function that are sufficiently smaller than this area are uniformly distributed on the surface of the protective layer.

DESCRIPTION OF EMBODIMENTS FIG. 3 shows one form of an embodiment of the present invention. 1 is a transparent substrate made of a material that is optically homogeneous and has few internal foreign substances. For example, glass plates such as soda glass, borosilicate glass, pyrex glass, and quartz glass, and resin plates such as polyethyl terephthalate resin, polyvinyl chloride resin, polymethyl methacrylate resin, polycarbonate resin, and polyethersulfone resin may be used. I can do it. The thickness is
A range of about 0.5 mm to 5 mm is usually used. 2 is a recording thin film whose state changes due to light irradiation, such as a Ge-Te-Sb-S thin film (Phys.Rev.
Letters 21 (1968) 1450), amorphous amorphous, chalcogenide thin films such as As-Se-Ge-S thin films (see JP-A-52-46464), or Te and
Oxide-based thin film whose main component is TeOx (O<x<2) consisting of _TeO2
-7558) etc. are used. When these materials are irradiated with light, at least one of their refractive index and absorption coefficient changes without changing their shape. 3b
is an adhesive protective layer made of a transparent resin, and any coating agent that forms a transparent and smooth layer can be used, but the material must be selected in consideration of mechanical strength, adhesion to the recording thin film, etc. For example, nitrocellulose lacquer, melamine resin paint, epoxy resin paint, polyurethane resin paint, amino resin paint, polyester resin paint, polysiloxane resin paint, etc. are used. As a coating method, a spinner coating method, a dipping method, a spraying method, a bar coating method, a roll coating method, etc. can be applied depending on the material. The surface 102b of the protective layer made of transparent resin has a surface that is 1/1/2 with respect to the thickness t of this resin layer.
It forms an uneven surface that is roughened at a period of 10 tons or less. Such a surface can be formed by rough polishing the surface after forming the transparent resin layer. For example, sandpaper treatment, sandblasting treatment, etc. are effective. In particular, sandblasting is particularly effective because the entire surface of the disk can be treated simultaneously and uniformly. Another method is to treat the surface of the adhesive protective layer with an organic solvent for a short time to attack the surface and create a scattering surface. The organic solvent used must be selected depending on the material of the protective layer, but generally trifluorethylene,
Used for perchlorethylene, methyl ethyl ketone, etc.

Next, experimental results based on specific examples will be shown.

Example 1 A polymethyl methacrylate PMMA plate with a thickness of 1.2 mm made by the casting method as a base material.
A disk with a diameter of 300 mm is used. This substrate was rotated in a vacuum evaporator, and Te and TeO ₂ were deposited in two different amounts.
Vacuum deposition is performed from two evaporation sources, and the evaporation rates from these two evaporation sources are independently controlled.
Form a TeOx (x≒1.2) thin film. The surface on which this TeOx thin film is deposited is coated with urethane acrylate oligomer (for example, Nippon Gosei Chemical Industry Co., Ltd. product name:
-4200B) is applied to a thickness of 15 μm using the spinner coat method, and then irradiated with ultraviolet light for about 30 seconds using a 4KW high-pressure mercury lamp to polymerize and harden. UV-curable resin has a fast curing speed,
It can be easily cured using small-scale equipment. In addition, because curing shrinkage is small, no heat is used for curing, and no solvent is used, curing can be performed without physically or chemically affecting the recording thin film, and it can be used as a protective layer for optical recording. It is particularly useful for
When the surface of this adhesive protective layer is treated with sandplast using an abrasive of about 10,000 for about 60 seconds, fine scratches with an average period of about 1 μm and a depth of about 0.5 μm are created on the surface, and the surface becomes a light-scattering surface. In addition, when sandblasted for about 60 seconds using an abrasive of about 1000, the surface becomes uneven and scratched with an average period of about 10 μm and a depth of about 5 μm, making the surface a light-scattering surface. These disks were rotated at a rotation speed of 1800 rpm to generate He− with a wavelength of 633 nm.
Concentrate the Ne laser beam with a converging lens of NA0.5,
The reflected light was focused and converged onto the recording thin film surface through the PMMA plate of the substrate, and the reflected light was detected. He
-Ne laser light was set to about 1 mW, which is sufficiently lower than the threshold value for changing the recording thin film, and the reflected light intensity was monitored. A spike-like noise occurred when the disk was not sandblasted, but this noise did not occur when the disk was sandblasted with No. 1000 abrasive. However, when the disk was sandblasted with No. 1000 abrasive, spike-like noise did not occur, but temporally uniform noise similar to white noise increased.

Example 2 Approximately 50 c.c. of methyl ethyl ketone was applied to the surface of the adhesive protective layer of an optical recording disk prepared in the same manner as in Example 1 using a spinner method, and when it was air-dried, the surface became cloudy and became a light-scattering surface. Ta. When this surface was observed under a microscope, thin cracks with a period of about 1 μm and a width of less than 1 μm were observed all over the surface. When this disc was reproduced in the same manner as in Example 1, no spike noise was generated and no increase in white noise occurred.

Next, another embodiment of the present invention will be explained using FIG. 4. In FIG. 4, 1 is a transparent substrate;
2 is a recording thin film. Reference numeral 3c denotes an adhesive protective layer made of transparent resin, and its surface 201c is filled with light-scattering particles having a size of 1/10 t or less of the thickness t of the adhesive protective layer uniformly and without gaps. By adopting such a configuration, the surface of the adhesive protective layer can be made substantially light-scattering, and the object of the present invention can be achieved. Specific examples are shown below.

Example 3 A disk made of polycarbonate resin with a thickness of 1.2 mm and a diameter of 120 mm was used as a base material, and concave grooves with a width of 0.6 μm and a depth of 70 nm were formed in a spiral shape on the surface with a pitch of 1.6 μm. A recording thin film was formed by depositing an oxide thin film TeOx (x≈1.1) containing Te and TeO ₂ as main components in the same manner as described in Example 1 above.

On this recording thin film, an ultraviolet curable paint containing an acrylic urethane oligomer (product name: Covisan 893, manufactured by Thiokol Co., Ltd.) as a main component is applied to a thickness of approximately 20 μm using the spinner coat method, and on top of this is coated with MgO with a particle size of 1 μm or less. Dispense the powder uniformly at a rate of about 20 mg/cm ² . After leaving it for about 5 minutes, irradiate it with ultraviolet light for about 60 seconds using a 4KW high-pressure mercury lamp to polymerize and harden the UV-curable paint. In this case, the MgO powder is embedded and fixed in the surface of the protective layer, and the surface becomes a light scattering surface. When observed under a microscope, it was observed that the MgO particles were fixed on the surface without any gaps.

This disk is rotated at a rotation speed of 1200 rpm, and the semiconductor laser beam with a wavelength of 830 nm is converged by a converging lens with an NA of 0.45, and the focus is controlled so that it is focused on the recording thin film surface through the polycarbonate plate of the substrate. A laser beam modulated with a rectangular wave with an output of 7 mW and a frequency of 2 MHz was irradiated and a signal was recorded while controlling to track a spiral groove of 0.6 μm and a depth of 70 nm. This signal recording section was again irradiated with a laser beam with an output of 1mM, and the reflected light was detected to reproduce the signal.
Disks that do not have MgO powder on the surface of the adhesion protective layer generate spike-like noise at 2MHz.
The C/N ratio of the reproduced signal (bandwidth 30KHz) is
On the other hand, when MgO powder was provided, no noise was generated and a C/N ratio of 52 dB was obtained. The weight of this disc is approximately 16g, which is approximately half the weight of conventional disc structures.

As shown in the above implementation, by uniformly providing a light scattering part of about 1/10 or less of the thickness on the surface of the adhesive protective layer over the entire disk surface, noise caused by reflected light from the surface of the protective layer is generated. This made it possible to prevent high-quality signal reproduction. It can also be said that the method of manufacturing the protective layer shown in these Examples is simpler and lower in cost than conventional methods.

Effects of the Invention As detailed above, according to the present invention, (1) recording and reproduction of high-quality signals with little noise during recording and reproduction can be performed, (2) a disk rotation system with small volume and weight; (3) It is possible to provide an optical recording disk and a method for manufacturing the same, which have a small burden on the transport system, are easy to handle, and (3) are low cost and easy to manufacture.

[Brief explanation of drawings]

1A and 1B are partial cross-sectional views showing a conventional example of an optical recording disk, FIG. 2 is an explanatory diagram explaining the problems of the conventional example, and FIG. 3 shows an embodiment of the optical recording disk of the present invention. FIG. 4 is a partial sectional view showing another embodiment of the present invention. 1... Transparent substrate, 2... Recording thin film, 3, 3a,
3b, 3c...Adhesive protective layer, 4...Lens, 5,
5a... Light path.

Claims (1)

[Scope of Claims] 1. A device comprising a transparent substrate, a recording thin film provided on the substrate whose state changes when irradiated with light, and a transparent resin layer provided on the recording thin film, the transparent resin layer being provided on the recording thin film. An optical recording disk characterized in that the surface of the layer is a light scattering surface. 2. The optical recording disk according to claim 1, wherein the recording thin film is made of a material that changes at least one of refractive index and absorption coefficient without changing its shape upon irradiation with light. 3. Claim 1, characterized in that the light scattering surface consists of an uneven surface in which the surface of the transparent resin layer is roughened at a period of 1/10 t or less with respect to the thickness t of the transparent resin layer. The optical recording disk described. 4. The light-scattering surface has light-scattering particles with a diameter of 1/10 t or less of the thickness t of the transparent resin layer embedded uniformly and close to each other on the surface of the transparent resin layer. An optical recording disk according to claim 1, characterized in that: 5. A recording thin film whose state changes when irradiated with light is provided on a transparent substrate by vacuum evaporation, a transparent resin layer is provided on this recording thin film, and the surface of this transparent resin layer is made light scattering by sandblasting. A method for manufacturing an optical recording disk, characterized in that: 6 A recording thin film whose state changes when irradiated with light is provided on a transparent substrate by vacuum evaporation, a transparent resin layer is provided on this recording thin film, and the surface of this transparent resin layer is treated with an organic medium to make it light scattering. A method for manufacturing an optical recording disk, characterized by: 7. The method of manufacturing an optical recording disk according to claim 6, wherein the transparent resin layer is formed by applying a photocurable resin and curing it by irradiation with light. 8. A recording thin film whose state changes when irradiated with light is provided on a transparent substrate using a vacuum evaporation method, a transparent resin layer is coated on this recording thin film, and a transparent resin layer is coated on the surface of this transparent resin layer.
A method for manufacturing an optical recording disk, which comprises removing light-scattering particles having a diameter of 0.1 t or less with respect to the thickness t of the transparent resin layer, and then hardening the transparent resin layer.