JPH0660443A - Production of optical disk substrate - Google Patents

Abstract

PURPOSE:To improve recording-reproducing characteristics by filling guide grooves of a rugged pattern on the surface of the medium with a hardening type resin layer before forming the optical recording medium so that depth or shape do not change. CONSTITUTION:Guide grooves of a rugged pattern on the surface of the medium are filled with a curing type resin layer before the optical recording medium is formed. The layer is formed by spin coating, and viscosity of monomers or mol.wt. of the resin to be applied is selected according to the film thickness of the film to be formed, and the applied coating is cured by irradiation of UV ray. By selecting the resin layer having the same refractive index as that of the resin layer which constitutes the rugged pattern, magento-optical effect can be increased by optical interference, which prevents reflection or absorption of light between the substrate and the resin layer. The resin is cured in an atmosphere containing no oxygen which gives high polymn, degree of the resin. Thereby, noises caused by fine rough pattern can be decreased, and recording and reproducing chatacteristics are improved, and thermal damage of the substrate surface is suppressed and adhesion property between the substrate and the recording medium can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical disk substrate.

[0002]

2. Description of the Related Art With the progress of the advanced information society in recent years, there is an increasing need for a high-density and large-capacity file memory. Optical recording is attracting attention as a memory that can meet this demand. Recently, magneto-optical recording, which is one of a read-only type represented by a compact disc, a write-once type used for a document file, and a rewritable type used for a document file or an image file, has recently been developed. ,
It was put to practical use. In particular, rewritable optical recording is
A wide range of applications are being considered, and research on how to improve its performance is being carried out at many research institutes. One of them is to improve the performance of magneto-optical disks. For example, it has been considered to form small recording bits in order to increase the recording density. In that case, it is necessary from the viewpoint of resolution to perform reproduction using light having a short wavelength. The signal-to-noise ratio (S / N) must be higher than in the past even if light having a small magnetic domain shape and a short wavelength is used. However, when light with a short wavelength is used, noise may increase due to minute irregularities on the substrate surface, and stable reproduction may not be possible in some cases. Heretofore, a search has been made for a recording material that can obtain a large magneto-optical effect in order to obtain a high S / N. One example is JP-A-62-222609.

[0003]

In the above-mentioned prior art, the study on the recording material is the main focus, and no consideration has been given to the generation of noise from the substrate, among the characteristics of the substrate.

An object of the present invention is to provide a high-performance optical disk by improving the disk performance, particularly the recording / reproducing characteristics, by using a process for improving the flatness of the substrate surface.

[0005]

The above object is to prepare a substrate for an optical disc having a guide groove having an uneven surface,
This can be achieved by forming an ultraviolet curable resin layer before forming the optical recording medium so that the depth and shape of the guide groove having irregularities on the surface do not change. The substrate for the optical disk used here may be plastic or a substrate in which a guide groove is formed on a glass disk by a photopolymer method with an ultraviolet curable resin, and does not depend on the material of the substrate.

In the present invention, it is important to select the physical properties of the resin to be formed so that the depth and shape of the uneven guide groove on the surface do not change. To form this layer, the monomer is applied using a spin coating method. In that case, what is important is the viscosity and molecular weight of the applied monomers. In order to form a thin layer of monomer with a spinner, the film thickness may be such that minute irregularities existing on the surface are filled.

As described above, in the production of a substrate for an optical disc having an uneven guide groove on the surface, the minute unevenness present on the surface is changed to the ultraviolet curable resin layer by changing the depth and shape of the uneven guide groove on the surface. The flattening of the substrate surface was realized by forming it so that it was not formed.

The viscosity and molecular weight of the monomer of the applied resin are
It is closely related to the film thickness of the film to be formed. After coating, the composition is irradiated with ultraviolet rays to be cured, but in that case, the life of the magneto-optical recording medium is affected because it causes a change in film thickness and a change in internal stress. As the resin layer formed on the substrate surface, an ultraviolet curable resin having the same refractive index as that of the substrate material or the resin layer forming the irregularities on the substrate surface was used. This is to increase the magneto-optical effect due to optical interference, and to prevent reflection and absorption of light between the substrate and the formed resin layer.

When the resin is cured, a resin layer is formed on the surface of the substrate.
After forming the (monomer layer), the resin was polymerized by irradiating the substrate surface with ultraviolet rays in a vacuum or in an environment where oxygen does not exist. This is because the degree of polymerization of the resin is high in the environment containing no oxygen. In addition, when a resin layer having a high hardness is formed on the surface of the substrate made of a substrate material having a low hardness, the mechanical strength of the substrate increases. Further, when a resin layer having high heat resistance is formed over a substrate having low heat resistance, heat damage on the surface of the substrate that occurs when a recording medium is manufactured by a sputtering method or a vacuum evaporation method can be suppressed. Further, when the adhesion between the substrate and the recording medium is poor, the adhesion between the substrate and the recording medium can be improved by this UV-curable resin layer.

[0010]

In the disk substrate obtained by the present invention, by forming an ultraviolet curable resin layer on the surface, the minute irregularities sufficiently filled with the guide grooves existing on the substrate are filled with the resin. It is possible to greatly reduce the disk noise generated due to the minute unevenness existing in the disk. In addition, by selecting the resin material, it is possible to further suppress the heat damage on the substrate surface, increase the mechanical strength of the substrate, and improve the adhesion between the substrate and the recording medium.

[0011]

【Example】

<Example 1> In this example, a plastic substrate is used. Polycarbonate was used as the substrate material. This substrate is manufactured by an injection molding method. An ultraviolet curable resin was spin-coated on the surface of this substrate. Then, this substrate was placed in a nitrogen gas atmosphere and ultraviolet rays were irradiated using a mercury lamp to cure the resin. A disk was manufactured using the substrate thus treated. Its structure is SiN
It has a four-layer structure of x / TbFeCoNb / SiNx / AlTa. The film formation was performed by a sputtering method, and the above four layers were continuously laminated.

Then, the noise of the disk thus manufactured when not recorded was measured. Frequency: f = 2.5M
The value in Hz is -62.0d when the present invention is used.
Bm was -5, but when not treated, -5
It was 9.5 dBm. By thus performing the flattening processing of the present invention, the noise level is reduced to about 2.5 dB (f = 2.5
MHz) could be reduced.

FIG. 1 shows a spectral distribution when recording is performed at a recording frequency of 2.5 MHz. As shown in this figure, the effect of the present invention is effective in the low frequency region of 5 MHz or less, and it is considered that the noise generated when untreated is the noise due to the fluctuation of the polarization plane caused by the unevenness of the substrate surface.

In addition to the above, as an effect of the present invention, the adhesion between the polycarbonate substrate and the recording medium was improved. Since the adhesion between the polycarbonate substrate and the recording medium, particularly silicon nitride, is weak, there is a problem that the recording medium peels off from the substrate over time. On the other hand, the ultraviolet curable resin has a strong adhesive force between plastics or with a recording medium, and therefore has a function as a binder. Further, for a substrate material having a low softening temperature such as an acrylic substrate, it is possible to suppress the deformation of the substrate itself, the groove, or the pit due to the increase in the surface temperature of the substrate during sputtering. Further, when a material having a low surface hardness was used, it was difficult to get scratches due to the same effect as hard coating.

Example 2 This example is a case of using a glass / 2p substrate in which uneven guide grooves are formed on the surface of a glass disk by a photopolymer method. An ultraviolet curable resin was spin-coated on the surface of this substrate. Then, this substrate was placed in a nitrogen gas atmosphere and ultraviolet rays were irradiated using a mercury lamp to cure the resin. Here, the same effect can be obtained if the atmosphere for curing the resin is not only nitrogen but also an atmosphere of an inert gas such as argon. The reason for curing in such an inert gas is to completely cure not only the surface of the film but also the inside of the film. A disk was manufactured using the substrate thus treated. Its structure is SiNx / Tb
It has a four-layer structure of FeCoNb / SiNx / AlTa. The film formation was performed by a sputtering method, and the above four layers were continuously laminated.

Then, the noise of the thus-produced disc when not recorded was measured. As a result, frequency: f
The value at = 2.5 MHz is -6 when the present invention is used.
While it was 5.0 dBm, it was -61.0 dBm when it was not treated. By thus performing the flattening process of the present invention, the noise level is reduced to about 4 dB (f =
2.5MHz) was able to be reduced.

FIG. 2 shows a spectral distribution when recording is performed at a recording frequency of 2.5 MHz. As shown in this figure, the present invention is effective in the low frequency region of 5 MHz or less, and it is considered that the noise generated when untreated is the noise due to the fluctuation of the polarization plane caused by the unevenness of the substrate surface.

[0018]

According to the present invention, by forming an ultraviolet-curable resin layer on the surface of a disk substrate, minute irregularities existing on the substrate can be filled with resin and can be removed. As a result, it is possible to greatly reduce the noise of the disc, which is caused by the minute irregularities existing on the substrate when the optical disc is formed. In addition, by selecting the resin material, it is possible to further suppress the heat damage on the substrate surface, increase the mechanical strength of the substrate, and improve the adhesion between the substrate and the recording medium.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing frequency dependence of carrier level and noise level measured by a spectrum analyzer.

FIG. 2 is a characteristic diagram showing frequency dependence of carrier level and noise level measured by a spectrum analyzer.

[Explanation of symbols]

 f ... Frequency (MHz).

Claims (5)

[Claims] 1. In the production of a substrate for an optical disc having an uneven guide groove on its surface, an ultraviolet curable resin layer is formed before the formation of an optical recording medium so that the depth and shape of the uneven guide groove on the surface do not change. A method for manufacturing an optical disk substrate, which is characterized in that 2. A method of manufacturing a substrate for an optical disc having an uneven guide groove on the surface, by forming an ultraviolet-curable resin layer on the surface so that the depth and shape of the uneven guide groove on the surface do not change. A method for manufacturing a substrate for an optical disc, characterized in that fine irregularities present on the surface of the substrate are flattened from the guide grooves. 3. In the production of a substrate for an optical disk having an uneven guide groove on the surface, an ultraviolet curable resin layer is formed before the formation of an optical recording medium so that the depth and shape of the uneven guide groove on the surface do not change. A method for manufacturing an optical disk substrate, characterized in that the molecular weight and the viscosity of the ultraviolet curable resin used for forming the substrate are controlled. 4. The method according to claim 1, 2 or 3, wherein the ultraviolet curable resin layer is formed before the formation of the optical recording medium so that the depth or shape of the guide groove of the unevenness on the surface does not change. A method for manufacturing an optical disk substrate using the ultraviolet curable resin having the same refractive index as that of the substrate material or the resin layer forming irregularities on the surface of the substrate. 5. The surface of the substrate according to claim 1, 2, 3 or 4, wherein after the resin layer is formed on the surface of the substrate, the surface of the substrate is irradiated with ultraviolet rays in a vacuum or in an environment where oxygen does not exist,
A method for manufacturing a substrate for an optical disc, which comprises polymerizing a resin.