JPH05250728A - Optical disc - Google Patents

Abstract

PURPOSE:To realize the economical fabrication of optical disc by providing a thin gold layer on the substrate side of a light reflective layer. CONSTITUTION:A cyanine photosensitive coloring matter layer of 0.1mum is formed, through coating, on a disc substrate 1 of polycarbonate resin. A gold layer of 6nm thick is then formed as a surface layer 3a of light reflective layer through sputtering followed by formation of a silver layer of 50nm thick, as a main reflective layer 3b, through vacuum deposition thus forming a light reflective layer 3 composed of the layers 3a, 3b. The light reflective layer 3 is then subjected to spin coating of ultraviolet ray curing acrylic resin paint which is subsequently cured by utraviolet ray to form a protective layer 4 thus obtaining an optical disc. According to the constitution, a highly reliable high quality optical disc can be obtained economically by reducing the amount of expensive gold to be used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk, and more particularly to an optical disk capable of optically reading an information signal recorded optically.

[0002]

2. Description of the Related Art A conventional optical disc is formed by providing a track for recording an information signal on a surface of a synthetic resin substrate and further providing a layer for reflecting light. When the signal on the track is scanned by the pickup, the wavelength and phase difference of the light reflected from the reflective layer are detected as the difference in the intensity.

In order to make information signals writable in such an optical disk, a thin film of, for example, a photosensitive cyanine dye is provided on the synthetic resin substrate side of the reflective layer, and light modulated by the information signal is irradiated to emit the cyanine dye. A signal is recorded by changing the light absorption wavelength, and an information signal is reproduced by detecting a change in the intensity of reflected light using an optical pickup having a specific wavelength. This type of optical disc has the advantage that a homogeneous thin film of a cyanine dye can be formed relatively easily and is inexpensive, but it is difficult to increase the reflectance with an aluminum reflective layer that has been widely used in conventional optical discs. Further, there is a problem that deterioration is likely to occur in a silver reflective layer that can obtain high reflectance.

Therefore, conventionally, a noble metal, particularly gold has been used to form a light reflecting layer having a high light reflectance and being hardly deteriorated. Moreover, in this case, the light reflectance is, for example, 70%.
In order to achieve the above, the thickness of the gold layer needs to be at least 100 nm or more, which is disadvantageous in that the manufacturing cost of the optical disk increases.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides an optical disk having a more economical light reflecting layer while maintaining the same light reflecting characteristics and deterioration resistance as the light reflecting layer made of gold in the conventional optical disk. The purpose is to provide.

[0006]

The above-mentioned objects of the present invention are as follows.
A light-reflective layer is formed on an information signal recording surface of a synthetic resin substrate, and the light-reflective layer is provided with an optical layer having a thickness of at least 5 nm on the substrate side. ..

As the synthetic resin substrate in the optical disk of the present invention, for example, a transparent synthetic resin such as methacrylic resin, polycarbonate resin, or polyolefin resin, which is molded into a disc shape with a groove, can be preferably used. However, the material and shape are not particularly limited.

The light reflecting layer in the optical disc of the present invention is composed of a surface layer made of a gold layer and a main reflecting layer. As a material for forming the main reflection layer, a material having a sufficiently high light reflectance may be used, and among them, a metal having high light brightness, for example, silver or copper is preferably used. The thickness of the main reflective layer depends on the type of material forming the main reflective layer, but may be a thickness sufficient to give a light reflectance of 70% or more, and is usually about 50 to 150 nm.

Further, in the light reflecting layer, it is necessary that the thickness of the gold layer on the substrate side, that is, the side on which the photosensitive dye layer is provided, is 5 nm or more. If the thickness of the gold layer is less than 5 nm, the effect of suppressing the deterioration of the high light reflectance material that substantially constitutes the light reflecting layer is insufficient, but if it is too thick, it is particularly advantageous in terms of improving the deterioration resistance. There is no. On the other hand, however, the total light reflectance of the light reflecting layer tends to be improved as the thickness of the gold layer becomes thicker, and it is usually about 6 to 50 nm. Further, a similar gold layer may be provided on the back side of the light reflecting layer, that is, the side where the protective coating layer is usually provided.

[0010]

The optical disk of the present invention maintains a sufficiently high reflectance even under an environment of high temperature and high humidity, and little deterioration of a recording signal.

[0011]

【Example】

(First Example) A cyanine-based photosensitive dye layer having a thickness of 0.1 μm was formed by coating on a circular substrate having a diameter of 12 cm and a thickness of 1.2 mm formed of a polycarbonate resin. Then, a gold layer having a thickness of 6 nm was formed thereon by a sputtering method, and then a silver layer having a thickness of 50 nm was further formed by an evaporation method to form a light reflecting layer. Then, an ultraviolet-curable acrylic resin coating material was spin-coated and photocured to form a protective layer having a thickness of 0.01 mm, and an optical disk A of the present invention was obtained.

An optical disc B having the same structure as the optical disc A except that the thickness of the gold layer was 4 nm was obtained in the same manner as above. Further, an optical disk C having the same structure as described above except that it has a light reflection layer consisting of a gold layer having a thickness of 130 nm by the same method as described above, and a light reflection layer consisting only of a silver layer having a thickness of 90 nm. Otherwise, the optical disc D has the same structure as the above.
And an optical disk E having the same structure as the above except that it has a light-reflecting layer consisting of an aluminum layer having a thickness of 100 nm.

Humidity of these optical disks is 90%
Table 1 shows the results of conducting an accelerated deterioration test at RH and 60 ° C. for 220 hours, and examining changes in the light reflectance and changes in the signal read error occurrence rate (BER) before and after the test. The optical disk E had too low a light reflectance, and thus the deterioration test was not performed.

[0014]

[Table 1] Table 1 ────────────────────────────────── Optical disk reflectance (%) BER (× 10 ^-4 ) After initial deterioration After initial deterioration ────────────────────────────────── A 69.2 70.1 7.40 11.3 B 70.4 71.8 ^* 4.87 18.6 ^* C 71.5 74.1 8.12 15.5 D 70.4 --- ^** 7.75 --- ^** E 60.0 --- --- --- ────────────────────── ────────────── *: A part of the disk is deteriorated **: The entire surface deteriorates in 120 hours and cannot be measured.

(Second Embodiment) Thickness 5 in the first embodiment
An optical disk F of the present invention having the same structure as the optical disk A was obtained except that a 60 nm-thick copper layer was used instead of the 0 nm silver layer. The deterioration resistance performance of the optical disk F was almost the same as that of the optical disk A.

[0016]

The optical disk of the present invention has an advantage that it can be manufactured economically while maintaining high quality and high reliability while using less expensive gold.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing the structure of an optical disc of the present invention.

[Explanation of symbols]

 1 Synthetic Resin Substrate 2 Photosensitive Dye Layer 3 Light Reflecting Layer 3a Surface Layer 3b Main Reflecting Layer 4 Protective Paint Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Ito 2680 Nishihanawa, Tatomi-cho, Nakakoma-gun, Yamanashi Prefecture Pioneer Video Co., Ltd.

Claims (2)

[Claims] 1. A light-reflecting layer formed on an information signal recording surface of a synthetic resin substrate, wherein the light-reflecting layer has at least a gold layer having a thickness of 5 nm or more on the substrate side. optical disk. 2. The optical disc according to claim 1, wherein the light reflection layer is a metal thin film.