JPH0292682A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain high reflectivity, high contrast, and to improve durability, weather resistance by forming a recording layer of an optically reflecting layer made of a thin metal film and a light absorbing layer on a nitrocellulose layer. CONSTITUTION:A nitrocellulose layer is formed on a substrate, an optically reflecting layer and a light absorbing layer are sequentially laminated to form a recording layer. When a light such as a laser light is radiated, the absorbing layer absorbs a recording light to rise at its temperature in case of melting, thereby thermally conducting or directly heating the nitrocellulose layer. Thus, the cellulose layer serves as an initiator to deform the recording layer, thereby causing recording. Thus, the boundary of bits becomes clear by the cellulose layer. Since an optically reflecting layer is provided, an optically recording layer having features of high reflectivity and high contrast is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium on which information is recorded and reproduced by irradiation with laser light.

[Prior Art] Optical recording media, which record and reproduce information using laser light, have recently become rapidly popular due to improvements in basic technologies such as semiconductor lasers, recording materials, and film-forming methods, as well as the ability to record large amounts of data. The path to practical application has been opened. Recording methods for the above-mentioned optical recording medium include (1) deforming the recording film to form pits or bubbles, and (2) changing optical properties such as reflectance of the recording film using thermal energy from laser beam irradiation. Methods to change this have been proposed.

In the recording method (1) above, studies have been made on highly sensitive recording materials in order to achieve high reflectance and high contrast. Also, regarding the configuration of the recording film, it is a single film! , composite membranes, etc. are being investigated. For example, JP-A-57-20
No. 7092 describes an optical recording medium that has a light absorption layer that absorbs light and burns it, a reflection layer that has a high light reflectance, and a heat amplification layer that has a low melting point and self-oxidation property and generates heat when burned. Disclosed.

Furthermore, JP-A No. 63-191332 discloses an optical recording medium with increased reflectance by interposing a transparent thin film layer with a refractive index lower than that of the plastic substrate between a plastic substrate and a recording film. Techniques related to media are disclosed.

[Problems to be Solved by the Invention] However, in the optical recording medium disclosed in JP-A No. 57-207092, when carbon black or a dye (for example, oleosol EL blue) is used as the light absorption layer, an optical recording medium with high reflectance cannot be obtained. Therefore, the reading of the information signal tends to become unstable. Furthermore, when this technology is applied to card-shaped optical recording media (optical cards), the optical cards are often subjected to external mechanical forces such as twisting and bending, are often exposed to high temperature and high humidity, and are often exposed to detergents. There was a problem with durability because it often came into contact with chemicals such as.

On the other hand, in the technique described in JP-A-63-191332,
The material of the recording film is not particularly limited as long as it satisfies the above conditions, but in order to obtain a sufficient effect, it is necessary to make the transparent thin film layer thick enough to form a reflective multi-interference film.
It was difficult to control the film thickness.

This invention was made in view of the above problems, and is an optical recording medium in which information is written by strongly absorbing light in a predetermined wavelength range and deforming the recording film by the light to form pits or bubbles. It has high reflectance and high contrast, good recording and playback characteristics can be easily obtained, and has mechanical durability and weather resistance (high temperature and high humidity resistance).
The objective is to provide an optical recording medium with excellent stability.

[Means for solving the problem] Recording by irradiating light (for example, laser light) for recording.

In the above optical recording medium, when the light absorption layer melts, the temperature rises, heats the nitrocellulose dynamic layer by heat conduction or directly, and the nitrocellulose linten layer acts as a detonator to deform the recording layer. Recording is done by doing this.

As the nitrocellulose derivative in this invention, a derivative in which the hydrogen atom of the hydroxyl group of nitrocellulose is replaced with another organic group is used. Cellulose derivatives that do not contain nitrate esters, such as cellulose acetate, are not used.

The degree of nitrification of the nitrocellulose layer is preferably in the range of 1 to 13%. If the amount exceeds this range, and the amount is too small, the effect as a detonator will be weakened, and if it is too large, the thermal stability of the nitrocellulose layer will decrease.

The optical recording medium of claim (2) of this application is defined by claim (1).
), a nitrocellulose layer, a light reflection layer and a light absorption layer are laminated in the above order on a substrate, and the light reflection layer has a reflectance of 15% or more and 80% with respect to the wavelength of light used for recording and reproduction. or less, and the transmittance is 105 or more and 85
% or less, and the absorption rate of the light absorption layer with respect to the wavelength of the recording/reproduction light is 15% or more, and the recording/reproduction light is a high reflectance optical recording medium when the substrate and the nitro cell light absorption layer are laminated in this order. can be easily obtained. In claim (2), the reflectance of the light reflective layer with respect to the wavelength of light used for recording and reproduction is preferably within the above range. If it exceeds this range and is too low, the optical contrast during recording will be particularly poor, while if it is too high, the writing sensitivity will decrease. Further, since this light reflecting layer must transmit light to the light absorbing layer, it is preferable that the transmittance for the above wavelength is within the above range.

Further, the absorption rate of the light absorption layer is preferably 15% or more. If it exceeds this range and is too low, light absorption will not take place and less heat will be generated, so recording may not be possible at all or high power will be required for recording, which is not preferable.

The material for the light absorption layer and light reflection layer of the optical recording medium of this application may be any highly durable metal thin film. P as a light reflecting layer
t%AusAgqCu1A121Crs A single element film or an alloy film of Nl and Ti is suitable. In addition, as a light absorption layer, Bi, Sb, In, Pb, Sn,
Single element films or alloy films of Te, Se and S are suitable. In particular, the light-reflecting layer is a noble metal thin film such as Au and Pt as described in claim (3), and the light-absorbing layer is an alloy thin film containing chalcogen elements such as Te and Se as described in claim (4).
For example, it is more preferable to use Te-Se alloy, Te-B1 alloy) because of its high durability.

Here, in the optical recording medium of the present invention, when a light reflection layer and a light absorption layer are laminated in this order, the light reflection layer substantially transmits the recording and reproduction light. (
It must be formed using a material and film thickness selected under the condition that the reflectance is less than 100%. In addition, if the layers are stacked in the reverse order, the light absorption layer is made of a material and a film thickness selected under conditions that substantially transmit the recording and reproducing light (absorption rate is less than 100%). must be formed.

Even when a protective layer is provided on the recording layer, the optical recording medium of the present invention maintains sufficiently high recording sensitivity due to the explosive power of the nitrocellulose layer, and is capable of recording with high contrast. The protective layer is preferably one selected from urethane-based, acrylic-based, and silicone-based synthetic resins in terms of writing sensitivity. Phenol-based and melamine-based synthetic resins have too high a hardness and are therefore undesirable because they either cannot record at all or require high power for recording.

In the optical recording medium of this application, when the recording layer is formed in the order of the light-reflecting layer and the light-absorbing layer with respect to the recording and reproducing light as described in claim (2), the light-reflecting layer is the same as the light-absorbing layer. It is not formed to increase the light absorption ability (enhancement effect), but is provided to give the optical recording medium the characteristic of high reflectance.

It is particularly preferable that the film thicknesses of the light reflection layer and the light absorption layer are set so that the reflectance before recording is in the range of 60% to 75%. If it exceeds this range or is too low, tracking may become unstable during recording or playback. On the other hand, if it is too high, recording light cannot be absorbed sufficiently, and recording may not be possible at all, or high power is required for recording, which is not preferable. Each layer of the present invention does not need to be a multiple interference film, and the thickness of each layer may vary somewhat within a range that provides high reflectance and high contrast.

Each layer shown above can be formed by sputtering method, vacuum evaporation method, C
It can be formed by a conventional method such as a VD method, and the film forming method is not particularly limited.

Any substrate can be used as long as it is transparent enough to transmit recording and reproducing light. For example, materials with excellent transparency such as glass, polyester resin, polyolefin resin, polyamide resin, polycarbonate resin, and polymethacrylic resin can be used. It is also possible to laminate each layer on the above-mentioned transparent substrate, and then laminate this substrate with an arbitrary opaque substrate to laminate a transparent (transparent) protective layer.

Two transparent substrates on which each layer has been formed may be bonded together with any adhesive with each layer on the inside.

The shape of the substrate may be circular, rectangular, etc., or may be disk-shaped, card-shaped, etc. The substrate may have irregularities such as guide grooves for tracking, for example.

Although the wavelength of the laser beam used for recording etc. is not particularly limited, a wavelength of 1 Goonm or less is suitable for use. Therefore, with current semiconductor lasers, the wavelength is 75
Those in the range 0 to 850n+11 are effectively used. In this case, the power used during recording is generally in the range of about 1 to 15 mW.

[Function] The light-absorbing layer of this application mainly absorbs recording light, melts as the temperature rises, and simultaneously deforms the light-reflecting layer to form pits. The light-reflecting layer has the function of adjusting the reflectance of the optical recording medium with respect to recording and reproducing light, and achieving high reflectance and high contrast. Furthermore, since the nitrocellulose layer has explosive power, high sensitivity can be achieved by providing this layer.

The present invention will be explained in more detail with reference to Examples below.

[Example 1] A card-shaped transparent sheet made of polycarbonate having land portions serving as recording portions and group portions serving as track guide grooves was molded by a hot press method. On this substrate, a solution obtained by dissolving nitrocellulose with a degree of nitrification of 10% in an ethanol ether solution was formed into a film by a spin cord method. A light reflecting layer made of Au and Tea are provided on this nitrocellulose layer. Sea. Two layers of light absorption layers were formed in the above order by sputtering method. the light reflecting layer;
The thickness of the light absorption layer was determined by calculation using the refractive index of each layer, etc. so that the reflectance was 40% and the absorption rate was 55%. The film forming conditions are shown below. First, check the inside of the chamber.
After evacuation to X 10-'Torr, Ar gas was introduced so that the gas pressure became 5X 10-'Torr.After this, DC power was applied to the Au target to form an Au layer with a film thickness of 100 mm. Next, Te −
High frequency power was applied to the Ss target to form a Te.Sel layer with a thickness of 20G on the Au layer.

Nitrocellulose layer, Au layer and T’ea. Set.

A card-shaped optical recording medium was created by bonding a transparent sheet with laminated layers and a white polycarbonate plate together using a urethane adhesive. When the recording and reproducing characteristics of this card-shaped optical recording medium were evaluated, the reflectance of the recording and reproducing light before recording was 40% and the reflectance after recording was 15%, and recording with high contrast was possible. In addition, an accelerated deterioration test was performed on this optical recording medium under the conditions of holding it at 75°C and 85% RH for 1000 hours, and archival life and shelf life were measured, but no signs of deterioration were observed in the recording and reproducing characteristics. Ta. Furthermore, a mechanical durability test of the recording film was conducted by subjecting this optical recording medium to bending, twisting, etc., but there was no effect on the recording/reproducing characteristics at all.

[Example 2] A solution obtained by dissolving nitrocellulose with a degree of nitrification of 12% in an ethanol ether solution was spun into a polycarbonate transparent disk having land portions as recording portions and group portions as track guide grooves: ) - The film was formed by the method. On this nitrocellulose layer is a light reflecting layer made of PT and Tea. A light absorption layer starting from Bho was formed by a sputtering method.

Next, the film forming conditions will be shown. As in Example 1, Ar gas was introduced into the evacuated chamber, and the gas pressure was set to sx.
It was set at 1G-'Torr. Here, DC power was applied to the PT target to form a PT layer having a thickness of 120 layers. Then, using an alloy target having a Te-B1 composition on the above pts, the film thickness was 200, and the atomic ratio was Tea. Bit. A light absorption layer was provided. The recording and reproducing characteristics of the disk-shaped optical recording medium produced by the above method were very good, and it was possible to write from 4 mf with a CNR of 45 dB, and the maximum CNR reached 50 dB.

Furthermore, an accelerated deterioration test was conducted under the conditions of holding this optical recording medium at 75° C. and 85% RH, and the archival life and shelf life were measured, but no signs of deterioration were observed in the recording and reproducing characteristics.

[Effects of the Invention] As explained above, according to the present invention, a nitrocellulose layer is provided on a substrate, and a recording layer formed of a light reflection layer made of a metal thin film and a light absorption layer is further provided. The pit boundaries become clear due to the nitrocellulose refractory layer, and by providing the light reflective layer, an optical recording medium having characteristics of high reflectance and high contrast can be obtained. In particular, according to the structure of claim (2), since the light reflecting layer is located on the side where the recording and reproducing light is irradiated rather than the light absorbing layer, an optical recording medium with a high reflectance can be easily obtained and the effect is great. Furthermore, when the materials according to claims (3) to (p) are used for the light reflection layer or the light absorption layer, they are suitable for optical cards because they have excellent mechanical durability and weather resistance (high temperature and high humidity resistance). .

Claims (4)

[Claims] (1) A nitrocellulose layer made of nitrocellulose or a derivative thereof is provided on a substrate, and a recording layer formed of a light reflection layer and a light absorption layer made of a thin metal film is provided on the nitrocellulose layer, An optical recording medium characterized in that information is recorded by irradiating the layer with recording light, thereby melting the light absorption layer and deforming each of the layers. (2) A nitrocellulose layer, a light reflective layer, and a light absorbing layer are laminated in the above order on the substrate, and the reflectance of the light reflective layer is 15% or more and 80% or less with respect to the wavelength of the recording/reproducing light, and the light is transmitted. an absorption rate of 10% or more and 85% or less, and an absorption rate of the light absorption layer for the wavelength of the recording/reproducing light is 15% or more, and the recording/reproducing light passes through the substrate and the nitrocellulose layer and absorbs the recording layer. The optical recording medium according to claim 1, characterized in that the optical recording medium is irradiated with. (3) The optical recording medium according to claim 1 or 2, wherein the light reflecting layer is made of a thin film of a noble metal element. (4) The optical recording medium according to any one of claims 1 to 3, wherein the light absorption layer is an alloy thin film containing a chalcogen element.