JPH0432448B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a highly sensitive information recording medium suitable for application to a high-density optical memory device that optically records and reproduces information.

BACKGROUND TECHNOLOGY AND PROBLEMS Conventionally, as described above, optical information recording media for optically recording and reproducing information include a thin film of a low-melting metal such as bismuth or tellurium as a recording layer on a transparent substrate such as glass or plastic. Alternatively, a thin film of these compounds is deposited and the recording layer is irradiated with a laser beam modulated according to the recorded information to melt and evaporate the thin film to form information pits and record the information. What is commonly done is However, such a metal thin film recording layer generally has a high reflectance, and although it uses a low melting point metal, it actually has a drawback that its recording sensitivity is low because its melting point is relatively high. Furthermore, metal thin films with excellent recording sensitivity are highly toxic and have serious drawbacks in their manufacture and handling.

On the other hand, a recording medium in which an organic dye layer that absorbs recording laser light is deposited instead of the metal thin film as the recording layer is disclosed, for example, in JP-A-56-16948. This information recording medium has a reflective film and an organic dye layer on a substrate, and information is recorded on it.In this case, although the above-mentioned toxicity has been improved, it can withstand long-term storage. has the disadvantage of low recording sensitivity. In addition, since it is necessary to irradiate the recording laser beam from the surface of this recording layer, dust and dirt that adhere to this surface,
There is a drawback that the read signal is greatly affected by the presence of scratches and the like, degrading the signal quality.

Furthermore, as another information recording medium, an auxiliary layer containing an organic dye or the like is used in combination with the metal thin film described above to improve recording sensitivity, as disclosed in, for example, Japanese Patent Laid-Open No. 54-89605. Disclosed. A recording medium with this structure has a transparent substrate, an auxiliary layer provided on the transparent substrate, and an information recording layer having a reflective characteristic disposed on the auxiliary layer. The information recording layer is irradiated through the base and is melted and evaporated according to the recorded information to form information pits. Since the auxiliary layer in this case contains an organic dye that absorbs laser light, it improves the low heat conversion rate of laser light caused by the high reflectance of the metal thin film as described above. It is designed to produce an exothermic effect. However, even in the information recording medium having such a structure, the recording layer uses a thin metal film with a low melting point, and the problem of toxicity has not been solved.

Furthermore, as another information recording medium, information is recorded by using a high melting point thin film and an organic material in combination, and by utilizing the bubbling phenomenon caused by decomposition and sublimation of the organic material, instead of using melting and evaporation of a low melting point metal thin film. The method was published in 1983
-Disclosed in Publication No. 65340. As shown in FIG. 1, this information recording medium has a light-reflecting material layer 2 formed on a transparent substrate 1, a light-transmitting material layer 3 deposited on this light-reflecting material layer 2, and a light-transmitting material layer 3 deposited on this light-reflecting material layer 2. Due to the three-layer structure in which a light absorber layer 4 is deposited on layer 3. In this case, the light absorbent layer 4 is made of titanium, platinum,
The light transmitting material layer 3 is made of a material having a high melting point such as rhodium, gold, nickel, chromium, panadium, etc.
It is made of an organic material that melts, decomposes, or sublimates at low temperatures to reduce the light energy required for recording, and is transparent to the recording/reading laser beam.
For recording on such an information recording medium, a laser beam modulated by information recording is transmitted to a light absorbent layer 4.
It is irradiated from the side, where it is converted into thermal energy, and this heat heats the light transmitting material 3 to generate decomposition gas, which causes bubbles to absorb light as shown in Figure 2. Information is recorded by forming a cavity 5 under the agent layer 4 and forming a pit 6 in which the layer 4 bulges in accordance with information recording. In this case, although the above-mentioned toxicity problem is solved, 1. Since the reflectance of the light absorbent layer 4 is high, the efficiency is poor and the recording sensitivity is not improved much.

2. Since recording and reading are performed from the light absorbent layer 4 side, signal defects increase due to dust, scratches, and other flaws on the surface.

3. Because the recording mode is in a bulging state where the thin film-like light absorbent layer 4 is floated by foaming, the light absorbent layer 4 is a thin film, and the foamed information recording portion, that is, the pit portion. 6 is mechanically weak and has low reliability.

It has the following disadvantages.

In addition, in order to prevent signal defects due to surface dust, scratches, etc. mentioned in item 2) above, it is possible to further provide a protective film on this light absorbing layer 4, but if such a protective film is provided, If it is thick, this will cause the disadvantage of suppressing the bulging deformation of the light absorber layer due to foaming, so it is made so thick that the surface of this protective film is located outside the focal depth of the objective lens of the focused beam system. I can't.

OBJECT OF THE INVENTION It is an object of the present invention to provide a non-toxic and highly sensitive information recording medium which improves the above-mentioned drawbacks.

Means for Solving the Problems As shown in FIG.
A light absorbing layer 12 containing a light absorbing agent that generates heat by absorbing recording light is formed on this substrate 11, and a metal light reflecting layer 13 is formed on this light absorbing layer 12. The heat generated by absorbing the recording light irradiated through the substrate 11 deforms the light irradiated portion of the light absorption layer 12 to record information.

For example, a laser beam is used as the recording and reading light, and a light absorbing agent such as an organic dye or pigment that absorbs the recording laser beam and a foaming agent are placed on the substrate 11 that is transparent to the laser beam. a light absorbing layer 12 made of, for example, a thermoplastic resin layer containing a reflective layer 12, a reflective layer 13 having a high reflectance for laser light on the light absorbing layer 12, and a reflective layer 13 on top of this as necessary. A protective film 14 is formed to protect the layer 13 from corrosion.

As the light absorbing agent in the light absorbing layer 12, an organic dye or an organic pigment whose light absorption wavelength almost matches the wavelength of the recording laser beam is used, and as a blowing agent, it decomposes upon heating and releases N ₂ and CO. A substance that generates a gas such as ₂ is used.

Recording and reading of information on the information recording medium with such a configuration is performed by irradiating recording laser light and readout laser light from the base 11 side as shown by arrow a in FIG. 3. That is, during recording, a focused laser beam modulated according to the information recording signal is irradiated from the substrate 11 side so as to be focused onto the light absorption layer 12. In this way, this light absorption layer 12
The light energy absorbed by the light absorbing agent, such as an organic dye or pigment, is converted into thermal energy and heats this layer in a pattern corresponding to the information recording signal. At this time, due to the temperature rise in this layer, the base material of the light absorption layer 12, that is, the thermoplastic resin, becomes locally plasticized, and the foaming agent is thermally decomposed to generate gas, so that fine air bubbles are created in this layer 12. This causes an apparent volume expansion, and as shown in FIG. 4, a pit 15 is formed in which the reflective layer 13 and the protective film 14 thereon are locally bulged, thereby recording. I will finish it. That is,
In this pit 15, a portion having different optical characteristics such as light reflection and interference from the portion other than the pit 15 is generated and recorded.

In addition, in order to read out the recording from the medium on which this recording has been made, that is, on which the recording pits 15 have been formed, a readout light such as a readout laser beam is emitted from the base 11 side as shown by the arrow b in FIG. The information is read by detecting changes in optical characteristics of the pits 15 due to differences in thickness and density, for example, by reflection from the reflective layer 13, interference, and the like.

The base 11 is made of a disc with a thickness of about 1 mm to 2 mm and is made of a base such as acrylic resin or polycarbonate resin that is transparent to both recording and reading laser beams. The coating thickness is about 200 to 3000 Å, preferably about 1000 Å. Further, as the light absorbing agent to be contained in the thermoplastic resin of the light absorbing layer 12, for example, when the recording laser is constituted by a semiconductor laser, a dithiobenzoin-based metal complex having light absorbing properties at a wavelength of around 8000 Å is used. . In addition, as a foaming agent, it is thermally decomposed at 100 to 3000℃ and produces _N2 or
For example, azobisisobutyrodinitrile, 1,1'-azobis-(cyclohexane-1-carbonitrile), etc., which efficiently generate CO ₂ gas, can be used.

These light absorbers and foaming agents are mixed with a thermoplastic resin dissolved in the same organic solvent, and
1 by a spin coating method.

The reflective layer 13 is formed by, for example, a vacuum evaporation method to
It is made of a metal thin film having a thickness of 1000 Å and having a high reflectance at least for the readout light, such as nickel, aluminum, or chromium.

Further, the protective film 14 can be formed by applying a metal oxide by, for example, a vacuum deposition method, or by applying a resin by a spin coating method.

Example 1 A light absorption layer 12 with a coating thickness of 1400 Å is placed on a substrate 11 made of a polycarbonate resin disk with a thickness of 1.5 mm.
was applied. This light-absorbing layer 12 is made of an acrylic resin dissolved in an organic solvent, a dithiobenzoin-based metal complex as a light-absorbing agent, and azobisisobutyrodinitrile, 1,1'-azobis-(cyclohexane-1- carbonitrile),
It was formed by coating on the substrate 11 by a spin coating method. Then, an Al layer having a thickness of 500 Å was formed as a reflective layer 13 on this light absorption layer 12 by vacuum deposition. Then, a metal oxide was formed thereon as a protective film 14 by vacuum evaporation.

When an information recording medium having such a structure is irradiated with a recording laser beam from the base 11 side as described above, this light is absorbed in the light absorption layer 12 and converted into heat, thereby causing foaming in this layer 12. The agent causes the layer 12 to expand, and the reflective layer 13 and protective layer 14 are locally lifted to form pits 15, as explained in FIG.

Effects of the Invention In the present invention, the light absorbing function and the deforming function, such as the foaming function, are performed by the same layer 12, so that during recording, the light is efficiently converted into heat by the light absorbing agent. It is efficiently transmitted to the foaming agent and causes it to foam, resulting in highly sensitive recording. Further, since the light absorption layer 12 itself is deformed, that is, foamed and expanded to form the pits 15, a cavity is formed under the reflective film 13 in the area where the pits 15 are formed, as in the conventional case explained in FIG. The pit is formed with almost no occurrence of oxidation, thereby increasing the mechanical strength of the pit. Therefore, a medium with high reliability and excellent storage stability can be obtained.

Further, according to the present invention, the reflective layer 13 is locally lifted by the volume expansion of the light absorbing layer 12 itself to form the pits 15, so that the formation of the pits 15 can be lifted reliably. Accordingly, even if the protective film 14 has a thickness sufficient to provide sufficient protection, the sensitivity will not decrease. Furthermore, in the information recording medium according to the present invention, recording and reading light can be irradiated from the base 11 side, so even if there is dust or scratches on the protective film 14, this will not cause signal defects. Information recording and reading with a high S/N ratio can be performed without any problems.

In addition, according to the present invention, it is possible to avoid the use of low melting point metals as mentioned at the beginning, and accordingly, the use of toxic materials can be avoided, and problems in the manufacturing process and pollution problems can be avoided. The industrial benefits will be large.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an example of a conventional information recording medium, FIG. 2 is a similar cross-sectional view showing the information recording state thereof, and FIG. 3 is a schematic enlarged view of an example of an information recording medium according to the present invention. FIG. 4 is a similar cross-sectional view showing a state in which information has been recorded thereon. 11 is a base, 12 is a light absorption layer, 13 is a reflection layer,
14 is a protective film.

Claims (1)

[Scope of Claims] 1. A transparent substrate; a light-absorbing layer formed on the substrate and containing a light-absorbing agent that generates heat by absorbing recording light; and a metal formed on the light-absorbing layer. Information recording comprising a light reflecting layer, and recording information by causing deformation in the light irradiated part of the light absorbing layer by heat generated by absorbing recording light irradiated through the substrate. Medium.