JP2001319375A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical information recording medium which enhances repetitive characteristics of high density optical recording and reproduction and still playback characteristics and can highly maintain signal quality. SOLUTION: The optical information recording medium 1A is an optical disk obtained by successively stacking at least a mask layer 3 and a reflecting layer 4 on a light transmissive substrate 2A, 2C. In the optical disk in which the mask layer comprises a thermochromic material having a disk super- resolution function by which the light transmittance of a part to be continuously irradiated with laser beam for reproduction incident from the substrate side increases partially when the part attains to the decoloring temperature or above, the diameter of a spot of light is substantially reduced, the laser beam for reproduction is allowed to emerge to the reflecting layer side and light returned from the reflecting layer side is allowed to emerge to the substrate side to reproduce an information signal, an organic crystalline material having a lower melting point than the decoloring temperature of the thermochromic material is contained in the thermochromic material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium such as an optical disk capable of optically reproducing or recording / reproducing high-density information, and more particularly to prevention of deterioration of a reproduction signal.

[0002]

2. Description of the Related Art In recent years, a large-capacity recording / reproducing technique for an optical information recording medium such as an optical disk has been developed.
Among them, a disk mask method (also called a disk super-resolution method) is a technique for reproducing high-density optical information by reducing the effective irradiation spot diameter of an irradiation laser beam on an optical information recording medium. It has been developed as shown in the following example. For example, Japanese Patent Application Laid-Open No. 7-18269 discloses an optical recording medium that realizes super-resolution of a disk using a thermochromic substance.
No. 3 and JP-A-7-311978. In this technique, when laser light is applied, only the central part of the irradiated part of the mask layer containing the thermochromic material becomes partially transparent due to a rise in temperature. The target irradiation spot diameter is reduced, thereby enabling high-density reproduction that could not be reproduced until now. Further, a technique relating to an improved method for reproducing and using this large amount of recorded information many times is disclosed in, for example, Japanese Patent Application Laid-Open No. 10-147068. In this technique, an attempt has been made to improve the still reproduction characteristic by setting an optimum range of the absorbance of the mask layer with respect to a laser beam to be used.

[0003]

By the way, in mask reproduction of an optical disk using a mask layer containing an organic thermochromic material as a main component, the biggest problem is the signal quality at the time of laser reproduction, especially at the time of still reproduction. That is, measures to prevent deterioration are not sufficient. The above-mentioned related gazette has a description about this countermeasure, but it is not sufficient for practical use.
In addition, when a structure in which a dye and a developer are dissolved in a solvent is applied on a transparent substrate and further covered with a transparent thin plate such as a cover glass, the structure is considerably larger than the case of only a solid without liquid. It was expected that the still characteristics would be improved. This is due to the fact that the liquid does not overheat due to the heat dissipation effect, and the damage to the thermochromic material is reduced, and even if the thermochromic material is damaged, the thermochromic material itself is liquid and easy to move. Since the chromic material is supplied one after another, it is considered that the thermochromic material is locally free from damage.

However, in order to maintain the above-described structure, there is no effective means for sandwiching a liquid material between the disk substrate and the cover on the optical disk.
It was difficult to adopt it as an optical disk. The present invention has been made in view of the above problems, and has been made in order to effectively solve the problems. The purpose of the present invention is to improve the repetition characteristics and the still reproduction characteristics of high-density optical recording and reproduction, and improve the signal reproduction. An object of the present invention is to provide an optical information recording medium capable of maintaining high quality.

[0005]

The invention defined in claim 1 is an optical information recording medium comprising at least a mask layer and a reflective layer sequentially laminated on a light transmitting substrate, wherein the mask layer However, when the temperature of the irradiated portion where the reproducing laser light incident from the substrate side is continuously irradiated becomes higher than the decoloring temperature, the light transmittance of a part of the irradiated portion is increased and the light spot diameter is reduced. A thermometer having a disk super-resolution function for reproducing an information signal by substantially reducing the size of the laser beam for reproduction to the reflection layer side and emitting the return light from the reflection layer side to the substrate side. An optical disc comprising a chromic material, wherein the thermochromic material comprises:
An optical information recording medium characterized by containing an organic crystalline substance having a melting point lower than the color erasing temperature of the thermochromic material. This makes it possible to improve the repetition characteristics and still reproduction characteristics of high-density optical recording and reproduction, and to maintain high signal quality.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical information recording medium according to the present invention will be described below in detail with reference to the accompanying drawings. First,
The principle of the characteristic mask layer of the present invention will be described. The thermochromic material contained in the mask layer generally contains an electron donating color compound and an electron accepting developer. In the thermochromic mask process in which the electron-donating color compound and the electron-accepting color developer react with each other by receiving heat and are cooled and reacted in reverse, both the electron-donating color-forming compound and the electron-accepting color developer are reacted. Need only be present in the solvent in the hot parts where the reaction takes place, not in the cold parts where the reaction has not taken place. Therefore, in a temperature range in which the substance is solid at room temperature and in which a thermochromic reaction occurs (a thermochromic development temperature range), the electron-donating color compound and the electron-accepting substance are contained in a substance (hereinafter referred to as a solid solvent) in a solution state. If a color developer is present, in practice, as described in the section of the problem to be solved by the invention described above [the solution of the dye and the developer dissolved in a solvent is applied on a transparent substrate, and further, If the structure is covered with a transparent thin plate such as a cover glass, the still characteristic is considerably improved as compared with the case where only a solid without liquid is used].

In order to create a solution state from a temperature slightly lower than the thermochromic expression temperature range, the melting point of the solid solvent needs to be lower than the thermochromic expression temperature range. Further, this solid solvent is limited to a crystalline substance because it needs to show a clear melting point. The mask layer made of a thermochromic material containing a solid solvent manufactured under the above conditions is heated by laser heating when reproducing optical disk information, and first, the solid solvent is in a liquid state near its melting point. , And the electron donating color developing compound and the electron accepting developer are dissolved in the liquid. Further, when the temperature is raised as described above, an electron reaction between the electron donating color developing compound and the electron accepting developer occurs, and the color is erased. Next, when the laser heating stops and cooling starts, an electron reverse reaction between the electron donating color developing compound and the electron accepting color developer occurs, causing coloring. Further, when cooled in this way, the melting point of the solid solvent is reached, and this solid solvent solidifies again together with the electron donating color compound and the electron accepting developer. Such a repetition of temperature rise and cooling is a still regeneration process. Even when the solid state and the liquid state are repeated in this manner, in the medium of the present invention, both the electron donating color compound and the electron accepting developer,
Since the thermal deterioration is very small, high durability reproduction characteristics can be obtained.

Next, an example in which the optical information recording medium of the present invention is applied to a ROM type optical disk and a RAM type optical disk will be described. <ROM type> In the case of a ROM type optical disk,
Concavo-convex pits serving as information signals are formed on one surface of a light-transmitting substrate in advance. On the uneven pit surface of this substrate,
A mask layer containing a thermochromic material, a reflective layer of a metal film, and a protective layer are sequentially laminated. The dielectric film is provided between the respective layers according to the purpose. The thermochromic material has a low transmittance since the absorbance is large at a temperature lower than the threshold with respect to the wavelength of the laser beam used for reproduction, and a mask layer containing the thermochromic material is provided on the uneven pits. When the laser light is incident from the substrate side, the transmitted light including the concave and convex pit information is absorbed by the mask layer and does not return as sufficient reflected light. On the other hand, at a temperature higher than the threshold, the absorbance decreases,
When the transmittance increases and the laser beam is incident from the substrate side, the transmitted light including the concave / convex pit information is returned as a sufficient reflected light without being absorbed by the mask layer. That is, at the time of reproduction, the mask layer in the central portion of the laser beam irradiation becomes higher in temperature than that of the mask layer around the laser beam irradiation by the laser heating having the Gaussian distribution. Therefore, the threshold value of this mask layer should be optimized. Accordingly, it is possible to reproduce only the concave / convex pits located at the center of the laser beam and mask the peripheral concave / convex pit information to prevent reproduction.

FIG. 1 is an enlarged sectional view showing a ROM type optical disk which is an example of the optical information recording medium of the present invention. As shown, the optical disc 1A has a light-transmitting substrate 2A made of, for example, a transparent resin, and pits, irregularities, grooves (grooves) and the like are recorded in advance on one surface of the substrate 2A as information signals. . A mask layer 3, a reflective layer 4, and a protective layer 5 are sequentially laminated on the surface on which the information signal is recorded. The substrate 2A is typically made of polycarbonate resin, polymethacrylate resin, epoxy resin, or the like.
What is used as an optical disk substrate can be used. The method for forming the pits and grooves is not particularly limited, and the pits and grooves are formed by a usual method. Various materials can be used as the thermochromic material contained in the mask layer 3. For example, a mixture of an electron donating color compound and an electron accepting developer is suitable. Examples of the electron donating color compound include a fluoran compound, a spiropyran compound, a phthalide compound, and a lactam compound. Examples of the electron-accepting developer include a phenol compound and a bisphenol compound. A solid solvent of an organic crystalline material having a melting point lower than the decoloring temperature of the thermochromic material is co-evaporated into the thermochromic material. As this solid solvent, a crystalline organic substance is suitable. Particularly, 4-diethylamino-benzaldehyde-1,1-diphenyl-hydrazone having a melting point in the range of 90 ° C. to 100 ° C. is suitable. The reflection layer 4 is the same as a reflection film material generally used for an optical disk, and includes gold, aluminum,
It consists of thin films of metals and alloys. This reflection layer 4
On top of this, a protective layer 5 is provided as necessary for the purpose of protecting the medium. This protective layer 5 can be formed by spin coating an ultraviolet curable resin.

FIG. 2 is an enlarged sectional view showing a modification of the ROM type optical disk shown in FIG. In this optical disc 1B, between the light-transmitting substrate 2A and the mask layer 3, or
Alternatively, dielectric layers 7 and 8 made of a transparent inorganic substance are provided between the mask layer 3 and the reflection layer 4. This is used according to the need for heat dissipation, light coherence, and the like. As the dielectric layers 7, 8, metal oxides, non-metal oxides, metal halides, metal sulfides and the like are mainly used. Specific examples include silicon dioxide, magnesium fluoride, zinc sulfide and the like.

<Case of RAM Type> Next, the present invention
An example in which the present invention is applied to an optical disk of the type will be described.
In the case of a RAM type optical disk, a new recording layer is added, and this recording layer is made of a phase change medium, a magneto-optical medium, and an organic write-once medium, and can be used as a RAM type or WO type optical disk. A groove serving as a guide groove is formed in advance on one surface of the light-transmitting substrate used here. A mask layer containing a thermochromic material, the recording layer, a reflective layer made of a metal film, and a protective layer are sequentially laminated on the groove surface of the light transmitting substrate.
The dielectric film is inserted between the respective layers according to the purpose. The thermochromic material contained in the mask layer,
Since the absorbance is large at a temperature lower than the threshold with respect to the wavelength of the laser beam used for optical reproduction, the transmittance is low, the recording layer is on this mask layer, and the laser beam enters from this substrate side. And the laser light hardly reaches the recording layer. Even if the reflected light containing the information of the recording layer is slightly transmitted, the light is absorbed by the mask layer again and does not return as a sufficient reflected light. On the other hand, at a temperature higher than the threshold value, the absorbance of the mask layer decreases, the transmittance increases, and when laser light is incident from the substrate side, the transmitted light containing the information of the recording layer is masked. The light is returned as sufficient reflected light without being absorbed by the layer. In other words, at the time of reproduction, the mask layer in the central portion of the light irradiation becomes higher in temperature than that of the mask layer around the light irradiation due to heating of the laser light having the Gaussian distribution, so that the threshold of the thermochromic material is optimized. By reproducing only the recorded information located at the center of the laser beam,
It is possible to mask peripheral information so as not to reproduce it.

FIG. 3 is an enlarged sectional view showing a RAM type optical disk which is another example of the optical information recording medium of the present invention.
1 and 2 are denoted by the same reference numerals and described. Optical disc 1C shown
Has a light-transmitting substrate 2C made of, for example, a transparent resin, and a groove is recorded in advance on one surface of the substrate 2C as a guide groove. The mask layer 3, the recording layer 9, the reflective layer 4, and the protective layer 5 are sequentially laminated on the surface on which the groove is formed. As the substrate 2C, those usually used as an optical disk substrate, such as a polycarbonate resin, a polymethacrylate resin, and an epoxy resin, can be used. The method of forming the groove is not particularly limited, and the groove is formed by an ordinary method. Various materials can be used as the thermochromic material contained in the mask layer 3. For example, a mixture of an electron donating color compound and an electron accepting developer is suitable. Examples of the electron donating color compound include a fluoran compound, a spiropyran compound, a phthalide compound, and a lactam compound. Examples of the electron-accepting developer include a phenol compound and a bisphenol compound. Into the thermochromic material, a solid solvent made of the same organic crystalline substance as described above, which is a feature of the present invention, is co-deposited. As this solid solvent, a crystalline organic substance is suitable. Particularly, 4-diethylamino-benzaldehyde-1,1-diphenyl-hydrazone having a melting point in the range of 90 ° C. to 100 ° C. is suitable. The recording layer 9 can be made of a phase-change material, a magneto-optical material, an organic write-once material, or the like.
AgInSbTe-based alloys and the like can be mentioned. Examples of the magneto-optical material include a TbFeCo-based material, and examples of the organic light-once material include an azo metal complex-based dye, a cyanine-based dye, and a phthalocyanine-based dye. The reflective layer 4 is similar to a reflective film material generally used for an optical disk, and is formed of a thin film of a metal or alloy such as gold, aluminum, or the like. A protective layer 5 is provided on the reflective layer 4 as needed for the purpose of protecting the medium. This protective layer 5 can be formed by spin coating an ultraviolet curable resin.

FIG. 4 is an enlarged view showing a modification of the RAM type optical disk shown in FIG. In this optical disc 1D,
Dielectric layers 7 and 8 made of a transparent inorganic substance are provided between the recording layer 9 and the mask layer 3 or between the recording layer 9 and the reflection layer 4. This is used according to the need for heat dissipation, light coherence, and the like. Mainly, metal oxides,
Non-metal oxides, metal halides, metal sulfides and the like are used. Specific examples include silicon dioxide, magnesium fluoride, zinc sulfide and the like.

Hereinafter, embodiments of the optical information recording medium according to the present invention will be described in detail. <Example 1> First, a polycarbonate resin light-transmitting substrate provided with 8/16 modulated signals as minute pits (3T mark length 0.26 μm) was injection-molded with a metal stamper. GN-2 (manufactured by Yamamoto Kasei) as an electron donating color compound, bisphenol A as an electron accepting developer, and 4-diethylamino-benzaldehyde-1,1- as a solid solvent (organic crystalline substance).
Diphenyl-hydrazone was co-deposited by a vacuum deposition method. At this time, the ratio of the GN-2, the bisphenol A and the 4-diethylamino-benzaldehyde-1,1-diphenyl-hydrazone was about 1 on a monitor. : 2: 0.1, a mask layer containing a thermochromic material with a thickness of 350 nm was formed. Next, aluminum was formed as a reflective layer on the mask layer to a thickness of 70 nm by a vacuum sputtering method. Further, as a protective film, an ultraviolet curing resin XR11 (manufactured by Sumitomo Chemical Co., Ltd.) is formed to a thickness of about 7 μm by a spinner method.
Type optical discs were produced.

The optical disk was reproduced by a player equipped with an objective lens having a numerical aperture of 0.6 and a semiconductor laser having a wavelength of 635 nm. The linear velocity for reproduction was set to 3.5 m / s, and the reproduction power was set to 1.5 to 2.0 mW. At this time, 1.
At a reproduction power of 0 mW or less, the signal could not be read because the transmittance of the mask layer did not increase. Further, to measure the signal amplitude I _14T of 14T is the signal amplitude I _3T and the longest mark 3T is the shortest mark, was determined the ratios I _3T / I _14T. As a result, in the first playback, I _3T
/ I _14T = 0.60, and at the _10,000th reproduction, I
_3T / I _{14 T} = 0.60, there was no change between the two, and it was proved that the signal quality was not degraded, and good results could be obtained.

Example 2 A light-transmitting substrate made of a polycarbonate resin provided with a groove having a track pitch of 0.74 μm as a guide groove is injection-molded with a metal stamper, and an electron-donating color is formed on the groove-formed surface. Vacuum deposition of GN-2 (manufactured by Yamamoto Kasei) as a compound, bisphenol A as an electron-accepting developer, and 4-diethylamino-benzaldehyde-1,1-diphenyl-hydrazone as a solid solvent (organic crystalline substance). At this time, the ratio of the above-mentioned GN-2, the above-mentioned bisphenol A and the above-mentioned 4-diethylamino-benzaldehyde-1,1-diphenyl-hydrazone was set to about 1: 2: 0.1 on a monitor. Then, a mask layer containing a thermochromic material with a thickness of 370 nm was formed. Next, ZnS—SiO ₂ was formed as a dielectric layer to a thickness of 75 nm on the mask layer by a vacuum sputtering method. Ag ₅ In ₅ Sb ₆₀ Te ₃₀ was formed thereon as a recording layer to a thickness of 20 nm by vacuum sputtering. Further, as a dielectric layer, Z
The nS-SiO ₂ was formed to a thickness of 17nm by vacuum sputtering. An aluminum-titanium alloy (Al _97.5 Ti _2.5 wt%) was formed thereon as a reflective layer to a thickness of 150 nm by a vacuum sputtering method. Further, a UV curable resin XR11 (manufactured by Sumitomo Chemical Co., Ltd.) is formed as a protective film to a thickness of about 6 μm by a spinner method.
A phase-change optical disk was manufactured.

The above optical disk was recorded and reproduced by a player equipped with an objective lens having a numerical aperture of 0.6 and a semiconductor laser having a wavelength of 635 nm. First, recording was performed by modulating a laser beam into a divided pulse pattern at a linear velocity of 3.5 m / s. The peak power was set at 14 mW, the erasing power was set at 7.0 mW, and the bottom power was set at 0.5 mW. The recording signal is 8/16
With modulation, the clock frequency was 38.6 MHz. Further, to measure the signal amplitude I _14T of 14T is the signal amplitude I _3T and the longest mark 3T is the shortest mark, was determined the ratios I _3T / I _14T. As a result, in the first playback, I _3T
/ I _14T = 0.50, and I
_3T / I _{14 T} = 0.50, there was no change between the two, and it was demonstrated that the signal quality was not degraded, and good results could be obtained.

<Example 3> A ROM type optical disk was manufactured and reproduced in the same manner as in Example 1 except that the ratio of the solid solvent contained in the mask layer was changed as follows. The result at this time is shown in FIG. As shown in the figure, as a result, when the weight ratio of the dye: the developer: the solid solvent (4-diethylamino-benzaldehyde-1,1-diphenyl-hydrazone) is 1: 2: 0.1, the sample number is as follows. The result with the least reproduction deterioration was obtained.

[0019]

As described above, according to the optical information recording medium of the present invention, the following excellent functions and effects can be exhibited. In the thermochromic material of the mask layer,
Since an organic crystalline substance having a melting point lower than the decoloring temperature of the material is included, the repetition characteristics of high-density optical recording and reproduction and the still reproduction characteristics can be improved, and the signal quality can be maintained high.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing a ROM type optical disk as an example of the optical information recording medium of the present invention.

FIG. 2 is an enlarged sectional view showing a modified example of the ROM type optical disk shown in FIG.

FIG. 3 is RA as another example of the optical information recording medium of the present invention.
It is an expanded sectional view showing an M type optical disk.

FIG. 4 is an enlarged view showing a modification of the RAM type optical disc shown in FIG.

FIG. 5 is a diagram showing evaluation results when an optical disk is manufactured by changing the ratio of a solid solvent.

[Explanation of symbols]

1A, 1B, 1C, 1D ... optical disk (optical information recording medium), 2A, 2C ... substrate, 3 ... mask layer, 4 ... reflection layer,
5: protective layer, 7, 8: dielectric layer, 9: recording layer.

Claims (1)

[Claims] 1. An optical information recording medium comprising a light-transmitting substrate and at least a mask layer and a reflective layer sequentially laminated on the light-transmitting substrate, wherein the mask layer is provided with a reproducing laser beam incident from the substrate side. When the temperature of the continuously irradiated portion becomes equal to or higher than the decoloring temperature, the light transmittance of a portion of the irradiated portion is increased, the light spot diameter is substantially reduced, and the reproduction laser beam is reduced. An optical disc made of a thermochromic material having a disc super-resolution function of reproducing an information signal by emitting a return light from the reflective layer side to the substrate side by emitting to the reflective layer side, wherein the thermochromic material is An optical information recording medium comprising an organic crystalline substance having a melting point lower than the decolorizing temperature of the thermochromic material.