JP2734005B2 - Rewritable optical information recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium capable of rewriting data and conforming to a compact disk format.

[Prior art] Data is recorded by irradiating a laser beam, and the recorded data can be reproduced with a laser beam having a lower power than the laser beam at the time of recording. Data can be erased with laser light that is stronger than reproduction light.
As a so-called rewritable optical information recording medium, a recording layer of a magneto-optical material such as Gd, Tb, or Fe is provided on one main surface of a substrate, and a metal layer having high reflectivity is provided on the upper surface of this layer. Further, a configuration in which a protective layer is formed on the upper surface of the metal layer is already known. The pit format formed in the recording layer in this case is a domain inversion type. Others
The pits formed in the recording layer include a type in which amorphous and crystal are repeated and a photoisomerization type of an organic material, depending on the type of recording material forming the recording layer.

[Problems to be Solved by the Invention] The rewritable optical information recording medium which has been conventionally developed or put into practical use is a compact disk player (CD player) for reproducing a compact disk (CD) which is currently most widely used. Difficult to play.

That is, the first type based on domain reversal of the magneto-optical material is a method of reproducing by reading a change in reversal rate due to the Kerr effect, but the reversal rate is low and the CD player cannot reproduce. Further, in the second type in which amorphous and crystal are repeated, the difference between the amount of reflected laser light at a pit (mark) formed on the recording layer due to a phase change and the amount of reflected light at other portions is small. For this reason, since the modulation degree of the reproduction signal is low and the disc reflectance is low, the CD
Cannot be adapted to the CD format specified for, and playback on a CD player is not possible. And the third type by photoisomerization of organic material is also the same as the type that repeats the crystal from the amorphous, and cannot satisfy the CD format for the same reason as the second type, and the CD player It is not possible to regenerate it.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to provide a rewritable optical information recording medium capable of obtaining a reproduction signal having a high reflectance and a high modulation degree of laser light conforming to the CD format. Is to provide.

[Means for Solving the Problems] That is, in order to achieve the above object, the gist of the first means adopted in the present invention is that a light transmitting layer 1 is provided between a light transmitting substrate 1 and a light reflecting layer 3 which reflects laser light. A light absorbing material that generates heat by absorbing laser light and melts, and has a softening point temperature of 50 to 15
0 ° C., the number average molecular weight is in the range of 500 to 25,000, and the recording layer 2 is mixed with a thermoplastic resin which is deformed by melting due to local heat generation of the light absorbing material. Rewritable optical information recording medium.

Further, the gist of the second means is that, in the first means, the real part n _rec of the complex refractive index of the recording layer 2 and its film thickness d _rec
And ρ = n _rec d _rec / λ given by the wavelength λ of the reproduction light is 0.05
≦ ρ ≦ 0.6 and the imaginary part k _{rec of the} complex refractive index is
A rewritable optical information recording medium characterized by being 0.3 or less.

Furthermore, the gist of the third means is that a light absorbing layer having a light absorbing material that generates heat by absorbing laser light and melts between the light transmitting substrate 1 and the light reflecting layer 3 that reflects laser light. 2a
And the softening point temperature is 50 ~ 150 ° C, the number average molecular weight is 500 ~ 2500
0, the thermoplastic resin layer 2b having a thermoplastic resin that is deformed by melting due to local heat generation of the light absorbing material of the light absorbing layer 2a, and is rewritable. An optical information recording medium.

Further, the gist of the fourth means is that, in the third means, the real part n _abs of the complex refractive index of the light absorbing layer 2a and the film thickness d
ρ = n _abs d _abs / λ given by _abs and the wavelength λ of the reproduction light is
0.05 ≦ ρ ≦ 0.6 and the imaginary part k of the complex refractive index
An rewritable optical information recording medium characterized by having _abs of 0.3 or less.

[Operation] FIGS. 2 and 3 show the concept of recording, reproducing, and erasing data on an optical information medium by the first and second means.

That is, at the time of recording, the recording layer 2 is irradiated with a converged laser beam to induce a thermal change in the light absorber of the recording layer 2 with high laser power. At this time, the light absorbing material included in the recording layer 2 changes light energy into heat energy, and at the same time, changes pressure due to melting sublimation, evaporation, and the like. The heat energy softens the thermoplastic resin contained in the recording layer 2 and, at the same time, causes a local concave deformation as shown in FIG. 3, for example, due to an increase in pressure by the light absorbing material. Thereafter, the concave deformation generated at this time is fixed as the resin cools, and remains as pits 5.

At the time of reproduction, the optical pickup 8 irradiates a laser beam 7 having such a power that the light absorbing material contained in the recording layer 2 gives only heat of a softening point or less to the thermoplastic resin from the optical pickup 8, and the recording pit 5 The data of the pit 5 is read out based on the difference between the amount of reflected light at the point and the amount of reflected light at other portions. At this time, the pit 5 is not deformed.

Further, in erasing, the recording layer 2 is irradiated with a laser beam having such a power that the light absorbing material itself generates heat in a thermally stable state and can heat the resin to the softening point or higher. At this time, no pressure increase was observed due to the light absorbing material in the recording layer 2, the thermoplastic resin component was softened, and the surface tension and the accumulated stress at the time of deformation caused the portion forming the pit 5 to be in FIG. Is restored to the state at the time of non-recording as shown by.

In the optical information recording medium according to the first and second means, a light absorbing material and a thermoplastic resin are mixed and dispersed in the recording layer 2, but these are separately formed as a light absorbing layer 2a and a thermoplastic resin layer 2b. The optical information recording medium provided by the third and fourth means is provided as a layer. Recording of data on this optical information recording medium,
The principle of reproduction and erasure is basically the same as that of the optical recording medium. That is, as shown in FIG. 6, the heat and pressure increase generated in the light absorbing layer 2a during recording softens and deforms the thermoplastic resin layer 2b in contact therewith, and the pits 5 are formed.
When data is erased in the same manner as described above, as shown in FIG.
2b is softened and deformed, and the pit 5 is restored.

The softening point temperature and the number average molecular weight of the thermoplastic resin contained in the recording layer 2 or the thermoplastic resin forming the thermoplastic resin layer 2b are limited to the above ranges for the following reasons.

That is, when the softening point temperature is lower than the above temperature range, it is difficult to maintain the pits already formed when data is repeatedly reproduced, and it is also difficult to maintain the pits 5 when the temperature of the atmosphere is high. This is because On the other hand, when the softening point temperature exceeds the above-mentioned temperature range, it is difficult to form the pits 5 at the time of recording and to erase the recorded data, and the C / N value of the reproduced signal becomes low.

On the other hand, the range of the number average molecular weight of the thermoplastic resin is also limited to the above range for substantially the same reason.
That is, when the thermoplastic resin contained in the recording layer 2 is equal to or less than the above range, it is difficult to maintain already formed pits when the optical recording medium is stored in a normal state,
This is because the recording data is broken when receiving a slight external force. On the other hand, when the number average molecular weight exceeds the above range, it is difficult to form pits 5 and erase recorded data at the time of recording, and the C / N value of the reproduced signal becomes low.

As described above, in the optical information recording medium according to the present invention in which data is recorded, reproduced, erased, and re-recorded, the pit form after recording is similar to the pit form of a CD formed by means such as a press. As a result, compared with the conventional rewritable optical information recording medium, it is possible to reproduce a signal having a high laser light reflectance and a high C / N.

Further, in the second means and the fourth means, ρ = n _rec d
_{The reason that rec} / λ or ρ = n _abs d _abs / λ is set to 0.05 ≦ ρ ≦ 0.6 and the imaginary part k _rec or k _abs of the complex refractive index is set to 0.3 or less is that the range is such that the laser beam at the time of reproduction is The reason for this is that the reflectance can be the highest, the degree of modulation of the reproduced signal is high, and the recording error is reduced.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 schematically shows the structure of an optical information recording medium according to the first and second means. That is, the recording layer 2 is formed on the translucent substrate 1 made of a resin such as polycarbonate. Further, a light reflection layer 3 made of a metal film is formed thereon, and a protective layer 4 made of a resin or the like is provided thereon, thereby forming an optical disk as shown in the figure.

As described above, the recording layer 2 is formed of a mixed material of a light absorbing material that absorbs a laser beam and a thermoplastic resin having a softening point of 50 to 150 ° C. and a number average molecular weight of 500 to 25,000. It is a layer in which these materials are uniformly dispersed.
FIG. 2 is an enlarged view of a portion A in FIG. 1 and shows a state before recording or after erasing the recording. FIG. 3 shows a recorded state of the same part.

FIG. 4 schematically shows the structure of the optical information recording medium by the third and fourth means. That is, a thermoplastic resin layer 2b made of a thermoplastic resin having a softening point temperature of 50 to 150 ° C. and a number average molecular weight in the range of 500 to 25,000 is formed on the light transmitting substrate 1 made of a resin such as polycarbonate. A light absorbing layer 2a made of a light absorbing material that absorbs laser light is formed thereon. FIG. 5 is an enlarged view of a portion B in FIG. 4, showing a state before recording or after erasing the recording. FIG. 6 shows a recorded state of the same part.

In the optical information recording medium according to the third and fourth means, the thermoplastic resin layer 2b may contain a light absorbing material. Further, a hard layer may be provided between the substrate and the reflective layer and the layer having the light absorbing material in order to prevent deformation of the substrate and the reflective layer during recording.

The softening point temperature of the thermoplastic resin forming the thermoplastic resin layer 2b is desirably 80 to 150 ° C, and the number average molecular weight is more desirably in the range of 1,000 to 20,000.

 Next, examples of the present invention will be described specifically.

(Example 1) Pellet polycarbonate (manufactured by Teijin Chemicals Limited,
Panlite), width 0.8μm depth 0.12μm pitch 1.6μ
A 1.2 mm thick translucent substrate 1 made of polycarbonate and having a spiral pre-groove of m was formed by injection molding.

To form a recording layer 2 in which a thermoplastic resin and a light absorbing material are mixed and dispersed on the substrate 1, 1.08 g of a styrene acrylic resin (softening point 105 ° C., number average molecular weight 2500) is dissolved in 30 ml of diisobutyl ketone. To this solution was added 0.542 g of 1,1 'dibutyl 3.3.3' 3 'tetramethyl 4.5.4' 5 'dibenzoindodicarbocyanine perchlorate (NK3219, manufactured by Nippon Kogaku Dyestuffs Co., Ltd.). Was applied by a spin coating method to form a recording layer 2 having a thickness of 210 nm. In this recording layer 2, ρ = 0.44, k _rec = 0.025
It is.

Next, on this recording layer 2 by a sputtering method,
A light reflecting layer 3 made of a Cu film having a thickness of 60 nm is provided, and an ultraviolet curable resin (Dai Nippon Ink Chemical Industry Co., Ltd., Die Cure Clear) is spin-coated on the light reflecting layer 3.
This was irradiated with ultraviolet rays and cured to provide a protective layer 4 having a thickness of 1 μm.

For the optical disk manufactured in this way, λ = 78
Using a 0 nm semiconductor laser, linear speed 1.2 m / sec, recording power 8.5
A 450 kHz pulse signal was recorded at mW. Insert this disc into 1.
Reproduction was performed using a 0 mW semiconductor laser, and when reflected light was detected, a reproduction signal having a CNR value of 50 dB was obtained. The reflectance at this time was 72.8%.

Next, an elliptical beam of 780 nm and 2.5 mW was applied on the recording pit.
After scanning at 1.2 m / s and erasing the above recorded data, a 720 kHz pulse signal was recorded again with a semiconductor laser having a linear velocity of 1.2 m / s and a power of 8.5 mW at a wavelength of 780 nm, and the CNR value was 48 dB.
Was obtained.

(Example 2) In Example 1, the light transmitting substrate 1 was formed of polymethyl methacrylate instead of polycarbonate, and the light reflecting layer 3 was formed of an Al film having a thickness of 60 nm. An optical disk was manufactured in the same manner as in Example 1. Note that ρ = 0.4 in the recording layer 2 of this optical disc.
4, k _rec = 0.025.

With respect to this optical disk, a pulse signal was recorded and reproduced in the same manner as in the first embodiment, and the reflected light was detected. The CNR value of the reproduced signal was 48 dB and the reflectance was 70.
5%. Next, after erasing the recorded data in the same manner, when the pulse signal was recorded again, a reproduced signal having a CNR value of 48 dB was obtained.

Example 3 In Example 1, the thickness of the recording layer 2 was set to 130 nm, and a 100 nm thick S layer was formed between the recording layer 2 and the light reflecting layer 3.
An optical disk was manufactured in the same manner as in Example 1 except that the iO ₂ layer was formed by a sputtering method, and the light reflection layer 3 was formed of a 60-nm-thick Au film. Note that ρ = 0.44 and k _rec = 0.02 in the recording layer 2 of this optical disk.
5

With respect to this optical disk, a pulse signal was recorded at a recording power of 8.5 mW in the same manner as in the first embodiment, its reproduction was performed, and the reflected light was detected.
The value was 50 dB, and the reflectance was 76.5%. Next, after similarly erasing the recorded data, a pulse signal was recorded again at a recording power of 8.5 mW, and a reproduced signal having a CNR value of 47 dB was obtained.

(Example 4) In Example 1, a 50-nm-thick SiO ₂ layer was formed between the light-transmitting substrate 1 and the optical recording layer 2 by a sputtering method, and the light-absorbing material contained in the recording layer 2 was used. As 0.
261 g of 1,1'-diethyl 3,3,3 ', 3'tetramethylindotricarbocyanine perchlorate (NK2885, manufactured by Nippon Kogaku Dyestuffs Co., Ltd.) was added. Except that a 100 nm thick SiO ₂ layer was formed between the recording layer 2 and the light reflecting layer 3 by sputtering, and the light reflecting layer 3 was formed of a 60 nm thick Ag film. An optical disk was manufactured in the same manner as in Example 1. Note that ρ in the recording layer 2 of this optical disk is
0.22, k _rec = 0.200.

For this optical disk, a pulse signal was recorded at a recording power of 9.0 mW in the same manner as in the first embodiment, and the pulse signal was reproduced and the reflected light was detected.
The value was 48 dB and the reflectance was 70.4%. Next, after similarly erasing the recorded data, a pulse signal was recorded again at a recording power of 9.0 mW, and a reproduced signal having a CNR value of 45 dB was obtained.

(Example 5) In Example 1 described above, a light absorbing material was added to a coating agent in which a thermoplastic resin for forming the recording layer 2 was dissolved in an amount of 0.1.
An optical disc was manufactured in the same manner as in Example 1 except that 360 g was added and the thickness of the recording layer 2 was set to 140 nm. Note that ρ and k in the recording layer 2 of this optical disc are
rec is ρ and k _rec is ρ = 0.32 and k _rec = 0.020.

For this optical disc, a pulse signal was recorded at a recording power of 10.0 mW in the same manner as in the first embodiment, and the pulse signal was reproduced and the reflected light was detected.
The value was 48 dB and the reflectance was 74.4%. Next, after similarly erasing the recorded data, a pulse signal was recorded again at a recording power of 10.0 mW, and a reproduced signal having a CNR value of 48 dB was obtained.

(Example 6) In Example 1, a light absorbing material was added to a coating agent in which a thermoplastic resin for forming the recording layer 2 was dissolved.
An optical disk was manufactured in the same manner as in the above example except that 08 g was added and the thickness of the recording layer 2 was 140 nm.
Note that ρ and k rec in the recording layer 2 of this optical disc are
Is ρ = 0.38 and k _rec = 0.030.

For this optical disc, a pulse signal was recorded at a recording power of 7.5 mW in the same manner as in the first embodiment, and the pulse signal was reproduced and the reflected light was detected.
The value was 54 dB and the reflectance was 70.3%. Next, after similarly erasing the recorded data, a pulse signal was recorded again at a recording power of 7.5 mW, and a reproduced signal having a CNR value of 45 dB was obtained.

(Example 7) In Example 1, the light absorbing material was added to the coating agent in which the thermoplastic resin for forming the recording layer 2 was dissolved.
An optical disk was manufactured in the same manner as in Example 1 except that 16 g was added and the thickness of the recording layer 2 was changed to 140 nm. Note that ρ and k in the recording layer 2 of this optical disc are
rec is ρ = 0.41 and k _rec = 0.040.

With respect to this optical disk, a pulse signal was recorded at a recording power of 7.0 mW in the same manner as in the first embodiment, the signal was reproduced, and the reflected light was detected.
The value was 55 dB and the reflectance was 70.9%. Next, after similarly erasing the recorded data, a pulse signal was recorded again at a recording power of 7.0 mW, and a reproduced signal having a CNR value of 42 dB was obtained.

(Example 8) In Example 1, 1.08 g of a polyamide resin (softening point: 105 ° C, number average molecular weight: 1500) was dissolved and used as a thermoplastic resin to be contained in the recording layer 2. An optical disk was manufactured in the same manner as in Example 1 except that the thickness was 130 nm. Note that ρ and k rec in the recording layer 2 of this optical disk are ρ = 0.37 and k _rec = 0.026.

For this optical disc, a pulse signal was recorded at a recording power of 10.5 mW in the same manner as in the first embodiment, and the pulse signal was reproduced. When the reflected light was detected, the CNR of the reproduced signal was measured.
The value was 50 dB, and the reflectance was 73.2%. Next, after similarly erasing the recorded data, a pulse signal was recorded again at a recording power of 10.5 mW, and a reproduced signal having a CNR value of 49 dB was obtained.

Example 9 In Example 1, polypropylene (softening point 130 ° C., number average molecular weight 3000) was used as the thermoplastic resin contained in the recording layer 2, and the film thickness of the recording layer 2 was 140 nm. An optical disk was manufactured in the same manner as in Example 1 except that the light reflecting layer 3 was formed of a Cu film having a thickness of 60 nm. Note that ρ and k rec in the recording layer 2 of this optical disk are ρ = 0.35 and k _rec = 0.026.

For this optical disc, a pulse signal was recorded at a recording power of 10.0 mW in the same manner as in the first embodiment, and the pulse signal was reproduced and the reflected light was detected.
The value was 49 dB and the reflectance was 72.4%. Next, after similarly erasing the recording data, a pulse signal was recorded again at a recording power of 10.0 mW, and a reproduced signal having a CNR value of 47 dB was obtained.

Example 10 A 1.2 mm-thick polycarbonate substrate (Panlite, manufactured by Teijin Chemicals Limited) having a spiral pre-groove having a width of 0.8 μm, a depth of 0.12 μm, and a pitch of 1.6 μm was formed by injection molding. .

On this substrate, 0.52 g of a polyamide resin (softening point: 105 ° C., number average molecular weight: 1500) was dissolved in 20 ml of butanol, and this was spin-coated on the substrate 1 to form a 50 nm-thick thermoplastic resin layer 2b. Formed.

Furthermore, 1.1 'dibutyl 3.3.3' 3 'tetramethyl 4.5.
195 mg of 4'5 'dibenzoindodicarbocyanine iodide (NK3251 manufactured by Nippon Kosaku Dyeing Co., Ltd.) was dissolved in 3 ml of 2-nitropropane, and the solution was applied on the plastic resin layer 2b to give a film thickness of 130 nm. The light absorbing layer 2a was formed. Ρ and k rec in this light absorbing layer 2a are ρ = 0.45, k _abs = 0.50
It is.

Next, on this light absorbing layer 2a, as a light reflecting layer 3, a film thickness is formed.
A 60 nm Ag film is formed by vacuum evaporation, and then a UV curable resin (Dainichi Ink Chemical Co., Ltd., Dicure Clear) is spin-coated on the upper surface, and cured by irradiating UV light onto the resin. A 10 μm protective layer was provided.

For the disc created in this way, λ = 780n
m semiconductor laser, linear speed 1.2m / sec recording power 11.5m
A 450 kHz pulse signal was recorded at W. This disc was read with a semiconductor laser with a recording power of 1.0 mW and a wavelength of 780 nm, and when reflected light was detected, the CNR value was 52 dB.
Was obtained. The reflectance at this time is 71.5
%Met.

A 780nm 2.5mW elliptical beam over this recording pit is 1.2m / s
After erasing the recorded data, the linear velocity is again 1.2m
/ s, recording power 11.5mW, wavelength 780nm semiconductor laser, 720
When a kHz pulse signal was recorded, a reproduced signal having a CNR value of 51 dB was obtained.

Example 11 In Example 10, the translucent substrate 1 was formed of polymethyl methacrylate instead of polycarbonate, and 1.1 ′ dibutyl 3.3.3 ′ 3 ′ tetra as a light absorbing material for forming the light absorbing layer 2a. Methyl 4.5.4'5 'Same as Example 1 except that dibenzoindodicarbocyanine perchlorate (NK3219, manufactured by Nippon Kogaku Dyestuffs Co., Ltd.) was used, and that the light reflecting layer 3 was formed of an Au film. The optical disk was manufactured. The optical absorption layer of this optical disk
Ρ and k rec in 2a are ρ = 0.46 and k _abs = 0.05.

With respect to this optical disc, a pulse signal was recorded at a recording power of 11.0 mW in the same manner as in Example 10 above, the reproduction was performed, and the reflected light was detected.
The value was 53 dB and the reflectance was 72.0%. Next, after similarly erasing the recorded data, a pulse was recorded again at a recording power of 11.0 mW, and a reproduced signal having a CNR value of 50 dB was obtained.

Example 12 In Example 13, a 100-nm-thick SiO ₂ layer was formed between the light absorbing layer 2a and the light reflecting layer 3 by a sputtering method, and the light reflecting layer 3 was formed of a Cu film. An optical disk was manufactured in the same manner as in Example 10 except for the above.

With respect to this optical disc, a pulse signal was recorded at a recording power of 12.5 mW in the same manner as in Example 10 above, and the pulse signal was reproduced, and the reflected light was detected.
The value was 48 dB and the reflectance was 75.6%. Next, after similarly erasing the recording data, a pulse signal was recorded again at a recording power of 12.5 mW, and a reproduced signal having a CNR value of 46 dB was obtained.

(Example 13) A polycarbonate substrate (Panlite, manufactured by Teijin Chemicals Ltd.) having a thickness of 1.2 mm and a spiral pregroove having a width of 0.8 μm, a depth of 0.12 μm, and a pitch of 1.6 μm was formed by injection molding. .

Dissolve 0.75 g of polyamide resin in 20 ml of butanol,
Further, Rhodamine B was added thereto and spin-coated on the substrate 1 to form a thermoplastic resin layer 2b having a thickness of 70 nm.

Furthermore, 1.1 'dibutyl 3.3.3' 3 'tetramethyl 4.5.
150 mg of 4'5 'dibenzoindodicarbocyanine iodide (NK3251 manufactured by Nippon Kogaku Dyestuffs Co., Ltd.) is dissolved in 3 ml of 2-nitropropane, applied on the above-mentioned plastic resin layer 2b and coated with a light having a thickness of 95 nm. The absorption layer 2a was formed.

Next, on this light absorbing layer 2a, as the light reflecting layer 3, a film thickness of 60
nm of Cu is deposited by vacuum evaporation, and then an ultraviolet curable resin (Dai Nippon Ink Chemical Industry Co., Ltd., Die Cure Clear SD-17) is spin-coated thereon, and this is irradiated with ultraviolet light. It was cured and a 10 μm protective layer was provided.

For the optical disk manufactured in this way, λ = 78
Using a semiconductor laser of 0 nm, linear velocity 1.2 m / sec, recording power 1
A 450 kHz pulse signal was recorded at 0.5 mW. The disc was reproduced with a 1.0 mW, 780 nm semiconductor laser, and the reflected light was detected. As a result, a reproduced signal having a CNR value of 52 dB was obtained. The reflectance at this time was 69.5%.

The recorded pit is scanned with a 780nm 2.5mW circular beam at 1.2m / s to erase the recorded data, and then re-enter the linear velocity.
When a pulse signal of 72.0 kHz was recorded at the previous recording position using a 780 nm wavelength semiconductor laser having a recording power of 10.5 mW and a recording power of 1.2 m / s, a reproduced signal having a CNR value of 47 dB was obtained.

[Effects of the Invention] As described above, according to the present invention, compared with the conventional rewritable optical information recording medium, it is possible to obtain a higher laser light reflectance and a higher C / N reproduction signal. Thus, a writable optical information recording medium conforming to the CD format is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an enlarged half-section of an optical disk showing an embodiment of the present invention, and FIG. 2 is a view showing a portion A in FIG. 1 before recording or after data is erased. FIG. 3 is a schematic enlarged sectional view of the same part after recording, and FIG. 4 is a half-sectional schematic perspective view of an optical disc showing another embodiment in an enlarged thickness direction. 5 and FIG. 5 are schematic enlarged sectional views showing the part B of FIG. 4 before recording or after data erasure, and FIG. 6 is a schematic enlarged sectional view of the same part after recording. 1 ... Transparent substrate, 2 ... Recording layer, 2a ... Light absorbing layer, 2b
... Thermoplastic resin layer, 3... Light reflection layer, 4.
5 ... pit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Arai 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Yuden Co., Ltd. (72) Inventor Ariake Shin 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Yuden (56) References JP-A-61-176924 (JP, A) JP-A-63-37995 (JP, A) JP-A-59-232896 (JP, A) JP-A-62-30090 (JP, A A)

Claims (4)

(57) [Claims] A light absorbing material that generates heat by absorbing laser light and melts between a light-transmitting substrate (1) and a light reflecting layer (3) that reflects laser light, and a softening point temperature. A recording layer (2) mixed with a thermoplastic resin having a number average molecular weight of 50 to 150 ° C. and a number average molecular weight in a range of 500 to 25,000, and being deformed by melting due to local heat generation of the light absorbing material; A rewritable optical information recording medium characterized by the above-mentioned. 2. The method according to claim 1, wherein ρ = n _rec d _rec given by the real part n _rec of the complex refractive index of the recording layer (2), its thickness d _rec and the wavelength λ of the reproduction light. / λ is 0.05 ≦ ρ
A rewritable optical information recording medium, wherein ≦ 0.6 and the imaginary part k _rec of the complex refractive index is 0.3 or less. 3. A light-absorbing layer having a light-absorbing material that generates heat by absorbing laser light and melts between a light-transmitting substrate (1) and a light-reflecting layer (3) that reflects laser light. 2a), heat that has a softening point of 50 to 150 ° C. and a number average molecular weight in the range of 500 to 25000, and is deformed by melting due to local heat generation of the light absorbing material of the light absorbing layer (2a). A rewritable optical information recording medium, comprising a thermoplastic resin layer (2b) having a thermoplastic resin. 4. The method according to claim 3, wherein ρ = n _abs d given by the real part n _abs of the complex refractive index of the light absorbing layer (2a), its thickness d _abs and the wavelength λ of the reproduction light. _abs / λ is 0.05
≦ ρ ≦ 0.6 and the imaginary part k _{abs of the} complex refractive index is
A rewritable optical information recording medium characterized by being 0.3 or less.