JPH0375942B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a writable optical information recording medium having at least a light absorption layer and a reflection layer on a transparent substrate, and a method for recording information thereon.

[Conventional technology]

A so-called writable optical information recording medium, which can record data by irradiation with laser light, has a recording layer consisting of a metal layer such as Te, Bi, Mn, etc., or a pigment layer such as cyanine, merocyanine, phthalocyanine, etc. Data is recorded by forming pits by deforming, sublimating, vaporizing, or modifying the recording layer by irradiating it with laser light. In optical information recording media having this recording layer, voids are generally provided behind the recording layer in order to facilitate deformation, sublimation, evaporation, denaturation, etc. of the recording layer when forming pits. . Specifically, for example,
A stacked structure called an air sandwich structure is used in which two substrates are stacked with a space in between.

In this optical information recording medium, pits are formed by irradiating laser light from the side of the transparent substrate 1. When playing back the recorded data,
A laser beam having a weaker power than during recording is irradiated from the substrate 1 side, and the signal is read based on the difference in reflected light between the pit and other parts.

On the other hand, so-called ROM type optical information recording media, on which data is recorded in advance and cannot be subsequently written or erased, have already been widely put into practical use in the information processing and audio sectors. This type of optical information recording medium is
Without the above-mentioned recording layer, pits for reproducing recorded data are formed in advance on a polycarbonate substrate by means such as pressing, and then Au,
A reflective layer made of a metal film such as Ag, Cu, Al, etc. is formed, and this is further covered with a protective layer.

The most typical ROM-type optical information recording medium is the compact disk, or so-called CD, which is widely used in audio and information processing departments.
The recording and playback signal specifications for this CD are so-called CD
The format has been standardized, and playback devices that comply with this format are compact disc players (CD
It is extremely popular as a player).

Each of the above-mentioned optical information recording media takes the form of a disk, that is, an optical disk, having a hole in the center for clamping to a rotating shaft.

[Problem to be solved by the invention]

The optical information recording medium mentioned above is a recording means that uses the same laser beam as a CD, so when playing back,
It is highly desirable to comply with CD, which is already widely used.

However, the former optical information recording medium is CD
It has a recording layer that is not found in CDs, and it also has a void layer etc. to make it easier to form pits in this recording layer, so the reflectance of laser light is lower than that of CDs. For this reason, it is difficult to satisfy the above-mentioned CD format, which defines standards for so-called CDs. Therefore, in the past, it has not been possible to provide a writable optical information recording medium that is compatible with CDs.

The present invention has been made in order to solve the above-mentioned conventional problems, and has a high reflectance of 70% or more, and can write data so that an output signal with a modulation degree compliant with the CD format can be obtained when reproducing data. The purpose is to provide a possible optical information recording medium.

[Means to solve the problem]

That is, in order to achieve the above object, the gist of the means adopted in the present invention is to provide an optical information recording medium in which at least a light absorption layer and a reflection layer are sequentially formed on a light-transmitting substrate. Real part of refractive index nabs, film thickness dabs, and wavelength λ of reproduction light
ρ=nabs・dabs/λ given by is 0.05≦ρ
≦0.6, and the imaginary part of the complex refractive index of the light absorption layer
The present invention provides an optical information recording medium having a kabs of 0.3 or less, and an optical information recording method using the same, in which a laser absorption layer is irradiated with laser light from the transparent substrate side to form pits.

The light absorption layer may be formed in a part of the light-transmitting substrate, and the region without the light absorption layer may be used as a ROM region in which pits for signal reproduction are formed in advance.

[Effect]

The present inventors have developed an optical information recording medium in which a light-absorbing layer made of an organic dye and a light-reflecting layer made of a metal are provided on a light-transmitting substrate. In order to obtain a reproduced signal with I11/Itop of 0.6 or more and I3/Itop of 0.3 to 0.7, the real part of the complex refractive index nabs of the light absorption layer of the optical information recording medium and its film thickness dabs must be
and the wavelength λ of the reproduction light, ρ=nabs・
Focusing on the fact that dabs/λ is a very important parameter, we conducted experiments and simulations on this point, and as a result we were able to obtain the relationship shown in Figure 7. Figure 7 shows the wavelength λ as the reproduction light.
= Using 780nm semiconductor laser light as a reflective layer
When using a light absorption layer made of Au and having a certain value of k, the real part nabs of the complex refractive index of the light absorption layer of the optical information recording medium, its film thickness dabs, and the wavelength λ of the reproduction light are It is a graph showing the relationship between the given ρ=nabs·dabs/λ and the reflectance of light incident from the substrate side.

Looking at this graph, it can be seen that when ρ is smaller than 0.6, it is almost certainly possible to secure a reflectance of 70% or more. Areas where ρ is less than 0.05,
Even in a region exceeding 0.6, a reflectance of 70% or more may be obtained. However, if ρ is less than 0.05, the thickness of the light absorption layer dabs should be 0.05 μm.
Since it has to be made considerably thinner, it is difficult to form pits for recording data, and the reproduction signal as described above cannot be obtained. Also,
In the case of a region exceeding 0.6, it becomes difficult to control the film thickness to be uniform, leading to variations in recording characteristics, resulting in practical problems such as I3/Itop falling below 0.3 and jitter errors increasing. The problem arises. That is, by setting ρ to 0.05 to 0.6,
It can be seen that the reflectance can be increased to 70% or more, which is compliant with the CD format.

Furthermore, as a result of further examination of these results, the inventors found that simply setting ρ within the range of 0.5 to 0.6 does not necessarily guarantee a stable output signal as specified in the CD standard. We found that kabs is an important parameter. 8th
The figure shows the results when the imaginary part kabs is changed from a value close to 0 to 2.0 while changing the translucency of the light absorption layer and keeping ρ constant in an optical information recording medium that uses an Au film for the reflective layer. It is a graph showing changes in reflectance.

Looking at this graph, it can be seen that the closer kabs is to 0, the higher the reflectance. Based on the results of experiments and simulations, the present inventors have found that in order to maintain a stable high reflectance with ρ in the range of 0.5 to 0.6, the light-absorbing layer must have sufficiently high transparency. Imaginary part of the complex refractive index of the same layer
We found that kabs needs to be less than 0.3. If ρ is within the range of 0.05 to 0.6 and kabs is greater than 0.3, it is difficult to ensure a reflectance of 70% or more.

From these results, results as shown in FIG. 9 can be obtained. FIG. 9 is a graph showing the critical values of combinations of ρ and kabs that conform to the CD standard.

As can be seen from this graph, in order to provide an optical information recording medium that can obtain recording signals compliant with the CD standard, ρ=nabs・dabs/λ must be 0.05.
It can be seen that it is necessary that the value be in the range of ~0.6 and that kabs be 0.3 or less.

Furthermore, in order to obtain a sufficient degree of modulation, ρ=nabs・dabs/λ is preferably in the range of 0.1 or more, and in order to obtain stable recording characteristics with a large degree of modulation, the range of 0.45±0.1 is desirable. This is the most desirable range.

Furthermore, the kabs of the optical information recording medium of the present invention are
If it is 0.3 or less, the closer it gets to 0, the better the reflectance will be. Therefore, this range is most desirable. However, the closer it gets to 0, the worse the recording sensitivity becomes, so it is necessary that it be larger than 0.
Specifically, a range of 0.01 or more is desirable, and in fact, around 0.05 is desirable.

Note that the content of the present invention is applicable even when there are other layers. For example, if a transparent layer (for example, an enhancement layer such as SiO2, an undercoat layer, etc.) is provided between the substrate and the light absorption layer, this layer may be treated as a part of the substrate, and it may be treated as a part of the light absorption layer. If a layer is provided between the reflective layer (for example, an adhesive layer, a hard layer, etc.), consider these layers as the second absorbing layer, treat them as ρ = (nl・dl+n ₂・d ₂ )/λ, and calculate the In the case of layers, ρ=Σ(ni・di)/λ (however,
(i is an integer), it can be handled in the same way even if there are multiple layers.

Further, when k is not 0, it can be handled in the same way as in the case of a single layer by calculating the average value k from the ratio of film thicknesses as k=1/ΣdiΣdiki.

Further, when a groove is formed on the substrate, dabs is expressed as the average value of the film thickness of the light absorption layer in the groove and the film thickness of the light absorption layer in the land portion.

In an optical information recording medium that has a ROM area in which the light absorption layer is formed in a part of the light-transmitting substrate and pits for signal reproduction are formed in the area without the light absorption layer, the ROM area is A large amount of uniform data can be recorded in advance using a press or the like, and since there is no light absorption layer, there is no risk of erroneous erasure or erroneous recording of other data. Further, in the area having the light absorption layer, user's own data can be arbitrarily recorded. Since this recorded data can be played back with a signal that complies with the CD standard, similar to the information in the ROM area mentioned above, it can be played back using commercially available
It can be played on a CD player.

Note that the above effect is not limited to disk-shaped recording media, but can be similarly considered in card-shaped or tape-shaped optical information recording media.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

Examples of the schematic structure of the optical information recording medium according to the present invention are shown in FIGS. 1 to 3 and 4 to 6. In these drawings, 1 is a light-transmitting substrate, 2 is a light absorption layer formed thereon,
This layer absorbs the irradiated laser beam, generates heat, melts, evaporates, sublimates, deforms, or denatures, and has the function of forming pits on the surface of the light absorption layer 2 and the substrate 1. 3 is a reflective layer formed thereon;
4 indicates a protective layer provided on the outside thereof.

1 to 3 show cases in which the light absorption layer 2 is formed on almost the entire surface of the transparent substrate 1, but in FIGS. 4 to 6, the light absorption layer 2 is formed on almost the entire surface of the transparent substrate 1. In this case, the light absorption layer 2 is formed only in a part near the outer periphery, and this becomes the recordable area 11, and the ROM area 10 is formed in the part on the inner periphery side.

Preferred specific examples will be described below.

The material of the transparent substrate 1 is preferably a highly transparent material with a refractive index in the range of 1.4 to 1.6 with respect to laser light, and a resin with excellent impact resistance. Specific examples include polycarbonate, acrylic, etc., but are not limited to these.

The substrate is molded using the materials described above, for example, by injection molding or the like.

A pregroove may be formed in a spiral shape on such a substrate. The pre-group may be formed under any condition as long as it is normally considered, but a depth of 50 to 250 nm is preferable.

The pregroove is usually formed by pressing a stamper during injection molding of the substrate.

A melt-resistant layer or an enhancement layer such as SiO ₂ may be coated between the substrate 1 and the light absorption layer.

The material for the light absorption layer 2 is preferably a light-absorbing organic dye, such as a cyanine dye, a polymethine dye, a triarylmethane dye, a pyrylium dye, a phenanthrene dye, a tetradehydrocholine dye, a triarylamine dye, a squarylium dye, or a crocodile dye. Examples include dyes, phthalocyanine dyes, azulenium dyes, etc., but the present invention is not limited to these, and the effects of the present invention can also be obtained using known recording layer materials such as low melting point metals.

Note that the light absorption layer 2 may contain other dyes, resins (for example, thermoplastic resins such as nitrocellulose, thermoplastic elastomers), liquid rubber, and the like.

The light absorption layer 2 is a light-transmitting substrate on which pregrooves are formed, or a substrate in which the above-mentioned dye and optional additives are dissolved and solvated in a known organic solvent (for example, alcohol, acetylacetone, toluene, etc.). It is formed on the surface of a substrate that has other layers coated on top.

Formation methods in this case include vapor deposition method, LB method,
Examples include a spin coating method, but the spin coating method is preferable because the layer thickness can be controlled by adjusting the concentration, viscosity, and drying rate of the solvent of the light absorption layer.

In addition, the ROM area 10 as shown in FIGS. 4 to 6
In the optical information recording medium, pits 9 for signal reproduction (see FIG. 5) are formed in advance on the surface of the transparent substrate 1 in a portion that will become the ROM area 10 using a stamper, etc., and the outside of the pits 9 are recordable. It is obtained by coating only the region 11 with the above material to form the light absorption layer 2.

The reflective layer 3 is preferably a metal film, such as gold,
Silver, aluminum or alloys containing these,
It is formed by a method such as a vapor deposition method or a sputtering method.
Since it is necessary for the optical information recording medium to have a reflectance of 70% or more, it is desirable to form the optical information recording medium from a metal mainly composed of gold or an alloy containing gold. moreover,
Other layers such as an oxidation-resistant layer may be interposed to prevent oxidation of the reflective layer.

Note that it is desirable that the layer on the reflective layer side of the light absorption layer has a higher thermal deformation temperature and higher hardness than the layer on the substrate side. This configuration is effective in reducing the block error rate of recording signals.

It is desirable that the protective layer 4 be formed of a resin with excellent impact resistance. For example, it is formed by applying an ultraviolet curable resin using a spin coating method and curing it by irradiating it with ultraviolet rays. Alternatively, it may be formed of an elastic material such as urethane.

The optical information recording medium according to the present invention is not limited to one in which pits are formed in the light absorption layer 2 by irradiating the light absorption layer 2 with laser light. For example, if a layer closer to the reflective layer than the light absorbing layer is formed with a layer that is less susceptible to thermal deformation than a layer closer to the substrate 1, the energy of the light absorbing layer 2 caused by the laser beam will be transferred to the layer closer to the substrate 1. As a result, convex, wavy or concave pits are formed in the layer on the substrate 1 side.

In the case of this embodiment, as schematically shown in FIGS. 3 and 5, pits protruding toward the absorption layer are formed on the surface of the optical disc after recording, which is in contact with the light absorption layer 2 of the substrate 1. 5 can be confirmed, and it is known that the reproduced waveform of the pit 5 thus formed is similar to that of a CD.

Reproduction of the recorded signal is performed by irradiating a reading laser from the substrate side and reading the optical phase difference between the reflected light from the pit portion and the reflected light from the portion other than the pit.

A specific example of this configuration will be described below.

Example 1 A polycarbonate substrate 1 having a thickness of 1.2 mm, an outer diameter of 120 mmφ, and an inner diameter of 16 mmφ on which a spiral pre-group with a width of 0.8 μm, a depth of 0.08 μm, and a pitch of 1.6 μm was formed was molded by injection molding.

As an organic dye to form a light absorption layer,
0.65g of 1,1'dibutyl 3,3,3',3'tetramethyl 4,5,4',5'dibenzoindodicarbocyanine perchlorate (manufactured by Nippon Kanko Shiki Co., Ltd., product number
NK3219) was dissolved in 10 c.c. of diacetone alcohol solvent, and this was applied onto the above substrate 1 by spin coating to form a light absorption layer 2 consisting of a dye film with a thickness of 0.13 μm. The complex refractive index of this light absorption layer 2 is nabs=2.7 and kabs=0.05. As described later, the wavelength λ of the semiconductor laser of the reproduction light is
The wavelength is 780 nm, and ρ=nabs·dabs/λ=0.45.

An Au film with a thickness of 600 angstroms was formed on the entire surface of this disk by sputtering method.
A reflective layer 3 was formed. The complex refractive index of this reflective layer 3 is nref=0.16 and kref=4.67. Furthermore, an ultraviolet curable resin is spin-coated on this reflective layer 3, and is cured by irradiating ultraviolet rays to increase the thickness.
A protective layer 4 of 10 μm was formed.

A semiconductor laser with a wavelength of 780 nm was applied to the optical disk obtained in this way at a linear velocity of 1.2 m/sec and a recording power.
It was irradiated with 6.0 mW and the EFM signal was recorded. and,
Insert this optical disc into a commercially available CD player (Aurex
Reproduction was performed using XR-V73 (reproduction light wavelength λ = 780 nm). The reflectance of this optical disc is 72%, I11/Itop
was 0.65, and I3/Itop was 0.35.

The CD standard requires a reflectance of 70% or more and an I11/Itop of
0.6 or more, I3/Itop is defined as 0.3 to 0.7,
The optical disk according to this embodiment satisfies this standard.

Example 2 0.5g of 1,1'diethyl 3,3,3',
A solution of 3'tetramethyl 5,5'diethoxyindodicarbocyanine iodide in 10 c.c. of isopropyl alcohol solvent is applied by spin coating to form a light absorption layer 2 consisting of a dye film with a thickness of 0.10 μm. Formed. The complex refractive index of this light absorption layer 2 is
nabs=2.65, kabs=0.05, and ρ=nabs・
dabs/λ=0.34.

A Cu film with a thickness of 500 angstroms was formed on the entire surface of this disk by sputtering method.
A reflective layer 3 was formed. The complex refractive index of this reflective layer 3 is nref=0.12 and kref=4.89. Furthermore, an ultraviolet curable resin is spin-coated on this reflective layer 3, and is cured by irradiating ultraviolet rays to increase the thickness.
A protective layer of 10 μm was formed.

A semiconductor laser with a wavelength of 780 nm was applied to the optical disk obtained in this way at a linear velocity of 1.2 m/sec and a recording power.
It was irradiated with 6.0 mW and the EFM signal was recorded. and,
This optical disc was played on the same CD player used in Example 1 above. As a result, the reflectance of the optical disk was 71%, I11/Itop was 0.63, and I3/Itop was
It was 0.33. Therefore, the optical disc according to this embodiment also satisfies the CD standard like the above embodiment.

Example 3 A film with a thickness of 900 angstroms was applied to a polycarbonate substrate 1 molded in the same manner as in Example 1 above.
A GaAs film was formed by a sputtering method to form a light absorption layer 2. The complex refractive index of this light absorption layer 2 is nabs=3.6, kabs=0.07, and ρ=nabs・
dabs/λ=0.42.

An Ag film with a thickness of 550 angstroms was formed on the entire surface of this disk by sputtering method.
A reflective layer 3 was formed. The complex refractive index of this reflective layer 3 is nref=0.086 and kref=5.29. Furthermore, an ultraviolet curable resin is spin-coated on this reflective layer 3, and is cured by irradiating ultraviolet rays to increase the thickness.
A protective layer of 10 μm was formed.

A semiconductor laser with a wavelength of 780 nm was applied to the optical disk obtained in this way at a linear velocity of 1.2 m/sec and a recording power.
It was irradiated with 6.0 mW and the EFM signal was recorded. and,
This optical disc was played on the same CD player used in Example 1 above. As a result, the reflectance of the optical disk was 73%, I11/Itop was 0.63, and I3/Itop was
It was 0.35. Therefore, the optical disc according to this embodiment also satisfies the CD standard like the above embodiment.

Example 4 A 1.2 mm thick spiral pre-group with a width of 0.5 μm, a depth of 0.15 μm, and a pitch of 1.6 μm was formed.
A polycarbonate substrate 1 having an outer diameter of 120 mmφ and an inner diameter of 15 mmφ was molded by injection molding.

As an organic dye for forming a light absorption layer, 0.050 g of the same dye as in Example 1 and nitrocellulose were used.
0.005 g was dissolved in 10 c.c. of isopropyl alcohol solvent, and this was applied onto the above substrate 1 by spin coating to form a light absorption layer 2 consisting of a dye film with an average thickness of 0.025 μm. The complex refractive index of this light absorption layer 2 is nabs=2.0 and kabs=0.04. The wavelength of the semiconductor laser for reproduction light is λ = 780 nm, and ρ =
nabs・dabs/λ=0.064.

A film with a thickness of 500 mm is coated on the entire surface of this disk using a vapor deposition method.
A reflective layer 3 was formed by depositing an angstrom-thick Au film. The complex refractive index of this reflective layer 3 is nref=
0.16, kref=4.67. Furthermore, this reflective layer 3
An ultraviolet curable resin was spin-coated on top of the resin and cured by irradiating ultraviolet rays to form a protective layer 4 with a thickness of 10 μm.

EFM was applied to the thus obtained optical disk using a semiconductor laser with a wavelength of 780 nm as in Example 1.
The signal was recorded and played back on a commercially available CD player.
The reflectance of this optical disc is 82%, and I11/Itop is
0.60, I3/Itop is 0.31, and the optical disc according to this embodiment satisfies the CD standard.

Example 5 1,1′ dibutyl 3,3,3′,3′ tetramethyl 5,6,5 0.050 g of ′,6′ tetramethoxy indodicarbocyanine perchlorate and 0.005 g of nitrocellulose were dissolved in 10 c.c. of diacetone alcohol solvent, and this was applied onto the above substrate 1 by spin coating to form a film. A light absorption layer 2 made of a dye film with a thickness of 0.020 μm was formed. The complex refractive index of this light absorption layer 2 is nabs = 2.0, kabs = 0.29, the wavelength of the semiconductor laser of the reproduction light is λ = 780 nm, and ρ =
nabs・dabs/λ=0.051.

A film with a thickness of 500 mm is coated on the entire surface of this disk using a vapor deposition method.
A reflective layer 3 is formed by depositing an angstrom-thick Au film, and then an ultraviolet curable resin is spin-coated on the reflective layer 3 and cured by irradiating ultraviolet rays to form a protective layer 4 with a thickness of 10 μm. was formed.

EFM was applied to the thus obtained optical disk using a semiconductor laser with a wavelength of 780 nm as in Example 1.
The signal was recorded and played back on a commercially available CD player.
The reflectance of this optical disc is 70%, and I11/Itop is
0.61, I3/Itop is 0.30, and the optical disc according to this embodiment satisfies the CD standard.

Example 6 In the range of diameter 46 to 100 mmφ (ROM area 10),
A pre-pit 8 is molded that can reproduce a spiral CD format signal with a width of 0.6 μm, a depth of 0.10 μm, and a pitch of 1.6 μm, and the outer diameter is 100 to 117 mmφ.
(recordable area 11), width 0.7μm, depth
0.07μm, pitch 1.6μm spiral pre-group formed, thickness 1.2mm, outer diameter 120mmφ, inner diameter
A polycarbonate substrate 1 with a diameter of 15 mm was molded by injection molding.

As an organic dye for forming a light absorption layer, 0.8 g of the same dye as in Example 1 was added to an acetylacetone solvent.
10c.c. and apply this to the above substrate 1 with a diameter of 100mm.
Coating is performed only on the outer peripheral side of φ, that is, on the recordable area 11, by the spin coat method, and the film thickness is
A light absorption layer 2 consisting of a 0.17 μm dye film was formed.
The complex refractive index of this light absorption layer 2 is nabs=2.7,
kabs=0.05. The wavelength of the semiconductor laser for reproduction light is 780 nm, and ρ=nabs·dabs/λ=0.59.

A film with a thickness of 500 mm is coated on the entire surface of this disk using a vapor deposition method.
A reflective layer 3 is formed by depositing an angstrom-thick Au film, and then an ultraviolet curable resin is spin-coated on the reflective layer 3 and cured by irradiating ultraviolet rays to form a protective layer 4 with a thickness of 10 μm. was formed.

As in Example 1, an EFM signal was recorded in the recordable area of the optical disc thus obtained using a semiconductor laser with a wavelength of 780 nm, and the ROM area and the recordable area were reproduced with a commercially available CD player. The reflectance of the recordable area of this optical disc is
70%, I11/Itop is 0.62, I3/Itop is 0.32,
Reflectance of ROM area is 90%, I11/Itop is 0.80,
I3/Itop was 0.50. Therefore, in the optical disc according to this embodiment, both the ROM area and the recordable area satisfy the CD standard.

Example 7 In the range of diameter 46 to 100 mmφ (ROM area 10),
A pre-pit 8 is formed that can reproduce a spiral CD format signal with a width of 0.6 μm, a depth of 0.10 μm, and a pitch of 1.6 μm, and its outer diameter is 100 to 117 mmφ.
(recordable area 11), width 0.5μm, depth
Thickness 1.2mm, outer diameter 120mmφ, inner diameter 15mm with spiral pre-loop of 0.18μm and pitch 1.6μm formed.
A polycarbonate substrate 1 having a diameter of φ was molded by injection molding.

As an organic dye to form a light absorption layer,
1,1'diethyl3,3,3',3'tetramethyl5,
Dissolve 0.55 g of 7,5',7' tetramethoxy indodicarbocyanine perchlorate in 10 c.c. of diacetone alcohol solvent, and add this to the diameter of substrate 1 above.
The light absorbing layer 2 made of a dye film with an average thickness of 120 nm was formed by applying it by spin coating only on the portion on the outer peripheral side of 100 mmφ, that is, on the recordable area 11. The complex refractive index of this light absorption layer 2 is nabs=
2.9, kabs=0.20. The wavelength of the semiconductor laser for reproduction light is λ = 780 nm, and ρ = nabs・dabs/λ
=0.45.

A film with a thickness of 500 mm is coated on the entire surface of this disk using a vapor deposition method.
A reflective layer 3 is formed by depositing an angstrom-thick Au film, and then an ultraviolet curable resin is spin-coated on the reflective layer 3 and cured by irradiating ultraviolet rays to form a protective layer 4 with a thickness of 10 μm. was formed.

An EFM signal was recorded on the above-mentioned recordable area of the thus obtained optical disc using a semiconductor laser having a wavelength of 780 nm as in Example 1, and the ROM area and the recordable area were reproduced using a commercially available CD player. The reflectance of the recordable area of this optical disc is
70%, I11/Itop is 0.70, I3/Itop is 0.40,
The reflectance of the ROM area, I11/Itop, and I3/Itop were the same as in Example 6 above. Therefore, in the optical disc according to this embodiment, both the ROM area and the recordable area satisfy the CD standard.

Comparative Example 1 0.065 g of the same organic dye as in Example 1 was added to polycarbonate substrate 1 molded in the same manner as in Example 1 above.
was dissolved in 10 c.c. of isopropyl alcohol solvent and applied by spin coating.
A light absorption layer 2 consisting of a 0.01 μm dye film was formed.
ρ in this optical disk is nabs・dabs/λ
=0.035.

An Al film with a thickness of 600 angstroms was formed on the entire surface of this disk by sputtering method.
A reflective layer 3 was formed. The complex refractive index of this reflective layer 3 is nref=1.87 and kref=7.0. Furthermore, an ultraviolet curable resin is spin-coated on this reflective layer 3, and is cured by irradiating it with ultraviolet rays to increase the thickness.
A protective layer of 10 μm was formed.

An attempt was made to record an EFM signal on the optical disc thus obtained by irradiating a semiconductor laser with a wavelength of 780 nm at a linear velocity of 1.2 m/sec, but sufficient recording was not possible even with a recording power of 10 mW. Then, this optical disk was used in the same way as that used in Example 1 above.
Played on a CD player. As a result, the reflectance of the optical disk is 70%, but I11/Itop is 0.20 and I3/Itop is 0.20.
Itop was 0.08. In other words, even if kabs is 0.3 or less, if ρ is less than 0.05, it may be possible to secure a reflectance of 70%, but the modulation depth will not be adequate and the CD standard will not be satisfied. I understand.

Comparative Example 2 1.3 g of the same organic dye as in Example 1 was added to a polycarbonate substrate 1 molded in the same manner as in Example 1 above.
A solution dissolved in 10 c.c. of isopropyl alcohol solvent was applied by spin coating to form a light absorption layer 2 consisting of a dye film with a thickness of 0.26 μm. In this optical disc, ρ=nabs·dahs/λ=0.90.

An Au film with a thickness of 600 angstroms was formed on the entire surface of this disk by sputtering method.
A reflective layer 3 was formed. Further, an ultraviolet curable resin was spin-coated on this reflective layer 3, and was cured by irradiating ultraviolet rays to form a protective layer with a thickness of 10 μm.

A semiconductor laser with a wavelength of 780 nm was applied to the optical disk obtained in this way at a linear velocity of 1.2 m/sec and a recording power.
It was irradiated at 6.0 mV and the EFM signal was recorded. and,
This optical disc was played on the same CD player used in Example 1 above. As a result, the reflectance of the optical disc is 62%, I11/Itop is 0.60, I3/Itop
was 0.30, the eye pattern of the reproduced signal was not clear, and a lot of air was observed. From this result, it can be seen that even if kabs is 0.3 or less, if ρ is larger than 0.6, the reflectance becomes low and the CD standard cannot be satisfied.

Comparative Example 3 0.58 g of 1,1' diethyl 3,3,3',
3'Tetramethylindotricarbocyanine perchlorate (manufactured by Nippon Kanko Shiki Co., Ltd., product number NK2885)
was dissolved in 10 c.c. of isopropyl alcohol solvent and applied by spin coating.
A light absorption layer 2 consisting of a 0.12 μm dye film was formed.
The complex refractive index of this light absorption layer 2 is nabs=2.7,
kabs=1.6, and ρ=nabs·dabs/λ=0.42.

An Ag film with a thickness of 600 angstroms was formed on the entire surface of this disk by sputtering method.
A reflective layer 3 was formed. Further, an ultraviolet curable resin was spin-coated on this reflective layer 3, and was cured by irradiating ultraviolet rays to form a protective layer with a thickness of 10 μm.

A semiconductor laser with a wavelength of 780 nm was applied to the optical disk obtained in this way at a linear velocity of 1.2 m/sec and a recording power.
It was irradiated with 6.0 mW and the EFM signal was recorded. and,
When this optical disc was played on the same CD player used in Example 1 above, the reflectance was very small.
10% and could not be played. As described above, even if ρ is within the range of 0.05 to 0.6, if kabs is larger than 0.3, the reflectance becomes extremely low and the CD standard cannot be satisfied.

〔Effect of the invention〕

As explained above, according to the optical information recording medium according to the present invention, the reflectance is 70% in accordance with the CD standard.
The above is also expressed as the modulation degree. I11/Itop
It is possible to obtain an output signal with I3/Itop of 0.6 or more and I3/Itop of 0.3 to 0.7.

[Brief explanation of drawings]

FIG. 1 is a schematic half-sectional perspective view showing an example of the structure of an optical information recording medium, FIG. 2 is a sectional view of a main part of the optical information recording medium, and FIG. 3 is a diagram showing the optical information recording medium after recording. 4 is a schematic half-section perspective view showing another example of the structure of the optical information recording medium, FIG. 5 is a sectional view of section A of the same optical information recording medium, and FIG.
FIG. 7, a cross-sectional view of part B after recording of the optical information recording medium, shows that ρ=
A graph showing an example of the relationship between nabs・dabs/λ and reflectance, FIG. 8 is a graph showing the relationship between the imaginary part kabs of the complex refractive index and reflectance, and FIG. 9 is a graph showing an example of the relationship between ρ=
It is a graph showing the area that satisfies the CD standard in nabs/dabs/λ and kabs. 1...Substrate, 2...Light absorption layer, 3...Reflection layer,
4...protective layer, 10...ROM area, 11...recordable area.

Claims (1)

[Claims] 1. In an optical information recording medium in which at least a light absorption layer and a reflection layer are sequentially formed on a light-transmitting substrate, the real part nabs of the complex refractive index of the light absorption layer, the film thickness dabs, and reproduction ρ= given by wavelength λ of light
An optical information recording medium characterized in that nabs·dabs/λ satisfies 0.05≦ρ≦0.6, and the imaginary part kabs of the complex refractive index of the light absorption layer is 0.3 or less. 2. In claim 1, the light-absorbing layer is formed in a part of the transparent substrate,
An optical information recording medium having a ROM area in which pits for signal reproduction are formed in advance in an area without a light absorption layer. 3. In a method for recording information on an optical information recording medium in which at least a light absorption layer and a reflection layer are sequentially formed on a light-transmitting substrate, the real part nabs of the complex refractive index of the light absorption layer, the film thickness dabs, and the reproduction ρ=nabs・dabs/λ given by the wavelength λ of light is 0.05≦ρ≦
0.6, and the imaginary part of the complex refractive index of the light absorption layer
1. An optical information recording method using an optical information recording medium having a kabs of 0.3 or less, which comprises irradiating a laser absorption layer with laser light from the transparent substrate side to form pits.