JPS6325092A - Optical recording medium - Google Patents

Abstract

PURPOSE:To form a durable optical recording medium requiring no independent reflection layer composed of inorganic compounds, by employing a specific phthalo/naphthalocyanine coloring matter in a recording layer of an optical recording medium containing an organic coloring material film as a recording layer and controlling the thickness of the recording layer properly. CONSTITUTION:An optical recording medium comprises a recording layer of a thickness of 50-400n containing phthalo/naphthalocyanine coloring matter shown by the general formula (I) and a reflection layer composed of an inorganic compound. (In the formula, M represents a metal oxide or a metal halide, L1, L2, L3, L4 are respectively non-substituted benzene rings or benzene rings having at least one hydrocarbon groups of carbon number 1-12.) The total quantity of phthalo/naphthalocyanine coloring matter in the recording layer and another mixable coloring matter is at least 80-100wt%, preferably 90-100wt%, and most preferably 95-100wt%.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an optical recording medium that can be additionally recorded using a focused beam of a semiconductor laser. The present invention relates to an optical recording medium used for recording.

[Prior art]

The above-mentioned recordable optical recording medium includes a recording medium having an inorganic recording layer made of a thin film of a low-melting metal such as tellurium, a tellurium alloy, and a bismuth alloy, and, for example, U.S. Pat.
A recording medium having a phthalocyanine dye film as a recording layer as disclosed in No. 75 has been proposed.

However, these recording media have low productivity because they require formation of the recording layer in a vacuum using vacuum evaporation, sputtering, etc., and media with inorganic recording layers have high thermal conductivity of the recording layer. has a limit in terms of recording density. Furthermore, since these use toxic substances such as tellurium, there are concerns about toxicity. On the other hand, for media with a recording layer made of phthalocyanine dye, the optical properties of the recording layer do not match the oscillation wavelength of the semiconductor laser, so a so-called shift treatment, which is a process in which the recording film obtained by ordinary vapor deposition is exposed to heat or organic solvent vapor, is performed. However, this shifting process is complicated and requires a long process time of 1 to 72 hours, so it has not been put to practical use.

In order to solve the above-mentioned problems, a medium in which a recording film is formed by a coating method using a soluble organic dye has been proposed. A method of applying an organic dye that absorbs in water and is soluble in an organic solvent using a spin coding method has been developed, and some of it has been put into practical use.

However, among the dyes proposed so far,
For example, media with recording layers made of cyanine dyes or squalium dyes have poor durability. Furthermore, since the pigment film alone, such as a dithiol metal complex, has an essentially low reflectance, a separate reflective layer made of an inorganic compound such as a metal thin film or a metal oxide thin film is required.

In addition, Japanese Patent Application Laid-open No. 61-25886 discloses that an alkyl-substituted naphthalocyanine dye is used to coat A on a substrate or a recording film.
A two-layer structure medium provided with a reflective layer of jl is disclosed. Furthermore, for example, U.S. Pat. No. 4,492.750 relates to a medium using an alkyl-substituted naphthalocyanine dye, but in this patent, a reflective layer such as ^l is provided on a substrate of glass or polymethyl methacrylate. The solution was then treated with organic solvent vapor. An optical recording medium provided with an optical recording layer composition in which alkyl-substituted naphthalocyanine dye particles having a particle size of , oosμ to 0.1μ are dispersed in a resin binder is disclosed. In this way, it is not possible to form a recording layer made of an organic dye directly on the substrate, and it is necessary to form a reflective layer made of an inorganic compound such as A1 on the substrate separately from the recording layer using a vacuum process such as vapor deposition. Therefore, the manufacturing process of the optical recording medium becomes more complicated. What is even more problematic is that organic pigment films inherently have low thermal conductivity, so they are expected to provide high recording performance, but metallic or inorganic pigment films with high thermal conductivity When a reflective layer is provided, due to the high thermal conductivity of the metallic reflective layer,
Thermal energy generated by the writing laser beam irradiated onto the recording layer is dissipated through the metal reflective layer and is not effectively used to form pits (irregularities corresponding to signals), resulting in a significant reduction in recording quality. It is to put it away. Furthermore, when a reflective layer made of an inorganic compound such as A1 is provided, if a laser beam for recording or reading signals is irradiated from the substrate side, even if the substrate itself is transparent, the laser beam The beam is blocked by a metal reflective layer that does not substantially transmit light and does not reach the recording layer. Therefore, if a reflective layer is provided, signals cannot be recorded or reproduced through the substrate, and the recording This has to be done from the layer side. In such a case, even slight dust or scratches on the surface of the recording layer greatly interfere with normal recording and reproduction of signals made up of unevenness. Therefore, for practical use, an overcoat or the like is required as a protective layer on the recording layer. If it is possible to record and reproduce signals by irradiating a laser beam through a transparent substrate, the presence of dust and scratches on the side where the laser beam enters, that is, on the medium surface before the laser beam is focused, will be eliminated from the substrate. A protective layer is not necessary because it does not substantially affect the recording and reproduction of signals due to the gap equivalent to the thickness of The recording layer is coated with an organic dye, which is highly durable and allows signals to be recorded and reproduced without the need for a separate reflective layer made of an inorganic compound. It has been desired to develop an optical recording medium formed as a.

[Basic idea]

The inventors of the present invention have conducted intensive studies to improve the above-mentioned drawbacks of optical recording media with an organic dye film as a recording layer. By controlling the thickness of the layer to an appropriate thickness, it not only has durability that could not be achieved with conventional optical recording media using organic dyes, but also because the recording layer itself has the function of a reflective layer. In addition, the present invention was completed by discovering that an optical recording medium can be formed that does not require a separate reflective layer made of an inorganic compound as in the prior art.

[Disclosure of the invention]

That is, the present invention essentially consists of a recording layer provided on a transparent substrate and a cough recording plate, and the recording layer has the following general formula (T) (where M is a metal or a metal oxide). or represents a metal halide, L, LX, 1, Ls is an unsubstituted benzene ring or a benzene ring having a hydrocarbon group having 1 to 12 carbon atoms (hereinafter referred to as unsubstituted or substituted benzene ring), or Unsubstituted naphthalene ring or 1 carbon number
Represents a naphthalene ring having ~12 hydrocarbon groups (hereinafter referred to as unsubstituted or substituted naphthalene ring), 1,
At least one of LX, Ls, and L4 is an unsubstituted or substituted benzene ring, and at least one is an unsubstituted or substituted naphthalene ring, and further bonded to the benzene ring and naphthalene ring in one molecule. The recording layer has a thickness of 50 to 400r+n+ and is made of an inorganic compound, and contains a phthalo/naphthalocyanine dye represented by (the total number of carbon atoms in all hydrocarbon groups is 17 or more). An optical recording medium capable of recording and reading signals without having a reflective layer is provided.

The transparent substrate used in the optical recording medium of the present invention preferably has a light transmittance of 85% or more for writing and reading signals, and has small optical anisotropy. For example, acrylic resin, polycarbonate resin, allyl resin, polyester resin, polyamide resin, vinyl chloride resin, polyvinyl ester resin,
Preferred examples include plastics such as epoxy resins and polyolefin resins, and glass.

Among these, plastics are particularly preferred from the viewpoints of mechanical strength of the substrate, ease of providing guide grooves, address signals, etc., and economic efficiency.

The shape of these transparent substrates may be plate-like or film-like, or may be circular or card-like.

Note that the thickness is not particularly specified, but is about 50μ ~
Approximately 5 mm is preferable. Of course, the surface may have a guide groove indicating a recording position, an unevenness for an address signal, etc. Such a guide groove, an address signal, etc. may be added when making a substrate by injection molding or casting, or It can also be applied by applying an ultraviolet curing resin or the like thereon, overlapping it with a stand bar, and exposing it to ultraviolet light.

In the present invention, on such a substrate, a compound of the following general formula (where M represents a metal, a metal oxide or a metal halide, L, Lg, Li L4 is an unsubstituted benzene ring or a carbon Benzene ring having 1 to 12 hydrocarbon groups (hereinafter referred to as unsubstituted or substituted benzene ring) or unsubstituted naphthalene ring or having 1 to 1 carbon atoms
Represents a naphthalene ring having two hydrocarbon groups (hereinafter referred to as unsubstituted or substituted naphthalene ring), 1, Lg
, Li, 1, at least one is an unsubstituted or substituted benzene ring, and at least one is an unsubstituted or substituted naphthalene ring, and further bonded to the benzene ring and naphthalene ring in one molecule. The recording layer contains a phthalo/naphthalocyanine dye having a total number of carbon atoms in all hydrocarbon groups of 17 or more.

Specific examples of hydrocarbons having 1 to 12 carbon atoms bonded to the benzene ring or naphthalene ring in the phthalo/naphthalocyanine dye represented by general formula (4) and general formula (I) used in the recording layer in the present invention as methyl,
Ethyl, n-propyl, 1so-propyl, n-butyl, 1so-butyl, 5ec-butyl, tert-butyl, n-amyl, tso-amyl, 5ec-amyl, te
rt-amyl, n-hexyl, tso-hexyl, 1-
Methyl-1-ethylpropyl, 1,1-dimethylbutyl, n-heptyl, tert-heptyl, octyl, 2-
Examples include alkyl groups such as ethylhexyl, nonyl, decyl, and dodecyl, alkenyl groups such as vinyl and allyl, and substituted phenyl groups such as phenyl, tolyl (methylphenyl), and xylyl (dimethylphenyl).

On the other hand, as a specific example of M in the phthalo/naphthalocyanine dye represented by general formula (4) and general formula (I), C
Group Ib metals of the periodic table such as u; Mg,, Cas
Group III metals such as Srs Zn and Cd; Al,
Group III metals such as Ga, In, 11; G3
Group ■ metals such as 5Sn, Pbs Ti; Sb
Group ■ metals such as , Bi, V, Nb, Ta; Group ■ metals such as Se, Te, Crs MO% 't4; Group ■ metals such as Mn, Tc; Fe,
Co+ Ni+ Ru, Rh, Pd, Os, r
Examples include group II metals such as r+ Pt, and halides such as oxides, chlorides, bromides, and iodides of these metals. These metals, metal oxides, and metal halides are usually divalent, but may be a mixture of monovalent and trivalent, or may form a dimer via oxygen. formula(
In the phthalo/naphthalocyanine dye of 1), L++
L*+ 1 and L4 consist of an unsubstituted or substituted benzene ring or an unsubstituted or substituted naphthalene ring as described above, but from the viewpoint of the absorption wavelength of the dye film, 1, Lt, C2. It is preferable that two or more of L4 consist of the above-mentioned unsubstituted or substituted naphthalene rings, and it is most preferable that all three of them consist of the above-mentioned unsubstituted or substituted naphthalene rings.

In the present invention, the total number of carbon atoms in all hydrocarbon groups in one molecule of hydrocarbon groups having 1 to 12 carbon atoms bonded to the benzene ring or naphthalene ring is 17 or more, This is preferred from the viewpoint of the solubility of the phthalo/naphthalocyanine dye of the present invention in solvents.

Furthermore, when the number of carbon atoms in the substituent exceeds 12, the reflectance of the recording layer containing the substituent becomes low, which is not preferable. In addition,
The position where this hydrocarbon group is bonded is not particularly limited, and may be any position on the benzene ring or naphthalene ring. Preferred in terms of absorption and reflection, especially VO41
0, In, In-Cf, In-Br, AI! −(t
l, Af-Br.

Ga-CI+Ga-Br+Aj! -0-AI
, Ga-0-Ga, and In-0-In are preferred.

The phthalo/naphthalocyanine dye used in the present invention can be produced by a known method.

For example, naphthalocyanine dyes are disclosed in JP-A-60-23
No. 451, Zh, Obs, Khtm, 42,696-6
It can be synthesized according to the known method disclosed in 99 (19T2) and the like.

In order to fix (form) the recording layer on the transparent substrate in the optical recording medium of the present invention, for example, phthalo/naphthalocyanine dyes can be fixed by methods such as vacuum evaporation, sputtering, and ion blating. Since the method (2) requires complicated operations and is inferior in productivity, a so-called coating method is most preferred.

To fix the recording layer by coating, a dye solution consisting of the above-described phthalo/naphthalocyanine dye and an organic solvent described below is brought into contact with the substrate to fix the dye on the substrate. There is a method in which the dye liquid is allowed to flow down, or after the surface of the substrate is brought into contact with the liquid level of the dye liquid and then pulled up, the excess liquid is removed while rotating the substrate. There are methods such as letting it flow down onto the substrate. If necessary, forced drying may be performed after this. The organic solvent used in this case may be a conventional solvent that dissolves phthalo/naphthalocyanine dyes, such as benzene, toluene, xylene, ethylbenzene, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, acetylacetone, ethyl acetate, butyl acetate, amyl acetate, cellosolve. , methyl cellosolve, butyl cellosolve, cellosolve acetate,
Examples include diglyme, chloroform, carbon tetrachloride, methylene chloride, methylchloroform, trichlene, and dimethylformamide. In selecting a solvent, it is preferable to use a solvent that does not damage the guide grooves on the transparent substrate in addition to the solubility of the dye.

The concentration of the dye solution in the present invention varies depending on the type of solvent and coating method, but is usually 0.1 to 10% by weight, preferably 0.3X to 5% by weight. At this time, in the present invention, in order to increase the reflectance of the recording film and improve the sensitivity,
It is also possible to mix other soluble dyes into the dye solution within a range that does not impede the effects of the present invention, for example in a range of approximately 50% of the total amount of dyes used. Examples of dyes that can be used in combination include already known aromatic or unsaturated aliphatic group 7 diamine metal complexes, aromatic or unsaturated aliphatic dithiol metal complexes, tert-butylphthalocyanine, and those already proposed by the present applicant. Special application 1986-285
No. 826, Japanese Patent Application No. 1982-285827, Japanese Patent Application No. 1983-
Soluble phthalocyanine dyes disclosed in Japanese Patent Application No. 60-4537 and Japanese Patent Application No. 1983
Examples include soluble naphthalocyanine dyes, polymethine dyes, squalium dyes, naphthoquinone dyes, and anthraquinone dyes disclosed in Japanese Patent Application No. 116592, JP-A-60-186659, and Japanese Patent Application No. 60-195763. It will be done.

In the present invention, when forming a recording film, in order to improve the smoothness of the recording film and to reduce defects such as pinholes, the fukuro/naphthalocyanine dye of the present invention and, if necessary, the phthalo/naphthalocyanine dye, are used. In a solution with other dyes, soluble resins such as nitrocellulose, ethylcellulose, acrylic resin, polystyrene, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyvinyl butyral, polyester resin, leveling agents, antifoaming agents, etc. Additives may be added. However, if large amounts of these resin binders or additives are added, the reflectance of the recording layer may decrease, or the dye may not be dissolved uniformly in the recording film and may become dispersed. However, the recording quality decreases and the reflectance also decreases.For these reasons, the amount of the resin and additives added is less than 20% by weight, preferably 10% by weight or less, in the recording layer.
More preferably, it is 5% by weight or less. In particular, the amount of the resin binder in the recording layer is preferably less than 20% by weight.In other words, in the present invention, the total amount of the dyes that can be used in combination with the phthalo/naphthalocyanine dye in the recording layer as described above. The amount is at least 80% by weight to 10
0% by weight, preferably 90% to 100% by weight, more preferably 95% to 100% by weight.

Regarding the optical recording medium of the present invention, as described above, it is preferable to record and reproduce signals using a laser beam (light beam irradiated from the substrate side) passing through a transparent substrate. In such a case, if the thickness of the recording layer becomes too thick, the writing light will be absorbed and attenuated considerably as it passes through the thick recording layer. Therefore, the amount of light on this surface is insufficient, the temperature rise is insufficient, and the formation of unevenness corresponding to the signal cannot be achieved satisfactorily, resulting in a decrease in the intensity of the signal, or even if it can be recorded somehow. However, the S/N value (signal-to-noise ratio) value when reading out the signal is too small to be put to practical use.

On the other hand, if the thickness of the recording layer is too thin, as will be described later, a sufficient reflectance in the recording layer cannot be obtained due to light interference, and therefore a large S/N value cannot be obtained.

Therefore, it is necessary to form a recording layer with an appropriate thickness, and the thickness of the recording layer in the optical recording medium of the present invention is preferably 50 to 400 nm, more preferably 60 to 250 nm.

There are various methods for measuring film thickness, and it is quite difficult to obtain accurate measured values. It is preferable to use Note that it is particularly difficult to measure the film thickness when there are guide grooves on the substrate;
It is also possible to use the film thickness obtained when the dye is fixed on a substrate that does not have e) as a substitute.

The most characteristic feature of the present invention is that the recording layer formed in this way has a fairly high reflectance, and therefore the recording layer itself also functions as a reflective layer. It is something that we have at the same time.

Therefore, the optical recording medium of the present invention is capable of controlling the focus of a laser beam when recording or reading signals without providing any reflective layer made of an inorganic compound such as a metal thin film, metal oxide, or metal alloy thin film as in the past. This makes it possible to control the writing position of signals.

Generally, to write a signal on an optical recording medium, a laser beam is irradiated with a focused laser beam on the recording layer.

The dye in the recording layer in the irradiated area absorbs the laser beam and generates heat, which changes the quality of the recording layer, forms irregularities, and changes the reflectance, thereby performing writing. This change in reflectance is
Signals are read out by detection with a laser beam, but if the change in reflectance is small relative to -g, the signal-to-noise ratio (S/N) is undesirably small.

However, what should be noted here is that the mode in which the reflectance of the optical recording medium changes when recording is performed, that is, the way in which the reflectance changes when unevenness is formed, depends on the optical recording medium. This is completely different depending on the configuration of the recording layer. For example, in the case of a medium consisting of two layers, a light-reflecting layer and a light-absorbing layer, as disclosed in US Pat. No. 4,219,826, unevenness is formed in the light-absorbing layer. The covered reflective layer is exposed, and therefore the reflectance of the uneven portion increases after recording. Therefore, in such a case, it is sufficient that the initial reflectance (that is, before the unevenness is formed) is such that the laser beam can be controlled.

On the other hand, as in the present invention, the recording layer having a reflective layer is a so-called monolayer that serves as both a light reflective layer and a light absorbing layer.
), the situation is completely opposite,
Due to the formation of irregularities, the reflectance of that portion decreases. That is, the reflectance of the uneven portion becomes lower than the unique reflectance that the recording layer originally had. In such a case, in order to obtain a large S/N value, the original reflectance through the substrate is at least 10% or more, preferably 15% or more in the state before the signal is written.

However, the reflectance changes depending on the film thickness due to interference of reflected light from the front and back sides of the recording layer. This 10%
A reflectance of preferably 15% or more can be easily achieved by using the dye of the present invention and appropriately selecting the thickness of the recording layer. In this case, the reflectance is measured using light of the same wavelength as the emission wavelength of the semiconductor laser used for recording and reproduction, and the recording layer is fixed on a transparent substrate that does not have any unevenness such as guide grooves. Measurements were taken through a transparent substrate using a spectrophotometer with attached equipment.

The amount of resin binder is 40-99% by weight, preferably 60% by weight as disclosed in U.S. Pat.
In the region where the amount is ~90% by weight, the dye is not uniformly dissolved in the binder and the dye particles become dispersed, so unless organic solvent vapor treatment is performed, the spectral characteristics of the dye will not match the emission wavelength of the laser. On the other hand, in the case of the present invention, where the amount of resin binder is much lower, from 0 to less than 20% by weight, it is surprisingly difficult to use organic solvent vapor treatment despite using similar dyes. We discovered that it has large absorption in the laser emission wavelength range even if it is not used. The exact reason for this is unknown, but it is probably because the state of association between dye molecules or the crystal structure varies greatly depending on the amount of resin binder.An even more significant feature of the present invention is that the resin binder (
It is also possible to form the recording layer using substantially only the phthalo/naphthalocyanine dye.

Usually, when a film made of an organic dye alone is formed by vacuum evaporation, the resulting film is inferior in mechanical strength. Therefore, the mechanical strength of the pigment film has been improved by adding a large amount of resin as Pai Goo to the organic pigment, but the specific pigment of the present invention has a much smaller amount of binder or all (or no binder). It was found that a recording film made of phthalo/naphthalocyanine dye alone has sufficient mechanical strength to be used as an optical recording medium.

When putting the optical recording medium of the present invention into practical use, an antireflection layer may be provided to improve the S/N value, or an ultraviolet curing resin or the like may be coated on the recording layer for the purpose of protecting the recording layer. It is also possible to use a combination of methods such as pasting a protective sheet on the recording layer surface, or pasting two sheets together with the recording layer surfaces facing inside, but it is preferable to create an air gap on the recording layer when pasting them together. .

In addition, the laser beam used for recording and reading in the present invention has a wavelength of 730 to 870 nm, preferably 75 nm.
It is a semiconductor laser with an emission wavelength of 0 to 860 nm. For example, when recording at 5 m/s, the laser output on the substrate surface should be about 4 mW = 12 mW, and the read output should be about 1710 during recording.
It may be about 0.4 mW to 1.2 mW.

[Preferred form for carrying out the invention]

Hereinafter, preferred embodiments of the present invention will be explained with reference to Examples.

Example 1 (1) A phthalo/naphthalocyanine vanadyl consisting of an average of one Lert-butylbenzene ring and three tert-hexyl-naphthalene rings per molecule was placed in the center of an acrylic resin plate with a thickness of 1.25+ am and a diameter of 200 mm. After dropping a solution consisting of 1 part by weight of the dye and 99 parts by weight of chloroform, the acrylic resin plate was rotated at a speed of 200 rpm for 15 seconds. Next, this acrylic resin plate was dried in an atmosphere of 40° C. for 10 minutes to fix a recording layer substantially consisting only of the above-mentioned phthalo/naphthalocyanine vanadyl dye to the acrylic resin plate. The thickness of this recording layer was 110 nm when measured in cross section using a microscope.

The reflectance of light having a wavelength of 810 nm through the acrylic resin plate was 19%.

(2) How to make a semiconductor laser with an oscillation wavelength of 810 nm and an output of 81 at the substrate surface by placing the optical recording medium made on a turntable with the recording layer facing up and rotating it at a speed of 600 rpm. A 1 MHz pulse signal (duty 50%) is applied to the optical recording medium using an optical head that controls the laser beam to be focused from the bottom side of the optical recording medium, that is, from the substrate side, onto the recording layer through the acrylic resin plate.
Using the same device as the one used for recording, the output of the semiconductor laser was set to 0.71 on the substrate surface, and the recorded signal was reproduced in the same manner. At this time, the signal-to-noise ratio (S/
N) could perform extremely good signal writing and reading at 51 decibels.

(3) 60°C to check the durability of this optical recording medium.
After being left in an atmosphere of 90XRH for 4 months, signals were recorded on the red recording section in the same manner as above, and the signals recorded before the durability test and the signals recorded after the durability test were played back. S of 50.51 decibels respectively
/N was obtained, and the change due to the durability test was sufficiently small.

, (4) The shape of the pits in the signal recording area after the durability test was observed using a scanning electron microscope, and the pits recorded before and after the durability test were almost the same. The shape of the optical recording medium, which has a recording layer made of an inorganic thin film such as a Te-based film, has a high thermal conductivity, so there is almost no bulging at the edges of the focus, which is thought to be a cause of noise, and the focus is very clear. It was the shape.

Example 2, Comparative Example 1 Using an acrylic plate with a thickness of 1.2 mm and a diameter of 120 mm, a phthalo/naphthalocyanine dye consisting of one free or substituted benzene ring and a substituted naphthalocyanine ring shown in Table 1 and a solvent were used. An optical recording medium having a recording layer consisting essentially only of phthalo/naphthalocyanine dyes was prepared in the same manner as in Example 1 by using carbon tetrachloride and varying the dye concentration, and the reflectance and S/N were examined. The results are summarized in Table 1.

It is clear from Table 1 that the S/N value is 47 to 53 dB in all the examples of the present invention, whereas
In the comparative example, only 30 to 35 dB L was obtained. Normally, the S/N value required for optical recording media is at least 45 dB.
Based on the above, it can be seen that the comparative example cannot be put to practical use as a recording medium at all.

Example 3, Comparative Example 2 An acrylic resin plate with a thickness of 1.2 mm and a diameter of 120 mm, a four-layer plate consisting of the dye used in Example 1 as a dye and a resin binder of the type and amount shown in Table 2. An optical recording medium was prepared in the same manner as in Example 2 using a carbon chloride solution. The thickness and reflectance of the recording layer are
Signals were recorded and reproduced in the same manner as in Example 2 using this medium with zero orders summarized in the table. The results are summarized in Table 2.

In Comparative Example 2 (experiment numbers 12 to 14) in Table 2, recording was impossible. In other words, it was possible to control the focus of the laser beam during recording, and the formation of physical irregularities was observed;
It was not possible to extract the signal during playback (reading). In the comparative example, this is because the binder (resinu
s binder) is much larger than in the embodiments of the present invention, the initial reflectance is originally as small as 7 to 9%.
This seems to be because even though the unevenness is formed, the amount of decrease in reflectance caused by this is small, and therefore a change in reflectance that can be taken out as a signal is obtained.

〔Effect of the invention〕

In the optical recording medium of the present invention, since the recording layer itself has sufficient reflectance, signals can be written and read without providing a reflective layer such as a thin metal film or a thin metal oxide film.
Moreover, since the reflectance is large, a large S/N ratio can be obtained. Furthermore, the shape of the bit in the recording section shows no raised edges, which confirms that a large S/N ratio can be obtained and at the same time indicates the possibility of improving the recording density.

The optical recording medium of the present invention can be easily mass-produced by a coating method, is stable against heat and humidity, and can be used for a long period of time.

Claims (5)

[Claims] (1) It is substantially composed of a transparent substrate and a recording layer provided on the recording plate, and the recording layer has the following general formula (I) (where M is a metal, a metal oxide, or a metal oxide). Represents a halide, and L_1, L_2, L_3, and L_4 are unsubstituted benzene rings or benzene rings having one or more hydrocarbon groups having 1 to 12 carbon atoms (hereinafter referred to as unsubstituted or substituted benzene rings). or represents an unsubstituted naphthalene ring or a naphthalene ring having one or more hydrocarbon groups having 1 to 12 carbon atoms (hereinafter referred to as unsubstituted or substituted naphthalene ring), L_1, L_2
, L_3, L_4, at least one is an unsubstituted or substituted benzene ring, and at least one is an unsubstituted or substituted naphthalene ring, and further bonded to the benzene ring and naphthalene ring in one molecule. The recording layer has a thickness of 50 to 400 nm and contains a phthalo/naphthalocyanine dye (the total number of carbon atoms in all hydrocarbon groups is 17 or more), and a reflective layer made of an inorganic compound. An optical recording medium that can record and read signals without having layers. (2) The optical recording medium according to claim 1, wherein signals are recorded and read by a light beam passing through a transparent substrate. (3) The optical recording medium according to claim 1, wherein the resin binder in the recording layer is less than 20% by weight. (4) The optical recording medium according to claim 1, wherein two or more of L_1, L_2, L_3, and L_4 in the phthalo/naphthalocyanine dye represented by general formula (I) are unsubstituted or substituted naphthalene rings. (5) The optical recording medium according to claim 4, wherein three of L_1, L_2, L_3, and L_4 in the phthalo/naphthalocyanine dye represented by general formula (I) are unsubstituted or substituted naphthalene rings.