JPS6221584A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide an optical recording medium which eliminates the need for separately providing a reflective layer comprising an inorganic compound, by using a specified anthraquinone dye in a recording layer and controlling the film thickness of the recording layer to an appropriate value. CONSTITUTION:A transparent base and a recording layer having a film thickness of 50-400nm and comprising an anthraquinone dye of general formula (1), wherein each of R<1> and R<2>, which may be the same or different, is subst. or unsubst. alkyl, subst. or unsubst. aryl, subst. or unsubst. alkenyl or cycloalkyl, and each of Y<1> and Y<2>, which may be the same or different, is hydroxyl or hydrogen, are provided, in an optical recording medium for recording and reproducing signals by reflected light. Because the recording layer itself has a fairy high reflectance, focus control of a laser beam and track control of a signal- writing position in recording or reading signals can be performed without requiring a conventional reflective layer constituted of a thin metallic film or an inorganic compound.

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, and more specifically relates to a computer external memory, various types of information such as images, audio, etc. The present invention relates to an optical recording medium used for recording.

[Prior art]

As the above-mentioned write-once optical recording medium, recording media having an inorganic recording layer made of a thin film of a low-melting metal such as tellurium, tellurium alloy, bismuth alloy, etc. are beginning to be put into practical use. However, these recording media have low productivity because they require the formation of a recording layer in a vacuum using vacuum evaporation, sputtering, etc., and the recording density and recording sensitivity are low because the thermal conductivity of the recording layer is large. There are limits to this, and since it uses toxic substances such as tellurium, there are particular concerns about its toxicity when it is used for civilian purposes.

In order to solve these problems, optical recording media with an organic dye film as a recording layer have recently been studied, and materials such as metal phthalocyanine, dithiol metal complexes, polymethine dyes, and squalium dyes absorb at the oscillation wavelength of semiconductor lasers. Organic dyes that exhibit the following have been proposed. However, the organic dye-based optical recording media that have been proposed so far lack durability and have low reflectance, requiring a separate reflective layer made of an inorganic compound such as a metal thin film or a metal oxide thin film.

Since the reflective layer made of such an inorganic compound must be formed separately from the recording layer, there is a problem in that the manufacturing process of the optical recording medium becomes considerably complicated.

Furthermore, the high recording density and recording sensitivity of organic dye-based recording films, which are expected due to their low thermal conductivity, are reduced or canceled out by laminating such high-conductivity metal-based reflective layers on the recording layer. There was a fatal problem.

[Basic departure]

As a result of intensive studies to improve the above-mentioned drawbacks of optical recording media with an organic dye film as a recording layer, the authors found that they used a specific anthraquinone dye in the recording layer and By controlling the film thickness to an appropriate thickness, the recording layer itself has the function of anti-resistance layer, as well as the durability that could not be achieved in optical recording media using conventional organic dyes. Optical recording 1 that does not require a separate reflective layer made of an inorganic compound as in the past.
They discovered that a medium can be formed and completed the present invention.

[Disclosure of the invention]

That is, the present invention provides an optical recording medium for recording and reproducing signals using reflected light, which comprises a transparent substrate and the following general formula (I
) [In the formula (Il, R1 and R1 are the same or each independently a substituted or unsubstituted alkyl group, a substituted or unsubstituted ali'-
represents a substituted or unsubstituted alkenyl group or a cycloalkyl group, and (2) or Y2 are the same or each independently represent a hydroxy group or a hydrogen atom. ] 50 to 40 containing an anthraquinone dye represented by
Provided is an optical recording medium comprising a recording layer having a film thickness of 0 nm, capable of recording and reading signals without having a reflective layer made of an inorganic compound.

In the present invention, it is preferable to write and read signals using a light beam that passes through a transparent substrate, since this makes it less susceptible to dust, scratches, and the like. Therefore,
The transparent substrate used in the present invention preferably has a light transmittance of 8 for writing and reading signals.
It is desirable that the optical anisotropy is 5 or more and that the optical anisotropy is small.

Preferred examples include plastics such as acrylic resin, polycarbonate resin, allyl resin, polyester resin, polyamide resin, vinyl chloride resin, polyvinyl ester resin, epoxy resin, and polyolefin resin, and glass. Among these, plastics are particularly preferred from the viewpoints of mechanical strength of the substrate, ease of marking guide grooves, address signals, etc., and economical efficiency.

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

Of course, the surface thereof may have guide grooves for indicating the recording position and irregularities for address signals.

Such guide grooves, address signals, etc. can be added when making the substrate by injection molding or casting, or they can be added by applying an ultraviolet curable resin or the like onto the substrate, overlapping it with a stamper, and exposing it to ultraviolet rays. can.

In the present invention, a recording layer containing an anthraquinone dye represented by the general formula (I) is provided on such a substrate.

The anthraquinone compound (I) used in the present invention is prepared by the following formula cIT) [formula σI] in an aprotic polar solvent.
In, R1, R2, Yl, Y2 are R1, R in formula fIl
2, Yl.

It has the same meaning as Y2. ] The compound and the cyanide are combined with ammonium bicarbonate,
Sodium bicarbonate, potassium bicarbonate, sodium hydrogen sulfate,
Obtained by reaction in the presence of sodium bisulfite or the like.

In addition, the substituted or unsubstituted alkyl group represented by R1 or R in formula (I) includes a branched or straight-chain alkyl group having 1 to 20 carbon atoms, an aralkyl group, an alkoxyalkyl group, an acyloxyalkyl group, and a hydroxyl group. Alkyl group, halogenated alkyl group, cyanoalkyl group, aminoalkyl group, monoalkylaminoalkyl group, dialkylaminoalkyl group.

Examples include alkoxycarbonylalkyl groups, substituted or unsubstituted aryl groups, such as alkyl-substituted phenyl or naphthyl groups such as phenyl group, naphthyl group, tolyl group, xylyl group, methoxyphenyl group, ethoxyphenyl group, dimethoxy Alkoxy-substituted phenyl or naphthyl groups such as phenyl groups, halogen-substituted phenyl or naphthyl groups such as chlorophenyl groups, phenyl or naphthyl groups substituted with trifluoromethyl groups, alkylamino groups such as N,N-(diethylamino)phenyl groups Examples include substituted phenyl or naphthyl groups, and examples of alkenyl groups include allyl group, methacryl group, and crotyl group.

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

To fix the recording layer by coating, a dye solution consisting of the above-mentioned anthraquinone dye and an organic solvent described below is brought into contact with the substrate to fix the dye on the substrate. After letting the liquid flow down,
Alternatively, there is a method in which the surface of the substrate is brought into contact with the surface of the dye liquid and then pulled up, and then the excess liquid is removed while rotating the substrate, or a method in which the dye liquid is allowed to flow down onto the substrate while rotating the substrate. . If necessary, forced drying may be performed after this. The organic solvent used in this case may be a usual solvent that dissolves anthraquinone dyes, such as benzene, toluene, xylene, ethylbenzene, methyl ethyl ketone, thylisobutyl ketone, cyclohexanone, acetylacetone, ethyl acetate, butyl acetate, amyl acetate, cellosolve, methyl cellosolve. , butyl cellosolve, cellosolve acetate, diglyme, chloroform, carbon tetrachloride, methylene chloride, methyl chloroform, tricrene, dimethyl formamide, and the like. When selecting a solvent, in addition to the solubility of the dye, it is of course preferable to use a solvent that does not damage the guide grooves on the transparent substrate. Among the above-mentioned solvents, chloroform,
Particularly preferred are carbon tetrachloride, methylchloroform, trichlene, and the like.

The concentration of the dye liquid in the present invention varies depending on the type of solvent and coating method, but is usually 0.1 to 10% by weight, preferably 0.3 to 5% by weight. At this time, nitrocellulose, ethyl cellulose,
A soluble resin such as acrylic resin, a leveling agent, an antifoaming agent, and other additives may be added. However, adding too much resin component or additive tends to reduce the reflectance of the recording layer, and the amount added is 2 times the amount of the dye.
5 weight downwind is preferred.

In the optical recording medium of the present invention, as described above, it is preferable to record and reproduce signals using a light beam passing through a transparent substrate (a light beam irradiated from the substrate side). 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. surface). Therefore, the amount of light on this surface is insufficient and the temperature rise is insufficient, making it impossible to satisfactorily form unevenness corresponding to the signal.

As a result, the sensitivity decreases, and even if recording is possible, the s/N value (signal-to-noise ratio) value when reading out the signal is too small to be of 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 8/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 from 50 to 400 nm, more preferably from 60 to 250 nm.

There are various methods for measuring film thickness, and it is quite difficult to obtain an accurate measurement value, but it is preferable to use a value measured using an ellipsometer. Note that it is particularly difficult to measure the film thickness when there are guide grooves on the substrate, but the film thickness when the dye is fixed on the same substrate without unevenness such as guide grooves can be used 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.

To write a signal in the optical recording medium of the present invention, 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, forming irregularities and reducing the reflectance, thereby allowing writing to be performed. Signals are read by detecting this change in reflectance using a finer laser beam, but generally, if the change in reflectance is small, the signal-to-noise ratio (S/N) is undesirable.

To obtain a large S/N value, the original reflectivity through the substrate must be at least 1 before the signal is written.
The coefficient is 0 or more, preferably 15% or more. This 10%
Preferably, a reflectance of coefficient 15 or higher can be easily achieved by using the dye of the present invention and by appropriately selecting the thickness of the recording layer. 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.

In putting the optical recording medium of the present invention into practical use, the S/N
In order to improve the value, an anti-reflection layer is provided, an ultraviolet curing resin is coated on the recording layer to protect it, a protective sheet is pasted on the recording layer surface, and the recording layer surfaces are placed on the inside. Known means such as laminating two sheets together may also be used. It is preferable to provide an air gap on the recording layer when laminating the recording layer.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example-1 (11) 1,4-di(n-butylamino)-2 was placed in the center of an acrylic resin plate with a thickness of 1.25 mm and a diameter of 200 mm.
, 1 part by weight of 3-dicyano-5,8-di-hydroxyanthraquinone dye and 99 parts by weight of chloroform (C8P value 9.3), and then the acrylic resin plate was rotated at a speed of 2000 rpm for 15 seconds. . Next, this acrylic resin plate was dried in an atmosphere of 40° C. for 10 minutes to fix the recording layer on the acrylic resin plate. The thickness of this recording layer was 110 nm as measured by an ellipsometer. The reflectance of light having a wavelength of 830 nm through the acrylic resin plate was 21.

(2) Place the optical recording medium thus produced on a turntable with the recording layer facing up, and while rotating at a speed of 900 rpm, equip a semiconductor laser with an oscillation wavelength of 800 nm and an output of 8 mW at the substrate surface. Using this optical head, a 1 MHz pulse signal was recorded while controlling the laser beam to be focused on the recording layer from the underside of the optical recording medium through the acrylic resin plate. Next, using the same equipment, the output of the semiconductor laser was increased to 0.7 mW on the substrate surface.
The recorded signal was played back in the same manner.

The signal-to-noise ratio (S/N) at this time was 54 decibels, and very good signal writing and reading could be performed.

(3) To check the durability of this optical recording medium,
After leaving it in an atmosphere of ℃ and 95% RH for 4 months, record the signal on the unrecorded area using the same method as above, and compare the signal recorded before the durability test and the signal recorded after the durability test. When reproduced, an S/N of 52.53 dB was obtained for each, and the change due to the durability test was sufficiently small.

(4) The shape of the bit in the signal recording section after the durability test was observed using a scanning electron microscope, and the shape of the bit recorded before and after the durability test was almost the same. This is thought to be caused by the high thermal conductivity of optical recording media whose recording layer is an inorganic thin film such as a Te-based film, and there is almost no bulge on the edge of the bit that causes noise, making it very clean. It was in the shape of a bit.

Example-2 ~ IO The same method as in Example-1, using a polycarbonate plate with a thickness of 1.2 im s and a diameter of 120 m, using the anthraquinone dye shown in Table 1 and carbon tetrachloride as a solvent, and changing the dye concentration. An optical recording medium was prepared using the same method, and the reflectance and S/N were examined. The results are summarized in Table 1.

(1B) Example-11 Spiral recording guide groove with thickness 1.25i+m and diameter 200i+m (width 0.8pms depth 0.07pm,
1,4-di(n-hexylamino)-2,3-dicyano-5,8 was applied to both the acrylic resin plate with a pitch interval of 2.5 μm and the acrylic resin plate without guide grooves.
-Dihydroxyanthraquinone A 1% by weight carbon tetrachloride solution was applied and dried in the same manner as in Example 1 to produce an optical recording medium. However, for the acrylic resin plate having guide grooves, the recording layer was fixed on the surface having the guide grooves. The film thickness of this optical recording medium was 130 nm as measured by an ellipsometer, and the reflectance was 22q6. (With a substrate without guide grooves) Using these optical recording media, S/N measurements and durability tests by writing and reading signals and observation of bits were performed in the same manner as in Example-1.

The results are summarized in Table 2.

Table 2

Claims (2)

[Claims] (1) Transparent substrate and the following general formula (I) provided on the substrate ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) [In formula (I), R^1 and R^2 are the same or each independently represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkenyl group, or a cycloalkyl group, and Y^1 and Y^2 are the same or each independently a hydroxy group or Represents a hydrogen atom. ] 500-4 containing an anthraquinone dye represented by
An optical recording medium comprising a recording layer having a thickness of 0.00 nm and capable of recording and reading signals without having a reflective layer made of an inorganic compound. (2) The optical recording medium according to claim 1, wherein signals are recorded and read by a light beam passing through a transparent substrate.