JPH01228895A - Optically recording medium - Google Patents

Abstract

PURPOSE:To perform recording/reading of a signal and a large C/N value even if a reflecting layer is not separately provided by providing a recording layer containing specific quinoid compound on a transparent board thereby to provide large absorptivity and sufficient reflectivity for a laser light in the layer. CONSTITUTION:A recording film is formed by vacuum depositing, sputtering ion plating or fusion-bonding to solvent quinoid compound of formula I (X is O, S, SO, SO2, Se, Te, N-R, A-ring and C-ring are unsubstituted or having 4 or less of substituted groups, B-ring are unsubstituted or having 2 or less of substituted groups, R is hydrogen or 1-12C substituted group, and n is integer number of 1-5) on a board, and dipping or spin coating it. Less than 20wt.% of resin binder is contained in the film.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical recording medium on which additional recording is possible using a focused beam of a laser, particularly a semiconductor laser. The present invention relates to optical recording media that can be used to record various information such as external memory, images, and audio.

[Conventional technology]

As recordable optical recording media, recording media having an inorganic recording layer made of a thin film of a low-melting metal such as tellurium, tellurium alloy, or bismuth alloy have been provided, and some of them are in practical use.

However, media with recording layers made of these low-melting point metal thin films,
When recording signals due to the high thermal conductivity of the recording layer,
Thermal energy generated by the irradiated laser beam is dissipated through the metal thin film. As a result, the irradiation energy is not effectively utilized for recording the signal;
The recording sensitivity decreases, the recording bits become large, and the sizes of the bits become uneven, so there is a low limit to the recording density. In addition, the metals used in these recording layers, such as tellurium, are easily oxidized, leading to concerns about their durability, and there are also concerns about the fact that they are toxic substances.

On the other hand, since organic materials generally have lower thermal conductivity than metals, optical recording media with an organic dye film as a recording layer have been proposed for the purpose of improving recording sensitivity and increasing recording density. For example, media with recording layers containing organic dyes capable of absorbing in the semiconductor laser region, such as dithiol metal complexes, polymethine dyes, squalium dyes, naphthoquinone dyes, phthalocyanine dyes, and naphthalocyanine dyes, have been developed, and some of them have been put into practical use. There is.

[Problems to be Solved by the Invention] However, among the optical recording media that have a recording layer using an organic dye film that has been proposed so far, for example, cyanine dyes,
Alternatively, a medium in which squarium dye is used as the recording medium tends to have poor durability, and the threshold value during recording is not clear, so that the readout power cannot be increased.

On the other hand, phthalocyanine dyes or naphthalocyanine dyes are dyes that generally have excellent durability. For example, US Pat. No. 4,298,975 discloses a medium in which a recording film is formed by vapor-depositing a phthalocyanine dye. ing. However, the optical properties of the vapor-deposited film of the dye do not harmonize with the oscillation wavelength of the semiconductor laser, so the recording film obtained by vapor deposition usually has to be subjected to a process of exposure to heat or organic solvent vapor, so-called shifting. This shifting process is not only complicated, but also
Because it requires a long processing time, it has not been available as a practical product.

Further, U.S. Pat. No. 4,492,750 relates to a medium using an alkyl-substituted naphthalocyanine dye, in which a reflective M such as an aluminum thin film is provided on a substrate, and alkyl-substituted naphthalocyanine dye particles are placed thereon in a resin binder. Discloses a medium having a recording film layer dispersed therein. Furthermore, media with a dithiol metal complex as a recording layer also require a separate reflective layer made of an inorganic compound such as a metal thin film or metal oxide thin film, since the dye film alone has inherently low reflectance. There is.

In this way, it is not possible to form a recording layer made of an organic dye directly on the substrate, and a reflective layer made of an inorganic compound such as aluminum cannot be formed on the substrate separately from the recording layer. The fact that it has to be formed using a vacuum process such as vapor deposition not only makes the manufacturing process of optical recording media extremely complicated, but also reduces the sensitivity of the recording film due to the low thermal conductivity characteristic of organic recording films. This makes it impossible to improve performance and increase recording density. That is, by providing a metal-based or metal oxide-based reflective layer with high thermal conductivity, the thermal energy generated during recording is dissipated through the metal reflective layer and is not used effectively, resulting in a decrease in recording sensitivity. Therefore, it becomes impossible to increase the recording density. Furthermore, when a reflective layer is provided in this way, it goes without saying that the laser beam is blocked by the reflective layer provided on the substrate, so the laser beam for recording and detecting signals must be irradiated from the substrate side. I can't. Therefore, recording and detection of signals must necessarily be performed from the recording layer side. In this case, even a small amount of dust or damage on the surface of the recording layer can seriously interfere with the normal recording and detection of signals. Therefore, in practical use, an overcoat or the like is required as a protective layer on the recording layer. If it is possible to record and read signals by irradiating a laser beam through a transparent substrate, on the side where the laser beam enters, there may be no dust or damage on the media surface before the laser beam is focused. A protective layer is no longer necessary since its presence does not substantially affect signal recording and readout due to the distance corresponding to the thickness of the substrate. Optical recording media that must be provided with a reflective layer made of a metal such as aluminum or a metal oxide have a number of drawbacks.

As described above, optical recording media with conventional organic dye recording layers have various drawbacks, and it is strongly desired to develop and provide improved optical recording media that eliminate or avoid these drawbacks. .

[Means to solve the problem]

The inventors secured the advantages of high sensitivity and high recording density, which are characteristics of optical recording media that use organic dyes as recording layers, while
In order to improve the shortcomings of conventional optical recording media that use the above-mentioned organic dye as a recording layer, as a result of intensive study and research, we have succeeded in using a specific new dye in the recording layer, allowing the use of conventional organic dyes. This optical recording medium has durability that cannot be achieved, has a sharp recording threshold, can increase read power, and has the function of a reflective layer itself. The inventors discovered that it is possible to produce an optical recording medium that does not require a separate reflective layer made of an inorganic compound as in the past, and were able to complete this invention.

The present invention provides an optical recording medium capable of recording and detecting signals without having a reflective layer, which is substantially composed of a transparent substrate and a recording layer provided on the substrate, represents the following general formula (1)% formula % Te, N-R, ring A and ring C are unsubstituted or have 4 or less substituents, and ring B is unsubstituted or 2 R represents hydrogen or a substituent having 1 to 12 carbon atoms. n represents an integer from 1 to 5. ) is an optical recording medium containing a quinonoid compound represented by

The substrate used in the optical recording medium of the present invention is preferably one that transmits light for recording or reading signals.

It is desirable that the light transmittance is 85% or more and the optical anisotropy is small. For example, acrylic resin,
Preferred examples include plastics such as polycarbonate resins, allyl resins, polyester resins, polyamide resins, vinyl chloride resins, polyvinyl ester resins, epoxy resins, and polyolefin resins, and glass. Among these, plastic is more preferable than glass from the viewpoint of the mechanical strength of the substrate itself, ease of providing guide grooves, address signals, etc., and economic efficiency.

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

Of course, there are guide grooves on the surface of the substrate to indicate the recording position.
Alternatively, it may have bits for address signals and the like. Guide grooves or address signals can be added when manufacturing the board by injection molding or casting, or
It can also be applied by applying an ultraviolet curing resin onto the substrate, overlapping it with a stamper, and exposing it to ultraviolet light.

In this invention, the following general formula (
1) (wherein, X is O, S, So%So2, Se, Te, N-
R is represented by ring A and ring C are unsubstituted or have 4 or less substituents, ring B is unsubstituted or has 2 or less substituents, and R is hydrogen or the number of carbon atoms. Substituents having 1 to 12 are indicated. n represents an integer from 1 to 5. ) is provided as a record M consisting of a quinonoid compound represented by

In the quinonoid compound represented by the general formula (1) used in the recording layer of this invention, the A ring, B ring, and C ring may not have a substituent, and the solubility,
Although they may be substituted with various substituents to control crystallinity, stability, optical properties, film formability, etc., rings A and C may be substituted, respectively, from the viewpoint of stability of the recording film. 2-4
Those substituted with 2 substituents are preferred.

Specific examples of various substituents substituted on ring A, ring B, and ring C include halogens such as chlorine, bromine, and iodine, methyl, ethyl, n-butyl, 5ec-butyl, and tert.
- Hydrocarbon groups such as butyl, amyl, hexyl, octyl, dodecyl, cyclohexyl, methylcyclohexyl, ethynyl, propenyl, allyl, hexenyl, dodecenyl, cyclohexenyl, dicyclopentagenyl, phenyl, butylphenyl, benzyl, methyloxy , ether groups such as ethyloxy, butyloxy, amyloxy, dodecyloxy, phenoxy, dodecylbenzeneoxy, thioether groups such as methylthioxy, ethylthioxy, butylthioxy, phenylthioxy, amino, methylamino, dimethylamino, butylamino, dibutylamino, phenyl Amino groups such as amino, diphenylamino, benzylamino, methylcarboxy, ethylcarboxy, butylcarboxy, octylcarboxy,
Carboxylic acid ester groups such as benzenecarboxy, sulfonic acid ester groups such as butylsulfonic acid and dodecylbenzenesulfonic acid, amide groups such as ethylaminocarboxy, butylaminocarboxy, and phenylaminocarboxy, butylsulfonamide, phenylsulfonamide, benzylsulfone Sulfonamide groups such as amide, carbonyl groups such as acetyl, ethylcarbonyl, butylcarbonyl, octylcarbonyl, dodecylcarbonyl, phenylcarbonyl, silyl groups such as trimethylsilyl, tributylsilyl, triphenylsilyl, trimethoxysilyl, triphenoxysilyl, Examples include, but are not limited to, siloxy groups, nitro groups, mercapto groups, hydroxyl groups, carboxyl groups, sulfonic acid groups, cyano groups, etc. For example, halogenated alkyl groups, or alkoxyalkyl groups, etc. Of course, those in which the above-mentioned substituents are further substituted with other substituents are also included. When the polycyclic rings A, B, and C are substituted with two or more substituents, adjacent substituents are linked to each other in a cyclic manner, as shown by the following formula (2). You can leave it there.

When the A ring, B ring and C ring are substituted with various substituents, the types of substituents may be different or the same, and the number of B rings is 2 or more. , the types of substituents on each B ring may be the same or different.

On the other hand, X of the quinonoid compound of general formula (1) is o, s,
so, SO2, Se, and 10%N-R, but O, S, and N-R are preferred from the viewpoint of ease of synthesis, solubility, stability, etc. When X is NH, R represents a substituent having 1 to 12 carbon atoms, and more specific examples include an alkyl group, an alkenyl group, an aryl group, and the like.

Further, these alkyl groups, alkenyl groups, and aryl groups may contain atoms such as halogen, oxygen, sulfur, nitrogen, and silicon, and may be cyclic.

The absorption wavelength of the quinonoid compound of general formula (1) differs depending on the type and number of substituents, but it is also possible to control the absorption wavelength by the number of B rings, and the absorption wavelength of the recording film and the semiconductor laser. In terms of harmony with the oscillation wavelength, the number n of B rings is preferably 1 to 3.

For example, in the case where X is S in the quinonoid compound represented by the general formula (1), compound (3) where n=1, compound (4) where n=2, n=
Compounds (5) of No. 3 are each represented as follows.

n=1 n=2 n=3 (R).

(However, !, m, p, r, and s indicate the number of substituents.) Furthermore, the synthesis of the quinonoid compound used in this invention is as follows:
For example, it can be carried out according to the following synthetic route.

Soup: tert-butyl group In order to form and fix the recording film on the substrate in the optical recording medium of the present invention, for example, a method such as vacuum evaporation, sputtering, or ion-blating of a quinonoid compound, or a method of adding a quinonoid compound to a solvent is used. It can be formed by melting and coating methods such as dipping and spin coating.

Among the above fixing methods, the coating method is preferable from the viewpoint of ease of management of the recording film, ease of operation, productivity, etc.
To fix the recording layer by coating, a dye solution consisting of a quinonoid compound and an organic solvent is brought into contact with the substrate to fix the quinonoid compound onto the substrate. More specifically, for example, the dye solution is poured onto the substrate. or after bringing the substrate surface into contact with the dye liquid level and then pulling it up.
There are a method of removing excess dye liquid while rotating the substrate, and a method of causing the dye liquid to flow down onto the substrate while rotating the substrate. If necessary, forced drying may be performed after this application.

In the coating method, aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene, hexane, heptane,
Aliphatic hydrocarbons such as octane, decane, cyclohexane, methylcyclohexane, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, acetylacetone, esters such as ethyl acetate, butyl acetate, amyl acetate, cellosolve acetate,
Alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, allyl alcohol, methyl cellosolve, ethyl cellosolve, butyl cellosolve, benzyl alcohol, ethers such as diethyl ether, dibutyl ether, diisopropyl ether, tetrahydrofuran, dioxane, diglyme, carbon tetrachloride, chloroform, Examples include halogenated hydrocarbons such as tricrene, dichloroethane, trichloroethane, and tetrachloroethane, dimethylformamide, and carbon disulfide.

When selecting a solvent, it is preferable to use a solvent that not only has solubility in the quinonoid compound but also does not damage the guide grooves or pre-pits on the substrate. The concentration of the dye solution during coating varies depending on the type of solvent and coating method, but is usually about 0.1-10% by weight.

In the optical recording medium of the present invention, in order to increase the reflectance of the recording film and further enhance the sensitivity, in addition to the quinonoid compound,
Other dyes may be added within a range that does not impede the effects of the invention, for example,
It is also possible to mix and use the dyes within a range of approximately less than 50% of the total amount of the dyes used. Dyes that can be used in combination include known aromatic or unsaturated aliphatic diamine metal complexes, aromatic or unsaturated aliphatic dithiol metal complexes, unsubstituted or substituted phthalocyanine or naphthalocyanine dyes, and polymethine dyes. Examples include pigments, squalium pigments, naphthoquinone pigments, and anthraquinone pigments.

In this invention, when forming a recording film, in order to improve the smoothness of the recording film or to reduce the occurrence of defects such as pinholes, the quinonoid compound of the invention is added to nitrocellulose, ethylcellulose, acrylic resin, polystyrene resin. It is also possible to form a recording film by adding resins such as, leveling agents, antifoaming agents, etc.

However, if large amounts of these resins or additives are added, the reflectance of the recording layer may decrease or the dyes in the recording film may become non-uniformly dispersed, which may impede the effects of the invention. There are cases where If these points are carefully considered, the amount of resin and additives added to the recording film will be 20%.
Less than % by weight, preferably less than 10% by weight, more preferably less than 5% by weight.

-II, in an optical recording medium, the thickness of the recording layer affects reflectance, recording sensitivity, etc., but the thickness of the recording layer of the invention is preferably 50 to 300 nm, more preferably 60 nm.
~250 nm.

As described above, in the optical recording medium of the present invention, it is preferable that signals are recorded and read out using a laser beam that passes through the substrate, that is, a laser beam that is irradiated from the substrate side.

Generally, in order to write a signal on an optical recording medium, when a laser beam is irradiated onto the recording layer with its focus adjusted, the recording layer in the area to be irradiated absorbs the laser beam and generates heat. Writing is performed by changing the quality of the recording layer by the generated heat and changing the reflectance.

Next, in order to read out the written signal, this change in reflectance is detected by a laser beam, but if this change in reflectance is small, the signal-to-noise ratio (
C/N) is small, which is not preferable.

In order to increase this change in reflectance, the reflectance before recording must be increased.

On the other hand, to make a recording film more sensitive, it must absorb laser beams better.

That is, the recording film must be highly reflective and highly absorbent to the laser beam.

The most distinctive feature of this invention is that when the quinonoid compound of the invention is used as a recording layer, the recording layer has a large absorption capacity in the oscillation wavelength range of a semiconductor laser, and
The recording layer itself has a fairly high reflectivity.

Therefore, the recording layer itself has the function of a reflective layer at the same time, and the optical recording medium of the invention has high sensitivity. There's no need.

FIG. 1 shows the optical properties of a thin film of compound (a) shown in the synthesis example above, which is one of the quinonoid compounds used in the invention.

It is confirmed that this compound has a large absorption ability over a wide range of 600 to 800 nm, and also has a large reflectance.

When putting the optical recording medium of this invention into practice, in order to protect the recording layer, it is necessary to apply an ultraviolet curing resin or the like to the surface of the recording layer, to laminate a protective sheet to the surface of the recording layer,
Alternatively, the optical recording medium 2 is made to face each other with the recording layer surfaces inside.
Measures such as pasting the sheets together may also be taken.

At this time, it is desirable to provide a thin gap on the surface of the recording layer and then bond the recording layer together.

In addition, in the optical recording medium of this invention, the laser beam used for recording and reading signals is usually 640~
Semiconductor lasers having an oscillation wavelength within the range of 850 nm are preferred.

For example, when recording at a linear velocity of 11 m/s, the laser output on the recording film is about 5 to 12 mW,
In the case of reading, the laser output may be set to about 1/1O of that during recording.

Hereinafter, the invention will be specifically explained with reference to Examples, but the invention is not limited by the Examples.

Example 1 1) Using ultraviolet curing resin on an acrylic resin substrate with a thickness of 1.2 mm and a diameter of 130 mm, the depth was 70% m and the width was 0.
．． 1.5% of the quinonoid compound (a) shown in the synthesis example above was placed in the center of the side surface with the guide grooves of a resin substrate on which spiral guide grooves of 6 μm and pitch of 1.6 μm were formed.
After dropping the chloroform solution, move the resin substrate at speed 1.
It was rotated for 10 seconds at 1000 rpm. Next, the resin substrate was dried by placing it in an atmosphere at 40° C. for 10 minutes, and a recording layer consisting essentially only of the quinonoid compound (a) was fixed on the resin substrate. The thickness of this recording layer was approximately 90 nm when measured in cross section using a microscope. Further, the absorption rate and reflectance of light with a wavelength of 780 nm passing through the resin substrate were 55% and 30%, respectively.

An optical recording medium was produced by bonding two similar recording plates thus produced facing each other with the recording layer surfaces facing each other with a gap of 500 μm provided therebetween.

2) This optical recording medium is placed on a turntable, and while rotating at a speed of +800 rpm, a laser beam is passed through the resin substrate and onto the guide groove using a drive device having an optical head equipped with a semiconductor laser having an oscillation wavelength of 780 nm. A pulse width of 90 ns was generated with a laser output of 8 mW on the recording surface while controlling the laser output to be focused on the recording layer.
- Recording of a 3.7 MHz pulse signal was performed on the outermost periphery of the medium. Next, using the same device, the recorded signal was read out with the output of the semiconductor laser set to 1 mW on the recording surface.

At this time, a signal-to-noise ratio (C/N) of 55 dB was obtained, and extremely good recording and detection could be performed.

In order to investigate the readout light stability of this recording film, we attempted to repeatedly and continuously read out the same track 1 million times using a 1 mW readout beam, but the magnitude of the recorded signal and the C/N value were No change was observed.

Next, in order to examine the recording frequency dependence of this optical recording medium, recording and reading were performed in exactly the same manner except that the recording frequency was changed, and the C/N value was determined.

Even if the recording frequency is increased to 9 MHz, the obtained C/
The N value did not decrease.

From this test result, it is clear that in the optical recording medium of the present invention, even if the recording frequency is increased, the C/N value decreases little and the recording density can be increased.

3) In order to test the durability of this optical recording medium,
After being left in an atmosphere at ℃ and 90% RH for 4 months, a signal was recorded on the unrecorded area using the same method as in 2) above, and the recorded signal was read out again before the start of the durability test, and after the durability test. When the recorded signals were read out, C/N values of 54 dB and 55 dB were obtained, respectively, and almost no deterioration of the recording film was observed in this durability test.

4) The shape of the signal recording part bit was observed using a scanning electron microscope, and both the bit recorded before the durability test and the bit recorded after the durability test had the same shape. The raised edge of the bit, which is frequently observed in optical recording media used as a recording layer and causes noise, was hardly observed in the optical recording media tested, and the bit shape was very beautiful.

Example 2 Quinonoid compounds (b), (c), (d) represented by the following formula in place of the quinonoid compound (a) of Example 1
, (e) and a drive device equipped with a semiconductor laser having the oscillation wavelength shown in Table 1, optical recording media were produced and evaluated in the same manner as in Example 1.

The test results are summarized in Table 1 on the next page.

The C/N value required for optical recording media is usually at least
It is said to be 45 dB or more.

As is clear from Examples 1 and 2, the optical recording media of the present invention both achieved excellent C/N values of 50 dB or more, and in the reproduction light stability and durability tests, almost no characteristics were observed. did not change, which is an excellent result.

〔Effect of the invention〕

Since the optical recording medium of the present invention uses a novel quinonoid compound in the recording film, the recording layer has a large absorption capacity for semiconductor laser light, and the recording layer itself has sufficient reflectance.

Table 1 Therefore, it has high sensitivity and enables signal recording and readout without the need for a separate reflective layer such as a thin film of metal or metal oxide, and the initial reflectance is high. Give a large C/N value to Furthermore, even if the recording frequency is increased, the decrease in the C7N value is small, and no swelling is observed at the edge of the bit, giving the possibility of increasing the recording density. In addition, it is easy to mass-produce using a coating method, has excellent reproduction light stability and durability, and can be used for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the spectral characteristics, absorption rate, and reflectance of the quinonoid compound (a) film of the invention.

Claims (1)

[Claims] 1. An optical recording medium capable of recording and detecting signals without having a reflective layer, which essentially consists of a transparent substrate and a recording layer provided on the substrate. , an optical recording medium characterized in that the recording layer contains a quinonoid compound represented by the following general formula (1). ▲There are mathematical formulas, chemical formulas, tables, etc.▼(1) (Here, X is O, S, SO, SO_2, Se, Te, N
-R, ring A and ring C are unsubstituted or have 4 or less substituents, ring B is unsubstituted or has 2 or less substituents, R is hydrogen, or Substituents having 1 to 12 carbon atoms are indicated. n represents an integer from 1 to 5. ) 2. In the quinonoid compound of general formula (1), X is
The optical recording medium according to claim 1, which is O, S, or NR. 3. In the quinonoid compound of general formula (1), n is 1
The optical recording medium according to claim 1, which is an integer of ˜3. 4. Claim 1 in which the A ring and the C ring each have two or more substituents in the quinonoid compound of general formula (1).
The optical recording medium described. 5. In the quinonoid compound of general formula (1), X is
2. The optical recording medium according to claim 1, wherein the ring is S or NR, n is an integer of 1 to 3, and the A ring and the C ring each have two or more substituents. 6. The optical recording medium according to claim 1, wherein the recording layer contains less than 20% by weight of a resin binder.