JPH04344345A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide the optical recording medium having an excellent jitter characteristic by using dyes having the prescribed value or below of the calorific value at the time of the pyrolysis in air for the dyes to be used for a recording layer. CONSTITUTION:This optical recording medium is constituted by successively laminating the recording layer contg. the dyes and a coating layer on a transparent substrate consisting of an injection molded resin. The dyes, such as polymethine dyes, phthalocyanine dyes and naphthalocyanine dyes, having absorption at the oscillation wavelength of a semiconductor laser, are used as the dyes to be used for the recording layer contg. the dyes. The dyes having <=3500cal/g calorific value at the time of the pyrolysis of the dyes in the air are preferable as the dyes and the dyes having <=3000cal/g are more preferable. An error rate and jitter value increase when bit length recording is executed if the calorific value is higher than the above-mentioned range and, therefore, such calorific value is undesirable.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium, and more particularly to an optical recording medium capable of recording a large amount of information. More specifically, the present invention relates to a single-plate type optical recording medium having a dye as a recording layer, in which various information can be recorded by pit length.

0002

[Prior Art] A write-once optical recording system using a dye as a recording layer can form a recording film by spin coating, and is superior to an optical recording medium using an inorganic thin film as a recording film, which requires vacuum technology. It is excellent in terms of productivity, economy, yield, etc., and is already in practical use. Conventional optical recording media with a recording layer made of dye are usually air-filled with the recording layer side inside to protect the recording layer.
The same substrate or protective substrate was laminated with a gap therebetween to form an optical recording medium (laid medium). Laminated media have the disadvantage that the thickness of the medium is too large and requires a complicated lamination process. In order to improve these drawbacks, studies on single-plate write-once optical recording media have been conducted, for example, in JP-A No. 2-132656 and JP-A No. 2-1.
Published in 68446. In a single-plate optical recording medium, a protective layer is provided directly on the dye-containing recording layer in order to protect the dye-containing recording layer. In such a case, the protective layer affects pit formation during recording, resulting in distortion of the recorded waveform and a large error rate. Especially in pit length recording, which can increase the recording capacity, information is recorded on the edge of the pit, so even if it is possible to record,
The error rate was large, and the jitter value of each pit was also large, resulting in poor reliability. Furthermore, the laser power during recording
The margins were not large, the dependence on writers and readers was high, and it was difficult to maintain compatibility.

0003

[Problems to be Solved by the Invention] The present inventors have discovered that if a small dye whose calorific value during thermal decomposition is below a certain level is used in the recording layer, it will be possible to create a single-plate type post-recording system in which a protective layer is provided directly on the recording layer. We have found that the problem of pit length recording, which has been difficult in the past, can be solved in a possible optical recording medium. That is, it was discovered that even in such a case, the error rate and jitter value are excellent, and the laser power margin during recording is also large, leading to the completion of the present invention.

0004

[Means for Solving the Problems] That is, the present invention provides a single-plate optical recording medium that can be written once upon a time using a pit length, in which a recording layer containing a dye and a coating layer are sequentially laminated on a transparent injection molded resin substrate. The present invention is a single-plate type optical recording medium capable of pit length, wherein the dye used in the recording layer has a calorific value of 3500 cal/g or less when thermally decomposed in air. The transparent injection molded substrate used in the present invention is preferably one that transmits light for recording and reading signals. It is desirable that the light transmittance is 85% or more and the optical anisotropy is small. Preferred examples include substrates using thermoplastic resins such as acrylic resins, polycarbonate resins, polyamide resins, vinyl chloride resins, and polyolefin resins. Among these, injection molded resin substrates made of acrylic resin, polycarbonate resin, and polyolefin resin are preferred from the viewpoint of mechanical strength of the substrate, ease of adding guide grooves and reproduction-only signals, and economic efficiency. Preferably, polycarbonate resin substrates are particularly preferred.

The shape of these substrates may be plate-like, film-like, circular or card-like. Of course, the surface of the substrate may have guide grooves representing recording positions, pits representing recording positions, pits for information exclusively for reproduction, etc. It is preferable to provide such guide grooves, pits, etc. when making the substrate by injection molding or casting, but they can also be provided by applying an ultraviolet curable resin onto the substrate, overlapping it with a stamper, and exposing it to ultraviolet light. can.

In the optical recording medium of the present invention, a recording layer containing a dye and a coating layer are sequentially laminated on the transparent injection molded resin substrate. The pigments include polymethine pigments, phthalocyanine pigments, naphthalocyanine pigments, naphthoquinone pigments,
Examples include dyes having absorption in the oscillation wavelength range of semiconductor lasers, such as azulene dyes and dithiol metal complex dyes. Among these pigments, pigments with a calorific value of 3500 cal/g or less when thermally decomposed in the air are preferred;
A dye of 3000 cal/g or less is more preferable. If the calorific value during thermal decomposition of the dye exceeds 3,500 cal/g, the error rate and jitter value will become too large when pit length is recorded, which is undesirable. There are various methods for measuring the amount of heat generated during the decomposition of a dye, but the amount of heat generated during the thermal decomposition of the dye in air in the present invention is determined from the peak area of the amount of heat generated using a commercially available differential thermal analyzer. Say the value.

There is no clear relationship between the amount of heat generated during thermal decomposition of a dye and the structure of the dye, and therefore, in the present invention, there is no particular limitation on the structure of the dye. However, in consideration of the durability of the medium, phthalocyanine dyes and naphthalocyanine dyes are preferred. In the present invention, the recording layer containing the above-mentioned dye can usually be formed by means such as spin coating, vapor deposition, and sputtering, but from the viewpoint of ease of film formation, spin coating is preferable. law is preferred. When forming the above dye by spin coating, use solvents that do not damage the injection molded substrate, such as aliphatic or alicyclic hydrocarbons such as hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, diethyl ether, etc. −
Non-polar solvents such as ethers such as ester, dibutyl ether and diisopropyl ether, and alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, allyl alcohol and methyl cellosolve. The dye may be dissolved in a polar solvent and coated. In this case, the dye may be selected so as to be soluble in the above-mentioned solvent, or a substituent may be introduced to improve solubility.

When forming a recording layer containing a dye, other substituted phthalocyanines, substituted naphthalocyanines, substituted porphyrin dyes, and cyanine dyes are added to the low calorific value dye of the present invention in order to improve the recording properties. , dithiol metal complexes, anthraquinone dyes, resins such as nitrocellulose, ethylcellulose, acrylic resins, polystyrene resins, urethane resins, leveling agents, antifoaming agents, etc. that impair the effects of the present invention. They can also be used together within the range. In the present invention, the thickness of the recording layer containing the dye is usually 30 to 500 nm, and 50 to 2 nm.
50 nm is more preferred. The coating layer provided on the recording layer in the present invention is a layer that has the function of protecting the recording layer containing a dye in order to make a single-plate type medium, and usually has a thickness of 2 μm or more and 15 μm or less. It is sufficient if the film is thick and hard. If the thickness of this coating layer is less than 2 μm, the ability to protect the recording layer from scratches etc. will be significantly reduced. On the other hand, if the thickness of the coating layer exceeds 15 .mu.m, the pits are likely to be distorted when the pit length is recorded, resulting in large jitter values and error rates.

[0009] The coating layer in the present invention may be a film having functions other than the function of protecting the recording film, such as a reflection function, a heat insulation function, and a light enhancement function. In such a case, the coating layer may be a multilayer of two or more layers. The thickness of the layer having these functions is approximately 30 to 500 nm. Specific examples of the coating layer include resins, metals, inorganic films, etc. Examples of the resin include acrylic resins, polycarbonate resins, ultraviolet curable resins, electron beam curable resins, and polysiloxane resins. Inorganic films include aluminum oxide, silicon oxide, silicon nitride, aluminum nitride, borium nitride, magnesium fluoride, silicon carbide, etc.; metals include aluminum, gold, silver, copper, platinum, nickel, etc., and these metals as one component. Examples include alloys such as However, since these metal films do not have a sufficient protective function, it is usually preferable to further provide a coating layer made of the above-mentioned resin or inorganic film on the metal film. These coating layers can be applied by spin coating, vapor deposition,
The film can be formed by means such as sputtering.

In the present invention, while rotating the optical recording medium, a focused laser beam, particularly a semiconductor laser beam, is emitted.
Recording is performed by irradiating the recording film with light. There are generally two methods for recording. One is to form a pit at the recording bit "1" (inter-pit recording), and the other is to record by turning on and off the recording laser power at the recording bit "1". It's a method. In the latter case, pits of various lengths are formed depending on the difference in the number of "0"s between a recording bit "1" and the next "1" (pit length recording). Although pit length recording has the advantage of increasing recording capacity compared to pit-to-pit recording, pits of various lengths must be accurately recorded at predetermined lengths, which places a heavy burden on the recording film.

In an optical recording medium using a dye, the recording layer absorbs light and generates heat during recording. The dye in the recording area is melted and decomposed by this heat. According to studies conducted by the present inventors, decomposition gas of the dye is generated at this time, but if the recording layer is covered with a protective layer, pressure is applied to the recording section. Particularly when the amount of heat generated during melting and decomposition of the dye is large, a large pressure is applied. On the other hand, at that time, it is assumed that the substrate directly below the recording section and the recording layer around the recording section are in a melted state due to heat generated during recording. When the substrate directly below the recording section in this molten state and the recording layer around the recording section are affected by the pressure caused by the decomposed gas, the waveform becomes distorted and the error rate and jitter value increase. Presumed. In the present invention, as described above, by using a dye that has a calorific value of 3,500 cal/g or less during thermal decomposition of the dye in the air, the error rate and jitter when recording pit length can be sufficiently reduced. It is. The above specific recording film used in the present invention is suitable for the pit length recording. The type of pit length when pit length recording is performed is determined by the modulation method of the recording code. Examples of modulation methods are FM, MFM, M2FM, 8-10
, EFM, etc. have been proposed, but the EFM method used in compact discs and the like is preferred from the viewpoint of compatibility of electronic components, although the method is not limited to these. The optical recording medium of the present invention records and reads signals by irradiating a laser beam through the substrate, and the wavelength of the laser beam used is usually a semiconductor laser having an oscillation wavelength of 640 to 850 nm. is preferred. When recording, while rotating the medium, the laser output on the recording film is
The output power of the laser should be about 12 mW, and when reading out, the laser output should be about 1/10 of that of recording. Further, in the optical recording medium of the present invention, printing or the like can be performed on the coating layer.

0012

[Examples] The present invention will be specifically explained below with reference to Examples, but the embodiments of the present invention are not limited thereto. Example 1 Spiral guide groove with a thickness of 1.2 mm and a diameter of 120 mm (depth 70 nm, width 0.6 μm, pitch 1.6 μm)
A 4% by weight octane solution of Pd-tetra-(1-isopropyl-isoamyloxy)tetra-(bromo)phthalocyanine dye was placed in the center of the surface having the guide groove of the injection-molded polycarbonate resin substrate having After dripping,
This resin substrate was rotated for 10 seconds at a speed of 1000 rpm. Next, this resin substrate was dried in an atmosphere of 40° C. for 10 minutes, and a recording layer consisting essentially only of the phthalocyanine dye was formed on the resin substrate. The thickness of this recording layer is 1
It was 20 nm. As a coating layer, a reflective layer of gold with a thickness of 80 nm was first formed by sputtering on this recording layer, and then a 5 μm thick ultraviolet curable resin (manufactured by Dainippon Ink Co., Ltd., Daicure Clear SD-1
A medium was prepared by providing the protective layer 7). That is, in this case, the coating layer consists of two layers: a reflective layer and a protective layer. The reflectance of this optical recording medium for 780 nm light is 6
It was 8%.

[0013] Place this optical recording medium on a turntable,
780 nm while rotating at a linear velocity of 1.4 m/s.
Using a drive with an optical head equipped with a semiconductor laser with an oscillation wavelength of EFM in the same manner as used for compact discs while varying the laser power of the
The modulated signal was recorded. Next, using the same device, the output of the semiconductor laser was set to 1 mW on the recording surface, and the recorded signal was read out. When recording with a laser output of 7 mW, the error rate of the readout signal is the minimum at 3 x 10-3, and the jitter value for a 3T length pit and pit-to-pit jitter is 18 ns each. , 20 ns, and almost no distortion was observed in the waveform of the recording/reproducing signal, allowing extremely good recording and reading. In addition, differential thermal analysis of this dye in air (measuring device: Seiko Electronics, TG/
The measurement result of the calorific value during thermal decomposition using DTA220, atmosphere: air, 100 ml/min, temperature increase rate: 10° C./min) was 1850 cal/g based on the area of the exothermic peak.

Comparative Example 1 In place of the dye in Example 1, Pd-tetra-(1
A medium was prepared in the same manner as in Example 1 except that the -isopropyl-isoamyloxy)phthalocyanine dye was used. Incidentally, the measurement result of the calorific value during thermal decomposition of this dye in air was 3900 cal/g. Also, the reflectance of this medium was 72% at a wavelength of 780 nm. Next, Example 1
Recording and reading were evaluated in the same manner. laser
The block error rate was the lowest under the recording condition of power -7 mW, but the value was 5 × 10-2, and the jitter between 3T pits and pits was 45 ns and 52 ns, respectively.
ns, and good recording was not possible. Further, distortion was observed in the recording/reproducing waveform. This waveform distortion is a large error.
This causes the rate and large jitter.

Examples 2 to 5, Comparative Examples 2 to 3 Example 1 except that a phthalocyanine dye having the substituents and center metal shown in Table 1 below was used instead of the dye used in Example 1.
Media were created and evaluated using the same method. Table 2 summarizes the evaluation results when recording was performed under conditions that minimized the calorific value of the dye used and the error rate of the medium.

[0016]

[Table 1]

[0017]

[Table 2]

In the reproduced waveform of the recorded signal, almost no distortion was observed in the media of Examples 2 to 5 of the present invention, but large distortion was observed in the media of Comparative Examples 2 and 3.

Example 6, Comparative Example 4 The dyes used in Example 1 and Comparative Example 1 were mixed in a weight ratio of 50:50 (Example 6) and 25:75 (Comparative Example 4). The calorific value during decomposition was measured using the same method as in Example 1, and found to be 2900 cal/g and 3600 cal/g, respectively.
It was cal/g. Next, a medium was prepared using this mixed dye in the same manner as in Example 1, and the error rate and jitter were reduced.
The dependence of the value on the recording laser power was also investigated including the medium of Example 1. The results are summarized in Table 3.

[0020]

[Table 3]

As is clear from Table 3, in Example 6, the error rate and jitter value are good even when the recording laser power varies. However, in Comparative Example 4, when the recording laser power fluctuates, both the error rate and the jitter value suddenly increase, and the margin width of the recording laser power is narrow.

[0022]

Effects of the Invention As is clear from the examples, in the present invention, in a single-plate optical recording medium consisting of a recording layer containing a dye and a coating layer, a dye that generates a small amount of heat during thermal decomposition can be used. By using it in the recording layer, it has excellent error rate and jitter characteristics when recording pit length, and has low recording power.
It can be seen that the margin width is also large.

Claims (5)

[Claims] 1. In a single-plate optical recording medium, which is formed by sequentially laminating a recording layer containing a dye and a coating layer on a transparent injection molded resin substrate, and which is recordable by adjusting the pit length, The amount of heat generated during thermal decomposition in air is 3.
1. A single-plate optical recording medium capable of pit length recording, characterized in that the pit length is 500 cal/g or less. 2. The optical recording medium according to claim 1, wherein the dye used in the recording layer has a calorific value of 3000 cal/g or less when thermally decomposed in air. 3. The optical recording medium according to claim 2, wherein the coating layer comprises a metal reflective layer and a protective layer, and has a reflectance of 60% or more. 4. The optical recording medium according to claim 3, wherein the recording method for pit length recording is the same EFM modulation method as used for compact discs. 5. The optical recording medium according to claim 4, wherein the dye used in the recording layer is a soluble phthalocyanine dye.