JPH10151854A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a crosstalk to the minimum possible extent and also record data to the high density level. SOLUTION: This optical recording medium consists of a recording layer containing a laser beam absorbing coloring matter formed, directly or through another layer, on a transparent base with grooves and a metal reflective layer formed, directly or through another layer, on the recording layer. In this case, Wg and P meet formula 0.24r<=Wg<=0.35r, 0.68r<=P<=0.83r, given the diameter of a recording beam expressed by λ/NA as r [λ is a recording wavelength (μm); Na is the numerical aperture of an objective lens], a pitch (track pitch) at which the grooves of the base are arranged as P (μm); and the width of the grooves as Wg (μm,). In addition, the coloring matter is a styryl coloring matter as expressed by formula. In the formula, A is a group of atoms consisting of substituted or non-substituted 5- or 6-membered rings including one nitrogen atom; Q is a group of atom consisting of non-substituted or substituted benzene rings or naphthalene rings condensed to 5-membered or 6-membered rings; R1-R3 are a 1-12C non-substituted or substituted alkyl group; R1, R2 may form a ring with a benzene ring to which an amino group is bonded; n is 1 or 2; and X is a univalent anion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical recording medium having a recording layer containing a dye and a reflective layer on a transparent substrate, and more particularly to an optical recording medium capable of recording at high density.

[0002]

2. Description of the Related Art A recordable optical recording medium in which a dye is used as a recording layer and a metal reflective layer is provided on the recording layer in order to increase the reflectance is disclosed in, for example, Optical Data Storage 1989.
Technical Digest Series Vol. 1, 45 (1989), and a medium using a cyanine dye or a phthalocyanine dye in the recording layer is marketed as a CD-R medium. These media are characterized in that they can be recorded by a 780 nm semiconductor laser and can be reproduced by a commercially available CD player or CD-ROM player equipped with a 780 nm semiconductor laser.

[0003] However, these media have a capacity of only about 650 MB, and when recording large-capacity information such as digital moving pictures, the recording time is as short as 15 minutes or less. or,
As the miniaturization of devices progresses, the capacity of conventional media becomes insufficient if the media is miniaturized. While the above-mentioned CD-R medium performs recording and reproduction using a semiconductor laser having a wavelength of about 780 nm, a semiconductor laser of 630 to 650 nm has recently been developed, and a higher density recording and / or reproducing method has been developed. Alternatively, an optical recording medium capable of reproducing and recording a high-quality moving image of 2 hours on a medium having a diameter of 120 mm has been developed as a DVD. This medium has a recording capacity of 4.7 GB / side,
At present, it is a read-only medium created by transferring pits to a substrate. Therefore, there is a demand for a recordable optical recording medium having a large capacity close to the recording capacity of a DVD as described above.

In general, to increase the recording capacity of a recordable medium, the recording laser beam may be reduced. As the wavelength of the laser used is shorter and the numerical aperture (NA) of the objective lens is larger, the beam diameter becomes smaller, which is preferable for high-density recording. There is a limit. For example, the beam diameter of the DVD described above is not small for the recording density as compared with the conventional CD. Therefore, at the time of recording, pits smaller than the beam diameter must be accurately formed as compared with the case of the CD-R, so that thermal interference and crosstalk between the pits at the time of recording increase, and high It becomes difficult to record the density. Therefore, there is a demand for accurately forming small and small pits without sacrificing the degree of modulation during recording.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-density optical recording medium capable of recording at a high density with a small crosstalk even if the track pitch is reduced with respect to the recording beam diameter. It is.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have non-trivially selected dyes, recording beam diameters, track pitches and groove shapes, and completed the present invention. .

That is, the present invention provides a recording layer containing a dye absorbing laser light, directly or through another layer, on a transparent substrate having a groove, In an optical recording medium having a metal reflective layer via a layer, the diameter of a recording beam represented by λ / NA is represented by r [where λ is a recording wavelength (μm), N
A represents the numerical aperture of the objective lens], when the groove pitch (track pitch) of the substrate is P (μm), and the width of the groove is Wg (μm), Wg and P satisfy the following expressions: .24r ≦ Wg ≦ 0.35r 0.68r ≦ P ≦ 0.83r, and the dye contained in the recording layer is a styryl dye represented by the following formula (1). High-density optical recording medium,

[0008]

Embedded image [Where A represents an atomic group consisting of a substituted or unsubstituted 5- or 6-membered ring containing one nitrogen atom, and Q represents the 5
An atomic group consisting of an unsubstituted or substituted benzene ring or a naphthalene ring fused to a 6-membered or 6-membered ring;
Represents an unsubstituted or substituted alkyl group having 1 to 12 carbon atoms,
R1, R2 may form a ring with a benzene ring which is an amino group is bonded, n a is 1 or 2, X ^- is a monovalent represents an anion] lambda is 0.635～0.655Myuemu, NA 0.60
The high-density optical recording medium according to the above item, wherein ± 0.05.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The optical recording medium of the present invention comprises a recording layer containing at least a dye absorbing laser light and a metal reflective layer on a transparent substrate, and has a sensitivity to short wavelength light. Therefore, even if the track pitch is made smaller than the recording beam diameter, high-density recording with reduced crosstalk can be performed without sacrificing the modulation degree.

When a dye is used for the recording layer, the recording layer can be formed by spin coating. When a recording layer is formed by a spin coating method on a substrate having a groove,
The thickness of the recording layer in the groove portion is usually larger than the thickness of the recording layer in the portion between the grooves (lands).

Usually, the recording sensitivity depends on the thickness of the recording layer.
In particular, in the case of a medium in which a metal reflective layer is provided on a recording layer, heat is diffused into the reflective layer, and the recording sensitivity is reduced. The thinner the recording layer, the greater the effect of this thermal diffusion, and the more the sensitivity tends to decrease. That is, a large difference occurs in the recording sensitivity between the groove and the land. Therefore, a thin pit can be formed even if the beam diameter of the recording laser beam is large, and recording with small crosstalk can be performed.

However, no matter how thin pits can be recorded, the track pitch cannot be reduced.
This is because, even if the track pitch is reduced indefinitely, if the diameter of the laser beam at the time of reproduction is large, not only the degree of modulation becomes small, but also the crosstalk becomes too large to make reproduction possible. That is, crosstalk is related to the beam diameter and track pitch during reproduction, and the width of recorded pits. Usually, the beam diameter during recording and during reproduction is the same, so the track pitch is reduced.
This is because even if recording with small crosstalk can be performed with a narrow pit, crosstalk increases during reproduction.

In the present invention, in order to perform recording so as to reduce crosstalk without sacrificing the degree of modulation during reproduction, if the recording beam diameter represented by λ / NA is r, the track pitch (P) Is preferably set to 0.68r to 0.83r, and the groove width (Wg) is set to 0.24r to 0.35r. Here, the width of the groove means a half width. If the track pitch is less than 0.68r, the crosstalk becomes too large, the modulation is reduced, and the jitter and error rate are increased.
If it exceeds 0.83r, the recording density in the radial direction does not increase, and the desired recording capacity cannot be obtained. On the other hand, when the width of the groove is less than 0.24r, the degree of modulation is small,
If it exceeds 0.35r, crosstalk is undesirably increased.

The beam diameter at the time of recording and reproduction in the present invention becomes smaller as the wavelength of the laser used becomes shorter and the numerical aperture (NA) of the objective lens becomes larger, which is preferable for high-density recording. As a high-output laser that can be used for recording from the viewpoint that the optical system can be simplified and the economical efficiency of the apparatus, a 0.635 to 0.655 μm semiconductor laser is preferable, and 0.635 to 0.640 μm is preferable. Most preferred. Further, the NA of the lens is 0.60 ± 0.05 from the point of aberration due to thickness unevenness of the substrate and inclination of the substrate.

The transparent substrate used in the optical recording medium of the present invention preferably has a transmittance of light for recording and reading signals of 85% or more and a small optical anisotropy. For example, a known resin substrate such as an acrylic resin, a polycarbonate resin, and a polyolefin resin may be used. These substrates may be plate-like or film-like,
The shape may be circular or card-like. The surfaces of these substrates have grooves and / or pits indicating recording positions. Such grooves and pits are preferably provided at the time of molding the substrate, but may also be provided by providing an ultraviolet curable resin layer on the substrate. The track (groove) pitch and groove width are as described above,
The depth of the groove is preferably about 70 to 180 nm.

In the present invention, the recording layer contains a dye, but the physical properties of the dye used in the recording layer are important in terms of recording sensitivity, reflectivity, and the like. In particular, a dye that provides a large degree of modulation when pits are formed and has excellent threshold characteristics is particularly preferred. From this point, styryl dyes represented by the above formula (1) are preferable, and some of them are commercially available, so that they are easily available.

More specifically, the styryl dye of the above formula (1) used in the present invention is a compound represented by a substituted or unsubstituted 5- or 6-membered ring containing one nitrogen atom represented by A. Examples of the atomic group include structures such as oxazole (a), thiazole (b), selenazole (c), pyrrole (d), pyridine (e), and imidazole (f) represented by the following formula [Chemical Formula 3].

[0018]

Embedded image

A is pyrrole (d), imidazole (f)
In the case of the above, the substituents R4, R5 and R6 represent an unsubstituted or substituted alkyl group having 1 to 12 carbon atoms, and Q represents a benzene ring or a naphthalene ring fused to the 5- or 6-membered ring of A,
The benzene ring or naphthalene ring may have a substituent, and specific examples of the substituent include chlorine, bromine, fluorine, halogen such as iodine, an alkyl group, an alkoxy group,
Examples thereof include an alkylthio group, an aryl group, an aryloxy group, and an arylthio group.

[0020] Further, in the above formula (1), X ^- halogen ion, perchlorate ion, phosphonium ion, sulfonium ion, monovalent such known dithiol metal complex anion as a singlet oxygen quencher Anion.

In the present invention, a recording layer containing the above-described dye is provided directly on the substrate or via another inorganic or organic layer (undercoat layer). The method for providing the recording layer includes, for example, a spin coating method, a dipping method, a spraying method, and a vapor deposition method, and the spin coating method is preferable.

As a coating solvent for forming a film by the spin coating method, a solvent that does not damage the substrate is preferable.
Preferred solvents include, for example, alcohol solvents such as ethyl alcohol, propyl alcohol, butyl alcohol, furfuryl alcohol, ethylene glycol monomethyl ether, and tetrafluoropropanol.

When forming the recording layer, a binder can be used together if necessary. Preferred binders include nitrocellulose, cellulose acetate, ketone resin, acrylic resin, polyvinyl butyral, polycarbonate, polyolefin and the like. Further, other dyes can be added for improving recording characteristics and the like. Although the thickness of the recording layer affects the degree of modulation and the reflectance, in the present invention, the thickness is 40 nm to 300 nm, preferably 60 nm to 20 nm.
0 nm.

When the recording layer is formed on the substrate, a layer made of an inorganic substance or a polymer may be provided on the substrate in order to improve the solvent resistance, reflectance, recording sensitivity, etc. of the substrate.

In the present invention, a reflective layer is provided directly on the recording layer or via another layer. As the reflective layer, metals such as gold, silver, aluminum, copper, and platinum and alloys containing these metals are used. However, from the viewpoint of reflectance and durability, gold, aluminum, silver or these metals are mainly used. Is preferred. The thickness of the reflective layer is usually
It is 40 nm to 300 nm, preferably 60 nm to 200 nm. The method for forming the reflective layer includes, for example, vacuum deposition, sputtering, and ion plating.

In the present invention, a light interference layer may be provided between the recording layer containing the dye and the reflective layer in order to improve the characteristics such as the reflectance and the degree of modulation. Examples of a material for forming the light interference layer include an inorganic dielectric, a polymer, and a dye.

In the present invention, since the numerical aperture of the objective lens is large, the thickness of the substrate is set to 0.5 to reduce aberration.
It is preferably about 0.8 mm. At this time, in order to improve the strength and mechanical properties of the medium, two sheets may be attached to each other using an adhesive. In bonding, the bonding can be performed without forming a protective layer on the reflective layer or after forming the protective layer. As the protective layer, an ultraviolet curable acrylic resin, an ultraviolet curable epoxy resin, a silicone hard coat resin, or the like is used. In addition, as an adhesive for bonding, an ultraviolet curable acrylic resin, an ultraviolet curable epoxy resin, a hot melt adhesive, or the like is used.

The thus obtained optical recording medium of the present invention can perform recording and reproduction at a much higher density than the beam diameter by focusing the laser beam on the recording layer. Signals for recording include, for example, CDs and DVs.
The modulation signal used for D or the like is preferable for achieving the effects of the present invention.

[0029]

EXAMPLES The present invention will be described below in more detail with reference to examples, but embodiments of the present invention are not limited thereto. (Example 1) Spiral groove having a thickness of 0.6 mm and a diameter of 120 mm (depth: 145 nm, width: 0.30 μm, pitch: 0.1 mm)
While rotating this resin substrate on the grooved surface of an injection-molded polycarbonate substrate having a thickness of 74 μm), 2- (p-dimethylaminostyryl) -1,
3,3-trimethylindolium-3.5 of iodide dye
A weight% tetrafluoropropanol solution was dropped to form a recording layer substantially composed of only a dye on the substrate. The thickness of the recording layer was 170 nm.

[0030]

Embedded image

On this recording layer, a reflective layer having a thickness of 80 nm
After forming a gold thin film by sputtering, an ultraviolet curing adhesive was applied on the reflective layer. The same 0.6 mm substrate as described above was superimposed on the adhesive, rotated at high speed to remove excess adhesive, and then irradiated with ultraviolet rays to produce an optical recording medium.

This optical recording medium is put on a turntable,
While rotating at a linear speed of 2.8 m / s, the laser beam was passed through the substrate and the recording layer on the groove using a drive equipped with a semiconductor laser having an oscillation wavelength of 640 nm and an objective lens with an NA of 0.64. After recording the same EFM modulated signal as the CD with the shortest pit length of 0.4 μm while changing the recording laser power while controlling so that it converges on the laser, the laser output was set to 1 mW using the same device and the signal was recorded. Reading was performed. Note that an equalization process was performed when reading. Recording power is 8.4
At the laser output of mW, the error rate was the smallest (optimal recording power), the error rate was 5 × 10 ⁻⁴ , and the jitter at that time was 7% of the channel bit clock at both the rise and fall of the pit. . The reflectance of the unrecorded area is 52%, the modulation of the longest pit is 64%, the modulation of the shortest pit (I3 / I11: the ratio of the amplitude of the shortest pit to the amplitude of the longest pit) is 0.24, and the crosstalk is 64%. There was very good recording and reproduction. Almost no distortion was observed in the reproduced waveform. In this case, Wg is 0.30
r and P are 0.74r.

(Examples 2 to 4 and Comparative Examples 1 to 3) A medium was prepared and evaluated in the same manner as in Example 1 except that a groove-shaped substrate shown in Table 1 was used. The results are summarized in [Table 2]. As is clear from Table 2, extremely good recording and reproduction were achieved in the example of the present invention, but in the comparative example, the crosstalk was large, the modulation degree of the shortest pit was small, and the error rate and the error rate were small. Jitter was large and could not be recorded and played well.

[0034]

[Table 1]

[0035]

[Table 2]

(Examples 5 to 8) As the dyes used in the recording layer, styryl dyes of A to D represented by the following formula [Chemical Formula 5];
Track pitch 0.8 μm, groove width 0.35 μm, depth 17
A medium was prepared and evaluated in the same manner as in Example 1 except that a 0 nm substrate was used. However, a drive equipped with an optical head composed of an objective lens having an NA of 0.60 was used. The results are summarized in [Table 3]. In this case, Wg is 0.33r, and P is
0.75r.

[0037]

Embedded image

[0038]

[Table 3]

[0039]

As is clear from the examples of the present invention and the comparative examples, in the present invention, the track pitch in an optical recording medium having at least a recording layer containing a styryl dye and a reflective layer on a substrate is described. And groove width λ / NA
By defining the recording beam diameter (λ is the recording wavelength and NA is the numerical aperture of the objective lens) represented by the following expression, crosstalk can be made as small as possible and high-density recording can be performed.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI C07D 263/56 C07D 263/56 263/60 263/60 277/64 277/64 277/84 277/84

Claims (2)

[Claims] 1. A recording layer containing a dye that absorbs laser light, directly or through another layer, on a transparent substrate having a groove, and directly or through another layer on the recording layer. In an optical recording medium having a metal reflective layer, the diameter of the recording beam represented by λ / NA is r [where λ is the recording wavelength (μm), NA is the numerical aperture of the objective lens], and the groove of the substrate is When the pitch (track pitch) is P (μm) and the width of the groove is Wg (μm), Wg and P satisfy the following formula: 0.24r ≦ Wg ≦ 0.35r 0.68r ≦ P ≦ 0.83r, and a dye contained in the recording layer is a styryl dye represented by the following formula (1) [formula 1]. Embedded image [Where A represents an atomic group consisting of a substituted or unsubstituted 5- or 6-membered ring containing one nitrogen atom, and Q represents the 5
An atomic group consisting of an unsubstituted or substituted benzene ring or a naphthalene ring fused to a 6-membered or 6-membered ring;
Represents an unsubstituted or substituted alkyl group having 1 to 12 carbon atoms,
R1, R2 may form a ring with a benzene ring which is an amino group is bonded, n a is 1 or 2, X ^- represents a monovalent anion] 2. λ is 0.635 to 0.655 μm, NA
Is 0.60 ± 0.05.
3. A high-density optical recording medium according to claim 1.