JPH10149583A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform high density recording by adjusting the diameter of a recording beam, the track pitch of a substrate groove, the shape of the groove and a pigment. SOLUTION: In this optical recording medium provided with a recording layer containing the pigment for absorbing laser beams directly or through an another layer on a transparent substrate provided with the groove and the reflection layer of metal directly or through the other layer on the recording layer, at the time of defining the diameter of the recording beam indicated by λ/NA as (r) [λ indicates a recording wavelength (# m) and NA indicates the opening number of an objective lens,] the track pitch of the groove of the substrate as P(μm) and the width of the groove as Wg(μm,) Wg and P are turned to be 0.24r<Wg<0.35r and 0.68r<P<0.83r and the pigment contained in the recording layer is turned to a trimethyl cyanine pigment.

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 T
A medium using a cyanine-based dye or a phthalocyanine-based dye for the recording layer is marketed as a CD-R medium, which is disclosed in Chemical Digest Series Vol. 1, 45 (1989). 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, but is currently a read-only medium made by transferring pits to a substrate. Therefore, DVD
There is a demand for a recordable optical recording medium having a large capacity close to the recording capacity of the 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 CD-R, so that thermal interference and crosstalk between the pits at the time of recording increase, and Since the modulation degree of the shortest pit becomes small, jitter and error rate become large, and it becomes difficult to perform high-density recording. Therefore, there is a demand for accurately forming small and small pits without sacrificing the degree of modulation during recording.

An optical recording medium having a trimethine cyanine dye as a recording layer is disclosed in Japanese Patent Application Laid-Open No. 6-40162.
However, this publication only discloses a trimethine cyanine dye as a dye having a recording sensitivity to short-wavelength laser light for high-density recording, and various conditions for increasing the recording capacity are specifically described. Nothing is disclosed.

[0006]

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

[0007]

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 made non-trivial selections on the recording beam diameter, track pitch, groove shape, and dye, and completed the present invention. .

That is, the present invention relates to (1) a recording layer containing a dye absorbing laser light, directly or through another layer on a transparent substrate having a groove; Alternatively, in an optical recording medium having a metal reflective layer via another layer, the diameter of a recording beam represented by λ / NA is r [where λ is the recording wavelength (μm), and NA is the numerical aperture of the objective lens. When the groove pitch (track pitch) of the substrate is P (μm) and the groove width is Wg (μm), Wg and P satisfy the following formula and are contained in the recording layer. Wherein the dye is a trimethine cyanine dye, 0.24r ≦ Wg ≦ 0.35r 0.68r ≦ P ≦ 0.83r (2) where λ is 0.635-0. 655 μm, NA = 0.
The high-density optical recording medium according to (1), wherein 60 ± 0.05.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical recording medium of the present invention comprises a recording layer containing a dye absorbing at least laser light on a transparent substrate, and a metal reflective layer. Even if the track pitch is reduced, high-density recording with reduced crosstalk can be performed without sacrificing the degree of modulation.

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,
Assuming that the recording beam diameter represented by λ / NA is r, the track pitch (P) should be 0.68r to 0.83r and the groove width (Wg) should be 0.24r to 0.35r. preferable. 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 becomes small,
If it exceeds 35r, crosstalk increases, which is not preferable.

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,
Further, the depth of the groove is preferably about 70 to 180 nm.

In the present invention, the recording layer contains a dye, and the physical properties of the dye used in the recording layer are important in terms of recording sensitivity, reflectance, and the like. It is particularly important in terms of the degree of modulation and the like, and specific examples are dyes that absorb light having a wavelength used for recording.For example, porphyrin dyes, polymethine dyes, cyanine dyes, azo dyes,
And naphthoquinone dyes.

In high-density recording, a dye having a large degree of modulation when pits of the same size are formed and having excellent threshold characteristics is particularly preferable. In this respect, a trimethine cyanine dye is preferable. .

The trimethine cyanine dye is a compound represented by the following formula (1) [Chemical Formula 1], some of which are commercially available, and thus can be easily obtained.

[0019]

Embedded image [Where Y and Y 'are CR4 R5, O, S, Se, NR
R1 to R6 are hydrogen or an unsubstituted or substituted alkyl group having 1 to 12 carbon atoms, A1 to A4 are hydrogen or an alkyl group having 1 to 4 carbon atoms, A1 and A2, or A3 and A4 May form an unsubstituted or substituted benzene ring or naphthalene ring. X represents a monovalent anion;
X may be omitted when is a monovalent anionic substituent. More specifically, the trimethinecyanine dye used in the present invention may be a 5-membered ring moiety composed of nitrogen and Y (Y '). , An indoline ring (Y, Y '= CR4 R5, A1
And A2 or A3 and A4 form a benzene ring), a benzoindoline ring (Y, Y '= CR4 R5, A1 and A2 or A
3 and A4 form a naphthalene ring), a thiazole ring (Y,
Y '= S), benzothiazole ring (Y, Y' = S, A1
And A2 or A3 and A4 form a benzene ring), a naphthothiazole ring (Y, Y '= S, A1 and A2, or A3 and A4
Form a naphthalene ring), an oxazole ring (Y, Y ′ =
O), benzoxazole ring (Y, Y '= O, A1 and A
2 or A3 and A4 form a benzene ring), naphthoxazole ring (Y, Y '= O, A1 and A2 or A3 and A4 form a naphthalene ring), imidazole ring (Y, Y' = N
R6), a benzimidazole ring (Y, Y '= NR6, A
1 and A2 or A3 and A4 form a benzene ring), a naphthoimidazole ring, a selenazole ring (Y, Y '= Se),
Examples include a benzoselenazole ring and a naphthoselenazole ring. The benzene or naphthalene ring formed by A1 and A2 or A3 and A4 may have a substituent. Specific examples of the substituent include halogen such as chlorine, bromine, fluorine, and iodine, an alkyl group, an alkoxy group, an alkylthio group, an aryl group, an aryloxy group, and an arylthio group. X represents a halogen ion, a perchlorate ion, a phosphonium ion, a sulfonium ion,
Examples of the singlet oxygen quencher include a monovalent anion such as a known dithiol metal complex anion.

In the present invention, a recording layer containing a dye absorbing laser light is provided directly on a 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 a recording layer is formed on a substrate, a layer made of an inorganic substance or a polymer is provided on the substrate as described above in order to improve the solvent resistance, reflectance, recording sensitivity, etc. of the substrate. May be.

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 and these metals are mainly used. Is preferred. The thickness of the reflective layer is usually 40 n
m to 300 nm, preferably 60 nm to 200 nm. Examples of the method for forming the reflective layer include 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 reflection 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 optical recording medium of the present invention thus obtained 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.

[0028]

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 150 nm, width 0.28 μm, pitch 0.
While rotating the resin substrate, a 3.5% by weight tetrafluoropropanol solution of a benzoindolinetrimethine cyanine dye represented by the following formula [Chemical Formula 2] was dropped on the grooved surface of the injection-molded polycarbonate substrate having a thickness of 74 μm). A recording layer consisting essentially of a dye was formed on the substrate. The thickness of the recording layer was 160 nm.

[0029]

Embedded image

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

Put this optical recording medium 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 638 nm and an objective lens with an NA of 0.63. 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 as to focus on the laser, the laser output was set to 1 mW using the same device, and the recorded signal was recorded. Reading was performed. Note that an equalization process was performed when reading. Recording power is 8.
When the laser output is 2 mW, the error rate is the smallest (optimum recording power), the error rate is 6 × 10 ^-4 , and the jitter at that time is 7% of the channel bit clock at both the rise and fall of the pit. there were. 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 shortest pit amplitude to the longest pit amplitude) is 0.23, and the crosstalk is 65%. There was very good recording and reproduction. Almost no distortion was observed in the reproduced waveform. In this case, Wg is 0.28
r and P are 0.73r.

(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.

[0033]

[Table 1]

[0034]

[Table 2]

(Examples 5 to 7) Trimethine cyanine dyes A to C represented by the following formula [Chemical Formula 3] were used as dyes for the recording layer, a track pitch of 0.8 μm, and a groove width of 0.36 μm.
A medium was prepared and evaluated in the same manner as in Example 1 except that a substrate having a depth of 150 nm was used. The results are summarized in [Table 3]. However, a drive equipped with an optical head composed of an objective lens having an NA of 0.60 was used. In this case, Wg is
0.34r and P are 0.75r.

[0036]

Embedded image

[0037]

[Table 3]

[0038]

As is clear from the examples and comparative examples of the present invention, in the present invention, a specific dye is used in an optical recording medium having at least a dye-containing recording layer and a reflective layer on a substrate. Is included in the recording layer, and the track pitch and the groove width are defined with respect to the recording beam diameter represented by λ / NA (λ is the recording wavelength, NA is the numerical aperture of the objective lens), thereby enabling crosstalk. Can be as small as possible,
High-density recording is possible.

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 groove width is Wg (μm), Wg and P satisfy the following formula, and the dye contained in the recording layer is
A high-density optical recording medium characterized by being a trimethine cyanine dye. 0.24r ≦ Wg ≦ 0.35r 0.68r ≦ P ≦ 0.83r 2. λ is 0.635 to 0.655 μm, NA
2. The high-density optical recording medium according to claim 1, wherein the ratio is 0.60 ± 0.05.