JP2003045079A - Optical recording medium - Google Patents

Abstract

(57) [Problem] To use a blue laser having a laser wavelength λ of 405 nm and increase the objective lens NA to 0.85 to reduce the laser spot diameter. Provided is a novel write-once optical recording medium having a structure adapted to a system for recording and reproducing by incidence. SOLUTION: A guide groove having a depth of 3 / 8λ is provided, a reflective layer is provided on a synthetic resin substrate using a material having a heat deformation temperature of 150 ° C. or more, and a laser beam having a wavelength of 500 nm or less is provided on the reflective layer. A recording layer mainly composed of an organic dye that absorbs and changes the quality of the dye, a protective layer is provided on the recording layer, and a cover layer is provided on the protective layer. It was possible to develop a write-once optical disc that was capable of good recording and reproduction even with a method of performing recording and reproduction by using an optical disk and that had excellent weather resistance.

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 using a dye material for a recording layer, and more specifically, a wavelength of 500 nm.
Recording density for recording / reproducing using the following laser light 10
GB / in ² or more High density optical recording medium

[0002]

2. Description of the Related Art In recent years, not only computer information but also information such as voices, still images and moving images have been digitized,
The amount of information handled is becoming extremely large. Along with this, it has become necessary to increase the capacity of optical recording media for storing such information. In response to this, an optical recording medium such as a DVD-RAM or a DVD-RW having a capacity 7 times or more that of the conventional CD-R or CD-RW has been commercialized. As a means for realizing this high density, by reducing the laser wavelength (λ) or increasing the numerical aperture NA of the lens for the purpose of reducing the recording / reproducing laser spot diameter, , DV
D-RAM and DVD-RW have been commercialized.

However, the amount of information tends to increase further in the future. For example, a medium having the same size as a DVD and a capacity of at least 23 GB or more for recording video information of HDTV (high definition television) for two hours or more. Is coveted. In order to meet these demands, an optical recording that uses a blue laser with a laser wavelength λ of 405 nm and reduces the laser spot diameter by increasing the objective lens NA to 0.85 to record higher density information A medium has been proposed (Jpn.J.Appl.Phys.Vol.39 (2000) pp.756-76).
1, Part1, No.2B, Feb.2000). This optical recording medium is a rewritable optical recording medium using a phase change material for the recording layer, and the optical recording medium has a structure in which a reflective layer, a recording layer and a cover layer are provided in this order on a substrate. This is because the laser wavelength is decreased, the lens numerical aperture NA is increased, and the spot diameter is decreased. As a result, the spot aberration is increased. It was difficult to achieve this, and it was thought that the aberration would be reduced by reducing the thickness of the substrate on which light is incident. As one of the methods, a method has been proposed in which recording / reproducing is performed by irradiating a laser beam from the cover layer side, that is, the surface opposite to the conventional surface.

[0004]

DISCLOSURE OF THE INVENTION In order to develop a write-once type optical recording medium having a structure adapted to the above-mentioned recording system, we have prepared an optical recording medium using a dye material for a recording layer, and made various studies. Was done. However, we were not able to perform sufficient recording and playback experiments. Considering a number of factors in this optical recording medium, we speculate that there are the following causes.

It is conceivable that mechanical distortion caused by thermal influence occurred during the manufacturing process of the recording medium, during storage of the medium, or during recording / reproduction experiment of the medium. Further, it is conceivable that the guide groove (groove) provided on the substrate for tracking did not have an appropriate depth. This is because the groove depth is λ / 8 (25n
Since it was set to m), the difference in the dye amount between the land and the groove was small, and the dye amount in the groove corresponding to the recording pit was also small, and it is considered that the uniformity of the recording layer was insufficient.

An object of the present invention is to solve the above-mentioned causes and to provide a new write-once type optical recording medium having a structure adapted to a method of recording and reproducing by injecting a laser beam from the cover layer side. is there.

[0007]

An optical recording medium according to the present invention will be described below with reference to FIG. The inventors of the present invention have conducted various studies to solve the above problems. As a result, a reflective layer is provided on a synthetic resin substrate having a guide groove, and a laser beam having a wavelength of 500 nm or less is absorbed on the reflective layer. By providing a recording layer mainly composed of a degradable organic dye, further providing a protective layer on the recording layer, and providing a cover layer on the protective layer, laser light is incident from the cover layer side for recording and reproduction. We have been able to develop a write-once optical disc that allows good recording and reproduction even with the method.

The material used for the substrate 1 has a heat distortion temperature of 150 ° C.
The above is preferable. The blue laser has a higher energy density than the red laser, and the spot portion during recording becomes extremely hot. This is because if the heat distortion temperature (18.6 kg / cm 2) of the material used for the substrate 1 is 150 ° C. or lower, the substrate may be deformed during recording and a good tracking signal may not be obtained. Further, it is possible that mechanical distortion occurs due to thermal influence during the manufacturing process. By increasing the heat distortion temperature of the material used for the substrate 1, the tracking characteristics can be improved when the recording medium is rotated.

Suitable as the substrate material of the present invention is
For example, polyamide, polyether sulfone, polyarylate, polysulfone, amorphous polyolefin, polyimide, polyamideimide, polyetherimide, polyetheretherketone, econol and the like can be mentioned. Furthermore, in consideration of productivity, it is preferable to manufacture by an injection molding method or the like. Suitable as the substrate material of the present invention are, for example, polyamide, polyether sulfone, polyarylate, amorphous polyolefin, polysulfone, Amorphous polyolefins, polyamideimides, polyetherimides, polyetheretherketones, econols and the like.

Further, in the conventional optical recording medium, the laser beam is incident from the substrate side, and therefore the substrate material is required to have optical characteristics. However, the optical recording medium according to the present invention does not allow the laser beam to pass through the substrate. Since the material is not required to have optical characteristics, it is possible to add an additive to the substrate material. For example, glass fibers, carbon fibers, alumina fibers, silicon carbide fibers, potassium titanate whiskers and other additives are added to the substrate material for the purpose of improving the rigidity of the substrate, or the life of the substrate material is extended. Therefore, it is possible to add an ultraviolet absorber or carbon black.

A guide groove (groove) for tracking is formed on the substrate 1, and the groove depth (L) is L.
It is preferable to set it in the vicinity of = 3λ / 8. In a conventional dye-based recording medium, the groove depth L = λ / 8 is set so that a good tracking signal can be obtained due to reflection interference of light. However, when the blue laser is used for recording and reproduction,
Since the wavelength λ becomes shorter, L becomes smaller, and when L = λ / 8, accurate substrate molding becomes difficult. In addition, since L is small, the amount of dye in the groove is small, and good C / N cannot be obtained during reproduction. Therefore, it was found that when L was increased to L = 3λ / 8, the difficulty of substrate molding was eliminated. Also, since L became deeper and the dye layer in the groove increased, good C / N at the time of reproduction could be obtained. L
= 3λ / 8, the sign is opposite to that of L = λ / 8,
As with L = λ / 8, the tracking signal has a peak value,
There was no problem and tracking was possible. The relationship between the groove width (WG) and the land width (WL) is preferably WG> WL. This is because as the WG becomes larger, the amount of dye in the groove increases and a better C / N can be obtained during reproduction.

By attaching a resin substrate having excellent smoothness, a glass substrate, or a metal substrate manufactured in a separate process to the surface side of the substrate 1 where the guide groove is not formed, the rigidity is improved. It is conceivable to avoid problems such as distortion, warpage, and flexure of the medium. Furthermore, it is also possible to bond the media manufactured in the same process with the recording surface facing outward.

Since the reflective layer 2 provided on the substrate 1 functions as a reflective layer, it needs to have a reflectance of 20% or more with respect to the recording / reproducing wavelength. The thickness of the reflective layer 2 is 10
nm to 500 nm is preferable, and further 20 n
It is desirable that it is m to 200 nm. The reflective layer 2 is preferably manufactured by a sputtering method or a vapor deposition method. If the recording layer 3 has a reflectance of 15% or more with respect to the recording / reproducing wavelength, the reflecting layer 2 can be omitted.

The dye used in the recording layer 3 may be any dye compatible with a blue laser, and among them, porphyrin dyes, coumarin dyes, pyrazole azo dyes, porphycene dyes and the like are preferable. The recording layer 3 is the substrate 1
Alternatively, those having an affinity with the reflective layer 2 are more preferable. The thickness of the recording layer 3 is preferably 50 to 200 nm. Further, the recording layer 3 can be produced by a method such as a method of dissolving these dyes in a solvent and spin coating, a method of heating the dyes under reduced pressure and depositing them. An ultraviolet absorber, a light stabilizer, etc. may be added to the recording layer 3 in order to improve the stability of these dyes, and the decomposition heat quantity of the dyes is controlled in order to record a fine signal recording signal. You may add an additive.

Further, it is desirable to protect the substrate material 1, the reflection layer 2 and the recording layer 3 from damage due to an external force by providing the protective layer 4 on the recording layer 3. However, by providing the protective layer 4, it becomes difficult to secure the uniformity of the film thickness on the laser light incident side over the entire medium. In the optical recording medium according to the present invention, the NA of the laser used for recording / reproducing becomes large and the laser wavelength becomes small, so that the spherical aberration of the laser light is affected by the thickness tolerance of the protective layer 4 which transmits the light. This is because it becomes easier. In order to solve such a problem, it is desirable to further provide a cover layer 5 on the protective layer 4. The cover layer 5 can be formed by spin-coating a cured resin, and at this time, it may have a property of eroding the recording layer 3. It is also possible to adhere the polymer on the sheet by adhesion so as to cover the protective layer. Also,
The fact that the cover layer has the function of protecting the medium from deterioration factors such as oxygen or ultraviolet rays does not hinder the purpose of the present invention.

The hard cover layer 6 may be provided on the cover layer 5. For example, silicon nitride, silicon oxide, zinc sulfide, etc. can be used, and the thickness is 100n.
It is preferably m or less. The hard cover layer 6 can be manufactured by a method such as sputtering or ion plating.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of an optical recording medium obtained in an embodiment of the present invention will be specifically described below with reference to FIG.

[0018]

EXAMPLE 1 FIG. 1 is a sectional view showing the structure of an information recording medium obtained in Example 1 of the present invention. Groove width (WG) 210 nm, land width (W) on the surface of amorphous polyolefin (APO resin,) plate with diameter 120 mm and thickness (T) 1.1 mm
The substrate 1 formed with L) 170 nm and track pitch (W) 380 nm was produced by injection molding. Disc identification information, address information, etc. are pre-recorded on this substrate by wobbles in the groove. These pieces of information can also be formed by prepits. Grooves were used as tracks for recording information.

This substrate 1 was placed in a sputtering chamber in a sputtering apparatus which was excellent in film thickness uniformity and reproducibility. Using Ag as a target, thickness 100 in argon gas
A reflection layer 2 having a thickness of 2 nm was formed.

Next, 0.5 g of the porphycene dye was dissolved in 40 g of octafluoropentanol, and this was ultrasonically dispersed at 40 ° C. for 30 minutes, then filtered with a 0.2 μm filter, and the number of revolutions was 1300 rpm on the reflection layer 2. Spin coat with 80
Recording layer 3 was formed by drying in an oven at ℃ for 30 minutes.

Next, on the recording layer 3, 4-morpholine-2,
An aqueous solution of 5-dibutoxydiazonium trifluoromethanesulfonate and polyvinylpyrrolidone was spin-coated and dried to form a protective layer 4 having a thickness of 200 nm on the recording layer 3.

Next, an ultraviolet curable resin was spin-coated on the protective layer 4 and cured by UV irradiation to form a cover layer 5 with a thickness of 0.1 mm.

The write-once type optical recording medium 10 manufactured as described above is rotated at a linear velocity of 6 m / s to obtain a wavelength of 4
A semiconductor laser beam of 05 nm was condensed by an objective lens having a numerical aperture of 0.85, and noise was measured when reproducing with a reproducing power of 0.3 mW. For noise, the noise level of the reproduced signal at a frequency of 12 MHz was measured with a spectrum analyzer. Here, RBW is 30 kHz, VBW is 100H
z. The measured noise level was −75.0 dBm.

[0024]

According to the present invention, the wavelength of 50
It is possible to provide a write-once type optical recording medium that can obtain good tracking characteristics and C / N in a system of performing recording / reproducing by entering a laser beam of 0 nm or less.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical recording medium according to the present invention.

[Simple explanation of symbols]

1 substrate 2 reflective layer 3 recording layers 4 protective layer 5 cover layers 6 hard coat layer 10 write-once type optical recording medium T board thickness t Cover layer thickness L groove depth WG groove width WL land width W track pitch

Continued front page    (72) Inventor Yoshiyuki Nagataki             Hitachima, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. (72) Inventor Toshinori Sugiyama             Hitachima, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. (72) Inventor Rejin Tamura             Hitachima, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. (72) Inventor Kazuhiro Fujikawa             Hitachima, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. (72) Inventor Mitsuru Ito             Hitachima, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. F-term (reference) 2H111 EA03 EA12 EA22 EA37 EA39                       FA12 FA14 FA30 FA38 FB42                 5D029 JA04 JB21 JC01 KA01 KB03                       KC11 KC13 WB17 WC05

Claims (3)

[Claims] 1. A tracking guide groove for recording is formed on a synthetic resin substrate in which land portions and groove portions are regularly arranged adjacent to each other, and a metal reflective layer is provided on the substrate. A recording layer that absorbs and modifies laser light having a wavelength of 500 nm or less is provided on the reflective layer, and a cover layer containing a constituent resin is provided on the recording layer. An optical recording medium of a dye-based optical recording medium, wherein the substrate material has a heat distortion temperature of 150 ° C or higher. 2. An optical recording medium, wherein the recording layer contains an organic dye that absorbs and modifies laser light having a wavelength of 500 nm or less. 3. The depth (L) of the groove provided on the substrate is L = 3λ / 8 (λ: recording / reproducing) in the organic dye-based optical recording medium which irradiates the recording / reproducing laser beam from the cover layer side. Optical recording medium represented by a laser wavelength).