OPTICAL RECORDING MEDIUM AND OPTICAL RECORDING-REPRODUCING METHOD USING THEREOF CROSS REFERENCES TO RELATED APPLICATIONS
The present invention contains subject matter related to Japanese Patent Application JP 2004-312944 filed in the Japanese Patent Office on October 27, 2004, the entire contents of which being incorporated herein by reference.
BACKGROUND OF THE INVENTION Field of the Invention:
The present invention relates to an optical recording medium, more particularly an optical recording medium using an organic dye as a recording layer, and an optical recording-reproducing method using thereof. Description of the Related Art:
As an optical recording medium, an optical recording medium using an optical organic dye material in a recording layer is configured to have a recording layer whose principal ingredient is an organic dye, and also a reflection layer, a protection layer, and the like according to a necessity, on a transparent substrate such as a plastic, and information is recorded in high density by scanning laser light on a surface of this recording layer and by forming a pit only in a portion of the irradiated surface.
An organic dye recording medium which is represented by a CD-R (write-once type CD: Compact Disc, registered trademark) is
dely accepted in the market as a backup of data, image, and the like and also as a music use since a structure is simple and it is possible to manufacture at a low cost. However, there is a desire for a recording medium having a further larger capacity along with a rapid progress of a computer in recent years, and a demand for the optical recording medium using the organic dye is shifting from the CD-R and the like to a DVD-R and DVD+R (right-once type DVD: Digital Versatile Disc, registered trademark).
Recording of information onto the optical recording medium using the organic dye is performed in heat mode. When the laser light is irradiated to the recording layer, the organic dye of the irradiated portion is resolved by absorbing the laser light to generate heat. Since the portion where the organic dye is resolved has a different reflectivity from an unresolved portion, a pit is to be formed inside the recording layer. Accordingly, a mechanism to absorb the heat becomes important in the optical recording medium using the organic dye.
An amount of heat necessary for resolving the organic dye inside the recording layer is determined by a light absorption spectrum. Generally, when the absorption of light becomes large in a certain wavelength, a recording sensitivity becomes high although a reflectivity is decreased. On the contrary, when the absorption becomes small, the reflectivity becomes high although the recording sensitivity is decreased.
Although a reflectivity characteristic and a recording
Sensitivity characteristic of the recording layer are important in the optical recording medium using the organic dye, those characteristics have a mutually close correlation as described hereinbefore and therefore give a big influence on a recording characteristic of the optical recording medium. In the DVD, the laser light of a shorter wavelength of 650nm (DVD-R) or 655nm (DVD+R) than the CD is used in order to increase a recording density, and the organic dye which has been previously used for the CD-R may not be used for the DVD-R and DVD+R due to a reason that the absorption is so large in this wavelength range as to shift greatly from the optimum recording sensitivity.
Moreover, even in the DVD-R and DVD+R, high speed recording is demanded similarly to the CD-R. In a recording material to perform the high speed recording, it is required that not only the reflectivity is high, but also the recording sensitivity is a high sensitivity, and a resolving speed of a dye due to heat is fast.
Various dye materials suitable for application to the DVD-R and the like have been proposed (for example, refer to patent references 1 and 2) .
However, a recording-reproducing characteristic at the time of high speed recording is not sufficiently studied.
In addition, a deterioration of a signal characteristic at the time of low speed recording is observed when the material is optimized to the high speed recording by simply increasing the
resolving speed of the dye, and also similarly an opposite case is that a signal characteristic at the time of high speed recording is deteriorated when the material is optimized to the low speed recording.
Furthermore, there is a possibility that a light stability characteristic deteriorates in the organic dye recording medium of high sensitivity.
Therefore, it is very difficult to satisfy simultaneously all of the recording characteristic and the light stability characteristic over low speed to high speed recording in one single organic dye recording medium.
[Patent Reference 1] Japanese patent application publication No. 2002-52829
[Patent Reference 2] Japanese patent application publication No. 2003-231359
SUMMARY OF THE INVENTION
The present invention aims at providing with an optical recording medium which enables to obtain an excellent recording characteristic over low speed recording to high speed recording in the optical recording medium of the write-once type such as the DVD-R and DVD+R, and an optical recording-reproducing method using thereof.
In order to solve the above-described problems, an optical recording medium according to an embodiment of the present invention is configured to have a recording layer that contains
an organic dye, wherein the recording layer has at least an organic dye that is expressed by a general formula shown in the following chemical formula 1 (in this formula, Rl represents an alkyl group of carbon number 1 through 4, R2 and R3 represent respectively an alkyl group of carbon number 1 through 4 and a benzyl group or group forming three to six-member ring by coupling, each of Yl and Y2 independently represents an organic group, and X represents C104, BF4, PF6, and SbF6) and an organic dye that is expressed by a general formula shown in the following chemical formula 2 (in this formula, Rl and R4 represent an alkyl group of carbon number 1 through 4, R2 and R3 represent respectively an alkyl group of carbon number 1 through 4 and a benzyl group or group forming three to six-member ring by coupling, each of Yl and Y2 independently represents an organic group, and X represents C104, BF4, PF6, and SbF6) . [Chemical Formula 1]
(FORMULA REMOVED)

Further, an optical recording-reproducing method according
to an embodiment of the present invention uses the optical recording medium having the above-described configuration of the embodiment of the present invention.
The optical recording medium according to the embodiment of the present invention is configured to have the recording layer mixing the organic dyes expressed in the general formulas of the above-described chemical formula 1 and chemical formula 2 as described hereinbefore, and thereby it is possible to suppress a jitter over the low speed recording to high speed recording that is from a IX speed to a 16X speed, which has not been previously obtained, and an excellent recording-reproducing characteristic can be obtained.
Furthermore, it is possible to provide with an optical recording-reproducing method that enables excellent recording and reproduction at least over IX speed recording to 16X speed recording by performing the recording and reproduction using such optical recording medium.
According to the optical recording medium of the embodiment of the present invention, an excellent recording-reproducing characteristic can be obtained over the low speed recording to high speed recording as explained hereinbefore.
Moreover, in the optical recording medium of the embodiment of the present invention, the jitter and reflectivity can be maintained in an excellent range by choosing a grooving
depth D of a groove formed in a substrate to become:
100nml00nm , and the reflectivity in D = 200nm is lower than 45% that is a lower limit of the standard of the write-once type DVD.
Then, it is understood that the groove depth satisfying the signal characteristic and reflectivity simultaneously is:
100ww<200wn
Also, in case of suppressing the jitter into less than 8%, it is desirable that the groove depth D is:
110nm l{W\ + W2 + W3) < 0.35 In addition, it is desirable that the weight ratio is in the following range in order to suppress the jitter lower.
0.1≤W3/ (W1 + W2 + Wl) < 0.3
In the above-described example, the study is made to a case that the material shown in the above-described chemical formula 5 is used as the deactivation agent, but an almost similar effect can be obtained even in a case that another deactivation agent such as a deactivation agent, for example, shown in the following chemical formula 6 or chemical formula 7 is used.
(FORMULA REMOVED)

Furthermore, in order to improve the light stability, a phthalocyanine dye and azo system dye that are stable to light may be added inside the recording layer in addition to the above-described deactivation agent.
Next, a study is made to the optical density (OD) of the recording layer. A compounding ratio of the recording layer materials is set such that the weight ratio of the organic dyes shown in the above-described chemical formula 3 and chemical formula 4 is W2/(W1 + W2) = 0.5 and also the weight ratio of the deactivation agent shown in the above-described chemical formula 5 is W3>/(W1 + W2 + W3) = 0.2 in order to produce an optical recording media whose optical density of the recording layer is changed.
In this example, the optical recording medium is produced under five conditions in which the optical densities (OD) of the organic dye film in the maximum wavelength of the absorption are 0.25, 0.40, 0.50, 0.60, and 0.70, and the jitter values are measured respectively at the time of IX speed recording and at the time of 16X speed recording. A result of this measurement is shown in FIG. 7.
From the result shown in FIG. 7, it is understood that the jitter at the time of 16X speed recording is lower than 9% when
the optical density (OD) of the recording layer is 0.25 and the jitter becomes 9% in case that the optical density is made to be OD=0.70. Therefore, it is understood that a range of the optical density OD in which a sufficient signal quality can be obtained is:
0.25 < OD < 0.70
Also, in case of suppressing the jitter into 8% or less, it is desirable that the optical density OD is:
0.35 < OD < 0.60 Moreover, in case of suppressing the jitter further into 7% or less, it is more desirable that the optical density OD is:
0.35 < OD < 0.60
According to the optical recording medium of the embodiment of the present invention, it becomes possible to provide with the optical recording medium in which the signal characteristic satisfying sufficiently the standard of the write-once type DVD can be obtained over the wide range of recording speed from the IX speed to the 16X speed in an optical system of the DVD type as explained hereinbefore.
In addition, it is possible to provide with the optical recording medium of the organic dye type having more excellent light stability by adding the deactivation agent.
It should be noted that the optical recording medium according to the embodiment of the present invention is not limited to each embodiment described hereinbefore but a similar
Effect can be obtained even when the present invention is applied to an optical recording medium that conforms or approximately conforms to the standard of the DVD+R type, or an optical recording medium that conforms or approximately conforms to the standard of the DVD-R type.
Here, numerical values including a light wavelength for recording and reproduction, a numerical aperture of a condensing lens, a IX line speed, and a tolerance of a shortest mark length according to the standard of the DVD+R type and DVD-R type optical recording medium are shown in the following table 2.
(TABLE REMOVED)

It should be noted that the light wavelength of 655nm +10nm/-5nm for recording and reproduction of the DVD+R means that the tolerance is +10nm and also -5 ran, and similarly the light wavelength of 650nm +10nm/-5nm for recording of the DVD-R means that the tolerance is +10nm and also -5nm in the above-described table 2.
In addition, it should be clear that various modifications
and alterations other than those described hereinbefore are possible within a scope not departing from the configuration of the present invention such that the present invention can be also applied to a case that a recording layer made of a dye material, for example, is made into a two-layers configuration in a configuration of an optical recording medium.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.

What is claimed is:
1. An optical recording medium comprising a recording layer that contains an organic dye, wherein said recording layer has at least:
an organic dye expressed by a general formula shown in the following chemical formula 1 (in this formula, Rl represents an alkyl group of carbon number 1 through 4, R2 and R3 represent respectively an alkyl group of carbon number 1 through 4 and a benzyl group or group forming three to six-member ring by coupling, each of Yl and Y2 represents independently an organic group, and X represents CIO4, FB4, PF6, and SbF6) ; and
an organic dye expressed by a general formula shown in the following chemical formula 2 (in this formula, Rl and R4 represent an alkyl group of carbon number 1 through 4, R2 and R3 represent respectively an alkyl group of carbon number 1 through 4 and a benzyl group or group forming three to six-member ring by coupling, each of Yl and Y2 represents independently an organic group, and X represents C104, FB4, PF6, and SbF6) . [Chemical Formula 1]
(FORMULA REMOVED)
2. An optical recording medium according to claim 1, wherein the optical recording medium is comprised such that a grooving depth D of a groove provided in a substrate of said optical recording medium is 100nm < D < 200nm .
3. An optical recording medium according to claim 1, wherein the optical recording medium is comprised such that a width Wg of the groove provided in the substrate of said optical recording medium is 230nm < Wg < 400nm .
4. An optical recording medium according to claim 1, wherein the optical recording medium is comprised such that the organic dye shown in said chemical formula 1 is a material of a structural formula shown in the following chemical formula 3.
[Chemical Formula 3]
(FORMULA REMOVED)

5. An optical recording medium according to claim 1,
wherein the optical recording medium is comprised such that the
organic dye shown in said chemical formula 2 is a material of a
structural formula shown in the following chemical formula 4.
[Chemical Formula 4]
(FORMULA REMOVED)

6. An optical recording medium according to claim 1,
wherein the optical recording medium is comprised as:
0.1 < W2I(W\ + W2) < 0.8 when a weight of the organic dye shown in said chemical formula 1 is put as Wl and a weight of the organic dye shown in said chemical formula 2 is put as W2.
7. An optical recording medium according to claim 1,
wherein the optical recording medium is comprised such that a
deactivation agent is added to said recording layer.
8. An optical recording medium according to claim 7,
wherein the optical recording medium is comprised as:
0.08 < W3 /(Wl + W2 + W3) < 0.35
when a weight of the organic dye shown in said chemical formula 1 is put as Wl, a weight of the organic dye shown in said chemical formula 2 as W2, and a weight of said deactivation agent as W3.
9. An optical recording medium according to claim 1,
wherein the optical recording medium is comprised as:
0.25 < OD < 0.70 when an optical density in a maximum wavelength of an absorption of said organic dye is put as OD.
10. An optical recording-reproducing method which uses an
optical recording medium comprising a recording layer that
contains an organic dye, wherein said optical recording medium
has at least following in said recording layer:
an organic dye expressed by a general formula shown in said chemical formula 1 (in this formula, Rl represents an alkyl group of carbon number 1 through 4, R2 and R3 represent respectively an alkyl group of carbon number 1 through 4 and a benzyl group or group forming three to six-member ring by coupling, each of Yl and Y2 represents independently an organic group, and X represents CIO4, FB4, PF6, and SbF6) ; and
an organic dye expressed by a general formula shown in said chemical formula 2 (in this formula, Rl and R4 represent an alkyl group of carbon number 1 through 4, R2 and R3 represent
Respectively an alkyl group of carbon number 1 through 4 and a benzyl group or group forming three to six-member ring by coupling, each of Yl and Y2 represents independently an organic group, and X represents C104, FB4, PF6, and SbF6) .
11. An optical recording-reproducing method according to claim 10, wherein a wavelength of light for recording and reproduction of said optical recording medium is 655nm+10nm/-5nm, a numerical aperture NA of a focusing lens that focuses said laser light onto said optical recording medium is 0.6510.01, a shortest mark length of information to be recorded onto said optical recording medium is 0.4 0um±0.003um, a IX line speed is 3.49±0.03m/s, and a track pitch of said optical recording medium is 0.74um±0.03um.
12. An optical recording-reproducing method according to claim 10, wherein a wavelength of light for reproduction of said optical recording medium is 650nm±5nm, a wavelength of light for recording is 650nm+10nm/-5nm, a numerical aperture NA of a focusing lens that focuses said laser light onto said optical recording medium is 0.60±0.01, a shortest mark length of information to be recorded onto said optical recording medium is 0.40um±0.003um, a IX line speed is 3.49m/s±0.03m/s, and a track pitch of said optical recording medium is 0.74um±0.03um.