Optical recording medium

Details Optical recording medium Optical recording medium

2002-08-20

2004-04-06

Mulvaney, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064800, C430S270200

Reexamination Certificate

active

06716509

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical recording medium, particularly to an optical recording medium for recording layer comprising at least one asymmetric trimethine-cyanine dye with specific functional group and an additive, which can enhance the writing sensitivity of DVD-R.
2. Description of the Related Art
An optical recording medium capable of once recording by a laser ray has been known. In the structure of the CD-R recording medium, a recording layer comprising an organic dye, a reflection layer and a protective layer are laminated on a transparent substrate by order. The recording information on the disc is performed by irradiating a laser at a wavelength of 780 nm to 830 nm to cause exothermic deformation of the recording layer. The information is usually reproduced by irradiating with the same laser ray, and the reflecting difference between the recorded area and unrecorded area is detected for the recording layer.
It is known that a laser ray with a shorter wavelength has a reduced light spot. Therefore, studies have being made to develop the optical disc capable of recording and reproducing by a laser beam of a wavelength of 620 nm to 690 nm to increase the recording density. Recordable digital video (DVD-R), which is capable of recording and reading in high density, is propagated as new media of the next generation. Since the wavelength zone for performing the recording and reproducing in DVD-R differs from that of the CD-R, the criteria for selecting the recording material to be employed for the CD-R cannot be applied to the DVD-R. Hence, new selection criteria are required to be established from a viewpoint peculiar to the DVD-R.
Trimethine-based cyanine dye is a popular material for the DVD-R recording layer. U.S. Pat. No. 5,976,658, and U.S. Pat. No. 6,291,045 described the use of trimethine-based cyanine dye having symmetry or asymmetry indolenine structure for DVD-R. However, the dye material should be selected carefully, while the writing wavelength of laser beam of DVD-R machines is changed from 635 nm to 650 nm (or further). Because the wavelength of laser power is getting longer, the dye absorbance of film state for 650 nm should be increased a little more. The dye, which is suitable for writing wavelength of 635 nm laser beam, is not performed well while the writing wavelength of laser beam is 650 nm because of low sensitivity at the region that might cost higher writing power to record information or record failed.
SUMMARY OF THE INVENTION
Said in U.S. Pat. No. 6,338,888, increase the sensitivity of recording could be reached by increasing the absorption of organic layer at the wavelength of writing laser. According to the opinion, we declare a new composition with specific additives which could enhance the recording sensitivity.
The first object of the present invention is to provide an asymmetric indolenine cyanine dye with electron-withdrawing group which is substituted on one ring of indolenine or benzoindolenine by the formula [1], [2], [3], [4], which are shown in scheme 1.
The second object of the present invention is to provide an optical recording medium with a recording layer, which comprises at least one asymmetric trimethine-cyanine dye with electron-withdrawing substituted group (EWG) and an additive which is a kind of asymmetric trimethine-cyanine dye with electron-donating substituted group (EDG).
The third object of the present invention is to provide a process to prepare asymmetric trimethine-cyanine dye with electron-withdrawing group and the one with electron-donating substituted group (EDG).
The fourth object of the present invention is to provide an optical recording medium with improved write/read characteristics at the writing wavelength of 650 nm or further.
According to the invention, the asymmetric trimethine-cyanine dye with electron-withdrawing substituted group used in the recording layer is any one represented by the general formulas [1], [2], [3], and [4] which were shown in scheme 1. “EWG” represents any electron-withdrawing substituted group, such as cyano and nitro group. “R
3
” and “R
2
” are independently selected from substituted or unsubstitued alkyl, phenyl, benzyl, alkylphenyl and phenoxyalkyl group. “R
3
” and “R
4
” are independently selected from hydrogen atom, halogen atom, alkoxy, hydroxyl or alkyl group. “Y” is selected from hydrogen atom, halogen atom or alkyl group, and “X” is an anion selected from the group consisting of F
−
, Cl
−
, Br
−
, I
−
, ClO
4
−
, BF
4
−
, PF
6
−
, SbF
6
−
, OTs
−
, OMs
−
, SCN
−
, alkylsulfonate and alkylcarboxylate. The material has a maximum absorption wavelength from 575 nm to 600 nm. It is used as a recording material for DVD-R machine with the laser wavelength from 620 nm to 690 nm.
The material used in the recording layer also selectively comprises the trimethine-cyanine dye of the following general formula [5]:
“A” and “B”, may be the same or different from each other, represent any one of the following general formulas [6], [7], [8], and [9]:
“D” may be any one of the substituted or unsubstitued alkyl, carboxyl, alkoxycarbonyl, alkylcarboxyl, alkoxyl, alklhydroxyl, aralkyl, alkenyl, alkylamide, alkylamino, alkylsufonamide, alkylcarbamoyl, alkylsulfamoyl, hydroxyl, halogen atom, hydrogen atom, alkylalkoxyl, alkylhalide, alkylsulfonyl, alkylcarboxyl or alkylsulfonyl which are bonded to a metallic ion or alkyl, phenyl, benzyl, alkylphenyl or phenoxyalkyl group. “p” represents the number of substituent groups, which is an integer of 1 or more.
“R
5
” and “R
6
” may be the same or different from each other and are individually substituted or unsubstitued alkyl, phenyl, benzyl, alkylphenyl or phenoxyalkyl group. “Z” is hydrogen atom, halogen atom or alkyl group, and “X” is an anion selected from the group consisting of F
−
, Cl
−
, Br
−
, I
−
, ClO
4
−
, BF
4
−
, PF
6
−
, SbF
6
−
, OTs
−
, OMs
−
, SCN
−
, alkylsulfonate, and akylcarboxylate.
The material as an additive used in the dye layer also selectively comprises any trimethine-cyanine dye represented by the following general formulas [10], [11], [12], and [13]:
“EDG” represents any electron-donating substituted group such as amino, alkylamino, and methoxy group. “R
7
” and “R
8
” are the same or different from each other and are individually substituted or unsubstitued alkyl, phenyl, benzyl, alkylphenyl and phenoxyalkyl group. “R
9
” and “R
10
” are independently selected from hydrogen atom, halogen atom, cyano or nitro group. “Y” is hydrogen atom, halogen atom or alkyl group, and “X” is an anion selected from the group consisting of F
−
, Cl
−
, Br
−
, I
−
, ClO
4
−
, BF
4
−
, PF
6
−
, SbF
6
−
, OTs
−
, OMs
−
, SCN
−
, alkylsulfonate and alkylcarboxylate. The material has a maximum absorption wavelength from 575 nm to 620 nm. It is used as a recording material for DVD-R machine with the laser wavelength from 620 nm to 690 nm. The dye layer comprising not only the trimethine-cyanine dye containing “EWG” but also the trimethine-cyanine dye containing “EDG” has the advantage of increasing the recording sensitivity, so that the writing power of laser can be reduced while recording information in DVD-R.
The method of preparing dye solution according to this invention can be described as follows.
(1) A cyanine dye represented by general formula [1], [2], [3], or [4] was dissolved in an organic solvent, such as fluorinated alcohol, diaceton alcohol, methylethyl ketone, methanol, toluene, cyclohexanone, acetylacetone, and dioxane. The concentration of the dye solution was 0.5% to 20% by weight.
(2) A dye mixture, which contains cyanine dye represented by general formula

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