Stock material or miscellaneous articles – Circular sheet or circular blank
Utility Patent
1999-02-16
2001-01-02
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064400, C428S064800, C428S913000, C430S270140, C430S270160, C430S270190, C430S945000, C369S283000, C369S288000
Utility Patent
active
06168843
ABSTRACT:
TECHNICAL FIELD
This invention relates to an optical recording medium and more particularly, to a highly light resistant optical recording medium capable of writing and reading with a near-infrared laser of 770 to 830 nm, an optical recording medium capable of writing and reading with a red laser of 630 to 690 nm, or an optical recording medium capable of writing and reading with a near-infrared laser of 770 to 830 nm and a red laser of 630 to 690 nm.
BACKGROUND ART
The present inventors have been engaged in the development of write-once type compact discs (CD-R) as a recordable optical recording medium corresponding to the compact disc (CD) standard.
As the dye for the CD-R's, cyanine dyes have been widely employed because of their solubility and wavelength characteristics. The cyanine dyes, however, have the drawback of poor light resistance or fastness. As a solution to this problem, attempts have been made to add quenchers and to form salts with Ni and Cu dithiolene metal complexes. These methods leave the problems that light resistance is not fully improved and productivity is low on account of poor solubility.
Under such circumstances, JP-B 37580/1995 proposes an optical recording medium comprising a chromium-containing azo compound. This medium, however, is insufficient in light resistance. JP-B 37580/1995 also discloses an optical recording medium comprising a cyanine dye and an azo metal chelate compound of an azo compound with a metal. Further, JP-A 55189/1990 discloses an optical recording medium comprising a recording layer composed of a cyanine dye and a diol hexa-coordinate metal complex salt compound of naphthalenino-azobenzene. Mixtures of a cyanine dye and an azo metal compound as used in these examples provide insufficient light resistance. Also, JP-A 51182/1991 discloses an optical recording medium comprising on a transparent substrate a recording layer containing a photo-stabilized organic dye in the form of a bonded compound of an anion of an electron-accepting azo metal complex salt compound with a cation of a cyanine dye having absorption in the wavelength region of recording light. However, neither the cyanine dye cation nor the compound bonded therewith is specified therein, and the desired characteristics are not obtained when certain cyanine dye cations are combined. The only exception is
FIG. 2
showing the absorption spectrum of a recording layer. But we confirmed that no satisfactory characteristics were obtained when such a dye was applied to CD-R.
Higher density optical recording media are desired in the recent years. Exemplary media are CD-R of the next generation wherein the recording wavelength of CD-R is reduced from the current 780 nm to a shorter wavelength of 680 nm to 635 nm and write-once type digital video discs (DVD-R) capable of recording and reading at 650 nm. With the interchangeability with the existing CD-R taken into account, CD-RII capable of reading at a short wavelength too has been proposed. The requirements on the dyes used in these standards are considered substantially equal to those on the currently used dyes except the wavelength. However, since development works have hitherto been made so as to match with 780 nm, there are known few dyes which can satisfy desired characteristics including light resistance, solubility and recording sensitivity on the shorter wavelength side of 680 nm to 635 nm.
For use in recording layers of optical recording media adapted to record signals at a laser wavelength of 680 nm to 635 nm, mention may be made of cyanine dyes, which undergo substantial photo-degradation and lack stability. Dyes having higher light resistance include metal azo complexes as described in JP-B 51682/1995, JP-A 268994/1991, and JP-A 156408/1996, for example. Despite high light resistance, these dyes have the problems of low recording sensitivity and low solubility, and that when used in optical recording media, the dyes fail to afford a good balance between Rtop and modulation among disc characteristics on account of a broader half band width of their absorption spectrum.
DISCLOSURE OF THE INVENTION
A primary object of the invention is to provide an optical recording medium which has improved light resistance and a sufficient solubility in coating solvents which do no attack polycarbonate substrates, especially fluorinated alcohol solvents and cellosolve solvents capable of improving a tact time, and exhibits excellent recording/reading characteristics complying with the CD standard to light having a wavelength selected from the range of 770 nm to 830 nm, especially a wavelength of 780 nm. A second object is to provide an optical recording medium which has improved light resistance and exhibits excellent recording/reading characteristics at a wavelength selected from the range of 630 nm to 690 nm, especially 635 nm to 680 nm; and a third object is to provide an optical recording medium which, in addition to the above advantages, exhibits excellent recording characteristics sufficient to enable recording and reading in accordance with the CD standard, with light having a conventional wavelength selected from the range of 770 nm to 830 nm, especially a wavelength of 780 nm.
This and other objects are achieved by the present invention which is defined below as (1) to (17).
(1) An optical recording medium comprising a recording layer containing a salt-forming dye between an ion of an azo metal complex of the following formula (I) and an ion of a cyanine dye of the following formula (II), the salt-forming dye having a complex index of refraction in the wavelength region of recording light and/or reading light whose imaginary part k is up to 0.20;
wherein in formula (I), A is an aromatic ring group having an active hydrogen-bearing group at a position adjacent to the diazo group or a nitrogenous heteroaromatic ring group having therein a metal ion-coordinatable nitrogen atom at a position adjacent to the carbon atom in the ring attached to the diazo group; B is an aromatic ring group having an active hydrogen-bearing group at a position adjacent to the diazo group; m is equal to 1 or 2; and M
1
is a center metal, with formula (I) schematically illustrating the coordination of A—N═N—B thereto;
in formula (II), Q
1
and Q
2
each are a group of atoms forming a 5-membered nitrogenous heterocyclic ring which may have a fused ring; L is a methine chain; R
1
and R
2
each are an alkyl group.
(2) The optical recording medium of (1) wherein in formula (II), the nitrogenous heterocyclic ring completed by Q
1
or Q
2
which may have a fused ring is an indolenine ring, thiazoline ring or oxazoline ring, and L is trimethine or pentamethine.
(3) The optical recording medium of (1) or (2) wherein the ion of cyanine dye of formula (II) is an ion of an indolenine type cyanine dye.
(4) The optical recording medium of any one of (1) to (3) wherein the center metal represented by M
1
in formula (I) is vanadium, cobalt, nickel or copper.
(5) An optical recording medium comprising a recording layer containing an azo oxovanadium metal complex between an azo compound of the following formula (III) and oxovanadium;
A—N═N—B (III)
wherein A is an aromatic ring group having an active hydrogen-bearing group at a position adjacent to the diazo group or a nitrogenous heteroaromatic ring group having therein an oxovanadium-coordinatable nitrogen atom at a position adjacent to the carbon atom in the ring attached to the diazo group; and B is an aromatic ring group having an active hydrogen-bearing group at a position adjacent to the diazo group.
(6) The optical recording medium of (5) wherein A in formula (III) is an aromatic ring group having an active hydrogen-bearing group at a position adjacent to the diazo group.
(7) An optical recording medium comprising a recording layer containing an azo metal complex obtained by combining at least one of an azo compound of the following formula (IV) and a compound of the following formula (V) with a metal compound;
wherein X is an active hydrogen-bearing group, R
1
and R
2
eac
Kambe Emiko
Kitagawa Sumiko
Monden Atsushi
Shinkai Masahiro
Evans Elizabeth
Lasker, Esq. R. J.
Laubscher & Laubscher
TDK Corporation
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