Optical data storage medium containing a diaza hemicyanine...

Details Optical data storage medium containing a diaza hemicyanine... Optical data storage medium containing a diaza hemicyanine...

2002-03-20

2004-04-27

Mulvaney, Elizabeth (Department: 1774)

Stock material or miscellaneous articles

Circular sheet or circular blank

C428S064400, C428S064800, C430S270160, C430S270170

Reexamination Certificate

active

06726972

ABSTRACT:

The invention relates to a preferably once recordable optical data storage medium containing a diaza hemicyanine dye as the light-absorbing compound in the information layer, and to a process for its production.
Recordable optical data storage media using special light-absorbing substances or mixtures thereof are particularly suitable for use in high-density recordable optical data storage media which operate with blue laser diodes, and in particular GaN or SHG laser diodes (360-460 nm), and/or for use in DVD-R or CD-R discs, which operate with red (635-660 nm) or infrared (780-830 nm) laser diodes, and the application of the above-mentioned dyes to a polymer substrate, in particular polycarbonate, by spin-coating or vapour deposition.
There has recently been an enormous growth in the sales of recordable compact discs (CD-R, 780 nm), which represent the technically established system.
The next generation of optical data storage media—DVDs—is currently being introduced onto the market. By using shorter-wave laser radiation (635 to 660 nm) and a higher numerical aperture NA, the storage density can be increased. The recordable format is in this case the DVD-R.
Today, optical data storage formats which use blue laser diodes (based on GaN, JP 08191171 or Second Harmonic Generation SHG JP 09050629) (360 nm to 460 nm) with a high laser power, are being developed. Recordable optical data storage media will therefore also be used in this generation. The achievable storage density depends on the focussing of the laser spot in the information plane. The spot size is proportional to the laser wavelength &lgr;/NA. NA is the numerical aperture of the objective lens used. The aim is to use the smallest possible wavelength &lgr; for obtaining the highest possible storage density. Based on semiconductor laser diodes, 390 nm are presently possible.
The patent literature describes dye-based recordable optical data storage media which are equally suitable both for CD-R and DVD-R systems (JP-A 11 043 481 and JP-A 10 181 206). In order to obtain high reflectivity, a high modulation level of the readout signal and sufficient sensitivity during recording, use is made of the fact that the IR wavelength 780 nm of the CD-R is located at the base of the long-wavelength slope of the absorption peak of the dye and the red wavelength 635 nm or 650 nm of the DVD-R is located at the base of the short-wavelength slope of the absorption peak of the dye. In JP-A 02 557 335, JP-A 10 058 828, JP-A 06 336 086, JP-A 02 865 955, WO-A 09 917 284 and U.S. Pat. No. 5,266,699 this concept is extended to cover the working wavelength range of 450 nm on the short-wavelength slope and the red and IR range on the long-wavelength slope of the absorption peak.
In addition to the above-mentioned optical properties, the recordable information layer consisting of light-absorbing organic substances must have a morphology which is as amorphous as possible, in order to keep the noise signal during recording or reading as small as possible. For this purpose it is particularly preferable, when applying the substances by spin-coating from a solution or by vapour deposition and/or sublimation, to prevent crystallization of the light-absorbing substances during the subsequent top-coating with metallic or dielectric layers in vacuo.
The amorphous layer of light-absorbing substances should preferably have high thermal stability, since otherwise additional layers of organic or inorganic material applied by sputtering or vapour deposition onto the light-absorbing information layer form blurred boundaries due to diffusion and thus have an adverse effect on the reflectivity. In addition, if a light-absorbing substance has inadequate thermal stability at the boundary to a polymeric substrate, it can diffuse into the latter and again have an adverse effect on the reflectivity.
If the light-absorbing substance has too high a vapour pressure, it can sublime during the above-mentioned sputtering or vapour deposition of additional layers in a high vacuum and thus reduce the desired layer thickness. This in turn has a negative effect on reflectivity.
The object of the invention is therefore to provide suitable compounds which meet the high demands (such as light stability, a favourable signal-to-noise ratio, damage-free application to the substrate material, etc.) for use in the information layer of a recordable optical data storage medium, in particular for high-density recordable optical data storage formats in a laser wavelength range of 340 to 680 nm.
Surprisingly, it has been found that light-absorbing compounds from the diaza hemicyanine group of dyes are particularly suitable for satisfying the above-mentioned requirement profile.
The invention therefore relates to an optical data storage medium containing a preferably transparent substrate which has optionally already been coated with one or more reflecting layers and onto the surface of which a photorecordable information layer, optionally one or more reflecting layers and optionally a protective layer or an additional substrate or a top layer are applied, which data storage medium can be recorded on and read using blue or red light, preferably laser light, wherein the information layer contains a light-absorbing compound and optionally a binder, characterized in that at least one diaza hemicyanine dye is used as the light-absorbing compound.
Blue laser light is particularly preferred.
The light-absorbing compound should preferably be thermally modifiable. Preferably the thermal modification is carried out at a temperature of <600° C., particularly preferably at a temperature of <400° C., very particularly preferably at a temperature of <300° C., and in particular at a temperature of <200° C. Such a modification can for example be the decomposition or chemical modification of the chromophoric centre of the light-absorbing compound.
A diaza hemicyanine of the formula (I) is preferred
in which
K represents a radical of the formulae (II) to (IV)
X
1
represents O or S,
X
2
represents O, S, CH or N—R
2
,
X
3
represents N, CH or C—CN,
R
1
, R
2
and R
12
independently of one another represent C
1
- to C
16
-alkyl, C
3
- to C
6
-alkenyl, C
5
- to C
7
-cycloalkyl or C
7
- to C
16
-aralkyl,
A together with X
2
and the C-atom bound therebetween represents a five-membered aromatic or quasi-aromatic heterocyclic ring which can contain 1 to 4 hetero atoms and/or can be benzo- or naphtho-fused and/or substituted by non-ionic radicals,
R
3
, R
4
, R
5
and R
6
independently of one another represent hydrogen, C
1
- to C
16
-alkyl, C
4
- to C
7
-cycloalkyl, C
7
- to C
16
-aralkyl or a heterocyclic radical or
NR
3
R
4
or NR
5
R
6
independently of one another represent a five- or six-membered saturated ring which is attached via N and can additionally contain an N or O atom and/or be substituted by non-ionic radicals,
R
7
represents hydrogen, C
1
- to C
16
-alkyl, C
1
- to C
16
-alkoxy or halogen or
R
7
and R
5
form a two- or three-membered bridge which can contain an O or N atom and/or be substituted by non-ionic radicals,
R
8
represents hydrogen, C
1
- to C
16
-alkyl, C
1
- to C
16
-alkoxy, halogen, cyano, C
1
- to C
4
-alkoxycarbonyl, O—CO—R
10
, NH—CO—R
10
, O—SO
2
—R
10
or NH—SO
2
—R
10
,
R
9
represents hydrogen, C
1
- to C
4
-alkyl or C
6
- to C
10
-aryl,
R
10
represents hydrogen, C
1
- to C
16
-alkyl, C
4
- to C
7
-cycloalkyl, C
7
- to C
16
-aralkyl, C
1
- to C
16
-alkoxy, mono- or bis-C
1
- to C
16
-alkylamino, C
6
- to C
10
-aryl, C
6
- to C
10
-aryloxy, C
6
- to C
10
-arylamino or a heterocyclic radical,
R
11
represents hydrogen, C
1
- to C
4
-alkyl or C
6
- to C
10
-aryl and
An
−
represents an anion.
Suitable non-ionic radicals are for example C
1
- to C
4
-alkyl, C
1
- to C
4
-alkoxy, halogen, cyano, nitro, C
1
- to C
4
-alkoxycarbonyl, C
1
- to C
4
-alkylthio, C
1
- to C
4
-alkanoylanino, benzoylamino, mono- or di-C
1
- to C
4
-alkylamino.
Alkyl, alkoxy, aryl and heterocyclic radicals can optionally contain additional radicals such as alkyl, halogen, nitro, cy

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