Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2002-02-04
2004-06-01
Mulvaney, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064800, C430S270140
Reexamination Certificate
active
06743494
ABSTRACT:
The invention is situated in the field of optical data storage devices, in particular optical data storage devices, which can be written to and read from by means of lasers. The invention relates to a recording medium for the recording layer of such a data storage device, to a method for the production of the recording medium and to an optical data storage device with a recording layer consisting of the recording medium, each in accordance with the generic term of the corresponding independent claim.
Optical data storage devices, which can be written to and read from by means of lasers (e.g., CD-R, DVD-R, DVD-RAM, DVD-RW or HD) usually comprise a disc-shaped, transparent carrier usually consisting of polycarbonate and on one side comprising a usually spiral-shaped recording groove and on this side usually being coated with three layers. These three layers are a recording layer, a reflective layer and a protective varnish layer. The recording layer is located directly on the carrier material on the side of the carrier structured by the groove and consists of a recording medium. This medium contains a dye or a mixture of dyes, the optical characteristics of which are changeable by a laser beam (writing beam). The reflecting layer is located on the recording layer and usually consists of a metal (e.g., silver, gold or aluminium). The protective varnish layer is located on the reflective layer and usually consists of a resin varnish, which is hardenable with ultraviolet light.
For writing, the data storage device is moved relative to a laser beam (writing beam) in the direction of the groove (rotated) and is written to by the laser, whereby the laser is directed onto the reflective layer through the carrier and the recording layer. In this, the wavelength range and the energy of the writing beam are designed in such a manner, that the absorption of the laser light in the recording layer leads to a local heating-up, through which between the carrier material and recording layer a bubble-shaped pit is produced and through which the chemical reaction in the recording layer leads to local change of the optical characteristics (e.g., de-colouring/bleaching) of the dye contained in this layer. The recording on the optical data storage device essentially consists of a sequence of points changed by the writing beam with a pit and chemically changed dye or dye mixture and unchanged points.
For reading, the data storage device is again moved relative to a laser beam in the direction of the groove, whereby the laser beam has a lower intensity than the writing beam and once again is directed onto the reflective layer through the carrier and the recording layer. Variations in the reflection of the laser beam (stronger and weaker reflection) at changed or unchanged points are evaluated as reading signals.
A production process for such data storage devices, for example, evolves in the following process steps:
Manufacturing of the polycarbonate carrier by injection moulding,
coating of the rotating carrier with a solution, in which the components of the recording medium are contained dissolved or as a colloid in an organic solvent or solvent mixture, wherein the solution is distributed over the carrier by means of centrifugal force and superfluous solution is centrifugally thrown off,
removal of the solvent or solvent mixture by volatilising,
application of the reflective layer by “sputtering”,
application and hardening of a protective varnish.
The steps mentioned above are usually carried out in a continuous process, into which advantageously also checking steps are integrated. Such checking steps serve for mostly optical checks of intermediate products and for elimination of defective products.
Continually increasing demands are made of the data storage devices described above, which demands above all relate to speed of writing and reading, to quality of writing and reading, to durability and last but not least, to the price. Writing and reading characteristics as well as durability and price of the data storage devices are to a great degree dependent on the characteristics of the recording layer, so that the demands of this layer are many and diverse. In particular, this layer is to make possible a suitable chemical reaction for the writing process, which for rapid writing is to require as little energy as possible, and simultaneously it should be chemically as stable as possible for a high durability. The chemical stability of the recording layer is also important, because it determines to a great extent, whether for the reflective layer a very noble and expensive metal has to be utilised or whether a less noble metal is sufficient. Furthermore, the solution of the recording medium, which is used for the production of the recording layer, has to have precisely defined rheological characteristics for the application by means of centrifugal force in such a manner, that the resulting layer has an accurately defined and as uniform as possible thickness, and it also has to be able to be dried rapidly and without any problems.
The dyes usually utilised in the recording layers of data storage devices and being changeable in their optical characteristics by a writing beam are, for example, cationic methine or poly-methine dyes (cyanin dyes, phthalo-cyanin dyes, azo dyes or metallized formazanes), which are commercially available, for example, as chlorides, bromides, fluorides, perchlorates, tetrafluoro borates or with anions of sulphone or carbonic acids. In order for the optical characteristics of the dyes to be easily changed by the writing beam, the recording medium in addition to the dye also contains a so-called quencher.
Dyes, which are suitable for utilisation in recording layers of data storage devices are described, for example, in the publications: EP-0403797, WO-93/22142, WO-98/14612, WO-99/37717, WO-99/05221, WO-98/34988, U.S. Pat. No. 5,900,348 (methine and poly-methine or cyanin dyes), JP-52047824, JP-58069255, JP-07314897 (phthalo-cyanin dyes), U.S. Pat. No. 5,731,054, U.S. Pat. No. 5,922,504 (metallised formazane dyes). It is also suggested to utilise mixtures of dyes, which contain two or three of the dyes mentioned.
Quenchers are also available on the market, for example under the trade name IRG 23 or IRG 003 by Nippon Kayako Co. Ltd.
It now becomes manifest that solutions, which contain the above mentioned known dyes and quenchers, are not very stable, because the quenchers are decomposable. For this reason, the solutions for the production of the recording layers cannot be made up in larger quantities and put into storage and in particular they cannot be unrestrictedly recycled. It also becomes manifest, that data storage devices with recording layers, which only contain the mentioned dyes and quenchers, can only be written to with limited speeds. Furthermore, such recording layers have a corrosive effect on the reflective layer in such a manner, that the latter has to be manufactured out of silver or gold to assure a sufficient durability of the data storage device.
The publication U.S. Pat. No. 5,436,113 describes an optical data storage device having a recording layer containing a phenol for stabilization.
It is the object of the invention to create a recording medium for recording layers of data storage devices, which recording medium comprises a significantly increased stability in comparison with known recording media, this both in the recording layer as well as in the solution utilised for the production of the recording layer.
This object is achieved by the recording medium for recording layers of optical data storage devices, by the process for the manufacture of the recording medium and by the data storage device, as they are defined in the corresponding independent claims.
The invention is based on the idea of stabilising the recording medium by the addition of a stabiliser in the form of a phenol with one or several hydroxy groups, which phenol is advantageously substituted. The phenol is present in the recording medium as a phenolate ion and is a substitute for a par
Bakardjieva-Eneva Jana
Rakovski Slavtcho
Zafirov Atanas
Interaxia AG
Mulvaney Elizabeth
Rankin, Hill Porter & Clark LLP
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