Radiation imagery chemistry: process – composition – or product th – Erasable imaging
Patent
1989-04-14
1991-10-29
Bowers, Jr., Charles L.
Radiation imagery chemistry: process, composition, or product th
Erasable imaging
430270, 430343, 430495, 430945, 430962, G11B 724, G03C 173, G03C 1825
Patent
active
050615823
DESCRIPTION:
BRIEF SUMMARY
It is known to store information in digital form wherein a "laser sensitive" material is exposed to the action of a laser beam to provide a "bit" of information. For example optical data storage discs are known where exposure to a laser beam causes photo-ablation, physical deformation, or magnetic or optical density changes. The recorded information can then be read by sensing the change which has occurred. A problem exsists, whatever medium is used for the recording, in that the profile of intensity of the laser beam is usually gaussian ie. the beam is of lesser intensity at its edges. For best operation, it would be preferable if the profile were of the "top-hat" type, that is constant intensity across the beam. Bit edges would then be more sharply defined allowing greater bit packing density and hence greater optical data storage.
In our co-pending U.K. patent application No. 8607715, we describe the use of photochromic fulgides and fulgimides to provide enhanced contrast in photo resist technology. The term "fulgide" as used herein includes fulgimides and other similar bistable photochromic compounds. In this application, there is described a technique in which a photochromic fulgide is employed. The fulgide can exist in two photochemically interconvertible states, one of which is a UV absorbing colourless compound which by the absorption of UV light changes to a second, UV transparent, visible light absorbing (coloured), compound. The second compound, by absorption of visible light, can be made to revert to the colourless form. In contrast enhanced resist technology, a film of UV absorbing material is locally exposed to UV light, and is thus converted to a UV transparent material which acts as a mask for the layer or layers beneath.
This approach is known in lithography as the portable conformable mask (PCM). It can be seen therefore that, by their nature, photochromic materials produce an artificial contrast enhancement effect. This may be used in one of two ways, either with a thin photochromic film, acting as a PCM on layers below in which it is intended to produce an image, or with a single photochromic layer where the outer surface acts as an automatic contrast enhancer for the material below.
It is an object of the present invention to provide an improved recording medium for optical data storage.
According to the present invention, there is provided an optical data storage medium comprising a support and at least a first layer consisting of a photochromic fulgide (as herein defined) having first and second stable states, the photochromic fulgide whilst in its first state being responsive to light of a first wavelength to change state and to become transparent to said first wavelength light and, in said second state, being responsive to light of a second wavelength to revert to its first state.
The invention will be described further, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic cross-section of a portion of an optical data storage medium in accordance with the present invention; and
FIGS. 2, 3 and 4 are similar view of further embodiments of optical data storage medium each in accordance with the present invention.
Referring firstly to FIG. 1, there is shown a fragmentary portion of an optical data storage medium constructed in accordance with the present invention. The medium comprises a support 10 which may be in the form of a circular disc having on its upper surface a layer 12 of a photochromic fulgide material. Such materials are known per se and are described in, inter alia, "The Allen Clark Research Centre Annual Review 1977" page 66 by R. J. Hurditch and C. J. Kirkly and also in a paper by H. G. Heller published by the Royal Society of Chemistry, Special Publication, vol. 60 (1986) pp 120-135.
As stated above the term "fulgide" as used herein includes fulgimides and other chemically similar bistable photochromic compounds.
The photochromic fulgide layer 12 has two stable states. In its first state, it is colourless and absorbs light of
REFERENCES:
patent: 4186002 (1980-01-01), Heller et al.
patent: 4737427 (1988-04-01), Miyazaki et al.
patent: 4737449 (1988-04-01), Heller et al.
"The Allen Clark Research Centre Annual Review 1977", by R. J. Hurditch et al., pp. 66-74.
Royal Society of Chemistry, Special Publication, vol. 60 1986, pp. 120-135, by H. G. Heller.
Bennion Ian
Brettle Jack
Groves-Kirkby Christopher J.
Bowers Jr. Charles L.
Buscher Mark R.
Plessey Overseas Limited
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