Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2001-03-30
2003-05-27
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S001000, C430S002000, C430S945000, C369S288000, C359S003000
Reexamination Certificate
active
06569600
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an optical recording element which is capable of storing and retrieving information.
BACKGROUND OF THE INVENTION
The modem information revolution has led to an ever increasing demand for data storage systems. As a case in point, CD and DVD disks represent successful high volume data storage technologies. One major advantage of these technologies is that reading or writing of data is accomplished by shining light on the disk so there is no physical contact between the media and the optical head. However, the total storage capacity of these disks is limited by the size of the smallest marks on the surface of the media that can be read by the wavelength of light employed. Many attempts have been made to develop data storage systems with progressively smaller marks. However, the required equipment is prohibitively expensive, and the data access rates tend to be unacceptably slow.
One way to increase the storage capacity of a medium is to record the information depthwise, rather than just on the surface. There could be used holography, two-photon optics, and similar methods for illuminating media in three dimensions, with the goal of producing marks in three dimensions, and thereby providing very high data capacity systems.
Bleaching and photoreactions (e.g., photochromicity) of organic dyes has also been used as a means to record optical data, both in a single layer in writeable CD-type media, and depthwise (dissolved in a bulk piece of polymer). However, a large amount of optical power is required in these systems to produce readable marks, therefore the rate of recording of such media is slow. Also, many photochromic systems also tend to fade over time.
Holographic recording has also been achieved by optically induced birefringence in suitable polymers, a process which relies on photo-alignment of the side chains within the polymers. Once again, a large amount of optical power is required, and this process is inefficient and slow. In addition, the fidelity of the recorded information may degrade with time since optically induced orientation tends to relax over time in polymers.
JP 2000-086588 discloses a recording medium using changes in circular dichroism based on the interconversion of chiral norbornadiene and quadricyclane derivatives. However, this technique requires enantiomerically enriched compounds that are difficult to synthesize. Furthermore, this application does not disclose the use of sensitizers for photoinduced electron transfer.
U.S. Pat. No. 5,759,721 discloses a holographic recording medium which uses a photopolymerization technique which can also be used for recording information optically in three dimensions.
There is a problem with this process, however, in that photopolymerization is usually accompanied by shrinkage of the material which is a consequence of the process of forming new chemical bonds among the constituents. Any dimensional changes that occur on writing limit the resolution that can be achieved, and reduce the data capacity of the medium. In addition, photopolymerization generally requires the use of low molecular weight reactants so that media made from these materials tend to be undesirably soft or sticky. Furthermore, the most common method of photopolymerization, free radical polymerization, is subject to interference by atmospheric oxygen which causes undesirable inconsistencies in the process.
It is an object of this invention to increase the storage capacity of a optical recording material. It is another object of this invention to provide an optical recording material which can record information depthwise, rather than just on the surface. It is still another object of this invention to provide an optical recording material which does not substantially change dimensions upon recording.
SUMMARY OF THE INVENTION
These and other objects are achieved in accordance with the invention which comprises an optical recording material which when exposed to actinic radiation produces a change in optical properties in the exposed regions, thereby providing a pattern of intelligence for storing and retrieving information, the recording material comprising:
a) a binder,
b) a reactant which is capable of undergoing a chemical transformation upon a one electron oxidation, thus causing the change in optical properties in the exposed regions, and
c) a sensitizer capable of absorbing actinic radiation to cause an initial one electron oxidation of the reactant.
In accordance with the invention, an optical recording material is obtained which possesses several advantages over the prior art.
1. The invention involves a photoinitiated chain reaction in a solid polymer that creates changes in the optical properties of the material. However, because our invention relies on photoisomerization rather than photopolymerization, the dimensional changes accompanying recording are negligible. (No new bonds are formed between molecules.)
2. The invention involves a recording process that is efficient in the use of light. Because the process involves a photoinitiated chain reaction, many new molecules are formed per photon absorbed (chemical amplification). A relatively large change in optical properties is obtained with only a small exposure to the recording beam.
3. The material of the invention is a simple, stable polymer, which can be conveniently fabricated into films and slabs.
4. The optical changes in the material of the invention are large, permanent, localized, and can easily be detected, forming the basis for an optical storage medium. The invention is especially suited to three dimensional optical data recording systems such as holography and two-photon optics.
5. Unlike free radical polymerization, cation radical rearrangements of the invention are not sensitive to molecular oxygen, and will not be subject to the inconsistent performance which is commonly observed for free radical photopolymerizations that are currently used in the art.
DETAILED DESCRIPTION OF THE INVENTION
Any binder may be used in the invention provided it dissolves the reactant and sensitizer. Suitable binders include a monomeric glass as defined in U.S. Pat. Nos. 4,499,165 and 4,626,361, the disclosures of which are hereby incorporated by reference, such as sucrose octaacetate; or a polymeric material such as, for example, poly(alkyl methacrylate), poly(alkyl acrylate), polystyrene, polycarbonate, cellulose acetate or poly(vinyl butyral). In general, the binder should be optically transparent in the spectral region where the sensitizer absorbs, i.e., should not have significant absorption at the excitation wavelengths, and should not interfere with the chemical transformation of the reactant. The binder may also contain a plasticizer, a preservative, etc.
The optical recording element of the invention may be in the form of a self-supporting slab or disk. It may also be coated on a support such as poly(ethylene terephthalate), poly(ethylene naphthoate), polystyrene, cellulose acetate, inorganic supports such as glass, quartz, silicon, etc. In a preferred embodiment, the support is a polyester or glass.
The surface of the substrate may be treated in order to improve the adhesion of the recording layer to the support. For example, the surface may be corona discharge treated prior to applying the optical recording material. Alternatively, an under-coating or subbing layer, such as a layer formed from a halogenated phenol or a partially hydrolyzed vinyl chloride-vinyl acetate copolymer, can be applied to the surface of the support.
The recording layer thickness may range from about 1 &mgr;m to about 1 cm, preferably from about 100 &mgr;m to about 1000 &mgr;m.
As noted above, the reactant used in the invention is capable of undergoing a chemical transformation upon a one electron oxidation, thus causing the change in optical properties in the exposed regions of the optical recording material. Such compounds undergo a photoinduced cation radical rearrangement to product species, a process which defines the recording event. With the product form
Dinnocenzo Joseph P.
Erdogan Turan
Farid Samir Y.
Robello Douglas R.
Angebranndt Martin
Cole Harold E.
Eastman Kodak Company
Leipold Paul A.
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