Radiation imagery chemistry: process – composition – or product th – Liquid crystal process – composition – or product
Patent
1997-02-28
1999-01-12
McPherson, John A.
Radiation imagery chemistry: process, composition, or product th
Liquid crystal process, composition, or product
430290, 430330, G03C 556
Patent
active
058585850
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for amplifying information generated by changing the configuration of side groups in polymers by means of high-energy light. The process according to the invention allows the original intensity of an image, which is partially lost at the end of the writing operation, to be restored or even increased.
One possible way of optical data storage uses laser light for generating images by thermal destruction of organic layers (M. Emmelius, G. Pawlowski, H. J. Vollmann, Angew. Chem. 101, 1475-1502 (1989); T. N. Gerasimova, V. V. Shelkovnikov, Russ. Chem. Rev. 61, 55-66 (1992)).
A disadvantage of this method is the limited scope for modifying and erasing images once written.
Another possible way of optically storing information is to irradiate polymers containing side groups, which change their configuration on exposure to light. Such "photoaddressable" polymers are known in principle: for example, WO 93/3073 describes homopolymers containing azobenzene side groups, EP-A 333 022 describes cholesteric liquid-crystalline polymers, EP-A 369 432 describes liquid crystalline polymers and DE-A 38 10 722 describes amorphous polymers which are suitable for optical information storage. When the irradiation is complete, however, the light-induced modification of the irradiated zones drops, the degree of this drop naturally depending, inter alia, on the polymer type, leaving at best a small residue of the induced modification which is stable for an extended period. When the temperature is raised above the glass transition temperature Tg of the polymer, the residual modification is said to be further reduced and disappears completely when the clearing point is reached (J. Stumpe, L. Muller, L. Laisker, D. Kreysig, G. Hauck, H. D. Koswig, S. Kostromin, V. Shibaev; Proceedings of the 20th Freiburg Congress on Liquid Crystals 1991).
Surprisingly, it has now been found that the effect remaining at the end of the writing operation and after relaxation of the light-induced modification can be re-amplified if the polymer is warmed to a temperature which is below the clearing point and in the region of the glass transition temperature Tg. The effect according to the invention can in fact be detected below the glass transition temperature, but is only achieved within a time span of practical interest above the Tg.
The invention thus relates to a process for amplifying the light-induced modification in a side-chain polymer by warming to a temperature between the glass transition temperature and the clearing point.
The clearing point is defined as the temperature at which the nematic into the isotropic phase. It can be measured by DSC analysis (2nd heating curve, 10.degree. C./minute). The assignment of the phase types can be deduced by comparison with known data from X-ray diffraction analysis of the homopolymers.
Examples of so-called side-group polymers which are suitable for the process according to the invention are described in the earlier German Patent Application P 43 39 862.6. In the glass state before irradiation, they should be optically isotropic, transparent, non-scattering and amorphous and after irradiation they should be transparent and semipermanently birefringent and dichroic owing to light-induced alignment of the side groups which is reversible in the glass state (the term "amorphous" for the purposes of the invention also includes states containing microdomains which are so small that they cannot be detected; this is generally the case if their diameter is less than 1/20 of the wavelength of light). They have a main chain which acts as backbone and covalently bonded side-groups branching off from this and have the following features: configuration can be changed induced by a light; shape-anisotropic side group, other than (1), having high anisotropy of the molecular polarizability; chain and the side groups (1) and (2).
Examples of groups whose configuration can be changed induced by light are groups containing double bonds whose cis- and trans-configurations can be converted into o
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Bieringer Thomas
Claussen Uwe
Eisenbach Claus Dieter
Fischer Karl
Fischer Thomas
Bayer Aktiengesellschaft
McPherson John A.
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