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Radical photoinitiators for holographic data storage

IP.com Disclosure Number: IPCOM000016456D
Publication Date: 2003-Jun-23
Document File: 2 page(s) / 10K

Publishing Venue

The IP.com Prior Art Database

Related People

Gabriele Weidenbr├╝ck: CONTACT

Abstract

This disclosure relates to photoinitiators, which generate radicals and initiate polymerization of monomer upon irradiation with blue laser radiation, suitable for holographic data storage. The wavelength range of the blue laser is 390 - 420 nm, preferably 400-410 nm and particularly 405 nm. It was found that suitable classes of photoinitiators, which combine high reactivity with low absorbance at 405 nm are aminoacetophenones, acylphosphineoxides, bisacylphosphineoxides, oxime esters, and borate-dye combinations. Suitable dyes for blue laser radiation are for example coumarines, xanthones, thioxanthones , where oxime ester derivatives having a thioxanthone chromophor as part of the molecular structure are particularly preferred.

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Radical photoinitiators for holographic data storage

This disclosure relates to photoinitiators, which generate radicals and initiate polymerization of monomer upon irradiation with blue laser radiation, suitable for holographic data storage. The wavelength range of the blue laser is 390 - 420 nm, preferably 400-410 nm and particularly 405 nm.

The holographic data storage system is preferably comprised of a matrix network of low-refractive index matrix precursors and high-refractive index photopolymerizable monomers. The media matrix is formed by in-situ polymerization which yields as cross-linked network in the presence of the photopolymerizable monomers which remain "dissolved" and unreacted. The matrix containing unreacted, photopolymerizable monomers can also be formed by other means, for example by using a solid-resin matrix material in which the photoreactive, liquid monomer is homogeneously distributed. Then, monochromatic exposure generates the holographic pattern, which according to the light intensity distribution, polymerizes the photoreactive monomers in the solid pre-formed matrix. The unreacted monomers (where light intensity was at a minimum) diffuse through the matrix, producing a modulation of the refractive index that is determined by the difference between the refractive indices of the monomer and the matrix and by the relative volume fraction of the monomer. The thickness of the recording layer is in the range of several micrometers up to a thickness of one millimeter. Because of such thick holographic data storage layers it is required that the photoinitiator combines high photoreactivity with low absorbance, in order to render the layer transparent at the laser wavelength to assure that the extent of photopolymerization is as little as possible dependent on the exposure depth into the recording layer.

It was found that suitable classes of photoinitiators, which combine high reactivity with low absorbance at 405 nm are aminoacetophenones, acylphosphineoxides, bisacylphosphineoxides, oxime esters, and borate-dye combinations, wherein the dye absorbs the laser radiation. Suitable dyes for blue laser radiation are for example coumarines, xanthones, thioxanthones (such as isopropyl thioxhanthone, diethylthioxanthone, 2-isopropylthio- xanthone, 3-isopropylthioxanthone, 2-chlorothioxanthone, 2-dodecylthio- xanthone, 1-chloro-4-propoxythioxanthone, 2,4-diethylthioxanthone, 2,4...