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Radical photoinitiators for holographic data storage

IP.com Disclosure Number: IPCOM000029578D
Publication Date: 2004-Jul-08
Document File: 5 page(s) / 86K

Publishing Venue

The IP.com Prior Art Database

Abstract

The following text relates to photoinitiators, in particular 1-[4-(phenylthio)phenyl]-2-(O-benzoyloxime)-1,2-octanedione and derivatives thereof and 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-1-(O-acetyloxime)-ethanone and derivatives thereof and oxime sulfonate compounds in combination with sensitizers, 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. Holographic storage systems (holographic recording media) are for example used to record and to retrieve large amount of data with fast access time. The photoinitiators as described below are for example in particular suitable for systems as described for example in WO 03/021358.

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Radical photoinitiators for holographic data storage 

The following text 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. Holographic storage systems (holographic recording media) are for example used to record and to retrieve large amount of data with fast access time.

The photoinitiators as described below are for example in particular suitable for systems as described for example in WO 03/021358.

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 matrix precursor and photoactive monomer can be selected such that (a) the reaction by which the matrix precursor is polymerized during the cure is independent from the reaction by which the photoactive monomer will be polymerized during writing of a pattern, e.g. data, and (b) the matrix polymer and the polymer resulting from polymerization of the photoactive monomer (the photopolymer) are compatible with each other.  The matrix is considered to be formed when the photorecording material, i.e. the matrix material plus the photoactive monomer, photoinitiator and/or additives, exhibits an elastic modulus of at least about 105 Pa, generally about 105 Pa to about 109 Pa.

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 in particular oxime esters, combinations of oxime su...