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A photopolymer in search of a developer.

Researchers at the University of Alicante in Spain have developed a new photopolymer which may be used as a holographic recording material. It is said to have a lower potential toxicity than conventional materials and is characterized as being environmentally friendly, since it does not contain any petroleum-derived solvents or other components classified as toxic, biotoxic, explosive, radioactive, oxidising, corrosive, inflammable or environmentally hazardous, and no such substances are used to prepare it.

Photopolymers are made up of a photopolymerization initiator, sensitizing dye and one or more polymerizable monomers in a polymer matrix which acts as a support. They are usually based on methyl methacryhc or other esters derived from acrylic acid so they are toxic. Since they need to be produced in hydrophobic conditions, inflammable organic solvents must be used, thus implying a problem of safety, difficulty in handling and a high risk of environmental contamination.

Furthermore, when these materials reach the end of their useful life, toxic inflammable organic solvents are needed to recycle them.

Other photopolymers use acryla-mide as the polymerizable monomer. These materials are distinguished by their high toxicity and carcinogenic properties. Derivatives of acrylic acid, epoxidic acrylates or silicon gels impregnated with esters of methacrylic acid have also been used, all of which are insoluble in water.

The Alicante developers claim it is possible to automate all the stages of their photopolymer preparation and it enables holograms to be obtained in a single stage without the need for subsequent processing.

The light sensitive photopolymer hasthe following composition:

* Metallic or ammonium salts of acrylic acid soluble in water are used as monofunctional monomers.

* Optionally, 1,2-dihydroxiethyl-ene-bis-acrylamide is used as a bi-functional monomer. This substance is soluble in water and acts as cross-linker.

* A metallic or ammonium salt of riboflavin 5'-monophosphate, a non-toxic substance soluble in water which allows the recording material to be used in the wavelength range of 200-550 nm is used as sensitizing dye capable of undergoing a photochemical oxidation or reduction reaction after absorbing light at the appropriate wavelength.

* 4,4'-azo-bis(4-cianopentanoic) acid, which enables the length of the polymeric chains formed during recording to be controlled, is used as chain transfer agent.

* Triethanolamine, which enables the energetic sensitivity of the recording material to be controlled is used as deactivator of free radicals.

* Glycerine is used to modify the thickness of the photopolymer layer

* Deionised or distilled water is used as regulator of the molecular diffusion processes that take place in the material.

* A hydrophilic organic polymer, soluble in water, is used as the matrix containing all the other components. It is selected from the following: xanthan gum, polyvinyl alcohol, the sodium salt of 3carboximethyl cellulose, methyl cellulose, ethyl cellulose, gelatin.

The final mixture is deposited in open moulds made of a chemically inert material, or on a transparent or partially transparent support. They are placed on a level surface in a dark chamber which allows the temperature and humidity to be controlled. After the water content has partially evaporated, a flexible plastic film between 20 and 2,000 micrometers thick is obtained and may be removed from the mould. This is the light sensitive holographic recording material.

It is claimed that this holographic recording material can be used to record holograms by means of any holographic technique. The holograms are obtained by exposure to light in a single stage and without the need for subsequent processing. The material exposed to light may be protected with totally or partially transparent plastic so as to guarantee its mechanical properties.

The application envisioned for the technology include holographic inter-ferometry; 3D holography for security and other applications; fabrication of holographic optical elements such as lenses, filters, systems for processing -images and optical fibre network intercommunication devices, and holographic data storage.

The technology is patented by the University (see below), which is looking for companies interested in acquiring this technology for its commercial exploitation. Any of the various forms of technology transfer (patent license agreement, transfer of user, manufacturing or commercializing rights to third parties, etc.) would be considered.

Contact: Alvaro Berenguer Berenguer SGITT-OTRJ (University of Alicante) Phone: +34 96 590 3467 E-Mail: URL: otri/es/areas/ttot/ttototachr. htm

RELATED ARTICLE: Alicante's Photopolymer Patent

The University of Alicante has a Spanish patent on its new photopolymer. Patent number is ES2288386, titled Registration method for environmentally compatible holgraphic material based on metallic acrylate, includes photopolymerizable material sensitive to light comprising metallic salt or ammonia of acrylic acid.


The method includes photopolymerizable material sensitive to light comprises a metallic salt or ammonia of acrylic acid, 1,2-dihydroxy-ethylene-bis-acrylamide, triethanolamine, a polymer having a number average molecular weight of between 25000 and 200000 e.g. xantana rubber, polivinilico alcohol, sodium salt of carboxy methyl cellulose, methyl cellulose, gelatin, a metallic salt of ammonia of 5'-riboflavin monophosphate, deionized water, cyanopentanoic acid and glycerin. The photopolymerizable material is subjected to the holographic registration process and the information of registration is stored and is recoverable later.
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Publication:Holography News
Date:May 1, 2011
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