Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K4/00—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K4/00—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens
  • G21K2004/06—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens with a phosphor layer
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K4/00—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens
  • G21K2004/10—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens with a protective film

Definitions

• the present invention relates to a binderless storage phosphor screen with vapour deposited phosphors.
• a well known use of storage phosphors is in the production of X-ray images.
• US-A-3 859 527 a method for producing X-ray images with a photostimulable phosphor, which are incorporated in a panel is disclosed.
• the panel is exposed to incident pattern-wise modulated X-ray beam and as a result thereof the phosphor temporarily stores energy contained in the X-ray radiation pattern.
• a beam of visible or infra-red light scans the panel to stimulate the release of stored energy as light that is detected and converted to sequential electrical signals which (are) be processed to produce a visible image.
• the phosphor should store as much as possible of the incident X-ray energy and emit as little as possible of the stored energy until stimulated by the scanning beam. This is called “digital radiography” or "computed radiography”.
• a protective layer can be coated onto the phosphor containing layer by directly applying thereto a coating solution containing a film-forming organic solvent-soluble polymer such as nitrocellulose, ethylcellulose or cellulose acetate or poly(meth)acrylic resin and removing the solvent by evaporation.
• a film-forming organic solvent-soluble polymer such as nitrocellulose, ethylcellulose or cellulose acetate or poly(meth)acrylic resin
• a protective overcoat is produced with a radiation-curable composition.
• a radiation curable coating as protective top layer in a X-ray conversion screen is described e.g. in EP-A-209 358 and JP-A-86 176 900 and US-A-4 893 021.
• the protective layer comprises a UV cured resin composition formed by monomers and/or prepolymers that are polymerised by free-radical polymerisation with the aid of a photoinitiator.
• the monomeric products are preferably solvents for the prepolymers used.
• an intensifying screen is disclosed carrying a radiation cured protective layer and having a determined unevenness.
• the use of polymeric beads containing fluoro-moieties in intensifying screens is disclosed so as to have screens with good transportability.
• US-A-5 401 971 storage phosphor screens are disclosed comprising a protective layer coated from a solution in butanone of a miscible blend of poly(vinylidene fluoride-co-tetrafluoroethylene) and poly(1 to 2 carbonalkyl) methacrylate.
• vapour deposited phosphor it is, throughout this text, meant a phosphor that is deposited on a substrate by any method selected from the group consisting of thermal vapour deposition, chemical vapour deposition, electron beam deposition, radio frequency deposition and pulsed laser deposition. This vapour deposition is preferably carried out under conditions as described in EP-A-1 113 458.
• vapour deposited phosphor layers contain needle shaped phosphors separated by voids as disclosed in, e.g., the above mentioned EP-A-1 113 458, the phosphor layer is quite sensitive for mechanical impact. It is common practice to apply a protective layer on top of the phosphor layer to enhance the strength, but it was now found that the strength of the surface of the screen could even be enhanced further if the protective layer was coated from a solution that has a viscosity so that the coating solution of the protective layer seeps into the voids between the phosphor needles.
• the solution of the protective layer was adapted so that , with phosphor needles having a length, L , said protective layer fills said void for at most 0.10 times L.
• the viscosity of the coating solution of the protective layer is adjusted so that the protective layer fills the voids for at most 0.05 times L. The needed viscosity depends on the width of the voids between the phosphor needles and is easily determined by, e.g,. measuring it on an electronmicrosopic image of the screen.
• any coating composition of a protective coating can be used in the preparation of the protective layer of a screen of this invention as long as the viscosity of this composition is adapted so that said protective layer fills the voids between phosphor needles with a length, L, for at most 0.10 times L.
• the protective layer is prepared by applying a radiation curable solution.
• the present invention thus incorporates also a method for producing a binderless phosphor screen comprising the steps of :
• Very useful radiation curable compositions for forming a protective coating according to the present invention contain as primary components: (1) a crosslinkable prepolymer or oligomer or a mixture of crosslinkable prepolymers or oligomers, (2) a reactive diluent monomer or mixture of reactive diluent monomers, and (3) in the case of an UV curable formulation a photoinitiator.
• the usual amounts of these primary components calculated on the total coating composition are 30-100% by weight for the prepolymer, 10-70% by weight for the reactive diluent and 0-10% by weight for the photoinitiator.
• minor amounts e.g. 5% by weight
• of nonreactive organic solvent for the prepolymer may be present.
• any radiation curable composition known in the art as e.g., the composition disclosed in EP-A-510 753, it is preferred to have a coating solution containing fluorinated compounds so that the finished protective layer comprises at least 1 % mol/mol of fluorinated moieties.
• the coating composition is so that composition the finished protective layer comprises between 5 % and 50 % (mol/mol) of fluorinated moieties.
• the fluorinated moieties can be present either in said crosslinkable prepolymer or oligomer or in said reactive diluent monomer or in both.
• the fluorinated moieties are added by using as diluent monomer a fluorinated monomer or by adding a fluorinated monomer to the mixture of diluent monomers.
• the fluorinated monomers can be used as diluent monomer(s) or can be used in combination with non-fluorinated diluent moieties.
• Very useful non-fluorinated diluent monomers for use in this invention are : methyl (metha)acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, n-hexyl acrylate, lauryl acrylate, tetrahydrofurfurylmethacrylate and the like.
• fluorinated moieties are present in the crosslinkable prepolymer or oligomer then preferably a mixture of fluorinated and non-fluornitaed prepolymers is used.
• fluorinated prepolymers - useful to bring fluorinated moieties in the protective layer of this invention - are,e.g, fluorinated polyester acrylates wherein the polyester includes fluorinated moieties brought in the polyester via fluorinated di- or poly-ols or via fluorinated di- or poly-carboxylic acid.
• Very suitable fluorinated diols and polyesters derived therefrom are those described in, e.g., US-A-4 957 986, US-A-5 004 790 and US-A-5 109 103.
• suitable diols are, e.g., 3,3,4,4,5,5,6,6-octafluorooctan-1,8-diol, or 2,2,3,3-tetrafluoro-1,4-butanediol
• most suitable diols are diols with formula HOCH 2 (CF 2 ) n CH 2 OH, wherein 2 ⁇ n ⁇ 10.
• Suitable fluorinated poly- or diacids are those corresponding to the formula HOOC(CF 2 ) n COOH or the methylesters thereof.
• terephthalic acid carrying -O-(CH 2 ) 10 -(CF2) 9 -CF 3 as a side group can be used to produce a fluorinated prepolymer useful in a screen of this invention.
• the polyester can then be functionalised with acrylates as described in EP-A-207 257. It is also possible to introduce the fluorinated moieties via the acrylation step; when using polyesters as described in, e.g., EP-A-207 257, these are functionalised by using fluorinated acrylates, as those shown above.
• non-fluorinated prepolymers or oligomers When fluorinated prepolymers or oligomers are used, these can be mixed with non-fluorinated prepolymers or oligomers.
• suitable non-fluorinated prepolymers for use in a radiation-curable composition applied according to the present invention are the following unsaturated polyesters, e.g. polyester acrylates; urethane modified unsaturated polyesters, e.g. urethane-polyester acrylates.
• Liquid polyesters having an acrylic group as a terminal group e.g. saturated co-polyesters which have been provided with acryltype end groups are described in published EP-A-207 257.
• UV ultraviolet radiation
• a photoinitiator is present in the coating composition to serve as a catalyst to initiate the polymerisation of the monomers and their optional cross-linking with the pre-polymers resulting in curing of the coated protective layer composition.
• a photosensitizer for accelerating the effect of the photoinitiator may be present.
• Photoinitiators suitable for use in UV-curable coating compositions belong to the class of organic carbonyl compounds, for example, benzoin ether series compounds such as benzoin isopropyl, isobutylether; benzil ketal series compounds; ketoxime esters; benzophenone series compounds such as benzophenone, o-benzoylmethylbenzoate; acetophenone series compounds such as acetophenone, trichloroacetophenone, 1,1-dichloroacetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone; thioxanthone series compounds such as 2-chlorothioxanthone, 2-ethylthioxanthone; and compounds such as 2-hydroxy-2-methylpropiophenone, 2-hydroxy-4'-isopropyl-2-methylpropiophenone, 1-hydroxycyclohexylphenylketone; etc.
• benzoin ether series compounds such as benzo
• a particularly preferred photoinitiator is 2-hydroxy-2-methyl-1-phenyl-propan-1-one which product is marketed by E. Merck, Darmstadt, Germany under the trade name DRACUT 1173.
• photopolymerisation initiators may be used alone or as a mixture of two or more.
• Suitable photosensitisers are particular aromatic amino compounds as described e.g. in GB-A-1 314 556, GB-A-1 486 911, USA-4 255 513 and merocyanine and carbostyril compounds as described in US-A-4 282 309.
• a storage stabiliser e.g. a colorant, and other additives, and then dissolved or dispersed therein to prepare the coating liquid for the protective layer.
• additives may be present, e.g. surfactants, solid lubricants, e.g. waxes, de-foamers and plasticisers.
• the protective layer of this invention can include spacing particles for further increasing the transportability and adjusting the electrostatic properties.
• Suitable spacing agents in the form of friction reducing polymer beads selected from the group consisting of solid polystyrene, solid polyalkylene and a solid organic fluorinated polymer.
• the spacing agents are beads incorporating fluorinated moieties.
• Such beads have been described in US-A-4 059 768.
• the trend is towards more and more compact apparatus, so that the distance between the (moving) storage phosphor screen and mechanical (moving) parts of the scanner can become very low and can become measured in 10 to 100 ⁇ m.
• beads used as spacing particles in a storage phosphor screen of this invention have preferably a volume median diameter, d v50 , so that 5 ⁇ m ⁇ dv50 ⁇ 25 ⁇ m and a numeric median diameter, d n50 , so that 1 ⁇ d v50 /d n50 ⁇ 1.20.
• the beads are preferably adapted to the thickness, t, of the protective layer on the storage panel of this invention so that and said polymeric beads have a volume median diameter, d v50 , so that 1.25 ⁇ d v50 /t ⁇ 4.0.
• the phosphor layer of a binderless storage phosphor screen according to this invention can be prepared by vacuum deposition of the storage phosphor crystals on the substrate as well as by combining (mixing) the ingredients for the storage phosphor (phosphor precursors) and then evaporating this mixture so as to have the phosphor formed in situ during evaporation.
• the storage phosphor in a binderless storage phosphor screen according to this invention can be any storage phosphor known in the art.
• the storage phosphor in a binderless storage phosphor screen of this invention is an alkali metal phosphor Suitable phosphors are, e.g., phosphors according to formula I : M 1+ X.aM 2+ X' 2 bM 3+ X'' 3 :cZ wherein:
• Highly preferred storage phosphors for use in a binderless phosphor screen of this invention are CsX:Eu stimulable phosphors, wherein X represents a halide selected from the group consisting of Br and Cl prepared by a method comprising the steps of :
• CsBr:Eu stimulable phosphor is used prepared by a method comprising the steps of :
• the phosphor layer of the binderless screen can be prepared by bringing the finished phosphor on the support by any method selected from the group consisting of thermal vapour deposition, chemical vapour deposition, electron beam deposition, radio frequency deposition and pulsed laser deposition. It is also possible to bring the alkali metal halide and the dopant together and depositing them both on the support in such a way that the alkali metal phosphor is doped during the manufacture of the screen.
• the invention encompasses a method for manufacturing a phosphor screen containing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br and Cl comprising the steps of :
• the deposition can proceed from a single container containing a mixture of the starting compounds in the desired proportions.
• the method encompasses further a method for manufacturing a storage phosphor screen containing a CsX:Eu stimulable phosphor, wherein X represents a halide selected from the group consisting of Br and Cl comprising the steps of :

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Conversion Of X-Rays Into Visible Images (AREA)
• Luminescent Compositions (AREA)
• Measurement Of Radiation (AREA)

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Cited By (3)

Citations (2)

• 2001
  • 2001-12-03 EP EP20010000694 patent/EP1316969B1/fr not_active Expired - Lifetime
  • 2001-12-03 DE DE60142438T patent/DE60142438D1/de not_active Expired - Lifetime
• 2002
  • 2002-11-15 JP JP2002332029A patent/JP2003232899A/ja active Pending

Patent Citations (2)

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