EP0967620B1 - Article luminescent aux rayons X avec une netteté de film améliorée - Google Patents

Article luminescent aux rayons X avec une netteté de film améliorée Download PDF

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Publication number
EP0967620B1
EP0967620B1 EP19990201521 EP99201521A EP0967620B1 EP 0967620 B1 EP0967620 B1 EP 0967620B1 EP 19990201521 EP19990201521 EP 19990201521 EP 99201521 A EP99201521 A EP 99201521A EP 0967620 B1 EP0967620 B1 EP 0967620B1
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EP
European Patent Office
Prior art keywords
binder
phosphor
layer
screen
coating
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EP19990201521
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German (de)
English (en)
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EP0967620A1 (fr
Inventor
Rudy Van Den Bergh
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Agfa Gevaert NV
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Agfa Gevaert NV
Agfa Gevaert AG
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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
    • G21K2004/08—Conversion screens for the conversion of the spatial distribution of X-rays or particle radiation into visible images, e.g. fluoroscopic screens with a binder in the 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 radiation-sensitive luminescent articles offering improved sharpness of diagnostic film images.
  • penetrating radiation which is high energy radiation belonging to the class of X-rays, ⁇ -rays and high energy elementary particle radiation, e.g. ⁇ -rays, electron beam or neutron radiation.
  • penetrating radiation For the conversion of penetrating radiation into visible light and/or ultraviolet radiation luminescent substances are used called phosphors.
  • an X-ray radiograph is obtained by X-rays transmitted imagewise through an object and converted into light of corresponding intensity in a so-called intensifying screen (X-ray conversion screen) wherein phosphor particles absorb the transmitted X-rays and convert them into visible light and/or ultraviolet radiation whereto a photographic film is more sensitive than to the direct impact of the X-rays.
  • intensifying screen X-ray conversion screen
  • the light emitted imagewise by said screen irradiates a contacting light-sensitive silver halide photographic emulsion layer which, after exposure, is developed to form therein a silver image in conformity with the X-ray image.
  • the X-ray film For use in common medical radiography the X-ray film comprises a transparant film support double-side coated with a silver halide emulsion layer. During the X-ray irradiation said film is arranged in a cassette between two X-ray conversion screens each of them making contact with their corresponding silver halide emulsion layer.
  • An autoradiograph is a photographic record formed through the intermediary of penetrating radiation emitted by radioactive material contained in an object, e.g. microtome cut for biochemical research.
  • Phosphors suitable for use in the conventional radiographic system must have a high prompt emission on X-ray irradiation and low afterglow in favour of image-sharpness. It is clear that said plates or panels carrying the phosphors serve only as intermediate imaging elements and do not form the final record and that the final image is made or reproduced on a separate recording medium or display as radiographic film materials. The phosphor plates or sheets can thus be repeatedly re-used and the expected life of the plate is limited mainly by mechanical damage such as scratches.
  • X-ray conversion screens generally comprise in order : a support, a layer comprising phosphor particles dispersed in a suitable binder and a protective coating coated over the phosphor containing layer in order to protect said layer during use.
  • the protective layer preferably has a relief structure that reduces friction as well as the tendency to show sticking phenomena with contacting materials, thus favouring loading and unloading of a film from a cassette and reducing the building up of static electricity.
  • the contact between the film and the conventional screens which depends on the contact area and the distance between both the screens and the photographic film, is important in order to obtain good image quality.
  • Phosphor having complicated crystal structures as, e.g., alkaline earth fluoro-halides, tend to decompose (partially) under vacuum deposition and the production of screens by vacuum deposition, while using phosphors with complicated crystal structure is about impossible and leads to inferior results.
  • vacuum deposition works only well with a limited number of phosphors.
  • vacuum deposited phosphor layers have to receive special treatments to give them good physical properties. Therefore other ways reducing the thickness of the phosphor layers in screens comprising a coated layer of phosphor particles dispersed in a binder have been disclosed.
  • One way to get thinner coated phosphor layers without changing the coated amounts of pigment and of binder makes use of a method of compressing the coated layer containing both ingredients at a temperature not lower than the softening point or melting point of the thermoplastic elastomer as has been described in EP-A 0 393 662. By this method the void ratio becomes remarkably reduced. This procedure although yielding better image quality thus requires an additional manipulation of the screen or panel. This additional manipulation is however less desirable from an economical point of view.
  • luminescent article comprises a self-supporting or supported layer of phosphor particles dispersed in a binding medium and a protective coating thereover characterised in that the binding medium substantially consists of one or more rubbery and/or elastomeric polymers, in that the ratio by volume of phosphor to binding medium is at least 70:30 and at most 92:8 and in that the packing ratio is less than 67%.
  • the binding medium substantially consists of one or more rubbery and/or elastomeric polymers, in that the ratio by volume of phosphor to binding medium is at least 70:30 and at most 92:8 and in that the packing ratio is less than 67%.
  • rubbery binders should be dissolved in toluene or a mixture of toluene and alkanes such as hexane in order to provide optimal solvation of the binder in the coating solution, thereby providing optimal flow characteristics and drying properties of the coating solution.
  • said polymer is soluble in ethylacetate for at least 20 % by weight (% wt/wt) and in a further preferred embodiment said binder comprises at least 60 % by weight of said polymer.
  • a polymer being at least one member selected from the group consisting of vinyl resins, polyesters and polyurethane resins.
  • Last but not least the wavelength of the light emitted by the intensifying screen is decisive for the sharpness obtainable with such screens: light having shorter wavelengths as the one emitted by blue and ultraviolet light emitting phosphors clearly leads to a better sharpness than light emitted from green-light emitting phosphors for images observed after processing of the radiographic films held in contact with the screens during X-ray irradiation and conversion illumination.
  • a luminescent article which luminescent article comprises a self-supporting or supported layer of phosphor particles dispersed in a binding medium and, adjacent thereto, a protective coating characterized in that, besides a binder, the said protective coating comprises titanium dioxide as a white pigment.
  • titanium dioxide white pigment is present in the said binder, preferably comprising an urethane acrylate, an improvement in sharpness of images is obtained after processing of light-sensitive silver halide photographic film materials held in contact with the said article during X-ray irradiation and subsequent conversion illumination.
  • said pigment When said pigment is present in an amount by weight of up to 5 %, more preferably up to 2 % and still more preferably up to 1 % versus said binder, no loss in speed for said processed film material is observed.
  • a luminescent article comprising a self-supporting or supported layer of phosphor particles dispersed in a binding medium and, adjacent thereto, a protective coating characterized in that the protective coating, besides a binder, comprises titanium dioxide as a white pigment, particularly in order to obtain an improved sharpness.
  • Said white pigment present in the protective overcoat layer is thus composed of titanium dioxide (rutile or anatase type titanium dioxide).
  • a luminescent phosphor can be used.
  • Said white pigment preferably has an average particle size diameter of less than 2 ⁇ m, more preferably less than 1 ⁇ m and still more preferably from 0.1-0.5 ⁇ m.
  • said white pigment is present in an amount by weight of up to 2 % versus the said binder and even more preferred in an amount by weight of up to 1 % versus the said binder.
  • Useful radiation curable compositions for forming a protective coating of the luminescent article according to the present invention contain as primary components :
  • Suitable 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.
  • 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 copolyesters which have been provided with acryltype end groups are described in EP-A 0 207 257 and Radiat. Phys. Chem., Vol. 33, No. 5, p. 443-450 (1989).
  • the latter liquid co-polyesters are substantially free from low molecular weight, unsaturated monomers and other volatile substances and are of very low toxicity (ref.
  • UV ultraviolet radiation
  • a photoinitiator is present in the coating composition to serve as a catalyst to initiate the polymerization 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-benzoylmethyl-benzoate; acetophenone series compounds such as acetophenone, trichloroacetophenone, 1,1-dichloroacetophenone, 2,2-diethoxyaceto-phenone, 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
  • 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 tradename DAROCUR 1173.
  • the above mentioned photopolymerization initiators may be used alone or as a mixture of two or more.
  • suitable photosensitizers are particular aromatic amino compounds as described e.g. in GB-A's 1,314,556 and 1,486,911 and in US-A 4,255,513 and merocyanine and carbostyryl compounds as described in US-A 4,282,309.
  • the binder of the said protective overcoat layer in the luminescent article according to the present invention comprises a urethane acrylate.
  • a coating dispersion is prepared therefore, composed of a urethane acrylate oligomer and an acrylate oligomer, which both, together, form the binder of the aid protective layer and which are present in a ratio by weight of at least 2:1, more preferably about 7:3 and which together represent at least 80 %, and even up to 90 % by weight of the total amount of the protective layer.
  • urethane acrylate and acrylate oligomers are GENOMEER T1600, trade name product from RAHN, Switzerland, and SERVOCURE RTT190, trade name product available from SERVO DELDEN BV, The Netherlands.
  • a flow modifying agent, a surfactant and a photo initiator are further added, together with the white pigment, the presence of which is essential in order to reach the objects of the present invention.
  • a more detailed description about the composition of the said protective overcoat layer can be found in the Examples hereinafter.
  • the roughness of the topcoat layer of the intensifying screens or luminescent articles according to the present invention offers the advantage that sticking phenomena between a film and an intensifying screen(s) in a cassette are substantially avoided even after intimate contact due to pressure build-up in the cassette system.
  • an X-ray conversion phosphor screen having a topcoat with embossed structure favours its practically frictionless loading and unloading of a cassette and reduces considerably the charging by static electricity.
  • the micro-channels formed by the embossed structure of the protective coating allow air to escape between phosphor screen and contacting film whereby image quality (image sharpness) is improved by better screen-film-screen contact without large air bubble inclusions.
  • the coating of the protective layer proceeds by screen-printing (silk-screen printing).
  • the protective coating composition is applied by a rotary screen printing device as has been described in detail in EP-A 0 510 753.
  • a storage stabilizer for the radiation-curable coating composition there may be added a storage stabilizer, a colorant, and other additives. These additives may be dissolved or dispersed therein in order to prepare the coating liquid for the protective layer.
  • colorants that can be used in the protective layer include MAKROLEX ROT EG, MAKROLEX ROT GS and MAKROLEX ROT E2G.
  • MAKROLEX is a registered tradename of Bayer AG, Leverkusen, Germany.
  • the photoinitiator which needs to be added to the coating solution will to a more or less extent also absorb the light emitted by the phosphor thereby impairing the sensitivity of the radiographic screen, particularly when a phosphor emitting UV or blue light is used.
  • a photoinitiator has to be chosen of which the absorption range overlaps to a minimum degree with the emission range of the phosphor; a preferred photoinitiator is then DAROCUR 1173 (tradename), already mentioned hereinbefore.
  • the protective coating of the present luminescent article is given an embossed structure following the coating stage by passing the uncured or slightly cured coating through the nip of pressure rollers wherein the roller contacting said coating has a micro-relief structure, e.g. giving the coating an embossed structure so as to obtain relief parts.
  • a suitable process for forming a textured structure in a plastic coating by means of engraved chill roll is described in US-A 3,959,546.
  • the textured or embossed structure is obtained already in the coating stage by applying the paste-like coating composition with a gravure roller or screen printing device operating with a radiation-curable liquid coating composition the Hoeppler-viscosity of which at a coating temperature of 25 °C is between 450 and 20,000 mPa.s.
  • the radiation-curing is effected immediately or almost immediately after the application of the liquid coating.
  • the rheologic behaviour or flow characteristics of the radiation-curable coating composition can be controlled by means of so-called flowing agents.
  • alkylacrylate ester copolymers containing lower alkyl (C1-C2) and higher alkyl (C6-C18) ester groups can be used as shear controlling agents lowering the viscosity.
  • pigments such as colloidal silica raises the viscosity.
  • a variety of other optional compounds can be included in the radiation-curable coating composition of the present radiographic article such as compounds suitable to reduce static electrical charge accumulation, plasticizers, matting agents, lubricants, defoamers and the like as has been described in EP-A 0 510 753.
  • compounds suitable to reduce static electrical charge accumulation plasticizers, matting agents, lubricants, defoamers and the like as has been described in EP-A 0 510 753.
  • edges of the screen may be reinforced by covering the edges (side surfaces) with a polymer material being formed essentially from a moisture-hardened polymer composition prepared according to EP-A 0 541 146 by a process comprising the steps of :
  • Support materials for radiographic screens in accordance with the present invention include cardboard, plastic films such as films of cellulose acetate, polyvinyl chloride, polyvinyl acetate, polyacrylonitrile, polystyrene, polyester, polyethylene terephthalate, polyamide, polyimide, cellulose triacetate and polycarbonate; metal sheets such as aluminum foil and aluminum alloy foil; ordinary papers; baryta paper; resin-coated papers; pigment papers containing titanium dioxide or the like; and papers sized with polyvinyl alcohol or the like.
  • a plastic film is preferably employed as the support material.
  • the plastic film may contain a light-absorbing material such as carbon black, or may contain a light-reflecting material such as titanium dioxide or barium sulfate.
  • the former is appropriate for preparing a high-resolution type radiographic screen, while the latter is appropriate for preparing a high-sensitivity type radiographic screen.
  • Examples of preferred supports include polyethylene terephthalate, clear or blue colored or black colored (e.g., LUMIRROR C, type X30 supplied by Toray Industries, Tokyo, Japan), polyethylene terephthalate filled with TiO 2 or with BaSO 4 .
  • Metals as e.g. aluminum, bismuth and the like may be deposited e.g. by vaporization techniques to get a polyester support having radiation-reflective properties.
  • These supports may have thicknesses which may differ depending on the material of the support, and may generally be between 60 and 1000 ⁇ m, more preferably between 80 and 500 ⁇ m from the standpoint of handling.
  • the screens are fixed inside a cassette allowing the arrangement of a double-side coated silver halide emulsion film inbetween.
  • one silver halide emulsion layer is exposed by the fluorescent light of a front screen (the screen most close to the X-ray source) and the other silver halide emulsion layer is exposed by the fluorescent light emitted by the back screen which is the screen struck by the X-rays that have penetrated already the photographic material.
  • Front and back screen may be asymmetrical in that e.g. their sensitometric properties, thickness, phosphor coverage and phosphor composition may be different.
  • the present radiographic screens may be used in non-destructive testing (NDT), of metal objects, where more energetic X-rays and ⁇ -rays are used than in medical X-ray applications.
  • NDT non-destructive testing
  • the fluorescent phosphor layer with a metal layer or metal support, wherein the metal has an atomic number in the range of 46 to 83 as described e.g. in US-A's 3,872,309 and 3,389,255.
  • the metal layer in contact with the phosphor-containing layer acts as an emitter of photo-electrons and secondary X-rays when struck by highly energetic X-rays or gamma rays.
  • the secondary lower energy X-rays and photo-electrons are absorbed in the adjacent ) phosphor-containing layer at a higher efficiency than the highly energetic X-rays and gamma rays emitted by an industrial X-ray apparatus, such results in an increase in photographic speed.
  • Said metal layers or supports have the additional advantage of reducing the scattered radiation whereby image-sharpness is improved.
  • image-sharpness is improved by incorporating in the X-ray intensifying screen between the phosphor-containing layer and the support and/or at the rear side of the support a pigment-binder layer containing a non-fluorescent pigment being a metal compound, e.g. salt or oxide, of a heavy metal whose atomic number (Z) is at least 46.
  • a pigment used for that purpose is lead oxide (PbO) being applied e.g. at a coverage of 100 to 400 g of lead per m 2 .
  • said luminescent article has phosphor particles having a composition selected from the group consisting of Gd 2 O 2 S.Tb; YTaO 4 .Nb; BaFBr.Eu and CaWO 4 .
  • the choice of the phosphor or phosphor mixture is not limited to the UV or blue emitting phosphors, but that also green emitting phosphors as e.g. Gd 2 O 2 S:Tb can be used.
  • the invention is even useful when prompt emitting phosphors emitting red light are used as especially in this case the problem of sharpness or definition becomes more and more stringent as radiation having a longer wavelength may lead to more lack of sharpness due to scattering which is more expressed for green and red light than for blue light.
  • the thickness thereof may be within the range of from 10 to 1000 ⁇ m, preferably from 50 to 500 ⁇ m and more preferably from 100 to 300 ⁇ m.
  • the coverage of the phosphor or phosphors present as a sole phosphor or as a mixture of phosphors whether or not differing in chemical composition and present in one or more phosphor layer(s) in a screen is preferably in the range from about 300 to 1500 g/m 2 .
  • Said one or more phosphor layers may have the same or a different layer thickness and/or a different weight ratio amount of pigment to binder and/or a different phosphor particle size or particle size distribution.
  • the optimum mean particle size for a given application is a compromise between imaging speed and image sharpness desired.
  • Preferred average grain sizes of the phosphor particles are in the range of 2 to 30 ⁇ m and more preferably in the range of 2 to 20 ⁇ m.
  • any phosphor or phosphor mixture may be coated depending on the objectives that have to be attained with the manufactured intensifying phosphor screens. It is possible to mix fine grain phosphors with more coarse grain phosphors to increase the packing density.
  • Preferred phosphors are e.g. yttriumtantalate phosphors, the preparation of which is described in EP-A's 0 011 909 and 0 202 875 and in US-A 5,064,729 or barium fluorobromide phosphors the preparation of which proceeds analogously as the preparation of barium fluorochloride phosphors described e.g. in GB-A's 1,161,871 and 1,254,271 and in US-A 4,088,894. plasticizers, fillers and subbing or interlayer layer compositions that have been described in extenso in the EP-A 0 510 753.
  • phosphor particles are mixed with dissolved rubbery and/or elastomeric polymers, in a 5 suitable mixing ratio in order to prepare a dispersion.
  • the luminescent article comprises phosphor particles dispersed in a binding medium wherein said binding medium is a polymeric binder and wherein said phosphor particles are present in a volume ratio of at least 80/20.
  • the polymeric binder of the phosphor layer(s) of the luminescent article according to the present invention is at least one member selected from the group consisting of vinyl resins, polyesters and polyurethane resins.
  • ethylenic monomers examples include acrylates, methacrylates, vinyl esters, olefins, styrenes, crotonic acid esters, itaconic acid diesters, maleic acid diesters, fumaric acid diesters, acrylamides, acryl compounds, vinyl ethers, vinyl ketones, vinyl heterocyclic compounds, glycidyl esters, unsaturated nitriles, polyfunctional monomers, and various unsaturated acids.
  • Particular vinylpolymers are chosen as a function of the solubility criterium and elongation at break criterium herein before.
  • PLEXISOL B372 (trade name), an acrylic resin supplied by ROHM GmbH,Germany ; ACRONAL 500L (copolymer of acrylic acid esters), ACRONAL 4F (poly-(n-butylacrylate)), ACRONAL 4L (poly-(n-butylacrylate)), ACRONAL 700L (co(n-butylacrylate/vinylisobutylether) and ACRONAL A150F (poly-(n-butylacrylate)) (trade names) all supplied by BASF, Germany; DURO-TAK 373-0036 (trade name), an acrylate resin supplied by National Starch & Chemical USA.
  • a second class of useful polymers in this invention are polyesters with Tg ⁇ 0.
  • This class comprises all polymers in which the main polymer backbones are formed by the esterification condensation of polyfunctional alcohols and acids. Particular polyesters are chosen as a function of the solubility criterium and elongation at break criterium herein before.
  • Very useful polyesters are commercially available from Hüls, Germany under trade name DYNAPOL (e.g. DYNAPOL S1420, with Tg - 15 °C ; from TOYOBO, Japan under trade name VYLON (e.g. VYLON 550 with Tg - 10 °C) ; from SHELL, UK under trade name VITEL.
  • a third class of useful polymers for incorporation in a binder mixture for a screen according to the present invention are polyurethanes.
  • This class comprises all polymers based on the reaction product of an organic isocyanate with compounds containing hydroxyl groups.
  • Particular polyurethanes are chosen as a function of the solubility criterium and elongation at break criterium herein before.
  • Very useful polyurethanes are commercially available from BAYER, Germany, under the trade name DESMOLAC (e.g. DESMOLAC 2100, DESMOLAC 4200, DESMOLAC 4125, non reactive linear polyurethanes).
  • some polymeric additives in low amounts can be present.
  • Very suitable polymeric additives are e.g. DISPERSE AYD 9100, a trade name of Daniel Products Company, Jersey City, New Jersey 07304, USA.
  • This polymeric additive is a low molecular weight thermoplastic acrylic resin and is very useful to control the quality of the dispersion of the phosphor particles, binder(s) and solvent.
  • cellulosic polymers as, e.g., CAB-381-2, a trade name of Eastman Chemicals USA, can be used to fine tune mechanical properties of the coated and dried phosphor layer.
  • the coating dispersion may further contain a filler (reflecting or absorbing) or may be colored by a colorant capable of absorbing light within the spectrum emitted by the phosphor in the X-ray conversion screen or luminescent article of the present invention.
  • colorants include Solvent Orange 71 (Diaresin Red 7), Solvent Violet 32 (Diaresin Violet A), Solvent Yellow 103 (Diaresin Yellow C) and Solvent Green 20 (all four supplied by Mitsubishi Chemical Industries, Japan), Makrolex Rot GS, Makrolex Rot EG, Makrolex Rot E2G, Helioechtgelb 4G and Helioechtgelb HRN (all five marketed by Bayer, Leverkusen, Germany), Neozapon85rot G and Zaponechtbraun BE (both marketed by BASF, Ludwigshafen, W. Germany).
  • one or more additional layers are occasionally provided between the support and the phosphor containing layer, having subbing or interlayer layer compositions, in order to improve the bonding between the support and the phosphor layer, or to improve the sensitivity of the screen or the sharpness and resolution of an image provided thereby.
  • a subbing layer or an adhesive layer may be provided by coating polymer material such as gelatin over the surface of the support on the phosphor layer side.
  • a light-reflecting layer may be provided, e.g. by vacuum-depositing an aluminium layer or by coating a pigment-binder layer wherein the pigment is e.g. titanium dioxide.
  • carbon black dispersed in a binder may be used but also any known anti-halation dye.
  • additional layer(s) may be coated on the support either as a backing layer or interposed between the support and the phosphor containing layer(s). Several of said additional layers may be applied in combination.
  • volume ratio of phosphor particles (PP)/binder (B) is higher as 80/20 makes it possible to manufacture screens with high elasticity, low brittleness, high sharpness, high speed and low noise.
  • the volume ratio of PP/B is known to be independent of the densities of the phosphor particles (the pigment) and of the binder, while a PP/B ratio in weight is dependent on the densities of phosphor and binder.
  • the pigment to binder volume ratio can not be increased to the high values as mentioned above, due mainly to physical properties, as e.g. adhesion and brittleness.
  • the ratio of pigment to binder was clearly limited by the lack in physical properties of the coated phosphor layers or by the presence of "screen structure mottle".
  • the dispersion of phosphor(s) in the polymeric binder described above is uniformly applied to a substrate by a known coating technique, e.g. doctor blade coating, roll coating, gravure coating or wire bar coating, and dried to form a luminescent layer fluorescing by X-ray irradiation and called hereinafter fluorescent layer.
  • a known coating technique e.g. doctor blade coating, roll coating, gravure coating or wire bar coating
  • Radiographic screens according to the present invention can also be made in the form of gradual screens, i.e. screens having a gradual intensification along their length and/or width.
  • Graduality can be achieved by gradually increasing the thickness of the phosphor layer over the length or width of the screen or by incorporating into the protective layer or into an interlayer between the protective layer and phosphor containing layer a gradually increasing amount of dye capable of absorbing the light emitted by the phosphor.
  • graduality is obtained by halftone printing of a dye or ink composition absorbing the light emitted by the screen.
  • the halftone printing can proceed on the phosphor containing layer which thereupon is covered with the protective coating or proceeds by applying the protective coating by halftone printing, e.g. by gravure roller or silk screen printing.
  • the primer layer is provided on the substrate beforehand, and then the phosphor dispersion is applied to the primer layer and dried to form the fluorescent layer.
  • the coating dispersion After applying the coating dispersion onto the support, the coating dispersion is heated slowly to dryness in order to complete the formation of a phosphor layer. In order to remove entrapped air in the phosphor coating composition in an amount as much as possible it can be subjected to an ultrasonic treatment before coating.
  • a protective layer is generally provided on top of the fluorescent layer, said protective layer having been described in detail hereinbefore.
  • a protective layer is generally provided on top of the fluorescent layer, said protective layer having been described in detail hereinbefore.
  • Example 1 SENSITOMETRY AND IMAGE QUALITY FOR INTENSIFYING SCREENS.
  • a silver bromoiodide emulsion (2 mole % of silver iodide, 98 mole % of silver bromide) was used containing silver halide grains with an average grain size (equivalent circular diameter) of 1.25 ⁇ m and an average thickness of 0.22 ⁇ m as the one described in US-A 5,595,864.
  • the emulsion ready for coating contained per kg an amount of silver halide corresponding to 190 g of silver nitrate and 74 g of gelatin.
  • the emulsion was spectrally sensitized by adding 660 mg of anhydro-5,5'-dichloro-3,3'-bis(n.sulfobutyl)-9-ethyloxacarbocyanine hydroxide per mole of silver halide.
  • As stabilizing agents the silver halide emulsion contained per kg 545 mg of 5-methyl-7-hydroxy-s-triazolo[1,5-a]pyrimidine and 6.5 mg of 1-phenyl-5-mercaptotetrazole.
  • the above emulsion was coated on both sides of a polyethylene terephthalate support, carrying on both sides a subbing layer.
  • each of the dried silver halide emulsion layers a protective layer was applied containing 1.1 g/m 2 of gelatin, hardened with formaldehyde and containing perfluorocaprylic acid as an antistatic agent. The hardening proceeded by adding 0.03 grams of formaldehyde per gram of gelatin. Each silver halide emulsion layer contained an amount of silver halide equivalent with 7 g of silver nitrate per m 2 .
  • the intensifying screen for use as luminescent article according to the present invention was containing Gd 2 O 2 S:Tb as a green emitting phosphor.
  • the screen was coated on a terephthalate support containing carbon black as light-absorbing material having a low percentage reflectance of 0-5%.
  • the screens were coated from a coating composition comprising Gd 2 O 2 S:Tb phosphor.
  • the phosphor used for these examples had a mean particle size of 5 ⁇ m.
  • the composition was doctor blade coated onto a subbed 200 ⁇ m thick black polyethylene terephthalate support and dried.
  • the coating composition was such that besides polymer P1 and polymer P2 as defined hereinbefore, DISPERSE AYD trade name of Daniel Products Company, Jersey City, New Jersey 07304, USA, as a low molecular weight thermoplastic acrylic resin with Tg > 0 was used as dispersing agent, in ratio amounts by weight of 5:1:1.
  • a subbing layer was prepared on basis of Vitel PE200 (trade name of SHELL, The Netherlands) and hardened with hardener DESMODUR N75 (tradename of Bayer AG, Leverkusen, Germany).
  • the phosphor/binder ratio by mass was 97/3 and the coating weight of the phosphor was 40 mg/cm 2 .
  • the protective coating having a thickness of 10 ⁇ m was coated adjacent to the phosphor layer by screen printing. Its composition has been described hereinafter.
  • GENOMEER T1600 (urethane acrylate oligomer as a binder) trade name of RAHN, Switzerland 70 g SERVOCURE RTT190 (acrylate oligomer used as a binder) trade name of SERVO DELDEN BV, The Netherlands 30 g MODAFLOW (flow modifier, used as coating aid) trade name of MONSANTO, Germany 3.0 g ANTIMOUSSE 416 (surfactant) trade name of RHONE POULENC, Germany 0.15 g NUVOPOL PI3000 (photo initiator) trade name of RAHN, Switzerland 5.0 g TITAN AN2 (white pigment having TITANIUM DIOXIDE composition, particle size: 0.3 ⁇ m), trade name of BAYER AG, Leverkusen, Germany x % (said x % is given by weight versus the total amount of binder (GENOMEER and SERVOCURE) and is given in real figures in Table 1
  • the X-ray exposure proceeded with 28 kVp X-rays, normally used in mamography, with a filter of 35 mm plexi at the screen-film system and a FFA of 400 cm dlogK of 0.10.
  • the density is plotted versus the corrected logK value, wherein said value is corrected for air absorption.
  • the developing liquid had the following composition: hydroquinone 30 g 1-phenyl-3-pyrazolidine-1-one 1.5 g acetic acid 99 % 9.5 ml potassiumsulphite 63.7 g potassiumchloride 0.8 g EDTA-2Na 2.1 g potassium carbonate 32 g potassiummetabisulfite 9 g potassium hydroxyde 14 g diethyleneglycol 25 ml 6-methylbenztriazol 0.09 g glutardialdehyd 50% 9.5 ml 5-nitroindazole 0.25 g demineralized water to make 1 l.
  • the starter solution to be added had the following composition: acetic acid 99 % 15.5 ml KBr 16 g demineralized water up to 100 ml
  • the overall developing time was 12 seconds at 37 °C in the total processing cycle of 45 seconds.
  • the developed photographic strips were fixed in a conventional fixing bath comprising, ammonium thiosulfate and potassium metabisulfite, and then rinsed in water and allowed to dry.
  • Sensitometric properties and values of speed and sharpness obtained for the film-screen combinations Nos. 1-5 are given in Table 2.
  • This Table shows the speed values S, calculated from the sensitometric curve by means of the square law in order to determine the dose necessary to get a netto density of 1.0.
  • SWR values used in connection with Table 2 were determined at 1; 2; 4 and 6 line pairs per mm (SWR1, SWR2, SWR4 and SWR6 respectively).
  • the determination of the SWR value for intensifying screens was performed with the same kVp after a Funk type K 0.01 mm Pb - 8 lp/mm raster, with a FFA of 400 cm dlogK of 0.10.

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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)
  • Silver Salt Photography Or Processing Solution Therefor (AREA)
  • Luminescent Compositions (AREA)

Claims (9)

  1. Article luminescent comprenant une couche autoportante ou déposée sur un support, contenant des particules de luminophore dispersées dans un liant, et, en position adjacente, un revêtement protecteur, caractérisé en ce qu'en plus du liant, ledit revêtement protecteur comprend du dioxyde de titane à titre de pigment blanc.
  2. Article luminescent selon la revendication 1, dans lequel ledit liant comprend un acrylate d'uréthane.
  3. Article luminescent selon la revendication 1 ou 2, dans lequel ledit pigment blanc est présent en une quantité pondérale s'élevant jusqu'à 5 % par rapport audit liant.
  4. Article luminescent selon la revendication 1 ou 2, dans lequel ledit pigment blanc est présent en une quantité pondérale s'élevant jusqu'à 2 % par rapport audit liant.
  5. Article luminescent selon la revendication 1 ou 2, dans lequel ledit pigment blanc est présent en une quantité pondérale s'élevant jusqu'à 1 % par rapport audit liant.
  6. Article luminescent selon l'une quelconque des revendications 1 à 5, dans lequel lesdites particules de luminophore sont dispersées dans un liant, à savoir un liant polymère, lesdites particules étant présentes dans un rapport en volume d'au moins 80/20.
  7. Article luminescent selon la revendication 6, dans lequel ledit liant polymère (i) comprend au moins un polymère possédant une valeur Tg ≤ 0 °C, (ii) possède un poids moléculaire moyen (MGavg) entre 5000 et 107, (iii) est soluble dans de l'acétate d'éthyle à concurrence d'au moins 5 % en poids.
  8. Article luminescent selon la revendication 6 ou 7, dans lequel ledit liant polymère représente au moins un membre choisi parmi le groupe constitué par des résines vinyliques, des polyesters et des résines de polyuréthanes.
  9. Article luminescent selon l'une quelconque des revendications 6 à 8, dans lequel lesdites particules de luminophore possèdent une composition choisie parmi le groupe constitué par Gd2O2S:Tb ; YTaO4.Nb ; BaFBr:Eu et CaWO4.
EP19990201521 1998-06-26 1999-05-10 Article luminescent aux rayons X avec une netteté de film améliorée Expired - Lifetime EP0967620B1 (fr)

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EP1316972B1 (fr) * 2001-12-03 2012-09-19 Agfa HealthCare NV Ecran luminescent sans liant doté d'une couche intermédiaire pigmentée
US6815092B2 (en) 2001-12-05 2004-11-09 Agfa-Gevaert Radiation image storage panel
EP1318525A3 (fr) * 2001-12-05 2007-03-28 Agfa-Gevaert Ecran pour l'enregistrement d'une image obtenue par rayonnement
KR101475745B1 (ko) * 2013-05-07 2014-12-23 한국과학기술원 고분자 중합체를 이용한 gos 섬광체, 및 그의 제조 방법

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JPS5858500A (ja) * 1981-10-01 1983-04-07 株式会社東芝 増感紙
JPS62247298A (ja) * 1986-04-19 1987-10-28 富士写真フイルム株式会社 放射線像変換パネル

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