Patent Application
20080044555
According to the present invention a method of manufacturing a radiation image storage phosphor layer on a support layer is provided wherein said method comprises a vapor depositing step of raw materials of an alkali metal halide salt and a lanthanide dopant salt or a combination thereof in order to ensure vapor deposition of a binderless storage phosphor layer from one or more resistance-heated crucible(s) in a vapor deposition apparatus, wherein one or more shutter(s) are positioned on, and, optionally, between said crucible(s) and said support, wherein in said method, at the time said vapor depositing step starts while opening a shutter, a start temperature is measured on and registered by means of a thermocouple positioned close to the support at the back side of the support, opposite to the side of the support where vapor becomes deposited, of less than 250° C., but not less than 100° C., when an additional heating is applied.
In a particular embodiment in the preparation method of phosphor or scintillator panels according to the present invention said a start temperature as measured on and registered by means of a thermocouple positioned close to the support at the back side of the support, opposite to the side of the support where vapor becomes deposited, is less than 220° C., but not less than 130° C., when an additional heating is applied.
In a further particular embodiment in the preparation method of phosphor or scintillator panels according to the present invention said start temperature as measured on and registered by means of a thermocouple positioned close to the support at the back side of the support, opposite to the side of the support where vapor becomes deposited, is less than 200° C., but not less than 150° C., when an additional heating is applied.
In the method according to the present invention, said additional heating proceeds by means of resistive heating or radiation heating. Said additional heating—in form of pre-heating before starting vaporization or while performing vaporization—thus proceeds by means of electrically resistive heating or radiation heating—i.e. by lamps as e.g. halogen lamps or infrared lamps. Radiation heating by lamps before and/or during vaporization usually proceeds at the side of the support or substrate, where vapor deposits, before and/or during vaporization by lamps positioned next to the crucible(s), preferably at positions surrounding the crucible(s) or between the crucible(s) and the support, just outside is the space of the vapor stream or cloud. Otherwise resistive heating is usually performed at the back side of the support, wherein the resistive heaters are positioned so that they cannot be hit by the vapor stream escaping from the crucible(s) and passing along the substrate so that no deposition onto the substrate or the resistive heaters occurs. It is however not excluded to depart from these particular arrangements and to have an opposite arrangement, or that use is exclusively made use from radiation heaters or resistive heaters.
In a further embodiment according to the method of the present invention, a temperature as measured on and registered by means of a thermocouple is performed by contactless measuring.
As an alkali metal halide salt, according to the method of the present invention use is made of CsBr and wherein as a lanthanide dopant salt use is made of EuX2, EuX3, EuOX or—as a mixed salt with divalent and trivalent europium—EuXz, wherein 2<z<3.
In another embodiment as a combination of an alkali metal halide salt and a lanthanide dopant salt, according to the method of the present invention, use is made of a salt according to the formula CsxEuyX′x+αy, wherein x/y>0.25, wherein α≧2 and wherein X′ is a halide selected from the group consisting of Cl, Br and I and combinations thereof.
In said vapor deposition apparatus, according to the method of the present invention, a pressure is further maintained in the range from 10−5 to 1 Pa, throughout said vapor deposition process.
A phosphor panel of the present invention comprises a support that can be any support known in the art, but in view of the desired high humidity resistance of the screens, a support with very low water vapor permeability is preferably used: any solid of an organic or inorganic nature, which can moreover assume any geometrical shape, such as foils, fibers (e.g. carbon fiber reinforced resin sheets and more particularly sheets, each of which includes carbon fibers arranged in a direction and impregnated with a heat resistant resin such that directions of the carbon fibers in the carbon fiber reinforced resin sheets are different from each other), and particles can be used. Particular organic supports may be chosen from a polyimide sheet, epoxy compounds, thermoplastic and thermosetting compounds of different compositions, polyether, polyester and polycarbonate compositions, without however being limited thereto. As an inorganic non-metallic support chemically reinforced glass or crystallized glass can be used. Inorganic metallic supports, suitable for use are, e.g. metal substrates such as those of aluminum, titanium, lead, iron, copper, steel, molybdenum, beryllium; supports of metallic and non-metallic oxides such as those of aluminum, titanium, lead, copper, beryllium, manganese, tungsten, vanadium, and silicon oxides. It is recommended to subject the support to cleaning procedures as to washing and degreasing before applying a protective layer unit and/or a phosphor deposit thereupon. A preferred support is a support of anodized aluminium and the supports as disclosed in U.S. Pat. No. 6,815,095 and US-Application 2003/0134087.
According to the method of the present invention, said support thus comprises a metal support, optionally coated with additional coatings.
More particularly said metal support, according to the method of the present invention, is aluminum or titanium. A support layer in form of a titanium sheet or an alloy thereof, or a support comprising a titanium layer or a titanium alloy layer may be applied as has e.g. been proposed as a particularly suitable support with respect to corrosion resistance in U.S. Ser. No. 60/809,424 filed May 30, 2006.
In case of an aluminum support, according to the method of the present invention, said aluminum support may be subjected to an anodizing step, followed by a sealing step, wherein said aluminum support is treated with a solution containing a chromium compound in at least one of said steps, e.g. as has been described in U.S. Ser. Nos. 60/794,548 and 60/794,426, both filed Apr. 24, 2006. A radiation image storage phosphor panel having as a layer arrangement of consecutive layers an anodized aluminum support layer, a phosphor layer comprising needle-shaped phosphor crystals, and a protective layer, may be manufactured, wherein said anodized aluminum support layer has a ratio of average surface roughness ‘Ra’ versus anodized layer thickness ‘t’ in the range from 6:1000 to 6:10, in favor of less corrosion and acceptable adhesion between support layer and storage phosphor. Such a radiation image storage phosphor panel advantageously has an aluminum support layer, which is, in a first preparation step, treated by an anodizing and a sealing step, and is treated with a chromium compound in at least one of said steps.
In another embodiment as an additional coating a sublayer is optionally present, comprising an inorganic compound, e.g. as the one described in U.S. Ser. No. 60/794,431, filed Apr. 24, 2006. In favor of lowering corrosion of a radiation image storage phosphor panel comprising, as a layer arrangement of consecutive layers, an anodized aluminium support, a sublayer and a phosphor layer having needle-shaped phosphor crystals may be built, wherein said sublayer comprises an inorganic metal oxide or a metal compound and wherein said sublayer has a thickness of less than 20 μm. Apart from the fact that said metal is selected from the group consisting of tin, copper, nickel, chromium, scandium, yttrium, tantalum, vanadium, titanium, niobium, cobalt, zirconium, molybdene and tungsten, said aluminum support advantageously contains magnesium.
According to the method of the present invention, as an additional coating a precoat layer is optionally present, comprising an organic polymer, e.g. as has been described in U.S. Ser. No. 60/794,427 filed Apr. 24, 2006. As thaught therein in favor of adhesion, and applicable in the present invention, a radiation image storage phosphor panel comprises as an arrangement of layers, in consecutive order, an anodized aluminum support, a precoat layer and a phosphor layer comprising needle-shaped phosphor crystals, wherein said precoat layer comprises an organic polymer, and wherein said precoat layer has a thickness of less than 20 μm. Apart from use of a poly-p-xylylene as an organic polymer, said polymer is selected from the group consisting of cellyte, poly-acrylate, poly-methyl-methacrylate, poly-methylacrylate, polystyrene, polystyrene-acrylonitrile, polyurethane, hexafunctional polyacrylate, poly-vinylidene-difluoride, silane-based polymers and epoxy functionalized polymers.
Coated upon a support layer, as an intermediate layer between support and phosphor layer a parylene layer as disclosed in US-A 2004/0051441 and US-A 2004/0051438 or another, e.g. dye-containing layer as in U.S. Pat. No. 6,927,404 may be recommended, wherein such a parylene layer may also be present between phosphor layer and outermost protective layer or topcoat as in U.S. Pat. No. 6,710,356 or as described in U.S. Pat. No. 6,822,243. A good adhesion between the two protective layers is advantageously provided when use is made of a phosphoric acid ester compound as disclosed in US-A 2005/0067584. The parylene layers mentioned above are particularly recommended to be applied as layers protecting the doped alkali metal halide phosphor from moisture, as is such phosphors are known to be very sensitive to humidity of the environment. In the case wherein between the support material and the phosphor layer a parylene layer is present, the surface roughness of the covered support shows a better smoothness its surface roughness decreases (preferably 0.5 or less and even more preferably 0.1 or less), as described in US-A 2004/0051438 which may be in favor of depositing columnar crystals or needles having smaller diameters, thereby leading to an improved packing density of the said needles per square unit of the surface area of the vapor deposited photostimulable phosphor layer and improved sharpness or image definition. Dimensions of such columnar, needle-shaped or cylindrical phosphors as disclosed in U.S. Pat. No. 6,967,339 may advantageously be strived at.
In favor of a good adhesion between support and phosphor layer measures may, in another embodiment, be taken as proposed in EP-Application No. 06 101 437, filed Feb. 9, 2006, wherein a sublayer in form of a binderless non-vapor deposited layer, at least comprising a halide compound, is providing good adhesiveness.
In a particular embodiment of the present invention the surface of the phosphor layer may be smaller than the surface of the support so that the phosphor layer does not reach the edges of the support. Thus a panel with a support having a surface larger than the main surface of the phosphor layer, so that the phosphor layer leaves a portion of the support free, wherein the protective layer comprising layer A and topcoat layer B may cover at least in part the portion of the support left free by the phosphor layer. An advantage of such a construction resides in the fact that the edges of the phosphor layer do not touch mechanical parts of the apparatus and are thus less easily damaged during use of the panel, more particularly e.g. during transport in the scanner. Another advantage of this construction is that no special edge reinforcement is necessary, although, if desired, further edge reinforcement may be applied. Although a construction of a phosphor panel wherein the surface of the phosphor layer is smaller than the surface of the support, so that the phosphor layer does not reach the edges of the support, represents a specific embodiment of the present invention, such a construction can be beneficial for the manufacture of any phosphor panel covered with any protective layer known in the art.
In favor of repetitive cleaning of storage panels and in order to avoid scratches while handling a storage phosphor plate, measures may be taken as proposed in EP-Applications Nos. 06 118 157 and 06 118 158, filed Jul. 31, 2006. As in these applications a protective coating having a photo- or electron beam curable composition may be applied, wherein said composition comprises a polymer or copolymer and a (meth)acrylate type monomer having more than one (meth)acrylate group per monomer molecule and at least one ethyleneoxy group per (meth)acrylate group in said monomer has been proposed therein. Such top-coat layer for a photostimulable phosphor screen comprising a support, a storage phosphor layer and an outermost top-coat, is more particularly suitable for use in favor or repeated cleanability when such a top-coat layer comprises a cellulose ester polymer. Otherwise a photo-curable composition comprising a polymer or copolymer and a (meth)acrylate type monomer with more than one (meth)acrylate group per monomer molecule and two or more ethyleneoxy groups per (meth)acrylate group in said monomer may be suitable for use as a topcoat layer for storage phosphor screens or panels, more particularly when said polymer is polymethyl methacrylate or a copolymer thereof, thereby avoiding scratches. When a storage phosphor screen with a topcoat layer has protruding beads it is important that the beads do not touch mechanical parts of the scanner and that this is true even when the storage panel shows some wobble during transport in the scanner. Therefore beads when used as spacing particles in a storage phosphor screen of the present invention preferably have a median volume diameter, dv50, so that 0.5 μm≦dv50≦25 μm and a median numeric diameter, dn50, so that 0.1≦dv50/dn50≦1.20. Further the beads are preferably adapted to the thickness, t, of the layer B on the storage panel of the present invention so that said polymeric beads have a median volume diameter, dv50, wherein 0.25≦dv50/t≦4.0.
While the present invention will hereinafter in the examples be described in connection with preferred embodiments thereof, it will be understood that it is not intended to limit the invention to those embodiments.
CsBr:Eu photostimulable phosphor screens were prepared by a vapor deposition process, on flexible chromium sealed anodized aluminum plates, in a vacuum chamber by means of a resistive heating of crucibles, having as starting materials a mixture of CsBr and EuOBr as raw materials. Said deposition process onto said flexible anodized aluminum supports was performed in such a way that said support was rotating over the vapor stream.
An electrically heated oven and two refractory trays or boats—one placed on the left side, the other on the right side, were used, in which 330 g of a mixture of CsBr and EuOBr as raw materials in a 99.5%/0.5% CsBr/EuOBr percentage ratio by weight were present as raw materials in each of said crucibles in order to become vaporized.
As crucibles an elongated boat having a length of 100 mm was used, having a width of 35 mm and a side wall height of 50 mm composed of “tantalum” having a thickness of 0.5 mm, composed of 3 integrated parts: a crucible container, a “second” plate with slits and small openings and a cover with slit outlet. The longitudinal parts were fold from one continuous tantalum base plate in order to overcome leakage and the head parts are welded. Said second plate was mounted internally in the crucible at a distance from the outermost cover plate which was less than ⅔ of said side wall height of 45 mm. Under vacuum pressure (a pressure of 2×10−1 Pa equivalent with 2×10−3 mbar) maintained by a continuous inlet of argon gas into the vacuum chamber, and at a sufficiently high temperature of the vapor source (760° C.) the obtained vapor was directed towards the moving sheet support and was deposited thereupon successively while said support was rotating over the vapor stream. Said temperature of the vapor source was measured by means of thermocouples present outside and pressed under the bottom of said crucible and by tantalum protected thermocouples present in the crucible. Before starting evaporation in the vapor deposition apparatus, while heating the raw mixture in the boat or crucible and to make them ready for evaporation, shutters are covering the boats, trays or crucibles.
The chromium sealed anodized aluminum support having a thickness of 800 μm, a width of 18 cm and a length of 24 cm, was covered with a parylene C precoat at the side whereupon the phosphor should be deposited, positioned at a distance—measured perpendicularly—of 22 cm between substrate and crucible vapor outlet slit.
Plates were taken out of the vapor deposition apparatus after having run same vapor deposition times, leading to phosphor plates having phosphor layers of about equal thicknesses.
In another experiment (see CB74120) only one crucible was used, having as dimensions a length of 130 mm, a width of 45 mm and a side wall height of 60 mm. The said crucible was filled with 600 g of a mixture of CsBr and EuOBr as raw materials in a 99.5%/0.5% CsBr/EuOBr percentage ratio by weight.
In the Table 1 hereinafter it has been indicated where, if applied, an additional heating was performed: in all of the experiments, except for CB74120, CB74310 and CB74312 an additional heating in form of a pre-heating step was applied at the back side of the support, i.e. by electrically resistive heaters at the side opposite to the side of the front side of the support where vapor was deposited while evaporating the raw materials. In experiments CB74310 and CB74312 additional heating in form of a pre-heating step was applied at the phosphor side of the support (by radiation heating with halogen lamps) where vapor was deposited while evaporating the raw materials.
“TtcKs shutter” represents the starting temperature measured at the back side of the support plate—i.e. opposite to the front side where vaporized materials becomes deposited while performing vaporization—and measured on and registered by a thermocouple type K from RODAX, Antwerp, Belgium, before opening the shutter, present on the crucible positioned on the left (see Table 1: shutter left) or right (see Table 1: shutter left) side in the vapor deposition apparatus.
From all of the data summarized in the Table 1, it is clear that the thermocouple temperature just before starting evaporation (i.e. with closed shutters) is in the range between 100° C. and 250° C., when said temperature is measured on the back side of the support, i.e. opposite to the front side where the binderless phosphor layer becomes deposited.
All of the temperatures T in Table 1 have been represented in degrees Celsius (° C.).
With respect to image sharpness as is reflected by MTF-values at 3 line pairs per mm: CB74120, prepared from only one large crucible, without extra—or additional—substrate heating, represents a panel that leads to results with respect thereto that are about just acceptable, whereas other preheated support plates provide high speed and better image sharpness as becomes clear from the results, summarized in Table 2 hereinafter.
Data about coating weight of the phosphor layer, MTF-values at 1 lp/mm and 3 lp/mm indicative for sharpness, and relative speed as well as absolute speed obtained after correction for the phosphor coating weight have been set out in the Table 2 hereinafter, as well as relative speed (SAL %), defined as speed for each of the screens, derived from Scan Average Levels, compared with the speed as derived from said “Scan Average Levels” of an MD10® reference photostimulable phosphor screen manufactured by Agfa-Gevaert, Mortsel, Belgium and corrected absolute speeds (expressed as SAL_corr.abs), i.e. corrected for coating weight differences.
CB74120, although offering still acceptable results—see e.g. its high speed—expressed as SAL_rel., and, after correction expressed as SAL_corr.abs wherein a higher figure stands for higher speed, tends to a decrease in sharpness (higher MTF-values stand for sharper images) versus CB-plates 74113, 74114, 74115, 74118, 74310 and 74312.
As an advantageous effect of the present invention it has been established, as set forth above in the description and in the examples, that in the conditions within a temperature range of less than 250° C., but not less than 100° C., measured on and registered by means of a thermocouple at the back side of the support where no raw materials become deposited, while starting vaporization by opening the shutters of crucibles in a resistive heating evaporation process, that an optimized speed and sharpness is measured for the storage phosphor plate thus obtained, when an additional heating is applied.
Having described in detail preferred embodiments of the current invention, it will now be apparent to those skilled in the art that numerous modifications can be made therein without departing from the scope of the invention as defined in the appending claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06119068.2 | Aug 2006 | EP | regional |
This application claims the benefit of U.S. Provisional Application No. 60/839,339 filed Aug. 22, 2006, which is incorporated by reference. In addition, this application claims the benefit of European Application No. 06119068.2 filed Aug. 17, 2006, which is also incorporated by reference. The entire contents of literatures cited in this specification are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60839339 | Aug 2006 | US |
