Needle image plate or panel suitable for use in CR or DR imaging.

Abstract

 A CR image plate or DR scintillator plate or panel having a glass support and having said glass support covered, in part, with a phosphor or scintillator layer, wherein said phosphor or scintillator layer and part of the said glass support left free from being covered by said phosphor or scintillator layer are coated with an organic polymeric protective layer, shows an improved adhesion between said glass support and said organic polymeric protective layer when said glass support is roughened up to an R_a value of more than 0.5 µm, upon at least part of the side of the support onto which the phosphor or scintillator layer is coated.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a screen or panel as an element for medical radiographic image formation, improved with respect to robustness, required for a frequently reused element. More particularly said element is suitable for use in computed, as well as in direct radiography.

BACKGROUND OF THE INVENTION

[0002] A well-known use of phosphors is in the production of X-ray images. In a conventional radiographic system an X-ray radiograph is obtained by X-rays transmitted image-wise 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 to which a photographic film is more sensitive than to the direct impact of X-rays.

[0003] According to another method of recording and reproducing an X-ray pattern as disclosed e.g. in US-A 3,859,527 a special type of phosphor is used, known as a photostimulable phosphor, which being incorporated in a panel, is exposed to incident pattern-wise modulated X-ray beam and as a result thereof temporarily stores energy contained in the X-ray radiation pattern. At some interval after the exposure, 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 can be processed to produce a visible image. For this purpose, 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". In both kinds of radiography it is preferred to be able to choose the phosphor that will be used on the basis of its speed and image quality over a long time period without having to bother about its hygroscopicity, the more as such a panel is normally reused over such a long time period.

[0004] Therefore it is highly desired to have the possibility of producing a phosphor panel, be it for use in direct radiography or in computed radiography, that is impervious to water vapour. In US-A 4,741,993 a radiation image storage panel is disclosed having at least one stimulable phosphor layer on a support and a protective layer provided on the stimulable phosphor layer, wherein the protective layer comprises at least two layers of which regains under a relative humidity of 90% on a sorption isotherm at 25°C are different by 0.5% or more. According to that invention, a radiation image storage panel which has good humidity resistance and can be used for a long term is obtained. Although a protective layer as disclosed in US-A 4,741,993 does provide good humidity protection, the need for providing phosphor panels with even better humidity resistance has been a remaining object.

[0005] Image quality of computed radiography (CR) can be improved by scanning the storage phosphor plate in transmission (see Fig.1) instead of in reflection. After making the X-ray image by exposure, the CR imaging plate (IP) is scanned in transmission, i.e. the NIP (needle image plate) is stimulated from the back or rear side and the emission light is detected at the front side. For this reason a transparent substrate is requested for the IP. For a transparent powder imaging plate a transparent plastic substrate may be used.

[0006] Another way to improve image quality of CR is by scanning the storage phosphor plate and collecting the PSL light both in transmission and in reflection. This technique is commonly called dual side reading as has e.g. been described in US-A's 6,344,657; 6,462,352; 6,465,794 and 6,479,834.

[0007] In the production of a needle imaging plate, however, a thermal vapor deposition process is used, in which the substrate is subjected to temperatures of 150°C or more for a time period varying from minutes to hours. Plastics are not dimensionally stable at these temperatures. Hence, glass is a desired substrate for transparent needle imaging plates (NIPs). As NIPs are hygroscopic, due to the presence of an alkali metal halide matrix in the phosphor, a suitable protection against moisture degradation is required. Therefore, NIPs are often covered with a poly p-xylylene layer, known as a "parylene" layer. Use of parylene layers as humidity protective layers of hygroscopic photo-stimulable phosphor screen layers has been disclosed in e.g. US-Application 2003/0038249. Also in DE-A-196 25 912 and GB-A-2 287 864 phosphor screens containing a parylene layer are disclosed. Although screens prepared according to the disclosures above do yield screens with an acceptable to even a very good overall quality, the need for a phosphor screen combining good humidity resistance and good resistance against physical damage, especially scratch resistance during use remains present. This problem is posed the more after frequent use of desired CsBr-based phosphor plates and as a result thereof the image quality thereof is reduced as a function of time. When the plates have to be cleaned or when they are taken out of the cassette the parylene layer, normally offering an adequate protection against moisture for the hygroscopic CsBr-based phosphor, may be damaged because parylene has a very low scratch resistance resulting again in a stability problem of the image plate. Coating of a layer onto the parylene layer may thus be desirable as has e.g. been described in US-A 6,710,356. From that radiation cured polymeric layer coated onto said parylene layer in order to further essentially prevent the phosphor plate against physical damage as a scratch resistant layer it is known that, over a long period of frequent use, adhesion of organic or inorganic polymer layers towards parylene coating is low. A remarkable adhesion improvement has been attained as has been described in US-A 7,193,226.

[0008] It was observed, however, that the adhesion between the glass substrate and parylene was bad. As a consequence, although severe measures have been taken hitherto, water may still diffuse into the NIP layer along the (side) edges, especially when the parylene overlaps with the glass substrate over a small or limited distance. As a result the NIP absorbs water at the edges and looses sensitivity very fast in the edge regions, more particularly in hot and humid conditions. When the moisture sensitive phosphor or scintillator layer has become deposited onto a glass support, an ever lasting problem has thus been encountered, in that due to inadequate moisture stopping power of the parylene coating at the borders of the glass support the phosphor layer becomes damaged in that region, especially due to moisture, penetrating into the phosphor layer at the insufficiently protected sites, as a consequence of initially insuffcient or degrading adhesiveness of the parylene layer onto the glass support.

SUMMARY OF THE INVENTION

[0009] It is thus an object of the present invention to provide the moisture sensitive phosphors, more preferably of the lanthanide doped alkali metal halide type, in a phosphor layer of a screen, plate or panel for radiographic diagnostic images, coated onto a glass support, with a protective parylene coating that is initially adequate and that does not deteriorate in adhesiveness onto said glass support, so that images with an enabling diagnostic value are obtained, even when the screen, plate or panel is frequently reused, after exposure with X-rays and read-out of said plate or panel.

[0010] It is another object of the present invention to offer a transparent NIP that is stable in hot, humid conditions and that does not undergo edge degradation.

[0011] The above-mentioned advantageous effects are realized by providing a CR or DR image plate or panel having the specific characteristics set out in claim 1. Specific features for preferred embodiments of the invention are set out in the dependent claims.

[0012] Further advantages and embodiments of the present invention will become apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] 

Fig.1 shows (left side) the exposure and (right side) the scanning of the storage phosphor plate in transmission, together with the detection of emitted light upon photostimulation by a laser source.

Fig.2 shows a reference "Flat-Field" as obtained from the exposed comparative transparent NIP from example 1.

Fig.3 shows a "Flat-Field" as obtained from the exposed comparative transparent NIP from example 1 after 10 days of conditioning in a climatic chamber at 30°C and 80% R.H.

Fig.4 shows the force to pull off the ParC^® layer increasing by mechanical roughening of the glass and increasing with roughness within one type of roughening.

Fig.5 provides a schematic representation of a NIP plate with an active phosphor area and a non-covered area with roughened edges.

Fig.6 schematically shows the degree of overlap between glass and poly-p-xylylene varying between 2 and 10 mm, wherein the ParC^® was covered with a spray-coated polyurethane acrylate (PUA) top-coat, with 2 mm overlap at both the right and the left edges.

Fig.7 shows "flat-field" images for a (fresh) reference screen and an inventive screen after a one week conditioning in a climatic chamber at 30°C and 80%RH.

Fig.8 shows sensitivity profiles over the NIP as obtained for a (fresh) reference screen and an inventive screen after a one week conditioning in a climatic chamber at 30°C and 80%RH.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The object as set forth hereinbefore has been fully achieved by increasing the specific surface of the glass, available for interaction with the parylene top-coat. More particularly the specific surface of the glass has been increased by increasing the roughness of the glass support by chemical etching or by a mechanical treatment, such as e.g. sand-blasting.

[0015] As described in US-Application 2003/0038249 a phosphor panel has been described wherein the panel further comprises a support with a surface larger than said main surface of said phosphor layer, so that said phosphor layer leaves a portion of said support free, and said layer A covers at least a part said portion of said support left free by said phosphor layer. In the examples the phosphor was deposited on a glass support.

[0016] Roughening may be carried out by using a SiC grinding medium having a grain number between 400 and 1200. Roughening and subsequent etching of the surface of the layer carrier may otherwise be performed.

[0017] A step of etching may be carried out using hydrofluoric acid, in a particular embodiment in a 1:1 mixture of distilled water. Following a grinding or sand-blasting operation the glass plate may be cleaned several times in distilled water, for example in an ultrasonic bath, and may be finally immersed for, e.g., 3 to 10 minutes in an etching bath, that preferably consists of a 1:1 mixture of H₂O and HF, and moved to and fro in the acid. Otherwise the method of using a chemical such as sodium etching may not be applied as having a problem with safety.

[0018] One type of glass usable in the invention may be the typically termed "soda-lime" glass. In general, soda-lime glass contains a percentage of sodium oxide and calcium oxide dispersed in silicon dioxide (silica), which forms the major component of the glass. Generally, during the etching process, the soda-lime components are dissolved and removed by the etching solution leaving the skeletized glass structure remaining. However, depending on the etching ability of the solution and the duration of the etching treatment, the silica itself may also be dissolved to a certain extent.
Soda-lime glasses useful in the invention may contain from about 5 to about 45% by weight of soda-lime with about 20 to about 25% by weight soda-lime preferred. While such glasses are preferred for use in the present invention, it will be understood by those skilled in the art that sheets and shapes of various other types of glass well known to the art may be processed to achieve the unique glass structure described herein and to thereby acquire the high clarity/low reflectivity/cleaning properties taught by the present invention. For example, glasses containing other alkali or mineral oxides such as potassium oxides, barium oxides, strontium oxides and aluminum oxides, with or without a small percentage of lead, may also be used. Also, glasses which have been tempered using conventional tempering treatments yield excellent results when employed as support materials in the present invention and soda-lime glass as in the instant description of the invention is only exemplary and is not limited thereto.

[0019] Prior to undergoing any etching, the surface of the glass must be cleaned to remove any oils, greases and any other contaminants which may interfere with the etching process. Any suitable heavy duty industrial glass cleaning solution may be used as a cleaning agent, such as, for example, a 50/50 volume ratio solution of ammonia and water. The glass to be treated is then generally immersed in the cleaning solution at about 45° to about 65°C to assist the cleaning action, with the solution agitated for about 10 minutes. After removal from the cleaning solution, the glass sheet is then normally rinsed with clean water, at room temperature.

[0020] The surface of the glass may further undergo a pre-etching step in order to remove a weathered surface layer which is usually comprised of surface oxides. This pre-treatment step enhances the wetting with the treatment chemicals. A typical soda-lime glass sheet, including about 23% soda-lime, may be pre-etched in an acid solution comprising e.g. about 0.5 to about 12.0 % of hydrofluoric acid, with about 2 to about 4% preferred. After such a pre-etching step, the glass is rinsed with water at about 25°C and thereafter diffusion etched using a diffusion etching solution, the glass being treated for between 15 seconds to 25 minutes, depending on temperature and concentration. The aqueous solution that may diffusion etch may include a strong fluoride ion agent, such as hydrogen fluoride, and a weak fluoride ion agent, such as ammonium fluoride. The said agents may be combined with a "moderator" which may control the activity of the fluoride ions in solution. The "moderator" e.g. may be an organic hydroxy group or an ester group containing compound, including at least one hydroxy or ester group. Generally, the glass is treated by contacting the sheet with an aqueous solution. In one embodiment, the sheet is immersed in the solution, which can be either in a one dip or in a multi dip operation. The time per dip may range from seconds to minutes depending on the concentrations, processing temperatures, and glass to be treated. It is preferable to utilize multiple dips for providing a finer etched structure with greater uniformity.

[0021] Control of the processing temperatures is very important in order to achieve the proper surface structure in the present invention. Generally, temperatures between 0°C and 35°C are preferred for the diffusion etching treatment. While such etching may be carried out above and below this range, below 0°C the reaction rate is unnecessarily slowed, while above 35°C the reaction rate may cause more severe etching than desired. Generally, the lower temperatures are preferred because at the lower reaction rates, it takes longer to etch the glass, enhancing control of the etching process and therefore providing a more finely etched surface structure which tends to yield a glass with increased clarity.

[0022] In order to adhere a particular fluorine-containing polymer film to a substrate support, following methods may be applied:

1) a method for physically roughening a surface of substrate by e.g. sand blasting;

2) a method for surface-treating a fluorine-containing resin film by chemical treatment such as e.g. sodium etching, plasma treatment, photochemical treatment;

3) a method for adhering by using an adhesive, and other methods as has e.g. been described in US-A 6,716,497.

[0023] With respect to the methods 1 and 2 above, surface-treating steps are required, and the steps are complicated and productivity is poor. Also kinds and shapes of substrate supports are restricted. Further the obtained adhesive force is insufficient, and heat resistance which the fluorine-containing resin inherently possesses is easily lowered. Also the method of using a chemical such as sodium etching has a problem with safety as already mentioned hereinbefore. Use of an adhesive in the third method, as e.g. a usual hydrocarbon type (non-fluorine-containing) adhesive does not have enough adhesive power and its heat resistance is insufficient. Thus a hydrocarbon type adhesive cannot stand under conditions for adhering a fluorine-containing polymer film which requires molding and processing at high temperature, and peeling due to decomposition of the adhesive and coloring occur. Since the above-mentioned composite material produced by using an adhesive also is insufficient in heat resistance, chemical resistance and water resistance of its adhesive layer, it cannot maintain adhesive force due to a change in temperature and environment, and lacks in reliability.

[0024] In another embodiment the "texturing" of the glass substrate may be carried out, as described in US-A 6,715,318 using a known mechanical polishing method, with precisely controlled operational conditions. However, in the case of a glass substrate having a glass or a crystallized glass, the texturing may be carried out more simply by roughening the glass substrate surface by etching.
When etching, in theory the surface of a multi-component glass substrate should be etched uniformly. Although irregular or abnormal evenness of etching patterns on microscopic scale are not desired, there may be some unevenness as, in general, the composition of the surface layer of a glass substrate is not necessarily uniform on a microscopic scale, and moreover, more particularly during polishing, abrasive grains may be pushed strongly against the glass substrate surface, may adhere thereto or become embedded therein, and hence at such sites, it will look as if the glass substrate support surface is irregular. There may thus be parts of the glass support substrate surface that are easily dissolved by an etching solution and parts that are not so easily dissolved, and as a result the etching may proceed not so uniformly as desired.

[0025] As in US-A 6,471,880 a process may be provided for etching glass objects by a chemical treatment. The process includes (a) at least one stage of chemical treatment of e.g. a glass support, and (b) at least one stage of rinsing said glass support etched by the treatment of step (a) with an aqueous solution of one or more alkali metal or alkaline earth metal cation salts. The chemical etching solution employed in stage (a) is e.g. obtained by mixing a composition comprising from 20% to 99% by weight of potassium bifluoride, from 1% to 80% by weight of at least one water-soluble divalent or trivalent cation salt selected from divalent and trivalent cation salts; and optionally one or more of the following compounds, i.e. up to 15% by weight of ammonium bifluoride, sodium bifluoride in a proportion by weight of less than or equal to that of potassium bifluoride, provided that, when the composition comprises both ammonium bifluoride and sodium bifluoride, the total amount of these two bifluorides does not exceed that of potassium bifluoride, from 5% to 60% by weight of at least one water-insoluble filler chosen from inorganic and organic products which are stable in an acidic medium, or from 0.2% to 6% by weight of one or more surface-active agents which are stable in an acidic medium.

[0026] Minutely roughening a surface of a substrate glass support, by an etching method for the purpose of enhancing adhesion of a coating film to the surface of the said substrate glass support may moreover be applied as has been described in US-A 5,242,544. An easily vaporizable material such as a fat or wax may be used, and the substrate surface be scattered with numerous microscopic droplets of the masking material by exposing the substrate surface to vapor of such masking material and simultaneously to vapor of another material, e.g. water or an alcohol, which is immiscible with the masking material and serves the purpose of preventing agglomeration of droplets of the masking material on the substrate surface. After having etched the substrate with a suitable etching fluid, the masking material is removed. As the result the etched surface of the substrate is scattered with numerous microscopic islets.

[0027] As a glass support PARSOL^® green may e.g. be used, said glass type belonging to the range of colored glass substrates sold by Saint-Gobain Vitrage under the trade name "PARSOL", which have various thermal properties and colors. With respect thereto reference can be made to the glasses described in the PCT patent application WO 93/07095 and in the French patent application 92/15537 filed December 23, 1992, in the name of Saint-Gobain Vitrage International. Making use of glass substrates already having a certain functionality is very advantageous, because in this way it is possible to synergistically combine both esthetic and thermal effects of the substrate on the one hand and the stack of thin layers on the other.

[0028] With respect to the particular organic polymeric protective layer, overlapping the phosphor layer and the glass support, incompletely covering said glass support as in the present invention, general information in literature with respect to poly-p-xylylene or "parylene" polymer films can be found in e.g. Martin H. Kaufman, Herman F. Mark, and Robert B. Mesrobian, "Preparation, Properties and Structure of Polyhydrocarbons derived from p-Xylene and Related Compounds," vol. XIII, 1954, pp. 3-20 (no date) and Andreas Griener, "Poly (1,4-xylylene)s: Polymer Films by Chemical Vapour Deposition," 1997, vol. 5, No. 1, Jan., 1997, pp. 12-16. "Parylene", a generic name for thermoplastic polymers and copolymers based on p-xylylene and substituted p-xylylene monomers, has been shown to possess suitable physical, chemical, electrical, and thermal properties for use in integrated circuits. Deposition of such polymers by vapourisation and decomposition of a stable dimer, followed by deposition and polymerisation of the resulting reactive monomer, is discussed by Ashok K. Sharma in "Parylene-C at Subambient Temperatures", published in the Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 26, at pages 2953-2971 (1988). "Parylene" polymers are typically identified as Parylene-N, Parylene-C, and Parylene-F corresponding to non-substituted p-xylylene, chlorinated p-xylylene, and fluorinated p-xylylene, respectively. Properties of such polymeric materials, including their low dielectric constants, are further discussed by R. Olson in "Xylylene Polymers", published in the Encyclopedia of Polymer Science and Engineering, Volume 17, Second Edition, at pages 990-1024 (1989). Parylene-N is deposited from non-substituted p-xylyene at temperatures below about 70-90°C.

[0029] The substituted dimers are typically cracked at temperatures which degrade the substituted p-xylylene monomers, and the parylene-C and parylene-F films must be deposited at temperatures substantially lower than 30°C.

[0030] In a preferred embodiment according to the present invention the protective coating is adhered to the phosphor screen or panel and to the glass support by chemical vapour deposition (CVD) and the vapour deposited film is thus a vacuum deposited polymeric film and more particularly a poly-p-xylylene film. A poly-p-xylylene has repeating units in the range from 10 to 10000, wherein each repeating unit has an aromatic nuclear group, whether or not substituted. Each substituent group, if present, can be the same or different and can be any inert organic or inorganic group which can normally be substituted on aromatic nuclei. Illustrations of such substituent groups are alkyl, aryl, alkenyl, amino, cyano, carboxyl, alkoxy, hydroxylalkyl, carbalkoxy and like radicals as well as inorganic radicals such as hydroxyl, nitro, halogen and other similar groups which are normally substitutable on aromatic nuclei. Particularly preferred of the substituted groups are those simple hydrocarbon groups such as the lower alkyl such as methyl, ethyl, propyl, butyl, hexyl and halogen groups particularly chlorine, bromine, iodine and fluorine as well as the cyano group and hydrogen. Applied on screens or panels, in part (the largest part) on the phosphor layer and on the glass support (the smallest part) as in the present invention, these polymers are formed on phosphor screens or panels by pyrolysis and vapour deposition of a di-p-xylylene. These materials are the subject of several US-Patents such as US-A 3,117,168 entitled "Alkylated Di-p-Xylylenes", US-A 3,155,712 entitled "Cyanated Di-p-Xylylenes" and US-A 3,300,332 entitled "Coated Particulate Material and Method for Producing Same". Pyrolysis of the vaporous di-p-xylylene occurs upon heating the dimer from about 450°C to about 700°C and preferably about 550°C to about 700°C. Regardless of the pressure employed pyrolysis of the starting di-p-xylylene begins at about 450°C. At temperatures above 700°C cleavage of the constituent groups may occur, resulting in a tri- or polyfunctional species causing cross-linking of highly branched polymers. It is preferred that reduced or sub-atmosphere pressures are employed for pyrolysis to avoid localized hot spots. For most operations pressures within the range of 0.0001 to 10 millimetres of Hg are practically used. However desired greater pressures may be employed. Likewise inert inorganic vapour diluents such as nitrogen, argon, carbon dioxide and the like can be employed to vary the optimum temperature of operation or to change the total effective pressure of the system. The diradicals formed in the manner described above are made to impinge upon the surface of the particulate material having surface temperatures below 200°C and below the condensation temperature of the diradicals present thereby condensing thereon and spontaneously polymerising.

[0031] As a basic agent the commercially available di-p-xylylene composition sold by the Union Carbide Co. under the trademark "Parylene" is thus preferred. The preferred compositions for the protective moistureproof protective layer covering the phosphor screens or panels thus are the unsubstituted "Parylene N", the monochlorine substituted "Parylene C", the dichlorine substituted "Parylene D" and the "Parylene HT" (a completely fluorine substituted version of Parylene N, opposite to the other "parylenes" resistant to heat up to a temperature of 400°C and also resistant to ultra-violet radiation, moisture resistance being about the same as the moisture resistance of "Parylene C" as described in the note about "High Performance Coating for Electronics Resist Hydrocarbons and High Temperature" written by Guy Hall, Specialty Coating Systems, Indianapolis, available via www.scscookson.com. Technology Letters have also been made available by Specialty Coating Systems, Cookson Company, as e.g. the one about "Solvent Resistance of the Parylenes", wherein the effect of a wide variety of organic solvents on Parylenes N, C, and D was investigated. In a preferred embodiment in the present invention said parylene layer is a halide-containing layer and more preferably said parylene layer is selected from the group consisting of a parylene D, a parylene C and a parylene HT layer.

[0032] According to the present invention a CR image plate or DR scintillator plate or panel having a glass support and having said glass support covered, in part, with a phosphor or scintillator layer coated thereupon, wherein said phosphor or scintillator layer and part of the said glass support left free from being covered by said phosphor or scintillator layer are coated with an organic polymeric protective layer, characterized in that said glass support is roughened up to an R_a value of more than 0.5 µm, upon at least part of the side onto which the phosphor or scintillator layer is coated onto said support.

[0033] In another embodiment the image plate or panel according to the present invention is characterized in that said glass support is roughened up to an R_a value of 1.0 µm or more.

[0034] Said R_a value, expressing the surface roughness attained by roughening the glass support, is measured by means of a perthometer. This instrument is built in order to microscopically follow the surface irregularities consisting of a series of "hills" and "valleys". The Ra value thus expresses the average height of these respective "high" and "low" points of the surface, i.e., a high Ra value indicates a rough surface, whereas a low Ra value indicates a smooth surface. The European standard DIN 4768 provides additional details of the surface roughness test.

[0035] In a still more particular embodiment the glass support of the image plate or panel according to the present invention has in addition, roughened upstanding edges.

[0036] According to the present invention, said organic polymeric protective layer overlaps the surface of said glass support onto which the phosphor layer is provided over a distance of at least 2 mm.

[0037] For the image plate or panel according to the present invention, the preferred organic polymeric protective layer is a poly-p-xylylene layer.

[0038] In a more particular embodiment according to the present invention, in the image plate or panel said organic layer is covered with a polyurethane acrylate layer. In favour of a good adhesion onto said "parylene" layer, in the image plate or panel according to the present invention, between said poly p-xylylene layer and said polyurethane acrylate layer, an organic coating layer is present, having at least one phosphoric acid ester compound.

[0039] That polyurethane acrylate layer, acting as a second protective layer is coated by adding at least one ester compound of phosphoric acid to an organic coating solution, followed by curing said panel by UV and/or electron beam exposure, wherein said at least one phosphoric acid ester compound is represented by the general formula (I) hereinafter:

wherein each of R¹, R² and R³ are same or different, and are selected from the group consisting of hydrogen, a saturated or unsaturated, substituted or unsubstituted aliphatic group and a substituted or unsubstituted aromatic group.

[0040] Said phosphoric acid ester compound providing good adhesion onto the parylene layer is, more particularly, selected from the group of compounds consisting of methacryl-ethyl phosphate, acrylethyl phosphate, di-methacrylethyl phosphate, methacrylethyl-methacrylpropyl-phosphate, di-acrylethyl phosphate, methacrylpropyl phosphate, acrylpropyl phosphate, dimethacrylpropyl phosphate, methacrylethyl-methacryl-propyl phosphate, dodecyl-polyethyleenglycolphosphate, polyethylene glycol-tridecylether phosphate, monoalkylphenyl- polyethyleenglycol phosphate, dioctylphenyl-polyethyleenglycol phosphate, 2-(phosphonoxy) ethyl-2-propenoate, 4-(phosphonoxy) butyl-2-propenoate, and phosphinicobis(oxy-2,1-ethane diyl)-di-2-propenoate, , tris-acryloyl-oxyethyl phosphate, nonylphenol ethoxylate phosphate, phenol ethoxylate phosphate, diethyl(ethoxycarbonyl-methane)phosphonate, ethoxylated fatty alcohol phosphate E, ethoxylated tridecyl phosphate mixture, mixture of mono,di,tri-tridecylethyleneglycol phosphate, polyethylene glycol tridecyl ether phosphate, diethyl ethyl phosphonate, dimethyl propyl phosphonate, diethyl N,N - bis(2-hydroxyethyl) amino methyl phosphonate, phosphonic acid methyl(5-methyl-2-methyl-1,3,2-dioxaphosphorinan-5-y) ester,P,P'-dioxide, phosphonic acid, methyl(5-methyl-2-methyl-1,3,2-dioxaphosphorinan-5-yl)methyl, methyl ester,P-oxide, triethyl phosphate, 2-ethylhexyl diphenyl phosphate, iso-decyl diphenyl phosphate, iso propylated triphenyl phosphate, iso propylated triphenyl phos-phate, iso butylated triphenyl phosphate, triphenyl phosphate, cresyl diphenyl phosphate, tributyl phosphate and tricresyl phosphate.

[0041] In the method of preparing an image plate or panel according to the present invention, said glass support is roughened up by chemical etching or by a mechanical treatment. More in particular, said mechanical treatment is performed by sand blasting. According to the method of the present invention, in a still more particular embodiment sand blasting is performed under pressure with aluminum oxide or glass beads. In another embodiment according to the method of the present invention said chemical etching is performed by a fluoride containing agent.

[0042] In the method of preparing an image plate or panel according to the present invention, said poly-p-xylylene layer is coated onto said phosphor or scintillator layer by chemical vapor deposition.

[0043] In another embodiment according to the method of the present invention said poly-p-xylylene layer is coated onto said phosphor or scintillator layer by a laminating step. In that case a foil of parylene is prepared by the steps of chemical vapor deposition of p-xylylene onto glass, pretreated with an easy-peel release agent, followed by peeling off said foil and laminating said foil onto the phosphor or scintillator layer and the portion of the roughened glass support left free from being covered by said phosphor or scintillator layer. It is recommended to perform said laminating step by a step of heating said laminate foil or layer while being laminated onto the phosphor or scintillator layer. In another embodiment said laminating step is followed by a step of heating said laminate layer in order to make it sticking onto the phosphor or scintillator layer and on the roughened glass support. The foil or layer normally has a thickness in the range from 1 µm up to 10 µm. Heating of said foil, during or after laminating, is advantageously performed with a radiation source having an emission spectrum in the range 1000°K to 3500°K and a power density of 12000 W/m², at a distance in the range from 5 cm to 20 cm from said laminate foil or layer. In another embodiment heating is performed in an oven and laminating proceeds by means of a heated plate in the said oven. In still another embodiment heating is performed by means of rollers, at least one of which is heated, and wherein laminating proceeds between said rollers or after said rollers. Heating steps as mentioned hereinbefore are performed at a temperature in the range from 100°C up to 200°C. When applying such a method of laminating a thin foil of parylene onto the phosphor or scintillator layer in a screen or panel as in the present invention, upon said laminated parylene layer as an organic polymeric protection layer, a second protective layer is advantageously coated by chemical vapour deposition of e.g. a second poly-p-xylylene layer.

[0044] Whatever a method is applied in order to coat the "parylene" layer, i.e. by chemical vapour deposition or laminating or both by laminating followed by chemical vapour deposition, in the method according to the present invention, as an additional organic coating layer between the outermost poly-p-xylylene layer and the further applied anti-abrasive or scratch-free polyurethane acrylate layer, such an additional organic coating layer is applied directly by a coating solution containing film-forming nitrocellulose, ethylcellulose, cellulose acetate or poly(meth)acrylic resin as organic solvent-soluble polymer wherein removing said solvent is performed by evaporation.

[0045] In a particular embodiment according to the method of the present invention, said polyurethane acrylate layer is applied by spray coating.

[0046] According to the method of the present invention said phosphor or scintillator layer is a binderless layer, deposited by vapour deposition of raw materials selected from the group consisting of one or more matrix compound(s), one or more dopant compound(s) and a combination thereof, aligned in parallel, having needle-shaped form and oriented under an angle in a range between 60° and 90° with respect to said glass support. As matrix compound(s) alkali metal halide salts and as dopant(s) lanthanides or non-matrix monovalent ions are preferred, in order to prepare a lanthanide doped alkali metal halide phosphor or scintillator such as e.g. CsBr:Eu, CsI:Na, CsI:Tl and RbBr:Tl, without being limited thereto. In case of laminating the "parylene" layer onto such needle-shaped phosphor or scintillator layer in CR image plate or DR scintillator plate or panel respectively, said phosphor or scintillator layer with vapour deposited needles and a space or gap in form of voids between said needles, covered with a protective layer composed of such an organic polymeric compound, in favour of image sharpness, advantageously fills said space or gap partially with said organic polymeric compound over a depth of not more than 1 µm, while the rest of said space or gap is filled with a gaseous compound.

[0047] In another embodiment according to the method of the present invention said phosphor or scintillator layer is coated as a binder medium layer of a ground needle-shaped phosphor or scintillator in non-aligned powdery form or as a binder medium layer of a powdery phosphor. In that case the phosphor or scintillator, apart from being a lanthanide or otherwise doped alkali metal halide phosphor or scintillator may also be a lanthanide doped alkaline earth metal halide phosphor or scintillator such as a europium doped barium fluorohalide type phosphor, such as e.g. BaFBr:Eu, BaFBr(I):Eu, Ba(Sr)FBr:Eu, Ba(Sr)FBr(I):Eu, without being limited thereto.

[0048] In still another embodiment according to the method of the present invention said phosphor or scintillator layer is coated by solidifying a molten binderless layer of ground or vapour deposited phosphors or scintillators, thus forming a crystalline layer comprising said phosphor in a homogeneously solidified form. In that case use may be made of lanthanide or otherwise doped alkali metal halide as well as lanthanide doped alkaline earth metal halide phosphors or scintillators.

Examples

[0049] While the present invention will hereinafter be described in connection with preferred embodiments thereof, it will be understood that it is not intended to limit the invention to those embodiments.

Sample preparation

[0050] A 750 µm thick CsBr:Eu²⁺ phosphor layer was deposited on an 8 mm thick "Parsol^® green" glass substrate by thermal vapour deposition.

[0051] The glass support was placed in a vacuum evaporation apparatus. Subsequently the stimulable phosphor raw materials, CsBr and EuOBr, were charged in a crucible, used as an evaporation source. The crucible was introduced in the vacuum chamber and high vacuum was created.

[0052] Next, argon gas was introduced while keeping the pumps on, in order to maintain the vacuum, thereby providing a pressure of about 3 Pa at most. The evaporation source was heated to an evaporation temperature of about 700°C, so that the CsBr:Eu was evaporating and condensing onto the rotating substrate which was suspended above the evaporation crucible. The deposition was stopped when a thickness for the stimulable phosphor layer of 750 µm was attained.
The phosphor layer was subsequently annealed for 4 hours at 170°C in air in order to improve the PSL activity.

[0053] In order to protect the CsBr:Eu²⁺ layer from moisture a 10 µm "ParC^® " (Parylene C) coating was applied by chemical vapour deposition. The NIP was finished with a 3 µm scratch-resistant, spray-coated protective layer of poly-urethane acrylate.

Experiments:

[0054] A first prototype Flat-panel NIP showed strong degradation starting from the edges as there was found a poor adhesion between the glass substrate and the parylene top-coat so that water could diffuse into the NIP layer at the edges, especially when the parylene layer did overlap with the glass substrate over a limited distance only. This was recognized to be the cause of degradation of the phosphor layer, starting from the edges.

[0055] In the experiments described below, attempts have been done in order to investigate whether edge degradation could be avoided by promoting the adhesion between the glass and the parylene interface by mechanically roughening the glass.

Comparative example 1

[0056] A transparent NIP prototype, R45-0507-01, was produced with an active area of 432 mm x 432 mm on a smooth Parsol^® -green glass substrate (size 450 mm x 450 mm). The overlap between the ParC^® and the glass substrate was about 1mm. A poly-urethane acrylate scratch-resistant top-coat was applied on top of the parylene moisture barrier layer.

[0057] Flat-field images were made. The term "flat field" should be understood herein as "uniformly exposed", i.e. exposed with a constant intensity and with a homogeneous energy distribution over the active area of the NIP, wherein in a standard procedure use is made therefore of RQA 5 (International Electrotechnical Commission - IEC61267:1994) beam quality. The thus homogeneously exposed NIP was scanned in transmission with a prototype scanning device allowing such scanning in transmission. The scanning device was calibrated under normal room conditions (22°C, 45% R.H. - relative humidity).

[0058] Fig. 2 shows the resulting flat-field image as reference image.

[0059] Comparative example 1 transparent NIP was subjected to a climatic test. It was stored in a climatic chamber or conditioning room at a temperature of 30°C and a relative humidity of 80% for a period of ten days.

[0060] After the climatic testing period a flat-field image was made in the same way as the reference flat-field image. The result is shown in Fig.3.

[0061] From the sensitivity profile before and after climatic changes, it was concluded for the comparative test that the sensitivity in central region of the NIP dropped to about 89% of the original value. However there was a continuous image plate degradation starting at the four corners of the image plate and expanding concentrically towards the center. The sensitivity degradation in the four corners was more than 80% at the end of the experiment.
The image plate did not recover when the climatic conditions were changed to standard conditions (22°C; 40-50% RH).

Inventive Examples

[0062] The region of the Parsol^® green glass substrate just outside of the transparent NIP active area was sand-blasted with different pressures, making use therefore of aluminum oxide particles or glass beads as roughening agents. The roughness (Ra) was measured and the glass was covered with a 10 µm ParC^® layer. For each type of roughening, the force to pull off a 26 mm wide ParC^® strip was measured with a manometer.

[0063] The results are listed in the Table 1 below. The figure in the last column of the Table 1 shows that the force to pull off the parC^® layer.

Table 1

Roughening	Ra (µm)	Force (grams)
No	< 0.01	2
A1203 - EKF 150 4 bar	3.41	85
A1203 - EKF 151 1 bar	1.18	25
A1203 - EKF 152 2 bar	1.94	52.5
A1203 - EKF 150 4 bar	3.11	70
Glass beads 4 bar	5.39	75

[0064] It is clear from the result in the Table 1 that the force to pull off the ParC^® layer was improved by mechanical roughening of the glass and increased with increasing roughness within one type of roughening as has also been shown in the Fig.4.

[0065] In order to investigate the effect on stability and, more particularly, edge stability, CR flat-panels with an active area of 18 cm x 24 cm were made on 25 cm x 25 cm Parsol^® -green glass substrates with roughened edges. The edges were roughened by sand-blasting with aluminium oxide type EKF150 with a pressure of 4 bar according to the schedule in Fig.5, giving a schematic representation of a NIP plate with an active phosphor area and a non-covered area with roughened edges.

[0066] The degree of overlap of glass by Parylene was varied between 2 and 10 mm. The Parylene was covered with a spray-coated PUA top-coat, with 2 mm overlap at both the right and the left edges as shown in Fig.6.

[0067] The NIPs were subjected to the above described standard climatic stability test. Before placing the NIPs in the climatic chamber at 30°C; 80% R.H., reference flat-field images were made by by read-out in reflection after homogeneous RQA5 exposure. After 2, 7 and 30 days of exposure to the hot, humid climatic conditions respectively, new flat-field images were made.

[0068] A homogeneous sensitivity drop of ca. 10% was observed over the complete NIP area. No strong degradation of the edges was observed, as can be seen in the flat-field images below in the Table 2.

Table 2

NIP	% sensitivity drop after 7 days
R_25_0611_01	10.25
R_25_0611_02	10.19
R_25_0611_03	9.86
R_25_0611_04	10.08
R_25_0611_05	11.43
R_25_0611_06	8.07

[0069] From these experiments it was concluded that no significant edge degradation occurred within one week (Fig.7) and that a more or less homogeneous sensitivity drop of about 10% was observed (Fig.8) after keeping the NIP's for 1 week at 30C/80% RH.

[0070] Making the glass sufficiently rough and having an overlap of at least 2 mm between glass and parylene was shown to be sufficient in order to avoid edge degradation.

Advantageous effects of the present invention

[0071] Making the glass substrate support sufficiently rough and having between glass and the parylene layer an overlap of at least 2 mm, providing glass substrates with roughened edges is a sufficient measure in order to avoid edge degradation. Forces to pull off the parylene layer have been shown to be remarkably improved by mechanical roughening of the glass and to be increased by increasing its roughness within one type of roughening method, as, e.g. within the sandblasting method.

[0072] Covering the parylene layer with a spray-coated polyurethane acrylate, moreover offers an additional protection, more in particular against scratches and damaging after frequent reuse.

[0073] It is further concluded that no significant edge degradation is observed as well as an acceptable sensitivity drop of about 10%, as observed after keeping NIPs for one week in a severe climatic conditing room at 30°C and at a high relative humidity of 80%, when making the glass sufficiently rough and having an overlap of the glass by parylene of at least 2 mm in order to avoid edge degradation.

[0074] 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.

Claims

1. A CR image plate or DR scintillator plate or panel having a glass support and having said glass support covered, in part, with a phosphor or scintillator layer coated thereupon, wherein said phosphor or scintillator layer and part of the said glass support left free from being covered by said phosphor or scintillator layer are coated with an organic polymeric protective layer, characterized in that said glass support is roughened up to an R_a value of more than 0.5 µm, upon at least part of the side onto which the phosphor or scintillator layer is coated onto said support.

2. Image plate or panel according to claim 1, characterized in that said glass support is roughened up to an R_a value of 1.0 µm or more.

3. Image plate or panel according to claim 1 or 2, wherein said glass support has in addition, roughened upstanding edges.

4. Image plate or panel according to any one of the claims 1 to 3, wherein said organic polymeric protective layer overlaps the surface of said glass support onto which the phosphor layer is provided over a distance of at least 2 mm.

5. Image plate or panel according to any one of the claims 1 to 4, wherein said organic polymeric protective layer is a poly-p-xylylene layer.

6. Image plate or panel according to any one of the claims 1 to 5, wherein said organic layer is covered with a polyurethane acrylate layer.

7. Image plate or panel according to claim 6, wherein between said poly p-xylylene layer and said polyurethane acrylate layer, an organic coating layer is present, having at least one phosphoric acid ester compound.

8. Method of preparing an image plate or panel according to any one of the claims 1 to 4, wherein said glass support is roughened by chemical etching or by a mechanical treatment.

9. Method of preparing an image plate or panel according to any one of the claims 5 to 7, wherein said glass support is roughened by chemical etching or by a mechanical treatment.

10. Method according to claim 8 or 9, wherein said mechanical treatment is performed by sand blasting.

11. Method according to claim 8 or 9, wherein said chemical etching is performed by treating with a fluoride containing agent.

12. Method according to any one of the claims 9 to 11, wherein said poly-p-xylylene layer has been coated onto said phosphor or scintillator layer by chemical vapor deposition.

13. Method according to any one of the claims 9 to 12, wherein said poly-p-xylylene layer has been coated onto said phosphor or scintillator layer by a laminating step.

14. Method according to any one of the claims 9 to 13, wherein said organic coating layer between said poly-p-xylylene layer and said polyurethane acrylate layer is applied directly by a coating solution containing film-forming nitrocellulose, ethylcellulose, cellulose acetate or poly(meth)acrylic resin as organic solvent-soluble polymer and removing said solvent by evaporation.

15. Method according to any one of the claims 9 to 14, wherein said polyurethane acrylate layer is applied by spray coating.

16. Method according to any one of the claims 8 to 15, wherein said phosphor or scintillator layer is a binderless layer, deposited by vapour deposition of raw materials selected from the group consisting of one or more matrix compound(s), one or more dopant compound(s) and a combination thereof, aligned in parallel, having needle-shaped form and oriented under an angle in a range between 60° and 90° with respect to said glass support.

17. Method according to any one of the claims 8 to 15, wherein said phosphor or scintillator layer is coated as a binder medium layer of a ground needle-shaped phosphor or scintillator in non-aligned powdery form or as a binder medium layer of a powdery phosphor.

18. Method according to any one of the claims 8 to 15, wherein said phosphor or scintillator layer is coated by solidifying a molten binderless layer of ground or vapour deposited phosphors or scintillators.

Drawing