JP2000056097A - X-ray luminescent article giving improved film sharpness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a luminescent article containing a phosphor-binder layer and a protective film adapted to it, e.g. a plate, a panel or a web. SOLUTION: This luminescent article contains a self-support or supported layer of phosphor grains dispersed in a binding medium and an adjacent protective film, and the protective film contains a binder and titanium dioxide as a white pigment. High-energy neutrons are emitted in a multiplication deceleration region formed with lead and beryllium by this method, low-energy neutrons are generated and radiated via a neutron multiplication reaction ((n, 2n) reaction), the number of neutrons is secured without being reduced even when a high-energy neutron source has a small output, and an expected nondestructive inspection can be made.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to radiation-sensitive luminescent articles that provide improved sharpness of diagnostic film images.

[0002]

2. Description of the Related Art In radiography, the inside of a subject is reproduced by X-rays, γ-rays, and high-energy elemental particle radiation, such as β-rays, electron beams, or penetrating radiation, which is high-energy radiation belonging to the group of neutron radiation. Is done. To convert the transmitted radiation into visible and / or ultraviolet radiation, luminescent materials called phosphors are used.

In a conventional radiographic system, X
X-ray radiographs are obtained by X-rays transmitted through a subject according to an image, and converted into light of a corresponding intensity in a so-called intensifying screen (X-ray conversion screen). In the intensifying screen the phosphor particles absorb the transmitted X-rays and convert it to visible and / or ultraviolet radiation. Photographic films are more sensitive to them than to the direct impact of X-rays.

In fact, the light emitted imagewise by the screen illuminates the contacting photosensitive silver halide photographic emulsion layer, which is developed after exposure to coincide with the X-ray image. A silver image is formed.

For use in general medical radiography, X-ray films comprise a transparent film support coated on both sides with a silver halide emulsion layer. During X-ray irradiation, the film is placed in a cassette between two X-ray conversion screens, each of which is contacted with a corresponding silver halide emulsion layer.

One-side coated silver halide emulsion films combined in contact with only one screen are known for autoradiography, applications where improved image resolution is critical, such as mammography and industrial radiography. It is often used in the specific field of non-destructive testing (NDT). Autoradiographs are photographic records formed through the transmission of transmitted radiation emitted by radioactive materials contained in a subject (eg, a microtome cut for biochemical studies).

[0007] Phosphors suitable for use in conventional radiographic systems must have high promptness upon X-ray irradiation and low afterglow which favors image sharpness. That said plate or panel carrying the phosphor acts only as an intermediate imaging material and does not form a final record, and that the final image is made or reproduced on another recording medium or display as a radiographic film material It is clear. The phosphor plate or sheet can thus be reused repeatedly and the expected life of the plate is limited mainly by mechanical damage such as scratches.

X-ray conversion screens generally comprise a support, a layer containing phosphor particles dispersed in a suitable binder, and a protective coating applied over the phosphor-containing layer to protect said layer during use in this order. Including.

As the X-ray conversion screens are used repeatedly in the above X-ray recording systems, it is important to provide them with a suitable topcoat to protect the phosphor-containing layer from mechanical and chemical damage. Therefore, the protective layer has a relief structure that reduces the tendency to exhibit sticking phenomena with contacting materials and reduces friction, which is favorable for loading and unloading films from the cassette and reduces the generation of static electricity.

[0010] Once the cassette is loaded, the contact between the film and the general screen (it depends on the distance and contact area between both screens and photographic film)
Is important for obtaining good image quality.

Optimization of the relationship between the physical properties of the topcoat layer of the screen and the image quality is described, for example, in EP-A05
No. 10754, wherein the coating is provided with a liquid radiation-curable composition and obtained by giving the coating an embossed structure by means of a rotary screen printing device or gravure roller and by curing said coating by UV or electron beam curing. A luminescent screen having an embossed protective layer is described.

The increased thickness itself, in particular from the point of view of the phosphor layer, can result in increased unsharpness of the emitted light.
This is undesirable if the weight ratio between the amount of phosphor particles and the amount of binder decreases for the same coverage of said phosphor particles (also called "pigments"). Increasing the weight ratio of pigment to binder to provide a sharper image by reducing the amount of binder may be necessary, for example, due to insufficient elasticity and brittleness of the coated phosphor layer in the screen. Leading to unacceptable operating characteristics.

[0013] Several different methods have been proposed for producing thin screens with high absorption (ie, low binder to phosphor ratio). The lowest binder to phosphor ratio is obtained when a "single crystal" screen (ie, a screen without any binder) is used. Extremely high resolution (ie, image sharpness) can be obtained using such a screen. Such a screen can be produced, for example, by vacuum deposition of a phosphor material on a support. However, this manufacturing method cannot be used to manufacture high quality screens using all available phosphors. The above process leads to best results when phosphor crystals with high crystal symmetry are used. Phosphors having a complex crystal structure, such as alkaline earth fluorine-halides, tend to (partly) decompose under vacuum deposition, and the production of screens by vacuum deposition has a phosphor with a complex crystal structure. Is almost impossible and leads to poor results. This means that vacuum deposition works well only with a limited number of phosphors. In addition, vacuum deposited phosphor layers must undergo special treatment to give them good physical properties.

Therefore, another method for reducing the thickness of a phosphor layer in a screen comprising a coated layer of phosphor particles dispersed in a binder has been disclosed. One method for obtaining a thinly coated phosphor layer without changing the coating weight of the binder and of the pigment is at a temperature above the melting or softening point of the thermoplastic elastomer as described in EP-A 0 393 662. It is to utilize a method of compressing a coating layer containing both components. The porosity is significantly reduced by this method. This method produces good image quality,
Request additional operation of the screen or panel. However, this additional operation is undesirable from an ecological point of view. EP-A 0 647 258 discloses, as an alternative, in a luminescent article comprising a self-supporting or supported layer of phosphor particles dispersed in a dispersion medium, wherein the binding medium comprises one or more rubbery and / or elastomeric polymers; The volume ratio of phosphor to binding medium is at least 70:30, up to 92:
8 and a fill factor of less than 67% is provided. EP-A 064
8254 shows detailed characteristics of the rubbery polymer, for example,
CARIFLEX, KRATON, SOLPRENE, TUFPRENE, EUROPRENE,
It is provided as those block copolymers well known by trade names such as BUNA BL. However, a small amount of binder leading to a high loading of the phosphor does not result in any brittle layer in this case, and the phosphor layer requires only a minimal amount of binder to provide structural integrity to the layer. Should be included. This method does not burden the "elasticity" of the screen. Although having good physical properties even with their high pigment-to-binder ratio, screens are sensitive to the formation of "fixed screen noise", also called "screen structure mottle", in the phosphor layer . Furthermore, these rubbery binders are dissolved in toluene or a mixture of alkane and toluene, such as hexane, to provide optimal solvation in the coating solution, thereby providing optimal flow and drying properties of the coating solution. Should. The use of these solvents is undesirable from an ecological point of view, and a solution has been provided in US-A 5,663,005. A screen comprising a self-supported or supported layer of phosphor particles dispersed in a polymeric binder, wherein the phosphor particles are present in the binder in a volume ratio of at least 80/20. the polymeric binder comprises at least one polymer of Tg ≦ 0 ° C., an average molecular weight of 5000 to 10 ⁷ _{(MG avg),} at least 5 wt% for (% wt / wt) is dissolved in ethyl acetate And at least 1% of a self-supporting layer of said polymer comprising 82% by volume of phosphor particles and having a thickness of 100 mg / cm ² of phosphor particles.
A screen characterized by an elongation at break.

In a preferred embodiment, the polymer is soluble in ethyl acetate for at least 20% by weight (% w / w), and in a more preferred embodiment the binder comprises at least 60% by weight of the polymer. Particularly preferred are polymers that are at least one material selected from the group consisting of vinyl resins, polyesters, and polyurethane resins.

The image quality, in particular the sharpness, in addition to being mainly determined by the filling factor and the thickness of the phosphor layer as described above, also depends in particular on the optimum scattering phenomena in the phosphor layer. Their scattering phenomena depend in particular on the crystal size distribution of the phosphor particles, their morphology and the choice and amount of binder present in the phosphor layer, which again is crucial to the achievable packing factor for the phosphor particles. It is. As is well known, the sensitivity of the screen is determined by the chemical composition of the phosphor, its crystal structure, crystal size characteristics, the weight of the phosphor coated on the phosphor layer and the thickness of the phosphor layer.

Although sharp images with little noise can be obtained using phosphor particles of small average particle size, it is common knowledge that luminous efficiency decreases with decreasing particle size. Thus, the optimal average particle size for a given application is a compromise between the desired image sharpness and imaging speed.

Last but not least, the wavelength of light emitted by intensifying screens is crucial to the sharpness obtained with such screens: emitted by phosphors that emit blue and ultraviolet light. Light having short wavelengths, such as those leading to better sharpness than light obtained after processing of a radiographic film that is held in close contact with the screen during x-ray and conversion illumination. Apart from that, the scattering of the fluorescent radiation generated by the screen is reduced by incorporating filters or antihalation dyes into the screen and / or the silver halide film material, whereby US-A 3,809,906,3.
It is known to compensate for the lack of resolution of a photosensitive silver halide emulsion layer as disclosed in 873209, 4130428 and 4130429. Further improvements to image sharpness, preferably without speed loss, are appreciated.

[0019]

It is an object of the present invention to provide a luminescent article, for example in the form of a plate, panel or web, comprising a phosphor-binder layer and a protective coating applied thereto, said article comprising: Has excellent image resolution without speed loss.

[0020] Other objects and advantages of the present invention will become apparent from the following description and examples.

[0021]

According to the present invention, in a luminescent article comprising a self-supporting or supported layer of phosphor particles dispersed in a binding medium and a protective coating adjacent thereto, said protective coating comprises a binder. In addition to the above, there is provided a light-emitting article comprising titanium dioxide as a white pigment.

Photosensitive silver halide photographic film material which is held in contact with said article during X-ray irradiation and subsequent conversion illumination when said titanium dioxide white pigment is present in said binder, preferably comprising urethane acrylate After the processing, the image sharpness is improved.

When the pigment is present in an amount of up to 5% by weight, preferably up to 2% by weight, more preferably up to 1% by weight, based on the binder, there is no speed loss for the treated film material. Not observed.

[0024]

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, there is provided a luminescent article comprising a self-supporting or supported layer of phosphor particles dispersed in a binding medium and a protective coating adjacent thereto for obtaining particularly improved sharpness. In addition, a luminescent article is obtained in which the protective coating contains titanium dioxide as a white pigment in addition to the binder. The white pigment present in the protective overcoat layer is composed of titanium dioxide (rutile or anatase type titanium dioxide). In addition, luminescent phosphors can be used as white pigments. The white pigment is less than 2 μm, preferably less than 1 μm, more preferably 0.1 to
It preferably has an average particle size diameter of 0.5 μm.

In the protective overcoat layer of the luminescent article according to the present invention, the white pigment is present in an amount of 2% by weight or less based on the binder, preferably in an amount of 1% by weight or less based on the binder.

Useful radiation curable compositions for forming protective coatings on luminescent articles according to the present invention include as major components: (1) a crosslinkable prepolymer or oligomer; (2) a reactive diluent monomer. And for UV curable formulations (3) Photoinitiator.

Examples of suitable prepolymers for use in the radiation-curable composition applied according to the invention are as follows: unsaturated polyesters, such as polyester acrylates; urethane-modified unsaturated polyesters, such as urethane-polyesters Acrylate. Liquid polyesters having acrylic groups as end groups, such as saturated copolyesters provided with acrylic end groups, are described in EP-A 0 0
207257 and Radiat. Phys. Chem., Vol. 33, No. 5,
p.443-450 (1989). The latter liquid copolyesters are substantially free of low molecular weight, unsaturated monomers and other volatiles and have very low toxicity (cf. the periodicals "Adhaesion" 1990 Heft 12, 12
page). DE-A 28 38 691 gives a process for the production of a variety of radiation-curable acrylic polyesters.
Mixtures of two or more of the prepolymers may be used.
An overview of UV curable coating compositions can be found, for example, in the periodicals “Coat
ing ”9/88, pp. 348-353.

When the radiation curing is carried out in the ultraviolet (UV), a photoinitiator is present in the coating composition to effect polymerization of the monomers and their optional crosslinking with the prepolymer, which results in the curing of the coating protective layer composition. Acts as a catalyst to get started. A photoinitiator may be present to enhance the effect of the photoinitiator. Photoinitiators suitable for use in UV-curable coating compositions are a group of organic carbonyl compounds, for example benzoin ether compounds such as benzoin isopropyl, isobutyl ether; benzyl ketal compounds; ketoxime esters; benzophenone, o-benzoyl. Benzophenone-based compounds such as methyl-benzoate; acetophenone-based compounds such as acetophenone, trichloroacetophenone, 1,1-dichloroacetophenone, 2,2-diethoxyacetophenone, and 2,2-dimethoxy-2-phenylacetophenone; 2-chlorothioxanthone; Thioxanthone-based compounds such as 2-ethylthioxanthone; 2-hydroxy-2-methylpropiophenone, 2-hydroxy-4'-isopropyl-2-methylpropiophenone, 1- It belongs to such mud alkoxy compounds such as phenyl ketone.

A particularly preferred photoinitiator is 2-hydroxy-
2-methyl-1-phenyl-propan-1-one, a product of which is sold under the trade name DAROCUR 1173 by E. Merck, Darmstadt, Germany. The photopolymerization initiators may be used alone or as a mixture of two or more. Examples of suitable photoinitiators are, for example, GB-A 1314
556 and 1486911 and U.S. Pat.
Aromatic amino compounds and US-A as described in No. 3
And carbostyril compounds as described in US Pat.

In a specific example, the binder of the protective overcoat layer in the luminescent article according to the present invention comprises urethane acrylate. A coating dispersion composed of a urethane acrylate oligomer and an acrylate oligomer is prepared, which together form the co-protective layer binder, which are at least 2: 1, more preferably about 7:
Present in a weight ratio of 3 together they represent at least 80% by weight, up to 90% by weight of the total amount of protective layer. Well-known urethane acrylates and acrylate oligomers are GENOMEER T1600 (RAHN, trade name from Switzerland), and
SERVOCURE RTT190 (SERVO DELDEN BV, trade name available from the Netherlands). Flow modifiers, surfactants and photoinitiators are further added with the white pigment, the presence of which is essential to achieve the objectives of the present invention. A more detailed description of the composition of the protective overcoat layer can be found in the examples below.

The roughness of the topcoat layer of the intensifying screen or luminescent article according to the present invention is substantially such that the phenomenon of sticking between the film in the cassette and the intensifying screen is after adhesion due to pressure enhancement in the cassette system. Provides the advantage of being avoided.

A related feature of the thickness and roughness of the protective coating that gives the screen of the present invention the desirable and unexpected properties of excellent image sharpness and ease of operation is EP-A05.
10754.

The use of an X-ray conversion phosphor screen with a top coat having an embossed structure for the transport properties of the film in the cassette is preferred for a virtually frictionless loading and unloading of the cassette, and significantly reduces electrostatic charging. The microgrooves formed by the embossed structure of the protective coating pass between the film where air is in close contact with the phosphor screen, thereby providing image quality (image sharpness)
Good screen without containing large bubbles-
It can be improved by film-screen adhesion.

According to a preferred embodiment, the coating of the protective layer is performed here by screen printing (silk screen printing).

In a preferred embodiment, the protective coating composition is EP-A
Applied by a rotating screen printing device as described in 0510753.

[0036] Storage stabilizers, colorants, and other additives may be added to the radiation-curable coating composition. These additives may be dissolved or dispersed therein to prepare a coating solution for the protective layer. Examples of coloring agents that can be used for the protective layer are MAKROLEX ROT EG, MAKROLEX ROT GS and MAKROLEX R
Including OT E2G. MAKROLEX is a registered trademark of Bayer AG, Leverkusen, Germany.

When using ultraviolet light as a curing source, the photoinitiator that needs to be added to the coating solution more or less absorbs the light emitted by the phosphor, and thus emits, in particular, UV or blue light. Impairs the sensitivity of radiographic screens when used. In the case of the use of a green emitting phosphor, a photoinitiator whose absorption range overlaps the emission range of the phosphor the least must be selected. A preferred photoinitiator is DAROCUR 1173 (trade name) described above.

After the protective coating of the luminescent article is provided with the embossed structure, the coating step is performed by passing the uncured or slightly cured coating through a nip of a pressure roller. The roller in contact with the coating has a micro relief structure, for example giving the coating an embossed structure to obtain a relief. A suitable method for forming a textured structure on a plastic coating by means of an engraved chill roll is described in U.S. Pat. No. 3,959,546.

According to another example, the texture or embossed structure is a gravure roller or screen printing device operated with a radiation-curable liquid coating composition (Hoeppler viscosity at a coating temperature of 25 ° C. is 450-20,000 mPa.s). At the coating stage by applying the paste-like coating composition.

To avoid flattening of the embossed structure under the influence of gravity, viscosity and surface shear stress, radiation curing is performed immediately or almost immediately after application of the liquid coating. The rheological behavior or flow properties of the radiation-curable coating composition can be controlled by so-called flowing agents. For that purpose, alkyl acrylate ester copolymers containing lower alkyl (C1-C2) and higher alkyl (C6-C18) ester groups can be used as viscosity reducing shear control agents. The addition of a pigment, such as colloidal silica, increases the viscosity.

Various other optional compounds, such as plasticizers, matting agents, lubricants, defoamers, etc., suitable for reducing the build-up of static electricity as described in EP-A 0 510 753 may be added to the radiographic article. Radiation curable coating composition. Said document gives a description of the apparatus and method for curing, along with an overview of X-ray conversion screen phosphors, photostimulable phosphors and binders in phosphor-containing layers.

The edges of the screen, which are particularly vulnerable by a number of operations, are described in EP-A 0 0 0 by a method comprising the following steps:
May be reinforced by covering the edges (sides) with a polymeric material essentially formed from a wet-cured polymer composition prepared according to 541146: (A) Chemistry capable of performing an addition reaction with amino groups Organic substance 1 containing 30 to 99 parts by weight of at least one olefinically unsaturated compound having a weight average molecular weight [Mw] of at least 1500, and (B) a blocked amino group ~
70 parts by weight (from which the compound having free primary and / or secondary amino groups is formed under the influence of moisture),
However, the copolymer of component (A) (i) is 393 to 980.
(Ii) a molecularly bound carboxyl anhydride moiety having an anhydride equivalent weight of the copolymer that is 0 and the binder composition contains 0.25-10 anhydride moieties for each blocked amino group; Coating the resulting mixture on at least one side (edge) of the phosphor screen, and (iii) removing the coating mixture consisting essentially of components (A) and (B) and moisture (H ₂ O). Bring into contact.

The support materials for the radiographic screens according to the invention include cardboard; cellulose acetate, polyvinyl chloride, polyvinyl acetate, polyacrylonitrile, polystyrene, polyester, polyethylene terephthalate, polyamide, polyimide, cellulose triacetate and Plastic films such as polycarbonate films; metal sheets such as aluminum foil and aluminum alloy foil; plain paper; barita paper; resin-coated paper; pigmented paper containing titanium dioxide and the like; and paper sized with polyvinyl alcohol and the like. . Preferably, a plastic film is used as the support material.

The plastic film may include a light absorbing material such as carbon black, or may include a light reflecting material such as titanium dioxide or barium sulfate.
The former is suitable for making high-resolution radiographic screens, while the latter is suitable for making high-sensitivity radiographic screens.

Examples of preferred supports include polyethylene terephthalate, transparent or blue-colored or black-colored polyethylene terephthalate (for example, Toray I, Tokyo, Japan).
LUMIRROR C, type X, supplied by ndustries
30), including polyethylene terephthalate filled with TiO ₂ or BaSO ₄ . For example, a metal such as aluminum or bismuth may be deposited by, for example, a vapor deposition method to obtain a radiation-reflective polyester support.

These supports can have different thicknesses depending on the material of the support, and are generally 60 to 1000 μm, more preferably 80 to 50 μm, depending on the handling characteristics.
It can be 0 μm.

In typical medical radiography, the screen is fixed in a cassette in which a double-sided silver halide emulsion film can be placed. In the radiographic exposure process, one silver halide emulsion layer is exposed by the fluorescence of the front screen (the screen closest to the X-ray source) and the other silver halide emulsion layer is a screen exposed by the X-rays transmitted through the photographic material. It is exposed by the fluorescent light emitted by some back screens.

The front and back screens may be asymmetric in that, for example, their sensitometric properties, thickness, phosphor coverage and phosphor composition may differ.

Usually, the screens described above are applied for medical X-ray diagnostic applications, but according to a specific example, the radiographic screens of the present invention have higher energy X-ray or γ than in medical X-ray applications. It may be used in non-destructive inspection (NDT) of metal objects using lines. It has been found that it is advantageous to combine the fluorescent phosphor layer with a metal layer or metal support in screens applied for industrial radiography. In this case, the metal is US-A 38
It has an atomic number in the range from 46 to 83 as described in 72309 and 3389255.

The metal layer in contact with the phosphor-containing layer acts as an emitter for photoelectrons and secondary X-rays when exposed to high energy X-rays or gamma rays. The second low energy X-rays and photoelectrons are absorbed by the adjacent phosphor-containing layer with higher efficiency than the high energy X-rays and gamma rays emitted by industrial X-ray equipment, which results in an increase in photographic speed. The metal layer or support has the additional advantage of reducing scattered radiation, thereby improving image sharpness.

Research Disclosure September 1979, item 1
According to a particular example described in 8502, image sharpness supports a pigment-binder layer containing a non-fluorescent pigment which is a metal compound (eg, a salt or oxide of a heavy metal having an atomic number (Z) of at least 46). It is improved by incorporation into an X-ray intensifying screen on the back of the body and / or between the phosphor-containing layer and the support. A preferred pigment used for that purpose is, for example, lead oxide (PbO) applied at a lead coverage of 100 to 400 g / m ² .

According to the invention, the luminescent article is Gd ₂ O ₂
S: Tb; YTaO ₄ : Nb; BaFBr: Eu and C
having a phosphor having a composition selected from the group consisting of AWO _4. The choice of phosphor or phosphor mixture is not limited to UV or blue emitting phosphors, for example Gd ₂ O ₂ S:
Obviously, a green emitting phosphor such as Tb can be used. The present invention is useful even when a prompt light emitting phosphor that emits red light is used. Particularly in this case, the problem of sharpness or sharpness becomes more severe. This is because the lack of sharpness is increased due to the scattering of radiation having a long wavelength appearing more in green and red light than in blue light. Also, when screens containing green or red emitting phosphors are used, combining these screens with photosensitive silver halide film materials spectrally sensitized to the wavelength of the converted illumination light emitted by the combined screens It is also clear that is advantageous. It is well known that silver halide crystals are sensitive to the ultraviolet and blue regions of the wavelength spectrum, and that this sensitivity is more deeply shifted as the halide composition changes from chloride to bromide and to iodide. But EP-A
0467155,04887010,0568686,
0592558, 0614542 and US-A 510
Obviously, even the spectral sensitivity in the blue region of the wavelength spectrum, as shown at 8887, is appreciated.

In terms of the sensitivity (also called speed) of the screen, its thickness is 10 to 1000 μm, preferably 50 to 500 μm, more preferably 100 to 300 μm.
m.

The coverage of the phosphor present as a single phosphor or as a mixture of phosphors may be about 300, regardless of the chemical composition and the presence of one or more phosphor layers in the screen.
It is preferably in the range of １1500 g / m ² .

The one or more phosphor layers may have the same or different layer thicknesses and / or different pigment to binder weight ratios and / or different phosphor particle sizes or different particle size distributions.

Thus, the optimal average particle size for a given application is a compromise between the desired image speed and image sharpness. The preferred average particle size of the phosphor particles is from 2 to 30.
μm, more preferably in the range of 2 to 20 μm.

The phosphor layer may be coated with any phosphor or phosphor mixture depending on the subject that must be achieved with the sensitized phosphor screen produced. Fine particle phosphors can be mixed with coarse particle phosphors to increase packing density.

Suitable phosphors are, for example, yttrium tantalate phosphors (the preparation of which is described in EP-A 0011909).
And 0202875 and U.S. Pat. No. 5,064,729) or barium fluorobromide phosphors (the preparation of which is described, for example, in GB-A 1161871 and 1).
254271 and U.S. Pat. No. 4,088,894).

Preferred barium fluorobromide phosphorescence
The body has the following empirical formula: BaFBr: Eu _0.05Having.
The manufacture of the phosphor comprises at least one of the europium actives.
Part is trivalent, and the phosphor is, for example, Radiology, Vo
X-ray as described in l.148, p.833-838, September 1983
Implemented to have a high promptness on exposure.

Both the listed prompt phosphors are in the near UV and blue regions of the visible spectrum, ie, predominantly 360-450 n
m, which is used in combination with a photosensitive silver halide photographic film material. The material has an inherent sensitivity in the spectral range, for example GB
A double-sided coated silver halide emulsion layer film of the type described in A 1477637. Said phosphors can be individually coated on one or more phosphor layers of a luminescent screen or article according to the invention, or the phosphor composition is EP
-80/20-as described in A 0435241
It may be made from a mixture of both phosphors in a weight ratio of 20/80. The use of the mixture makes it possible to produce an X-ray conversion screen having a higher brightness than a phosphor screen containing only tantalate phosphor, resulting in the patient receiving a lower X-ray dose in medical diagnosis.
Further improvements in image sharpness can be realized with thermoplastic rubber binders when using said phosphor mixtures. Because the thin phosphor is EP-A 064
7258 and 0648254 (corresponding US-A 556)
9530), as possible with high phosphor to binder ratios. In the last mentioned patent, especially SHEL
L, KRATON-G rubber from the Netherlands is recommended as the only type of rubber designed for use without vulcanization.

It is clear that within the scope of the present invention the choice of phosphor or phosphor mixture is not limited to the preferred phosphors listed here.

The luminescent article or radiographic screen according to the present invention can be manufactured by the following manufacturing method.
The phosphor layer can be prepared by any coating method utilizing a solvent for the binder of the phosphor-containing layer together with useful dispersants, plasticizers, fillers and primer or interlayer compositions widely described in EP-A 0510753. Can also be applied to the support.

According to the present invention, the phosphor particles are mixed with the dissolved rubber and / or elastomeric polymer in a suitable mixing ratio to prepare a dispersion.

According to one embodiment of the present invention, the luminescent article comprises phosphor particles dispersed in a binding medium, wherein the binding medium is a polymeric binder, wherein the phosphor particles have at least 80 /
It is present in a volume ratio of 20.

In a more preferred embodiment, the polymeric binder of the phosphor particles of the luminescent article according to the present invention comprises (i) at least one polymer having Tg ≦ 0 ° C .;
A thickness having an average molecular weight (MG _avg ) of 10 ⁷ and (iii) dissolved in ethyl acetate for at least 5% by weight (% w / w), and (iv) having 100 mg / cm ² of phosphor particles. A self-supporting layer of said polymer comprising 82% by volume of phosphor particles having an elongation at break of at least 1% as described in US Pat. No. 5,663,005.

In a further preferred embodiment, the polymer binder of the phosphor layer of the luminescent article according to the present invention is at least one resin selected from vinyl resins, polyesters and polyurethane resins. The first of the polymers used as binders
Is a vinyl resin. Plastics
According to Whittington's dictionary, this type is a vinyl group CH
₂ = Includes all resins and polymers made from monomers containing CH-. Examples of such ethylene monomers are acrylate, methacrylate, vinyl ester, olefin, styrene, crotonic acid ester, itaconic acid diester, maleic acid diester, fumaric acid diester, acrylamide, acrylic compound, vinyl ether, vinyl ketone, vinyl heterocyclic compound, glycidyl Includes esters, unsaturated nitriles, polyfunctional monomers, and various unsaturated acids. In particular, the vinyl polymer is chosen as a function of the elongation at break and the solubility at base described above.

Commercially available examples of vinyl resins useful in the present invention are PLEXISOL B372 (trade name), ROHM Gmb
H, acrylic resin supplied by Germany; ACRONAL
500L (Acrylic acid ester copolymer), ACRONAL 4F
(Poly- (n-butyl acrylate)), ACRONAL 4L
(Poly- (n-butyl acrylate)), ACRONAL 700L
(Co (n-butyl acrylate / vinyl isobutyl ether)) and ACRONAL A150F (poly- (n-butyl acrylate)), trade name, all supplied by BASF, Germany; DURO-TAK 373-0036, trade name ) 、 National
Starch & Chemical is an acrylate resin supplied by the United States. The solubility and Tg in EtAc (ethyl acetate) are given in Table 1 immediately below.

[0068]

[Table 1]

A second class of polymers useful in the present invention are polyesters with Tg ≦ 0. This class includes all polymers in which the polymer backbone is formed by esterification condensation of a polyfunctional alcohol and an acid. The particular polyester is selected as a function of the elongation at break criteria and the solubility criteria described above. An extremely useful polyester is Huels
, Germany, trade name DYNAPOL (eg DYNAPOL S1420,
Tg-15 ° C); TOYOBO, Japan, trade name VYLON (eg VYLON 550, Tg-10 ° C); SHELL, UK,
Commercially available from VITEL.

A third type of polymer useful for incorporation into a binder mixture for a screen according to the present invention is a polyurethane. This class includes all polymers based on the reaction products of compounds containing hydroxyl groups with organic isocyanates. The particular polyurethane is selected as a function of the elongation at break criteria and the solubility criteria described above. Extremely useful polyurethanes are BAYER, Germany, trade name DESMOLAC (eg DESMOLAC 2100, DESMOLAC 42
00, DESMOLAC 4125, a non-reactive linear polyurethane).

If the above polymer is a functional group, the literature (M. Ooka and H. Ozawa: Progress in Organic coat)
ings, 23 (1994) 325-338 and references therein). For example, curing can be performed with di- or polyisocyanates.

In order to fine-tune the (physical and optical) properties of the screens containing the polymers according to the invention, some polymeric additives are used in low amounts (ie, to reduce the total amount of polymeric substances present in the binder). Less than 40% by weight). Highly suitable polymeric additives are, for example, DIS
PERSE AYD 9100, Daniel Products Company, JerseyCi
ty, New Jersey 07304, a US brand name. This polymeric additive is a low molecular weight thermoplastic acrylic resin, which is extremely useful for controlling the quality of the dispersion of phosphor particles, binder and solvent. For example, CAB-381-2, Eastman Ch
The addition of cellulose polymers such as the emicals US trade name can be used to fine tune the mechanical properties of the coated and dried phosphor layers.

The coating dispersion may further contain a filler (reflection or absorption), or the luminescent article of the present invention or X.
It may be colored by a colorant capable of absorbing light in the spectrum emitted by the phosphor in the line conversion screen. An example of a colorant is Solvent Orange 71 (D
iaresin Red 7), Solvent Violet 32 (Diaresin Violet
A), Solvent Yellow 103 (Diaresin Yellow C) and Sol
vent Green 20 (all four are Mitsubishi Chemical Ind
ustries, supplied by Japan), Makrolex Rot G
S, Makrolex Rot EG, Makrolex Rot E2G, Helioechtg
elb 4G and Helioechtgelb HRN (all five are Bayer,
Leverkusen, sold by Germany), Neozaponfe
uerrot G and Zaponechtbraun BE (both BASF, Ludw
igshafen, sold by Germany).

In the manufacture of a sensitized radiographic screen as in the present invention, to improve the bond between the support and the phosphor layer, or to improve the sensitivity of the screen or the resolution and sharpness of the image imparted to it. One or more additional layers are sometimes provided between the support and the phosphor-containing layer having an undercoat or interlayer composition. For example, a subbing or adhesive layer may be provided by coating a polymeric material such as gelatin on the surface of the support on the phosphor layer side. The light-reflecting layer may be provided, for example, by vacuum-depositing an aluminum layer or by coating a pigment-binder layer whose pigment is, for example, titanium dioxide.
For the production of the light absorbing layer acting as an antihalation layer, carbon black dispersed in a binder may be used, but any known antihalation dye may be used. Such additional layers may be coated on the support as a backing layer or may be interposed between the support and the phosphor-containing layer. Some of the additional layers may be applied in combination.

The use of polymers in the binder of the phosphor layer with a phosphor particle (PP) / binder (B) volume ratio higher than 80/20 results in high elasticity, low brittleness, high sharpness, high speed and low noise. It is possible to manufacture a screen having. It is known that the volume ratio of PP / B is independent of the density of the phosphor particles (pigment) and the binder, while the PP / B weight ratio depends on the density of the phosphor and the binder.

In the binder alone or for more than 40%, for example, US Pat. No. 2,502,529,288737
9,3617285,3043710,330031
When using other well-known binder polymers, such as those disclosed in U.S. Pat.
The pigment-to-binder volume ratio cannot be increased to such high values by physical properties such as adhesion and brittleness. For the binder polymers used hitherto, the pigment-to-binder ratio is determined by the deficiency in the physical properties of the coated phosphor layer or the "screen structure motor".
Is clearly limited by the presence of

The phosphor dispersion in the polymeric binder is uniformly applied to the support by known coating techniques, such as doctor blade coating, roll coating, gravure coating or wire bar coating, dried and fluoresced by X-ray irradiation. Is formed (hereinafter, referred to as a fluorescent layer). No further mechanical treatment, such as compression, which results in reduced porosity, is required within the scope of the present invention.

The radiographic screen according to the invention can also be made in the form of a gradual screen, ie a screen having a gradual intensification along its length and / or width. Graduality is achieved by increasing the thickness of the phosphor layer over the length or width of the screen or by increasing the amount of dye capable of absorbing the light emitted by the phosphor between the protective layer and the phosphor-containing layer. It can be achieved by incorporating it into an intermediate layer or into a protective layer.

According to another convenient technique, the graduality is obtained by halftone printing of a dye or ink composition that absorbs the light emitted by the screen. Gradation can be obtained to any degree by changing the screen dot size in halftone printing, ie, by gradually changing the percentage dot area over the length or width of the screen. Halftone printing is carried out on a phosphor-containing layer on which a protective coating has been applied, or by applying a protective coating by halftone printing, for example by gravure rollers or silk screen printing.

In the manufacture of a phosphor screen having a primer layer between the support and the fluorescent layer, the primer layer is previously provided on the support, and the phosphor dispersion is then applied to the primer layer, dried and To form

After applying the coating dispersion on the support, the coating dispersion is gradually heated to a dry state to complete the formation of the phosphor layer. In order to remove as much air as possible incorporated in the phosphor coating composition, it can be subjected to sonication before coating.

After the formation of the fluorescent layer, a protective layer is generally provided on the fluorescent layer. The protective layer has already been described in detail.

The present invention will be described with reference to the following examples, but the present invention is not limited thereto.

[0084]

EXAMPLE 1 Sensitometry and Image Quality for an Intensifying Screen

1. Film having a mean grain size (equivalent circular diameter) of 1.25 .mu.m and a mean thickness of 0.22 .mu.m, such as those described in US Pat. No. 5,595,864, in making radiographic photosensitive silver halide photographic films. Silver bromoiodide emulsion containing silver particles (2 mol% silver iodide, 90 mol
% Silver bromide). The emulsion prepared for coating contained an amount of silver halide corresponding to 190 g of silver nitrate per kg and 74 g of gelatin. The emulsion contained 660 mg of anhydro-per mol of silver halide.
Spectral sensitized by adding 5,5'-dichloro-3,3'-bis (n.sulfobutyl) -9-ethyloxacarbocyanine hydroxide.

1 kg of silver halide emulsion as stabilizer
545 mg of 5-methyl-7-hydroxy-s-
It contained 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 a subbing layer on both sides. To each of the dried silver halide emulsion layers was applied a protective layer containing 1.1 g / m ² of gelatin, cured with formaldehyde and containing perfluorocaprylic acid as an antistatic agent. Hardening is 0.03g per 1g gelatin
By adding formaldehyde.
Each silver halide emulsion layer contained an amount of silver halide equivalent to 7 g / m ² of silver nitrate.

[0087] 2. Luminescent Screen An intensifying screen for use as a luminescent article according to the present invention contains Gd ₂ O ₂ S: Tb as a green luminescent phosphor.

The screen was coated on a terephthalate support containing carbon black as a light absorbing material having a low percentage reflectance of 0-5%.

Solvents Used for Screen Production The following solvent mixtures were used in the production of the screens. The composition (% by volume) is given below. Methyl ethyl ketone 48 Methoxypropanol 15 Ethyl acetate 37

Polymers Used for Screen Production The following polymers were used for screen production. PLEXISOL B732 (acrylic resin supplied by Rohm GmbH, Germany, hereafter designated as P1, said polymer having a Tg of 0 ° C. and at least 5
% Soluble by weight), and-CELLIT (cellulose acetate butyrate, CELLI
T, trade name from Eastman Chemicals, hereinafter designated as P2).

Screen Preparation The screen was coated from a coating composition containing a Gd ₂ O ₂ S: Tb phosphor. The phosphor used for these examples had an average particle size of 5 μm. The composition was doctor blade coated on a primed 200 μm thick black polyethylene terephthalate support and dried. The coating composition comprises T1 in addition to polymer P1 and polymer P2 described above.
D as low molecular weight thermoplastic acrylic resin having g> 0
ISPERSEAYD (Daniel Products Company, Jersey City
, New Jersey 07304, U.S.A.) was used as a dispersant in a 5: 1: 1 weight ratio.

The subbing layer is manufactured on the basis of Vitel PE200 (SHELL, trade name of the Netherlands) and has a curing agent DESMODUR N75.
(Bayer AG, Leverkusen, trade name of Germany).

The phosphor / binder volume ratio in the phosphor layer is 97/3 and the phosphor coating weight is 40 mg / c.
It was m ^2.

A protective coating having a thickness of 10 μm was applied by screen printing next to the phosphor layer. The composition is described below.

Composition of Protective Coating The following products and their amounts were used to coat a 10 m ² protective layer: GENOMEER T1600 (urethane acrylate oligomer as binder) RAHN, trade name of Switzerland 70 g SERVOCURE RTT190 (used as binder) Acrylate oligomer) SERVO DELDEN BV, trade name of the Netherlands 30 g MODAFLOW (flow control agent used as coating aid) MONSANTO, trade name of Germany 3.0 g ANTIMOUSSE 416 (surfactant) RHONE POULENC, trade name of Germany 0.15 g NUVOPOL PI3000 (photoinitiator) RAHN, trade name of Switzerland 5.0 g TITAN AN2 (white pigment having titanium dioxide composition, average particle size: 0.3 μm) Trade name of BAYER AG, Leverkusen, Germany X% (X% above) Is the total amount of binder (GENOMEER and SERVOCURE)
Given by the weight of the corresponding screen /
The actual numbers are given in Table 2 below for Screen Nos. 1-5 used for film combinations).

[0096] 3. X of the luminescent article or screen in a film / screen combination (both described above) in an exposed radiographic film
The line exposure was performed such that the luminescent article or screen was placed in the cassette and held in intimate contact with the one-side coated silver halide emulsion film. X-ray exposure is 0.10 of 400
The test was performed with 28 kVp X-rays commonly used for mammography using a 35 mm plexi filter in a FFA of cm logK and a screen-film system. In the resulting curve the density is plotted against a modified log K value (the value has been modified for air absorption).

[0097] 4. Processing of the Exposed Material The exposed silver halide emulsion material adhered to the screen Nos. 1 to 4 was processed in the following developer, and then fixed and rinsed at the indicated temperature and processing time.

The developer had the following composition: hydroquinone 30 g 1-phenyl-3-pyrazolidin-1-one 1.5 g acetic acid 99% 9.5 ml potassium sulfite 63.7 g potassium chloride 0.8 g EDTA-2Na 2 0.1 g potassium carbonate 32 g potassium metabisulfite 9 g potassium hydroxide 14 g diethylene glycol 25 ml 6-methylbenztriazole 0.09 g glutardialdehyde 50% 9.5 ml 5-nitroindazole 0.25 g Make up to 1 l with deionized water.

The starting solution added had the following composition: Acetic acid 99% 15.5 ml KBr 16 g Make up to 100 ml with deionized water.

The total development time was 12 seconds at 37 ° C. for a total processing cycle of 45 seconds. Here, the developed photographic strips were fixed in a conventional fixing bath containing ammonium thiosulfate and potassium metabisulfite, then rinsed with water and dried.

The sensitometric properties and speed and sharpness values obtained for Film-Screen combination No. 1-5 are given in Table 2. This table shows the speed value S calculated from the sensitometric curve by the square law to determine the dose required to obtain a net value of 1.0.

After processing, the SWR used in connection with Table 2
The values are expressed as 1, 2, 4, and 6 wire pairs per mm (SW
R1, SWR2, SWR4 and SWR6).
The measurement of the SWR value for the intensifying screen was performed using a Funk type K with an FFA of 0.10 and a 400 cm log K.
Same after 0.01mm Pb-8lp / mm raster
Vp.

[0103]

[Table 2]

As is evident from the data summarized in Table 2, the presence of the white pigment TiO _{2 in} an amount of up to 2% by weight, based on the total amount of binder present in the protective coating adjacent to the phosphor layer, resulted in a speed loss. Without leading to improved sharpness.

Example 2 The following data summarized in Table 3 show the effect of adding an enormous amount of white pigment (the same anatase-type titanium dioxide pigment as in Example 1). Film, screen (35mg / cm
Excluding a ² coating weight), the amount of TiO ₂ (X% relative to Table 2 of the binder), exposure and processing of film materials No.6-9 was the same as Example 1.

[0106]

[Table 3] Table As is apparent from gathered data to 3, the presence of 5 wt% or more of the amount of the white pigment TiO ₂ with respect to the total amount of binding agent present in the protective coating adjacent to the phosphor layer, especially 5%
There is a speed loss for the amount of white pigment for the above binders, but leads to improved sharpness (see especially the effect on sharpness at higher line pairs per mm). However, when such a loss in speed is tolerated, the sharpness increase is quite noticeable.

Claims (5)

[Claims] 1. A luminescent article comprising a self-supporting or supported layer of phosphor particles dispersed in a binding medium and a protective coating adjacent thereto, said protective coating comprising, in addition to a binder, titanium dioxide as a white pigment. A light-emitting article comprising: 2. The luminescent article according to claim 1, wherein said binder comprises urethane acrylate. 3. The luminescent article according to claim 1, wherein the white pigment is present in an amount of 5% by weight or less based on the binder. 4. The method according to claim 1, wherein the phosphor particles are dispersed in a binding medium that is a polymeric binder, and wherein the phosphor particles have at least 80 /
The luminescent article according to any one of claims 1 to 3, wherein the luminescent article is present in a volume ratio of 20. 5. The polymeric binder comprises (i) at least one polymer having Tg ≦ 0 ° C., and (ii) 500
Average molecular weight of 0~10 ⁷ _{(MG avg)} have, (iii)
The luminescent article of claim 4, wherein the luminescent article is soluble in ethyl acetate for at least 5% by weight.