DE3206776A1 - X-ray intensifier screen - Google Patents

Description

Ring amplifier screen

The invention relates to a transparent X-ray intensifier as well as fluorescent masses with an isotropic phosphor, which for light that is emitted by the phosphor, is transparent and a polymeric binder.

It is known to use transparent X-ray intensifying screens with alkali halides, alkaline earth halide, metal sulfide and metal selenide phosphors produced by various processes. Such transparent screens have proven to be useful because they utilize incident X-rays more effectively than thick conventional, high scattering factor screens which "waste" a significant amount of radiation by diffusion of the light emitted near the back of the screen as well as by internal absorption. Thick transparent screens with a reduced number of reflections allow the light to hit the top of the screen with minimal deflections achieved to produce a screen image on the photographic film which is in contact with the screen. A bigger one Ratio of the X-ray energy emitted by the phosphor is absorbed and converted into light, is used to generate images without loss of sharpness.

There are also thin transparent screens made by Vapor phase deposition with only one phosphor has become known. These transparent screens have lower sensitivities than the screens with a high scatter factor with the same phosphor occupancy. Furthermore, it has been shown that these transparent screens are brittle without a protective binder and can be easily damaged. Finally, it is also known to produce thicker screens by hot pressing, but this has been the case shown that such screens only at great expense can be produced.

From US Pat. No. 3,023,313 there is also the use of a polymeric binder with a refractive index that is so close as possible with the refractive index of an alkali metal halide phosphor is to produce X-ray intensifying screens with increased j sensitivity., known. Due to considerable Differences between the refractive index of the selected binder and the refractive index of the phosphor must however, reflective pigments can be added to the mixture to avoid the creation of "blurry" images and ura to improve the resolution. These screens are for Light is not really transparent, so that some reduction in the utilization of absorbed X-rays can be observed. The screens known from US Pat. No. 3,023,313 have a carrier which preferably has a highly reflective coating.

From the reference "Applied Optics", 12, (1973), pages • 1865 - 1870 is the theoretical calculation of the modulation transfer function (MTF) known for the resolving power of X-ray intensifying screens with transparent phosphors and a black background. It is known from the literature that, although the MTF value if a black background is used, 501 of the exposing radiation will be absorbed by the background. This means that the sensitivity of the X-ray intensifying screen is decreased.

From the literature reference "J. C ₍ pt. Soc. Am", 6_3, (1973), pages 714-720) the calculation of the theoretical efficiencies and the MTF values of various screen-receiver systems is known, whereby in the litigation it is reported that if a dark Lichthafschut2 background is applied to the back of the transparent screen, the MTF value only

little is being improved. On the other hand, will the back be perfect ' If designed to be reflective, the MTF value is reduced, but the effectiveness of the screen is more advantageous Way doubled, as can be seen from Fig. 8 of the reference.

An experimental confirmation of the calculations of the reference "J. Opt. Soc. Am." 63, (1973) pages 714 - 720 results by measuring the MTF value of a transparent, hot-pressed zinc sulfide screen with a colored gelatin underlayer is coated. It turned out to be an excellent one Agreement between the measured and calculated MTF values established. The author of the quoted literature passage believes that attempts to improve the MTF of a transparent screen are undesirable Lead to a loss of effectiveness.

When choosing between a small increase in the MTF value, associated with an undesirable loss of effectiveness (with an absorbent backsheet) and a large one Increase in effectiveness, combined with only a little less MTF (reflective sub-layer) value is given by the author Umbrella with the high effectiveness with a reflective underlayer clearly given preference.

Thus it follows that transparent X-ray intensifying screens, which lead to a high resolution while maintaining Sensitivity and effectiveness, and which are resistant to physical damage and are easy and economical to manufacture are extremely desirable X-ray intensifying screens represent.

It has been found that the X-ray intensifying screens in the The features specified in the claims are extremely advantageous X-ray intensifying screens.

An X-ray intensifying screen according to the invention thus exists from a carrier and at least one applied layer of:

A) 50 to 90 percent by weight of an isotropic or practically isotropic Fluorescent substance stimulated by X-rays and

B) 10 to 50 wt .- $ of a polymer, which is characterized is that it has a refractive index over at least 801 of the emission spectrum of the phosphor that is not by more than 0.02 units of the refractive index of the phosphor deviates.

The layer is practically transparent to the light emitted by the phosphor.

The polymer is composed of:

a) 5 to 100 mol % repeating units of the formula:

-fCH -C) -

-C

C-O

I 2 O-R

where mean:

R is a hydrogen atom or an alkyl radical and

R is an alkyl, cycloalkyl, aryl or aralkyl radical or an aryl radical which is replaced by an alkyl and / or alkoxy

radical is substituted or a heterocyclic * Rest and

b) O to 95 MoI-! of repeating units of the following Formula:

R ¹

OO

S-CH-R ³

Ar-R ⁴

where mean:

Ar is an arylene radical;

R is a hydrogen atom or an alkyl radical;

R is a hydrogen atom or an alkyl, aryl or aralkyl radical and

R is a hydrogen atom or a halogen atom or an alkyl, alkoxy, amino, sulfide, sulfoxide, sulfonate or heterocyclic radical.

The carrier of the intensifying screen has a refractive index which is equal to the refractive index of the phosphor or up to 0.05 units above the refractive index of the phosphor, the optical reflection density of the carrier to light emitted by the phosphor is at least 1.7.

An X-ray intensifying screen according to the invention can be produced according to the following process steps: "

3 ^: 2 O 6 7 7 6

/ U a mixture of:

a) 50 to 90 wt. t of an isotropic or practically isotropic ₍ phosphor that is excited by X-rays "and

b) 10 to 50% by weight of a mixture of copol) merizable Monomers with

to 100 mol% of a copolymerizable monomer of Formula:

R ¹

C)

C = O

I 2
0R ^

where mean:

R is a hydrogen atom or an alkyl radical and

2
R is an alkyl, cycloalkyl, aryl or aralkyl radical

or an aryl radical substituted by an alkyl and / or alkoxy radical or a heterocyclic radical Rest and

c) 0 to 95 mol-i of a copolymerizable monomer of Formula:

R ¹

(CH ₇ -C)

I. C-O

S-CH-R ³
Ar-R ⁴

where mean:

Ar is an arylene radical; R is a hydrogen atom or an alkyl radical;

R is a hydrogen atom or an alkyl, aryl or aralkyl radical and

R is a hydrogen or halogen atom or a

Alkyl, alkoxy or amino radical or a sulfide, sulfoxide, sulfonate or heterocyclyl radical, which is practically transparent to the light emitted by the phosphor, and which if it is polymerized, has a refractive index over at least 801 of the emission spectrum of the phosphor, which is by no more than 0.02 Units deviating from the refractive index of the phosphor is applied to a carrier, which has a refractive index which is equal to the refractive index of the phosphor or by up to 0.05 units above the refractive index of the phosphor, the carrier also an optical reflection density to the light emitted by the phosphor of has at least 1.7.

B) The mass applied to the carrier is polymerized to produce a polymer.

To produce a Röntgenvt according to the invention; rs umbrella practically all isotropic or practically isotropic phosphors that are excited by X-rays and can be used are transparent or practically transparent to the light emitted by the excited phosphor. Below this

As used expression "isotropic phosphor" or "practically isotropic phosphor" is to be understood here as a crystalline phosphor which has the same or practically the same optical properties in all directions of the crystal and which is practically free from defects such as cracks or crevices and inclusions, which lead to light scattering. Suitable phosphors include, for example, activated alkali metal halides, such as: KCl: Sb, CsBr. "Tl, KIiTl, KBr: T1, KCIrTl, RbCIrTl, RbBf: T1 and RbIrTl; alkaline earth metal halides, e.g. BaF and BaFCl; such as CaF ₂ : Eu, SrCl ₂ : Sm, SrF ₂ : Eu, BaFCIrSr, Eu, BaFCIrEu and SrF _?: Sm; activated metal silicates, such as BaSiO ₃ IEu ₁ CaSiO.rMn and Zn ₂ SiO ₄ IMn; mixed metal fluorides, e.g. KCdF ₃ IMn and CsCdF ₃ IMn; metal sulfates, ζ. Β. metal sulfates activated with lanthanides, ζ. B. BaSO.rSr, Eu, SrSO ₄ : Eu, BaSO ₄ rEu, ZnSO ₄ rMn and Cs ₃ SO ₄ ICe; metal gallates, e.g. ZnGa ₃ O ₄ IMn; and phosphates, e.g. phosphates activated with lanthanides, e.g. Ba ₂ P ₄ O ₇ IEu and Ca ₃ (PO ₄ ) ₂ : Ce.

Further examples of phosphors which can be used according to the invention are given in US Pat. No. 4,100,101; 2,303,963; 3,163,610; 3 163 603 and 3,506,584 and from the R.C. pastor and employees, mat. Res. Bull., J_5, (1980), pp. 469-475.

Typical transparent phosphors which can be used according to the invention include, for example, RbIiTl; KIiTl; BaFCIiSr, Eu; BaSO ₄ ISr, Eu; CsCdF ₃ Mn; BaF ₂ ; KCdF ₃ IMn and SrF ₂ .

The following have proven to be particularly advantageous phosphors: TbIiTl; KIiTl; BaFCIiSr, Eu; CsCdF ₃ IMn; BaSO ₄ ISr, Eu and BaSO ₄ IPb.

The phosphors described can be prepared according to the usual known methods Manufacture processes for the production of isotropic phosphors, e.g. B. by introducing the anions and cations that make up the phosphor form-, in a reaction solution, one being up to "1 molar

Maintain an excess of anion or cation in the reaction mixture and local excesses of cations or anions are avoided, so that phosphor crystals of at least 0.5 microns can grow slowly, as is known, for example, from US Pat. No. 3,668,142. Other manufacturing methods of isotropic phosphors that are excited by X-rays and are practically transparent to the emitted light are processes in which precipitation occurs at elevated temperatures and superatmospheric pressures, such as them are known, for example, from US Pat. No. 2,285,464, as well as processes in which a precipitation takes place with subsequent Heating, fusion and grinding of the obtained particles to the desired one Particle size and method with ignition in the presence of a superplasticizer. The process known from US Pat. No. 3,668,142 has proven to be a particularly advantageous process for the production of isotropic phosphors.

The intensifying screens according to the invention can be modified so that they can be used, for example, in an apparatus and in the context of Imaging processes can be used as they are from the US-PS 3,859,527 and DE-PS 29 51 501 and 29 28 246 are known. In this modification, one becomes substantial or practical isotropic storage phosphor in a binder applied to a carrier, which has the properties described below having. The phosphor is excited by a radiation pattern of a first wavelength. Then the phosphor becomes one Exposure to radiation of a second wavelength, which leads to the storage medium having radiation of a third wavelength an intensity pattern emitted representative of the stored image. The binder used to make this umbrella is used is matched to the refractive index of the phosphor at the second wavelength and the support of the screen is selected such that it emits radiation at the second wavelength not reflected. The refractive index of the third wavelength is preferably selected so that it does not

3 2Ö 6 776

Corresponds to the refractive index of the phosphor and the carrier of the screen can absorb the radiation at this third shaft length reflect. This means that the radiation is at the third wavelength that is emitted when the phosphor passes through the second wavelength is excited, is not captured by total internal reflection or by the carrier, but from exits the screen and from a photo-amplification tube with captured by suitable optics or by other photosensors, which respond effectively to radiation at the third wavelength. Screens of this type have proven particularly suitable for radiographic purposes and other applications in which a Pattern of high energy radiation is absorbed by the phosphor, then by scanning the screen with a Laser beam is released which has a wavelength which is equal to the wavelength at which the refractive index of the Phosphor and the refractive index of the binder match, and where the support of the screen has a low ;; Has reflectivity. The laser beam ideally follows the path the high energy radiation, so that the resolution of the image of the screen is determined by the dimensions of the Laser beam. The light released from the phosphor by the laser beam is captured by a suitable photosensor, amplified, and the signal is displayed on a cathode tube or on an image recording medium below Creation of an image recorded. Phosphors suitable for this purpose are, for example, barium alkaline earth metal fluorohalides, as described, for example, in German Pat Have spectrum.

The luminescent crystals can, if necessary, be activated by customary activation methods in order to achieve the desired sensitivity achieve. One method is to add a solution of a small amount (0.05% by weight) of the activating ion in one

Solvent, for example isopropanol, to a vigorously stirred solution of the isotropic host in a solvent, for example water at very low temperatures (-30 to + 2O ⁰ C) ^- , which is followed by the isolation of the precipitated, activated phosphor.

The isotropic or practically isotropic phosphors that are for the production of the X-ray intensifying screens according to the invention are preferably cubic or substantially or practically cubic. The for the production of the invention X-ray intensifying screens are suitable isotropic phosphors advantageously have a crystal size of 1 to 50 microns, especially 10 to 20 microns.

The various polymers with a refractive index within 0.02 of the refractive index of the phosphor over at least 801 of the emission spectrum.

The selection of the polymer used in the individual case for production the intensifying screen depends on the refractive index of the isotropic phosphor selected in the individual case at its emission wavelength. The refraction index of the phosphor can be determined by measuring the transmission spectrum of the phosphor mixed with a number of Cargille liquids, such as those found in McCrone's book, Draftz and Delly, "The Particle Atlas", Ann Arbor Science Publishers, Inc. 1967 known and determination of the wavelength, in which the refractive index of the fluorescent substance corresponds to the index of the Liquid matches. A phosphor dispersion curve can be obtained by recording the wavelength of the maximum Transmission for the series on the Cargille family of dispersion curves, contained in the quoted book "The Particle Atlas". The phosphor dispersion curve thus obtained is used directly to find the refractive index,

that for the polymer of the new transparent X-ray intensifying screen is required.

The polymer with the required index of refraction, i.e. H. a refractive index within 0.02 of the refractive index of the Luminous substance over at least 80 * of its emission spectrum, can consist of a single polymerized monomer or but from a mixture of 2 or more copolymerized monomers. In general, the polymers consist of two together copolymerized monomers, one of which if there is is polymerized, provides a polymer of a higher than required refractive index and one of which if it is is polymerized, provides a lower than required refractive index. The ratio of the two monomers to one another is adjusted so that a polymer with the required refractive index is obtained. Calculated approaches can be by measuring the transmission curve of a coating curve of the fluorescent composition used for making an intensifying screen is used, check with a spectrophotometer. A wavelength of maximum transmission, the lower than that of the phosphor emission wavelength indicates that the refractive index of the polymeric binder is too low. In contrast, a wavelength of maximum transmission that is greater than the wavelength of the fluorescent emission indicates that the refractive index of the polymer is too high.

Monomers which, when polymerized, lead to a refractive index that is greater than that of the selected phosphor, generally provide a refractive index above 1.6, preferably in the range from 1.60 to 1.75.

Examples of monomers that provide polymers with a refractive index that is greater than that of the selected phosphor and as a result can be mixed with monomers that lead to

Polymers with a lower refractive index lead, and can be used according to the invention, are for example S- (1-naphthylmethyl) thioacrylate; Naphthyl acrylate; 1-bromo-2-naphthyl acrylate and naphthyl line thacrylate. A particularly advantageous monomer for preparing the polymers is S- (1-naphthylmethyl) thioacrylate.

Monomers which, when polymerized, lead to a refractive index which is lower than the index of the phosphor, provide im generally a refractive index of up to 1.60, preferably from 1.40 to 1.60. Examples of monomers that polymerize provide an index of refraction that is lower than that of the selected phosphor and, as a result, are capable of mixing are suitable with monomers that have a higher refractive index, are, for example, copolymerizable ethylenically unsaturated Monomers such as: acrylates and methacrylates, ζ. B. methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, • butyl methacrylate and cyclohexyl methacrylate; Vinyl esters, amides, nitrides, ketones, halides, ethers, olefins and diolefins such as for example acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, Acrylamide, methacrylamide, vinyl chloride, methyl vinyl ketone, fumaric acid, maleic acid and itaconic acid esters, 2-chloroethyl vinyl ether, Dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, N-vinylsuccinamide, N-viny! Phthalimide, N-viny! Pyrrolidone, Butadiene and ethylene. Preferred monomers are acrylates and methacrylates, cyclohexyl methacrylate being found to be a particularly advantageous monomer.

The ratio in which the described monomers of high refractive index and low refractive index to each other can be mixed to produce a polymer with the required refractive index can vary widely. That polymerized monomer with the low refractive index preferably makes up 5 to 100 mol-I of the polymer to be produced,

it has proven particularly advantageous to use 15 to mol% of this monomer. The polymerized Monomer with the high refractive index preferably makes up 95 mol% of the polymer to be produced, in particular up to 85 mole-t.

A particularly advantageous polymer for producing an intensifying screen according to the invention consists of 5 to 100 mol-I from recurring units of the following formula:

R ¹

I.
CO

where mean:

R is a hydrogen atom or an alkyl radical, preferably with 1 to 4 carbon atoms, for example a methyl, Ethyl, propyl, isopropyl or butyl radical and

R is an alkyl radical, preferably with 1 to 12 carbon atoms, z. B. a methyl, ethyl, propyl or butyl radical; a cycloalkyl radical, e.g. B. a cyclopentyl · or Cyclohexyl radical; an aryl radical, preferably with 6 to 22 carbon atoms, e.g. B. a phenyl, naphthyl, Anthryl, perylenyl or acenaphthenyl radical; an aralkyl radical, preferably having 5 to 20 carbon atoms, e.g. B. a benzyl, phenylethyl, phenylpropyl, phenylbutyl, tolylbutyl or naphthymethyl radical or an aryl radical, which is substituted by an alkyl radical, preferably by an alkyl radical with 1 to 20 carbon atoms, z. B. e-inen methyl, ethyl, isopropyl or hexyl radical;

or an alkoxy radical, preferably with 1 to 20 carbon atoms, ζ. B. methoxy or ethoxy; or a heterocyclic one Remainder, preferably a 5- to 7-membered ring, which is saturated can be, for example a pyrrolidonyl, morpholinyl, Piperidinyl, tetrahydrofuryl, dioxanyl or quinaldinyl radical or an unsaturated heterocyclic radical, e.g. B. a Pyrrolyl, isoxazolyl, imidazolyl, isothiazolyl, furazanyl or pyrazolinyl radical.

A particularly advantageous polymer for making a intensifying screen according to the invention can also be 0 to 95 MoI-I have recurring units of the following formula:

R ¹
-G)-

C = O

S-CH-R ³
Ar-R ⁴ .

where mean:

Ar is an arylene radical, preferably having 6 to 22 carbon atoms, e.g. B. a phenylene, naphthylene or anthrylene radical or a rsrylenylene or acenaphthylenylene radical;

R is a hydrogen atom or an alkyl radical as already for R given;

R is a hydrogen atom or an alkyl, aryl or aralkyl radical, as already indicated for R ″ and

R is a hydrogen atom or an alkyl radical, preferably

with 1 to 20 carbon atoms, ζ. B. a methyl, Ethyl, isopropyl or hexyl radical or an alkoxy radical, preferably having 1 to 20 carbon atoms, e.g. B. a Methoxy or ethoxy radical or an amino radical or a Halogen atom, for example a chlorine or bromine atom or a sulfide, sulfoxide or sulfonate radical or a heterocyclic radical, preferably a radical consisting of a 5 to 7-membered ring which may be saturated, e.g. B. a pyrrolidinyl, mofpholinyl, piperidinyl, tetrahydrofuryl, Dioxanyl or quinaldinyl radical or an unsaturated ring, for example a pyrrolyl, isoxazolyl, Imidazolyl, isothiazolyl, furazanyl or pyrazolinyl ring.

If we are talking about "alkyl residues", "aryl residues" and "arylene residues", so unsubstituted and substituted alkyl, aryl and arylene radicals are to be understood, e.g. B. methoxyethyl, Chlorophenyl and bromonaphthyl radicals.

Examples of polymers which are advantageously suitable for producing intensifying screens according to the invention are:

Poly (T-naphthylmethyl methacrylate-co-S-O-naphthylmethyl) thioacrylate /;

Poly / T-naphthylmethyl methacrylate-co-i-bromo-Z-naphthyl acrylate ?; Poly / S-C1-naphthylmethyl) thioacrylate-co-benzyl methacrylate ?; Poly / S- (2-naphthylmethyl) thioacrylate-co-bfinzylm «thacrylate / and Poly / t-butyl methacrylate /.

According to a particularly advantageous embodiment of an inventive In the intensifying screen, the polymer consists of 5 to 100 mol% of a polymerizable, copolymerizable Naphthylmethyl methacrylate monomer and from 0 to 95 mole-t a polymerizable, copolymerizable naphthylmethy.lthioacrylate monomer. According to a further advantageous embodiment

of the invention consists of the polymer that is used to produce the Intensifying screen is used, to 5 to 100 MoI-I from polymerized 1-naphthylmethyl methacrylate and from 0 to 95 MoI-I from polymerized S- (I-naphthylmethyl) thioacrylate.

As already stated, an X-ray intensifying screen according to the invention contains an isotropic or practically isotropic one Phosphor that is excited by X-rays and is transparent or practically transparent to light emanating from that Phosphor is emitted, and a polymeric binder selected so that its refractive index is within of 0.02 corresponds to the refractive index of the phosphor, and is highly transparent.

An intensifying screen according to the invention generally has a mean free path for light scattering greater than 1 mm, preferably greater than 3 mm, for example at Phosphor: binder ratios of 2.5 or above. The highly transparent screen material enables the use of relatively thick screens that absorb more of the incident X-ray beam, which leads to a higher sensitivity.

Furthermore, the increased absorption of X-rays reduces quantum mottle and enables improvement the overall image quality. Furthermore, the polymeric binder protects the brittle phosphors from physical Damage. For the production of intensifying screens according to the invention In addition, a wide variety of carrier materials can be used which have a refractive index of is the same as the refractive index of the phosphor Wavelength of maximum emission or its refractive index up to 0.05 units above the refractive index of the phosphor at its wavelength of maximum emission, and the optical reflection densities of at least 1.7 over that of

have light emitted from the phosphor. Suitable carrier materials are polymeric substances, e.g. B. poly (methyl methacrylate) (Lucite); furthermore tourmaline (Elbite), furthermore urea-formaldehyde resins (Formica) and polyolefins, e.g. B. polyethylene and polypropylene, polycarbonates, cellulose acetates, cellulose acetate butyrate, poly (ethylene terephthalate); Glass, e.g. B. a glass in which 801 of its surface are covered with holes a depth of 0.381 mm and a width of 0.127 mm (Corning Fotoforra) and metal ,, z. B. a carrier made of black anodized aluminum.

The required optical reflection density of 1.7 against light emitted from the phosphor can be achieved by using support materials that are naturally dark in color, by using materials that during their Dyed or pigmented to produce a uniform dark shade or by using Materials that have undergone a surface treatment, e.g. B. a coating with a dye, a pigment or with colored or pigmented fabrics, by anodizing in the case of metals or by a combination of the surface treatments mentioned.

A preferred support with both the required optical density and the required refractive index exists for example from a conventional carrier material with a thin polymer layer on the surface on which the fluorescent Mass is applied. The thin polymer layer can, for example, consist of a polymer with a refractive index of the same or up to 0.05 units above the refractive index of the phosphor exist at one wavelength, maximum emission and a finely divided pigment, for example carbon black in an amount, sufficient to produce an optical density of 1.7 to light emitted by the phosphor.

An X-ray intensifying screen according to the invention

with a highly transparent screen material of high Sensitivity and a light-absorbing support with the required optical reflection density leads to a high Contrast and a high resolution. The use of a carrier with the same or slightly larger (up to 0.05 larger) refractive index, compared to the index of the phosphor layer, reduces the flickering of the image and increases the contrast. The mixture of the fluorescent Composition is preferably made by combining the isotropic phosphor in the form of a free-flowing powder a polymerizable monomer or mixture of copolymerizable Monomers that polymerize lead to the required index of refraction.

The weight ratio of phosphor to monomers can be very different, but is preferably 50:50 to 90:10 and in particular 70:30 to 80:20. In general, the weight ratio of phosphor to monomer is maximized, resulting in a honey-like, viscous mixture that is castable. If necessary, the mixture obtained is degassed in order to remove trapped air bubbles. If necessary, the mixture also contains 0.001 to 1.0% by weight, preferably 0.1 to 0.5% by weight, of a photoinitiator such as 4,4'-bis-chloromethylbenzophenone, benzoin ethyl ether or benzoyl peroxide. If necessary, further additives can be incorporated into the mixtures, for example resins, stabilizers, surface-active compounds and mold release agents to improve the film-forming properties, the coating properties, the adhesion of the layer produced on the carrier, the separability of the mixture from non-carrier materials, to improve the mechanical strength and ser chemical resistance.

32U6776

■ - 26 -

The mixture obtained can be according to customary known processes, z. B. by roller coating, coating with an application brush, by solvent coating or by Apply the coating to a carrier in a predetermined thickness by means of a coating funnel. A method for Production of an X-ray intensifying screen according to the invention consists in applying the mixture to a support, which to cover the applied layer with a cover sheet, for example with a glass cover sheet with suitable spacers for generating the predetermined coating thickness and spreading the mixture by applying pressure to the cover sheet up to the spacer limit.

The optimum in individual cases Besehichtungsstärke of lamps ¹ -Stoff monomer mixture depends on various factors such. B. the intended use of the material to be produced, the desired sensitivity, the degree of image quality, the selected phosphor, the selected monomer or the selected monomeric mixture in the ratio of phosphor to monomers and the nature of the other components that may be in the layer produced can be present. Suitable layer thicknesses are from 25 to 2500 microns, preferably from 400 to 1200 microns. Advantageous coating thicknesses are from 110 to 5400 g / m ² , in particular from 540 to 2200 g / m ² .

The applied layer of a monomer or a monomeric mixture and a phosphor is then preferably ^{polymerized at a temperature of 20 to 30 °} C. by irradiation with a lamp which emits ultraviolet light in the near UV range. However, other polymerization processes can also be used, for example thermal polymerization, polymerization by irradiation with electron beams and polymerization by means of high-energy gamma rays.

After the polymerization is complete, the polymerized mixture is preferably allowed to cool to room temperature or below and an applied cover sheet for spreading the applied The coating compound and the setting of the coating thickness are removed. In some cases the separation can be initiated by carefully placing a knife between supports and coversheet introduces polymerized to the carrier from the applied Separate mixture until Newton's see rings on the Introduction point are to be observed. The cover sheet can be lifted off, whereby the cover sheet can be further briefly cooled if necessary, z. B. with 2 crushed dry ice. However, further cooling should be carried out carefully, since the cover sheet is overcooled can easily cause the polymerized, applied screen mixture to burst.

The polymer obtained has a refractive index within 0.02 of the refractive index of the phosphor above 801 of its Emission spectrum, which achieves a strong transparency with respect to the light emitted by the excited phosphor will. The polymer protects the phosphor from mechanical damage and provided the polymer is hydrophobic against damage due to the effects of moisture.

The invention thus enables the production of highly transparent X-ray intensifying screens with advantageous sensitivity, high contrast and high resolution. Furthermore, the invention enables the production of highly sensitive X-ray intensifying screens from high resolution to comparatively inexpensive and simple ones Way without the addition of reflective pigments.

The manufacturing methods and examples described below are intended to illustrate the invention in more detail.

Manufacturing 1

A RblrTl phosphor (0.0004) was produced by adding a solution of 0.33 g of thallium (I) acetate in 500 ml of isopropanol at a rate of 36 ml / min to a vigorously stirred solution of 6 36 g of rubid undo did in 46O g Water. The temperature of the isopropanol solution was kept at -29 ⁰ C, and the temperature of the aqueous solution C. to about 15 ⁰ There are 200g of precipitated rubidium iodide phosphor separated to obtain the supernatant isopropanol-water mixture was carefully separated, which was stored for the recovery of non- precipitated rubidium iodide in further subsequent preparations. (The above isopropanol-water mixture, which remains with the precipitated phosphor, can contaminate the precipitated phosphor by further precipitation of a phosphor of different composition, which can lead to undesired light scattering in the fluorescent composition produced). The precipitated, thallium-activated Rbl phosphor, which had been freed from the excess isopropanol-water mixture, was then washed twice with isopropanol in a high-speed mixer, whereupon the precipitate was separated off after each wash using glass filter paper. The phosphor was then dried in vacuo and filled into a bottle. The sensitivity of the phosphor RbI: T1 (0.0004) produced in this way corresponded approximately to the sensitivity of KIrTl. Sensitivities were measured which were 6 and 7 greater than that of a commercially available CaW0 ₄ phosphor of the DuPont No. 501 type when carrying out the X-ray powder test which is described in the aforementioned US Pat. No. 3,668.

Manufacturing 2

It has an AI: manufactured T1 phosphor (0.0003), by adding a solution of 0.4 thallium (I) acetate in 1.6 liters of isopropanol at a temperature of -29 ⁰ C to a solution of 800 g potassium iodide

was added in 600 g of distilled water at a temperature of SO ⁰ C with vigorous stirring. The temperature of the reaction solution was kept at about 14 ^° C. The rate of addition was 35 ml / min. The obtained crystals of the precipitated phosphor were free from defects and had a cubic structure with crystal sizes ranging from 10 to 20 microns. The sensitivity of the phosphor, measured after precipitation, after washing and drying according to the process known in US Pat. No. 3,668,142, was about 7 greater than the sensitivity of commercially available calcium tungstate. .

Manufacturing 3

A mixture of 66 g of cyclopentadiene and 500 ml of methylene chloride was stirred with 90 g of acryloyl chloride at dry ice temperature (-78.5 ⁰ C) and gradually brought within a period from 24 hours to room temperature. The reaction product obtained was then distilled. The Bicycloheptancarbonylchlorid obtained was treated with 1- (naphthylmethyl) mercaptan reacted by refluxing in methylene chloride (boiling point 40 - 41 ⁰ C), wherein an equivalent Diisopropylethy.lamin was slowly added to the mixture. The reaction product was then distilled in vacuo, to which an oil bath at a temperature of 25O ⁰ C was used. Under these conditions, the cyclopentadiene split off, whereby S- (1-naphthylmethyl) thioacrylate was obtained in good yield. Thin-layer chromatography carried out (hexane / ether in the ratio 50:50, silica gel) of the product obtained gave an R _f value of 0.69 to 0.72.

Manufacturing 4

1-naphthylmethyl methacrylate was produced by catalytic Transesterification of an excess amount of methyl methacrylate with the alcohol 1-Naphthy1methanol. The resulting by-product, namely, methanol became continuously by azeotropic distillation

removed and / or by using molecular sieves so that * the reversible reaction led to the desired reaction side became. After the reaction had practically ended, the excess methyl methacrylate was removed by distillation under atmospheric pressure separated «A comparatively small amount (5 to 2 hours) of the unconverted higher alcohol 1-naphthylmethanol remained in the 1-naphthylmethyl methacrylate obtained.

Manufacturing 5

In an alternative synthesis of 1-naphthylmethyl methacrylate, 1- (chloromethyl) naphthalene was reacted with one equivalent of potassium methacrylate in dimethyl sulfoxide. The potassium methacrylate used can first be prepared in isolation or generated in situ from potassium hydroxide and methacrylic acid. The reaction takes place at 70 ^° C. within about 30 minutes. The 1-naphthylmethyl methacrylate obtained in this way can be isolated in this way in a yield of 93-98Λ. It is practically free from contamination.

Manufacturing 6 Aluminum plates were in 12-15Hger H ₀ SO. at 70 ⁰ C and

2 A4

12 to 14 Ampe "re / 0.1929 m anodized. The porous deposit was made with Aluminum Black BK dye, d, h. treated with a dye from Sandoz Colors and Chemicals and then sealed with hot water or a nickel acetate solution. The carrier thus obtained had an optical density of 2.34 when coated with a blend of rubidium iodide and polymer matched refractive index. Although the refractive index of anodized aluminum is not exactly known, it is probably around 1.76, i.e. H. by less than 0.05 units higher than the refractive index of rubidium iodide at 425 nm the range of the maximum Emission.

The following examples are intended to further illustrate the invention.

example 1

A mixture of 100 g of thallium-activated potassium iodide phosphor (0.003) prepared as described in preparation 2 and 40 g of a 4: 1 mixture of S- (1-naphthylmethyl) thioacrylates prepared as described in preparation 3, and 1-naphthylmethyl methacrylate, prepared as described in preparation 4, with a content of 0.3 wt -.% of 4,4'-bis-chlormethylbenzochinon. was degassed in a vacuum. A portion of the mixture was then photopolymerized between two sheets of glass to produce an unsupported screen. The unsupported screen thus produced was placed in a commercially available spectrophotometer (type Cary 17), whereupon the optical density of the screen was measured using an unsupported screen made of only photopolymerized polymer (without phosphor) as a reference screen.

The optical density of the unsupported screen was used to to calculate the mean free path of light through the screen. The calculated mean free path was at least 2.3 mm.

Another portion of the mixture was in different layer thicknesses on black anodized aluminum supports, as in manufacture 6 described, produced, applied and polymerized under glass cover plates. Radiographic recordings were then made by exposing Io-Dose film in contact with the produced screens as rear screens with 70 kVp X-rays.

A comparative photograph was made by exposing lo-dose film in contact with a commercially available intensifying screen of the DuPont Par Speed Intensifying Screen type, to the relative

To determine the sensitivities of the screens produced. The * Sensitivity difference was determined using the known density-log Ε curve for the lo-dose film from the densities that resulted from the exposed and developed films. The following results were obtained:

Screen thickness (Micron)

Coating strength (g / m?)

Relative sensitivity PAR = 100 +

10 microns lead testobjektauf- solution

404

750

1115

655 1215 1810

175 265 325

3.15 1 / mm

2.24-2.5

2.0

DuPont Par Speed Intensifying Screen. Example 2

A mixture of 35.5 g of thallium activated rubidium iodide phosphor (0.0004), prepared as described in Preparation 1, and 10 g of a mixture of 1-naphthylmethyl methacrylate and 1-bromo-2-naphthyl acrylate in the ratio 60:40 with 0 3t 4,4 ^f -Bischloromethylbenzophenon was applied to a black anodized aluminum support and covered with a glass plate, whereupon the layer was photopolymerized. When the polymerization had ended, the glass plate was removed. The transparent screen thus obtained had a thickness of 500 microns with a coverage of 89 g of phosphor per 0.0929 m.

Radiographic recordings made with this screen as a back screen using a lo-dose film at 70 kVp, gave relative radiographic sensitivity (calculated as described in Example 1) of 255, in comparison

with 285 for a DuPont Hi-Plus umbrella with Lo-Dose film.

When using a bone bead test object in the comparison got better picture quality when using the transparent Screen achieved.

Example 3

A mixture of 250 g of the thallium activated rubidium iodide and 65 g of a mixture of 1-naphthylmethyl methacrylate and S-O-naphthylraethyU-thiocatrylate in a ratio of 3: 1, the also contained 0.3% by weight, 4,4'-bis-chloromethylbenzophenone, was degassed in vacuo, whereupon the mass was further processed as follows: Part of the mass was on a black anodized aluminum carrier applied. Another part was applied to the optically flat surface of a reflective aluminum support and a third part of the mass became Production of a self-supporting film used. In all three In some cases, the layers of the same thickness were photopolymerized. The screens made in this way were used for manufacture from radiographic recordings used together with the DuPont Hi-Plus screen using Io-Dose film, 70 kVp X-rays and a 20μ lead stick test object. The resolving power of the radiographic images was as follows:

Hi-Plu> screen 4.0 1 / mm

black aluminum support 4.0 1 / mm

reflective aluminum support 1.8 1 / mm

carrier-free screen 1.8 1 / mm

The resolving power of the screen with a black substrate was dramatically increased, both in comparison with the resolving power of the screen with a reflective substrate and in comparison with the unsupported screen.

Example 4

A mixture of 136.8 g of thallium activated rubidium iodide (0.0004), 40 g of a mixture of 1-naphthylmethyl methacrylate with up to 25 liters of 1-naphthylmethanol and S- (1-naphthylmethyl) thioacrylate in a mixing ratio of 3: 1 and 0.3 wt 4,4'-bis-chloromethylbenzophenone was degassed in vacuo. the Mixture was then applied to a support of strips of black polished Formica, black anodized aluminum, black Corning photo molded glass, 80% of which is a pitted surface a diameter of 0.127 mm and a depth of 0.381 mm and dark blue tourmaline in one A matrix of black plastic material of the Lucite type is applied. The mixture would be applied evenly over the carrier, so that the different types of girders were covered equally. A glass cover sheet was then placed on the mixture and the mixture was photopolymerized. The cover sheet was then removed, whereupon the optical reflection densities of the various districts were measured. A 70 kV prediographic was used Image of a 10 micron wide lead dissolution test object made using the screen as the back screen and using DuPont Lo-Dose film. the radiographic recordings made using this transparent screen were compared with one Comparative radiographic image made with Lo-Dose film using an opaque Hi-Plus screen.

The radiographic sensitivity was determined as described in Example 1. The following results were obtained:

Carrier Refraction Optical Re-Radiographic Resolution

index r., flexion density sensitive- (1 / mm)

; , _2 speed

Lucite 1.49 2.25 315 2.5-2.8

3.15 3.15

3.15-3.55

3.55

3.55

From the results obtained, it is found that the optimum Combination of sensitivity and resolution then is achieved when the fluorescent mixture of a selected transparent phosphor-polymer combination on a black anodized aluminum surface was applied. Furthermore, the results obtained show that the transparent screen with a black anodized aluminum support has a resolution that is the same as that of a commercially available one opaque control screen and a radiographic sensitivity that is practically the same as that of a commercially available one opaque control screen. In contrast, the transparent screen according to the invention showed a considerably small amount of quantum speckles (quantum mottle) than the commercially available opaque screen.

Photo form
Glass 1.87 250 Tourmaline 1.64 2.57 250 Formica 1.65 2.17 245 Black
anodized
Aluminum 1.76 2.34 245 Hi-plus
umbrella
comparison
(opaque) 285

Example 5

A mixture of 180 g of finely divided Ba ^ g. Sr _{Q Q.} FCl: Eu (0.006) phosphor and 51 g of a mixture of benzyl methacrylate and 1-naphthylmethyl methacrylate (in a weight ratio of approximately 50:50) were degassed in vacuo and then applied to a black anodized aluminum support. A glass cover plate was applied to the applied layer, after which the mixture was polymerized through the glass plate by irradiation with a UV lamp with a considerable emission at 365 nm. After removing the glass plate, the size of the layer and its weight were determined. 915 g of phosphor were used on a 1m support surface. The mean free path for 38Onm radiation was determined spectrophotometrically to be 304 microns.

The screen was used as a back screen together with a front screen

2 from 58 g Gd ₂ O ₂ S: Tb / O, O929m (on a highly reflective carrier) used for the production of radiographic recordings of 70 kVp of a standard "Bone-Wu3.st" test object with a Kodak X-OMAT R X-ray film. For purposes of comparison to determine the image quality, a further picture was taken, with both the front screen and the rear screen consisting of Gd-O ₂ S: Tb screens. The sensitivity achieved using the comparative screens was 400 and the resolving power 2.24 1 / mm. The transparent back screen resulted in a sensitivity of 350 and a resolution of 2.24 1 / mm. The mottling of both radiographic images was assessed roughly the same. However, the sharpness and the bead visibility were considerably better in the case of the radiographic photograph made using the transparent screen.

Claims (8)

Dr. RKR. νλτ. J. BrandKH J'ATHNTANWAI / r HOOO MÜNCHEN 22 Reg. NT. 2 THIQRSClISTR. 8 TJOIjKFON; (08Ö) 20S2O7 EASTMAN KODAK COMPANY. tblbx «π 23325 (f> mwo <i> 343 State Street Rochester, New York State United States of America monchkn February 25, 1982 25/28 X-ray intensifying screen patent claims (\.) X-ray intensifying screen made from a carrier and at least one fluorescent layer applied to it: A.) 50 to 90% by weight of an isotropic phosphor which is excited by X-rays and which is transparent to the light emitted by the phosphor and B.) 10 to 50% by weight of a polymeric binder, characterized in that 1.) the polymeric binder has a refractive index that is no more than at least 80i of the emission spectrum of the phosphor 0.02 units deviates from the refractive index of the phosphor and is made up of: a.) 5 to 100 MoI-S recurring units of the Formula: R ¹ C = O I 2 0-R BANK DETAILS! UBUTHfHK BANK ACl, PILtAM)! MÜ NCHEN, ACCOUNT NO. 2710101 «BLZ 70O70010) 3205776 in which: R is a hydrogen atom or an alkyl radical and R, an alkyl or cycloalkyl radical, an aryl or Aralkyl radical or an aryl radical substituted by an alkyl or alkoxy radical or a heterocyclic radical and b.) from 0 to 95 mol% of repeating units the formula: R ¹ c-o S-CH-R ³
Ar-R ⁴ in which: Ar is an arylene radical; R is a hydrogen atom or an alkyl radical; R is a hydrogen atom, an alkyl, aryl or alkoxy radical and R is a hydrogen atom, an alkyl, alkoxy, amino, sulfide, sulfoxide, sulfonate or heterocyclic radical or a halogen atom and that 2.) the carrier has a refractive index which is equal to the refractive index of the phosphor or · um to 0.05 units above the refractive index of the luminous 320S776 Substance is and also an optical reflection density compared to the light emitted by the phosphor of at least 1.7. 2. X-ray intensifying screen according to claim 1, characterized in that the recurring units of the Formula: R ¹ C-O S-CH-R ³
Ar-R ⁴ derived from a naphthylmethylthioacrylate monomer. 3. X-ray intensifying screen according to claim 2, characterized in that the polymeric binder is composed of a) 5 to 100 MoI-S repeating units that differ from derive a naphthylmethyl methacrylate monomer and b) 0 to 95 MoI-I repeating units that differ from derive a naphthylmethylthioacrylate monomer. 4. X-ray intensifying screen according to claim 3, characterized in that that the polymeric binder is made up of: a) 1-naphthylmethyl methacrylic units and b) S- (I-naphthylmethyl) thioacrylate units. 5. X-ray amplifier screen according to one of claims 1 to 4, characterized in that the carrier has a black anodized aluminum surface. 6. Fluorescent mass made of: A) 50 to 90 wt -.% Of an isotropic phosphor which is excited by X-rays, and which is to light emitted by the phosphor, transparent, and B) 10 to 50 Gew.-i of a polymer, characterized in that the polymer has a Re frkt ions index aufitfeistj which over " at least 80% of the emission spectrum of the phosphor by no more than 0.02 units of the refractive index differs from the fluorescent material and is made up of: a) 5 to 100 mol% of recurring units of the formula: R ¹ C = O in which: R is a hydrogen atom or an alkyl radical and 2
R is an alkyl or cycloalkyl radical, a Aralkyl radical or one optionally substituted by an alkyl or alkoxy radical Aryl radical or a heterocyclic radical and b) O to 95 MoI-I recurring units of the Formula: R ¹ I.
CO S-CH-R ³ Ar-R ⁴ in which: Ar is an arylene radical; R is a hydrogen atom or an alkyl radical; 3
R is a hydrogen atom, an alkyl, aryl or aralkyl radical and R is a hydrogen atom, an alkyl, alkoxy, _t amino, sulfide, sulfoxide, sulfonate or heterocyclic radical or a halogen atom. 7. Fluorescent composition according to claim 1, characterized in that the repeating units of the formula: R ¹ C = O S-CH-R ³ Ar-R ⁴ derived from a naphthylmethylthioacrylate monomer. 8. Fluorescent composition according to claim 7, characterized in that the polymer is composed of: a) 5 to 99 mol% of repeating units that are derive from a naphthylmethyl methacrylate monomer and b) 1 to 95 mole-i repeating units that differ from derive a naphthylmethylthrloacrylate monomer.