JPH03134597A - Radiation sensitized screen and its manufacturing - Google Patents

Abstract

PURPOSE:To obtain a sensitive screen causing no sharpness degrading even when the thickness of the screen is fairly large by dispersing fluorescent particles into a solution of a binder agent, by forming spinning liquid into thread in order to form a fiber and by placing a sheet, which is formed by cutting and bundling the fibers, on a carrier body. CONSTITUTION:A spinning liquid consisting of a binder agent and fluorescent particles is regulated by dispersing the fluorescent particles into a molten body of the binder agent or a solution of the binder agent. A protein such as a gelatine, for instance, is used as the bonder agent. A tungstate fluorescent body (CaWO4 and the like), for instance, is also used as a fluorescent body for radiation sensitivity. In case that the solution of the binder agent is used as the spinning liquid, a lower alcohol such as a methanol, for instance, is used as a solvent. Mixing ratio of the binder agent and a stimulated phosphorescence differs according to characteristics of a target radiation sensitive screen, but in anyway, is selected from a range of 1:1 to 1:100 (in weight ratio). The fiber is formed by the spinning liquid consisting of the regulated fluorescent body and the binder agent. Those fibers are cut by a certain length and bundled together and then a bundle of the fibers are made to be a shape of a sheet to be placed on a carrier body.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to radiation intensifying screens and methods of manufacturing the same.

[Technical Background of the Invention and Prior Art] Radiation intensifying screens are used in various fields such as medical radiography such as X-ray photography for the purpose of medical diagnosis, and industrial radiography for the purpose of non-destructive testing of materials. In order to improve the sensitivity of the Jm shadow system in radiography, it is used by superimposing it closely on one or both sides of a radiographic film such as an X-ray film. This radiation intensifying screen basically consists of a support and a phosphor layer formed on one side of the support. Note that the surface of this phosphor layer opposite to the support (
The surface facing away from the support is generally provided with a transparent protective film to protect the phosphor layer from chemical alteration or physical attack.

The phosphor layer is composed of a binder containing and supporting phosphor particles in a dispersed state. The phosphor layer is generally attached onto the support using a coating method under normal pressure as described below. That is, a coating solution is prepared by mixing and dispersing phosphor particles and a binder in a suitable solvent, and this coating solution is subjected to radiation sensitization under normal pressure using a coating means such as a doctor blade, roll coater-knife coater, etc. Either by directly coating the screen support and then removing the solvent from the coating film, or by applying the coating solution in advance on a temporary support such as a glass plate under normal pressure and then removing the solvent from the coating film. The phosphor layer is attached to the support by forming a phosphor-containing resin thin film, peeling it from the temporary support, and bonding it to the support of the radiation intensifying screen. .

The phosphor in the phosphor layer has the property of emitting high-intensity light when excited by radiation such as X-rays.

Therefore, the phosphor emits high-intensity light depending on the amount of radiation that passes through the subject, and the radiographic film placed in contact with the surface of the phosphor layer of the radiation-sensitizing screen is sensitive to this phosphor. Since exposure is also caused by body luminescence, sufficient exposure of photographic film can be achieved with a relatively small dose of radiation.

It is desired that a radiation intensifying screen having the basic structure as described above has high sensitivity and provides images with good image quality (sharpness, granularity, etc.).

The sensitivity of a radiation intensifying screen basically depends on the total amount of light emitted by the phosphors contained in the panel. It also depends on the content of A high content of phosphor also means high absorption of radiation such as X-rays, resulting in higher sensitivity and at the same time improved image quality (particularly graininess).

The content of phosphor in the phosphor layer can be increased by increasing the thickness of the phosphor layer, but on the other hand, increasing the thickness of the phosphor layer increases the amount of phosphor located deep in the phosphor layer. The emitted light spreads by scattering before reaching the radiographic film, exposing not only the area actually excited by the radiation but also the surrounding area, which reduces the sharpness of the resulting image. A problem arises in which there is a significant decrease.

[Summary of the Invention] Another object of the present invention is to provide a radiation intensifying screen in which the sharpness does not decrease even when the thickness of the phosphor layer increases, and a method for manufacturing the same.

The above-mentioned object is a radiation-sensitizing screen according to the present invention having at least one phosphor layer comprising a support and a binder and a phosphor provided on the support: A radiation-sensitizing screen, at least one of which has a structure in which fibers made of the above-mentioned binder and the above-mentioned phosphor are bundled with substantially the same length in the thickness direction of the screen, and a support. A method for producing a radiation intensifying screen having at least one phosphor layer consisting of a binder and a phosphor provided on the support, comprising: a) a binder in a solution or melt; b) forming the spinning solution into a thread shape and forming a fiber made of the binder and the phosphor by using a parent solvent or cooling; C) cutting and bundling the fibers to form a bundle of fibers in which the fibers are bonded to each other on their sides, d) cutting the M1m bundle substantially perpendicular to the length direction to form a sheet; e. ) This can be achieved by a method for producing a radiation intensifying screen characterized by the step of attaching the above sheet onto a support.

In the radiation-sensitizing screen of the present invention, the phosphor layer has a structure in which fibers made of a binder and phosphor are bundled with the same length in the thickness direction of the screen. The light emitted from the phosphor travels through the fiber toward the surface and does not spread inside the phosphor layer. Therefore,
Even if the thickness of the phosphor layer increases, the sharpness does not decrease. In addition, a substance with a high refractive index is used as a binder,
If the sides of the fiber are coated with a low-refractive-index material or colored with a color that absorbs the emitted light, the emitted light from the phosphor within the book fiber is effectively trapped within the fiber. Since the fibers do not advance to the screen surface and enter adjacent fibers from the side surfaces of the fibers (that is, cause crosstalk), deterioration of sharpness can be prevented.

Preferred embodiments of the present invention are listed below.

(1) A radiation intensifying screen, wherein the binder is a substance having a refractive index of 1.55 or more in the visible to near ultraviolet region.

(2) The binder is polycarbonate containing 4.4°-dihydroxydiphenyl-1,1-ethane, polycarbonate containing 4,4°-dihydroxytriphenyl-2°2.2-ethane, polystyrene, poly-0 - At least one bond selected from the group consisting of methoxystyrene, polyvinylidene chloride, polypentachlorophenyl methacrylate, polyphenyl α-bromoacrylate, poly2,6-dichlorostyrene, polysulfone, and polyphenyl α-naphthyl methacrylate. A radiation-sensitizing screen characterized in that it is an agent.

(3) A radiation intensifying screen characterized in that the side surfaces of the fibers are coated with a substance having a refractive index of 1.49 or less in the visible to near ultraviolet region.

(4) A radiation-sensitizing screen characterized in that the side surfaces of the fibers are colored so as to absorb light in the visible to near ultraviolet region.

(5) A method for producing a radiation-sensitizing screen, characterized in that in step b), the spinning solution is formed into a thread by discharging it from a nozzle.

(6) A method for producing a radiation intensifying screen, characterized in that in step b), the spinning solution is stretched to form a thread.

[Detailed Description of the Invention] The radiation intensifying screen of the present invention and its manufacturing method will be described in detail below.

First, the radiation intensifying screen of the present invention will be explained with reference to the attached page 41.

FIG. 1 schematically shows a cross-sectional view of an example of the radiation intensifying screen of the present invention. In FIG. 1, 1 is a protective film, 2 is a phosphor layer, and 3 is a support. Phosphor layer 2
are fibers 2a, 2b, 2c made of a binder and phosphor particles.
, --2z have a structure in which the lengths are aligned in the thickness direction of the screen and are bundled. The light emitted from the phosphor inside the fibers 2b of the phosphor layer 2 does not spread within the phosphor layer 2, but travels inside the Ml fibers 2b toward the surface and passes through the protection 11.
Expose the radiographic film through the QI.

At this time, if the side surface of the fiber 2b is colored with a dye that absorbs this emitted light, the emitted light that attempts to leak to the outside of the fiber 2b from the side surface of the fiber 2b will be absorbed by this dye. Light emission does not enter into 2c from the side. Similarly, if the side surface of the fiber 2b is coated with a low refractive index material, the light emitted from the side surface of the fiber 2b to the outside of the fiber 12b will be reflected inside the fiber 2b by total internal reflection. The light emitted from the phosphor inside can travel to the surface while being confined inside the fiber 2b.

As shown in No. 1 [31], the radiation intensifying screen of the present invention is characterized in that the phosphor layer is composed of fibers made of a binder and phosphor particles. Therefore, when manufacturing the radiation intensifying screen of the present invention, it is first made of a binder and phosphor particles! Forms a-fibers.

The fibers made of the binder and the phosphor particles are produced by a method similar to that used for spinning ordinary synthetic fibers. That is,
A spinning solution consisting of a binder and phosphor particles is prepared, and the spinning solution is drawn and cooled, or spun by being discharged from a nozzle into a coagulating solution.

A spinning solution consisting of a binder and phosphor particles is prepared by dispersing the phosphor particles in a binder melt or binder solution.

Examples of binders used in the present invention include proteins such as gelatin, polysaccharides such as dextran, or natural polymeric substances such as gum arabic; and polyvinyl butyral, polyvinyl acetate, nitrocellulose, ethylcellulose, and vinylidene chloride.・Vinyl chloride copolymer, polyalkyl (meth)acrylate, vinyl chloride/vinyl acetate copolymer, polyurethane, cellulose acetate butyrate, polyvinyl alcohol, linear polyester, 4,4゛-dihydroxydiphenyl-1,
Polycarbonate with 1-ethane, polycarbonate with 4.4°-dihydroxytriphenyl-2,2,2-ethane, polystyrene, poly・O-methoxystyrene, polyvinylidene chloride, polypentachlorophenyl・
Examples include binders typified by synthetic polymeric substances such as methacrylate, polyphenyl α-bromoacrylate, poly2,6-dichlorostyrene, polysulfone, and polyphenyl α-naphthyl methacrylate.

Fibers formed using a binder with a relatively high refractive index of 1.55 or more in the wavelength region of the emitted light of the phosphor (visible to near ultraviolet region) are made using a binder with a relatively high refractive index such as a fluorine-based resin. By coating the fiber with a substance with a low refractive index, the light emitted from the phosphor inside the fiber is guided to the surface while being confined within the fiber, and the light is prevented from leaking from the side to other adjacent fibers. You can avoid it. Therefore, in the present invention, it is preferable to use a binder having a high refractive index. It is generally known that the refractive index of a polymer compound increases when an aromatic group, bromide, chloride, sulfone group, ketone, etc. are present in the repeating structure (chain) of the polymer. Specifically, examples of binders having a high refractive index include polycarbonate having 4.4°-dihydroxydiphenyl-1,1-ethane, 4,4'-dihydroxytriphenyl-2, 2,
Polycarbonate with 2-ethane, polystyrene, polyO-methoxystyrene, polyvinylidene chloride, polypentachlorophenyl methacrylate, polyphenyl α-bromoacrylate, poly2,6-dichlorostyrene, polysulfone and polyphenyl α-naphthyl. - It is preferable to use methacrylate in the present invention.

A spinning solution is prepared by dispersing phosphor particles in the melt or solution of the binder described above.

The phosphor used in the present invention will be described below.

Examples of radiation-sensitizing phosphors preferably used in the present invention include the following phosphors.

Tungstate-based phosphors (CaWO4, MgWO,
CaWO4: Pb, etc.), terbium-activated rare earth oxysulfide phosphor [Y20□S:Tb, Gd2O2S:Tb
, La2o. S: Tb, (YGd)20. S:Tb,
(Y, Gd) 202 S: Tb, Tm, etc.], terbium-activated rare earth phosphate phosphor (YPO4: Tb, Gd
PO4: Tb, LaPO4:Tb, etc.), terbium-activated rare earth oxyhalide phosphor (LaOBr:
Tb, La0Br: Tb, Tm, LaOCM +Tb
.

La0Cf: Tb, Tm, Gd0Br: Tb, Gd
0C1:Tb, etc.), thulium-activated rare earth oxyhalide phosphors (LaOBr:Tm, La0C1:Tm, etc.), barium sulfate phosphors [Ba5O,: Pb, Ba
5O,: Eu”, (BaS r)SO2: Eu2+
etc.], divalent europium-activated alkaline earth metal phosphate phosphor [Ba3(PO4)2:Eu24, (B
a, 5r)3 (PO4)2 :Eu2+, etc.], divalent europium-activated alkaline earth metal fluoride halide phosphor [BaFCu:Eu'', BaFBr:Eu2÷B
aCl2: Eu”, Tb, BaFBr
: Eu”Tb, BaF2- BaCl12-
KCj! : Eu”BaF2・BaC
l12-xBasO4・KCj2:Eu” (
Ba, Mg)F2-BaCl2□-KCu:Eu2+
etc.], iodide-based phosphors (Csl:Na, Csl:Tl
, NaI, KI:Tl2, etc.), sulfide-based phosphor [ZnS
: Ag, (Zn, Cd)S:Ag, (Zn, Cd
)S: Cu, (Zn.

Cd)S: Cu, Afi, etc.], hafnium phosphate phosphors (HfP207: Cu, etc.). However, the phosphor used in the present invention is not limited to these, and may be any phosphor that emits light in the visible to near ultraviolet region when irradiated with radiation.

When using a binder solution as a spinning solution, examples of solvents used include lower alcohols such as methanol, ethanol, n-propanol, and n-butanol; chlorine-containing hydrocarbons such as methylene chloride and ethylene chloride; acetone. , methyl ethyl ketone, methyl isobutyl ketone, and other ketones; esters of lower fatty acids and lower alcohols, such as methyl acetate, ethyl acetate, and butyl acetate; ethers, such as dioxane, ethylene glycol monoethyl ether, and ethylene glycol monomethyl ether; and mixtures thereof. can be mentioned.

The mixing ratio of the binder and the stimulable phosphor in the spinning solution varies depending on the characteristics of the intended radiation-sensitizing screen, the type of phosphor, etc., but regardless of whether a melt or solution of the binder is used, it is generally is the mixing ratio of binder and phosphor,
It is selected from the range of 1:1 to 1:100 (weight ratio), and particularly preferably selected from the range of 1:8 to 1:40 (weight ratio).

In addition, the spinning solution contains a dispersant to improve the dispersibility of the phosphor in the spinning solution, and a dispersant to adjust the viscosity or a bond between the binder and the phosphor in the fiber after formation. Various additives such as plasticizers may be mixed to improve bonding strength. Examples of dispersants used for such purposes include phthalic acid, stearic acid, caproic acid, lipophilic surfactants, and the like. Examples of plasticizers include phosphate esters such as triphenyl phosphate, tricresyl phosphate, and diphenyl phosphate; phthalate esters such as diethyl phthalate and dimethoxyethyl phthalate; ethyl phthalyl ethyl glycolate, butyl phthalyl butyl glycolate, etc. and polyesters of polyethylene glycol and aliphatic dibasic acids, such as polyesters of triethylene glycol and adipic acid and polyesters of diethylene glycol and succinic acid.

Fibers are formed from a spinning solution consisting of the phosphor and binder prepared as described above.

In the step of forming the fibers, a method commonly used in the spinning process of synthetic 1a fibers and the like can be used.

For example, in the case of a spinning solution prepared from a binder solution, spinning can be carried out by discharging it from a nozzle into a coagulating solution to remove the solvent from the spinning solution, or by adjusting the viscosity of the spinning solution appropriately and stretching it. The fiber is made into a thread, which is submerged in a coagulating solution to remove the solvent and then spun. In addition, in the case of a spinning solution in which phosphor particles are dispersed in a molten binder, it can be spun by being cooled by being discharged from a nozzle into the air or into a cooling liquid, or it can be stretched into a thread and then cooled. It is then spun.

In this manner, the side surfaces of the spun fiber made of the binder and the phosphor particles are preferably coated with a low refractive index substance or colored with a color that absorbs emitted light. Such coating or coloring can be carried out by submerging the fibers spun as described above in a coating agent or colorant solution.

As a coating material, the wavelength range of emitted light (visible to near ultraviolet)
A fluororesin, a low-molecular liquid substance, or the like, which has a relatively low refractive index of about 1.30 to 1.49, is used. Further, it is preferable to use a dye, dye, pigment, or the like having an absorption band in this wavelength range as a coloring agent to color the side surface of the fiber so as to absorb the light emitted by the phosphor.

The fibers made of the binder and phosphor particles spun as described above are cut into appropriate lengths and bundled, and the fibers are adhered to each other on the sides to form the fiber bundle. It is preferable to provide adhesive properties to the side surfaces of the fibers in advance so that the fibers adhere to each other on the side surfaces. Such adhesion of the fiber side surface can be imparted by submerging the fiber in an adhesive after the above-mentioned coating, coloring, etc. This adhesive, coating,
Of course, the sides of the fibers may be coated with a material that functions as any two or all of the colorants.

Next, a bundle of fibers made of a binder and phosphor particles is cut perpendicularly to the longitudinal direction of the fibers to form a sheet, and this is placed on a support to form a phosphor layer.

When cutting, the thickness of the sheet cut from the fiber bundle becomes the same as the thickness of the phosphor layer, so it is cut in a tight manner using a high-strength cutter or the like to achieve the desired layer thickness. The thickness of the phosphor layer varies depending on the characteristics of the intended radiation-sensitizing screen, the type of phosphor, the mixing ratio of the binder and the phosphor, etc., but considering the purpose of the present invention, the thickness of the phosphor layer in conventional screens Preferably thicker than the layer, usually 20μ
m to 2 mm. However, the thickness of this layer is preferably 100 μm to 1 mm.

The sheet thus obtained is pressed onto a support or attached to the support using an adhesive,
Use as a phosphor layer.

In addition, in the radiation intensifying screen of the present invention, a conventionally known binder and a binder dispersed therein are added to the phosphor layer made of the above-mentioned fibers for the purpose of adjusting sharpness and improving sensitivity. A phosphor layer made of phosphor particles may be provided.

The support for the radiation intensifying screen of the present invention can be arbitrarily selected from materials known as supports for conventional radiation intensifying screens. Examples of such materials include cellulose acetate, polyester, polyethylene terephthalate, polyamide, polyimide, triacetate,
Films of plastic materials such as polycarbonate,
Metal sheets such as aluminum foil and aluminum alloy foil, regular paper, baryta paper, resin coated paper, pigment paper containing pigments such as titanium dioxide, paper sized with polyvinyl alcohol, etc., alumina, zirconia, magnesia, titania, etc. Examples include ceramic plates or sheets.

In known radiation-sensitizing screens, a phosphor layer is provided in order to strengthen the bond between the support and the phosphor layer, or to improve the sensitivity or image quality (sharpness, granularity) of the radiation-sensitized screen. A polymeric substance such as gelatin is coated on the surface of the side support to form an adhesion-imparting layer, or a light-reflecting layer made of a light-reflecting substance such as titanium dioxide, or a light-reflecting layer made of a light-absorbing substance such as carbon black. It is known to provide an absorbent layer or the like. The support A used in the present invention can also be provided with these various layers, and their configurations can be arbitrarily selected depending on the purpose, use, etc. of the desired radiation intensifying screen. .

Furthermore, in order to improve the sharpness of the obtained image, an adhesive layer, a light reflection layer, a light absorption layer, etc. are provided on the surface of the support on the phosphor layer side (the surface of the support on the phosphor layer side). microscopic irregularities may be formed on the surface.

In a normal radiation intensifying screen, as mentioned above, a transparent protective film is provided on the surface of the phosphor layer on the side opposite to the side that contacts the support to physically and chemically protect the phosphor layer. It is being It is preferable to provide such a transparent protective film also in the radiation intensifying screen of the present invention.

The transparent image 21 membrane may be made of, for example, a cellulose derivative such as cellulose acetate or nitrocellulose; or a synthetic polymer material such as polymethyl methacrylate, polyvinyl butyral, polyvinyl formal, polycarbonate, polyvinyl acetate, or vinyl chloride/vinyl acetate copolymer. It can be formed by applying a solution prepared by dissolving a transparent polymer substance in a suitable solvent onto the surface of the phosphor layer. Alternatively, polyethylene terephthalate,
A plastic sheet made of polyethylene naphthalate, polyethylene, polyvinylidene chloride, polyamide, etc.; and a protective film-forming sheet such as a transparent glass plate are formed separately and adhered to the surface of the phosphor layer using an appropriate adhesive. It can also be formed by the following method.

The thickness of the protective film is generally in the range of about 0.1 to 20 μm.

In the radiation-sensitizing screen of the present invention produced as described above, the phosphor layer has a structure in which fibers made of a binder and phosphor are bundled with the same length in the thickness direction of the screen. Therefore, the emitted light emitted from the phosphor located deep in the phosphor layer travels through the fibers toward the surface and does not spread inside the phosphor layer. Therefore, the radiation-sensitizing screen of the present invention is a radiation-sensitizing screen in which the sharpness of the obtained image does not deteriorate even if the thickness of the phosphor layer increases.

[Brief explanation of the drawing]

FIG. 1 schematically shows a cross-sectional view of an example of the radiation intensifying screen of the present invention. ■=Retention 3M film, 2: Phosphor layer, 3: Support, 2a,
2b, 2c, = 2z: fibers made of binder and phosphor.

Claims (1)

[Scope of Claims] 1. A radiation intensifying screen comprising a support and at least one phosphor layer provided on the support and comprising a binder and a phosphor; at least one of the phosphor layers One is a radiation-sensitizing screen characterized in that the fibers made of the binder and the phosphor are bundled with substantially the same length in the thickness direction of the screen. 2. A method for producing a radiation intensifying screen comprising a support and at least one phosphor layer provided on the support and comprising a binder and a phosphor, comprising: a) solution or melting of the binder; a step of preparing a spinning solution in which the phosphor particles are dispersed in the spinning solution; b) forming the spinning solution into a thread shape and forming fibers made of the binder and the phosphor by removing the solvent or cooling; c) cutting and bundling the fibers to form a bundle of fibers in which the fibers are bonded to each other on their sides; d) forming the bundle of fibers,
A method for producing a radiation intensifying screen, comprising the steps of: cutting the sheet substantially perpendicularly to the length direction to form a sheet; e) attaching the sheet to a support.