JPH1164596A - Radiation sensitized screen - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screen having a high sharpness in which a transparent protecting film has no abrasion or scratch by forming the transparent protecting film on a support body from polyethylene naphthalate. SOLUTION: This screen is formed of a phosphor layer and a transparent layer provided on a support body in this order. The transparent protecting film is a thin film for physically and chemically protecting the phosphor layer. As the transparent protecting film to be stuck, a thin film consisting of polyethylene naphthalate is used, and polyester having a main frame represented by the formula is preferable. The transparent film can be formed by adhering a separately formed transparent polyethylene naphthalate film to the surface of the phosphor layer by use of a proper adhesive. The thickness of the protecting film is generally about 0.5-0.7 μm, and the transmissivity to the protecting film of the total emission of the phosphor is preferably 50% or more. The protecting film can be also formed by separately preparing a protecting film forming sheet of polyethylene naphthalate, and adhering it to the surface of the phosphor layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiographic intensifying screen (hereinafter, simply referred to as a screen), and more particularly, to a screen having a transparent protective film having high strength and high sharpness. .

[0002]

2. Description of the Related Art As means used for medical radiography for medical diagnosis and industrial radiography for nondestructive inspection of substances, there are screens and silver halide photographic materials (hereinafter simply referred to as photosensitive materials). Radiography, which is also referred to as a material.

In radiography, radiation is applied to a phosphor on a screen to excite it to convert it into visible light, and form a radiographic image on a photosensitive material for diagnosis and inspection.

The screen has a basic structure comprising a support, a phosphor layer and a protective film provided on one side of the support. The phosphor layer is composed of phosphor particles and a binder containing and supporting the phosphor particles in a dispersed state, and the phosphor particles have a property of emitting high-luminance light when excited by radiation such as X-rays. Things. Therefore, the phosphor emits light of high luminance in accordance with the amount of radiation that has passed through the subject, and the photosensitive material placed on top of the phosphor layer of the screen so as to be in contact with the surface of the phosphor layer also emits light of this phosphor. Since the photosensitive material is exposed, the photosensitive material can be sufficiently exposed with a relatively small radiation dose.

In such a radiographic method, for example, a photosensitive material is pressed in such a manner as to be sandwiched between two screens attached to both sides of a cassette and irradiated with radiation through a subject, and the radiation of the subject is irradiated onto the photosensitive material. Although an image is formed, abrasion occurs on the protective film after about 5,000 uses. In addition, since the corner of the film often scratches the protective film when loading the photosensitive material,
These abrasions and scratches directly or indirectly mix dyes and stains in the light-sensitive material into the screen, coloring the screen, appearing on radiographic images as image defects and causing misdiagnosis. For this reason, many screens use a relatively durable polyethylene terephthalate film with a thickness of about 10 μm as the protective film. On the other hand, in order not to lower the sharpness, the thinner the protective film, the better. However, the strength against scratches, scratches and the like naturally decreases. Therefore, development of a screen that is resistant to abrasion and has excellent sharpness has been desired.

[0006]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a screen having high sharpness without scratches or scratches on the transparent protective film.

[0007]

The above objects of the present invention have been attained by the following constitutions.

[0008] 1. A radiation intensifying screen having a phosphor layer and a transparent protective film on a support in this order, wherein the transparent protective film is formed from polyethylene naphthalate.

Hereinafter, the present invention will be described more specifically.

First, the transparent protective film of the present invention will be described.

The screen of the present invention has a phosphor layer and a transparent protective film on a support in this order. The transparent protective film is a transparent thin film for physically and chemically protecting the phosphor layer. It is.

In the present invention, the transparent protective film adhered on the phosphor layer of the screen is a transparent protective film made of polyethylene naphthalate, which has a main skeleton represented by the following structural formula. It is preferably polyester.

[0013]

Embedded image

The transparent protective film can be formed, for example, by bonding a separately formed transparent polyethylene naphthalate film to the surface of the phosphor layer using a suitable adhesive.

In the present invention, the thickness of the transparent protective film is preferably from 0.5 to 7 μm, more preferably from 1 to 7 μm.
5 μm.

Although the thickness of the transparent protective film varies depending on the emission wavelength of the phosphor, the transmittance of the total light emission to the transparent protective film is 50%.
% Or more, more preferably 80% or more.

The transparent protective film of the present invention is formed by preparing a polyethylene naphthalate plastic sheet protective film-forming sheet separately and bonding it to the surface of the phosphor layer using an appropriate adhesive. Can also.

By using such a thin transparent protective film, particularly in the case of a radiographic intensifying screen, the distance from the phosphor to the silver halide emulsion is shortened, which contributes to the improvement of the sharpness of the obtained radiographic image. Will be.

Further, polyethylene naphthalate has the following advantages over polyethylene terephthalate.
Since the heat shrinkage is small, it is stable even when heated, such as when sticking to the phosphor layer. 2. High chemical resistance, especially high strength against caustic soda. 3. Since the moisture permeability and gas permeability are low, the effect of preventing deterioration of the phosphor layer due to moisture or gas is large.

The phosphors preferably used for the screen of the present invention include the following.

Tungstate-based phosphor (CaWO ₄ ,
MgWO ₄ , CaWO ₄ : Pb, etc.), terbium-activated rare earth oxysulfide-based phosphor [Y ₂ O ₂ S: Tb, Gd ₂ O ₂ S: T
b, La ₂ O ₂ S: Tb, (Y, Gd) ₂ O ₂ S: Tb,
(Y, Gd) O ₂ S: Tb, Tm, etc.], terbium-activated rare earth phosphate-based phosphor (YPO ₄ : Tb, GdPO ₄ : T
b, LaPO ₄ : Tb, etc.), terbium-activated rare earth oxyhalide phosphor (LaOBr: Tb, LaOB)
r: Tb, Tm, LaOCl: Tb, LaOCl: T
b, Tm, GdOBr: Tb, GdOCl: Tb, etc.),
Thulium-activated rare earth oxyhalide phosphor (La
OBr: Tm, LaOCl: Tm, etc.), barium sulfate-based phosphor [BaSO ₄ : Pb, BaSO ₄ : Eu ²⁺ , (B
a, Sr) SO ₄ : Eu ²⁺ etc.] divalent eurobium-activated alkaline earth metal phosphate phosphor [Ba ₂ (P
O ₄ ) ₂ : Eu ²⁺ , (Ba ₃ (PO ₄ ) ₂ : Eu ²⁺ etc.), 2
-Valent europium-activated alkaline earth metal fluorohalide-based phosphor [BaFCl: Eu ²⁺ , BaFBr: E
u ²⁺ , BaFCl: Eu ²⁺ , Tb, BaFBr: E
u ²⁺ , Tb, BaF ₂ .BaCl ₂ .KCl: Eu ²⁺ ,
(Ba, Mg) F ₂ .BaCl ₂ .KCl: Eu ²⁺ etc.],
Iodide phosphors (CsI: Na, CsI: Tl, Na
I, KI: Tl, etc.), sulfide-based phosphors [ZnS: Ag,
(Zn, Cd) S: Ag, (Zn, Cd) S: Cu,
(Zn, Cd) S: Cu, Al, etc.), hafnium phosphate-based phosphor (HfP ₂ O ₇ : Cu, etc.), tantalate-based phosphor [YTaO ₄ , YTaO ₄ : Tm, YTaO ₄ : Nb,
(Y, Sr) TaO _4-x : Nb, LuTaO ₄ , LuTa
O ₄ : Nb, (Lu, Sr) TaO _4-x : Nb, GdTa
O ₄ : Tm, Gd ₂ O ₃ .Ta ₂ O ₅ .B ₂ O ₃ : Tb, etc.].

The phosphor preferably used in the present invention preferably has a main peak of the emission spectrum in the wavelength range of 300 to 650 nm when emitted by radiation excitation, and emits violet to red light. And more preferably a phosphor having a main peak of an emission spectrum in a wavelength range of 500 to 600 nm.

The average particle size of these phosphors is 1 to
A range of 10 μm is preferred.

As a method for classifying the particle size of the phosphor, a sieve method using a sieve, a method in which a phosphor is placed in a nylon mesh bag and shaken in water or by pouring a phosphor coating solution through a sieve is used. An elutriation method, a sedimentation method in which a phosphor is stirred in water and allowed to stand, and after a certain time, a supernatant or a precipitate is removed. The method of measuring the particle size distribution of the classified phosphor is as follows: volume analysis method such as sieving and coulter counter, image analysis method using a microscope, sedimentation method using gravity and centrifugation, inertial force method such as cascade impactor and cyclone, There are a surface area analysis method such as the Kalman method and the Nudesen method, an adsorption method such as the BET method and the flow method, and a method utilizing electromagnetic wave scattering such as a light diffraction method.

The binder resin of the phosphor coating solution preferably used in the present invention is, for example, a polystyrene-based thermoplastic elastomer, a polyolefin-based thermoplastic elastomer, a polyurethane-based thermoplastic elastomer, a polyester-based thermoplastic elastomer, a polyamide-based thermoplastic elastomer. , Polybutadiene-based thermoplastic elastomer, ethylene-vinyl acetate-based thermoplastic elastomer, polyvinyl chloride-based thermoplastic elastomer, natural rubber-based thermoplastic elastomer, fluoro-rubber-based thermoplastic elastomer, polyisoprene-based thermoplastic elastomer, chlorinated polyethylene-based thermoplastic Elastomers, styrene-butadiene rubber, silicone rubber-based thermoplastic elastomers, and the like are included.

Of these, polyurethane-based thermoplastic elastomers and polyester-based thermoplastic elastomers have good dispersibility since they have a strong bonding force with the phosphor.
Further, it is preferable because it has high ductility and the bending resistance of the radiation intensifying screen becomes good.

Examples of the solvent for the phosphor coating solution preferably used in the present invention include, for example, methanol, ethanol,
Lower alcohols such as n-propanol and n-butanol; hydrocarbons containing chlorine atoms such as methylene chloride and ethylene chloride; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; aromatic compounds such as toluene and benzene; methyl acetate and ethyl acetate And esters of lower fatty acids such as butyl acetate and lower alcohols, ethers such as dioxane, ethylene glycol monoethyl ester and ethylene glycol monomethyl ester, and mixtures thereof.

Examples of the phosphor dispersant used in the screen of the present invention include, for example, phthalic acid, stearic acid,
Examples include caproic acid and lipophilic surfactants.

Examples of the plasticizer used in the phosphor coating solution preferably used in the present invention include, for example, phosphates such as triphenyl phosphate, tricresyl phosphate and diphenyl phosphate, and phthalic acids such as diethyl phthalate and dimethoxyethyl phthalate. Ester, glycolic acid ester such as ethylphthalylethyl glycolate, butylphthalic acid glycol, etc., polyester of triethylene glycol and adipic acid, polyester of polyethylene glycol such as polyester of diethylene glycol and succinic acid and polyester of aliphatic dibasic acid And the like.

In preparing a screen, first, a binder and a phosphor are added to an appropriate organic solvent, and the mixture is stirred and mixed using a disper or a ball mill to form a coating solution in which the phosphor is uniformly dispersed in the binder. Prepare. A coating film is formed by uniformly applying the thus prepared phosphor coating solution on a support.

This coating operation can be performed by using a usual coating means, for example, a doctor blade, a roll coater, a knife coater or the like.

Next, the formed coating film is dried by gradually heating to complete the formation of the phosphor layer on the support.

Further, the phosphor layer does not necessarily need to be formed by directly applying a coating solution on the support as described above, and the coating solution may be applied on another temporary support or a protective film in the same manner as described above. After the phosphor layer is formed by drying, the phosphor layer may be bonded to the support by pressing the phosphor layer on the support or using an adhesive.

As the support or the temporary support, for example, those made of various materials such as glass, wool, cotton, paper, and metal can be used. What can be done is preferred. From this point, for example, cellulose acetate film, polyester film, polyethylene terephthalate film, polyamide film, polyimide film, triacetate film, plastic film such as polycarbonate film, aluminum foil, metal sheet such as aluminum alloy foil, general paper and, for example, photographic Base paper, coated paper or printing base paper such as art paper, baryta paper, resin coated paper, paper sized with polysaccharide as described in Belgian Patent 784,615, titanium dioxide, etc. Pigmented paper containing pigments, and processed paper such as paper sized with polyvinyl alcohol are particularly preferred.

The thickness of the phosphor layer varies depending on the characteristics of the target screen, the kind of the phosphor, the mixing ratio of the binder and the phosphor, etc., but is usually in the range of 20 μm to 1 mm, preferably 50 μm. ３００300 μm.

In order to strengthen the bond between the support and the phosphor layer,
Or screen sensitivity or image quality (sharpness,
In order to improve the granularity, etc.), an undercoat layer is applied to the surface of the support on which the phosphor layer is provided to impart adhesiveness by applying a polymer substance such as polyester or gelatin, or light reflection such as titanium dioxide is provided. There may be provided a light reflecting layer made of a conductive material, a light absorbing layer made of a light absorbing material such as carbon black, or the like. These configurations can be arbitrarily selected according to the purpose, use, and the like.

In order to increase the filling rate of the phosphor in the phosphor layer,
The obtained phosphor layer may be placed on a support and compressed at a temperature higher than the softening temperature or melting point of the binder. In this case, it is effective to prepare the phosphor layer on a temporary support and adhere the phosphor layer on the support while compressing the obtained phosphor layer.

As a compression apparatus used for the compression processing, generally known apparatuses such as a calender roll and a hot press can be mentioned.

For example, the compression treatment using a calender roll is performed by placing the obtained phosphor layer on a support and passing the phosphor layer at a constant speed between rollers heated to a temperature higher than the softening temperature or melting point of the binder. . However, the compression device is not limited to these, and any device may be used as long as it can compress the sheet while heating it.

The pressure during compression is preferably at least 30 kgw / cm ² . The compression may be performed after the protective layer is applied.

[0041]

Hereinafter, embodiments of the present invention will be described.
As a matter of course, the present invention is not limited to the embodiments described below.

Example 1 Preparation of Comparative Screen (1) Phosphor Gd ₂ O ₂ S: Tb400 having an average particle diameter of 3 μm, which was classified by elutriation and measured by a Coulter counter.
g, binder polyurethane 10 g and solvent methyl ethyl ketone 50 g were mixed and dispersed in a ball mill for 6 hours to prepare a phosphor coating solution. The coating solution was uniformly applied with a knife coater on a polyethylene terephthalate (250 μm) support placed horizontally on a glass plate so that the layer thickness after drying was 120 μm to form a phosphor layer. 1 μm
9 μm thick with a polyester-based adhesive layer applied
The transparent polyethylene terephthalate film was adhered on the phosphor layer with the adhesive layer facing down to prepare a comparative screen (1) as a protective film.

Preparation of Comparative Screen (2) Phosphor Gd ₂ O ₂ S: Tb400 having an average particle diameter of 3 μm, which was classified by elutriation and measured by a Coulter counter.
g, binder polyurethane 10 g and solvent methyl ethyl ketone 50 g were mixed and dispersed in a ball mill for 6 hours to prepare a phosphor coating solution. The coating solution was uniformly applied with a knife coater on a polyethylene terephthalate (250 μm) support placed horizontally on a glass plate so that the layer thickness after drying was 120 μm to form a phosphor layer. 1 μm
3μm with a polyester adhesive layer applied
The transparent polyethylene terephthalate film was adhered on the phosphor layer with the adhesive layer facing down to prepare a comparative screen (2) as a protective film.

Preparation of Screen (3) of the Present Invention A phosphor Gd ₂ O ₂ S: Tb400 having an average particle diameter of 3 μm, which was classified by elutriation and measured by a Coulter counter.
g, binder polyurethane 10 g and solvent methyl ethyl ketone 50 g were mixed and dispersed in a ball mill for 6 hours to prepare a phosphor coating solution. The coating solution was uniformly applied with a knife coater on a polyethylene terephthalate (250 μm) support placed horizontally on a glass plate so that the layer thickness after drying was 120 μm to form a phosphor layer. 1 μm
3μm with a polyester adhesive layer applied
The transparent polyethylene naphthalate film was adhered on the phosphor layer with the adhesive layer facing down to prepare a screen (3) as a protective film.

1) Sharpness A sample screen was placed in contact with a single-sided photosensitive material of SR-IC manufactured by Konica Corporation, placed at a position 2 m from the X-ray tube, and exposed to the front with respect to the X-ray source. The material was placed behind the screen. The X-ray tube used was DRX made by Toshiba
−2724 HD-P, using a tungsten target, focus spot size 0.6 mm × 0.6
mm, and passes through a 3 mm aluminum equivalent material including an aperture to generate X-rays. A voltage of 80 kV is applied to the three phases by a pulse generator, and a rectangular chart for MTF measurement (made of molybdenum, thickness: 80 μm, spatial frequency: 0 / mm to 1) is used as an X-ray as a light source through a 7 cm water filter.
0 lines / mm). After the photographing, the photosensitive material was developed to obtain a measurement sample. The development process is performed by a Konica roller transport type automatic developing machine (SRX-502).
-35 ° C. using DF developer and fixation with 200 ml of fixing solution (ammonium thiosulfate (70% weight / volume),
Water was added to 20 g of sodium sulfite, 8 g of boric acid, 0.1 g of disodium ethylenediaminetetraacetate (dihydrate), 15 g of aluminum sulfate, 2 g of sulfuric acid, and 22 g of glacial acetic acid to make 1 liter, and the pH was adjusted to 10.02. ) At 25 ° C for a total treatment time of 4 ° C.
Processing took 5 seconds.

Next, the obtained measurement sample was scanned with a microdensitometer. At this time, the aperture used a slit of 10 μm in the scanning direction and 1000 μm in the direction perpendicular thereto, and the density profile was measured at a sampling interval of 10 μm. This operation was repeated 20 times to calculate an average value, which was used as a profile for calculating the CTF. Thereafter, the peak of the rectangular wave at each frequency of the density profile was detected, the density contrast at each frequency was calculated, and further the Kortman correction was performed to obtain the MTF.

The value of MTF was measured at a spatial frequency of 2.0 cycles / mm, and expressed as a relative value with the value of Comparative Screen 1 being 100. The higher the value, the better the sharpness. The results are shown in Table 1.

2) Evaluation of strength of protective film (whether or not there are scratches and scratches)
DC-14 (manufactured by Konica Corporation) was loaded, and a film SR-C for direct radiography (manufactured by Konica Corporation) was used for 10,000.
Conveyed. The 10,000th sheet was photographed and developed, and the presence or absence of image defects was visually evaluated according to the following evaluation criteria.
It was shown to.

Evaluation criteria ○: no image defect ×: image defect

[0050]

[Table 1]

From Table 1, it can be seen that the screen of the present invention has no image defects due to scratches and dye contamination on the transparent protective film, and is excellent in sharpness.

[0052]

According to the present invention, it is possible to provide a screen excellent in sharpness without image defects due to scratches and dye contamination.

Claims (1)

[Claims] 1. A radiographic intensifying screen comprising a support and a phosphor layer and a transparent protective film in this order, wherein the transparent protective film is formed from polyethylene naphthalate.