JPS6031100A - Radiation picture converting panel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a radiation image conversion panel, and more particularly to a stimulable phosphor layer comprising a stimulable phosphor dispersed in a binder. The present invention relates to a radiation image conversion panel having improved light resistance and mechanical properties by completely containing polyvinyl formal resin in the binder.

(Prior Art) Radiographic images such as X-ray images are often used for disease diagnosis. In order to obtain this X-ray image, the X-edge that has passed through the subject is irradiated onto a phosphor layer, thereby producing visible light, and this visible light is then exposed to the K
Tili! Developed by irradiating a film using salt,
A so-called radiograph is used. However, in recent years,
In particular, due to problems such as the depletion of iron resources on a global scale, methods have been devised to take out images directly from the phosphor layer without using a film coated with silver salt.

This method involves making a phosphor absorb the radiation that has passed through the object, and then exciting the phosphor with, for example, light or thermal energy to absorb the radiation that has been accumulated by the phosphor through the absorption. is emitted as fluorescent light, this fluorescent light is detected, and 11! There is a method to image II. Specifically, for example, U.S. Pat. No. 3,859,527 and JP-A-55-12144 disclose a radiation image conversion method using a photostimulable phosphor and using visible light or infrared rays as excitation light. .

This method uses a radiation image conversion panel in which a photostimulable phosphor layer is formed on a support. Radiation energy corresponding to the radiation transmittance of each part is accumulated to form a latent image 1~ Then, the accumulated radiation energy of each part is radiated by scanning this photostimulable phosphor layer with photostimulation excitation light. This is converted into light, and an image is obtained using an optical signal based on the intensity of this light. This final image may be reproduced as a note copy or on a CRT.

By the way, the above-mentioned radiation image conversion panel uses a flexible material such as a plastic film as a support, and has a stimulable phosphor layer formed by dispersing a stimulable phosphor in a binder on this support. It was established. In order to physically or physically protect this stimulable phosphor layer, a protective layer is provided on the surface of the stimulable phosphor layer, and if necessary, a protective layer is provided between the stimulable phosphor layer and the support. A pulling layer is provided to improve the adhesion between the two.

When a radiation image conversion panel with such a configuration is used, the radiation image recording process involves accumulating radiation energy to form a latent image as described above, and scanning the latent image with stimulated excitation light to create an image. In the process of reproducing the radiation image to be taken out, it is incorporated into the imaging device and the reading device, respectively. At this time, a bending force may be applied to the radiation image conversion panel so that it is automatically sent from the imaging device to the reading device using a roller conveyor, for example. In this case, the panel will be bent during handling since the support is made of a flexible material. In particular, after the image is taken out, this channel is reused after erasing the afterimage with strong erasing light, so it is repeatedly incorporated into the above-mentioned apparatus. This process is repeated several thousand times. Therefore, the above-mentioned panel may be bent repeatedly. If this happens, cracks may occur in the stimulable phosphor layer, or the phosphor layer may partially peel off from the support, and such a layer may be used as a phosphor layer. If used, images corresponding to these parts will be accompanied by noise. In order to prevent cracking or peeling from occurring due to such bending, the stimulable phosphor layer should have flexibility and strong adhesion to the support. but,
Regarding this flexibility, if it is too large, when the radiographic image conversion panel is used repeatedly, it may be difficult to incorporate it into the device, for example, when supporting it on a frame or transporting it with rollers, etc. It must be moderate, as pressure and other local forces are applied to the surface, making it more likely to be damaged.

Furthermore, as mentioned above, the radiation image conversion panel is irradiated with stimulated excitation light during reading in the radiation image reproduction process, and is also irradiated with erasing light for erasing afterimages for reuse. 106-10-Lux-asc irradiation. When the excitation light for reading or the much more powerful erasing light is irradiated onto the photostimulable phosphor layer over a long period of time, for example several thousand times, an organic material is usually used as the binder. Therefore, remove the ones that cause photodecomposition and turn yellow. In this case, for example, fluorescent X-rays generated from a photostimulable phosphor have a peak at 390 nm and a half-width of 360 nm.
When the spectrum is from 410 nm to 410 nm, this overlaps with the absorption region of the binder, so a part of the fluorescent X-rays are absorbed by the binder. Furthermore, similar problems arise when using stimulated excitation light that is close to the absorption region of the binder. When the binder absorbs one or both of the photostimulable excitation light and the light generated from the photostimulable phosphor in this way, the reading sensitivity of the radiation image conversion panel is reduced. Not only that, but as a result of the binder being subjected to photochange, the binder becomes hard, reducing the flexibility of the stimulable phosphor layer and its adhesion to the support.

As mentioned above, the binder used in the stimulable phosphor layer of the radiation image conversion panel is important in terms of durability and light resistance, such as resistance to cracking when bent, adhesion, and resistance to scratching. Excellent qualities are required. This property is much stricter than the properties required of a binder used in the phosphor layer of a general phosphor intensifying screen. In the case of a general phosphor intensifying screen, it is used by pasting it on a cassette, and the phosphor layer does not need to be particularly flexible against bending or be careful not to get scratched as mentioned above. Also, the above-mentioned light resistance is not required.

As the binder for the stimulable phosphor layer of the radiation image conversion panel as described above, it is possible to reuse the binder conventionally used for the phosphor layer of general phosphor intensifying screens. It is being done. As such, for example, JP-A-55-163
No. 500, No. 56-11400, proteins such as gelatin, polysaccharides such as dextrin or gum arabic, cellulose conductors such as nitrocellulose, vinyl chloride-vinylidene chloride copolymer polymethyl methacrylate, Examples include vinyl chloride-vinyl acetate copolymer, polyurethane, polyvinyl acetate, and polyvinyl alcohol. However, these binders do not have the durability and light resistance required for the binders of the stimulable phosphor layers of the radiation image conversion panels as described above. Among these materials, for example, in the case of nitrocellulose, it is easily yellowed by the excitation light and erasing light, and does not have the flexibility and adhesive properties described above, so it cannot be used.

On the other hand, JP-A-57-24900 discloses a radiation conversion panel using a mixture of polyester-urethane resin and cellulose acetate as a binder for the purpose of improving the durability against bending and light resistance. However, the light resistance of the resin cellulose acetate contained in the binder of this radiation image conversion panel is particularly poor, resulting in yellowing, which causes the deterioration of sensitivity as described above, and the resulting sensitivity unevenness. It has the following drawback.

As mentioned above, the binder in the stimulable phosphor layer of the conventional radiation image conversion panel does not have sufficient durability and light resistance.
Improvement was desired.

(Objective of the Invention) The first object of the present invention is that the photostimulable phosphor layer has good light resistance to photostimulation excitation light and erasure light, and therefore, even when repeatedly irradiated with these lights for a long time, Sensitivity decreases or
Another object of the present invention is to provide a radiation image conversion panel whose durability against bending does not deteriorate due to hardening of the binder.

A second object of the present invention is to provide a radiation image conversion panel in which the stimulable phosphor layer does not crack or peel off from the support when bent. There is a particular thing.

A third object of the present invention is to provide a radiation image conversion panel in which the stimulable phosphor layer is less likely to be damaged by pressure or other factors during use, and is therefore easy to handle.

(Structure of the Invention) The above object is to have light resistance as a binder for a photostimulable phosphor in a radiation image conversion panel, and to provide any flexible material intermediate between e.g. nitrocellulose, cellulose acetate and polyurethane resin. This is achieved by using a range of polyvinyl formal resins having properties.

The radiation image conversion panel of the present invention has a support and a stimulable phosphor layer formed by dispersing a stimulable phosphor in a binder. The conversion panel is characterized in that the binder contains a polyvinyl formal resin represented by the following general formula.

During the general ceremony! , y and J are 0.50≦χ/Cz+y+,>)
≦0.80.0.05≦ν/(χ+2+7)≦0.45
, okuJ/(2+1ν1))≦0.30 and 100≦z
+y−10, , )≦3000.

The present invention will be explained in detail below.

The polyvinyl formal resin which is the binder used in the stimulable phosphor layer of the radiation image conversion panel of the present invention is represented by the above general formula.

Polyvinyl formal resin is generally synthesized by reacting formaldehyde with polyvinyl alcohol obtained by saponifying polyvinyl acetate, so it becomes a copolymer of vinyl formal, vinyl alcohol, and vinyl acetate monomer components. Its properties change significantly depending on the proportion of its components. That is, when increasing the vinyl formal component, the solubility in ordinary solvents,
Water resistance and heat softening properties are improved, and when the vinyl alcohol component is increased, solubility in common solvents and water resistance are improved, but adhesive strength and light resistance are reduced. Therefore, when polyvinyl formal resin is used as a binder for the stimulable phosphor layer of a radiation image conversion panel, the ratio of the above three components is extremely important, and this ratio determines the performance of the stimulable phosphor layer. Varies significantly.

Since the properties of the stimulable phosphor layer vary depending on the ratio of the three components, the polyvinyl formal resin used in the present invention has a copolymerization ratio of each monomer within the range shown below. By selecting from the above, the durability and light resistance can be improved. That is, in the above general formula, the ratio of the vinyl formal component is determined to be 0.50≦-/C-10v10)≦0.80. This is because the proportion of vinyl formal components decreases and χ/
(χ12+7) < 0.50, the proportion of vinyl alcohol component or vinyl acetate component increases as a result, and when the proportion of vinyl alcohol component increases, the hydrophilicity of the polyvinyl formal resin of these copolymers decreases. increases, and when it is used as a binder for the above-mentioned stimulable phosphor layer, its water resistance is significantly reduced. Therefore, the stimulable phosphor layer containing the binder will not swell under high humidity. This is undesirable because it reduces the adhesion to the support and makes it more likely to be scratched, and also because the solubility of this polyvinyl formal resin in organic solvents decreases, causing the resin solution to have photostimulability. This is because it is difficult to prepare a dispersion liquid with good coating properties in which a phosphor is dispersed, and therefore a stimulable phosphor layer cannot be coated on a support. On the other hand, when the proportion of vinyl acetate component increases, the adhesive strength or light resistance of polyvinyl formal [fat] decreases significantly, and when it is used as a binder for the above-mentioned stimulable phosphor layer, its durability against bending decreases. This is because the light resistance to photostimulation excitation light and erasure light decreases. Furthermore, the proportion of vinyl formal component increases, and χ/(21+y+i)>080
This is because the synthesis yield of the polyvinyl formal resin becomes poor, which is disadvantageous in terms of the binder for the stimulable phosphor layer and the shite industry.

In addition, the proportion of vinyl alcohol component is 0.05≦n/(χ
10v1)) ≦0.45. This is because the proportion of vinyl alcohol component increases, y/(χ+2+,)))0
．． If it is 45, the hydrophilicity of the polyvinyl formal resin will increase as mentioned above, which is not preferable, and the proportion of the vinyl alcohol component will decrease, and if it is 0.05, the synthesis yield of the polyvinyl formal resin will be poor. This is because it is industrially disadvantageous as a binder for a stimulable phosphor layer.

Further, the ratio of the vinyl acetate component is determined to be O<i/(20v1J)≦0.30. This is because the proportion of vinyl acetate component increases and J,/(z+y+,))>0.3
This is because if it is 0, as mentioned above, the adhesive strength and light resistance of the polyvinyl formal resin will decrease, which is not preferable.

The object of the present invention can be achieved by using a polyvinyl formal resin in which the ratio of each component is selected from the above range as a binder for the photostimulable phosphor layer, but the binder for the photostimulable phosphor layer Considering the dispersibility into the resin, the ease of coating the stimulable phosphor layer, etc., it is more preferable to select the polyvinyl formal resin from the following range. That is, the proportions of vinyl formal component, vinyl alcohol component, and vinyl acetate component are each 0.60≦χ/(
χ+y 10 times)≦079.0.10≦y/(χ++7)
It is more preferable that ≦0.35 and 0〈/(χ10ν1))≦0.25.

Furthermore, if the photostimulable phosphor is easily deteriorated by moisture, it is necessary to reduce the moisture permeability of the above-mentioned photostimulable phosphor layer, and for this purpose, the above-mentioned polyvinyl formal resin should be selected from the range shown below. It is even more preferable to do so. That is, the proportions of vinyl formal component, vinyl alcohol component, and vinyl acetate component are each 0.65≦χ
/(χ1ν1J)≦0.79.0. lO≦y/(210ν+, ))≦0.30 and 0.05≦7/(2+l+7
)≦0.20 is even more preferable.

Polyvinyl formal 411k used in the present invention has a degree of polymerization (χ+y+i) of 1 in addition to the above-mentioned matters.
00 to 3000 is used, but the above polymerization degree is 1jSO to 3000 from the viewpoint of the bending strength or the softening point of the resin representing its flexibility when used as a binder for the stimulable phosphor layer. 2000 is more preferable.

The binder used in the stimulable phosphor layer of the radiation image conversion panel of the present invention may be only a polyvinyl formal resin, but it may also be combined with one or more other resins that are highly compatible with the polyvinyl formal resin. They may be used in combination. Examples of such resins include phenolic resins, melamine resins, epoxy resins, maleic acid resins, alkyd resins, ester gums, sulfonamide resins, and nitrocellulose. These resins and the polyvinyl formal resin used in the present invention can form a photostimulable phosphor layer by mixing the respective resin solutions and coating and drying the mixed solution. By changing the mixing ratio of these, the physical properties such as flexibility when used in the photostimulable phosphor layer can be changed, and the physical properties that are best for the photostimulable phosphor layer can be changed. can be adjusted so that they are complementary. Particularly preferable physical properties of the stimulable phosphor layer of such a radiation image conversion panel include a ratio of 4:6 (weight ratio) of the polyvinyl formal resin used in the present invention to the other resins mentioned above. ) In particular, those using a large amount of polyvinyl formal resin in a ratio of 6:4 or more can be mentioned.

To manufacture the radiation image conversion panel of the present invention, first, a photostimulable phosphor described below is dispersed in a suitable organic solvent to prepare a dispersion of the photostimulable phosphor. Examples of organic solvents for this purpose include alcohols such as methanol, ethanol, and n-propanol; chlorinated hydrocarbons such as methylene chloride and ethylene chloride; ketones such as acetone and methyl ethyl ketone; and methyl acetate, ethyl acetate, and butyl acetate. Examples include, but are not limited to, esters, dioxane, ethers such as ethylene glycol, monoethyl ether, ethyl glycol monomethyl ether, and mixtures thereof.

Next, a polyvinyl formal resin solution prepared in advance is added to the above-mentioned stimulable phosphor dispersion liquid, and a coating liquid is prepared by dispersing and mixing using a ball mill, impeller mill, roll mill, glass beads, or ultrasonic dispersion machine. . As the solvent for dissolving the polyvinyl formal resin, methanol,
Examples include, but are not limited to, alcohols such as ethanol, benzyl alcohol, and n-propanol, ketones such as acetone and methyl ethyl ketone, ethers such as dioxane, ethylene glycol monoethyl ether, and ethylene glycol monomethyl ether, and mixtures thereof. isn't it. In addition, when using polyvinyl formal resin and other resin together, prepare the other resin solution and add this together with the polyvinyl formal resin solution.
It may be added to the above dispersion and operated in the same manner as above.

The mixing ratio of the resin and the photostimulable phosphor in the coating solution varies depending on the characteristics required depending on the intended use of the radiation image conversion panel, the type of the photostimulable phosphor, etc., but is generally 1:
Selected from the range of 1 to 1:30 (weight ratio), 1:
A range of 0.5 to 1:20 (weight ratio) is more preferable.A dispersant may be added to the above coating liquid for the purpose of improving the dispersibility of the photostimulable phosphor particles.

Such dispersants include phthalic acid, stearic acid,
Caproic acid, lipophilic surfactants, etc. are used. Also,
When the coating liquid is applied and dried to form a photostimulable phosphor layer, a plasticizer is added to the coating liquid in order to improve the binding force between the binder made of resin and the photostimulable phosphor particles. may be added. Such plasticizers include phosphate esters such as triphenyl phosphate and diphenyl phosphate;
Glycolic acid esters such as diethyl phthalate, ethyl phthalyl ethyl glycolate, and butylphthalyl butyl glycolate are used.

Furthermore, in order to improve the sharpness of the image formed on the radiation image conversion panel, for example, Japanese Patent Laid-Open No. 55-146447
White powder may be dispersed in the stimulable phosphor layer as described in JP-A-55-16.
As described in No. 3500, a coloring agent that absorbs photostimulable excitation light is dispersed in the photostimulable phosphor layer to enhance the sharpness of the image, It may be appropriately colored in order to absorb photostimulation excitation light. Examples of such colorants include Cyanine Blue NR8 (manufactured by Toyo Ink), Lionol Blue SL (manufactured by Yoyo Ink), and Sumia Acrylic Blue F-GSL (manufactured by Sumitomo Chemical).

In order to form a photostimulable phosphor layer using the above coating liquid, apply this coating liquid to the support using a doctor blade, a roll coater,
It is applied uniformly using a knife coater and dried by an appropriate means to form a coating film. The above supports include general paper, baryta paper, resin coated paper, pigment paper containing pigments such as titanium dioxide, processed paper such as paper sized with polyvinyl alcohol, etc., polyester such as polyethylene, polypropylene, and polyethylene terephthalate. Alternatively, a sheet made of other polymeric materials, a metal sheet such as an aluminum plate, an iron plate, a copper plate, etc. can be used. Note that a subbing layer of gelatin may be provided in advance on the surface of the support to which the coating liquid is applied. In addition, in order to improve the sharpness of the image of the radiation image conversion panel,
The support or the subbing layer may be colored as disclosed in No. 5-163500. Furthermore, in order to improve the sharpness and sensitivity of this radiation image conversion panel, a light reflecting layer is provided between the support and the stimulable phosphor layer as disclosed in JP-A-56-11393. You can also do it.

The thickness of the stimulable phosphor layer formed by coating and drying the above coating solution depends on the characteristics of the radiation image conversion panel, the type of stimulable phosphor, the binder and the stimulable phosphor layer. It varies depending on the mixing ratio of the light source, etc., but generally it is 10μm to 100μm.
0 μm is suitable, preferably 80 μm to 600 μm.
It is μm.

The photostimulable phosphor layer formed as described above can be used as is, but generally a protective layer is provided on the surface of the photostimulable phosphor layer (the surface opposite to the support side). The fluorescent phosphor layer is physically and chemically protected. This protective layer contains cellulose derivatives such as cellulose acetate and nitrocellulose,
Polymethyl methacrylate, polyvinyl butyral, polyvinyl formal, polycarbonate, vinyl acetate,
Examples include those obtained by dissolving a resin such as vinyl chloride-vinyl acetate copolymer or polyester in a suitable solvent, coating the solution on the above-mentioned stimulable phosphor layer, and drying it. Further, a thin film of polyethylene terephthalate, polyester, polyvinyl butyral, polyvinyl formal, polyethylene, vinylidene chloride, nylon, or the like may be adhered to the surface of the stimulable phosphor layer with a suitable adhesive. The thickness of the protective layer is 2-40
The thickness is preferably about μm. Furthermore, the protective layer is preferably one that is less susceptible to deterioration due to stimulation excitation light and erasure light, similar to the binder used in the photostimulable phosphor layer, and from this point of view, polymethyl methacrylate, polyvinyl butyral, polyvinyl Particularly preferred are formal, polyester, nylon, polyethylene, polyethylene terephthalate, and the like.

Here, the photostimulable phosphor used in the present invention will be described in detail. This photostimulable phosphor is a phosphor that emits photostimulable light when it is irradiated with radiation and then irradiated with photostimulation excitation light, as described above, but from a practical point of view it is preferable that
Examples of such photostimulable phosphors include BaSO, which is described in JP-A-48-80487.
4: Fluorescent substance represented by Ax (provided that it is at least one of Dlr, Tb and Tm, and 0.001≦χ and 1 mol%), described in JP-A-48-80488 MgSO4: A phosphor represented by Ax (where A, Ho, or Dy, and 0.001≦χ≦1), SrSO4 described in JP-A-48-80489: Ag (However, AkeDV, T
At least one of b and 'rm, and χ is 0.0
01≦χ<1 mol%. ), NaSO4+ described in JP-A No. 51-29889
(: Mn*DV and T in a804 and BaSO4 etc.
Fluorescent substance doped with at least 111 of b, JP-A-5
Boo, LiF described in No. 2-30487.
, MgSO4 and CaF! Liff1840 described in Japanese Patent Application Laid-Open No. 53-39277
y: Fluorescent material such as Cu, Ag, etc., JP-A-54-4788
LitOt・(BdOlh)x described in No. 3:
Cu (however, χ is 2<χ≦3), and L120' (Bt
Ot) *: Cu, Ag (However, 1 is 2〈χ≦3)
SrS: Co 18 m s 8 r8 : E, as described in U.S. Pat. No. 3,859.527.
u + Sm s La2O2S: Eu @ Sm
and (Zn + Cd) S : Mn * X (
(where X is halogen).

In addition, Zn described in JP-A No. 55-12142
8: Cu, PJ phosphor, general formula is BaO*z
k120H: barium aluminate phosphor represented by gu (however, 0.8≦2≦10), and the general formula is MIO
-χ810. : A (However, Mll is Mg+Ca, S
r, Zn, Cd or Ba, and A is Ce.

Tb + Eu + Tm * Pb r Tl,
At least one of Bi and Mn, χ is 0.5
≦χ≦2.5. ) are alkaline earth metal silicate-based phosphors. In addition, the general formula is (Bal-z-yMgxc) FX: 4E-+(
However, X is at least one of Br and CI, and χ
, y, and number are numbers that satisfy the following conditions, respectively: 0<χ+y≦0.6, χy〆0, and 10≦L≦5×10. )
The general formula of the alkaline earth fluorohalide phosphor described in JP-A-55-12144 is LnOX: 26A (where Ln represents at least one of La, Y, Gd and Lu, and is CI and/or Br, AHC* and/or T
b is a phosphor, χ is 0 (K (representing a number satisfying 0, 1) ) FX: >k (however, y
ll is Mg + at least one of C1, S, r, Zn and Cd, X is at least one of CI r Br and ■, A is Eu + Tbr Ca
*Tm + DV *Pr + Ho, Nd
, Yb and Er, 2 and y
represents a number satisfying the conditions 0≦χ≦0,6 and 0≦y≦0.2. ), Japanese Patent Application Laid-Open No. 55-84
The general formula described in No. 389 is BaFX: zc
e, yA (However, X is at least one of CA' + Br and I, A is In, TV.

At least one of the backs of Gd, Sm and Zr, and χ and y are 0<z≦2×10 and O<y≦5, respectively.
×10. ), Japanese Patent Application Laid-open No. 1983-
The general formula described in No. 160078 is M”FX-g
A: yLn (However, 1 digit Mg, CaBr, Zn and Cd
At least l'P1, A is Boo + MgO
, CaO+ SrO+BaO, ZnOI Al2O@@
YIO @ w La, o, l I ntos I S
102.

Tl0I, Zr01ρso, , 5nO1+ N
btOs * At least 41 species of TatOs and The, Ln is Eu, Tb.

Co, Tm, Dy + Pr 1) TO, Nd, Yb
, Er +8m and Gd, and χ and y are 5×10≦χ≦0.5 and O<
This is a number that satisfies the condition y≦0.2. ) rare earth element-activated divalent metal fluoro-ride phosphor, whose general formula is ZnS:A%Cd8:A, (Zn,C
d) 8:A, ZnEl:A, X and Cd5eA,
X (However, A is Cu, Ag, Au.

or Mn, and X is halogen. ), the general formula CI) described in JP-A No. 57-148285, the general formula (I) "Ms (PO4)t -NXx:
>A general formula (TI) MS (pa41: yh (where M and N are respectively Mg + Ca + Sr *
B' At least one of tZn and Cd,
, CJ! '.

At least one of Br and I, A is Eu, Tb
.

Ce +Tm ID)r +Pr,)(e,Nd
, Yb, Er, sb, TllMn and Sn. Also, 2 and yokeQ (Z≦
This is a number that satisfies the condition 6.0≦y≦1. ), and the general formula [IIT) or [IV] general formula [river] nReX@ ・? FLAX4: zE
u general formula (:lV)? LR@XS ・mAX'2:
zEu + 7Sm (in the formula, Rake L * r Gd
r Y + at least one of Lu, A is an alkaline earth metal, at least one of Ba, Sr, and Ca; X and X' are at least one of F, C1, and Br;
Represents a species. Moreover, 2 and y are I X 1o-'<
2 < 3 X 10", I X to-'< y <
It is a number that satisfies the condition that I
Examples include a phosphor that satisfies the condition 7X10<n7m.

As described above, a radiation image conversion panel having a stimulable phosphor layer in which the stimulable phosphor is dispersed in a binder made of the resin on the support is completed, and these panels are stored together. be done. When using this, first the photographing device is attached to the frame. Next, for example, a human body is used as a subject, and radiation such as X-rays is irradiated onto the subject, and the transmitted light is irradiated onto the radiation image conversion panel. As a result, a latent image is formed on the stimulable phosphor layer by absorbing the X-rays in proportion to the intensity of the X-rays corresponding to the X-ray transmittance of each part of the subject, and the latent image is recorded. Next, when this recorded latent image is read out, the radiation image conversion panel on which the image has been recorded is sent to a reading device by, for example, a roller conveyor or a cassette equipped with the panel, where the photostimulable excitation light is converted into photostimulable fluorescence. The body layer is irradiated with the radiation, whereby the absorbed radiation energy is emitted and fluorescence is generated based on this, and this optical signal is photoelectrically converted and converted into a visible image by appropriate means. This used item is reused. At that time, since there is an afterimage on the stimulable phosphor layer, in order to erase this, an erasing light stronger than the above-mentioned stimulable excitation light is applied to the stimulable phosphor layer immediately after using the radiation image conversion panel or just before reusing it. Irradiates the light body layer.

In this manner, each time the radiation image conversion panel is used, the imaging device is set in the frame, and the panel is automatically sent to the reading device and irradiated with excitation light and erasure light. At this time, the support of the radiation image conversion panel is made of a flexible material and may be bent during handling, but since the binder contains polyvinyl formal resin with appropriate flexibility, There are no mechanical cracks in the stimulable phosphor layer, no partial peeling, and no damage to the stimulable phosphor layer. In addition, since polyvinyl formal resin has light resistance, it is less likely to be deteriorated by either or both of the above-mentioned photostimulation excitation light and erasing light. There is no absorption of the generated stimulated fluorescence, so the readout sensitivity of the latent image is not reduced, and cracks are less likely to occur due to curing of the resin. There is a flexibility measurement value based on the test method described below that indicates the occurrence of mechanical cracks, partial peeling, or susceptibility to scratches, and according to this, it is found that the radiographic image of the present invention indicates the flexibility of the panel. The flexibility is 0.29 to 0.50/g, which is far superior to the conventional nitrocellulose or cellulose acetate, which is 0.11 to 0.25, respectively, as a binder. In this way, it is possible to have the optimum characteristic values for the above requirements, but by changing χ and J in the above general formula, it is possible to obtain a material that is hard to scratch but weak in bending and adheres to the support. This is because it is possible to provide an arbitrary flexibility between nitrocellulose and cellulose acetate, which are not good, and polyurethane resin, which has sufficient flexibility against bending but is easily damaged. Also,
Regarding light resistance, when using the test method described below, the sensitivity ratio of the radiation image conversion channel of the present invention was 96 to 92%, and compared with conventional polyester-urethane-cellulose acetate or polyurethane resin as a binder. 80 or 65, respectively, and exhibits far better characteristics than these conventional products, in which not only the deterioration of the resin but also the occurrence of cracks due to the hardening of the resin are inevitable.

Next, the present invention will be explained in detail.

Example 1 Divalent europium-activated odorized barium fluoride stimulable phosphor (
A photostimulable phosphor dispersion liquid was prepared by dispersing 300 parts by weight of BaFBr2Eu'') in parts by weight of cyclohexanone.
)=O175, y/Cz+y+, ))=0.15 and )/(K+7)=0.10 polyvinyl formal resin loading part is dissolved in cyclohexanone 130]ii part to prepare a polyvinyl formal resin solution. was prepared.

Next, the polyvinyl formal resin solution was added to the stimulable phosphor dispersion, and 2 parts by weight of tricresyl phosphate was added as a plasticizer, and the mixture was sufficiently dispersed and mixed using an ultrasonic dispersion machine to obtain a coating liquid. .

Composition of coating solution aFBr: Eu" 300 parts by weight Polyvinyl formal resin 30 parts by weight Tricresyl phosphate 2 parts by weight Cyclohexanone 180 parts by weight This coating solution was held horizontally on a 250 μm thick polyethylene terephthalate plate using a doctor blade. The coating was applied uniformly. After coating, the coating was air-dried for a day and night, and then dried in a drying box by gradually increasing the temperature from room temperature to 100"ct. In this way, a stimulable phosphor layer with a thickness of 300 μm+7') was formed on the polyethylene terephthalate support.

Next, polymethylmethac IJ was applied to the surface of the photostimulable phosphor layer.
A solution obtained by dissolving 170 parts by weight of L/-to-I in 170 parts by weight of total was applied, and this was dried in a drying box by gradually increasing the temperature from room temperature to 100°C.
A protective layer with a thickness of m was formed.

Radiographic image conversion panel test piece A thus obtained
The flexibility measurement, cracking test, and photostimulable phosphor layer peeling test described below were carried out using the same, as well as the light resistance test against one or both of photostimulation excitation light and erasure light. The results are shown in Table 1.

In addition, in order to check the light resistance (yellowing due to deterioration of the binder) of the radiation image conversion panel, the spectral reflectance of the photostimulable phosphor layer was measured over time, and the results are shown in the figure (curve A ).

Example 2 The polyvinyl formal resin of Example 1 was replaced with an average polymerization degree of 750. z/(z+1+))=0.61.7/
(z+y+i) = 0.32,)/(z+y+,
)) = 0.07 A radiation image conversion panel test piece B of this example was obtained in the same manner as in Example 1, except that a polyvinyl formal resin of 0.07 was used.

The same measurements and tests as in Example 1 were performed using this radiation image conversion panel test piece B. The results are shown in Table 1 and the figure (curve B).

Example 3 Instead of the polyvinyl formal resin of Example 1, the average degree of polymerization was 750, -/(thin+2+Jn=0.69, y/(x
+y+i) = 0.09, J/(z+y+i)
A radiographic image conversion/reflection test piece Ct of this example was obtained in the same manner as in Example 1, except that 6 parts by weight of a polyvinyl formal resin (U = 0.22) and 6 parts by weight of a phenol resin (Priauchen 5010) were used.

The same measurements and tests as in Example 1 were performed using this radiation image conversion panel test piece C. The results are shown in Table 1 and the figure (curve C).

Comparative examples to be compared with the radiographic image conversion panel test pieces of these Examples were prepared as follows, and the same measurements and tests as above were conducted. The results are shown in Table 1 and Figure (curve p-s
).

Comparative Example 1 This was carried out in the same manner as in Example 1, except that instead of the polyvinyl formal resin in Example 1, a polyurethane resin (N-3022 manufactured by Nippon Polyurethane Co., Ltd.) was used after being dissolved in cyclohexanone (130 weight tons). A radiation image conversion panel test piece P of a comparative example was obtained.

Comparative Example 2 As a substitute for the polyvinyl formal resin of Example 1, nitrocellulose (9) with an average degree of polymerization of 250 and a degree of nitrification of 10% was dissolved in a mixed solvent of 80 parts by weight of methyl ethyl ketone and 1 part by weight of ethyl acetate. A radiographic image conversion panel test piece Q of this comparative example was obtained in the same manner as in Example 1 except that it was used.

Comparative Example 3 Methylene chloride soluble polyester-urethane resin weighted part with an average molecular weight of 7000 synthesized using a dihydroxy polyester at both ends consisting of adipic acid and ethylene glycol and tolylene diisocyanate instead of the polyvinyl formal resin of Example 1 10 parts by weight of cellulose acetate having a degree of acetylation of 64% and an average degree of polymerization of 280 were dissolved in a mixed solvent of 6 parts by weight of methylene chloride and 5 parts by weight of methanol. A radiation image conversion panel test piece R of this comparative example was obtained in the same manner as in Example 1, except that the cellulose acetate solution was mixed with the cellulose acetate solution.

Comparative Example 4 In place of the polyvinyl formal resin of Example 1, cellulose acetate with an average degree of polymerization of 260 and a degree of acetylation of 60% was used after being dissolved in a mixed solvent of 110 parts by weight of chloride and a weighted part of methanol. In the same manner as in Example 1, this Comparative Example of Radiation Image Conversion Honeyluer -F't38-1 Judging from the results of the flexibility measurement and the peeling test of the photostimulable phosphor layer shown in the table above, Examples 1- The radiation image conversion panel test pieces A-C of No. 3 have higher durability against bending than the radiation image conversion panel test pieces P, Q, and S of comparative examples because they do not develop cracks or peel off due to bending. The risk of cracks etc. occurring due to bending can be reduced. On the other hand, in all of the comparative examples, the stimulable phosphor layer was likely to peel off, and in the test specimens Q and S, cracks also occurred in the stimulable phosphor layer. Here, since the test piece P is more flexible than that of this example, when the radiation image conversion panel is conveyed by rollers in the reading device, the panel is locally pressed, so that the stimulable phosphor layer easily scratched. In addition, the results of the light resistance test showed that test pieces A-C of Examples 1 to 3 had lower sensitivity to the main stimulation excitation light, 10,000 yen of erasure light, or both than test pieces P, Q, and S of comparative examples. It has almost no color and has excellent light resistance. This is even clearer than the figure. That is, test pieces A to C of Examples 1 to 3 show almost no decrease in reflectance to 390 μm 1 liter) light, whereas test piece P-8 of the comparative example shows a large decrease in reflectance.

This is the result of yellowing of the binder resin due to deterioration, and absorption of fluorescence and photostimulation excitation light generated by the photostimulable phosphor. Especially test piece Q of a radiation image conversion panel using nitrocellulose or cellulose acetate as a binder.
Since the deterioration of the S-resin is significant, it is almost impossible to use it practically.

In addition, test pieces A to C of Examples 1 to 3 were exposed to photostimulated excitation light,
Since the deterioration of the binder due to erasing light is small, there is no difference in the crack test results before and after the light resistance test, whereas the comparative example test piece Q-8 has a difference in the crack test results before and after the light resistance test. A large difference was observed, and this is understood to be because the binder deteriorated due to the light, and the resin of the binder hardened, reducing its flexibility and becoming brittle. In particular, nitrocellulose and cellulose acetate are susceptible to cracking and cannot be put to practical use.

Example 4 Instead of the polyvinyl formal resin of Example 1, the average degree of polymerization was 800, "/CZ+y+2) -0,56, y/C
:a+y+,>)=0.40,i/(z+y-+1)=
A radiation image conversion panel test piece of this example was obtained in the same manner as in Example 1 except that 4 0.04% polyvinyl formal resin was used. This radiation image conversion tunnel test piece and radiation image conversion panels A and B obtained in Example 1.2
A water resistance test was conducted using That is, the above panel pieces A, B, and D were heated at a constant temperature of 50° C. and a relative humidity of 95%.
Changes in appearance, peel test and sensitivity measurement results were investigated before and after storage for several days. The results are shown in Table 2.

Comparative Example 5 In place of the polyvinyl formal resin of Example 1, the average degree of polymerization was 800, ”/('+1,)) = 0.45
,y/(z+y+,L)=0.50,)/(x+=+,
)) A radiation image conversion panel test piece T of this comparative example was obtained in the same manner as in Example 1 except that the polyvinyl formal resin loading part of = 0.05 was dissolved in 130 parts by weight of m-cresol. Ta. Using this panel test piece T, changes in appearance before and after the water resistance test and changes in the results of the sensitivity measurement were examined in the same manner as in Example 4. The results are shown in Table 2.

2. Surface Weight From the results of the appearance inspection in Table 2, panel test piece A of this example
, B and D showed no change in appearance even after being left under high temperature and high humidity for a long time, whereas in panel test piece T of the comparative example, swelling of the stimulable phosphor layer was observed. This seems to be due to the vinyl alcohol component in the polyvinyl formal resin as the binder. When the stimulable phosphor layer swells in this way, it becomes excessively flexible, so as explained above, when installing the radiation image conversion panel, it is easily damaged by local external pressure when setting it in the frame. Become. In addition, for panel test pieces A, B, and D of this example, there was no difference in the peel test results before and after the water resistance test, and there was no peeling at all in either case, but in the peel test of panel test piece T of the comparative example, after the water resistance test. The degree of peeling was increased compared to the previous one. This is because the swelling of the photostimulable phosphor layer deteriorates the adhesiveness between the support and the photostimulable phosphor layer, and this makes it almost impossible to use it practically. The swelling of the stimulable phosphor layer is also thought to be due to the presence of a large amount of vinyl alcohol in the binder resin.

In addition, panel test pieces A, B, and D of the examples of the present invention had no significant difference in sensitivity measurement results before and after the water resistance test, and no significant decrease in sensitivity was observed, but panel test pieces T of the comparative example
A significant decrease in sensitivity was observed before and after the water resistance test. This is because the photostimulable phosphor layer of the panel test piece of the comparative example has high moisture permeability, so that the photostimulable phosphor deteriorates due to moisture, and this makes it almost impossible to use it practically. The reason for the low moisture permeability of this stimulable phosphor layer is thought to be the result of the binder resin containing a large amount of vinyl alcohol component.
Ru.

In addition, from the sensitivity measurement results before and after the water resistance test, among the panel test pieces A, B, and D of the example, A was particularly excellent, followed by B.

Example 5 Instead of the polyvinyl formal resin of Example 1, the average degree of polymerization was 950, χ/(χ+7+i) = O, Z 3,
y/(z+y+))=0.15, z/(z+y+,))
A radiation image conversion panel test piece E of this example was obtained in the same manner as in Example 1, except that a polyvinyl formal resin of =0.12 was used.

Example 1 Using this radiation image conversion/tunnel test piece E
The same measurements and tests were conducted. The results are shown in Table 3.

Example 6 In place of the polyvinyl formal resin of Example 1, the average degree of polymerization was 1000, z/Cz+y+i) = o, 6. i
,y/(χ+ν+,>)=O,OC+,J/(χ+y+
A radiation image conversion panel test piece F of this example was obtained in the same manner as in Example 1 except that polyvinyl formal resin of 1) = o, 2r was used.

The same measurements and tests as in Example 1 were conducted using this radiation image conversion panel test piece F. The results are shown in Table 3.

Comparative Example 6 14 Instead of the polyvinyl formal resin of Example 1, the average degree of polymerization was 950, χ/(z-1-y+z) = 0.51
, 2/(z+y+,)) = O,t 5,)/(”
A radiographic image conversion channel test piece U of this comparative example was obtained in the same manner as in Example 1 except that a polyvinyl formal resin with +P+2)=0.34 was used.

The same measurements and tests as in Example 1 were performed using this panel test piece U. The results are shown in Table 3. Panel test pieces E of Examples 7 and 8 are shown in Table 3.

As with Examples 1 to 6 above, the durability against bending is high, and the risk of cracks etc. occurring due to bending can be reduced accordingly. On the other hand, the panel test piece U of Comparative Example 6 has low durability against bending and cracks occur in the stimulable phosphor layer when bent.

This is considered to be because the adhesive strength of the polyvinyl formal resin decreased due to an increase in the proportion of vinyl acetate component in the polyvinyl formal resin as a binder. Furthermore, from the results of the light resistance test, the panel test pieces E and F of Example 7゜8 showed almost no decrease in sensitivity to either or both of the photostimulation excitation light and the erasure light compared to the panel test piece U of the comparative example. , has excellent light resistance.

This is also considered to be due to an increase in the proportion of vinyl acetate component in the polyvinyl formal resin as a binder.

In addition, from the results on the sensitivity side after the light resistance test, among the panel test pieces E and F of the examples, E was particularly excellent in terms of light resistance.

The above measurement method and test method are as follows.

(1) Measurement of flexibility Fix one end of a radiographic imaging panel test piece with a width of 20 mm and a length of 50 mm horizontally with its photostimulable phosphor layer facing upwards. The amount of bending of the above panel piece was measured when the position of the panel was loaded with a tension gauge. The larger this value, the more flexible the panel is.

(2) Crack test A photostimulable phosphor was prepared by wrapping a 50-width radiograph mound suppression panel test piece around a glass tube with a diameter of 15 mm so that the photostimulable phosphor layer surface was facing outward. The number of cracks occurring in the layer was observed. Panel specimens with a large number of cracks have low flexibility and low durability against bending.

(3) Peeling test of phosphor layer The stimulable phosphor layer of a 60w square radiation image conversion panel test piece was cut with a knife at 5B intervals. Next, a 30× cellophane tape was adhered onto the photostimulable phosphor layer, and then the above panel test piece was fixed and the ends of the cellophane tape were strongly pulled to remove the cellophane tape from the photostimulable phosphor layer. Peeled off. The area of the stimulable phosphor layer peeled off from the support together with this cellophane tape was calculated, and this was divided by the area of the cellophane tape originally adhered to the test piece to determine the peeling rate (%).The peeling rate is high. This indicates that the adhesion of the stimulable phosphor layer to the support is low.

(4) Light resistance test against photostimulation excitation light and erasure light 150W
A radiation image conversion panel test piece was placed approximately 40 points from a halogen lamp (manufactured by Ushio Inc.), and the illumination intensity was 1.5.
This panel test piece was irradiated with light at X 10' Lux-see. Before irradiating this panel test piece with light and 6
The sensitivity of the panel test piece to X-rays after irradiation for 0 hours was measured, and the ratio of the sensitivity after light irradiation to the sensitivity before light irradiation was calculated. The higher this ratio is, the higher the light resistance of the panel to stimulated excitation light or erasure light is, and the more difficult it is for the binder to yellow due to decomposition. kOh, the sensitivity of the above panel test piece to x@ is 80 KVOX for this panel test piece.
After irradiating the beam at 10 mR, excitation is stimulated with Ar laser light,
This was done by measuring the intensity of the generated stimulated luminescence.

Furthermore, after irradiating the above panel test piece with either or both of stimulated excitation light and erasure light, a crack test similar to that in (2) above was conducted to examine the deterioration of flexibility.This result is the result of (2) above. If it is worse than that, it means that the binder has been degraded by one or both of the stimulated excitation light and the erasing light.

(Effects of the Invention) As explained above, according to the present invention, a polyvinyl formal resin is used as a binder for the stimulable phosphor layer of the radiation image conversion panel. Even when used repeatedly, its flexibility reduces cracking or peeling of the photostimulable phosphor layer from the support, and its excellent light resistance allows repeated use of this radiation image conversion panel to reduce photostimulable excitation light. Even when the erasing light is repeatedly irradiated, the sensitivity of reading the latent image of the stimulable phosphor layer is suppressed from decreasing.

[Brief explanation of drawings]

The figure shows a radiation image conversion panel test piece A according to an example of the present invention.
B, C and Comparative Example Radiographic Image Conversion Panel Test Pieces P, Q
, R, and S are graphs showing measurement results of spectral reflectance over time. Agent Yoshimi Kuwahara

Claims (2)

[Claims] (1) In a radiation image conversion channel having a stimulable phosphor layer formed by dispersing a stimulable phosphor in a binder on a support, the binder is represented by the following general formula: A radiation image conversion panel characterized by containing polyvinyl formal resin. General formula (where χ, ν and J are 0.50≦χ/c2B+y+,
i) <o, so, o, o5≦y/(z-1-y+z)≦
0145, minus J/(χ1F+J) S is an integer satisfying 0.30 and 100≦χ+2+7≦3000. (2) In the polyvinyl formal resin, in the general formula! , 7, and J are 0.60≦χ/(i+y+
, i)≦0.79.0, 10≦y/Cz+y+, >)≦
0.35.0〈)/(Z+)f+)n≦0.25 and 1
The radiation image conversion panel according to claim 1, wherein the panel is an integer satisfying 50≦z+2+)≦2000.