JP3369070B2 - Method for producing rare earth oxysulfide phosphor for X-ray intensifying screen - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth oxysulfide phosphor used in an X-ray intensifying screen, and more particularly to a method for producing a rare earth oxysulfide phosphor having excellent water resistance.

[0002]

2. Description of the Related Art X-ray intensifying screens are generally used in close contact with both sides of an X-ray film by increasing the absorption of X-rays in various radiographs such as medical radiographs and industrial radiographs.

Generally, an X-ray intensifying screen has a structure as shown in FIG. Support made of plastic, etc. (mounting paper)
1 and a reflective layer 2 and a phosphor layer 3 provided thereon (a layer coated with a coating liquid in which a phosphor is dispersed in an organic binder)
And a transparent protective layer 4 of about 10 μm that covers the phosphor layer 3.
Consists of. In X-ray photography, the X-ray film has an emulsion layer 5 coated on both sides with a thickness of about 20 to 30 μm.
And a pair of intensifying screens (a front intensifying screen and a back intensifying screen) so that the protective film of the X-ray intensifying screen is in contact with each other. For the purpose of improving the sharpness of the X-ray image, it is important that the X-ray film and the intensifying screen are in close contact with each other.

Further, the protective film is required to be transparent so as to prevent absorption and scattering of light emission, and
The thickness is preferably about 10 μm. However, as the thickness of the protective film becomes thinner, pinholes are more likely to form in the film, and if moisture penetrates into the protective film through the pinholes, the intensifying screen may deteriorate or the emulsion layer of the X-ray film may be affected. May have adverse effects. For example, in the case of intensifying screens for ortho films in which rare earth oxysulfide phosphors such as Gd2O2S: Tb and Y2O2S: Tb are used, if these are stored in a high humidity state, water flows in from the pinholes of the protective film, The minute amount of water causes the surface of the phosphor to be hydrolyzed to generate hydrogen sulfide gas.
This hydrogen sulfide gas reacts with silver halide, which is a component of the film emulsion, to produce black silver sulfide. This black silver sulfide lowers the brightness of the phosphor in that portion, which causes deterioration of the image quality of the X-ray image.

In order to improve the water resistance of the phosphor for X-ray intensifying screens, the present inventors have found that aluminum,
Attempts have been made to coat inorganic materials such as phosphates such as magnesium and strontium, borates, hydroxides and fluorides.
However, according to this method, the coating with the inorganic substance does not form a uniform film, but in reality, since the particulate inorganic substance adheres to the surface of the phosphor particle, the coating on the surface of the phosphor particle is heterogeneous. There are many gaps nearby. As a result, it was not possible to impart sufficient water resistance to a sufficient phosphor.

As a method for forming a continuous film on the surface of phosphor particles, we have added organosilicon and water to phosphor slurry suspended in alcohol in a heated state to hydrolyze, and silicon dioxide on the surface of phosphor particles. A method of forming a thin film has been disclosed. (JP-A-3-6289) According to this method, a uniform thin film of silicon dioxide is formed on the surface of the phosphor particles, and sufficient water resistance can be imparted to the phosphor. However, in this method, alcohol is used as a solvent for suspending the phosphor, and since organic silicon is expensive, the manufacturing cost is high and it is not suitable for mass production.

[0007]

Therefore, the present invention has been made in view of the above-mentioned circumstances, and an object thereof is to improve the water resistance of a rare earth oxysulfide phosphor used in an X-ray intensifying screen. Moreover, it is an object of the present invention to provide a manufacturing method which is economical and suitable for mass production.

[0008]

Means for Solving the Problems The present inventors have once formed a hydroxide film on the surface of a phosphor and then heat-treating the phosphor to form the hydroxide film into an oxide film, thereby forming a phosphor. It was found that a rare earth oxysulfide-based phosphor having a small amount of sulfur was obtained on the surface of particles, and hydrogen sulfide was not generated between sulfur on the surface of the phosphor even when water was applied, and the present invention was completed.

That is, in the method for producing a rare earth oxysulfide phosphor of the present invention, an oxysulfide of at least one element selected from the group consisting of yttrium, lanthanum, and gadolinium is used as a matrix, and terbium is used as an activator. In the method for producing a rare earth oxysulfide phosphor, a pulverized phosphor powder is brought into contact with an oxidizing agent in water to once form a hydroxide layer on the phosphor particle surface, and then 200 to 5
It is characterized by heating at a temperature in the range of 00 ° C.

The base of the oxysulfide phosphor used in the present invention is most preferably gadolinium oxysulfide (gadolinium oxysulfide).

The oxidizing agent used in the present invention is preferably hydrogen peroxide, and the amount thereof is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the phosphor.

In the present invention, the heating temperature in the heating step is 30.
It is preferably in the range of 0 to 400 ° C.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The phosphor matrix used in the present invention is an oxysulfide of at least one element selected from the group consisting of yttrium, lanthanum, and gadolinium, and has a general formula (Y, La, Gd). It is represented by 2O2S. In the present invention, terbium was selected as the activator (Y, La, Gd).
The 2O2S: Tb phosphor will be described, but the activator is not limited to terbium, and an oxysulfide phosphor to which another activator is added has the same effect.

The present invention is a method for treating a prepared phosphor powder, and the rare earth oxysulfide phosphor used in the present invention is obtained by a usual method including the steps of raw material mixing, firing and pulverization. Can be used, and the method for preparing the phosphor is not particularly limited.

<Suspension pH> First, the rare earth oxysulfide phosphor powder is suspended in a sufficient amount of pure water, and ammonia, caustic soda and the like are added to the suspension to adjust the suspension to be basic.
In order to bring the phosphor into contact with the oxidizing agent in water, the pH of the suspension is preferably in the range of 7-10. This is because when the pH is lower than this range, the oxidizing power of the oxidant decreases, and conversely, when the pH is higher than this range, the phosphor tends to agglomerate and the coating property on the intensifying screen deteriorates.

<Oxidizing agent> As the oxidizing agent, hydrogen peroxide, sodium persulfate, sodium hypochlorite, ozone water, chlorine water and the like can be used, but hydrogen peroxide or ozone water is particularly preferably used. be able to. The oxidation reaction of hydrogen peroxide or ozone water does not generate anything other than oxygen and water and does not remain as impurities, but other oxidizers leave metal or impurities such as halogen elements after the oxidation reaction. This is because it is necessary to sufficiently wash and remove this.

When hydrogen peroxide is used as the oxidizing agent, the pH of the suspension is most preferably in the range of 8-9.

<Amount of oxidizing agent added> The suspension is made basic and the oxidizing agent is added with stirring. When hydrogen peroxide is used as the oxidant, the amount of hydrogen peroxide added is 100
It is preferably prepared so as to be 0.1 to 10 parts by weight with respect to parts by weight. When hydrogen peroxide is used as an oxidant in the gadolinium oxysulfide phosphor, the relationship between the amount of the oxidant, water resistance (%), and screen brightness is plotted in FIG. The addition amount in FIG. 1 is the amount based on 100 parts by weight of the gadolinium oxysulfide phosphor.

According to FIG. 1, when hydrogen peroxide is not added,
Water resistance is 85%, but hydrogen peroxide concentration is 0.01
95 parts by weight, 100% if 0.1 parts by weight or more
Therefore, the effect of surface oxidation of hydrogen peroxide is maximized. Moreover, the screen brightness is about 97 when hydrogen peroxide is not added.
%, But is 100% in the range of 0.01 to 0.1 part by weight of hydrogen peroxide. However, addition of more than this lowers the screen brightness. this is,
This is because not only the surface of the phosphor particles but also the interior of the phosphor is oxidized by the oxidizing agent, and as a result, the emission brightness of the phosphor is reduced.

From the viewpoint of water resistance only, 0.01 to 10
Effective in a wide range of weight%, but actually X
Taking the screen brightness due to lines into consideration, the range of 0.03 to 0.3 parts by weight is more preferable, and the concentration of the oxidant is most preferably 0.1 part by weight.

<Relationship between heating temperature and water resistance> The surface-treated phosphor is solid-liquid separated and heated in a temperature range of 200 to 500 ° C. By this heating, the hydroxide on the phosphor surface is dehydrated to become an oxide, and the phosphor surface can be stabilized. The heating should be performed at a temperature lower than 500 ° C., since the oxysulfide of the phosphor matrix is partially decomposed at a temperature higher than 500 ° C. On the contrary, at 200 ° C. or lower, dehydration of the hydroxide does not occur and heating is meaningless. Therefore, the heating temperature is 300
The temperature range of ˜400 ° C. is more preferable.

FIG. 2 shows the case of heating the phosphor after the oxidant treatment,
The relationship between water resistance and heating temperature was plotted. In this case, the heating time was all 10 hours.

<Water Resistance Test Method> Water resistance was evaluated as follows. First, a part of the phosphor surface of an X-ray intensifying screen having a phosphor having a thickness of 200 μm is forced to absorb water, and the X-ray film is directly adhered in the cassette without providing a protective film. Leave for days. After that, the X-ray film is removed, and the screen brightness of the part that absorbs moisture and the screen brightness of the part that does not absorb water are measured, and the screen brightness of the part that absorbs moisture is measured with respect to the brightness of the part that does not absorb water. The relative value was defined as water resistance (%). Here, the screen brightness was determined as a relative emission brightness (%) using the phosphor of Example 1 as a brightness reference.

[0024]

The method for producing a phosphor of the present invention is mainly to oxidize the phosphor surface in a basic suspension to once form a hydroxide, and then dehydrate the hydroxide by heating at a high temperature. As a result, an oxide layer is formed on the phosphor surface. In this way, the sulfur on the surface of the phosphor particles is replaced with the oxide. In that respect, it becomes possible to prevent the generation of hydrogen sulfide due to sulfur on the surface of the phosphor particles. As a result, since the intensifying screen using the phosphor of the present invention does not generate hydrogen sulfide, there is no or less the problem of reacting with silver halide in the emulsion of the X-ray film to generate black silver sulfide. .

[0025]

【Example】

[Example 1] Pure water was added to 175 g of terbium-activated gadolinium oxysulfide phosphor powder, and the total length was 600 m.
l of phosphor suspension slurry is prepared. Ammonia water is added thereto to adjust the pH to 8, 0.050 ml of 35% hydrogen peroxide water is added, and the slurry is stirred for 1 hour. In this case, the addition ratio of the oxidizing agent to the phosphor is 0.01% by weight. The slurry is separated and dehydrated, and the phosphor cake
It was heated at 00 ° C. for 15 hours and passed through a sieve to obtain the phosphor of the present invention.

[Examples 2 to 4] Pure water was added to 200 g of terbium-activated gadolinium oxysulfide phosphor powder to prepare a phosphor suspension slurry of 600 ml in total.
Ammonia water is added to this to adjust the pH to 8, and 35%
Example 2 of the present invention was performed in the same manner as in Example 1 except that hydrogen peroxide water was added so that the concentration of hydrogen peroxide with respect to the phosphor was 0.1, 1.0, and 10% by weight, respectively. ~ 4 phosphors were obtained.

40 g of the phosphors of Examples 1 to 4 thus obtained and 5% nitrocellulose butyl acetate solution 10
g was thoroughly mixed to prepare a phosphor coating solution. The phosphor coating solution thus obtained was coated on a mount with a thickness of 200 μm using a doctor blade to prepare an intensifying screen. Examples 1 to 4
The water resistance and screen brightness of the phosphor of No. 1 were measured and the results are shown in Table 1.

[0028]

[Table 1]

Here, in Comparative Example 1, a conventional phosphor, which is not subjected to the steps of oxidizing agent treatment-separation-heating in the present invention, was applied to a mount in exactly the same manner as described above to prepare an intensifying screen. It is a thing.

As is clear from Table 1, according to the method of the present invention, the water resistance is improved and the screen brightness is also improved as compared with Comparative Example 1.

Although only the case of gadolinium oxysulfide is shown as an example, the phosphor matrix used in the present invention may be an oxysulfide of at least one element selected from the group consisting of yttrium, lanthanum and gadolinium. Shows the same effect. Although only terbium is shown as the activator, the use of other activators has the same effect on water resistance.

[0032]

As described above, according to the method for producing an oxysulfide phosphor of the present invention, the sulfur content on the particle surface of the phosphor is replaced by an oxide, so that the intensifying screen is stored in a high humidity state. However, hydrogen sulfide gas is not generated by the reaction between water and sulfur on the phosphor surface, and the problem of producing black silver sulfide by reacting with silver halide in the emulsion layer of the X-ray film is prevented. You can That is, the water resistance can be greatly improved. In addition, the screen brightness can be improved by several percent.

Further, even if the surface of the phosphor particles is uniformly coated with organic silicon, the water resistance can be improved, but expensive raw materials such as a solvent and organic silicon had to be used. On the other hand, in the method of the present invention, since the raw material used is inexpensive, the water resistance can be economically improved, and the method is suitable for mass production.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing the structure of an X-ray intensifying screen.

FIG. 2 is a characteristic diagram showing the relationship between the amount of oxidant added and water resistance and screen brightness.

FIG. 3 is a characteristic diagram showing the relationship between heating temperature and water resistance.

[Explanation of symbols]

1 ・ ・ ・ ・ ・ ・ Mount 2 .... Reflective layer 3 ・ ・ ・ ・ ・ ・ Phosphor layer 4 ... Protective layer 5 ・ ・ ・ ・ ・ ・ Emulsion layer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-53-39985 (JP, A) JP-A-6-201834 (JP, A) JP-A-4-59888 (JP, A) JP-A-4-59888 236294 (JP, A) JP 7-316551 (JP, A) JP 55-94986 (JP, A) JP 5-320637 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C09K 11/01-11/89 G21K 4/00

Claims (4)

(57) [Claims] 1. A method for producing a rare earth oxysulfide phosphor having an oxysulfide of at least one element selected from the group consisting of yttrium, lanthanum and gadolinium as a matrix and terbium as an activator By contacting the phosphor powder having been subjected to the treatment with an oxidizing agent in water, a hydroxide layer is once formed on the surface of the phosphor particles, and then 200 to
A method for producing a rare earth oxysulfide phosphor, which comprises heating at a temperature in the range of 500 ° C. 2. The X according to claim 1, wherein the matrix of the phosphor is gadolinium oxysulfide.
A method for producing a rare earth oxysulfide phosphor for a linear screen. 3. The X-ray intensifying screen according to claim 1, wherein the oxidizing agent is hydrogen peroxide, and the amount thereof is 0.01 to 10 parts by weight with respect to 100 parts by weight of the phosphor. For producing rare earth oxysulfide phosphors for use in automobiles. 4. The method for producing a rare earth oxysulfide-based phosphor for an X-ray intensifying screen according to claim 1, wherein the heating temperature is in the range of 300 to 400 ° C.