Transparent radiation-shielding composition, radiation shielding material, and method for manufacturing same

Abstract

The present disclosure provides an inexpensive radiation-shielding composition having superior transparency to visible light compared to conventional compositions. The present disclosure is directed to a transparent radiation-shielding composition comprising: a matrix comprising a polar solvent, a polar polymer, or a combination thereof; and ions of a metal compound ionized in the matrix. The metal compound is a water-soluble metal compound that can be ionized and dissolved as ions in the polar solvent, and the polar polymer is a water-soluble polymer that can be dissolved in the polar solvent.

Description

Transparent radiation-shielding composition, radiation-shielding material, and method for producing the same

[0001] The present invention relates to a transparent radiation-shielding composition, a radiation-shielding material, and a method for producing the same.

[0002] Radiation shielding is required in medical treatment, health checkups, X-ray equipment, nuclear facilities, etc. Lead has traditionally been used, but because it is opaque and harmful, composites of metal compound particles and resin have recently been widely used instead.

[0003] For the purpose of providing a transparent radiation shielding material against neutron rays, gamma rays, and X-rays, an epoxy resin molded product has been proposed, which is obtained by curing an epoxy resin composition containing nanoparticles of a metal element and / or a metal compound with an acid anhydride (Patent Document 1).

[0004] With the aim of providing a radiation protector for protecting the hippocampus from radiation exposure, a radiation protector has been proposed that includes a head shielding portion that blocks radiation entering through the head and a face shielding portion that blocks radiation entering through the face (Patent Document 2).

[0005] In order to provide a radiation shielding material having a high density and a refractive index that is kept within a range close to that of a transparent resin, ３ As described above, a radiation shielding material containing a solid solution of fluoride having a refractive index of 1.55 or less has been proposed (Patent Document 3).

[0006] With the aim of providing a lead-free radiation shielding material, a radiation shielding material has been proposed that includes a polymer component and a heavy metal component such as bismuth that is bound to the polymer component or embedded in the matrix of the polymer component (Patent Document 4).

[0007] JP 2022-037678 A JP 2012-225702 A JP 2018-179679 A JP 2019-138915 A

[0008] However, in the prior art including Patent Documents 1 to 4, it was necessary to prepare a radiation-shielding material using a dispersion of metal or metal compound particles having an average diameter of several μm to several tens of μm in a liquid or a solid such as a plastic, or to use nano-sized metal oxide particles smaller than the wavelength of visible light to make the X-ray shielding material transparent to visible light. However, dispersions of metal or metal compound particles have low transparency to visible light, and even when nano-sized particles are used, adding a large number of particles for use as a radiation-shielding material tends to cause aggregation, resulting in insufficient transparency to visible light. Furthermore, the use of nano-sized metal oxide particles requires costs such as raw material costs and costs for dispersibility control, making it difficult to achieve both radiation shielding and transparency to visible light at low cost. Therefore, there is a demand for an inexpensive radiation-shielding composition that has better transparency to visible light than conventional compositions.

[0009] The gist of the present invention is as follows: (1) A transparent radiation-shielding composition comprising: a host material containing a polar solvent, a polar polymer, or a combination thereof; and ions of a metal compound ionized in the host material, wherein the metal compound is a water-soluble metal compound that can be ionized in the polar solvent and dissolved as ions; and the polar polymer is a water-soluble polymer that can be dissolved in the polar solvent. (2) The radiation-shielding composition according to (1), wherein the polar solvent is water, glycerin, ethylene glycol, propylene glycol, methanol, ethanol, biomass ethanol, or a combination thereof. (3) The radiation-shielding composition according to (1) or (2), wherein the metal compound is barium acetate, barium bromide, barium chloride, barium hydroxide, barium nitrate, sodium tungstate, sodium polytungstate, potassium tungstate, bismuth acetate, bismuth bromide, sodium borate, sodium polyborate, or a combination thereof. (4) The radiation-shielding composition according to any one of (1) to (3) above, wherein the polar polymer is starch, polyacrylic acid, carrageenan, polyvinyl alcohol, polyvinylpyrrolidone, cellulose nanofiber, carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylamide, agarose, agar, water-dispersible rubber latex, or a combination thereof. (5) The radiation-shielding composition according to any one of (1) to (4) above, wherein the content of the metal compound is 3 to 50 mass% based on the total amount of the composition. (6) A radiation-shielding material comprising the radiation-shielding composition according to any one of (1) to (5) above. (7) The radiation-shielding material according to (6) above, which is a radiation-shielding curtain. (8) A method for producing a transparent radiation-shielding composition, comprising mixing a polar solvent and a water-soluble metal compound that is soluble in the polar solvent to form a first composition in which the water-soluble metal compound contains ions ionized in the polar solvent.(9) The method for producing a water-soluble metal compound according to (8), comprising: mixing the first composition with a polar polymer soluble in the polar solvent to dissolve the polar polymer in the polar solvent in the first composition, thereby forming a second composition in which the water-soluble metal compound contains ions ionized in a solution of the polar solvent and the polar polymer. (10) The method for producing a water-soluble metal compound according to (9), comprising removing at least a portion of the polar solvent from the second composition to form a third composition in which the water-soluble metal compound contains ions ionized in a solution of the polar solvent and the polar polymer or in the polar polymer.

[0010] According to the present invention, it is possible to provide an inexpensive radiation-shielding composition that has better transparency to visible light than conventional compositions.

[0011] FIG. 1 shows a photograph and a schematic diagram of an example of the first composition contained in a glass bottle. FIG. 2 shows a photograph and a schematic diagram of a conventional radiation-shielding material containing metal particles or metal compound particles contained in a glass bottle. FIG. 3 shows a photograph of an example of pellets of the present composition. FIG. 4 shows a photograph of the conventional radiation-shielding material. FIG. 5 shows a photograph of pellets of a composition containing no metal compound. FIG. 6 shows diffraction charts measured with a powder X-ray diffractometer for the present composition, the conventional radiation-shielding material shown in FIG. 4, and the raw powder (barium sulfate powder) of the metal compound contained in the conventional radiation-shielding material shown in FIG. 4. FIG. 7 is a schematic diagram illustrating a method for measuring the X-ray shielding rate when the present composition is a liquid, gel, or the like that cannot maintain a certain shape unless placed in a container. FIG. 8 is a schematic diagram illustrating a measurement method for determining the radiation-shielding rate of only the sample (measurement target). FIG. 9 is a schematic diagram illustrating a method for measuring the radiation-shielding rate when the present composition is a self-standing solid or the like. FIG. 10 is a graph of the X-ray shielding ratios of compositions prepared in Examples and Comparative Examples at tube voltages of 40 to 120 kV. FIG. 11 is a graph of the X-ray shielding ratios of compositions (pellets) prepared in Examples and Comparative Example 5 at tube voltages of 40 to 120 kV. FIG. 12 is a graph of the X-ray shielding ratios of liquid compositions prepared with a metal compound content of 1 mmol and using barium acetate, barium chloride, and barium bromide as the metal compound. FIG. 13 is a graph of the X-ray shielding ratios of liquid compositions prepared with a metal compound content of 2.5 mmol and using barium acetate, barium chloride, and barium bromide as the metal compound. FIG. 14 is a graph of the X-ray shielding ratios of liquid compositions prepared with a metal compound content of 5 mmol and using barium acetate, barium chloride, and barium bromide as the metal compound. FIG. 15 is a graph of the X-ray shielding ratios of compositions prepared in Examples. FIG. 16 is a graph of the visible light transmittance of pellets prepared in Examples and Comparative Examples in the visible light region. Fig. 17 is a photograph of the appearance of a conventionally used radiation protection glove, on which the X-ray shielding factor was measured. Fig. 18 is a photograph of the appearance of a composition (pellet) prepared in an example. Fig. 19 is a photograph of the appearance of a composition (pellet) containing no metal compound. Fig. 20 is a graph of the X-ray shielding factor of compositions (pellets) prepared in examples and comparative examples.FIG. 21 is a graph showing the visible light transmittance of the compositions (pellets) prepared in the examples and comparative examples.

[0012] The present disclosure relates to a transparent radiation-shielding composition (hereinafter also referred to as the present composition), which includes a host material including a polar solvent, a polar polymer, or a combination thereof, and ions of a metal compound ionized in the host material, wherein the metal compound is a water-soluble metal compound that can be ionized in the polar solvent and dissolved as ions, and the polar polymer is a water-soluble polymer that can be dissolved in the polar solvent.

[0013] The present inventors have discovered that when a polar solvent is mixed with a water-soluble metal compound (hereinafter also referred to as a metal compound) that is soluble in the polar solvent, the metal compound ionizes and dissolves in the polar solvent as ions, and a composition in which the metal compound ionizes and dissolves in the polar solvent as ions (hereinafter also referred to as a first composition or a two-component system) has high transparency to visible light and radiation-shielding properties. The first composition can be liquid. The viscosity of the first composition can be adjusted depending on the type of polar solvent and the content of the metal compound.

[0014] The present inventors have also discovered that a composition obtained by adding a polar polymer to the above-described first composition and dissolving the composition in a polar solvent (hereinafter also referred to as a second composition or a three-component system) has the same transparency to visible light and radiation shielding properties as the above. In the second composition, the metal compound exists as an ion in a mixture of a polar solvent and a polar polymer. The second composition can be a relatively high-viscosity liquid or gel. The state of the second composition can be liquid, gel, or solid. The state of the second composition can be adjusted depending on the type and content of the polar solvent and polar polymer, as well as the content of the metal compound.

[0015] The present inventors have further found that a composition obtained by removing at least a portion of the polar solvent from the second composition (hereinafter also referred to as a third composition or a three-component system) also has the same transparency to visible light and radiation-shielding properties as those described above. The third composition can be solid. The third composition is obtained by removing at least a portion of the polar solvent from the second composition, but may or may not contain residual polar solvent. The state of the third composition can be adjusted depending on the amount of residual polar solvent, the type of polar solvent and polar polymer, the content of polar polymer, and the content of metal compound. In the third composition, the metal compound exists as an ion in the polar polymer. By including a polar polymer in the composition, the viscosity or strength of the radiation-shielding material made of the composition can be changed, and the composition can be made transparent even when solid.

[0016] The composition can be the first composition, the second composition, the third composition, or a combination thereof described above.

[0017] In the present composition, the metal compound is ionized and exists as ions in a matrix containing a polar solvent, a polar polymer, or a combination thereof, and therefore does not block visible light. Furthermore, it has been found that, depending on the metal content of the metal compound contained in the present composition, radiation-shielding properties equivalent to those of conventional radiation-shielding materials containing metal particles or metal compound particles can be obtained.

[0018] Conventional radiation shielding materials containing metal components contain metal components as metal particles or metal compound particles, and even if these particles are reduced to nano-sized particles to block visible light, their transparency to visible light tends to decrease, and nano-sized particles tend to aggregate, which can affect transparency. In contrast, in the present composition, the metal compounds are ionized and contained as ions, so they have high transparency to visible light. Furthermore, in the present composition, the metal compounds exist as ions, so there is no need to use nano-sized metal compound particles to achieve transparency, which is advantageous in terms of cost and workability.

[0019] Transparency can be evaluated visually. FIG. 1 shows a photograph and a schematic diagram of the appearance of an example of the first composition contained in a glass bottle. FIG. 2 shows a photograph and a schematic diagram of the appearance of a radiation-shielding material containing conventional metal particles or metal compound particles contained in a glass bottle. As can be seen from FIGS. 1 and 2 , the conventional radiation-shielding material containing metal particles or metal compound particles is opaque because the metal particles or metal compound particles are dispersed in a solvent and not dissolved, whereas the first composition is transparent because the metal compound is ionized in the polar solvent and dissolved as ions. The second composition containing a polar polymer and the third composition not containing a polar solvent are also transparent.

[0020] FIG. 3 shows a photograph of an example of pellets of the second composition, which is in a gel state close to a solid and is made of 26% by mass of glycerin, 26% by mass of sodium polytungstate (SPT), and 47% by mass of starch. FIG. 4 shows a photograph of the appearance of pellets of a conventional radiation shielding material (47% by mass of polystyrene and 53% by mass of barium sulfate particles). FIG. 5 shows a photograph of the appearance of pellets of a composition containing no metal compound (36% by mass of glycerin and 64% by mass of starch). As can be seen from FIG. 4, the conventional radiation shielding material is opaque because the metal compound particles are dispersed in a non-polar solvent and not dissolved. However, as can be seen from FIG. 3, the second composition is transparent as the pellets of FIG. 5, which do not contain a metal compound, because the water-soluble metal compound is present as ions in a polar polymer.

[0021] Transparency can be evaluated by measuring visible light transmittance using an ultraviolet-visible spectrophotometer. The present composition can have excellent visible light transmittance in the visible light region of wavelengths from 400 to 800 nm. The third composition can have a higher visible light transmittance. The present composition exhibits a visible light transmittance of preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and even more preferably 80% or more. The visible light transmittance of ordinary glass is approximately 90%, while the visible light transmittance of conventional radiation-shielding materials containing metal particles or metal compounds is approximately 30%.

[0022] Whether a metal compound is ionized and exists as an ion in a matrix of a polar solvent, a polar polymer, or a combination thereof can be evaluated by powder X-ray diffraction. When a radiation shielding material containing conventional metal particles or metal compound particles is analyzed with a powder X-ray diffractometer, a diffraction chart having peaks reflecting the crystalline structure of the metal particles or metal compound particles is obtained. On the other hand, when the present composition, in which the metal compound is ionized and dissolved as ions in the matrix, is analyzed with a powder X-ray diffractometer, no peaks attributable to the metal compound are observed in the diffraction chart. Thus, although the ionized metal compound contained in the present composition does not appear as a peak in a powder X-ray diffraction chart, qualitative and quantitative analysis of the metal compound is possible by SEM-EDS (scanning electron microscope-energy dispersive X-ray spectroscopy).

[0023] FIG. 6 shows diffraction charts measured with a powder X-ray diffractometer for pellets of the gel-like second composition prepared by mixing 23 mass % of glycerin, 36 mass % of barium bromide, and 41 mass % of starch, pellets of the conventional radiation shielding material shown in FIG. 4, and raw material powder of the metal compound (barium sulfate powder) contained in the conventional radiation shielding material shown in FIG. 4.

[0024] In the X-ray diffraction chart measured for the conventional radiation shielding material, peaks reflecting the crystalline structure of barium sulfate are observed, which are the same as those in the diffraction chart measured for the raw material powder. Conventional radiation shielding materials are opaque because the metal compound particles (barium sulfate powder) exist as particles having a crystalline structure in polystyrene, and peaks reflecting the crystalline structure of the metal compound are observed. On the other hand, in the X-ray diffraction chart measured for the second composition, no peaks of the metal compound are observed. In the second composition, the metal compound (barium bromide) exists as ions in a solution of glycerin, a polar solvent, and starch, a polar polymer, and does not substantially have a crystalline structure, so no peaks reflecting the crystalline structure of the metal compound are observed in the diffraction chart. Similarly, no peaks reflecting the crystalline structure of the metal compound are observed in the diffraction charts for the first and third compositions.

[0025] When the metal compound is ionized and exists as ions in the base material, it becomes transparent, so the transparency may also be evaluated by the presence or absence of diffraction peaks in powder X-ray diffraction.

[0026] The present composition can have good radiation-shielding properties over a wide range of tube voltages. Since the photoelectric effect decreases as energy increases, the radiation-shielding effect of the present composition tends to decrease as the tube voltage increases. However, for example, a radiation-shielding material made of the present composition and having a thickness of 10 mm can exhibit an X-ray shielding rate of preferably 20% or more, more preferably 25% or more, even more preferably 30% or more, even more preferably 35% or more, and even more preferably 45% or more at an X-ray tube voltage of 120 kV, and an X-ray shielding rate of preferably 30% or more, more preferably 40% or more, even more preferably 50% or more, even more preferably 60% or more, and even more preferably 70% or more at an X-ray tube voltage of 40 kV. For example, a radiation-shielding material made of the present composition and having a thickness of 0.5 mm can exhibit an X-ray shielding rate of preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more at an X-ray tube voltage of 40 kV. For example, a radiation-shielding material having a thickness of 0.3 mm that is made of the composition of the present invention can exhibit an X-ray shielding rate of preferably 5% or more, more preferably 10% or more, even more preferably 15% or more, and still more preferably 20% or more at an X-ray tube voltage of 40 kV.

[0027] Figures 7 to 9 show the method for measuring the radiation shielding factor. Figure 7 is a schematic diagram showing the method for measuring the X-ray shielding factor when the present composition is a liquid, gel, or the like that cannot maintain a fixed shape unless placed in a container. A 4.5 mm thick lead plate 30 with a 15 mm diameter hole is placed on the detector. The present composition, which serves as sample 20 (measurement target), is placed in a glass container to a depth of 10 mm. The glass container containing the present composition is placed on the lead plate 30, and radiation is irradiated at a predetermined tube voltage from a radiation source 10, such as an X-ray source, 1000 mm away from the detector 40, and a first radiation intensity is measured with the detector 40. Additionally, as shown schematically in Figure 8, to determine the radiation shielding factor of the sample alone, an empty glass container alone is placed on the lead plate 30, and radiation is irradiated in the same manner as above, and a second radiation intensity is also measured with the detector 40.

[0028] The difference between the measured first radiation intensity and the second radiation intensity is added to the first radiation intensity to determine the radiation intensity that has passed through the sample, and the radiation transmittance can be measured using the following formula (1): Radiation transmittance (%)=(Radiation intensity that has passed through the sample) / (Radiation intensity directed toward the sample)×100 (1).

[0029] The radiation shielding rate can be calculated by the following formula (2): Radiation shielding rate (%)=100%−radiation transmittance (%) (2).

[0030] 9 is a schematic diagram showing a method for measuring the radiation shielding factor when the present composition is self-supporting as a high-viscosity gel, solid, etc. The present composition as a sample 20 (to be measured) is placed directly on a lead plate 30, and the radiation shielding factor can be measured in the same manner as above.

[0031] The radiation intensity when measuring the radiation shielding rate can be adjusted by the tube voltage. The tube voltage may be determined depending on the intensity of the radiation to be shielded using the present composition, and for example, when the radiation is X-rays, the tube voltage may be 40 to 120 kV. Generally, the tube voltage when taking an X-ray of a hand is about 40 kV, and the tube voltage when taking an X-ray of a chest is about 120 kV.

[0032] The radiation that can be shielded by the present composition can be x-rays, gamma rays, alpha rays, beta rays, or neutron rays.

[0033] Conventionally, lead glass has been used for radiation shielding in, for example, medical settings and the nuclear power industry. However, although the higher the lead content of lead glass, the higher the radiation shielding properties, the more its transparency to visible light may be insufficient. Furthermore, since lead glass contains a large amount of lead, the higher the lead content, the heavier it becomes. Furthermore, since lead glass is glass, it is prone to breakage.

[0034] In contrast, the present composition has excellent transparency to visible light while maintaining radiation shielding properties, and therefore can be used effectively in applications requiring transparency equivalent to or greater than that of lead glass. Because the present composition is transparent, when used as a radiation shielding material, the interior shielded by the composition can be easily viewed while working, thereby improving workability and safety. The present composition can be used, for example, in place of or in combination with lead glass, which has traditionally been used in medical settings, nuclear power fields, and the like, thereby enabling a reduction in the amount of lead used or realization of lead-free use.

[0035] The present composition can be used, for example, as a material for the lenses and frames of radiation-protective eyeglasses used to prevent exposure of the crystalline lens during catheterization in medical settings, or as a window material for observing the inside of examination equipment using radiation such as X-rays. Because the present composition does not require the inclusion of lead, it is easier to reduce its weight compared to conventional lead glass. Furthermore, because the present composition is a liquid, gel, or resin-based solid, it is less likely to break and is highly safe. Furthermore, in examinations using isotopes, higher energy radiation such as gamma rays may be used. In such examinations, the radiation shielding effect of lead glass may be insufficient. Therefore, excellent radiation shielding effect can be achieved by combining lead glass with a shielding material composed of the present composition.

[0036] A radiation-shielding material containing the present composition (hereinafter also simply referred to as a radiation-shielding material) can be obtained. The radiation-shielding material containing the present composition may be the present composition alone or a composite material containing the present composition and other materials.

[0037] The radiation shielding material can be a thin sheet-like sheet member having a layer of the present composition. The sheet member may be a strip-shaped sheet member. The layer of the present composition may have flexibility and rubber elasticity that allows elastic deformation. Therefore, the layer of the present composition can be folded or rolled like a cloth, and is less likely to break or chip when folded or rolled. In the present application, having flexibility means being less likely to break or chip when folded or rolled.

[0038] The radiation-shielding material may have, for example, a two-layer structure in which the composition is disposed on at least a portion of one side of a first substrate, or a three-layer structure in which the composition is disposed on at least a portion of both sides of a first substrate, or these layer structures may further include another layer.The radiation-shielding material may have, for example, a three-layer structure in which the composition is disposed on at least a portion between a first substrate and a second substrate, or these layer structures may further include another layer.

[0039] The first substrate and the second substrate can independently be flexible sheet or film materials such as fabrics such as woven fabrics and nonwoven fabrics, paper, or resins. The first substrate and the second substrate can independently be relatively rigid sheet materials such as glass plates and plastic plates. The first substrate and the second substrate can be made of the same material or different materials. The thickness of the first substrate and the second substrate can be the same as or different from the thickness of the present composition.

[0040] A transparent radiation-shielding material can be formed by disposing the liquid first composition between a first substrate and a second substrate that are transparent to visible light. If the second composition is a liquid or a gel with relatively low strength and cannot stand on its own, a transparent radiation-shielding material can be formed by disposing it between a first substrate and a second substrate that are transparent to visible light. If the second composition is a gel or a solid with relatively high strength, it can stand on its own and may be used alone as a radiation-shielding material, or may be sandwiched between a first substrate and a second substrate that are transparent to visible light. Since the third composition is a solid and can stand on its own, it may be used alone as a radiation-shielding material, or may be sandwiched between a first substrate and a second substrate that are transparent to visible light.

[0041] The second composition may be used as a liquid, gel, or solid, or may be used as a solid third composition by drying the polar solvent, and can be transparent to visible light and have radiation-shielding properties in any of the liquid, gel, or solid states. Therefore, the second composition can be placed in a liquid state between a first substrate and a second substrate that are transparent to visible light to form a transparent radiation-shielding material, or can be used as a free-standing radiation-shielding material in a gel or solid state, or the polar solvent can be dried to form a solid, transparent third composition that can be used as a radiation-shielding material. The solid third composition can form a transparent radiation-shielding material even in places where a liquid cannot be used.

[0042] Two or three of the first, second and third compositions may be used in combination.

[0043] The radiation-shielding material preferably has a substantially uniform thickness over the entire region, and the entire surface of the radiation-shielding material is flat. The thickness of the radiation-shielding material is not particularly limited, but the upper limit of the thickness may be 100 mm or less, 50 mm or less, 10 mm or less, 1.0 mm or less, 0.8 mm or less, or 0.5 mm or less. The lower limit of the thickness of the radiation-shielding material may be 0.1 mm or more, or 0.3 mm or more. The thicknesses of the first substrate and the second substrate in the radiation-shielding material may independently be 0.005 mm to 0.2 mm or 0.01 mm to 0.1 mm.

[0044] The thickness of the present composition contained in the radiation shielding material can be adjusted depending on the intended use. The first composition can be preferably used in applications requiring a relatively large thickness, and can have a thickness of, for example, 1 to 100 mm, 2 to 50 mm, 3 to 20 mm, 4 to 15 mm, or 5 to 10 mm. The second composition and the third composition can be preferably used in applications requiring a relatively small thickness, and can have a thickness of, for example, 0.1 to 1 mm, 0.2 to 0.9 mm, 0.3 to 0.8 mm, or 0.4 to 0.7 mm. The second composition and the third composition can exhibit mechanical properties such as flexibility and high strength even at the above-mentioned thin thicknesses.

[0045] The radiation shielding material may be used in clothing such as radiation protection suits, other products other than clothing, for example, articles worn by people such as gloves or neck guards, and various articles other than articles worn by people.

[0046] The radiation-shielding material is preferably a radiation-shielding curtain. The radiation-shielding curtain may be used in an X-ray inspection device for baggage at an airport. The radiation-shielding curtain may be placed at the entrance and exit of the X-ray inspection device. Since the composition can have a radiation-shielding effect and flexibility, a radiation-shielding curtain containing the composition has a radiation-shielding effect that prevents X-rays emitted inside the X-ray inspection device from leaking to the outside, and flexibility that allows baggage transported on a conveyor belt to pass through smoothly.

[0047] Since the present composition can be transparent, a radiation-shielding curtain containing the present composition can also be transparent. Conventional radiation-shielding curtains used in X-ray inspection devices are opaque, making it impossible to see inside the X-ray inspection device. However, by using a radiation-shielding curtain containing the present composition, it is possible to see inside the X-ray inspection device where baggage is irradiated with X-rays. As a result, when a problem occurs, such as baggage not coming out from inside the X-ray inspection device, the condition of the baggage inside the X-ray inspection device can be easily confirmed through the transparent radiation-shielding curtain without having to stop the X-ray inspection device.

[0048] For example, the present composition may be sandwiched between a first substrate and a second substrate, and the laminate of the first substrate and the second substrate with the present composition sandwiched therebetween may be pressed together with a press or roller, and then heated and dried in a hot air drying oven.

[0049] The first substrate and the second substrate are transported using a supply roller or the like, the present composition is supplied to the upper surface of the first substrate being transported below, and the second substrate is placed on top of the supplied present composition, and the first substrate and the second substrate with the present composition sandwiched therebetween can be pressed together using a press or roller.

[0050] The laminate of the pressed first substrate, the present composition, and the second substrate is dried with hot air. This dries the present composition sandwiched between the first substrate and the second substrate, and a layer of the present composition is formed between the first substrate and the second substrate. In this way, a sheet-shaped radiation-shielding material having a layer of the present composition tightly adhered between the first substrate and the second substrate can be produced.

[0051] The radiation-shielding material may be composed of a single layer of the present composition. In this case, the radiation-shielding material may be produced by molding only the layer of the present composition, or the radiation-shielding material having only the layer of the present composition may be produced by forming a layer of the present composition on a first substrate and then peeling off the first substrate. In this case, the first substrate can be used as a release sheet.

[0052] The polar solvent is preferably water, glycerin, ethylene glycol, propylene glycol, methanol, ethanol, biomass ethanol, or a combination thereof. The use of such a preferred polar solvent allows for good dissolution of the metal compound. The polar solvent is preferably a liquid with a relatively low molecular weight, more preferably having a molecular weight of 18 to 92. A solvent in the preferred molecular weight range allows for good dissolution of the metal compound.

[0053] The polar solvent is more preferably biodegradable. From the viewpoint of biodegradability, the polar solvent is more preferably water, glycerin, or biomass ethanol. Furthermore, for example, glycerin has a high boiling point, so that it can dissolve metal compounds while heating, and is therefore preferred in that it can dissolve metal compounds at higher concentrations.

[0054] The polar solvent preferably has a relative dielectric constant of 3 or more, more preferably 10 or more, even more preferably 20 or more, even more preferably 30 or more, and even more preferably 40 or more. By using a polar solvent having a relative dielectric constant within the above-mentioned preferred range, a larger number of metal compounds can be dissolved. The relative dielectric constant of water is 80, the relative dielectric constant of glycerin is 47, the relative dielectric constant of ethylene glycol is 39, the relative dielectric constant of propylene glycol is 32, the relative dielectric constant of methanol is 33, and the relative dielectric constant of ethanol is 24. The relative dielectric constant can be measured based on JIS C2138:2007.

[0055] The polar solvent preferably has a boiling point of 100° C. or higher, more preferably 180° C. or higher, even more preferably 190° C. or higher, and even more preferably 200° C. or higher. By using a polar solvent having a boiling point within the above-mentioned preferred range, it is possible to heat the solvent while suppressing evaporation, and therefore it is possible to dissolve a higher concentration of the metal compound in the polar solvent.

[0056] When it is desired to remove the solvent from the composition, the polar solvent may have a boiling point of 100°C or less, 90°C or less, 80°C or less, or 70°C or less. By using a polar solvent having a boiling point within the above range, the polar solvent can be more easily removed by natural evaporation, heat treatment, or the like. By removing the solvent, a highly viscous or solid composition can be more easily formed. In particular, in the case of a second composition containing a polar polymer, even after the polar solvent is removed, the metal compound remains as ions in the polar polymer, so a transparent, solid third composition having radiation-shielding properties can be obtained.

[0057] The present composition may contain multiple polar solvents with different boiling points. A third composition may be obtained by evaporating only the polar solvent with the lower boiling point from a second composition containing multiple polar solvents with different boiling points. For example, a second composition may be produced by heating and stirring two or more polar solvents, such as water with a boiling point of 100°C or less and glycerin with a boiling point higher than 100°C, along with a polar polymer and a metal compound. The polar solvent with a boiling point of 100°C or less, such as water, may then be evaporated to obtain a third composition containing a polar solvent with a boiling point higher than 100°C, such as glycerin, a polar polymer, and a metal compound. The polar solvent remaining in the third composition can ionize the metal compound as a metal ion and impart flexibility to the present composition. Removal of some of the polar solvents contained in the second composition can be achieved by utilizing the difference in boiling points of the polar solvents.

[0058] The boiling point of water is 100°C, that of glycerin is 290°C, that of ethylene glycol is 197°C, that of propylene glycol is 188°C, that of methanol is 64°C, and that of ethanol is 78°C.

[0059] The content of the polar solvent in the composition may be, for example, 0% by mass, or greater than 0 to 97% by mass, 5 to 96% by mass, 10 to 95% by mass, 15 to 94% by mass, 20 to 90% by mass, or 25 to 85% by mass, based on the total amount of the composition. The content of the polar solvent in the composition may be, for example, 20 to 30% by mass, 60 to 95% by mass, 70 to 90% by mass, or 90 to 97% by mass, based on the total amount of the composition. The content of the polar solvent in the first composition and in the composition when forming the composition may be within a range capable of dissolving the metal compound added. The content of the polar solvent in the second composition may be adjusted depending on the amount of polar polymer added to the composition within a range capable of dissolving the metal compound. The third composition may contain a portion of the polar solvent contained in the second composition, or may be substantially free of the polar solvent.

[0060] The content of the remaining polar solvent in the third composition may be varied depending on the desired flexibility. For example, when the third composition is obtained by evaporating a polar solvent, such as water, having a relatively low boiling point among the multiple polar solvents contained in the second composition, the greater the content of the remaining polar solvent with a relatively high boiling point, such as glycerin, ethylene glycol, or propylene glycol, the greater the flexibility of the third composition. When the third composition is to be flexible, the composition contains 20 to 60 mass %, 25 to 55 mass %, or 30 to 50 mass % of a polar solvent with a relatively high boiling point, such as glycerin, ethylene glycol, or propylene glycol, relative to the total weight of the composition. When the third composition is not to be flexible, the content of the remaining polar solvent may be reduced, and the content of the polar solvent relative to the total weight of the composition may be 15 mass % or less, 10 mass % or less, 5 mass % or less, or substantially zero.

[0061] The metal compound is a water-soluble metal compound that can be ionized in a polar solvent and dissolved as ions. The metal compound has positive and negative charges and can exist as ionized ions in the matrix. The metal element contained in the metal compound is preferably a Period 6 element or boron. Metal compounds containing Period 6 elements are effective in shielding against X-rays, gamma rays, alpha rays, and beta rays, while metal compounds containing boron are effective in shielding against neutron rays. The Period 6 elements are preferably Period 6 elements from barium to bismuth, i.e., barium, lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, thallium, lead, and bismuth. The higher the atomic number of an element, the better the radiation shielding properties. However, elements with atomic numbers greater than Period 6 can become a radiation source when irradiated with radiation, so the metal contained in the metal compound is preferably a Period 6 element.

[0062] The metal element contained in the metal compound is more preferably barium, tungsten, lead, bismuth, boron, or a combination thereof, with barium, tungsten, or bismuth being more preferred from an environmental standpoint (non-toxicity), and tungsten or barium being even more preferred from a cost and environmental standpoint (non-toxicity) standpoint.

[0063] The metal compound is preferably barium acetate, barium bromide, barium chloride, barium hydroxide, barium nitrate, sodium tungstate, sodium polytungstate (SPT), potassium tungstate, bismuth acetate, bismuth bromide, sodium borate, sodium polyborate, or a combination thereof, which can be more easily dissolved in a polar solvent.

[0064] The content of the metal compound can be an amount according to the desired radiation-shielding properties, as long as it is soluble in a polar solvent. The higher the content of the metal compound in the composition, the greater the radiation-shielding properties. Furthermore, the higher the content of the metal compound in the composition, the less likely the radiation-shielding properties will be reduced even if the tube voltage is increased. Note that the thicker the radiation-shielding material formed using the composition, the greater the radiation-shielding properties, so the content of the metal compound may be small. The thinner the radiation-shielding material formed using the composition, the smaller the radiation-shielding properties, so the greater the content of the metal compound.

[0065] The thickness of the radiation-shielding material formed using the present composition is not particularly limited and can be a thickness depending on the desired radiation-shielding properties, for example, 1 to 1000 mm, 2 to 750 mm, 3 to 500 mm, 4 to 250 mm, or 5 to 100 mm.

[0066] The content of the metal compound is preferably 3 to 50 mass%, 5 to 48 mass%, 10 to 46 mass%, 15 to 44 mass%, or 20 to 42 mass%, based on the total amount of the composition. When the content of the metal compound is within the above range, the metal compound can be more effectively dissolved as ions in the polar solvent, thereby achieving a radiation shielding effect. The content of the metal compound contained in the present composition is also preferably 3 to 50 mass%, 5 to 48 mass%, 10 to 46 mass%, 15 to 44 mass%, or 20 to 42 mass%, based on the total amount of the composition. When the content of the metal compound is within the above range, the metal compound can be more effectively dissolved as ions in the polar solvent, thereby achieving a radiation shielding effect. ３ The amount of the metal compound is preferably 0.5 to 10 mmol, more preferably 1 to 8 mmol, even more preferably 2 to 6 mmol, and even more preferably 2.5 to 5 mmol, per 1000 ppm of the polar solvent. When the content of the metal compound is within the above-mentioned preferred range, the metal compound having a radiation-shielding effect can be more effectively dissolved as ions in the polar solvent.

[0067] The metal compound prepared for dissolution in a polar solvent may be a powder that is soluble in a polar solvent, may be in the form of an aggregate, and may be, for example, a commercially available metal compound powder of about 100 μm to 1 mm. In the present composition, the metal compound exists as ions, so there is no need to use nano-sized metal compound particles to achieve transparency, which is advantageous in terms of cost and workability.

[0068] The polar polymer is a water-soluble polymer that can be dissolved in a polar solvent. The polar polymer may be soluble in a polar solvent and may have a dielectric constant similar to that of the polar solvent. Depending on the content or molecular weight of the polar polymer, the viscosity of the composition can be adjusted to a high or low viscosity, or the hardness of the gel composition can be adjusted, and a substantially solid composition can also be obtained. Furthermore, a hard composition can be obtained by crosslinking the polar polymer.

[0069] The polar polymer is preferably starch, polyacrylic acid, carrageenan, polyvinyl alcohol, polyvinylpyrrolidone, cellulose nanofiber, carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylamide, agarose, agar, water-dispersible rubber latex, or a combination thereof. The polar polymer is also preferably biodegradable. In terms of biodegradability, the polar polymer is more preferably starch, carrageenan, agarose, or agar.

[0070] A biodegradable first composition can be obtained by using a biodegradable polar solvent when forming a first composition. A biodegradable second composition can be obtained by using a biodegradable polar solvent and a biodegradable polar polymer when forming a second composition. For example, since glycerin and starch are both biodegradable, a composition that is visible light transparent, has radiation shielding properties, and is biodegradable can be obtained by using glycerin as the polar solvent and starch as the polar polymer. When the polar solvent is removed from the second composition to form a third composition, a biodegradable third composition can be obtained by using a biodegradable polar polymer.

[0071] By using cellulose nanofibers as the polar polymer, the cellulose nanofibers can be dispersed in a polar solvent to form a transparent dispersion liquid, and at least a portion of the polar solvent can be removed by drying or heat treatment to obtain a transparent, biodegradable, fibrous third composition.

[0072] The content of the polar polymer can be an amount depending on the desired viscosity or strength of the resulting composition. The content of the polar polymer may be, for example, 0.1 to 60 mass%, 0.5 to 57 mass%, 1 to 54 mass%, 10 to 52 mass%, 20 to 50 mass%, or 30 to 48 mass%, based on the total amount of the composition. When the content of the polar polymer is within the above range, the second composition or the third composition can be successfully formed.

[0073] The content ratio (mass ratio) of the polar polymer to the polar solvent may be within a range in which the polar polymer is soluble in the polar solvent, and can be determined depending on the desired viscosity or hardness of the resulting composition. The content ratio (mass ratio) of the polar polymer to the polar solvent is preferably 1.5 to 2.0, more preferably 1.6 to 1.9, and even more preferably 1.7 to 1.8. By achieving this preferred ratio, it is possible to more easily form a composition having the desired viscosity or hardness while dissolving the polar polymer and metal compound in the polar solvent.

[0074] The composition may contain any other ingredients, such as gelling agents, thickeners, and other polysaccharides.

[0075] The present disclosure is also directed to a method for producing a transparent radiation-shielding composition (hereinafter also referred to as the present production method), which includes mixing a polar solvent with a water-soluble metal compound that is soluble in the polar solvent to form a first composition containing ions formed by ionization of the metal compound.

[0076] By mixing a polar solvent with a water-soluble metal compound that is soluble in the polar solvent, the metal compound can be ionized in the polar solvent and dissolved as ions. The method for mixing the polar solvent and the metal compound is not particularly limited, but the mixture can be performed at room temperature or while heating. By mixing the polar solvent and the metal compound while heating, a higher concentration of the metal compound can be dissolved in the polar solvent in a shorter time. The heating temperature can be adjusted depending on the boiling point of the polar solvent, and is, for example, 60 to 200°C.

[0077] Preferably, the first composition is mixed with a polar polymer and the polar polymer is dissolved in the polar solvent in the first composition to form a second composition. In the second composition, the metal compound exists as an ion in the solution of the polar solvent and the polar polymer. The method for mixing the first composition with the polar polymer is not particularly limited, but can be performed at room temperature or while heating. Mixing the first composition with the polar polymer while heating can more effectively dissolve the polar polymer in the polar solvent. The heating temperature can be adjusted depending on the boiling point of the polar solvent, for example, 60 to 200°C. A polar polymer such as carrageenan may also be mixed at the same time as mixing the polar solvent with the metal compound, but as described above, mixing the first composition with the polar polymer makes it easier to uniformly dissolve the polar polymer in the polar solvent.

[0078] More preferably, the first composition and the polar polymer are mixed at room temperature, and the mixture is heated and melt-kneaded to form the second composition. This prevents the polar polymer, such as starch, from forming lumps when added. The melt-kneading temperature can be adjusted depending on the boiling point of the polar solvent, and is preferably, for example, 60 to 200°C.

[0079] Preferably, at least a portion of the polar solvent is removed from the second composition to prepare a third composition. In the third composition, the metal compound exists as an ion in a solution of the polar solvent and the polar polymer or in the polar polymer. The third composition can be solid. The method for removing at least a portion of the polar solvent from the second composition is not particularly limited, but can be performed at room temperature or with heating. Heating can remove at least a portion of the polar solvent from the second composition in a shorter time. The heating temperature can be adjusted depending on the boiling point of the polar solvent, and is, for example, 60 to 300°C or 80 to 200°C.

[0080] The second composition or the third composition can be processed to obtain a molded product such as pellets. The processing can be a conventional resin molding method such as injection molding or pressing. For example, a compression molding method can be used in which the second composition or the third composition is placed in a heated mold, and when it softens and acquires a suitable fluidity, pressure is applied to fill the mold with the second composition or the third composition, and further heating and pressure are continued to harden the second composition or the third composition in the mold. Even in the pelletized second composition or the third composition, the metal compounds exist as ions in the matrix.

[0081] The above-mentioned contents are applicable to the polar solvent, metal compound, and polar polymer used in this production method, and also to the compositions including the first composition, second composition, and third composition obtained by this production method.

[0082] (Examples of Two-Component System) (Example 1) 93.5% by mass of glycerin (manufactured by Kanto Chemical Co., Ltd., product number: 56-81-5, the same applies hereinafter) and 6.5% by mass of barium acetate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product number: 543-80-6, the same applies hereinafter) were mixed while heating to 80°C to form a transparent liquid composition.

[0083] Example 2 92.6% by mass of glycerin and 7.4% by mass of barium bromide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product number: 10553-31-8, the same applies below) were mixed while being heated to 80° C. to form a transparent liquid composition.

[0084] Example 3 93.8% by mass of glycerin and 6.2% by mass of barium chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product number: 10326-27-9, the same applies below) were mixed while being heated to 80° C. to form a transparent liquid composition.

[0085] Example 4 91.8% by mass of glycerin and 8.2% by mass of sodium tungstate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product number: 10213-10-2, the same applies below) were mixed while being heated to 80° C. to form a transparent liquid composition.

[0086] Example 5 91.8% by mass of glycerin and 8.2% by mass of sodium polytungstate (SPT) (manufactured by MEASURE WORKS Co., Ltd., product number: 12141-67-2, the same applies hereinafter) were mixed while being heated to 80° C. to form a transparent liquid composition.

[0087] Table 1 shows the types and contents of the polar solvents and metal compounds, as well as the transparency and X-ray shielding ratio of the obtained compositions in Examples 1 to 5. The X-ray shielding ratio was measured by the method shown in Figures 7 and 8 (at a depth of 10 mm in the composition).

[0088]

[0089] Examples 6 to 10 Transparent liquid compositions were prepared in the same manner as in Examples 1 to 5, except that water was used as the polar solvent instead of glycerin. Figure 1 shows a photograph of the appearance of the liquid composition prepared in Example 6 placed in a glass bottle.

[0090] Table 2 shows the types and contents of the polar solvents and metal compounds, as well as the transparency and X-ray shielding ratio of the obtained compositions in Examples 6 to 10. The X-ray shielding ratio was measured by the method shown in Figures 7 and 8 (at a depth of 10 mm in the composition).

[0091]

[0092] (Three-Component Example) (Example 11) 24% by weight of glycerin and 34% by weight of barium acetate were mixed while heating to 80°C to form a transparent first composition. Next, 42% by weight of starch powder (pregelatinized tapioca flour, manufactured by Sanwa Starch Industry Co., Ltd., the same applies hereinafter) was added to the first composition at room temperature, mixed, and then heated to 120°C for melt-kneading to form a transparent second composition. The obtained second composition was press-molded to form a transparent, solid, disk-shaped pellet (film-like composition) having a thickness of 0.5 mm and a diameter of 20 mm.

[0093] Example 12 A transparent first composition was formed by mixing 23% by mass of glycerin and 36% by mass of barium bromide while heating to 80° C. Next, 41% by mass of starch was added to the first composition while heating to 120° C., and mixed to form a transparent second composition in the same manner as in Example 11, thereby obtaining disk-shaped transparent solid pellets (film-like composition) having a thickness of 0.5 mm and a diameter of 20 mm.

[0094] Example 13 A transparent first composition was formed by mixing 26% by mass of glycerin and 28% by mass of barium chloride while heating to 80° C. Next, 46% by mass of starch was added to the first composition while heating to 120° C., and mixed to form a transparent second composition in the same manner as in Example 11, thereby obtaining disk-shaped transparent solid pellets (film-like composition) having a thickness of 0.5 mm and a diameter of 20 mm.

[0095] Example 14 A transparent first composition was formed by mixing 26% by mass of glycerin and 26% by mass of sodium tungstate while heating to 80° C. Next, 47% by mass of starch was added to the first composition while heating to 120° C., and mixed to form a transparent second composition in the same manner as in Example 11, thereby obtaining disk-shaped transparent solid pellets (film-like composition) having a thickness of 0.5 mm and a diameter of 20 mm.

[0096] Example 15 26% by mass of glycerin and 26% by mass of sodium polytungstate (SPT) were mixed while heating to 80°C to form a transparent first composition. Next, 47% by mass of starch was added to the first composition while heating to 120°C and mixed to form a transparent second composition in the same manner as in Example 11, and transparent, solid, disc-shaped pellets (film-like composition) with a thickness of 0.5 mm and a diameter of 20 mm were obtained. Figure 3 shows a photograph of the appearance of the obtained pellets.

[0097] Example 16 81% by mass of water and 18% by mass of sodium polytungstate (SPT) were mixed while heating to 80°C to form a transparent first composition. Next, 1% by mass of carrageenan (manufactured by Tokyo Chemical Industry Co., Ltd., 11114-20-8) was added to the first composition while heating to 80°C, and mixed to form a transparent second composition. The obtained second composition was cooled at room temperature to obtain a transparent, gel-like pellet (film-like composition) in a disk shape with a thickness of 0.5 mm and a diameter of 20 mm.

[0098] Table 3 shows the types and contents of the polar solvents, metal compounds, and polar polymers, as well as the transparency and X-ray shielding ratios of the resulting compositions in Examples 11 to 16. The X-ray shielding ratios were measured by the method shown in Figure 9 (composition thickness: 0.5 mm).

[0099]

[0100] Comparative Example 1 100% by mass of glycerin was prepared.

[0101] Comparative Example 2 100% by mass of water was prepared.

[0102] (Comparative Example 3) A liquid composition was prepared by mixing 94.1% by mass of glycerin and 5.9% by mass of barium sulfate (W-10, average particle size 10 μm, manufactured by Takehara Chemical Industry Co., Ltd.) while heating to 120° C. The barium sulfate particles were dispersed in the glycerin without dissolving, and the prepared composition was opaque.

[0103] Comparative Example 4 A liquid composition was prepared by mixing 94.2% by mass of glycerin and 5.8% by mass of tungsten oxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 1314-35-8, average particle size 10 μm, the same applies below) while heating to 120° C. The tungsten oxide particles were dispersed in the glycerin without dissolving, and the prepared composition was opaque.

[0104] Comparative Example 5 47% by mass of polystyrene (G100, manufactured by Toyo Styrene Co., Ltd., relative dielectric constant 2.4) and 53% by mass of barium sulfate were mixed while heating to 200°C to form a composition (pellet). The resulting composition was opaque. The resulting composition was cooled at room temperature to obtain gel-like pellets (film-like composition) having a thickness of 0.5 mm and a diameter of 20 mm. FIG. 4 shows a photograph of the appearance of the resulting pellets.

[0105] (Comparative Example 6) A liquid composition was formed by mixing 94.2% by mass of water and 5.9% by mass of barium sulfate while heating to 80°C. The barium sulfate particles were not dissolved in the water but remained dispersed, and the resulting composition was opaque. Figure 2 shows a photograph of the appearance of the resulting liquid composition in a glass bottle.

[0106] Table 4 shows the types and contents of the polar solvents and metal compounds in Comparative Examples 1 to 6, as well as the transparency and X-ray shielding ratio of the obtained compositions. The X-ray shielding ratio was measured for Comparative Examples 1 to 4 and 6 by the method shown in Figures 7 and 8 (composition depth: 10 mm), and for Comparative Example 5 by the method shown in Figure 9 (composition thickness: 0.5 mm). While the X-ray shielding ratio of Comparative Example 1 was 29%, the above-mentioned Example 1 exhibited an X-ray shielding ratio of 56% while maintaining transparency, demonstrating 1.93 times the shielding performance.

[0107]

[0108] Comparative Example 7 36% by mass of glycerin and 64% by mass of starch were mixed while heating to 120° C. to form a transparent composition (pellet) having a thickness of 0.5 mm and a diameter of 20 mm. Fig. 5 shows a photograph of the appearance of the obtained pellet.

[0109] (Comparative Example 8) 17% by mass of glycerin and 53% by mass of barium sulfate were mixed at room temperature to form a composition, and then 30% by mass of starch was mixed therein while heating to 120° C. to form a composition (pellet) having a thickness of 0.5 mm and a diameter of 20 mm. The resulting composition was opaque.

[0110] Comparative Example 9: 17% by mass of glycerin and 53% by mass of tungsten oxide were mixed at room temperature to form a composition, and then 30% by mass of starch was mixed therein while heating to 120° C. to form a composition (pellet) having a thickness of 0.5 mm and a diameter of 20 mm. The resulting composition was opaque.

[0111] Table 5 shows the types and contents of the polar solvents, metal compounds, and polar polymers, as well as the transparency and X-ray shielding ratios of the resulting compositions in Comparative Examples 7 to 9. The X-ray shielding ratios were measured by the method shown in Figure 9 (composition thickness: 0.5 mm).

[0112]

[0113] (Evaluation of Diffraction Charts by Powder X-Ray Diffraction) FIG. 6 shows diffraction charts of the pellets (glycerin / barium bromide / starch) prepared in Example 12, the pellets (polystyrene / barium sulfate) prepared in Comparative Example 5, and the barium sulfate powder used in Comparative Example 5, measured using a horizontal sample multipurpose X-ray diffractometer (Ultima IV, Rigaku Corporation).

[0114] The X-ray diffraction chart measured for the pellets prepared in Comparative Example 5 showed peaks reflecting the crystalline structure of barium sulfate, the same as those in the diffraction chart measured for the barium sulfate powder. On the other hand, the X-ray diffraction chart measured for the pellets prepared in Example 12 showed no peaks of metal compounds.

[0115] (Evaluation of X-ray shielding ratio) Fig. 10 shows a graph of the X-ray shielding ratio at tube voltages of 40 to 120 kV for the liquid composition (glycerin / barium acetate) prepared in Example 1, the liquid composition (glycerin / sodium tungstate) prepared in Example 4, the liquid composition (glycerin / barium sulfate) prepared in Comparative Example 3, and the liquid composition (glycerin / tungsten oxide) prepared in Comparative Example 4. The X-ray shielding ratio was measured by the method shown in Figs. 7 and 8. The liquid compositions prepared in Examples 1 and 4 were transparent, but showed X-ray shielding ratios equivalent to those of the opaque liquid compositions prepared in Comparative Examples 3 and 4.

[0116] CH, which exists as an ion in glycerin ３ A liquid composition containing COOBa (Example 1) and BaSO4 present as particles in glycerin ４ The X-ray shielding rate was almost the same as that of the liquid composition containing the compound (Comparative Example 3).

[0117] In addition, Na, which exists as an ion in glycerin, ２ WO ４ ・2H ２ A liquid composition containing WO (Example 4) and WO present as particles in glycerin ３ The X-ray shielding rate was almost the same as that of the liquid composition containing the compound (Comparative Example 4).

[0118] FIG. 11 shows a graph of the X-ray shielding factor at tube voltages of 40 to 120 kV for the pellets prepared in Example 15 (glycerin / sodium polytungstate (SPT) / starch), the pellets prepared in Comparative Example 5 (polystyrene / barium sulfate), and the pellets prepared in Comparative Example 7 (glycerin / starch). The X-ray shielding factor was measured by the method shown in FIG. 9. The pellets prepared in Example 15 were transparent, but showed an X-ray shielding factor equivalent to that of the opaque pellets prepared in Comparative Example 5. The X-ray shielding factor of the composition prepared in Comparative Example 7, which did not contain a metal compound, was almost 0%.

[0119] (Evaluation of X-ray shielding rate depending on type and content of metal compound) (Example 17) 91.9 mass % of water and 1 mmol (8.1 mass %) of barium acetate were mixed while being heated to 80°C to form a transparent liquid composition.

[0120] Example 18 90.8% by weight of water and 1 mmol (9.2% by weight) of barium bromide were mixed while heating to 80° C. to form a clear liquid composition.

[0121] Table 6 shows the types and contents of the polar solvents and metal compounds, as well as the transparency and X-ray shielding ratio of the obtained compositions in Examples 17 and 18. The X-ray shielding ratio was measured by the method shown in Figures 7 and 8 (at a depth of 10 mm in the composition).

[0122]

[0123] 12 shows a graph of the X-ray shielding ratio of liquid compositions prepared in Examples 17 and 18, in which the types of metal compounds were barium acetate and barium bromide and the metal compound contents were standardized to 1 mmol. The X-ray shielding ratio of the composition in which the metal compound was barium bromide was higher than that of the composition in which the metal compound was barium acetate. The X-ray shielding ratio tended to decrease as the tube voltage increased.

[0124] Example 19 81.1% by weight of water and 2.5 mmol (18.9% by weight) of barium acetate were mixed while heating to 80° C. to form a clear liquid composition.

[0125] Example 20 84.6% by weight of water and 2.5 mmol (15.4% by weight) of barium chloride were mixed while heating to 80° C. to form a clear liquid composition.

[0126] Example 21 79.3% by weight of water and 2.5 mmol (20.7% by weight) of barium bromide were mixed while heating to 80° C. to form a clear liquid composition.

[0127] Table 7 shows the types and contents of the polar solvents and metal compounds, as well as the transparency and X-ray shielding ratio of the obtained compositions in Examples 19 to 21. The X-ray shielding ratio was measured by the method shown in Figures 7 and 8 (at a depth of 10 mm in the composition).

[0128]

[0129] 13 shows a graph of the X-ray shielding ratios of liquid compositions prepared in Examples 19 to 21 in which the types of metal compounds were barium acetate, barium chloride, and barium bromide and the content of the metal compounds was standardized to 2.5 mmol. The X-ray shielding ratio of the composition in which the metal compound was barium bromide was high, and the X-ray shielding ratios of the compositions in which the metal compound was barium acetate and barium chloride were equivalent. The X-ray shielding ratio tended to decrease slightly as the tube voltage increased.

[0130] Example 22 66.0% by weight of water and 5 mmol (34.0% by weight) of barium acetate were mixed while heating to 80° C. to form a clear liquid composition.

[0131] Example 23 72.4% by weight of water and 5 mmol (27.6% by weight) of barium chloride were mixed while heating to 80° C. to form a clear liquid composition.

[0132] Example 24 64.4% by weight of water and 5 mmol (35.6% by weight) of barium bromide were mixed while heating to 80° C. to form a clear liquid composition.

[0133] Table 8 shows the types and contents of the polar solvents and metal compounds, as well as the transparency and X-ray shielding ratio of the obtained compositions in Examples 22 to 24. The X-ray shielding ratio was measured by the method shown in Figures 7 and 8 (at a depth of 10 mm in the composition).

[0134]

[0135] 14 shows a graph of the X-ray shielding ratio of liquid compositions prepared in Examples 22 to 24 using barium acetate, barium chloride, and barium bromide as the metal compounds, with the metal compound content standardized to 5 mmol. The X-ray shielding ratio of the composition in which the metal compound was barium bromide was high, while the X-ray shielding ratios of the compositions in which the metal compound was barium acetate and barium chloride were equivalent. The X-ray shielding ratio was stable regardless of the tube voltage.

[0136] (Evaluation of Carrageenan as a Polar Polymer) Fig. 15 shows a graph of the X-ray shielding rate of the composition (pellets) prepared in Example 16. The X-ray shielding rate was 60% or more regardless of the tube voltage.

[0137] (Evaluation of Visible Light Transmittance) Figure 16 shows a graph of the visible light transmittance of the pellets prepared in Example 15 (glycerin / sodium polytungstate (SPT) / starch), Comparative Example 5 (polystyrene / barium sulfate), and Comparative Example 7 (glycerin / starch) measured with an ultraviolet-visible spectrophotometer (U-4100, manufactured by Hitachi High-Tech Corporation) in the visible light region of wavelengths of 400 to 800 nm. The pellets prepared in Example 15 contained metal compounds as ions, and therefore exhibited a visible light transmittance of 65% or more, equivalent to the pellets prepared in Comparative Example 7, which did not contain metal compounds. The visible light transmittance of the pellets prepared in Comparative Example 5, which contained barium sulfate as particles, was approximately 30%.

[0138] (Comparative Example 10) The X-ray shielding rate of the circled wrist, back of the hand, and fingertips of a conventionally used 0.5 mm thick radiation protection glove (G-3, manufactured by Hoshina Seisakusho Co., Ltd.) shown in Figure 17 was measured at a tube voltage of 100 kV. As shown in Table 9, the X-ray shielding rate of the radiation protection glove was approximately 50%.

[0139]

[0140] Example 25: 90.4% by weight of water, 2.8% by weight of glycerin, 1.5% by weight of barium bromide, and 5.3% by weight of starch powder were stirred at 90°C for 2 hours to form a transparent second composition. The second composition was then placed in a petri dish and dried at 40°C for 24 hours to evaporate the water, forming a transparent solid third composition. The resulting third composition was press-molded to a thickness of 0.3 mm, a diameter of 50 mm, and a density of 1.4 g / cm. ３ A transparent, solid, disc-shaped pellet (film-like composition) was formed. Fig. 18 shows a photograph of the appearance of the obtained pellet.

[0141] Comparative Example 10: 91.7% by weight of water, 2.8% by weight of glycerin, and 5.4% by weight of starch powder were stirred at 90°C for 2 hours to form a transparent second composition. The second composition was then placed in a petri dish and dried at 40°C for 24 hours to evaporate the water, forming a transparent solid third composition. The resulting third composition was press-molded into a 0.3 mm thick, 50 mm diameter, and 1.2 g / cm3 density. ３A transparent, solid pellet (film-like composition) having a disk shape was formed. Fig. 19 shows a photograph of the appearance of the obtained pellet.

[0142] Table 10 shows the types and contents of the polar solvents and metal compounds, as well as the transparency and X-ray shielding ratio of the obtained compositions in Example 25 and Comparative Example 10. The X-ray shielding ratio was measured by the method shown in Figure 9 (composition thickness: 0.3 mm).

[0143]

[0144] 20 shows a graph of the X-ray shielding efficiency at tube voltages of 40 to 120 kV for the pellets (glycerin / starch / barium bromide) prepared in Example 25 and the pellets (glycerin / starch) prepared in Comparative Example 10. Both the pellets prepared in Example 25 and Comparative Example 10 were transparent, but the X-ray shielding efficiency of the pellets prepared in Comparative Example 10, which did not contain a metal compound, was low, while the pellets prepared in Example 25 showed a high X-ray shielding efficiency.

[0145] 21 shows a graph of the visible light transmittance in the visible light region of 400 to 800 nm wavelength, measured with an ultraviolet-visible spectrophotometer (U-4100, manufactured by Hitachi High-Tech Corporation) for the pellets (glycerin / starch / barium bromide) prepared in Example 25 and the pellets (glycerin / starch) prepared in Comparative Example 10. The pellets prepared in Example 25 and Comparative Example 10 both showed a visible light transmittance of about 90%.

[0146] 10 Radiation source 20 Sample 30 Lead plate 40 Detector

Claims

1. A base material containing a polar solvent and a polar polymer, and Ions of the metal compound ionized in the aforementioned base material Includes, The aforementioned metal compound is a water-soluble metal compound that can dissolve as an ion by ionization in the polar solvent. The polar polymer is a water-soluble polymer that is soluble in the polar solvent. A transparent radiation shielding composition.

2. The radiation shielding composition according to claim 1, wherein the polar solvent is water, glycerin, ethylene glycol, propylene glycol, methanol, ethanol, biomass ethanol, or a combination thereof.

3. The radiation shielding composition according to claim 1 or 2, wherein the metal compound is barium acetate, barium bromide, barium chloride, barium hydroxide, barium nitrate, sodium tungstate, sodium polytungstate, potassium tungstate, bismuth acetate, bismuth bromide, sodium borate, sodium polyborate, or a combination thereof.

4. The radiation shielding composition according to claim 1 or 2, wherein the polar polymer is starch, polyacrylic acid, carrageenan, polyvinyl alcohol, polyvinylpyrrolidone, cellulose nanofiber, carboxymethylcellulose, hydroxyethylcellulose, polyacrylamide, agarose, agar, water-dispersible rubber latex, or a combination thereof.

5. The radiation shielding composition according to claim 1 or 2, wherein the content of the metal compound is 3 to 50% by mass, based on the total amount of the composition.

6. A radiation shielding material comprising the radiation shielding composition according to claim 1 or 2.

7. The radiation shielding material according to claim 6, which is a radiation shielding curtain.

8. A polar solvent and a water-soluble metal compound soluble in the polar solvent are mixed to form a first composition containing ions formed by the ionization of the water-soluble metal compound in the polar solvent, and The first composition is mixed with a polar polymer soluble in the polar solvent to dissolve the polar polymer in the polar solvent in the first composition, thereby forming a second composition containing ions formed by the ionization of the water-soluble metal compound in the solution of the polar solvent and the polar polymer. A method for producing a transparent radiation shielding composition containing [the specified element].

9. The manufacturing method according to claim 8, comprising removing at least a portion of the polar solvent from the second composition to prepare a third composition in which the water-soluble metal compound contains ions ionized in the solution of the polar solvent and the polar polymer or in the polar polymer.