Radiation-shielding composition, composition, and coating or coating material

Abstract

The present invention relates to a radiation-shielding composition including a polyvinyl alcohol-based resin. The present invention also relates to: a coating or a coating material containing the radiation-shielding composition; a medical device, electronic member, member for nuclear power generation, or member for aviation or space use having a layer using the coating or coating material; a shaped object containing the radiation-shielding composition; and a medical device, electronic member, member for nuclear power generation, or member for aviation or space use having said composition. The present invention further relates to a composition containing a polyvinyl alcohol-based resin and at least one selected from the group consisting of compounds containing at least one of Gd, B and Li.

Description

Radiation shielding composition, composition and paint or coating material

[0001] The present invention relates to radiation shielding compositions, compositions and paint or coating materials.

[0002] Radiation can be broadly divided into electromagnetic radiation and particle radiation. The main types of electromagnetic radiation are gamma rays and X-rays, while the main types of particle radiation include alpha rays (helium nuclei) and beta rays (electrons) produced by radioactive isotopes, as well as high-energy electrons, protons, neutrons, and heavy particles (heavy ions) produced in the space environment and accelerator facilities. Of these, electrically neutral neutrons cannot be blocked by matter due to electromagnetic interactions, so shielding materials tailored to their properties will be required to protect the human body and other objects.

[0003] Neutrons are produced by nuclear fission in nuclear reactors, and continue to be produced by spontaneous fission and (α, n) reactions in spent nuclear fuel. They are also produced by high-energy particle-nuclear reactions in particle accelerators used for medical and research purposes, and by photonuclear reactions (nuclear reactions between photons and atomic nuclei) in medical X-ray linacs with energies exceeding 20 million electron volts (20 MeV). Neutrons are relevant in a variety of fields, including energy and medicine, and are also used in industry for non-destructive testing and in medicine, such as cancer treatment.

[0004] High-energy neutrons penetrate deep into the human body and impart large amounts of energy to the elements that make up the body, resulting in a large dose conversion factor, which represents the radiation risk to the human body, and thus have a significant impact on external exposure to the human body. Neutrons from medical accelerators, nuclear reactors, spent nuclear fuel, etc. are mainly generated in the energy range known as fast neutrons, with kinetic energies of approximately one million electron volts (MeV). Therefore, efficient shielding of fast neutrons is highly effective in reducing external exposure to neutron radiation. It is known that deceleration by elastic scattering with hydrogen atoms, which have approximately the same mass as the neutrons, is effective in shielding fast neutrons, and materials with a high hydrogen content have been used as fast neutron shielding materials. For example, among resins, polyethylene, especially high-density polyethylene, has a relatively high hydrogen atom ratio and is known to have excellent neutron shielding performance.

[0005] For example, Patent Document 1 discloses a boron compound, preferably boron carbide B ４ Patent Document 2 describes a neutron absorbing material made of ultra-high molecular weight polyethylene embedded with C. Patent Document 2 also describes a neutron shielding structure that includes an inner layer made of polyethylene containing a substance that absorbs neutrons, an intermediate layer made of polyethylene that is disposed on the inner layer, and an outer layer made of polyethylene that is disposed on the intermediate layer.

[0006] Japanese Unexamined Patent Publication No. 3-107797 Japanese Unexamined Patent Publication No. 2015-010826

[0007] However, from the viewpoint of pursuing safety of nuclear reactors and the like, materials with better neutron shielding performance are required.

[0008] Therefore, an object of the present invention is to provide a radiation-shielding composition that is particularly excellent in neutron shielding performance.

[0009] As a result of extensive investigations, the present inventors have found that a radiation-shielding composition using a polyvinyl alcohol-based resin has high neutron shielding performance, and have thus completed the present invention.

[0010] That is, the present invention relates to the following Aspects 1 to 22. Aspect 1 of the present invention is a radiation-shielding composition containing a polyvinyl alcohol-based resin. Aspect 2 of the present invention is the radiation-shielding composition according to Aspect 1, wherein the radiation includes one or more selected from the group consisting of neutrons, protons, and heavy particles. Aspect 3 of the present invention is the radiation-shielding composition according to Aspect 1 or 2, wherein the polyvinyl alcohol-based resin contains a saponified ethylene-vinyl ester-based copolymer. Aspect 4 of the present invention is the radiation-shielding composition according to Aspect 3, wherein the saponified ethylene-vinyl ester-based copolymer has an ethylene content of 0.1 to 77 mol %. Aspect 5 of the present invention is the radiation-shielding composition according to Aspect 3, wherein the ethylene content of the saponified ethylene-vinyl ester-based copolymer is 20 to 60 mol %. Aspect 6 of the present invention is the radiation-shielding composition according to any one of Aspects 1 to 5, wherein the polyvinyl alcohol-based resin contains a modified polyvinyl alcohol-based resin containing a 1,2-diol structural unit in a side chain. Aspect 7 of the present invention is the radiation-shielding composition according to any one of Aspects 1 to 6, further containing an inorganic filler. Aspect 8 of the present invention is the radiation-shielding composition according to aspect 7, wherein the inorganic filler is 30 mass % or more. Aspect 9 of the present invention is a radiation-shielding composition comprising Gd ２ O ３ , B ２ O ３ , B ４A radiation-shielding composition according to Aspect 7 or 8, which comprises at least one selected from the group consisting of C and LiF. Aspect 10 of the present invention is the radiation-shielding composition according to any one of Aspects 1 to 9, which is an aqueous or solvent-based resin emulsion. Aspect 11 of the present invention is a paint or coating material containing the radiation-shielding composition according to any one of Aspects 1 to 10. Aspect 12 of the present invention is a molded article containing the radiation-shielding composition according to any one of Aspects 1 to 10. Aspect 13 of the present invention is a medical device having a layer formed using the paint or coating material according to Aspect 11. Aspect 14 of the present invention is an electronic component having a layer formed using the paint or coating material according to Aspect 11. Aspect 15 of the present invention is a nuclear power generation component having a layer formed using the paint or coating material according to Aspect 11. Aspect 16 of the present invention is an aerospace component having a layer formed using the paint or coating material according to Aspect 11. Aspect 17 of the present invention is a medical device having the molded article according to Aspect 12. Aspect 18 of the present invention is an electronic component having the molded article according to Aspect 12. Aspect 19 of the present invention is a nuclear power generation component having the molded article according to aspect 12. Aspect 20 of the present invention is an aviation or space component having the molded article according to aspect 12. Aspect 21 of the present invention is a composition containing a polyvinyl alcohol resin and at least one compound selected from the group consisting of compounds containing at least one of Gd, B, and Li. Aspect 22 of the present invention is the composition according to aspect 21, which is used as a radiation shielding composition.

[0011] According to the present invention, it is possible to provide a radiation-shielding composition that is particularly excellent in neutron shielding performance.

[0012] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified as desired without departing from the spirit of the present invention. Furthermore, the term "to" indicating a range of values ​​is used to mean that the values ​​before and after it are included as the lower and upper limits.

[0013] (Radiation-shielding composition) The radiation-shielding composition according to an embodiment of the present invention contains a polyvinyl alcohol-based resin. As a result of extensive studies, the present inventors have found that polyvinyl alcohol-based resins are particularly excellent in neutron shielding performance and are suitable as radiation-shielding compositions. In particular, they have found that polyvinyl alcohol-based resins have better neutron shielding performance than polyethylene, despite having a lower hydrogen ratio (weight ratio of hydrogen atoms in the molecule) than polyethylene, and have thus completed the present invention. The reason for this is presumably that hydroxy groups contained in the polyvinyl alcohol-based resin form hydrogen bonds, thereby improving the density of the resin and increasing the hydrogen density (intermolecular cohesive force) in the resin.

[0014] The radiation-shielding composition according to the embodiment of the present invention has excellent radiation-shielding performance. Examples of target radiation include neutrons, protons, gamma rays, X-rays, α-rays, β-rays, electrons, protons, and heavy particles. The target radiation preferably includes one or more selected from the group consisting of neutrons, protons, and heavy particles. Like neutrons, protons and heavy particles are effective radiations when they are decelerated by collision with atomic nuclei. Therefore, the radiation-shielding composition according to the embodiment of the present invention is considered to have excellent radiation-shielding performance, particularly for neutrons, as well as excellent radiation-shielding performance for protons and heavy particles. In other words, the radiation-shielding composition according to the embodiment of the present invention has excellent radiation-shielding performance, particularly for decelerating radiation by collision with atomic nuclei. More preferred aspects of the radiation-shielding composition are described below.

[0015] (Polyvinyl Alcohol Resin) The polyvinyl alcohol resin (hereinafter also referred to as PVA resin) used in this embodiment has vinyl alcohol structural units corresponding to the degree of saponification and vinyl ester structural units in the unsaponified portion.

[0016] The radiation-shielding composition contains at least a PVA-based resin, and may consist of a PVA-based resin. That is, the proportion of the PVA-based resin in the radiation-shielding composition is preferably 11% by mass to 100% by mass, for example, although it depends on the content of the inorganic filler described below. From the viewpoint of storage stability of the coating material, the proportion of the PVA-based resin is preferably 11% by mass or more, more preferably 20% by mass or more, more preferably 30% by mass or more, more preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and most preferably 70% by mass or more. On the other hand, from the viewpoint of radiation-shielding properties, the upper limit is preferably 100% by mass or less, more preferably 90% by mass or less, more preferably 80% by mass or less, and most preferably 70% by mass or less.

[0017] Examples of PVA-based resins include unmodified PVA, copolymer-modified PVA obtained by copolymerizing various monomers during the production of vinyl ester-based resins and then saponifying the copolymerized PVA, and various post-modified PVAs obtained by post-modifying unmodified PVAs to introduce various functional groups. Such modification can be carried out within a range that does not result in a loss of a degree of polymerization sufficient for polymer formation of the PVA-based resin. In some cases, the modified PVA may also be further post-modified.

[0018] When a copolymerized modified PVA is obtained, examples of monomers used in copolymerization with a vinyl ester monomer during the production of a vinyl ester resin include olefins such as propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, and itaconic acid, or their salts, or their mono- or dialkyl esters; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallylsulfonic acid, or their salts; alkyl vinyl ethers; N-acrylamidomethyltrimethylammonium chloride; allyltrimethylammonium chloride; dimethylallyl vinyl ketone; N-vinylpyrrolidone; vinyl chloride; vinylidene chloride; polyoxyethylene (meth)allyl ether; and polyoxypropylene (meth)allyl ether. Examples of suitable hydroxyalkylene (meth)allyl ethers include polyoxyalkylene (meth)acrylates such as polyoxyethylene (meth)acrylate and polyoxypropylene (meth)acrylate; polyoxyalkylene (meth)acrylamides such as polyoxyethylene (meth)acrylamide and polyoxypropylene (meth)acrylamide; polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl) esters; polyoxyalkylene vinyl ethers such as polyoxyethylene vinyl ether and polyoxypropylene vinyl ether; polyoxyalkylene allylamines such as polyoxyethylene allylamine and polyoxypropylene allylamine; polyoxyalkylene vinylamines such as polyoxyethylene vinylamine and polyoxypropylene vinylamine; and hydroxy group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, and 5-hexen-1-ol, or derivatives thereof, such as acylated products. Here, (meth)allyl means allyl or methallyl, (meth)acrylic means acrylic or methacrylic, and (meth)acrylate means acrylate or methacrylate, respectively.Furthermore, examples of monomers that can be copolymerized with vinyl ester monomers include 3,4-dihydroxy-1-butene, 3,4-diacyloxy-1-butene, 3-acyloxy-4-hydroxy-1-butene, 4-acyloxy-3-hydroxy-1-butene, 3,4-diacyloxy-2-methyl-1-butene, 4,5-dihydroxy-1-pentene, 4,5-diacyloxy-1-pentene, 4,5-dihydroxy-3-methyl-1-pentene, 4,5-diacyloxy-3-methyl-1-pentene, 5,6- Examples of such compounds include compounds having a diol, such as dihydroxy-1-hexene, 5,6-diacyloxy-1-hexene, glycerin monoallyl ether, 2,3-diacetoxy-1-allyloxypropane, 2-acetoxy-1-allyloxy-3-hydroxypropane, 3-acetoxy-1-allyloxy-2-hydroxypropane, glycerin monovinyl ether, glycerin monoisopropenyl ether, vinyl ethylene carbonate, and 2,2-dimethyl-4-vinyl-1,3-dioxolane. From the viewpoint of radiation shielding properties, the content of these monomers, such as olefins such as propylene, is preferably 45 mol% or less, more preferably 40 mol% or less, even more preferably 35 mol% or less, and particularly preferably 30 mol% or less.

[0019] Examples of post-modified PVAs into which functional groups have been introduced by post-modification include those having acetoacetyl groups by reaction with diketene, those having polyalkylene oxide groups by reaction with ethylene oxide, those having hydroxyalkyl groups by reaction with an epoxy compound, and those obtained by reacting an aldehyde compound having various functional groups with a PVA-based resin.

[0020] The modified PVA-based resin may be a PVA-based resin containing a structural unit having a primary hydroxyl group in the side chain. PVA-based resins containing a structural unit having a primary hydroxyl group in the side chain tend to have excellent melt-processability and are therefore preferred. Examples of PVA-based resins containing a structural unit having a primary hydroxyl group in the side chain include modified PVA-based resins having a 1,2-diol structural unit in the side chain and modified PVA-based resins having a hydroxyalkyl group structural unit in the side chain, with modified PVA-based resins having a 1,2-diol structural unit in the side chain being more preferred. Modified PVA-based resins containing a 1,2-diol structural unit in the side chain can be produced by known production methods. For example, they can be produced by the methods described in JP 2002-284818 A, JP 2004-285143 A, and JP 2006-95825 A.

[0021] When the PVA-based resin is a modified PVA-based resin, the modification rate in the modified PVA-based resin, i.e., the content of structural units derived from various monomers in the copolymer or functional groups introduced by post-modification, cannot be generally determined because the properties vary greatly depending on the type of functional group, but may be, for example, 0.1 to 20 mol %.

[0022] The PVA-based resin used in this embodiment may be one type or a mixture of two or more types. When two or more types of PVA-based resins are used, for example, a combination of two or more types of unmodified PVA-based resins differing in saponification degree, viscosity-average degree of polymerization, melting point, etc., a combination of an unmodified PVA-based resin and a modified PVA-based resin, or a combination of two or more types of modified PVA-based resins differing in saponification degree, viscosity-average degree of polymerization, melting point, type of functional group, modification rate, etc., may be mentioned.

[0023] From the viewpoint of achieving superior neutron shielding performance, the PVA resin preferably contains a saponified ethylene-vinyl ester copolymer (hereinafter also referred to as EVOH). EVOH is generally a resin obtained by saponifying a copolymer of ethylene and a vinyl ester monomer (ethylene-vinyl ester copolymer), and corresponds to the copolymer-modified PVA described above. EVOH is, for example, primarily composed of ethylene-derived structural units and vinyl alcohol structural units, and also contains vinyl ester structural units remaining unsaponified.

[0024] The ethylene content of EVOH, as measured in accordance with ISO 14663, is preferably 0.1 to 77 mol%, more preferably 20 to 60 mol%, more preferably 23 to 50 mol%, more preferably 25 to 48 mol%, more preferably 25 to 45 mol%, more preferably 25 to 40 mol%, more preferably 25 to 35 mol%, more preferably 25 to 32 mol%, and particularly preferably 29 to 32 mol%. That is, the ethylene content is preferably 0.1 mol% or more, more preferably 20 mol% or more, more preferably 23 mol% or more, more preferably 25 mol% or more, and particularly preferably 29 mol% or more. The ethylene content is preferably 77 mol% or less, preferably 60 mol% or less, more preferably 50 mol% or less, more preferably 48 mol% or less, more preferably 45 mol% or less, more preferably 40 mol% or less, even more preferably 35 mol% or less, and particularly preferably 32 mol% or less. When the ethylene content is equal to or greater than the lower limit, the crystallinity is improved and the arrangement of hydroxyl groups can be adjusted to facilitate hydrogen bonding, improving radiation shielding properties.When the ethylene content is equal to or less than the upper limit, the number of hydroxyl groups in the material can be increased, increasing the number of hydrogen bonds between hydroxyl groups, improving radiation shielding properties.

[0025] The EVOH may further contain structural units derived from the various monomers described above as monomers to be copolymerized with the vinyl ester monomer, in addition to ethylene structural units and vinyl alcohol structural units (including unsaponified vinyl ester structural units). EVOH may also be one into which functional groups have been introduced by the above-described post-modification.

[0026] The saponification degree of the PVA-based resin used in this embodiment (measured in accordance with JIS K 6726), including the saponification degree when the PVA-based resin is EVOH, is preferably, for example, 60 to 100 mol%. The preferred range of the saponification degree varies depending on the modified species. For example, in the case of an unmodified PVA-based resin, it is generally 70 mol% or more, with the upper limit being, for example, 99.9 mol% or less. That is, the saponification degree of the unmodified PVA-based resin may be 70 mol% to 99.9 mol%. Furthermore, the saponification degree of EVOH is generally 90 to 100 mol%, preferably 95.0 to 100 mol%, and particularly preferably 99 to 100 mol%. When the saponification degree of the PVA-based resin is equal to or greater than the lower limit, the PVA-based resin can be easily and uniformly mixed with the inorganic filler described below. Furthermore, a relatively high saponification degree can further improve neutron shielding performance. The degree of saponification may be 100 mol %, but from the viewpoint of ease of industrial production, it may be equal to or less than the upper limit mentioned above.

[0027] The melt flow rate (MFR) (210°C, 2160 g load) of the PVA-based resin (including EVOH) is typically 0.5 to 100 g / 10 min, preferably 1 to 50 g / 10 min, and particularly preferably 3 to 35 g / 10 min. That is, the MFR of the PVA-based resin may be 0.5 g / 10 min or more, preferably 1 g / 10 min or more, and particularly preferably 3 g / 10 min or more. The MFR of the PVA-based resin may be 100 g / 10 min or less, preferably 50 g / 10 min or less, and particularly preferably 35 g / 10 min or less. Having an MFR equal to or greater than the above-mentioned lower limit can improve moldability during melt extrusion and other processes. Having an MFR equal to or less than the above-mentioned upper limit can improve the strength of the molded product when molded into a film, sheet, or molded product.

[0028] The viscosity-average degree of polymerization (measured in accordance with JIS K 6726) of the PVA-based resin used in this embodiment is generally 250 to 3000, preferably 400 to 1700, particularly preferably 450 to 1100, and even more preferably 450 to 800. That is, the viscosity-average degree of polymerization of the PVA-based resin may be, for example, 250 or more, preferably 400 or more, and particularly preferably 450 or more. The viscosity-average degree of polymerization of the PVA-based resin may be 3000 or less, preferably 1700 or less, particularly preferably 1100 or less, and even more preferably 800 or less. Having a viscosity-average degree of polymerization equal to or greater than the above-mentioned lower limit ensures the strength of films, coating films, and other molded articles. Having a viscosity-average degree of polymerization equal to or less than the above-mentioned upper limit allows for the use of general-purpose molding methods, enabling the resin to be used in a variety of applications.

[0029] The PVA resin used in this embodiment can be produced by polymerizing a vinyl ester monomer such as vinyl acetate and then saponifying the polymer. To obtain a copolymerized modified PVA, a monomer composition containing a vinyl ester monomer and a monomer used in copolymerization is polymerized and then saponified.

[0030] Examples of the vinyl ester monomer that can be used include vinyl propionate, vinyl butyrate, vinyl caproate, vinyl caprylate, vinyl caprate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl stearate, vinyl cyclohexanecarboxylate, vinyl piperate, vinyl octylate, vinyl monochloroacetate, vinyl adipate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl benzoate, vinyl cinnamate, and vinyl trifluoroacetate. From the viewpoints of cost and availability, vinyl acetate is preferably used as the vinyl ester monomer.

[0031] The polymerization of vinyl ester monomers can be carried out by any known polymerization method, such as solution polymerization, suspension polymerization, or emulsion polymerization. Among these, solution polymerization, which can efficiently remove reaction heat, is preferably carried out under reflux. As a solvent for solution polymerization, for example, an alcohol is used, and preferably a lower alcohol having 1 to 3 carbon atoms is used.

[0032] The saponification of the obtained polymer can also be carried out by a known saponification method. That is, for example, the saponification can be carried out using an alkali catalyst or an acid catalyst while the polymer is dissolved in an alcohol or water / alcohol solvent. Examples of alkali catalysts that can be used include hydroxides and alcoholates of alkali metals such as potassium hydroxide, sodium hydroxide, sodium methylate, sodium ethylate, potassium methylate, and lithium methylate. For example, a transesterification reaction using an alkali catalyst in an absolute alcohol solvent is preferably used in terms of the reaction rate and the ability to reduce impurities such as fatty acid salts.

[0033] The reaction temperature for the saponification reaction is, for example, 20 to 60°C. If the reaction temperature is too low, the reaction rate tends to be slow and the reaction efficiency tends to decrease, while if the reaction temperature is too high, the temperature may exceed the boiling point of the reaction solvent, which tends to reduce safety in terms of production. When saponification is performed under high pressure using a highly pressure-resistant tower-type continuous saponification tower or the like, saponification can be performed at a higher temperature, for example, 80 to 150°C, and it is possible to obtain a product with a high degree of saponification in a short time even with a small amount of saponification catalyst.

[0034] (Inorganic Filler) The radiation-shielding composition preferably further contains an inorganic filler. For example, by incorporating a compound containing an element having good neutron absorption performance as a filler, the neutron shielding performance of the radiation-shielding composition can be further improved. From this viewpoint, the inorganic filler preferably contains a compound containing one or more elements selected from the group consisting of Gd, B, and Li. The compound is not particularly limited, but examples thereof include oxides, composite oxides, sulfides, hydroxides, etc. containing each element. All of these elements have a high absorption cross section for neutrons. Among these elements, Gd and B have larger absorption cross sections, and it is more preferable that the inorganic filler contains at least one selected from the group consisting of compounds containing at least one of Gd and B. Among these elements, Gd has the largest absorption cross section, and it is most preferable that the inorganic filler contains a compound containing Gd. In another aspect, from the viewpoints of stability and toxicity, the inorganic filler is selected from the group consisting of Gd ２ O ３ , B ２ O ３ , B ４ It is preferable that the electrolyte contains at least one selected from the group consisting of C and LiF.

[0035] Examples of compounds containing Gd include oxides, composite oxides, sulfides, and hydroxides containing Gd. More specifically, gadolinium oxide (GdO) ２ O ３ , gadolinium gallium garnet Gd ３ Ga ５ O １２ , gadolinium ferrite GdFeO ３ , Gd ３ Fe ５ O １２ , gadolinium hydroxide Gd(OH) ３ , cerium-activated gadolinium silicate Gd ２ SiO ５ : Ce, europium activated gadolinium borate GdBO ３ : Eu, europium-activated gadolinium oxide Gd ２ O ３: Eu, gadolinium sulfate activated with europium Gd ２ O ２ S: Eu, europium-activated gadolinium aluminate (Gd) ３ Al ５ O １２ : Eu, europium-activated gadolinium gallate Gd ３ Ga ５ O １２ : Eu, europium-activated gadolinium vanadate GdVO ４ : Gadolinium gallate Gd activated with Eu and cerium or chromium ３ Ga ５ O １２ : Ce, Cr, terbium activated gadolinium oxide Gd ２ O ３ : Tb, terbium activated gadolinium sulfate Gd ２ O ２ S: gadolinium sulfate activated with Tb and praseodymium (Gd) ２ O ２ S: Pr, terbium-activated gadolinium gallate Gd ３ Ga ５ O １２ : Tb, terbium activated gadolinium aluminate Gd ３ Al ５ O １２ : Tb, etc., and from the viewpoint of excellent stability in the atmosphere, oxides of Gd are preferred, and Gd ２ O ３ is more preferred.

[0036] Examples of compounds containing B include oxides, composite oxides, sulfides, hydroxides, carbides, nitrides, and phosphides containing B, and more specifically, boron carbide B ４ C, boron nitride BN, boron phosphide BP, boron sulfide B ２ S ３ , Boron phosphate BPO ４ , boron oxide B ２ O ３ From the viewpoint of excellent stability in the atmosphere, B ４ C, B ２ O ３ is preferred.

[0037] Examples of compounds containing Li include oxides, composite oxides, sulfides, fluorides, and hydroxides containing Li, and lithium oxide, Li ２ O, Lithium peroxide Li ２ O ２ , lithium aluminate LiAlO ２ , lithium metaborate LiBO ２ , lithium tetraborate Li ２ B ４ O ７ , lithium germanate Li ２ GeO ３ , lithium molybdate Li ２ MoO ４ , lithium niobate LiNbO ３ , lithium metasilicate Li2SiO ３ , lithium tantalate LiTaO ３ , lithium titanate Li2TiO ３ , lithium vanadate LiVO ３ , lithium tungstate LiWO ４ , lithium zirconate Li ２ ZrO ３ , lithium fluoride LiF, lithium nitride Li ３ N, Lithium hydroxide LiOH.H ２ O, Lithium methoxy LiOCH ３ LiF and Li are preferred because of their excellent stability in the atmosphere. ２ O is preferred.

[0038] The radiation-shielding composition may contain, as inorganic fillers, compounds containing elements capable of absorbing neutrons, protons, and heavy particles, as well as compounds containing elements capable of absorbing various types of radiation other than neutrons, protons, and heavy particles, known additives, etc., depending on the desired performance. Specific examples of compounds containing elements capable of absorbing various types of radiation other than neutrons, protons, and heavy particles include compounds containing one or more elements selected from the group consisting of lead, iron, Bi, Y, Zr, Nb, Mo, Hf, Ta, W, and lanthanoid elements. Examples of compounds containing these elements include composite oxides, sulfides, hydroxides, etc. Among these, ZrO is preferred from the viewpoint of being able to simultaneously absorb gamma rays generated by nuclear reactions and being easy to handle. ２ is particularly preferred.

[0039] The proportion of the compound containing one or more elements selected from the group consisting of Gd, B, and Li in the inorganic filler may be 0% by mass depending on the desired performance, but from the viewpoint of improving the shielding performance against neutrons and protons, it is preferably 20% by mass or more, more preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, particularly preferably 60% by mass or more, and may be 100% by mass.

[0040] The content of the inorganic filler in the radiation-shielding composition is preferably, for example, 10 to 90% by mass. That is, from the viewpoint of improving the radiation-shielding property, the content of the inorganic filler is preferably 10% by mass or more, more preferably 20% by mass or more, and particularly preferably 30% by mass or more. From the viewpoints of the strength, shape stability, and moldability of various molded products, the content of the inorganic filler in the radiation-shielding composition is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, still more preferably 50% by mass or less, and particularly preferably 40% by mass or less.

[0041] The shape of the inorganic filler is not particularly limited, but powdered inorganic fillers are generally preferred. The average particle size of the inorganic filler is, for example, preferably 1 to 50 μm, more preferably 2 to 30 μm, and even more preferably 2 to 20 μm. That is, the average particle size of the inorganic filler is preferably 1 μm or more, more preferably 2 μm or more. Furthermore, the average particle size of the inorganic filler is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. By having the average particle size be equal to or less than the above upper limit, the particle arrangement in the coating film can be precisely designed, thereby improving radiation shielding properties. By having the average particle size be equal to or greater than the above lower limit, the inorganic filler can be uniformly dispersed in the coating film or molded product. Here, the average particle size refers to the median diameter (d50) measured using a laser diffraction particle size distribution analyzer in accordance with JIS 8825: Particle Size Analysis - Laser Diffraction and Scattering Method.

[0042] When the radiation-shielding composition contains a polyvinyl alcohol-based resin and an inorganic filler, the radiation-shielding composition can be produced by mixing them by a known method, such as melt-kneading, aqueous or solvent-based dispersion of the resin and the filler, or mixing an aqueous or solvent-based resin emulsion with the inorganic filler. In terms of lowering the heating temperature in the mixing step, aqueous or solvent-based dispersion of the resin and the filler, or mixing an aqueous or solvent-based resin emulsion with the inorganic filler is preferred, and mixing an aqueous or solvent-based resin emulsion with the inorganic filler is particularly preferred. That is, the polyvinyl alcohol-based resin is preferably contained in the radiation-shielding composition in the form of an emulsion. Mixing an emulsion-form polyvinyl alcohol-based resin with the inorganic filler lowers the heating temperature in the mixing step, allowing a larger amount of filler to be contained, thereby further improving neutron shielding performance.

[0043] When a radiation-shielding composition is produced by mixing an aqueous or solvent-based resin emulsion with an inorganic filler, examples of methods for producing the aqueous or solvent-based resin emulsion include a high-pressure homogenizer method and an extrusion-forced mechanical emulsification method. Among these, the extrusion-forced mechanical emulsification method is advantageous in terms of continuous productivity for efficient production.

[0044] The radiation-shielding composition may further contain additives other than the polyvinyl alcohol-based resin and the inorganic filler, such as a stabilizer (thickener), a surfactant, a colorant, a plasticizer, and a lubricant, as long as the additives do not impair the effects of the present invention.

[0045] (Applications) The radiation-shielding composition according to the embodiment of the present invention has excellent radiation-shielding performance, particularly excellent neutron-shielding performance, and is therefore suitable for use in protecting people, articles including robots, etc. that may be exposed to radiation. More specifically, the radiation-shielding composition according to the embodiment of the present invention is suitable for use in nuclear power generation-related applications such as components for nuclear reactors or their periphery, and vessels and containers for storing nuclear waste and nuclear fuel debris, aerospace applications such as components for aircraft and spacecraft, and artificial satellites and lunar and Mars-related infrastructure, medical applications such as components for medical accelerators and peripheral components for medical devices that utilize radiation, and electronic materials containing semiconductors as components.

[0046] The neutron transmittance of a molded article made of the radiation-shielding composition according to an embodiment of the present invention is preferably less than 25%, particularly preferably less than 22%, and even more preferably less than 20%, when the thickness of the molded article is 1 mm. When the thickness of the molded article is 5 mm, the neutron transmittance of the molded article is preferably less than 18%, particularly preferably less than 17.8%, and even more preferably less than 17.6%. The neutron transmittance is measured by the method described in the examples.

[0047] In the various applications described above, the radiation-shielding composition may be used as various articles or components by molding into a desired shape, or by preparing a paint or coating material containing the radiation-shielding composition and applying the paint or coating material to various components, etc. That is, the present invention also relates to a paint or coating material containing the radiation-shielding composition according to an embodiment of the present invention. The paint or coating material containing the radiation-shielding composition can be produced, for example, by a method similar to that for producing a known paint or coating material containing a PVA-based resin. Furthermore, by applying or coating the paint or coating material containing the radiation-shielding composition to various components, etc. and drying it as necessary, a layer made of the paint or coating material can be formed on various components, and these are suitable for various applications such as medical devices, electronic components, nuclear power generation components, or aviation or space components. When the radiation-shielding composition contains an inorganic filler, it is preferable to prepare a radiation-shielding composition with properties suitable for a paint or coating material by, for example, emulsion-mixing a PVA-based resin, an inorganic filler, and optional additives, etc.

[0048] Furthermore, a molded product obtained by molding the radiation-shielding composition according to an embodiment of the present invention has excellent radiation-shielding performance, particularly excellent neutron-shielding performance, and is therefore suitable for use as various articles such as medical devices, electronic components, components for nuclear power generation, or components for aviation or space applications, or components constituting these articles.

[0049] (Composition containing a polyvinyl alcohol-based resin and at least one selected from the group consisting of compounds containing at least one of Gd, B, and Li) The present invention also relates to a composition containing a polyvinyl alcohol-based resin and at least one selected from the group consisting of compounds containing at least one of Gd, B, and Li. As described above, the inventors have found that PVA-based resins have excellent neutron shielding performance. Furthermore, compounds containing at least one of Gd, B, and Li have excellent neutron absorption performance. Therefore, the composition has excellent neutron shielding performance. In particular, a composition containing a polyvinyl alcohol-based resin and a compound containing Gd has particularly excellent neutron shielding performance. In another embodiment, a composition containing a polyvinyl alcohol-based resin and a compound containing Gd is ２ O ３ , B ２ O ３ , B ４ Compositions containing at least one selected from the group consisting of C and LiF have excellent neutron absorption performance and are also preferred in terms of stability and toxicity. These compositions are suitable for use in radiation shielding compositions.

[0050] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified.

[0051] (Examples 1 to 5) The resins shown in Table 1 were used as the PVA-based resin. Gd ２ O ３A PVA-based resin and a filler were mixed using powder (manufactured by Nippon Yttrium Co., Ltd., product name: gadolinium oxide 99.9%, average particle size 2.32 μm) so that the filler content in the composition would be the value shown in Table 1, to obtain compositions (radiation-shielding compositions). For evaluation, in Examples 1 to 3 and 5, a uniformly dispersed kneaded product measuring 5 cm long, 5 cm wide, and 5 mm thick was obtained by melt-kneading (molding temperature 210°C) using a twin-screw extruder, and this was used for evaluation. In Example 4, a separately prepared emulsion of EVOH3 (solid content concentration 22%) and an inorganic filler were uniformly stirred and mixed using a batch mixer, and then allowed to dry, to obtain a uniformly dispersed kneaded product measuring 5 cm long, 5 cm wide, and 5 mm thick (inorganic filler content 87% by mass), which was used for evaluation.

[0052] The emulsion used in Example 4 was produced by a forced extrusion mechanical emulsification method using a twin-screw extruder, and was obtained as an emulsion solution of EVOH3 with a solid content of 22% and an average particle size of 2 μm.

[0053] The details of the resins shown in Table 1 are as follows: PVA1: "Nichigo G-Polymer (registered trademark) BVE8049P" manufactured by Mitsubishi Chemical Corporation, a modified PVA resin containing a 1,2-diol structural unit in the side chain, saponification degree 99.2%, hydrogen ratio 9.4% by mass EVOH1: "Soarnol (registered trademark) DT2904RB" manufactured by Mitsubishi Chemical Corporation, EVOH with an ethylene content of 29 mol%, saponification degree 99.9%, hydrogen ratio 10.2% by mass EVOH2: "Soarnol (registered trademark) AT4403B" manufactured by Mitsubishi Chemical Corporation, EVOH with an ethylene content of 44 mol%, saponification degree 99.9%, hydrogen ratio 10.8% by mass EVOH3: "Soarnol (registered trademark) AT4403B" manufactured by Mitsubishi Chemical Corporation, EVOH with an ethylene content of 44 mol%, saponification degree 99.9%, hydrogen ratio 10.8% by mass EVOH4: "Soarnol (registered trademark) AT4403B" manufactured by Mitsubishi Chemical Corporation, EVOH with an ethylene content of 44 mol%, saponification degree 99.9%, hydrogen ratio 10.8% by mass EVOH5: "Soarnol (registered trademark) AT4403B" manufactured by Mitsubishi Chemical Corporation, EVOH with an ethylene content of 44 mol%, saponification degree 99.9%, hydrogen ratio 10.8% by mass EVOH6: "Soarnol (registered trademark) AT4403B" manufactured by Mitsubishi Chemical Corporation, DC3212B," EVOH with an ethylene content of 32 mol%, saponification degree of 99.9%, and hydrogen ratio of 10.3% by mass. EVOH4: Tosoh Corporation, "MELTHEN H0051K," ethylene content: 89 mol%, saponification degree: 99 mol%, MFR: 6.5 g / 10 min (190°C, load: 2160 g), and hydrogen ratio of 13.1% by mass.

[0054] Comparative Example 1 The same procedure as in Example 1 was repeated, except that high-density polyethylene (manufactured by Mitsubishi Chemical Corporation, "Novatec HD HJ360", hydrogen ratio 14.3% by mass) was used instead of PVA1. The high-density polyethylene and the filler were uniformly melt-kneaded to obtain a molded product having a length of 5 cm, a width of 5 cm, and a thickness of 5 mm, which was used for evaluation.

[0055] Example 6 As shown in Table 2, a composition (radiation-shielding composition) prepared by mixing EVOH1 and an inorganic filler was melt-kneaded (molding temperature: 210°C) in a twin-screw extruder in the same manner as in Example 2, to obtain a uniformly dispersed kneaded product having a size of 5 cm long x 5 cm wide x 1 mm thick, which was used for evaluation.

[0056] Example 7 The same emulsion solution as used in Example 4, containing 70% by mass of EVOH (EVOH3) with a solid content of 22% and an average particle size of 2 μm, and an inorganic filler (Gd ２ O ３ The mixture was uniformly stirred and mixed with 30% by mass of a powder (product name: gadolinium oxide 99.9%, average particle size 2.32 μm, manufactured by Nippon Yttrium Co., Ltd.) in a batch mixer, and then allowed to dry to obtain a uniformly dispersed kneaded product (inorganic filler content 66% by mass) measuring 5 cm in length, 5 cm in width, and 1 mm in thickness, which was used for evaluation.

[0057] Example 8 As shown in Table 2, EVOH4 and an inorganic filler were homogeneously melt-kneaded in the same manner as in Example 6, except that EVOH4 was used instead of EVOH1, to obtain a molded product having a length of 5 cm, a width of 5 cm, and a thickness of 1 mm, which was used for evaluation.

[0058] Comparative Example 2 As shown in Table 2, the same procedure as in Example 6 was repeated except that high-density polyethylene (manufactured by Mitsubishi Chemical Corporation, "Novatec HD HJ360", hydrogen ratio 14.3 mass%) was used instead of EVOH1. The high-density polyethylene and the inorganic filler were uniformly melt-kneaded to obtain a molded product having a length of 5 cm, a width of 5 cm, and a thickness of 1 mm, which was used for evaluation.

[0059] (Evaluation) For each composition, a plate-shaped molded product for evaluation was prepared as described above, and neutron transmittance was evaluated. Gold foil was placed on each of the front and back (both main surfaces) of the molded sample for evaluation, and neutrons were irradiated from the front side of the sample toward the sample in a direction parallel to the plate thickness direction. Either main surface of the sample can be designated as the surface. The accelerator neutron source was generated under the following conditions. The gold foils placed on the front and back of the sample were positioned so that they did not overlap when viewed parallel to the plate thickness direction of the sample (i.e., the neutron irradiation direction). When irradiated with neutrons, the gold foil was activated. The neutron transmittance (shielding factor) was evaluated based on the ratio of the radioactivity intensity of the gold foil on the front side of the sample, which was directly irradiated with neutrons, to the radioactivity intensity of the gold foil on the back side, which was irradiated with neutrons that had passed through the sample. In other words, the smaller this ratio (transmittance), the better the neutron shielding performance of the sample. The results are shown in Tables 1 and 2. (Accelerator neutron source) Accelerator: Sumitomo Heavy Industries Cyclotron HM-18HC Accelerated particle: Proton 18 MeV Target: Be Nuclear reaction: 7Be(p,n)7B reaction Irradiation current: ~120 μA Irradiation time: 3 hours

[0060]

[0061]

[0062] The results in Table 1 confirm that the compositions of Examples 1 to 3 and 5, which contained a PVA-based resin, exhibited superior neutron shielding performance compared to the composition of Comparative Example 1, which had the same filler content, and were therefore suitable for use as radiation-shielding compositions. This is believed to be due to an increased amount of hydrogen bonding between hydroxyl groups in the polyvinyl alcohol, resulting from the crystalline portion derived from polyethylene. In particular, the composition of Example 2, which contained EVOH1 with an ethylene content of 29 mol%, and the composition of Example 3, which contained EVOH2 with an ethylene content of 44 mol%, exhibited superior neutron shielding performance compared to the composition of Example 1, which contained PVA1, and the composition of Example 5, which contained EVOH4 with an ethylene content of 89 mol%. The composition of Example 4 was obtained as an emulsion-mixed liquid composition before standing and drying, and had properties suitable for use as a paint or coating material. By preparing the composition as an emulsion-mixed liquid, the heating temperature during the mixing process could be lowered, allowing for the incorporation of a larger amount of filler, resulting in superior neutron shielding performance.

[0063] A similar tendency was also observed in comparison between Examples 6 to 8, in which the sample thickness was changed to 1 mm, and Comparative Example 2.

[0064] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese patent applications filed on February 28, 2023 (Patent Application No. 2023-030175) and February 28, 2024 (Patent Application No. 2024-028793), the contents of which are incorporated herein by reference.

Claims

1. A radiation-shielding composition containing a polyvinyl alcohol-based resin.

2. The radiation shielding composition of claim 1 , wherein the radiation comprises one or more selected from the group consisting of neutrons, protons, and heavy particles.

3. 2. The radiation-shielding composition according to claim 1, wherein the polyvinyl alcohol-based resin comprises a saponified ethylene-vinyl ester-based copolymer.

4. 4. The radiation-shielding composition according to claim 3, wherein the ethylene content of the saponified ethylene-vinyl ester copolymer is 0.1 to 77 mol %.

5. 4. The radiation-shielding composition according to claim 3, wherein the ethylene content of the saponified ethylene-vinyl ester copolymer is 20 to 60 mol %.

6. 2. The radiation-shielding composition according to claim 1, wherein the polyvinyl alcohol-based resin comprises a modified polyvinyl alcohol-based resin containing a 1,2-diol structural unit in a side chain.

7. The radiation-shielding composition of claim 1 , further comprising an inorganic filler.

8. The radiation-shielding composition according to claim 7 , comprising the inorganic filler in an amount of 30 mass % or more.

9. The inorganic filler is Gd ２ O ３ , B ２ O ３ , B ４ The radiation-shielding composition according to claim 7, comprising at least one selected from the group consisting of C and LiF.

10. The radiation-shielding composition according to claim 1 , which is a water-based or solvent-based resin emulsion.

11. A paint or coating material comprising the radiation-shielding composition according to any one of claims 1 to 10.

12. A molded article comprising the radiation-shielding composition according to any one of claims 1 to 10.

13. A medical device having a layer formed using the paint or coating material according to claim 11.

14. An electronic component having a layer formed using the paint or coating material according to claim 11.

15. A component for nuclear power generation having a layer formed using the paint or coating material according to claim 11.

16. An aeronautical or space component having a layer formed using the paint or coating material according to claim 11.

17. A medical device comprising the molded article according to claim 12.

18. An electronic component comprising the molded article according to claim 12.

19. A component for nuclear power generation, comprising the molded article according to claim 12.

20. An aeronautical or space component comprising the molded article according to claim 12.

21. A composition comprising a polyvinyl alcohol resin and at least one compound selected from the group consisting of compounds containing at least one of Gd, B, and Li.

22. 22. The composition of claim 21 used as a radiation shielding composition.