Coating composition and radiation shielding coating composition

Abstract

The present invention relates to a coating composition containing an emulsion (I) that contains: a saponified ethylene-vinyl ester copolymer product (A) containing 10 mol% or greater of ethylene-derived structural units; and a polyvinyl alcohol resin (B) containing less than 10 mol% of ethylene-derived structural units. The contained proportion of the polyvinyl alcohol resin (B) is 5 to 90 mass% with respect to the total of 100 mass% of the saponified ethylene-vinyl ester copolymer product (A) and the polyvinyl alcohol resin (B). The saponification degree of the polyvinyl alcohol resin (B) is 70 to 97 mol%.

Description

Coating composition and radiation shielding coating composition

[0001] The present invention relates to a coating composition and a radiation shielding coating composition.

[0002] Traditionally, saponified ethylene-vinyl ester copolymers have been used as gas barrier layers in various packaging films due to their excellent oxygen gas barrier properties (see, for example, Patent Document 1). Furthermore, because saponified ethylene-vinyl ester copolymers have excellent solvent resistance, it is difficult to dissolve them in a solvent to form a coating liquid (paint) when forming a laminate, and they are typically laminated by melt extrusion. However, when laminating them to materials other than thermoplastic resins or to materials with complex shapes, a paint with fluidity is required.

[0003] Ethylene-based polymers with a high proportion of hydrogen atoms are also attracting attention as radiation shielding materials. Radiation can be broadly divided into electromagnetic radiation and particle radiation. The main electromagnetic radiation is gamma rays and X-rays, while the main particle radiation is alpha rays (α rays = helium nuclei) and beta rays (β rays = electrons) generated by radioactive isotopes, as well as high-energy electrons, protons, neutrons, and heavy particles (heavy ions) generated in space and accelerator facilities. Of these, electrically neutral neutrons are not blocked by matter due to electromagnetic interactions, so shielding materials tailored to their properties will be required to protect the human body and other areas.

[0004] 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.

[0005] 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.

[0006] For example, Patent Document 2 discloses a boron compound, preferably boron carbide B ４ Patent Document 3 describes a neutron absorbing material made of ultra-high density polyethylene embedded with C. Patent Document 3 also describes a neutron shielding structure that includes an inner layer made of polyethylene containing a neutron absorbing substance, an intermediate layer made of polyethylene disposed on the inner layer, and an outer layer made of polyethylene containing a neutron absorbing substance disposed on the intermediate layer.

[0007] Japanese Unexamined Patent Publication No. 2022-139179 Japanese Unexamined Patent Publication No. 3-107797 Unexamined Japanese Patent Application No. 2015-010826

[0008] However, paints made from polyethylene emulsion or silicone have the problem that when inorganic fillers, which have a high specific gravity and tend to settle, are added, the dispersion stability of the inorganic fillers and the like are poor, and the coating film forming properties are also poor.

[0009] Therefore, one of the objects of the present invention is to provide a coating composition that has excellent film-forming properties and, when a film is formed, has excellent water resistance.

[0010] As a result of extensive research, the present inventors have found that a coating composition containing an emulsion containing a saponified ethylene-vinyl ester copolymer and a polyvinyl alcohol resin in a specific ratio has excellent coating film formability and excellent water resistance when the coating film is formed.

[0011] That is, the present invention relates to the following aspects 1 to 10.

[0012] A first aspect of the present invention is a coating composition containing an emulsion (I) containing a saponified ethylene-vinyl ester copolymer (A) having a content of structural units derived from ethylene of 10 mol% or more, and a polyvinyl alcohol resin (B) having a content of structural units derived from ethylene of less than 10 mol%, wherein the content of the polyvinyl alcohol resin (B) is 5 to 90 mass% relative to 100 mass% of the total of the saponified ethylene-vinyl ester copolymer (A) and the polyvinyl alcohol resin (B), and the polyvinyl alcohol resin (B) has a degree of saponification of 70 to 97 mol%.

[0013] A second aspect of the present invention is the coating composition of the first aspect, wherein the emulsion particles in the emulsion (I) have an average particle size of 0.1 to 20 μm.

[0014] A third aspect of the present invention is the coating composition of the first or second aspect, wherein the saponified ethylene-vinyl ester copolymer (A) has a content of ethylene-derived structural units of 10 to 77 mol %.

[0015] A fourth aspect of the present invention is the coating composition according to any one of the first to third aspects, wherein the polyvinyl alcohol resin (B) has a degree of saponification of 85 to 95 mol %.

[0016] A fifth aspect of the present invention is the coating composition according to any one of the first to fourth aspects, wherein the polyvinyl alcohol resin (B) has an average degree of polymerization of 1,800 to 2,500.

[0017] A sixth aspect of the present invention is the coating composition according to any one of the first to fifth aspects, further comprising an inorganic filler (C).

[0018] A seventh aspect of the present invention is the coating composition of the sixth aspect, which contains 100 to 2,000 parts by mass of an inorganic filler (C) per 100 parts by mass of the saponified ethylene-vinyl ester copolymer (A).

[0019] Aspect 8 of the present invention is the inorganic filler (C) of aspect 6 or 7, wherein the inorganic filler (C) is a calcium-based compound, a titanium-based compound, a vanadium-based compound, a chromium-based compound, a manganese-based compound, an iron-based compound, a cobalt-based compound, a nickel-based compound, a copper-based compound, a zinc-based compound, a zirconium-based compound, a niobium-based compound, a molybdenum-based compound, a technetium-based compound, a ruthenium-based compound, a rhodium-based compound, a palladium-based compound, a silver-based compound, a cadmium-based compound, an indium-based compound, a tin-based compound, an antimony-based compound, a barium-based compound, a lanthanum-based compound, or a chromium-based compound. The coating composition contains at least one selected from the group consisting of platinum-based compounds, cerium-based compounds, neodymium-based compounds, samarium-based compounds, gadolinium-based compounds, lithium-based compounds, boron-based compounds, hafnium-based compounds, tantalum-based compounds, tungsten-based compounds, rhenium-based compounds, osmium-based compounds, indium-based compounds, platinum-based compounds, gold-based compounds, thallium-based compounds, lead-based compounds, bismuth-based compounds, polonium-based compounds, sand, soil, clay, ores, minerals, mortar, cement, concrete, asphalt, and ceramics.

[0020] A ninth aspect of the present invention is a radiation-shielding coating composition containing the coating composition according to any one of the first to eighth aspects.

[0021] A tenth aspect of the present invention is the radiation shielding coating composition according to the ninth aspect, wherein the radiation includes one or more selected from the group consisting of neutrons, protons, and heavy particles.

[0022] According to the present invention, there is provided a coating composition that exhibits excellent film-forming properties and excellent water resistance when a coating film is formed. The present inventors have also found that this coating composition exhibits better neutron shielding ability than coating compositions using high-density polyethylene, which is considered to have high neutron shielding ability due to its high hydrogen atom ratio. Thus, the present invention also provides a radiation-shielding coating composition that contains this coating composition and has excellent radiation-shielding ability.

[0023] 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.

[0024] <<Coating Composition>> The coating composition of this embodiment contains an emulsion (I) containing a saponified ethylene-vinyl ester copolymer (A) having an ethylene-derived structural unit content of 10 mol% or more and a polyvinyl alcohol-based resin (B) having an ethylene-derived structural unit content of less than 10 mol%. Here, the content of the polyvinyl alcohol-based resin (B) relative to 100% by mass of the total of the saponified ethylene-vinyl ester copolymer (A) and the polyvinyl alcohol-based resin (B) is 5 to 90% by mass. The saponification degree of the polyvinyl alcohol-based resin (B) is 70 to 97 mol%. Each component will be described in order below.

[0025] <Saponified Ethylene-Vinyl Ester Copolymer (A)> The saponified ethylene-vinyl ester copolymer (hereinafter abbreviated as EVOH) (A) used in the present embodiment is generally a resin obtained by saponifying a copolymer of ethylene and a vinyl ester monomer (ethylene-vinyl ester copolymer). EVOH mainly contains, for example, ethylene-derived structural units and vinyl alcohol structural units, and also contains vinyl ester structural units remaining unsaponified.

[0026] The content of ethylene-derived structural units in EVOH (A) (ethylene content), as measured in accordance with ISO 14663, is 10 mol% or more, preferably 10 to 77 mol%, more preferably 20 to 60 mol%, and even more preferably 23 to 50 mol%, 25 to 48 mol%, and 25 to 45 mol%, in the following stepwise order. That is, the ethylene content of EVOH (A) is 10 mol% or more, preferably 20 mol% or more, more preferably 23 mol% or more, and particularly preferably 25 mol% or more. Furthermore, the ethylene content of EVOH (A) is preferably 77 mol% or less, more preferably 60 mol% or less, even more preferably 50 mol% or less, and even more preferably 48 mol% or less and 45 mol% or less, in the following stepwise order. When the ethylene content of EVOH (A) is 10 mol% or more, the water resistance and gas barrier properties of the coating film are appropriately exhibited. In addition, an ethylene content of EVOH (A) of 77 mol% or less is preferable because it improves crystallinity and allows the arrangement of hydroxyl groups to be adjusted to one that facilitates hydrogen bonding, thereby improving radiation shielding properties. In addition, an ethylene content of EVOH (A) of 77 mol% or less can increase the number of hydroxyl groups in the material, thereby increasing the number of hydrogen bonds between hydroxyl groups and further improving radiation shielding properties. When the ethylene content of EVOH (A) is 10 to 77 mol%, the water resistance and gas barrier properties of the formed coating film tend to be superior. In addition, the radiation shielding properties also tend to be superior.

[0027] EVOH (A) may contain structural units derived from ethylene, vinyl alcohol structural units (including unsaponified vinyl ester structural units), and structural units derived from various monomers used in copolymerization with vinyl ester-based monomers. EVOH (A) may also contain structural units derived from various monomers used in copolymerization with vinyl ester-based monomers by post-modification. Examples of the monomers used in copolymerization include various monomers exemplified as monomers used in copolymerization with vinyl ester-based monomers in the production of polyvinyl alcohol-based resin (B) described below. The same techniques as those used in the post-modification of polyvinyl alcohol-based resin (B) described below can also be used for the post-modification.

[0028] The saponification degree of EVOH (A) is generally 90 to 100 mol%, preferably 95 to 100 mol%, and particularly preferably 99 to 100 mol%. When the saponification degree is equal to or greater than the lower limit, the inorganic filler (C), which will be described later, can be easily mixed uniformly into the resin composition. Furthermore, a relatively high saponification degree can further improve the radiation-shielding performance. The saponification degree may be 100 mol%, but may be equal to or less than the upper limit from the viewpoint of ease of industrial production.

[0029] The melt flow rate (MFR) (210°C, 2160 g load) of EVOH (A) is usually 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 EVOH (A) 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 EVOH (A) may be 100 g / 10 min or less, preferably 50 g / 10 min or less, and particularly preferably 35 g / 10 min or less. When the MFR of EVOH (A) is equal to or greater than the above-mentioned lower limit, molding processability during melt extrusion and the like can be improved. When the MFR of EVOH (A) is equal to or less than the above-mentioned upper limit, the strength of the molded product can be improved when molded into a film, sheet, or molded product.

[0030] The EVOH (A) used in this embodiment may be one type or a mixture of two or more types. When two or more types of EVOH (A) are used, for example, a combination of two or more types of unmodified EVOHs differing in saponification degree, viscosity-average degree of polymerization, melting point, etc., a combination of an unmodified EVOH and a modified EVOH, or a combination of two or more types of modified EVOHs differing in saponification degree, viscosity-average degree of polymerization, melting point, type of functional group, modification rate, etc., may be mentioned.

[0031] EVOH is a resin obtained by copolymerizing ethylene with a vinyl ester monomer and then saponifying the copolymer, and is a water-insoluble thermoplastic resin known as a saponified ethylene-vinyl alcohol copolymer or ethylene-vinyl acetate copolymer. Any known polymerization method, such as solution polymerization, suspension polymerization, or emulsion polymerization, can be used, but solution polymerization using methanol as a solvent is generally used. The resulting ethylene-vinyl ester copolymer can also be saponified by a known method.

[0032] <Polyvinyl Alcohol-Based Resin (B)> The polyvinyl alcohol-based resin (hereinafter abbreviated as PVA-based resin) (B) used in this embodiment is composed primarily of vinyl alcohol structural units, and contains unsaponified vinyl ester structural units and, as necessary, structural units derived from other copolymerizable monomers. In this embodiment, the content of ethylene-based structural units (ethylene content) in the PVA-based resin (B) is less than 10 mol%, preferably less than 5 mol%, more preferably less than 2 mol%, and particularly preferably 0 mol%. If the ethylene content of the PVA-based resin (B) is too high, it becomes water-insoluble and fails to exhibit satisfactory surfactant and protective colloid properties. However, if the ethylene content is less than 10 mol%, it exhibits satisfactory surfactant and protective colloid properties, enabling the formation of a uniform EVOH emulsion.

[0033] Examples of the PVA-based resin (B) include unmodified PVA, copolymer-modified PVA obtained by copolymerizing various monomers during the production of a vinyl ester-based resin and then saponifying the copolymer, and various post-modified PVAs obtained by post-modifying unmodified PVA 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.

[0034] When a copolymerized modified PVA is obtained, examples of monomers used for copolymerization with a vinyl ester monomer during the production of a vinyl ester resin include olefins such as ethylene, 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, polyoxypropylene (meth)allyl ether, and the like. Examples of the hydroxyl group-containing α-olefins include oxyalkylene (meth)allyl ethers; 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 derivatives of hydroxyl group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, and 5-hexen-1-ol, or acylated products thereof. 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 ethylene and propylene, is preferably less than 10 mol%, more preferably 5 mol% or less, even more preferably 2 mol% or less, and particularly preferably 0 mol%.

[0035] 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.

[0036] 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.

[0037] When the PVA-based resin (B) 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 %. However, as described above, the content of ethylene-derived structural units (ethylene content) in the PVA-based resin (B) is less than 10 mol %.

[0038] The PVA-based resin (B) used in this embodiment may be one type or a mixture of two or more types. When two or more types of PVA-based resin (B) are used, examples thereof include a combination of two or more unmodified PVA-based resins having different saponification degrees, viscosity-average degrees of polymerization, melting points, etc.; a combination of an unmodified PVA-based resin and a modified PVA-based resin; and a combination of two or more modified PVA-based resins having different saponification degrees, viscosity-average degrees of polymerization, melting points, types of functional groups, modification rates, etc.

[0039] The saponification degree of the PVA-based resin (B) is 70 to 97 mol%, preferably 80 to 96 mol%, and more preferably 85 to 95 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, the preferred range is generally 87 mol% or more, with the upper limit being, for example, 90 mol% or less. When the saponification degree of the PVA-based resin (B) is within the above range, it is possible to exhibit good protective colloid properties and surfactant properties, and a uniform and stable EVOH emulsion can be formed. Furthermore, by using a PVA-based resin (B) with a high saponification degree, excellent gas barrier properties are likely to be obtained when a coating film is formed.

[0040] The viscosity of a 4% by mass aqueous solution of the PVA resin at 20° C. is preferably 5 to 70 mPa s, more preferably 15 to 60 mPa s, and even more preferably 20 to 50 mPa s. If the viscosity is too low, the stability of the emulsion composition tends to decrease.

[0041] When an unmodified PVA resin is used as the PVA-based resin, the viscosity of a 4% by mass aqueous solution of the unmodified PVA resin at 20° C. is preferably 5 to 70 mPa s, more preferably 15 to 60 mPa s, and even more preferably 30 to 50 mPa s. If the viscosity is too low, the stability of the emulsion composition tends to decrease.

[0042] When a modified PVA-based resin is used as the PVA-based resin, the viscosity of a 4% by mass aqueous solution of the modified PVA-based resin at 20° C. is preferably 5 to 50 mPa s, more preferably 13 to 40 mPa s, and even more preferably 17 to 30 mPa s. If the viscosity is too low, the stability of the emulsion composition tends to decrease.

[0043] The viscosity of the 4 mass % aqueous solution is measured in accordance with JIS K 6726 3.11.2.

[0044] The average degree of polymerization (measured in accordance with JIS K 6726) of the PVA-based resin (B) used in this embodiment is generally 250 to 3,000, preferably 800 to 3,000, particularly preferably 1,200 to 2,800, and even more preferably 1,800 to 2,500. That is, the average degree of polymerization of the PVA-based resin (B) may be, for example, 250 or more, preferably 800 or more, more preferably 1,200 or more, and particularly preferably 1,800 or more. The average degree of polymerization of the PVA-based resin (B) may be 3,000 or less, preferably 2,800 or less, and particularly preferably 2,500 or less. When the average degree of polymerization of the PVA-based resin (B) is within the above range, the EVOH emulsion exhibits good protective colloid properties, enabling the emulsion particles to exhibit uniform dispersion stability.

[0045] The PVA-based resin (B) used in this embodiment can be produced by, for example, polymerizing a vinyl ester-based monomer such as vinyl acetate and saponifying the polymer. To obtain a copolymerized modified PVA, a monomer composition containing a vinyl ester-based monomer and a monomer used in copolymerization is polymerized and saponified.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] <Emulsion (I)> The emulsion (I) used in this embodiment contains the above-mentioned EVOH (A), PVA-based resin (B), and further a dispersion medium. Typically, the EVOH (A) is a dispersoid, the PVA-based resin (B) is a dispersant, and particles of the EVOH (A) in the dispersion medium are dispersed and stabilized by the PVA-based resin (B).

[0051] The content of the PVA-based resin (B) in the emulsion (I) used in this embodiment is 5 to 90% by mass, preferably 7 to 80% by mass, and more preferably 9 to 65% by mass, based on 100% by mass of the total of the EVOH (A) and the PVA-based resin (B). When the content of the PVA-based resin (B) is 5% by mass or more based on 100% by mass of the total of the EVOH (A) and the PVA-based resin (B), the emulsion (I) exhibits excellent dispersion stability when an inorganic filler or the like is incorporated and dispersed therein. Furthermore, the emulsion (I) exhibits excellent coating film formability. When the content of the PVA-based resin (B) is 90% by mass or less based on 100% by mass of the total of the EVOH (A) and the PVA-based resin (B), the resulting coating film exhibits excellent water resistance and gas barrier properties. The content of EVOH (A) is usually 5 to 25% by mass, preferably 6 to 20% by mass, and particularly preferably 8 to 18% by mass, of the entire emulsion (I).

[0052] The dispersion medium is not particularly limited as long as it is a water-soluble component within a substance and concentration range that does not affect the stability of the emulsion composition, and any aqueous solution containing such a component may be used, including water alone, a polysaccharide aqueous solution, a cellulose (CNF) aqueous solution, etc., and a small amount of a water-soluble organic solvent may be used in combination. Examples of organic solvents include methanol, ethanol, acetone, etc. Among these, water is preferred from the standpoints of safety and supply.

[0053] The content of the dispersion medium is not particularly limited, but is preferably 25% by mass or more, more preferably 35% by mass or more, and even more preferably 40% by mass or more, based on the total amount of emulsion (I), and is preferably 95% by mass or less, more preferably 85% by mass or less, and even more preferably 75% by mass or less.

[0054] When a dispersion medium is a combination of water and an organic solvent, the content of water relative to the total amount of the dispersion medium is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. Among these, it is most preferable to use only water as the dispersion medium.

[0055] The average particle size of the emulsion particles (dispersoid) in the emulsion (I) used in this embodiment is preferably 0.1 to 20 μm, more preferably 1 to 10 μm, and even more preferably 2 to 5 μm. When the average particle size is within the above range, the dispersion stability of the emulsion particles (dispersoid) in the emulsion (I) is improved. The average particle size is the median size of the emulsion particles (dispersoid) measured in accordance with JIS Z 8825.

[0056] Typical methods for producing emulsion (I) include (i) a high-pressure homogenizer method and (ii) a forced extrusion mechanical emulsification method. (ii) The forced extrusion mechanical emulsification method is preferred in terms of production efficiency because it allows the resin melting process to be carried out continuously. (ii) The forced extrusion mechanical emulsification method is an emulsification method in which EVOH (A), PVA-based resin (B), and other emulsion components are melt-kneaded in a twin-screw extruder (kneading temperature, for example, 95 to 220°C), and a dispersion medium is introduced through the extruder vent. Alternatively, the dispersant PVA-based resin (B) may be added as an aqueous solution through the vent. The temperature of the vent where the dispersion medium and the aqueous solution of PVA-based resin (B) are added is preferably adjusted to 100°C or below to suppress evaporation.

[0057] The coating composition may also contain components other than the emulsion (I), such as an inorganic filler (C), an organic filler, various additives, etc. Examples of the various additives include leveling agents, antifoaming agents, antisettling agents, lubricants, abrasives, rust inhibitors, antistatic agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, stabilizers (thickeners), surfactants, colorants, plasticizers, lubricants, etc. Among these, the inclusion of an inorganic filler (C) is preferred because it can be easily applied to a variety of uses.

[0058] <Inorganic Filler (C)> Examples of the inorganic filler (C) include generally calcium-based compounds, titanium-based compounds, vanadium-based compounds, chromium-based compounds, manganese-based compounds, iron-based compounds, cobalt-based compounds, nickel-based compounds, copper-based compounds, zinc-based compounds, zirconium-based compounds, niobium-based compounds, molybdenum-based compounds, technetium-based compounds, ruthenium-based compounds, rhodium-based compounds, palladium-based compounds, silver-based compounds, cadmium-based compounds, indium-based compounds, tin-based compounds, antimony-based compounds, barium-based compounds, Examples of suitable materials include lanthanum-based compounds, cerium-based compounds, neodymium-based compounds, samarium-based compounds, gadolinium-based compounds, lithium-based compounds, boron-based compounds, hafnium-based compounds, tantalum-based compounds, tungsten-based compounds, rhenium-based compounds, osmium-based compounds, indium-based compounds, platinum-based compounds, gold-based compounds, thallium-based compounds, lead-based compounds, bismuth-based compounds, polonium-based compounds, sand, soil, clay, ores, minerals, mortar, cement, concrete, asphalt, and ceramics.

[0059] When the coating composition of this embodiment is used as a radiation-shielding coating composition described later, from the viewpoint of further improving radiation shielding performance such as neutron shielding performance, the inorganic filler (C) preferably contains a compound containing one or more elements selected from the group consisting of Gd, B, and Li. Examples of the compound include, but are not particularly limited to, 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 the largest absorption cross sections, and it is more preferable that the inorganic filler (C) contains a compound 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 viewpoint of stability and toxicity, the inorganic filler is preferably 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.

[0060] The Gd-containing compound includes oxides, composite oxides, sulfides, hydroxides, etc. containing Gd, and more specifically, gadolinium oxide (Gd 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 Gd３ 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.

[0061] 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.

[0062] Examples of compounds containing Li include oxides, composite oxides, sulfides, and hydroxides containing Li, such as lithium fluoride (LiF) 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 Li ２ SiO ３ , lithium tantalate LiTaO ３ , lithium titanate Li ２ TiO ３ , lithium vanadate LiVO ３ , lithium tungstate LiWO ４ , lithium zirconate Li ２ ZrO ３ , lithium nitride Li ３N, 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.

[0063] When the coating composition of this embodiment is used as a radiation-shielding coating composition described later, in addition to a compound containing an element capable of absorbing neutrons, protons, and heavy particles, compounds containing an element capable of absorbing various types of radiation other than neutrons, protons, and heavy particles, known additives, etc. may be contained as the inorganic filler (C) depending on the desired performance. Specific examples of compounds containing an element 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.

[0064] The proportion of the compound containing one or more elements selected from the group consisting of Gd, B, and Li in the inorganic filler (C) 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, more preferably 50% by mass or more, particularly preferably 60% by mass or more, and may be 100% by mass.

[0065] The content of the inorganic filler (C) in the coating composition of this embodiment is preferably, for example, 100 to 2000 parts by mass per 100 parts by mass of the saponified ethylene-vinyl ester copolymer (A). That is, from the viewpoint of coatability, the content of the inorganic filler (C) in the coating composition is preferably 100 parts by mass or more, more preferably 150 parts by mass or more, and even more preferably 200 parts by mass or more per 100 parts by mass of the saponified ethylene-vinyl ester copolymer (A). Furthermore, from the viewpoint of coatability, the content of the inorganic filler (C) in the coating composition is preferably 2000 parts by mass or less, more preferably 1800 parts by mass or less, and even more preferably 1600 parts by mass or less per 100 parts by mass of the saponified ethylene-vinyl ester copolymer (A).

[0066] Furthermore, when the coating composition of this embodiment is used as a radiation-shielding coating composition, the content of the inorganic filler (C) is preferably, for example, 100 to 2,000 parts by mass relative to 100 parts by mass of the saponified ethylene-vinyl ester copolymer (A). That is, from the viewpoint of improving the radiation shielding property, the content of the inorganic filler (C) in the radiation-shielding coating composition is preferably 100 parts by mass or more, more preferably 150 parts by mass or more, and particularly preferably 200 parts by mass or more, relative to 100 parts by mass of the saponified ethylene-vinyl ester copolymer (A). Furthermore, from the viewpoints of the strength, shape stability, and moldability of various molded products, the content of the inorganic filler (C) in the radiation-shielding coating composition is preferably 2,000 parts by mass or less, more preferably 1,800 parts by mass or less, even more preferably 1,600 parts by mass or less, and particularly preferably 1,400 parts by mass or less, relative to 100 parts by mass of the saponified ethylene-vinyl ester copolymer (A).

[0067] The shape of the inorganic filler (C) is not particularly limited, but a powder form is generally preferred. The average particle size of the inorganic filler (C) 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 (C) is preferably 1 μm or more, more preferably 2 μm or more. Furthermore, the average particle size of the inorganic filler (C) 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. Therefore, when used as a radiation-shielding coating composition, the radiation shielding properties can be improved. By having the average particle size be equal to or greater than the above lower limit, the inorganic filler (C) can be uniformly dispersed in the coating film or molded product. Here, the average particle size refers to the median diameter (d50) measured by a laser diffraction particle size distribution measuring device in accordance with JIS Z 8825: Particle size analysis - laser diffraction and scattering method.

[0068] Furthermore, when the coating composition of this embodiment contains an inorganic filler (C), it can be mixed by a known method, such as a method of mixing components such as EVOH (A) and melt-kneading them, or a method of mixing an emulsion (I) containing EVOH (A) and a PVA-based resin (B) with an aqueous or solvent-based dispersion of the inorganic filler (C). The method of mixing the inorganic filler (C) with the emulsion (I) is preferred because it is easy to handle as a coating composition.

[0069] The coating composition of this embodiment contains the emulsion (I) and forms a coating film by applying it to a molded article (substrate). The molded article on which a coating film is formed using the coating composition of this embodiment is not particularly limited, and examples include metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel, and zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.) plated steel, PBT (polybutylene terephthalate) / PET (polyethylene terephthalate) alloy resin, ABS (acrylonitrile butadiene styrene) resin, AES (acrylonitrile ethylene propylene diene styrene) resin, PC (polycarbonate) resin, high-heat PC resin, acrylic resin, polystyrene resin, and other resins, as well as various molded articles containing difficult-to-adhere substrates such as polyolefin resins such as polypropylene and polyethylene, and polyester resins such as PET resin and PBT resin. Other examples include molded articles made of paper, mortar, concrete, wood, ceramic materials, and the like.

[0070] To form a coating film on these molded articles using the coating composition of this embodiment, the coating composition of this embodiment is applied to the surface of the molded article (substrate) and dried. The coating film thickness after curing is preferably in the range of 20 to 1000 μm. Methods for applying the coating composition include brush coating, spray coating, dip coating, spin coating, and flow coating. Heating during drying can also be performed using known heating means. Examples of heating means that can be used include drying ovens such as hot air ovens, electric ovens, and infrared induction heating ovens. The heating temperature is not particularly limited, but is preferably about 60 to 210°C. The heating time is not particularly limited, but is preferably about 5 to 20 minutes.

[0071] After application of the coating composition, and before heating, preheating, air blowing, etc. may be carried out under heating conditions that do not substantially cure the coating, in order to prevent the occurrence of coating defects. The preheating temperature is preferably about 30 to 100°C. The preheating time is preferably about 30 seconds to 15 minutes. Air blowing can usually be carried out by blowing air heated to a temperature of about 30 to 100°C onto the coated surface for about 30 seconds to 15 minutes.

[0072] After the coating film is formed, it can be cured (stored) to further increase the hardness of the coating film. The curing conditions can be, for example, at 0 to 60°C for about 1 to 10 days.

[0073] The coating composition of the present embodiment can be suitably used in a wide range of fields, including applications such as coatings on various vehicles such as automobiles, buses, and railway cars, construction machinery, agricultural machinery, electrical equipment, precision electronic devices, medical equipment, floors, walls, and roofs of buildings, and also on constituent materials thereof such as metal products, mortar and concrete products, woodworking products, plastic products, and ceramic building materials such as calcium silicate boards and gypsum boards. Among these, it is preferably used as a radiation-shielding coating composition.

[0074] <<Radiation-Shielding Coating Composition>> The radiation-shielding coating composition according to this embodiment contains the coating composition described above. After extensive research, the present inventors have found that polyvinyl alcohol-based resins (PVA-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 (PVA-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. This is presumably because hydroxy groups contained in polyvinyl alcohol-based resins (PVA-based resins) form hydrogen bonds, improving the density of the resin and increasing the hydrogen density (intermolecular cohesive force) in the resin. Note that the term "polyvinyl alcohol-based resins (PVA-based resins)" as used herein encompasses EVOH.

[0075] The radiation-shielding composition according to this embodiment contains an emulsion (I) containing EVOH (A) and a PVA-based resin (B), and therefore 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 when shielded. Therefore, the radiation-shielding coating composition according to this embodiment is considered to have excellent neutron-shielding performance, among other types of radiation, as well as excellent proton-shielding performance and proton-shielding performance and heavy particle-shielding performance. In other words, the radiation-shielding coating composition according to this embodiment is particularly excellent in the ability to shield radiation by decelerating it through collision with atomic nuclei.

[0076] The radiation-shielding coating composition of this embodiment comprises the coating composition described above, and the contents of each component and other components may be the same as those in the coating composition described above. In addition, the radiation-shielding coating composition of this embodiment preferably contains an inorganic filler (C) containing a compound containing one or more elements selected from the group consisting of Gd, B, and Li, in order to further enhance radiation shielding.

[0077] (Applications) The radiation-shielding coating composition according to this embodiment 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 coating composition according to this embodiment is suitable for use in nuclear power generation-related applications such as components for nuclear reactors or the periphery of nuclear reactors, 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 infrastructure related to the Moon and Mars, medical applications such as components for medical accelerators and peripheral components for medical devices that utilize radiation, etc.

[0078] The present specification also discloses the following aspects: (i) Use of a coating composition for shielding radiation, the coating composition comprising an emulsion (I) containing a saponified ethylene-vinyl ester copolymer (A) having a content of structural units derived from ethylene of 10 mol % or more and a polyvinyl alcohol resin (B) having a content of structural units derived from ethylene of less than 10 mol %, wherein the content of the polyvinyl alcohol resin (B) is 5 to 90 mass % relative to 100 mass % of the total of the saponified ethylene-vinyl ester copolymer (A) and the polyvinyl alcohol resin (B), and the degree of saponification of the polyvinyl alcohol resin (B) is 70 to 97 mol %. (ii) A radiation shielding method, comprising forming, on a substrate, a coating film made from a coating composition containing an emulsion (I) that contains a saponified ethylene-vinyl ester copolymer (A) having a content of structural units derived from ethylene of 10 mol% or more and a polyvinyl alcohol resin (B) having a content of structural units derived from ethylene of less than 10 mol%, wherein the content of the polyvinyl alcohol resin (B) is 5 to 90 mass% relative to 100 mass% of the total of the saponified ethylene-vinyl ester copolymer (A) and the polyvinyl alcohol resin (B), and the saponification degree of the polyvinyl alcohol resin (B) is 70 to 97 mol%.

[0079] 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.

[0080] The following components were prepared as component (A) (EVOH (A)), component (B) (PVA-based resin (B)), inorganic filler (C), and aqueous polyolefin dispersion. <Component (A)> EVOH (A-1) (saponification degree 99 mol%, ethylene content 32 mol%, MFR 12 g / 10 min (210°C, load 2160 g)) <Component (B)> PVA-based resin (B-1) (unmodified PVA resin, average degree of polymerization 2200, saponification degree 88 mol%, 4% by mass viscosity at 20°C 40 to 46 mPa·s) PVA-based resin (B-2) (unmodified PVA resin, average degree of polymerization 2500, saponification degree 76 mol%, 4% by mass viscosity at 20°C 44 to 52 mPa·s) PVA-based resin (B-3) (unmodified PVA resin, average degree of polymerization 1700, saponification degree 88 mol%, 4% by mass viscosity at 20°C 20.0 to 24.5 mPa·s) PVA resin (B-4) (unmodified PVA resin, average polymerization degree 1700, saponification degree 98 mol%, 4% by mass viscosity at 20°C 25 to 30 mPa·s) <Inorganic filler (C)> Gd ２ O ３ Powder (manufactured by Nippon Yttrium Co., Ltd., product name: gadolinium oxide 99.9%, average particle size 2.32 μm) <Polyolefin aqueous dispersion> - Low-density polyethylene dispersion (manufactured by Mitsui Chemicals, Inc., product name: Chemipearl M200, solid content concentration 20%)

[0081] Example 1 100 parts of the above EVOH (A-1) was continuously fed from the hopper of a twin-screw extruder [product number KZW15TW-60MG, manufactured by Technovel Co., Ltd., L / D = 60], melt-kneaded under the following extrusion temperature conditions, and continuously extruded (screw rotation speed: 300 rpm) for a heating time of 180 seconds while continuously feeding 43 parts of the above PVA-based resin (B-1) and 507 parts of water as a dispersion medium from a feed port provided in the extruder, to obtain emulsion (I-1). Emulsion (I-1) refers to emulsion (I) prepared in Example 1. In Table 1, "EVOH / PVA" refers to the mass ratio of EVOH to PVA-based resin. In Example 1, the mass ratio of EVOH (A-1) to PVA-based resin (B-1) was 70 / 30. That is, in Example 1, the content of the PVA-based resin (B-1) relative to the total of EVOH (A-1) and PVA-based resin (B-1): 100% by mass was 30% by mass. The dispersed particle diameter (median diameter) of the emulsion (I-1) was measured using a laser diffraction particle diameter measuring device (product number LA-950V2, manufactured by Horiba, Ltd.) and was found to be 2.57 μm. Extrusion temperature (°C): C1 / C2 / C3 / C4 / C5 / C6 / C7 / C8 = 170 / 220 / 220 / 195 / 95 / 95 / 95 / 95

[0082] The emulsion (I-1) obtained above and Gd ２ O ３ The powder was mixed with emulsion (I-1) / Gd ２ O ３ The powders were mixed uniformly in a batch mixer at a mass ratio of 70 / 30 (650 parts / 279 parts) to obtain a coating composition. This coating composition was applied to a substrate (PET film) and allowed to dry at 90°C for 10 minutes to obtain coating films with thicknesses of 30 μm and 1 mm, and the following evaluations were performed. The results are shown in Table 2. Note that "-" in each evaluation result indicates that the measurement was not performed.

[0083] (Examples 2 to 7 and Comparative Examples 1 to 4) Emulsions (I) in Examples 2 to 7 and Comparative Examples 1 to 4 were prepared in the same manner as in Example 1, except that the amounts and types of each component were changed as shown in Tables 1 and 2. Subsequently, the inorganic filler (Gd ２ O ３ The coating compositions and coating films of Examples 2 to 7 and Comparative Examples 1, 2, and 4 were obtained in the same manner as in Example 1, except that the cellulose acylate powder was mixed in, and similar evaluations were carried out. The results are shown in Table 1. In Comparative Examples 1 and 4, no coating films could be formed.

[0084] Comparative Example 3 The emulsion (I-1) used in Example 1 was replaced with 470 parts of the above-mentioned polyolefin aqueous dispersion (manufactured by Mitsui Chemicals, Inc., product name: Chemipearl M200), and this was mixed with Gd ２ O ３ A coating composition was obtained in the same manner as in Example 1, except that 113 parts of the powder was mixed with the coating composition. This coating composition was applied to a substrate (PET film) and allowed to stand and dry at 90°C for 10 minutes in an attempt to obtain coating films with thicknesses of 30 µm and 1 mm, but no coating films could be formed.

[0085] [Coating film formability] The resulting coating films of 30 μm and 1 mm thickness were folded by hand 10 times, and the surface condition was visually observed and evaluated according to the following criteria. Evaluation results of ⊚, ◯, or △ were deemed to be acceptable. ⊚: No cracks observed ◯: Partial cracks observed at the folded portion △: Cracks observed at the folded portion and in other portions ×: No flexibility, could not be folded

[0086] [Water resistance of coating film] A drop of water was dropped onto the resulting 30 μm thick coating film using a dropper, and after 5 seconds the area where the water droplet was located was rubbed with a finger. The surface condition of the coating film after rubbing was visually observed and evaluated according to the following criteria. Evaluation results of ⊚, ◯, or △ were deemed to be acceptable. ⊚: The coating film did not dissolve where the water droplet was dropped, and the substrate was not exposed. ◯: The substrate was exposed in less than half of the coating area where the water droplet was dropped. △: The substrate was exposed in more than half of the coating area where the water droplet was dropped. ×: The coating film dissolved where the water droplet was dropped, and the substrate was completely exposed.

[0087] [Gas Barrier Properties] In accordance with JIS K7126-2 (2006), the oxygen transmission rate (OTR, unit: cc / m) of the 30 μm thick coating film obtained above was measured using an oxygen transmission rate measuring device (OX-TRAN2 / 21 model manufactured by MOCON) under conditions of 23° C. and 50% relative humidity. ２ / day / atm) was measured.

[0088] [Neutron Shielding Performance] For each coating composition, a plate-shaped molded product for evaluation was prepared as described above, and the neutron transmittance was evaluated. Gold foil was placed on 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 front 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 (i.e., the neutron irradiation direction). When irradiated with neutrons, the gold foil was activated. The neutron 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 penetrated the sample. In other words, the higher the neutron shielding factor, the better the neutron shielding performance of the sample. The results are shown in Table 2.

[0089] (Accelerator neutron source) Accelerator: Cyclotron HM-18HC manufactured by Sumitomo Heavy Industries, Ltd. Accelerated particle: Proton 18 MeV Target: Be Nuclear reaction: ７ Be(p, n) ７ B reaction Irradiation current: ~120 μA Irradiation time: 3 hours

[0090] [Substrate Deterioration] Each of the coating compositions of Examples 1, 3, and 7 was applied to a PP substrate (made of polypropylene, 15 x 15 cm x 1 mm thick) and allowed to dry at 90°C for 10 minutes to obtain a coating film of the thickness shown in Table 2, which was then irradiated with gamma rays under the following conditions. The rupture stress of the PP substrate before and after gamma ray irradiation was measured using an autograph. The results are shown in Table 2. As also shown in Table 2, the rupture stress of the PP substrate before gamma ray irradiation was 29.0 MPa.

[0091] ATOX Corporation Technology Development Center ６０ Conducted at a Co gamma ray irradiation facility. Radiation source: ６０ Co sealed radiation source - Dose rate 1 kGy / h Accumulative dose 100 kGy

[0092] (Breaking stress measurement) Autograph AG-IS (Shimadzu Corporation) Measurement sample size: After irradiation, the sample was punched out with a No. 3 dumbbell. Pulling speed: 200 mm / min. Distance between chucks: 4 mm

[0093] Comparative Example 5 The substrate deterioration property of a PP substrate (made of polypropylene, 15 x 15 cm x 1 mm thick) was evaluated as it was without using any coating composition, and this was taken as Comparative Example 5. The results are shown in Table 2.

[0094]

[0095]

[0096] The coating compositions of Examples 1 to 7 passed the evaluation of film-forming ability and also passed the evaluation of water resistance when a coating film was formed. Furthermore, the coating compositions of Examples 1 to 4 and 6 to 7 also had gas barrier properties when a coating film was formed. On the other hand, the coating composition of Comparative Example 1 had a low PVA-based resin content of 3 mass% relative to the total of EVOH and PVA-based resin, and therefore poor dispersion stability of the inorganic filler, making it impossible to form a coating film. The coating composition of Comparative Example 2 had a high PVA-based resin content of 95 mass% relative to the total of EVOH and PVA-based resin, and therefore good film-forming ability, but poor water resistance and gas barrier properties when a coating film was formed. The coating composition of Comparative Example 3, which used a polyolefin aqueous dispersion, failed to form a coating film due to poor dispersion stability of the inorganic filler. The coating composition of Comparative Example 4 used a PVA-based resin with a high saponification degree of 98 mol%, making it impossible to form an emulsion and therefore unable to form a coating film. Furthermore, the coating compositions of Examples 1 to 6 exhibited high neutron shielding performance.

[0097] Furthermore, the coating compositions of Examples 1, 3 and 7 effectively suppressed or prevented the deterioration of the substrate due to gamma ray irradiation.

[0098] 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 a Japanese patent application (Patent Application No. 2023-183314) filed on October 25, 2023, the contents of which are incorporated herein by reference.

Claims

1. A coating composition comprising an emulsion (I) containing an ethylene-vinyl ester copolymer saponified product (A) having a content of structural units derived from ethylene of 10 mol % or more, and a polyvinyl alcohol resin (B) having a content of structural units derived from ethylene of less than 10 mol %, wherein the content of the polyvinyl alcohol resin (B) relative to a total of 100 mass % of the ethylene-vinyl ester copolymer saponified product (A) and the polyvinyl alcohol resin (B) is 5 to 90 mass %, and the degree of saponification of the polyvinyl alcohol resin (B) is 70 to 97 mol %.

2. The coating composition according to claim 1, wherein the average particle size of the emulsion particles in said emulsion (I) is 0.1 to 20 μm.

3. The coating composition according to claim 1, wherein the saponified ethylene-vinyl ester copolymer (A) has an ethylene-derived structural unit content of 10 to 77 mol %.

4. The coating composition according to claim 1, wherein the polyvinyl alcohol resin (B) has a degree of saponification of 85 to 95 mol %.

5. The coating composition according to claim 1, wherein the average degree of polymerization of the polyvinyl alcohol resin (B) is 1,800 to 2,500.

6. The coating composition according to claim 1, further comprising an inorganic filler (C).

7. The coating composition according to claim 6, which contains 100 to 2,000 parts by mass of said inorganic filler (C) per 100 parts by mass of said saponified ethylene-vinyl ester copolymer (A).

8. The inorganic filler (C) is a calcium-based compound, a titanium-based compound, a vanadium-based compound, a chromium-based compound, a manganese-based compound, an iron-based compound, a cobalt-based compound, a nickel-based compound, a copper-based compound, a zinc-based compound, a zirconium-based compound, a niobium-based compound, a molybdenum-based compound, a technetium-based compound, a ruthenium-based compound, a rhodium-based compound, a palladium-based compound, a silver-based compound, a cadmium-based compound, an indium-based compound, a tin-based compound, an antimony-based compound, a barium-based compound, a lanthanum-based compound, a cerium-based compound, The coating composition according to claim 6, comprising at least one selected from the group consisting of neodymium-based compounds, samarium-based compounds, gadolinium-based compounds, lithium-based compounds, boron-based compounds, hafnium-based compounds, tantalum-based compounds, tungsten-based compounds, rhenium-based compounds, osmium-based compounds, indium-based compounds, platinum-based compounds, gold-based compounds, thallium-based compounds, lead-based compounds, bismuth-based compounds, polonium-based compounds, sand, soil, clay, ores, minerals, mortar, cement, concrete, asphalt, and ceramics.

9. A radiation shielding coating composition comprising the coating composition according to any one of claims 1 to 8.

10. The radiation shielding coating composition according to claim 9, wherein the radiation includes one or more selected from the group consisting of neutrons, protons and heavy particles.