Composition for electrostatic coating and radiation-shielding paint composition

Abstract

To provide a composition for electrostatic coating, which is used in electrostatic coating, has high metal adhesion, and forms a coated surface with superior smoothness.SOLUTION: A composition for electrostatic coating comprises ethylene-vinyl ester-based copolymer saponified particles (A) and an inorganic filler (B).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a composition for electrostatic coating and a radiation shielding coating composition. [Background technology]

[0002] Conventionally, there has been known a technique for imparting chemical resistance and rust prevention to a substrate by applying a powder coating to the substrate. Examples of such powder coatings include those based on thermoplastic resins such as polyethylene resins (see, for example, Patent Document 1) and those based on thermosetting resins such as epoxy resins.

[0003] Furthermore, ethylene-based polymers with a high ratio of hydrogen atoms have been 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) that are produced by radioactive isotopes, and high-energy electrons, protons, neutrons, and heavy particles (heavy ions) that are produced in the space environment and accelerator facilities. Of these, neutrons, which are electrically neutral, cannot be blocked by matter due to electromagnetic interactions. Therefore, in order to protect the human body and other objects, shielding materials that are specifically tailored to the properties of neutrons will be required.

[0004] Neutrons are produced by nuclear fission in nuclear reactors, and continue to be produced by spontaneous nuclear 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 (20MeV). 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 compose the human body, resulting in a large dose conversion factor that indicates the radiation risk to the human body, and thus having a very large 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 called fast neutrons, with kinetic energy of about 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 due to elastic scattering between neutrons and hydrogen atoms, which have almost the same mass as 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 large hydrogen atom ratio and is known to have excellent neutron shielding performance.

[0006] For example, Patent Document 2 describes a boron compound, preferably boron carbide B 4 A neutron absorbing material consisting of ultra-high molecular weight polyethylene embedded with C is described. Furthermore, Patent Document 3 describes a neutron shielding structure comprising an inner layer made of polyethylene containing a substance that absorbs neutrons, an intermediate layer made of polyethylene arranged on the inner layer, and an outer layer made of polyethylene containing a substance that absorbs neutrons arranged on the intermediate layer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2006-219507 A [Patent Document 2] Japanese Patent Application Publication No. 3-107797 [Patent Document 3] JP 2015-010826 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, according to the findings of the present inventors, for example, a powder coating based on a polyethylene resin as described in Patent Document 1 has a problem that when the substrate to be coated is metal, the coating (coating film) has low adhesion to the metal, and when an inorganic filler is added, the inorganic filler falls off from the coating surface. Also, a coating surface with high smoothness is required.

[0009] Therefore, one of the objects of the present invention is to provide an electrostatic coating composition for use in electrostatic coating, which has high adhesion to metals and can provide a coating surface with excellent smoothness. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors have found that an electrostatic coating composition containing saponified ethylene-vinyl ester copolymer particles and an inorganic filler can provide a coating surface that has high adhesion to metals and excellent smoothness. The inventors also found that this composition exhibits better neutron shielding ability than a coating composition using high-density polyethylene, which is considered to have high neutron shielding ability due to its high ratio of hydrogen atoms.

[0011] That is, the present invention relates to the following aspects 1 to 9.

[0012] A first aspect of the present invention is a composition for electrostatic coating that contains saponified ethylene-vinyl ester copolymer particles (A) and an inorganic filler (B).

[0013] A second aspect of the present invention relates to the electrostatic coating composition of the first aspect, wherein the average particle size of the saponified ethylene-vinyl ester copolymer particles (A) is 0.1 to 20 μm.

[0014] A third aspect of the present invention relates to the electrostatic coating composition according to the first or second aspect, wherein the saponified ethylene-vinyl ester copolymer particles (A) are spherical.

[0015] A fourth aspect of the present invention is the electrostatic coating composition in any one of the first to third aspects, wherein the content of ethylene-derived structural units in the saponified ethylene-vinyl ester copolymer particles (A) is 10 to 77 mol %.

[0016] A fifth aspect of the present invention is a composition for electrostatic coating, in which the mass-based mixing ratio (A) / (B) of the saponified ethylene-vinyl ester copolymer particles (A) to the inorganic filler (B) is 10 / 90 to 90 / 10 in any one of the first to fourth aspects.

[0017] A sixth aspect of the present invention is a composition for electrostatic coating according to any one of the first to fifth aspects, in which the saponified ethylene-vinyl ester copolymer particles (A) and the inorganic filler (B) are dispersed in a dispersion medium.

[0018] A seventh aspect of the present invention is any one of the first to sixth aspects, wherein the inorganic filler (B) 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 electrostatic 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.

[0019] An eighth aspect of the present invention is a radiation shielding coating composition containing the electrostatic coating composition according to any one of the first to seventh aspects.

[0020] A ninth aspect of the present invention is the radiation shielding coating composition according to the eighth aspect, wherein the radiation includes one or more selected from the group consisting of neutrons, protons, and heavy particles. Effect of the Invention

[0021] According to the present invention, it is possible to provide a composition for electrostatic coating which has high adhesion to metals and gives a coated surface with excellent smoothness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] 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 gist of the present invention. In addition, the symbol "to" indicating a numerical range is used to mean that the numerical values ​​before and after the symbol are included as the lower and upper limits.

[0023] <<Electrostatic coating composition>> The electrostatic coating composition of the present embodiment contains saponified ethylene-vinyl ester copolymer particles (A) and an inorganic filler (B). Each component will be described in turn below.

[0024] <Saponified ethylene-vinyl ester copolymer particles (A)> The EVOH constituting the saponified ethylene-vinyl ester copolymer (hereinafter abbreviated as EVOH) particles (A) used in this 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, structural units derived from ethylene and vinyl alcohol structural units, and also contains vinyl ester structural units that remain unsaponified. Hereinafter, the EVOH constituting the EVOH particles (A) may be referred to as EVOH (A). Note that the various properties of EVOH (A) such as the ethylene content and degree of saponification are the same as those of the EVOH particles (A).

[0025] Since the electrostatic coating composition of this embodiment contains EVOH particles (A), it exhibits high adhesion even when applied to metals to which adhesion is difficult to obtain, and furthermore, a coating surface with excellent smoothness is obtained. This is presumably because the hydroxyl groups contained in the EVOH particles (A) enhance the affinity with metals. In addition, since the hydroxyl groups contained in the EVOH particles (A) also have high affinity with the inorganic filler (B), it is thought that they also contribute to suppressing the inorganic filler from falling off. Furthermore, since the electrostatic coating composition of this embodiment contains EVOH particles (A), it also has excellent gas barrier properties when a coating film is formed.

[0026] The content of ethylene-derived structural units in EVOH (A) (ethylene content) is 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%, as measured based on ISO 14663. That is, the ethylene content of EVOH (A) is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 23 mol% or more, and particularly preferably 25 mol% or more. 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, as measured based on the following steps. When the ethylene content of EVOH (A) is the above lower limit or more, the crystallinity is improved, and the arrangement of hydroxyl groups can be adjusted to an arrangement that facilitates hydrogen bonding, thereby improving the radiation shielding property. By keeping the ethylene content below the upper limit, the number of hydroxyl groups in the material can be increased, which increases the number of hydrogen bonds between hydroxyl groups and improves radiation shielding properties. In addition, when the ethylene content of EVOH (A) is within the above range, the water resistance and gas barrier properties of the coating film formed tend to be superior.

[0027] EVOH (A) may further contain structural units derived from various monomers as monomers used for copolymerization with vinyl ester monomers, in addition to structural units derived from ethylene and vinyl alcohol structural units (including unsaponified vinyl ester structural units). EVOH (A) may also be one into which a functional group has been introduced by post-modification.

[0028] That is, EVOH (A) includes unmodified EVOH (unmodified EVOH), copolymerized modified EVOH (copolymerized modified EVOH), and various post-modified EVOHs in which various functional groups are introduced into unmodified EVOH by post-modification. Such modification can be carried out within a range in which the degree of polymerization sufficient for the formation of a polymer of EVOH is not lost. In some cases, the modified EVOH may be further post-modified.

[0029] When obtaining a copolymer-modified EVOH, examples of the monomers used for copolymerization with vinyl ester-based monomers during the production of vinyl ester-based resins include olefins such as propylene, isobutylene, α-octene, α-dodecene, α-octadecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid or their salts, their mono- or dialkyl esters, etc.; nitriles such as acrylonitrile, methacrylonitrile; amides such as acrylamide, methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid or their salts; alkyl vinyl ethers; N-acrylamidomethyltrimethylammonium chloride; allyltrimethylammonium chloride; dimethylallyl vinyl ketone; N-vinylpyrrolidone; vinyl chloride; vinylidene chloride; polyoxyalkylene (meth)allyl ethers such as polyoxyethylene (meth)allyl ether, polyoxypropylene (meth)allyl ether; polyoxyalkylene (meth)acrylates such as polyoxyethylene (meth)acrylate, polyoxypropylene (meth)acrylate; polyoxyalkylene (meth)acrylamides such as polyoxyethylene (meth)acrylamide, polyoxypropylene (meth)acrylamide; polyoxyethylene (1-(meth)acrylamide-1,1-dimethylpropyl) ester; polyoxyalkylene vinyl ethers such as polyoxyethylene vinyl ether, polyoxypropylene vinyl ether; polyoxyalkylene allyl amines such as polyoxyethylene allyl amine, polyoxypropylene allyl amine; polyoxyalkylene vinyl amines such as polyoxyethylene vinyl amine, polyoxypropylene vinyl amine; hydroxy group-containing α-olefins such as 3-buten-1-ol, 4-penten-1-ol, 5-hexen-1-ol or their derivatives such as acylates. Here, (meth)allyl means allyl or methallyl, (meth)acrylic means acrylic or methacrylic, and (meth)acrylate means acrylate or methacrylate, respectively. In addition, 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 the diol-containing compounds include 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 is preferably less than 10 mol %, more preferably 5 mol % or less, even more preferably 2 mol % or less, and particularly preferably 0 mol %.

[0030] Examples of post-modified EVOH in 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 epoxy compounds or the like, and those obtained by reacting EVOH with aldehyde compounds having various functional groups.

[0031] When EVOH (A) is a modified EVOH, the modification rate in the modified EVOH, 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 characteristics vary greatly depending on the type of functional group, but may be, for example, 0.1 to 20 mol %.

[0032] The saponification degree of EVOH (A) is generally from 90 to 100 mol %, preferably from 95.0 to 100 mol %, and particularly preferably from 99 to 100 mol %. When the saponification degree is equal to or higher than the lower limit, the EVOH particles (A) can be easily mixed uniformly with the inorganic filler (B) described later. In addition, when the saponification degree is relatively high, the radiation shielding performance can be further improved. The saponification degree may be 100 mol%, but may be equal to or lower than the upper limit from the viewpoint of ease of industrial production.

[0033] The melt flow rate (MFR) of EVOH (A) (210°C, load 2160g) is usually 0.5 to 100g / 10min, preferably 1 to 50g / 10min, and particularly preferably 3 to 35g / 10min. That is, the MFR of EVOH (A) may be 0.5g / 10min or more, preferably 1g / 10min or more, and particularly preferably 3g / 10min or more. The MFR of EVOH (A) may be 100g / 10min or less, preferably 50g / 10min or less, and particularly preferably 35g / 10min or less. When the MFR of EVOH (A) is the above lower limit or more, the molding processability during melt extrusion and the like can be improved. When the MFR of EVOH (A) is the above upper limit or less, the strength of the molded product when molded into a film, sheet, or molded product can be improved.

[0034] 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 EVOH with different saponification degrees, viscosity average polymerization degrees, melting points, etc.; a combination of unmodified EVOH and modified EVOH; a combination of two or more types of modified EVOH with different saponification degrees, viscosity average polymerization degrees, melting points, types of functional groups, modification rates, etc. may be mentioned. In addition, the EVOH particles (A) may be one type or a mixture of two or more types.

[0035] In the electrostatic coating composition of this embodiment, the EVOH particles (A) are not particularly limited as long as they are particulate, and examples of the shape include spherical, scaly, cubic, plate-like, columnar, needle-like, and fibrous shapes. Among these, from the viewpoint of adhesion to metals and smoothness of the coating surface, it is preferable that the EVOH particles (A) are spherical. Incidentally, the spherical shape does not only mean a geometrically perfect sphere, but may also be an ellipsoid, and is more preferable to be close to a perfect sphere. In this embodiment, the particle is considered to have a spherical shape when the ratio of the longest diameter (major axis diameter) to the shortest diameter (minor axis diameter) of the three mutually perpendicular diameters of the particle is 2 or less, preferably 1.3 or less. The average particle size of the EVOH particles (A) is preferably from 0.1 to 20 μm, particularly preferably from 1 to 10 μm, and further preferably from 2 to 5 μm. When the average particle size is within the above range, the dispersion stability is improved. The average particle size is the median size measured in accordance with JIS Z8825.

[0036] The content of the EVOH particles (A) in the electrostatic coating composition of this embodiment is not particularly limited, but is preferably, for example, 10 to 90% by mass based on the total mass of the solid content of the electrostatic coating composition. That is, from the viewpoint of surface smoothness, the content of the EVOH particles (A) in the electrostatic coating composition is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and particularly preferably 50% by mass or more based on the total mass of the solid content of the electrostatic coating composition. In addition, from the viewpoint of metal adhesion, the content of the EVOH particles (A) in the electrostatic coating composition is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less based on the total mass of the solid content of the electrostatic coating composition.

[0037] EVOH is a resin obtained by copolymerizing ethylene and a vinyl ester monomer and then saponifying it, and is a water-insoluble thermoplastic resin known as a saponified ethylene-vinyl alcohol copolymer or ethylene-vinyl acetate copolymer. Any known polymerization method can be used for the polymerization, such as solution polymerization, suspension polymerization, dispersion polymerization, etc., but solution polymerization using methanol as a solvent is generally used. The saponification of the obtained ethylene-vinyl ester copolymer can also be performed by a known method.

[0038] The method for obtaining the EVOH particles (A) contained in the electrostatic coating composition of the present embodiment is not particularly limited, but a preferred embodiment includes a method (hereinafter also referred to as method (I)) in which the EVOH particles (A) are dispersed in a dispersion medium, and then the EVOH particles (A) are recovered from the dispersion (I). The method (I) will be described below.

[0039] In the method (I), first, a dispersion (I) containing EVOH particles (A), a dispersant and a dispersion medium is prepared.

[0040] The content of the dispersant in the dispersion (I) is usually 5 to 43 parts by mass, preferably 11 to 43 parts by mass, and more preferably 25 to 43 parts by mass, based on 100 parts by mass of the EVOH particles (A). The content of the EVOH particles (A) is usually from 5 to 50% by mass, preferably from 10 to 45% by mass, and particularly preferably from 15 to 40% by mass, based on the total mass of the dispersion (I).

[0041] Examples of the dispersant include polyvinyl alcohol resins (PVA resins), surfactants, and the like. Among these, PVA resins are preferred in terms of dispersion stability.

[0042] As the above-mentioned PVA-based resin, in addition to unmodified PVA, there are copolymerization-modified PVA obtained by copolymerizing various monomers during the production of vinyl ester-based resin and saponifying it, and various post-modified PVAs obtained by introducing various functional groups into unmodified PVA by post-modification. In addition, the content (ethylene content) of the structural unit derived from ethylene in the PVA-based resin is preferably less than 10 mol%.

[0043] The saponification degree of the PVA-based resin is preferably, for example, 85 to 95 mol%, and the viscosity of a 4 mass% aqueous solution at 20 °C is preferably 10 to 70 mPa·s. The viscosity of the 4 mass% aqueous solution is measured in accordance with JIS K 6726 3.11.2.

[0044] As the dispersion medium (hereinafter also referred to as the first dispersion medium) used when preparing the dispersion (I), usually, in a substance and concentration range that does not affect the stability of the dispersion (I), if it is a water-soluble component, it is not particularly limited, and any aqueous solution containing them may be used, such as only water, an aqueous solution of polysaccharide, an aqueous solution of cellulose (CNF), etc., and a small amount of a water-soluble organic solvent may be used in combination. Examples of the organic solvent include methanol, ethanol, acetone, etc. Among them, water is preferable from the viewpoints of safety and supply.

[0045] The content of the first dispersion medium is not particularly limited, but is preferably 25 mass% or more, more preferably 35 mass% or more, and even more preferably 40 mass% or more based on the total amount of the dispersion (I). Also, it is preferably 95 mass% or less, more preferably 85 mass% or less, and even more preferably 75 mass% or less.

[0046] When using a dispersion medium in which water and an organic solvent are used in combination, the content ratio of water to the total amount of the dispersion medium is preferably 60 mass% or more, more preferably 70 mass% or more, and even more preferably 90 mass% or more. Among these, it is most preferable to use only water as the dispersion medium.

[0047] As the method for producing the dispersion (I), usually (i) the high-pressure homogenizer method and (ii) the method using an extruder can be mentioned. The method (ii) using an extruder is preferable in terms of production efficiency because the melting process of the resin can be continuously carried out. The method (ii) using an extruder is a method in which EVOH (A), a dispersant, and other components in the dispersion are melt-kneaded (the kneading temperature is, for example, 95 to 220 ° C) with a twin-screw extruder, and a dispersion medium is introduced from the extruder vent. In some cases, the dispersant may be added as an aqueous solution from the vent. The temperature of the vent portion where the aqueous solution of the dispersion medium and the dispersant is added is preferably adjusted to 100 ° C or lower in order to suppress evaporation.

[0048] In method (I), subsequently, EVOH particles (A) are recovered from the dispersion (I). The method for recovering EVOH particles (A) from the dispersion (I) is not particularly limited. For example, a method of recovering EVOH particles (A) by subjecting the filtrate obtained by filtering the dispersion (I) to solid-liquid separation such as centrifugation after diluting it as necessary can be mentioned.

[0049] <Inorganic filler (B)> As the inorganic filler (B) used in the electrostatic coating composition of the present embodiment, 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, 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, earth, clay, ore, mineral, mortar, cement, concrete, asphalt, ceramics, etc. can be mentioned.

[0050] When the electrostatic coating composition of this embodiment is used as a radiation shielding coating composition described later, from the viewpoint of further improving the neutron shielding performance, it is preferable that the inorganic filler (B) 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, the absorption cross section of Gd is larger than that of the other elements, and it is more preferable that the inorganic filler (B) contains a compound containing Gd.

[0051] The above-mentioned compound containing Gd includes oxides, composite oxides, sulfides, hydroxides, etc. containing Gd. 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, gadolinium aluminate activated with europium (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, cerium or chromium 3 Ga 5 O 12 : Gadolinium oxide activated with Ce, Cr, and terbium 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 Among them, the oxide of Gd is preferable because of its excellent stability in the air. 2 O 3 is more preferred.

[0052] Examples of compounds containing B include oxides, composite oxides, sulfides, hydroxides, carbides, nitrides, and phosphides containing B. 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 2 O 3 is preferred.

[0053] Examples of compounds containing Li include oxides, composite oxides, sulfides, and hydroxides containing Li. 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 3 N, Lithium hydroxide LiOH H 2 Lithium methoxyl LiOCH 3 Li is preferred because of its excellent stability in air. 2 O is preferred.

[0054] When the coating composition of the present embodiment is used as a radiation shielding coating composition described later, in addition to the compound containing an element having an absorption performance for neutrons, protons, and heavy particles, a compound containing an element having an absorption performance for various radiations other than neutrons, protons, and heavy particles, or a known additive may be contained as an inorganic filler (B) according to the desired performance. Specific examples of the compound containing an element having an absorption performance for various radiations 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 them, 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.

[0055] The proportion of the compound containing one or more elements selected from the group consisting of Gd, B, and Li in the inorganic filler (B) may be 0 mass% depending on the desired performance, but from the viewpoint of improving the shielding performance against neutrons and protons, it is preferably 20 mass% or more, more preferably 30 mass% or more, more preferably 40 mass% or more, more preferably 50 mass% or more, particularly preferably 60 mass% or more, and may be 100 mass%.

[0056] The content of the inorganic filler (B) in the electrostatic coating composition of this embodiment is not particularly limited, but is preferably, for example, 10 to 90 mass% based on the total mass of the solid content of the electrostatic coating composition. That is, from the viewpoint of metal adhesion, the content of the inorganic filler (B) in the electrostatic coating composition is preferably 10 mass% or more, more preferably 15 mass% or more, and even more preferably 20 mass% or more based on the total mass of the solid content of the electrostatic coating composition. In addition, from the viewpoint of surface smoothness, the content of the inorganic filler (B) in the electrostatic coating composition is preferably 90 mass% or less, more preferably 85 mass% or less, even more preferably 80 mass% or less, and particularly preferably less than 50 mass% based on the total mass of the solid content of the electrostatic coating composition.

[0057] In addition, when the electrostatic coating composition of this embodiment is used as a radiation-shielding coating composition described later, the content of the inorganic filler (B) is preferably, for example, 10 to 90 mass% based on the total mass of the solid content of the radiation-shielding coating composition. That is, from the viewpoint of improving the radiation shielding property, the content of the inorganic filler (B) in the radiation-shielding coating composition is preferably 10 mass% or more, more preferably 15 mass% or more, and even more preferably 20 mass% or more based on the total mass of the solid content of the radiation-shielding coating composition. In addition, from the viewpoint of the strength, shape stability, and moldability of various molded products, the content of the inorganic filler (B) in the radiation-shielding coating composition is preferably 90 mass% or less, more preferably 85 mass% or less, even more preferably 80 mass% or less, and particularly preferably less than 50 mass% based on the total mass of the solid content of the radiation-shielding coating composition.

[0058] In addition, when the mixing ratio (mass ratio) of the EVOH particles (A) and the inorganic filler (B) based on mass is (A) / (B), (A) / (B) is preferably 10 / 90 to 90 / 10, more preferably 15 / 85 to 85 / 15, and further preferably 20 / 80 to 80 / 20. When the mixing ratio is within this range, the metal adhesion and surface smoothness are good, and the affinity between the EVOH particles (A) and the inorganic filler (B) is good and they are mixed uniformly, which is preferable.

[0059] The shape of the inorganic filler (B) is not particularly limited, but in general, a powder is preferably used. The average particle size of the inorganic filler (B) 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 (B) is preferably 1 μm or more, and more preferably 2 μm or more. The average particle size of the inorganic filler (B) 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, and the surface smoothness is also excellent. Therefore, when used as a radiation shielding coating composition, the radiation shielding property can be improved. By having the average particle size be equal to or more than the above lower limit, the inorganic filler (B) can be uniformly dispersed in the coating film or molded product. Here, the average particle size refers to the median size (d50) measured by a laser diffraction type particle size distribution measuring device in accordance with JIS 8825: Particle size analysis - Laser diffraction and scattering method.

[0060] Furthermore, when the inorganic filler (B) is incorporated into the electrostatic coating composition of this embodiment, it can be mixed by a known method, such as a method of mixing components such as EVOH (A) and melt-kneading and mixing, or a method of dispersing EVOH (A) and the inorganic filler (B) in a dispersion medium.

[0061] The electrostatic coating composition of this embodiment contains the above-mentioned EVOH particles (A) and inorganic filler (B). From the viewpoint of ease of handling as a coating composition, the electrostatic coating composition of this embodiment is preferably in a form in which the EVOH particles (A) and the inorganic filler (B) are dispersed in a dispersion medium.

[0062] Here, the dispersion medium (hereinafter also referred to as the second dispersion medium) that can be used in the electrostatic coating composition is preferably a polar solvent, such as lower alcohols and water. Among these, from the viewpoints of safety and supply, as well as uniform dispersion and anti-sedimentation effect in the resulting electrostatic coating composition, alkylene glycol is preferred, and propylene glycol is particularly preferred. In addition, when the above-mentioned method (I) is applied as a method for preparing EVOH particles (A), the dispersion medium (first dispersion medium) used in preparing the above-mentioned dispersion (I) and the dispersion medium (second dispersion medium) that can be used in the electrostatic coating composition may be the same as or different from each other.

[0063] The electrostatic coating composition may contain components other than EVOH (A) and inorganic filler (B), such as organic fillers, various additives, etc. Examples of the various additives include dispersants, leveling agents, defoamers, antisettling agents, lubricants, abrasives, rust inhibitors, antistatic agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, stabilizers (thickeners), surfactants, colorants, plasticizers, lubricants, etc.

[0064] The molded article on which the coating film is formed by the electrostatic coating composition of this embodiment is not particularly limited, and examples thereof include metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel, 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 polyolefin resins such as polypropylene and polyethylene, PET resin, PBT resin, and other polyester resins, and other molded articles containing poorly adherent substrates. In addition, the molded article may be made of paper, mortar, concrete, wood, ceramic materials, and the like. It should be noted that the electrostatic coating composition of this embodiment has high adhesion to metals, but it is naturally understood that it can be applied to various coated objects other than metals without any particular restrictions.

[0065] To form a coating film on these molded articles using the electrostatic coating composition of this embodiment, the electrostatic coating composition of this embodiment is applied to the surface of the molded article (substrate) and then dried. The electrostatic coating composition can be applied, for example, by supplying a dispersion of the electrostatic coating composition to an electrostatic coating device and spraying it together with compressed air, propane gas, and oxygen.

[0066] The thickness of the coating film after curing is preferably in the range of 20 to 1000 μm. The drying may be performed by heating, which can be performed by a known heating means. For example, a drying oven such as a hot air oven, an electric oven, or an infrared induction heating oven can be used as the heating means. 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.

[0067] After coating the electrostatic coating composition, and before heating, pre-heating, 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 150° 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 150° C. onto the coated surface for about 30 seconds to 15 minutes.

[0068] 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.

[0069] The electrostatic coating composition of the present embodiment can be suitably used in a wide range of fields, including applications for various vehicles such as automobiles, buses, and railroad cars, construction machinery, agricultural machinery, electrical equipment, precision electronic devices, medical equipment, floors, walls, and roofs of buildings, and also for coating the 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.

[0070] <Radiation shielding paint composition> The radiation shielding coating composition according to this embodiment comprises the above-mentioned electrostatic coating composition. As a result of intensive research, the present inventors have found that EVOH is particularly excellent in neutron shielding performance and is suitable as a radiation shielding composition. In particular, they have found that EVOH has better neutron shielding performance than polyethylene, even though it has a smaller hydrogen ratio (weight ratio of hydrogen atoms in the molecule) than polyethylene. The reason for this is presumably that the hydroxyl groups contained in EVOH form hydrogen bonds to improve the density of the resin, thereby improving the hydrogen density (intermolecular cohesive force) in the resin.

[0071] The radiation-shielding composition according to the present embodiment contains EVOH particles (A), and therefore has excellent radiation-shielding performance. Examples of the target radiation include neutrons, protons, gamma rays, X-rays, α rays, β rays, electrons, protons, heavy particles, and the like. 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 radiations that are effective for shielding when they are decelerated by collision with atomic nuclei. Therefore, the radiation-shielding coating composition according to the present embodiment is considered to have excellent neutron shielding performance among radiations, and also excellent shielding performance for protons and heavy particles. In other words, the radiation-shielding coating composition according to the present embodiment is particularly excellent in the performance of shielding radiation by decelerating it by collision with atomic nuclei.

[0072] The radiation-shielding coating composition of this embodiment is composed of the above-mentioned electrostatic coating composition, and the contents of each component and other components may be the same as those in the above-mentioned electrostatic coating composition. In addition, in order to further enhance radiation shielding, the radiation-shielding coating composition of this embodiment preferably contains an inorganic filler (B) containing a compound containing one or more elements selected from the group consisting of Gd, B, and Li.

[0073] (Application) 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 and articles, including robots, 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, vessels and containers for storing nuclear waste and nuclear fuel debris, aerospace applications, such as components for aircraft and spacecraft, artificial satellites and Moon- and Mars-related infrastructure, medical applications, such as components for medical accelerators and peripheral components for medical devices that utilize radiation, and the like. EXAMPLES

[0074] Hereinafter, the present invention will be described more specifically 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.

[0075] (Component (A) (EVOH (A)), Component (B) (inorganic filler (B)), PVA-based resin, and polyolefin aqueous dispersion), the following were prepared. <Component (A)> · EVOH (saponification degree 99 mol%, ethylene content 32 mol%, MFR 12 g / 10 min (210 °C, load 2160 g)) (in Table 1, it is represented as "A-1"). <Component (B)> · Gd 2 O 3 powder (manufactured by Nippon Yttrium Co., Ltd., product name: gadolinium oxide 99.9%, average particle diameter 2.32 μm) <PVA-based resin> · PVA-based resin (unmodified PVA resin, average degree of polymerization 2,400, saponification degree 87 - 89%, 4 mass% viscosity at 20 °C 40 - 46 mPa·s) <Polyolefin aqueous dispersion> · Low-density polyethylene dispersion (manufactured by Mitsui Chemicals, Inc., product name: Chemparl M200, solid content concentration 40%) (in Table 1, it is represented as "PE").

[0076] (Example 1) (Preparation preparation of EVOH particles (A)) 15.4 parts of the above EVOH (A) was continuously supplied from the hopper of a twin-screw extruder [product number KZW15TW-60MG, manufactured by TechnoBel, L / D = 60], melt-kneaded under the following extrusion temperature conditions, and from the supply port provided in the extruder, 6.6 parts of the above PVA-based resin and 78 parts of water were continuously supplied while continuously extruding under the condition of a heating time of 180 seconds (screw rotation speed: 300 rpm) to obtain dispersion i. Note that dispersion i represents dispersion (I) prepared in Example 1. The dispersed particle diameter (median diameter) of the EVOH particles (A) in the dispersion i was measured with a laser diffraction particle diameter measuring device (product number LA-950V2, manufactured by Horiba, Ltd.) and found to be 2.57 μm. Extrusion temperature (℃): C1 / C2 / C3 / C4 / C5 / C6 / C7 / C8=170 / 220 / 220 / 195 / 95 / 95 / 95 / 95

[0077] (Preparation of electrostatic coating composition) In order to recover EVOH particles (A) from the obtained dispersion i, the dispersion i was filtered through a 125 mesh, and the filtrate was diluted 10 times with purified water and centrifuged (1000 rpm, 3 minutes) for solid-liquid separation to extract EVOH particles (A). Then, EVOH particles (A) and Gd 2 O 3 The obtained mixture was mixed with propylene glycol in a ratio of mixture / propylene glycol = 30% by mass / 70% by mass to obtain EVOH particles (A) and Gd 2 O 3 The powder (inorganic filler (B)) was dispersed in propylene glycol to obtain a composition for electrostatic coating.

[0078] Electrostatic coating was performed using a Micro Mist coater manufactured by Nagase Techno Engineering Co., Ltd. The coating conditions were nozzle diameter 50 μm, voltage 12 kV, flow rate 0.1 cm / min, nozzle height 50 mm, pitch 2 mm, speed 50 mm / s, and stage temperature 100° C., and the electrostatic coating composition was electrostatically coated on an aluminum plate (thickness 300 μm). After that, the plate was pre-dried at 120° C. for 5 minutes, and then heat-treated at 200° C. for 5 minutes and dried. The coating (coating) had a thickness of 30 μm. The following evaluations were then performed. The results are shown in Table 1.

[0079] (Examples 2 to 4) The electrostatic coating compositions and electrostatic coating were prepared in each of Examples 2 to 4 in the same manner as in Example 1, except that the amount of each component or the coating (coating) thickness was changed as shown in Table 1, and the same evaluations were performed. The results are shown in Table 1.

[0080] Comparative Example 1 70 parts of the above-mentioned polyolefin aqueous dispersion and Gd 2 O 3 This electrostatic coating composition was electrostatically coated under the same coating conditions as in Example 1, and the same evaluations were carried out. The results are shown in Table 1.

[0081] [Painting stability] Spraying was continued for 5 minutes and an evaluation was made as to whether clogging occurred during painting. ◎: High fluidity, and coating was performed evenly without clogging 〇: Fluidity has decreased and the coating area has become smaller. ×: Clogged and unable to paint

[0082] [Adhesion] Rub your finger over the painted surface to reveal the Gd 2 O 3 The state of separation of the powder (inorganic filler (B)) was observed and evaluated according to the following criteria. ◎: Inorganic filler (B) does not adhere to fingers even when rubbed hard ○: Inorganic filler (B) does not adhere to fingers even when rubbed ×: Inorganic filler (B) adheres to fingers when rubbed

[0083] [Smoothness] The coated surface was observed with a laser microscope, the height of any side of the obtained image was measured, and the arithmetic mean surface roughness Ra was calculated. For Comparative Example 1, the adhesion was poor, so the smoothness was not evaluated.

[0084] [Gas barrier properties] In each of the Examples and Comparative Examples, except that a PET film (thickness 38 μm) was used instead of an aluminum plate (thickness 300 μm), the coating film was electrostatically coated in the same manner as above, and the oxygen transmission rate (OTR, unit: cc / m) was measured at 23°C and 50% relative humidity using an oxygen transmission rate measuring device (MOCON OX-TRAN2 / 21 type) in accordance with JIS K7126-2 (2006). 2 / day / atm) was measured. The thickness of the coating electrostatically applied to the PET film (thickness 38 μm) was the same as the thickness of the coating electrostatically applied to an aluminum plate (thickness 300 μm). In addition, for Comparative Example 1, the gas barrier property was not evaluated because the adhesion was poor.

[0085] [Evaluation of neutron shielding performance] For each electrostatic coating composition, a plate-shaped evaluation sample (an aluminum plate electrostatically coated with the electrostatic coating composition) was prepared as described above, and the neutron transmittance was evaluated. Gold foil was set on the front and back (both main surfaces) of the evaluation sample, and neutrons were irradiated from the front side of the sample toward the sample in a direction parallel to the plate thickness direction. It is arbitrary which main surface of the sample is to be the front. The accelerator neutron source was generated under the following conditions. The gold foils set on the front and back of the sample were arranged so that they did not overlap each other when viewed parallel to the plate thickness direction of the sample (i.e., the neutron irradiation direction). When irradiated with neutrons, the gold foil becomes activated. The neutron shielding factor was evaluated from the ratio of the radioactivity intensity of the gold foil on the front side of the sample, which is directly irradiated with neutrons, to the radioactivity intensity of the gold foil on the back side, which is irradiated with neutrons that have passed through 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 1. (accelerator neutron source) Accelerator: Sumitomo Heavy Industries Cyclotron HM-18HC Accelerated particle: Proton 18MeV Target:Be Nuclear reactions that occur: 7 Be(p,n) 7 Reaction B Irradiation current: ~120μA Irradiation time: 3 hours

[0086] [Table 1]

[0087] When electrostatic coating compositions of Examples 1 to 4 were electrostatically coated on metal, they gave a coating surface with high adhesion and excellent smoothness. They also had good coating stability and gas barrier properties, and showed high neutron shielding performance. On the other hand, the electrostatic coating composition of Comparative Example 1 had poor adhesion when electrostatically coated onto metal.

Claims

1. A composition for electrostatic coating comprising saponified ethylene-vinyl ester copolymer particles (A) and an inorganic filler (B).

2. 2. The electrostatic coating composition according to claim 1, wherein the average particle size of the saponified ethylene-vinyl ester copolymer particles (A) is 0.1 to 20 μm.

3. 2. The electrostatic coating composition according to claim 1, wherein the saponified ethylene-vinyl ester copolymer particles (A) are spherical.

4. 2. The electrostatic coating composition according to claim 1, wherein the content of structural units derived from ethylene in the saponified ethylene-vinyl ester copolymer particles (A) is 10 to 77 mol %.

5. The electrostatic coating composition according to claim 1, wherein the mass-based mixing ratio (A) / (B) of the saponified ethylene-vinyl ester copolymer particles (A) to the inorganic filler (B) is 10 / 90 to 90 / 10.

6. 2. The electrostatic coating composition according to claim 1, wherein the saponified ethylene-vinyl ester copolymer particles (A) and the inorganic filler (B) are dispersed in a dispersion medium.

7. The inorganic filler (B) is selected from the group consisting of 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, lanthanum-based compounds, cerium-based compounds, ne The electrostatic coating composition according to claim 1, which contains at least one selected from the group consisting of odium-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.

8. A radiation shielding coating composition comprising the electrostatic coating composition according to any one of claims 1 to 7.

9. The radiation shielding coating composition according to claim 8, wherein the radiation includes at least one selected from the group consisting of neutrons, protons, and heavy particles.

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