Bismuth sulfide particles, method for producing the same, and use thereof

Abstract

The present invention provides a bismuth sulfide which is easy to reflect infrared rays and has a blackness equivalent to or higher than that of carbon black. The present invention is a bismuth sulfide particle including agglomerated secondary particles formed by agglomeration of primary particles, and having a cumulative 50% particle diameter (D1) of 0.2 μm or more and 10 μm or less in a volume cumulative distribution measured by a laser diffraction / scattering particle size distribution measuring device. The present invention includes a process of heating a bismuth compound and a sulfur compound in a dispersion medium in the presence of a protective agent at 30°C or higher and 100°C or lower.

Description

Technical Field

[0001] This invention relates to bismuth sulfide particles and their manufacturing methods, as well as black pigments containing bismuth sulfide particles, infrared reflective materials, laser reflective materials for laser imaging detection and scattering (LiDAR), solvent compositions, resin compositions, coating compositions, coating films, etc. Background Technology

[0002] Carbon black is a well-known general-purpose black pigment. Due to its high blackness, carbon black is widely used as a colorant in coatings, plastics, and other products.

[0003] However, because carbon black absorbs infrared radiation, items coated with black paint containing carbon black and plastic products containing carbon black will easily experience a rise in surface temperature when exposed to sunlight outdoors, resulting in faster deterioration of the products.

[0004] Furthermore, because carbon black absorbs infrared light, it is difficult to apply to LiDAR, a technology that has gained attention in recent years in fields such as autonomous driving. LiDAR is known as a technology for detecting the distance, position, and shape of surrounding objects. LiDAR determines the distance and direction of an object by illuminating it with laser light (near-infrared light) and measuring the time it takes for the laser light to reach the object and reflect back. Therefore, to ensure the accuracy of LiDAR measurements, the object needs to reflect the laser light (near-infrared light). However, when a car body is painted with a black coating containing carbon black, the laser light (near-infrared light) is absorbed by the car body surface, which cannot sufficiently ensure the intensity of the reflected laser light (near-infrared light), thus compromising the accuracy of LiDAR measurements.

[0005] Based on the above, and considering the need to suppress the surface temperature rise of black objects and the applicability of lidar to black objects, it is required that the material be "black but reflective of infrared light" (i.e., black infrared reflective material).

[0006] Several candidate materials exist for black infrared reflective materials, and bismuth sulfide is one of them. Bismuth sulfide is generally known as a black material that is difficult to absorb infrared radiation (in other words, it is easily transmitted or reflected). For example, Patent Document 1 describes the use of bismuth sulfide particles as a black pigment in coatings used in light-absorbing films for liquid crystal displays. These bismuth sulfide particles are obtained by adding an aqueous solution of sodium thiosulfate dissolved in an aqueous solution containing bismuth nitrate pentahydrate and sodium hydroxide, while stirring and heating.

[0007] Furthermore, Non-Patent Document 1 describes the synthesis of black bismuth sulfide particles by adding hydrochloric acid to an aqueous solution containing dissolved bismuth oxide and thiocarbamoyl dihydrazide, followed by the addition of polyvinyl alcohol (PVA), and then performing hydrothermal synthesis at a temperature of 200°C. Additionally, Non-Patent Document 2 describes the synthesis of black bismuth sulfide particles by reflux of an aqueous solution containing dissolved bismuth nitrate pentahydrate, thiourea, and polyethylene glycol (PEG) at a temperature of 130°C.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 5-264984

[0011] Non-patent literature

[0012] Non-patent literature 1: Journal of Physics and Chemistry of Solids vol.71 (2010), pp.712-715

[0013] Non-patent literature 2: Materials Letters vol.91 (2013), pp.100-102 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] For bismuth sulfide particles manufactured using the aforementioned existing technologies, the blackness has not met expectations, requiring further improvement. For this reason, bismuth sulfide with high infrared reflectivity and a blackness equivalent to or exceeding that of carbon black is desired.

[0016] Methods for solving problems

[0017] The inventors conducted in-depth research in order to obtain bismuth sulfide particles with high blackness. As a result, they found that when bismuth compounds and sulfur compounds are reacted to synthesize bismuth sulfide at a temperature below 100°C, the presence of a protective agent can reduce the degree of primary particle aggregation of bismuth sulfide particles. As a result, bismuth sulfide particles with higher blackness than those of the past can be obtained, thus completing the present invention.

[0018] That is, the present invention is as follows.

[0019] [1] A bismuth sulfide particle comprising agglomerated secondary particles formed by the aggregation of primary particles, wherein the cumulative 50% particle size (D1) in the volume cumulative distribution measured by a laser diffraction / scattering particle size distribution measuring device is greater than 0.2 μm and less than 10 μm.

[0020] [2] According to the bismuth sulfide particles described in [1], wherein the ratio (D1 / D2) of the cumulative 50% particle size (D1) in the cumulative volume distribution to the cumulative 50% particle size (D2) in the cumulative number distribution of the primary particles as determined by scanning electron microscopy is greater than 1 and less than 6.

[0021] [3] Bismuth sulfide particles according to [1] or [2], wherein the cumulative 50% particle size (D2) is 0.2 μm or more and 3 μm or less.

[0022] [4] Bismuth sulfide particles according to any one of [1] to [3], wherein the ratio of the difference between the cumulative 90% particle size (D90) and the cumulative 10% particle size (D10) to the cumulative 50% particle size (D50) in the cumulative particle size distribution measured by a Coulter counter type particle size distribution measuring device (D3 = (D90-D10) / D50) is 3.0 or less.

[0023] [5] Bismuth sulfide particles according to any one of [1] to [4], wherein the element X is selected from Al, Ce, La, Fe and Y in such a way that the ratio of the number of moles of X atoms to the number of moles of bismuth atoms (X / Bi molar ratio) is greater than 0 and less than 0.15.

[0024] [6] According to the bismuth sulfide particles described in [5], wherein element X is Al.

[0025] [7] Bismuth sulfide particles according to any one of [1] to [6], wherein the shape of the bismuth sulfide particles observed by a scanning electron microscope is a shape formed by the aggregation of one end of more than 10 needle-like constituent elements and / or a shape having a plurality of protrusions of plate-like plates and / or needle-like plates on the surface of an approximately spherical body.

[0026] [8] A black pigment comprising bismuth sulfide particles as described in any one of [1] to [7].

[0027] [9] A matte pigment comprising bismuth sulfide particles as described in any one of [1] to [7].

[0028]

[10] An infrared reflective material comprising bismuth sulfide particles as described in any one of [1] to [7].

[0029]

[11] A laser reflective material for lidar, comprising bismuth sulfide particles as described in any one of [1] to [7].

[0030]

[12] A solvent composition comprising bismuth sulfide particles as described in any one of [1] to [7] and a solvent.

[0031]

[13] A resin composition comprising bismuth sulfide particles and resin as described in any one of [1] to [7].

[0032]

[14] A coating composition comprising bismuth sulfide particles as described in any one of [1] to [7] and a coating resin.

[0033]

[15] A coating comprising the coating composition described in

[14] .

[0034]

[16] The coating according to

[15] , wherein the bismuth sulfide particles described in any one of [1] to [7] are contained at a pigment volume concentration of 15% or more.

[0035]

[17] A method for manufacturing bismuth sulfide particles, comprising: heating a bismuth compound and a sulfur compound in a dispersion medium in the presence of a protective agent at a temperature above 30°C and below 100°C.

[0036]

[18] The method for manufacturing bismuth sulfide particles according to

[17] includes, in the presence of a protective agent, a step of maintaining the temperature at or above 10°C and below 40°C for more than 1 hour and less than 24 hours before the step of heating the bismuth compound and the sulfur compound in the dispersion medium.

[0037]

[19] The method for manufacturing bismuth sulfide particles according to

[17] or

[18] includes a step of mixing a compound of at least one element X selected from Al, Ce, La, Fe and Y with a bismuth compound.

[0038]

[20] The method for manufacturing bismuth sulfide particles according to

[19] , wherein element X is Al.

[0039]

[21] The method for manufacturing bismuth sulfide particles according to

[19] or

[20] , wherein a compound of element X is mixed such that the ratio of the number of moles of X atoms to the number of moles of bismuth atoms (X / Bi molar ratio) is greater than 0 and less than 10.

[0040]

[22] The method for manufacturing bismuth sulfide particles according to any one of

[17] to

[21] , wherein the above-mentioned protective agent is a water-soluble polymer.

[0041]

[23] In the method for manufacturing bismuth sulfide particles according to

[22] , the water-soluble polymer is polyvinyl alcohol and / or polyethylene glycol.

[0042]

[24] The method for manufacturing bismuth sulfide particles according to any one of

[17] to

[23] , wherein the bismuth compound and the sulfur compound are mixed such that the ratio of the number of moles of sulfur atoms to the number of moles of bismuth atoms (S / Bi molar ratio) is 3.5 or more and 20 or less.

[0043] Invention Effects

[0044] The bismuth sulfide particles of the present invention have higher blackness compared to conventional bismuth sulfide particles, thus enabling the production of black pigments, coatings, and films with higher blackness than before. Furthermore, the bismuth sulfide particles of the present invention have infrared reflectivity, therefore, they can be used as infrared reflective materials, laser reflective materials for lidar, black pigments for heat insulation, and black laser reflective materials for lidar.

[0045] In addition, the bismuth sulfide particles of the present invention have high matting properties, making them useful as matting pigments.

[0046] Furthermore, the bismuth sulfide particles of the present invention can be used, for example, with solvents and resins (e.g., coating resins) to achieve solvent compositions and resin compositions (e.g., coating resin compositions).

[0047] Furthermore, the manufacturing method of the present invention involves heating a bismuth compound and a sulfur compound in a dispersion medium, in the presence of a protective agent, and at a specified temperature, enabling the production of bismuth sulfide particles with high blackness using a simple method. Moreover, the method involves heating a bismuth compound, a sulfur compound, and a compound containing at least one element X selected from Al, Ce, La, Fe, and Y at a specified temperature in the presence of a protective agent; by including element X in the bismuth sulfide particles, bismuth sulfide particles with even higher blackness can be produced. Attached Figure Description

[0048] [ Figure 1 [Image is a scanning electron microscope image of bismuth sulfide particles from Example 1.]

[0049] [ Figure 2 [This is a volume cumulative particle size distribution map obtained by measuring the bismuth sulfide particles of Example 1 using a laser diffraction / scattering particle size distribution measuring device.]

[0050] [ Figure 3 This is a cumulative particle size distribution diagram obtained by measuring the primary particle size of bismuth sulfide particles in Example 1 using a scanning electron microscope.

[0051] [ Figure 4 [This is a cumulative particle size distribution diagram obtained by measuring the number of bismuth sulfide particles in Example 1 using a Coulter counter-type particle size distribution measuring device.]

[0052] [ Figure 5 [This is a cumulative particle size distribution diagram obtained by measuring the number of bismuth sulfide particles in Example 6 using a Coulter counter-type particle size distribution measuring device.]

[0053] [ Figure 6[Reflectance spectra of coatings using bismuth sulfide particles from Example 1 and coatings using carbon black (reference example).]

[0054] [ Figure 7 [Image: Powder X-ray diffraction pattern of bismuth sulfide particles in Example 1] Detailed Implementation

[0055] The bismuth sulfide particles of the present invention are compounds identified as bismuth sulfide (Bi2S3, etc.) by powder X-ray diffraction patterns. In the powder of these bismuth sulfide particles, there exists a composition consisting of L... * The value indicates that the blackness is sufficiently high, and the reflectance at wavelengths of 780–2500 nm, measured using a UV-Vis-NIR spectrophotometer, is also sufficiently high.

[0056] The bismuth sulfide particles of the present invention comprise condensed secondary particles formed by the aggregation of primary bismuth sulfide particles. Condensed secondary particles are particles formed by the aggregation of multiple (two or more) primary particles through intermolecular forces, etc. For such bismuth sulfide particles of the present invention, not all may be in the form of condensed secondary particles; some may be primary particles.

[0057] The cumulative 50% particle size (referred to as "D1") in the volumetric cumulative distribution of the bismuth sulfide particles of the present invention, as measured by a laser diffraction / scattering particle size distribution measuring device, is 0.2 μm or more and 10 μm or less. The cumulative 50% particle size (D1) of the bismuth sulfide particles of the present invention is preferably 0.6 μm or more and 8.0 μm or less, more preferably 1.0 μm or more and 6.0 μm or less, and even more preferably 1.0 μm or more and 5.0 μm or less. If the primary particles have the same particle size, the larger the secondary particle size, the greater the degree of aggregation. In this regard, for the bismuth sulfide particles of the present invention, the cumulative 50% particle size (D1) is 10 μm or less, indicating a relatively small degree of aggregation. The smaller the degree of aggregation of bismuth sulfide particles, the greater the blackness of the bismuth sulfide particles (and consequently, the black pigment, coating, or film containing bismuth sulfide particles). Therefore, the cumulative 50% particle size (D1) is an important indicator.

[0058] The cumulative 50% particle size (D1) of the bismuth sulfide particles of the present invention refers to the cumulative 50% particle size in the volumetric cumulative distribution when the particle size distribution is measured using a laser diffraction / scattering particle size distribution measuring device LA-950 (manufactured by Horiba Corporation) as a sample, where a dispersion of bismuth sulfide particles in a dispersion medium such as water is used. Detailed measurement conditions are described below. It should be noted that the above dispersion was prepared using an ultrasonic cleaner UT-305 (manufactured by Sharp Corporation) as the disperser.

[0059] [Measurement Conditions]

[0060] Sample refractive index: 2.13

[0061] Solvent refractive index: 1.33

[0062] Cycle speed: 10

[0063] Ultrasonic intensity: 1

[0064] Ultrasound duration: 2 minutes

[0065] Stirring intensity: 10

[0066] Transmittance (R) relative to laser (650nm): 95-70%

[0067] Transmittance (B) relative to LED light (405nm): 90-80%

[0068] The cumulative 50% particle size (referred to as "D2") in the cumulative distribution of the number of primary particles of the bismuth sulfide particles of the present invention, as measured by electron microscopy, is preferably 0.2 μm or more and 3 μm or less, more preferably 0.5 μm or more and 2 μm or less. The cumulative 50% particle size (D2) is the median particle size of the primary particles of bismuth sulfide observed by electron microscopy. If the cumulative 50% particle size (D2) is within the above-mentioned range, the cumulative 50% particle size (D1) of the bismuth sulfide particles of the present invention is easily obtained as the desired value (10 μm or less), and is therefore preferred. The cumulative 50% particle size (D2) refers to the cumulative 50% particle size when the diameter (longest diameter) of each of 100 randomly selected primary particles is measured using a scanning electron microscope S-4800 (manufactured by Hitachi High Technology Co., Ltd.) and expressed as the cumulative distribution of the number of primary particles.

[0069] For the bismuth sulfide particles of the present invention, the ratio of D1 to the cumulative 50% particle size (D2) of the primary particles (D1 / D2) is preferably greater than 1 and less than 6, more preferably greater than 1 and less than 5, and even more preferably greater than 1 and less than 4.

[0070] The D1 / D2 ratio mentioned above represents the degree of aggregation of bismuth sulfide particles when the size of primary particles is also taken into account. The smaller the value, the less aggregation (in other words, closer to the primary particle state, closer to monodisperse). As mentioned above, there is a correlation between the degree of aggregation of primary bismuth sulfide particles and the blackness of bismuth sulfide particles (and consequently, black pigments, coatings, and films containing bismuth sulfide particles). By reducing the value of D1 / D2 (specifically below 6), the blackness can be further improved.

[0071] The bismuth sulfide particles of the present invention, as observed by an electron microscope, preferably have a shape similar to that of a sea urchin (purple sea urchin). More specifically, they are preferably a shape formed by aggregating one end of 10 or more needle-like constituent elements, or a shape having multiple protrusions of plate-like plates and / or needle-like plates on a surface that is approximately spherical. Figure 1 The image shows an electron microscope photograph of bismuth sulfide particles of the present invention, which have a sea urchin-like shape.

[0072] For bismuth sulfide particles with a sea urchin-like shape, numerous tiny spaces are formed from the particle's surface inwards through needle-like constituent elements. Light incident on the surface of the bismuth sulfide particles is repeatedly reflected multiple times within these tiny spaces, thus reducing the reflectivity of light (especially visible light) at the particle surface. Here, for the bismuth sulfide particles of the present invention, the degree of primary particle aggregation is highly suppressed, resulting in a state where a larger portion of the primary particle surface is exposed. Therefore, the effect of reducing visible light reflectivity brought about by the sea urchin-like shape can be fully utilized, resulting in a high degree of blackness.

[0073] For the bismuth sulfide particles of the present invention, regarding the cumulative 50% particle size (D50), cumulative 90% particle size (D90), and cumulative 10% particle size (D10) calculated from the cumulative particle size distribution measured using a Coulter counter-type particle size distribution measuring device, the ratio of the difference between the cumulative 90% particle size (D90) and the cumulative 10% particle size (D10) to the cumulative 50% particle size (D50) (this ratio is referred to as "D3", D3 = (D90 - D10) / D50) is preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.2 or less. The aforementioned Coulter counter-type particle size distribution measuring device can be, for example, a Multisizer4 (manufactured by Beckman Coulter).

[0074] The D3 mentioned above is an indicator of the width of the particle size distribution. The smaller the value, the narrower the distribution, and the larger the value, the wider the distribution.

[0075] In the bismuth sulfide particles of the present invention where D1 / D2 is greater than 1 and less than 6, a small D3 (narrow particle size distribution) indicates a low ratio of coarse and fine particles. The coarse particles can be understood as highly aggregated secondary particles; therefore, a smaller D3 indicates a lower degree of aggregation of the coarse particles. This further improves the blackness of the bismuth sulfide particles of the present invention.

[0076] Furthermore, as described above, with respect to the bismuth sulfide particles of the present invention, it is understood that by causing incident light to be reflected multiple times within the tiny spaces formed by the needle-like constituent elements, the reflectivity of light is reduced, thus resulting in a black appearance. Here, it is preferable to reduce the presence ratio of particles with very small primary particle sizes, or secondary particles aggregated from such particles (collectively referred to as fine particles), from the viewpoint of avoiding a situation where a high presence ratio would prevent the aforementioned tiny spaces from being sufficiently constructed and the light reflectivity from being sufficiently reduced. In other words, by reducing the presence ratio of fine particles, the blackness of the bismuth sulfide particles of the present invention can be further improved.

[0077] The bismuth sulfide particles of the present invention preferably contain at least one element X selected from Al, Ce, La, Fe and Y, more preferably Al or Ce, and even more preferably Al.

[0078] The element X is preferably included in such a way that the ratio of the number of moles of X atoms to the number of moles of bismuth atoms in the bismuth sulfide particles of the present invention (i.e., the X / Bi molar ratio) is greater than 0 and less than 0.15, and more preferably in such a way that it is greater than 0 and less than 0.05. The X / Bi ratio can be calculated, for example, from the result obtained by measuring the bismuth sulfide particles of the present invention using fluorescence X-ray analysis. As an apparatus for performing the fluorescence X-ray analysis, for example, the ZSX (registered trademark) Primus IV (manufactured by Rigaku Corporation) can be cited.

[0079] It is understandable that if bismuth sulfide particles contain element X, then some of the bismuth atoms will be replaced by element X, or element X will enter the space between the bismuth atoms, thus forming an impurity energy level in the band gap, thereby further improving the blackness.

[0080] The bismuth sulfide particles of the present invention may contain 0.1% by mass and less than 5% by mass of carbon. This carbon content primarily originates from the protective agent used in the manufacture of the bismuth sulfide of the present invention. The aforementioned carbon content can be determined using an elemental analysis apparatus, for example, a Vario EL cube (manufactured by Elementar).

[0081] For the bismuth sulfide particles of the present invention, various inorganic and organic compounds can be used to coat the surface. Examples of inorganic compounds include metal oxides and / or metal hydroxides of silicon, aluminum, titanium, zirconium, tin, and antimony. Examples of organic compounds include organosilicon compounds, organometallic compounds, polyols, amines, and carboxylic acids (specifically, trimethylolmethane, trimethylolethane, trimethylolpropane, pentaerythritol, dimethylethanolamine, triethanolamine, stearic acid, oleic acid, and their salts). The surface of the bismuth sulfide particles can be coated with the aforementioned inorganic compound, followed by a further coating with the aforementioned organic compound. The amount of inorganic and organic compounds coated can be appropriately set.

[0082] As a method for coating the surface of bismuth sulfide particles with inorganic or organic compounds, conventional surface treatment methods similar to those used for coating general pigments such as titanium dioxide pigments can be used. Specifically, it is preferable to add inorganic or organic compounds to a slurry of bismuth sulfide particles for coating, and more preferably to neutralize the inorganic or organic compounds in the slurry, causing them to precipitate on the surface of the bismuth sulfide particles for coating. Alternatively, coating can be performed by dry mixing of bismuth sulfide particle powder with inorganic or organic compounds.

[0083] The bismuth sulfide particles of the present invention can be manufactured, for example, by heating a bismuth compound and a sulfur compound in a dispersion medium, in the presence of a protective agent, at a temperature of 30°C or higher and 100°C or lower. If the heating temperature is below 30°C, the reaction does not proceed; if it is above 100°C, a hydrothermal apparatus becomes necessary. From the viewpoint of avoiding the above situations, the above temperature range is preferred. A heating temperature of 30°C or higher and 85°C or lower is more preferably 30°C or higher and 70°C or lower.

[0084] It is understood that the aforementioned protective agent adsorbs onto the surface of the bismuth sulfide particles that have undergone a heating reaction in the dispersion medium. It is also understood that the steric hindrance of the adsorbed protective agent inhibits the aggregation of the bismuth sulfide particles.

[0085] Examples of bismuth compounds that can be used include bismuth sulfate, bismuth nitrate, bismuth nitrate pentahydrate, bismuth subnitrate, bismuth hydroxide, bismuth oxide, bismuth chloride, bismuth bromide, bismuth iodide, bismuth oxychloride, bismuth subcarbonate, and basic bismuth carbonate. These bismuth compounds are not limited to the form of powder; solutions or suspensions prepared by dissolving the powder in various solvents (water, formic acid, methanol, ethanol, 1-propanol, 2-propanol, etc.) can also be used.

[0086] Furthermore, the aforementioned bismuth compounds can be manufactured using known methods. For example, if it is bismuth hydroxide, it can be manufactured as follows: Bismuth nitrate pentahydrate and nitric acid are mixed and heated. Sodium hydroxide is added to the mixture, and it is allowed to mature, thereby obtaining a suspension containing bismuth hydroxide. The resulting suspension is then subjected to solid-liquid separation, and the solid component (specifically, bismuth hydroxide) is washed.

[0087] Regarding sulfur compounds, sulfur itself can be used, or organosulfur compounds such as potassium thiocyanate, sodium thiocyanate (thiocyanates), sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate (thiosulfates), thiourea, and thioacetamide can be used. These sulfur compounds can be anhydrides or hydrates; either form is acceptable. Furthermore, the sulfur compounds are not limited to powder form; solutions or suspensions prepared by pre-dissolving the powder in various solvents (water, formic acid, methanol, ethanol, 1-propanol, 2-propanol, etc.) can also be used. Additionally, known acids or bases can be added to dissolve the powder suspended in the solvent.

[0088] The protective agent is a substance that functions as a dispersion stabilizer for the synthesized bismuth sulfide particles. In this invention, substances known as protective agents can be used. Examples include proteins such as gelatin, gum arabic, casein, sodium caseinate, and ammonium caseinate; natural polymers such as starch, dextrin, agar, and sodium alginate; celluloses such as hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, and ethyl cellulose; vinyl compounds such as polyvinyl alcohol and polyvinylpyrrolidone; acrylic compounds such as sodium polyacrylate and ammonium polyacrylate; and synthetic polymers such as polyethylene glycol. One or more of these can be used. Among these, water-soluble polymers are preferred. Examples of such water-soluble polymers include gelatin, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, and polyethylene glycol. Polyvinyl alcohol, polyethylene glycol, and polyvinylpyrrolidone are particularly preferred. Alternatively, a solution prepared by dissolving the protective agent in various solvents (water, formic acid, methanol, ethanol, 1-propanol, 2-propanol, etc.) can be used.

[0089] The aforementioned dispersion medium is primarily composed of water, meaning that the water content is 50% by mass or more. The water content in the aqueous dispersion medium is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass. Examples of components other than water include various organic solvents dissolved in water (methanol, ethanol, 2-propanol, butanol, acetone, methyl ethyl ketone, tetrahydrofuran, etc.).

[0090] The mixing of the above-mentioned raw materials can be carried out in any order. That is, the bismuth compound, sulfur compound, and dispersion medium can be mixed in advance, and a protective agent can be added thereto; the sulfur compound, protective agent, and dispersion medium can be mixed in advance, and the bismuth compound can be added thereto; or the bismuth compound, protective agent, and dispersion medium can be mixed in advance, and the sulfur compound can be added thereto. Alternatively, all raw materials can be added to the dispersion medium at once for mixing, or the bismuth compound, sulfur compound, and protective agent can be mixed into the dispersion medium one by one. Among these, it is preferable to mix the protective agent and dispersion medium in advance, add the bismuth compound thereto, and then add the sulfur compound. By doing so, the raw materials can be dissolved more uniformly in the solvent. The temperature of the raw material mixing can be set appropriately. Generally, it can be carried out at the temperature of the unheated aqueous dispersion medium, for example, in the range of 5 to 30°C. Alternatively, the aqueous dispersion medium can be heated, for example, in the range of 10 to 50°C.

[0091] In the above-described raw material mixing process, the sulfur compound and bismuth compound are preferably mixed in an S / Bi molar ratio of 3.5 or more and 20 or less, more preferably 4 or more and 12.5 or less, and even more preferably 4.5 or more and 10 or less. By achieving the above range, bismuth sulfide particles with higher blackness can be produced. The above-described S / Bi molar ratio is calculated by dividing the number of moles of sulfur atoms in the sulfur compound by the number of moles of bismuth atoms in the bismuth compound.

[0092] In the above-described raw material mixing process, the mixing amount of the protective agent can be appropriately adjusted according to the type of protective agent. For example, if polyvinyl alcohol is used as the protective agent, it is preferable to mix it at a concentration of 250% by mass or more and 3000% by mass or less relative to the bismuth compound used as the raw material, and more preferably at a concentration of 400% by mass or more and 2000% by mass or less. If polyethylene glycol is used as the protective agent, it is preferable to mix it at a concentration of 1500% by mass or more and 5000% by mass or less relative to the bismuth compound used as the raw material, and more preferably at a concentration of 2000% by mass or more and 4000% by mass or less.

[0093] In addition, the above-mentioned raw material mixing process may include additives such as dispersants, emulsifiers, thickeners, defoamers, and anti-settling agents, as needed.

[0094] For the mixture obtained through the above mixing process, it is preferable to adjust the pH appropriately according to the raw materials used. For example, if bismuth hydroxide, sodium thiosulfate, polyvinyl alcohol, and water are used as raw materials, it is preferable to adjust the pH of the mixture obtained after the mixing process to below 5. More preferably, the pH should be adjusted to below 4, and even more preferably, the pH should be adjusted to below 3. There are no particular limitations on the pH adjusting agent; known acids or bases such as sulfuric acid, nitric acid, hydrochloric acid, sodium hydroxide, and potassium hydroxide can be used. It should be noted that the sulfur compounds mentioned above do not include the sulfuric acid used herein.

[0095] To mix the above raw materials, known mixers such as stirrers, blenders, homogenizers, and agitators can be used.

[0096] The heating time at the above temperature can be set arbitrarily, preferably 0.5 hours or more and 10 hours or less.

[0097] Furthermore, prior to the heating step described above, a step may be included to hold the mixture obtained through the mixing step described above. The holding temperature is set below the heating temperature, and preferably 10°C or higher and 40°C or lower, more preferably 12°C or higher and 30°C or lower, and even more preferably 15°C or higher and 25°C or lower. Additionally, the holding time is preferably 1 hour or higher and 24 hours or lower, more preferably 2 hours or higher and 20 hours or lower, and even more preferably 3 hours or higher and 18 hours or lower. By doing so, the blackness of the bismuth sulfide particles of the present invention can be further improved.

[0098] The aforementioned holding process can be performed at any stage, as long as it occurs before the aforementioned heating process. That is, the holding process can be performed after the raw material mixing or after the aforementioned pH adjustment process, preferably after the aforementioned pH adjustment process. Furthermore, if heating is performed during the mixing process, this temperature can be maintained. In addition, in the aforementioned holding process, known mixers such as stirrers, blenders, homogenizers, and agitators can be used to mix the liquid.

[0099] The mechanism by which the blackness of the bismuth sulfide particles of the present invention is further improved through the above-described holding process can be understood as follows. By heating after the holding process, a nucleation process for bismuth sulfide particles and a growth process for the nuclei obtained through the nucleation process can be separated. The particle size distribution of the bismuth sulfide particles obtained in the above manner is narrower than that of the bismuth sulfide particles obtained without the above-described holding process (i.e., the D3 is smaller). As mentioned above, if the D3 is smaller, the blackness of the bismuth sulfide particles is further improved. Therefore, it can be understood that the blackness of the bismuth sulfide particles of the present invention is further improved through the above-described holding process.

[0100] Furthermore, the method for manufacturing bismuth sulfide particles of the present invention preferably further includes a step of mixing a compound of at least one element X selected from Al, Ce, La, Fe, and Y with a bismuth compound. That is, it is a method of heating the bismuth compound, the sulfur compound, and the compound of at least one element X selected from Al, Ce, La, Fe, and Y at a specified temperature in a dispersion medium in the presence of a protective agent, thereby containing element X in the bismuth sulfide particles. Element X is more preferably Al or Ce, and even more preferably Al.

[0101] For compounds containing Al as element X, examples include aluminum hydroxide, aluminum oxide, aluminum chloride, aluminum nitrate, aluminum sulfate, sodium aluminate, etc. For compounds containing Ce as element X, examples include cerium(III) oxide (Ce₂O₃), cerium(IV) oxide (CeO₂), cerium(III) sulfate octahydrate (Ce₂(SO₄)₃·8H₂O), cerium(III) sulfate tetrahydrate (Ce(SO₄)₂·4H₂O), cerium(III) chloride heptahydrate (CeCl₃·7H₂O), cerium(III) nitrate hexahydrate (Ce(NO₃)₃·6H₂O), etc. For compounds containing La as element X, examples include lanthanum nitrate hexahydrate (La(NO₃)₃·6H₂O), lanthanum oxide (La₂O₃), lanthanum chloride (La₂Cl₃), etc. As compounds in which Fe is element X, ferric nitrate nonahydrate (Fe(NO3)3·9H2O), metallic iron, iron(II) oxide (FeO), iron(III) oxide (Fe2O3), iron(III) oxide (Fe3O4), ferric sulfate (II) sulfate (FeSO4) or its hydrate, ferric sulfate (III) sulfate (Fe2(SO4)3) or its hydrate, ferric chloride (II) chloride (FeCl2) or its hydrate, ferric chloride (III) chloride (FeCl3) or its hydrate, etc. As compounds in which Y is element X, for example, yttrium nitrate hexahydrate (Y(NO3)3·6H2O), yttrium oxide (Y2O3), yttrium fluoride (III) fluoride (YF3), yttrium chloride (III) chloride (YCl3), yttrium bromide (III) bromide (YBr3), etc., can be used. The compounds of element X mentioned above are not limited to the form of powder. They can also be solutions or suspensions formed by dissolving the powder in various solvents (water, formic acid, methanol, ethanol, 1-propanol, 2-propanol, etc.).

[0102] The compounds of element X can be mixed at any time. That is, it is preferable to mix them in any of the steps of mixing the bismuth compound, sulfur compound, dispersion medium and protective agent, holding step and heating step. In addition, when bismuth hydroxide is manufactured as a bismuth compound, it can also be mixed at this time.

[0103] Furthermore, when mixing a compound of element X during the manufacture of bismuth hydroxide, there are no particular restrictions on the order of mixing. That is, bismuth nitrate pentahydrate and the compound of element X can be mixed and dissolved in nitric acid, or nitric acid and the compound of element X can be mixed and the bismuth nitrate pentahydrate can be dissolved in it, or bismuth nitrate pentahydrate, nitric acid and the compound of element X can be mixed at the same time, or an aqueous solution of sodium hydroxide can be mixed with the compound of element X.

[0104] The compounds of element X are preferably mixed in such a way that the ratio of the number of moles of X atoms to the number of moles of bismuth atoms (X / Bi molar ratio) is greater than 0 and less than 10, more preferably greater than 0 and less than 8, and even more preferably greater than 0 and less than 5.

[0105] After the above heating process, the mixture can be evaporated to dryness as needed, or the mixture can be separated into solid and liquid components. For solid-liquid separation, known filtration methods can be used, such as pressure filtration devices commonly used in industry, such as rotary presses, filter presses, vacuum filtration devices, and Moore filters. Centrifugation can also be used. In this case, washing with pure water can be performed as needed.

[0106] Additionally, a step of drying the solid component obtained through the above-described solid-liquid separation may be included. When a drying step is included, the drying temperature and drying time can be set arbitrarily. For example, the drying temperature is preferably 30°C or higher and 120°C or lower, and the drying time is preferably 0.5 hours or higher and 10 hours or lower. In the drying step, for example, a dryer, oven, electric furnace, spray dryer, freeze dryer, vacuum dryer, etc., may be used.

[0107] For bismuth sulfide particles manufactured using the above method, the particle size can be appropriately adjusted using known pulverizers, classifiers, etc.

[0108] Bismuth sulfide particles manufactured using the methods described above can be identified as bismuth sulfide using methods such as X-ray diffraction. For example, they can be identified based on the spectra measured using the Ultima IV X-ray diffraction apparatus (trade name) (manufactured by Rigaku Corporation).

[0109] The bismuth sulfide particles of the present invention have high blackness, thus they can be used as a black pigment. Furthermore, the bismuth sulfide particles of the present invention have infrared reflectivity, thus they can also be used as an infrared reflective material. When used as a black pigment or an infrared reflective material, the bismuth sulfide particles of the present invention can be used in combination with other colorants and infrared reflective materials. Infrared radiation, as referred to here, means electromagnetic waves with wavelengths from 780 nm to 2500 nm.

[0110] Furthermore, the bismuth sulfide particle reflective lidar of the present invention uses lasers in the infrared region with wavelengths (e.g., wavelengths of 905 nm and / or 1550 nm), and is therefore also suitable for use as a laser reflective material for lidar.

[0111] Furthermore, the bismuth sulfide particles of the present invention have matting properties, and therefore can also be used as matting pigments. When the bismuth sulfide particles of the present invention are formulated as matting pigments, conventional matting pigments, colorants, additives, dispersants, etc., can also be incorporated.

[0112] The bismuth sulfide particles and the infrared reflective material containing them of the present invention can be mixed with a solvent to form a dispersion or suspension (solvent composition). Examples of solvents that can be used in the dispersion or suspension include aqueous solvents, alcohols (methanol, ethanol, butanol, 2-propanol, ethylene glycol, etc.), esters (ethyl acetate, etc.), ethers (butyl cellosolve, propylene glycol-1-monomethyl ether, etc.), ketones (acetone, methyl ethyl ketone, etc.), aromatic hydrocarbons (toluene, xylene, mineral spirits, etc.), aliphatic hydrocarbons, and other non-aqueous solvents, or mixtures thereof. The dispersion or suspension may, as needed, contain additives such as dispersants, emulsifiers, antifreeze agents, pH adjusters, thickeners, and defoamers. The concentration of bismuth sulfide in such a solvent composition can be appropriately set.

[0113] Furthermore, the solvent composition described above can be directly applied to a substrate and dried to form a film. As for the coating method, conventional methods such as spin coating, spray coating, roller coating, dip coating, flow coating, doctor blade coating, electrostatic coating, bar coating, mold coating, brush coating, and droplet coating can be used without limitation. The tools used for coating the solvent composition can be appropriately selected from known tools such as spray guns, rollers, brushes, bar coaters, and doctor blades. Examples of substrates include ceramic products, glass products, metal products, plastic products, and paper products.

[0114] In the mixing process for producing the aforementioned dispersions and suspensions, a known mixer can be used. Furthermore, degassing can be performed during the mixing process as needed. Examples of mixers commonly used in industry include twin-screw mixers, three-roll mills, sand mills, and planetary mixers. For laboratory-scale applications, agitators, hybrid mixers, homogenizers, and paint shakers can be used. In this case, pulverizing media composed of glass, alumina, zirconium oxide, zirconium silicate, etc., can be used as needed.

[0115] Furthermore, the preparation of the aforementioned dispersions and suspensions may include a solid-liquid separation process, and the aforementioned mixing and solid-liquid separation processes may be repeated. In the solid-liquid separation process, known filtration methods can be used, such as pressure filtration devices commonly used in industry, such as rotary presses, filter presses, vacuum filters, and vacuum leaf filters. Alternatively, centrifugal separation may also be employed.

[0116] The bismuth sulfide particles and the infrared reflective material containing them of the present invention can be mixed with a resin to form a resin composition. Examples of resins that can be used in the above-described resin composition include, but are not particularly limited to, the following resins.

[0117] Examples of thermoplastic resins include:

[0118] (1) General-purpose plastic resins (e.g., (a) polyolefin resins (polyethylene, polypropylene, etc.), (b) polyvinyl chloride resin, (c) acrylonitrile butadiene styrene resin, (d) polystyrene resin, (e) methacrylic acid resin, (f) polyvinylidene chloride resin, etc.);

[0119] (2) Engineering plastic resins (e.g., (a) polycarbonate resins, (b) polyethylene terephthalate resins, (c) polyamide resins, (d) polyacetal resins, (e) modified polyphenylene ethers, (f) fluoropolymers, etc.);

[0120] (3) Super engineering plastic resins (e.g., (a) polyphenylene sulfide resin (PP), (b) polysulfone resin (PSF), (c) polyethersulfone resin (PES), (d) amorphous polyarylate resin (PAR), (e) liquid crystal polymer (LCP), (f) polyether ether ketone resin (PEEK), (g) polyamide imide resin (PAI), (h) polyether imide resin (PEI), etc.); etc.

[0121] Examples of thermosetting resins include (a) epoxy resins, (b) phenolic resins, (c) unsaturated polyester resins, (d) polyurethane resins, (e) melamine resins, and (f) silicone resins.

[0122] Examples of thermoplastic elastomers include styrene-based, olefin / alkene-based, vinyl chloride-based, polyurethane-based, and amide-based elastomers.

[0123] In addition, the above-mentioned resin composition may, as needed, contain various additives such as lubricants, light stabilizers, antistatic agents, bactericides, dispersants, fillers, flame retardants, antifreeze agents, pH adjusters, thickeners, ultraviolet absorbers, and antioxidants. The concentration of bismuth sulfide in such a resin composition can be appropriately set, and it can also be formed into a high-concentration masterbatch.

[0124] The above-described resin composition can be obtained by incorporating the bismuth sulfide particles of the present invention into the molten resin using a mixer. As the mixer, commonly used mixers can be used, such as single-screw extruders, twin-screw extruders, intensive mixers like Banbury mixers, roll forming machines, etc.

[0125] The bismuth sulfide particles of the present invention and black pigments, matte pigments, infrared reflective materials, and laser reflective materials for lidar containing the bismuth sulfide particles can be mixed with coating resins to form coating compositions. There are no particular limitations on the coating resin; any resin commonly used in coating applications can be used. For example, various coating resins such as phenolic resins, alkyd resins, acrylic alkyd resins, acrylic resins, acrylic emulsion resins, polyester resins, polyester polyurethane resins, polyether resins, polyolefin resins, polyurethane resins, acrylic polyurethane resins, epoxy resins, modified epoxy resins, silicone resins, acrylic silicone resins, fluoropolymers, ethylene vinyl acetate copolymers, acrylic-styrene copolymers, amino resins, methacrylic resins, polycarbonate resins, and polyvinyl chloride resins can be used.

[0126] Depending on the requirements, the coating composition of the present invention may contain various additives, solvents, etc. Examples of additives include commonly used dispersants, emulsifiers, antifreeze agents, pH adjusters, thickeners, defoamers, film-forming aids, etc. Examples of solvents include water solvents, alcohols (methanol, butanol, ethylene glycol, etc.), esters (ethyl acetate, etc.), ethers, ketones (acetone, methyl ethyl ketone, etc.), aromatic hydrocarbons (toluene, xylene, mineral oil, etc.), aliphatic hydrocarbons, and other non-aqueous solvents, or mixtures thereof. The concentration of bismuth sulfide in such a coating composition can be appropriately set.

[0127] In the above-mentioned mixing process with resin, the same method as the mixing process used in the preparation of the above-mentioned dispersion and suspension can be used.

[0128] A coating film can be formed by applying the solvent composition or coating composition of the present invention to a substrate and allowing it to cure. This coating film can be used as a black coating film, or as an infrared reflective coating film, or as an infrared blocking coating film, and further, as a heat-insulating coating film.

[0129] The method for applying the solvent composition and coating composition of the present invention can be performed without limitation using conventional methods such as spin coating, spray coating, roller coating, dip coating, flow coating, doctor blade coating, electrostatic coating, bar coating, mold coating, brush coating, and droplet coating. The tools used for applying the solvent composition and coating composition can be appropriately selected from known tools such as spray guns, rollers, brushes, bar coaters, and doctor blades. After coating, drying and curing yields a coating film. Alternatively, baking can be performed after drying. The baking conditions can be appropriately set; for example, a baking time of approximately 1 to 120 minutes in an oxidizing atmosphere at a temperature range of 40°C to 200°C. By setting these conditions, sufficient baking can be performed in the drying oven of a coil coating line.

[0130] Examples of materials that can serve as base materials for coating solvent compositions and coating compositions include ceramic products, glass products, metal products, plastic products, and paper products.

[0131] For the coating of the present invention, by forming a coating in which bismuth sulfide of the present invention is used as a black pigment, L * a * b * L of the coating in the colorimetric system * The value should be below 10.0, preferably below 5.0. Here, L refers to... * The value is CIE1976Lab(L) * a * b * The lightness index (L) in a colorimetric system represents lightness. The smaller the value, the lower the lightness. * The smaller the value, the higher the blackness of the bismuth sulfide particles, and consequently, the blackness (an indicator of the degree of blackness) of black pigments, coatings, and films containing bismuth sulfide particles. The term "CIE 1976Lab(L)" refers to this. * a * b * The CIELAB color system is a color space recommended by the CIE (International Commission on Illumination) in 1976, and is sometimes abbreviated as CIELAB.

[0132] Determining the L of the coating * To prepare a coating composition with a pigment mass concentration (PWC) of 50.00%, an 8 mil applicator was used to apply it onto black-and-white chart sheet to form a coating film. A clear coating was then applied onto this coating film using the same 8 mil applicator to form a clear coating film. For the coating film on a white background, the L value was measured using a colorimeter at a light angle of 45°. *Value. As a color difference meter, for example, a multi-angle colorimeter BYK-Maci (manufactured by BYK-GARDNER) etc. can be used.

[0133] In addition, for the coating film using the bismuth sulfide particles of the present invention, the L * a * b * value of the coating film in the colorimetric system can be -2.0 or more and 2.0 or less, and the b * value of the coating film can be -3.0 or more and 4.5 or less. The coating film using the bismuth sulfide particles of the present invention can be formed into a black coating film that suppresses red, green, yellow, and blue. Here, the so-called a * value, b * value, is an index representing the hue chroma (in Japanese: 色相彩度) of the L * a * a * b * colorimetric system. The larger the a * value is towards the positive side, the stronger the red color is, and the larger it is towards the negative side, the stronger the green color is. In addition, the larger the b * value is towards the positive side, the stronger the yellow color is, and the larger it is towards the negative side, the stronger the blue color is. Regarding the above a * value, b * value, it can be measured in the same manner as the L * value.

[0134] In addition, the coating film of the present invention has infrared reflection characteristics by containing the bismuth sulfide particles of the present invention.

[0135] Furthermore, for the above coating film, the solar reflectance can be 25.0% or more, preferably 35.0% or more. If it is such a value, it can be said that the heat insulation of the above coating film is high enough. The solar reflectance can be calculated according to JIS K 5602 from the reflectance at wavelengths of 780 - 2500 nm of the coating film.

[0136] When measuring the reflectance of the coating film, for example, the coating film can be formed on black and white chart paper in the same manner as when measuring the L * value of the coating film. For the coating film formed on the white background of the black and white chart paper, use a spectrophotometer to measure the reflectance. As a spectrophotometer, for example, an ultraviolet-visible-near-infrared spectrophotometer V-670 (trade name) (manufactured by JASCO Corporation) etc. can be used.

[0137] The coating of the present invention preferably contains 15% or more and 95% or less of the bismuth sulfide particles of the present invention, based on a pigment volume concentration (PVC). For such a coating, a specular gloss of 5 or less at 60° of geometric conditions as measured according to JIS K5600-4-7:1999 can be achieved, forming a so-called matte coating. Furthermore, a specular gloss of 30 or less at 85° can also sufficiently suppress so-called bottom gloss. The aforementioned PVC is more preferably 30% or more and 70% or less, and even more preferably 30% or more and 50% or less.

[0138] When determining the specular gloss of a coating film, for example, a paint composition with a pigment volume concentration (PVC) of 15% to 95% is prepared and applied to a tin-plated iron sheet using an 8-mil applicator to form a coating film. For this coating film, a haze gloss meter is used to measure the gloss values ​​at 20°, 60°, and 85°. For example, a haze gloss meter such as Cat. No. 4601 (manufactured by BYK-GARDNER) can be used.

[0139] Example

[0140] The following are embodiments of the present invention, but the present invention is not limited to these embodiments.

[0141] (Example 1)

[0142] <Preparation of Bismuth Hydroxide>

[0143] 116.8 g of 60% nitric acid (manufactured by NACALAI TESQUE, INC.) was added to 277.6 g of pure water (room temperature, specifically 5–30°C), followed by 146.1 g of bismuth nitrate pentahydrate (manufactured by Kanto Chemical Co., Ltd.), and the mixture was stirred. At room temperature (specifically 5–30°C), 1459.5 g of pure water was added to this mixture to prepare a bismuth nitrate solution. The above bismuth nitrate solution and 3 equivalents of sodium hydroxide aqueous solution were added to 4 L of pure water heated to 70°C, while maintaining the pH at 6.5–7.5. The mixture was then allowed to mature for 10 minutes to obtain a solution containing bismuth hydroxide. Solid-liquid separation was performed by filtration, and the solution was washed with pure water to recover the bismuth hydroxide.

[0144] <Preparation of Bismuth Sulfide>

[0145] At room temperature (specifically 5–30°C), pure water was added to the bismuth hydroxide obtained above to prepare 32 mL of a 0.96 mol / L bismuth hydroxide slurry. Additionally, at room temperature (specifically 5–30°C), pure water was added to 40 g of polyvinyl alcohol (manufactured by Fujifilm and Koko Pure Chemical Industries, Ltd.) with a degree of polymerization of 1500 to prepare 506 mL of a 102.8 g / L polyvinyl alcohol aqueous solution. Furthermore, at room temperature (specifically 5–30°C), pure water was added to sodium thiosulfate (manufactured by NACALAI TESQUE, INC.) to prepare 85 mL of a 1.88 mol / L sodium thiosulfate aqueous solution.

[0146] Next, sodium thiosulfate aqueous solution and bismuth hydroxide slurry were added to the above-mentioned polyvinyl alcohol aqueous solution in the order of addition and stirring. The S / Bi molar ratio in this mixture was 5, and the amount of polyvinyl alcohol added relative to bismuth hydroxide was 500% by mass. 20 g of 30% by mass nitric acid was added. The pH of the mixture after adding nitric acid was 1.95. The resulting mixture was heated to 70°C and stirred for 2 hours to obtain a black precipitate of bismuth sulfide. The black precipitate was recovered by filtration and washed with pure water to obtain bismuth sulfide (sample 1). The carbon content of sample 1 was determined using an automated elemental analyzer described later, and the result was 1.88% by mass.

[0147] (Example 2)

[0148] The amount of polyvinyl alcohol (manufactured by Fujifilm and Kojun Chemical Co., Ltd.) with a degree of polymerization of 1500 in Example 1 was changed to 60 g, and the concentration was changed to 154.2 g / L. Otherwise, the procedure was the same as in Example 1 to obtain bismuth sulfide (sample 2). The amount of polyvinyl alcohol added was 750% by mass relative to bismuth hydroxide. The carbon content of the obtained sample 2 was determined using an automated elemental analyzer described later, and the result was 2.25% by mass.

[0149] (Example 3)

[0150] The amount of polyvinyl alcohol (manufactured by Fujifilm and Koichi Chemicals Co., Ltd.) with a degree of polymerization of 1500 in Example 1 was changed to 80 g, and the concentration was changed to 205.6 g / L. Otherwise, the procedure was the same as in Example 1 to obtain bismuth sulfide (sample 3). The amount of polyvinyl alcohol added was 1000% by mass relative to bismuth hydroxide. The carbon content of the obtained sample 3 was determined using an automated elemental analyzer described later, and the result was 3.19% by mass.

[0151] (Example 4)

[0152] The polyvinyl alcohol (manufactured by Fujifilm and Kojun Chemical Co., Ltd.) with a degree of polymerization of 1500 in Example 2 was replaced with polyvinyl alcohol (manufactured by Polyscience Co., Ltd.) with an average molecular weight of 125,000. Otherwise, the procedure was the same as in Example 1 to obtain bismuth sulfide (sample 4). The amount of polyvinyl alcohol added in this formulation was 500% by mass relative to bismuth hydroxide. The carbon content of the resulting sample 4 was determined using an automated elemental analyzer described later, and the result was 2.27% by mass.

[0153] (Example 5)

[0154] The polyvinyl alcohol (manufactured by Fujifilm and Kohden Chemical Co., Ltd.) with a degree of polymerization of 1500 in Example 1 was replaced with polyethylene glycol (manufactured by Fujifilm and Kohden Chemical Co., Ltd.) with an average molecular weight of 20000, and the addition amount was 240 g, resulting in a concentration of 616.7 g / L. Otherwise, the procedure was the same as in Example 1 to obtain bismuth sulfide (sample 5). The amount of polyethylene glycol added in this formulation was 3000% by mass relative to bismuth hydroxide. The carbon content of the obtained sample 5 was determined using an automated elemental analyzer described later, and the result was 0.77% by mass.

[0155] (Example 6)

[0156] At room temperature (specifically 5–30°C), pure water was added to the bismuth hydroxide obtained in Example 1 (Preparation of Bismuth Hydroxide) to prepare 32 mL of a 0.96 mol / L bismuth hydroxide slurry. Additionally, at room temperature (specifically 5–30°C), pure water was added to 40 g of polyvinyl alcohol (manufactured by Fujifilm and Koko Pure Chemical Industries, Ltd.) with a degree of polymerization of 1500 to prepare 506 mL of a 102.8 g / L polyvinyl alcohol aqueous solution. Furthermore, at room temperature (specifically 5–30°C), pure water was added to sodium thiosulfate (manufactured by NACALAI TESQUE, INC.) to prepare 85 mL of a 1.88 mol / L sodium thiosulfate aqueous solution.

[0157] Next, the temperature of the polyvinyl alcohol aqueous solution was adjusted to 20°C, and bismuth hydroxide slurry was added while stirring. Then, sodium thiosulfate aqueous solution was added while stirring. The S / Bi molar ratio in this mixture was 5, and the amount of polyvinyl alcohol added relative to bismuth hydroxide was 500% by mass. 20g of 30% by mass nitric acid was added. The pH of the mixture after adding nitric acid was 1.95. After adding nitric acid, the temperature of the mixture was maintained at 20°C while stirring for 4 hours (holding process). The resulting mixture was then heated to 70°C and stirred for 2 hours (heating process) to obtain a black precipitate of bismuth sulfide. Add 2440g of pure water to the aqueous solution containing the black precipitate, stir, and centrifuge using a high-speed cooling centrifuge, Himac CR21GII (manufactured by Hitachi Construction Machinery Co., Ltd.), at 10000 rpm for 10 minutes. Discard the supernatant, add 2440g of pure water and stir. Recover the black precipitate by filtration, wash with pure water, and obtain bismuth sulfide (sample 6).

[0158] (Example 7)

[0159] The stirring time of the mixture after adding nitric acid in Example 6 was changed from 4 hours to 17 hours. Otherwise, the same procedure was followed as in Example 6 to obtain bismuth sulfide (sample 7).

[0160] (Example 8)

[0161] The temperature of the polyvinyl alcohol aqueous solution and the temperature of the mixture after adding nitric acid in Example 6 were changed from 20°C to 15°C, and the stirring time of the mixture after adding nitric acid was changed from 4 hours to 17 hours. Otherwise, the same procedure as in Example 6 was followed to obtain bismuth sulfide (sample 8).

[0162] (Example 9)

[0163] The temperature of the polyvinyl alcohol aqueous solution and the temperature of the mixture after adding nitric acid in Example 6 were changed from 20°C to 28°C, and the stirring time of the mixture after adding nitric acid was changed from 4 hours to 17 hours. Otherwise, the same procedure as in Example 6 was followed to obtain bismuth sulfide (sample 9).

[0164] (Example 10)

[0165] The temperature of the polyvinyl alcohol aqueous solution and the temperature of the mixture after adding nitric acid in Example 6 were changed from 20°C to 40°C, and the stirring time of the mixture after adding nitric acid was changed from 4 hours to 17 hours. Otherwise, the same procedure as in Example 6 was followed to obtain bismuth sulfide (sample 10).

[0166] (Example 11)

[0167] The temperature of the polyvinyl alcohol aqueous solution and the temperature of the mixture after adding nitric acid in Example 6 were changed from 20°C to 28°C, and the stirring time of the mixture after adding nitric acid was changed from 4 hours to 2 hours. Otherwise, the same procedure as in Example 6 was followed to obtain bismuth sulfide (sample 11).

[0168] (Example 12)

[0169] The bismuth hydroxide in Example 6 was replaced with bismuth oxide (manufactured by Kanto Chemical Co., Ltd.), and otherwise the same procedure was followed as in Example 6 to obtain bismuth sulfide (sample 12).

[0170] (Example 13)

[0171] <Preparation of bismuth hydroxide containing Al>

[0172] 116.8 g of 60% nitric acid (manufactured by NACALAI TESQUE, INC.) was added to 277.6 g of pure water at room temperature (specifically 5–30°C), followed by 146.1 g of bismuth nitrate pentahydrate (manufactured by Kanto Chemical Co., Ltd.) and 0.123 g of sodium aluminate (Wako Grade 1, manufactured by Fujifilm Wako Pure Chemical Co., Ltd.), and the mixture was then added. At this point, the molar ratio of Al atoms to bismuth atoms (i.e., the Al / Bi molar ratio) was 0.5. A bismuth nitrate mixture was then prepared by adding 1459.5 g of pure water to this mixture at room temperature (specifically 5–30°C). Add the above bismuth nitrate mixture and 3 equivalents of sodium hydroxide aqueous solution to 4L of pure water heated to 70°C, while maintaining the pH at 6.5-7.5, and then allow it to mature for 10 minutes to obtain a suspension containing bismuth hydroxide with Al. Then, perform solid-liquid separation by vacuum filtration, wash with pure water, and recover the bismuth hydroxide containing Al (sample A).

[0173] <Preparation of Al-containing bismuth sulfide>

[0174] At room temperature (specifically 5–30°C), pure water was added to sample A to prepare 32 mL of a 0.96 mol / L bismuth hydroxide slurry containing Al. Additionally, at room temperature (specifically 5–30°C), pure water was added to 40 g of polyvinyl alcohol (manufactured by Fujifilm and Koko Pure Chemical Industries, Ltd.) with a degree of polymerization of 1500 to prepare 506 mL of a 102.8 g / L polyvinyl alcohol aqueous solution. Furthermore, at room temperature (specifically 5–30°C), pure water was added to sodium thiosulfate (manufactured by NACALAI TESQUE, INC.) to prepare 85 mL of a 1.88 mol / L sodium thiosulfate aqueous solution.

[0175] Next, the polyvinyl alcohol aqueous solution was adjusted to 20°C, and the Al-containing bismuth hydroxide slurry was added while stirring. Then, sodium thiosulfate aqueous solution was added while stirring. The S / Bi molar ratio in this mixture was 5, and the amount of polyvinyl alcohol added was 500% by mass relative to the Al-containing bismuth hydroxide. 20g of 30% by mass nitric acid was added. The pH of the mixture after adding nitric acid was 1.95. After adding nitric acid, the temperature of the mixture was maintained at 20°C while stirring for 17 hours (holding process). The resulting mixture was then heated to 70°C and stirred for 2 hours (heating process) to obtain a black precipitate of Al-containing bismuth sulfide. Add 2440g of pure water to the aqueous solution containing the black precipitate, stir, and centrifuge using a high-speed cooling centrifuge, Himac CR21GII (manufactured by Hitachi Construction Machinery Co., Ltd.), at 10000 rpm for 10 minutes. Discard the supernatant, add 2440g of pure water and stir. Recover the black precipitate by filtration, wash with pure water, and obtain bismuth sulfide containing Al (sample 13).

[0176] The obtained Al-containing bismuth sulfide particles were dried at 100°C for 3 hours to obtain a dry powder. The dried powder was then thoroughly pulverized in an agate mortar and packed into an aluminum ring. The ring was then pressed into shape using a hydraulic press. The results were analyzed using a ZSX Primus IV fluorescence X-ray analyzer (manufactured by Rigaku Corporation). The Al / Bi molar ratio was found to be 0.003.

[0177] (Example 14)

[0178] <Preparation of bismuth hydroxide containing Al>

[0179] In the preparation of Al-containing bismuth hydroxide in Example 13, the amount of sodium aluminate (Wako Grade 1, manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.) was changed from 0.123 g to 0.493 g. Otherwise, Al-containing bismuth hydroxide (sample B) was obtained in the same manner as in Example A. The ratio of the number of moles of Al atoms to the number of moles of bismuth atoms (i.e., the Al / Bi molar ratio) was 2.0.

[0180] <Preparation of Al-containing bismuth sulfide>

[0181] In the preparation of Al-containing bismuth sulfide in Example 13, sample A was replaced with sample B. Otherwise, Al-containing bismuth sulfide (sample 14) was obtained in the same manner as in Example 13. The Al / Bi molar ratio of the obtained Al-containing bismuth sulfide was 0.010.

[0182] (Example 15)

[0183] <Preparation of Ce-containing bismuth hydroxide>

[0184] In the preparation of Al-containing bismuth hydroxide in Example 13, 0.123 g of sodium aluminate (Wako Grade 1, manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.) was replaced with 2.616 g of cerium(III) nitrate hexahydrate (Wako Premium Grade, manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.). Otherwise, bismuth hydroxide containing Ce (sample C) was obtained in the same manner as in the preparation of Al-containing bismuth hydroxide in Example 13. The molar ratio of Ce atoms to bismuth atoms (i.e., Ce / Bi molar ratio) was 2.0.

[0185] <Preparation of Ce-containing bismuth sulfide>

[0186] In the preparation of Al-containing bismuth sulfide in Example 13, sample A was changed to sample C. Otherwise, bismuth sulfide containing Ce (sample 15) was obtained in the same manner as in the preparation of Al-containing bismuth sulfide in Example 13. The Ce / Bi molar ratio of the obtained Ce-containing bismuth sulfide was 0.004.

[0187] (Example 16)

[0188] <Preparation of Ce-containing bismuth sulfide>

[0189] At room temperature (specifically 5–30°C), pure water was added to the bismuth hydroxide obtained in the preparation of bismuth hydroxide in Example 1 to prepare 32 mL of 0.96 mol / L bismuth hydroxide slurry. Additionally, pure water (room temperature, specifically 5–30°C) was added to 40 g of polyvinyl alcohol (manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) with a degree of polymerization of 1500 to prepare 506 mL of a 102.8 g / L polyvinyl alcohol aqueous solution. Furthermore, pure water (room temperature, specifically 5–30°C) was added to sodium thiosulfate (manufactured by NACALAI TESQUE, INC.) to prepare 85 mL of a 1.88 mol / L sodium thiosulfate aqueous solution. Finally, 0.67 g of cerium(III) hexahydrate (Wako Special Grade, manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.) was dissolved in 20 g of 30% nitric acid to prepare a cerium nitrate aqueous solution.

[0190] The polyvinyl alcohol aqueous solution was adjusted to 20°C, and bismuth hydroxide slurry was added while stirring. Next, sodium thiosulfate aqueous solution was added while stirring. The S / Bi molar ratio in this mixture was 5, and the amount of polyvinyl alcohol added relative to bismuth hydroxide was 500% by mass. Next, the above-mentioned cerium nitrate aqueous solution was added. The pH of the mixture after adding cerium nitrate aqueous solution was 1.95. At this point, the ratio of the number of moles of Ce atoms to the number of moles of bismuth atoms (i.e., the Ce / Bi molar ratio) was 5.0. After adding nitric acid, the temperature of the mixture was maintained at 20°C while stirring for 17 hours (holding process). The resulting mixture was heated to 70°C and stirred for 2 hours (heating process) to obtain a black precipitate of bismuth sulfide containing Ce. 2440 g of pure water was added to the aqueous solution containing the black precipitate. After stirring, the mixture was centrifuged using a high-speed refrigerated centrifuge (Himac CR21GII, manufactured by Hitachi Construction Machinery Co., Ltd.) at 10000 rpm for 10 minutes. The supernatant was discarded, and 2440 g of pure water was added and stirred. The black precipitate was recovered by filtration and washed with pure water to obtain bismuth sulfide containing Ce (sample 16). The Ce / Bi molar ratio of the obtained bismuth sulfide containing Ce was 0.005.

[0191] (Comparative Example 1)

[0192] At room temperature (specifically 5–30°C), 356.8 mL of a 0.08 mol / L bismuth hydroxide slurry was prepared by adding pure water to bismuth hydroxide. Separately, at room temperature (specifically 5–30°C), 223.5 mL of a 0.68 mol / L sodium thiosulfate aqueous solution was prepared by adding pure water to sodium thiosulfate (manufactured by NACALAI TESQUE, INC.). Next, the sodium thiosulfate aqueous solution was added to the bismuth hydroxide slurry. 20 g of 30% nitric acid was added. The pH of the mixture after adding nitric acid was 2.00. The resulting mixture was heated to 70°C and stirred for 2 hours to obtain a black precipitate of bismuth sulfide. The bismuth sulfide was recovered by filtration and washed with pure water to obtain bismuth sulfide (sample 17).

[0193] <Particle Size Distribution Determination>

[0194] Add 20 ml of pure water to 1.0 g of sample and disperse for 1 minute using an ultrasonic cleaner UT-305 (manufactured by Sharp Corporation) to prepare a dispersion. The particle size distribution of this dispersion was measured using a laser diffraction / scattering particle size distribution measuring device LA-950 (manufactured by Horiba Corporation) under the following conditions. The volumetric cumulative particle size distribution measured using the laser diffraction / scattering particle size distribution measuring device for sample 1 is shown below. Figure 2 .

[0195] Sample refractive index: 2.13 (bismuth sulfide)

[0196] Solvent refractive index: 1.33 (pure water)

[0197] Cycle speed: 10

[0198] Ultrasonic intensity: 1

[0199] Ultrasound duration: 2 minutes

[0200] Stirring intensity: 10

[0201] Transmittance (R) to laser (650nm): 95-70%

[0202] Transmittance (B) to LED light (405nm): 90-80%

[0203] <Cumulative 50% particle size (D1) in the volumetric cumulative distribution of bismuth sulfide particles>

[0204] Based on the particle size distribution obtained above, the cumulative 50% particle size (D1) in the volume cumulative distribution of bismuth sulfide particles is calculated.

[0205] <Determination of primary particle size>

[0206] The above samples were dried at 100°C for 3 hours to obtain dried powder. The dried powder was observed using a scanning electron microscope S-4800 (manufactured by Hitachi High Technology Co., Ltd.), and 100 primary bismuth sulfide particles were selected. Then, the longest straight portion of each of these primary particles was measured. The cumulative particle size distribution of sample 1, measured using a scanning electron microscope, is shown below. Figure 3 .

[0207] <Cumulative 50% particle size (D2) in the cumulative number distribution of primary particles>

[0208] Based on the first particle size obtained above, the cumulative 50% particle size (D2) in the cumulative distribution of the number of first particles is calculated.

[0209] <Determination of Particle Size Distribution Using a Coulter Counter>

[0210] Mix 80g of NOPCOSPERSE 5600 (manufactured by S.N. Nopco) to 7920g of ISOTON II diluent (manufactured by Beckman Coulter) and stir for at least 1 hour. After stirring, filter the solution through a 0.45μm membrane filter (JHWP09025 2-3051-16, manufactured by Merck) to prepare the electrolyte.

[0211] Weigh the sample to ensure the solid component is equivalent to 0.1g, and mix it with the electrolyte to prepare a 20.0g sample mixture. Disperse the sample mixture for 5 minutes using an ultrasonic disperser (360W, AU-180C EYELA (registered trademark), manufactured by Tokyo Riko Instruments Co., Ltd.) to prepare a dispersion. Weigh 2.0g of the dispersion and mix it with 18.0g of the electrolyte to prepare a diluent. Measure 3cc of the diluent and mix it with 200g of the electrolyte to prepare the test sample. The testing apparatus used is a MultisiZer4 (manufactured by Beckman Coulter), and the test sample is stirred while being measured. Detailed test conditions are as follows. The cumulative particle size distribution of samples 1 and 6, measured using a Coulter counter-type particle size distribution measuring device, is shown below. Figure 4 , Figure 5 .

[0212] Pore ​​size: 30μm

[0213] Particle size range measured: 0.6–18 μm

[0214] Measurement conditions: 80 μL quantification

[0215] <The ratio (D3) of the difference between the cumulative 90% particle size (D90) and the cumulative 10% particle size (D10) in the cumulative particle size distribution to the cumulative 50% particle size (D50)>

[0216] Based on the cumulative particle size distribution obtained above using the Coulter counter-type particle size distribution measuring device, the cumulative 10% particle size (D10), cumulative 50% particle size (D50), and cumulative 90% particle size (D90) are calculated respectively, and D3 is calculated according to the following formula (1).

[0217] D3=(D90-D10) / D50 (1)

[0218] <Methods for determining carbon content>

[0219] The sample was dried at 100°C for 3 hours to obtain a dried powder. The carbon content of the dried powder was determined using an automated elemental analysis apparatus, Vario EL cube (manufactured by Elementar), under conditions of a combustion tube temperature of 950°C and a reduction tube temperature of 600°C.

[0220] <Determination of Powder X-ray Diffraction Patterns>

[0221] The sample was dried at 100°C for 3 hours to obtain a dried powder. The dried powder was then thoroughly pulverized using an agate mortar, and the sample was placed in a testing chamber for analysis using a horizontal multi-functional X-ray diffractometer, Ultima IV (trade name) (manufactured by Rigaku Corporation). The obtained spectra were compared with the ICSD (Inorganic Crystal Structure Database) provided by the Japan Chemical Information Association to identify the sample. The spectra were obtained under the following testing conditions.

[0222] (1) Optical System

[0223] (I) Diverging slit: 1°

[0224] (II) Scattering slit: 1°

[0225] (III) Receiving slit: 0.15mm

[0226] (IV) Monochrome receiving slit: 0.8mm

[0227] (2) X-rays

[0228] (I) Wavelength: CuKα line

[0229] (II) Tube current: 50mA

[0230] (III) Tube voltage: 50kV

[0231] (3) Measurement range: 5 to 70 degrees Celsius

[0232] (4) Scanning method

[0233] (I) Scanning speed: 5° / minute

[0234] (II) Step width: 0.02 degrees

[0235] <Paint Making>

[0236] Weigh 5.0 g of samples 1-5 and 17 (converted to solid content), and place them in a glass container with 11.9 g of the acrylic silicone resin complex (solid content 42% by mass) listed in Table 1 and 12.0 g of pure water. Mix the mixture for 2 minutes using a mixing mixer to prepare the coating. The solid content of samples 1-5 and 17 was calculated from the mass change before and after drying at 100°C for 1 hour.

[0237] [Table 1]

[0238]

[0239] Weigh Xg of samples 6–16 to obtain a solid content of 5.0g. Weigh Yg of ethanol to obtain X + Y = 6.89g. Place the samples, ethanol, 16.5g of the complex listed in Table 2, and 12.0g of pure water into a glass container and mix for 2 minutes using a mixing mixer to prepare the coating. The solid content of samples 6–16 is calculated from the mass change before and after drying at 100°C for 1 hour.

[0240] [Table 2]

[0241]

[0242] <Preparation of Coatings Using Carbon Black (Reference Example)>

[0243] The coating was prepared using commercially available carbon black (trade name MA-100: manufactured by Mitsubishi Chemical Corporation). Specifically, the raw materials were placed in a 70mL mayonnaise bottle according to Table 3 and dispersed using a paint conditioner (manufactured by Red Devil Inc.) to prepare a mill base. Next, 20.0g of alkyd resin (ALUKIDIR (registered trademark) J-524-IM-60: manufactured by DIC Corporation) was added to the above mill base and dispersed using a paint conditioner (manufactured by Red Devil Inc.) to obtain the coating.

[0244] [Table 3]

[0245]

[0246] <Coating Preparation>

[0247] Using an 8 mil applicator, the coatings used for samples 1-5 and 17 were applied onto black and white chart paper (Form 5C, manufactured by Opacity Chart Leneta Company, Inc.) and dried at 60°C for 30 minutes to form a coating film. Next, using an 8 mil applicator, the transparent complex described in Table 4 was applied from the above coating film and dried at 80°C for 30 minutes to prepare an evaluation coating film.

[0248] [Table 4]

[0249]

[0250] Using an 8 mil applicator, the coatings used in samples 6–16 were applied onto black and white chart paper (Form 5C, manufactured by Opacity Chart Leneta Company, Inc.) and dried at 60°C for 30 minutes to form a coating film. Next, using an 8 mil applicator, the transparent complexes described in Table 5 were applied from the above coating film and dried at 80°C for 30 minutes to prepare an evaluation coating film.

[0251] [Table 5]

[0252]

[0253] <Preparation of a coating using carbon black (reference example)>

[0254] Using an 8 mil applicator, the coating containing the aforementioned carbon black was applied to black and white chart paper (Form 5C, manufactured by Opacity Chart Leneta Company, Inc.). After standing for 30 minutes, it was dried at 110°C for 40 minutes to produce an evaluation coating.

[0255] <Preparation of Solvent Dispersions>

[0256] Sample 1 was weighed to a solid content of 10 g and dispersed in 20 mL of propylene glycol-1-monomethyl ether at 35 kHz using a UT-305S ultrasonic disperser (manufactured by Sharp Corporation) for 10-30 minutes. The dispersion was then filtered or centrifuged. This dispersion and filtration process was repeated twice, and the sample was recovered. Propylene glycol-1-monomethyl ether was added to the obtained sample to achieve a solid content concentration of 55% by mass, and the mixture was stirred for 2 minutes using a mixing mixer to obtain a solvent dispersion. The solid content of Sample 1 and the recovered sample after filtration was calculated from their masses before and after drying at 120°C for 1 hour.

[0257] <Making of Matte Coatings>

[0258] Weigh the solvent dispersion to obtain 5.0 g of solid content and place it in a glass container. Add the clear coating (nax Admila α280 Correction Clear, manufactured by NIPPON PAINT CO.,LTD.) and binder (nax Admila α901 Binder, manufactured by NIPPON PAINT CO.,LTD.) listed in Table 6 to the container, respectively, so that the pigment volume concentration (PVC) of the matte coating is 15%, 30%, 50%, and 70%. Mix for 2 minutes using a mixing mixer to obtain the matte coating. Dry the clear coating and binder separately at 100°C for 1 hour and calculate the mass change before and after drying.

[0259] [Table 6]

[0260]

[0261] <Preparation of Matte Coating>

[0262] Using an 8mil applicator, the above-mentioned matte coating was applied to a tin-plated iron sheet (150×100×0.3mm, Taiyu Machinery Co., Ltd.), and dried at 60°C for 30 minutes to obtain a matte coating film.

[0263] < L of the coating * value, a * value, b * Value determination >

[0264] For the coatings described above, the coating on the white background of black and white chart paper was measured using a multi-angle colorimeter BYK-maci (manufactured by BYK-GARDNER) at an illumination angle of 45° and a light reception angle of 45°. * value, a * value, b * value.

[0265] <Determination of Infrared Reflectance of Coating>

[0266] In the above coating, for the coating on the white background of black and white chart paper, the reflectance at wavelengths of 780 to 2500 nm was measured using a UV-Vis-NIR spectrophotometer V-670 (manufactured by Nippon Spectrophotometer Co., Ltd.) with a Spectralon standard reflector plate (manufactured by Labsphere).

[0267] <Calculation of solar reflectance of coating>

[0268] Based on the reflectivity of the above coating at wavelengths of 780–2500 nm, calculate the solar reflectivity in the wavelength range of 780–2500 nm according to JIS K 5602.

[0269] <Specular gloss of matte coating>

[0270] In the above-mentioned matte coating, the specular gloss was measured at 20°, 60° and 85° using a haze gloss meter Cat. No. 4601 (manufactured by BYK-GARDNER).

[0271] Table 7 shows the preparation conditions of samples 1–17 (presence and type of protective agent), the cumulative 50% particle size of bismuth sulfide particles (D1), the cumulative 50% particle size of primary particles (D2) and their ratio (D1 / D2), and the ratio (D3) of the difference between the cumulative 90% particle size (D90) and the cumulative 10% particle size (D10) in the cumulative particle size distribution measured using a Coulter counter-type particle size distribution measuring device to the cumulative 50% particle size (D50). Hereinafter, PVA represents polyvinyl alcohol, and PEG represents polyethylene glycol. It should be noted that empty columns in Table 7 indicate samples not measured.

[0272] [Table 7]

[0273]

[0274] The L on the white background of the coatings made using samples 1-17 and the coatings made using carbon black. * value, a * value, b * The values ​​and solar reflectance at wavelengths of 780–2500 nm are shown in Table 8.

[0275] [Table 8]

[0276]

[0277] Table 7 shows that for samples 1-4 and 6-16 manufactured using PVA as a protective agent, the cumulative 50% particle size (D1) of bismuth sulfide particles is less than 10 μm. Table 8 shows that the coatings made using these samples have a lower L... * A value below 10 indicates high blackness. Furthermore, it is known that Sample 5, manufactured using PEG as a protective agent, also exhibits sufficient blackness, similar to Samples 1–4 and Samples 6–16.

[0278] On the other hand, for sample 17 manufactured without a protective agent, as shown in Table 7, the cumulative 50% particle size (D1) of bismuth sulfide particles is large, becoming much larger than 10 μm. Furthermore, as shown in Table 8, the coating film made using this sample has a lower L... * A value that is large, becoming much larger than 10, does not have sufficient blackness.

[0279] Furthermore, as shown in Table 8, the coatings prepared using samples 13-16 containing different elements as recorded in Table 7 have L... * The value is less than the L value of the coating film made using a sample that does not contain different elements (e.g., sample 1). * It has a high blackness value.

[0280] Furthermore, according to Table 8, for the coatings using samples 1 to 16, the coating's a * Values ​​above -2.0 and below 2.0 indicate the coating's b... * A value between -3.0 and 4.5 indicates that black is suppressed by red, green, yellow, and blue.

[0281] Table 9 shows the specular gloss of the matte coating made using sample 1 at 20°, 60°, and 85°.

[0282] [Table 9]

[0283]

[0284] As shown in Table 9, for the matte coating using Sample 1, the specular gloss at 60° was below 5 under any PVC temperature, effectively eliminating gloss. Furthermore, the specular gloss at 85° was below 30, also effectively suppressing surface gloss.

[0285] A scanning electron microscope image of sample 1 after drying is shown below. Figure 1 Based on scanning electron microscope images, it was confirmed that samples 1-16 all have a shape consisting of more than 10 needle-like constituent elements assembled at one end. Furthermore, the reflectance spectrum of the coating film (reference example) prepared using sample 1 and carbon black is shown below. Figure 6 For the coatings used in samples 1-5, the solar reflectance of the coatings in the wavelength range of 780-2500 nm is over 40%, which can be considered to have sufficiently high infrared reflectance. On the other hand, the coatings made using carbon black cannot be said to have sufficient infrared reflectance. Furthermore, the powder X-ray diffraction pattern of sample 1 is shown below. Figure 7 For samples 1–17, powder X-ray diffraction patterns confirmed that they were all compounds identified as Bi₂S₃.

[0286] Industrial availability

[0287] The bismuth sulfide particles of the present invention exhibit high blackness, making them useful as black pigments. Furthermore, the bismuth sulfide particles of the present invention have high infrared reflectivity, making them useful as black infrared reflective materials. Additionally, the bismuth sulfide particles of the present invention have high matting properties, making them useful as matting pigments. Moreover, utilizing the above-mentioned properties, the bismuth sulfide particles of the present invention can be used in display barrier materials, resist inks, and the like.

Claims

1. A bismuth sulfide particle comprising agglomerated secondary particles formed by the aggregation of primary particles, wherein the cumulative 50% particle size D1 in the volumetric cumulative distribution, as determined by a laser diffraction / scattering particle size distribution measuring device, is ≥0.2 μm and ≤10 μm. The ratio D1 / D2 of the cumulative 50% particle size D1 in the volume cumulative distribution to the cumulative 50% particle size D2 in the number cumulative distribution of primary particles determined by scanning electron microscopy is greater than 1 and less than 6. The bismuth sulfide particles observed using a scanning electron microscope have a shape with multiple protrusions of plate-like plates and / or needle-like plates on the surface of an approximately spherical body.

2. The bismuth sulfide particles according to claim 1, wherein, The cumulative 50% particle size D2 is above 0.2 μm and below 3 μm.

3. The bismuth sulfide particles according to claim 1 or 2, wherein, The ratio of the difference between the cumulative 90% particle size D90 and the cumulative 10% particle size D10 to the cumulative 50% particle size D50, D3 = (D90 - D10) / D50, is less than 3.

0. The cumulative 50% particle size D50, cumulative 90% particle size D90, and cumulative 10% particle size D10 are values ​​calculated based on the cumulative particle size distribution measured using a Coulter counter-type particle size distribution measuring device.

4. The bismuth sulfide particles according to claim 1, wherein, The element X is selected from Al, Ce, La, Fe and Y in such a way that the ratio of the number of moles of X atoms to the number of moles of bismuth atoms, i.e., the X / Bi molar ratio, is greater than 0 and less than 0.

15.

5. The bismuth sulfide particles according to claim 4, wherein, Element X is Al.

6. A black pigment comprising bismuth sulfide particles as described in claim 1.

7. A matting pigment comprising bismuth sulfide particles as described in claim 1.

8. An infrared reflective material comprising bismuth sulfide particles as described in claim 1.

9. A laser reflective material for lidar, comprising bismuth sulfide particles as described in claim 1.

10. A solvent composition comprising bismuth sulfide particles as described in claim 1 and a solvent.

11. A resin composition comprising the bismuth sulfide particles and resin as described in claim 1.

12. A coating composition comprising the bismuth sulfide particles of claim 1 and a coating resin.

13. A coating comprising the coating composition of claim 12.

14. The coating according to claim 13, wherein, The PVC coating contains bismuth sulfide particles as described in claim 1 at a pigment volume concentration of 15% or more and 95% or less.

15. A method for manufacturing bismuth sulfide particles according to claim 1, comprising: The process of mixing a sulfur compound and a bismuth compound in a dispersion medium in the presence of a protective agent, wherein the S / Bi molar ratio is 3.5 or more and 20 or less, and heating the bismuth compound and the sulfur compound at a temperature of 30°C or more and 100°C or less.

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