Aluminum pigment composition

Abstract

To provide a novel aluminum pigment composition that has improved brightness.SOLUTION: A aluminum pigment composition for solving the problem is an aluminum pigment composition in which, in 100 scanning electron microscope images of 100 aluminum flake particles individually photographed at 7000x and tilted 45 degrees, the ratio of an average of 100 total areas determined by the contour of the particulate aluminum component adhering to the surface of each aluminum flake particle to an average of 100 areas determined by the overall contour of each aluminum flake particle is 9.7% or less. Preferably, the ratio is 4.9% or less. Preferably, a surface roughness Rz of the aluminum flake particle may be 40 nm or less. Preferably, an average particle size d50 of the aluminum flake particle may be 4 μm to 15 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aluminum pigment composition. [Background technology]

[0002] Aluminum pigments have traditionally been widely used in a variety of fields as pigments that combine a unique metallic appearance not found in other pigments with excellent hiding power for the substrate. In recent years, mirror-like, luxurious appearances have become increasingly important in the painting of automobile bodies, automobile interior parts, metallic coatings for optical equipment, and the like. Such coatings using aluminum pigments are expected to become even more important in the future, from the perspective of demonstrating value equal to or greater than the original functions of the products.

[0003] One method for achieving the above-described excellent appearance characteristics is the removal of fine particle components. A method for classifying the raw atomized powder of aluminum pigment using a sedimentation method to remove fine particles has been proposed (see, for example, Patent Document 1). However, although the aluminum pigment obtained by this method removes fine particles derived from the raw atomized powder, it does not remove most of the fine particle components generated during the milling process. This causes the problem that the fine particle components generated during milling adhere to the surfaces of the aluminum particles, significantly reducing the design properties.

[0004] A method of regulating the particle size of aluminum flakes has been proposed as a method of achieving appearance characteristics with a small amount of fine particle components. Patent Document 2, for example, describes a method of achieving high-brightness aluminum flake pigments by obtaining aluminum flakes with an equality number n of 2.4 or more. However, even with this method, the fine particle components generated during the grinding process are hardly removed, resulting in a significant decrease in the gloss of the coating film.

[0005] In order to reduce the amount of fine particles generated during the grinding process, a method has been proposed in which the number of particles with a particle size of 1 μm or less is specified for the entire aluminum pigment (see, for example, Patent Document 3). However, although this method reduces the amount of fine particles in the entire aluminum pigment, it does not take into consideration the removal of the fine particles attached to the aluminum particle surface. Therefore, even with this method, the smoothness of the aluminum particle surface is low, and sufficient properties have not yet been obtained in terms of realizing high brightness in the regular reflection region, low scattered light, and high gloss of the coating film. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 02-073872 [Patent Document 2] Japanese Patent Application Publication No. 11-152423 [Patent Document 3] International Publication No. 2019 / 077904 Summary of the Invention [Problem to be solved by the invention]

[0007] One object of the present invention is to provide a novel aluminum pigment composition that provides a coating film having excellent mirror-like metallic design properties, which has long been in high demand. Another object of the present invention is to provide an aluminum pigment composition which not only enables the formation of a coating film having an excellent mirror-like metallic design, but also has high brightness in the specular reflection region, generates little scattered light, and produces a coating film with high gloss. [Means for solving the problem]

[0008] As a result of intensive research aimed at solving the problems of conventional aluminum pigments as described above, the present inventors focused on the fine aluminum particles adhering to the surfaces of aluminum flake particles, and discovered that a novel aluminum pigment composition that provides a coating film with a mirror-like metallic design can be obtained by taking 100 scanning electron microscope images of 100 aluminum flake particles individually under specified conditions, and setting the ratio of the average of the 100 areas defined by the overall outline of each aluminum flake particle to the average of the 100 areas defined by the overall outline of each aluminum flake particle to be 9.7% or less, thereby completing the present invention.

[0009] That is, the various aspects of the present invention are as follows. [1]. An aluminum pigment composition in which, in 100 scanning electron microscope images taken of 100 aluminum flake particles individually at a 45-degree angle at 7000x magnification, the ratio of the average of 100 images of the total area defined by the outlines of the fine particle aluminum components adhering to the surface of each aluminum flake particle to the average of 100 images of the area defined by the entire outline of each aluminum flake particle is 9.7% or less. [2]. The aluminum pigment composition according to item [1] above, wherein the ratio of the average of 100 total areas defined by the contours of the fine-particle aluminum components adhering to the surfaces of each aluminum flake particle to the average of 100 areas defined by the contours of the entire aluminum flake particle in the 100 scanning electron microscope images is 4.9% or less. [3]. The aluminum pigment composition according to item [1] or [2] above, wherein the surface roughness Rz of the aluminum flake particles is 40 nm or less. [4]. The aluminum pigment composition according to any one of the above items [1] to [3], wherein the aluminum flake particles have an average particle size d50 of 4 μm to 15 μm. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a novel aluminum pigment composition that produces a coating film having a mirror-like metallic design. Furthermore, according to a preferred embodiment of the present invention, it is possible to provide an aluminum pigment composition that has high brightness in the specular reflection region, generates little scattered light, and produces a coating film with high gloss, and that can realize a mirror-like metallic design. [Brief explanation of the drawings]

[0011] [Figure 1] This shows a photograph of an SEM image (a photograph in which the contours of the aluminum flake particles and the area of ​​the aluminum flake particles were detected and measured using image analysis software) obtained using a scanning electron microscope (Hitachi / S-2600H) of the aluminum flake particles of Example 1 and the fine aluminum components adhering to their surfaces. [Figure 2] This shows an SEM image of the aluminum flake particles of Example 1 and the fine particle aluminum components adhering to their surfaces, obtained using a scanning electron microscope (Hitachi / S-2600H) (a photograph in which the contours of the fine particle aluminum components were detected and the area was measured using image analysis software). [Figure 3] This shows an SEM image of the aluminum flake particles of Comparative Example 1 and the fine aluminum components adhering to their surfaces, obtained using a scanning electron microscope (Hitachi / S-2600H) (a photograph in which the contours of the aluminum flake particles were detected and the area was measured using image analysis software). [Figure 4] This shows an SEM image of the aluminum flake particles of Comparative Example 1 and the fine particle aluminum components adhering to their surfaces, obtained using a scanning electron microscope (Hitachi / S-2600H) (a photograph in which the contours of the fine particle aluminum components were detected and the area was measured using image analysis software). DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments for carrying out the present invention will be described in detail. The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to the following content. The present invention can be carried out by appropriately modifying it within the scope of its gist.

[0013] [Aluminum pigment composition] In the aluminum pigment composition of the present invention, the ratio of the average of the 100 total areas defined by the outlines of the fine-particle aluminum components adhering to the surfaces of each aluminum flake particle to the average of the 100 areas defined by the overall outline of each aluminum flake particle (hereinafter simply referred to as the "average ratio of the total area of ​​the fine-particle aluminum components") is 9.7% or less in 100 scanning electron microscope images of 100 aluminum flake particles individually photographed at a 45-degree angle at 7000x magnification. By setting the average ratio of the total area of ​​the fine-particle aluminum components to 9.7% or less, an aluminum pigment composition can be obtained that exhibits high brightness in the specular reflection region, little scattered light, and a high coating gloss. The average ratio of the total area of ​​the fine-particle aluminum components is preferably 9% or less, even more preferably 8% or less, even more preferably 7% or less, even more preferably 6% or less, and most preferably 4.9% or less. The smaller the average ratio of the total area of ​​the fine-particle aluminum components, the better, but it can be, for example, 0.1% or more.

[0014] [Fine particle aluminum component] Particulate aluminum components are tiny aluminum components attached to the surface of aluminum flake particles. The ratio of the average total area (of one or more fine particles) defined by the outline of the particulate aluminum components attached to the surface of each aluminum flake particle to the average area defined by the outline of the entire aluminum flake particle can be determined by acquiring an FE-SEM image of the surface of each aluminum flake particle and measuring it using image analysis software. In the FE-SEM image of the surface of each aluminum flake particle, first, the area defined by the outline of the entire aluminum flake particle is measured using image analysis software. For all 100 microscopic images, the area defined by the outline of the entire aluminum flake particle is measured in this way, and the average is calculated. Next, the total area (of one or more fine particles) defined by the outline of the particulate aluminum components attached to that aluminum flake particle is measured. For all 100 microscopic images, the total area defined by the outline of the particulate aluminum components attached to the aluminum flake particle is measured in this way, and the average is calculated. The ratio of the average total area defined by the outlines of the fine-particle aluminum components attached to each aluminum flake particle to the average area defined by the outline of the entire aluminum flake particle can then be calculated. The fine-particle aluminum components are counted as particles having an area ratio of 0.1% or more of the area defined by the outline of each aluminum flake particle. The reason for the 0.1% or more area ratio is that fine-particle aluminum components with an area ratio of 0.1% or more contribute significantly to the desired design, particularly the glossiness of the coating film. The inventors have found that the more fine-particle aluminum components with an area of ​​0.1% or more of the area defined by the outline of each aluminum flake particle, the more significantly the glossiness and design properties of the resulting coating film are reduced. This is because the amount of fine-particle aluminum components attached reduces the smoothness of the aluminum flake particle surface, causing diffuse reflection and resulting in a reduced glossiness.Furthermore, fine particle aluminum components having an area ratio of less than 0.1% relative to the area defined by the overall outline of each aluminum flake particle have little physical interaction with the aluminum flake particles, do not adhere strongly to the aluminum flake particle surface, and are easily peeled off. In this specification, the term "fine particle aluminum component" is intended to count only fine particle components that adhere strongly to the aluminum flake particle surface (remain without peeling off). Preparation of a sample of an aluminum pigment composition, acquisition of an SEM image, and image analysis can be specifically carried out by the methods described below.

[0015] The surface roughness Rz of the aluminum flake particles in the aluminum pigment composition is an index indicating the smoothness of the particle surface and can be measured using an SPM (Scanning Probe Microscope), including an atomic force microscope. In one embodiment, the surface roughness Rz of the aluminum flake particles is preferably 40 nm or less. When the surface roughness Rz of the aluminum flake particles is 40 nm or less, the particle surface is highly smooth, which increases the amount of specularly reflected light, resulting in a higher sense of brightness and, further, the gloss of the coating film. This Rz is more preferably 35 nm or less, and even more preferably 30 nm or less.

[0016] The average particle diameter d50 (μm) of the aluminum flake particles in the aluminum pigment composition is the median diameter and can be measured using a laser diffraction / scattering particle size distribution analyzer. In one embodiment, the average particle diameter d50 of the aluminum flake particles is preferably 4 μm to 15 μm. The average particle diameter d50 of the aluminum flake particles can be adjusted within the above numerical range depending on the final desired design. When the average particle diameter d50 of the aluminum flake particles is 4 μm or more, the particles are oriented in a certain direction in a coating film formed using the aluminum pigment composition, reducing light scattering and increasing brightness, which is preferable. Furthermore, when the average particle diameter of the aluminum flake particles is 15 μm or less, a dense metallic coating film can be obtained, which is preferable. In one embodiment, the average particle size of the aluminum flake particles is preferably 5 μm or more and 13 μm or less, and more preferably 6 μm or more and 12 μm or less. The average particle diameter d50 of the aluminum flake particles can be controlled by appropriately adjusting the particle diameter of the raw atomized aluminum powder, the mass per grinding ball, and the rotation speed of the grinding device in the process of grinding the raw atomized aluminum powder using a ball mill in the method for producing an aluminum pigment composition described below.

[0017] [Method for producing aluminum pigment composition] A method for producing an aluminum pigment composition is described below. The method typically includes grinding atomized aluminum powder using a grinding device equipped with a ball mill, exfoliating the adhered fine aluminum particles by ultrasonic irradiation, and removing the exfoliated fine aluminum particles using a wet classification device such as a liquid cyclone. In this grinding step, the atomized aluminum powder used as the raw material can be prevented from adhering to the surfaces of aluminum flake particles during the grinding step by appropriately adjusting and combining conditions such as using a raw material with a uniform particle size and a sharp particle size distribution, reducing the mass per grinding ball, and reducing the rotational speed of the grinding device. These conditions are described in more detail below.

[0018] Considering the need to suppress the generation of fine aluminum components adhering to the surfaces of aluminum flake particles and to achieve an average particle size (d50) in the range of 4 μm to 15 μm, particularly preferred milling conditions may include using atomized aluminum powder as the raw material, typically having an average particle size (d50) of 1.3 to 6.0 μm, preferably 1.3 to 4.5 μm, and more preferably 1.3 to 4.0 μm. Preferred milling conditions may also include the use of atomized aluminum powder having such an average particle size, and setting the mass per ball used in the milling apparatus to preferably 0.09 to 11.00 mg, more preferably 0.09 to 10.00 mg, and / or setting the rotation speed of the milling apparatus to 35% to 68%, more preferably 37% to 55%, of the critical rotation speed (Nc). The average particle size (d50) of the atomized aluminum powder is also a median size, and can be measured using a laser diffraction / scattering particle size distribution measuring device.

[0019] The specific gravity of the grinding balls used in a ball mill or the like is preferably 8 or less, more preferably 7 or less, and even more preferably 6 or less, from the viewpoint of facilitating the formation of a large proportion of planar particles and of increasing the surface smoothness of the aluminum particles and suppressing the adhesion of fine particle aluminum components. The specific gravity of the grinding balls is preferably greater than that of the grinding solvent. By making the specific gravity of the grinding balls greater than that of the grinding solvent, the grinding balls can be prevented from floating in the solvent, sufficient shear stress is obtained between the grinding balls, and grinding tends to proceed sufficiently.

[0020] As the grinding balls used in the method for producing an aluminum pigment composition, those with high surface smoothness, such as stainless steel balls, zirconia balls, glass balls, etc., are preferred from the viewpoints of adjusting the surface smoothness of the aluminum particles, suppressing the adhesion of fine particle aluminum components, and durability of the grinding balls. On the other hand, when using steel balls, alumina balls, etc. with low surface smoothness, it is preferred to use balls whose surface smoothness has been improved by, for example, mechanical polishing and chemical polishing, from the viewpoints of adjusting the surface smoothness of the aluminum particles, suppressing the adhesion of fine particle aluminum components, and durability of the grinding balls.

[0021] As mentioned above, the mass of each grinding ball is preferably 0.09 to 11.00 mg. By using grinding balls with a mass of 0.09 mg or more, it is possible to prevent the occurrence of so-called group motion, in which the grinding balls do not move individually but move as a group or in a lump, reducing the shear stress between the grinding balls and preventing grinding from progressing. Furthermore, by using grinding balls with a mass of 11.00 mg or less, it is possible to prevent excessive impact force from being applied to the aluminum particles, preventing the occurrence of warping, distortion, cracks, etc., and ultimately suppressing the occurrence of fine aluminum components adhering to the surfaces of aluminum flake particles.

[0022] The atomized aluminum powder used as the raw material preferably contains few impurities other than aluminum. The purity of the atomized aluminum powder is preferably 99.5% by mass or more, more preferably 99.7% by mass or more, and even more preferably 99.8% by mass or more.

[0023] The average particle size (d50) of the atomized aluminum powder used as the raw material is typically 1.3 to 6.0 μm, preferably 1.3 to 4.5 μm, and more preferably 1.3 to 4.0 μm. Having an average particle size of 1.3 μm or greater prevents excessive energy from being applied to the particles during grinding, preventing warping and distortion of the particles, maintaining good particle shape, and ultimately suppressing the occurrence of fine aluminum components adhering to the surfaces of aluminum flake particles. Furthermore, having an average particle size of 6.0 μm or less allows the average particle size of the aluminum flake particles in the ground product to be adjusted to 15 μm or less, which tends to favorably produce an aluminum pigment composition in which the average ratio of the total area of ​​the fine aluminum components is 9.7% or less. The shape of the atomized aluminum powder used as the raw material is preferably spherical or teardrop-shaped. Using these shapes tends to reduce the tendency for the aluminum particles to lose their shape during grinding. On the other hand, acicular powder and amorphous powder are not preferred because the shape of the aluminum particles tends to be distorted during grinding (although it is not intended to completely eliminate their use).

[0024] When producing an aluminum pigment composition using a grinding device equipped with a ball mill, it is preferable to use a grinding solvent. The type of grinding solvent is not limited to, but includes, for example, conventionally used hydrocarbon solvents such as mineral spirits and solvent naphtha, as well as low-viscosity solvents such as alcohols, ethers, ketones, and esters. Regarding the grinding conditions for the atomized aluminum powder, the volume of the grinding solvent relative to the mass of aluminum in the atomized aluminum powder is preferably 2.0 to 14.0 times, more preferably 3.0 to 11.0 times. A grinding solvent volume of 2.0 times or more relative to the mass of aluminum in the atomized aluminum powder is preferable because it can prevent warping, distortion, cracks, and the like that accompany long-term grinding of the atomized aluminum powder, and thus suppresses the generation of fine aluminum components adhering to the surfaces of aluminum flake particles. Furthermore, by setting the volume of the grinding solvent to 14.0 times or less the mass of aluminum in the atomized aluminum powder, the uniformity of the dispersion in the mill during grinding is improved, the atomized aluminum powder comes into efficient contact with the grinding media, and grinding tends to proceed smoothly.

[0025] The ratio of the total volume of the grinding balls to the volume of the grinding solvent (total volume of grinding balls / volume of grinding solvent) is preferably 0.6 to 3.0, and more preferably 0.9 to 2.0. When the ratio of the total volume of the grinding balls to the volume of the grinding solvent is 0.6 or more, the uniformity of the grinding balls in the mill during grinding improves, and grinding tends to proceed smoothly. Furthermore, when the ratio of the total volume of the grinding balls to the volume of the grinding solvent is 3.0 or less, the ratio of the grinding balls in the mill falls within a suitable range, and the stacking of the balls does not become too high, preventing problems with shape deterioration such as warping, distortion, and cracking of the particles due to grinding stress. This in turn suppresses the generation of fine aluminum components adhering to the surfaces of aluminum flake particles, and also prevents a decrease in brightness and increased scattered light, which is preferable.

[0026] When producing an aluminum pigment composition using a grinding device equipped with a ball mill, it is preferable to use a grinding aid in addition to the grinding solvent described above. The grinding aid may be any one that exhibits the properties of a non-leafing pigment, and includes, but is not limited to, higher unsaturated fatty acids such as oleic acid, higher aliphatic amines such as stearic amine, higher aliphatic alcohols such as stearyl alcohol and oleyl alcohol, higher fatty acid amides such as stearic acid amide and oleic acid amide, and higher fatty acid metal salts such as aluminum stearate and aluminum oleate. The grinding aid is preferably used in an amount of 0.5 to 25% by mass relative to the mass of the atomized aluminum powder.

[0027] The ball mill used to grind the atomized aluminum powder preferably has a diameter of 0.7 mm to 2.3 mm, and more preferably 0.8 mm to 1.5 mm. By using a ball mill with a diameter of 0.7 mm or more, the stacking of grinding balls does not become excessively low, and the pressure applied to the aluminum particles during grinding falls within an appropriate range, tending to allow grinding to proceed smoothly. Furthermore, by using a ball mill with a diameter of 2.3 mm or less, the stacking of grinding balls does not become excessively high, preventing problems with particle shape deterioration such as warping, distortion, and cracking due to the weight of the balls. This in turn suppresses the generation of fine aluminum components adhering to the surfaces of aluminum flake particles, and prevents a decrease in brightness and increased scattered light, which is preferable.

[0028] As described above, the rotation speed of the ball mill during grinding of the atomized aluminum powder is preferably 35% to 68% of the critical rotation speed (Nc), more preferably 37% to 55%. A rotation speed / critical rotation speed ratio of 35% or more is preferable because it maintains uniformity of the aluminum slurry liquid and ball movement within the ball mill. Furthermore, a rotation speed / critical rotation speed ratio of 68% or less prevents the grinding balls from being lifted up or falling under their own weight. This prevents excessive impact force on the aluminum particles from the grinding balls, preventing problems with particle shape deterioration such as warping, distortion, and cracking. This ultimately suppresses the occurrence of fine aluminum component particles adhering to the surfaces of aluminum flake particles. In one embodiment, the rotation speed of the ball mill during grinding of the atomized aluminum powder is preferably 5 rpm or more and 30 rpm or less, more preferably 10 rpm or more and 20 rpm or less. The critical rotation speed can be calculated from Nc (rpm) = 42.3 / √D (D is the inner diameter (m) of the ball mill) and is adjusted according to the inner diameter of the ball mill.

[0029] In another embodiment, the aluminum pigment composition can be produced by a vacuum deposition method instead of or in addition to the production method including the grinding of the atomized aluminum powder described above. Aluminum pigments produced by the vacuum deposition method are called vapor-deposited aluminum pigments. Vapor-deposited aluminum pigments are pigments produced by adhering aluminum evaporated by heating to a plastic film, then shredding the resulting very thin aluminum film into flakes. The production method for such vapor-deposited aluminum pigments is not limited, but examples include using a plastic film such as oriented polypropylene, crystalline polypropylene, or polyethylene terephthalate as a base film, applying a release agent thereto, and vapor-depositing aluminum onto the release agent. Next, after vapor deposition of the aluminum, a top coating agent is applied to the vapor-deposited surface to prevent oxidation of the vapor-deposited aluminum. The vapor-deposited aluminum film is then peeled from the base film, shredded into flake aluminum, and further classified to obtain the desired product.

[0030] The ultrasonic device is not particularly limited, and examples include one that directly applies ultrasonic waves generated from an ultrasonic vibrator to the aluminum powder slurry in an external circulation vessel via an ultrasonic horn; one that attaches an ultrasonic vibrator directly to the exterior of an external circulation vessel and applies ultrasonic waves to the slurry inside through the vessel wall; and one that attaches an ultrasonic vibrator directly to the exterior of an external circulation vessel, fills the vessel with an appropriate solvent, and applies ultrasonic waves to the slurry by passing the solvent through a pipe through which the slurry circulates. Among these, one that directly applies ultrasonic waves to the slurry in an external circulation vessel via an ultrasonic horn is preferred from the viewpoint of compactness and high productivity. The externally applied ultrasonic waves used in the present invention are a type of elastic vibration that propagates through an elastic body. Such ultrasonic waves are typically longitudinal waves that propagate compression and expansion in the direction of wave propagation, but transverse waves may also exist on the external circulation vessel wall and its contact surfaces. Note that, in the technical definition, ultrasonic waves also include sound waves that are not intended to be heard directly, and all sound waves that propagate through the surface or interior of a liquid or solid are also included in ultrasonic waves. The ultrasonic waves have a frequency of 15 to 10,000 kHz, preferably 20 to 3,000 kHz, and particularly preferably 30 to 1,000 kHz.The output is 5 to 20,000 W, preferably 10 to 10,000 W, and particularly preferably 12 to 6,000 W.

[0031] When removing adhered fine aluminum particles by ultrasonic irradiation, adding a surfactant to the slurry facilitates the removal of the adhered fine particles. The surfactant is not particularly limited, and examples include known surfactants such as anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, silicone surfactants, and fluorine-based surfactants. Among these, at least one surfactant selected from the group consisting of anionic surfactants and nonionic surfactants is preferred. Examples of anionic surfactants include alkyl sulfocarboxylates, α-olefin sulfonates, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether sulfates, polyoxyethylene dinonylphenyl ether sulfates, and polyoxyethylene lauryl ether sulfates. Polyoxyethylene lauryl ether sulfates (e.g., Hitenol TMLA-10 and LA-12 from Daiichi Kogyo Seiyaku) are particularly preferred. Preferred nonionic surfactants include polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkyl ether, polyoxyethylene acetylene glycol ether, and polyoxyethylene distyrenated phenyl ether, and particularly polyoxyethylene lauryl ether (e.g., Marpon ACL-3 and Marpon ACL-5 manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) is more preferred.

[0032] The wet classification device is not particularly limited as long as it is a device that forms a centrifugal field, and examples include a liquid cyclone, a decanter, and a centrifugal separator. Among these, a liquid cyclone is preferred as a wet classification device from the viewpoints of high productivity and industrial suitability, such as a compact device and reduced power costs. Classification conditions when using a liquid cyclone include flow rate (L / min) and operating pressure (MPa). The classification operation can be optimized by appropriately adjusting these conditions. In one embodiment, the flow rate for removing detached fine aluminum components using a liquid cyclone is preferably 2 to 20 L / min, more preferably 3 to 15 L / min. The operating pressure is preferably 0.2 to 0.9 MPa, more preferably 0.3 to 0.7 MPa.

[0033] The aluminum pigment composition of the present invention obtained as described above can be considered to be a metal pigment composition that contains aluminum flake particles (and the fine-particle aluminum components on the surfaces thereof, if any remain), and further contains, as the residual solid content (non-volatile content), the organic solvent used in the manufacturing process. The amount of organic solvent remaining in the aluminum pigment composition may be, for example, 0.5 to 95 mass %, or 1 to 90 mass %, or 2 to 80 mass %, or 5 to 70 mass % of the aluminum pigment composition.

[0034] [Paint composition] A coating composition according to one embodiment includes the aluminum pigment composition described above. The coating composition may contain, in addition to the aluminum pigment composition, mica, a coloring pigment, etc. The coating composition may also contain various resins and various additives such as antioxidants, light stabilizers, polymerization inhibitors, surfactants, etc. The coating composition can be produced by mixing the aluminum pigment composition with various other materials as needed. The coating composition can be used as a metallic coating.

[0035] [Coating film and article having said coating film] A coating film according to one embodiment contains the aluminum flake particles described above and can be formed by applying the coating composition described above to a predetermined substrate and drying it. Various articles can be selected as the substrate. The coating film according to this embodiment can be formed on the target substrate depending on the selected article. Examples of such articles include automobile bodies, automobile interior parts, home appliances, mobile phones, smartphones, PCs, tablets, cameras, televisions, and other optical devices. The method for forming the coating film is not particularly limited, and conventionally known methods can be applied as appropriate depending on the target article.

[0036] [Ink composition, printed matter] An ink composition according to one embodiment includes the aluminum pigment composition described above. The ink composition may contain, in addition to the aluminum pigment composition described above, a predetermined color pigment, a solvent, and the like. The ink composition may also contain various resins and various additives such as antioxidants, light stabilizers, polymerization inhibitors, and surfactants. The ink composition can be produced by mixing the aluminum pigment composition with various other materials as needed, and can be used as a metallic ink. Furthermore, a printed matter according to one embodiment includes the aluminum flake particles described above, and can be formed by printing using the ink composition described above in accordance with a known method. Examples of the printed matter include ink-printed matters in which a coating film is formed by gravure printing, offset printing, screen printing, or the like.

[0037] [Other uses] In addition, the aluminum pigment composition can be kneaded with a resin or the like and used as a water-resistant binder or filler.

[0038] [Preparation of observation specimens for aluminum flake particle surfaces (SEM images)] A scanning electron microscope (SEM) image for observing the surface of an aluminum flake particle is prepared as follows. For example, a paste-like aluminum pigment composition (2.0 g) obtained by the method described in the Examples and Comparative Examples below is collected in a glass filter and subjected to suction filtration while washing with hexane four times. The filtered material is then powdered by continuing suction for at least 30 minutes after filtration. 1.0 g of the resulting aluminum powder is added to a 100 ml beaker along with 2 ml of a 5% by weight solution of stearate in mineral spirits, and dispersed with a spatula. 50 ml of mineral spirits is added, and the mixture is heated in an oven at 45°C for two hours. The resulting sample is then subjected to suction filtration of the solution through another glass filter. n-Hexane is added to the mixture, and the mixture is dispersed. The mixture is then subjected to suction filtration for one hour and dried. The mixture is then dried in a desiccator for at least two hours, stirring occasionally with a spatula.

[0039] The sample thus obtained is dispersed with a spatula while adding isopropyl alcohol dropwise, and then the dispersion is poured slowly into a container filled with water. The entire water surface is stirred with a spatula to homogenize the entire sample, minimizing overlap of the aluminum flake particles. The sample is then placed on the sample stage of a scanning electron microscope (Hitachi S-2600H), minimizing overlap of the aluminum flake particles. The sample stage is typically disk-shaped, with a smooth, flat surface.

[0040] Aluminum flake particles placed on a sample stage are photographed using a scanning electron microscope at a magnification of 7000x, with the image tilted 45 degrees relative to the flat surface of the sample stage. The 45-degree tilt makes it easier to photograph the attached fine particle aluminum components. One hundred fields of view are photographed randomly for each of the 100 aluminum particles, ensuring that the image of each aluminum flake particle targeted for photographing is not covered by other aluminum flake particles, resulting in 100 scanning microscope images. Next, for the scanning microscope images of each aluminum flake particle photographed in this manner, the area defined by the overall outline of each aluminum flake particle and the total area defined by the outline of the fine particle aluminum components in each aluminum flake particle are measured using the following procedure.

[0041] Using the SEM image (7000x magnification) obtained using the above acquisition procedure and image analysis software Image-ProPLUS ver. 7.0 (Media Cybernetics), the overall outline of the aluminum flake particle is first detected, and the area defined by the overall outline of the aluminum flake particle is measured. Next, the outlines of all fine aluminum components attached to the aluminum flake particle are detected, and the total area is measured. Here, only fine aluminum components firmly attached to the surface of the aluminum flake particle, whose area ratio to the area defined by the overall outline of the aluminum flake particle is 0.1% or more, are counted. For all 100 microscopic images, the area defined by the overall outline of the aluminum flake particle and the total area defined by the outlines of the attached fine aluminum components are measured, and the respective average values ​​are calculated. The area ratio of the fine aluminum component is calculated from the average value of the area defined by the overall outline of the aluminum flake particle and the average value of the total area defined by the outlines of the fine aluminum component.

[0042] [Surface roughness of aluminum flake particles: Rz] The average roughness Rz of the aluminum flake particles contained in the aluminum pigment composition is measured by the following method. (1) Pretreatment A washing process is carried out to remove the solvent (mineral spirits or solvent naphtha in the examples and comparative examples described below) from the aluminum pigment composition. 100 mg of the paste-like aluminum pigment composition is placed in a screw tube, and 5 mL of toluene is added. The mixture is dispersed by hand shaking for several tens of seconds, and then centrifuged. The supernatant is removed, and 5 mL of toluene is added again, followed by dispersion and centrifugation in the same manner. A small amount (approximately a few mg) of the precipitated aluminum flake particles is collected, dispersed in 5 mL of toluene, and dropped onto a 1 cm square silicon wafer, followed by air drying. (2) Acquiring images for measurement The average roughness Rz of the aluminum flake particles is measured under the following conditions. Particles that can secure a 4 μm square field of view are selected, and images for measurement are obtained under the following conditions. Equipment: Bruker AXS Dimension Icon Measurement mode: Tapping mode Probe: NCH type Si single crystal probe (k=0.40N / m typ) Measurement field of view: 4μm square / 512pixel (3) Analysis and Rz calculation The analysis can be performed using the analysis software provided with the device. After performing a first-order tilt correction, the roughness analysis function is used to calculate Rz. Software: Nanoscope Analysis (analysis software included with the device) Post-measurement correction: First-order tilt correction Roughness measurement: Rz (automatic calculation)

[0043] [Average particle diameter: d50] The average particle size (d50) of the aluminum flake particles or raw atomized aluminum powder contained in the aluminum pigment composition is measured using a laser diffraction / scattering particle size distribution analyzer (e.g., LA-300 / HORIBA, Ltd.). Mineral spirits are usually used as the measurement solvent. Measurements are performed according to the instruction manual for the laser diffraction / scattering particle size distribution analyzer. It is important to note that the aluminum pigment sample should be subjected to ultrasonic dispersion for several minutes, for example, about 2 minutes, as a pretreatment, and then placed in a dispersion tank. It is desirable to confirm that the appropriate concentration has been achieved before starting the measurement. After the measurement is completed, the d50 is automatically displayed. [Example]

[0044] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. The methods for measuring various physical properties used in the examples and comparative examples are as follows. The acquisition of scanning electron microscope images (SEM images) for observing the surfaces of the aluminum flake particles, the measurement of the surface roughness Rz of the aluminum flake particles, and the measurement of the average particle diameter (d50) of the raw atomized aluminum powder and aluminum flake particles were carried out using the methods described above.

[0045] [Evaluation of brightness, scattered light amount, and glossiness] (1) Preparation of paint and painted board Using the aluminum pigment compositions obtained in the Examples and Comparative Examples described below, metallic base paints were prepared according to the following formulations. Aluminum pigment composition: 2g Mixed thinner (solvent mixture ratio - methyl ethyl ketone: 40% by mass, ethyl acetate: 40% by mass, isopropyl alcohol: 20% by mass): 6g Polyurethane resin (Sanyo Chemical Industries, Ltd., product name "Sanprene IB Series 1700D"): 8g Next, the metallic base paint was applied to a PET film using a bar coater (No. 6) so that the dry film thickness was 3 μm, and the film was dried at room temperature to obtain a metallic base coated plate for evaluation.

[0046] (2) Measurement of brightness, scattered light amount, and glossiness The brightness was evaluated using a goniochromatic colorimeter (manufactured by Suga Test Instruments Co., Ltd.). The brightness was measured at an incident angle of 45 degrees and a receiving angle of 5 degrees (L5), which is close to specularly reflected light and excludes light in the specular reflection region reflected on the coating surface. Brightness is a parameter proportional to the intensity of specularly reflected light from the aluminum pigment composition, and the larger the measured value, the higher the specularly reflected light intensity, which was judged to be superior. The amount of scattered light was evaluated using an MA68II multi-angle spectrophotometer (manufactured by X-Rite, Inc., USA). The geometric conditions were an incident angle of 45 degrees, and full-range reception angles (from the specular reflection angle) of 15 degrees, 25 degrees, 45 degrees, 75 degrees, and 110 degrees. The amount of scattered light is a parameter (L110) equivalent to the value of the amount of light received at 110 degrees from the specular reflection angle, L; the smaller the measured value, the less scattered light the coated panel has, and the better its optical properties are judged to be. Glossiness was evaluated using a UGV-5D (manufactured by Suga Test Instruments Co., Ltd.) When the reflectance was measured when the incident angle and receiving angle were both 60 degrees according to the 60-degree specular glossiness, the higher the 60-degree specular reflectance, the higher the glossiness of the coating film, and the better its optical properties were judged to be.

[0047] Example 1 A mixture consisting of 9.5 kg of raw atomized aluminum powder (average particle size: 2 μm), 45.8 kg of mineral spirits, and 570 g of oleic acid was loaded into a ball mill with an inner diameter of 2 m and a length of 30 cm, and the atomized aluminum powder was milled using 309 kg of zirconia balls with a diameter of 0.8 mm. The zirconia balls used contained 94% by mass or more of ZrO2 as the main component and had a circularity of 95% or more. The ball mill was set to a rotation speed of 13 rpm, and grinding was carried out for 90 hours. After grinding, the milled atomized aluminum powder slurry was washed with mineral spirits and passed through a 400-mesh vibrating sieve. The filtered slurry was concentrated to obtain a cake with a heating residue of 80% by mass. 750 g of the resulting cake and 8300 g of mineral spirits containing 0.15% of a nonionic surfactant (Marpon ACL-3, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.) were added to a 20-L reactor. The mixture was stirred while introducing nitrogen gas, and the temperature in the system was raised to 40°C. The reactor was then connected to a commercially available circulating ultrasonic disperser, and the slurry in the reactor was circulated at a rate of approximately 1 L / min using a metering pump. This circulating ultrasonic disperser directly irradiates the slurry in the vessel with ultrasonic waves via an ultrasonic horn. The vessel was constantly holding 100 ml of slurry, and the slurry circulated within the vessel was directly irradiated with ultrasound at a frequency of 30 kHz and an output of 200 W for 30 minutes to remove the fine aluminum particles adhering to the aluminum flake particles. A liquid cyclone (TR-10, manufactured by Murata Industries, Ltd.) was used to separate and remove the fine aluminum particles from the slurry after ultrasound irradiation. The remaining slurry was filtered and concentrated to obtain a cake with a heating residue of 76% by mass. A predetermined amount of solvent naphtha was added and mixed for 20 minutes to obtain an aluminum pigment composition with a heating residue of 65% by mass. The resulting aluminum pigment composition was evaluated for brightness, scattered light amount, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.6 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 43%. The "area ratio (%) of attached fine particle components" in Table 1 indicates the ratio of the average of 100 images of the total area determined by the outline of the fine particle aluminum components attached to the surface of each aluminum flake particle to the average of 100 images of the area determined by the entire outline of each aluminum flake particle in 100 scanning electron microscope images taken of 100 aluminum flake particles individually at a 45-degree angle at 7000x magnification.

[0048] Example 2 An aluminum pigment composition was obtained by the same procedure as in Example 1, except that 9.5 kg of raw material atomized aluminum powder (average particle size: 2.5 μm) and mineral spirits containing 0.15% of an anionic surfactant (Hitenol TMLA-10, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) were used. The resulting aluminum pigment composition was evaluated for brightness, scattered light intensity, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.6 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 43%.

[0049] Example 3 An aluminum pigment composition was obtained by the same procedure as in Example 1, except that 9.5 kg of raw material atomized aluminum powder (average particle size: 3.3 μm) was used, the ball mill rotation speed was set to 16 rpm, and grinding was carried out for 75 hours. The obtained aluminum pigment composition was evaluated for brightness, scattered light amount, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.6 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 53%.

[0050] Example 4 An aluminum pigment composition was obtained by the same procedure as in Example 1, except that 475 kg of 0.8 mm diameter zirconia balls were used, and grinding was carried out with 42.0 kg of mineral spirits and 522 g of oleic acid. The obtained aluminum pigment composition was evaluated for brightness, scattered light intensity, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.6 mg, the volume ratio of the milling balls to the volume of the milling solvent was 1.5, and the ratio of the rotation speed to the critical rotation number was 43%.

[0051] Example 5 Grinding was carried out using 295 kg of 1.0 mm diameter glass balls at a ball mill rotation speed of 13 rpm. Other conditions were the same as in Example 1, and an aluminum pigment composition was obtained. The resulting aluminum pigment composition was evaluated for brightness, scattered light intensity, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.3 mg, the volume ratio of the milling balls to the volume of the milling solvent was 2.0, and the ratio of the rotation speed to the critical rotation number was 43%.

[0052] Example 6 Using 409 kg of 1.3 mm diameter zirconia balls, the ball mill rotation speed was set to 11 rpm and grinding was carried out for 73 hours. Other conditions were the same as in Example 1, and an aluminum pigment composition was obtained. The resulting aluminum pigment composition was evaluated for brightness, scattered light intensity, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 6.9 mg, the volume ratio of the milling balls to the volume of the milling solvent was 1.2, and the ratio of the rotation speed to the critical rotation number was 37%.

[0053] Example 7 Using 9.5 kg of raw atomized aluminum powder (average particle size: 4.0 μm) and 522 kg of 0.8 mm diameter steel balls, 38.7 kg of mineral spirits, and 482 g of oleic acid, the ball mill was rotated at 12 rpm and milled for 54 hours. The steel balls used had their surface smoothness enhanced by mechanical and chemical polishing. The other conditions were the same as in Example 1, and an aluminum pigment composition was obtained. The resulting aluminum pigment composition was evaluated for brightness, scattered light intensity, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 2.1 mg, the volume ratio of the milling balls to the volume of the milling solvent was 1.3, and the ratio of the rotation speed to the critical rotation number was 40%.

[0054] Example 8 Using 9.5 kg of raw atomized aluminum powder (average particle size: 4.0 μm) and 409 kg of 1.3 mm diameter steel balls, 45.8 kg of mineral spirits, and 482 g of oleic acid, the ball mill was rotated at 13 rpm and milled for 54 hours. The steel balls used had their surface smoothness enhanced by mechanical and chemical polishing. The other conditions were the same as in Example 1, and an aluminum pigment composition was obtained. The resulting aluminum pigment composition was evaluated for brightness, scattered light intensity, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 9.0 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 43%.

[0055] Example 9 An aluminum pigment composition was obtained by the same procedure as in Example 1, except that ultrasonic waves with a frequency of 20 kHz and an output of 100 W were irradiated for 15 minutes. The brightness, scattered light amount, and gloss of the obtained aluminum pigment composition were evaluated as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.6 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 43%.

[0056] Comparative Example 1 An aluminum pigment composition was obtained in the same manner as in Example 1, except that neither the peeling of the adhering fine aluminum particles by ultrasonic irradiation nor the removal of the peeled fine aluminum particles by a liquid cyclone was performed. The obtained aluminum pigment composition was evaluated for brightness, scattered light amount, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.6 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 43%.

[0057] Comparative Example 2 An aluminum pigment composition was obtained in the same manner as in Example 1, except that the removal of the exfoliated fine aluminum component particles using a liquid cyclone was not performed. The obtained aluminum pigment composition was evaluated for brightness, scattered light amount, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.6 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 43%.

[0058] Comparative Example 3 An aluminum pigment composition was obtained in the same manner as in Example 1, except that the adhered fine particle aluminum component was not peeled off by ultrasonic irradiation. The brightness, scattered light amount, and gloss of the obtained aluminum pigment composition were evaluated as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.6 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 43%.

[0059] Comparative Example 4 Using 9.5 kg of raw atomized aluminum powder (average particle size: 6.1 μm) and 408 kg of 2.0 mm diameter steel balls, the ball mill was set to a rotation speed of 13 rpm and milled for 16 hours. Furthermore, an aluminum pigment composition was obtained by the same procedure as in Example 1, except that a cake with a heating residue of 82% by mass was obtained after milling was completed. The brightness, scattered light amount, and gloss of the obtained aluminum pigment composition were evaluated as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 32.9 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 43%.

[0060] Comparative Example 5 9.5 kg of raw material atomized aluminum powder (average particle size: 4.0 μm) was used, and the ball mill rotation speed was set to 24 rpm, and grinding was carried out for 55 hours. Other conditions were the same as in Example 1, and an aluminum pigment composition was obtained. The brightness, scattered light amount, and gloss of the obtained aluminum pigment composition were evaluated as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.6 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 80%.

[0061] Comparative Example 6 Using 450 kg of 3.0 mm diameter glass balls, the ball mill was rotated at 13 rpm and milled for 65 hours. Other conditions were the same as in Example 1, to obtain an aluminum pigment composition. The resulting aluminum pigment composition was evaluated for brightness, scattered light intensity, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 35.3 mg, the volume ratio of the milling balls to the volume of the milling solvent was 3.1, and the ratio of the rotation speed to the critical rotation number was 43%.

[0062] Comparative Example 7 An aluminum pigment composition was obtained by the same procedure as in Example 1, except that 522 kg of 1.3 mm diameter glass balls were used, and grinding was carried out with 38.7 kg of mineral spirits and 482 g of oleic acid. The obtained aluminum pigment composition was evaluated for brightness, scattered light intensity, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 2.9 mg, the volume ratio of the milling balls to the volume of the milling solvent was 4.2, and the ratio of the rotation speed to the critical rotation number was 43%.

[0063] Comparative Example 8 Using 9.5 kg of raw material atomized aluminum powder (average particle size: 4.0 μm) and 408 kg of 2.4 mm diameter steel balls, the ball mill was set to a rotation speed of 22 rpm and milled for 16 hours. The same procedures as in Example 1 were repeated except that a cake with a heating residue of 82% by mass was obtained after milling was completed, to obtain an aluminum pigment composition. The resulting aluminum pigment composition was evaluated for brightness, scattered light intensity, and glossiness as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 56.8 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 74%.

[0064] Comparative Example 9 An aluminum pigment composition was obtained by the same procedure as in Example 1, except that ultrasonic waves with a frequency of 10 kHz and an output of 50 W were irradiated for 30 minutes. The brightness, scattered light amount, and gloss of the obtained aluminum pigment composition were evaluated as described above. The evaluation results are shown in Table 1. In this example, the mass of each milling ball was 1.6 mg, the volume ratio of the milling balls to the volume of the milling solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 43%.

[0065] [Table 1]

[0066] The results shown in Table 1 demonstrate that the aluminum pigment composition of the present invention has high brightness, very little scattered light, and produces a coating film with high gloss. [Industrial Applicability]

[0067] The aluminum pigment composition of the present invention can be suitably used in high-quality metallic paints for automobile bodies and automobile interior parts, metallic paints for automobile repair, metallic paints for home appliances, metallic paints for optical devices such as mobile phones, smartphones, PCs, tablets, cameras, and televisions, PCMs, industrial metallic paints, high-quality metallic printing inks such as gravure printing, offset printing, and screen printing, and as a material for kneading high-quality metallic resins. More specifically, the present invention can provide a high-brightness, high-flop aluminum pigment composition that can impart high light reflectance and extremely high flop properties, i.e., optical anisotropy, to conventional coatings, prints, films, etc. in the above applications.

Claims

1. A method for producing an aluminum pigment composition, wherein in 100 scanning electron microscope images of 100 aluminum flake particles taken individually at a 45-degree angle at 7000x magnification, the ratio of the average of 100 total areas determined by the outlines of fine particle aluminum components adhering to the surfaces of each aluminum flake particle to the average of 100 areas determined by the overall outline of each aluminum flake particle is 9.7% or less, and the surface roughness Rz of the aluminum flake particles is 40 nm or less, grinding the atomized aluminum powder with a grinding device; a step of irradiating the milled atomized aluminum powder with ultrasonic waves to peel off fine aluminum components adhering to the surface of the milled atomized aluminum powder; and The method further comprises a step of removing the exfoliated fine aluminum particles using a wet classification device.

2. A method for producing an aluminum pigment composition as described in claim 1, wherein the ratio of the average of 100 total areas determined by the outlines of the fine particle aluminum components adhering to the surface of each aluminum flake particle to the average of 100 areas determined by the overall outline of each aluminum flake particle in the 100 scanning electron microscope images is 4.9% or less.

3. A method for producing an aluminum pigment composition according to claim 1 or 2, wherein the average particle diameter d50 of the aluminum flake particles is 4 μm to 15 μm.

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