JP7796482B2 - Aluminum pigment composition - Google Patents

Description

The present invention relates to an aluminum pigment composition.

Aluminum pigments have traditionally been widely used in a variety of fields as they combine a unique metallic look not found in other pigments with excellent hiding power for the substrate. In recent years, there has been growing emphasis on a mirror-like, luxurious appearance in the painting of automobile bodies, automobile interior parts, and metallic coatings for optical equipment. Such coatings using aluminum pigments are expected to become even more important in the future, as they demonstrate value equal to or greater than the original functionality of the product.

Removal of fine particle components is known as a method for achieving the excellent appearance characteristics described above. A method has been proposed in which the raw atomized powder of aluminum pigment is classified using a sedimentation method to remove fine particles (see, for example, Patent Document 1). However, although the aluminum pigment obtained by this method removes fine particles originating from the raw atomized powder, it does not remove most of the fine particle components generated during the milling process. This creates the problem that these fine particle components adhere to the surface of the aluminum particles, significantly reducing the design properties.

One method proposed for achieving appearance characteristics with minimal fine particle content is to make aluminum flakes of uniform particle size. Patent Document 2, for example, describes how high-brightness aluminum flake pigments have been achieved by obtaining aluminum flakes with an equality number n of 2.4 or greater. However, even with this method, the fine particle components generated during the grinding process are hardly removed, resulting in a significant reduction in the gloss of the coating film.

In order to reduce the fine particle content 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 that make up the entire aluminum pigment is specified (see, for example, Patent Document 3). However, while this method reduces the fine particle content of the entire aluminum pigment, it does not take into consideration the removal of the fine particle content that adheres to the aluminum particle surface. As a result, even with this method, the smoothness of the aluminum particle surface is low, and sufficient characteristics have not yet been achieved in terms of achieving high brightness in the specular reflection region, low scattered light, and high gloss in the coating film.

Japanese Patent Application Publication No. 02-073872 Japanese Patent Application Publication No. 11-152423 International Publication No. 2019/077904

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.

As a result of intensive research into resolving the problems associated with conventional aluminum pigments, the inventors focused on the fine aluminum particles adhering to the surfaces of aluminum flake particles. They then discovered that a novel aluminum pigment composition that produces 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 total area defined by the outlines of the fine aluminum components adhering to the surface of each aluminum flake particle to the average area defined by the overall outline of each aluminum flake particle over the 100 images to a ratio of 9.7% or less, thereby completing the present invention.

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 total areas defined by the outlines of the fine particle aluminum components adhering to the surface of each aluminum flake particle to the average of 100 areas defined by the overall 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 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 total area defined by the outlines of the entire aluminum flake particle in the 100 images of the scanning electron microscope is 4.9% or less.
[3].
Item [1] or [2], wherein the aluminum flake particles have a surface roughness Rz of 40 nm or less.
[4].
[4] The aluminum pigment composition according to any one of [1] to [3] above, wherein the average particle diameter d50 of the aluminum flake particles is 4 μm to 15 μm.

The present invention provides a novel aluminum pigment composition that produces a coating film with a mirror-like metallic design. Furthermore, a preferred embodiment of the present invention provides 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, making it possible to achieve a mirror-like metallic design.

FIG. 1 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 component adhering to the surface thereof. FIG. 1 shows a photograph of an SEM image (a photograph in which the contours of the fine particle aluminum components were detected and the area was 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 particle aluminum components adhering to the surface thereof. FIG. 1 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 Comparative Example 1 and the fine aluminum components adhering to the surfaces thereof. 1 shows a photograph of an SEM image (a photograph in which the contours of the fine particle aluminum components were detected and the area was measured using image analysis software) obtained using a scanning electron microscope (Hitachi/S-2600H) of the aluminum flake particles of Comparative Example 1 and the fine particle aluminum components adhering to the surface thereof.

The following describes in detail the modes for carrying out the present invention. 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 modified and carried out as appropriate within the scope of its essence.

[Aluminum pigment composition]
In the aluminum pigment composition of the present invention, the ratio of the average of the total area determined by the outlines of the fine-particle aluminum components adhering to the surface of each aluminum flake particle to the average of the area determined by the overall outline of each aluminum flake particle (hereinafter, sometimes 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.

[Fine particle aluminum component]
The particulate aluminum component is a minute aluminum component adhered to the surface of an aluminum flake particle. The ratio of the average total area (of one or more fine particles) defined by the outline of the particulate aluminum component adhered 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 obtaining 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 component adhered to that aluminum flake particle is measured. For all 100 microscopic images, the total area defined by the outline of the particulate aluminum component adhered 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 adhering 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 component is counted as particles having an area ratio of 0.1% or more relative to the area defined by the outline of the entire aluminum flake particle. The reason for the 0.1% or more area ratio is that fine-particle aluminum components having 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 there are with an area of 0.1% or more relative to the area defined by the outline of the entire aluminum flake particle, the more significantly the gloss and design properties of the resulting coating film are reduced. This is because a large amount of fine-particle aluminum components adhering to the aluminum flake particle reduces the smoothness of the 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).
Specifically, the preparation of a sample of the aluminum pigment composition, the acquisition of an SEM image, and the image analysis can be carried out by the methods described below.

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), which includes 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 smoothness of the particle surface is high, which increases the amount of specularly reflected light, resulting in a higher sense of brightness and potentially increasing the gloss of the coating film. This Rz is more preferably 35 nm or less, and even more preferably 30 nm or less.

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. An average particle diameter d50 of the aluminum flake particles of 4 μm or more is preferable because the particles are oriented in a certain direction in a coating film formed using the aluminum pigment composition, reducing light scattering and increasing brightness. Furthermore, an average particle diameter of the aluminum flake particles of 15 μm or less is preferable because a metallic coating film with a dense feel can be obtained.
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 step of grinding the raw atomized aluminum powder using a ball mill in the method for producing an aluminum pigment composition described below.

[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.

In addition to suppressing the generation of fine aluminum components adhering to the surfaces of aluminum flake particles, taking into consideration the requirement for an average particle size (d50) in the range of 4 μm to 15 μm, particularly preferred milling conditions may include using, as the raw material, an atomized aluminum powder typically having an average particle size (d50) of 1.3 to 6.0 μm, preferably an average particle size (d50) of 1.3 to 4.5 μm, and more preferably an average particle size (d50) of 1.3 to 4.0 μm. Preferred milling conditions may also include a combination of using an atomized aluminum powder having such an average particle size, 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.

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 larger proportion of planar particles, and of increasing the surface smoothness of the aluminum particles and suppressing the adhesion of fine particle aluminum components. It is preferable that the specific gravity of the grinding balls be greater than that of the grinding solvent. Having a larger specific gravity than the grinding solvent prevents the grinding balls from floating in the solvent, provides sufficient shear stress between the grinding balls, and tends to promote sufficient grinding.

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, and glass balls, are preferred from the perspectives of adjusting the surface smoothness of the aluminum particles, suppressing the adhesion of fine aluminum components, and improving the durability of the grinding balls. On the other hand, when using steel balls, alumina balls, etc. with low surface smoothness, it is preferable to use balls whose surface smoothness has been improved, for example, by mechanical polishing and chemical polishing, from the perspectives of adjusting the surface smoothness of the aluminum particles, suppressing the adhesion of fine aluminum components, and improving the durability of the grinding balls.

As mentioned above, the mass of each grinding ball is preferably 0.09 to 11.00 mg. Using grinding balls with a mass of 0.09 mg or more can prevent the occurrence of so-called group motion, a phenomenon in which the grinding balls do not move individually but rather move as a group or clump, reducing the shear stress between the grinding balls and preventing grinding from progressing. Furthermore, using grinding balls with a mass of 11.00 mg or less can prevent excessive impact forces from being applied to the aluminum particles, preventing warping, distortion, cracks, and the like, and ultimately suppressing the occurrence of fine aluminum components adhering to the surfaces of aluminum flake particles.

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.

The average particle size (d50) of the atomized aluminum powder used as 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 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 irregularly shaped powder are not preferred because the shape of the aluminum particles tends to collapse during grinding (although it is not intended to completely eliminate their usability).

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 the following, but examples include 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, and 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 can suppress 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.

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. A ratio of the total volume of the grinding balls to the volume of the grinding solvent of 0.6 or more improves the uniformity of the grinding balls in the mill during grinding, and grinding tends to proceed smoothly. Furthermore, a ratio of the total volume of the grinding balls to the volume of the grinding solvent of 3.0 or less ensures that the ratio of grinding balls in the mill falls within a suitable range, preventing excessive ball stacking and preventing shape deterioration such as particle warping, distortion, and cracking due to grinding stress. 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, making this preferable.

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 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.

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. Using a ball mill with a diameter of 0.7 mm or more prevents the grinding balls from stacking too low, keeping the pressure applied to the aluminum particles during grinding within an appropriate range, and tends to allow grinding to proceed smoothly. Furthermore, using a ball mill with a diameter of 2.3 mm or less prevents the grinding balls from stacking too 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, making this preferable.

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), and 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 scraped 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, and ultimately suppressing the occurrence of fine aluminum components 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 using Nc (rpm) = 42.3/√D (D is the inner diameter of the ball mill (m)) and is adjusted to match the inner diameter of the ball mill.

In another embodiment, the aluminum pigment composition can be produced by a vacuum deposition method instead of or in addition to the production method described above, which includes grinding atomized aluminum powder. Aluminum pigments produced by the vacuum deposition method are called vapor-deposited aluminum pigments. Vapor-deposited aluminum pigments are pigments made by adhering aluminum vaporized 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 to the film, 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 and shredded to produce aluminum flakes, which are then further classified to obtain the desired product.

The ultrasonic device is not particularly limited, and examples include one that applies ultrasonic waves generated from an ultrasonic vibrator directly 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's 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 piping system through which the slurry circulates. Among these, a device that applies ultrasonic waves directly to the slurry in an external circulation vessel via an ultrasonic horn is preferred due to its compact size and high productivity. The externally applied ultrasonic waves used in this invention are a type of elastic vibration that propagates through elastic bodies. 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 surfaces and interiors of liquids and solids are also included. The ultrasonic waves should 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 power is 5 to 20,000 W, preferably 10 to 10,000 W, and particularly preferably 12 to 6,000 W.

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, with polyoxyethylene lauryl ether (e.g., Marpon ACL-3 and Marpon ACL-5 manufactured by Matsumoto Yushi Seiyaku) being particularly preferred.

The wet classification device is not particularly limited as long as it is a device that forms a centrifugal field, but 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 standpoints of high productivity and industrial suitability, such as a compact device and reduced power costs. Classification conditions when using a liquid cyclone include the flow rate (L/min) and operating pressure (MPa). The classification operation can be optimized by appropriately adjusting these conditions. In one embodiment, the removal of detached fine aluminum component particles using a liquid cyclone is preferably performed at a flow rate of 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.

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 production process.
The amount of organic solvent remaining in the aluminum pigment composition may be, for example, 0.5 to 95% by mass, or 1 to 90% by mass, or 2 to 80% by mass, or 5 to 70% by mass of the aluminum pigment composition.

[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.

[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 and drying the coating composition described above to a predetermined substrate. 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 a conventionally known method can be applied as appropriate depending on the target article.

[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.

[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.

[Preparation of observation samples of 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 obtained aluminum powder is added to a 100 ml beaker along with 2 ml of a 5% by weight stearate mineral spirit solution and dispersed with a spatula. 50 ml of mineral spirit is added, and the mixture is heated in an oven at 45°C for 2 hours. The solution obtained in this manner is subjected to suction filtration through another glass filter. n-Hexane is added to the mixture, and the mixture is dispersed. The mixture is then suctioned and dried for 1 hour. The mixture is then dried in a desiccator for at least 2 hours, stirring occasionally with a spatula.

The sample thus obtained is dispersed with a spatula while adding isopropyl alcohol dropwise, and then the dispersion is gently poured little by little into a container filled with water. The entire water surface is stirred with a spatula to homogenize the entire mixture, ensuring that the aluminum flake particles do not overlap as much as possible. The sample is then placed on the sample stage of a scanning electron microscope (Hitachi S-2600H), ensuring that the aluminum flake particles do not overlap as much as possible. The sample stage is typically disc-shaped, with a smooth, flat surface.

A scanning electron microscope is used to photograph aluminum flake particles placed on a sample stage 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 at random for each of the 100 aluminum particles, ensuring that the image of the individual aluminum flake particle being photographed is not covered by other aluminum flake particles, resulting in 100 scanning microscope images. Next, for the scanning microscope images of the individual aluminum flake particles photographed in this way, 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.

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-particle aluminum components attached to the aluminum flake particle are detected, and the total area is measured. Here, only fine-particle 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-particle aluminum components are measured, and the respective average values are calculated. The area ratio of the fine-particle 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-particle aluminum components.

[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 treatment 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) Obtaining an Image for Measurement The average roughness Rz of the aluminum flake particles is measured under the following conditions.
Particles that can secure a field of view of 4 μm square are selected, and an image for measurement is obtained under the following conditions.
Device: Bruker AXS Dimension Icon
Measurement mode: Tapping mode
Probe: NCH type Si single crystal probe (k=0.40N/m type)
Measurement field of view: 4μm square/512pixel
(3) Analysis and Calculation of Rz 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)
Correction after measurement: First-order tilt correction Roughness measurement: Rz (automatic calculation)

[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 (for example, LA-300/HORIBA, Ltd.). Mineral spirits are usually used as the measurement solvent. Measurements are carried out in accordance with 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.

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 diameters (d50) of the raw material atomized aluminum powder and aluminum flake particles were carried out by the methods described above.

[Evaluation of brightness, scattered light amount, and glossiness]
(1) Preparation of Paint and Coated Plate 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: 2 g
Mixed thinner (solvent mixture ratio - methyl ethyl ketone: 40% by mass, ethyl acetate: 40% by mass, isopropyl alcohol: 20% by mass): 6g
Polyurethane resin (manufactured by Sanyo Chemical Industries, Ltd., product name "Sanprene IB Series 1700D"): 8 g
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 coating was dried at room temperature to obtain a metallic base coated plate for evaluation.

(2) Measurement of luminance, scattered light amount, and glossiness Luminance was evaluated using a goniochromatic colorimeter (manufactured by Suga Test Instruments Co., Ltd.). Luminance 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. Luminance is a parameter proportional to the intensity of specularly reflected light from the aluminum pigment composition, and a larger measured value indicates a higher specularly reflected light intensity and is therefore considered 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) corresponding to the value of the amount of light received at 110 degrees from the specular reflection angle, L, and the smaller the measured value, the less scattered light the coated panel had, which was judged to have better optical properties.
The glossiness was evaluated using a UGV-5D (manufactured by Suga Test Instruments Co., Ltd.) When the reflectance was measured when the incident angle and the receiving angle were both 60 degrees according to the 60-degree specular glossiness, it was judged that the greater the 60-degree specular reflectance, the higher the glossiness of the coating film and the more excellent its optical properties.

Example 1
A ball mill having an inner diameter of 2 m and a length of 30 cm was charged with 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, and the atomized aluminum powder was milled using 309 kg of zirconia balls having a diameter of 0.8 mm.
The zirconia balls used were those containing 94% by mass or more of _ZrO2 as a main component and having a circularity of 95% or more. The ball mill was rotated at 13 rpm, and grinding was carried out for 90 hours.
After completion of grinding, the slurry of the atomized aluminum powder milled in the mill was washed with mineral spirits and passed through a 400-mesh vibrating sieve. The passed slurry was filtered and concentrated to obtain a cake with a heating residue of 80% by mass. 750 g of the obtained cake and 8300 g of mineral spirits in which 0.15% of a nonionic surfactant (Marpon ACL-3 / Matsumoto Yushi Pharmaceutical Co., Ltd.) was dissolved 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. Thereafter, the reactor was 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 is a type in which ultrasonic waves are directly irradiated onto the slurry in the vessel via an ultrasonic horn. 100 ml of slurry was constantly held in the container, and the slurry circulated in the container 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 classify 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 defined 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 defined 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 tilt at 7000x magnification.

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 in which 0.15% of an anionic surfactant (Hitenol TMLA-10/manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was dissolved were used. 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%.

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%.

Example 4
An aluminum pigment composition was obtained by the same procedure as in Example 1, except that 475 kg of zirconia balls with a diameter of 0.8 mm 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 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 1.5, and the ratio of the rotation speed to the critical rotation number was 43%.

Example 5
Grinding was carried out using 295 kg of glass balls with a diameter of 1.0 mm, with the ball mill rotation speed set to 13 rpm. 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 1.3 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%.

Example 6
Using 409 kg of zirconia balls with a diameter of 1.3 mm, 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 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 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%.

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 polishing and chemical polishing. The same procedures as in Example 1 were carried out under the other conditions to obtain an aluminum pigment composition. 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 2.1 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%.

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 polishing and chemical polishing. The same procedures as in Example 1 were carried out under the other conditions to obtain an aluminum pigment composition. 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 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%.

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%.

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%.

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%.

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 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%.

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 rotated at 13 rpm and milled for 16 hours. The same operations as in Example 1 were carried out, 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 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%.

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. The same procedures as in Example 1 were carried out under the other conditions, to obtain an aluminum pigment composition. 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 grinding ball was 1.6 mg, the volume ratio of the grinding balls to the grinding solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 80%.

Comparative Example 6
Using 450 kg of glass balls with a diameter of 3.0 mm, the ball mill was rotated at 13 rpm and milled for 65 hours. The same operations as in Example 1 were carried out under the other conditions to obtain an aluminum pigment composition. 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 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%.

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 amount, 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%.

Comparative Example 8
Using 9.5 kg of raw atomized aluminum powder (average particle size: 4.0 μm) and 408 kg of steel balls with a diameter of 2.4 mm, the ball mill was rotated at 22 rpm and milled for 16 hours. The same operations as in Example 1 were carried out, 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 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 grinding ball was 56.8 mg, the volume ratio of the grinding balls to the grinding solvent was 0.9, and the ratio of the rotation speed to the critical rotation number was 74%.

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%.

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 with high gloss.

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, PCM, 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, or films in the above applications.

Claims (3)

A method for producing an aluminum pigment composition, wherein 100 scanning electron microscope images are taken of 100 aluminum flake particles individually at a magnification of 7000x and tilted at an angle of 45 degrees, and the ratio of the average of 100 images of the total area defined by the outlines of 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, 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 particle aluminum components adhering to the surface of the milled atomized aluminum powder; and a step of removing the peeled fine particle aluminum components with a wet classification device. 2. The method for producing an aluminum pigment composition according to claim 1, wherein the ratio of the average of 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 100 areas defined by the outlines of the entire aluminum flake particle in the 100 scanning electron microscope images is 4.9% or less. The method for producing an aluminum pigment composition according to claim 1 or 2, wherein the aluminum flake particles have an average particle diameter d50 of 4 μm to 15 μm.