WO2025079174A1 - Black coating material composition, coated article, and method for forming low-gloss coating film - Google Patents

Abstract

The purpose of the present disclosure is to provide: a black coating material composition which can be coated by means of air spraying and which can yield a low-gloss coating film having high blackness; a coated article; and a method for forming a low-gloss coating film. A black coating material composition according to the present embodiment contains a black pigment, a dispersion medium and a resin. The black pigment includes a black organic pigment. The dispersion medium includes a good dispersion medium that readily wets the black organic pigment and a poor dispersion medium that wets the black organic pigment less than the good dispersion medium. The boiling point of the good dispersion medium is lower than the boiling point of the poor dispersion medium. The content of the good dispersion of medium is 50 parts by mass or more relative to 100 parts by mass of the black organic pigment. The content of the black organic pigment is 60 parts by mass or more relative to 100 parts by mass of the resin.

Description

Black paint composition, coated article, and method for forming low gloss coating film

This disclosure relates to a black paint composition that has air spray applicability, a painted article, and a method for forming a low gloss paint film.

　Conventionally, optical devices such as cameras are required to have anti-reflection properties against sunlight and other light entering from the outside in order to prevent the occurrence of ghosts or flares, and the inner walls of optical devices such as cameras are covered with black materials. To achieve anti-reflection properties, the black materials are required to have, for example, low gloss (low luster, low reflectivity) and high blackness. Examples of black materials that are used include cloth, film, plated film, and coating film.

A paint for optical elements that contains a high refractive index epoxy resin and black particles has been disclosed as a paint for forming a coating film as a black component (see, for example, Patent Document 1).

JP 2011-252949 A

When using cloth, film or plated membrane as the black material, there was a problem that application or plating could not be performed if the target product had a complex shape or was small.

The paint of Patent Document 1 contains a matting agent to improve low gloss. The matting agent is, for example, an extender pigment such as silica or talc, or resin beads, and reduces reflectance by forming irregularities on the surface of the paint film, thereby improving low gloss. However, in paints containing matting agents, the whiteness derived from the extender pigment or resin beads appears in the appearance of the paint film, making it difficult to improve the blackness and reduce the reflectance, and the anti-reflection required for optical instruments may not be obtained. In addition, air spray applicability is sometimes required for excellent work efficiency. However, since the paint of Patent Document 1 uses silica as a matting agent, there is a possibility that uneven gloss may occur during air spray application.

The present disclosure aims to provide a black paint composition that has air spray applicability and can produce a low-gloss coating film with low gloss and high blackness, a coated article, and a method for forming a low-gloss coating film.

The black paint composition according to the present invention is a black paint composition containing a black pigment, a dispersion medium, and a resin, characterized in that the black pigment contains a black organic pigment, the dispersion medium contains a good dispersion medium that easily wets the black organic pigment, and a poor dispersion medium that is less wettable by the black organic pigment than the good dispersion medium, the boiling point of the good dispersion medium is lower than the boiling point of the poor dispersion medium, the content of the good dispersion medium per 100 parts by mass of the black organic pigment is 50 parts by mass or more, and the content of the black organic pigment per 100 parts by mass of the resin is 60 parts by mass or more.

In the black paint composition according to the present invention, it is preferable that the resin contains a urethane resin, an acrylic resin, an epoxy resin, a silicone resin, an ester resin, a fluororesin, or a melamine resin.

In the black paint composition according to the present invention, it is preferable that the resin contains an olefin resin.

In the black paint composition according to the present invention, the poor solvent preferably contains at least water.

In the black paint composition according to the present invention, it is preferable that the black pigment further contains a black inorganic pigment in addition to the black organic pigment. This can further improve anti-reflection properties in the infrared range.

The black paint composition according to the present invention includes compositions that do not contain a matting agent or in which the content of the matting agent per 100 parts by mass of the resin is more than 0 parts by mass and not more than 50 parts by mass.

The coated article according to the present invention is a coated article having a substrate and a low-gloss coating film provided on the surface of the substrate, the low-gloss coating film being a dried product of the black paint composition according to the present invention, and characterized in that it has protruding portions that contain aggregates of the black organic pigment.

In the coated product of the present invention, the average diameter of the convex portions is preferably 1 to 40 μm. This allows the coating film to have lower gloss.

In the coated product according to the present invention, it is preferable that the substrate is made of polypropylene resin, and that the resin contains an olefin resin.

The method for forming a low gloss coating film according to the present invention is a method for forming a low gloss coating film, comprising a coating step in which the black paint composition according to the present invention is sprayed onto the surface of a substrate by air spraying, and a drying step, the coating step including a mixture formation step in which all or a part of the good dispersion medium among the dispersion medium is volatilized after the black paint composition is sprayed from the air spray and before it reaches the surface of the substrate, forming a mixture containing aggregates of the black organic pigment, the resin, and at least the poor dispersion medium as a non-volatilized dispersion medium, and an attachment step in which the mixture reaches the surface of the substrate and adheres to it, and the drying step includes a step of volatilizing the non-volatilized dispersion medium contained in the mixture.

The present disclosure provides a black paint composition that has air spray applicability and can produce a low-gloss coating film with low gloss and high blackness, a coated article, and a method for forming a low-gloss coating film.

1 is a SEM image (magnification: 150x) showing the surface state of the coating film of an item coated with the coating composition of Example 1. 1 is a SEM image (magnification: 150x) showing the surface state of the coating film of an item coated using the coating composition of Comparative Example 2. 1 is an image of Sample 1 after being left to stand for two weeks. 1 is an image of Sample 2 after being left to stand for two weeks.

Below, one aspect of the present invention will be described with reference to the attached drawings. The embodiment described below is an example of the present invention, and the present invention is not limited to the following embodiment. Note that components with the same reference numerals in this specification and drawings indicate the same components. Various modifications may be made as long as the effects of the present invention are achieved.

The black paint composition according to the present embodiment is a black paint composition containing a black pigment, a dispersion medium, and a resin, the black pigment containing a black organic pigment, the dispersion medium containing a good dispersion medium that easily wets the black organic pigment, and a poor dispersion medium that is less wettable than the good dispersion medium, the boiling point of the good dispersion medium is lower than the boiling point of the poor dispersion medium, the content of the good dispersion medium relative to 100 parts by mass of the black organic pigment is 50 parts by mass or more, and the content of the black organic pigment relative to 100 parts by mass of the resin is 60 parts by mass or more. The black paint composition according to the present embodiment is a black paint composition containing two or more dispersion media (good dispersion media and poor dispersion media) that have different wettability with the black organic pigment, so that in the liquid state before coating, the black organic pigment is wetted with the good dispersion medium, and is dispersed and stabilized in the dispersion medium containing the good dispersion medium and the poor dispersion medium in the form of primary particles or secondary particles. In the black paint composition before coating, the black organic pigment may be dispersed in the form of primary particles, secondary particles, or a mixture of primary particles and secondary particles. Even if the black organic pigment is in the form of secondary particles, in the black paint composition before application, the black organic pigment is wetted with a good dispersion medium and becomes aggregates that are sufficiently smaller than the diameter of the spray gun, so it can be applied by air spray coating without clogging.

In this specification, "good dispersion medium", "poor dispersion medium", and "wetting" are technical terms used in the technical fields of paints and pigments. The pigment dispersion process has three steps: (i) wetting step, (ii) crushing step, and (iii) dispersion stabilization step. (i) Wetting step is a step in which the cohesive force of the pigment particles is reduced by wetting the surface of the pigment particles with the dispersion medium. Here, in the technical fields of paints and pigments, "wetting" means that when the pigment and the dispersion medium are mixed, the interface between the pigment and the air is replaced by the interface between the pigment and the dispersion medium. Wetting can also be said to be a phenomenon in which the dispersion medium adheres to the surface of the pigment particles and enters the gaps between the pigment particles, and the pigment particles are covered with the dispersion medium. When the pigment particles are covered with the dispersion medium, the cohesive force of the pigment particles is reduced and the pigment particles change from a coarse particle to a fine particle state. The phenomenon in which the dispersion medium adheres to the surface of the pigment particles and enters the gaps between the pigment particles is sometimes expressed as the pigment becoming familiar with the dispersion medium. (ii) The disintegration process is a process in which mechanical forces such as shear force or impact force of a disperser are applied to the pigment particle aggregates whose cohesive force has been reduced in the wetting process to disaggregate them into smaller aggregates. (iii) The dispersion stabilization process is a process in which the particles dispersed in the disintegration process are prevented from re-aggregating. In the technical field of paints and pigments, a dispersion medium that is easily wetted to the particle surface of a certain pigment, can reduce the cohesive force of the pigment particles in the wetting process, and can make the pigment particles finer and less likely to re-aggregate in the disintegration process is called a "good dispersion medium" for that pigment. Conversely, a dispersion medium that is difficult to wet to the particle surface of a certain pigment, cannot reduce the cohesive force of the pigment particles in the wetting process, cannot make the pigment particles finer in the disintegration process, or is prone to re-aggregation even if the pigment particles are made finer in the disintegration process is called a "poor dispersion medium" for that pigment.

The resin is a component that is responsible for the strength of the coating film, and serves to fix the protrusions resulting from the aggregates of the black organic pigment that reaggregate due to the difference in evaporation rate between the good dispersion medium and the poor dispersion medium, on the substrate by forming a film with the resin. For example, a resin called a coating film-forming resin can be suitably used as the resin. A coating film-forming resin is a resin that forms a coating film by drying or curing as necessary after application. In the black paint composition according to this embodiment, the coating film-forming resin may be used alone or in combination of two or more types. The resin may be dispersed in a dispersion medium or dissolved in a solvent.

In the black paint composition according to this embodiment, the resin preferably contains a urethane resin, an acrylic resin, an epoxy resin, a silicone resin, an ester resin, a fluororesin, or a melamine resin. Of these, it is preferable that the resin contains a urethane resin.

In the black paint composition according to this embodiment, the resin preferably contains an olefin resin. Olefin resin is a general term for polymer compounds synthesized from at least alkenes as monomers, and is also called polyolefin resin. Examples of olefin resins include polyethylene, polypropylene, polybutylene, ethylene vinyl acetate copolymer, chlorinated polyolefins, non-chlorinated polyolefins, acrylic modified polyolefins, and urethane modified polyolefins. By blending an olefin resin, it is possible to improve adhesion to a polypropylene resin substrate. In the black paint composition according to this embodiment, the content of the olefin resin in the total mass of the resin is preferably 70 mass% or more, and more preferably 80 mass% or more. The upper limit of the content of the olefin resin in the total mass of the resin is not particularly limited, but is preferably 100 mass% or less.

The proportion of resin in the total solid content of the black paint composition is preferably 10 to 50 mass%, and more preferably 10 to 35 mass%. If the resin content is less than 10 mass%, the strength of the coating film may be insufficient. If the resin content exceeds 50 mass%, the gloss of the coating film after drying may increase.

The black pigment contains at least a black organic pigment. The black organic pigment is, for example, aniline black, perylene black, cyanine black, or lactam black. The black organic pigment may be used alone or in combination with two or more. Of these, the black organic pigment is preferably aniline black or perylene black, and more preferably aniline black. The content of the black organic pigment relative to 100 parts by mass of resin is 60 parts by mass or more, and more preferably 80 parts by mass or more. If the content of the black organic pigment relative to 100 parts by mass of resin is less than 60 parts by mass, the unevenness of the resulting coating film becomes small or the unevenness is not expressed, and the gloss and reflectance become higher than the desired range. In addition, a coating film having the desired blackness cannot be obtained. The upper limit of the content of the black organic pigment relative to 100 parts by mass of resin is not particularly limited, but is preferably 300 parts by mass or less, and more preferably 200 parts by mass or less. If the content of black organic pigment exceeds 300 parts by mass per 100 parts by mass of resin, the strength of the coating film may be insufficient.

In the black paint composition according to this embodiment, the black pigment preferably further contains a black inorganic pigment in addition to the black organic pigment. By using a black organic pigment and a black inorganic pigment in combination, it is possible to further improve the anti-reflection properties in the infrared region, specifically in the wavelength region exceeding 780 nm. Examples of black inorganic pigments include carbon black, titanium black, acetylene black, graphite, nickel, silicon carbide, silicon nitride, and iron oxide. The black inorganic pigment may be used alone or in combination of two or more types. Of these, the black inorganic pigment is preferably carbon black or titanium black, and more preferably carbon black, because it is less likely to aggregate. The content of the black inorganic pigment relative to 100 parts by mass of resin is preferably 0 to 50 parts by mass, and more preferably 0 to 20 parts by mass. If the content of the black inorganic pigment relative to 100 parts by mass of resin exceeds 50 parts by mass, the stability of the paint may deteriorate.

The good dispersion medium may be any component that easily wets the organic pigment, and is preferably, for example, a component used as a wetting agent to be added to the pigment dispersion liquid. There is no particular limit to the components that are used as wetting agents and are suitable as good dispersion media, but examples include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol. These may be used alone or in combination of two or more types.

The good dispersion medium is a dispersion medium that is easily wetted with the black organic pigment, for example, ethanol, isopropyl alcohol, methanol, and normal propanol. The good dispersion medium may be used alone or in combination of two or more. Of these, from the viewpoint of safety, it is more preferable that the good dispersion medium is ethanol or a mixed dispersion medium having ethanol as the main component. Here, the main component means that the content of ethanol in the mixed dispersion medium is 50 mass% or more. It is more preferable that the content of ethanol in the mixed dispersion medium is 80 mass% or more. As a mixed dispersion medium having ethanol as the main component, industrial ethanol obtained by adding methanol and/or isopropyl alcohol to ethanol may be used. From the viewpoint of safety, the boiling point of the good dispersion medium is preferably 50 to 100°C, more preferably 60 to 90°C. The content of the good dispersion medium per 100 mass parts of black organic pigment is 50 mass parts or more, more preferably 60 mass parts or more. If the content of the good dispersion medium per 100 mass parts of black organic pigment is less than 50 mass parts, the stability of the paint may be poor. In addition, since the unevenness of the coating film is reduced, the gloss and reflectance may be higher than the desired range. Furthermore, a coating film having the desired blackness may not be obtained. The upper limit of the content of the good dispersion medium per 100 parts by mass of the black organic pigment is not particularly limited, but is preferably 150 parts by mass or less, and more preferably 100 parts by mass or less. If the content of the good dispersion medium per 100 parts by mass of the black organic pigment exceeds 150 parts by mass, the product may dry too quickly, making work difficult.

The poor dispersion medium is a dispersion medium that is less wettable by black organic pigments than the good dispersion medium and has a higher boiling point than the good dispersion medium. Examples of the poor dispersion medium are water, normal octanol, isooctanol, butyrocellosolve, texanol, and propylene glycol monobutyl ether. The poor dispersion medium may be used alone or in combination of two or more. Of these, it is more preferable that the poor dispersion medium contains at least water from the viewpoint of safety. When the resin is in the form of a dispersion liquid in which the resin is dispersed in a dispersion medium that can be a poor dispersion medium such as water, the content of the poor dispersion medium also includes the content of the dispersion medium contained in the dispersion liquid of the resin. From the viewpoint of work efficiency, the boiling point of the poor dispersion medium is preferably 95 to 300°C, more preferably 100 to 200°C, and even more preferably 100 to 120°C. In this embodiment, it is preferable that the good dispersion medium contains ethanol as a main component and the poor dispersion medium contains water. The content of the poor dispersion medium relative to 100 parts by mass of the black organic pigment is preferably 200 to 1200 parts by mass, and more preferably 300 to 1000 parts by mass. If the content of the poor dispersion medium relative to 100 parts by mass of the black organic pigment is less than 200 parts by mass, the gloss and reflectance may be higher than the desired range. If the content of the poor dispersion medium relative to 100 parts by mass of the black organic pigment exceeds 1200 parts by mass, the working efficiency may be poor. Furthermore, it is particularly preferable that the content of the poor dispersion medium relative to 100 parts by mass of the black organic pigment is in the range of 600 to 800 parts by mass. By setting it in such a range, the reflectance in the visible light region can be further reduced.

In the black paint composition according to this embodiment, the poor dispersion medium may also function as an auxiliary. Examples of poor dispersion mediums that function as auxiliary agents include butyl cellosolve or propylene glycol monobutyl ether, which function as film-forming assistants, or Texanol, which functions as a coating strength enhancer. These may be used in combination as necessary.

When selecting a good dispersion medium and a poor dispersion medium, the degree of wettability, such as "easy to wet" and "difficult to wet", can be judged, for example, by the ease with which pigment particles re-aggregate when the pigment and the dispersion medium are mixed. The confirmation method is not particularly limited, but can be confirmed, for example, by the following method. The pigment is added to any liquid that can be used as a dispersion medium, and the pigment is dispersed using a grinding medium. After dispersion, the dispersion is filled into a sealed container such as a glass bottle and left to stand, and the presence or absence of pigment sedimentation is confirmed. After standing for a predetermined time, a liquid in which no pigment sedimentation or separation is observed is a dispersion medium that is easy to wet for the pigment and can be selected as a good dispersion medium, and a liquid in which pigment sedimentation is observed and separation is observed is a dispersion medium that is difficult to wet for the pigment and can be selected as a poor dispersion medium. In this confirmation method, the grinding medium is not particularly limited, but can be, for example, zirconia beads or glass beads. The diameter of the grinding medium is not particularly limited, but can be, for example, 1 to 10 mm. The dispersion processing time is not particularly limited, but can be, for example, 60 to 120 minutes. The time for which the solution is left to stand is not particularly limited, but is, for example, 30 to 60 days.

The black paint composition according to this embodiment includes a form in which the matting agent is not contained or the content of the matting agent per 100 parts by mass of resin is more than 0 parts by mass and not more than 50 parts by mass. The matting agent is, for example, an extender pigment or beads. The extender pigment is a white or colorless pigment also called a filler, for example, silica, talc, or dolomite, and the particle size is not particularly limited, but is, for example, 5 to 200 μm. The beads are particles of resin such as silicone resin, polyethylene resin, or nylon resin, and the particle size is not particularly limited, but is, for example, 5 to 100 μm. If the content of the matting agent per 100 parts by mass of resin exceeds 50 parts by mass, clogging of the air spray may occur, significantly reducing the paint workability. In addition, appearance defects such as cracks in the coating film may occur. When a matting agent is blended, the content of the matting agent per 100 parts by mass of resin is more preferably 1 to 10 parts by mass. Conventional black paint compositions have been formulated with a matting agent to form unevenness on the surface of the paint film, resulting in a low-gloss paint film. However, the black paint composition of this embodiment is formulated with two or more types of dispersion media that differ in their wettability with the black organic pigment, and the difference in evaporation rate between the two or more dispersion media is utilized to create unevenness on the surface of the paint film, resulting in a low-gloss paint film. Therefore, the black paint composition of this embodiment can provide a low-gloss paint film with little gloss, even without the incorporation of a matting agent.

The black paint composition according to this embodiment may contain various auxiliary agents as necessary within the scope of not impairing the effects of the present invention. Examples of auxiliary agents include dispersants, thickeners, defoamers, and surface conditioners. It is preferable that the black paint composition according to this embodiment contains at least a dispersant as an auxiliary agent, since this can more stably ensure the dispersion stability of the black organic pigment.

The coated article according to this embodiment has a substrate and a low-gloss coating film formed on the surface of the substrate, and the low-gloss coating film is a dried product of the black paint composition according to this embodiment and has protruding portions that contain aggregates of black organic pigment.

The material of the substrate is not particularly limited, but examples thereof include ABS resin (acrylonitrile, butadiene, styrene copolymer synthetic resin), AS (acrylonitrile-styrene) resin, acrylic resin such as PMMA (polymethyl methacrylate) resin, polyester resin such as PET (polyethylene terephthalate) resin and PBT (polybutylene terephthalate) resin, polycarbonate resin, vinyl chloride resin, epoxy resin, phenolic resin, fluororesin, PP (polypropylene) resin, and mixed resins thereof. The shape of the substrate is, for example, a film, a plate, or a three-dimensional shape. When the substrate is three-dimensional, the surface of the substrate on which the low gloss coating film is formed is, for example, the inner wall surface of the barrel of a camera lens, the end surface of a lens, or the inner wall surface of the housing of a HUD (head-up display).

In the coated product according to this embodiment, it is preferable that the substrate is made of polypropylene resin and that the resin contains an olefin resin. By including an olefin resin as the resin for forming the coating film, better adhesion to the PP substrate can be ensured.

The low gloss coating film is a coating film having low gloss properties, and is a dried product of the black paint composition according to this embodiment. In this specification, low gloss properties refer to a property of having low gloss and low reflectance in the visible light region, specifically in the wavelength region of 300 to 780 nm. For example, the preferred properties of a low gloss coating film will be explained using the example of a low gloss coating film used as a coating film on the inner wall surface of an optical device such as a camera. The 20° gloss, 60° gloss, and 85° gloss are preferably all 2.0 or less, more preferably 1.5 or less, and particularly preferably 0.3 or less. The reflectance in the visible light region is the average value obtained by measuring the reflectance of each wavelength at intervals of 0.5 nm in the range of 300 to 780 nm, and is preferably 0.7 to 3.0%, and more preferably 0.9 to 1.5%. Here, the 20° gloss, 60° gloss, and 85° gloss can be measured, for example, using a micro-gloss (manufactured by BYK). The reflectance in the visible light region can be measured, for example, using a spectrophotometer (U-4100, manufactured by Hitachi High-Technologies Corporation).

The low gloss coating film according to the present embodiment preferably has a high blackness in addition to low gloss. The blackness (My value) is preferably 170 to 225, more preferably 175 to 210. The blackness (My value) can be measured, for example, with a spectrophotometer (CM-700D, manufactured by Konica Minolta). The blackness (My value) was calculated by measuring the Y value with a spectrophotometer (CM-700D, manufactured by Konica Minolta) and using the following formula 1.
(Math 1) My=100×log(100/Y)

The low gloss coating film has a convex portion containing an aggregate of black organic pigment. The low gloss coating film preferably has an uneven structure having a plurality of convex portions and a concave portion between adjacent convex portions. The convex portion is a portion where the coating film components containing the aggregate of black organic pigment are deposited in a relatively large amount in the film thickness direction. The coating film components deposited on the convex portion may contain other coating film components in addition to the aggregate of black organic pigment. The other coating film components are, for example, a resin, or a black inorganic pigment, a matting agent, or various auxiliary agents that are blended as necessary. The concave portion is a portion where the coating film components are deposited in a relatively small amount in the film thickness direction compared to the adjacent convex portion. The coating film components deposited on the concave portion include a resin, or a black inorganic pigment, a matting agent, or various auxiliary agents that are blended as necessary, and may or may not contain aggregates of black organic pigment. The convex portions create unevenness on the surface of the coating film, which can achieve the gloss, reflectance in the visible light region, and blackness described above. The arithmetic mean roughness of a low gloss coating is preferably 4 to 80 μm, and more preferably 4 to 40 μm. The arithmetic mean roughness is a value measured using a laser microscope or the like in accordance with JIS B 0601:2001.

The average diameter of the convex portions is preferably 1 to 40 μm, and more preferably 5 to 30 μm. If the average diameter of the convex portions is less than 1 μm, the strength of the convex portions may be insufficient and the convex portions may collapse, making it impossible to achieve the desired gloss, reflectance in the visible light region, and blackness. If the average diameter of the convex portions exceeds 100 μm, the gloss may increase. The average diameter of the convex portions is determined by measuring the diameters of all convex portions present in an area of 1000 μm x 1000 μm in an image of the surface of the coating film observed with an electron microscope such as a transmission electron microscope (TEM) or a scanning electron microscope (SEM).

The average height of the convex portions is preferably 10 to 200 μm, more preferably 15 to 150 μm, and even more preferably 15 to 100 μm. The average height of the convex portions is the difference in height between the apex of the convex portion and the lowest part of the concave portion adjacent to the convex portion. The average height of the convex portions is the average height of the convex portions in a range of 1000 μm x 1000 μm obtained by using, for example, an atomic force microscope (AFM) and the accompanying analysis software.

The method for forming a low gloss coating film according to this embodiment is a method for forming a low gloss coating film, comprising a coating step in which the black paint composition according to this embodiment is sprayed onto the surface of a substrate by air spray, and a drying step. The coating step includes a mixture formation step in which all or a part of the good dispersion medium among the dispersion mediums is volatilized after the black paint composition is sprayed from the air spray and before it reaches the surface of the substrate, forming a mixture containing aggregates of the black organic pigment, a resin, and at least a poor dispersion medium as a non-volatile dispersion medium, and an adhesion step in which the mixture reaches the surface of the substrate and adheres to it, and the drying step includes a step of volatilizing the non-volatile dispersion medium contained in the mixture.

In the coating process, the solids concentration of the black paint composition is not particularly limited, but taking into account the efficiency of air spray coating, it is preferable to prepare it at 20 to 40 mass%, and more preferably at 25 to 35 mass%.

The coating process preferably employs air spray coating. Air spray coating is easy to process, even if the substrate to be coated has a complex or small shape. Conventional paint compositions contain a matting agent to obtain a low-gloss coating film, which can cause problems such as clogging of the air spray device and makes it difficult to obtain a highly jet-black coating film due to the white color of the matting agent. However, the paint composition of this embodiment can obtain a low-gloss coating film without the use of a matting agent or even with only a small amount of matting agent, making it not only suitable for air spray coating, but also capable of obtaining a highly jet-black coating film because no matting agent is used.

The coating process includes a mixture formation process. Next, the mechanism of the mixture formation process will be described. In the method for forming a low-gloss coating film according to this embodiment, air spray coating is adopted to utilize the difference in evaporation rate between a good dispersion medium and a poor dispersion medium. Since the boiling point of a good dispersion medium is lower than that of a poor dispersion medium, the evaporation rate of a good dispersion medium is faster than that of a poor dispersion medium. In air spray coating, the coating composition sprayed from the air spray moves through the air and reaches the surface of the substrate. The inventors have found that by utilizing the difference in evaporation rate of the dispersion medium during the time that the coating composition moves through the air to form aggregates of the black organic pigment, it is possible to obtain a low-gloss coating film by expressing unevenness on the surface of the coating film. More specifically, in the mixture formation process, all or part of the good dispersion medium evaporates before the coating composition is sprayed from the air spray and reaches the surface of the substrate, causing the composition to be in a state of excess poor dispersion medium, and the black organic pigment that was wetted by the good dispersion medium and dispersed in the state of fine particles is forcibly re-aggregated. As a result, a mixture is formed that contains agglomerates of the black organic pigment reaggregated, a resin, and at least a poor dispersion medium as a non-volatile dispersion medium. This embodiment includes a form in which the non-volatile dispersion medium contains only a poor dispersion medium and does not contain a good dispersion medium, and a form in which the non-volatile dispersion medium further contains a good dispersion medium in addition to the poor dispersion medium. In addition, the non-volatile dispersion medium may contain other dispersion media that act as auxiliary agents other than the good dispersion medium and the poor dispersion medium.

The coating process includes an adhesion process after the mixture formation process. In the adhesion process, the mixture reaches and adheres to the surface of the substrate. In the adhesion process, the mixture is deposited on the surface of the substrate to form a wet film. The surface of the wet film has an uneven structure due to protrusions resulting from aggregates of the black organic pigment.

The drying process includes a process of volatilizing the non-volatile dispersion medium contained in the mixture. In the drying process, the non-volatile dispersion medium is removed while maintaining the uneven structure of the wet film, and a dry coating film having an uneven structure is formed. This dried coating film is a low-gloss coating film. The drying method may be forced drying or natural drying. Of these, forced drying is more preferable in terms of increasing the coating film strength. The drying conditions for forced drying are not particularly limited, but are, for example, 60 to 90°C and 20 to 60 minutes. The film thickness of the low-gloss coating film after drying is not particularly limited, but is preferably 15 to 45 μm, and more preferably 20 to 40 μm.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass", respectively, unless otherwise specified. The number of parts added is a value calculated as solid content.

Example 1
The resin used was 10.95 parts by mass in terms of solid content of urethane dispersion resin (Takelac W-6110, manufactured by Mitsui Chemicals, Inc., solid content concentration 30% by mass), the good dispersion medium was 6.60 parts by mass of industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.), the poor dispersion medium was 53.40 parts by mass of pure water, and the poor dispersion medium and auxiliary agent were 6.60 parts by mass of butyl cellosolve and 0.30 parts by mass of Texanol. , 6.00 parts by mass of dispersant (DISPERBYK-184, manufactured by BYK), 11.70 parts by mass of aniline black (NCC1031, manufactured by Noma Chemical Industry Co., Ltd.) as a black organic pigment in solid content, 6.00 parts by mass of thickener (Thixol K-502, manufactured by Kyoei Chemical Co., Ltd.), 0.10 parts by mass of defoamer (SN DEFORMER 1315, manufactured by San Nopco Co., Ltd.) were mixed, and stirred and mixed with Disper (manufactured by Chuo Rika Co., Ltd.) to obtain a black paint composition. The content of the good dispersion medium relative to 100 parts by mass of black organic pigment was 56.4 parts by mass. In addition, the content of the black organic pigment relative to 100 parts by mass of resin was 107 parts by mass. In addition, no matting agent was added.

Example 2
A black coating composition was obtained in the same manner as in Example 1, except that the amount of urethane dispersion resin (Takelac W-6110, manufactured by Mitsui Chemicals, Inc., solid content concentration 30% by mass) was changed to 9.00 parts by mass in terms of solid content. The content of the good dispersion medium per 100 parts by mass of the black organic pigment was 56.4 parts by mass. The content of the black organic pigment per 100 parts by mass of the resin was 130 parts by mass.

Example 3
A black coating composition was obtained in the same manner as in Example 1, except that the amount of urethane dispersion resin (Takelac W-6110, manufactured by Mitsui Chemicals, Inc., solid content concentration 30% by mass) was changed to 6.00 parts by mass in terms of solid content, and the amount of pure water, which is a poor dispersion medium, was changed to 59.40 parts by mass. The content of the good dispersion medium per 100 parts by mass of the black organic pigment was 56.4 parts by mass. The content of the black organic pigment per 100 parts by mass of the resin was 195 parts by mass.

Example 4
A black coating composition was obtained in the same manner as in Example 1, except that the amount of urethane dispersion resin (Takelac W-6110, manufactured by Mitsui Chemicals, Inc., solid content concentration 30% by mass) was changed to 13.95 parts by mass in terms of solid content, and the amount of pure water, which is a poor dispersion medium, was changed to 48.40 parts by mass. The content of the good dispersion medium per 100 parts by mass of the black organic pigment was 56.4 parts by mass. The content of the black organic pigment per 100 parts by mass of the resin was 83.9 parts by mass.

(Example 5)
A black coating composition was obtained in the same manner as in Example 1, except that the amount of urethane dispersion resin (Takelac W-6110, manufactured by Mitsui Chemicals, Inc., solid content concentration 30% by mass) was changed to 18.45 parts by mass in terms of solid content, and the amount of pure water, which is a poor dispersion medium, was changed to 44.20 parts by mass. The content of the good dispersion medium per 100 parts by mass of the black organic pigment was 56.4 parts by mass. The content of the black organic pigment per 100 parts by mass of the resin was 63.4 parts by mass.

Example 6
A black coating composition was obtained in the same manner as in Example 1, except that the amount of aniline black (NCC1031, manufactured by Noma Chemical Industry Co., Ltd.) was changed from 11.70 parts by mass to 9.70 parts by mass, and 2.00 parts by mass of carbon black (SPECIAL BLACK5, manufactured by Orion Engineered Carbons Co., Ltd.), a black inorganic pigment, was further added. The content of the good dispersion medium per 100 parts by mass of the black organic pigment was 68 parts by mass. The content of the black organic pigment per 100 parts by mass of the resin was 88.6 parts by mass.

(Example 7)
In Example 1, the amount of aniline black (NCC1031, manufactured by Noma Chemical Industry Co., Ltd.) was changed from 11.70 parts by mass to 9.70 parts by mass, and 2 parts by mass of titanium black (TilackD TS-M, manufactured by Akaho Chemical Industry Co., Ltd.), a black inorganic pigment, was further blended. A black paint composition was obtained in the same manner as in Example 1. The content of the good dispersion medium per 100 parts by mass of the black organic pigment was 68 parts by mass. In addition, the content of the black organic pigment per 100 parts by mass of the resin was 88.6 parts by mass.

(Example 8)
A black coating composition was obtained in the same manner as in Example 1, except that the amount of aniline black (NCC1031, manufactured by Noma Chemical Industry Co., Ltd.) was changed from 11.70 parts by mass to 9.70 parts by mass, and 2.00 parts by mass of perylene black (Spectrasense Black K0088, manufactured by BASF Corporation) was further added as a black organic pigment. The content of the good dispersion medium per 100 parts by mass of the black organic pigment was 56.4 parts by mass. The content of the black organic pigment per 100 parts by mass of the resin was 107 parts by mass.

(Example 9)
In Example 1, the amount of industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) which is a good dispersion medium was changed from 6.60 parts by mass to 6 parts by mass, and the amount of aniline black (NCC1031, manufactured by Noma Chemical Industry Co., Ltd.) which is a black organic pigment was changed from 11.70 parts by mass to 12 parts by mass. A black paint composition was obtained in the same manner as in Example 1. The content of the good dispersion medium per 100 parts by mass of the black organic pigment was 50 parts by mass. In addition, the content of the black organic pigment per 100 parts by mass of the resin was 109.6 parts by mass.

Example 10
A black coating composition was obtained in the same manner as in Example 1, except that in Example 1, industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) was not used as a good dispersion medium, and instead 6.6 parts by mass of isopropyl alcohol (isopropyl alcohol, manufactured by Ando Parachemie Co., Ltd.) was used.

Example 11
A black coating composition was obtained in the same manner as in Example 1, except that in Example 1, industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) was not used as a good dispersion medium, and instead 6.6 parts by mass of methanol (methanol, manufactured by Kyoei Chemical Co., Ltd.) was used.

Example 12
A black coating composition was obtained in the same manner as in Example 1, except that in Example 1, industrial ethanol (mixed ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) was not used as a good dispersion medium, and instead, 6.6 parts by mass of normal propanol (1-propanol, manufactured by Hayashi Pure Chemical Industries Co., Ltd.) was used.

Example 13
A black paint composition was obtained in the same manner as in Example 1, except that the poor dispersion medium and auxiliary agents butyl cellosolve and texanol were not added, and the amount of pure water, which is the poor dispersion medium, was changed from 53.40 parts by mass to 60.3 parts by mass.

(Example 14)
The resin was an olefin resin emulsion (Aptrock BW-5635, manufactured by Mitsubishi Chemical Corporation, solid content concentration 30% by mass) of 10.95 parts by mass in terms of solid content, the good dispersion medium was industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) of 6.60 parts by mass, the poor dispersion medium was pure water of 53.4 parts by mass, and the poor dispersion medium and auxiliary agent was butyl cellosolve of 6.60 parts by mass and Texanol of 0.30 parts by mass. 6.00 parts by mass of dispersant (DISPERBYK-184, manufactured by BYK), 11.70 parts by mass of aniline black (NCC1031, manufactured by Noma Chemical Industry Co., Ltd.) as a black organic pigment in solid content, 6.00 parts by mass of thickener (Thixol K-502, manufactured by Kyoei Chemical Co., Ltd.), 0.10 parts by mass of defoamer (SN DEFORMER 1315, manufactured by San Nopco Co., Ltd.) were mixed, and a black paint composition was obtained by stirring and mixing with Disper (manufactured by Chuo Rika Co., Ltd.). The content of the good dispersion medium relative to 100 parts by mass of black organic pigment was 56.4 parts by mass. In addition, the content of the black organic pigment relative to 100 parts by mass of resin was 107 parts by mass. In addition, no matting agent was mixed.

(Example 15)
The resin was a polyurethane dispersion resin (Takelac W-6110, manufactured by Mitsui Chemicals, Inc., solid content concentration 30% by mass) of 2.48 parts by solids, and an olefin resin emulsion (Aptlock BW-5635, manufactured by Mitsubishi Chemical Corporation, solid content concentration 30% by mass) of 9.30 parts by solids. The resin was a good dispersion medium, and industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) of 6.60 parts by mass was used. Pure water was used as a poor dispersion medium, and 52.57 parts by mass was used. 6.60 parts by mass of Chilcelsolve and 0.30 parts by mass of Texanol, 6.00 parts by mass of dispersant (DISPERBYK-184, manufactured by BYK), 11.70 parts by mass of aniline black (NCC1031, manufactured by Noma Chemical Industry Co., Ltd.) as a black organic pigment in terms of solid content, 6.00 parts by mass of thickener (Thixol K-502, manufactured by Kyoei Chemical Co., Ltd.), and 0.10 parts by mass of defoamer (SN Defoamer 1315, manufactured by San Nopco Co., Ltd.) were mixed and stirred and mixed with Disper (manufactured by Chuo Rika Co., Ltd.) to obtain a black paint composition. The content of the good dispersion medium relative to 100 parts by mass of black organic pigment was 56.4 parts by mass. In addition, the content of the black organic pigment relative to 100 parts by mass of resin was 99 parts by mass. In addition, no matting agent was added.

(Example 16)
In Example 14, a black paint composition was obtained in the same manner as in Example 14, except that industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) was not used as a good dispersion medium, and instead, 6.6 parts by mass of isopropyl alcohol (isopropyl alcohol, manufactured by Ando Parachemie Co., Ltd.) was used.

(Example 17)
In Example 14, a black coating composition was obtained in the same manner as in Example 14, except that industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) was not used as a good dispersion medium, and instead, 6.6 parts by mass of methanol (methanol, manufactured by Kyoei Chemical Co., Ltd.) was used.

(Example 18)
A black coating composition was obtained in the same manner as in Example 14, except that industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) was not used as a good dispersion medium in Example 14, and instead, 6.6 parts by mass of normal propanol (1-propanol, manufactured by Hayashi Pure Chemical Industry Co., Ltd.) was used.

Example 19
In Example 14, a black paint composition was obtained in the same manner as in Example 14, except that the poor dispersion medium and auxiliary agents butyl cellosolve and texanol were not added, and the amount of pure water, which is the poor dispersion medium, was changed from 53.40 parts by mass to 60.3 parts by mass.

(Example 20)
In Example 15, the amount of the urethane dispersion resin blended as the resin was changed to 5.55 parts by mass, the amount of the olefin resin blended was changed to 5.40 parts by mass, and instead of blending industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) as a good dispersion medium, 6.6 parts by mass of isopropyl alcohol (isopropyl alcohol, manufactured by Ando Parachemie Co., Ltd.) was blended, a black paint composition was obtained in the same manner as in Example 15.

(Example 21)
In Example 15, the amount of the urethane dispersion resin blended as the resin was changed to 5.55 parts by mass, the amount of the olefin resin blended was changed to 5.40 parts by mass, and instead of blending industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) as a good dispersion medium, 6.6 parts by mass of methanol (methanol, manufactured by Kyoei Chemical Co., Ltd.) was blended, a black paint composition was obtained in the same manner as in Example 15.

(Example 22)
In Example 15, the amount of the urethane dispersion resin blended as the resin was changed to 5.55 parts by mass, the amount of the olefin resin blended was changed to 5.40 parts by mass, and instead of blending industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.) as a good dispersion medium, 6.6 parts by mass of normal propanol (1-propanol, manufactured by Hayashi Pure Chemical Industry Co., Ltd.) was blended, a black coating composition was obtained in the same manner as in Example 15.

(Example 23)
In Example 15, the amount of the urethane dispersion resin blended as the resin was changed to 5.55 parts by mass, the amount of the olefin resin blended was changed to 5.40 parts by mass, the poor dispersion medium and auxiliary agents butyl cellosolve and Texanol were not blended, and the amount of pure water, which is a poor dispersion medium, was changed from 53.40 parts by mass to 60.3 parts by mass. A black paint composition was obtained in the same manner as in Example 15.

(Comparative Example 1)
A black coating composition was obtained in the same manner as in Example 1, except that aniline black (NCC1031, manufactured by Noma Chemical Industry Co., Ltd.) was not used as the black organic pigment, and 11.7 parts by mass of carbon black (SPECIAL BLACK 5, manufactured by Orion Engineered Carbons Co., Ltd.) was used instead, which is a black inorganic pigment.

(Comparative Example 2)
A black paint composition was obtained in the same manner as in Example 1, except that the amount of the resin, urethane dispersion resin (Takelac W-6110, manufactured by Mitsui Chemicals, Inc., solid content concentration 30% by mass), was changed from 10.95 parts by mass to 18 parts by mass in solid content, and the amount of the black organic pigment, aniline black (NCC1031, manufactured by Noma Chemical Industry Co., Ltd.), was changed from 11.70 parts by mass to 9 parts by mass. The content of the good dispersion medium per 100 parts by mass of the black organic pigment was 68 parts by mass. The content of the black organic pigment per 100 parts by mass of the resin was 53.9 parts by mass.

(Comparative Example 3)
In Example 1, the amount of ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.), which is a good dispersion medium, was changed from 6.60 parts by mass to 5 parts by mass, and the amount of aniline black (NCC1031, manufactured by Noma Chemical Industry Co., Ltd.), which is a black organic pigment, was changed from 11.70 parts by mass to 12 parts by mass. A black paint composition was obtained in the same manner as in Example 1. The content of the good dispersion medium per 100 parts by mass of the black organic pigment was 41.7 parts by mass. In addition, the content of the black organic pigment per 100 parts by mass of the resin was 109.6 parts by mass.

(Comparative Example 4)
A black paint composition was obtained in the same manner as in Example 1, except that pure water, which is a poor dispersion medium, was not added, and the amount of industrial ethanol (Mixed Ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.), which is a good dispersion medium, added was changed from 6.60 parts by mass to 2 parts by mass.

The compositions of the main components (resin, black pigment, good dispersion medium, and poor dispersion medium) of the black paint compositions of Examples 1 to 9 and Comparative Examples 1 to 4 are shown in Table 1.

The black paint compositions of Examples 1 to 9 were applied to the surface of a substrate (ABS plate, thickness 2 mm) using an air spray device (WIDER1 series, manufactured by Anest Iwata Corporation) and forced dried at 70°C for 30 minutes to form a coating film. For the black paint compositions of Comparative Examples 1 to 4, coating films were also formed in the same manner as for the black paint compositions of the Examples. However, the black paint composition of Comparative Example 1 could not be applied due to clogging caused by carbon black. The following evaluations were performed on the resulting coating films, which were the cured products of the black paint compositions of Examples 1 to 9 (hereinafter sometimes referred to as the coating films of Examples 1 to 9) and the coating films, which were the cured products of the black paint compositions of Comparative Examples 2 to 4 (hereinafter sometimes referred to as the coating films of Comparative Examples 2 to 4). The evaluation results are shown in Table 2.

The compositions of the main components (resin, black pigment, good dispersion medium, and poor dispersion medium) of the black paint compositions of Examples 10 to 19 are shown in Table 3. In addition, the black paint compositions of Examples 10 to 19 were evaluated in the same manner as in Example 1, and the evaluation results are shown in Table 4.

(Glossiness)
The 20°, 60°, and 85° glossiness were measured as follows. Measurements were performed three times at angles of 20°, 60°, and 85° using a micro-gloss (manufactured by BYK), and the average value was calculated. The evaluation criteria were as follows: a 20°, 60°, and 85° glossiness of 2.0 or less was deemed to be of a practical level, and a 20°, 60°, and 85° glossiness of more than 2.0 was deemed to be of an unsuitable level for practical use.

(Reflectance in the visible light range)
The reflectance in the visible light region was measured as follows. The visible light region was measured using a spectrophotometer (U-4100 manufactured by Hitachi High-Technologies Corporation). The reflectance was measured every 0.5 nm in the range of 400 to 780 nm, and the average value was calculated. The evaluation criteria were as follows: a reflectance of 3.0% or less on average was deemed to be at a practical level, and a reflectance of more than 3.0% on average was deemed to be at an unsuitable level for practical use.

(Blackness)
The blackness was measured as follows. The blackness (My value) was calculated by measuring the Y value with a spectrophotometer (CM-700D, manufactured by Konica Minolta) and using the following formula 1. The judgment criteria were that an My value of 170 or more was a practical level, and an My value of less than 170 was an unsuitable level for practical use.
(Math 1) My=100×log(100/Y)

As shown in Table 2, the coating films of Examples 1 to 9 all had a 20°, 60°, and 85° gloss of 2.0 or less, an average reflectance in the visible light region of 0.7 to 3.0%, and a blackness of 176 or more, and thus had low gloss and high blackness. The reflectance in the visible light region and the 85° gloss tended to decrease as the content of the black organic pigment relative to 100 parts by mass of resin increased. On the other hand, the coating film of Comparative Example 2 had a black organic pigment content of less than 60 parts by mass relative to 100 parts by mass of resin, so that the unevenness of the coating film was reduced and the gloss and reflectance were higher than those of the coating films of the Examples. In addition, the blackness was lower than that of the coating films of the Examples. The coating film of Comparative Example 3 had a content of the good dispersion medium of less than 50 parts by mass relative to 100 parts by mass of black organic pigment, so that the gloss and reflectance were higher than those of the coating films of the Examples. In addition, the blackness was lower than that of the coating films of the Examples. The coating film of Comparative Example 4 had a content of good dispersion medium of less than 50 parts by mass per 100 parts by mass of black organic pigment, so the gloss and reflectance were higher than those of the coating film of the Example. Also, the blackness was lower than that of the coating film of the Example.

As shown in Table 4, the coatings of Examples 10 to 23 all had a 20°, 60°, and 85° gloss of 2.0 or less, an average reflectance in the visible light region of 0.7 to 3.0%, and a blackness of 176 or more, similar to the coatings of Examples 1 to 9, and thus had low gloss and high blackness. Examples 10 to 12 are examples in which the type of good dispersion medium was changed from Example 1. Example 13 is an example in which the type of poor dispersion medium was changed from Example 1. Examples 14 and 15 are examples in which the resin was changed from urethane resin to only olefin resin, and to a combination of urethane resin and olefin resin, respectively, compared to Example 1. Examples 16 to 18 are examples in which the type of good dispersion medium was changed from Example 14. Example 19 is an example in which the type of poor dispersion medium was changed from Example 14. Examples 20 to 22 are examples in which the type of good dispersion medium was changed from Example 15. Example 23 is an example in which the type of poor dispersion medium was changed from Example 15.

(Adhesion)
The black paint compositions of Examples 14 and 15 were applied to the surface of a substrate (PP plate, thickness 2 mm) using an air spray device (WIDER1 series, manufactured by Anest Iwata Corporation), and forced drying was performed at 70°C for 30 minutes to form a coating film, thereby obtaining a coated product. The adhesion of the coating film to the substrate was evaluated for the obtained coated product. The evaluation method and evaluation criteria for adhesion were as follows. Adhesion was evaluated and judged according to the cross-cut method shown in JIS K-5600-5-6:1999 "General Test Methods for Paints - Part 5: Mechanical Properties of Coatings - Section 6: Adhesion (Cross-cut Method)". First, six cuts were made horizontally at intervals of 1 mm to form a 25-cell grid pattern, and six more cuts were made vertically. Next, cellophane tape was applied, rubbed with fingertips to adhere, and then the end of the tape was grabbed and peeled off. The judgment was made according to which of the classifications 0 to 5 the surface condition of the grid pattern after evaluation fell into. The results of the adhesion evaluation are shown in Table 5. As shown in Table 5, it was confirmed that the black coating compositions of Examples 14 and 15 had high adhesion to the PP substrate.

(Surface condition of the coating film)
The surface state of the coating film of the example and the comparative example was observed by SEM. FIG. 1 is an SEM image showing the surface state of the low gloss coating film of Example 1, and FIG. 2 is an SEM image showing the surface state of the coating film of Comparative Example 2. In FIG. 1 and FIG. 2, the magnification is 150 times, and the scale at the lower right is 20 μm. In FIG. 1 and FIG. 2, the black parts are recesses, and the parts with higher brightness than the recesses (parts that look relatively white or gray) are protrusions. The coating film shown in FIG. 1 had an uneven structure having a plurality of protrusions and recesses between adjacent protrusions. It was also confirmed that the average diameter of the protrusions was 18 μm, which was within the range of 1 to 40 μm. It was also confirmed that the average diameter of the protrusions of the other examples was within the range of 1 to 40 μm. The coating film shown in FIG. 2 had almost no unevenness.

(Height of protrusion)
The height of the convex portions of the low gloss coating film of Example 1 was measured as follows. The measurement was performed using a digital microscope VHX-6000 manufactured by Keyence Corporation. As a result, the height of the convex portions was 80 to 134 μm.

(arithmetic mean roughness)
The arithmetic mean roughness of the coating film surface was measured for the low gloss coating film of Example 1 and the coating film of Comparative Example 2. The measurement was performed using a digital microscope (Model VHX-6000, manufactured by Keyence Corporation). As a result, the arithmetic mean roughness of the low gloss coating film surface of the Example was 22.50 to 39.80 μm, whereas the arithmetic mean roughness of the coating film surface of the Comparative Example was 1.40 to 1.60 μm, and it was confirmed that the arithmetic mean roughness value of the low gloss coating film surface of the Example was greater than that of the coating film surface of the Comparative Example.

(Selection of Dispersion Medium)
For reference, an example of a method for selecting a good dispersion medium and a poor dispersion medium will be described. 20 parts by mass of aniline black was added to 80 parts by mass of pure water, and dispersed for 1 hour with 5 mm zirconia beads using a bead mill (manufactured by Toray Industries, Inc., type Treceram beads φ5 mm), to obtain a dispersion liquid as sample 1. 20 parts by mass of aniline black was added to 80 parts by mass of industrial ethanol (mixed ethanol NP, purity 85.5%, manufactured by Yamaichi Chemical Industry Co., Ltd.), and dispersed for 1 hour with 5 mm zirconia beads using a bead mill (manufactured by Toray Industries, Inc., type Treceram beads φ5 mm), to obtain a dispersion liquid as sample 2. Samples 1 and 2 were each filled into a glass bottle with a volume of 100 ml, sealed, and left to stand for 2 weeks. After standing for 2 weeks, the presence or absence of aniline black precipitation was confirmed. FIG. 3 is an image of sample 1 after standing for 2 weeks, and FIG. 4 is an image of sample 2 after standing for 2 weeks. As shown in Figure 3, in sample 1, due to the settling of aniline black, a lower layer with a relatively high concentration of aniline black and an upper layer with a relatively low concentration of aniline black were formed, separating the sample into two layers. For this reason, pure water was selected as a poor dispersion medium. As shown in Figure 4, in sample 2, aniline black did not settle and maintained a uniformly dispersed state without being separated into two layers. For this reason, industrial ethanol was selected as a good dispersion medium.

Claims (10)

A black pigment;
A dispersion medium;
A black paint composition comprising:
the black pigment comprises a black organic pigment,
the dispersion medium includes a good dispersion medium that is easily wetted with the black organic pigment, and a poor dispersion medium that is less wetted with the black organic pigment than the good dispersion medium,
The boiling point of the good dispersion medium is lower than the boiling point of the poor dispersion medium,
The content of the good dispersion medium per 100 parts by mass of the black organic pigment is 50 parts by mass or more,
A black paint composition, characterized in that the content of the black organic pigment per 100 parts by mass of the resin is 60 parts by mass or more. The black paint composition according to claim 1, characterized in that the resin contains a urethane resin, an acrylic resin, an epoxy resin, a silicone resin, an ester resin, a fluororesin or a melamine resin. The black paint composition according to claim 1 or 2, characterized in that the resin contains an olefin resin. The black paint composition according to claim 1 or 2, characterized in that the poor solvent contains at least water. The black paint composition according to claim 1 or 2, characterized in that the black pigment further contains a black inorganic pigment in addition to the black organic pigment. The black paint composition according to claim 1 or 2, characterized in that the black paint composition does not contain a matting agent or the content of the matting agent per 100 parts by mass of the resin is more than 0 parts by mass and not more than 50 parts by mass. A coated article having a substrate and a low gloss coating film provided on a surface of the substrate,
3. A coated article, wherein the low gloss coating film is a dried product of the black paint composition according to claim 1 or 2, and has convex portions containing aggregates of the black organic pigment. The coated article according to claim 7, characterized in that the average diameter of the convex portions is 1 to 40 μm. The substrate is made of polypropylene resin,
8. The coated article according to claim 7, wherein the resin comprises an olefin resin. A method for forming a low gloss coating film, comprising a coating step of spraying the black coating composition according to claim 1 or 2 onto a surface of a substrate by air spray, and a drying step,
The coating step includes a mixture forming step in which the good dispersion medium of the dispersion medium is all or partly volatilized after the black paint composition is sprayed from the air spray and before the black paint composition reaches the surface of the substrate, thereby forming a mixture containing an aggregate of the black organic pigment, the resin, and at least the poor dispersion medium as a non-volatile solvent, and an attachment step in which the mixture reaches and adheres to the surface of the substrate,
A method for forming a low gloss coating film, wherein the drying step includes a step of volatilizing the non-volatilized dispersion medium contained in the mixture.