JP2024081131A - Composite metal pigment composition and method for producing same - Google Patents

Abstract

The present invention provides a composite metal pigment composition having improved coagulation properties and storage tank stability and a low content of volatile organic solvents.
A composite metal pigment composition comprising a metal particle and a composite particle having a metal oxide coating formed on the surface thereof,
(1) The composite particles have a scale-like shape,
(2) The composite particles have a volume-based average particle diameter _D50 of 1 to 30 μm when the particle size distribution of the composite particles is measured using a laser diffraction particle size distribution analyzer;
(3) The composite particles have an average particle thickness of 20 to 400 nm;
(4) The composite metal pigment composition has a volatile content of 20 to 90% by mass, and 50 to 100% by mass of the volatile content is water;
(5) The composite metal pigment composition has a volatile organic solvent content of 0 to 20 parts by mass per 100 parts by mass of solids,
(6) The above composite metal pigment composition, in which when the composite metal pigment composition is dispersed in water and filtered through a 200 mesh filter, the residue is 0.1 mass% or less of the solid content.
[Selection diagram] None

Description

The present invention relates to a composite metal pigment composition comprising metal particles and composite particles having a metal oxide coating formed on the surface thereof, and a method for producing the same. More specifically, the present invention relates to a composite metal pigment composition that effectively suppresses aggregation and deformation of the composite particles while reducing the amount of volatile organic compounds (VOCs), and that has a high level of balance between low VOCs, excellent storage stability when used in water-based paints, suppression of bumps, design properties, hiding properties, and other excellent coating properties, and a method for producing the same.

2. Description of the Related Art Metallic pigments have been used for metallic paints, printing inks, plastic blends, and the like, for the purpose of achieving cosmetic effects that emphasize a metallic appearance.
In recent years, in the field of paints, the need to switch to water-based paints that use less organic solvents has been increasing as a measure to conserve resources, improve the working environment, and eliminate pollution. In order to improve the stability of metal pigments in water-based paints, pigments using composite particles in which metal particles are coated with metal oxides such as amorphous silica have been proposed. Even in such water-based paints, further reduction in VOCs is required. In order to reduce VOCs, it is effective to improve the non-volatile content (solid content) in the manufacturing process, but if strong centrifugation or pressing or filtration under strong pressure is performed in the filtration process, the particles of the metal pigment may deform or aggregate, or even defects may occur in the metal oxide coating such as silica, resulting in poor water resistance and reduced storage stability. It is also possible to improve the non-volatile content by volatilizing the organic solvent by heating or reducing pressure, but in this case, the surface dries early, causing the particles to stick to each other and aggregate, making it difficult to disperse in solvents or water without aggregation. As described above, composite metal pigment compositions in which the non-volatile content has been increased or other VOCs have been reduced using conventional methods have problems such as poor dispersibility during paint preparation, inability to express the desired color tone, and poor storage stability, and there has been a strong demand for solutions to these problems.

For example, Patent Document 1 describes the provision of PVD metallic effect pigments that exist in the form of a powder or in a highly concentrated form, and describes that the PVD pigment powder should be substantially free of agglomeration, should have good redispersibility, etc. However, agglomeration after redispersion is not directly evaluated, and dispersibility in aqueous solvents is not reported.
Patent Document 2 describes the preparation of coated aluminum effect pigments by suction filtration through a Büchner funnel, and also describes the use of the aluminum effect pigments to form an aqueous paint system, but does not report on the quality of dispersibility.
Patent Document 2 describes a paste that has a low VOC ratio and is preferable for environmental reasons, in which the water ratio is preferably 20% to 100% by weight, more preferably 30% to 90% by weight, and extremely preferably 40% to 80% by weight, based on the weight of the solvent in the paste. However, there is no description of a specific manufacturing method, dispersibility in paint, or performance as a coating film, and it is difficult to imagine that the paste will be able to exhibit sufficient practical performance when used as a water-based paint.
Patent Document 3 describes a metal pigment composition containing composite particles having metal particles and a coating layer, in which the particle size distribution D50 of the composite particles is 3 μm or more and 30 μm or less, the average thickness of the composite particles is 20 nm or more and 300 nm or less, and the proportion of the composite particles having a specific particle size is small. However, further improvement in VOC reduction is expected.

JP 2017-533982 A Patent No. 5512830 JP 2022-150635 A

In view of the limitations of the above-mentioned conventional techniques, the object of the present invention is to provide a composite metal pigment composition with a low content of volatile organic solvents, which has excellent dispersibility in water-based paints, can form coating films with excellent color tone, brightness, hiding power, etc., and can produce water-based paints with excellent storage stability, and which has a high level of balance between these properties, and a method for producing the same.

As a result of intensive research, the inventors discovered that the above-mentioned objectives can be achieved by a composite metal pigment composition with a low content of volatile organic solvents, in which the organic solvent used during production is replaced with water under specific conditions to improve coagulation properties and storage tank stability, and thus completed the present invention.

That is, the first invention of the present application and its aspects are as follows.
[1]
A composite metal pigment composition comprising metal particles and composite particles having a metal oxide coating formed on a surface thereof,
(1) The composite particles have a scale-like shape,
(2) The composite particles have a volume-based average particle diameter _D50 of 1 to 30 μm when the particle size distribution of the composite particles is measured using a laser diffraction particle size distribution analyzer;
(3) The composite particles have an average particle thickness of 20 to 400 nm;
(4) The composite metal pigment composition has a volatile content of 20 to 90% by mass, and 50 to 100% by mass of the volatile content is water;
(5) The composite metal pigment composition has a volatile organic solvent content of 0 to 20 parts by mass per 100 parts by mass of solids,
(6) The above composite metal pigment composition, in which when the composite metal pigment composition is dispersed in water and filtered through a 200 mesh filter, the residue is 0.1 mass% or less of the solid content.
[2]
(7) The composite metal pigment composition according to [1], in which 12.5 g of the metal pigment composition as a nonvolatile matter, 9.2 g of isopropyl alcohol, and 9.2 g of purified water are thoroughly mixed to prepare a mill base, and then 170 g of a water-soluble resin, 20.0 g of isopropyl alcohol, and 50 g of purified water are added to this mill base and thoroughly mixed to obtain 200 g of water-based metallic paint, which is then placed in a flask and the cumulative amount of hydrogen gas generated is measured for up to 24 hours in a constant temperature water tank at 60°C. The gas generated is 20 ml or less.
[3]
The composite metal pigment composition according to [1] or [2], wherein the proportion of non-aggregated primary particles in the composite particles is 35% or more on a number basis.
[4]
The composite metal pigment composition according to any one of [1] to [3], wherein the proportion of non-aggregated primary particles in the composite particles is 40% or more on a number basis.
[5]
The composite metal pigment composition according to [1], wherein the proportion of bent composite particles in the composite particles is 10% or less on a number basis.
[6]
The composite metal pigment composition according to [2], wherein the proportion of bent composite particles in the composite particles is 10% or less on a number basis.
[7]
The composite metal pigment composition according to [3] or [4], wherein the proportion of bent composite particles in the composite particles is 10% or less on a number basis.
[8]
The composite metal pigment composition according to any one of [1] to [7], wherein at least one layer in the metal oxide coating is a silicon compound-containing layer.
[9]
The composite metal pigment composition according to any one of [1] to [8], wherein the average layer thickness of the metal oxide coating is 5 to 150 nm.
[10]
The composite metal pigment composition according to any one of [1] to [8], wherein the metal particles contain aluminum or an aluminum alloy.
[11]
The composite metal pigment composition according to [9], wherein the metal particles contain aluminum or an aluminum alloy.
[12]
The composite metal pigment composition according to any one of [1] to [10], wherein the composite particle further has a coating layer containing at least one selected from a metal, a metal oxide, a metal hydrate, and a resin other than the metal oxide coating.
[13]
The composite metal pigment composition according to [11], wherein the composite particle further has a coating layer containing at least one selected from a metal, a metal oxide, a metal hydrate, and a resin other than the metal oxide coating.
[14]
The composite metal pigment composition according to [12] or [13], characterized in that the further coating layer according to [12] or [13] is an outermost layer of the composite particle.
[15]
The composite metal pigment composition according to any one of [12] to [14], wherein the further coating layer is an organic phosphorus compound.

The second and third inventions of the present application and their various aspects are as follows.
[16]
A method for producing a composite metal pigment composition comprising the following steps 1) to 3):
The above production method comprises the steps of: 1) dispersing metal particles in a solvent; 2) coating the metal particles with a metal oxide; and 3) washing and filtering the composite particles having the metal particles and the metal oxide coating formed on the surfaces thereof obtained in step 2), and replacing the organic solvent with water. Step 3) is carried out at 5 to 80° C. and in a state in which the solid content is 80 mass % or less.
[17]
The method according to [16], wherein the composite metal pigment composition is the composite metal pigment composition according to any one of [1] to [15].
[18]
A method for producing a composite metal pigment composition comprising the following steps 1) to 3):
1) a step of dispersing metal particles in a solvent; 2) a step of coating the metal particles with a metal oxide; and 3) a step of washing and filtering the composite particles having the metal particles obtained in step 2) and the metal oxide coating formed on their surfaces, and replacing the solvent with water. The above-mentioned manufacturing method is characterized in that step 3) comprises filtering the treatment liquid obtained in step 2) to reduce the volatile content to 70% by weight or less, followed by washing, filtering, and replacing the organic solvent with water.
[19]
The method according to [18], wherein the composite metal pigment composition is the composite metal pigment composition according to any one of [1] to [15].
[20]
The method according to any one of [16] to [19], characterized in that after step 3), an organic phosphoric acid compound is mixed with the composite metal pigment composition obtained to form a further coating layer.
[21]
A water-based paint comprising the composite metal pigment composition according to any one of [1] to [10].
[22]
A water-based paint comprising the composite metal pigment composition according to any one of [11] to [14].
[23]
A water-based paint comprising the composite metal pigment composition according to [15].
[24]
A method for producing a water-based paint, comprising using the composite metal pigment composition according to any one of [1] to [15].

According to the present invention, it is possible to obtain a novel composite metal pigment composition that has not been available in the prior art.
The composite metal pigment composition of the first invention of the present application effectively suppresses aggregation, deformation, etc. of composite particles, and when used in water-based paints, it can reduce the amount of volatile organic compounds (VOCs) in the paint, while achieving a high level of balance that exceeds the limits of conventional technology and provides excellent coating film properties such as storage stability, suppression of bumps, design properties, and hiding properties.
According to the manufacturing method of the second invention of the present application, it is possible to efficiently produce a composite metal pigment composition that effectively suppresses aggregation, deformation, etc. of composite particles, and when used in water-based paints, etc., reduces the amount of volatile organic compounds (VOCs) in the paint, while providing excellent coating film properties such as storage stability, suppression of bumps, designability, and hiding power at a high level that exceeds the limits of conventional technology.

The present invention will be described below with reference to typical or preferred embodiments, but the present invention is not limited to these embodiments. Unless otherwise specified, these embodiments can be freely combined within the scope of the present invention defined in the appended claims.

The first invention of the present application is a composite metal pigment composition comprising metal particles and composite particles having a metal oxide coating formed on the surface thereof,
(1) The composite particles have a scale-like shape,
(2) The composite particles have a volume-based average particle diameter _D50 of 1 to 30 μm when the particle size distribution of the composite particles is measured using a laser diffraction particle size distribution analyzer;
(3) The composite particles have an average particle thickness of 20 to 400 nm;
(4) The composite metal pigment composition has a volatile content of 70 to 95% by mass, and 50 to 100% by mass of the volatile content is water;
(5) The composite metal pigment composition has a volatile organic solvent content of 0 to 20 parts by mass per 100 parts by mass of solids,
(6) When the composite metal pigment composition is dispersed in water and filtered through a 200 mesh filter, the residue is 0.1 mass% or less of the solid content,
Preferably, (7) the above composite metal pigment composition, in which 200 g of an aqueous metallic paint containing 12 g of the metal pigment composition as a nonvolatile matter, 18 g of methoxypropanol, 110 g of an aqueous acrylic resin, 18 g of melamine resin, and 12 g of water is placed in a flask, and the cumulative amount of hydrogen gas generated is measured in a constant temperature water bath at 60°C for up to 24 hours, and the amount of gas generated is 20 ml or less.

Composite Particles Constituting the Composite Metal Pigment Composition The composite metal pigment composition according to the first invention of this application comprises composite particles having metal particles and a metal oxide coating formed on the surface thereof.
That is, in this specification, the term "composite metal pigment composition" contains, as essential components, composite particles having metal particles and a metal oxide coating formed on the surface thereof, and further contains specific non-solid components.
The composite metal pigment composition according to the first aspect of the present invention may contain other components, such as an organic treating agent, and a solvent including water and/or a hydrophilic solvent.

Metal Particles The composite particles constituting the composite metal pigment composition according to the first invention of the present application include metal particles and a metal oxide coating formed on the surface thereof. That is, one or more layers of metal oxide coating are formed on the surface of the metal particle that is the core of the composite particle. The metal oxide coating usually has a layered structure.

The material of the metal particles (core particles) constituting the composite particles is not particularly limited, and may be any metal known or commercially available metal pigment, such as aluminum, aluminum alloy, zinc, iron, magnesium, nickel, copper, silver, tin, chromium, stainless steel, etc. In this specification, the metal of the metal particles constituting the composite particles includes not only simple metals but also alloys and intermetallic compounds.
The metal particles may be used alone or in combination of two or more kinds.
The metal particles in the first aspect of the present invention preferably contain aluminum or an aluminum alloy, and more preferably are composed of 95 mass % or more of aluminum element.

The average particle size of the metal particles is not particularly limited, but is preferably an average particle size that can provide D ₅₀ in the particle size distribution of the composite particles described below. In other words, it is preferable to set the volume average particle size (D ₅₀ ) of the metal particles so that D ₅₀ is 1 to 30 μm when the volume distribution of the composite particles is measured using a laser diffraction particle size distribution meter, or so as to facilitate this.
The average particle size of the metal particles can be controlled in the process of grinding, sieving and filtering a raw atomized metal powder (e.g., aluminum powder) using a ball mill or the like by appropriately adjusting the particle size of the raw atomized metal powder, the mass per grinding ball when a ball mill is used, the rotation speed of the grinding device, the degree of sieving and filter pressing, etc.

Although there are no particular limitations on the thickness or shape of the metal particles, they are preferably scaly (flake-like) with an average particle thickness of 10-300 nm, which allows the composite particles constituting the composite metal pigment composition according to the first invention of the present application to easily have a scaly shape, so that high hiding power and the like can be more reliably obtained.
The average thickness of the metal particles is preferably a thickness that can provide the average thickness of the composite particles described below, specifically, 10-300 nm. This effectively suppresses aggregation and deformation of the composite particles, making it easy to achieve excellent design properties, gloss, suppression of bumps in the coating film, stability in water-based paint, etc. From the above viewpoints, the average thickness of the metal particles is preferably 15-250 nm, more preferably 20-200 nm.

Here, the average particle thickness of the metal particles can be measured by a method known in the art, for example, by forming a coating film using a metal pigment composition containing composite particles having metal particles and a metal oxide coating on the surface thereof, obtaining a FE-SEM image (field emission scanning electron microscope image) of the cross section, and analyzing the image. More specifically, it can be measured by the method described in the examples of this application.

The aspect ratio of the scaly metal particles (shape coefficient obtained by dividing the average particle size by the average thickness) is preferably 30 to 1500, more preferably 50 to 1000, and particularly preferably 80 to 700. By making the aspect ratio of the metal particles 30 or more, a higher sense of brilliance can be obtained. Furthermore, by making the aspect ratio of the metal particles 1500 or less, the mechanical strength of the flakes can be maintained and a stable color tone can be obtained.
The average thickness of the metal particles, like the volumetric _D50 , can be controlled by appropriately adjusting the particle size of the raw atomized metal powder (e.g., aluminum powder) in the process of grinding, sieving, and filtering the raw atomized metal powder using a ball mill or the like, the mass per grinding ball when a ball mill is used, the rotation speed of the grinding device, the degree of sieving and filter pressing, and the like.

The metal particles do not necessarily have to be composed of metal only, and as long as they do not impair the effects of the first invention of the present application, for example, synthetic resin particles, or inorganic particles such as mica or glass whose surfaces are coated with metal can also be used. In the first invention of the present application, it is preferable that the particles contain aluminum or an aluminum alloy, in particular because of their high weather resistance, low specific gravity, and ease of availability.

Particularly suitable metal particles constituting the composite particles are aluminum flakes, which are commonly used as metallic pigments. Aluminum flakes having the surface properties, particle size, and shape required for metallic pigments, such as surface gloss, whiteness, and brilliance, are suitable. Aluminum flakes are usually commercially available in a paste state. Paste-like aluminum flakes may be used as they are, or may be used after removing fatty acids and the like from the surface with an organic solvent or the like. Also usable is so-called aluminum vapor-deposited foil having a volume average particle size (D ₅₀ ) of 3 to 20 μm and an average thickness (t) of 10 to 110 nm.

Metal Oxide Coating The composite particles constituting the composite metal pigment composition of the first invention of this application have a metal oxide coating formed on the surface of the metal particles.
The metal oxide coating is a film composed of a layer containing a metal oxide, and may be formed on the entire surface of the metal particle surface or only on a part of the surface. From the viewpoints of water resistance and storage stability when used in a paint, it is preferable that the metal oxide coating is formed on the entire surface.
The metal oxide coating may be entirely composed of a metal oxide, or only a portion of the metal oxide coating may contain components other than the metal oxide.

The metal oxide constituting the metal oxide coating is a compound containing oxygen and at least one metal element as its constituent elements.
Therefore, the metal oxide may be a metal oxide in the narrow sense having only oxygen and at least one metal element as its constituent elements, but as long as it contains oxygen and at least one metal element as its constituent elements, it may also contain elements other than the oxygen and metal element as its constituent elements, such as a metal hydroxide, oxide hydrate, oxynitride, etc. Also, it may be a compound containing an organic group.
The metal oxide may be a so-called single oxide having only one type of metal element as a constituent element, or may be a composite oxide having two or more types of metal elements as constituent elements.
At least one metal element that constitutes the metal oxide may be a typical metal or a transition metal, or may be a so-called metalloid element. Among them, a metal oxide having silicon as a constituent element is particularly suitable as a metal oxide that constitutes the metal oxide coating.

Specific examples of suitable metal oxides constituting the metal oxide coating include silicon oxide, aluminum oxide, boron oxide, zirconium oxide, cerium oxide, iron oxide, titanium oxide, chromium oxide, tin oxide, molybdenum oxide, vanadium oxide, their oxide hydrates, their hydroxides, and mixtures thereof. Among these, silicon oxide, aluminum oxide, and mixtures thereof, as well as their oxide hydrates and hydroxides, are preferably used. Particularly preferably, silicon oxides such as silicon oxide, silicon hydroxide, and/or silicon oxide hydrate can be used.

The use of silicon oxide in the metal oxide coating is particularly advantageous from the standpoint of realizing good storage stability in aqueous paints, improving water resistance when formed into a coating film, and suppressing gas generation.
By using silicon oxide for the metal oxide coating, the metal oxide coating is usually a layer composed of a compound containing Si-O- bonds (siloxane bonds). Examples of such layers include layers containing at least one of silane-based compounds and silicon oxides. Examples of such compounds include silane-based compounds [H ₃ SiO(H ₂ SiO) _n SiH ₃ ] (where n is any positive integer), as well as silicon oxides represented by SiO ₂ , SiO _{2.nH 2} O (where n is any positive integer). These silane-based compounds and silicon oxides may be either crystalline or amorphous, but are particularly preferably amorphous. Therefore, as a layer containing silicon oxide (silica, etc.), a layer containing, for example, amorphous silica can also be suitably adopted.

The metal oxide coating using silicon oxide may be a layer formed using an organosilicon compound (including a silane coupling agent) as a starting material. In this case, the metal oxide coating may contain unreacted organosilicon compounds or components derived therefrom, as long as the effect of the first invention of the present application is not hindered. In a typical example of this case, the metal oxide coating may be formed by hydrolyzing the organosilicon compound.

When silicon oxide is used, the mass of the metal oxide coating is not particularly limited, but is preferably 1 to 20 parts by mass, and more preferably 2 to 15 parts by mass, per 100 parts by mass of the metal particles. By making the silicon content of the metal oxide coating 1 part by mass or more per 100 parts by mass of the metal particles, the corrosion resistance, water dispersibility, stability, etc. of the composite metal pigment composition can be maintained at a high level. By making the silicon content of the metal oxide coating 20 parts by mass or less per 100 parts by mass of the metal particles, aggregation of the composite particles and deterioration of the color tone such as hiding power and metallic luster can be prevented.

The metal oxide coating of the composite particles contained in the composite metal pigment composition according to the first invention of the present application is preferably particularly hydrophilic. The composite particles usually form a composite metal pigment composition in the form of being dispersed in an aqueous solvent (water or a mixed solvent containing water and an organic solvent), but if the metal oxide coating has a hydrophilic surface, the composite particles can be highly dispersed in such an aqueous solvent. Moreover, since metal oxides such as silicon oxides (amorphous silica, etc.) are very stable in aqueous solvents, a composite metal pigment containing composite particles that are highly stable in aqueous solvents can be provided. From this perspective, it is desirable that at least one layer, preferably the outermost layer, of the composite particles contained in the composite metal pigment composition according to the first invention of the present application is a metal oxide coating, and it is particularly desirable that the silicon compound-containing layer (particularly a layer composed of a compound containing Si-O bonds) is a metal oxide coating. Metal oxides also have excellent affinity with metal particles, so when a composite particle has a coating layer consisting of multiple layers, in addition to the outermost metal oxide coating, a metal oxide layer, particularly preferably a silicon compound-containing layer (particularly a Si-O-based coating layer), may be separately formed as a layer other than the outermost layer, particularly preferably a layer in contact with the metal particle.

The thickness of the metal oxide coating of each composite particle is not particularly limited, so long as the average particle thickness of the composite particles is in the range of 20 to 400 nm, as described below. The average thickness of the metal oxide coating is usually about 5 to 150 nm, particularly 10 to 100 nm, and preferably 20 to 70 nm. By having an average thickness of the metal oxide coating of 5 nm or more, a coating film having sufficient water resistance and suppressing the occurrence of corrosion or discoloration of the metal particles in the water-based paint can be obtained. On the other hand, by having an average thickness of the metal oxide coating of about 150 nm or less, the brightness, distinctness, and hiding power of the coating film can be maintained at a high level.

When the metal oxide coating of each composite particle contains a silicon compound-containing layer, the thickness of the silicon compound-containing layer is not particularly limited as long as the average thickness of the composite particles is in the range of 2 to 400 nm, as described below. From the viewpoint of exerting the function of the layer, the average thickness of the silicon compound-containing layer may usually be in the range of 5 to 150 nm, and is preferably in the range of 10 to 100 nm, and more preferably in the range of 20 to 70 nm.

Specific examples of the organosilicon compound that can be used in the present embodiment are described below, but the organosilicon compound is not limited to these specific examples.
The organosilicon compound may contain at least one organosilicon compound represented by the following general formula (1) and at least one selected from the group consisting of so-called silane coupling agents represented by any of the following general formulae (2), (3) and (4) and partial condensates thereof.

Si( ^OR1 ) ₄ ... (1)
(In the formula, R ¹ is a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms, and when there are two or more R ^1s , all of them may be the same, some of them may be the same, or all of them may be different.)
^R2mSi ( _OR3 ⁾ _4-m ... (2)
(In the formula, ^R2 is a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms which may optionally contain a halogen group, and ^R3 is a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. ^R2 and ^R3 may be the same or different, and when there are two or more ^R2s or ^R3s , they may all be the same, some may be the same, or all may be different. 1≦m≦3.)
R ⁴ _p R ⁵ _q Si(OR ⁶ ) _4-p-q ... (3)
(In the formula, R ⁴ is a group containing a reactive group capable of chemically bonding with another functional group, R ⁵ is a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms which may optionally contain a halogen group, and R ⁶ is a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. When there are two or more R ^{4 s} , R ^{5 s} , or R ^{6 s} , they may all be the same, some may be the same, or all may be different. 1≦p≦3, 0≦q≦2, and 1≦p+q≦3.)
R ⁷ _r SiCl _4-r ... (4)
(In the formula, ^R7 is a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms which may optionally contain a halogen group, and when there are two or more ^R7s , all of them may be the same, some of them may be the same, or all of them may be different. 0≦r≦3.)

Examples of the hydrocarbon group in R ¹ of formula (1) include methyl, ethyl, propyl, butyl, hexyl, octyl, etc., which may be branched or linear. Among these hydrocarbon groups, methyl, ethyl, propyl, and butyl are particularly preferred. In addition, the four R ¹ may all be the same, some may be the same, or all may be different.
Preferable examples of such organosilicon compounds of formula (1) include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, etc. Among these, tetraethoxysilane is particularly preferable.

Examples of the hydrocarbon group in ^R2 in formula (2) include methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, dodecyl, oleyl, stearyl, cyclohexyl, phenyl, benzyl, naphthyl, etc., which may be branched or linear, and may contain halogen groups such as fluorine, chlorine, and bromine. Among these, hydrocarbon groups having 1 to 18 carbon atoms are particularly preferred. In addition, when there are two or more ^R2s , they may all be the same, some may be the same, or all may be different. The number of ^R2s in the molecule in formula (2) is m=1 to 3, that is, 1 to 3, but it is more preferable that m=1 or 2.
Examples of the hydrocarbon group in ^R3 in formula (2) include methyl, ethyl, propyl, butyl, hexyl, octyl, etc., which may be branched or linear. Among these hydrocarbon groups, methyl, ethyl, propyl, and butyl are particularly preferred. In addition, when there are two or more ^R3s , they may all be the same, some may be the same, or all may be different.
Preferred examples of such an organosilicon compound (silane coupling agent) of formula (2) include methyltrimethoxysilane, methyltriethoxysilane, methyltributoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldibutoxysilane, trimethylmethoxysilane, trimethylethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, n-propyltributoxysilane, butyltrimethoxysilane, butyltriethoxysilane, butyltributoxysilane, dibutyldimethoxysilane, dibutyldiethoxysilane, dibutyldibutoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, dihexyldimethoxysilane, dihexyldiethoxysilane, octyltrimethoxysilane, octyltrimethoxysilane, octyltrimethoxysilane, octyltriethoxy ... ethoxysilane, dioctyldimethoxysilane, dioctyldiethoxysilane, dioctylethoxybutoxysilane, decyltrimethoxysilane, decyltriethoxysilane, didecyldimethoxysilane, didecyldiethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, dioctadecyldimethoxysilane, dioctadecyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, trifluoropropyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 3-chloropropyltributoxysilane, and the like.

Examples of the reactive group capable of chemically bonding with another functional group in ^R4 of formula (3) include a vinyl group, an epoxy group, a styryl group, a methacryloxy group, an acryloxy group, an amino group, a ureido group, a mercapto group, a polysulfide group, and an isocyanate group.
In addition, when there are two or more ^R4s , they may all be the same, some may be the same, or all may be different. The number of ^R4s in the molecule is p=1 to 3 in formula (3), that is, 1 to 3, and more preferably p=1.
Examples of the hydrocarbon group of ^R5 in formula (3) include methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, dodecyl, oleyl, stearyl, cyclohexyl, phenyl, benzyl, naphthyl, etc., which may be branched or straight-chain and may contain a halogen group such as fluorine, chlorine, or bromine. Among these, a hydrocarbon group having 1 to 18 carbon atoms is particularly preferred. When there are two or more ^R5s , they may all be the same, some may be the same, or all may be different.
Examples of the hydrocarbon group in R ⁶ of formula (3) include methyl, ethyl, propyl, butyl, hexyl, octyl, etc., which may be branched or linear. Among these hydrocarbon groups, methyl, ethyl, propyl, and butyl are particularly preferred. In addition, when there are two or more R ^6s , they may all be the same, some may be the same, or all may be different.

Preferred examples of such organosilicon compounds (silane coupling agents) of formula (3) include vinyltrimethoxysilane, vinyltriethoxysilane, vinyl-tris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-methyl-3-aminopropyl-trimethoxysilane, N-2-(aminoethyl)-3-amino Propylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, 3-ureidopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanatepropyltriethoxysilane, etc.

Examples of the hydrocarbon group in R ⁷ in formula (4) include methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, dodecyl, oleyl, stearyl, cyclohexyl, phenyl, benzyl, naphthyl, etc., which may be branched or linear, and may contain halogen groups such as fluorine, chlorine, and bromine. Among these, hydrocarbon groups having 1 to 12 carbon atoms are particularly preferred. In addition, when there are two or more R ^7s , they may all be the same, some may be the same, or all may be different. The number of R ^7s in the molecule in formula (4) is r=0 to 3, that is, 0 to 3, but it is more preferable that r=1 to 3.
Preferred examples of such organosilicon compounds (silane coupling agents) of formula (4) include methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, octyldimethylchlorosilane, phenyltrichlorosilane, vinyltrichlorosilane, and tetrachlorosilane.

The organosilicon compound represented by the above general formula (1) may be used alone or in combination of two or more. The silane coupling agent represented by any of the general formulas (2), (3), and (4) may be used alone or in combination of two or more. When using two or more in combination, only the silane coupling agent represented by any of the general formulas (2), (3), and (4) may be used in combination of two or more, or silane coupling agents represented by two or more different general formulas may be used in combination.

The hydrolysis product of the organosilicon compound and/or its condensation reaction product can be obtained by stirring and mixing the organosilicon compound with the amount of water required for the hydrolysis reaction and a hydrolysis catalyst. In this case, a hydrophilic solvent can also be used if necessary. The conditions for the hydrolysis reaction (i.e., the reaction for forming the silicon compound-containing layer) will be described later.

As a raw material for the hydrolysis and/or condensation reaction to obtain a hydrolysate of an organosilicon compound and/or a condensation product thereof, a partially condensed oligomer may be used.
The condensation reaction of the hydrolyzate of the organosilicon compound may be carried out simultaneously with the hydrolysis reaction of the organosilicon compound, or may be carried out in separate steps, and if necessary, using a different catalyst. In this case, heating may be performed as necessary.

Physical Properties of Composite Particles and Composite Metal Pigment Composition In the composite metal pigment composition according to the first aspect of the present invention, the composite particles constituting the composition satisfy the following physical property requirements.
(1) The composite particles have a scale-like shape.
(2) The volume-based average particle diameter _D50 of the composite particles is 1 to 30 μm when the particle size distribution of the composite particles is measured using a laser diffraction particle size distribution analyzer.
(3) The composite particles have an average particle thickness of 20 to 400 nm.
The composite metal pigment composition according to the first aspect of the present invention further satisfies the following requirements as a composition.
(4) The composite metal pigment composition has a volatile content of 20 to 90 mass %, and 50 to 100 mass % of the volatile content is water.
(5) The composite metal pigment composition has a volatile organic solvent content of 0 to 20 parts by mass per 100 parts by mass of the solid content.
(6) When the composite metal pigment composition is dispersed in water and filtered through a 200 mesh filter, the residue is 0.1 mass% or less of the solid content.
Preferably, (7) 200 g of an aqueous metallic paint containing 12 g of the metal pigment composition as a nonvolatile matter, 18 g of methoxypropanol, 110 g of an aqueous acrylic resin, 18 g of melamine resin, and 12 g of water is placed in a flask, and the cumulative amount of hydrogen gas generated is measured for up to 24 hours in a constant temperature water bath at 60°C; the amount of gas generated is 20 ml or less.

Each of these physical property requirements will now be described.

(1) The composite particles have a scale-like shape.
The composite particles contained in the composite metal pigment composition according to the first invention of the present application are scaly in shape. By containing the scaly composite particles, the composite metal pigment composition according to the first invention of the present application can effectively form a coating film having excellent properties such as high hiding power.
Scaly composite particles tend to be easily deformed during processes such as stirring, separation, and filtration during production, and are particularly prone to deformation due to strong centrifugation or filtration under strong pressure to increase the non-volatile (solid) content. However, in the present invention, deformation of the scaly composite particles can be effectively suppressed while achieving a high non-volatile (solid) content.

Here, the composite particle being scaly means that the particle has a shape having a high aspect ratio, preferably within the numerical range described below.
The scaly composite particles can be produced by using scaly metal particles as a raw material in the production of the composite particles. As such metal particles, for example, known or commercially available paste-like aluminum flakes can be used.

The scaly composite particles contained in the composite metal pigment composition according to the first invention of the present application preferably have an aspect ratio (shape coefficient obtained by dividing the average particle size by the average thickness) of 30 to 700. By having an aspect ratio of the composite particles of 30 or more, it becomes easier to obtain a higher sense of brilliance. Furthermore, by having an aspect ratio of the composite particles of 700 or less, the mechanical strength of the composite particles is maintained, making it easier to obtain a stable color tone. The aspect ratio is more preferably 50 to 600, and even more preferably 80 to 500.

(2) The volume-based average particle diameter _D50 is 1 to 30 μm when the particle size distribution of the composite particles is measured using a laser diffraction particle size distribution analyzer. The volume-based average particle diameter _D50 is 1 to 30 μm when the particle size distribution of the composite particles is measured using a laser diffraction particle size distribution analyzer. This effectively suppresses particle aggregation and deformation, and the coating film formed using the composite metal pigment composition or an aqueous paint containing the same can achieve excellent design, gloss, suppression of bumps, stability in the aqueous paint, etc. This volume-based _D50 is also generally referred to as the median diameter.
From the viewpoint of obtaining excellent design, gloss, suppression of bumps, stability in water-based paints, and the like, the volume-based _D50 when the particle size distribution of the composite particles is measured by a laser diffraction particle size distribution meter is preferably 2 to 25 μm, and particularly preferably 3 to 20 μm.
In the physical property requirements, the "composite particle" refers to an aggregate (aggregate) of multiple composite particles that are aggregated or adhered to each other.
Here, when the particle size distribution of the composite particles is measured by a laser diffraction particle size distribution analyzer, the volume-based _D50 refers to the particle size at a cumulative degree of 50% in the volume cumulative particle size distribution. The laser diffraction particle size distribution analyzer is not particularly limited, but an "LA-300" (manufactured by Horiba, Ltd.) or the like can be used. As the measurement solvent, a hydrophilic solvent such as water, isopropanol, or methoxypropanol can be used. For example, a composite metal pigment composition containing a sample composite particle can be subjected to ultrasonic dispersion for about 2 minutes as a pretreatment, and then the composite metal pigment composition can be placed in a dispersion tank to confirm that it has been properly dispersed, and then _D50 can be measured.
The volumetric _D50 of the composite particles constituting the composite metal pigment composition can be controlled, for example, by appropriately adjusting the particle size and charge amount of the raw atomized metal powder, the amount of the grinding solvent such as mineral spirits, the type and amount of the grinding aid, the mass and input amount per grinding ball when a ball mill is used, the rotation speed of the grinding device, the degree of sieving and filter pressing, etc. in the process of grinding, sieving and filtering the raw atomized metal powder (e.g., aluminum powder) using a ball mill or the like, and by appropriately adjusting the pH, concentration, stirring temperature, stirring time, type of stirring device, stirring power/degree (type and diameter of stirring blade, rotation speed, presence or absence of external stirring, etc.) during hydrolysis of the raw material such as an organosilicon compound in the process of coating with a metal oxide coating (and other coating layers as necessary).

(3) Average particle thickness of the composite particles is 20 to 400 nm The average thickness of the composite particles contained in the composite metal pigment composition according to the first invention of the present application is 20 to 400 nm. This, together with the satisfaction of the above requirements (1) and (2), effectively suppresses aggregation and deformation of the composite particles, and realizes excellent design properties, gloss, suppression of bumps, stability in water-based paints, etc. in the coating film.
From the above viewpoint, the average thickness of the composite particles is preferably 20 to 300 nm, and more preferably 20 to 250 nm.
In this physical property requirement, the "composite particle" refers to an aggregate (aggregate) when a plurality of composite particles are aggregated or adhered to each other.
The average thickness of the composite particles can be calculated by measuring the average particle thickness of the metal particles and the thickness of the metal oxide coating, and then using these values in accordance with the following formula:
Average particle thickness of composite particles = Average particle thickness of metal particles + Thickness of metal oxide coating x 2
The average particle thickness of the metal particles can be measured by the method described in (2) above.
The thickness of the metal oxide coating can be measured by a method known in the art, for example, by STEM (scanning transmission electron microscope). More specifically, it can be measured by the method described in the examples of the present application.
The average thickness of the composite particles contained in the composite metal pigment composition can be controlled, similarly to the volumetric standard D ₅₀ , by appropriately adjusting the pH, concentration, stirring temperature, stirring time, type of stirring device, stirring power/degree (type and diameter of stirring blade, rotation speed, presence or absence of external stirring, etc.) during the pretreatment of the raw material aluminum paste and the hydrolysis of the raw material such as the organosilicon compound in the process of processing the raw material metal powder, the process of coating with metal oxide coating such as a silicon compound-containing layer (and other coating layers as necessary), etc. In addition, the particle size tends to increase due to aggregation during the metal oxide coating treatment, but particle expansion leads to a decrease in color tone, a decrease in hiding power, and a decrease in the appearance of the coating film, so it is particularly effective to prevent particle expansion by pretreatment of the raw material aluminum paste used in the treatment.

(4) The composite metal pigment composition has a volatile content of 20 to 90 mass %, and 50 to 100 mass % of the volatile content is water.
The volatile content of the composite metal pigment composition according to the first aspect of the present invention is 20 to 90 mass %, and 50 to 100 mass % of the volatile content is water.
The composite metal pigment composition according to the first invention of the present application has a volatile content of 20 to 90% by mass, and 50 to 100% by mass of the volatile content is water, so that the paint can be made low in VOC (volatile organic compounds) while improving the handleability when preparing the paint and the dispersibility in the paint, and a paint that can form a coating film with a good appearance can be realized. More specifically, by having a volatile content of 90% by mass or less and a water content in the volatile content of 50% by mass or more, the content of VOCs such as solvents can be sufficiently reduced, so that even when a paint is formed using this, it is easy to realize a paint with a sufficiently reduced VOC content. On the other hand, by having a volatile content of 20% by mass or more, uniform dispersion when forming the paint can be easily achieved, and the occurrence of bumps in the coating film can be effectively suppressed.
The volatile content is preferably 25 to 80% by mass, more preferably 30 to 70% by mass, and particularly preferably 40 to 65% by mass. The water content in the volatile content is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and particularly preferably 90 to 100% by mass.

The volatile content of the composite metal pigment composition is the mass ratio of the volatile content contained in the composite metal pigment composition. The volatile content can be determined by heating a predetermined amount of the composite metal pigment composition to volatilize the volatile content, measuring the mass after the volatilization, calculating the mass reduced by the volatilization, and determining the ratio of the mass to the mass before heating. More specifically, it can be measured by, for example, the method described in the examples of this application.
The moisture content in the volatile matter can be determined by measuring the amount of volatile organic solvent contained in the volatile matter of the composite metal pigment composition by GC (gas chromatography) or LC (liquid chromatography), and calculating the difference between the volatile matter and the volatile organic solvent content.

The volatile content of the composite metal pigment composition can be appropriately adjusted by removing the volatile content of the solvent and the like used in dispersing the metal particles and forming the metal oxide coating during the production of the composite metal pigment composition by filtration, washing, volatilization, etc. The moisture content in the volatile content can be appropriately adjusted by adding water during dispersing the metal particles and forming the metal oxide coating during the production of the composite metal pigment composition, or by using or adding water during filtration and washing.

(5) The volatile organic solvent content of the composite metal pigment composition is 0 to 20 parts by mass per 100 parts by mass of the solid content. The volatile organic solvent content of the composite metal pigment composition according to the first invention of the present application is 0 to 20 parts by mass per 100 parts by mass of the solid content.
In the manufacture of a paint, the composite metal pigment composition is blended so that the solid content of the composite metal pigment composition is a predetermined amount in order to exhibit the performance as a pigment. Therefore, in order to reduce the VOC (volatile organic compounds) of the paint, it is necessary to reduce the volatile organic solvent content per solid content of the composite metal pigment composition to be blended, and it is necessary to make it 20 parts by mass or less per 100 parts by mass of the solid content. The volatile organic solvent content is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably 3 parts by mass or less.
In addition, the volatile organic solvent used in the present application is preferably a hydrophilic specific solvent in an amount of 80 mass% or more. Since the specific solvent is hydrophilic, by making the specific solvent account for 80 mass% or more of the volatile organic solvent, it becomes easy to disperse the composite metal pigment composition according to the first invention of the present application in water, and it becomes easier to form a uniform water-based paint.
The concept of a hydrophilic solvent is commonly understood among those skilled in the art, and for example, a solvent having a solubility in water of 20 g/g or more at room temperature can be preferably used as a hydrophilic solvent. Also, a solvent having an sp value (solubility parameter) of 10.5 or more can be preferably used as a hydrophilic solvent.

The specific solvent preferably accounts for 80 to 100% by mass, more preferably 85 to 100% by mass, and particularly preferably 90 to 100% by mass of the volatile organic solvent in the composite metal pigment composition.
The amount (ratio) of the specific solvent can be appropriately adjusted by adjusting the composition of the solvent used in the production of the composite metal pigment composition. The amount (ratio) of the specific solvent can usually be calculated from the amounts of various solvents used in the production of the composite metal pigment composition and the amounts of various solvents removed, but when the steps of filtration, volatilization, etc. during production are complicated and calculation is difficult, the solvent can be extracted from the obtained composite metal pigment composition with a solvent such as THF (tetrahydrofuran) and measured by LC-MS (liquid chromatography mass spectrometry) or the like.

Suitable examples of the specific solvent include methoxypropanol, isobutanol, normal butanol, isopropanol, and normal propanol.
These specific solvents may be used alone or in combination of two or more.
A metal pigment composition having the volatile content, solid content, moisture, filtration residue, and hydrogen gas generation amount specified in the first invention of the present application can be realized, for example, by adopting the manufacturing method of the second invention of the present application. As described below, it is essential to optimize the procedure and conditions of the coating treatment step so as to suppress corrosion and aggregation of the composite metal pigment, as well as the procedure and conditions of the steps of washing the composite particles, filtering, and replacing the solvent with water.

(6) When the composite metal pigment composition is dispersed in water and filtered through a 200 mesh filter, the residue is 0.1 mass% or less of the solid content.
When the composite metal pigment composition according to the first aspect of the present invention is dispersed in water and filtered through a 200 mesh filter, the residue is 0.1 mass % or less of the solid content.
Since the mesh size of a 200-mesh filter is approximately 74 μm, most composite particles having a volume-based average particle size _D50 of 1 to 30 μm and an average particle thickness of 20 to 400 nm will pass through a 200-mesh filter if there is no adhesion or aggregation between the particles. Therefore, the residue when a composite metal pigment composition is filtered through a 200-mesh filter is composite particles in which the particles are adhered to each other and aggregated, and it is preferable that the proportion of these particles in the solid content is low.
The composite metal pigment composition according to the first invention of the present application, when dispersed in water and filtered through a 200 mesh filter, leaves a residue of 0.1 mass% or less of the solid content, so that adhesion and aggregation of particles is effectively suppressed, and the composition can be dispersed in a solvent or water to form a paint in which aggregation is suppressed, and a coating film with excellent appearance can be formed in which bumps are effectively suppressed.
The amount of residue is preferably 0.05% by mass or less, more preferably 0.01% by mass or less, and particularly preferably 0.005% by mass or less, of the solid content.

The amount of the residue can be determined by thoroughly dispersing the composite metal pigment composition in water, filtering the composition through a 200 mesh filter, measuring the dry mass of the residue, and comparing this with the mass of the solid content in the initial composite metal pigment composition to determine the proportion of the residue in the solid content. More specifically, the amount can be determined by, for example, the method described in the examples of the present application.
The amount of residue remaining after filtration through a 200 mesh filter can be reduced by suppressing adhesion and aggregation of the composite particles by various methods described in the present specification. In particular, the use of the production method according to the second aspect of the present invention to effectively prevent aggregation and deformation of the composite particles while reducing the amount of volatile organic solvents is also effective in reducing the amount of residue.
(7) 200 g of an aqueous metallic paint containing 12 g of the metal pigment composition as nonvolatile matter, 18 g of methoxypropanol, 110 g of aqueous acrylic resin, 18 g of melamine resin, and 12 g of water was placed in a flask, and the cumulative amount of hydrogen gas generated was measured for 24 hours in a constant temperature water bath at 60°C; the amount of gas generated was 20 ml or less.
Preferably, 200 g of an aqueous metallic paint containing 12 g of the composite metal pigment composition according to the first invention of the present application as a non-volatile matter, 18 g of methoxypropanol, 110 g of an aqueous acrylic resin, 18 g of melamine resin, and 12 g of water is placed in a flask, and the cumulative amount of hydrogen gas generated is measured in a constant temperature water bath at 60°C for up to 24 hours; the amount of gas generated is 20 ml or less.
A gas generation of 20 ml means that the metal pigment is firmly covered with a metal oxide coating, which results in good storage stability of the paint and improved mechanical stability. The amount of gas generation is more preferably 15 ml or less, even more preferably 10 ml or less, and particularly preferably 5 ml or less. There is no lower limit, and the less the better. The method for preparing the water-based metallic paint and the method for measuring the amount of gas generation will be described in detail in the examples.

Preferred physical properties of composite particles, etc. In the composite metal pigment composition according to the first invention of the present application, the composite particles constituting the composition preferably have some or all of the following physical properties, characteristics, etc. in addition to the physical property requirements (1) to (7) above.

The proportion of non-aggregated primary particles in the composite particles is preferably 35% or more by number in the composite metal pigment composition according to the present embodiment. The proportion of non-aggregated primary particles in the entire composite particles contained in the composite metal pigment composition is preferably 35% or more by number. The proportion of primary particles being 35% or more means that the aggregation of individual particles is suppressed, and the degree of aggregation is smaller not only for primary particles but also for aggregated particles. This makes it easier for the coating film formed using the composite metal pigment composition to exhibit excellent design, gloss, and suppression of bumps, and to improve stability in water-based paints.
Furthermore, by suppressing the aggregation of the individual particles in this manner, only mild stirring is required for dispersion, and deformation of the particles due to stirring can be significantly reduced.

From the viewpoint of promoting the above-mentioned effect, the proportion of non-aggregated primary particles in the aggregate of composite particles is more preferably 40% or more, even more preferably 60% or more, and particularly preferably 80% or more, on a number basis.
Generally, the higher the ratio of the non-aggregated primary particles in the composite particles, the more preferable it is. There is no particular upper limit, and ideally, the ratio is 100%.
The proportion of non-aggregated primary particles in the composite particles can be measured by a method known in the art, for example, by forming a coating film using a metal pigment composition consisting of an aggregate of metal particles and composite particles having a metal oxide coating on the surface thereof, obtaining an FE-SEM image (field emission scanning electron microscope image) of the cross section, and analyzing the image, or by an evaluator counting the number of primary particles and aggregated particles in the FE-SEM image. More specifically, it can be measured, for example, by the method described in the examples of the present application.

The proportion of non-aggregated primary particles in the composite particles can be improved, for example, by employing the production method of the second aspect of the present invention.
In addition, it can be controlled by appropriately selecting and treating the metal particles constituting the composite particles, and by appropriately setting the type of metal oxide coating formed on the metal particles and the manufacturing conditions. As an existing technique, attempts have been made to strengthen mechanical dispersion by increasing the stirring rotation speed during the coating treatment and setting the Reynolds number to a certain value or more, but this method has limitations in dispersing fine particles such as those handled in this application, and there is a problem that thin, flaky particles are broken or deformed due to strong stress during stirring.
On the other hand, by subjecting the metal particles to a pretreatment to improve dispersibility before coating the metal particles with metal oxide, it is possible to suppress particle aggregation during the coating treatment, thereby significantly increasing the proportion of primary particles without aggregation.
For example, when the raw metal particles are supplied dispersed in a solvent, the aggregation that occurs during the coating process can be significantly suppressed by replacing the solvent with the same solvent as that used in the coating process, and then, if desired, by carrying out a heating process for a certain period of time to allow the solvent to fully blend with the metal particle surfaces. Furthermore, adding a small amount of a surfactant at this time is also effective in suppressing aggregation.

These treatments improve the dispersibility of the metal particles themselves, so there is no need for excessive stirring during the coating process, and primary particles without aggregation can be produced even with mild stirring. This makes it possible to significantly reduce deformation of particles during the coating process, making it easier to achieve excellent design properties, gloss, reduced bumps, and stability in water-based paints in the coating film.

In addition to the above, factors that affect the proportion of primary particles without agglomeration include the particle size of the raw atomized metal powder (e.g., aluminum powder) in the process of grinding, sieving, and filtering the raw atomized metal powder using a ball mill or the like, the mass per grinding ball when using a ball mill, the rotation speed of the grinding device, the degree of sieving and filter pressing, and the pH, concentration, stirring temperature, stirring time, type of stirring device, and stirring power/degree (type and diameter of stirring blades, rotation speed, presence or absence of external stirring, etc.) during hydrolysis of the raw material such as an organosilicon compound in the process of coating with an oxide metal coating (and other coating layers as necessary) such as a silicon compound-containing layer. By adjusting these appropriately, the proportion of primary particles without agglomeration can also be controlled.

The proportion of bent composite particles in the total composite particles is 10% or less on a number basis.
In the composite metal pigment composition according to the present embodiment, the proportion of bent composite particles in the total composite particles contained in the composite metal pigment composition is preferably 10% or less, which makes it easier for the coating film formed using the composite metal pigment composition to exhibit excellent design, gloss, and suppression of bumps, as well as to improve the stability in water-based paints.

The proportion of bent composite particles is understood to be an index related to the degree of deformation or damage of the composite particles. If the proportion of bent composite particles is 10% or less, the degree of deformation or damage of the composite particles is small, and the proportion of untreated surfaces (surfaces on which metal oxide coating is not formed) of each composite particle is small, thereby improving stability in water-based paints, and furthermore, it becomes easy to form a uniform and sufficient coating on each particle, which further reduces the cohesion of each particle, so that a coating film formed using the composite metal pigment composition can be obtained that shows excellent design, gloss, and suppression of bumps on the coating film surface.
The proportion of bent composite particles in the aggregate of composite particles is preferably as small as possible. This proportion is preferably 6% or less, more preferably 3% or less, and particularly preferably 1% or less. The proportion of bent composite particles is preferably as low as possible, and there is no particular lower limit, but it is ideally 0%.

The proportion of bent composite particles in a composite metal pigment composition can be measured by a method known in the art, for example, by forming a coating film using a metal pigment composition consisting of an aggregate of composite particles having metal particles and a metal oxide coating on the surface thereof, obtaining an FE-SEM image (field emission scanning electron microscope image) of the cross section, and analyzing the image. More specifically, particles in which the ratio of the straight-line distance between both ends of the cross section of the metal particle in the FE-SEM image to the path length between both ends along the cross section of the metal particle is 0.8 times or less are determined as bent particles, and the proportion of the number of such particles can be measured. More specifically, the proportion can be measured, for example, by the method described in the examples of the present application.
The proportion of bent composite particles in the total composite particles can be reduced, for example, by employing the production method of the second aspect of the present invention.
In addition, in the process of applying the metal oxide coating (and other coating layers as necessary), the amount of the raw aluminum paste can also be controlled by appropriately adjusting pretreatment for improving the dispersibility of the raw aluminum paste, the stirring time, the type of stirring device, the power/degree of stirring (type and diameter of stirring blades, number of revolutions, presence or absence of external stirring, etc.), etc.
Furthermore, by pretreating the raw aluminum paste, the dispersibility of the particles themselves during the reaction can be improved, so that only mild stirring is required for dispersion, significantly reducing deformation of the particles due to stirring.

Second Coating Layer: The coating layer of the composite particles contained in the composite metal pigment composition according to the first invention of the present application is not particularly limited other than that it has at least one metal oxide coating, but a coating layer other than the metal oxide coating (hereinafter referred to as the "second coating layer") can also be formed as necessary.
The second coating layer preferably contains at least one of metals (alkali metals; alkaline earth metals; manganese, iron, cobalt, nickel, copper, silver, etc.), metal oxides (titanium oxide, zirconium oxide, iron oxide, etc.), metal hydrates, and resins (acrylic resins, alkyd resins, polyester resins, polyurethane resins, polyvinyl acetate resins, nitrocellulose resins, fluororesins, and other synthetic resins). As the second coating layer, for example, a molybdenum-containing coating, a phosphate compound coating, etc. can be formed. By providing the second coating layer, the corrosion resistance of the metal particles can be improved and the formation of a metal oxide coating such as a silicon compound-containing layer can be promoted.

The second coating layer is preferably formed (if formed) between the metal particles and the metal oxide coating such as the silicon compound-containing layer. Therefore, for example, a layer structure of "metal particles/second coating layer/metal oxide coating" can be preferably adopted. Although not particularly limited, examples of molybdenum-containing coatings include those disclosed in JP 2003-147226 A, WO 2004/096921 A, Japanese Patent No. 5979788, and Japanese Patent No. 2019-151678 A. Examples of phosphate compound coatings include those disclosed in Japanese Patent No. 4633239. A preferred example of a molybdenum-containing material constituting a molybdenum-containing coating is a mixed coordination type heteropolyanion compound disclosed in JP 2019-151678 A.
In another variation, the second coating layer can be formed on the outside of the metal particles and the metal oxide coating, such as the silicon compound-containing layer. In yet another variation, the components of the second coating layer (such as the molybdenum-containing compound and the phosphate compound) can be included in the metal oxide coating, such as the silicon compound-containing layer, along with the silicon compound.

The mixed coordination heteropolyanion compound preferably used in the embodiment for forming a second coating layer (typically a molybdenum-containing coating) other than the metal oxide coating of the composite particles contained in the composite metal pigment composition according to the first invention of the present application is not particularly limited, but specific examples include the following.

The mixed coordination heteropolyanion of the mixed coordination heteropolyanion compound that can be used has a structure in which some of the polyatoms of a heteropolyanion made of one type of element are replaced with another element, and exhibits physical properties different from those of a mixture of the individual heteropolyanions.

When expressed by _{a chemical formula, if the mixed coordination heteropolyanion is expressed as [XpMqNrOs ] t} ^, the heteropolyanion _becomes [ _XpMqOs ] ^t , _and is further distinguished from the _isopolyanion [ _MqOs ] ^t . However, the heteroatom X represents an element of the IIIB, _IVB , or VB group such as B, Si, or Ge, P, or As, among which B, Si, or P is preferred. The polyatoms M and N represent transition metals such as Ti, Zr, V, Nb, Ta, Mo, or W, and Ti, Zr, V, Nb, Mo, or W is preferred.
Furthermore, p, q, r, and s represent the number of atoms, and t represents the oxidation number.
Since heteropolyanion compounds have many structures, mixed coordination type heteropolyanion compounds can have even more structures, but typical and preferred mixed coordination type heteropolyanion compounds include the following mixed coordination type heteropolyacids: H ₃ PW _x Mo _12-x O _{40.nH 2} O (phosphotungstomolybdic acid, n-hydrate), H _3+x PV _x Mo _12-x O _{40.nH 2} O (phosphovanadomolybdic acid, n-hydrate), H ₄ SiW _x Mo _12-x O _{40.nH 2} O (silicotungstomolybdic acid, n-hydrate), H _4+x SiV _x Mo _12-x O _{40.nH 2} O (silicovanadomolybdic acid, n-hydrate), etc. (where 1≦x≦11, n≧0).

Specific preferred examples of these heteropolyanion compounds include H ₃ PW ₃ Mo ₉ O _{40.nH 2} O, H ₃ PW ₆ Mo ₆ O _{40.nH 2} O, H ₃ PW ₉ Mo ₃ O _{40.nH 2} O, H ₄ PV ₁ Mo ₁₁ O _{40.nH 2} O, H ₆ PV ₃ Mo ₉ O _{40.nH 2} O, H ₄ SiW ₃ Mo ₉ O _{40.nH 2} O, H ₄ SiW ₆ Mo ₆ O _{40.nH 2} O, H ₄ SiW ₉ Mo ₃ O _{40.nH 2} O, H ₅ SiV ₁ Mo ₁₁ O _{40.nH 2} O, and H ₇ Examples of the heteropolyacid include mixed coordination type heteropolyacids such as SiV ₃ Mo ₉ O _{40.nH 2} O (where n≧0).
The mixed coordination heteropolyanion compound may be used in the form of an acid (so-called mixed coordination heteropolyacid) or in the form of a (partial or complete) salt having a specific cation as a counter ion.

When the mixed coordination heteropolyanion compound is used in the form of a salt having a specific cation as a counter ion, the counter cation source may be at least one selected from alkali metals such as lithium, sodium, potassium, rubidium, cesium, etc.; alkaline earth metals such as magnesium, calcium, strontium, barium, etc.; metals such as manganese, iron, cobalt, nickel, copper, zinc, silver, cadmium, lead, aluminum, etc.; inorganic components such as ammonia; and amine compounds which are organic components. Among the inorganic components, salts of alkali metals, alkaline earth metals, and ammonia are preferred.
Furthermore, when at least one selected from these alkali metals, alkaline earth metals, and ammonia is used as the counter cation source, it is more preferable to use it in the form of a salt with at least one selected from H ₃ PW _x Mo _{12-x O 40.nH 2} O (phosphotungstomolybdic acid, n- _hydrate ), H _3+x PV _x Mo _12-x O _{40.nH 2} O (phosphovanadomolybdic acid, n-hydrate), H ₄ SiW _x Mo 12-x O _{40.nH 2} O (silicotungstomolybdic acid, n-hydrate), and H _4+x SiV _x Mo _12-x O 40.nH ₂ O (silicovanadomolybdic acid, n-hydrate).

In addition, amine compounds, which are organic components, are also preferably used as a counter cation source for mixed coordination heteropolyanion compounds, and specific examples thereof include those represented by the following general formula (5).

(R ⁸ -N(-R ¹⁰ )-) _n -R ⁹ ... (5)
(wherein R ⁸ , R ⁹ and R ¹⁰ may be the same or different and are a hydrogen atom or a monovalent or divalent hydrocarbon group having 1 to 30 carbon atoms and optionally containing an ether bond, an ester bond, a hydroxyl group, a carbonyl group or a thiol group; optionally R ⁸ and R ⁹ may join together to form a 5- or 6-membered cycloalkyl group or a 5- or 6-membered ring which may additionally contain a nitrogen or oxygen atom as a bridging member; or optionally R ⁸ , R ⁹ and R ¹⁰ may join together to form a multi-membered multiple ring which may contain one or more additional nitrogen and/or oxygen atoms as bridging members. R ⁸ , R ⁹ and R ¹⁰ are not hydrogen atoms at the same time; and n represents an integer of 1 to 2.)

Examples of the amine compound that is a counter cation source for the mixed coordination heteropolyanion compound include linear or branched alkyl primary, secondary, or tertiary amines, tertiary amines having mixed hydrocarbon groups, alicyclic primary amines, primary amines having aromatic ring substituents, alicyclic secondary amines, secondary amines having aromatic ring substituents, asymmetric secondary amines, alicyclic tertiary amines, tertiary amines having aromatic ring substituents, amines having ether bonds, alkanolamines, diamines, cyclic amines, aromatic amines, etc., or any mixture thereof.

Among these amine compounds, a preferred specific example is at least one selected from primary, secondary, or tertiary amines or alkanolamines having 4 to 20 carbon atoms, such as butylamine, hexylamine, cyclohexylamine, octylamine, tridecylamine, stearylamine, dihexylamine, di-2-ethylhexylamine, linear or branched ditridecylamine, distearylamine, tributylamine, trioctylamine, linear or branched tritridecylamine, tristearylamine, N,N-dimethylethanolamine, N-methyldiethanolamine, triethanolamine, and morpholine.
It is more preferable to use at least one selected from the amine compounds represented by the general formula (5) in the form of a salt of at least one selected from H ₃ PW _x Mo ₁₂ -x O _{40.nH 2} O (phosphotungstomolybdic acid, n-hydrate), H _3+x PV _x Mo _12-x O _{40.nH 2} O (phosphovanadomolybdic acid, n-hydrate), H ₄ SiW _x Mo _12-x O _{40.nH 2} O (silicotungstomolybdic acid, n-hydrate), and H _4+x SiV _x Mo _12-x O _{40.nH 2} O (silicadomolybdic acid, n-hydrate).
Among the above mixed coordination type heteropolyanion compounds, the mixed coordination type heteropolyacids such as H ₃ PW _x Mo _12-x O _{40.nH 2} O (phosphotungstomolybdic acid, n-hydrate), H _3+x PV _x Mo _{12-x O 40.nH 2} O (phosphovanadomolybdic acid, n-hydrate) and H ₄ SiW _x Mo _12-x O _{40.nH 2} O (silicotungstomolybdic acid, n-hydrate) or organic amine salts of these mixed coordination type heteropolyacids are most preferred.

The second coating layer other than the metal oxide coating of the composite particle contained in the composite metal pigment composition according to this embodiment may be a layer containing another corrosion inhibitor in order to further improve the corrosion resistance of the core metal particle (preferably an aluminum particle or an aluminum alloy particle). The corrosion inhibitor to be added is not particularly limited, and any known corrosion inhibitor can be used. The amount used may be within a range that does not inhibit the desired effect of the first invention of this application. Examples of such corrosion inhibitors include acidic phosphate esters, dimer acids, organic phosphorus compounds, and metal salts of molybdic acid. In this case, it is also a preferred embodiment to form a second coating layer on the outermost layer of the composite metal pigment. In this way, it is possible to compensate for the corrosion resistance of parts where the effect of the metal oxide coating, such as the corrosion resistance, is low, that is, parts not covered by the coating layer or parts where the coating layer is thin or not dense.

The metal oxide coating and/or second coating layer of the composite particles contained in the composite metal pigment composition, or as a separate layer, may further contain an organic oligomer or polymer from the viewpoint of adhesion and chemical resistance when a coating film is formed.
In addition, from the viewpoint of storage stability, the metal oxide coating and/or the second coating layer of the composite particle, or as a separate layer, may contain at least one selected from the group consisting of inorganic phosphoric acids and their salts, and acidic organic (or acidic) phosphorous esters and their salts.
These compounds are not particularly limited, but for example, those disclosed in JP-A-2019-151678 can be used.

Composite metal pigment composition The composite metal pigment composition of the first invention of the present application comprises composite particles comprising metal particles and one or more layers of metal oxide coatings on the surfaces thereof, the composite particles satisfying the above requirements (1) to (3), and the composite metal pigment composition satisfying the above requirements (4) to (7). No other requirements are imposed on the composition. However, in addition to the composite particles, the composition may contain, as the residual solid content (non-volatile content), unreacted organosilicon compounds, compounds that form a second coating layer, oligomers or polymers derived from these, etc., and may also contain solvents used in the manufacturing process.
The composite metal pigment composition may contain a silicon compound which is a hydrolysate and/or a condensate of an organosilicon compound (for example, at least one organosilicon compound represented by the above general formula (1), at least one silane coupling agent represented by any one of the above general formulas (2), (3) and (4), and partial condensates thereof).
The composite metal pigment composition may contain a compound that forms an optional second coating layer (in the optional embodiment in which a molybdenum-containing coating is formed as the second coating layer, a molybdenum-containing compound, such as a mixed coordination heteropolyanion compound).
An optional organic oligomer or polymer may be present in the composite metal pigment composition.
In the composite metal pigment composition, at least one member selected from the group consisting of optional inorganic phosphoric acids and their salts, and acidic organic (phosphite) esters and their salts may be present.
Solvents, including water/hydrophilic solvents, used during the manufacturing process may be present in the composite metal pigment composition.

The composite metal pigment composition may optionally contain optional components other than those described above. Examples of optional components include at least one of an antioxidant, a light stabilizer, and a surfactant.

Antioxidants that can be used include phenolic compounds, phosphorus compounds, and sulfur compounds.

As light stabilizers, those used as antioxidants as mentioned above can be used, but representative examples that can be used include benzotriazole compounds, benzophenone compounds, salicylate compounds, cyanoacrylates, oxalic acid derivatives, hindered amine compounds (HALS), and hindered phenol compounds.

Examples of surfactants include nonionic surfactants such as polyoxyalkylene alkyl ethers, polyoxyalkylene alkylphenyl ethers, polyoxyalkylene alkylamino ethers, sorbitan fatty acid esters, polyoxyalkylene sorbitan fatty acid esters, polyalkylene glycol fatty acid esters, and glycerin fatty acid esters; anionic surfactants such as sulfate ester salts, sulfonate salts, and phosphate ester salts; and cationic surfactants such as quaternary ammonium salts. One or more of these surfactants may be used. Particularly preferred examples of these surfactants include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, or mixtures thereof.

Manufacturing method of composite metal pigment composition There is no particular limitation on the manufacturing method of the composite metal pigment composition according to the first invention of the present application, but it is particularly preferable to manufacture it by the manufacturing method of the second invention of the present application. The manufacturing method of the second invention of the present application is particularly suitable for manufacturing the composite metal pigment composition according to the first invention of the present application, since it can manufacture a composite metal pigment composition having an appropriate volatile matter concentration and a low volatile organic solvent content while effectively suppressing the aggregation and deformation of the composite particles.
The application of the production method of the second invention of the present application is not limited to the production of the composite metal pigment composition of the first invention of the present application, but can be suitably used for the production of various composite metal pigment compositions.

The manufacturing method of the second aspect of the present invention is as follows:
A method for producing a composite metal pigment composition comprising the following steps 1) to 3):
1) a step of dispersing metal particles in a solvent; 2) a step of coating the metal particles with a metal oxide; and 3) a step of washing and filtering the composite particles having the metal particles and the metal oxide coating formed on the surfaces thereof obtained in step 2), and replacing the solvent with water. Step 3) is carried out at 5 to 80° C. and in a state in which the solid content is 80 mass % or less.
Alternatively, the production method of the second aspect of the present invention includes the steps of:
A method for producing a composite metal pigment composition comprising the following steps 1) to 3):
1) a step of dispersing metal particles in a solvent; 2) a step of coating the metal particles with a metal oxide; and 3) a step of washing and filtering the composite particles having the metal particles and the metal oxide coating formed on the surfaces thereof obtained in step 2), and replacing the solvent with water. The above-mentioned production method is characterized in that step 3) comprises filtering the treatment liquid obtained in step 2) to reduce the volatile content to 70% by weight or less, followed by washing, filtering, and replacing the organic solvent with water.
It is also.

In step 1), metal particles are dispersed in a solvent . By dispersing the metal particles in the solvent, it becomes easier to suppress particle aggregation in the subsequent step 2), in which the metal particles are coated with a metal oxide. As a result, the dispersibility of the resulting composite particles is also good, and the proportion of primary particles without aggregation can be significantly increased.
The method for dispersing the metal particles in the solvent is not particularly limited, but a method such as adding the metal particles to the solvent and then stirring or irradiating with ultrasonic waves is preferably employed.
It is also preferable to carry out a pretreatment in order to improve the dispersibility of the metal particles.

Stirring can be performed using a known or commercially available stirring device. For example, at least one of a kneader, a kneading machine, a rotary vessel stirrer, a stirred reaction tank, a V-shaped stirrer, a double cone stirrer, a screw mixer, a sigma mixer, a flash mixer, an airflow stirrer, a ball mill, an edge runner, etc. can be used.

Among these agitators, it is preferable to use a device that uses an agitating blade (impeller). The agitating blade exerts a circulation effect that causes the entire system containing the metal particles and solvent to flow, as well as a pressure shear effect, which results in more effective dispersion by suppressing aggregation of the metal particles.

The shape of the impeller is not particularly limited, and for example, anchor type, propeller type, turbine type, fan turbine type, paddle type, inclined paddle type, and gate type can be used. In addition, impellers of these shapes can be combined in multiple stages.

The stirring speed is preferably set at a level that does not expose the stirring blades due to vortexes generated by stirring. In addition, a cylindrical tank, a square tank, or a tank equipped with baffles can be suitably used to suppress vortexes generated by stirring.

The linear stirring speed (tip speed of the stirring blade) is preferably 0.5 to 30 m/s, and more preferably 1 to 20 m/s. By having the linear stirring speed in the range of 0.5 to 30 m/s, the dispersibility of the metal particles can be increased, and it becomes easier to obtain a composite metal pigment composition with less aggregation of individual particles, excellent design, gloss, and coating appearance, and little gas generation. In addition, by having the linear stirring speed in the above range, damage to the metal particles (e.g., scaly aluminum powder) can be prevented, and particle aggregation can be effectively suppressed.

The ultrasonic treatment is not particularly limited, but can be performed usually at 10 to 1000 W, preferably 50 to 800 W, for usually 20 seconds to 10 minutes, preferably 30 seconds to 5 minutes.

In the pretreatment, for example, when the raw metal particles are supplied dispersed in an inert solvent, the solvent can be replaced with the same solvent used in the coating treatment. If desired, a heating treatment can be performed for a certain period of time to allow the solvent to fully blend with the metal particle surface, thereby greatly suppressing the aggregation that occurs in the step 2) of coating the metal particles with a metal oxide. The heat treatment temperature is preferably about 30 to 60°C, and the treatment time is preferably optimized between 3 hours and 7 days. Since hydrophilic solvents such as ethanol, isopropanol, and methoxypropanol are preferably used in the coating treatment step, the same hydrophilic solvent as that used in the reaction is preferably used in the pretreatment.
Furthermore, adding a small amount of a surfactant at this time is also effective in suppressing aggregation due to the pretreatment. The surfactant is not particularly limited, but nonionic surfactants and anionic surfactants are preferred, and the use of nonionic surfactants is particularly preferred.

1) The process of dispersing metal particles in a solvent can be carried out usually at 10 to 80°C, preferably 15 to 70°C, and most preferably at around room temperature (about 20 to 60°C). In addition, 1) the process of dispersing metal particles in a solvent can be carried out for 5 minutes to 20 hours, preferably 10 minutes to 5 hours (including ultrasonic treatment if performed).

2) Step of Coating Metal Particles with Metal Oxide By carrying out the step 2) of coating metal particles with metal oxide following the step 1) of dispersing metal particles in a solvent, a metal oxide coating can be formed on the metal particles.
As described above, it is preferable to use silicon oxide for the metal oxide coating. Therefore, hereinafter, the step of forming a silicon compound-containing layer will be described as a specific example of step 2) taking as an example an embodiment in which at least one layer in the metal oxide coating is a silicon compound-containing layer.

Formation process of silicon compound-containing layer In the formation process of the silicon compound-containing layer, for example, a mixed liquid containing metal particles, a silicon-containing raw material containing at least one type of organosilicon compound, a solvent, and other optional components as necessary is reacted to form the silicon compound-containing layer.
Since the metal particles are dispersed in a solvent in step 1), a silicon-containing raw material is usually added to this in step 2).

As the metal particles, the above-mentioned metal particles can be used, but aluminum or aluminum alloy particles are particularly suitable. As for the particle shape, as described above, it is preferable to use flake-like metal particles. As the metal particles, publicly known or commercially available ones (typically paste-like aluminum flakes) can be used.

The content (solid content) of metal particles in the above mixed liquid is not particularly limited and can be set appropriately depending on the type, particle size, etc. of the metal particles used.

As the silicon-containing raw material, an organosilicon compound can be used. The organosilicon compound is not limited, but preferably, the above-mentioned compounds can be used.
At least one of the organosilicon compounds represented by the above formula (1) (a typical example is tetraalkoxysilane) and/or condensates thereof, and the silane coupling agents represented by any of the above formulas (2) to (4) can be suitably used.
Hereinafter, an example will be described in which tetraalkoxysilane is used as the organosilicon compound represented by the above formula (1). In the following, tetraalkoxysilane and/or its condensate may be collectively referred to simply as "tetraalkoxysilane."

When using a tetraalkoxysilane represented by the above formula (1) in combination with a silane coupling agent represented by any one of the above formulas (2) to (4), a method of using a mixture of the two (referred to as the "first method") can be adopted. Alternatively, a method including a step of treating metal particles with one agent to form a first silicon compound-containing layer, and treating the metal particles with the other agent to form a second silicon compound-containing layer (referred to as the "second method") can also be adopted.

The first method includes, for example, a method including a step of forming a silicon compound-containing layer by appropriately adjusting the pH of a mixture containing metal particles, a tetraalkoxysilane represented by the above formula (1), and a silane coupling agent represented by any one of the above formulas (2) to (4), thereby causing a hydrolysis/condensation reaction of the tetraalkoxysilane and the silane coupling agent.

The second method includes, for example, a step of forming a first silicon compound-containing layer (e.g., a silica coating made of amorphous silica) on the surface of the metal particles by appropriately adjusting the pH of a mixed solution containing metal particles and a tetraalkoxysilane represented by the above formula (1) to cause a hydrolysis/condensation reaction of the tetraalkoxysilane, and a step of forming a second silicon compound-containing layer on the surface of the first silicon compound-containing layer by adjusting the pH of a mixed solution containing metal particles and a silane coupling agent represented by any one of the above formulas (2) to (4) to cause a hydrolysis/condensation reaction of the silane coupling agent.

The amount of the tetraalkoxysilane or condensate thereof represented by the above formula (1) used can be appropriately set depending on the type of tetraalkoxysilane used. For example, from the viewpoint of the coating treatment effect and from the viewpoint of suppressing aggregation of metal particles or reduction in brilliance, the amount used may be 2 to 200 parts by mass, and more preferably 5 to 100 parts by mass, per 100 parts by mass of metal particles (solid content).

The amount of the silane coupling agent represented by any of the above formulas (2) to (4) used is not particularly limited, but may usually be about 0.1 to 20 parts by mass, and preferably 1 to 5 parts by mass, per 100 parts by mass of metal particles (solid content). By using an amount of about 0.1 to 20 parts by mass, it is possible to obtain the desired coating treatment effect and desirable coating film properties.

The solvent in the mixed solution, i.e., the solvent for the hydrolysis reaction and/or condensation reaction of the organosilicon compound, may be appropriately selected depending on the type of silicon-containing raw material used, but typically water, a hydrophilic organic solvent, or a mixed solvent thereof can be used. By using these solvents, the uniformity of the reaction and the uniformity of the resulting hydrolysis product and/or condensation reaction product can be improved. In the embodiment in which the silicon compound-containing layer is formed directly on the metal particles, it is particularly preferable that the solvent of the mixed solution contains a hydrophilic organic solvent from the viewpoint of avoiding the reaction between the metal particles and water from proceeding too rapidly. In this embodiment, a mixed solvent of water and a hydrophilic organic solvent can be preferably used.

Examples of hydrophilic organic solvents include, but are not limited to, alcohols such as methanol, ethanol, propanol, butanol, isopropanol, and octanol; ether alcohols and esters thereof such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monoethyl ether, propylene glycol monomethyl ether, and dipropylene glycol monomethyl ether; glycols such as ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, polyoxyethylene glycol, polyoxypropylene glycol, and ethylene propylene glycol; ethyl cellosolve, butyl cellosolve, acetone, methoxypropanol, ethoxypropanol, and other alkoxy alcohols. These can be used alone or in combination of two or more.

The amount of solvent used in the silicon compound-containing layer formation process (excluding the amount of solvent used when pre-dispersing metal particles) is not limited, but is usually about 100 to 10,000 parts by mass per 100 parts by mass of metal particles (solid content), and is preferably 200 to 2,000 parts by mass. By using an amount of solvent of 100 parts by mass or more, the increase in viscosity of the mixed liquid (slurry) is suppressed, and appropriate stirring is possible. In addition, by using an amount of solvent of 10,000 parts by mass or less, the recovery and regeneration costs of the treatment liquid can be prevented from becoming high. Note that the amount of solvent used here refers to the total amount of solvent used for forming the first silicon compound-containing layer and the second silicon compound-containing layer in the case of the second method described above.

The above mixture may contain other additives as necessary within the range that does not impair the effects of the first invention of the present application. Examples of such additives include catalysts such as hydrolysis catalysts and dehydration condensation catalysts, as well as surfactants and metal corrosion inhibitors.

Among these, a hydrolysis catalyst can be preferably used. By adding a hydrolysis catalyst, the pH of the mixed liquid can be adjusted and the organosilicon compound can be efficiently hydrolyzed and dehydrated and condensed, and as a result, a silicon compound-containing layer can be efficiently and reliably formed on the surface of the metal particles.

The hydrolysis catalyst is not particularly limited and may be a known or commercially available one. Examples of the hydrolysis catalyst that can be used include inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid; organic acids such as benzoic acid, acetic acid, chloroacetic acid, salicylic acid, oxalic acid, picric acid, phthalic acid, and malonic acid; and phosphonic acids such as vinylphosphonic acid, 2-carboxyethanephosphonic acid, 2-aminoethanephosphonic acid, and octanephosphonic acid. These hydrolysis catalysts may be used alone or in combination of two or more.
Examples of the hydrolysis catalyst that can be used include inorganic alkalis such as ammonia, sodium hydroxide, and potassium hydroxide; inorganic alkali salts such as ammonium carbonate, ammonium hydrogen carbonate, sodium carbonate, and sodium hydrogen carbonate; amines such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, N,N-dimethylethanolamine, ethylenediamine, pyridine, aniline, choline, tetramethylammonium hydroxide, and guanidine; and salts of organic acids such as ammonium formate, ammonium acetate, monomethylamine formate, dimethylamine acetate, pyridine lactate, guanidinoacetic acid, and aniline acetate. These hydrolysis catalysts can be used alone or in combination of two or more.

The amount of hydrolysis catalyst added is not particularly limited, but is usually 0.01 to 20 parts by mass per 100 parts by mass of metal particles (solid content), and is preferably 0.02 to 10 parts by mass. When the amount added is 0.01 parts by mass or more, the amount of deposition of the silicon compound-containing layer can be sufficient. Also, when the amount added is 20 parts by mass or less, aggregation of the metal particles can be effectively suppressed.

In the production of the composite metal pigment composition according to the first aspect of the present invention, the preparation of the mixture is preferably carried out under stirring at an appropriate intensity.
The temperature of the mixed solution may be either room temperature or heated. In general, the temperature of the mixed solution may be 20 to 90°C, and is preferably controlled in the range of 30 to 80°C. When the temperature is 20°C or higher, the formation rate of the silicon compound-containing layer can be increased and the processing time can be shortened. On the other hand, when the temperature is 90°C or lower, the reaction can be easily controlled and the probability of obtaining the desired composite particles can be increased.

The agitator for agitating the mixture is not particularly limited, and any known agitator capable of efficiently and uniformly agitating the mixture containing aluminum particles and an organosilicon compound can be used. Specific examples include kneaders, mixers, rotary vessel agitators, stirred reaction tanks, V-type agitators, double cone agitators, screw mixers, sigma mixers, flash mixers, airflow agitators, ball mills, edge runners, etc.

The temperature of the mixed liquid containing the metal particles and the organosilicon compound when stirring is usually about 10 to 90°C, and preferably 30 to 80°C. By keeping this temperature at 10°C or higher, the reaction time required to obtain a sufficient treatment effect can be shortened. Also, by keeping this temperature at 90°C or lower, it becomes easier to control the reaction to obtain the desired composite metal pigment composition.

The stirring time of the mixed solution is not particularly limited as long as it is sufficient to form the desired silicon compound-containing layer. For example, this stirring time is preferably 0.5 to 10 hours, and more preferably 1 to 5 hours. By setting the stirring time to 0.5 hours, a sufficient treatment effect can be obtained. Furthermore, by setting the stirring time to 10 hours or less, an increase in treatment costs can be suppressed.

In the above-mentioned mixed solution, the silicon-containing raw material is subjected to a hydrolysis/condensation reaction to form a silicon compound-containing layer on the surface of the metal particles (or via the second coating layer). This hydrolysis/condensation reaction can be carried out by, in particular, adjusting the pH of the mixed solution.

When adjusting the pH, the pH value of the mixed solution changes, particularly at the stage where the silicon compound-containing layer is formed on the metal particle surface (or via the second coating layer), so it is desirable to adjust the pH value appropriately so that it remains within a certain range. In this case, it is desirable to adjust the pH value by adding a hydrolysis catalyst, but the pH value may also be adjusted using other acidic or alkaline compounds as long as this does not impair the properties of the composite metal pigment composition according to the first invention of this application.

When a basic hydrolysis catalyst is used as the hydrolysis catalyst, the pH value is preferably 7 to 13. A pH value of 7 or more allows the silicon compound-containing layer to be formed quickly. On the other hand, a pH value of 13 or less can suppress the aggregation of metal particles and the decrease in brilliance, and can prevent the generation of hydrogen gas due to corrosion.

When an acidic hydrolysis catalyst is used as the hydrolysis catalyst, the pH value is preferably 1.5 to 7, and more preferably 2 to 6. A pH value of 1.5 or more allows the reaction to be appropriately controlled, making it easier to obtain a composite metal pigment composition containing the desired composite particles. On the other hand, a pH value of 7 or less allows the deposition rate of the silicon compound-containing layer to be maintained high.

Regardless of whether the first or second method is used, the hydrolyzate and/or condensate of the organosilicon compound represented by the general formula (1) is preferably added in an amount of 0.01 to 50 parts by mass, more preferably 1 to 30 parts by mass, based on the state after the hydrolysis and condensation reaction is completed, based on 100 parts by mass of the metal particles (solid content). In addition, the hydrolyzate and/or condensate derived from the silane coupling agent represented by any of the general formulas (2) to (4) and/or their partial condensates is/are added in an amount of 0.01 to 10 parts by mass, more preferably 0.05 to 2 parts by mass, based on the state after the hydrolysis and condensation reaction is completed, based on 100 parts by mass of the metal particles (solid content).

The amount of the hydrolysate and/or condensate of the organosilicon compound represented by general formula (1) to be added can be calculated by multiplying the mass of the organosilicon compound represented by general formula (1) used in the production of the composite metal pigment composition by the mass ratio before and after the reaction when the organosilicon compound is completely hydrolyzed and subjected to a condensation reaction.
For example, when tetraethoxysilane (TEOS) is used as the organosilicon compound represented by general formula (1), the amount of hydrolyzate of the organosilicon compound and/or its condensate to be added can be calculated using the mass ratio before and after the hydrolysis and condensation reactions described below.
(Hydrolysis)
Si( _OC2H5 ) ₄ (molecular weight: ₂₀₈ ) + _4H2O
→ Si(OH) ₄ (molecular weight: ₉₆ ) + ( _C2H5OH ) ₄
(Condensation)
Si(OH) ₄ (molecular weight: 96) + Si(OH) ₄ (molecular weight: 96)
→ ( _SiO2 ) ₂ (molecular weight: 60 x 2) + _4H2O
The mass before and after the above hydrolysis and condensation reactions is 60/208 = 0.288 times, so for example, when 10 parts by mass of TEOS is used per 100 parts by mass of metal particles (solid content), the amount of the hydrolysate and/or condensate added will be 0.288 times that amount, or 2.88 parts by mass.

Similarly, the amount of hydrolysate and/or condensate thereof of a silane coupling agent represented by any one of general formulas (2) to (4) added can be calculated by multiplying the mass of the silane coupling agent represented by any one of general formulas (2) to (4) and/or its partial condensate used in the production of the composite metal pigment composition by the mass ratio before and after the reaction when the silane coupling agent and/or its partial condensate are all hydrolyzed and subjected to a condensation reaction.
For example, when methyltrimethoxysilane is used as the silane coupling agent represented by the general formula (2), the amount of the hydrolyzate and/or condensate of the silane coupling agent to be added can be calculated using the mass ratio before and after the hydrolysis and condensation reactions described below.
(Hydrolysis)
_CH3Si ( _OCH3 ) ₃ (molecular weight: 136) + _3H2O
→ _CH3Si (OH) ₃ (molecular weight: 94) + ( _CH3OH ) ₃
(Condensation)
_CH3Si (OH) ₃ (molecular weight: 94) + _CH3Si (OH) ₃ (molecular weight: 94)
→ ( _SiCH3O1.5 ) ₂ (molecular weight: 67 _x 2) + _3H2O
The mass before and after the above hydrolysis/condensation reaction is 67/136 = 0.49 times. Therefore, for example, if 1.23 parts by mass of methyltrimethoxysilane is used per 100 parts by mass of metal particles (solid content), the amount of the hydrolyzate and/or condensate added will be 0.49 times that amount, or 0.60 parts by mass.

3) Step of washing the composite particles, filtering, and replacing the organic solvent with water After the step 2) of coating the metal particles with a metal oxide is completed, the composite particles obtained can be recovered to obtain the desired composite metal pigment composition, and the step 3) of washing the composite particles, filtering, and replacing the organic solvent with water can be carried out.
In producing the composite metal pigment composition of the first invention of the present application, it is not essential to carry out step 3), but it is preferable to carry it out.
The mixed liquid obtained in step 2) contains the coated composite particles, the solvent (volatile matter), and impurities such as reaction residues and catalysts. In the method for producing a composite metal pigment composition of the second invention of the present application, in order to remove the impurities and adjust the volatile matter and water ratios to predetermined values, the mixed liquid obtained in step 2) is washed and filtered, and the organic solvent is replaced with water in step 3).
In the above step 3), it is essential to suppress the aggregation and deformation of the composite particles. To this end, step 3) needs to be carried out with the temperature of the treatment liquid at 5 to 80°C and the solid content of the treatment liquid at 80% by mass or less. By setting the temperature at 5°C or more, the solubility of impurities in the solvent increases and the viscosity decreases, making cleaning easier. By setting the temperature at 80°C or less and the solid content at 80% by mass or less, the aggregation and deformation of the metal particles can be suppressed. The temperature of the treatment liquid is preferably 10 to 75°C, more preferably 15 to 70°C. The solid content is preferably 75% by mass or less, more preferably 70% by mass or less.
The pH value of the treatment solution used in carrying out the above step 3) is preferably 1.5 to 13, more preferably 3 to 13, and even more preferably 5 to 12. By setting the pH within this range, corrosion and aggregation of metal particles can be easily suppressed.
The step 3) includes the case where the washing, filtration, and the operation for replacing the organic solvent with water are carried out independently, or the case where a plurality of operations are carried out simultaneously. The order of carrying out each operation can be appropriately selected, and includes the case where each operation is carried out multiple times.

The washing in step 3) can be carried out by a method commonly used in the art, for example, the slurry or cake containing the composite particles obtained in step 2) can be washed with an organic solvent or water. By washing, unreacted substances, solvents that are undesirable in the final composite metal pigment composition, etc. can be removed from the slurry, cake, etc. containing the composite particles.
In washing, it is preferable to stir the composite metal pigment in a container in order to increase the frequency of contact between the washing liquid and the composite metal pigment, or to run the washing liquid through a filtering device to perform washing simultaneously with filtration. There are no particular limitations on the conditions for stirring, but for example, the same conditions as those described above in relation to step 1) can be adopted. In addition, when performing washing simultaneously with filtration, one preferable example is to use a Nutsche type filter or the like and run the washing liquid continuously or intermittently to perform washing.
The temperature during washing in step 3) is 5 to 80° C., preferably 10 to 75° C., and more preferably 15 to 70° C. The washing time is not particularly limited, but it can usually be carried out for 5 to 180 minutes, and preferably 10 to 120 minutes.

In the washing, it is preferable to use a hydrophilic organic solvent and water for the purpose of removing impurities and the solvent used in the previous steps, and for convenience when using the composite metal pigment composition in a water-based paint later. A hydrophilic organic solvent having a boiling point of 80 to 150°C is particularly preferable, and washing with such an organic solvent makes it easier to satisfy the requirement (4) in the first invention of the present application that the volatile content of the composite metal pigment composition is 20 to 90 mass% and that 50 to 100 mass% of the volatile content is water, and makes it easier to obtain a paint with excellent color tone. Preferred examples of hydrophilic solvents having a boiling point of 80 to 150°C include methoxypropanol, isopropanol, isobutanol, normal butanol, normal propanol, etc.
There is no particular limit to the amount of washing liquid used for washing, and it is usually preferable to use 0.5 to 10 times the amount of the composite particles. There is no particular limit to the number of washings, and washing may be performed only once, but it is preferable to wash multiple times, for example, 2 to 5 times. When washing multiple times, it is also preferable to alternate between washing and filtration.

The filtration in step 3) can be carried out by a method commonly used in this technical field. For example, a polypropylene filter cloth having an air permeability of usually 10 to 100 ml/cm ² /min, preferably 20 to 80 ml/cm ² /min, a metal filter, a glass filter, a ceramic filter, or the like having an equivalent mesh size can be used to carry out filtration by suction filtration or pressure filtration using a Nutsche type filter, or a method such as a filter press, a belt press, or a centrifugal filter can be appropriately adopted. By carrying out the filtration, unreacted substances and solvents that are undesirable in the final composite metal pigment composition can be removed from the composite particles obtained in step 2).
The temperature and pressure of the filtration in step 3) are not particularly limited, but when a Nutsche type filter is used, the temperature is 5 to 80° C., preferably 10 to 90° C., and more preferably 15 to 80° C. The pressure is usually 0.11 to 0.9 MPa, and preferably 0.15 to 0.5 MPa.
The solid content of the filtered slurry, cake, etc. containing the composite particles must be 80% by mass or less, preferably 75% by mass or less, and more preferably 70% by mass or less.
From the viewpoint of improving the washing efficiency, it is preferable that the solid content of the slurry, cake, etc. containing the composite particles after filtration is high. To achieve this, the pressure during filtration can be set high. However, since high pressure during filtration may cause aggregation or deformation of the composite particles, it is preferable to set the pressure taking this point into consideration.

Furthermore, filtration may be appropriately combined with a solid-liquid separation method other than filtration, such as centrifugation or decantation.
There is no particular limit to the number of times filtration is performed, and filtration may be performed only once, but it is preferable to alternate between washing and filtration multiple times. By alternately performing washing and filtration multiple times, unreacted materials and solvents that are undesirable in the final composite metal pigment composition can be more effectively removed, making it easier to satisfy the requirement in the first invention of this application (4) that the volatile content of the composite metal pigment composition is 20 to 90 mass % and that 50 to 100 mass % of the volatile content is water.
During the filtration, a gas may be passed through the surface and voids of the slurry or cake to volatilize the solvent.

The step of replacing the organic solvent with water in step 3) can be carried out by a method commonly used in the art, such as adding water or a mixture of water and an organic solvent to the treatment liquid and then filtering the liquid, filtering the treatment liquid to increase the solid content and reduce the organic solvent content, and then adding a predetermined amount of water or a mixture of water and an organic solvent, or a combination of these methods.
A specific example of step 3) is a method in which the treated liquid obtained in step 2) is filtered with a Nutsche type filter, the filtered sediment is washed by flowing an organic solvent of the same type as the reaction solvent in an amount of about 0.5 to 5 times the amount of the filtered sediment, then the filtered sediment is washed by flowing water in an amount of 0.5 to 5 times the amount of the filtered sediment (and the organic solvent is replaced with water), and finally, washing, solvent replacement, and filtration are performed using a washing liquid having a predetermined moisture content to obtain a predetermined solid content.
In the above example, one preferred method is to first filter the reaction solution obtained in step 2) to remove impurities and the reaction solvent, then pass a solvent containing a large amount of organic solvent through the reaction solution to remove impurities with a high affinity for the organic solvent, and then add water or a mixture of water and organic solvent to remove impurities with a high affinity for water. In this case, the volatile content of the reaction solution is preferably reduced to 70% by weight or less, more preferably to 65% by weight or less, and particularly preferably to 60% by weight or less by filtering the reaction solution.

Other steps: When producing the composite metal pigment composition of the first invention of the present application, preferably by the method for producing the composite metal pigment composition of the second invention of the present application, in addition to the above steps 1) to 3), the method may include a step of crushing metal particles, a step of forming a coating layer other than a metal oxide coating, etc.

Pulverization, sieving, filtration, etc. of metal particles Prior to the above-mentioned step 1) of dispersing metal particles in a solvent, the metal particles may be pulverized, sieved, and/or filtered. By pulverizing, sieving, and/or filtering the metal particles, the particle size of the metal particles becomes more uniform and fine, which is preferable from the viewpoint of producing a composite metal pigment composition containing uniform and fine composite particles.
Here, an example will be described in which aluminum powder is used as the metal particles.
The aluminum powder is generally obtained by pulverizing atomized aluminum powder and/or aluminum foil in the presence of a grinding aid or an inert solvent into a so-called flake-like form using a method commonly used in the pigment industry, such as a dry ball mill method, a wet ball mill method, an attritor method, or a stamp mill method, and then passing through any necessary steps, such as sieving (classification), filtration, washing, and mixing.
Examples of the grinding aid include fatty acids, fatty amines, fatty amides, and fatty alcohols. In general, oleic acid, stearic acid, and stearylamine are preferred. Examples of the inert solvent include hydrophobic substances such as mineral spirits, solvent naphtha, toluene, and xylene, which can be used alone or in combination. The grinding aid and the inert solvent are not limited to these.
As the pulverization step, pulverization by a wet ball mill method is preferred from the viewpoint of preventing dust explosions and ensuring safety.

When aluminum particles are used as the metal particles, commercially available paste-like aluminum flakes obtained through such grinding, sieving, and filtration can be used. The paste-like aluminum flakes may be used as is, or may be used after removing fatty acids and the like from the surface with an organic solvent or the like.

Formation process of the second coating layer The composite particles constituting the composite metal pigment composition of the first invention of the present application preferably have, in addition to the metal oxide coating, another coating layer (second coating layer), preferably a coating layer containing at least one selected from metals, metal oxides, metal hydrates and resins. The second coating layer (if formed) is preferably formed between the metal particles and the metal oxide coating such as a silicon compound-containing layer. Therefore, a layer structure of "metal particles/second coating layer/metal oxide coating" can be preferably adopted.
The second coating layer is not particularly limited, but may be a molybdenum-containing coating, a phosphate compound coating, etc. A preferred example of a molybdenum-containing material constituting the molybdenum-containing coating is the mixed coordination heteropolyanion compound disclosed in JP 2019-151678 A. Examples of the components of the second coating layer, including the mixed coordination heteropolyanion compound, are as described above.
In the following, an embodiment in which a molybdenum-containing coating is formed as a second coating layer between metal particles and a metal oxide coating such as a silicon compound-containing layer will be described as an example.

When a molybdenum-containing coating is formed as a second coating layer between metal particles and a metal oxide coating such as a silicon compound-containing layer, a mixed liquid containing metal particles and a molybdenum compound (typically a mixed coordination type heteropolyanion compound) can be stirred prior to the formation of a metal oxide coating such as a silicon compound-containing layer to form a molybdenum-containing coating on the surface of the metal particles.

The method for forming a molybdenum-containing coating on the surface of metal particles is not particularly limited, and any method capable of uniformly stirring a mixed liquid containing metal particles and a molybdenum compound in an aqueous solvent may be used. For example, a molybdenum-containing coating can be formed on the surface of metal particles by stirring or kneading a mixed liquid containing metal particles and a molybdenum compound in a slurry or paste state. In the mixed liquid, the molybdenum compound may be dissolved or dispersed.

The agitator for agitating the mixture containing metal particles and a molybdenum compound is not particularly limited, and any known agitator capable of efficiently and uniformly agitating the mixture containing metal particles and a molybdenum compound can be used. Specific examples include kneaders, mixers, rotary vessel agitators, agitation reaction tanks, V-type agitators, double cone agitators, screw mixers, sigma mixers, flash mixers, airflow agitators, ball mills, edge runners, etc. Examples of the agitator blades include, but are not limited to, anchor blades, paddle blades, propeller blades, turbine blades, etc.

The amount of the molybdenum compound used can be set appropriately depending on the type of molybdenum compound used. This amount is generally 0.02 to 20 parts by mass per 100 parts by mass of metal particles (solid content), and is preferably 0.1 to 10 parts by mass. By setting the content to 0.02 parts by mass or more, a sufficient treatment effect can be obtained. Furthermore, by setting the content to 20 parts by mass or less, the brilliance of the resulting composite metal pigment composition can be maintained at a high level.

The solvent used to mix the metal particles and the molybdenum compound is usually water, a hydrophilic organic solvent, or a mixture of these.

Examples of hydrophilic organic solvents include alcohols such as methanol, ethanol, propanol, butanol, isopropanol, and octanol; ether alcohols and esters thereof such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monoethyl ether, propylene glycol monomethyl ether, and dipropylene glycol monomethyl ether; glycols such as ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, polyoxyethylene glycol, polyoxypropylene glycol, and ethylene propylene glycol; ethyl cellosolve, butyl cellosolve, acetone, methoxypropanol, ethoxypropanol, and other alkoxy alcohols. These can be used alone or in combination of two or more.

The amount of solvent used in the process of forming the second coating layer (excluding the amount of solvent used in the case where the metal particles are pre-dispersed) is not particularly limited, but is usually preferably 50 to 5,000 parts by mass, and more preferably 100 to 2,000 parts by mass, per 100 parts by mass of the metal particles (solid content). By using an amount of solvent of 50 parts by mass or more, uneven distribution of the molybdenum compound and aggregation of the metal particles can be suppressed. Also, by using an amount of solvent of 5,000 parts by mass or less, a sufficient treatment effect of the molybdenum compound on the metal particles can be obtained.

The temperature of the mixed liquid containing the metal particles and the molybdenum compound when stirring is usually about 10 to 100°C, and preferably 30 to 80°C. By keeping this temperature at 10°C or higher, the reaction time required to obtain a sufficient treatment effect can be shortened. Also, by keeping this temperature at 100°C or lower, it becomes easier to control the reaction to obtain the desired composite metal pigment composition.

The stirring time of the mixed solution is not particularly limited as long as it is sufficient to form the desired molybdenum-containing coating. For example, this stirring time is preferably 0.5 to 10 hours, and more preferably 1 to 5 hours. By setting the stirring time to 0.5 hours, a sufficient treatment effect can be obtained. Furthermore, by setting the stirring time to 10 hours or less, an increase in treatment costs can be suppressed.

After the stirring of the mixture containing the metal particles and the molybdenum compound is completed, the particles on which the second coating layer is formed can be collected. In this case, known washing, solid-liquid separation, etc. can be appropriately performed as necessary. For example, it is preferable to wash the mixture using a hydrophilic organic solvent, and then filter it using a filter or the like to remove water and unreacted substances from the cake containing the metal particles having a molybdenum-containing coating. In this way, the molybdenum-containing coating, which is the second coating layer, can be formed. When forming other second coating layers, the above method can also be used.

In an embodiment in which a metal oxide coating (hereinafter, a silicon compound-containing layer will be described as an example) is formed on metal particles after a second coating layer (hereinafter, a molybdenum-containing coating will be described as an example), after stirring of the mixed liquid containing the metal particles and the molybdenum compound is completed, a dispersion of a silicon compound source (typically an organosilicon compound represented by the above formula (1), such as tetraalkoxysilane and/or a condensate thereof, and at least one silane coupling agent represented by any one of the above formulas (2) to (4)) in water and/or a hydrophilic organic solvent may be directly added to the system and stirred without recovering the particles on which the second coating layer has been formed. In this case, a dispersion of an organosilicon compound represented by the above formula (1), such as tetraalkoxysilane and/or a condensate thereof, may be added to the system containing the particles on which the second coating layer has been formed, and then a dispersion of at least one silane coupling agent represented by any one of the above formulas (2) to (4) may be added and stirred.

To form the second coating layer on the outermost layer of the composite metal pigment, a corrosion inhibitor such as an acidic phosphoric acid ester, a dimer acid, an organic phosphorus compound, or a metal salt of molybdic acid is added to the obtained composite metal pigment composition at about room temperature in an amount of 1 to 20 parts by weight per 100 parts by weight of the composition and mixed uniformly. In order to form a uniform layer, it is preferable to add these corrosion inhibitors by dissolving/dispersing them in the hydrophilic organic solvent used when forming the oxidized metal coating layer at 20 to 80% by weight. The amount of the corrosion inhibitor is more preferably 2 to 10% by weight, more preferably 3 to 7% by weight, per 100 parts by weight of the composition.

Uses of the composite metal pigment composition The composite metal pigment composition of the first invention of the present application and the composite metal pigment composition produced by the production method of the second invention of the present application can be added to an aqueous paint or ink in which resins, which are coating film-forming components (binders), are dissolved or dispersed in a medium mainly composed of water, to produce a metallic aqueous paint or ink that reduces VOCs and has excellent storage stability for the paint or ink, and can provide a coating film that is excellent in suppressing bumps, designability, hiding properties, etc. The antioxidant, light stabilizer, and surfactant may be added when the composite metal pigment composition is blended with the aqueous paint or ink, or resin, etc.

When the composite metal pigment composition is used in paints or inks, it may be added directly to the water-based paint or ink, or may be dispersed in water or a solvent mainly composed of water beforehand and then added. Examples of solvents other than water that can be used include Texanol, diethylene glycol monobutyl ether, and propylene glycol monomethyl ether, but from the viewpoint of reducing VOCs, it is better to use as little of these solvents as possible.
Examples of resins include acrylic resins, polyester resins, polyether resins, epoxy resins, fluororesins, and rosin resins. Examples of binders for paints or inks include rubbers in addition to resins. These resins are preferably emulsified, dispersed, or dissolved in water. To achieve this, carboxyl groups, sulfone groups, and the like contained in the resins can be neutralized. Preferred resins include acrylic resins and polyester resins.
If necessary, resins such as melamine-based curing agents, isocyanate-based curing agents, and urethane dispersions can be used in combination. Furthermore, it may be combined with coloring pigments such as inorganic pigments, organic pigments, and extender pigments, silane coupling agents, titanium coupling agents, dispersants, anti-settling agents, leveling agents, thickeners, and defoamers that are generally added to paints. In order to improve dispersibility in paints, a surfactant may be further added, and in order to improve the storage stability of the paint, an antioxidant, a light stabilizer, and a polymerization inhibitor may be further added.

Examples of color pigments include phthalocyanine, quinacridone, isoindolinone, perylene, azo lake, iron oxide, yellow lead, carbon black, titanium oxide, pearl mica, etc.

The content of the composite metal pigment composition according to the first invention of the present application or the composite metal pigment composition produced by the production method of the second invention of the present application in the above-mentioned water-based paint or water-based ink (resin composition) is not limited, but usually the amount of solids is 0.1 to 30 mass%, and it is particularly preferable that the amount is 1 to 20 mass%. By making this content 0.1 mass% or more, a high decorative (metallic) effect can be obtained. In addition, by making this content 30 mass% or less, it is possible to prevent the properties of the water-based paint or water-based ink, such as weather resistance, corrosion resistance, mechanical strength, etc., from being impaired.

The content of the solvent, including water, is not particularly limited, but may be 20 to 200% by mass relative to the binder content. By keeping the solvent content within this range, the viscosity of the paint or ink can be adjusted to an appropriate range, making handling and film formation easier. Of these, the proportion of water is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

The coating method or printing method for the water-based paint is not particularly limited. For example, various coating methods or printing methods can be appropriately adopted taking into consideration the form of the water-based paint, the surface shape of the material to be coated, etc. Coating methods include, for example, spraying, roll coating, brush coating, doctor blade coating, etc. Printing methods include, for example, gravure printing, screen printing, etc.

A coating film formed from a water-based paint or the like may be formed on a primer layer or an intermediate coat layer formed by electrocoating or the like. In addition, if necessary, a top coat layer or the like may be formed on a coating film formed from a water-based paint or the like.

In the case of these layer configurations, each coating layer may be applied and cured or dried before the next coating layer is applied, or each coating layer may be applied by so-called wet-on-wet coating and then the next coating layer may be applied without curing or drying. For water-based paints and the like containing the composite metal pigment composition according to the first invention of the present application or the composite metal pigment composition produced by the production method of the second invention or the third invention of the present application, it is preferable to adopt a method including a step of applying a base coating layer, curing or drying it, and then forming a coating layer from the water-based paint or the like, in that a coating film having good mirror-like luster can be obtained.
The coating composition of each coating layer may be cured by heat or by room temperature, and the coating composition of each coating layer may be dried by, for example, hot air or by natural drying at room temperature.

The thickness of the coating layer made of water-based paint, etc. is not particularly limited, but is usually preferably about 0.5 to 100 μm, and more preferably about 1 to 50 μm. When the coating layer is 0.5 μm or thicker, the ink or paint can be sufficiently hidden from the base. Furthermore, when the coating layer is 100 μm or thinner, drying becomes easier, and the occurrence of defects such as popping and dripping can be suppressed.

The composite metal pigment composition of the first invention of this application, the composite metal pigment composition obtained by the manufacturing method of the second invention of this application, and the coating film obtained using the same have excellent design, gloss, suppression of bumps, stability in water-based paints, etc. at high levels, so they can be suitably used in various applications where metal pigments have traditionally been used, such as paints, inks, and resin kneading agents, more specifically, in automobile bodies, automobile repair materials, automobile parts, home appliances, plastic parts, paints for PCM, highly weather-resistant paints, heat-resistant paints, anti-corrosion paints, paints for ship bottoms, offset printing inks, gravure printing inks, screen printing inks, etc.

The present invention will be explained in more detail below with reference to the following examples. However, please note that these examples are merely illustrative and that the present invention is in no way limited by the explanations of these examples.

Example 1
In a ¹ m2 reaction tank with a diameter of 2 m and an anchor-type stirring blade with a blade diameter of 1 m, 135 kg of commercially available aluminum paste (manufactured by Asahi Kasei Corporation, product name "GX-3100 (average particle size 11 μm, non-volatile content 74%)") was added 465 kg of methoxypropanol (hereinafter abbreviated as "PM"), and the mixture was stirred with the stirring blade at 100 rpm, and the aluminum paste was uniformly dispersed in the PM while externally circulating 10 L/min of the dispersion liquid withdrawn from the bottom back to the reaction tank from the top of the reaction tank.
Next, a solution of 1 kg of phosphotungstomolybdic acid (H ₃ PW ₆ Mo ₆ O ₄₀ ) hydrate dissolved in 5 kg of PM was gradually added, and the mixture was stirred for 1 hour while maintaining the slurry temperature at 40° C. External circulation was continued during the reaction.
After that, 15 kg of tetraethoxysilane was added as an organic silicon compound, and then 15 kg of 25% ammonia water and 200 kg of purified water were added over 3 hours. Then, 1.3 kg of methyltrimethoxysilane was added as a silane coupling agent, and the mixture was stirred for 3 hours. External circulation was continued during the reaction.
After the reaction was completed, the slurry was cooled to 30°C, and then pressure-filtered using a Nutsche filter with a diameter of 600 mm to obtain a filtrate with a volatile content of 55% by mass. Next, 100 kg of PM was added to the Nutsche filter containing the filtrate, and then pressure-filtered to wash and filter the filtrate with a volatile content of 55% by mass. The obtained filtrate was added to a stirring tank containing 300 kg of water and dispersed again, and then pressure-filtered using a Nutsche filter until the volatile content was 55% by weight. Next, 200 kg of water was added to the Nutsche filter containing the filtrate, and pressure-filtered to wash, filter, and replace the organic solvent with water to obtain a composite aluminum pigment composition with a volatile content of 45% by mass, 98% by mass of the volatile content being water, and the volatile organic solvent content was 1.3 parts per 100 parts of solid content.
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.

Example 2
A composite aluminum pigment composition with a volatile content of 45% was obtained in the same manner as in Example 1, except that the aluminum paste was changed to (manufactured by Asahi Kasei Corporation, product name "GX-4100 (average particle size 10 μm, non-volatile content 74%)").

Example 3
A composite aluminum pigment composition with a volatile content of 45% was obtained in the same manner as in Example 1, except that the aluminum paste was changed to (manufactured by Asahi Kasei Corporation, product name "FD-5090 (average particle size 9 μm, non-volatile content 75%)").

Example 4
The same procedures as in Example 1 were carried out except that 100 kg of PM was added, washed and filtered under pressure to obtain a filtrate with a volatile content of 55% by mass, and the filtrate was kept in the Nutsche filter (without being added to a stirring tank containing 300 kg of water and dispersed again), and 400 kg of water was added and filtered under pressure to wash, filter, and replace the organic solvent with water, thereby obtaining a composite aluminum pigment composition with a volatile content of 45% by mass, 97% by mass of the volatile content being water, and the volatile organic solvent content being 1.6 parts per 100 parts of solids.
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.

Example 5
A composite aluminum pigment composition having a volatile content of 45% by mass, 98% by mass of the volatile content being water, and a volatile organic solvent content of 1.6 parts per 100 parts of solids was obtained in the same manner as in Example 4, except that 100 kg of a mixed liquid of water/PM:3/2 was added instead of 100 kg of PM, and then washed and filtered.
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.

Example 6
The slurry after the reaction was filtered, and the filtrate was placed in a Nutsche filter. 200 kg of water was then added to the filter, which was then subjected to pressure filtration to wash, filter, and replace the organic solvent with water, thereby obtaining a composite aluminum pigment composition having a volatile content of 45% by mass, 95% by mass of the volatile content being water, and a volatile organic solvent content of 4.1 parts per 100 parts of solids.
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.

Example 7
A composite aluminum pigment composition having a volatile content of 45% by mass, 80% by mass of the volatile content being water, and a volatile organic solvent content of 16.4 parts per 100 parts of solid content was obtained in the same manner as in Example 6, except that 300 kg of PM was added to the slurry after the reaction and then filtered.
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.

Example 8
The same procedure as in Example 6 was repeated, except that 300 kg of water was added to the slurry after the reaction and then filtered, to obtain a composite aluminum pigment composition having a volatile content of 45% by mass, 80% by mass of the volatile content being water, and a volatile organic solvent content of 16.4 parts per 100 parts of solid content.
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.

Example 9
The same procedure as in Example 4 was repeated, except that the final filtration was stopped when the volatile content reached 60% by mass, to obtain a composite aluminum pigment composition having a volatile content of 60% by mass, 98% by mass of which was water, and a volatile organic solvent content of 3.0 parts per 100 parts of solids.
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.

Example 10
The same procedure as in Example 4 was repeated, except that the final filtration was stopped when the volatile content reached 80% by weight, to obtain a composite aluminum pigment composition having a volatile content of 80% by weight, 98% by weight of which was water, and a volatile organic solvent content of 4.0 parts per 100 parts of solids.
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.

Example 11
To the composite aluminum pigment composition having a volatile content of 45 mass% obtained in Example 1, 5 parts by mass of an alkyl acidic phosphate ester (product name: GF-215DPM, manufactured by Toho Chemical Industry Co., Ltd.) was added per 100 parts by mass of the composition, and the mixture was uniformly mixed at room temperature in a mixer to obtain a composite aluminum pigment composition.
Composition of GF-215DPM: Mixture of the following: 56% by mass
・Alkyl acid phosphate ester ・Morpholine salt
・Alkyl acid phosphate ester
Morpholine Propylene glycol monomethyl ether: 44% by mass
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.

Example 12
To the composite aluminum pigment composition having a volatile content of 45% by mass obtained in Example 10, 5 parts by mass of an alkyl acidic phosphate ester was added per 100 parts by mass of the composition in the same manner as in Example 11, and the mixture was mixed uniformly in a mixer at room temperature to obtain a composite aluminum pigment composition.
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.

Comparative Example 1
Using the same apparatus as in Example 1, 465 kg of PM was added to 135 kg of commercially available aluminum paste (manufactured by Asahi Kasei Corporation, product name "GX-3100": average particle size 11 μm, non-volatile content 74%) to form a dispersed slurry, and while stirring the slurry, a solution in which 1 kg of tungstomolybdic phosphonate (H ₃ PW ₆ Mo ₆ O ₄₀ ) hydrate was dissolved in 5 kg of PM was gradually added, and the slurry was stirred for 1 hour while maintaining the temperature at 40° C. After cooling, the slurry was filtered to obtain an aluminum pigment composition with a volatile content of 40%.
In Comparative Example 1, the features of the manufacturing method of the composite metal pigment composition of the present invention, "Step 2) the step of coating the metal particles with metal oxide" and "Step 3) the step of replacing the organic solvent with water", were not carried out.

Comparative Example 2
In the same manner as in Example 1, after the reaction was completed, the slurry was cooled to 30°C and then pressure-filtered using a Nutsche filter with a diameter of 600 mm to obtain a filtrate with a volatile content of 55% by mass. Next, 300 kg of PM was added to the Nutsche filter containing the filtrate, and the filtrate was washed and filtered by pressure filtration for a long period of time to obtain a filtrate with a volatile content of 74% by mass. At this time, the water content of the volatile content was 0% by mass, and a composite aluminum pigment composition was obtained in which the volatile organic solvent content was 35.1 parts per 100 parts of solid content.
After the reaction, the steps from cooling and filtering the slurry to finally obtaining the composite aluminum pigment composition were carried out in a room temperature atmosphere, and the temperature of the composition did not exceed 80° C. In addition, the pH value of the filtrate was within the range of 5 to 12.
In Comparative Example 2, the content of the volatile organic solvent was reduced by performing pressure filtration for a long period of time, and "Step 3) Step of replacing the organic solvent with water" was not performed.

Comparative Example 3
Water was added to the composite aluminum pigment composition obtained in Comparative Example 2 to obtain a composite aluminum pigment composition having a volatile content of 45 mass%, a water content in the volatile content of 42 mass%, and a volatile organic solvent content of 47.3 parts per 100 parts of solids.
In Comparative Example 3, water was simply added to the aluminum pigment composition obtained in step 2, and step 3) "step of replacing the organic solvent with water" was not carried out.

Comparative Example 4
The composite aluminum pigment composition obtained in Comparative Example 2 was vacuum dried at 90°C to obtain a composite aluminum pigment composition having a volatile content of 5 mass%, a water content in the volatile content of less than 1 mass%, and a volatile organic solvent content of 5.3 parts per 100 parts of solids.
In Comparative Example 4, the content of the volatile organic solvent was reduced by vacuum drying, but "step 3) step of replacing the organic solvent with water" was not carried out.

Comparative Example 5
Water was added to the composite aluminum pigment composition obtained in Comparative Example 4 to obtain a composite aluminum pigment composition having a volatile content of 45% by mass, 89% by mass of the volatile content being water, and a volatile organic solvent content of 9.1 parts per 100 parts of solids.
In Comparative Example 5, water was simply added to the aluminum pigment composition obtained in step 2, and step 3) "step of replacing the organic solvent with water" was not carried out.

(Evaluation of Composite Metal Pigment Composition)
Average particle size: _D50
The average particle size (D ₅₀ ) of the composite particles (silicon oxide-coated aluminum particles) in the composite aluminum pigment composition obtained in each of the above Examples and Comparative Examples was measured using a laser diffraction/scattering type particle size distribution measuring device (LA-300/manufactured by Horiba, Ltd.).
Isopropanol was used as the measurement solvent.
The measurements were carried out in accordance with the equipment's instruction manual, but it should be noted that the composite metal pigment composition sample was subjected to ultrasonic dispersion for 2 minutes as a pretreatment, and then placed in a dispersion tank. After confirming that it was dispersed to the appropriate concentration, the measurements were started.
After the measurement was completed, the _D50 was calculated by the instrument software and automatically displayed.

Solid content and volatile content 10 g of the composite aluminum pigment composition obtained in each of the above Examples and Comparative Examples was heated at 105° C. for 3 hours to volatilize the volatile content, and then the mass was measured. This was taken as the mass of the solid content, and the proportion of the solid content was calculated, and the proportion of the volatile content was calculated.

Residue : 50 g of the composite aluminum pigment composition obtained in each of the above Examples and Comparative Examples was dispersed in 1,000 ml of water using a spatula, and then filtered through a 200-mesh nylon net (manufactured by NBC). The residue was thoroughly washed with acetone and then dried at 105° C. for 10 minutes, after which the mass was measured, and this was regarded as the mass of the residue to determine its proportion.

(Evaluation of paints and coatings)
Using the composite aluminum pigment compositions obtained in the above Examples and Comparative Examples, water-based metallic paints were prepared according to the compositions and methods described below, and the paints and coating films obtained therefrom were evaluated according to the methods described below. The results are shown in Table 1.
A water-based metallic paint was prepared having the following components:
・Composite aluminum pigment composition ・Isopropyl alcohol ・Purified water ・Water-soluble acrylic resin (※1)
*1: Watersol S-744, manufactured by DIC Corporation
(Resin 40% by weight, isopropyl alcohol 30% by weight, water 30% by weight)
In the preparation, 12.5 g of the composite aluminum pigment as a nonvolatile content, 9.2 g of isopropyl alcohol, and 9.2 g of purified water were first thoroughly mixed to prepare a mill base, and then 170 g of the water-soluble resin, 20.0 g of isopropyl alcohol, and 50 g of purified water were added to the mill base and thoroughly mixed. After mixing, 5 to 10% by mass of purified water was added to adjust the viscosity to 600 to 700 mPa·s (B-type viscometer, No. 3 rotor, 60 rpm, 25°C).
In addition, since the pigment composition of Comparative Example 1 does not have a metal oxide coating, the paint dispersibility is poor, and it is difficult to evaluate the coating film (Evaluation 2 below) by the same method. For this reason, in the coating film evaluation of Comparative Example 1, a sample prepared by the following method was used.
Pigment composition of Comparative Example 1 Methoxypropanol Polyoxyethylene lauryl ether (nonionic surfactant) (*3)
·purified water,
- Water-soluble acrylic resin (*4)
・Melamine resin (※5)
*3: Actinol L5, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.
*4: Alumatex WA911, manufactured by Mitsui Chemicals, Inc.
*5: Cymel 350, manufactured by Japan Cytec Industries Co., Ltd.

In the preparation, 12.0 g of composite aluminum pigment as non-volatile matter, 18.0 g of methoxypropanol, 6.0 g of polyoxyethylene lauryl ether, 12.0 g of purified water, 110 g of water-soluble acrylic resin, and 18.0 g of melamine resin were added and thoroughly mixed. After mixing, the pH was adjusted to 7.7 to 7.8 with dimethylethanolamine, and the viscosity was adjusted to 650 to 750 mPa·s (B-type viscometer, No. 3 rotor, 60 rpm, 25°C) with a carboxylic acid thickener and purified water.

The water-based metallic paint thus prepared was used to carry out the following evaluations.
Evaluation 1 (storage stability (gas generation))
200 g of the water-based metallic paint prepared according to the above recipe was placed in a flask, and the cumulative amount of hydrogen gas generated was measured for 24 hours in a thermostatic water bath at 60° C. The amount of gas generated was evaluated according to the following criteria and used as an index of storage stability in the paint.
○: 5ml or less △: 5ml to 10ml or less ×: 10ml to 20ml or less ××: More than 20ml

・Evaluation 2 (coating film evaluation)
The water-based metallic paint prepared according to the above formula was air spray painted onto a 12 cm x 6 cm steel plate (manufactured by Miki Coating Co., Ltd.) that had been coated with an undercoat paint so that the dry film thickness would be 6 μm, and after pre-drying at 90°C for 10 minutes, an organic solvent-based top coat paint having the following composition was dispersed with a spatula for 3 minutes, and then the paint viscosity was adjusted to 20.0 seconds using a Ford cup No. 4. The paint was air spray painted onto the plate so that the dry film thickness would be 20 μm, and the plate was dried at 140°C for 30 minutes to prepare a painted plate, which was then subjected to the following evaluations.
(Composition of organic solvent-based top coat paint)
Acrydic 44-179 (DIC Corporation, acrylic clear resin) 141g
・Super Beckamin J-820 (DIC, melamine resin) 35.3g
123.5g toluene

2-i (paint film)
The number of bumps on the entire surface of the topcoat film of the resulting coated plate was counted and evaluated according to the following criteria.
〇: No visible particles △: 10 particles or less ×: More than 10 particles

2-ii (Brightness)
The resulting coated panels were evaluated using a laser metallic feel measuring device Alcove LMR-200 manufactured by Kansai Paint Co., Ltd. The optical conditions were a laser light source with an incident angle of 45 degrees and light receivers at receiving angles of 0 degrees and -35 degrees. The measured value was the IV value at a receiving angle of -35 degrees where the maximum light intensity was obtained from the reflected light of the laser, excluding the light in the specular reflection region reflected by the coating surface. The IV value is a parameter proportional to the intensity of specularly reflected light from the coating, and represents the magnitude of light brightness.
The obtained IV values were evaluated based on the following criteria.
◯: The decrease from the standard (Comparative Example 1) was less than 20.
Δ: The decrease from the standard (Comparative Example 1) was 20 or more and less than 40. ×: The decrease from the standard (Comparative Example 1) was 40 or more.

2-iii (Concealment)
The prepared water-based metallic paint was applied to a polyethylene terephthalate sheet (PET sheet) using a 2 mil applicator so as to give a dry film thickness of 15 μm, and the coating film was dried at 140° C. for 30 minutes and visually evaluated.
◯: Equivalent to slightly lower than the standard (Comparative Example 1).
Δ: Lower than the standard (Comparative Example 1).
×: Much lower than the standard (Comparative Example 1).

(Evaluation of aggregation and deformation of composite particles)
In order to make it easier to judge the state of particle aggregation, etc., the amount of aluminum paste in the paint formulation used to prepare the coated plate in Evaluation 2 was reduced to 1/10, but the paint was prepared under the same conditions as in Evaluation 2, and a coated plate was prepared under the conditions for Evaluation 2.
The above coated plate was cut into 1 cm square pieces using a shearing machine.
The cross section of the obtained coating film was subjected to ion milling treatment using an ion milling device (IB-09010CP manufactured by JEOL Ltd.) set so as to be able to irradiate the ion beam up to a portion 20 μm away from the cross section of the coating film, and a precision-polished cross section sample was prepared by ion milling treatment.
The cross section of the obtained coating film (coated plate) was observed with an FE-SEM (Hitachi/S-4700) to observe the overlapping state of the particles and the deformation state of the particles, and evaluated according to the following procedure.

Primary particle ratio (aggregated state)
First, the degree of particle overlap was easily distinguished by observing at a magnification of about 1000 to 3000 times. When the degree of overlap could not be distinguished at this magnification, the degree of overlap was evaluated by changing the magnification appropriately. In this observation method, the observation was performed at a maximum magnification of about 30,000 times. Multiple fields of view were observed from the cross section of the same sample piece so that the number of particles observed was 500 or more.
In addition, when the particles were close to each other and it was difficult to judge whether or not agglutination occurred, if the length of the contact area between the particles was 1/4 or less of the particle diameter of the smaller particle (the particle with the shorter major axis), it was judged that there was no agglutination, and if it was more than 1/4, it was judged that there was agglutination.

Percentage of bent particles (deformed state)
The degree of deformation of the particles was easily observed at a magnification of about 1000 to 3000 times. If the deformation could not be determined at this magnification, the degree of deformation was evaluated by changing the magnification appropriately. In this observation method, the observation was performed at a maximum magnification of about 30,000 times. Multiple fields of view were observed from the cross section of the same sample piece so that the number of particles observed was 500 or more. The presence or absence of deformation was determined to be present when the shortest distance between both ends of the particle was 0.8 times or less the length of the particle.

Average Particle Thickness of Metal Particles Using the FE-SEM image (10,000x) obtained by the above acquisition procedure and image analysis software Win Roof version 5.5 (manufactured by MITANI CORPORATION), the particle thickness in the cross section of the aluminum particle was measured and the average thickness was calculated.
An FE-SEM image for measuring the thickness of an aluminum particle in its cross section was displayed, and an ROI line was selected and aligned with the 5 μm scale of the image, and the length and unit were input and set via registration/change.
Next, an image of the cross section of the aluminum particle on which thickness measurement was to be performed was displayed, a rectangular ROI was selected, and the rectangular ROI was aligned with the cross section of the particle and binary processing was performed.
Next, the subject was asked to select the measurement item of the vertical chord length, and then the measurement was carried out. The value (vertical chord length value) automatically measured by the image analysis software was displayed on the image.
In this way, 300 particles were selected using the image analysis software Win Roof version 5.5, and the thickness and major axis of the cross section of the aluminum particles were automatically measured. Next, the arithmetic mean value of the thickness was calculated for the 300 particles, and the average thickness t of the particles was obtained. Note that the thickness uniformity of the aluminum particles is high, and the thickness difference due to the cut part of the particle is small. Therefore, the influence of the difference in the cut part of the particle on the average particle thickness measurement can be ignored.

Average particle thickness of composite particles, thickness of metal oxide coating For the coated plate used to obtain the above FE-SEM image, the average thickness of the particle coating layer was measured at a magnification of 200,000 times using a STEM (scanning transmission electron microscope). When the surface of the coating layer is uneven, the area of the coating layer was measured using image analysis software Win Roof version 5.5, and the average thickness of the coating layer was obtained by dividing it by the perimeter of the coated particle. In addition, when the particle is large, it is not necessary to measure the area of the entire coating layer, and the average thickness of the coating layer can be obtained with sufficient accuracy by measuring the area of the coating layer in a region of about 1 μm along the particle surface and dividing it by the particle surface length. In addition, since the average thickness of the coating layer is almost uniform regardless of the particle, the average value was calculated for 10 particles. In addition, the average thickness of the composite particle was calculated according to the following calculation formula from the thickness of the particle coating layer and the average particle thickness of the metal particles obtained above.
Average particle thickness of composite particles = Average particle thickness of metal particles + Thickness of coating layer x 2

The evaluation results are shown in Table 1. The composite metal pigment compositions according to the present invention obtained in each example, which satisfy all of the requirements in items (1) to (7) above, have a high solid content, good stability as a paint, little gas generation (good storage stability), excellent brightness and hiding power, and further effectively suppressed bumps in the coating film.

The composite metal pigment composition of the first invention of this application, the composite metal pigment composition obtained by the manufacturing method of the second invention of this application, and the coating film obtained by using them, when used in water-based paints, etc., emit little VOC from the paint, and have excellent coating film properties such as storage stability, suppression of bumps, design, and hiding power at a high level that exceeds the limits of conventional technology. Therefore, they can be suitably used in various applications where metal pigments have traditionally been used, such as paints, inks, resin kneading agents, etc., more specifically, in automobile bodies, automobile repair materials, automobile parts, home appliances, etc., plastic parts, PCM paints, highly weather-resistant paints, heat-resistant paints, anti-corrosion paints, paints for ship bottoms, offset printing inks, gravure printing inks, screen printing inks, etc., and have high applicability in various industrial fields such as the transportation machinery industry such as automobiles, the electrical and electronic industry such as home appliances, the paint industry, and the printing industry.

Claims (24)

A composite metal pigment composition comprising metal particles and composite particles having a metal oxide coating formed on a surface thereof,
(1) The composite particles have a scale-like shape,
(2) The composite particles have a volume-based average particle diameter _D50 of 1 to 30 μm when the particle size distribution of the composite particles is measured using a laser diffraction particle size distribution analyzer;
(3) The composite particles have an average particle thickness of 20 to 400 nm;
(4) The composite metal pigment composition has a volatile content of 20 to 90% by mass, and 50 to 100% by mass of the volatile content is water;
(5) The composite metal pigment composition has a volatile organic solvent content of 0 to 20 parts by mass per 100 parts by mass of solids,
(6) The above composite metal pigment composition, in which when the composite metal pigment composition is dispersed in water and filtered through a 200 mesh filter, the residue is 0.1 mass% or less of the solid content. (7) The composite metal pigment composition according to claim 1, in which 12.5 g of the metal pigment composition as a nonvolatile content, 9.2 g of isopropyl alcohol, and 9.2 g of purified water are thoroughly mixed to prepare a mill base, and then 170 g of a water-soluble resin, 20.0 g of isopropyl alcohol, and 50 g of purified water are added to the mill base and thoroughly mixed to obtain 200 g of water-based metallic paint, which is then collected in a flask and the cumulative amount of hydrogen gas generated is measured in a thermostatic water bath at 60°C for up to 24 hours, and the amount of gas generated is 20 ml or less. The composite metal pigment composition according to claim 1, wherein the proportion of non-aggregated primary particles in the composite particles is 35% or more by number. The composite metal pigment composition according to claim 1, wherein the proportion of non-aggregated primary particles in the composite particles is 40% or more by number. The composite metal pigment composition according to claim 1, wherein the proportion of bent composite particles in the composite particles is 10% or less by number. The composite metal pigment composition according to claim 2, wherein the proportion of bent composite particles in the composite particles is 10% or less by number. The composite metal pigment composition according to claim 3, wherein the proportion of bent composite particles in the composite particles is 10% or less by number. The composite metal pigment composition according to any one of claims 1 to 7, wherein at least one layer in the metal oxide coating is a silicon compound-containing layer. The composite metal pigment composition according to claim 8, wherein the average layer thickness of the metal oxide coating is 5 to 150 nm. The composite metal pigment composition according to claim 8, wherein the metal particles contain aluminum or an aluminum alloy. The composite metal pigment composition according to claim 9, wherein the metal particles contain aluminum or an aluminum alloy. The composite metal pigment composition according to claim 10, wherein the composite particles further have a coating layer containing at least one selected from a metal, a metal oxide, a metal hydrate, and a resin other than the metal oxide coating. The composite metal pigment composition according to claim 11, wherein the composite particles further have a coating layer containing at least one selected from a metal, a metal oxide, a metal hydrate, and a resin other than the metal oxide coating. The composite metal pigment composition according to claim 12, characterized in that the further coating layer according to claim 12 is in the outermost layer of the composite particle. The composite metal pigment composition according to claim 14, characterized in that the further coating layer is an organic phosphorus compound. A method for producing a composite metal pigment composition comprising the following steps 1) to 3):
The above production method comprises the steps of: 1) dispersing metal particles in a solvent; 2) coating the metal particles with a metal oxide; and 3) washing and filtering the composite particles having the metal particles and the metal oxide coating formed on the surfaces thereof obtained in step 2), and replacing the organic solvent with water. Step 3) is carried out at 5 to 80° C. and in a state in which the solid content is 80 mass % or less. The manufacturing method according to claim 16, wherein the composite metal pigment composition is the composite metal pigment composition according to any one of claims 1 to 7. A method for producing a composite metal pigment composition comprising the following steps 1) to 3):
1) a step of dispersing metal particles in a solvent; 2) a step of coating the metal particles with a metal oxide; and 3) a step of washing and filtering the composite particles having the metal particles obtained in step 2) and the metal oxide coating formed on their surfaces, and replacing the solvent with water. The above-mentioned manufacturing method is characterized in that step 3) comprises filtering the treatment liquid obtained in step 2) to reduce the volatile content to 70% by weight or less, followed by washing, filtering, and replacing the organic solvent with water. The manufacturing method according to claim 18, wherein the composite metal pigment composition is the composite metal pigment composition according to any one of claims 1 to 7. The method according to claim 16 or 18, characterized in that after step 3), an organic phosphoric acid compound is mixed with the composite metal pigment composition obtained to form a further coating layer. A water-based paint characterized by using the composite metal pigment composition according to any one of claims 1 to 7. A water-based paint characterized by using the composite metal pigment composition according to claim 11. A water-based paint characterized by using the composite metal pigment composition according to claim 15. A method for producing a water-based paint, comprising using the composite metal pigment composition according to any one of claims 1 to 7.