JP2025011960A - Resin-bonded aluminum pigments, paints, and inks - Google Patents

Abstract

To provide a resin-attached aluminum pigment which has excellent designability, and excellent adhesion and chemical resistance.SOLUTION: There is provided a flat resin-attached aluminum pigment in which the surface of aluminum particles are coated with a resin layer containing a monomer having one or more radical-polymerizable double bonds and/or a polymer of an oligomer, wherein resin particles having a circle-equivalent diameter of 5 to 50 nm are attached onto an arbitrary edge part of the resin-attached aluminum pigment.SELECTED DRAWING: Figure 2

Description

The present invention relates to a resin-attached aluminum pigment, and to paints and inks containing the resin-attached aluminum pigment.

Traditionally, aluminum pigments have been used in metallic paints, printing inks, plastic blends, etc., to achieve a cosmetic effect that emphasizes a metallic look. In particular, thin-film aluminum with an average particle size of 20 μm or less and a particle thickness of 0.1 μm or less has excellent design properties. On the other hand, by coating these aluminum pigments with resin, it is possible to improve chemical resistance to chemicals, such as alkali resistance.

As a method for improving the alkali resistance of aluminum pigments as described above, a method of subjecting the aluminum pigments to a specific surface treatment has been proposed.
For example, Patent Document 1 describes that a pigment having excellent chemical resistance to chemicals such as alkalis can be provided by setting the ratio of the total area of resin particles having an equivalent circle diameter of 25 nm or more on the surface of the coating resin that coats the surfaces of aluminum particles to a specific range. However, there is no description about aggregability due to interactions between aluminum particles or dispersibility of the pigment in paint.

Patent Document 2 describes how a metal pigment can be provided that has improved affinity and adhesion with binder resins such as paints, and improved peel resistance of coatings and printed surfaces, without substantially reducing gloss, by leaving part of the surface of the metal pigment particles intact and forming synthetic resin protrusions in various places on the remaining surface of the metal pigment particles. However, there is no description of chemical resistance to alkalis and other chemicals, nor is there any description of cohesiveness due to interactions between aluminum particles, or dispersibility of the pigment in paint.

International Publication No. 2018/047360 JP 2001-115061 A

The present invention aims to provide a resin-attached aluminum pigment that has not necessarily been fully realized by the above-mentioned conventional techniques, and aims to provide a resin-attached aluminum pigment that has excellent design properties, adhesion, and chemical resistance by improving the dispersibility of the resin-attached aluminum pigment in paint.

As a result of intensive research aimed at solving the above-mentioned problems, the inventors have discovered that by arranging resin particles near the edges of a resin-adhered aluminum pigment, it is possible to obtain a resin-adhered aluminum pigment that has improved paint dispersibility, excellent design properties, and excellent adhesion and chemical resistance to chemicals such as alkalis, and have thus completed the present invention.
That is, the gist of the present invention is as follows.
[1] A flat resin-attached aluminum pigment in which the surfaces of aluminum particles are coated with a resin layer containing a polymer of a monomer/oligomer having one or more radically polymerizable double bonds,
The resin-adhered aluminum pigment has resin particles having a circle-equivalent diameter of 5 to 50 nm adhered to any edge portion of the resin-adhered aluminum pigment.
[2] A flat resin-attached aluminum pigment in which the surfaces of aluminum particles are coated with a resin layer containing a polymer of a monomer/oligomer having one or more radically polymerizable double bonds,
The resin-adhered aluminum pigment has, on an edge portion of the resin-adhered aluminum pigment, 3 to 1,000 resin particles having a circle-equivalent diameter of 5 to 50 nm adhered per 5 μm of the edge portion.
[3] The resin-adhered aluminum pigment according to the above [2], wherein 3 to 100 resin particles having a circle-equivalent diameter of 5 to 50 nm are adhered to an edge portion of the resin-adhered aluminum pigment per 5 μm of the edge portion.
[4] The resin-adhered aluminum pigment according to the above [2], wherein 10 to 100 resin particles having a circle-equivalent diameter of 5 to 50 nm are adhered to an edge portion of the resin-adhered aluminum pigment per 5 μm of the edge portion.
[5] The resin-adhered aluminum pigment according to the above [2], wherein the average surface roughness Ra of the resin layer is 2.0 to 7.0 nm.
[6] The resin-adhered aluminum pigment according to the above [2], wherein the proportion of the portion of the resin layer where the thickness τ of the resin layer is 5 nm or less is 5% or less, as observed by cross-sectional observation of the resin-adhered aluminum pigment.
[7] The resin-adhered aluminum pigment according to the above [2], wherein the average cross-sectional thickness τ' of the aluminum particles is 0.03 to 0.18 μm, and the average particle diameter d50 of the aluminum particles is 5 to 15 μm.
[8] A paint containing the resin-adhered aluminum pigment according to any one of [2] to [7] above.
[9] An ink containing the resin-adhered aluminum pigment according to any one of [2] to [7] above.

The present invention makes it possible to provide a resin-attached aluminum pigment that has not necessarily been fully realized with conventional technology, and improves the dispersibility of the resin-attached aluminum pigment in paint, providing a resin-attached aluminum pigment with excellent design properties, adhesion, and chemical resistance.

1 is an example of a SEM photograph of the resin-adhered aluminum pigment of Example 1. 2 is an example of an SEM photograph of the resin-adhered aluminum pigment of Example 1, which is a higher magnification of the SEM photograph of FIG. 1 . 1A and 1B are both examples of AFM photographs of the resin-adhered aluminum pigment of Example 1, where 1A is a bird's-eye view and 1B is a Height image. 1 is an example of a TEM photograph of a cross section of the resin-adhered aluminum pigment of Example 1. 1 is an example of a microscope photograph of a metallic base coated plate using the resin-adhered aluminum pigment of Example 1. 1 is an example of a SEM photograph of the resin-adhered aluminum pigment of Comparative Example 1. 1 is an example of a TEM photograph of a cross section of a resin-adhered aluminum pigment of Comparative Example 1. 1 is an example of a microscope photograph of a metallic base coated plate using the resin-adhered aluminum pigment of Comparative Example 1.

The following describes an example of a preferred embodiment of the present invention. However, the following embodiment is merely an example for explaining the present invention, and the present invention is not limited to the following embodiment.

The resin-adhered aluminum pigment of the present invention has excellent adhesion and chemical resistance while maintaining excellent design properties.

The specific shapes of the aluminum particles that are the raw material for the resin-adhered aluminum pigment of the present invention are described below.

The aluminum particles used in the present invention (hereinafter, sometimes referred to as "flake aluminum powder") are not limited in type, and may be those generally used as aluminum pigments, and may have a flat shape such as a scaly, angular, or rounded shape. If high design properties (e.g., properties such as brightness, brilliance, flip-flop feel, and hiding power) are to be maintained, the effect of the present invention will be more pronounced if high design grade aluminum particles (vapor deposition metallic paint or ink grade) are used.

There is no particular limitation on the method for producing flake aluminum powder, but it can be obtained by grinding granular powder or small pieces of metallic aluminum together with a few percent of a grinding aid using a mechanical method such as the stamp mill method, dry ball mill method, wet ball mill method, attritor method, or vibrating ball mill method.

As a method for producing highly decorative flake aluminum powder, for example, the method described in WO 99/54074 can be mentioned, and the flake aluminum powder obtained by this method, which has a smooth surface and a uniform thickness, can be particularly preferably used as the raw material for the aluminum pigment of the present invention.

The particle size of the aluminum particles used as the raw material for the resin-adhered aluminum pigment of the present invention varies depending on the application. When the resin-adhered aluminum pigment of the present invention is used for paints and printing inks, aluminum particles with an average particle size d50 (μm) of about 1 to 100 μm can be suitably used. Recently, applications in which high designability of metal pigments is particularly required include automobiles, general home appliances, and information appliances such as mobile phones, and in these applications, metal pigments are used to paint metals such as iron and magnesium alloys or plastics. In order to ensure high designability, the preferred average particle size (d50) of the aluminum particles of the resin-adhered aluminum pigment of the present invention used for these applications is 5 to 35 μm, and more preferably 5 to 15 μm.

The average particle diameter d50 (μm) of the aluminum particles of the present invention can be measured using a general laser diffraction/scattering type particle size distribution measuring device, and can be measured, for example, as follows.
The average particle size (d50) of the particles of the flaky aluminum powder is measured using a laser diffraction/scattering type particle size distribution measuring device (LA-300/Horiba, Ltd.) Mineral spirits can be used as the measurement solvent.
It is preferable that the resin-adhered aluminum pigment sample is subjected to ultrasonic dispersion for 2 minutes as a pretreatment, and then charged into a dispersion tank and the measurement is started after confirming that the appropriate concentration has been reached.

The average cross-sectional thickness τ' (μm) of the aluminum particles of the present invention can be determined by using an FE-SEM image of the cross section of the coating film and measuring it with the aid of image analysis software.
Specifically, 100 particles are randomly selected from an FE-SEM image of the cross section of the coating film, the cross-sectional thickness of the particles is automatically measured, and the arithmetic average value of the 100 particles is calculated.
The average cross-sectional thickness τ' (μm) of the aluminum particles of this embodiment is preferably 0.03 to 0.20 μm, and more preferably 0.03 to 0.15 μm.

The specific composition and shape of the resin attached to the surface of the aluminum pigment of the present invention will be described below.

The resin attached to the resin-attached aluminum pigment of this embodiment is not particularly limited, but is preferably a polymer of a monomer (hereinafter referred to as a monomer) and/or an oligomer having one or more radically polymerizable double bonds.

The monomer is not particularly limited, and a conventionally known monomer can be used. Specific examples include, but are not limited to, unsaturated carboxylic acids (e.g., acrylic acid, methacrylic acid, itaconic acid, fumaric acid, citraconic acid, crotonic acid, maleic acid, or maleic anhydride), mono- or diesters of phosphorus or phosphonic acid (e.g., 2-methacryloyloxyethyl phosphate, di-2-methacryloyloxyethyl phosphate, tri-2-methacryloyloxyethyl phosphate, 2-acryloyloxyethyl phosphate, di-2-acryloyloxyethyl phosphate, tri-2-acryloyloxyethyl phosphate, diphenyl-2-acryloyloxyethyl phosphate, dibutyl-2-methacryloyloxyethyl phosphate, dioctyl-2-acryloyloxyethyl phosphate, 2-meth ... propyl phosphate, bis(2-chloroethyl)vinyl phosphonate, diallyl dibutyl phosphonosuccinate, 2-methacryloyloxyethyl phosphate, 2-acryloyloxyethyl phosphate), coupling agents (e.g., γ-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, vinyltrichlorosilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyl tris(β-methoxyethoxy)silane, isopropyl isostearoyl diacryl titanate, acetoalkoxyaluminum diisopropylate, zircoaluminate), nitriles of unsaturated carboxylic acids (e.g., acrylonitrile, methacrylonitrile), or esters of unsaturated carboxylic acids (e.g., acrylic acid Methyl, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methoxyethyl acrylate, butoxyethyl acrylate, glycidyl acrylate, cyclohexyl acrylate, 1,6-hexanediol diacrylate, 1,4-butadiol diacrylate, triethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, trimethylolpropane triacrylate, tetramethylolpropane tetraacrylate, tetramethylolpropane methane triacrylate, trimethylolpropane trimethacrylate, tetramethylolmethane trimethacrylate, di-trimethylolpropane tetraacrylate, pentaerythritol tetraacrylate, di-pentaerythritol hexaacrylate, di-pentaerythritol pentaacrylate, di-pentaerythritol pentaacrylate monopropionate, triacrylformal, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, stearyl methacrylate, hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, methoxyethyl methacrylate, butoxyethyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate), and the like can be suitably used.
Furthermore, cyclic unsaturated compounds (e.g., cyclohexene) and aromatic unsaturated compounds (e.g., styrene, α-methylstyrene, vinyltoluene, divinylbenzene, cyclohexene vinyl monoxide, divinylbenzene monoxide, vinyl acetate, vinyl propionate, allylbenzene, or diallylbenzene) can also be suitably used.
Furthermore, cyclic unsaturated compounds (e.g., cyclohexene) and aromatic unsaturated compounds (e.g., styrene, α-methylstyrene, vinyltoluene, divinylbenzene, cyclohexene vinyl monoxide, divinylbenzene monoxide, vinyl acetate, vinyl propionate, allylbenzene, or diallylbenzene) can also be suitably used. The oligomer having one or more radically polymerizable double bonds can be a polymer of these monomers.

In the method for producing a resin-adhered aluminum pigment of this embodiment, the amount of the monomer and/or oligomer added to the aluminum particles is preferably, for example, 5% or more, and more preferably 8% or more, 10% or more, or 15% or more. By adding the amount of the monomer and/or oligomer at or above the lower limit, a resin layer is formed on the surface of the aluminum particles, and resin particles are formed at the edge portions of the resin-adhered aluminum pigment. If the amount of the monomer and/or oligomer added is below the lower limit, a resin layer and resin particles are not sufficiently formed on the surface of the aluminum particles.

In the method for producing a resin-adhered aluminum pigment of this embodiment, it is preferable to use a radical polymerization initiator (hereinafter, referred to as a polymerization initiator).
The polymerization initiator is generally known as a radical generator, and the type thereof is not particularly limited.
Examples of the polymerization initiator include, but are not limited to, peroxides such as benzoyl peroxide, lauoyl peroxide, and bis-(4-t-butylcyclohexyl)peroxydicarbonate, and azo compounds such as 2,2'-azobis-isobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, and 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile.

The amount of polymerization initiator used is a factor that determines the molecular weight of the resin particles. If the amount of polymerization initiator is 0.5 molar equivalents or less relative to the amount of monomer, the molecular weight will increase due to the small amount of polymerization initiator, leading to a decrease in design. If the amount is 2.0 molar equivalents or more, the amount of polymerization initiator will be excessive, causing a termination reaction between the initiators, and the resulting resin particles will tend to slide off, which may cause bumps (irregularities on the coating surface) in the coating. For these reasons, it is preferable that the amount of polymerization initiator used be, for example, 0.5 molar equivalents or more and less than 2.0 molar equivalents relative to the monomer.

The solvent is not limited to the following examples, but any organic solvent that is inactive to the metal pigment may be used to disperse the metal pigment in the organic solvent. Examples of the organic solvent include aliphatic hydrocarbons such as hexane, heptane, octane, and mineral spirits; aromatic hydrocarbons such as benzene, toluene, xylene, and solvent naphtha; ethers such as tetrahydrofuran and diethyl ether; alcohols such as ethanol, 2-propanol, and butanol; esters such as ethyl acetate and butyl acetate; glycols such as propylene glycol and ethylene glycol; glycol ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, and ethylene glycol monobutyl ether; and glycol esters such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, and ethylene glycol monomethyl ether acetate. These organic solvents may be used alone or in combination of two or more. In the present invention, the organic solvent is also used as a reaction solvent when the above-mentioned monomers and/or oligomers are polymerized to form a resin.

In one embodiment of the present invention, the resin-adhered aluminum pigment has resin particles having a circle-equivalent diameter (more specifically, area-equivalent circle diameter; Heywood diameter) of 5 to 50 nm attached to any edge portion thereof, i.e., compared to the surface of a flat aluminum particle, the resin particles are specifically attached to at least a portion of the edge portion.
In one embodiment of the present invention, the resin-adhered aluminum pigment has resin particles having a circle-equivalent diameter of 5 to 50 nm attached to its edge portion, preferably 10 to 1,000 particles, more preferably 3 to 100 particles, and even more preferably 10 to 100 particles per 5 μm length in any portion constituting the edge portion (any part of the outer periphery of the resin-adhered aluminum pigment).
The edge portion refers to the end (outer edge portion) and the area immediately adjacent thereto of a flat, resin-coated aluminum pigment having a scaly, angular, rounded or other shape as shown in FIG.
In the manufacturing process of the resin-attached aluminum pigment of the present invention, it is preferable to carry out the polymerization reaction while maintaining the primary particle state by using various high-speed stirring means such as a kneader, a two-roll mill, a three-roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, an annular bead mill, or an attritor, from dispersing aluminum particles in a solvent until the polymerization of the monomer and the end of the reaction. This process increases the interaction between particles, allows the resin particles to be selectively attached to the edge portions, and maintains the smoothness of the surface.

The agitation speed of the resin-adhered aluminum pigment of the present invention is preferably 700 to 10,000 rpm, more preferably 700 to 2,000 rpm, since a load of 10,000 rpm or more may damage the aluminum particles, and a speed of 700 rpm or less may cause aggregation of the aluminum particles when the resin is attached.

The resin-attached aluminum pigment of the present invention is characterized by high design retention and chemical resistance to chemicals such as alkali, compared to thin-film aluminum pigments. This is characterized by having a resin layer and forming fine resin particles at the edge portion by reacting a monomer at a high polymerization initiator concentration (e.g., 0.5 molar equivalents or more and less than 2.0 molar equivalents) with a monomer amount sufficient for maintaining alkali resistance and design (e.g., the amount of monomer and/or oligomer added to the aluminum particles is 5% or more) under high-speed stirring. High-speed stirring increases the interaction between the aluminum pigments, making it difficult for the resin particles to adhere to areas other than the edge portions of the aluminum particles, and it is believed that the selective formation of resin particles at the edge portions improves the dispersibility of the resin-attached aluminum pigment in the paint. It is believed that the improved paint dispersibility improves the hiding power and color tone of the paint, resulting in a paint with excellent design.
The resin-adhered aluminum pigment can be evaluated for the number of resin particles at the edge from its SEM image, for the formation of a smooth resin layer from AFM measurement data, and for the formation of the resin layer from TEM images. These evaluation methods are explained below with specific examples, but the equipment used and measurement conditions can be changed within the range in which appropriate evaluation results can be obtained.

[Amount of resin particles present per 5 μm at edge portion (A) measured by SEM]
The resin-coated aluminum pigment is diluted with an excess of pentane, hand-dispersed for 1 minute, and the resulting solution is air-dried to obtain a measurement sample of the resin-coated aluminum pigment.
Next, gold is vapor-deposited onto the measurement sample, and the pigment side surface is observed from an angle of 45° using a scanning electron microscope (e.g., SEM JSM7800F manufactured by JEOL Ltd.) and evaluated. The measurement magnification is, for example, 10,000 times. The resin-adhered aluminum pigment is observed in 30 fields of view, and the projected area circle equivalent diameter (circle equivalent diameter) of the resin particles is measured. The amount of resin particles with a circle equivalent diameter of 5 to 50 nm present at the edge portion of the resin-adhered aluminum pigment is determined using image analysis software (e.g., Win Roof version 5.5 (manufactured by MITANI CORPORATION)), and then the number of resin particles, which are primary particles, present on the 5 μm edge portion is determined, and the arithmetic average value (A) is calculated.

The equivalent circle diameter of the resin particles present on the edge portions of the resin-adhered aluminum pigment of the present invention is preferably 5 to 50 nm, and more preferably 5 to 40 nm.
The number (A) of resin particles present per 5 μm length of the edge portion is preferably 3 to 1,000, more preferably 3 to 100, and even more preferably 10 to 100.

The average surface roughness Ra of the resin layer surface of the resin-adhered aluminum pigment of the present invention is 2.0 to 7.0 nm.
The average surface roughness Ra referred to in the present invention can be calculated by a surface morphology observation method using a general atomic force microscope. Specifically, it is calculated, for example, by the following method.
As a method for observing the surface morphology of the resin-attached aluminum pigment, an atomic force microscope (hereinafter abbreviated as AFM) (for example, Dimension Icon (manufactured by Bruker)) can be used. As a pretreatment, for example, a sample of the resin-attached aluminum pigment is washed with excess methanol, vacuum dried, dispersed again in acetone, dropped onto a Si wafer, and naturally dried. The quantitative determination of the surface roughness by AFM is defined as the "average surface roughness Ra (nm)" for a resin-attached aluminum pigment that does not overlap with other resin-attached aluminum pigments, with a measurement field of view of 2 μm and 512 pixels. The term surface roughness is based on JIS-B-0601:2013.
The average surface roughness Ra of the resin-attached aluminum pigment of the present invention is usually 10.0 nm or less, preferably 7.0 nm or less. When the average surface roughness Ra is 7.0 or less, the regular reflectance of light on the surface is high, so that the pigment shows extremely excellent light brightness and good flop-flop properties. In addition, an average surface roughness Ra of 7.0 or less indicates that no resin particles are present on the surface of the resin-attached aluminum pigment except for the edge portions, or that only a very small amount of resin particles are attached.

In the resin-adhered aluminum pigment of the present invention, the thickness τ of the resin layer measured by cross-sectional observation of the resin-adhered aluminum pigment is preferably 5 to 30 nm, and more preferably 10 to 20 nm. When the thickness τ of the resin layer is within this range, it exhibits extremely high brightness and also has good chemical resistance. Furthermore, in the resin-adhered aluminum pigment of the present invention, the proportion of the portion of the resin layer where the thickness of the resin layer is 5 nm or less is preferably 5% or less.

[Proportion (B) of aluminum pigment interfaces with resin layer thickness τ of 5 nm or less as determined by TEM measurement]
The average thickness τ of the resin layer referred to in the present invention is first pretreated by ultrasonically cleaning the resin-adhered aluminum pigment with excess methanol and chloroform, then vacuum drying, dispersing and cleaning again in acetone, and then naturally drying. Then, after embedding in epoxy resin and completely curing, trimming and cutting out slices are performed, and the cross section is observed with a transmission electron microscope (hereinafter abbreviated as TEM) to observe the resin coating layer. Observation is performed in four fields of view at 200,000 times magnification per field, and the resin adhesion site of 5 nm or less where the resin adhesion is insufficient is obtained from the outline of the resin layer using image analysis software Win Roof version 5.5 (manufactured by MITANI CORPORATION). Next, the interface length of the aluminum pigment in the field of view is obtained, and the proportion of the resin layer thickness of 5 nm or less where the resin adhesion is insufficient is calculated, and defined as [the proportion (B) of the interface of the aluminum pigment where the resin layer thickness is 5 nm or less].

The ratio (B) of the interface of the aluminum pigment having a resin layer thickness τ of 5 nm or less obtained by cross-sectional observation of the resin-adhered aluminum pigment of the present invention is preferably 5% or less, and more preferably 1% or less. When (B) satisfies such conditions, the aluminum particles are entirely coated with resin, improving chemical resistance.

In addition, the resin-adhered aluminum pigment of the present invention has a resin layer formed on the surface of the aluminum particles, which improves the chemical resistance in the coating film. When the color difference ΔE is calculated according to 6.3.2 of JIS-Z-8730 (1980) to evaluate chemical resistance, it is preferable that ΔE is less than 1.0.

The resin-adhered aluminum pigments of the present invention can be used in paints and inks.
The resin-adhered aluminum pigment of the present invention can be suitably used for automobiles, general home appliances, information appliances such as mobile phones, printing, and coatings for metals such as iron and magnesium alloys, plastics, and other substrates, and can exhibit high design properties. Inks containing the resin-adhered aluminum pigment of the present invention can be suitably used for metallic paints, printing inks, paints for plastic kneading, and the like, and can exhibit high design properties.

Additives commonly used in the paint industry, such as pigments, dyes, wetting agents, dispersants, color separation inhibitors, leveling agents, slip agents, rheology control agents, viscosity modifiers, anti-skinning agents, anti-gelling agents, defoamers, thickeners, anti-sagging agents, anti-mold agents, UV absorbers, film-forming aids, and surfactants, may also be added to the novel resin-attached aluminum pigment of the present invention as appropriate.

Next, the present invention will be described in detail with reference to examples. In the following description, "%" indicates % by weight.

Example 1
100 g of commercially available aluminum paste (manufactured by Asahi Kasei Corporation, SB-10 "average particle size 10 μm, non-volatile content 74% by mass") was placed in a 1-liter four-neck flask, 500 g of mineral spirits was added, and while bubbling nitrogen gas, a high-speed stirring disperser was used to stir a shear disk with a diameter of 8 cm at 1000 rpm, and the temperature in the system was raised to 70 ° C. Next, 1.11 g of acrylic acid was added and stirring was continued for 30 minutes at 70 ° C. Next, 10.0 g of trimethylolpropane trimethacrylate, 1.11 g of di-trimethylolpropane tetraacrylate, 9.5 g of 2,2'-azobis-2,4-dimethylvaleronitrile (polymerization initiator), and 50 g of mineral spirits were dropped over 1 hour, and polymerization was carried out for a total of 5 hours while maintaining the temperature in the system at 70 ° C. The amount of unreacted trimethylolpropane trimethacrylate and di-trimethylolpropane tetraacrylate in the filtrate sampled at this point was analyzed by gas chromatography, and it was found that 99% or more of the added amount had reacted. After the polymerization was completed, the treated slurry was filtered to obtain a resin-adhered aluminum pigment. The heating residue of the aluminum pigment (according to JIS-K-5910) was 60.5% by weight.
Figures 1 and 2 show FE-SEM images of the resin-adhered aluminum pigment of Example 1. As shown in Figures 1 and 2, resin particles are adhered to the surface of the resin-adhered aluminum pigment of Example 1, and many of them are adhered specifically to edge portions.

Example 2
A resin-adhered aluminum pigment was obtained in the same manner as in Example 1, except that the amount of 2,2'-azobis-2,4-dimethylvaleronitrile (polymerization initiator) was changed to 11.9 g.

Example 3
A resin-adhered aluminum pigment was obtained in the same manner as in Example 1, except that the amounts of trimethylolpropane trimethacrylate, di-trimethylolpropane tetraacrylate, and 2,2'-azobis-2,4-dimethylvaleronitrile (polymerization initiator) were changed to 13.3 g, 1.5 g, and 12.7 g, respectively.

Example 4
A resin-adhered aluminum pigment was obtained in the same manner as in Example 1, except that in Example 3, 15.8 g of 2,2'-azobis-2,4-dimethylvaleronitrile (polymerization initiator) was used.

Example 5
A resin-adhered aluminum pigment was obtained in the same manner as in Example 1, except that the aluminum paste used in Example 1 was changed to 100 g (manufactured by Asahi Kasei Corporation, FD-5060 "average particle size 6 μm, non-volatile content 72 mass%"), 5.2 g of trimethylolpropane trimethacrylate, 0.6 g of di-trimethylolpropane tetraacrylate, and 4.9 g of 2,2'-azobis-2,4-dimethylvaleronitrile (polymerization initiator).

Example 6
A resin-adhered aluminum pigment was obtained in the same manner as in Example 5, except that the amount of 2,2'-azobis-2,4-dimethylvaleronitrile (polymerization initiator) was changed to 7.4 g.

Example 7
A resin-adhered aluminum pigment was obtained in the same manner as in Example 1, except that the amounts of trimethylolpropane trimethacrylate, di-trimethylolpropane tetraacrylate, and divinylbenzene were changed to 9.0 g, 1.11 g, and 1.0 g, respectively.

Example 8
A resin-adhered aluminum pigment was obtained in the same manner as in Example 1, except that the aluminum paste (manufactured by Asahi Kasei Corporation, MH-8801 "average particle size 15 μm, non-volatile content 65 mass%), trimethylolpropane trimethacrylate 9.8 g, di-trimethylolpropane tetraacrylate 8.8 g, and 2,2'-azobis-2,4-dimethylvaleronitrile (polymerization initiator) 8.4 g were changed to 100 g.

Comparative Example 1
100 g of commercially available aluminum paste (manufactured by Asahi Kasei Corporation, SB-10 "average particle size 10 μm, non-volatile content 74% by mass") was placed in a 1-liter four-neck flask, 500 g of mineral spirits was added, and the mixture was stirred for 1 hour while bubbling nitrogen gas, and the temperature in the system was raised to 70 ° C. Then, 1.11 g of acrylic acid was added and the mixture was stirred for 30 minutes at 70 ° C. Next, using a circulating ultrasonic disperser, ultrasonic waves were directly irradiated through an ultrasonic horn to the slurry liquid in the container, and vibration dispersion was performed for 1 hour. Next, 13.3 g of trimethylolpropane trimethacrylate, 1.5 g of di-trimethylolpropane tetraacrylate, 2.0 g of 2,2'-azobis-2,4-dimethylvaleronitrile (polymerization initiator), and 50 g of mineral spirits were dropped by a metering pump over 1 hour, and polymerization was performed for a total of 8 hours while maintaining the temperature in the system at 70 ° C. The amount of unreacted trimethylolpropane trimethacrylate and di-trimethylolpropane tetraacrylate in the filtrate sampled at this point was analyzed by gas chromatography, and it was found that 99% or more of the added amount had reacted. After the polymerization was completed, the treated slurry was filtered to obtain a resin-adhered aluminum pigment. The heating residue of the aluminum pigment (according to JIS-K-5910) was 65.2% by weight.
Fig. 6 shows an FE-SEM image of the resin-adhered aluminum pigment of Comparative Example 1. As shown in Fig. 6, no resin particles are adhered to the surface of the resin-adhered aluminum pigment of Comparative Example 1.

Comparative Example 2
In Comparative Example 1, a resin-adhered aluminum pigment was obtained in the same manner as in Comparative Example 1, except that the aluminum paste (manufactured by Asahi Kasei Corporation, FD-5060 "average particle size 6 μm, non-volatile content 72 mass%"), trimethylolpropane trimethacrylate, and di-trimethylolpropane tetraacrylate were changed to 10.4 g and 1.2 g, respectively.

Comparative Example 3
In Comparative Example 1, 100 g of aluminum paste (manufactured by Asahi Kasei Corporation, MH-8801 "average particle size 15 μm, non-volatile content 65 mass%"), 4.7 g of trimethylolpropane trimethacrylate, and 0.5 g of di-trimethylolpropane tetraacrylate were changed to obtain a resin-adhered aluminum pigment in the same manner as in Comparative Example 1.

Comparative Example 4
A resin-adhered aluminum pigment was obtained in the same manner as in Comparative Example 1, except that the amounts of trimethylolpropane trimethacrylate and di-trimethylolpropane tetraacrylate were changed to 1.4 g and 0.1 g, respectively.

[Evaluation 1 (average particle size: d50 measurement)]
The average particle size (d50) of the aluminum particles was measured using a laser diffraction/scattering type particle size distribution measuring device (LA-300/HORIBA, Ltd.).
Mineral spirits 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 aluminum particles used as samples were ultrasonically dispersed for 2 minutes as a pretreatment, and then placed in a dispersion tank. After confirming that the appropriate concentration had been achieved, the measurements were started.
After the measurement was completed, d50 was automatically displayed.

[Evaluation 2 (Measurement of average cross-sectional thickness τ' of aluminum particles)]
(1) Preparation of Coated Plates Using the aluminum pigments obtained in the Examples and Comparative Examples, metallic base paints were prepared according to the following compositions.
Aluminum pigment: 2g
Thinner (Musashi Paint Co., Ltd., product name "Plaace Thinner No. 2726"): 50g
Acrylic resin (manufactured by Musashi Paint Co., Ltd., product name "Plaace No. 7160"): 33 g
The above paint was applied to an ABS resin plate using an air spray device so that the dry film thickness was 20 μm, and then dried in an oven at 60° C. for 30 minutes to obtain a metallic base-coated plate.
A top coat paint prepared according to the following composition was applied onto the metallic base coated plate using an air spray device.
・Hitaroid Varnish 3685S (Hitachi Chemical): 25g
Mixed thinner (solvent mixing ratio: toluene: 45% by mass, butyl acetate: 30% by mass, ethyl acetate: 20% by mass, 2-acetoxy-1-methoxypropane: 5% by mass): 20 g
・Duranate TPA100 (Asahi Kasei Chemicals): 5g
After the above coating, the plate was dried in an oven at 60° C. for 30 minutes to obtain a coated plate for evaluation.

(2) Preparation of Cross Section of Coating Film Using the coated plate for evaluation produced as described above, a cross section of the coating film was prepared according to the following procedure.
Using scissors, the coated plate for evaluation was cut into pieces measuring 2 cm square.
The cut 2 cm square coated evaluation panels were repeatedly cut along the cross section of the coating using a large rotary microtome (RV-240, manufactured by Yamato Koki Kogyo Co., Ltd.) to remove microscopic aluminum and acrylic resin protruding from the cross section.
The cross section of the coating film obtained as described above 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, thereby preparing a cross section of the coating film for obtaining an FE-SEM image as described below.

(3) Obtaining particle cross section (FE-SEM image) The coating film cross section (coated plate) obtained in the above ((2) Preparation of coating film cross section) was attached parallel to an SEM sample stage, and an FE-SEM image of the coating film cross section was obtained using a field emission type FE-SEM (Hitachi/S-4700).
The conditions for FE-SEM observation and acquisition were such that the acceleration voltage was adjusted to 5.0 kV and the image magnification was 10,000 times.
In addition, before acquiring (capturing) the FE-SEM image, electronic axis alignment processing was performed to prevent distortion of the boundary between the aluminum particles and the acrylic resin in the FE-SEM image.

(4) Analysis (measurement of average cross-sectional thickness of aluminum particles on particle cross section)
Using the FE-SEM images (10,000 magnification) obtained in the procedure for obtaining particle cross sections (FE-SEM images) described above ((1)-(3)) and image analysis software Win Roof version 5.5 (manufactured by MITANI CORPORATION), the particle thicknesses at the cross sections of the aluminum particles were measured, and the average cross-sectional 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 using the register/change function.
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 manner, using the image analysis software Win Roof version 5.5, 100 aluminum particles having an average particle diameter within ±50% of d50 ((IV) Average particle diameter: d50) described below were selected, and the thickness of the cross section of the aluminum particles was automatically measured. The arithmetic mean value of the 100 particles was calculated, and the average cross-sectional thickness τ' of the aluminum particles was determined.

[Evaluation 3 (amount of resin particles present per 5 μm at edge portion (A) measured by FE-SEM)]
The resin-coated aluminum pigment was diluted with an excess of pentane, hand-dispersed for 1 minute, and the resulting solution was air-dried to obtain a measurement sample of the resin-coated aluminum pigment.
Next, a field emission FE-SEM (Hitachi/S-4700) was used to obtain an FE-SEM image of the cross section of the coating film of the measurement sample, and the pigment side surface was observed from an angle of 45° and evaluated. The measurement magnification was 20,000 times. The resin-adhered aluminum particles were observed in 30 fields of view, and the number of primary particles (single resin particles) and secondary particles (aggregates of primary particles) resin particles with an area circle equivalent diameter (circle equivalent diameter) of 5 to 50 nm present in an edge portion range of 5 μm at a distance between two points on the edge portion was determined using the image analysis software Win Roof version 5.5, and the arithmetic average value (A) was calculated.

[Evaluation 4 (Measurement of average surface roughness Ra of resin-adhered aluminum pigment surface)]
The surface morphology of the resin-attached aluminum pigment was observed using an atomic force microscope (AFM; Dimension Icon (manufactured by Bruker)). As a pretreatment, the resin-attached aluminum pigment sample was washed with excess methanol, vacuum dried, and dispersed again in acetone, then dropped onto a Si wafer and naturally dried. A line profile (300 scans) of one visual field of 4 μm square was obtained using the AFM. The same operation was performed for a total of four or more visual fields, and the arithmetic average value was obtained and taken as Ra.
3(a) and (b) show AFM images of the surface morphology of the resin-adhered aluminum pigment of Example 1.

[Evaluation 5 (proportion of aluminum pigment interfaces with a resin layer thickness τ of 5 nm or less as determined by TEM measurement (B))]
The average thickness τ of the resin layer in the present invention was first pretreated by ultrasonically cleaning the aluminum pigment to which the resin was attached with excess methanol and chloroform, then vacuum drying, dispersing and cleaning again in acetone, and then naturally drying. Then, the aluminum pigment was embedded in epoxy resin and completely cured, and then trimming and cutting out a section was performed, and the cross section was observed with a TEM to observe the resin coating layer. Observation was performed in four fields of view at 200,000 times magnification per field, and the resin adhesion site of 5 nm or less where the resin adhesion was insufficient was obtained from the outline of the resin layer using image analysis software Win Roof version 5.5. Next, the interface length of the aluminum pigment in the field of view was obtained, the proportion of the site with insufficient resin adhesion was calculated, and the arithmetic average proportion (B) was obtained.
Figure 4 shows a TEM photograph of a cross section of the resin-adhered aluminum pigment of Example 1. Figure 7 shows a TEM photograph of a cross section of the resin-adhered aluminum pigment of Comparative Example 1. As is clear from Figures 4 and 7, a resin layer is formed on the surface of the aluminum particle.

[Evaluation 6 (evaluation of coating film adhesion, chemical resistance, gloss retention, and pigment dispersibility)]
Using the resin-adhered aluminum pigments obtained in Examples 1 to 8 and Comparative Examples 1 to 4, metallic coating compositions were prepared according to the following formulations.
Resin-attached aluminum pigment: 1.3 g (solid mass)
Thinner (a mixture of 30 parts of butyl acetate, 45 parts of toluene, 20 parts of isopropyl alcohol, and 5 parts of ethyl cellosolve): (D) g (the total amount of the resin-adhered aluminum pigment and (D) was adjusted to 33 g).
Clear (a mixture of 29 parts of Acrydic A-166 (manufactured by DIC), 3 parts of nitrocellulose (industrial nitrocellulose 1/2 AS, manufactured by Companhia Nitro Qumica Brasileira), and 68 parts of the above thinner) (binder resin component): 42 g
The resulting coating composition was spray-coated onto an ABS resin plate to a film thickness of 15 μm, and then dried at 55° C. for 30 minutes to prepare a coated plate for evaluation.
Using the above-mentioned coating plates for evaluation, the adhesion, chemical resistance, and gloss retention were evaluated.

(Adhesion of coating film)
Using the coated plate prepared above, cellophane tape (registered trademark: CT405AP-18, manufactured by Nichiban Co., Ltd.) was attached to the coating film and pulled at a 45 degree angle, and the degree of peeling of the resin-adhered aluminum pigment particles was visually observed. Depending on the observation results, the following evaluation was made.
○ (Good): No peeling △ (Acceptable): Slight peeling × (Not acceptable): Peeling

(Chemical resistance of coating film)
The lower half of the coated plate prepared above was immersed in a beaker containing 2.5N NaOH aqueous solution and left at 23°C for 24 hours. After the test, the coated plate was washed with water and dried, and the immersed and unimmersed parts were color-measured according to condition d (8-d method) of JIS-Z-8722 (1982), and the color difference ΔE was calculated according to JIS-Z-8730 (1980) 6.3.2. Evaluation was made according to the value of the color difference ΔE as follows (the smaller the value, the better).
○ (Good): Less than 1.0 △ (Acceptable): 1.0 or more but less than 2.0 × (Unacceptable): 2.0 or more

[Evaluation 7 (FF property (brightness, brilliance), hiding power of coating film)]
Using the resin-adhered aluminum pigments obtained in Examples 1 to 8 and Comparative Examples 1 to 4, metallic paints were prepared according to the following compositions.
Resin-attached aluminum pigment: 5.0 g
Thinner (product name "Acrydic 2000GL" manufactured by Kansai Paint Co., Ltd.): 13.0 g
Acrylic resin (product name "Acrydic 2000" manufactured by Kansai Paint Co., Ltd.): 97.0 g
Next, the metallic base paint was applied to a PET film using a 3 mil applicator and dried at room temperature for 30 minutes to obtain a metallic base-coated plate.
Figure 5 shows a microscope photograph of a metallic base coated plate using the resin-adhered aluminum pigment of Example 1. Figure 8 shows a microscope photograph of a metallic base coated plate using the resin-adhered aluminum pigment of Comparative Example 1. It is clear from Figure 5 that the individual resin-adhered aluminum pigments are uniformly dispersed in the coated plate of Example 1, whereas the resin-adhered aluminum pigments have low dispersibility and are overlapped in the coated plate of Comparative Example 1.

(2) Measurement of ΔF/F property (brightness, brilliance) The coating film formed by applying the above-prepared coating material to a PET sheet was evaluated for ΔF/F property using a variable angle colorimeter (manufactured by Suga Test Instruments Co., Ltd.). The incident angle was set to 45 degrees, and the light receiving angle of 15 degrees (L15), which is close to the regular reflection light, and the light receiving angle of 60 degrees (L60), which is close to the base color, were measured, excluding the light in the specular reflection area reflected by the coating film surface of the coating plate for evaluation. The ratio (L15/L60) was taken as ΔF/F property.

(3) Evaluation of paint dispersibility and hiding power The coating film formed by applying the above-mentioned prepared paint to a PET sheet was visually evaluated. Specifically, the above-mentioned prepared paint was prepared using a standard aluminum paste and a resin-coated aluminum paste, and two coated strips were drawn on a PET sheet, and a light was irradiated from the uncoated side to evaluate hiding power.
(The standard aluminum paste pigment is aluminum particles before being resin-coated.)
⊚: Has the same hiding power as the standard aluminum paste pigment.
◯: The hiding power is slightly decreased compared to the standard aluminum paste pigment.
Δ: The hiding power is low compared to the standard aluminum paste pigment.

The results of evaluations 1 to 7 are shown in Table 1.

Claims (9)

A flat resin-attached aluminum pigment in which the surfaces of aluminum particles are coated with a resin layer containing a polymer of a monomer and/or oligomer having one or more radically polymerizable double bonds,
The resin-adhered aluminum pigment has resin particles having a circle-equivalent diameter of 5 to 50 nm adhered to any edge portion of the resin-adhered aluminum pigment. A flat resin-attached aluminum pigment in which the surfaces of aluminum particles are coated with a resin layer containing a polymer of a monomer and/or oligomer having one or more radically polymerizable double bonds,
The resin-adhered aluminum pigment has, on an edge portion of the resin-adhered aluminum pigment, 3 to 1,000 resin particles having a circle-equivalent diameter of 5 to 50 nm adhered per 5 μm of the edge portion. The resin-adhered aluminum pigment according to claim 2, wherein 3 to 100 resin particles having a circle equivalent diameter of 5 to 50 nm are attached to the edge portion of the resin-adhered aluminum pigment per 5 μm of the edge portion. The resin-adhered aluminum pigment according to claim 2, wherein 10 to 100 resin particles having a circle equivalent diameter of 5 to 50 nm are attached to the edge portion of the resin-adhered aluminum pigment per 5 μm of the edge portion. The resin-attached aluminum pigment according to claim 2, wherein the average surface roughness Ra of the resin layer is 2.0 to 7.0 nm. The resin-adhered aluminum pigment according to claim 2, wherein the proportion of the portion of the resin layer where the thickness τ of the resin layer is 5 nm or less is 5% or less, as observed by cross-sectional observation of the resin-adhered aluminum pigment. The resin-adhered aluminum pigment according to claim 2, wherein the average cross-sectional thickness τ' of the aluminum particles is 0.03 to 0.18 μm, and the average particle diameter d50 of the aluminum particles is 5 to 15 μm. A paint containing the resin-attached aluminum pigment according to any one of claims 2 to 7. An ink containing the resin-attached aluminum pigment described in any one of claims 2 to 7.

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