JP7263768B2 - Black zinc dust and method for producing the same - Google Patents

Description

The present invention relates to black zinc dust and a method for producing the same. More particularly, the present invention relates to black zinc powder useful for industrial steel parts, anti-corrosion coatings for building members, and a method for producing the same.

Zinc dust is suitably used in industrial steel parts such as automobile parts and electrical parts, and anticorrosion undercoatings for protecting members of buildings from corrosion. The resin layer containing zinc dust works as an anti-corrosion layer that protects the steel material from rust by sacrificing zinc due to its electrochemical properties.
For the above industrial steel parts and building members, there are cases where a black color tone is required as a naturally harmonious dark color instead of a glaring plating color. In the painting of such members, a method is usually used in which a zinc dust paint is applied as an undercoat, dried, and then a colored topcoat such as a black paint is applied and dried. There has been a demand for a paint that exhibits anti-corrosion properties and blackness with a single application. Various techniques for increasing the blackness of anticorrosive paints have been studied to address such problems. For example, Patent Document 1 describes a black zinc dust coating composition obtained by blending 50 to 86 parts by weight of zinc powder and 1 to 10 parts by weight of conductive carbon black with respect to 100 parts by weight of a coating film-forming component containing a resin. is disclosed. In Patent Document 2, zinc powder having an oxygen content of 1.0 wt% or less obtained by quenching zinc vapor is placed in an oxygen-containing atmosphere at a temperature of 80 to 400 ° C. and a pressure of 1 to 20 atm for a certain period of time to obtain zinc powder. A method is disclosed for obtaining zinc oxide powder for black pigments with an oxygen content of 2.5-18.0 wt % by oxidizing the surface.

JP-A-6-49393 JP-A-2-22125

As described above, various methods have been developed to increase the blackness of zinc dust paints. However, for example, the method of mixing a pigment such as carbon black with zinc dust has the problem that the content of zinc in the coating film decreases, resulting in a decrease in anticorrosion performance. In addition, the conventional method of darkening the color tone of the zinc powder itself was not sufficient in terms of blackness.

The present invention has been made in view of the above-mentioned current situation, and an object of the present invention is to provide black zinc dust that can sufficiently exhibit both anticorrosion performance and blackness.

The present inventors have made various studies on black zinc dust, and found that a step of obtaining a slurry containing zinc dust and at least one selected from the group consisting of fatty acids having branched chains and salts thereof; is refined and blackened by media treatment, so that the L* value in the CIELAB color system measured with a spectral colorimeter is 40 or less, and the total amount of black zinc powder is 100. It was found that a black zinc powder having a content of 70% by mass or less relative to the mass % was obtained, and such a zinc powder sufficiently exhibited both anticorrosion performance and blackness, and the above problems were successfully solved. The present invention has been arrived at by conceiving that it is possible.

That is, the present invention provides a black color having an L* value of 40 or less in the CIELAB color system measured with a spectral colorimeter and a content of metallic zinc of 70% by mass or less with respect to 100% by mass of the total amount of black zinc dust. It is zinc dust.

The present invention also provides black zinc powder in which part of the metallic zinc is oxidized, wherein the content of metallic zinc is 70% by mass or less with respect to the total amount of 100% by mass of the black zinc powder, and is measured with a spectrophotometer. It is also a black zinc powder having an L* value of 40 or less in the CIELAB color system.

The black zinc powder preferably has a median diameter (D50) of 6.0 μm or less.

The present invention also includes a step A of obtaining a slurry containing zinc dust and at least one selected from the group consisting of fatty acids having branched chains and salts thereof; It is also a method for producing black zinc dust including step B.

The fatty acid and its salt preferably have 8 to 24 carbon atoms.

The amount of the fatty acid and its salt to be used is preferably 0.01 to 5.0% by mass with respect to 100% by mass of zinc powder.

In step B, it is preferable to perform the media treatment over 200% of the media treatment time at which the median diameter (D50) of the resulting zinc dust is maximized.

The present invention further provides a paint containing the above black zinc powder and a binder.

The content of the black zinc dust is preferably 5 to 95% by mass with respect to 100% by mass of the solid content in the paint.

The paint is preferably used for anticorrosion purposes.

The black zinc powder of the present invention has the above-described structure and can sufficiently exhibit both anticorrosion performance and blackness, so it can be used as an anticorrosion paint for industrial steel parts, car parts, and building members. It can be used preferably.

1 is an SEM photograph (magnification: 2000 times) of black zinc powder of Example 1. FIG. 4 is an SEM photograph (magnification: 2000 times) of the black zinc dust of Example 2. FIG. 2 is an SEM photograph (magnification: 2000 times) of the black zinc powder of Example 3. FIG. 10 is an SEM photograph (magnification: 2000 times) of the black zinc dust of Example 4. FIG. 10 is an SEM photograph (magnification: 2000 times) of the black zinc dust of Example 5. FIG. 10 is an SEM photograph (magnification: 2000 times) of black zinc powder of Example 6. FIG. 4 is an SEM photograph (magnification: 2000 times) of zinc powder of Comparative Example 1. FIG. 4 is an SEM photograph (magnification: 2000 times) of the carbon black of Comparative Example 2. FIG. 3 is an SEM photograph (magnification: 2000 times) of zinc powder of Comparative Example 3. FIG.

Preferred embodiments of the present invention will be specifically described below, but the present invention is not limited to the following description, and can be appropriately modified and applied without changing the gist of the present invention. In addition, the form which combined 2 or 3 or more of each preferable form of this invention described below also corresponds to the preferable form of this invention.

<Black zinc powder>
The black zinc dust of the present invention has a metal zinc content of 70% by mass or less with respect to 100% by mass of the total black zinc dust. This can improve the blackness of the zinc dust. Also, the content of metallic zinc is preferably 5% by mass or more. This makes the black zinc dust more excellent in anticorrosion performance. The content of metallic zinc is preferably 10 to 65% by mass, more preferably 15 to 60% by mass, and still more preferably 55% by mass or less.

The black zinc dust of the present invention has an L* value of 40 or less in the CIELAB color system measured with a spectral colorimeter. The larger the L* value in the CIELAB color system, the whiter the sample, and the smaller the L* value in the CIELAB color system, the darker the sample. The L* value in the CIELAB color system is preferably 35 or less, more preferably 32 or less, and still more preferably 30 or less. If the L* value in the CIELAB colorimetric system is 32 or less, it exhibits blackness equal to or higher than that of carbon black.

The present invention also relates to black zinc powder obtained by partially oxidizing metallic zinc, and the black zinc powder contains zinc oxide. The content of zinc oxide in the black zinc dust is not particularly limited, but is preferably 30 to 95% by weight with respect to 100% by weight of the total black zinc dust. As a result, the L* value of the black zinc dust in the CIELAB color system is in a more preferable range. The zinc oxide content is more preferably 40 to 85% by mass.

The particle size of the black zinc powder of the present invention is not particularly limited, but the median size (D50) is preferably 6.0 μm or less. This can further improve the blackness of the zinc dust and the hiding power of the coating film against the substrate when the coating film is formed. The median diameter (D50) is more preferably 5.0 μm or less, still more preferably 4.0 μm or less. The median diameter (D50) of the black zinc powder is preferably 0.1 µm or more.
The median diameter (D50) of black zinc dust can be measured by the method described in Examples.

In addition, the black zinc dust of the present invention may contain at least one selected from the group consisting of fatty acids having branched chains described below and salts thereof (hereinafter also referred to as fatty acids having branched chains (salts)). . The method for producing the black zinc dust of the present invention is not particularly limited, but when produced by the production method described later, the resulting black zinc dust contains fatty acids (salts) having a branched chain.

When the black zinc dust contains a fatty acid (salt) having a branched chain, its content is not particularly limited, but it is preferably 0.01 to 5.0% by weight with respect to 100% by weight of the zinc dust. . More preferably 0.05 to 3.5% by mass, still more preferably 0.1 to 2.8% by mass, and particularly preferably 0.2 to 2.3% by mass.

The black zinc powder of the present invention contains a zinc compound such as metallic zinc and zinc oxide, but may contain other components other than the metallic zinc, the zinc compound, and the fatty acid (salt) having a branched chain. Examples of the other components include, but are not particularly limited to, pigments such as carbon black; lubricants other than fatty acids (salts) having a branched chain described later;
The total content of other components is preferably 0 to 5% by mass with respect to 100% by mass of the total zinc content (sum of metallic zinc in black zinc dust and zinc derived from zinc compounds). It is more preferably 0 to 1% by mass, still more preferably 0 to 0.5% by mass, and most preferably 0% by mass.
Among the other components, the content of pigments such as carbon black is preferably 0 to 5% by mass with respect to 100% by mass of the total amount of zinc. It is more preferably 0 to 1% by mass, still more preferably 0 to 0.5% by mass, and most preferably 0% by mass.

<Method for producing black zinc dust>
The present invention comprises a step A of obtaining a slurry containing zinc dust and at least one selected from the group consisting of fatty acids having branched chains and salts thereof, and finely and blackening the zinc dust in the slurry by media treatment. It is also a method for producing black zinc dust including step B.

1. Process A
Step A is a step of obtaining a slurry containing a fatty acid (salt) having a branched chain and zinc powder. It is possible to sufficiently suppress the sticking of zinc dust to each other as an obstacle, thereby sufficiently finely miniaturizing and blackening in the step B, as a result, sufficiently exhibiting both anticorrosive performance and blackness. black zinc powder is obtained.

The fatty acid having a branched chain may be one having a hydrocarbon group having a branched structure and a carboxyl group. Further, examples of salts thereof include alkali metal salts such as sodium and potassium; alkaline earth metal salts such as calcium and magnesium; salts such as zinc and aluminum; and the like. Among these, fatty acids having branched chains are preferred.

The number of carbon atoms in the branched fatty acid (salt) is preferably 8-24. As a result, the slipperiness as a lubricant is further enhanced, and finer particles and blackening can be performed more efficiently. The number of carbon atoms is more preferably 10-22, still more preferably 12-20.

As the hydrocarbon group having a branched structure, an alkyl group having a branched structure is preferred.
The number of carbon atoms in the alkyl group having a branched structure is preferably 7-23, more preferably 9-21, still more preferably 11-19.

Specific examples of the alkyl group having a branched structure include isopropyl group, sec-butyl group, isobutyl group, tert-butyl group, 1-methylbutyl group, 1-ethylpropyl group, 2-methylbutyl group, isoamyl group, and neopentyl group. , 1,2-dimethylpropyl group, 1,1-dimethylpropyl group, tert-amyl group, 1,3-dimethylbutyl group, 3,3-dimethylbutyl group, 2-ethylbutyl group, 2-ethyl-2-methyl propyl group, 1-methylheptyl group, 2-ethylhexyl group, 1,5-dimethylhexyl group, t-octyl group, isooctyl group, sec-nonyl group, tert-nonyl group, neononyl group, isodecyl group, sec-decyl group , tert-decyl group, neodecyl group, isoundecyl group, sec-undecyl group, tert-undecyl group, neoundecyl group, isododecyl group, sec-dodecyl group, tert-dodecyl group, neododecyl group, isotridecyl group, sec-tridecyl group, tert -tridecyl group, neotridecyl group, isotetradecyl group, sec-tetradecyl group, tert-tetradecyl group, neotetradecyl group, isopentadecyl group, sec-pentadecyl group, tert-pentadecyl group, neopentadecyl group, isohexadecyl group, sec-hexadecyl group, tert-hexadecyl group, neohexadecyl group, isoheptadecyl group, sec-heptadecyl group, tert-heptadecyl group, neoheptadecyl group, isooctadecyl (isostearyl) group, sec-octadecyl group, tert-octadecyl group , neo-octadecyl group, isononadecyl group, sec-nonadecyl group, tert-nonadecyl group, neo-nonadecyl group, isoicosyl group, sec-icosyl group, tert-icosyl group, neoicosyl group, isoheneicosyl group, sec-henicosyl group, tert-henicosyl group, neohenicosyl group, isodocosyl group, sec-docosyl group, tert-docosyl group, neodocosyl group, isotricosyl group, sec-tricosyl group, tert-tricosyl group, neotricosyl group, isotetracosyl group, sec-tetracosyl group, tert-tetracosyl group, neotetracosyl group , isopentacosyl group, sec-pentacosyl group, tert-pentacosyl group, neopentacosyl group, isohexacosyl group, sec-hexacosyl group, tert-hexacosyl group, neohexacosyl group, isoheptacosyl group, sec-heptacosyl group, tert-heptacosyl group, neoheptacosyl group, isooctacosyl group, sec-octacosyl group, tert-octacosyl group, neooctacosyl group, n-nonaccosyl group, isononacosyl group, sec-nonacosyl group, tert-nonacosyl group, neononacosyl group, n-triacontyl group, isotriacontyl group, sec-triacontyl group group, tert-triacontyl group, and the like.

A preferred branched structure of the fatty acid (salt) having a branched chain is the following formula (1);

(In the formula, R ¹ , R ² and R ³ represent a hydrogen atom or an alkyl group having 1 to 22 carbon atoms, provided that at least two of R ¹ , R ² and R ³ have 1 to 22 alkyl group).
The alkyl groups for R ¹ , R ² and R ³ may have a straight chain structure or a branched structure.
Specific examples of the alkyl group having a branched structure include the alkyl groups described above.
Linear alkyl groups include methyl, ethyl, n-propyl, n-butyl, n-pentyl (amyl), n-hexyl, n-heptyl, n-octyl and n-nonyl. group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, n-henicosyl group, n-docosyl group and the like.

In the compound represented by the above formula (1), at least two alkyl groups of R ¹ , R ² and R ³ preferably have 1 to 18 carbon atoms. More preferably 2 to 16, still more preferably 4 to 14, even more preferably 5 to 12, particularly preferably 6 to 10.

Specific examples of fatty acids having a branched chain include isobutyric acid, isovaleric acid (isopentanoic acid), 2-ethylbutyric acid, ethylmethylacetic acid, isocaproic acid (isohexanoic acid), isoenanthic acid (isoheptanoic acid), isocaprylic acid (isooctanoic acid ), isoperargonic acid (isononanoic acid), isocapriic acid (isodecanoic acid), isoundecanoic acid, isolauric acid (isododecanoic acid), isotridecylic acid (isotridecanoic acid), isomyristic acid (isotetradecanoic acid), isopentadecylic acid (iso pentadecanoic acid), isopalmitic acid (isohexadecanoic acid), isomargaric acid (isoheptadecanoic acid), isostearic acid (isooctadecanoic acid, 2-heptylundecanoic acid), isononadecanoic acid (isononadecanoic acid), isoarachidic acid (isoicosanoic acid), isodocosane acid, isohexacosanoic acid, 2-ethylhexanoic acid, 2-propylhexanoic acid, 2-butylhexanoic acid, 2-ethylheptanoic acid, 2-propylheptanoic acid, 2-butylheptanoic acid, 2-ethyloctanoic acid, 2-propyl octanoic acid, 2-butyloctanoic acid, 2-pentyldecanoic acid, 2-heptyloctanoic acid, 2-hexylnonanoic acid, 2-heptylnonanoic acid, 2-hexyldecanoic acid, 2-hexyldodecanoic acid, 2-octyldecanoic acid, 2-hexyltridecanoic acid, 2-heptyldodecanoic acid, 2-octylundecanoic acid, 13-methyltetradecanoic acid, 12-methyltetradecanoic acid, 15-methylhexadecanoic acid, 14-methylhexadecanoic acid, 10-methylhexadecanoic acid, 18 -Methyl eicosanoic acid, phytanic acid, salts thereof, and the like.
Among them, isoenanthic acid, isocaprylic acid, isopelargonic acid, isocapric acid, isoundecanoic acid, isolauric acid, isotridecylic acid, isomyristic acid, isopentadecylic acid, isopalmitic acid, isomargaric acid, isostearic acid, isononadecylic acid, isoarachine Acids and salts thereof, more preferably isolauric acid, isotridecylic acid, isomyristic acid, isopentadecylic acid, isopalmitic acid, isomagaric acid, isostearic acid, isononadecylic acid, isoarachidic acid, and particularly preferably isostearin is an acid.

The amount of the fatty acid (salt) having a branched chain is not particularly limited, but it is preferably 0.01 to 5.0% by mass based on 100% by mass of the zinc dust. By using a fatty acid (salt) having a branched chain, it is possible to exert its effect as a lubricant with a smaller amount than in the case of using a straight-chain fatty acid. More preferably 0.05 to 3.5% by mass, still more preferably 0.1 to 2.8% by mass, and particularly preferably 0.2 to 2.3% by mass.

The zinc dust is not particularly limited, but preferably has an average particle size of 0.1 to 80 μm. It is more preferably 0.5 to 60 μm, still more preferably 1 to 50 μm.
The average particle diameter can be measured by the particle size distribution analyzer described in the Examples.

In step A above, it is preferable to prepare a slurry using a solvent.
As the solvent, commonly used solvents can be used, for example, hydrocarbons such as pentane, hexane, heptane, octane, toluene, xylene, mineral turpentine, mineral spirit, solvent naphtha; methanol, ethanol, isopropanol, 2- Alcohols such as methyl-2-propanol, butanol, hexanol, methoxybutanol, methoxymethylbutanol, capryl alcohol, lauryl alcohol, myristyl alcohol, oleyl alcohol, stearyl alcohol, isopalmityl alcohol, isostearyl alcohol, and these alcohols Esters such as acetate and propionate, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, hexylene glycol, octylene glycol, and neopentyl glycol, glycerin , glycol ethers such as dipropylene glycol monomethyl ether, diethylene glycol methyl ether, and ethylene glycol hexyl ether; and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. Hydrocarbons are preferred, and xylene is more preferred.
The amount of the solvent used is preferably 10 to 600% by mass with respect to 100% by mass of zinc dust. More preferably 50 to 400% by mass, still more preferably 100 to 250% by mass.

From the viewpoint of preventing zinc dust particles from adhering to each other in the slurry, the amount of water used in step A is preferably 5% by mass or less with respect to 100% by mass of zinc dust. It is more preferably 1% by mass or less, and most preferably 0% by mass.

The slurry obtained in the step A may contain components other than the fatty acid (salt) having a branched chain, zinc powder and the solvent.
Other components include, for example, lubricants (grinding aids) other than branched chain fatty acids (salts), dispersants, and the like.
The content of other components is preferably 0 to 1.0% by mass with respect to 100% by mass of zinc dust. More preferably 0.05 to 0.5% by mass, still more preferably 0.1 to 0.3% by mass.

Examples of other lubricants include solid paraffin, polyethylene wax, aliphatic amines, aliphatic amides, aliphatic esters, aliphatic alcohols, graphite, silica powder, talc, zinc phosphate, talc, and mica.
The content of other lubricants is preferably 0 to 1.0% by mass with respect to 100% by mass of zinc powder. It is more preferably 0 to 0.5% by mass, still more preferably 0 to 0.3% by mass, and most preferably 0% by mass.

2. Process B
Step B is a step of making the zinc dust in the slurry obtained in Step A finer and blackened by media treatment. By media-treating the zinc dust in the slurry, the zinc dust is pulverized and oxidized, resulting in blackening.

The proportion of zinc dust in the slurry is preferably 15 to 60% by mass with respect to 100% by mass of the slurry. As a result, the zinc dust can be made finer and blackened more sufficiently. The proportion of zinc dust in the slurry is more preferably 20 to 55% by mass, still more preferably 30 to 50% by mass.

The media processing method is not particularly limited and can be performed by a commonly used method.
For example, planetary mills, bead mills, vibration mills, etc. can be used. Among these, the method using a bead mill is preferable.

As the beads used in the bead mill, any of glass beads, alumina beads, zirconia beads, titania beads, silicon nitride beads and the like may be used. Zirconia beads and alumina beads are preferred.

When using a bead mill, it is preferable to use beads having a diameter of 0.03 to 0.5 mm.
Although the amount of beads used in a bead mill is not particularly limited, it is 10 to 1000% by mass with respect to 100% by mass of zinc powder used. Thereby, the zinc dust and the beads sufficiently collide with each other, and the median diameter (D50) of the obtained zinc dust can be set in a more suitable range. The amount of beads used is more preferably 20 to 950% by mass, still more preferably 30 to 900% by mass.

When using a bead mill, it is preferable to use a rotating disk, and the rotation speed of the rotating disk is preferably 100 to 10000 rpm. It is more preferably 200 to 6000 rpm, still more preferably 250 to 4000 rpm, and particularly preferably 300 to 3500 rpm.
The peripheral speed of the rotating disk is preferably 3 to 50 m/s. It is more preferably 5 to 40 m/s, still more preferably 7 to 30 m/s, and particularly preferably 8 to 20 m/s.

In the above step B, as the media treatment of the zinc dust progresses, the median diameter of the zinc dust (the D50 value of the particle size distribution) increases and reaches a peak, after which the zinc dust is further pulverized and the median diameter (D50) decreases. do.
The present inventors set the media processing time based on the media processing time at which the median diameter (D50) of the zinc dust is maximized, thereby efficiently producing black zinc dust with a suitable median diameter (D50). I found that That is, in the above step B, it is preferable to perform the media treatment over 200% of the media treatment time that maximizes the median diameter (D50) of the zinc dust. Also, it is preferable to perform media processing in 2000% or less of the time. More preferably 210 to 1000% of the time, still more preferably 225 to 800% of the time, still more preferably 250 to 600% of the time, even more preferably 275 to 500% of the time, especially Preferably it is 300-400% of the time.
The median diameter (D50) of the black zinc dust can be obtained by the method described in Examples.

The temperature at which step B is performed is not particularly limited, but it can be performed at a temperature of 10 to 150°C.

The method for producing black zinc dust of the present invention may include steps other than steps A and B. Other steps include a step of removing the solvent and the like contained in the slurry obtained in steps A and/or B, a step of washing and drying, and the like.

<Uses of black zinc powder>
The black zinc dust of the present invention can be suitably used for industrial steel parts, car parts, anti-corrosion coatings for building members, coloring pigments, and the like.
The black zinc dust of the present invention can be suitably used as a substitute for black pigments such as carbon black among the above colored pigments.

<Paint>
The present invention further provides a paint containing the black zinc powder of the present invention and a binder (hereinafter also referred to as resin).
The paint is preferably used for undercoating, anticorrosion, coloring, and the like.
The paint preferably contains black zinc dust in an amount of 5 to 95% by mass based on 100% by mass of the solid content in the paint. It is more preferably 10 to 95% by mass, still more preferably 20 to 95% by mass, and particularly preferably 30 to 95% by mass.
In the present specification, the term "solid content" means solid or liquid residue at normal temperature excluding volatile components such as solvent and water, so-called non-volatile content, and dried at 150 ° C. for 1 hour. The solid content can be calculated by measuring the evaporation residue obtained.

Also, the content of the binder is preferably 1 to 99% by mass as a solid content with respect to 100% by mass of the black zinc powder. More preferably 3 to 90% by mass, still more preferably 5 to 80% by mass.

Examples of the binder (resin) include silicates such as sodium silicate, potassium silicate, and lithium silicate; alkali silicone, silicone, silicone emulsion, water-soluble silicone, acrylic resin, acrylic resin emulsion, epoxy resin emulsion, phenolic resin emulsion, silicone resin. , alkyl silicate, silane coupling agent, polystyrene resin, chlorinated rubber, epoxy resin, phenolic resin, polyurethane resin, polyester resin, phenol-modified alkyd resin, melamine resin, melamine/alkyd resin, alkyd resin, fluorine resin, aqueous urethane resin , water-based acrylic resins, water-based acrylic resin emulsions, water-based melamine resins, water-based modified epoxy resins, and water-based modified epoxy ester resins.
Among them, melamine/alkyd resins, epoxy resins, polyurethane resins, acrylic resins, polyester resins, alkyd resins, silicone resins, water-based urethane resins, water-based acrylic resins, water-based acrylic resin emulsions, water-based melamine resins, water-based modified epoxy resins, water-based modified Epoxy ester resins are preferred. More preferred are melamine/alkyd resins, epoxy resins, polyurethane resins, acrylic resins, silicone resins, water-based urethane resins, and water-based modified epoxy resins, and even more preferred are epoxy resins, polyurethane resins, water-based urethane resins, water-based modified epoxy resins, and melamine.・It is an alkyd resin.

The paint may contain other components than the black zinc powder and the binder.
The total content of other components in the paint is preferably 0 to 5% by mass with respect to the total 100% by mass of black zinc powder and resin. More preferably 0 to 1% by mass, still more preferably 0 to 0.5% by mass.

Examples of the other components include solvents, pigments, dispersants, wetting agents, leveling agents, thixotropic agents, thickeners, anti-sagging agents, antifungal agents, film-forming aids, stabilizers, and the like.
Solvents include those mentioned above.
Examples of pigments include aluminum powder, magnesium powder, nickel powder, cobalt powder, silicon oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium carbonate, zirconium oxide, barium sulfate, barium carbonate, silica, calcium carbonate, talc, mica, Clay, kaolin, bentonite, carbon black, aniline black, gunjo, watching red, cyanine blue, phthalocyanine green and the like.
Examples of dispersants include cationic surfactants such as octadecylamine acetate, alkyltrimethylammonium chloride, alkyldimethylbenzylammonium chloride; Examples include nonionic surfactants such as ethylene fatty acid esters.

As described above, the paint of the present invention may contain the above pigments as other components, but since the black zinc dust of the present invention has a high degree of blackness, it is possible to achieve a sufficient black color without using any pigment other than zinc dust. demonstrate degree.
The ratio of pigments other than zinc dust in the paint is preferably 5% by mass or less with respect to 100% by mass of the paint. It is more preferably 1% by mass or less, still more preferably 0.5% by mass or less, and most preferably 0% by mass.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited only to these examples. Unless otherwise specified, "part" means "mass part" and "%" means "mass %".

Various measurements were performed as follows.
<Median diameter of particle size distribution (D50)>
The median diameter (D50) of the particle size distribution was measured with a laser diffraction/scattering particle size distribution analyzer Microtrac MT-3300 EXII (manufactured by Nikkiso Co., Ltd.). Xylene was used as the solvent for the measurement, the black zinc powder had a refractive index of 2.4, and the solvent had a refractive index of 1.5.

<Measurement of metallic zinc>
Accurately weigh 0.4 g of the sample to the order of 0.1 mg, transfer it to a 300 mL Erlenmeyer flask, add 60 mL of iron (III) chloride / sodium acetate mixture and a rotor, wash the rim of the Erlenmeyer flask with 50 mL of distilled water, Seal the Erlenmeyer flask. Subsequently, it is dissolved by stirring with a magnetic stirrer, and 50 mL of Reinhardt's solution and 200 mL of distilled water are added. Two drops of an orthophenanthroline indicator solution are added, and the solution is titrated with a 0.1 mol/L potassium permanganate solution (reagent for volumetric analysis). Metallic zinc is calculated by the following formula.
Titration volume (mL) of 0.1 mol/L potassium permanganate solution x factor/sample mass (g) x 0.016345 x 100
0.016345 in the above formula means the mass (g) of metallic zinc corresponding to 1 mL of 0.1 mol/L potassium permanganate solution.
Various reagents used for measurement are prepared and used as follows.
(Iron (III) chloride/sodium acetate mixture)
Distilled water is added to 332 g of sodium acetate trihydrate to make up to 1 L. 16 g of iron (III) chloride hexahydrate is added to 20 mL of this sodium acetate solution and distilled water is added to make 60 mL.
(Mr. Reinhardt's solution)
Add 80 g of manganese (II) sulfate tetrahydrate (reagent special grade) or manganese (II) sulfate pentahydrate (reagent grade) and 500 mL of distilled water to a beaker. While cooling the beaker with ice water, phosphoric acid (concentration: about 85%, density: about 1.69 g/mL, reagent special grade) 150 mL and sulfuric acid (concentration: about 95%, density: about 1.84 g/mL, reagent special grade) ) 150 mL is decanted and made up to 1 L with distilled water.
(Indicator orthophenanthroline solution)
150 mg of 1,10-phenanthroline monohydrate (o-phenanthroline monohydrate) and 75 mg of iron (II) sulfate heptahydrate are dissolved in 10 mL of distilled water.

<Measurement of total zinc content (total content of metallic zinc in black zinc powder and zinc derived from zinc compound)>
Accurately weigh about 1 g of the sample to the order of 0.1 mg and transfer it to a beaker, add 50 mL of distilled water, 5 mL of hydrochloric acid, and 1 mL of nitric acid to dissolve it by heating, cool it down, wash it with distilled water and transfer it to a 250 mL volumetric flask. , add distilled water up to the marked line. 25 mL of this solution was taken into a conical beaker, 10 mL of buffer solution was added, the pH value was adjusted to 5.5 to 5.7 with ammonia water (1+1), distilled water was added to make 250 mL, and xylenol orange was used as an indicator. About 0.5 mL of the solution (1 g/L) is added and titrated with a 0.05 mol/L EDTA solution. Total zinc is calculated by the following formula (2).
Total zinc (%) = 0.003269 x EDTA titer (mL) x factor/(sample mass (g) x 25 mL/250 mL) x 100 (2)
Here, 0.003269 in the above formula (2) means the mass (g) of total zinc corresponding to 1 mL of 0.05 mol/L EDTA solution.
Also, the factor in the above formula (2) is calculated by the following formula (3).
Factor = Zinc (g) used for standardization / (0.003269 x EDTA titer (mL)) (3)
Here, 0.003269 in the above formula (3) means the mass (g) of zinc corresponding to 1 mL of 0.05 mol/L EDTA solution.
Furthermore, orientation in the above formula (3) means the following operations.
Approximately 0.12 g of zinc or JIS purest zinc metal, which is a standard substance for volumetric analysis, is accurately weighed to the order of 0.1 mg, transferred into a beaker, and then added with approximately 20 mL of distilled water and 10 mL of hydrochloric acid and heated to dissolve. . After cooling, add 10 mL of buffer solution, adjust the pH value to 5.5-5.7 with aqueous ammonia (1+1), and then add distilled water to make about 250 mL. About 0.5 mL of a xylenol orange solution (1 g/L) is added as an indicator and titrated with a 0.05 mol/L EDTA solution.

Various reagents used for measurement are prepared and used as follows.
(hydrochloric acid)
Concentration: about 35%, density: about 1.18 g/mL reagent special grade.
(nitric acid)
Concentration: about 60%, density: about 1.38 g/mL reagent special grade.
(Ammonia water (1+1))
Concentration: about 25%, density: about 0.91 g/mL reagent special grade and distilled water are mixed at a volume ratio of 1:1 to prepare.
(buffer)
Dissolve 250 g of ammonium acetate (reagent special grade) in 1 L of distilled water, add acetic acid (reagent special grade) to adjust the pH value to 5.
(Xylenol orange solution (1 g/L))
Dissolve 0.1 g of xylenol orange in distilled water to make 100 mL.
(0.05mol/L EDTA solution)
Prepare by dissolving about 19 g of disodium dihydrogen dihydrogen ethylenediaminetetraacetate dihydrate (reagent special grade) in about 1 L of distilled water.

<Evaluation of anticorrosion (rust prevention) performance>
Black zinc powder obtained in the example, or 10 g of the sample of the comparative example, thermosetting alkyd resin J-524-A (solid content concentration 50%, manufactured by DIC) 1.18 g, butylated melamine resin J-820 0.40 g of (solid concentration 75%, manufactured by DIC) and 21.72 g of xylene were shaken with a paint shaker to prepare a paint having a zinc concentration of 92% as a solid content in the paint. Subsequently, the prepared paint is applied to one side of an SPCC-SB steel plate (0.8 t × 35 × 150 mm) using a hobby airbrush MX2370 (manufactured by Anest Iwata Co., Ltd.), and left to dry for 30 minutes at room temperature. A coating film was formed on the steel plate by baking at 140°C for 20 minutes, and a cross-cut was made from the coating film surface to the steel plate with a cutter blade, and an outdoor exposure test was conducted for 168 hours. The test was started on a rainy day, and after the start of the test, red rust generated from the cross-cut portion was visually observed over time, and a qualitative evaluation of ◯, Δ, and × was performed. ○ means no red rust within 168 hours, △ means no red rust within 72 hours but red rust develops up to 168 hours, and x means red rust within 72 hours.

<SEM Observation>
Using a scanning electron microscope (manufactured by JEOL Ltd., JSM-6510A), SEM observation was performed at an acceleration voltage of 15 kV.

<Example 1>
Isostearic acid (manufactured by Nissan Chemical Industries, Ltd., Fine Oxocol) 1.37 g (2 wt% to Zn) was added to and dissolved in 136.5 g of xylene, followed by 68.4 g of zinc powder #3 (manufactured by Sakai Chemical Industry Co., Ltd.). A slurry was prepared by repulping so that the zinc concentration in the prepared slurry was 33%. After the treatment, it was filtered and dried to prepare black zinc dust.
In addition, the zinc concentration in the prepared slurry can be calculated by the following formula (4).
Zinc concentration (%) = zinc (g) / (zinc (g) + isostearic acid (g) + xylene (g)) x 100 (4)

<Examples 2 to 6>
Black zinc dust was prepared in the same procedure as in Example 1, except that the conditions were changed to those shown in Table 1.

<Comparative Example 1>
Zinc dust was prepared in the same manner as in Example 1, except that isostearic acid was changed to stearic acid and the media treatment time was changed to 1440 minutes (24 hours).

The black zinc powder prepared in Examples 1 to 6 and the zinc powder prepared in Comparative Example 1, Mitsubishi carbon black (manufactured by Mitsubishi Chemical Corporation, MA100, 24 nm, 110 m ² /g) as Comparative Example 2, and Comparative Example 3 Zinc dust #3BL (manufactured by Sakai Chemical Industry Co., Ltd.) was subjected to the above physical property evaluation, anticorrosion performance evaluation, and SEM observation. Table 1 shows the physical property evaluation and anticorrosion performance evaluation results. SEM observation results are shown in FIGS.

As shown in the examples, by media-treating a slurry containing a fatty acid (salt) having a branched chain and zinc dust, part of the metallic zinc, which is the zinc dust, is oxidized, resulting in a CIELAB colorimetry measured with a spectrophotometer. Black zinc having an L* value of 40 or less in the system, a content of metallic zinc of 70% by mass or less relative to the total amount of black zinc dust of 100% by mass, and a median diameter (D50) of 6.0 μm or less. It was found that such zinc powder can sufficiently exhibit both anti-corrosion performance and blackness. Further, by comparing Examples 2, 3, and 5, it is clear that when the bead mill treatment time is the same, the lower the zinc concentration (%) in the prepared slurry, the finer and blacker the black zinc dust is obtained. be. In addition, by comparing Examples 1 and 2, or Examples 3 and 4, or Examples 5 and 6, when the zinc concentration (%) in the prepared slurry is the same, the longer the bead mill treatment time, the finer and the blackness becomes. It is clear that black zinc dust with a high On the other hand, in Comparative Example 1 using stearic acid, which is a fatty acid having no branched chain, the zinc concentration (%) in the prepared slurry was the same as in Example 1, and the bead mill treatment time was extended to 1200%. In spite of this, it was not possible to make it finer and blacken it. Furthermore, with the conventionally known zinc powder of Comparative Example 3, which was blackened by air oxidation, it was not possible to obtain black zinc powder having an L* value of 40 or less in the CIELAB color system. It was also found that the carbon black of Comparative Example 2 was excellent in blackness, but insufficient in anticorrosion performance.

Claims (10)

The L* value in the CIELAB color system measured with a spectral colorimeter is 40 or less, the content of metallic zinc is 70% by mass or less with respect to the total amount of 100% by mass of black zinc dust, and it has a branched chain A black zinc powder containing 0.01 to 5.0% by mass of at least one selected from the group consisting of fatty acids and salts thereof with respect to 100% by mass of black zinc powder. Black zinc powder in which a part of metallic zinc is oxidized,
The content of metallic zinc is 70% by mass or less with respect to the total amount of 100% by mass of black zinc dust, and the L* value in the CIELAB color system measured with a spectrocolorimeter is 40 or less. Item 1. Black zinc powder according to item 1. The black zinc dust according to claim 1 or 2, wherein the black zinc dust has a median diameter (D50) of 6.0 µm or less. A step A of obtaining a slurry containing zinc dust and at least one selected from the group consisting of fatty acids having branched chains and salts thereof; and a step B of making the zinc dust in the slurry fine and black by media treatment. A method for producing black zinc dust, comprising: 5. The method for producing black zinc dust according to claim 4, wherein the fatty acid and its salt have 8 to 24 carbon atoms. 6. The method for producing black zinc powder according to claim 4 or 5, wherein the amount of the fatty acid and its salt used is 0.01 to 5.0% by mass with respect to 100% by mass of the zinc powder. Claims 4 to 6, characterized in that in the step B, the media treatment is performed for a time exceeding 200% of the media treatment time at which the median diameter (D50) of the resulting zinc dust is maximized. A method for producing black zinc dust according to any one of A paint comprising the black zinc powder according to any one of claims 1 to 3 and a binder. 9. The paint according to claim 8, wherein the content of said black zinc dust is 5 to 95% by mass with respect to 100% by mass of solid content in the paint. 10. The paint according to claim 8 or 9, wherein the paint is used for anticorrosion purposes.

Images