JP7344430B2 - Black zinc powder and its manufacturing method - Google Patents

Description

The present invention relates to black zinc powder and a method for producing the same. More specifically, the present invention relates to a black zinc powder useful for industrial steel parts, anticorrosive coatings for building components, and a method for producing the same.

Zinc dust is suitably used in industrial steel parts such as automobile parts and electrical parts, and anticorrosive undercoat paints for protecting members of buildings and the like from corrosion. The resin layer containing zinc powder acts as an anti-corrosion layer that protects the steel from rust by sacrificing zinc due to its electrochemical properties.
The above-mentioned industrial steel parts and building members may be required to have a black tone, which is a dark color that harmonizes with nature, rather than a glaring plating color. When painting such parts, the method usually used is to apply a zinc powder paint as an undercoat, let it dry, then apply a colored topcoat such as black paint, and dry it. There was a need for a paint with a high degree of corrosion resistance and blackness that could be achieved with just one application. In response to such problems, various techniques for increasing the blackness of anticorrosive paints have been studied. For example, Patent Document 1 discloses a black zinc powder coating composition comprising 50 to 86 parts by weight of zinc dust and 1 to 10 parts by weight of conductive carbon black to 100 parts by weight of a coating film-forming component containing a resin. is disclosed. Patent Document 2 discloses that zinc powder with an oxygen content of 1.0 wt% or less obtained by rapid cooling of 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 form zinc powder. A method for obtaining zinc oxide powder for black pigment with an oxygen content of 2.5 to 18.0 wt% by oxidizing the surface is disclosed.

Furthermore, with recent global warming, there is an urgent need to develop infrared shielding paints. One of the causes of global warming is infrared rays from the sun. The amount of infrared rays accounts for approximately 50% of the sunlight that reaches the earth, and its thermal effect is large. Even with a small amount of light, it has a wavelength suitable for effective thermal movement of substances, and by absorbing infrared rays, it can cause various effects. The temperature of these items increases. Therefore, attempts have been made to significantly suppress the temperature rise of various articles and buildings by applying infrared shielding paints containing inorganic and organic pigments that diffuse heat through absorption of infrared rays or shield them through reflection. . For example, technology is being considered to shield infrared rays using gray or black paints containing carbon black or black pigments.

Japanese Patent Application Publication No. 6-49393 Japanese Patent Application Publication No. 2-22125

As mentioned above, various methods for increasing the blackness of zinc dust paints and techniques for shielding infrared rays with gray or black paints have been developed. However, for example, the method of mixing pigments such as carbon black with zinc powder has the problem that the zinc content in the coating film decreases, resulting in a decrease in anticorrosion performance. There was a need for the development of a paint that could fully demonstrate its properties.

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

The present inventors conducted various studies on black zinc powder, and found that black zinc powder, which has a total light reflectance of 17% or less at a specific wavelength in the infrared region, has excellent anticorrosion performance and infrared rays when made into a coating. The inventors have discovered that both the shielding effect and the shielding effect can be sufficiently exhibited, and have come up with the idea that the above-mentioned problems can be successfully solved, leading to the present invention.

That is, the present invention is a black zinc powder having a total light reflectance of 17% or less at wavelengths of 800 nm, 1400 nm, and 2000 nm as measured with a spectrophotometer.

The black zinc powder preferably has a total light reflectance of 17% or less in a wavelength range of 800 nm to 2000 nm as measured with a spectrophotometer.

The above-mentioned black zinc powder contains a coating film containing black zinc powder and melamine/alkyd resin at a mass ratio (black zinc powder/melamine/alkyd resin) of 0.6 and having a film thickness of 27 μm. It is preferable that the total light transmittance at wavelengths of 800 nm, 1400 nm, and 2000 nm are all 15% or less when measured with a spectrophotometer.

The black zinc powder preferably has a total light reflectance of 15% or less in the wavelength range of 800 nm to 2000 nm as measured by a spectrophotometer of the coating film.

The black zinc powder preferably has an L* value of 40 or less in the CIELAB color system measured with a spectrophotometer.

The black zinc powder preferably has a metal zinc content of 70% by mass or less based on 100% by mass of the total amount of black zinc powder.

The black zinc powder is preferably one in which metallic zinc is partially oxidized.

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

The present invention also provides a step A of obtaining a slurry containing at least one selected from the group consisting of branched chain fatty acids and salts thereof and zinc dust, and in which the zinc dust concentration is 45% by mass or less; It is also a method for producing black zinc powder, which includes step B of making the zinc powder fine and blackening it by media treatment.

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

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

In step B, the media treatment is preferably performed for a time exceeding 200% of the media treatment time at which the median diameter (D50) of the obtained zinc dust is maximum.

The present invention also provides a resin composition containing black zinc powder and a binder.

The content of the black zinc powder is preferably 30 to 95% by mass based on 100% by mass of solid content in the resin composition.

The present invention also provides a coating material containing the above resin composition.

The above-mentioned paint is preferably used for anticorrosion purposes.

The above paint is preferably used for coloring purposes.

The black zinc powder of the present invention has the above-mentioned structure and can sufficiently exhibit both anticorrosion effect and infrared shielding effect. It can be suitably used for colored paints and the like.

1 is a spectrum of total light reflectance for black zinc powders of Examples 1 to 4 and carbon black and zinc powders of Comparative Examples 2 to 5. This is a spectrum of the total light transmittance of each coating film when a coating film with a thickness of 27 μm was formed for the black zinc powder of Examples 1 to 4 and the carbon black and zinc powder of Comparative Examples 2 to 5.

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 applied with appropriate modifications within the scope of the gist of the present invention. Note that combinations of two or more of the individual preferred embodiments of the present invention described below also correspond to preferred embodiments of the present invention.

<Black zinc powder>
The black zinc powder of the present invention has a total light reflectance of 17% or less at wavelengths of 800 nm, 1400 nm, and 2000 nm as measured with a spectrophotometer. Thereby, infrared rays can be effectively shielded, and when used in a paint, the infrared ray shielding effect can be sufficiently exhibited. The total light reflectance at the above wavelength is preferably 16% or less, more preferably 15% or less, still more preferably 14% or less.

The black zinc powder preferably has a total light reflectance of 17% or less in a wavelength range of 800 nm to 2000 nm as measured with a spectrophotometer. It is more preferably 16% or less, still more preferably 15% or less, particularly preferably 14% or less.

The above-mentioned black zinc powder contains a coating film containing black zinc powder and melamine/alkyd resin at a mass ratio (black zinc powder/melamine/alkyd resin) of 0.6 and having a film thickness of 27 μm. It is preferable that the total light transmittance at wavelengths of 800 nm, 1400 nm, and 2000 nm are all 15% or less when measured with a spectrophotometer. Thereby, when used in a paint, it is possible to fully exhibit an infrared shielding effect. The total light transmittance at the above wavelength is preferably 10% or less, more preferably 7% or less, and even more preferably 6% or less.

The black zinc powder preferably has a total light reflectance of 15% or less in the wavelength range of 800 nm to 2000 nm as measured by a spectrophotometer of the coating film. It is more preferably 10% or less, still more preferably 7% or less, particularly preferably 6% or less.

The black zinc powder of the present invention preferably has an L* value of 40 or less in the CIELAB color system measured with a spectrophotometer. 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 more preferably 35 or less, still more preferably 32 or less, particularly preferably 30 or less. If the L* value in the CIELAB color system is 32 or less, the blackness will be equal to or higher than that of carbon black.

The black zinc powder of the present invention preferably has a metal zinc content of 70% by mass or less based on 100% by mass of the total amount of black zinc powder. This can improve the blackness of the zinc powder and further improve the infrared shielding effect. Moreover, it is preferable that the content rate of metal zinc is 5 mass % or more. This makes the black zinc powder more excellent in anticorrosion performance. The content of metallic zinc is more preferably 10 to 65% by mass, still more preferably 15 to 60% by mass, even more preferably 55% by mass or less, particularly preferably 50% by mass or less, and most preferably is 48% by mass or less.

The present invention also provides a black zinc powder in which a part of metallic zinc is oxidized, and the black zinc powder contains zinc oxide. The content of zinc oxide in the black zinc powder is not particularly limited, but it is preferably 30 to 95% by mass based on 100% by mass of the total amount of black zinc powder. As a result, the L* value of the black zinc powder in the CIELAB color system falls within a more preferable range. The content of zinc oxide is more preferably 40 to 85% by mass.

Although the particle size of the black zinc powder of the present invention is not particularly limited, it is preferable that the median diameter (D50) is 6.0 μm or less. Thereby, the blackness of the zinc dust can be further improved, and the reflectance of wavelengths in the infrared region can be more sufficiently reduced. Furthermore, if the median diameter of the black zinc powder is 6.0 μm or less, the hiding power of the coating film against the base layer during coating film formation can be further improved. The median diameter (D50) is more preferably 5.0 μm or less, still more preferably 4.0 μm or less, particularly preferably 3.0 μm or less. It is preferable that the median diameter (D50) of the black zinc powder is usually 0.1 μm or more.
The median diameter (D50) of black zinc powder can be measured by the method described in Examples.

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

When the black zinc powder 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 mass based on 100% by mass of zinc dust. . It is more preferably 0.05 to 3.5% by weight, still more preferably 0.1 to 2.8% by weight, particularly preferably 0.2 to 2.3% by weight.

The black zinc powder of the present invention contains metallic zinc and zinc compounds such as zinc oxide, but may contain other components other than metallic zinc, zinc compounds, and the branched chain fatty acid (salt). The other components mentioned above are not particularly limited, and include, for example, pigments such as carbon black; other lubricants other than the branched chain fatty acids (salts) described below, and the like.
The total content of other components is preferably 0 to 5% by mass based on 100% by mass of the total zinc amount (total of metallic zinc in the black zinc powder and zinc derived from zinc compounds). It is more preferably 0 to 1% by weight, still more preferably 0 to 0.5% by weight, and most preferably 0% by weight.
Among the other components mentioned above, the content of pigments such as carbon black is preferably 0 to 5% by mass based on 100% by mass of the total zinc amount. It is more preferably 0 to 1% by weight, still more preferably 0 to 0.5% by weight, and most preferably 0% by weight.

<Production method of black zinc powder>
The present invention comprises a step A of obtaining a slurry containing at least one selected from the group consisting of branched chain fatty acids and salts thereof and zinc dust, and having a zinc dust concentration of 45% by mass or less; It is also a method for producing black zinc powder, which includes step B of making the zinc powder fine and blackening it by media treatment.

1. Process A
Step A is a step of obtaining a slurry containing a fatty acid (salt) having a branched chain and zinc dust. By using the fatty acid (salt) having a branched chain as a lubricant, the branched chain of the fatty acid (salt) is It is possible to sufficiently prevent the zinc powder from sticking to each other as an obstacle, and as a result, sufficient fineness and blackening can be achieved in process B, and as a result, both corrosion prevention performance and infrared shielding effect are sufficiently achieved. It is thought that a black zinc powder that exhibits this effect can be obtained.

The branched fatty acid may be any fatty acid having a branched structure and a hydrocarbon group and a carboxyl group. Examples of the salt 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 to 24. Thereby, the slipperiness as a lubricant is further improved, and finer particles and blackening can be performed more efficiently. The number of carbon atoms is more preferably 10 to 22, and still more preferably 12 to 20.

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

Specifically, the alkyl group having the above branched structure includes an isopropyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, a 1-methylbutyl group, a 1-ethylpropyl group, a 2-methylbutyl group, an isoamyl group, and a 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, tert-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 , neooctadecyl group, isononadecyl group, sec-nonadecyl group, tert-nonadecyl group, neononadecyl 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, neodocsyl group, isotrichosyl 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, isoheptacyl group, sec-heptacyl group, tert-heptacyl group, neoheptacosyl group, isooctacosyl group group, sec-octacosyl group, tert-octacosyl group, neooctacosyl group, n-nonacosyl 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 preferable branched structure of the fatty acid (salt) having a branched chain is represented by 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. However, at least two of R ¹ , R ² , and R ³ have 1 to 22 carbon atoms. It is an alkyl group of 22).
The alkyl groups in R ¹ , R ² and R ³ above may have a linear structure or a branched structure.
Specific examples of the alkyl group having a branched structure include the alkyl groups described above.
Straight chain alkyl groups include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group (amyl group), n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group. 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 group, n-icosyl group, n-henicosyl group, n-docosyl group, etc.

In the compound represented by the above formula (1), the number of carbon atoms in at least two alkyl groups among R ¹ , R ² and R ³ is preferably 1 to 18. 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 with branched chains include isobutyric acid, isovaleric acid (isopentanoic acid), 2-ethylbutyric acid, ethylmethylacetic acid, isocaproic acid (isohexanoic acid), isoenanthic acid (isoheptanoic acid), and isocaprylic acid (isooctanoic acid). ), isoperargonic acid (isononanoic acid), isocapric acid (isodecanoic acid), isoundecanoic acid, isolauric acid (isododecanoic acid), isotridecylic acid (isotridecanoic acid), isomyristic acid (isotetradecanoic acid), isopentadecanoic acid (isodecanoic acid) 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), isodocosan 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, and salts thereof.
Among these, preferred are isoenanthic acid, isocaprylic acid, isoperargonic acid, isocapric acid, isoundecanoic acid, isolauric acid, isotridecylic acid, isomyristic acid, isopentadecylic acid, isopalmitic acid, isomargaric acid, isostearic acid, isononadecylic acid, and isoarachinic acid. acids, and salts thereof, more preferably isolauric acid, isotridecylic acid, isomyristic acid, isopentadecylic acid, isopalmitic acid, isomargaric acid, isostearic acid, isononadecylic acid, isoarachidic acid, and particularly preferably isostearic acid. It is an acid.

The amount of the branched fatty acid (salt) used is not particularly limited, but it is preferably 0.01 to 5.0% by mass based on 100% by mass of zinc dust. By using a fatty acid (salt) having a branched chain, the effect as a lubricant can be exhibited in a smaller amount than when using a straight chain fatty acid. It is more preferably 0.05 to 3.5% by weight, still more preferably 0.1 to 2.8% by weight, particularly preferably 0.2 to 2.3% by weight.

The above zinc powder is not particularly limited, but preferably has an average particle size of 0.1 to 80 μm. More preferably, it is 0.5 to 60 μm, still more preferably 1 to 50 μm, and most preferably 1 to 40 μm.
The above average particle diameter can be measured using the particle size distribution measuring device described in Examples.

The zinc dust concentration in the slurry prepared in the above step A is 45% by mass or less. Thereby, the zinc powder can be sufficiently made fine and blackened in Step B, and the infrared ray shielding effect can be sufficiently exhibited. The zinc dust concentration is preferably 10 to 45% by mass, more preferably 15 to 40% by mass, even more preferably 20 to 40% by mass, particularly preferably 25 to 40% by mass, and most preferably It is 25 to 35% by mass.

In the above step A, it is preferable to prepare a slurry using a solvent.
As the solvent, commonly used solvents can be used, such as hydrocarbons such as pentane, hexane, heptane, octane, toluene, xylene, mineral turpentine, mineral spirit, and solvent naphtha; methanol, ethanol, isopropanol, 2- Alcohols such as methyl-2-propanol, butanol, hexanol, methoxybutanol, methoxymethylbutanol, caprylic alcohol, lauryl alcohol, myristyl alcohol, oleyl alcohol, stearyl alcohol, isopalmityl alcohol, isostearyl alcohol, and these alcohols esters such as acetate ester and propionate ester, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, hexylene glycol, octylene glycol, neopentyl glycol, glycerin Examples include trihydric alcohols 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 based on 100% by mass of zinc dust. The amount is more preferably 50 to 400% by weight, and even more preferably 100 to 250% by weight.

From the viewpoint of preventing the zinc dust from sticking to each other in the slurry, the amount of water used in the step A is preferably 5% by mass or less based on 100% by mass of the zinc powder. More preferably it is 1% by mass or less, and most preferably 0% by mass.

The slurry obtained in the above step A may contain components other than the fatty acid (salt) having a branched chain, zinc dust, and the solvent.
Examples of other components include lubricants (grinding aids) other than branched chain fatty acids (salts).
The content of other components is preferably 0 to 1.0% by mass based on 100% by mass of zinc powder. The amount is more preferably 0.05 to 0.5% by weight, and even more preferably 0.1 to 0.3% by weight.

Examples of the other lubricants include solid paraffin, polyethylene wax, aliphatic amine, aliphatic amide, aliphatic ester, aliphatic alcohol, graphite, silica powder, zinc phosphate, talc, mica, and the like.
The content of other lubricants is preferably 0 to 1.0% by mass based on 100% by mass of zinc dust. It is more preferably 0 to 0.5% by weight, still more preferably 0 to 0.3% by weight, and most preferably 0% by weight.

2. Process B
Step B is a step in which the zinc powder in the slurry obtained in Step A is made fine and blackened by media treatment. By media-treating the zinc dust in the slurry, the zinc dust is made fine and oxidized, resulting in a black color.

The proportion of zinc powder in the slurry is preferably 10 to 45% by mass based on 100% by mass of the slurry. This allows the zinc powder to be finely refined and blackened more fully. The proportion of zinc powder in the slurry is more preferably 15 to 40% by mass, still more preferably 20 to 40% by mass, particularly preferably 25 to 40% by mass, and most preferably 25 to 35% by mass. be.

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

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

When using a bead mill, the beads used preferably have a diameter of 0.03 to 1.5 mm, more preferably 0.03 to 0.5 mm.
When using a bead mill, the amount of beads used is not particularly limited, but is 10 to 1000% by mass based on 100% by mass of zinc dust. Thereby, the zinc dust and beads can sufficiently collide, and the median diameter (D50) of the resulting zinc dust can be set in a more suitable range. The amount of beads used is more preferably 20 to 950% by mass, and even 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 10,000 rpm. More preferably 200 to 6000 rpm, still more preferably 250 to 4000 rpm, particularly preferably 300 to 3500 rpm.
The circumferential speed of the rotating disk is preferably 3 to 50 m/s. More preferably 5 to 40 m/s, still more preferably 7 to 30 m/s, particularly preferably 8 to 20 m/s.

In step B above, as the media treatment of zinc dust progresses, the median diameter (D50 value of particle size distribution) of zinc powder increases and reaches a peak, and then the zinc powder is further crushed 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 powder becomes maximum, thereby efficiently producing black zinc powder with a suitable median diameter (D50). I found out that it can be obtained. That is, in the above step B, it is preferable to carry out the media treatment for a time exceeding 200% of the media treatment time at which the median diameter (D50) of the zinc dust becomes the maximum. Furthermore, 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, even more preferably 250 to 600% of the time, even more preferably 275 to 500% of the time, especially Preferably it is 300 to 400% of the time.
The median diameter (D50) of the black zinc powder can be determined 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 powder of the present invention may include steps other than steps A and B. Other steps include a step of removing the solvent etc. contained in the slurry obtained in step A and/or B, a step of washing and drying, and the like.

<Applications of black zinc powder>
The black zinc powder of the present invention can be suitably used for industrial steel parts, car parts, anticorrosion paints for building members, coloring pigments, and the like.
The black zinc powder of the present invention can be suitably used as a substitute for black pigments such as carbon black among the above-mentioned colored pigments. Further, as described above, the black zinc powder of the present invention has an excellent infrared ray shielding effect, and therefore can be suitably used as a substitute for infrared ray shielding pigments.

<Resin composition>
The present invention further provides a resin composition containing the black zinc powder of the present invention and a binder (hereinafter also referred to as resin).
The content of the black zinc powder is preferably 30 to 95% by mass based on 100% by mass of solid content in the resin composition. More preferably, it is 35 to 95% by mass.
In addition, "solid content" in this specification means the so-called non-volatile content, which is a solid or liquid residue at room temperature excluding volatile components such as solvent and water, and is dried at 150 ° C. for 1 hour. The solid content can be calculated by measuring the evaporation residue obtained. The content of the binder is preferably 1 to 99% by mass as a solid content based on 100% by mass of black zinc powder. The content is more preferably 3 to 90% by weight, and even more preferably 5 to 80% by weight.
The above resin composition can be suitably used for paints, resin molded articles, etc., which will be described later.

<Paint>
The present invention also provides a coating material containing the above resin composition.
A paint containing the black zinc powder of the present invention and a binder is also one of the present inventions.
The above paint is preferably used for undercoating, anticorrosion, infrared shielding, coloring, and the like.
The content of black zinc powder in the paint is preferably 30 to 95% by mass based on 100% by mass of the solid content in the paint. More preferably, it is 35 to 95% by mass.
Further, the content of the binder is preferably 1 to 99% by mass as a solid content based on 100% by mass of black zinc powder. The content is more preferably 3 to 90% by weight, and even more preferably 5 to 80% by weight.

Examples of the binder (resin) include silicates such as sodium silicate, potassium silicate, and lithium silicate; alkali silicone, silicone emulsion, water-soluble silicone, acrylic resin, acrylic resin emulsion, epoxy resin emulsion, phenol resin emulsion, silicone resin, alkyl Silicates, silane coupling agents, polystyrene resins, chlorinated rubber, epoxy resins, phenolic resins, polyurethane resins, polyester resins, phenol-modified alkyd resins, melamine resins, melamine/alkyd resins, alkyd resins, fluorine resins, water-based urethane resins, water-based Examples include acrylic resin, aqueous acrylic resin emulsion, aqueous melamine resin, aqueous modified epoxy resin, and aqueous modified epoxy ester resin.
Among them, preferred are melamine/alkyd resin, epoxy resin, polyurethane resin, acrylic resin, polyester resin, alkyd resin, silicone resin, water-based urethane resin, water-based acrylic resin, water-based acrylic resin emulsion, water-based melamine resin, water-based modified epoxy resin, and water-based modified epoxy resin. 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 above-mentioned paint may contain components other than the black zinc powder and the binder.
The total content of other components in the paint is preferably 0 to 5% by mass based on 100% by mass of the black zinc powder and resin. It is more preferably 0 to 1% by mass, and even more preferably 0 to 0.5% by mass.

Examples of the other components include a solvent, a pigment, a dispersant, a wetting agent, a leveling agent, a thixotropic agent, a thickener, an anti-sagging agent, a fungicide, a film-forming aid, and a stabilizer.
Examples of the solvent include the above-mentioned solvents.
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, Examples include clay, kaolin, bentonite, carbon black, aniline black, gunjo, watching red, cyanine blue, and phthalocyanine green.
Examples of dispersants include cationic surfactants such as octadecylamine acetate, alkyltrimethylammonium chloride, and alkyldimethylbenzylammonium chloride; polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl amide, polyoxy Examples include nonionic surfactants such as ethylene fatty acid esters.

As mentioned above, the paint of the present invention may contain the above-mentioned pigments as other components, but since the black zinc powder of the present invention has a high degree of blackness and a high infrared shielding effect, it may be used in addition to zinc powder. Demonstrates sufficient blackness without using pigments such as colored pigments or infrared shielding pigments.
The proportion of pigments other than zinc dust in the paint is preferably 5% by mass or less based on 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.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples. In addition, unless otherwise specified, "%" shall mean "mass %."

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

<Measurement of L* value>
The L* value in the CIELAB color system was measured using a spectrophotometer (manufactured by Nippon Denshoku Kogyo Co., Ltd., SE 6000).

<Measurement of metallic zinc>
Weigh 0.4 g of the sample accurately to the 0.1 mg digit, transfer it to a 300 mL Erlenmeyer flask, add 60 mL of a mixed solution of iron (III) chloride and sodium acetate and a rotor, and rinse the rim of the Erlenmeyer flask with 50 mL of distilled water. Seal the Erlenmeyer flask. Next, stir with a magnetic stirrer to dissolve, and 50 mL of Reinhardt's solution and 200 mL of distilled water are added. Add two drops of indicator orthophenanthroline solution, titrate with 0.1 mol/L potassium permanganate solution (volume analysis reagent), and take the end point when the color of the solution changes from orange to pale yellow. Metallic zinc is calculated using the following formula.
Titration amount of 0.1 mol/L potassium permanganate solution (mL) x factor/sample mass (g) x 0.016345 x 100
0.016345 in the above formula means the mass (g) of metal zinc equivalent to 1 mL of 0.1 mol/L potassium permanganate solution.
The various reagents used in the measurement are prepared and used as follows.
(Iron(III) chloride/sodium acetate mixture)
Add distilled water to 332 g of sodium acetate trihydrate to make 1 L. Add 16 g of iron (III) chloride hexahydrate to 20 mL of this sodium acetate solution and make up to 60 mL with distilled water.
(Mr. Reinhardt's liquid)
Add 80 g of manganese (II) sulfate tetrahydrate (special grade reagent) or manganese (II) sulfate pentahydrate (special grade reagent) and 500 mL of distilled water to a beaker. While cooling the beaker with ice water, add 150 mL of phosphoric acid (concentration: approx. 85%, density: approx. 1.69 g/mL, reagent grade) and sulfuric acid (concentration: approx. 95%, density: approx. 1.84 g/mL, reagent grade). ) Gently pour 150 mL and make 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 compounds)>
Weigh out approximately 1 g of the sample accurately to the nearest 0.1 mg, transfer it to a beaker, add 50 mL of distilled water, 5 mL of hydrochloric acid, and 1 mL of nitric acid, heat to dissolve, and after cooling, wash the entire volume into a 250 mL volumetric flask with distilled water. , add distilled water up to the mark. Take 25 mL of this solution into a conical beaker, add 10 mL of buffer, adjust the pH value to 5.5 to 5.7 with aqueous ammonia (1+1), add distilled water to make 250 mL, and use xylenol orange as an indicator. Approximately 0.5 mL of the solution (1 g/L) is added, titrated with 0.05 mol/L EDTA solution, and the end point is defined as the point at which the color of the liquid changes from purple to red to yellow. Total zinc is calculated by the following formula (2).
Total zinc (%) = 0.003269 x EDTA titration (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 equivalent to 1 mL of 0.05 mol/L EDTA solution.
Moreover, the factor in the above formula (2) is calculated by the following formula (3).
Factor = Zinc used for standardization (g) / (0.003269 x titration amount of EDTA (mL)) (3)
Here, 0.003269 in the above formula (3) means the mass (g) of zinc equivalent to 1 mL of 0.05 mol/L EDTA solution.
Furthermore, orientation in the above formula (3) means the following operation.
Accurately weigh approximately 0.12 g of zinc or JIS purest zinc ingot as a standard material for volumetric analysis to the 0.1 mg digit, transfer it to a beaker, add approximately 20 mL of distilled water and 10 mL of hydrochloric acid, and heat to dissolve. . After cooling, add 10 mL of buffer solution, adjust the pH value to 5.5 to 5.7 with aqueous ammonia (1+1), and then add distilled water to make about 250 mL. Approximately 0.5 mL of xylenol orange solution (1 g/L) is added as an indicator and titrated with 0.05 mol/L EDTA solution, and the end point is defined as the point at which the color of the liquid changes from purple to red to yellow.

The various reagents used in the measurement are prepared and used as follows.
(hydrochloric acid)
Concentration: approximately 35%, density: approximately 1.18 g/mL, special grade reagent.
(nitric acid)
Special grade reagent with concentration: approximately 60% and density: approximately 1.38 g/mL.
(Ammonia water (1+1))
It is prepared by mixing a special grade reagent with a concentration of about 25% and a density of about 0.91 g/mL and distilled water at a volume ratio of 1:1.
(buffer)
Dissolve 250 g of ammonium acetate (reagent grade) in 1 L of distilled water, and adjust the pH value to 5 by adding acetic acid (reagent grade).
(Xylenol orange solution (1g/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 ethylenediaminetetraacetic acid dihydrate (special grade reagent) in about 1 L of distilled water.

<Corrosion prevention (rust prevention) performance evaluation>
10 g of the black zinc powder obtained in the example or a sample of the comparative example, 1.18 g of thermosetting alkyd resin J-524-A (solid content concentration 50%, manufactured by DIC Corporation), butylated melamine resin J-820 (solid content concentration 75%, manufactured by DIC) 0.40 g and xylene 21.72 g were shaken in a paint shaker to prepare a paint having a powder concentration of 92% as solid content in the paint. Subsequently, the prepared paint was applied to one side of an SPCC-SB steel plate (0.8t x 35 x 150mm) using a hobby airbrush MX2370 (manufactured by Anest Iwata), and left to dry at room temperature for 30 minutes. A coating film was formed on the steel plate by baking at 140° C. for 20 minutes, a cross cut was made from the coating surface to the steel plate using 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 qualitatively evaluated as ○, △, or ×. ○ means that no red rust occurs within 168 hours, △ means that red rust does not occur within 72 hours, but red rust occurs within 168 hours, and × means that red rust occurs within 72 hours.

<Measurement of total light ray reflectance>
The total light reflectance (spectral reflectance) was measured using a spectrophotometer model V-770 (manufactured by JASCO Corporation). More specifically, the powder obtained in each example and comparative example was placed in a special cell, attached to a spectrophotometer, and the total light ray reflectance (spectral reflectance) in the wavelength range of 800 nm to 2000 nm was measured. .

<Measurement of total light transmittance>
The total light transmittance was measured using a spectrophotometer model V-770 (manufactured by JASCO Corporation). More specifically, 2.5 g of powder obtained in Examples and Comparative Examples, 4.74 g of thermosetting alkyd resin J-524-A (solid content concentration 50%, manufactured by DIC Corporation), and butylated melamine resin. 2.40 g of J-820 (solid content concentration 75%, manufactured by DIC) and 1.34 g of xylene were placed in a 75 ml mayonnaise bottle and shaken for 10 minutes in a paint conditioner to obtain a paint. The obtained paint was applied onto a slide glass so that the film thickness was 27 μm (prepared with bar coater No. 12), and by drying, the powder/binder weight ratio was 0.6 and the paint film was A melamine alkyd resin paint film with a powder concentration of 37.5% was prepared, and the total light transmittance in the wavelength range of 800 nm to 2000 nm was measured using a spectrophotometer.

<Measurement of haze (cloudiness)>
The haze (%) of the coating film was measured using a haze meter HM-150 model (manufactured by Murakami Color Research Institute). The higher the haze value, the lower the transparency.

<Example 1>
1.37 g (2wt% to Zn) of isostearic acid (manufactured by Nissan Chemical Industries, Ltd., Fine Oxocol) was added and dissolved in 136.5 g of xylene, and then 68.4 g of zinc powder #3 (manufactured by Sakai Chemical Industries, Ltd.) was added. was repulped to make a slurry with a zinc concentration of 33%, and the slurry was processed at 3000 rpm ( After performing media treatment for 360 minutes at a circumferential speed of 8.6 m/s), the mixture was filtered and dried to prepare black zinc powder.
Note that the zinc concentration in the prepared slurry can be calculated using the following formula (4).
Zinc concentration (%) = zinc (g) / (zinc (g) + isostearic acid (g) + xylene (g)) x 100 (4)
When the obtained black zinc powder was measured using a spectrophotometer, the total light reflectance at wavelengths of 800 nm, 1400 nm, and 2000 nm was 10.9%, 11.0%, and 11.1%, respectively. .
In addition, using the obtained black zinc powder, a melamine alkyd resin paint with a powder/binder weight ratio of 0.6 and a coating film thickness of 27 μm (prepared with bar coater No. 12) was applied on a slide glass. When the film was prepared and measured using a spectrophotometer, the total light transmittance at wavelengths of 800 nm, 1400 nm, and 2000 nm was 0.3%, 0.3%, and 0.1%, respectively. Further, the haze (%) of the coating film at this time was 80%. In addition, when carbon black is blended under the above blending conditions (Comparative Example 2), the total light transmittance at wavelengths of 800 nm, 1400 nm, and 2000 nm is 0.1%, 0.2%, and 0.1%, respectively. It was confirmed that it has infrared shielding performance equivalent to carbon black.

<Examples 2 to 4>
A black zinc powder was prepared in the same manner as in Example 1 except that the conditions were changed to those 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).

<Comparative example 4>
As shown in Table 1, zinc dust was prepared in the same manner as in Example 2 except that the amounts of zinc dust, xylene, and isostearic acid were changed.

<Comparative example 5>
As shown in Table 1, zinc powder was prepared in the same manner as in Comparative Example 4 except that the bead milling time was changed.

The black zinc powder prepared in Examples 1 to 4 and the zinc powder prepared in Comparative Examples 1, 4, and 5, and Mitsubishi carbon black (manufactured by Mitsubishi Chemical Corporation, MA100, 24 nm, 110 m ² /g) as Comparative Example 2, As Comparative Example 3, zinc powder #3BL (manufactured by Sakai Chemical Industry Co., Ltd.) was evaluated for the physical properties of the powder and the optical properties and anticorrosion performance of the coating film. Table 1 shows the results of the above physical property evaluation and anticorrosion performance evaluation. The spectrum of the total light reflectance of the powder and the results of SEM observation of the total light transmittance of the coating film are shown in FIGS. 1 and 2.

It was revealed that the black zinc powders obtained in Examples 1 to 4 exhibited an excellent infrared shielding effect and good antirust performance when a coating film was formed.
On the other hand, in Comparative Example 1 in which stearic acid, which is a fatty acid without a branched chain, was used, zinc powder could not be made fine or blackened even if the media treatment time was 1440 minutes (24 hours). . Furthermore, in Comparative Example 4, the L* value in the CIELAB color system is comparable to that of carbon black, and the total light transmittance at a wavelength of 800 nm is 17% or less; The total light reflectance exceeds 17%, and the total light transmittance of the coating film with a film thickness of 27 μm is about twice that of Example 4, in which the total light reflectance at the three wavelengths mentioned above is all 17% or less. It has become. These results revealed that by suppressing the total light reflectance at all of the three wavelengths mentioned above to 17% or less, it is possible to effectively suppress the infrared transmittance when forming a coating film. .

Claims (16)

The content of metallic zinc is 5 to 70% by mass with respect to 100% by mass of the total amount of black zinc powder,
A black zinc powder characterized in that the total light reflectance at wavelengths of 800 nm, 1400 nm, and 2000 nm measured with a spectrophotometer is all 17% or less. The black zinc powder according to claim 1, wherein the black zinc powder has a total light reflectance of 17% or less in a wavelength range of 800 nm to 2000 nm as measured with a spectrophotometer. A coating film containing the black zinc powder and melamine/alkyd resin at a mass ratio (black zinc powder/melamine/alkyd resin) of 0.6 and having a thickness of 27 μm was measured using a spectrophotometer. The black zinc powder according to claim 1, wherein the total light transmittance at wavelengths of 800 nm, 1400 nm, and 2000 nm is all 15% or less. 4. The black zinc powder according to claim 3, wherein the black zinc powder has a total light reflectance of 15% or less in a wavelength range of 800 nm to 2000 nm as measured by a spectrophotometer of the coating film. The black zinc powder according to any one of claims 1 to 4, which has an L* value of 40 or less in the CIELAB color system measured with a spectrophotometer. 6. The black zinc powder according to claim 1 , wherein the black zinc powder is partially oxidized metallic zinc. The black zinc powder according to any one of claims 1 to 6 , wherein the black zinc powder has a median diameter (D50) of 6.0 μm or less. Step A of obtaining a slurry containing at least one selected from the group consisting of branched chain fatty acids and salts thereof and zinc dust and having a zinc dust concentration of 45% by mass or less; A method for producing black zinc powder, comprising a step B of refining and blackening by treatment. The method for producing black zinc dust according to claim 8 , wherein the fatty acid and its salt have 8 to 24 carbon atoms. The method for producing black zinc dust according to claim 8 or 9, characterized in that the amount of the fatty acid and its salt used is 0.01 to 5.0% by mass based on 100% by mass of zinc dust. 10. The step B is characterized in that the media treatment is performed for a time exceeding 200% of the time taken as 100% for the media treatment time at which the median diameter (D50) of the obtained zinc powder is maximum. A method for producing black zinc powder according to any one of the above. A resin composition comprising the black zinc powder according to any one of claims 1 to 7 and a binder. The resin composition according to claim 12 , wherein the content of the black zinc powder is 30 to 95% by mass based on 100% by mass of solid content in the resin composition. A coating material comprising the resin composition according to claim 12 or 13 . The paint according to claim 14 , wherein the paint is used for anticorrosion purposes. The paint according to claim 14 , wherein the paint is used for coloring purposes.

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