Black zinc particles, method for producing the same, and use thereof

Abstract

The present invention relates to a black granular zinc composite. 【Solution means】(a) Zinc element or zinc alloy metal in an amount c in the range of 58.0 to 85.0% by weight with respect to the composite, (b) ZnO, and (c) a further material, this further material (the amount of c) c Zn、M is in the range of 4.5 to 17.0% by weight with respect to the total amount of the composite material, and components (b) and (c) are at least partially mixed with the zinc element or zinc alloy metal (a). The black zinc particles are used as a corrosion inhibitor pigment. The particles are produced by a dry grinding process under severe conditions where they are incorporated into the pigment after the grinding process in the presence of an abrasion aid. add ​

Description

Technical Field

[0001] The present invention relates to black zinc particles that can be used for a cathode corrosion prevention film.

Background Art

[0002] Zinc powder is suitably used for anticorrosive undercoats (primers) that protect industrial steel materials such as automotive parts and electrical parts, and members such as buildings from corrosion. A resin layer containing zinc powder or zinc flakes acts as an anticorrosive layer that protects steel materials from rust by sacrificing zinc due to the electrochemical properties of zinc. The above-mentioned industrial steel parts such as buildings like buildings and bridges, as well as automotive applications, especially screw coatings and building members, may need to have a black color tone as a dark color in natural harmony rather than a shiny plating color in some applications. In the painting of screws mounted on such members, especially automobiles, it is most common to apply a zinc powder or zinc flake paint as an undercoat paint, dry it, and then apply a colored topcoat paint such as a black paint and dry it. Here, the black color of a conventional anticorrosive paint using a black pigment is used. However, scratches on the topcoat are not desirable because the zinc-containing undercoat looks gray to silver and is conspicuous. Therefore, a black zinc pigment is required to reduce this contrast.

[0003] There is a demand for a paint that increases the blackness within a single coating and exhibits corrosion resistance. In response to such problems, various techniques for increasing the blackness of anticorrosive paints have been conventionally studied. For example, JPH0649393A describes a black zinc powder 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. JPH0222125A discloses a method of placing zinc powder having an oxygen content of 1.0 mass% or less obtained by rapidly cooling zinc vapor in an oxygen-containing atmosphere at a temperature of 80 to 400 ° C and a pressure of 1 to 20 for a certain period of time. A method of obtaining zinc oxide powder for a black pigment having an oxygen content of 2.5 to 18.0 wt% by oxidizing the surface is disclosed.

[0004] As described above, various methods for increasing the blackness of zinc powder paints have been developed. However, for example, in the method of mixing zinc powder with a pigment such as carbon black, there is a problem that the zinc content in the coating film decreases and the anticorrosive performance decreases. In addition, the conventional method of blackening the color tone of zinc powder itself is not sufficient in terms of blackness.

[0005] DE102014105434A1 discloses a black zinc coating by combining zinc flakes with a spinel-type dark pigment. However, such a solution is costly to implement and requires a fairly large amount of dark pigment to obtain an actual dark coating. However, these pigments may hide the electrical contact of the zinc flakes, and therefore, the conductivity may decrease. Furthermore, the viscosity of the paste containing these mixtures may be difficult to adjust in an appropriate range, which reduces the flexibility of the coating formulation.

[0006] Dark metallic pigments are also disclosed in EP2173819A2, where metal flakes are coated with a matrix material such as silica and dark pigments having low IR absorption. However, such pigments can hardly be used as anticorrosive pigments even when zinc is used as the metal flake, and they are difficult and expensive to manufacture.

[0007] US7,021,573B2 discloses a dry grinding process of zinc powder using a fluorocarbon polymer. Black zinc particles cannot be obtained in this document.

[0008] WO1999 / 9058274A1 discloses a dry grinding process using graphite particles as a solid lubricant in the absence of an organic lubricant such as a long-chain fatty acid. It was reported that flaky zinc pigments with high corrosion stability were obtained, but black zinc pigments were not obtained.

[0009] WO2021 / 216943A1 discloses black zinc pigments composed of elemental zinc, zinc oxide and a lubricant, which can also be used in aqueous coatings. However, this document does not disclose the detailed method of how to manufacture such pigments. The same applicant has a commercially available black zinc pigment (Blitz (trademark) Zinc Z2031), which has limited stability in the salt spray test.

[0010] Japanese Patent Application Laid-Open No. 2020-105575 and Japanese Patent Application Laid-Open No. 2021-038331 disclose black zinc pigments obtained by wet grinding using a branched fatty acid as a lubricant. Such a lubricant is considered to promote the oxidation of zinc particles during grinding. The particles are preferably strongly over-ground using a grinding time exceeding 200% of the grinding time, where the maximum value of the d50 value of the particle size distribution of the zinc pigment is obtained. The resulting final zinc pigment is very fine, with a d of less than 6 μm 50have values. Because of their small size, these pigments may cause safety problems when finally dried into a powder. In addition, they may cause viscosity problems when incorporated into a coating formulation and thus may limit the versatility of the formulation.

[0011] Supplementary to the same method as these documents is disclosed in JP2020-105338A. However, the grinding time was less than 200% and more than 30% of the time of the maximum d of the ground zinc pigment, resulting in relatively large zinc flakes that were not black. 50 value, resulting in relatively large zinc flakes that were not black. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0012] Accordingly, an object of the present invention is to provide a black zinc pigment suitable for preventing cathode corrosion, particularly passing a salt spray test, having at least the blackness of conventional state-of-the-art pigments but improved corrosion stability. MEANS FOR SOLVING THE PROBLEMS

[0013] This object is solved by providing the following black granular composite: (a) elemental zinc or zinc alloy in an amount c in the range of 58.0 to 85.0% by weight with respect to the composite, Zn,M and (b) Zn-oxide, and (c) a further material, the amount c of this further material (c) add being in the range of 4.5 to 17.0% by weight with respect to the total amount of the composite material, a black granular composite comprising wherein components (b) and (c) are at least partially commingled with elemental zinc metal (a). BRIEF DESCRIPTION OF THE DRAWINGS

[0014]

Figure 1

Figure 2

DETAILED DESCRIPTION OF THE INVENTION

[0015] Further preferred embodiments are disclosed in claims 2 to 13.

[0016] A further object is to provide a method for producing these pigments that is inexpensive.

[0017] This object has been solved by providing a method for producing a black composite material, comprising the following steps: (a) Providing a mixture comprising zinc powder, a wear aid, which consists of a further material (c) or a precursor thereof, and a lubrication aid, into a grinding aggregate (mill aggregate) equipped with grinding balls (mill balls); (b) Dry-grinding the mixture of (a) above for a time t m without using a fluorocarbon polymer during the grinding process; (c) Separating the ground mixture from the grinding aggregate, and (d) Optionally further steps, such as sieving and / or pasting.

[0018] A further object was to provide the use of a black zinc pigment.

[0019] This object is solved by using the black granular composite described in the claims as a corrosion-inhibiting pigment in a heavy corrosion-inhibiting formulation.

[0020] DETAILED DESCRIPTION: Black zinc granules: The black granular composite of the present invention is: (a) An amount c in the range of 58.0 to 85.0% by weight relative to the composite Zn,M of the element zinc or a zinc alloy, (b) Zn-oxide, and (c) A further material, the amount c of this further material (c) add is in the range of 4.5 to 17.0% by weight relative to the total amount of the composite material, comprising, Components b) and (c) are at least partially commingled with the elemental zinc metal (a).

[0021] The black granular composite has an unformed shape. Thus, it is different from zinc flakes which are usually obtained by dry or wet grinding of zinc powder into flake form.

[0022] The term "black" refers to the diffuse L value measured on a panel, preferably < 36.0, more preferably < 35.0, most preferably < 34.0, using D65 / 10° conditions. The panel is prepared as follows: 56.5 g of the black zinc composite is stirred into 43.5 g of a solvent-based silicate lacquer (having a solids content of about 55% by weight). Optionally, the viscosity may be adjusted to the range of 30 s to 50 s measured with a flow cup according to DIN53211 by adding dipropylene glycol (up to 10 g). This lacquer is applied onto a metal substrate (steel Q-panel R46) by drawdown (applied nominal dry film thickness: 24 μm, speed 3 cm / min) in two opposite direction applications. The panel is ventilated at 100 °C for about 30 minutes and fired in an oven at 300 °C for 40 minutes. *

[0023] Regarding the term "black granular composite", terms such as "black zinc", "black zinc pigment" are also used interchangeably within the present invention.

[0024] The zinc component can be either pure zinc or a zinc alloy. Preferably, zinc has a purity of 99.99% by weight, more preferably 99.995% by weight.

[0025] As the zinc alloy, an alloy of the general formula (I) is preferably used: ZnAl x Mg y M f z (I) Here, x, y, and z represent the contents of the respective metals in wt%, based on the total content of the alloy. x is in the range of >0 to 10, preferably in the range of 2.5 to 7, y is in the range of ≧0 to 7, preferably in the range of 0.5 to 6, and z is in the range of 0 to <2.5, preferably in the range of 0.01 to 0.5, more preferably in the range of 0.02 to 0.1. M f represents a further optional alloy metal and can be treated as a total, preferably Ca, Sn, Si, In, Bi, Mn, K, Sr, Ba, and mixtures thereof, more preferably Ca, Sn, Si, In, Bi, and mixtures thereof.

[0026] The balance of the alloy is formed by zinc and unavoidable impurities.

[0027] Preferably, the zinc alloy has a composition of 87.0 to 98.0 mass% zinc, 0.0 to 10.0 mass%, preferably 2.0 to 8.0 mass% aluminum, and 0.0 to 6.0 mass% of their magnesium mixture, respectively based on the total amount of metals in the zinc alloy. In a more preferred embodiment, the proportions of Sn, Ca, Si, In, Bi, Mn, K, Sr, Ba, and mixtures thereof are less than 0.3 wt%, more preferably less than 0.1 wt%, respectively based on the total amount of the zinc alloy. Particles based on any alloy and pure zinc may further contain naturally occurring unavoidable impurities of the respective metal components.

[0028] c Zn,MThe term means the amount of elemental zinc and optionally additional elemental alloying metals (M) that can be detected by volumetric titration. The volumetric titration is based on the reduction of Fe(III) ions to Fe(II) ions with the oxidation of the elemental metal, and this method is described in detail in the experimental section. The Fe(II) ions can be titrated by potassium permanganate or cerimetry. In the case of other metal alloy components M, the alloy composition needs to be determined first (e.g., by X-ray diffraction), and then the correction of the titration results can be carried out assuming uniform oxidation of all metal elements. The amount c of elemental zinc Zn,M is in the range of 58.0 to 85.0% by weight, in a preferred embodiment in the range of 59.0 to 80.0% by weight, and in the most preferred embodiment in the range of 60.0 to 78.0% by weight, each based on the complex.

[0029] If it is less than 58.0% by weight, the amount is too low, resulting in insufficient corrosion behavior and a behavior where it does not last long as a sacrificial anode in the corrosion film. If it exceeds 85.0% by weight, the complex is not dark enough, and since the amount of elemental metal is large and at least partially present in a very fine form and correspondingly the amount of each metal oxide is small, it may cause safety problems.

[0030] Without being bound by theory, it is assumed that zinc or zinc alloy is formed at least partially as nanoparticles with an average size of less than 60 nm, preferably less than 50 nm. Such metal nanoparticles can be sufficiently embedded in zinc oxide and / or further material (c). The presence of such nanoparticles is considered to be mostly the reason for the black color of the composite particles.

[0031] Component (b) Zn-oxide mostly results from the oxidation of zinc particles. The production of these particles involves dry grinding of zinc powder under severe conditions that oxidize a significant amount of zinc. After the grinding process, the composite particles come into contact with the ambient atmosphere that usually causes further oxidation on the surface of the particles.

[0032] The term "Zn-oxide" herein represents the oxide ZnO, the hydroxide Zn(OH)₂, and any mixture of Zn-oxide species and Zn-hydroxide species, where the formal oxidation state of zinc can be between (0) and (II), preferably between (I) and (II). In particular, on the surface of the black granular zinc composite, such mixed species can occur under the influence of oxygen and water during and after the grinding process.

[0033] In the case of zinc alloys, other metal components such as aluminum or magnesium can also be partially oxidized. The amount of these oxides can be conveniently estimated by first determining the amount of c Zn,M and the amount of the additional material (c), and then subtracting these amounts from the total amount of the black composite particles, and it may be necessary to correct for the residue of organic lubricants such as fatty acids.

[0034] Another method for determining the amount of Zn-oxide involves, for example, as described in paragraph

[0063] of JP-A-2020-105575, determining the total zinc (including alloy metals if present) content by titrating the black granular composite in a hydrochloric acid medium with EDTA, and recalculating the amount of ZnO by subtracting the elemental metal content determined by Fe(II) oxidation (in combination with permanganometry or cerimetry).

[0035] The amount c ZnO,M-ox of the component (b) ZnO (and other metal oxides derived from alloy components if present) is preferably in the range of 10.0 to 35.0% by weight, more preferably in the range of 13.0 to 34.0% by weight, and most preferably in the range of 15.0 to 32.0% by weight, each based on the total amount of the composite particles. A part of the Zn-oxide is located on the surface of the black zinc pigment, while another part is found inside the particles and is at least partially mixed with the elemental metal.

[0036] In a preferred embodiment, at least 30 atomic % of the total Zn-oxide content is present inside the particles, more preferably at least 40 atomic %, and most preferably at least 50 atomic %, based on the total Zn-oxide content.

[0037] Such amounts can be determined by SEM (scanning electron microscopy) in combination with EDX (energy-dispersive X-ray spectroscopy) of the cross-section of the black zinc granulates.

[0038] The further material (c) was used as an abrasion aid during this grinding of the zinc powder in the dry grinding process.

[0039] Since the further material (c) is intended to be used as an abrasion aid during the dry grinding process, it is a raw material having a certain hardness. This further material preferably has a hardness on the Mohs scale in the range of more than 2.5 to about 9.5, more preferably in the range of 4 to 7. The hardness values are based on the respective bulk materials. It has to be higher than the hardness of elemental zinc (2.5) in order to abrade the zinc powder. However, the hardness should not be too high, as the inside of the ball mill or the beads could be adversely affected or even damaged by this material.

[0040] The abrasion aid can strongly deform the zinc powder particles and itself either not change in its particle form or be ground into smaller fragments. In the final black zinc granulates, this material may be mixed with elemental zinc and also with ZnO.

[0041] Preferably, the further material (c) is at least partially mixed with the elemental zinc particles after the entire manufacturing process. The mixed abrasion aid can also be detected by SEM in combination with EDX of the cross-section of the black zinc granulates. The mixed particles are found inside such granulates.

[0042] Preferably, at least 50 atomic % of the wear assistant, more preferably at least 60 atomic %, even more preferably at least 70 atomic %, and most preferably at least 80 atomic % is mixed with elemental zinc particles.

[0043] Only a very small part of the wear assistant may be present on the surface of the composite granule after the grinding process.

[0044] The further material (c) does not form an encapsulating coating layer or a coating of separate particles on the zinc particle surface. Optionally, particles of the material (c) may be present on the surface of the zinc composite granule, but it is preferred that less than 20% of the mass of the material (c) is present in such a form.

[0045] Preferably, the further material (c) is selected from the group consisting of: (i) Metal oxides or metal hydroxides such as SiO2, TiO2, Al2O3, Al(OH)3, magnetite, Fe2O3, ZrO2 and mixtures thereof, or (ii) Silicates or aluminosilicates, for example, synthetic mica, natural mica, preferably biotite or muscovite, nepheline - cyanite, Zn - silicate and mixtures thereof; (iii) Metal phosphates, (iv) BaSO4 or a mixture of any of the (i) - (iv) species.

[0046] The material (c) should have a compact shape, for example, spherical, flaky (flake - like), or amorphous shape. Needle - like formation should be avoided. Usually, the material (c) is selected from common inorganic metal oxide pigments, fillers or desiccants in the coating industry.

[0047] In certain embodiments, the material (c) may contain ZnO or may consist of ZnO. These ZnO particles may be mixed with any of the other materials (c) described above.

[0048] In the most preferred embodiment, the further material (c) is SiO2 or nepheline - cyanite or a mixture thereof.

[0049] The further material (c) may be surface - modified and may in particular be hydrophobized. Hydrophobization can be achieved, for example, by an organofunctional silane having an alkyl or aryl moiety.

[0050] Most preferably, hydrophobized SiO2 or hydrophobized nepheline - cyanite or a mixture thereof is used as the further material (c).

[0051] Examples of organofunctional silanes that impart hydrophobization to the further material (c) are silazanes selected from dimethyldichlorosilane, trimethoxy - i - butylsilane, trimethoxyoctylsilane, hexadecyltrimethoxysilane, octyltriethoxysilane, 1,1,1 - trimethyl - N - trimethylsilyl - silanamine and N - methyl - aza - 2,2,4 - trimethylsilacyclopentane, or siloxanes selected from octamethyltetracyclosiloxane, decamethylpentacyclosiloxane or polydimethylsiloxane, and combinations thereof.

[0052] Examples of commercially available products for the further material (c) are amorphous silica particles such as Syloid Al 1 (Grace), Aerosil R 972 or Aerosil 9201, Sipernat D10, Sipernat D13, Sipernat D14, manufactured by Evonik, amorphous or precipitated silica particles. Examples of nepheline - cyanite are Minex products from Sibelco (Belgium), or Silibond or Treminex products from Quarzwerke Group (Germany). An example of BaSO4 is Blanc Fixe N or G from Solvay. Examples of metal phosphates are Heucophos (trademark) products from Heubach (Germany), for example, ZnCaSrAl orthophosphate silica hydrate, for example ZCPPlus, or modified zinc orthophosphate, for example ZPO.

[0053] According to the present invention, c add The amount of the further material (c), called, is in the range of 4.5 to 17.0% by weight, preferably in the range of more than 4.5 to 15.0% by weight, more preferably in the range of 5.0 to 14.0% by weight, most preferably in the range of 6.0 to 13.0% by weight, based on the total amount of the composite material respectively. Suitable ranges are also 6.0 to 17.0% by weight and 7.0 to 17.0% by weight, based on the total amount of the composite material respectively.

[0054] If it is less than 4.5% by weight, the blackness degree is too low, and if it exceeds 17% by weight, the amount of active Zn is too low, so the corrosion prevention is too low.

[0055] The amount c of the abrasion aid add and the amount c of the metal oxide ZnO,M The total of is preferably in the range of 15.0 to 42.0% by weight, more preferably in the range of 20.0 to 41.0% by weight, most preferably in the range of 22.0 to 40.0% by weight, based on the total amount of the black granular zinc composite material respectively. Zinc and optionally further metal alloy components c present in the compound Zn,MThe elemental content represents the cathode mass available when the pigment is used as a sacrificial anode. However, due to the fairly high specific surface of the pigment, this cathode material is relatively readily available. This can be represented by a parameter called c Zn,M,spec. and is defined herein as c Zn,M,spec = c Zn,M / BET.

[0056] The term "BET" here is the specific surface area measured by a known method based on the Brunauer - Emmett - Teller (BET) theory, applying a three - point measurement using nitrogen as the adsorbed gas. Preferably, c Zn,M,spec is in the range of 14.0 - 87.0 wt%×g / m 2 more preferably in the range of 15.0 - 87.0 wt%×g / m 2 even more preferably in the range of 20.0 - 87.0 wt%×g / m 2 even more preferably in the range of 21.0 - 70.0 wt%×g / m 2 and most preferably in the range of 23.0 - 65.0 wt%×g / m 2 range.

[0057] The particle size can preferably be determined by laser particle size measurement using a Malvern Mastersizer 2000 instrument. As a measure of the average diameter, the median value d 50 can be used. The size is determined as the volume - weighted sphere equivalent value according to the Fraunhofer approximation and according to the instructions of the manufacturer of the measuring instrument. Preferably, the d 50 of the composite particles is in the range of 5.0 - 30 μm, more preferably in the range of 6.5 - 30 μm, even more preferably in the range of 7 - 30 μm, still more preferably in the range of 8 - 27 μm, and most preferably in the range of 9 - 25 μm.

[0058] A d 50 less than 5.0 μmHowever, the particles become too fine, which may cause safety problems when finally dried into powder. In addition, they may cause viscosity problems when incorporated into the coating formulation, thus limiting the versatility of the corrosion pigment formulation.

[0059] Particles exceeding 30 μm are hardly achievable due to the stringent conditions of their production.

[0060] Manufacturing method: The manufacturing method of the black zinc composite material includes the following steps: (a) Providing a mixture containing zinc powder, a wear assistant, which comes from a further material (c), and a lubrication assistant in a grinding aggregate equipped with grinding balls; (b) Dry-grinding the mixture of (a) over a time t m wherein no fluorocarbon polymer is used during the grinding process; (c) Separating the ground mixture from the grinding aggregate; (d) Optionally, further steps such as sieving and / or pasting.

[0061] In this method, the zinc powder used preferably has a substantially spherical shape. The zinc powder obtained after atomization of the melt preferably has a median particle size d in the range of 2 μm to 500 μm 50、粒子 and more preferably in the range of 5 μm to 200 μm, even more preferably in the range of 10 μm to 100 μm. Preferably, the metal powder obtained by atomization has a narrow particle size distribution. The spherical metal particles of the alloy for use according to the present invention have a D 50、粒子 value in the range of 1 μm to 15 μm, preferably 1.0 to 10 μm, a D 10 value in the range of 25 μm to 75 μm, preferably 30 μm to 40 μm, and a D 50 value in the range of 75 μm to 90 μm, preferably 80 μm to 90 μm. 90 It is preferred to have these values.

[0062] The dry grinding process is carried out under rather stringent conditions. The grinding time t of grindingm is preferably in the range of 12 to 36 hours, more preferably in the range of 13 to 30 hours, and most preferably in the range of 15 to 24 hours. These grinding times are generally much longer than the normal grinding times used, for example, in the production of zinc flakes.

[0063] What is important is the use of an additive as an abrasion aid in the grinding process. The abrasion aid is also referred to herein as an "abrasion aid additive".

[0064] The abrasion aid facilitates the formation of very fine zinc or zinc alloy particles.

[0065] These fine particles are expected to be dark gray to black. Due to the severe conditions of grinding, the abrasion aid may be powdered and ultimately mixed with elemental zinc or zinc alloy. Also, they reduce the occurrence of cold welding of zinc powder particles as compared to the normal milling (grinding) of zinc powder without an abrasion aid.

[0066] The grinding process is preferably carried out under conditions of reduced oxygen content as compared to ambient conditions. For example, the grinding atmosphere may contain 3 to 15% by volume of oxygen in an inert gas atmosphere such as nitrogen or argon.

[0067] The zinc metal or zinc alloy metal component is partially oxidized during the grinding process. After the grinding process, the compound black pigment is further contacted with oxygen or water under ambient conditions, and metal oxides are formed on its surface. However, a part of the metal oxides formed during the grinding process can be formed especially from small zinc particles and thus is mixed with elemental zinc metal.

[0068] The median diameter d of the abrasion aid particles used before grinding 50、摩耗is preferably in the range of 0.05 to 12 μm, more preferably in the range of 1.0 to 8.0 μm. These sizes refer to the primary particle size and not to aggregates that will be separated or crushed during the grinding process anyway. Since the wear aid particles may be at least partially crushed, it is most likely that the final intermediate particle size will be smaller than the initial particle size.

[0069] Preferably, the wear aid additive is used in an amount of 4.5 to 17.0% by weight, more preferably 6.0 to 13.0% by weight, each based on the amount of zinc powder. If it is less than 4.5% by weight, the formed particles are not sufficiently black. If an amount exceeding 17% by weight is used, the amount of elemental zinc or elemental alloy metal is too low.

[0070] The wear aid is preferably selected from the following: (i) a group consisting of metal oxides or metal hydroxides such as SiO2, TiO2, Al2O3, Al(OH)3, magnetite, Fe2O3, ZrO2 and mixtures thereof, or (ii) silicates or aluminosilicates, for example, synthetic mica, natural mica, preferably biotite or muscovite, nepheline - syenite, Zn - silicate and mixtures thereof; (iii) metal phosphates, (iv) BaSO4 or a mixture of any of (i) to (iv) thereof.

[0071] Preferably, the wear aid is at least partially mixed with the elemental zinc particles after the entire manufacturing process. The mixed wear aid can be detected by SEM (scanning electron microscopy) combined with EDX (energy - dispersive X - ray spectroscopy) of the cross - section of the black zinc particles. The mixed particles will be present inside such granular bodies. Preferably, at least 50 atomic% of the wear aid, more preferably at least 60 atomic%, even more preferably at least 70 atomic%, and most preferably at least 80 atomic% is mixed with the elemental zinc particles.

[0072] Only a very small portion of the wear aid may be present on the surface of the composite granulate after the grinding process.

[0073] A further component of the grinding mixture is a lubricant such as a fatty acid.

[0074] Preferably, saturated fatty acids such as stearic acid, oleic acid, linoleic acid, castor oleic acid, palmitic acid, arachidic acid, myristic acid, lauric acid, capric acid, elaidic acid, erucic acid, linolenic acid, myristic acid, palmitoleic acid and mixtures thereof are used as lubricants. Most preferably, saturated fatty acids such as palmitic acid, stearic acid and mixtures thereof are used here.

[0075] It is preferred to use fatty acids having unbranched alkyl groups. In this case, at least 90% of the fatty acid is unbranched, while up to 10%, preferably up to 4%, most preferably up to 2% of the fatty acid may be branched.

[0076] The amounts of these well-known lubricants are usually quite small in this manufacturing process, preferably in the range of 0.1 to 3.0% by weight, more preferably in the range of 0.2 to 2.5% by weight, even more preferably in the range of 0.3 to 2.0% by weight, most preferably in the range of 0.5 to 1.0% by weight, respectively, based on the total amount of the zinc metal or zinc alloy and the wear aid used. Such small amounts are advantageous for the formation of the black composite zinc pigment, and the wear aid additive, and the formed metal oxide are also partially mixed with the elemental metal.

[0077] The dry grinding process is preferably used compared to the wet grinding process because no solvent is used (avoidance of solvent release) and the process is more energy-efficient.

[0078] The comminuted aggregate is preferably any type of comminution media mill suitable for dry comminution, such as a ball mill or an impact mill, a pin mill, a blast mill, a beater mill or an attrition disk mill. Such mills are commercially available, for example, from Netzsch in Germany.

[0079] The milling balls (grinding balls) of the ball mill (ball milling) are preferably made of steel and have a diameter of about 2.5 to about 6.0 mm. If it is less than 2.5 mm, the energy of comminution is too low, and if it exceeds 6.0 mm, the comminution of zinc powder is not optimal.

[0080] The rotational speed is preferably in the range of 55% to 75% with respect to the critical rotational speed n crit and the critical rotational speed can be determined according to a well-known formula:

Equation

[0081] where D is the diameter of the drum and g is the gravitational constant.

[0082] More preferably, the rotational speed is in the range of 60% to 70% with respect to the critical rotational speed.

[0083] If it is less than 55%, the energy input to the abrasive is too low, and if it exceeds 75%, the malleability becomes not optimal.

[0084] According to the present invention, no fluorocarbon polymer is used during the comminution process. More specifically, fluorocarbon polymers such as PTFE are not used as lubricants in the dry comminution process. According to US7,023,572B2, zinc flakes having no black color can be produced by using a fluorocarbon polymer and a cooling ball mill as lubricants.

[0085] The black granular zinc composite can be used in heavy corrosion prevention formulations, especially applicable to automobiles and construction, particularly buildings and bridges, etc. Particularly preferred is the dip spin formulation which can be preferably used for the coating of screws in automotive applications. In particular, in automotive applications, such formulations can be used to coat clips, washers, metal panels, screws, bolts, fasteners, brakes or automotive chassis components.

[0086] Further aspect: Furthermore, in some embodiments, material (c) comprises or consists of ZnO or Zn(OH)₂ or a mixture thereof. For these specific embodiments, the present invention has the following aspects:

[0087] The first aspect relates to a black granular zinc composite comprising: (a) Elemental zinc or zinc alloy in an amount C in the range of 58.0 - 85.0% by weight relative to the composite, Zn,M and (b) Zn-oxide, Component (b) is at least partially mixed with zinc or zinc alloy metal (a).

[0088] A second aspect according to this first aspect is a black granular zinc composite material, wherein the amount c Zn,M is in the range of 60.0 - 75.0% by weight relative to the composite.

[0089] A third aspect according to any of the foregoing aspects is a black granular zinc composite, wherein c Zn、spec = c Zn The specific activity Zn amount c defined as c / BET Zn,spec. is in the range of 14.0 - 90% by weight × g / m 2

[0090] A fourth aspect according to any of the foregoing aspects is a black granular zinc composite material, wherein the specific activity Zn amount c Zn,spec is in the range of 25 - 87% by weight × g / m 2 ​​

[0091] A fifth aspect according to any of the foregoing aspects is a black composite material, wherein component (a) is of the formula ZnAl x Mg y M f z (I) and is a zinc alloy represented by wherein x, y, and z represent the content of each metal in weight % with respect to the total content of the alloy, x is in the range of >0 to 10, y is in the range of >0 to 7, z is in the range of 0 to 0.5, and M f represents a further metal, which may be treated as a total and is selected from the group consisting of Ca, Sn, Si, In, Bi, Mn, K, Sr, Ba, and mixtures thereof.

[0092] A sixth aspect according to any of the foregoing aspects is a black composite material, wherein at least 15 mol% of ZnO, Zn(OH)2 or a mixture thereof of component (b) is present inside the composite when analyzed in cross-section using SEM and EDX.

[0093] A seventh aspect according to any of the foregoing aspects is a black granular zinc composite according to any of the foregoing claims, wherein the amount of (b) Zn-oxide is in the range of 15.0 to 42.0% by weight with respect to the total amount of the composite material.

[0094] An eighth aspect according to any of the foregoing aspects is a black composite material in which at least a part of ZnO or Zn(OH)2 is used as an abrasion aid during the grinding of zinc powder in a dry grinding process.

[0095] A ninth aspect is a method for producing a black composite material, comprising the following steps: (a) providing a mixture containing zinc powder or zinc alloy powder, an abrasion aid made of ZnO, Zn(OH)2 particles or a mixture thereof, and a lubrication aid in a grinding aggregate equipped with grinding balls; (b) dry-grinding the mixture of (a) above for a time t m ; (c) Separating the pulverized mixture from the pulverized aggregate, and (d) Optionally, further steps, such as classifying and / or pasting, is a method comprising.

[0096] A tenth aspect according to aspect 9 is a method for producing a black composite material, wherein the wear aid is used in an amount of 4.5 to 17.0% by weight based on the amount of zinc powder.

[0097] An eleventh aspect according to aspect 9 or 10 is a method for producing a black composite material, wherein the wear aid d 50 , 摩耗 has a median size in the range of 0.05 to 12 μm.

[0098] A twelfth aspect according to any of aspects 9 to 11 is a method for producing a black composite material, wherein the milling time t m is in the range of 12 to 36 hours.

[0099] A thirteenth aspect according to any one of aspects 9 to 12 is a method for producing a black composite material, wherein the zinc alloy powder has the formula ZnAl x Mg y M f z (I) represented by wherein x, y and z represent the content of each metal in the total content of the alloy in wt%, x is in the range of >0 to 10, y is in the range of >0 to 7, z is in the range of 0 to 0.5, and M f is a further metal, which can be treated as a whole and is selected from the group consisting of Ca, Sn, Si, In, Bi, Mn, K, Sr, Ba and mixtures thereof.

Examples

[0100] Example 1: A 7 kg steel ball (diameter: 4.7 mm), 180 g of zinc alloy 1 powder <140 μm, 20 g of the abrasion aids described in Tables 1 and 2, and 1 g of stearic acid were introduced into a drum mill (length: 35 cm, width: 18 cm). Subsequently, the mixture was dry milled at 60 rpm for 16 hours with a 5% reduced oxygen content.

[0101] Subsequently, the product was saturated over 2 hours with an increased oxygen content. Finally, the obtained black zinc composite product was carefully separated from the metal balls through a sieve.

[0102] Example 2: A 7 kg steel ball (diameter: 4.7 mm), 180 g of zinc alloy 1 powder <140 μm, 20 g of the abrasion aids described in Tables 1 and 2, and 2 g of stearic acid were introduced into a drum mill (length: 35 cm, width: 18 cm). Subsequently, the mixture was dry milled at 60 rpm for 16 hours with a 5% reduced oxygen content. Subsequently, the product was saturated over 2 hours with an increased oxygen content.

[0103] Subsequently, the obtained black zinc composite product was carefully separated from the metal balls through a sieve.

[0104] Examples 3 - 24 and Comparative Examples 1 - 5: Further examples were carried out according to Example 1 or 2, however using the experimental parameters as listed in Table 1. In Table 2, the abrasion aids used therein are specified in more detail.

[0105] Comparative Example 6: The competing product Blitz (trademark) Zinc Z2031 (manufactured by Benda - Lutz, Sun Chemical) of black zinc.

[0106] Initial zinc powder: Some of the examples of the present invention used commercially available Standart (trademark) Zinc AS <45 μm (Eckart Suisse) as the initial zinc powder, as illustrated in Table 1.

[0107] In other examples, a zinc alloy (referred to as "zinc alloy 1 or 2" in Table 1) having a substantially spherical shape and obtained by atomizing in the usual manner was used. The composition of zinc alloy 1 was 94 wt% zinc, 5 wt% aluminum, and 1 wt% magnesium. Different fractions of this alloy were used as exemplified by the sieve parameters or air classification parameters in Table 1. The composition of zinc alloy 2 was 6 wt% aluminum, 6 wt% magnesium, and the balance zinc.

[0108]

Table 1

[0109]

Table 2

[0110] Characteristic evaluation: The examples and comparative examples were characterized with respect to their particle sizes and tested in various ways. The results are shown in Table 3.

[0111] Particle size measurement: Approximately 0.5 g of the black zinc pigment from the sample was dispersed in a Hydro 2000 G dispersion unit containing isopropanol, and then measured using a Malvern Mastersizer 2000 connected according to the manufacturing information, under ultrasonic shock in the measurement chamber during measurement. The particle size was determined according to the Fraunhofer approximation method based on the volume-weighted size of the equivalent sphere. The median value d 50 was used as a measure of the average particle size.

[0112] Panel preparation for corrosion test and color measurement: 56.5 g of the black pigment of the examples and comparative examples of the present invention was slowly stirred and dispersed in 43.5 g of a solvent-based silicate lacquer having a solid content of about 55 wt%. Optionally, the viscosity was adjusted to the range of 30 s to 50 s as measured by a flow cup according to DIN 53211 by adding dipropylene glycol (up to 10 g), and the lacquer was applied onto a metal substrate (steel Q-panel R46) by drawdown (applied nominal dry film thickness: 24 μm, speed 3 cm / min) by applying it twice in opposite directions. After the panel was ventilated at 100 °C for about 30 minutes, it was cooled and placed in an oven at 300 °C for 40 minutes. After cooling, the panel can be used for color measurement and salt spray test.

[0113] Salt spray test: Here, the described painted metal sheets were subjected to a salt spray test to examine their resistance to rust according to ASTM B117; ISO 9227 or ASTM G85. The formation of red rust after 504 hours was evaluated as the total percentage of the exposed area. The test was considered passed when the red rust area was 1.5% or less. If the red rust area was 0.8 or less, it was marked as "++", and if the red rust area was 0.8% or more and 1.5% or less, it was marked as "+". If the red rust area was >1.5% and ≦10.0, it was indicated as "-", and if it was >10.0%, it was indicated as "-".

[0114] Color measurement: The painted panels were also used for color measurement with a Konica Minolta 700d spectrophotometer. The diffuse L * value was determined using D65 / 10° conditions. Four corners and the center point of each panel were measured in a clockwise direction. Ten measurements were taken from each point, and the average value was calculated. The about 32 L * values are comparable to the visual appearance of carbon black. The L * samples with values <29.0 were marked as "++", and the L * samples with values ≧29.0 and <34.0 were marked as "+", and the L * samples with values ≧34.0 did not meet the test and were marked as "-".

[0115] Determination of Active Zinc Content (in the Case of Pure Zinc Compounds): The determination of the active zinc content was carried out by volumetric titration (volume titration). The zinc pigment sample was dispersed in a ferric sulfate solution, whereby Fe 3+ ions were reduced to Fe 2+ These Fe 2+ ions were titrated with a potassium permanganate solution (0.1N).

[0116] In the first step, the titer of potassium permanganate was measured. Therefore, approximately 0.5 g of Na-oxalate was weighed into a 250 ml beaker, dissolved in distilled water, and filled to the mark in a 250 ml volumetric flask. Next, 50 ml of this solution was pipetted into an Erlenmeyer flask. A 25 ml burette was filled with potassium permanganate (0.1N) and the zero point was adjusted. The Na-oxalate solution was heated to 50 °C with stirring and then titrated with the potassium permanganate solution. The volume required here is V1 (ml). The titer of the K-potassium permanganate solution was calculated as follows:

Equation

[0117] A blank test was carried out by adding 5 ml of acetone to an Erlenmeyer flask, then 50 ml of ferrous sulfate solution, and subsequently approximately 30 ml of sulfuric acid (30%). Then, 2 or 3 drops of potassium permanganate were added to this solution and stirred. If the color of the permanganate remained, there was no defect in the Fe solution and acetone.

[0118] For the determination of the zinc content, 100 mg of the zinc sample was weighed into a 250 ml Erlenmeyer flask. To enable better dispersion of the zinc particles, 5 ml of acetone was added and slightly warmed. Then, 50 ml of ferric sulfate solution of an appropriate concentration was added and stirred slightly until the solid dissolved. After adding 30 ml of sulfuric acid (30%), the color changed slightly to green. This solution was titrated with the potassium permanganate solution to obtain a volume V2 (ml).

[0119] The active zinc content is calculated as follows accordingly:

Number

[0120] For better reproducibility, titration was repeated several times (2 - 3 times), and the results were averaged. In the case of using zinc alloys containing Al and Mg, the determination of the elemental metal content c ,ZnM had to be corrected by a correction factor k1 defined as follows:

Number

[0121] Here, M Zn , M Al and M Mg are the molar masses respectively, M 合金 is the effective molar mass of the alloy, x is the content in mass % of Al, and y is the content in mass % of Mg in the zinc alloy.

[0122] This correction factor is based on the following assumptions: The particles are assumed to be homogeneous with respect to the elemental metal content, there is no segregation of alloying elements, the oxidation during the grinding process is homogeneous with respect to the metal, and there is no change in composition during titration.

[0123]

Table 3 - 1

Table 3 - 2

[0124] Discussion: All zinc pigment samples of Examples 1 - 24 of the present invention are sufficiently dark (L *<34.0), and passed the salt spray test. The commercially available Comparative Example 6 also had sufficient darkness, but as can also be seen in FIG. 1, it did not pass the salt spray test. As is well understood, at any of the illustrated times, the panel of Example 2 is much smoother compared to the panel of Comparative Example 6, and the area of red rust appears darker (the "hole part") in this black / white photograph.

[0125] However, further differences were observed: The pigment of Comparative Example 1 in which glass flakes were used as an abrasion aid was not sufficiently black and did not pass the salt spray test. All other comparative examples were sufficiently black but did not pass the salt spray test. In particular, Comparative Examples 2 to 5 were carried out using pure zinc powder, various additives, and a rather high milling time of 1200 minutes. The active zinc content of these samples was rather low. Compared with these experiments, Examples 12 to 14 were carried out under the same conditions except that a zinc alloy was used. These results are considered to indicate that the zinc alloy is preferable compared to pure zinc.

[0126] Generally, all examples using silica or nepheline-syanite compounds as abrasion aids showed excellent results. ZnO or TiO2 particles can also be used as abrasion aids, but here it is necessary to use either a higher grinding time (Examples 22 and 23) or a higher concentration (Example 24).

[0127] In FIG. 2, the internal structure of the pigment of Example 3 can be seen in the SEM cross-sectional micrograph. The silica particles used here as abrasion aids appear to have a dark contrast against zinc or zinc oxide. Most of the silica particles are located within the internal pigment, and thus it can be clearly seen that they are mixed with zinc and zinc oxide.

Claims

1. A black granular zinc composite, comprising: (a) an amount c in the range of 58.0 to 85.0% by weight relative to the complex Ｚｎ、Ｍ of elemental zinc or a zinc alloy, (b) a Zn-oxide, and (c) Further material, amount c of this further material (c) ａｄｄ is in the range of 4.5 to 17.0% by weight based on the total amount of the composite material wherein components (b) and (c) are at least partially commingled with said elemental zinc or zinc alloy (a).

2. The black granular zinc composite according to claim 1, wherein said further material (c) is selected from the group consisting of: (ii) a silicate or aluminosilicate selected from the group consisting of synthetic mica, natural mica, preferably biotite or muscovite, nepheline-syenite, Zn-silicate, and mixtures thereof; (i) SiO ２ , TiO ２ , Al ２ O ３ , Al(OH) ３ , magnetite, Fe ２ O ３ , ZrO ２ and a metal oxide or metal hydroxide selected from the group consisting of these and mixtures thereof, or (iii) a metal phosphate

3. (iv) BaSO ４ or a mixture of any of the species (i) to (iv) thereof.

4. Additional material (c) is SiO ２ The black granular zinc composite according to claim 1 or 2, which is nepheline - cyanite or a mixture thereof.

5. The further material (c), preferably SiO ２ is further hydrophobized, the black granular zinc composite according to claim 3.

6. The black granular zinc composite according to any one of claims 1 to 4, wherein the amount of said further material (c) ranges from 6.0 to 17.0% by weight based on the total amount of the composite material.

7. c Ｚｎ，Ｍ The black granular zinc composite according to any one of claims 1 to 5, wherein c is in the range of 59.0 to 80.0% by weight.

8. The black granular zinc composite according to any one of claims 1 to 6, wherein the total amount of (b) Zn-oxide and said further material (c) ranges from 15.0 to 42.0% by weight based on the total amount of the composite material.

9. c Ｚｎ、ｓｐｅｃ = c Ｚｎ The specific activity Zn amount c, defined as c / BET Ｚｎ、ｓｐｅｃ． is in the range of 14.0 to 87.0 wt% × g / m ２ of. The black granular zinc composite according to any one of claims 1 to 7.

10. The black granular zinc composite according to any one of claims 1 to 8, wherein said further material (c) does not form a coating layer or a coating of separate particles on the surface of the zinc particles.

11. d ５０ The black granular zinc composite according to any one of claims 1 to 9, wherein d is in the range of 6.5 to 30 μm.

12. The black granular zinc composite according to any one of claims 1 to 10, wherein component (a) is a zinc alloy represented by the formula ZnAl ｘ Mg ｙ M ｆ ｚ (I) and is a black granular zinc composite. Wherein, x, y and z represent the content of each metal in weight % with respect to the total content of the alloy, x is in the range of >0 to 10, y is in the range of >0 to 7, z is in the range of 0 to 0.5, and M ｆ represents a further metal, which may be treated as a total and is selected from the group consisting of Ca, Sn, Si, In, Bi, Mn, K, Sr, Ba and mixtures thereof

13. The black granular zinc composite according to any one of claims 1 to 11, wherein said further material (c) is used as an abrasion aid during the grinding of zinc powder in a dry grinding process.

14.

15. The composite has an L value of < 34.0 ＊ The black granular zinc composite according to any one of claims 1 to 12

16. A method for producing the black zinc composite according to claims 1 to 13, comprising the following steps: (a) providing a mixture comprising zinc powder or zinc alloy powder, an abrasion aid, which consists of further material (c), and a lubrication aid in a grinding aggregate equipped with grinding balls; (b) drying and pulverizing the mixture of (a) over a time t ｍ without using a fluorocarbon polymer during the pulverization process (c) separating the ground mixture from said grinding aggregate; and (d) optionally, further steps such as sieving and / or pasting

17. The method according to claim 14, wherein said abrasion aid is selected from the group consisting of: ​ (i) SiO ２ , TiO ２ , Al ２ O ３ , Al(OH) ３ , magnetite, Fe ２ O ３ , ZrO ２ and a metal oxide or metal hydroxide selected from the group consisting of these and their mixtures, or (ii)a silicate or aluminosilicate selected from the group consisting of synthetic mica, natural mica, preferably biotite or muscovite, nepheline - syenite, Zn - silicate, and mixtures thereof; (iii)metal phosphates, (iv) BaSO ４ or a mixture of any of the species (i) to (iv) thereof.

16. Use of the black granular zinc complex according to claims 1 to 13 as a corrosion - inhibiting pigment in a heavy - corrosion - preventing formulation.

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