Zinc alloy pigment for waterborne corrosion formulations

Abstract

This invention is about platy zinc alloy pigments having a composition represented by formula (I): ZnAlx(MIV y)m(M2 o)n, (I) or by formula (II): ZnAlx(MIV y)m(M1 z)p(M2 o)n,(II) wherein x = 2.000 to 20, y = 0.100 to 8.000, z = 0.100 to 7.000 and MIV = Si, Ge or Sn, and m is an integer representing the number of different MIV elements and is in a range of 1 to 3, M1 denotes other alloy components and is chosen from the group consisting of Mg, Ti, Cr, Ni, Mn, Li, Ce, Mm, Mo, Bi, In, Sr, Zr, Ca, B, Ga, Pb, Fe and p is an integer which denotes the number of different M1 elements and M2 denotes unavoidable impurities of further metals which are not classified as MIV and / or M1 and whereas o is in a range of 0.001 to less than 0.100 and n is an integer representing the number of different impurity elements and wherein the platy zinc alloy pigment has a median size d50,fl, an average thickness tfl and an aspect ratio d50,fl / tfl and the aspect ratio d50,fl / tfl has a value of at least 8.0.

Description

[0001] Zinc alloy Pigment for Waterborne Corrosion Formulations

[0002] The present invention relates to a corrosion protection pigment of new zinc alloy composition which can be used in waterborne corrosion formulations.

[0003] Zinc flakes or zinc alloy flakes have been used for decades as pigments for cathodic corrosion protection. Usually, the corrosion formulations are solvent based systems, but due to ecological demands there is a desire to further shift to water-based corrosion protection formulations. In such formulations it is difficult to stabilize the zinc flakes against attack by water in the corrosion formulation while simultaneously the zinc flakes must act as a corrosion protection pigment in the final application of a film on a steel or an aluminum substrate. Special coatings or treatments of the zinc flakes have been proposed to address this difficult balance.

[0004] JP 2005238001 A discloses zinc flakes for aqueous based corrosion formulations, wherein the zinc flakes are treated with an oligomeric tetraethoxysilane and a water-soluble silane coupling agent. The coated zinc pigment seems to act as a rust preventive pigment and is stable in water-based formulations. However, many components must be carefully adjusted to obtain the desired properties, making this composition difficult to control and causing problems in reproducibility.

[0005] EP 3315563 A1 discloses zinc flakes which are coated with metal oxides from silicon, titanium or zirconium, preferably of silicon oxide. These pigments also should be stable in aqueous based corrosion formulations and at the same time exhibit good corrosion protection. However, it is difficult to adjust the exact thickness of the metal oxide coating. Thick coatings impart gassing stability but prevent the use as effective corrosion pigment while for thin metal oxide coatings the contrary characteristics apply. Therefore, an optimal metal oxide thickness must be adjusted for every corrosion formulation system which is not practical as the metal oxide coating is made by pigment suppliers while the corrosion formulation is made by coating manufacturers. Additionally, the manufacture of such coated zinc flakes has not been reproducible.

[0006] US 2023 / 0323135 discloses a rust preventive coating composition comprising a zinc pigment which is at least partially treated with orthophosphoric acid. This document indicates that the silica coated zinc pigments either failed to have gassing stability or did not give satisfactory results as corrosion protection pigment. The coating composition disclosed in this document is expected to have stability also in aqueous based formulations. Dispersibility is achieved mainly by adding a further dispersing additive.

[0007] WO 2022 / 132845 A1 discloses a zinc pigment treated with organic heterocycle additives which is to be used in waterborne corrosion protection formulations.

[0008] The technical teachings of all these documents require an extra step of coating the zinc flakes with at least one certain additive. Despite additional costs this coating step must be extremely well controlled in order to achieve reproducible results in view of the difficult balance of protection of the zinc pigment against gassing and the enablement as active corrosion protection pigment in a final cured corrosion formulation. Therefore, a need exists to provide a zinc pigment which has good corrosion protection properties and at the same time is gassing stable in aqueous environments even without any further passivation coating or at least with a strongly reduced sensitivity in such passivation coating processes.

[0009] Zinc alloys have been used widely as corrosion protection pigments. EP 1233043 A1 proposed zinc alloy pigments with more than 50 wt.% of zinc and a balance of other components of less than 50 wt.%. Such other components of the alloy could be tin, aluminum or magnesium. Especially preferred were alloys like ZnAI7. The alloys disclosed therein were supposed to be usable also in waterborne corrosion coating formulations. However, the zinc alloys disclosed therein do not meet the criteria of gassing stability. Therefore, zinc pigments with enhanced gassing stability, good corrosion stability and a simple and cost-effective way of production are needed.

[0010] The needs are met by providing a platy zinc alloy pigments having a composition represented by formula (I):

[0011] ZnAlx(MIVy)m(M2o)n, (I) or by formula (II):

[0012] ZnAlx(MIVy)m(M1z)p(M2o)n,(ll) wherein x = 2.000 to 20, y = 0.100 to 8.000, z = 0.100 to 7.000 and

[0013] MIV= Si, Ge or Sn, and m is an integer representing the number of different MIVelements and is in a range of 1 to 3,

[0014] M1denotes other alloy components and is selected from the group consisting of Mg, Ti, Cr, Ni, Mn, Li, Ce, Mm, Mo, Bi, In, Sr, Zr, Ca, B, Ga, Pb, Fe and p is an integer which denotes the number of different M1elements and

[0015] M2denotes unavoidable impurities of further metals which are not classified as MIVand / or M1and whereas o is in a range of 0.001 to less than 0.100 and n is an integer representing the number of different impurity elements and wherein the platy zinc alloy pigment has a median size dso.fi , an average thickness tn and an aspect ratio dso.fi / tti and the aspect ratio dso.fi / tti has a value of at least 8.0.

[0016] Further preferred embodiments are disclosed in claims 2 to 13.

[0017] Furthermore the needs are met by providing a method of manufacture of platy zinc alloy pigments comprising: a) producing a powder of zinc alloy particles by atomization of a melt of components with envisaged element composition b) grinding the zinc alloy particles obtained in a) in a ball mill equipped with grinding balls in a solvent and a lubricating grinding agent to obtain platy zinc alloy pigments and c) optionally further classifying the platy zinc alloy particles obtained in b) and optionally combining with a defined amount of an organic solvent to obtain a paste of platy zinc alloy pigments.

[0018] A further preferred embodiment is disclosed in claim 15.

[0019] Furthermore the needs are met by a water-based corrosion coating formulation comprising the platy zinc alloy pigments.

[0020] Furthermore the needs are met by use of the platy zinc alloy pigments in a water-based corrosion coating formulation.

[0021] Detailed Description: Zinc alloy Pigments:

[0022] The zinc alloy pigments have a composition which can be represented by formula (I): ZnAlx(MIVy)m(M2o)n, (I) or by formula (II):

[0023] ZnAlx(MIVy)m(M1z)p(M2o)n, (II) wherein x is the amount of aluminum in wt.% and y the amount of a particular MIVelement in wt.%, each based on the total zinc alloy. Parameter x is in a range of 2.00 to 20.00, preferably in a range of 2.00 to 15.0, more preferably in a range of 2.00 to 13.00, furthermore preferably in a range of 3.00 to 10.0 and most preferably in a range of 3.00 to 7.00. Above of 7.0 the zinc alloys tend to be too reactive towards water and corrosion stabilization by addition of MIVelement may not be sufficient. Such alloys might need further stabilization by addition of corrosion protective additives. Particularly preferred are zinc alloy pigments with parameter x in a range of 3.00 to 7.00, which are not further coated with corrosion protective additives. The surface of such pigments is only coated with common lubricating grinding additives used for manufacture of these pigments by grinding.

[0024] Parameter y is in a range of 0.100 to 8.00, preferably in a range of 0.30 to 6.00 and more preferably in a range of 0.400 to 2.00. MIVis Si, Ge or Sn and most preferably is Si. Parameter m is an integer in a range of 1 to 3 and denotes the number of MIVelements which have an y-value of at least 0.100. In preferred embodiments MIVis Si and m = 1.

[0025] Formula (I) denotes ternary zinc alloys including aluminum and MIVwith a balance of zinc and M2denotes unavoidable impurities of further metals which are not MIV.

[0026] Formula (II) denotes quaternary zinc alloys including aluminum and M1which denotes another element as a further alloy component and includes or is selected from the group consisting of Mg, Ti, Cr, Ni, Mn, Li, Ce, Mm, Mo, Bi, In, Sr, Zr, Ca, B, Ga, Pb and Fe. Mm denotes to mixtures of rare earth metal elements. In more preferred embodiments M1is selected from the group consisting of Mg, Ti, Cr, Ni, Mn, Li, Ce, Mo, Bi, In, Sr, Zr, Ca, B, Ga, Pb and Fe.

[0027] Parameter z denotes the amount of a particular M1element in wt.% based on the total zinc alloy particle and z is in a range of 0.100 to 7.00 and preferably in a range of 0.150 to 3.00. Parameter p is an integer and denotes the number of different M1elements and is preferably in a range of 1 to 4, more preferably in a range of 1 to 3, even more preferably in a range of 1 to 2 and most preferably p=1 . Further preferred elements for M1are Mg, Ti, Cr, Ce, Mo and In and most preferred is Mg (with p = 1). If there are two or more of M1elements (p > 2) each of the different elements may have a different z-value. Preferably the sum of all z-values of all p M1elements is below of 7.00 and more preferably below of 5.00. Further the alloy contains a balance of zinc and M2denotes unavoidable impurities of further metals which are not classified as M1or MIV.

[0028] In contrast to the convention for metal alloys (ISO 1190-1), the quantity parameters in these formulas are subscripted for better clarity. However, specific alloys are shown as usual. In further embodiments M2is taken from the group containing or consisting of Ca, Na, K, Co, Cd, Pb, Fe, Cr, Mg, Mn, Cu, Hg, Ni, Sn, In, Ba, Sr, Si and mixtures thereof. The elements Sn or Si may only be classified as impurities here when MIVis different from any of these elements for a particular Zn alloy particle. These elements cover the major possible impurities associated with zinc aluminum alloys. The parameter o denotes the amount of a particular M2element in wt.%, based on the total zinc alloy pigment and is in a range of 0.001 to less than 0.100.

[0029] Formula (I) is to be understood in that any of the elements listed for MVIare denoted as an impurity M2when its concentration is below of 0.100 wt.% of the alloy. Formula (II) is to be understood in that any of the elements mentioned for M1or for MIVare denoted as an impurity M2when its concentration is below of 0.100 wt.% of the alloy. The parameter n denotes the number of different M2elements which can be analyzed to have a concentration within the limits of parameter o. If there are two or more of M2elements (n > 2) each of the different elements may have different values of o. Parameter n is typically in a range of 1 to 15 and preferably in a range of 4 to 9. The sum of all the o-values of all p M2elements preferably should not exceed 0.200, more preferably it should not exceed 0.150 and most preferably it should not exceed 0.100.

[0030] The elemental composition of the platy zinc alloy pigments is preferably determined by ICP-OES (inductive coupled plasma optical emission spectroscopy) using preferably an Avio 200 ICP-OES instrument (from Perkin Elmer) according to the instructions of the manufacturer of the measuring device. For the determination of a silicon amount the zinc alloy pigments should be subjected to a hydrofluoric acid digestion. Zinc, aluminum, possibly a M1metal and impurities can be usually analyzed by using a digestion with HCI and H2O2. Elements can be analyzed up to a minimum concentration level of 0.001 wt.%. Other impurities with lower concentration may be present but are difficult to determine.

[0031] In other embodiments the concentration of an element to qualify it as impurity M2is less than 0.850 wt.% which means that y is in a range of 0.085 to 8.00 and 0 is in a range of 0.001 to 0.085.

[0032] In preferred embodiments the zinc alloy pigments of formula (I) have parameter x in a range of 3.00 to 10.0 and more preferably in a range of 3.00 to 7.00 and parameter y in a range of 0.30 to 2.0.

[0033] For preferred embodiments of the quaternary zinc alloy pigments according to formula (II) M1is only one element (p = 1) and x is in a range of 2.000 to 8.00 and more preferably in a range of 3.00 to 7.00 and x / z is in a range of 0.9 to 1.1. Such kind of alloys are basically known to have a rather high corrosion stability, even without addition of MIVelements, particularly without Si. Examples thereof are ZnAHMgs or ZnAleMge.

[0034] In preferred embodiments the zinc alloy pigments of formula (II) have x in a range of 3.50 to 10.0 and more preferably in a range of 3.00 to 7.00, y in a range of 0.30 to 2.0 and z in a range of 0.15 to 3.0.

[0035] In preferred embodiments MIVis Si and the zinc alloy pigments have a wt.% ratio of Al to Si, x / y, in a range of 1 .5 to 20, further preferred in a range of 3 to 18 and most preferred in a range of 6 to 15.

[0036] The zinc alloy particles have a platelet-like form. They are obtained from the zinc alloy particles described before by milling, for example in a ball mill. The zinc alloy particles obtained by milling may be also called as “flakes”. The terms “platelet-like pigments”, “platy pigments”, “flaky pigments” or “flakes” are used synonymously throughout this document.

[0037] The particle size of the zinc alloy pigments can be determined by laser granulometry, preferably using a Helos BR apparatus. As a measure of the mean diameter the median value dso can be used. The sizes are determined as volume weighted sphere equivalents according to the Fraunhofer approximation and according to the instructions of the manufacturer of the measurement instrument.

[0038] The median size of the platy zinc alloy pigments is called dso.fi and preferably the dso.fi- values are in a range of 8 to 35 pm, more preferably in a range of 10 to 25 pm and most preferably in a range of 1 1 to 18 pm.

[0039] Platelet-like pigments have a thinnest dimension which is their thickness. The flaky zinc alloy particles preferably have an average thickness tfi in a range of 80 to 1 ,000 nm, more preferably in a range of 100 to 500 nm and most preferably in a range of 120 to 350 nm. These preferred thickness ranges are rather low when compared to other corrosion protection flakes like pure zinc flakes or ZnMg alloy flakes which is due to the higher ductility of ZnAI alloys. The mean thickness tfi of the zinc alloy flakes can be determined by counting particle thicknesses using a SEM (scanning electron microscope). The thickness distribution can be determined, for example, by the method described on page 24 of WO 2004 / 087816 A2. For a more refined method the procedure is as follows: the platy zinc alloy pigments in powder form are dispersed in a nitrocellulose-based lacquer and applied to an aluminum foil. The mixing ratio between powder and lacquer in the liquid system is about 1 :10. A section of a few cm2of the thus coated aluminum foil is separated out by irradiation with high-energy Ar ions using a broad-beam ion source to create a cross-section. To ensure sufficient conductivity, the separated cross-section is sputtered with thin carbon layer having a thickness of about 5 nm. The platy zinc alloy pigments in the cross-section are then imaged using a scanning electron microscope at magnifications ranging from 10,000x to 30,000x. If the thickness of the flakes varies along a single flake the maximum and the minimum thickness value of the flake may be determined and the average of these values is counted as thickness value of this particular flake. At least 100 flakes are measured and the arithmetic average thickness is determined.

[0040] The aspect ratio of the zinc alloy having platelet-like form is defined as dso.fi / tfi and is at least 8.0. More preferably the aspect ratio is in a range of 10.0 to 150, furthermore preferably in a range of 15.0 to 125 and most preferably in a range of 20 to 100.

[0041] Method of manufacture of zinc alloy pigments with platelet-like form:

[0042] A method of manufacture of platy zinc alloy pigments comprises the following steps: a) a powder of zinc alloy particles is produced by atomization of a melt of components with envisaged element composition b) the zinc alloy particles obtained in a) are ground in a ball mill equipped with grinding balls in a solvent and a lubricating grinding agent to obtain platy zinc alloy pigments and c) optionally the platy zinc alloy particles obtained in b) are optionally further classified and pasted to a defined amount with an organic solvent to obtain a paste of platy zinc alloy pigments.

[0043] The atomization step a) should be conducted at a temperature where all metal components are melted. MIVelements like silicon or germanium are preferably introduced not in elemental form but as an alloy, for example with aluminum, to avoid melting temperatures that are too high. The atomization step can be conducted in air atmosphere or in an atmosphere of an inert gas like Argon. In that case, however, a small amount of oxygen should be present in order to saturate the zinc alloy particles with respect to metal oxide on the surface of the zinc alloy particles.

[0044] The atomized zinc alloy particles may be further classified into different sizes after step a).

[0045] Preferably the zinc alloy particles have a median size dso.p in a range of 10 to 50 pm, more preferably in a range of 20 to 45 pm and most preferably in a range of 25 to 40 pm. If the zinc alloy particles are further comminuted to flakes the desired flake sizes are hardly reached if the dso.p is below of 10 pm. For zinc alloy particles with a dso.p above of 100 pm the obtained flaky pigments are too thick and in, for example fasteners applications, the limited stacking of such thick pigments would be of disadvantage.

[0046] The particle size distribution curve is determined by the same method as described above for the platy zinc alloy pigments.

[0047] The form of the zinc alloy particles may be spherical, brittle or ellipsoidal. In a preferred embodiment the zinc alloy particles have a spherical form.

[0048] The zinc alloy particles are ground under conditions of comminution grinding.

[0049] Preferred grinding aids are balls are made from steel, more preferably corrosion stable steel balls having an average diameter in a range of 6 to 10 mm.

[0050] The wt.% ratio of zinc alloy powder with respect to the steel balls is preferably in a range of 5 to 10 wt.% and more preferably in a range of 6 to 8 wt.%.

[0051] The grinding can take place in a solvent in a weight ratio of solvent to zinc alloy particles preferably in a range of 0.5 to 2.0 and more preferably in a range of 0.6 to 1 .2.

[0052] The solvent may be mineral spirit, solvent naphtha or mixture thereof and preferably is mineral spirit. In preferred embodiments the solvent is essentially free of aromatic compounds. Herein the term “essentially free” means a concentration of less than 0.5 wt.%, based on the whole solvent. Such solvents are preferred for toxicological reasons. Furthermore grinding aids such as lubricating grinding agents may be used in order to prevent cold welding of the zinc alloy particles. Preferred lubricating grinding agents as grinding aids are stearic acid, palmitic acid, 12-hydroxy stearic acid or mixtures thereof.

[0053] The critical speed of rotation nCrit is an important parameter which indicates when the balls begin to press against the mill wall due to centrifugal forces, at which point virtually no more grinding takes place: wherein g is the gravitational constant and D is the diameter of the drum.

[0054] The speed of rotation of the ball mill is preferably in a range of 25% to 85%, more preferably in a range of 40% to 70% of the critical number of revolutions nCrit.

[0055] Below of 25% the grinding of the zinc alloy powder is not effective while above of 85% the comminution of the Zn alloy powder may be too strong and additionally the ball mill may be mechanically overstressed by the strong centrifugal forces occurring.

[0056] The zinc alloy pigment pastes obtained in step c) preferably have a non-volatile content of 70 to 95 wt.% and more preferably of 80 to 92 wt.%. The solvent used for forming a paste is preferably mineral spirit.

[0057] Further aspects of this invention are dedicated to zinc alloy pigments which are produced by the above-mentioned process.

[0058] Therefore, a first aspect is dedicated to platy zinc alloy pigments having a composition represented by formula (I):

[0059] ZnAlx(MIVy)m(M2o)n, (I) or by formula (II):

[0060] ZnAlx(MIVy)m(M1z)p(M2o)n, (ll) wherein x = 2.000 to 20, y = 0.100 to 8.000, z = 0.100 to 7.000 and

[0061] MIV= Si, Ge or Sn, and m is an integer representing the number of different MIVelements and is in a range of 1 to 3,

[0062] M1denotes other alloy components and is selected from the group consisting of Mg, Ti, Cr, Ni, Mn, Li, Ce, Mm, Mo, Bi, In, Sr, Zr, Ca, B, Ga, Pb, Fe and p is an integer which denotes the number of different M1elements and

[0063] M2denotes unavoidable impurities of further metals which are not classified as MIVand / or M1and whereas o is in a range of 0.001 to less than 0.100 and n is an integer representing the number of different impurity elements and wherein the platy zinc alloy pigment has a median size dso.fi , an average thickness tn and an aspect ratio dso.fi / tti and the aspect ratio dso.fi / tti has a value of at least 8.0, which are manufactured by a process comprising the following steps: a) a powder of zinc alloy particles is produced by atomization of a melt of components with envisaged element composition b) the zinc alloy particles obtained in a) are ground in a ball mill equipped with grinding balls in a solvent and a lubricating grinding agent to obtain platy zinc alloy pigments and c) optionally the platy zinc alloy particles obtained in b) are optionally further classified and pasted to a defined amount with an organic solvent to obtain a paste of platy zinc alloy pigments.

[0064] A second aspect is dedicated to platy zinc alloy pigments according to aspect 1 , wherein M2is selected from the group consisting ofCa, Na, K, Co, Cd, Pb, Fe, Cr, Mg, Mn, Cu, Hg, Ni, Sn, In, Ba, Sr, Si and mixtures thereof.

[0065] A third aspect is dedicated to platy zinc alloy pigments according to any of preceding aspects 1 or 2, wherein parameter y in formula (I) or formula (II) is in a range of 0.30 to 6.00.

[0066] A fourth aspect is dedicated to platy zinc alloy pigments according to any of preceding aspects, wherein the pigments of formula (I) have a parameter x in a range of 3.00 to 10.00, preferably in a range of 3.00 to 7.00 and parameter y is in a range of 0.300 to 2.0.

[0067] A fifth aspect is dedicated to platy zinc alloy pigments according to any of preceding aspects, wherein the pigments of formula (I) or formula (II) have a parameter x in a range of 3.00 to 7.00.

[0068] A sixth aspect is dedicated to platy zinc alloy pigments according to any of preceding claims, wherein in formula (II) the elements for M1are selected from the group consisting of Mg, Ti, Cr, Ce, Mo, In and mixtures thereof and most preferred is Mg (with p = 1).

[0069] A seventh aspect is dedicated to platy zinc alloy pigments according to any of preceding claims, wherein the zinc alloy pigments of formula (II) have a parameter x in a range of 3.00 to 10.0, preferably in a range of 3.00 to 7.00, a parameter y in a range of 0.300 to 2.00 and a parameter z in a range of 0.150 to 3.00.

[0070] An eighth aspect is dedicated to platy zinc alloy pigments according to any of preceding claims, wherein for zinc alloy pigments according to formula (II) M1is only one element with p = 1 and parameter x is in a range of 3.00 to 10.00, preferably in a range of 3.00 to 7.00 and x / z is in a range of 0.9 to 1 .1 . A ninth aspect is dedicated to platy zinc alloy pigments according to any of preceding claims, wherein in formula (II) the sum of all z-values of all p M1elements is below of 7.00.

[0071] A tenth aspect is dedicated to platy zinc alloy pigments according to any of preceding claims, wherein MIVis Si and m = 1 .

[0072] An eleventh aspect is dedicated to a platy zinc alloy pigments according to any of preceding claims, wherein MIVis Si and the wt.% ratio of Al to Si x / y is in a range of 1 .5 to 20.

[0073] A twelfth aspect is dedicated to a platy zinc alloy pigments according to any of preceding claims, wherein their median size dso.fi is in a range of 8 to 35 pm.

[0074] A thirteenth aspect is dedicated to a platy zinc alloy pigments according to any of preceding claims, wherein the pigments have an average thickness in a range of 80 to 1 ,000 nm and preferably in a range of 100 to 500 nm.

[0075] A fourteenth aspect is dedicated to a platy zinc alloy pigments according to any of preceding claims, wherein the lubricating grinding agent of step b) of the method of manufacture is chosen from the group consisting of stearic acid, palmitic acid, 12-hydroxy stearic acid or mixtures thereof.

[0076] A fifteenth aspect is dedicated to a platy zinc alloy pigments according to any of preceding claims, wherein the zinc alloy particles obtained in step a) have a median size dso.p in a range of 10 to 50 pm.

[0077] A sixteenth aspect is dedicated to a platy zinc alloy pigments according to any of preceding claims, wherein the zinc alloy pigments are obtained as a paste using a solvent essentially free of aromatic compounds.

[0078] Coating composition for corrosion protection:

[0079] Another embodiment of this invention is a coating composition for corrosion protection comprising the zinc alloy pigments as described before. This formulation may be solvent based but preferably is an aqueous based formulation. Aqueous based coating compositions are those whose solvent is water or a mixture of water and one or more organic solvents compatible with water. That is, the coating composition for corrosion protection preferably contains water as a solvent, and may further contain an organic solvent, preferably a hydrophilic organic solvent, in addition to water.

[0080] In the case that the solvent is a mixture of water and an organic solvent (an aqueous solvent), the organic solvent is preferably a hydrophilic organic solvent. The hydrophilic organic solvent may be the same as the hydrophilic organic solvent used when producing the platy zinc alloy pigments and is contained in the resulting paste or composition.

[0081] Examples of the organic solvent that can be used in the coating composition for corrosion protection include, but are not limited to, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol and tripropylene glycol; glycol ethers such as monomethyl ether, monoethyl ether, dimethyl ether and diethyl ether of the glycols; alcohols such as ethanol, propanol, isopropanol, butanol, isobutanol, tert-butanol and diacetone alcohol; and ketones such as acetone and methyl ethyl ketone. Among the preceding, the organic solvent is preferably a glycol or glycol ether. The organic solvent may be used singly or in a combination of two or more.

[0082] The water or aqueous solvent content of the corrosion coating composition is not particularly limited, but generally it is preferably 20 wt.% or more, and more preferably 20 to 40 wt.%, based on the total weight of the corrosion coating composition. In the case of an aqueous solvent, it is preferred that the water content of the aqueous solvent is 50 wt.% or more, and the organic solvent content of the aqueous solvent is 50 wt.% or less, based on the total weight of the corrosion coating composition.

[0083] Generally, the coating composition for corrosion protection further contain a binder. The binder may be any type; any inorganic-based binder or organic-based binder resin can be used. The binder may be used singly or in combination of two or more.

[0084] Examples of the inorganic-based binder include, but are not limited to, a silane compound such as a silane-based coupling agent; silicates such as sodium silicate, potassium silicate and lithium silicate; metal alkoxide such as tetraethoxysilane, tetraethoxytitanium, tetraisopropoxytitanium, tetrapropoxyzirconium, triisopropoxyaluminum and dimethoxyzinc; and silicone resin. Examples of the silane-based coupling agent include, but are not limited to, vinylsilane-based coupling agents such as vinyltrimethoxysilane; acrylic silane-based coupling agents such as methacryloxypropyltrimethoxysilane; aminosilane-based coupling agents such as 3-amino-propyltrimethoxysilane; epoxysilane- based coupling agents such as p-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and y- glycidoxypropyltrimethoxysilane. Other examples of the inorganic-based binder that can be used are titanium-based coupling agents such as isopropyltriisostearoyl titanate; aluminum-based coupling agents such as acetoalkoxyaluminum diisopropylate; and zirconium-based coupling agents such as zirconium tributoxymonoacetylacetonate.

[0085] Among them, the inorganic-based binder is preferably a silane-based binder such as a silane-based coupling agent.

[0086] Examples of the organic-based binder resin include, but are not limited to, acrylic resins, epoxy resins, phenolic resins, polystyrene resins, polyurethane resins, oxazoline group- containing polymers, and polyvinylpyrrolidone.

[0087] The binder content of the coating composition for corrosion protection is not particularly limited and may be appropriately selected depending on the type of the binder or the like. When a silane-based binder is used, the silane-based binder content of the coating composition for corrosion protection is not particularly limited, but generally it is preferably 3 to 20 wt.%, and more preferably 4 to 16 wt.%, based on the total weight of the composition.

[0088] The coating composition for corrosion protection of the present embodiment contains the zinc alloy flakes as described before. In preferred embodiments the coating composition contains the zinc alloy flakes as the only metal pigments and contains no further metal pigments.

[0089] In other embodiments the coating composition for corrosion protection of the present embodiment may further contain another metal pigment.

[0090] Metal pigment other than the platy zinc alloy pigment (hereinafter, also referred to as “the other metal pigment”) may be any metal pigment. Examples thereof include, but are not limited to, a metal or metal alloy particle such as an aluminum or aluminum alloy particle, a manganese or manganese alloy particle, a nickel or nickel alloy particle, a titanium or titanium alloy particle, a tin or tin alloy particle, an iron or iron alloy particle, a cobalt or cobalt alloy particle, a tungsten or tungsten alloy particle, a vanadium or vanadium alloy particle, a molybdenum or molybdenum alloy particle, a tantalum or tantalum alloy particle, a niobium or niobium alloy particle, and a stainless steel particle. The other metal pigment may be used singly or in combinations of two or more. Preferably the other metal pigment has also a flake form. In other preferred embodiments the other metal pigment may be stabilized against attack of water by an additive or corrosion protection coating (like a silica or polymer coating) especially in case of an aluminum pigment.

[0091] The zinc alloy pigment content of the coating composition for corrosion protection (the amount of the zinc pigment of the present embodiment and optionally also the other metal pigment) is not particularly limited but generally is preferably in a range of 10 to 50 wt.% and more preferably in a range of 20 to 35 wt.%, each based on the weight of the total coating composition.

[0092] The coating composition for corrosion protection may further contain a metal oxide pigment, an organic pigment or a mixture thereof, Examples of the metal oxide pigment include, but are not limited to, a manganese oxide particle, a molybdenum oxide particle, a tungsten oxide particle, a tin oxide particle, an antimony oxide particle, an iron oxide particle, an aluminum oxide particle, a zinc oxide particle, a magnesium oxide particle, a niobium oxide particle, a vanadium oxide particle, a tantalum oxide particle, a silica particle, a titania particle, a zirconia particle, a silica alumina particle, a silica titania particle, and a silica magnesia particle.

[0093] The organic pigment may be of any type. Examples thereof include, but are not limited to, p-naphthol pigments, p-oxynaphthoic pigments, pyrazolone-based pigments, acetoacetic acid allylide-based monoazo pigments, acetoacetic acid allylide-based disazo pigments, benzimidazolone-based monoazo pigments, isoindolinone-based pigments, styrene-based pigments, isoindoline-based pigments, and phthalocyanine-based pigments.

[0094] In further embodiments the coating composition for corrosion protection may contain a filler. Examples of such fillers are glass flakes, talc, mica or aerosil.

[0095] The coating composition for corrosion protection may further contain further electrically conducting particles which are not metals. Examples of such particles are graphite, graphene, or carbon nanotubes.

[0096] The coating composition for corrosion protection may contain, as appropriate, further additives such as a surfactant, a thickener, a repairing agent (inhibitor), a lubricant, a dispersant, a wetting agent, a leveling agent, a rheology control agent, a pH regulator, a pH stabilizer, a film forming agent, a stabilizer, a thixotropic agent, an anti-foaming agent, an ultraviolet absorber, a flame retardant, an antiseptic agent, an antistatic agent, and a colorant. There are cases in which adding a surfactant to the coating composition for corrosion protection can improve the adhesion or the leveling of the resulting preventive film. The surfactant may be of any type. Examples thereof include, but are not limited to, non-ionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl phenol ether, polyoxyethylene alkylamide, polyoxyethylene higher alcohol ether, polyoxyalkylene alkyl ether, polyoxyethylene polyoxypropylene glycol, polyethylene glycol fatty acid ester, glycerin fatty acid ester, propylene glycol fatty acid ester, alkyl glyceryl ether, sorbitan fatty acid ester, and polyoxyethylene sorbitan fatty acid ester; cationic-based surfactants such as mono-, di- or trialkylamine salts, alkyltrimethylammonium halide, dialkyldimethylammonium halide and alkyldimethylbenzylammonium chloride; and anionic-based surfactants such as dialkyl sulfosuccinates. Among them, the surfactant is preferably a non-ionic surfactant. The surfactant may be used singly or in a combination of two or more.

[0097] The surfactant content of the coating composition for corrosion protection is not particularly limited, but generally it is preferably 0.01 to 10 wt.%, based on the total weight of the composition.

[0098] A thickener may also be added to the coating composition for corrosion protection for the purpose of adjusting the viscosity. The thickener may be of any type. Examples thereof include, but are not limited to, a cellulosic thickener such as an ether (a cellulose ether) of methylcellulose, hydroxymethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, ethylhydroxyethyl cellulose, methylethyl cellulose and hydroxypropyl cellulose; a cellulose nanofiber; xanthan gum; a urethane-based thickener; an acrylic thickener; a modified clay; a fatty acid salt; and a fatty acid amine. Among them, the thickener used is preferably a cellulose ether. The thickener may be used singly or in a combination of two or more.

[0099] The thickener content of the coating composition for corrosion protection is not particularly limited, but generally it is preferably 0.005 to 2 wt.%, based on the total weight of the composition.

[0100] A lubricant may also be added to the coating composition for corrosion protection for the purpose of adjusting the coefficient of friction of the surface of a rust preventive film obtained from the coating composition for corrosion protection. The lubricant may be of any type. Examples thereof include, but are not limited to, a wax such as polyolefin or modified polyolefin (polyethylene, modified polyethylene, polypropylene, modified polypropylene, etc.) or paraffin; a carnauba wax; fluorine resin; melamine cyanurate; or hexagonal boron nitride. The lubricant may be used singly or in a combination of two or more.

[0101] The lubricant content of the coating composition for corrosion protection is not particularly limited and can be appropriately selected to obtain a desired surface frictional coefficient. Generally, it is preferably 20 wt.% or less, based on the total weight of the coating composition for corrosion protection.

[0102] The coating composition for corrosion protection can be produced, by a known method commonly used, by uniformly stirring and mixing the zinc alloy pigment or a paste or composition containing the platy zinc alloy pigment with paint components such as water and / or the organic solvent, the binder, etc.

[0103] The coating composition for corrosion protection may be a 1 K- or a 2K-system. In case of a 2K system the zinc alloy flakes may be formulated either to the binder component or to the hardener component.

[0104] Preferred embodiments include aqueous based coating composition for corrosion protection wherein the formulation is suitable for heavy duty corrosion protection applications, architectural & construction applications, electricity & energy, wind power & offshore applications, agriculture construction earthmover (ACE) and truck & trailer applications.

[0105] Furthermore the needs are met by a use of the platy zinc alloy pigments in a water-based corrosion coating formulation. All embodiments and features mentioned above concerning the platy zinc alloy pigments and the composition of the aqueous based coating composition do also apply to such use.

[0106] The aqueous coating formulations containing the platy zinc alloy pigments described earlier can be represented by the following further aspects:

[0107] A seventeenth aspect is dedicated to an aqueous based corrosion coating formulation containing a binder, a solvent which is water or a mixture of water and one or more organic solvents compatible with water and about platy zinc alloy pigments having a composition represented by formula (I): ZnAlx(MIVy)m(M2o)n, or by formula (II):

[0108] ZnAlx(MIVy)m(M1z)p(M2o)n, (ll) wherein x = 2.000 to 20, y = 0.100 to 8.000, z = 0.100 to 7.000 and

[0109] MIV= Si, Ge or Sn, and m is an integer representing the number of different MIVelements and is in a range of 1 to 3,

[0110] M1denotes other alloy components and is chosen from the group consisting of Mg, Ti, Cr, Ni, Mn, Li, Ce, Mm, Mo, Bi, In, Sr, Zr, Ca, B, Ga, Pb, Fe and p is an integer which denotes the number of different M1elements and

[0111] M2denotes unavoidable impurities of further metals which are not classified as MIVand / or M1and whereas o is in a range of 0.001 to less than 0.100 and n is an integer representing the number of different impurity elements and wherein the platy zinc alloy pigment has a median size dso.fi , an average thickness tn and an aspect ratio dso.fi / tti and the aspect ratio dso.fi / tti has a value of at least 8.0.

[0112] An eighteenth aspect according to aspect 16 is dedicated to an aqueous based corrosion coating formulation, wherein M2is selected from the group consisting of Ca, Na, K, Co, Cd, Pb, Fe, Cr, Mg, Mn, Cu, Hg, Ni, Sn, In, Ba, Sr, Si and mixtures thereof.

[0113] A nineteenth aspect according to aspects 16 or 17 is dedicated to an aqueous based corrosion coating formulation, wherein parameter y in formula (I) or formula (II) is in a range of 0.30 to 6.00.

[0114] A twentieth aspect according to any of preceding aspects is dedicated to an aqueous based corrosion coating formulation, wherein the pigments of formula (I) have a parameter x in a range of 3.000 to 10.0, preferably in a range of 3.00 to 7.00 and parameter y in a range of 0.300 to 2.0.

[0115] A twenty-first aspect according to any of preceding aspects is dedicated to an aqueous based corrosion coating formulation, wherein the pigments of formula (I) or formula (II) have a parameter x in a range of 3.00 to 7.00.

[0116] A twenty-second aspect according to any of preceding aspects is dedicated to an aqueous based corrosion coating formulation, wherein in formula (II) the elements for M1are selected from the group consisting of Mg, Ti, Cr, Ce, Mo, In and mixtures thereof and most preferred is Mg.

[0117] A twenty-third aspect according to any of preceding aspects is dedicated to an aqueous based corrosion coating formulation, wherein the zinc alloy pigments of formula (II) have x in a range of 3.00 to 7.00, y in a range of 0.300 to 2.0 and z in a range of 0.150 to 3.0.

[0118] A twenty-fourth aspect according to any of preceding aspects is dedicated to an aqueous based corrosion coating formulation, wherein for zinc alloy pigments according to formula (II) M1is only one element with p = 1 and x is in a range of 3.00 to 10.0, preferably in a range of 3.00 to 7.00 and x / z is in a range of 0.9 to 1.1.

[0119] A twenty-fifth aspect according to any of preceding aspects is dedicated to an aqueous based corrosion coating formulation, wherein in formula (II) the sum of all z-values of all p M1elements is below of 7.00.

[0120] A twenty-sixth aspect according to any of preceding aspects is dedicated to an aqueous based corrosion coating formulation, wherein MIVis Si and m = 1 .

[0121] A twenty-seventh aspect according to any of preceding aspects is dedicated to an aqueous based corrosion coating formulation, wherein MIVis Si and the wt.% ratio of Al to Si x / y is in a range of 1 .5 to 20.

[0122] A twenty-eighth aspect according to any of preceding aspects is dedicated to an aqueous based corrosion coating formulation, wherein their median size dso.fi is in a range of 8 to 35 pm.

[0123] A twenty-ninth aspect according to any of preceding aspects is dedicated to an aqueous based corrosion coating formulation, wherein the pigments have an average thickness in a range of 80 to 1 ,000 nm and preferably in a range of 100 to 500 nm.

[0124] Preventive Film and an Article with a Preventive Film

[0125] In another embodiment a preventive film on an article is obtained by drying or heat-treating the coating composition for corrosion protection described above. An article with a preventive film has on a surface thereof, a preventive film obtained by drying or heat- treating the coating composition for corrosion protection described above; and is obtained by, for example, by applying the coating composition for corrosion protection to the article to be coated and drying or heat-treating the applied preventive coating composition.

[0126] The coating composition for corrosion protection can be applied to an article which is composed of any metal material or alloy material. Examples of the metal material and the alloy material include, but are not limited to aluminum, aluminum alloy, iron, iron alloy, carbon steel, alloy steel, and stainless steel. The coating composition for corrosion protection can also be applied to a metal material or an alloy material whose surface has been subjected to plating; chemical conversion treatment such as oxidation, nitridation and carbonization; and dry plating. Among them, the coating composition for corrosion protection can be suitably applied to an article to be coated that contains an iron or an iron alloy, or an article to be coated that has, on its surface, a film or layer containing iron or an iron alloy, and an excellent effect of improving the corrosion resistance can be obtained. Incidentally, a coating target or an article to be coated may be a raw material (a metal material or an alloy material itself), an intermediate product, a final product, or the like without particular limitation.

[0127] The coating composition for corrosion protection may be applied to an article to be coated by any known method. The coating composition for corrosion protection can be applied using a roller, a doctor blade, a bar coater, a brush, sprayer, or the like. Further, the application conditions may be appropriately selected without particular limitation.

[0128] The preventive film is formed by applying the coating composition for corrosion protection to an article to be coated and then drying or heat-treating it. Although the method and conditions for the drying and heat-treating may be appropriately selected, it is generally preferred to heat the coating composition for corrosion protection applied to an article at a temperature of 120 to 400 °C and more preferably 130 to 380 °C to remove the solvent and form the preventive film. This heating may be performed in any known method such as a convection heating method, an infrared heating method, or an induction heating method. The conditions of the heat treatment such as the time period and atmosphere of the heat treatment may also be appropriately selected without particular limitation. For example, the heat treatment may be performed in the atmosphere or may be performed in an inert gas such as nitrogen gas.

[0129] An article to be coated may be subjected to a treatment such as degreasing, water washing or the like as appropriate before the coating composition for corrosion protection is applied to the article to be coated. Such degreasing and water washing treatments can be performed by any known methods. The degreasing and water washing treatments may be appropriately selected and may be solvent degreasing using a hydrocarbon-based degreasing agent or the like, water washing treatment using an alkaline aqueous degreasing agent or the like, or washing treatment using supercritical water or the like, for example.

[0130] The application amount of the coating composition for corrosion protection is not particularly limited, but generally it is applied in such an amount that the average thickness of the preventive film after drying is preferably 1 to 200 pm, more preferably 4 to 100 pm. In terms of the amount of zinc alloy after drying, the coating composition for corrosion protection is applied in such an amount that the zinc alloy content of the preventive film after drying is preferably 3 to 200 g / m2, and more preferably 20 to 120 g / m2.

[0131] A EXAMPLES

[0132] Pre-Example 1 : Atomization of ZnAI5Si0.7 alloy

[0133] Appropriate amounts of zinc and aluminum ingots and ingots of the alloy AISi12 were melted and atomized at 540 °C under air atmosphere at a pressure of 6.5 bar vertically downwards through an annular nozzle. A zinc alloy was obtained and the powder particles had a dso.p of 31 pm as determined with a Helos BR instrument.

[0134] The elemental composition of main elements of the zinc alloy particles was determined with ICP-OES as follows: 200 mg of the dried zinc alloy powder were mixed in a PTFE beaker with 10 ml 65% HNO3 which was diluted with 10 ml of water. 2 mL of 40% HF were added slowly. After the reaction had subsided, the sample was briefly boiled under moderate heat to expel the nitrous gases. The ICP-OES measurement was conducted using an internal standard. The elemental composition was ZnAI5Si0.7.

[0135] Example 1 : Milling of Zn alloy powder of Pre-Example 1 to flakes.

[0136] A laboratory ball mill was charged with 7.5 kg of steel balls with a diameter of 8 mm. 400 ml of mineral spirit, 500 g of the zinc alloy powder obtained from Pre-Example 1 and 12.5 g stearic acid were added. The zinc alloy powder was milled in a ball mill for 24 h at 20 rpm wherein the ball mill was flooded with 11 l / h of air to ensure controlled saturation of new zinc alloy surfaces with oxygen. After milling the ground material was separated from the mill and finally a paste with 90% solid content in mineral spirit was fabricated. The dso.ti of the zinc alloy flakes was 14.5 pm. Comparative Example 1 : Commercially available Stapa Zinc 4 (Eckart Suisse) which represents a pure zinc flake with a dso.fi of about 15 pm.

[0137] Comparative Example 2: An alloy containing zinc, aluminum and magnesium in appropriate amounts were atomized as described in Pre-Example 1 . The resulting zinc alloy powder was milled according to Example 1 which resulted in flakes with a dso.fi of about 13 pm. The composition of the resulting zinc alloy flakes was analyzed by ICP and can be represented by formula ZnAI2.5Mg0.7.

[0138] Comparative Example 3: Stapa 4 ZnAI6Mg6 (flaky zinc alloy pigments manufactured by Eckart Suisse with dso.fi of about 11 pm).

[0139] Comparative Example 4: An alloy containing zinc and magnesium in appropriate amounts were atomized as described in Example 1 . The resulting zinc alloy powder was milled according to Example 2 which resulted in flakes with a dso.fi of about 14 pm. The composition of the resulting zinc alloy flakes was analyzed by ICP and is represented by formula ZnAI3Mg3.

[0140] Comparative Example 5: Stapa 4 ZnAI7 (most preferred example in EP 1233043 A1): Flaky zinc alloy pigments manufactured by Eckart Suisse with dso.fi of about 15 pm).

[0141] Comparative Example 6: Stapa 4 ZnAI3 (flaky zinc alloy pigments manufactured by Eckart Suisse with dso.fi of about 15 pm).

[0142] B Test methods:

[0143] Gassing Test:

[0144] The components listed in table 1 were mixed together and put in a 500 ml gassing flask which was sealed with a twin-chain gas bubble counter and maintained at 20 °C. The test was passed when after 24 h less than 15 ml gas (hydrogen) evolved (note 2). When less than 15 mL gas evolved after 24 h the test was passed very well (note 1).

[0145] Table 1 : Components of gassing test:

[0146] Panel preparation for corrosion test:

[0147] Parts of the pastes of zinc alloy pigment samples of the inventive Example 1 and of

[0148] Comparative Examples were slowly stirred into the formulation used for the gassing test in proportions of wt.% as displayed in table 2:

[0149] Table 2:Components of Salt Spray test:

[0150] 1-Methoxy-2-propanol was used to adjust the viscosity. The lacquer was applied by a draw-down, (nominal total dry film applied: 12 pm, speed 3 cm / min) on a metal substrate (steel Q-Panel R46) with two runs applied in opposite directions. The panel was ventilated at 140 °C for about 10 min, then cooled down and put for 20 minutes into an oven at 300 °C. After cooling down, the panels were used for the salt spray test. Salt Sprays Test:

[0151] The painted metal sheets as described above were now subjected to a salt spray test to investigate their resistance to rust in accordance with ASTM B117; DIN EN ISO 9227. The red rust formation after 1056 h was assessed as percentage of the whole exposed area.

[0152] The test was passed when the red rust area was < 1 .0% after that time (Ri 1 according to DIN EN ISO 4628-3).

[0153] C Results and Discussion:

[0154] Table 3: Results of testing

[0155] The results show that Example 1 yields the best results in the gassing test as well as in the corrosion test with respect to red rust and white rust formation. The ZnAI3 alloy (Comparative Example 6) yields a good gassing test, but poor corrosion test results. All other Comparative Examples do not pass the gassing test and yield corrosion test results which do not fulfill the R1 criteria of DIN EN ISO 4628-3.

Claims

Claims:1 . Platy zinc alloy pigments having a composition represented by formula (I):ZnAlx(MIVy)m(M2o)n, (I) or by formula (II):ZnAlx(MIVy)m(M1z)p(M2o)n, (ll) wherein x = 2.000 to 20, y = 0.100 to 8.000, z = 0.100 to 7.000 andMIV= Si, Ge or Sn, and m is an integer representing the number of different MIVelements and is in a range of 1 to 3,M1denotes other alloy components and is selected from the group consisting of Mg, Ti, Cr, Ni, Mn, Li, Ce, Mm, Mo, Bi, In, Sr, Zr, Ca, B, Ga, Pb, Fe and p is an integer which denotes the number of different M1elements andM2denotes unavoidable impurities of further metals which are not classified as MIVand / or M1and whereas o is in a range of 0.001 to less than 0.100 and n is an integer representing the number of different impurity elements and wherein the platy zinc alloy pigment has a median size dso.fi , an average thickness tn and an aspect ratio dso.fi / tti and the aspect ratio dso.fi / tti has a value of at least 8.0.

2. Platy zinc alloy pigments according to claim 1 , wherein M2is selected from the group consisting of Ca, Na, K, Co, Cd, Pb, Fe, Cr, Mg, Mn, Cu, Hg, Ni, Sn, In, Ba, Sr, Si and mixtures thereof.

3. Platy zinc alloy pigments according to any of preceding claims 1 or 2, wherein parameter y in formula (I) or formula (II) is in a range of 0.30 to 6.00.

4. Platy zinc alloy pigments according to any of preceding claims, wherein the pigments of formula (I) have x in a range of 3.00 to 10.0 and y in a range of 0.300 to 2.0.

5. Platy zinc alloy pigments according to any of preceding claims, wherein in formula (II) the elements for M1are selected from the group consisting of Mg, Ti, Cr, Ce, Mo, In and mixtures thereof and most preferred is Mg (with p = 1).

6. Platy zinc alloy pigments according to any of preceding claims, wherein the zinc alloy pigments of formula (II) have x in a range of 3.00 to 10.0, y in a range of 0.300 to 2.0 and z in a range of 0.150 to 3.0.

7. Platy zinc alloy pigments according to any of preceding claims, wherein for zinc alloy pigments according to formula (II) M1is only one element with p = 1 and x is in a range of 2.000 to 8.00 and x / z is in a range of 0.9 to 1 .1 .

8. Platy zinc alloy pigments according to any of preceding claims, wherein in formula (II) the sum of all z-values of all p M1elements is below of 7.00.

9. Platy zinc alloy pigments according to any of preceding claims, wherein MIVis Si and m = 1 .

10. Platy zinc alloy pigments according to any of preceding claims, wherein the pigments of formula (I) or formula (II) have a parameter x in a range of 3.00 to 7.00.11 . Platy zinc alloy pigments according to any of preceding claims, wherein MIVis Si and the wt.% ratio of Al to Si x / y is in a range of 1 .5 to 20.

12. Platy zinc alloy pigments according to any of preceding claims, wherein their median size dso.fi is in a range of 8 to 35 pm.

13. Platy zinc alloy pigments according to any of preceding claims, wherein the pigments have an average thickness in a range of 80 to 1 ,000 nm and preferably in a range of 100 to 500 nm.

14. Method of manufacture of platy zinc alloy pigments of claims 1 to 13, comprising: a) producing a powder of zinc alloy particles by atomization of a melt of components with envisaged element composition b) grinding the zinc alloy particles obtained in a) in a ball mill equipped with grinding balls in a solvent and a lubricating grinding agent to obtain platy zinc alloy pigments and c) optionally further classifying the platy zinc alloy particles obtained in b) and optionally combining with a defined amount of an organic solvent to obtain a paste of platy zinc alloy pigments.

15. Method of manufacture of platy zinc alloy pigments according to claim 14, wherein the zinc alloy particles obtained in step a) have a median size dso.p in a range of 10 to 50 pm.

16. Use of the platy zinc alloy pigments of claims 1 to 13 in a water-based corrosion protection formulation.

17. A water-based corrosion protection formulation containing the platy zinc alloy pigments of claims 1 to 13.

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