COATED METAL EFFECT PIGMENTS, METHOD OF PRODUCTION AND USE THEREOF

Abstract

This invention involves a coated flaky metal effect pigment comprising a metal effect flake as substrate coated by the following consecutive coating sequences: a) optionally a discontinuous or a continuous layer of Mo-oxide, b1) an inorganic metal oxide layer comprising mainly SiO.sub.2, c1) a hybrid layer comprising SiO.sub.2 modified by a diphenyl silane, a phenylsilane or mixtures thereof or c2) a hybrid layer comprising SiO.sub.2 modified by a diphenyl silane, a phenylsilane or mixtures thereof, b2) an inorganic metal oxide layer comprising mainly SiO.sub.2, and d) optionally a further top-coat of organofunctional silanes, titanates, aluminates or zirconates.

Claims

1. A coated flaky metal effect pigment comprising a metal effect flake as substrate, wherein the substrate is selected from aluminum or aluminum alloys and including the following consecutive coating layers: a) optionally a discontinuous or a continuous layer of Mo-oxide, b1) an inorganic metal oxide layer comprising over 50% SiO.sub.2, c1) a hybrid layer comprising SiO.sub.2 modified by a diphenyl silane, a phenyl silane or mixtures thereof, or c2) a hybrid layer comprising SiO.sub.2 modified by a diphenyl silane, a phenyl silane or mixtures thereof, and b2) an inorganic metal oxide layer comprising over 50% SiO.sub.2.

2. The coated flaky metal effect pigment according to claim 1, wherein the thickness of layer b1) or b2) is a least 15 nm.

3. The coated flaky metal effect pigment according to claim 1, wherein the layer c1) or c2) comprises SiO.sub.2 modified by a diphenyl silane and the .sup.29Si NMR-MAS signal ratio of D-silanes to Q-silanes is in a range of 1.8% to 10.5%.

4. The coated flaky metal effect pigment according to claim 1, wherein the .sup.29Si NMR-MAS signal ratio of T-silanes to Q-silanes is in a range of 0 to 3.0%.

5. The coated flaky metal effect pigment according to claim 1, wherein the characterization with .sup.13C-NMR-MAS spectroscopy yields signals attributable to diphenyl moieties of the D-silanes and optionally .sup.13C-NMR-MAS signals attributable to organic moieties connected with T-silanes and wherein the total amount of these .sup.13C-NMR signals is in a range of 80% to 100% of all .sup.13C-signals observed.

6. The coated flaky metal effect pigment according to claim 1, wherein the hybrid layer c1) or c2) comprises diphenyl dimethoxy silane.

7. (canceled)

8. The coated flaky metal effect pigment according to claim 1, wherein the total thickness of the coatings a), b) and c) is in a range of 30 to 60 nm.

9. The coated flaky metal effect pigment according to claim 1, wherein the metal effect flake is an aluminum flake, which was produced by milling technology.

10. The coated flaky metal effect pigment according to claim 1, wherein the flaky metal effect pigment has a total amount of the sum of SiO.sub.2 and of diphenyl silane in layers b1) and c1) or b2) and c2) of at least 95 wt.-%, based on the amount of the total coating.

11. A method of manufacture of a coated flaky metal effect pigment comprising the following steps: a) optionally coating a metallic substrate with a discontinuous or a continuous layer of Mo-oxide, the metallic substrate being selected from aluminum or aluminum alloys b1) coating the metallic substrate or the substrate obtained from step a) with an inorganic metal oxide layer comprising over 50% SiO.sub.2 in a sol-gel process, c1) forming a hybrid layer on layer b1) by sol-gel reaction of a tetraalkoxy silane of formula
Si(OR).sub.4(I) with a diphenyl silane of formula
Ph.sub.2Si(OR).sub.2,(IIa), a phenylsilane of formula
PhSi(OR).sub.3(IIb) or mixtures thereof wherein R is methyl, ethyl, n-propyl or isopropyl, n-butyl or iso-butyl and R independently is methyl or ethyl, or c2) coating the metallic substrate or the substrate obtained from step a) with a hybrid layer by sol-gel reaction of a tetraalkoxy silane of formula
Si(OR).sub.4(I) with a diphenyl silane of formula
Ph.sub.2Si(OR).sub.2,(IIa), a phenylsilane of formula
PhSi(OR).sub.3(IIb) or mixtures thereof, b2) coating the coated substrate c2) with an inorganic metal oxide layer comprising over 50% SiO.sub.2 in a sol-gel process.

12. The method of claim 11, wherein for step c1) or c2) the tetra alkoxy silane is tetra ethoxy silane (TEOS) and the diphenyl silane is diphenyl dimethoxy silane.

13. The method of claim 11, wherein the coatings c2) and b2) are coated in a two-pot synthesis by isolation of the coated substrate after step c2) from the reaction mixture and redispersing in a solvent before conducting coating step b2).

14. (canceled)

15. The coated flaky metal effect pigment according to claim 1, further comprising a further top-coat of organofunctional silanes, titanates, aluminates or zirconates.

16. The method of claim 11, wherein steps b1) or b2) use TEOS as precursor material.

17. The method of claim 11, further comprising coating the effect pigment obtained from c1) or b2) with an organofunctional silane, titanate, aluminate or zirconate.

18. A coating composition comprising a coated flaky metal effect pigment according to claim 1 and a carrier.

Description

DESCRIPTION

Coated Flaky Metal Effect Pigment:

[0037] The coated flaky metal effect pigment of this invention comprises a metal effect flake as substrate coated by the following consecutive coating sequences: [0038] a) optionally a discontinuous or a continuous layer of Mo-oxide, [0039] b1) an inorganic metal oxide layer comprising mainly SiO.sub.2, [0040] c1) a hybrid layer comprising SiO.sub.2 modified by a diphenyl silane, a phenyl silane or mixtures thereof, [0041] or [0042] c2) a hybrid layer comprising SiO.sub.2 modified by a diphenyl silane, a phenyl silane or mixtures thereof, [0043] b2) an inorganic metal oxide layer comprising mainly SiO.sub.2, and [0044] d) optionally a further top coat of organofunctional silanes, titanates, aluminates or zirconates.

[0045] When within this invention the inorganic metal oxide layer comprising mainly SiO.sub.2I b1) or b2) or both of them are meant it is referred to generally as layer b).

[0046] When either the hybrid layers c1) or c2) or both of them are meant it is referred to generally as layer c).

[0047] The flaky metal effect pigment substrates are preferably selected from aluminum, copper, zinc, zinc alloys, iron, chromium, titanium, zirconium, tin or mixtures or alloys thereof. Preferred alloys are gold-bronze or steel.

[0048] More preferred are aluminum, copper and gold-bronze and most preferred aluminum or aluminum alloys. Aluminum effect pigments are by far the most widespread effect pigments in the coating industry representing silver metal color tones in various realizations.

[0049] In certain embodiments the flaky metal effect pigment substrates, especially aluminum substrates may be produced by PVD (physical vapor deposition) means. These metal effect pigments represent by far the most brilliant pigments available. However, they are presently rarely used in automotive basecoat due to severe application problems. Furthermore, although their prices have decreased during the last decade they represent the most expensive metal effect pigments, especially aluminum effect pigments. Therefore, it is preferred to use flaky metal effect pigments, preferably aluminum effect pigments which were produced by milling technology. The milling technology is well known and especially a Hall process (wet milling) is preferred. The aluminum effect pigments can be of the silverdollar or of the cornflake type. Furthermore, the aluminum effect pigments may be very thin milled pigments with average thicknesses comparable to PVD pigments as described e.g. in EP 1621586 B1, WO 2004087816 A2 or WO 2008/077612 A2.

[0050] The flaky metal effect pigment substrates have a D.sub.50-value in a range of 2 to 100 m, more preferably in a range of 5 to 60 m, and most preferably in a range of 7 to 40 m. The D.sub.50 is the median value of the particle size distribution function. It indicates the size that is equal or smaller than 50% of the particles. These measurements are conducted e.g. by means of laser granulometry using a particle size analyzer manufactured by Sympatec GmbH (model: Helos/BR). The measurement is conducted according to data from the manufacturer. The particles measured with this method are calculated according to the Fraunhofer approximation as volume averaged equivalent spheres.

[0051] The thickness can be characterized by the median value h.sub.50 and is in a range of 15 to 600 nm, preferably in a range of 50 to 400 nm and more preferably in a range of 80 to 300 nm. Especially for aluminum pigments obtained by milling technology the h.sub.50-value is preferably in a range of 40 to 600 nm and more preferably in a range of 50 to 300 nm.

[0052] The thickness distribution and therefore the h.sub.50-value can be determined by AFM (atomic force microscopy) or preferably by SEM as described in EP 1813702 B1 (paragraphs [0124] to [0128]).

[0053] The flaky metal effect pigment substrates are called flaky, when their aspect ratio, defined as D.sub.50/h.sub.50 is larger than 5. Preferably the metal effect pigments have aspect ratios in the range of 10 to 1,000, more preferably in the range of 20 to 150 and most preferably in the range of 25 to 100.

[0054] The optional layer (a) from molybdenum oxide can be either a discontinuous layer or a continuous layer of metal oxide.

[0055] The term continuous layer (a) means that layer (a) encapsulates substantially completely, in particular completely, the respective metal substrate. The term discontinuous layer (a) means that layer (a) only partially encapsulates the respective metal substrate. A partial encapsulation means that the respective metal substrate is not fully coated. The partial encapsulation or discontinuity can be realized, e.g., in the form of islands of layer (a) on the respective metal substrate.

[0056] According to an embodiment of the invention, the layer (a) comprises or consists of metal oxide wherein said metal oxide is selected from the group consisting of molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate, molybdenum peroxides and mixtures thereof. The molybdenum oxide usually is a mixture of different species and may involve coordination type species. It may be represented by the compositional formulas:

MoO.sub.2mH.sub.2O.Math.nH.sub.2O or MoO.sub.3-m(O.sub.2).sub.m.Math.nH.sub.2O(III)

wherein Mo is molybdenum, O is oxygen, 0m2 and 1n<2.

[0057] Also molybdenum complexes involving different ligands selected from the group of water, O.sub.2, O and mixtures thereof may be included. All these species are included in the term Mo-oxide within this invention.

[0058] Furthermore, layer (a) may also contain elemental molybdenum in an amount of 0 to 30 atom-%, preferably 0 to 25 atom-% and most preferably 3 to 20 atom-%, each based on the total content of the molybdenum forming the metal oxide (a). The amount of elemental molybdenum may be determined with XPS.

[0059] Preferably, the molybdenum oxide coat is prepared by first preparing a solution of polymolybdic acid peroxide by dissolving molybdenum oxide or elemental molybdenum in a hydrogen oxide solution (see for example Solid States Ionics, pp. 507-512, 1992).

[0060] It is of utmost importance in this invention that the metal pigments are coated by individual layers of an inorganic metal oxide layer comprising mainly SiO.sub.2 only and of a hybrid layer, wherein SiO.sub.2 is modified by diphenyl silane, a phenyl silane or mixtures thereof. Very surprisingly such coated metal effect pigments had an enhanced gassing stability in a very strong gassing test even after strong mechanical treatment (Waring Blender test). The diphenyl silane or phenyl silane is a so-called network modifier which means that it is able to bond covalently to the silica via hydrolyzed SiOH (silanol) groups, but is does not form an organic network. The phenyl groups mainly impart hydrophobic properties to the silica network.

[0061] With SiO.sub.2 it is meant in this invention that it includes silica formed typically in a sol-gel process. The silica can contain water and can contain residual amounts of non-hydrolyzed alkoxy-groups.

[0062] The silica is preferably formed by a well-known sol-gel process which consists of a hydrolysis and a condensation step form silicon alkoxides:

hydrolysis: Si(OR).sub.4+H.sub.2O.fwdarw.HOSi(OR).sub.3+ROH.fwdarw..fwdarw..fwdarw.Si(OH).sub.4(IV)

condensation: Si(OH).sub.4.fwdarw.SiO.sub.2+2H.sub.2O(V)

[0063] The species Si(OH).sub.4 does not exist in solution but is used to illustrate that up to four hydrolysis steps are needed to finally obtain SiO.sub.2. R is preferably methyl, ethyl, n-propyl or isopropyl, n-butyl or iso-butyl, more preferably methyl or ethyl and most preferably ethyl.

[0064] The reaction in catalyzed by bases or acids. In EP 2510060 A1 it is disclosed that the catalysis can be conducted by a base and an acid catalyzed step.

[0065] Residues of such catalysator can also remain in the silica, especially of basic catalysts as the silica itself is acidic due to its silanol groups.

[0066] The inorganic metal oxide layer comprising mainly SiO.sub.2 (layer b) contains SiO.sub.2 in an amount in a range of more than 50 to 100 wt.-%, based on this layer b). Preferably the amount of SiO.sub.2 is in a range of 75 to 100 wt.-%, more preferably in a range of 85 to 100 wt.-% and most preferably in a range of 90 to 100 wt.-%, each based on layer b). Other metal oxides may be present in this layer such as ZrO.sub.2, TiO.sub.2, Al.sub.2O.sub.3, Ce-oxide, SnO.sub.2 or the like. In another embodiment layer b) consists of SiO.sub.2.

[0067] Without being bound to a theory the inventors assume that the single inorganic metal oxide layer b) containing mainly SiO.sub.2 layer imparts a certain mechanical stability to the metal effect pigment. In preferred embodiments this stability is achieved when the silica layer has a certain minimal thickness. It is therefore preferred when the mean thickness of the layer b) is at least 15 nm. Below 15 nm mean thickness the mechanical stability is not achieved. On the other side should the silica not exceed certain thicknesses as otherwise the optical properties of the metal effect pigments may be distorted. It is therefore preferred that the silica layer b) has preferably a mean thickness in a range of 15-40 nm, more preferably in a range of 16 to 30 nm and most preferably in a range of 17 to 25 nm.

[0068] The two different layers and their thickness' can be best determined via TEM (transmission electron microscope) analysis of a cross-section of the coated metal effect pigments. The coated effect pigments are embedded in a hard lacquer such as a cured epoxy binder. From this cross-section ultra-thin lamellas can be prepared by using an ultra-microtome. The lamellas can be collected in water and be mounted on TEM grids. Using the TEM and possibly additionally EDX the thickness of the layers can be determined. For determination of the mean thickness of the layers at least 10 pigment particles should be counted.

[0069] Without being bond to a theory the inventors assume that the hybrid layer is mainly enhancing the gassing stability of the coated metal effect pigment.

[0070] The incorporation of the diphenyl silane or the phenyl silane or mixtures thereof into the silica layer c) can be preferably formed by using a dialkoxy diphenyl silane or a trialkoxy phenyl silane. A reaction step leading to modified silica can be, for example, achieved via a transesterification step:

SiO(OR)OH+Si(OR).sub.2Ph.sub.2.fwdarw.SiO(OR)OSi(OR)Ph.sub.2+ROH(VIa)

or a condensation step of the pre-hydrolyzed diphenyl silane:

SiO(OR)OH+Si(OH)(OR)Ph.sub.2.fwdarw.SiO(OR)OSi(OR)Ph.sub.2+H.sub.2O(VIb)

[0071] R is independently of R methyl or ethyl. It is well known that organofunctional silanes modified by SiC bonds are less reactive in a sol-gel reaction than tetra alkoxy silanes. To balance this disadvantage, it is therefore preferred that diphenyl silane in the hybrid layer c) is formed by diphenyl dimethoxy silane, as the leaving methoxy group is known to be the most reactive group.

[0072] As outlined before both layers SiO.sub.2 b) and the hybrid layer SiO.sub.2 layer c) are needed in the total coating of the metal effect pigments. However, it is preferred to use the following variant of consecutive layers: [0073] a) optionally a discontinuous or a continuous layer of Mo-oxide, [0074] b1) a metal oxide layer comprising mainly SiO.sub.2, preferably an amount of SiO.sub.2 in a range of 75 to 100 wt.-%, referred to layer b), [0075] c1) a hybrid layer comprising SiO.sub.2 modified by a diphenyl silane, a phenyl silane or mixtures thereof, [0076] d) optionally a further top-coat of organofunctional silanes, titanates, aluminates or zirconates.

[0077] This variant turned out to be most stable and reproducible. Preferably a diphenyl silane is used as network modifying agent.

[0078] In the case of the second variant: [0079] a) optionally a discontinuous or a continuous layer of Mo-oxide, [0080] c2) a hybrid layer comprising SiO.sub.2 modified by a diphenyl silane, a phenyl silane or mixtures thereof, [0081] b2) a metal oxide layer comprising mainly SiO.sub.2, preferably an amount of SiO.sub.2 in a range of 75 to 100 wt.-%, referred to layer b), [0082] d) optionally a further top-coat of organofunctional silanes, titanates, aluminates or zirconates,
it is preferred that the coatings c2) and b2) are coated in a two-pot synthesis by isolation of the coated substrate after step c2) from the reaction mixture and redispersing in a solvent before conducting coating step b2) and the optional step d).

[0083] The amount especially of the diphenyl silane in the coating referred to the total Si-amount can be measured by solid state NMR-MAS (nuclear magnetic resonancemagic angle spinning) spectroscopy. Namely .sup.29Si NMR-MAS is a suitable tool, as it is well known that from the chemical shift of Si-atoms it is possible to distinguish between various Si species:

[0084] Q-silanes represent species where Si atoms are bound to oxygen atoms only. Namely one can distinguish the following species: Q.sup.2: O.sub.2Si(OH).sub.2; Q.sup.3: O.sub.3Si(OH) and Q.sup.4: (O.sub.4Si). The abbreviation Q denotes to the sum of all these species. The Q-silanes therefore represent the SiO.sub.2 amount of the total coating and their chemical shift can be observed in the .sup.29Si spectra in a range of about 120 to 87 ppm.

[0085] D-silanes represent species wherein two carbon atoms a bound to the silicon atom, which is in case of a diphenyl silane, for example, D.sup.2: O.sub.2SiPh.sub.2. These species have a chemical shift in a range of about 45 to 40 ppm.

[0086] In the present invention the integral .sup.29Si NMR-MAS signal ratio of D-silanes to Q-silanes is in case of the diphenyl silane preferably in a range of 1.5% to 10.5%, more preferably in a range of 1.8 to 10.0% and most preferably in a range of 2.0 to 7.0%.

[0087] Within these ranges the optimal ratio of diphenyl silane to silica had been found with respect to the desired properties. Therefore, surprisingly a relative low amount of diphenyl silane with respect to the total silica amount is needed for optimized properties.

[0088] For embodiments in which the optional further top-coat d) is made from of organofunctional silanes typically silanes are used which have only one SiC bond. These species are denoted as T-species in NMR terminology and have chemical shift of about 70 to 60 ppm.

[0089] In preferred embodiments of using diphenyl silanes as network modifier such species are used for the top-coating and the .sup.29Si NMR-MAS signal ratio of T-silanes to Q-silanes is in a range of 0 to 3.0% and more preferred in a range of 0.5-2.5%.

[0090] These rather low relative amounts of T-silanes are due to the fact, that these silanes are usually used as top-coat modification agents and thus they are coated not within the hybrid layer b) but just on the top of the pigment surface.

[0091] In FIG. 1 a .sup.29Si-NMR-MAS spectrum is shown for an inventive example together with fitted curves of the signals and the quantitative analysis of the peaks.

[0092] For embodiments using phenyl silane as network modifier the .sup.29Si NMR-MAS signal ratio of T-silanes to Q-silanes is in a range of 3.5% to 13.5%, more preferably in a range of 4.0 to 13.0% and most preferably in a range of 5.0 to 10.0%.

[0093] Surprisingly, it was estimated that the hybrid layer b) does not need to contain any oligomerized or polymerized organic material as it was described in WO 2007/01795 A1 or WO 2016/120015 A1. The mere modification of a SiO.sub.2 layer by diphenyl silane in combination with the two separate layers b) and c) seems to be enough to impart the desired stability to the coated metal pigments. Therefore, in preferred embodiments the coated metal effect pigments do not contain organic oligomers and/or polymers liked via a network former with the SiO.sub.2 layer.

[0094] The chemical nature of the organic parts of the coating can be further analyzed by .sup.13C NMR-MAS spectroscopy. In further embodiments the coated metal effect pigments exhibit, when characterized by this method, .sup.13C-NMR-MAS signals attributable to diphenyl moieties of the D-silanes or phenyl moieties of the T-silanes and optionally .sup.13C-NMR-MAS signals attributable to organic moieties connected with further T-silanes. It is preferred that the total amount of these .sup.13C-NMR signals is in a range of 80% to 100%, more preferably in a range of 90% to 100% and most preferably in a range of 95% to 100% of all .sup.13C-signals observed. Diphenyl silanes typically form peaks in the .sup.13C-NMR-MAS spectrum in the range of 125 to 140 ppm with two maxima at about 128 ppm and 134 ppm which are well known for phenyl groups.

[0095] Typical moieties of T silanes depend on the specific functionalities of these silanes but can be well attributed by the skilled artesian.

[0096] In further preferred embodiments only the .sup.13C-NMR-MAS signals attributable to diphenyl moieties of the D-silanes or phenyl moieties of T-silanes are in a range of 60 to 100% and more preferably in a range of 70 to 100% and most preferably in a range of 75 to 95% of all .sup.13C-signals observed in the NMR-MAS spectrum.

[0097] The amount of organic material of effect pigments can also be roughly quantified by the carbon content of the whole effect pigment after pyrolysis. In preferred embodiments the content of carbon is in a range of 1.3 to 7.5 wt.-%; more preferred in a range of 2.0 to 5.0 wt.-%, each referred to the total weight of the coated metal effect pigment.

[0098] In further preferred embodiments the flaky metal effect pigments according to this invention have a total amount of the sum of SiO.sub.2 and of diphenyl silane in layers b) and c) of at least 90 wt.-% 93 wt.-%, more preferred at least 95 wt.-%, 96 wt.-%, 97 wt.-%, each based on the amount of the total coating.

[0099] In further preferred embodiments the total coating containing layers a), b), c) and d) of the flaky metal effect pigment has an average thickness in a range of 30 to 60 nm, more preferred in a range of 35 to 50 nm and most preferred in a range of 30 to 45 nm. Thus, although at least two coatings are needed the total thickness of the coatings is rather low.

[0100] Above a total thickness of 60 nm the optical properties of the flaky metal effect pigments like gloss and flip-flop are generally getting unacceptable, especially when compared with pure silica coated metal effect pigments. Below of a total thickness of 30 nm the gassing stability and the mechanical stability is too low.

[0101] For the optional topcoat organofunctional silanes, titanates, aluminates or zirconates are used. This topcoat modifies the chemical nature and polarity of the effect pigment surface and ensures compatibility to the final coating binder system with respect to adhesion. Most preferred are organofunctional silanes. These organofunctional silanes may have organic moieties like amino, hydroxy, thiol, (meth)acrylate, vinyl, epoxy, isocyanate, urethane, which are capable to chemically interact or to form chemical bonds to corresponding functional groups of binders. But the organofunctional silanes can have also hydrophobic groups to impart a certain controlled hydrophobicity of the pigments surface.

[0102] Preferably the topcoat comprises organofunctional silanes with amino groups and alkyl or aryl groups. Examples for amino silanes are: [0103] aminopropyl trimethoxy silane (Dynasylan AMMO), aminopropyl triethoxy silane (Dynasylan AMEO) or N-(2-aminoethyl)-3-aminopropyl trimethoxy silane (Dynasylan DAMO), N-(2-aminoethyl)-3-aminopropyl triethoxy silane (Dynasylan DAMEO), N-ethylgamma-aminoisobutyl trimethoxy silane (Silquest A-Link 15), 4-amino-3,3-dimethylbutyltrimethoxysilane (Silquest Y-11637), N-cyclohexyl aminomethyl methyldiethoxy silane (GENIOSIL XL 924), (N-cyclohexylaminomethyl) triethoxysilane (GENIOSIL XL 926), (N-phenylaminomethyl) trimethoxysilane (GENIOSIL XL 973) and mixtures thereof.

[0104] In other preferred embodiments pre-condensated organofunctional silanes (hetero polysiloxanes) are used as described in WO 2015/086771 A1. Examples for such pre-condensated organofunctional silanes are, for example, commercially available as Dynasyian Hydrosil 2627, Dynasylan Hydrosil 2776 Dynasylan Hydrosil 2909, Dynasylan 1146 und Dynasylan Hydrosil 2907 from Evonik Industries AG, 45128 Essen, Germany. Preferred are water-based pre-condensated organofunctional silanes such as Dynasylan Hydrosil 2627, Dynasylan Hydrosil 2776, Dynasylan Hydrosil 2907 and Dynasylan Hydrosil 2909.

[0105] In other embodiments a further top-coat d) is not necessary. It is assumed that in this case some phenyl groups from the diphenyl silane are located on the top of the surface of the coated flaky effect pigment and thus render the surface chemistry and surface properties of the effect pigment in a favorable way.

[0106] A very preferred embodiment of this invention is a coated flaky metal effect pigment comprising an aluminum effect pigment obtained by milling as substrate which is coated by the following consecutive coating sequences: [0107] a) optionally a discontinuous or a continuous layer of Mo-oxide, [0108] b1) a metal oxide layer comprising mainly SiO.sub.2, preferably a layer consisting of SiO.sub.2, [0109] c1) a hybrid layer comprising SiO.sub.2 modified by a diphenyl silane, wherein the D/Q-ratio as determined by .sup.29Si-NMR-MAS spectroscopy is in a range of 2.0 to 7.0 and [0110] d) optionally a further top-coat of organofunctional silanes, titanates, aluminates or zirconates.

Manufacture of Flaky Coated Metal Effect Pigment:

[0111] A further embodiment of this invention is a method of manufacture of the coated flaky metal effect pigment comprising the following steps: [0112] a) optionally coating the metallic substrate with a discontinuous or a continuous layer of Mo-oxide [0113] b) coating the metallic substrate or the substrate obtained from step a) with an inorganic metal oxide layer mainly comprising SiO.sub.2 in a sol-gel process, preferably using TEOS as precursor material, [0114] c) forming a hybrid layer by sol-gel reaction of a tetra alkoxy silane of formula

Si(OR).sub.4(I) [0115] with a diphenyl silane of formula

Ph.sub.2Si(OR).sub.2,(IIa), [0116] a phenylsilane of formula

PhSi(OR).sub.3(IIb) [0117] or mixtures thereof [0118] wherein R and R independently is methyl or ethyl, or [0119] c2) coating the metallic substrate or the substrate obtained from step a) with a hybrid layer by sol-gel reaction of a tetraalkoxy silane of formula

Si(OR).sub.4(I) [0120] with a diphenyl silane of formula

Ph.sub.2Si(OR).sub.2,(IaI), [0121] a phenylsilane of formula

PhSi(OR).sub.3(IIb) [0122] or mixtures thereof [0123] b2) coating the coated substrate c2) with an inorganic metal oxide layer mainly comprising SiO.sub.2 in a sol-gel process, preferably using TEOS as precursor material, and [0124] d) optionally coating the effect pigment obtained from c1) or b2) with an organofunctional silane, titanate, aluminate or zirconate.

[0125] In preferred embodiments for step c) the tetra alkoxy silane is tetra ethoxy silane (TEOS) and the diphenyl silane is diphenyl dimethoxy silane.

[0126] The reaction is catalyzed by bases or acids. It can be also catalyzed by a combination of acids or bases in separate steps as outlined in EP 2510060 A1.

[0127] Preferably the sol-gel reaction is catalyzed by bases. Preferably, the basic catalyst is an organic base and more preferably an amine or ammonia. These may be primary, secondary or tertiary amines.

[0128] In a further preferred embodiment, the amine has 1 to 8, particularly preferably 1 to 6 and very particularly preferably 1 to 5 C atoms.

[0129] Amines with more than 8 carbon atoms are often too demanding to be used as effective catalysts.

[0130] According to a preferred variant of the invention, the amine is selected from the group consisting of dimethylethanol amine (DMEA), monoethanol amine, diethanol amine, triethanol amine, ethylene diamine (EDA), t-butyl amine, monoethanol amine, diethanol amine, monomethyl amine, dimethyl amine, trimethyl amine, monoethyl amine, diethylamine, triethyl amine, pyridine, pyridine derivative, aniline, aniline derivative, choline, choline derivative, urea, urea derivative, hydrazine derivative, and mixtures thereof.

[0131] Particularly preferably, the basic amine catalyst used is ethylene diamine, monoethyl amine, diethyl amine, monomethyl amine, dimethylamine, monoethanol amine, diethanol amine, trimethyl amine, triethyl amine or mixtures thereof.

[0132] In case of an acidic catalyst preferably formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, maleic acid, succinic acid, anhydrides of the abovementioned acids and mixtures thereof are used. Very particular preference is given to formic acid, acetic acid or oxalic acid and mixtures thereof.

[0133] In one embodiment the method of manufacturing an aluminum pigment according to the present invention has the step of forming a molybdenum coat on the surface of each aluminum particle by stirring a dispersive solution containing aluminum particles and a molybdenum compound.

[0134] A method of forming the molybdenum coat on the surface of each aluminum particle is not particularly restricted so far as the dispersive solution containing the aluminum particles and the molybdenum compound can be homogeneously stirred according to this method. More specifically, a method of forming the molybdenum coat on the surface of each aluminum particle by stirring or kneading the dispersive solution containing the aluminum particles and the molybdenum compound in a slurry state or a paste state can be listed.

[0135] A stirrer employed in the step of stirring the dispersive solution containing the aluminum particles and the molybdenum compound is not particularly restricted but a well-known stirrer capable of efficiently homogeneously stirring the dispersive solution containing the aluminum particles and the molybdenum compound can be employed. More specifically, a kneader, a kneading machine, a rotating container stirrer, a stirring reactor, a V-type stirrer, a double cone stirrer, a screw mixer, a sigma mixer, a flash mixer, an air current stirrer, a ball mill, an edge runner or the like can be listed.

[0136] While the molybdenum compound employed in the present invention is not particularly restricted but a well-known molybdenum compound capable of forming a molybdenum coat when added to the dispersive solution containing the aluminum particles and stirred, peroxidic polymolybdic acid, ammonium molybdate, phosphomolybdic acid or the like can be listed as a specific example. The said molybdenum compound may be solely used, or at least two types of such molybdenum compounds may be mixed with each other.

[0137] The peroxidic polymolybdic acid, a compound expressed in the following composition formula (I) in general, can be readily prepared by dissolving metal molybdenum powder or molybdenum oxide in a hydrogen peroxide solution of 5 to 40% in concentration.

[0138] A hydrophilic solvent is preferably employed as the solvent for the dispersive solution containing the aluminum particles and the molybdenum compound. More specifically, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, t-butyl alcohol, n-butyl alcohol, isobutyl alcohol can be used.

[0139] In a preferred embodiment the molybdenum compound, preferably a peroxidic polymolybdic acid, is first prepared separately and then added to the flaky metal pigment used as substrate which is dispersed in a solvent which can be used for the sol-gel process steps.

[0140] When forming the silica layer b) preferably the flaky metal effect pigment is first dispersed in a solvent and optionally water. The alkoxysilane, preferably tetraalkoxysilane is added and the addition of the catalyst, preferably takes place after dispersing the flaky metal effect pigment in the organic solvent and optionally heating the dispersion to reaction temperature. The water required for the hydrolysis can already be contained in the organic solvent or added at a later time.

[0141] Organic base is then typically introduced as a basic catalyst into the reaction mixture, which contains metal effect pigments, alkoxysilanes, preferably tetraalkoxy silanes and optionally water, in order to start the second stage of the process according to the invention.

[0142] The silica layer can also be formed by an acid catalyzed process or first an acid catalyzation followed by a base catalyzed sol-gel process as described in EP 2510060 A1. As acids typically formic acid, acetic acid, propionic acid, oxalic acid, malonic acid or maleic acid or the like can be used. In another embodiment, when first forming layer a) from a molybdenum-oxide the acidic medium imparted by a reagent such as e.g. peroxo molybdic acid is used as catalyzing medium for at least a first step of silica formation by sol-gel process.

[0143] When forming the hybrid layer c) the different speeds of the tetraalkoxy silane forming SiO.sub.2 and the diphenyl silane in sol-gel reactions need to be considered. Usually, the diphenyl silane is of slower speed and therefore it is preferably added first and the desired amount of tetraalkoxy silane is dosed to the reaction mixture at an appropriate velocity in order to essentially compensate the different reaction speeds of the precursor materials.

[0144] In the case of the second variant: [0145] a) optionally a discontinuous or a continuous layer of Mo-oxide, [0146] c2) a hybrid layer comprising SiO.sub.2 modified by a diphenyl silane, a phenyl silane or mixtures thereof, [0147] b2) an inorganic metal oxide layer mainly comprising SiO.sub.2, [0148] d) optionally a further topcoat of organofunctional silanes, titanates, aluminates or zirconates,
it is preferred that the coatings c2) and b2) are coated in a two-pot synthesis by isolation of the coated substrate after step c2) from the reaction mixture and redispersing in a solvent before conducting coating step b2) and the optional step d).

[0149] Preferred organic solvents are alcohols, glycols, esters, ketones and mixtures of these solvents. Particular preference is given to the use of alcohols or glycols or mixtures thereof, and very particular preference is given to the use of alcohols. Suitable alcohols are advantageously methanol, ethanol, isopropanol, n-propanol, t-butanol, n-butanol, isobutyl alcohol, pentanol, hexanol or mixtures thereof. Particular preference is given to using ethanol and/or isopropanol.

[0150] As glycol, use is advantageously made of butyl glycol, propyl glycol, ethylene glycol or mixtures thereof.

[0151] The present reaction mixture is preferably reacted at a temperature which is in a range from 20 C. to the boiling point of the particular solvent or solvent mixture. Particularly preferably, the reaction temperature is in a range from 50 C. to a temperature which is preferably 5 C. below the boiling point of the respective solvent or solvent mixture. A preferred reaction temperature range is the temperature range ranging from 75 C. to 82 C.

[0152] The coated flaky metallic effect pigments can be used in coatings, especially aqueous based coatings, printing inks, plastics or powder coatings.

[0153] Especially preferred is a use in automotive coatings. The invention also includes formulations such as lacquers, paints, printing inks containing the coated flaky metal pigments according to this invention. Especially preferred are aqueous-based formulations and most preferred automotive and industrial water-based basecoat formulations.

A EXAMPLES

Example 1: (SiO.SUB.2.-+Hybrid Layers)

[0154] 5.0 g Molybdic acid (MOO.sub.3*H.sub.2O) were dispersed in 15 g H.sub.2O.sub.2 and stirred until a clear solution is obtained (approx. 1 h). In a 1 l double jacketed reactor equipped with thermostat, reflux condenser and anchor stirrer 250 g Stapa Metallux 2156 (corresponding to 162.5 g Al; a silverdollar aluminum pigment paste from Eckart GmbH) were dispersed in 350 g isopropanol. The dispersion was heated up to 40 C. 0.33 g of the peroxo molybdic acid solution were added together with 2.0 g of water and the dispersion stirred for 60 minutes. 44.5 g tetraethoxy silane were added and the dispersion was heated to 80 C. 6.0 g ethylene diamine dissolved in 35 g water were continuously dosed during 60 min to the mixture and it was stirred for further 3 h. 14.9 g diphenyl dimethoxy silane dissolved in 100 ml isopropanol were added and then 47.8 g tetraethoxy silane were dosed into the mixtures over one hour. The dispersion was further stirred for 200 min and then the reaction mixture was cooled down to 40 C. and the pigments were separated by filtration through a Bchner funnel.

Example 2: The Same as Example 1 but without the Molybdenum Oxide Pretreatment

Comparative Example 1: According to Example 10 of EP 1619222 A1

[0155] 0.5 g metallic Molybdenum were dissolved in 10 g hydrogen peroxide. 142.5 g Stapa Metallux 2156 (equivalent to 100 g pigment), 600.0 g isopropanol and the molybdenum solution were dispersed in 1 l double jacketed reactor equipped with thermostat, reflux condenser and anchor stirrer and heated to 50 C. The mixture was left stirring for 60 min. The pH is brought to 8.6 with 3.5 g monoethanol amine and 30 g tetraethoxy silane and 10 g Dynasylan 9265 (phenyl trimethoxysilane) were added. The mixture was allowed to react for 10 h. The dispersion was cooled to 40 C. and the coated pigment isolated through filtering with a Bchner funnel.

Comparative Example 2

[0156] 5 g Molybdic acid were dissolved in 15 g hydrogen peroxide until a clear solution is obtained (duration approx. 1 h). 250 g Stapa Metallux 2156 and 400 g isopropanol are mixed in a double jacketed reactor equipped with agitator running at 300 rpm, reflux condenser and thermostat. Temperature was held at 25 C. and 0.281 g of the above prepared solution of molybdic acid in H.sub.2O.sub.2 and 30 g water were added and stirred for 60 min. 42.5 g tetraethoxy silane were added and the reaction mixture heated up to 80 C. Stirring was done for further 60 min. 13 g of phenyl triethoxysilane (Dynasylan 9265) were continuously added over a period of 3 h. After 30 min 6.36 g ethylendiamine in 20 g isopropanol were added. This was repeated twice. After the last base addition the mixture was allowed to react for 90 min. 8.5 g Hydrosil 2776 were added and after 60 min, the dispersion was cooled to 40 C. and the coated pigments were isolated through filtration.

Comparative Example 3: (Coating without Single First SiO.SUB.2 .Layer, Only One Hybrid Layer)

[0157] 5 g Molybdic acid (MOO.sub.3*H.sub.2O) were dispersed in 15 g H.sub.2O.sub.2 and stirred until a clear solution is obtained (approx. 1 h). In a 1 l double jacketed reactor equipped with thermostat, reflux condenser and anchor stirrer 250 g Stapa Metallux 2156 were dispersed in 350 g isopropanol. The dispersion was heated up to 40 C. and 0.33 g of the peroxo molybdic acid solution was added together with 3 g of water and the dispersion stirred for 60 minutes. 42.5 g tetraethoxy silane were added, the dispersion heated to 80 C. and stirred for 60 minutes. 13.3 g diphenyl dimethoxy silane was added over the period of 180 min. 6.0 g ethylene diamine and 20 g isopropanol were added and the mixture stirred for 30 min. The base addition was repeated two more times. After the last addition the dispersion was stirred for 90 min, 8.5 g Hydrosil 2776 were added and after additional 45 min the reaction mixture was cooled to 40 C. and the pigments were separated by filtration through a Bchner funnel.

Comparative Example 4

[0158] Commercially available Stapa IL Hydrolan 2156. This product is a SiO.sub.2 coated aluminum flake (based on Stapa Metallux 2156) without a Mo-oxide pretreatment and without any diphenyl silane. This product served as an internal standard especially for the hiding power test.

Comparative Example 5a

[0159] The coating of Example 3 according to WO 2007/017195 A2 was applied to Stapa Metallux 2156 as substrate. The threefold amounts of TEOS, water and of Dynalysan MEMO, TMPTMA and lauryl methacrylate with respect to 100 g of metal effect pigment were used, respectively.

Comparative Example 5b: (Prepared with Reference to WO 2016/120015 A1)

[0160] In a 1 l double jacketed reactor equipped with thermostat, reflux condenser and anchor stirrer 280 g of Stapa Metallux 2156 (corresponding to 182 g Al-pigment) were dispersed in 300 g isopropanol. The suspension is heated to 70 C., after which the constituents of the inorganic/organic hybrid layer (48.6 g tetraethyl orthosilicate (TEOS), 0.82 g Dynasylan MEMO, 3.47 g TMPTMA, 0.61 g allyl methacrylate, 0.26 g azobis(isobutyronitrile) (AIBN)) followed by 3 g of acetic acid in 17 g of distilled water were added. After 3 hours, 9.0 g of ethylenediamine in 3.0 g of isopropanol are added. After a further 2 hours, 1.4 g Dynasylan OCTEO and 1.8 g Dynasylan DAMO are added and the reaction mixture is stirred for 1 h before being cooled. The solid is isolated by filtration and collected as a paste.

Examples and Comparative Examples 6

[0161] In this series of examples the recipe of example 1 was used but the ratio of diphenyl silane to TEOS was varied while keeping the molar sum of both components constant. The exact parameters can be depicted from table 1.

TABLE-US-00001 TABLE 1 Amounts and calculated ratio of diphenyl silane (DiPS) and tetraethoxy silane (TEOS) referring to 250 g of initial MEX 2156 aluminum paste (162.5 g Al pigment) Sample mDiPS mTEOS Example 1 14.94 92.36 Example 6a 4.26 101.6 Example 6b 7.1 99.18 Example 6c 10.65 96.18 Comp. Ex. 6d 17.75 90.1 Comp. Ex. 6e 21.3 87.07 Comp. Ex. 6g 24.85 84.05

Example 7: (Inverse Layer Stack, Two-Pot Synthesis)

[0162] 5.0 g Molybdic acid (MoO.sub.3*H.sub.2O) were dispersed in 15 g H.sub.2O.sub.2 and stirred until a clear solution is obtained (approx. 1 h). In a 1 I double jacketed reactor equipped with thermostat, reflux condenser and anchor stirrer 250 g Stapa Metallux 2156 (corresponding to 162.5 g Al) were dispersed in 350 g isopropanol. The dispersion was heated up to 40 C. 0.33 g of the peroxo molybdic acid solution were added together with 3.0 g of water and the dispersion stirred for 60 minutes. 42.5 g TEOS were added and the and the dispersion was heated to 80 C. and stirred for one hour. 13.28 g of diphenyl dimethoxy silane dissolved in 100 ml isopropanol were dosed within 3 h to the mixture. Then 18 g ethylene diamine dissolved in 27 g water were added and the reaction mixture was further stirred for 3 hours. Then it was cooled down to about 40 C. and was separated from the solvent and washed and pasted with isopropanol to a paste with a pigment content of 65 wt.-%.

[0163] 250 g of the received coated aluminum pigment paste were again dispersed in 350 g isopropanol. 42.5 g TEOS was added and the mixture was heated under stirring to 80 C. 5.0 g of water and 4.0 g ethylene diamine dissolved in 40 g isopropanol were added and the mixture was stirred for further 5 hours. Then 8.5 g Hydrosil were added and after 60 min, the dispersion was cooled to 40 C. and the coated pigments were isolated through filtration.

B TESTING METHODS

I Mechanical Pre-Treatment

[0164] All metal effect pigments were dispersed in isopropanol to achieve a paste with an effect pigment content of 55 wt.-%. All of the inventive and comparative example pastes were first treated for 10 min in a KitchenAid prior to any further testing methods.

[0165] This treatment simulates moderate shear-forces typically occurring in mixer aggregates used in the large-scale production of metal effect pigments.

II. Gassing TestAccording to WO 2016/120015, p. 72

[0166] For a stringent gassing test, 15 g of the metal pigment paste with a solid content of 55 wt % were suspended in 11.0 g of butyl glycol with a stirring time of 5 minutes. This suspension was admixed with 14.4 g of colorless binder (ZK26-6826-402, manufacturer: BASF Coatings) and 0.6 g of 10 wt-% dimethylethanolamine solution (solvent: water) and stirred for 5 minutes. 22 g of the suspension were incorporated with stirring into a mixture of 195.0 g of mixing varnish for effect substance testing, milky/colorless (ZW42-6008-0101, manufacturer: BASF Coatings), 75.6 g of red aqueous basecoat tinting paste (ZU560-329, manufacturer: BASF Coatings, containing red iron oxide Fe.sub.2O.sub.3) and 6.0 g of black aqueous basecoat tinting paste (ZU 425-943, manufacturer: BASF Coatings, containing black iron oxide Fe.sub.2O.sub.3*FeO). Thereafter the pH of the suspension was adjusted to 9.0 using 10 wt.-% dimethyl ethanol amine solution (solvent water).

[0167] 265 g of the above composition were introduced into a gassing flask which was sealed with a twin-chamber gas bubble counter. The gas wash bottle was conditioned in a water bath at 40 C. for 1 hour, given a gastight seal, and tested over a maximum of 41 days. The resulting gas volume was read off on the basis of the displaced water volume in the upper chamber of the gas bubble counter. On evolution of at most 10 ml of hydrogen after 41 days, the test was deemed to have been passed. If the sample was not stable over the entire period, the time until outgassing of the sample was recorded.

[0168] If this first gassing test was not passed, no further tests were conducted at all, as passing this test is a prerequisite for inventive examples.

III. Hiding Power

[0169] First of all a test of the hiding power was made to rule out agglomerated or disoriented metal effect pigment probes.

[0170] For this test a drawdown on a Hostaphane film (Melinex O transparent, 175 m) was made using a paste containing the coated aluminum pigment in an amount corresponding to 0.65 g pigment which was mixed with about 3 g butyl acetate and this paste was homogenized with a test lacquer system containing yellow iron oxide pigments. This preparation was rolled down on the foil using a 50 m wire bar and dried.

[0171] The hiding power was evaluated visually according to a noting system against the standard sample represented by Comparative Example 4 (Hydrolan 2156). This test was passed when the note was at least 4 and no spots were seen. The standard sample usually had a hiding power noted 3. Some of the Comparative Examples showed spots when applied to the substrate. These spots were due to strong agglomeration of the metal pigments. In these cases the Waring Blender test was denoted as not passed without any further evaluation of optics. The second gassing test in these cases was also not conducted as it is well known that agglomerated metal pigments can show a relatively good gassing test, the result thereof may be only due to the surface reduction due to the otherwise fatal agglomeration of the pigments.

[0172] In Table 2a the results were denoted under Hiding power and no further results of Waring Blender were noted.

IV. Enhanced High Shear Test, Simulation of Circulation Line (Waring Blender)

[0173] The same test composition was prepared as in the first gassing test I but with the fourfold amounts. This composition was sheared in a Dissolver (VMA, type CA-20C of Getzmann) using a 5 cm dissolver disk at 20,000 rotations per minute for 10 min. Afterwards the optical properties were evaluated in comparison to the unsheared probes. This test simulates typical shear conditions of the circulation lines used in automotive industry. The optical properties were determined using a draw-down of this test composition with a 50 m wire bar. With a Byk-Mac the lightness L* at five different angles of observation of 15, 25 45, 75 and 110 was measured.

[0174] The flop index according to Alman is defined as follows in the relevant literature:

[00001]$\mathrm{Flop}\mathrm{index}=2.69.Math.\left(L^{*}15-L^{*}110\right)111/L^{*}450\text{.86}$ [0175] where L*15 is the luminance of the near-to-specular measuring angle, L*45 is the luminance of the measuring angle between near-to-specular and far-from-specular angle and L*110 is the luminance of the far-from-specular measuring angle.

[0176] A Flop and L* for each of the measured angles relative to the draw-down of the respective unsheared sample was evaluated and noted in table 2b. For the delta flop value the test was passed when Flop was <1.0 which was usually the case.

[0177] When evaluating the optical properties the occurrence of any L*-value>2.60 at any of the measured angles of observation of 15, 25 45, 75 and 110 was quoted as not being passed the test. The angles denote to the cis configuration relative to the incoming light (angle of incidence: 45). If the highest of the respective L*-values was <2.60 and >2.20 the test was denoted as being passed. If the highest of the respective L*-values was 2.20 the test was denoted as being well passed.

[0178] The before described gassing test was repeated for the samples after the enhanced high shear test. The whole enhanced shear test was only passed when the optical requirements were met, and the second gassing test was passed. All results are reported in table 2a,b.

TABLE-US-00002 TABLE 2a Results of testing gassing, hiding power and gassing after enhanced shear test (Waring-Blender) Gassing test I Hiding Enhanced (after moderate power shear test Sample shearing) noting Gassing Example 1 pass 4 passed Example 2 passed 4 passed Comp. Example 1 10 d failed Comp. Example 2 passed 4 <7 d, failed Comp. Example 3 failed failed Comp. Example 4 <7 d 3 <1 d, failed failed Comp. Example 5a failed Comp. Example 5b passed 4+ <1 d! failed Example 6a passed 4 passed Example 6b passed 4+ passed Example 6c passed 4+ passed Example 6d passed 4+ passed Comp. Ex. 6e passed 4+ failed Comp. Ex. 6f passed 4+ failed Example 7 passed 4 passed

TABLE-US-00003 TABLE 2b Results of testing optics after enhanced shear test (Waring-Blender) and overall results: Enhanced shear Waring Blender test - Optics Overall Overall results result of all Sample Flop L*.sub.15 L*.sub.25 L*.sub.45 L*.sub.75 L*.sub.110 Optics tests Example 1 0.12 2.10 0.14 0.85 0.23 0.00 passed passed Example 2 0.39 1.08 0.96 0.11 0.84 0.73 well passed passed Comp. failed Example 1 Comp. 0.70 2.19 0.05 1.26 0.66 0.30 passed failed Example 2 Comp. failed Example 3 Comp. failed Example 4 Comp. failed Example 5a Comp. failed Example 5b Example 6a 0.19 0.34 1.03 0.08 0.62 0.64 well passed passed Example 6b 0.29 1.68 2.00 0.44 0.50 0.51 well passed passed Example 6c 0.07 1.02 2.05 0.52 0.45 0.43 well passed passed Example 6d 0.31 0.81 2.58 1.08 0.20 0.39 passed passed Comp. Ex. 0.29 1.52 2.87 1.30 0.10 0.23 failed failed 6e Comp. Ex. 0.35 1.77 3.36 1.50 0.09 0.20 failed failed 6f Example 7 0.95 0.19 0.34 2.23 1.85 0.45 passed passed

[0179] Optical results missing in table 2 are due to the fact that the first gassing test was not passed (further evaluations were stopped) or that the gassing test after shearing was not passed after a very short period of some days.

V .SUP.29.Si NMR-MAS measurements

[0180] Some samples were prepared for NMR measurements. As the aluminum core disturbed the measurements due to the diamagnetic properties of the metal these sample were first completely oxidized. A weighted portion of the coated aluminum effect pigment was treated with 1 M HCl-solution at elevated temperature of about 60 C. for 48 hours to completely oxidize the aluminum core. Afterwards the pigments were separated from this solution, neutralized, washed with water, dried and homogenized.

[0181] The .sup.29Si NMR-MAS measurements were conducted with a 300 MHz Bruker (Avance II Bruker) using single pulse modus with a pulse length of 4.5 us and a relaxation time of 600 s. The measurements were conducted so long that a signal to noise of at least 150 was obtained wherein the signals referring to resonances of the Q2 to Q4 silanes in the region of 85 to 141 ppm were taken as signal and as noise the region between 40 to 0 ppm was chosen were no signals occurred. The powdered samples were measured in a 7 mm tube with a rotation frequency of 5,000 Hz and the chemical shift is noted against TMS (tetramethyl silane) as internal standard.

[0182] The results are depicted in table 3. In FIG. 1 the NMR spectrum is shown for example 6b. The intensities of different peaks were evaluated quantitatively according to standard fitting and integration procedures of NMR spectroscopy.

TABLE-US-00004 TABLE 3 Results of .sup.29Si NMR-MAS spectroscopy of certain samples Intensity sum of Intensity Intensity Q- D-Signal T-Signal signals (Ph.sub.2Si) (R-Si) (SiO.sub.2) Sample in % in % in % D/Q in % T/Q in % Ex. 1 9 0 91 9.9% Ex. 6b 3.3 1.7 95 3.5% 1.8% Ex. 6c 5.2 1.2 93.6 5.6% 1.3% Ex. 6d 7.9 1.9 90.2 8.8% 2.1%

VI Results

[0183] From table 2a it can be gathered that the pigments from comparative example 1 which was conducted according to example 10 of EP 1619222 did not even pass the first gassing test and therefore were not further tested. In this comparative example phenyl triethoxy silane was used as organic modifying silane agent, but only in a single hybrid coating without a pure SiO.sub.2 coating.

[0184] Similar results were obtained for the pigments of comparative examples 3, 4 and 5a. Comparative example 3 was conducted without a SiO.sub.2 layer and therefore demonstrated that also a single hybrid layer of SiO.sub.2 modified by diphenyl silane does not enable the aluminum effect pigment for a high gassing stability as already moderate shear forces by the treatment in the KitchenAid seemed to harm the coating.

[0185] This gassing test is already too strong for the standard product of comparative example 4 (Stapa IL Hydrolan 2156) and likewise for comparative example 5a which was made according to example 3 of WO 2007/017195 A2. According to this patent the coated products should have a certain gassing stability after the impact of moderate shearing. However, the gassing test used here was more severe than in this patent. Consequently, example 5b, which was made in reference to WO 2016/120015 A2 passed the first gassing test. However, the optical properties after the enhanced shear test were not satisfying as the L*.sub.25* was too high and furthermore the gassing test after the enhanced shear treatment was not passed.

[0186] Both comparative examples 5a and 5b are made according to technology where a hybrid layer is coated which involves methacrylate polymer formed together with SiO.sub.2 and wherein the methacrylate polymer is linked to the SiO.sub.2 via a methacrylate functional silane. This technology seems not to be adequate to enable coated metal pigments which pass the high demands of the present invention.

[0187] The comparative examples 2, 6e and 6f did also passed the first gassing test but failed in the enhanced shear test. Here comparative example 2, which is a further variant of comp. example 1 passed even the optical criteria of the enhanced shearing test but not the second gassing test.

[0188] The criteria for the flop was fulfilled by all samples tested but the L* criteria and the second gassing test turned out to be more severe. All the inventive examples 1, 2, and 6a-6d passed the enhanced shear test. Surprisingly also the example 7 passed the enhanced shear test with respect to the optical properties and gassing. In the sample of example 7 the inverse layer sequence was applied in that the aluminum substrate was first coated with the hybrid layer (diphenyl silane modification) followed by the SiO.sub.2 layer using a two-pot synthesis passed all tests. Generally, the results of the optical properties were better for the examples of the layer sequence first SiO.sub.2 and then the hybrid layer (examples 1, 2, 6a-6d). The best results were obtained for the examples 1, 2 and 6a to 6c. Here the E*-values were equal or below 2.2 for all measured angles (well passed). In these examples the ratio of the diphenyl silane to SiO.sub.2 was in an optimal range. In the comparative examples 6e and 6f the ratio of the diphenyl silane to SiO.sub.2 was apparently too high.