Sheet-like PVD aluminum pigment having protective coating and method for producing sheet-like PVD aluminum pigment having protective coating

Abstract

The present invention relates to a sheet-like PVD aluminum pigment having a protective envelope, where the protective envelope comprises a) a continuous, coated silicon oxide-containing coating (a), where the silicon oxide-containing coating comprises at least 60% by weight of silicon oxide, based on the total weight of the silicon oxide-containing coating, and b) a layer (b) of a metal oxide, where the metal oxide layer (b) comprises at least 60% by weight of silicon oxide, based on the total weight of the silicon oxide-containing coating. Wherein the metal oxide is selected from the group consisting of molybdenum oxide, molybdenum hydroxide, hydrated molybdenum oxide, tungsten oxide, tungsten hydroxide, hydrated tungsten oxide, and mixtures thereof, and c) optionally, an organo-chemically modified outer layer. The invention also relates to a method for producing said sheet-like metallic pigment and to the use thereof.

Description

[0001] This application is a divisional application of the international application with the title "Plate-like PVD aluminum pigments with protective encapsulation and method for manufacturing plate-like PVD aluminum pigments with protective encapsulation" of Evonik Industries AG filed on December 3, 2018 with the international application number PCT / EP2018 / 083317. The international application PCT / EP2018 / 083317 entered the Chinese national phase on May 25, 2020 with the national application number 201880076022.2. TECHNICAL FIELD

[0002] The present invention relates to plate-like PVD aluminum pigments with protective encapsulation. The present invention further relates to a method for manufacturing plate-like PVD aluminum pigments with protective encapsulation. BACKGROUND

[0003] PVD pigments are pigments obtained by physical vapor deposition (PVD), wherein a metal, for example aluminum, is vaporized in high vacuum and deposited as a metal foil on a substrate, for example a polyethylene terephthalate (PET) foil. The substrate is usually provided with a release coating to facilitate peeling off the metal film from the substrate. The deposited metal foil is subsequently passed through a solvent bath to peel off the resulting metal film and to obtain coarse particles of the metal foil. The metal particles can then be concentrated and washed and further comminuted, for example using a high-speed stirrer or ultrasound, to obtain plate-like PVD pigments of the desired particle size distribution.

[0004] PVD pigments have an extremely smooth surface and a mirror-like reflectivity of incident light. They represent the highest level of optical appearance in terms of brightness and flop of all metallic effect pigments. PVD pigments are available as aluminum pigments under the trademark of BASF SE or under the trademark of Carl Schlenk AG.

[0005] To maintain the high reflectivity of PVD pigments, the PVD pigments have to be protected from corrosion which can be initiated by water, humidity, chemicals etc. from the surrounding environment, e.g. paint, lacquer, coating etc. PVD pigments are much more sensitive to corrosion than flaky metal pigments obtained from a milling process, wherein spherical or irregularly shaped metal particles are physically flattened in a ball mill to obtain a flaky shape. One reason for the increased sensitivity of PVD pigments is their very high specific surface area. Furthermore, PVD pigments exhibit the best optical properties of metal effect pigments to make them sensitive to even small corrosion processes. Another reason for the increased sensitivity can be the fact that dispersions of commercially available PVD aluminum pigments always contain a certain amount of residual release coating material, which is usually a polymer. These residues have a negative influence on the coating process of a corrosion protection layer, e.g. silicon dioxide.

[0006] EP 1 619 222 A1 discloses aluminum pigments comprising aluminum particles, a molybdenum coating comprising molybdenum oxide and / or molybdenum hydrate covering the surface of each of the aluminum particles and further a silicon dioxide coating comprising amorphous silicon dioxide and / or a coating made from a silane coupling agent covering the molybdenum coating. The aluminum pigments are obtained by milling aluminum particles. EP 1 619 222 A1 does not relate to PVD aluminum pigments.

[0007] DE 10 2013 113 885 A1 relates to metal pigments comprising a metal substrate and a coating. The coating comprises a first coating layer comprising at least one metal oxide. The coating further comprises a second layer comprising at least one heteropolysiloxane comprising at least one aminosilane component and at least one silane component selected from the group consisting of alkylsilane, vinylsilane and arylsilane. The pigments according to the teaching of DE 10 2013 113 805 A1 exhibit an improved stability against corrosion and chemicals. However, it turned out that PVD-metal pigments treated with these heteropolysiloxanes do not provide corrosion resistance in certain applications.

[0008] DE 10 2010 007 147 A1 relates to metal effect pigments coated with silicon oxide using a sol-gel process. The pigments according to the teaching of DE 10 2010 007 147 A1 are manufactured in a two-step process, wherein the sol-gel reaction is carried out in the first step in the presence of an acid and in the second step in the presence of a base or vice versa. These pigments can represent a proper balance between covering power on the one hand and corrosion resistance on the other hand.

[0009] WO 2016 / 059033 A1 relates to PVD metal effect pigments coated with a metal oxide layer, wherein the metal oxide layer corresponds to 5 to 45 wt.-% of the total weight of the coated metal effect pigments. The metal oxide is selected from the group consisting of silicon dioxide, aluminum oxide, titanium dioxide, iron oxide, tin oxide, zinc oxide or mixtures thereof. The PVD metal effect pigments can be provided in concentrated dispersions having a coated PVD metal effect pigment content of 70 wt.-% or more based on the total weight of the dispersion. SUMMARY

[0010] It was an object of the present invention to provide PVD pigments having improved stability, especially against humidity in a hardening coating system. Furthermore, it was an object of the present invention to provide PVD pigments having a simple structure which can be easily manufactured.

[0011] The object of the present invention is solved by providing a platelet-shaped PVD aluminum pigment having a protective envelope, wherein the protective envelope comprises

[0012] (a) a continuous, overlying silicon oxide-containing coating, wherein the silicon oxide-containing coating comprises at least 60 wt.-% silicon oxide based on the total weight of the uncoated PVD pigment, and

[0013] (b) a metal oxide layer, wherein the metal oxide is selected from the group consisting of molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate, tungsten oxide, tungsten hydroxide, tungsten oxide hydrate and mixtures thereof, and

[0014] (c) optionally, an organic-chemically modified outer layer.

[0015] The silicon oxide-containing coating is also referred to as coating (a) or as layer (a).

[0016] The discontinuous layer of metal oxide or the continuous layer of metal oxide is also referred to as layer (b). Preferably, the discontinuous layer comprises or consists of a metal oxide or the continuous layer comprises or consists of a metal oxide, wherein the metal oxide is selected from the group consisting of molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate, tungsten oxide, tungsten hydroxide, tungsten oxide hydrate and mixtures thereof.

[0017] The term silicon oxide-containing coating (a) refers to any one of silicon dioxide, silicon hydroxide and silicon oxide hydrate and mixtures thereof. Also included is silicon dioxide made by sol-gel synthesis. Such sol-gel silicon dioxide can contain unreacted groups of alkoxides, such as methoxy or ethoxy groups. The unreacted groups can be present in the range of 1 % to 50 %, preferably 10 % to 30 %, of all Si-OH functions involved in the 100 % hydrolysis theory of all silicon alkoxides used for forming the coating (a).

[0018] The term "metal oxide" used in connection with layer (b) refers to any metal oxide or metal hydroxide or hydrated metal oxide or metal peroxide or any combination of mixtures of these classes. It can also contain elemental metals in an amount of 0 to 30 atom-%, preferably 0 to 25 atom-%, based on the total content of the metals constituting the metal oxide (b).

[0019] The term "layer (b)" used in connection with the metal oxide refers to layer (b) on a PVD aluminum substrate or on coating (a) or in the case where the metal oxide (b) is at least partially located in cracks or sink holes of coating (a).

[0020] The term "PVD aluminum pigment" refers to a single PVD aluminum pigment or to a plurality of PVD aluminum pigments.

[0021] The protective envelope described in the claims serves to encapsulate PVD aluminum pigments which have not been protected or stabilized against corrosion, i.e. unstabilized PVD aluminum pigments. Thus, the protective envelope protects the PVD aluminum pigments against corrosion. Preferably, the protective envelope also protects the PVD aluminum pigments when incorporated into an application medium, such as a cured coating, against hydrolysis caused by moisture penetrating the cured coating.

[0022] Conventional metal pigments obtained by, for example, milling processes are generally quite stable after incorporation into a cured coating system. In contrast, PVD pigments which are merely coated with a protective layer of silicon dioxide are susceptible to such oxidation processes.

[0023] Hydrolysis occurs, for example, when the application medium, for example an automotive interior coating containing PVD metal pigments, is subjected to elevated temperatures and elevated humidity for a long period of time. Even in a two-coat system consisting of a basecoat and a clear coat containing PVD aluminum pigments, moisture can penetrate the clear coat and can degrade the aluminum pigments. The conditions for these kinds of coatings are simulated, for example, in the VW test TL 226. Extremely thin PVD metal flakes are particularly sensitive to the effects of moisture on such coatings.

[0024] The present inventors have found that, surprisingly, very corrosion-prone PVD aluminum pigments can be surprisingly simply stabilized against corrosion when a coating (a) which is an encapsulating silicon oxide-containing coating comprising at least 60 wt.-% silicon oxide based on the total weight of the uncoated silicon oxide-containing coating and a layer (b) of a metal oxide, wherein the metal oxide is selected from the group consisting of molybdenum oxide, molybdenum hydroxide, hydrated molybdenum oxide, tungsten oxide, tungsten hydroxide, hydrated tungsten oxide and mixtures thereof and c) optionally an organic-chemically modified outer layer are applied.

[0025] In general, the present application relates to the following embodiments.

[0026] 1. A platelet-shaped PVD aluminum pigment having a protective envelope, wherein the protective envelope comprises:

[0027] a) a continuous, overlying silicon oxide-containing coating layer (a), wherein the silicon oxide-containing coating layer comprises at least 60 wt.-% silicon oxide, based on the total weight of the silicon oxide-containing coating layer, and

[0028] b) a layer of a metal oxide (b), wherein the metal oxide is selected from the group consisting of molybdenum oxide, molybdenum hydroxide, hydrous molybdenum oxide, tungsten oxide, tungsten hydroxide, hydrous tungsten oxide, and mixtures thereof, and

[0029] c) optionally, an organic-chemically modified outer layer.

[0030] 2. The platelet-shaped PVD aluminum pigment having a protective envelope according to embodiment 1, characterized in that the PVD aluminum pigment has a median diameter d 50 .

[0031] 3. The platelet-shaped PVD aluminum pigment having a protective envelope according to embodiment 1 or 2, characterized in that the PVD aluminum pigment has a median thickness h 50 .

[0032] 4. The platelet-shaped PVD aluminum pigment having a protective envelope according to any one of embodiments 1 to 3, characterized in that the amount of the metal oxide is 0.01 to 0.4 wt.-% for Mo and 0.01 to 0.8 wt.-% for W, each calculated as elemental molybdenum and / or tungsten and based on the weight of the uncoated PVD aluminum pigment.

[0033] 5. The platelet-shaped PVD aluminum pigment having a protective envelope according to any one of embodiments 1 to 4, characterized in that the silicon oxide-containing coating layer (a) amounts to 8 wt.-% to 25 wt.-%, based on the weight of the uncoated PVD aluminum pigment.

[0034] 6. The platelet-shaped PVD aluminum pigment having a protective envelope according to any one of embodiments 1 to 5, characterized in that the silicon oxide-containing coating layer (a) has an average thickness in the range of 15 to 60 nm.

[0035] 7. The platelet-shaped PVD aluminum pigment having a protective envelope according to any one of embodiments 1 to 6, characterized in that the silicon oxide-containing coating layer (a) consists of silicon oxide, preferably of silicon dioxide.

[0036] 8. A flaky PVD aluminum pigment with a protective envelope according to any one of embodiments 1 to 6, characterized in that the silicon oxide containing coating (a) consists of a coating, wherein the remainder compounds to 100 wt.-% in the silicon oxide containing coating (a) comprise or consist of organic groups to form a hybrid silicon oxide / organic coating.

[0037] 9. A flaky PVD aluminum pigment with a protective envelope according to embodiment 8, characterized in that the organic groups comprise organic oligomers and / or polymers.

[0038] 10. A flaky PVD aluminum pigment with a protective envelope according to any one of embodiments 1 to 6, characterized in that the silicon oxide containing coating (a) consists of silicon oxide, preferably silicon dioxide, and a mixture of organic functional silanes of the following formula

[0039] R (4-z) Si(X) z (I)

[0040] wherein z is an integer from 1 to 3, R is an unsubstituted, unbranched or branched alkyl chain having 1 to 24 C atoms or an aryl group having 6 to 18 C atoms or an arylalkyl group having 7 to 25 C atoms or mixtures thereof, and X is a halogen group and / or preferably an alkoxy group.

[0041] 11. A flaky PVD aluminum pigment with a protective envelope according to any one of embodiments 1 to 10, characterized in that the organic-chemically modified outer layer comprises at least one organic functional silane.

[0042] 12. A PVD aluminum pigment with a protective envelope according to any one of embodiments 1 to 11, characterized in that the PVD aluminum pigment is first coated with the silicon oxide containing coating (a) and then the layer (b) of the metal oxide is provided.

[0043] 13. A flaky PVD aluminum pigment with a protective envelope according to any one of embodiments 1 to 11, characterized in that the PVD aluminum pigment is first provided with the layer (b) of the metal oxide and then coated with the silicon oxide containing coating (a).

[0044] 14. A method for manufacturing a flaky PVD aluminum pigment with a protective envelope according to any one of embodiments 1 to 13, wherein the method comprises the following successive steps:

[0045] (a1) contacting a soluble alkylsilicon compound dissolved in a solvent and a flaky PVD aluminum pigment and forming a flaky PVD aluminum pigment coated with a substantially continuous silicon oxide containing coating by a sol-gel process,

[0046] (b1 ) contacting a soluble metal compound dissolved in a solvent and the flake-shaped PVD aluminum pigment obtained in step (a1 ) to coat the pigment of step (a1 ) with a metal oxide, wherein the metal of the soluble metal compound is selected from the group consisting of molybdenum, tungsten and mixtures thereof, to obtain a flake-shaped PVD pigment with a protective coating and

[0047] (c1 ) optionally forming an organo-chemically modified outer layer with at least one organofunctional silane

[0048] or

[0049] (a2) contacting a soluble metal compound dissolved in a solvent and the flake-shaped PVD aluminum pigment to obtain a flake-shaped PVD aluminum pigment with a metal oxide, wherein the metal of the soluble metal compound is selected from the group consisting of molybdenum, tungsten and mixtures thereof,

[0050] (b2) contacting a soluble alcohol silane compound dissolved in a solvent and the flake-shaped PVD aluminum pigment obtained in step (a2) to obtain a flake-shaped PVD aluminum pigment coated with a substantially continuous silicon oxide containing coating by a sol-gel process to obtain a flake-shaped PVD pigment with a protective coating and

[0051] (c2) optionally forming an organo-chemically modified outer layer with at least one organofunctional silane.

[0052] 15. Use of a flake-shaped PVD aluminum pigment according to any one of embodiments 1 to 13 in a formulation, preferably in an aqueous formulation.

[0053] 16. Formulation, characterized in that it contains a flake-shaped PVD aluminum pigment according to any one of embodiments 1 to 13. DETAILED DESCRIPTION

[0054] PVD aluminum pigment:

[0055] The PVD aluminum pigment has an aluminum content of preferably at least 98 wt.-%, preferably at least 99 wt.-%, more preferably at least 99.9 wt.-%, more preferably at least 99.99 wt.-%, each based on the total weight of the uncoated PVD aluminum pigment.

[0056] According to one preferred embodiment, the PVD aluminum pigment has a median diameter d 50 .

[0057] The median diameter d 50 means that 50% of the metal pigments have a diameter of the indicated size or less. The median diameter d 50The (volume average) can be measured by laser particle sizing, e.g. with a CILAS 1064 (Quantachrome GmbH, Germany).

[0058] According to another embodiment of the present application, the PVD aluminum pigments have a median thickness h of 15 to 75 nm, preferably 16 to 50 nm, more preferably 19 to 40 nm 50 The median thickness h 50 means that 50% of the metal pigments have the indicated size or lower thickness.

[0059] At h 50 values below 15 nm, the aluminum PVD pigments become too dark and lose their great hiding power. At values above 75 nm, the PVD pigments lose their good orientation in the application medium, so that the optical properties such as gloss and flop decrease, in addition the hiding power decreases with increasing thickness.

[0060] According to another embodiment of the present application, the PVD aluminum pigments have a median diameter d 50 of 6 to 18 pm and a median thickness h 50 of 16 to 50 nm, preferably 19 to 40 nm, most preferably 20 to 38 nm.

[0061] Such PVD-pigments exhibit a high hiding power and a liquid metal effect.

[0062] The median thickness of the PVD aluminum pigments can be adjusted when performing the physical vapor deposition. Furthermore, the median thickness h 50 of the PVD aluminum pigments can be measured by counting the individual pigment particles in a SEM according to the method described in detail in WO 2004087816 A2 (see especially page 9, lines 12 to 17 and page 24, line 12 to page 25, line 15).

[0063] According to another embodiment, the PVD aluminum pigments are shaped as or shaped with a diffraction grating, which has a period of preferably 5,000 to 20,000 lines per cm, more preferably 10,000 to 16,000 lines per cm. When shaped as or shaped with a diffraction grating, the PVD aluminum pigments have iridescent properties. The production of PVD aluminum pigments with a diffraction grating can be carried out according to US 5,624,076 A. These PVD pigments are also described as embossed pigments. The method for producing embossed pigments or pigments with a diffraction grating is according to US 5,624,076 A.

[0064] These embossed PVD pigments consist only of very thin aluminum platelets having a primary layer thickness of about 25 to 80 nm and preferably 30 to 70 nm. Embossed PVD pigments can be manufactured by pressing a grating structure onto a polymer film and then applying aluminum onto it by vapor deposition in high vacuum. The aluminum film is then removed from the polymer film as standard practice in the manufacture of metal effect pigments by PVD methods and the resulting film pieces are then comminuted to obtain the embossed PVD pigments. By this method also diffractive structures comprising up to 20,000 diffractive units per cm can be manufactured. The diffractive structure is preferably a groove structure arranged essentially parallel to each other, i.e. formed by valleys separated from each other by ridges or peaks. The peak to valley height of such a structure is preferably in the range of 150 nm to 400 nm, more preferably 175 nm to 350 nm. Of course, other diffractive structures can also be used. For example, the diffractive structure can be in the form of concentric groups of structures arranged within each other or a groove structure arranged in a spiral form. The only necessity is that the diffractive structure causes the desired optical effect or rainbow effect of polychromatic iridescence to the observer. The diffractive structure is preferably formed as a reflective grating.

[0065] The uncoated PVD aluminum pigments which look like mirror-like pigments have a high metallic appearance and a high reflectivity. The PVD pigments of the present invention have optical properties which are close to identical or at least very close to the optical properties of the uncoated PVD aluminum pigments. According to one preferred embodiment of the present invention, the PVD aluminum pigments are not colored with additional dyes or colored pigments. Thus, the coating (a) and the layer (b) or any additional layer preferably do not comprise additional dyes and / or colored pigments.

[0066] If the PVD aluminum pigments are embossed with a (a) diffractive grating as described above, only the color effect is induced. The continuous encapsulating silicon oxide containing coating (a):

[0067] The silicon oxide containing coating comprises at least 60 wt.-% silicon oxide, preferably silicon dioxide, based on the total weight of the silicon oxide containing coating. According to one preferred embodiment, the silicon oxide, preferably silicon dioxide, amounts to 70 wt.-% to 99 wt.-%, more preferably 75 wt.-% to 95 wt.-%, for example 88 wt.-% to 92 wt.-%, of the total weight of the silicon oxide containing coating.

[0068] According to another embodiment, the silicon oxide containing coating (a) consists of silicon oxide, preferably silicon dioxide.

[0069] The term "continuous layer (a)" means that layer (a) is substantially complete, in particular completely coats the respective PVD-aluminum substrate or the PVD-aluminum substrate pre-coated with layer (b). However, such a substantially complete coating can still contain some cracks in the coating, which can be generated after the chemical coating has been completed. The cracks can be generated, for example, by the drying step of the PVD-aluminum pigments coated with layer (a).

[0070] The silicon oxide-containing coating can comprise additional metal oxides, metal oxide hydroxides and / or hydrated metal oxides, wherein the metal is preferably selected from the group consisting of aluminum, zinc, tin, zirconium, cerium and mixtures thereof, more preferably from the group consisting of aluminum, zinc, tin, zirconium and mixtures thereof, more preferably from the group consisting of aluminum. The amount of additional metal oxides, metal oxide hydroxides and / or hydrated metal oxides can be up to 30 wt.-%, more preferably from 1 wt.-% to 25 wt.-%, more preferably from 5 to 20 wt.-%, more preferably from 8 wt.-% to 12 wt.-%, based on the total weight of the silicon oxide-containing coating.

[0071] The continuous silicon oxide-containing coating, preferably a silicon dioxide coating, preferably has an average thickness of from 15 nm to 60 nm, more preferably from 18 nm to 55 nm, more preferably from 20 nm to 50 nm, more preferably from 25 nm to 45 nm, most preferably from 30 nm to 40 nm.

[0072] If the transparent coating, such as the silicon oxide-containing coating, is thicker than 60 nm, the covering power is significantly reduced and the optical properties of the PVD aluminum pigments are also impaired. The covering power is the ability to cover the underground so that the underground does not shine through the applied application medium, such as lacquer, varnish or paint. If the thickness of the coating (a) is below 15 nm, the corrosion resistance stability of the PVD aluminum pigments decreases and the pigments become too thin so that there is no good covering power. Furthermore, the appearance of such thin metal pigments becomes too dark.

[0073] According to another embodiment of the present application, the silicon oxide-containing coating amounts to from 8 wt.-% to 25 wt.-%, preferably from 10 wt.-% to 22 wt.-%, more preferably from 12 wt.-% to 20 wt.-%, most preferably from 14 wt.-% to 18 wt.-%, each based on the weight of the uncoated PVD aluminum pigments. The person skilled in the art can adjust the optimal amount depending on the size and the specific surface area of the PVD aluminum pigments.

[0074] Below 8 wt.-%, the corrosion resistance stability is too low. Above 25 wt.-%, the high-end optical properties of the PVD aluminum pigments can be impaired.

[0075] In a further embodiment, the silicon oxide containing coating (a) contains silicon oxide, preferably silicon dioxide, in an amount of at least 60 wt.-%, more preferably at least 70 wt.-%, more preferably at least 80 wt.-%, more preferably at least 95 wt.-%, each based on the total weight of the silicon oxide containing coating (a).

[0076] In another embodiment, the remaining compounds to 100 wt.-% in the silicon oxide containing coating (a) comprise or consist of organic groups, thus forming a hybride silicon oxide / organic coating.

[0077] In certain embodiments, the organic material comprises or consists of organic oligomers and / or polymers. That is, the silicon oxide containing coating can be formed as a hybride layer of silicon oxide, preferably silicon dioxide, and organic oligomers and / or organic polymers, which are preferably interpenetrated. Such a hybride coating can be manufactured by simultaneously forming the silicon oxide, preferably by sol-gel synthesis, and forming the polymer or oligomer. Thus, the hybride layer is preferably a substantially homogeneous layer, wherein silicon oxide, preferably silicon dioxide, and organic oligomers and / or organic polymers are substantially homogeneously distributed within the coating (a). Metal effect pigments coated by such a hybride layer are disclosed in EP 1812519 B1 or WO 2016 / 120015 A1. Such a hybride layer enhances the mechanical properties of the coating (a).

[0078] According to another embodiment of the present application, the silicon oxide containing coating (a) contains 70 to 95 wt.-%, preferably 80 to 90 wt.-% silicon oxide, preferably silicon dioxide, and 5 to 30 wt.-%, preferably 10 to 20 wt.-% organic oligomers and / or organic polymers, each based on the total weight of the silicon oxide containing layer.

[0079] According to another embodiment of the present application, the silicon oxide, preferably silicon dioxide, and the organic oligomers and / or organic polymers are not covalently bound to each other.

[0080] According to another embodiment of the present application, the silicon oxide, preferably silicon dioxide, and the organic oligomers and / or organic polymers can be at least partially covalently bound to each other.

[0081] The at least partial covalent binding of the silicon oxide network to the organic oligomers and / or polymers can be achieved by means of at least one organic network former. A network former is an agent which can be bound both to the silicon oxide network and to the organic oligomers and / or polymers.

[0082] Organofunctional silanes are preferably used as organic network formers. The organofunctional silanes can be bound to the silica network after hydrolysis of the hydrolysable groups. By hydrolysis, the hydrolysable groups are usually replaced by OH groups, which subsequently form covalent bonds with OH groups in the inorganic silica network by condensation. The hydrolysable groups are preferably halogen, hydroxyl or alkoxy groups having 1 to 10 carbon atoms, preferably 1 to 2 carbon atoms, which can be linear or branched in the carbon chain, and mixtures thereof.

[0083] Suitable organofunctional silanes are, for example, the many representatives produced by Evonik (Untere Kanalstrasse 3, D-79618 Rheinfelden) and sold under the trade name "Dynasylan". For example, 3-methacryloyloxypropyltrimethoxysilane (Dynasylan MEMO) can be used to form (meth)acrylate or polyester, vinyltri(m)ethoxysilane (Dynasylan VTMO or VTEO) can be used to form vinyl polymers, 3-mercaptopropyltri(m)ethoxysilane (Dynasylan MTMO or 3201) can be used for copolymerization in rubber polymers, aminopropyltrimethoxysilane (Dynasylan AMMO) or N2-aminoethyl-3- aminopropyltrimethoxysilane (Dynasylan DAMO) can be used to form beta-hydroxylamine or 3-glycidyloxypropyltrimethoxysilane (Dynasylan GLYMO) can be used to form urethane or polyether networks.

[0084] Further examples of silanes with vinyl or (meth)acrylate functionality are: isocyanatotriethoxysilane, 3-isocyanatopropyltriethoxysilane, vinyl ethyldichlorosilane, vinyl methyl dichlorosilane, vinyl methyl diacetoxysilane, vinyl methyl diethoxysilane, vinyl triacetoxysilane, vinyl trichlorosilane, phenyl vinyl diethoxysilane, phenyl allyl diethoxysilane, phenyl allyl dichlorosilane, 3-methacryloyloxypropyltriethoxysilane, methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 2-methacryloyloxyethyltri(m)ethoxysilane, 2-acryloyloxyethyltri(m)ethoxysilane, 3-methacryloyloxypropyltri(methoxy-ethoxy)silane, 3-methacryloyloxypropyltri(butoxyethoxy)silane, 3-methacryloyloxypropyltri(propoxy)silane or 3-methacryloyloxypropyltri(butoxy)silane.

[0085] In a preferred extension of the application, both the silica, preferably silicon dioxide, and the organic network of oligomers and / or polymers are present, preferably exhibiting interpenetration.

[0086] For the present application, "oligomer" in the mixed layer means the term commonly used in polymer chemistry: i.e. a linkage of 2 to 20 monomer units (Hans-Georg Elias, "Makromolekύle" 4th edition 1981, Huethig & Wepf Verlag Basel). A polymer is a linkage of more than 20 monomer units.

[0087] The average chain length of the organic segments can be varied by changing the ratio of the monomer concentration to the concentration of the organic network former. The average chain length of the organic segments is from 2 to 10,000 monomer units, preferably from 3 to 5,000 monomer units, more preferably from 4 to 500 monomer units, and even more preferably from 5 to 30 monomer units.

[0088] Furthermore, in further embodiments, the organic polymer has an average chain length of from 21 to 15,000 monomer units, more preferably from 50 to 5,000 monomer units, and most preferably from 100 to 1,000 monomer units to be used as the organic component.

[0089] In another embodiment of the present application, the silicon oxide-containing layer (a) consists of a mixed layer of silicon oxide, preferably silicon dioxide, and an organofunctional silane having un-polymerized or oligomerized functional groups. Such organofunctional silanes are referred to as network modifiers and metal pigments coated with such hybrid layers are described in WO 2015 / 013762 A1.

[0090] Preferably, the network modifier is an organofunctional silane having the formula

[0091] R (4-z) Si(X) z (I)

[0092] In this formula, z is an integer from 1 to 3, R is an unsubstituted, unbranched or branched alkyl chain having from 1 to 24 C atoms or an aryl group having from 6 to 18 C atoms or an arylalkyl group having from 7 to 25 C atoms or mixtures thereof, and X is a halogen group and / or preferably an alkoxy group. Preferred are alkylsilanes with alkyl chains having from 1 to 18 C atoms or arylsilanes with phenyl groups. R can also be cyclically linked to Si, in which case z is usually 2. X is most preferably ethoxy or methoxy.

[0093] Preferred examples of such network-modifying organofunctional silanes are alkyl or aryl silanes.

[0094] Examples of these silanes are butyltrimethoxysilane, butyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane and mixtures thereof.

[0095] Layer (b) can be a discontinuous layer or a continuous layer of a metal oxide.

[0096] The term "continuous layer (b)" means that layer (b) substantially completely, in particular completely, coats the respective PVD-aluminum substrate, for example a continuous silicon oxide containing coating (a), which in turn coats the flaky PVD aluminum pigment.

[0097] The term "discontinuous layer" or "discontinuous layer (b)" means that layer (b) only partially coats the respective substrate, for example a continuous silicon oxide containing coating (a) or the flaky PVD aluminum pigment. Partial coating means that the respective substrate is not completely coated. The partial coating or discontinuity can for example be realized in the form of islands of layer (b) on the respective substrate.

[0098] According to one embodiment of the present application, layer (b) comprises or consists of a metal oxide, wherein the metal oxide is selected from the group consisting of molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate, molybdenum peroxide and mixtures thereof. Molybdenum oxide is usually a mixture of different species and can involve coordination species. It can be represented by the following compositional formula:

[0099] MoO3mH2O2.nH2O or MoO 3-m (O2) m .nH2O (II)

[0100] wherein Mo is molybdenum, O is oxygen, 0 < m < 1 and 1 < n < 2.

[0101] Molybdenum complexes comprising different ligands selected from the group consisting of water, O2, O and mixtures thereof can also be included.

[0102] Furthermore, layer (b) can also contain elemental molybdenum in an amount of 0 to 30 atomic %, preferably 0 to 25 atomic %, most preferably 3 to 20 atomic %, each based on the total content of molybdenum constituting the metal oxide (b).

[0103] The amount of elemental molybdenum can be determined by XPS.

[0104] Preferably, the molybdenum oxide coating is prepared by first dissolving molybdenum oxide or elemental molybdenum in a hydrogen oxide solution to prepare a solution of peroxomolybdic acid (see for example Solid States Ionics, pages 507-512, 1992).

[0105] According to another embodiment, layer (b) comprises or consists of a metal oxide, wherein the metal oxide is selected from the group consisting of tungsten oxide, tungsten hydroxide, tungsten oxide hydrate, tungsten peroxide and mixtures thereof. It is also possible to include tungsten complexes comprising different ligands selected from the group consisting of water, O2, O and mixtures thereof. Furthermore, layer (b) of this embodiment can also contain elemental tungsten in an amount of 0 to 30 atomic %, preferably 0 to 25 atomic %, most preferably 3 to 20 atomic %, each based on the total content of tungsten constituting the metal oxide (b). The amount of elemental tungsten can be determined by XPS.

[0106] Preferably, the tungsten oxide coating is prepared by first dissolving tungsten oxide or elemental tungsten in a hydrogen oxide solution to prepare a solution of peroxopolytungstate.

[0107] The inventors found that the corrosion resistance stability, especially the hydrolysis resistance stability, of PVD-aluminum pigments coated by coating (a) and layer (b) is enhanced, which is surprising. It is especially surprising that the stability is enhanced in case layer (b) can be discontinuous. The utility of a discontinuous layer in improving the protective encapsulation of flaky PVD aluminum pigments especially indicates that the effect is not due to a simple addition of the first complete encapsulation layer and the second complete encapsulation layer. Rather, the two layers seem to have a synergistic effect in the utility of imparting corrosion resistance stability to PVD aluminum pigments.

[0108] Although the synergistic effect is not understood, the specific combination of the silicon oxide containing coating, which mainly constitutes the protective encapsulation, and the small amount of metal oxide, metal hydroxide and / or hydrated metal oxide deposited as layer (b) can provide an improved protective encapsulation of flaky PVD aluminum pigments.

[0109] According to another preferred embodiment of the present application, the amount of layer (b) of metal oxide is 0.01 to 0.4 wt.-% calculated as elemental molybdenum or 0.01 to 0.8 wt.-% calculated as elemental tungsten, each based on the weight of the uncoated PVD aluminum pigment. According to another preferred embodiment, the amount of layer (b) of metal oxide is 0.015 to 0.35 wt.-%, more preferably 0.02 to 0.3 wt.-%, each calculated as elemental molybdenum and based on the weight of the uncoated PVD aluminum pigment. According to another preferred embodiment, the amount of layer (b) of metal oxide is 0.02 to 0.6 wt.-%, more preferably 0.05 to 0.5 wt.-%, each calculated as elemental tungsten and based on the weight of the uncoated PVD aluminum pigment.

[0110] Surprisingly, the anti-corrosion effect of coated PVD metal pigments can be obtained with very low amounts of metal oxide.

[0111] The amount of molybdenum or tungsten and the amount of SiO2 were determined by optical emission spectroscopy (ICP-OES).

[0112] According to a further embodiment of the invention, the layer (b) comprising or consisting of a metal oxide extends at least partially into the silicon oxide-containing coating.

[0113] This is believed to be important for improving the protective envelope by extending into the silicon oxide-containing coating (a), at least partially filling defects in the coating (a), such as cracks, e.g. microcracks, shrinkage pores, pinholes, pores, etc., and / or at least partially covering the coating (a).

[0114] According to a preferred embodiment of the present invention, the metal oxide forms a discontinuous layer (b). Preferably, the discontinuous layer (b) comprises or consists of islands of said metal oxide.

[0115] Islands are discrete areas of metal oxide that are not connected to other areas of metal oxide. Organic-chemically modified outer layer:

[0116] According to a further preferred embodiment, the platelet-shaped PVD aluminum pigments comprise an organo-chemically modified outer layer.

[0117] In a preferred embodiment, the organo-chemically modified outer layer comprises at least one organofunctional silane.

[0118] Preferably, the organo-chemically modified outer layer comprises at least a first silane having coupling groups.

[0119] The silane may alternatively be an organofunctional silane which enables chemical bonding to plastics, binders of paints or inks or the like.

[0120] Organofunctional silanes preferably used as surface modifiers and having suitable functional groups are commercially available and are produced, for example, by Evonik and under the trade name Other products are available from Momentive Performance Materials ( Silane) or purchased from Wacker ( product groups).

[0121] Examples of these products are 3-methacryloxypropyltrimethoxysilane (Dynasylan MEMO, Silquest A-174 NT), vinyltri(m)ethoxysilane (Dynasylan VTMO or VTEO, Silquest A-151 or A-171), methyltri(m)ethoxysilane (Dynasylan MTMS or MTES), 3-mercaptopropyltrimethoxysilane (Dynasylan MTMO; Silquest A-189), 3-glycidoxypropyltrimethoxysilane (Dynasylan GLYMO, Silquest A-187), tris[3-(trimethoxysilyl)propyl]isocyanurate (Silquest Y-11597), bis[3-(triethoxysilyl)propyl]]tetrasulfide (Silquest A-1289), bis[3-(triethoxysilyl)propyl disulfide (Silquest A-1589), beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (Silquest A-186), bis(triethoxysilyl)ethane (Silquest Y-9805), gamma-isocyanatopropyltrimethoxysilane (Silquest A-Link 35, GENIOSIL GF 40), methacryloxymethyltri(m)ethoxysilane (GENIOSIL XL 33, XL 36), (methacryloxymethyl)(m)ethyldimethoxysilane (GENIOSIL XL 32, XL 34), (isocyanatomethyl)methyl dimethoxysilane, (isocyanatomethyl)trimethoxysilane, 3-(triethoxysilyl)propyl succinic anhydride (GENIOSIL GF 20), (methacryloxymethyl)methyl diethoxysilane, 2-acryloxyethyl methyl dimethoxysilane, 2-methacryloxyethyltrimethoxysilane, 3-acryloxypropyl methyl dimethoxysilane, 2-acryloxyethyltrimethoxysilane, 2-methacryloxyethyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltripropoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltriacetoxysilane, 3-methacryloxypropyl methyl dimethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane (GENIOSIL XL 10), vinyltri(2-methoxyethoxy)silane (GENIOSIL GF 58), and vinyltriacetoxysilane.

[0122] As organofunctional silanes, use is preferably made of 3-methacryloyloxypropyltrimethoxysilane (Dynasylan MEMO, Silquset A-174 NT), vinyltri(m)ethoxysilane (Dynasylan VTMO or VTEO, Silquest A-151 or A-171), methyltri(m)ethoxysilane (Dynasylan MTMS or MTES), beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (Silquest A-186), bis(triethoxysilyl)ethane (Silquest Y-9805), gamma-isocyanatopropyltrimethoxysilane (Silquest A-Link 35, GENIOSIL GF 40), methacryloyloxymethyltri(m)ethoxysilane (GENIOSIL XL 33, XL 36), (methacryloyloxymethyl)(m)ethyldimethoxysilane (GENIOSIL XL 32, XL 34), 3-(triethoxysilyl)propyl succinic anhydride (GENIOSIL GF 20), vinyltrimethoxysilane (GENIOSIL XL 10) and / or vinyltri(2-methoxyethoxy)silane (GENIOSIL GF 58).

[0123] However, it is also possible to apply further and / or additional organofunctional silanes to the coated PVD aluminum pigments of the present application.

[0124] It is furthermore possible to use, for example, aqueous prehydrolysates available from Evonik. These include, inter alia, aqueous aminosiloxanes (Dynasylan Hydrosil 1151), aqueous amino- / alkyl-functional siloxanes (Dynasylan Hydrosil 2627 or 2909), aqueous diaminofunctional siloxanes (Dynasylan Hydrosil 2776), aqueous epoxy-functional siloxanes (Dynasylan Hydrosil 2926), amino- / alkyl-functional oligosiloxanes (Dynasylan 1146), vinyl- / alkyl-functional oligosiloxanes (Dynasylan 6598), oligovinylsilanes (Dynasylan 6490) or oligo short-chain alkyl-functional silanes (Dynasylan 9896).

[0125] According to a further embodiment of the present application, the organo-chemically modified outer layer comprises a second silane without coupling groups.

[0126] In a further preferred embodiment, the silane without coupling groups is an alkylsilane. The alkylsilane preferably has the formula according to formula (I) mentioned above as network modifier:

[0127] R (4-z) Si(X) z (I)

[0128] For the alkylsilane as part of the organomodified outer layer, R is an unsubstituted, unbranched or branched alkyl chain having 1 to 24 C atoms, preferably 6 to 18 C atoms, and X is preferably an alkoxy group, most preferably a methoxy or ethoxy group.

[0129] At or on the surface of the PVD aluminum pigments coated according to the invention with layers a) and b), in addition to the silanes and silane mixtures mentioned above, further organochemical modifiers such as substituted or unsubstituted alkyls, polyethers, thioethers, siloxanes etc. and mixtures thereof can be arranged.

[0130] In a preferred embodiment, the organofunctional silane mixture comprises at least one amino-functional silane and at least one silane without functional binding groups. An amino functionality is a functional group capable of one or more chemical interactions with most groups present in the binder. This can involve covalent bonds, for example with isocyanate or carboxylate functions of the binder, hydrogen bonds, such as with OH or COOR functions, or ionic interactions. Amino functionality is therefore highly suitable for chemically binding coated PVD aluminum pigments to various binders.

[0131] The following compounds are preferably suitable for this purpose: 3-aminopropyltrimethoxysilane (Dynasylan AMMO; Silquest A-1110), 3-aminopropyltriethoxysilane (Dynasylan AMEO), [3-(2-aminoethyl)aminopropyl]trimethoxysilane (Dynasylan DAMO, Silquest A-1120), [3-(2-aminoethyl)aminopropyl]triethoxysilane, triaminofunctional trimethoxysilane (Silquest A-1130), bis(γ-trimethoxysilylpropyl)amine (Silquest A-1170), N-ethyl-γ-aminoisobutyltrimethoxysilane (Silquest A-Link 15), N-phenyl-γ-aminopropyltrimethoxysilane (Silquest Y-9669), 4-amino-3,3-dimethylbutyltrimethoxysilane (Silquest A-1637), N-cyclohexylaminomethylmethyldiethoxysilane (GENIOSIL XL 924), N-cyclohexylaminomethyltriethoxysilane (GENIOSIL XL 926), N-phenylaminomethyltrimethoxysilane (GENIOSIL XL973), and mixtures thereof.

[0132] By surface modification it is possible, for example, to change and / or set the hydrophilicity or hydrophobicity of the surface of the pigments. For example, by surface modification it is possible to change and / or set the leafing or non-leafing properties of the PVD aluminum pigments of the present application. Leafing means that the PVD aluminum pigments of the present application occupy a position at or close to the upper interface or surface of the application medium, for example a coating material or paint.

[0133] The surface modification agent can also have reactive chemical groups, for example acrylate, methacrylate, vinyl, isocyanate, cyano, epoxy, hydroxyl or amino groups or mixtures thereof. These chemically reactive groups are capable of chemically bonding, in particular forming covalent bonds, to the application medium or components of the application medium, for example the binder. By this it is possible to improve, for example, the chemical and / or physical properties of the cured varnish, paint or printing ink, such as the resistance to environmental influences, for example humidity, sunlight, UV light, etc. or the resistance to mechanical influences, for example scratching, etc.

[0134] The chemical reaction between the chemically reactive groups and the application medium or components of the application medium can be initiated, for example, by energy irradiation in the form of UV radiation and / or heat.

[0135] In a further embodiment, the PVD aluminum pigments coated with the layers (a) and (b) can be further coated thereon with an organic coating to provide stronger corrosion resistance stability. Such an organic coating is preferably made of acrylate and / or methacrylate.

[0136] In a further embodiment, silanes having functional groups comprising polymerizable unsaturated carbon-carbon bonds, such as methacrylate silanes, acrylate silanes or vinyl silanes, can be used as external chemical organic modification and an additional polymer consisting of methacrylate or acrylate monomers can be formed thereon. Such polymerization is described, for example, in DE 102011103882 A1 or EP 1953195 A1.

[0137] Preferred coating systems for PVD aluminum pigments:

[0138] According to one preferred embodiment of the present application, the PVD aluminum pigments are first coated with a silicon oxide-containing coating (a) and then provided with the metal oxide of layer (b).

[0139] The order of the two coatings (a) and (b) of this embodiment can be determined by XPS (X-ray photoelectron spectroscopy) in combination with sputter techniques.

[0140] According to this embodiment, a continuous silicon oxide containing coating, which is preferably a silicon dioxide coating, is applied directly to the uncoated or unstabilized PVD aluminum pigments. The continuous silicon oxide containing coating completely coats the PVD aluminum pigments. When the metal vapor is deposited on the substrate during the production of the PVD aluminum pigments, usually a release layer is applied to the substrate to facilitate the peeling off. Thus, although the PVD aluminum pigments are usually washed after peeling off from the substrate, residues of the release layer can still be present on the surface of the PVD aluminum pigments. When it is mentioned that a continuous silicon oxide containing coating is applied directly to the uncoated or unstabilized PVD aluminum pigments, this also includes that any remaining release coating can also be coated by the continuous silicon oxide containing coating (a).

[0141] According to a preferred embodiment of the present application, the surface of the platelet-shaped PVD aluminum pigments is not separately treated or coated with an etch resist, for example with H2O2, an organic phosphorous compound, such as a phosphoric acid ester, a substituted phosphoric acid derivative, an organic phosphonic acid, phosphoric acid, boric acid, an etch resist pigment, chromic acid, and the like.

[0142] That is, the starting platelet-shaped PVD aluminum pigments are preferably uncoated or unstabilized PVD aluminum pigments, which are directly coated with a continuous silicon oxide containing coating, which coats the uncoated or unstabilized PVD aluminum pigments.

[0143] According to another preferred embodiment, layer (b) is a discontinuous layer comprising or consisting of a metal oxide or a continuous layer of a metal oxide, which is applied directly to coating (a), wherein the metal oxide is selected from the group consisting of molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate, tungsten oxide, tungsten hydroxide, tungsten oxide hydrate, and mixtures thereof.

[0144] Thus, according to a preferred embodiment of the present application, the uncoated or unstabilized platelet-shaped PVD aluminum pigments, preferably PVD aluminum pigments, are directly coated with coating (a), which means that the uncoated or unstabilized PVD aluminum pigments are directly coated with a continuous silicon oxide containing coating. The continuous silicon oxide containing coating is preferably a silicon dioxide coating. Furthermore, it is preferred that layer (b) is applied directly to coating (a), i.e. there is no intermediate layer between coating (a) and layer (b).

[0145] Preferably, the platelet-shaped PVD aluminum pigments, which are preferably uncoated or unstabilized platelet-shaped PVD aluminum pigments, are directly coated with a continuous silicon oxide containing coating (a), which directly coats the PVD aluminum pigments, and wherein the metal oxide layer (b) comprises or consists of tungsten oxide, tungsten hydroxide, tungsten oxide hydrate, or mixtures thereof.

[0146] More preferably, the platelet-shaped PVD aluminum pigments, which are preferably uncoated or unstabilized platelet-shaped PVD aluminum pigments, are directly coated with the continuous silica-containing coating layer (a) which directly coats the PVD aluminum pigments and wherein the metal oxide layer (b) comprises or consists of molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate or mixtures thereof.

[0147] The fact that both of these particular coating embodiments also lead to an enhanced corrosion stability is completely unexpected. In EP 1 619 222 A1 only the molybdenum oxide first coating and the subsequent silica coating are reported to enhance the gassing stability of conventional aluminum pigments.

[0148] This result is particularly surprising since the metal oxide of layer (b) does not directly contact the aluminum substrate which was originally thought to be necessary for any electrochemical interaction.

[0149] According to another preferred embodiment, layer (b) is a discontinuous layer comprising or consisting of a metal oxide, wherein the metal oxide is selected from the group consisting of molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate, tungsten oxide, tungsten hydroxide, tungsten oxide hydrate and mixtures thereof.

[0150] According to another preferred embodiment, layer (b) is a discontinuous layer comprising or consisting of a metal oxide selected from the group consisting of molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate and mixtures thereof.

[0151] Surprisingly, it is not necessary to apply a continuous layer of a metal oxide as layer (b).

[0152] A continuous layer (b) of a metal oxide means that this layer substantially completely, in particular completely, coats the continuous silica-containing coating layer (a).

[0153] A discontinuous layer (b) of a metal oxide comprises or consists of islands, which comprise or consist of the respective metal oxide, so that layer (b) only partially coats the continuous silica-containing coating layer (a).

[0154] According to another embodiment of the present application, the continuous silica-containing coating layer is directly applied to and physically contacts the platelet-shaped PVD aluminum pigments, preferably uncoated or unstabilized platelet-shaped PVD aluminum pigments.

[0155] According to another embodiment of the present application, layer (b) is directly applied to and physically contacts coating layer (a) and wherein layer (b) preferably comprises or consists of islands, which comprise or consist of the respective metal oxide.

[0156] In a further preferred embodiment, the PVD aluminum pigment (which is preferably an uncoated or unstabilized PVD aluminum pigment) is directly coated with a continuous silicon oxide-containing coating (a), which directly covers the PVD aluminum pigment, and wherein the layer (b) is a discontinuous or continuous layer comprising or consisting of tungsten oxide, tungsten hydroxide, hydrated tungsten oxide or a mixture thereof or molybdenum oxide, molybdenum hydroxide, hydrated molybdenum oxide or a mixture thereof. The thickness of the continuous silicon oxide-containing coating (a) is from 25 to 45 nm.

[0157] According to another embodiment of the invention, a continuous silicon oxide-containing coating is applied directly to and in physical contact with a flake-shaped PVD aluminum pigment, preferably an uncoated or unstabilized flake-shaped PVD aluminum pigment, wherein layer (b) is applied directly to and in physical contact with coating (a), and wherein layer (b) preferably comprises or consists of islands comprising or consisting of the respective metal oxide, and wherein the external organic-chemical modification is attached directly and in physical contact to the surface of this embodiment. Due to the discontinuity of layer (b), the external organic-chemical modification is also directly attached to coating (a) (if not coated by layer (b)) and layer (b).

[0158] In particular, if the organo-chemically modified outer layer comprises at least a first silane having coupling groups and optionally a silane without coupling groups, the silanol groups of these silanes can condense directly with the silanol groups of coating (a).

[0159] Although silanes with or without coupling groups can also react with molybdenum oxide, molybdenum hydroxide, or hydrated molybdenum oxide, or with tungsten oxide, tungsten hydroxide, or hydrated tungsten oxide, the chemical reaction between the silanol groups of the silane and the silanol groups of the subsequent silicon oxide-containing coating is chemically preferred. Therefore, silanes with or without coupling groups can be reliably bonded to the surface of coating (a) of the PVD aluminum pigments of the present invention. If layer b) follows layer a), the silane can also at least partially coat layer b).

[0160] According to a further preferred embodiment of the invention, the PVD aluminum pigments are first provided with a metal oxide layer (b) and subsequently coated successively with the silicon oxide-containing coating (a).

[0161] The sequence of the two coatings (a) and (b) of this embodiment can be determined by XPS (X-ray Photoelectron Spectroscopy) combined with sputtering technology.

[0162] In a preferred embodiment, the flake-shaped PVD aluminum pigment (which is preferably an uncoated or unstabilized flake-shaped PVD aluminum pigment) is directly coated with a layer (b) comprising or consisting of tungsten oxide, tungsten hydroxide, hydrated tungsten oxide or a mixture thereof, and wherein the continuous silicon oxide-containing coating (a) directly envelops the PVD aluminum pigment coated with the first layer (b).

[0163] In a further preferred embodiment, the flaky PVD aluminum pigments, which are preferably uncoated or unstabilized flaky PVD aluminum pigments, are directly coated with a metal oxide layer (b) consisting of or comprising molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate or mixtures thereof, and wherein the continuous silicon oxide containing coating layer (a) directly coats the PVD aluminum pigments coated with the first layer (b).

[0164] According to another embodiment of the present application, the layer (b) is directly applied to and physically contacts the flaky PVD aluminum pigments, preferably uncoated or unstabilized flaky PVD aluminum pigments, and wherein the layer (b) preferably comprises or consists of islands comprising or consisting of a respective metal oxide.

[0165] According to another embodiment of the present application, if the layer (b) is a continuous layer coating the PVD aluminum pigments, preferably uncoated or unstabilized flaky PVD aluminum pigments, the continuous silicon oxide containing coating layer (a) is directly applied to and physically contacts the layer (b).

[0166] According to another embodiment of the present application, if the layer (b) is a discontinuous layer only partially coating the flaky PVD aluminum pigments, preferably uncoated or unstabilized flaky PVD aluminum pigments, the continuous silicon oxide containing coating layer (a) is directly applied to and physically contacts the layer (b) and the flaky PVD aluminum pigments.

[0167] According to another embodiment of the present application, the layer (b) is directly applied to and physically contacts the flaky PVD aluminum pigments, preferably unstabilized flaky PVD aluminum pigments, wherein the coating layer (a) is directly applied to and physically contacts the layer (b), and wherein the layer (b) preferably comprises or consists of islands comprising or consisting of a respective metal oxide, and wherein an external organic-chemical modification is directly and physically attached on the surface of this embodiment. Due to the discontinuity of the layer (b), the coating layer (a) is also in direct physical contact with the flaky PVD aluminum pigments, preferably unstabilized flaky PVD aluminum pigments, if the flaky PVD aluminum pigments are not directly coated with the layer (b).

[0168] In a further preferred embodiment, the PVD aluminum pigments, which are preferably uncoated or unstabilized PVD aluminum pigments, are directly coated with a layer (b) which is a discontinuous or continuous layer consisting of or comprising molybdenum oxide, molybdenum hydroxide, molybdenum oxide hydrate or mixtures thereof or tungsten oxide, tungsten hydroxide, tungsten oxide hydrate or mixtures thereof, and wherein the continuous silicon oxide containing coating layer (a) directly coats the PVD aluminum pigments coated with the first layer (b), and the thickness of the continuous silicon oxide containing coating layer (a) is from 25 to 45 nm.

[0169] In particular, if the organo-chemically modified outer layer comprises at least a first silane with coupling groups and optionally a silane without coupling groups, the silanol groups of these silanes can directly condense with the reactive groups, such as hydroxyl or silanol groups, of layer (b).

[0170] Surprisingly, the protective encapsulation of the flaky PVD aluminum pigments is also improved or even superior when layer (b) is applied first and the coating (a) is applied after layer (b).

[0171] The protective encapsulation is even improved if layer (b) is applied directly as a discontinuous layer of metal oxide on the flaky PVD aluminum pigments, preferably on unstabilized flaky PVD aluminum pigments.

[0172] In a further embodiment, layer (b) can be applied both before and after the PVD aluminum pigments are coated with the silicon oxide-containing coating (a).

[0173] Manufacturing process:

[0174] The present application also relates to a process for manufacturing flaky PVD aluminum pigments with a protective coating as described in the above sections.

[0175] The protective encapsulation, wherein the process comprises the following successive steps:

[0176] (a1 ) contacting a soluble metal compound dissolved in a solvent and the flaky PVD aluminum pigments to obtain flaky PVD aluminum pigments with at least a metal oxide layer, wherein the metal of the soluble metal compound is selected from the group consisting of molybdenum, tungsten and mixtures thereof,

[0177] (b1 ) contacting a soluble metal compound dissolved in a solvent and the flaky PVD aluminum pigments obtained in step (a1 ) to envelope the pigments of step (a1 ) with at least a metal oxide layer, wherein the metal of the soluble metal compound is selected from the group consisting of molybdenum, tungsten and mixtures thereof, to obtain flaky PVD pigments with a protective encapsulation,

[0178] (c1 ) optionally forming an organo-chemically modified outer layer with at least one organofunctional silane;

[0179] or

[0180] (a2) contacting a soluble metal compound dissolved in a solvent and the flaky PVD aluminum pigments to obtain flaky PVD aluminum pigments with at least a metal oxide layer, wherein the metal of the soluble metal compound is selected from the group consisting of molybdenum, tungsten and mixtures thereof,

[0181] (b2) contacting the soluble alcohol silane dissolved in a solvent with the flaky PVD aluminum pigment obtained in step (a2) to obtain by a sol-gel process a flaky PVD aluminum pigment coated with a substantially continuous silica-containing coating to obtain a flaky PVD pigment having a protective envelope and

[0182] (c2) optionally forming an organic-chemically modified outer layer with at least one organofunctional silane.

[0183] The application of layer (b) can be controlled by the amount and / or dilution of the soluble metal compound used to generate the metal oxide, metal hydroxide and / or hydrous metal oxide of layer (b).

[0184] The two successive steps (al) and (bl) or (a2) and (b2) can be performed in a one-pot synthesis route or in a two-pot synthesis, wherein a step is included to separate the PVD aluminum pigment coated with the first coating from step (al) or step (a2) from the solvent and to re-disperse it in a solvent prior to the second coating step. In a two-step synthesis, the solvents used for the successive coating steps can be the same or can be different.

[0185] The solvent used to dissolve the soluble metal compound can be water or an organic solvent or a mixture thereof. Preferably, water is used as solvent. Since the amount of water used can also influence the sol-gel process used to form the coating (a), the concentration of the soluble metal compound should be high to use the lowest amount of water.

[0186] In a preferred embodiment, the soluble molybdenum compound is prepared by first dissolving molybdenum oxide or elemental molybdenum in a hydrogen oxide solution to prepare a solution of peroxomolybdic acid (see for example Solid States Ionics, pages 507-512, 1992). Likewise, the preferred soluble tungsten compound is prepared by first dissolving tungsten oxide or elemental tungsten in a hydrogen oxide solution to prepare a solution of peroxotungstic acid.

[0187] The silica of layer (a) is preferably applied using a sol-gel process.

[0188] Such a sol-gel process starts with an alkoxysilane which reacts under catalysis with a small amount of water to form silanol groups and alcohol. The PVD aluminum pigment is dispersed in an organic solvent (e.g. an alcoholic phase) and then the alkoxysilane, water and at least one basic or acidic catalyst are added with heat supply. The alkoxysilane can also be added to the PVD aluminum pigment dispersed in an organic solvent.

[0189] The silanol groups condense with the elimination of water to form a Si-O-Si network. This Si-O-Si network is subsequently precipitated in the form of a gel onto the metal effect pigments, so that they are encapsulated or coated by silicon oxide, preferably SiO2.

[0190] During the reaction, a dense network of silicon dioxide is formed on the surface of the pigments and completely coats the pigment particles. In addition, the silicon dioxide coating newly precipitated onto the surface of the pigments can be subjected to a further surface modification in particular. For example, a silane having at least one non-hydrolysable substituent, such as an alkylsilane, can be added after the application of the SiO2coating and can be hydrolysed in situ, the silane having at least one non-hydrolysable substituent being firmly anchored to the silicon dioxide layer on the surface of the pigments by a further condensation reaction.

[0191] The alkoxysilane used according to the application preferably comprises di-, tri- and / or tetraalkoxysilanes. Tetraalkoxysilanes are particularly preferred. When tetraalkoxysilanes are used, hydrolysis leads to the formation of four silanol groups, which, on condensation, result in a highly cross-linked, i.e. a silicon oxide coating, preferably a SiO2coating, having a good barrier effect. When di- or trialkoxysilanes are used, hydrolysis leads to the formation of two or three silanol groups, respectively, which are able to condense to form a Si-O-Si network. The use of di- or trialkoxysilanes enables the introduction of organic groups, such as alkyl or aryl groups or polymers, into the silicon oxide coating to form inorganic-organic hybrid layers. Di- or trialkoxysilanes can also be referred to as organosiloxanes.

[0192] The alkoxysilane according to the application is any monomeric or polymeric silicon compound having at least one alkoxy group. The tetraalkoxysilanes used advantageously comprise tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and condensates thereof, or mixtures of these.

[0193] It is particularly advantageous to use tetraethoxysilane and / or oligomers of tetraethoxysilane as tetraalkoxysilane.

[0194] A great advantage when using alkoxysilanes, preferably tetraalkoxysilanes, is that no salts are produced. This is advantageous both in terms of the environment and in terms of possible agglomeration processes during the sol-gel reaction, since salts interfere with the electrostatic stabilisation of the pigment particles.

[0195] The sol-gel reaction is generally catalysed by amines, such as ammonia or organic amines.

[0196] The amine can be a primary, secondary or tertiary amine.

[0197] In a preferred embodiment, the amine comprises 1 to 8 C atoms, more preferably 1 to 6, particularly preferably 1 to 5 C atoms.

[0198] Amines having more than 8 C atoms can be spatially too demanding to be used as effective catalysts.

[0199] According to a preferred embodiment of the present application, the amine is selected from dimethylethanolamine (DMEA), monoethanolamine, diethanolamine, triethanolamine, ethylenediamine (EDA), t-butylamine, mono-methylamine, di-methylamine, tri-methylamine, mono-ethylamine, di-ethylamine, tri-ethylamine, pyridine or derivatives thereof, aniline or derivatives thereof, choline or derivatives thereof, urea or derivatives thereof, hydrazine or derivatives thereof or mixtures thereof.

[0200] According to a most preferred embodiment of the present application, the amine is selected from ethylenediamine, mono-ethylamine, di-ethylamine, mono-methylamine, di-methylamine, tri-methylamine, tri-ethylamine or mixtures thereof.

[0201] The organic solvent used is preferably an alcohol, a diol, an ester, a ketone and mixtures of these solvents. The use of an alcohol or a diol or mixtures thereof is particularly preferred, the use of an alcohol being especially preferred.

[0202] As an alcohol, it is advantageous to use methanol, ethanol, isopropanol, n-propanol, t-butanol, n-butanol, isobutanol, pentanol, hexanol or mixtures thereof.

[0203] The use of ethanol and / or isopropanol is particularly preferred.

[0204] As a diol, it is advantageous to use butyl glycol, propyl glycol, ethylene glycol or mixtures thereof.

[0205] The reaction mixture present is preferably reacted at a temperature in the range from 20°C to the boiling point of the respective solvent or solvent mixture. The reaction temperature is particularly preferably in the range from 50°C to a temperature which is preferably 5°C below the boiling point of the respective solvent or solvent mixture. The preferred reaction temperature range is a temperature range from 70°C to 82°C.

[0206] The reaction time is preferably in the range from 2 to 20 hours, more preferably 3 to 8 hours.

[0207] The silicon oxide coating (a), preferably a silicon dioxide layer, can be applied under the conditions disclosed in DE 10 2010 007 147 A1.

[0208] The coating (a) consisting of a hybrid coating of silicon oxide, preferably silicon dioxide, and at least one organic oligomer and / or at least one organic polymer can be applied under the conditions disclosed in EP 1812519 B1 or WO 2016 / 120015 A1.

[0209] The organic-chemically modified layer can be applied under the conditions disclosed in DE 10 2013 113 885 A1.

[0210] The formation of layer (b) is preferably carried out by first treating the molybdenum oxide or tungsten oxide with hydrogen peroxide in an aqueous solution to dissolve the metal oxide. Here a mixture of several metal compounds is produced, including peroxide complexes.

[0211] The solution is added to PVD aluminum flakes dispersed in the organic solvent used for the sol-gel process to form layer (a). The addition can be carried out before or after the formation of the silicon oxide-containing layer (a) which coats the PVD aluminum flakes. The precipitation on the surface of the pigments can be achieved in the presence of a base or acid which is also used in the sol-gel reaction for the formation of layer (a).

[0212] The entire coating process to form layers (a) and (b) can be carried out as a one-pot synthesis. In other embodiments, a two-pot synthesis route can be used by first coating layer (a) or (b), then separating the coated PVD aluminum flakes from the solvent, dispersing them in a new solvent and coating with the second coating layer (b) or (a).

[0213] Use and formulations:

[0214] The present application also relates to the use of the flaky PVD aluminum pigments according to any of claims 1 to 13 in a formulation, preferably in an aqueous formulation.

[0215] The present application also relates to a formulation, wherein the formulation contains the flaky PVD aluminum pigments according to any of claims 1 to 13.

[0216] The formulation can be selected from the group consisting of a coating system, a paint, a lacquer, a printing ink, a powder paint, an architectural coating composition, a plastic, a security printing ink, a ceramic and a cosmetic.

[0217] Especially preferred is a lacquer for automotive interior parts. An aqueous paint or lacquer is also preferred.

[0218] According to a preferred embodiment, the flaky PVD aluminum pigments, preferably PVD aluminum pigments, are used in an aqueous formulation, such as an aqueous coating system, an aqueous paint, an aqueous printing ink, an aqueous security printing ink or an aqueous cosmetic.

[0219] Examples

[0220] The following examples are given to illustrate the present application only. The examples should not be construed as limiting the scope of the present application. The scope of the present application is only defined by the appended claims.

[0221] A Preparation

[0222] Experiments were carried out according to the following formulations. In Table 1 it is indicated which example is based on which formulation. The amount of molybdenum or tungsten acid can be described in Table 1.

[0223] 1.1 Preparation of the peroxomolybdate solution:

[0224] 5 g of powdered molybdic acid (hydrated molybdenum(VI) oxide, M0O3*H2O) was dissolved in 15 g of a 30% aqueous H2O2 solution at room temperature under stirring until a clear yellow solution was formed.

[0225] 1.2 Preparation of the peroxotungstic acid solution (according to P.C. Murrau, Anal. Chem., 1961, 33(8), pp. 1125-1126):

[0226] 0.5 g of metallic tungsten was dissolved in 4.5 g of a 30% aqueous H2O2 solution at room temperature under stirring until a clear yellow solution was formed.

[0227] Example A1 (invention):

[0228] 150 g of a commercially available PVD aluminum pigment (Metalure W-52012 IL; Eckart GmbH; containing 30 g of aluminum and residues of polyvinylpyrrolidone vinyl acetate used as a release coating) were dispersed in 450 g of isopropanol in a chemical reactor under stirring.

[0229] The specified amount (see Table 1) of the peroxomolybdic acid solution prepared according to section 1.1 was added and stirred for 30 minutes. The dispersion was heated to 70°C and stirred for another 25 minutes. Then 18.8 g of TEOS (tetraethoxysilane) and 18.8 g of water were added and stirred for 1 hour. Then 4.5 g of a 25% by weight aqueous ammonia solution were dosed into the reaction mixture over 1 hour. After a reaction period of 7 hours, 1.2 g of Dynasylan Octeo and subsequently 0.4 g of Dynasylan AMMO were added. The reaction mixture was stirred for another 120 minutes. The dispersion was cooled to room temperature and filtered using a Buchner funnel to isolate the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10% by weight.

[0230] Example A2 (invention):

[0231] In a jacketed 1 -liter glass reactor 150 g of a commercial PVD aluminum pigment (Metalure W-52012 IL; contains 30 g of aluminum and residues of a release coating) were dispersed under stirring in 365 g of isopropanol. The dispersion was heated to 70°C and stirred for another 25 minutes. Then 18.8 g of TEOS and 18.8 g of water were added and the dispersion was stirred for 1 hour. Then 4.5 g of a 25 wt.-% ammonia solution were dosed into the reaction mixture over 1 hour. After a reaction period of 7 hours the specified amount (see Table 1, column 5) of a peroxomolybdate solution prepared according to section 1.1 was added and stirred for 30 minutes. Then 1.2 g of Dynasylan Octeo and subsequently 0.4 g of Dynasylan AMMO were added. The reaction mixture was stirred for another 120 minutes. The dispersion was cooled to room temperature and filtered using a Buchner funnel to isolate the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

[0232] Example A3 (inventive):

[0233] Analogous to Example A1, except that a peroxotungstate solution prepared according to section 1.2 was used instead of the peroxomolybdate solution. The amounts are specified in Table 1.

[0234] Example A4 (inventive):

[0235] Analogous to Example A2, except that a peroxotungstate solution prepared according to section 1.2 was used instead of the peroxomolybdate solution. The amounts are specified in Table 1.

[0236] Comparative Example 2 (no treatment with peroxomolybdate or peroxotungstate solution):

[0237] In a jacketed 1 -liter glass reactor 150 g of a commercial PVD aluminum pigment (Metalure W-52012 IL; contains 30 g of aluminum and residues of a release coating) were dispersed under stirring in 365 g of isopropanol. The dispersion was heated to 70°C and stirred for another 45 minutes. Then 18.8 g of TEOS and 18.8 g of water were added and stirred for 1 hour. Then 4.5 g of a 25 wt.-% ammonia solution were dosed into the reaction mixture over 1 hour. After a reaction period of 5 hours 1.2 g of Dynasylan Octeo and subsequently 0.4 g of Dynasylan AMMO were added. The reaction mixture was stirred for another 120 minutes. The dispersion was cooled to room temperature and filtered using a Buchner funnel to isolate the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

[0238] Example B1 (inventive):

[0239] A commercially available PVD aluminum pigment dispersion (Metalure A-41010 BG; Eckart GmbH; containing 30 g of aluminum and residues of polyacrylates used as release coating) was dispersed under stirring in 300 g of isopropanol.

[0240] The specified amount (see Table 1) of the peroxomolybdate solution prepared according to section 1.1 was added and stirred for 30 minutes. The dispersion was heated to 70°C and stirred for another 45 minutes. 21.4 g of TEOS and 21.4 g of water were added and stirred for another 1 hour.

[0241] Then 6 g of a 25 wt.-% ammonia solution were dosed into the reaction mixture over a period of 1 hour. After a reaction period of 7 hours, 5 g of Hydrosil 2909 were added. The reaction mixture was stirred for another 2 hours, then cooled to room temperature and filtered using a Buchner funnel to isolate the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

[0242] Example B2 (invention):

[0243] A commercially available PVD aluminum pigment dispersion (Metalure A-41010 BG; Eckart GmbH; containing 30 g of aluminum and residues of polyacrylates used as release coating) was dispersed under stirring in 300 g of isopropanol.

[0244] 21.4 g of TEOS and 21.4 g of water were added and stirred for another 1 hour. Then 4.5 g of a 25 wt.-% ammonia solution were dosed into the reaction mixture over a period of 1 hour. After a reaction period of 5 hours, the specified amount (see Table 1, column 5) of the peroxomolybdate solution prepared according to 1.1 was added and stirred for 30 minutes. Then 5 g of Hydrosil 2776 were added. The reaction mixture was stirred for another 2 hours, then cooled to room temperature and filtered using a Buchner funnel to isolate the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

[0245] Example B3 (invention):

[0246] Similar to Example B1, except that a peroxotungstate solution prepared according to section 1.2 was used instead of the peroxomolybdate solution. The amounts are specified in Table 1.

[0247] Example B4 (invention):

[0248] Similar to Example B2, except that a peroxotungstate solution prepared according to section 1.2 was used instead of the peroxomolybdate solution. The amounts are specified in Table 1.

[0249] Comparative Example 1 (no treatment with peroxomolybdate or peroxotungstate solution):

[0250] 300 g of a commercially available PVD aluminium pigment dispersion (Metalure A-41010 BG; containing 30 g of aluminium and residues of polyacrylate used as release coating) was dispersed under stirring in 300 g of isopropanol.

[0251] 21.4 g of TEOS and 21.4 g of water were added and stirring was continued for another 1 h. Then 5 g of a 25 wt.-% ammonia solution were dosed into the reaction mixture over a period of 1 h. After a reaction period of 5 h, 5 g of Hydrosil 2776 were added. The reaction mixture was stirred for another 1 h, then cooled to room temperature and filtered using a Buchner funnel to isolate the coated PVD pigment. The pigment was finally combined with isopropanol to yield a pigment dispersion with a pigment content of 10 wt.-%.

[0252] B Test method:

[0253] The hydrolytic stability of the samples was tested according to the Volkswagen test TL 226, § 3.12.1 for coatings of automotive interiors according to the following method:

[0254] A dispersion of 10 g of the coated PVD pigment was dispersed in 2.5 g of butyl glycol with the aid of 0.5 g of a dispersing additive. 70 g of an aqueous acrylate binder system were added and the pH was adjusted to the range of 7.6 to 8.0. This basecoat should have a viscosity in the range of 80 to 120 mPas, measured with a Brookfield viscosimeter at a shear rate of 1000 1 / s. If necessary, the viscosity can be adjusted by further addition of water. A plastic substrate (ABS / PC Blend) was coated with this basecoat using a Langguth (Erichsen GmbH, model 480) under the following spray conditions:

[0255] pistol conditions: 1.1.0 / 4 passes

[0256] Drying time: 10 min at room temperature and 15 min at 80 °C

[0257] The thickness of this basecoat was about 2 to 4 pm. On this basecoat a clearcoat was sprayed in two passes with pistol parameters 2.1.2 and dried for 30 min at 80 °C.

[0258] The coated substrate was stored for 48 h at 80 °C.

[0259] The coated substrates were then subjected to 90°C and >96% humidity in a desiccator for 72 hours. The treated substrates were dried and the L*a*b* coordinates were measured at 5 angles (cis configuration) of i = 15°, 25°, 45°, 75° and 110° in comparison to the untreated substrate (Byk-Mac, Byk Instruments, Geretsried, Germany). The ΔΕ* at these angles was obtained and averaged according to the following equation:

[0260]

[0261] where i is the angle of measurement and ΔE i , Δa i and Δb i are the coordinate differences between the treated and untreated substrate at a specific angle i.

[0262] At ΔE* below 2.0, it is very well by test. At ΔE* from 2 to 5, it is by test. ΔE* above 5 to 15 is partially by in the sense that the pigments can be incorporated in certain 2-coat system coatings in applications that show less high criticality.

[0263] If ΔE* is above 15, it is not by test.

[0264] Method to determine the content of Mo or W:

[0265] 200 mg of the coated pigments were dissolved in a mixture of 10 ml nitric acid (65%) and 2 ml hydrofluoric acid (40%) diluted with about 10 ml water, which was heated below their boiling point. The concentration of molybdenum or tungsten was measured with emission spectroscopy (ICP-OES). Two times per sample were prepared and five single measurements were taken and averaged. All preparations and measurements were performed using a housing material that is compatible with hydrofluoric acid.

[0266] In addition, the concentration of the element silicon was measured using a scandium internal standard. The concentration was calculated as SiO2.

[0267] Table 1 : Summary of experimental parameters and results of the hydrolysis test for the examples and comparative examples

[0268]

[0269]

[0270] Conclusion:

[0271] All of the examples according to the invention exhibited significantly improved stability in the hydrolysis test compared to the respective comparative examples 1 and 2, which did not pass the hydrolysis test. The Mo-oxide / SiO2-coated systems generally had high stability (Examples 1 to 9). The order of the metal oxide coatings did not appear to have a significant effect.

[0272] The W-oxide / SiO2 coating pair has a thickness h of approximately 40 nm as determined by SEM. 50 The W-52012 PVD-Al-pigment showed excellent stability (Examples 10 to 13). The W-oxide / SiO2 coating was slightly better than the SiO2 / W-oxide coating. For the thinner PVD-Al-pigment (A-41010; thickness h measured by SEM) which showed a higher specific surface area, the W-oxide / SiO2 coating was slightly better than the SiO2 / W-oxide coating. 50 (The tungsten content is approximately 32 nm, so more tungsten material must be selected to achieve acceptable stability. At lower amounts, the test is only partially passed. The hydrolysis test results for those examples with a first W-oxide layer followed by a silicon dioxide coating are slightly better than those with the reverse coating order.

Claims

1. A flake-shaped PVD aluminum pigment having a protective coating, wherein the protective coating comprises: a) a continuous, enveloping silicon oxide-containing coating (a), wherein the silicon oxide-containing coating comprises at least 60 wt. % silicon oxide, based on the total weight of the silicon oxide-containing coating, and b) a layer (b) of a metal oxide, wherein the metal oxide is selected from molybdenum oxide, molybdenum hydroxide, hydrated molybdenum oxide, tungsten oxide, tungsten hydroxide, hydrated tungsten oxide, and mixtures thereof, and c) optionally, organo-chemically modifying the outer layer, wherein the silicon oxide-containing coating (a) has an average thickness in the range of 15 to 60 nm, wherein the PVD aluminum pigment has an aluminum content of at least 98% by weight, based on the total weight of the uncoated PVD aluminum pigment, wherein the PVD aluminum pigment has a median diameter d in the range of 6 to 18 μm 50 and a median thickness h ranging from 16 to 50 nm 50 , in: The silicon oxide-containing coating (a) consists of silicon oxide; or The silicon oxide-containing coating (a) is composed of a mixture of silicon oxide and an organofunctional silane serving as a network modifier of the formula R (4-z) Si(X) z (I) wherein z is an integer from 1 to 3, R is an unsubstituted, unbranched or branched alkyl chain having 1 to 24 C atoms or an aryl group having 6 to 18 C atoms or an arylalkyl group having 7 to 25 C atoms or a mixture thereof, and X is a halogen group and / or an alkoxy group.

2. The flake-shaped PVD aluminum pigment with a protective coating according to claim 1, characterized in that The amount of the metal oxides is 0.01 to 0.4% by weight for Mo and 0.01 to 0.8% by weight for W, calculated in each case as elemental molybdenum and / or tungsten and based on the weight of the uncoated PVD aluminum pigment.

3. The flake-shaped PVD aluminum pigment with a protective coating according to claim 1 or 2, characterized in that The silicon oxide-containing coating (a) amounts to 8% to 25% by weight, based on the weight of the uncoated PVD aluminum pigment.

4. The flake-shaped PVD aluminum pigment with a protective coating according to any one of claims 1 to 3, characterized in that The silicon oxide-containing coating (a) is composed of silicon dioxide.

5. The platelet-shaped PVD aluminum pigment having a protective coating according to any one of claims 1 to 4, wherein the silicon oxide is silicon dioxide.

6. The flake-shaped PVD aluminum pigment with a protective coating according to any one of claims 1 to 5, characterized in that The organo-chemically modified outer layer comprises at least one organofunctional silane.

7. The PVD aluminum pigment with a protective coating according to any one of claims 1 to 6, characterized in that The PVD aluminum pigments are first coated with a silicon oxide-containing coating (a) and then provided with a layer of the metal oxide (b).

8. The flake-shaped PVD aluminum pigment with a protective coating according to any one of claims 1 to 7, characterized in that The PVD aluminum pigment is first provided with a layer of the metal oxide (b) and subsequently coated with a silicon oxide-containing coating (a).

9. Use of the platelet-shaped PVD aluminum pigment according to any one of claims 1 to 8 in a formulation, in particular in an aqueous formulation.

10. A formulation, characterized in that The formulation contains the flake-shaped PVD aluminum pigment according to any one of claims 1 to 8.

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