Weather-resistant nacreous pigment

Abstract

Provide a weather-resistant pearlescent pigment that passes the enhanced weather resistance test procedure, without significant change in the interference color and without significant gloss degradation compared to the initial pearlescent pigment without top coating. 【Solution】A weather-resistant pearlescent pigment having a basic pearlescent luster with an interference color, comprising a transparent small plate-shaped substrate and at least one metal oxide layer with a refractive index exceeding 1.8, and having a weather-resistant top coating with at least one metal oxide and an organic functional surface modification on top of this basic pearlescent pigment. (a) For the basic pearlescent pigment, the weather-resistant top coating consists of a rare earth metal M from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof 1 of a first metal oxide, and (b) for the basic pearlescent pigment having a colored interference color or a silver interference color, the weather-resistant top coating contains a rare earth metal M from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof 1 of a first metal oxide, and a second metal oxide from a second metal M2 is selected from the group consisting of Si, Al, Zn, Mg, Zr, Sn, and mixtures or combinations thereof. In each case of (a) or (b), the organic functional surface modification includes an organic functional silane or a water-based precondensed organic functional silane.

Description

Technical Field

[0001] The present invention relates to weather-resistant nacreous pigments that have no gloss loss in tests with enhanced weather resistance (weather stability) and no substantial color change due to their top coatings.

Background Art

[0002] Nacreous pigments containing titanium dioxide in the top layer or composed of particulate TiO2 have a specific photocatalytic activity. In this case, when UV light acts on the nacreous pigment in the presence of water and oxygen, the UV activity of the nacreous pigment can induce accelerated decomposition of organic compounds, such as the binder matrix. Even the UV portion present in sunlight can cause this reaction, i.e., it is necessary to use particularly stabilized nacreous pigments for applications such as automotive finishes that are directly exposed to the weather. To counteract this effect, which is harmful for external applications, various protective coatings can be applied to the nacreous pigments to reduce their photoactivity.

[0003] EP0141174 describes improved weather-resistant nacreous pigments having a protective coating consisting essentially of a rare earth metal compound specified as cerium oxide and polysiloxane. Further, the application of the protective coating carried out in an aqueous suspension can also contain zinc salts and / or aluminum salts or silicates. The polysiloxane is coated together with a silicate or alumina coating.

[0004] EP0342533 discloses zirconium oxide-coated pigments to which a layer consisting of a hydrated metal oxide of cobalt, manganese or cerium can be applied. The pigments thus treated are said to be very suitable for use in non-aqueous coating systems, but according to EP632109, they remain inappropriate for water-thinnable coating materials as they form microblisters in the coating film.

[0005] According to the teachings of EP0632109, a three-layer protective layer is applied to a small plate-shaped substrate coated with a metal oxide. In the first step, SiO2 is applied, in the second step, a hydroxide or oxide hydrate of cerium, aluminum or zirconium is applied, and in the third step, at least one hydroxide or oxide hydrate of cerium, aluminum or zirconium, and also an organic coupling reagent is applied. Further, the coupling reagent must be hydrolyzed before binding to the pigment surface, and according to the teachings of EP0888410B1, only a maximum of 60% of the added coupling reagent can bind to the pigment surface.

[0006] EP0888410B1 discloses a modified nacreous pigment based on a small plate-shaped substrate coated with a metal oxide. According to the teachings of EP0888410B1, the top layer is composed of an oxide mixture or mixed oxide of silica, at least two oxides of alumina, cerium oxide, titanium oxide or zirconium oxide, and an aqueous oligomeric silane system.

[0007] EP0649886 provides nacreous pigments having a titanium dioxide or iron oxide coating, which are coated with a combination of cerium and aluminum oxide hydrate in an aqueous phase and then dried.

[0008] US2011 / 0118384A1 discloses a weather-resistant nacreous pigment having a protective layer from various metal oxides and further an acrylate copolymer.

[0009] According to the teachings of European Patent Application Publication No. 1203795, the nacreous pigment can include a layered structure. In the first layer, it contains a hydrated oxide of silicon or aluminum. In the subsequent second layer, it contains a hydrated oxide of silicon, aluminum, zirconium, or cerium, and the composition of the first layer is different from that of the second layer. This nacreous pigment further includes a third layer of at least one organic hydrophobic coupling reagent, and the organic hydrophobic coupling reagent does not react with, for example, the binder of the coating system.

[0010] EP1682622A1 discloses a weather-resistant nacreous pigment having a top coating including a first layer of cerium oxide, a subsequent SiO2 layer, and an organic surface modification.

[0011] US2019 / 0169439A1 discloses a weather-resistant nacreous pigment having a protective layer containing at least one rare earth metal oxide and at least one metal oxide selected from silicon, aluminum, zirconium, and mixtures thereof. The specifically mentioned rare earth metal oxide is Ce2O3 used in some examples.

[0012] US2014 / 4018439A1 discloses a weather-resistant nacreous pigment, where the top coating consists of cerium oxide as a single metal oxide layer followed by an organic functionalization.

[0013] US2015 / 0259563A1 discloses a weather-resistant nacreous pigment, where in the top coating, a cerium oxide layer follows a metal oxide layer of tin, and finally, an organic surface modification of oligomeric silane follows.

[0014] Since all weathering top coatings using cerium oxide have a yellowish absorption color, they are practically limited in the amount of this oxide. An excessive amount can cause an undesirable discoloration of the entire nacreous pigment.

[0015] On the one hand, the new requirements of customers include a more enhanced test method for weather resistance, which is a combination of two well-known methods. First, the nacreous pigment is coated on a KTL panel with an appropriate base coat according to automotive requirements using a 1K clear coat. These coatings are first processed for between 1000 and 4000 hours in a xenon test and immediately afterwards in a dew condensation test. This test procedure simulates very harsh conditions in a very photosensitive coating application system. In many cases, it can cause irreversible UV reactions and swelling phenomena, ultimately causing either undesirable color changes or significant deterioration of gloss characteristics in coating applications.

Summary of the Invention

Problems to be Solved by the Invention

[0016] Therefore, the object of the present invention is to provide a weather-resistant nacreous pigment that passes such an enhanced test procedure for weather resistance, does not change strongly in interference color compared to the initial nacreous pigment without top coating, and does not suffer significant gloss deterioration.

Means for Solving the Problems

[0017] This object can be solved by providing a weather-resistant nacreous pigment having a basic nacreous luster with an interference color, which comprises a transparent platelet substrate and at least one metal oxide layer having a refractive index > 1.8, and having a weathering top coating having at least one metal oxide and an organic functional surface modification on top of this basic nacreous pigment, (a) For a basic nacreous pigment having a silver interference color, the weathering top coating consists of a first metal oxide of a rare earth metal M from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof 1 and (b) For a basic nacreous pigment having a colored interference color or a silver interference color, a weather-resistant top coating contains a rare earth metal M from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof 1 a first metal oxide of, and a second metal M from the group consisting of Si, Al, Zn, Mg, Zr, Sn, and mixtures or combinations thereof 2 and contains a second metal oxide from (a) or (b) In each case, the organic functional surface modification contains an organic functional silane or a water-based precondensed organic functional silane.

Brief Description of the Drawings

[0018]

Figure 1

Mode for Carrying Out the Invention

[0019] Preferred embodiments of this weather-resistant nacreous pigment are further disclosed in claims 2 to 11.

[0020] A further object of the present invention is to provide a simple method for manufacturing a weather-resistant nacreous pigment.

[0021] This object can be solved by providing a method for manufacturing a weather-resistant nacreous pigment, which includes the following steps: (i) Suspending a basic nacreous pigment in a solvent, (iia) Coating the basic nacreous pigment from step (i) in a solvent with a rare earth metal oxide precursor at a predetermined pH1 to obtain a rare earth metal oxide layer, or (iib) Coating the basic nacreous pigment from step (i) in a solvent by one of the following methods: (iib1) Obtain a layer of rare earth metal oxide using a rare earth metal oxide precursor at a specified pH1, and then coat this nacreous pigment from the process with a precursor of a second metal oxide at a specified pH2 to obtain a second metal oxide, or, (iib2) Form a second metal oxide using a precursor of the second metal oxide at a specified pH2, and then coat this nacreous pigment with a rare earth metal oxide precursor at a specified pH1 to obtain a layer of rare earth metal oxide, or, (iib3) Use a rare earth metal oxide precursor together with a precursor of a second metal oxide at a specified pH3 for coating, where pH3 is equal to pH1 and pH2, or preferably between pH1 and pH2, (iii) Coat the nacreous pigment from step (iia) or (iib) in a solvent with an organofunctional silane or a water-based precondensed organofunctional silane, and (iv) Separate the coated nacreous pigment, optionally wash it with a solvent, and dry it at a temperature in the range of 80 °C to 160 °C.

[0022] A preferred embodiment of this treatment is disclosed in claim 13.

[0023] Basic nacreous pigment: Natural mica is usually the thinnest transparent substrate that requires a relatively large amount of refractive index metal oxide, especially TiO2, and relatively high photoactivity occurs. Therefore, a more resistant top coating is required here. On the other hand, the optical properties of basic nacreous pigments based on synthetic substrates have optically very high-quality properties. Optically very high-quality properties mean, in particular, the excellent gloss and color purity of the nacreous pigment in the application medium.

[0024] Therefore, the deterioration of these optical properties due to the top coating is a serious drawback. The transparent small plate-shaped synthetic substrate is preferably selected from synthetic mica small plates, glass small plates, SiO2 small plates, Al2O3 small plates, synthetic boehmite small plates, BiOCl small plates, and mixtures thereof, more preferably selected from synthetic mica small plates, glass small plates, Al2O3 small plates, and mixtures thereof. The synthetic substrate in the form of small plates (platelet shape) is particularly preferably selected from the group consisting of glass small plates, synthetic mica small plates, and mixtures thereof.

[0025] The above synthetic substrates are known from a series of patent applications and patents. For example, when the small plate-shaped synthetic substrate consists of a glass small plate, those produced according to the methods described in EP0289240A1, WO2004 / 056716A1, and WO2005 / 063637A1 are preferably used within the framework of the present invention. The glass small plate that can be used as the substrate can have, for example, a composition corresponding to the teachings of EP1980594B1.

[0026] These glass small plates, also called glass flakes as described in these documents, are characterized by a particularly homogeneous surface and thickness of the small plates. The thickness of the glass small plates preferably takes various values with a standard deviation of at most 20%, more preferably at most 15%, and even more preferably at most 10%. The average thickness of the glass small plates is in the range of 20 to 2,000 nm, preferably in the range of 100 to less than 1,000 nm.

[0027] These glass small plates are preferably those produced according to the following process (see EP0289240B1): - Supplying the flow of molten glass downward into a rotating cup, - Cause the molten glass to flow over the edge of the cup so that the molten glass is pushed into the gap between two plates surrounding the cup, where the movement of the material occurs radially and is brought about by the air flow between the plates, as a result, the radial flow is pushed radially, thereby keeping the radial flow flat and causing the material to be crushed into flakes when the material solidifies.

[0028] Optically particularly high-quality nacreous pigments based on synthetic substrates are also known from EP2217664B1. Here, it can be seen that substrates with a narrow size distribution surprisingly make it possible to provide nacreous pigments with particularly high color purity and high gloss.

[0029] In one embodiment of the present invention, the weather-resistant nacreous pigment according to the present invention has a cumulative frequency distribution of a volume average size distribution function having values of D 10 , D 50 and D 90 , and this cumulative frequency distribution has a span ΔD in the range of 0.7 to 1.4. The span ΔD is calculated according to formula (I): ΔD=(D 90 -D 10 ) / D 50 (I).

[0030] According to the present invention, the span ΔD is used to characterize the particle size distribution. The smaller the span, the narrower the particle size distribution. In a particularly preferred embodiment, the weather-resistant nacreous pigment according to the present invention has a span ΔD in the range of 0.75 to 1.3, more preferably in the range of 0.8 to 1.2, and even more preferably in the range of 0.85 to 1.1.

[0031] When the span ΔD exceeds 1.4, a sufficiently color-pure nacreous pigment cannot be obtained. Within the framework of conventional methods, nacreous pigments with a span of less than 0.7 in size distribution are very labor-intensive to manufacture and are therefore no longer economical.

[0032] The nacreous luster pigments having the span ΔD values listed above as preferred have excellent color purity. This particularly applies to nacreous luster pigments whose substrate has an average thickness of 500 to 2000 nm, more preferably 500 to 1200 nm.

[0033] Therefore, these parameters of the size distribution function, preferably these parameters of the average thickness of the nacreous luster pigment substrate, interact synergistically with the weathering coating according to the present invention. In such optically high-quality nacreous luster pigments, on the one hand, even slight optical losses as a result of insufficient stabilization can have a very distorting effect, or a weathering layer that is too thick or optically distorted (e.g., a swelling layer) can have a very distorting effect.

[0034] The weather-resistant nacreous luster pigments according to the present invention can have any average particle size D 50 The D 50 value of the pigments according to the present invention is preferably in the range of 3 to 80 μm. The pigments according to the present invention preferably have a D 50 value in the range of 5 to 63 μm, particularly preferably in the range of 7 to 56 μm, and extremely particularly preferably in the range of 9 to 40 μm.

[0035] The D 10 value of the pigments according to the present invention is preferably in the range of 1 to 25 μm. The pigments according to the present invention preferably have a D 10 value in the range of 2 to 21 μm, particularly preferably in the range of 3 to 18 μm, and extremely particularly preferably in the range of 4 to 14 μm.

[0036] The D 90 value of the pigments according to the present invention is preferably in the range of 6 to 250 μm. The pigments according to the present invention preferably have a D 90 value in the range of 15 to 210 μm.

[0037] The D 10 of the cumulative frequency distribution of the volume average particle size distribution function obtained by the laser diffraction method, D 50 or D 90The values indicate that 10%, 50% or 90% of each of the pigments according to the present invention has a diameter equal to or less than the indicated value. Here, the particle size distribution curve of the pigment is preferably determined according to the manufacturer's instructions using an apparatus from Malvern (Malvern) (apparatus: MALVERN Mastersizer 2000). When using a Mastersizer 3000 apparatus, it is recommended to measure in the "Mastersizer 2000" section within the organization. The scattered light signal was evaluated according to the Fraunhofer approximation.

[0038] The average thickness of the small plate-shaped transparent substrate to be coated is preferably in the range of 50 nm to 5000 nm, preferably in the range of 60 nm to 3000 nm, and particularly preferably in the range of 70 nm to 2000 nm.

[0039] In one embodiment of the present invention, the average thickness of the glass small plate as the small plate-shaped substrate to be coated is preferably in the range of 750 nm to 1500 nm. Such glass small plates are widely commercially available. Thinner glass small plates provide further advantages. Thinner substrates result in a smaller total layer thickness of the pigments according to the present invention. In the case of glass small plates, the average thickness is within the range of 100 nm to 700 nm, more preferably within the range of 150 nm to 600 nm, particularly preferably within the range of 170 nm to 500 nm, and extremely particularly preferably within the range of 200 nm to 400 nm, and thus it is also a preferred substrate according to the present invention.

[0040] In a further embodiment, the average thickness of the synthetic mica (synthetic mica) as the small plate-shaped substrate to be coated is preferably in the range of 100 nm to 700 nm, more preferably in the range of 120 nm to 600 nm, particularly preferably in the range of 140 nm to 500 nm, and extremely particularly preferably in the range of 150 nm to 450 nm.

[0041] When small platelet-shaped transparent substrates with an average thickness of less than 50 nm are coated, for example, with a high refractive index metal oxide, extremely brittle pigments are obtained, which may decompose even when incorporated into the application medium, resulting in a significant reduction in gloss. In addition, the time required to coat these thin substrates, for example, with a high refractive metal oxide, is very long due to the large specific surface area of these small platelet-shaped transparent substrates, i.e., the surface area per unit weight of the pigment, resulting in high manufacturing costs. When the average substrate thickness exceeds 5000 nm, the basic nacreous luster pigment may be too thick overall. This may be associated with a lower coating ability, i.e., the coated area per unit weight of the pigment according to the present invention, and a lower in-plane orientation in the application medium. The lower orientation results in a reduced gloss.

[0042] In a preferred embodiment, the standard deviation of the thickness of the synthetic substrate is 15% to 100%, particularly preferably 20 to 70%, and extremely particularly preferably 22 to 40%.

[0043] Below a standard deviation of 15%, color flip effect pigments are obtained. Above a standard deviation of 100%, much thicker pigments are contained in the entire pigment system, resulting in poor orientation and loss of gloss. The average thickness is determined using a cured coating film in which the effect pigment is oriented substantially parallel to the base. For this purpose, the cross-section of the cured coating film is examined under a scanning electron microscope (SEM), the thickness of at least 100 nacreous luster pigments is determined, and statistically averaged.

[0044] The small plate-shaped transparent substrate used according to the present invention can be a coated or uncoated small plate-shaped substrate. For example, a low refractive index layer in the form of, for example, Al2O3 and / or SiO2 can also be applied to the small plate-shaped transparent substrate. However, it is preferable that a high refractive index layer is applied as the outermost layer. An extremely thin layer of SnO2 that brings about the rutile formation of the subsequently applied TiO2 layer can also be applied to the small plate-shaped transparent substrate. Rutile formation means that the applied TiO2 does not exist in the anatase structure, but rather the formation of the rutile structure is induced. However, the rutile structure can also be obtained by applying SnO2 and TiO2 jointly, and as a result, a separate SnO2 layer is not absolutely necessary for the application of the TiO2 layer having the rutile structure.

[0045] According to a preferred variant of the present invention, an uncoated small plate-shaped substrate is used.

[0046] To obtain the normal nacreous luster effect based on interference, the small plate-shaped substrate is coated with at least one high refractive metal oxide layer. In the framework of the present invention, the high refractive index metal oxide layer means a layer having a refractive index > 1.8, preferably > 2.0.

[0047] The at least one high refractive layer preferably comprises or consists of a metal oxide, metal hydroxide, and / or hydrated metal oxide selected from the group consisting of TiO2, Fe2O3, Fe3O4, TiFe2O5, Fe2Ti3O9, FeTiO3, ZnO, SnO2, CoO, Co3O4, ZrO2, Cr2O3, VO2, V2O3, (Sn, Sb)O2, and mixtures thereof.

[0048] The at least one high refractive metal oxide layer particularly preferably comprises or consists of a metal oxide, metal hydroxide, and / or hydrated metal oxide selected from the group consisting of TiO2, Fe2O3, Fe3O4, TiFe2O5, Fe2Ti3O9, FeTiO3, and mixtures thereof.

[0049] In some embodiments, the transparent substrate is preferably coated with only one (number: 1) high refractive index metal oxide layer selected from the group consisting of TiO2, Fe2O3, TiFe2O5, Fe2Ti3O9, FeTiO3, and mixtures thereof.

[0050] In highly particularly preferred embodiments, the substrate is coated with only one (number: 1) high refractive index metal oxide layer consisting of rutile-modified TiO2. Rutile modification (or rutile TiO2) means in the sense of the present invention that at least 99 wt% of TiO2 is present as rutile, where the wt% indication refers to the total TiO2 content in each layer. In a further particularly preferred embodiment, the colored high refractive index coating contains rutile TiO2, i.e., rutile-modified TiO2, in an amount in the range of 30 to 80 wt% relative to the total weight of the pearlescent pigment. The third-order particularly strong interference color is typically in this range. The proportion of the rutile TiO2 coating is more preferably in the range of 40 to 70 wt% relative to the total weight of the pearlescent pigment, and even more preferably in the range of 45 to 60 wt%.

[0051] Such a proportion of rutile TiO2 corresponds to a preferred average thickness of the rutile TiO2 layer in the range from 80 to 280 nm, depending on the fineness and thus the specific surface area of the platelet substrate, respectively. The average thickness of the rutile TiO2 layer is particularly preferably in the range of 100 to 270 nm.

[0052] At these layer thicknesses, in principle, third-order interference colors can be obtained. Due to the large layer thickness of the rutile TiO2 layer, the pigment has particularly high photocatalytic activity. Thus, unwanted discoloration of the color or coating layer containing the TiO2-containing pigment occurs very easily under the action of UV radiation.

[0053] In some embodiments, the basic nacreous pigment has a so-called "spacer layer" between two high refractive index layers. This spacer layer is porous with large cavities and specific connections and has a very low effective refractive index. Such nacreous pigments are described in EP3034562B1, EP3034563B1, EP3034564B1 and WO2016 / 097421A1.

[0054] In the present invention, basic nacreous pigments having a "silver" or "colored" interference color are distinguished.

[0055] For the purposes of the present invention, a basic nacreous pigment having a "silver" interference color is a basic nacreous pigment in which the chroma value C * 15° is ≤20, preferably ≤18, more preferably ≤15, very preferably ≤10. The chroma value C of the basic nacreous pigment having a silver interference color according to the present invention * 15° is preferably in the range of 1 to ≤20, more preferably in the range of 2 to ≤19, more preferably in the range of 3 to ≤18, particularly preferably in the range of 4 to ≤17.

[0056] In the case of multilayer nacreous pigments, these effect pigments can have a colored appearance when viewed from outside the specular angle in addition to their silver interference color. This colored appearance can be induced by the inherent color of the coating material and its layer thickness, depending on the nature of the coating of the platelet-shaped transparent substrate. Due to the high gloss, the absorption color that may be present becomes stronger at the specular angle, and the overall appearance of the multilayer nacreous pigment according to the present invention is presented to the observer as silver. In other embodiments, the silver interference color may have a slightly pastel hue at the specular angle, but here the observer mainly perceives a silver appearance. The chroma value in this specification is determined from the following application: Nitrocellulose varnish (Dr.Renger Erco Bronzemischlack 2615e; Morton) containing 6.0% by weight of the basic nacreous pigment (the % by weight is based on the total weight of the varnish) is applied at a wet film thickness selected to provide sufficient hiding power, D 50Depending on the value and pigment opacity, apply to the BYK-Gardner black / white drawdown chart (Byko-Chart 2851), and then dry at room temperature. Then, using BYK-MAC (BYK Gardner), perform colorimetric evaluation on these drawdown charts, and measure against the black background of the drawdown chart. The incident angle is 45°, and the chroma value used is at an observation angle of 15°.

[0057] Similarly, the basic nacreous pigments with "colored interference colors" under these conditions are defined to have C * 15° > 20, preferably > 18, more preferably > 15, and very preferably > 10. These lower limits of the C * 15° values should be interpreted as complementary to the values that define the silver basic nacreous pigments disclosed above.

[0058] The color change of the basic nacreous pigments by top coating can affect the interference color. However, it is much more of a problem when the overall tone of the basic nacreous is affected. Therefore, within the scope of the present invention, the overall tone change by top coating is mainly emphasized. Such an overall tone change can be measured best on a white substrate, and the details are specified in the experimental section.

[0059] Weather-resistant top coating (weather-stabilized top coating): In the present invention, the term "rare earth metal oxide" also means rare earth metal hydroxides or hydrated rare earth metal oxides and mixtures thereof, despite being oxides. Similarly, the term "second metal oxide" of the top coating or any further metal oxide of the top coating also means the second metal hydroxide or the second metal oxide hydrate and mixtures thereof, despite being particulate oxides. The same applies to the corresponding specific chemical formulas. For example, "Sm2O3" also includes possible hydroxides or oxide hydrates of Sm(III) and mixtures thereof.

[0060] The metal oxides of the weather-resistant top coating can be fired before coating with organic functional groups. However, in most cases, these coatings are not fired, and thus, hydroxides and oxide hydrates may be present.

[0061] The rare earth metal oxides used for the corresponding metal oxides are selected from metals Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof. Preferably, the rare earth metal oxides used for the corresponding metal oxides are selected from metals La, Pr, Nd, Sm, Eu, Gd, Ho, Yb, and mixtures thereof, more preferably selected from Pr, Nd, Sm, Eu, Gd, Ho, Yb, and mixtures thereof, and most preferably selected from Nd, Sm, Yb, Eu, Ga, and mixtures thereof.

[0062] For rare earth metal oxides, it is preferably mainly metal oxides with a formal oxidation number of 3. Thus, for rare earth metal M 1 50 to 100 atomic% of the metal oxide is M 1 preferably based on the (III) oxidation state, more preferably 70 to 99 atomic%, each based on the total amount of M 1 ions. In this oxidation state, the metal ions can undergo redox reactions with the pores generated, for example, by the absorption of UV light by the TiO2 layer of the basic nacreous pigment: M 1 (III)+“+” → M 1 (IV)

[0063] Furthermore, most of the rare earth metal oxides of type M 1 2O3 are colorless or slightly colored, while Ce2O3 has a relatively strong golden yellow color tone. This allows the use of a larger amount of M 1 2O3 in principle, compared to the amount of Ce2O3 (here the amount relative to the moles of M 1 2O3 used), without reaching a strong color change compared to each basic nacreous pigment.

[0064] Therefore, the amount of the first metal oxide of the rare earth metal M 1 is preferably in the range of 0.3 to 4.0% by weight, more preferably in the range of 0.5 to 3.0% by weight, and most preferably in the range of 0.7 to 2.5% by weight, each based on the entire nacreous pigment.

[0065] The amount of particles strongly depends on the fineness and thickness of the basic nacreous pigment. Finer and thinner basic nacreous pigments have a higher specific surface area and can be optimized by those skilled in the art without undue burden. Within these ranges, sufficient resistance to more enhanced weather stability test methods is achieved on the one hand, and in addition, the change in interference color due to top coating is within the allowable range.

[0066] The amount of the rare earth metal can preferably be determined using XRF (X-ray fluorescence analysis) and can be expressed as the weight percentage of M 1 2O3 based on the total nacreous pigment.

[0067] In some embodiments, the weathering top coating further contains cerium metal oxide in a very limited amount. The amount of cerium oxide is preferably in the range of 0.0 to 30% by weight, more preferably in the range of 0.0 to 20% by weight, each calculated as Ce2O3 and referring to the total amount of rare earth metal oxides calculated as M 1 2O3 in the weathering top coating. Such a small amount can be within the allowable range regarding color change compared to the basic nacreous pigment.

[0068] In the case of the basic nacreous pigment of silver, usually, it is sufficient to use only the rare metal oxide coating as a single metal oxide coating on the outermost layer. Usually, such pigments have a rather thin thickness of the high refractive index metal oxide of the basic nacreous pigment. For example, a transparent silver nacreous pigment based on a TiO2 coating of a small platelet-shaped transparent substrate has a thickness of about 40 nm for the TiO2 layer. In this case, the photoactivity is not very high, and a single rare earth coating may be sufficient.

[0069] In the case of a basic nacreous pigment having an iridescent interference color, the thickness, and thus the amount of the high refractive index metal oxide, in particular titanium oxide, is higher, which usually results in an increase in photoactivity. In these cases, at least two metal oxide layers are proposed (variant b)). The first rare earth metal oxide layer is complemented by a second metal oxide coating. This second metal oxide metal is a metal M selected from Si, Al, Zn, Mg, Zr, Sn and mixtures or combinations thereof 2 is

[0070] Particularly preferred second metal oxides are SiO2, Al2O3, ZnO, MgO, ZrO2, SnO2 and mixtures or combinations thereof.

[0071] These materials are already known in the art to be used as weathering topcoat materials. They can be used as mixtures of two or more of them, or as two or more separate layers. More preferred are SiO2, Al2O3, ZnO, ZrO2 and mixtures or combinations thereof, and most preferred are SiO2, ZnO and mixtures or combinations thereof. In particular, the combination of SiO2 and ZnO deposited on the nacreous pigment as a subsequent layer or as a mixed layer has proven to be particularly effective.

[0072] All of these metal oxides are transparent in the visible wavelength range, and thus have a very small effect on the overall tone of the nacreous pigment.

[0073] Preferably, the amount of the second metal oxide of metal M 2 is in the range of 1.0 to 5.0% by weight, more preferably in the range of 2.0 to 3.5% by weight, each being a value relative to the total nacreous pigment.

[0074] Regarding the arrangement of the first and second metal oxides, in principle all arrangements can be used.

[0075] In a first preferred embodiment, the weathering top coating (b) has a structure characterized in that the first coating located on the basic nacreous pigment is a first rare earth metal oxide coating, followed by a second metal oxide coating.

[0076] Since these coatings have a thickness in the range of nm, it may be difficult to analyze a specific arrangement. Therefore, in a preferred embodiment, the weathering top coating (b) has a structure resulting from a first precipitation of a precursor of the first rare earth metal oxide, followed by a second precipitation of a precursor material of the second metal oxide.

[0077] In a further preferred embodiment, the weathering top coating (b) has a structure characterized in that both the first rare earth metal oxide and the second metal oxide are produced by co-precipitation of the two metal oxide precursors. By utilizing such co-precipitation, the relative amounts of the separate metal oxides in the top coating can vary slightly depending on the relative precipitation kinetics of the two precursor materials and the particle coating conditions. However, essentially, a mixed layer of the two metal oxides is formed.

[0078] In a third embodiment, the weathering top coating (b) has a structure characterized in that the first coating located on the basic nacreous pigment is a coating of the second metal oxide, followed by a coating of the first rare earth metal oxide.

[0079] In any of the variations, the weathering top coating is finished by applying an organic modification. Such modifications are well known in the art and are intended to adapt the nacreous pigment surface to the organic binder for the end use in the coating of the nacreous pigment.

[0080] Examples of such coupling agents include organofunctional silanes or aqueous precondensed organofunctional silanes. These coupling agents have proven to be very efficient and are well known in the art. Such particulate organofunctional silanes are described, for example, in EP1682622A1 and EP632109A1. The precondensed organofunctional silanes are described in detail in EP0888410B1 and US2014 / 0018439A1.

[0081] Method for producing weather-resistant pearlescent pigment: A further object of the present invention is solved by providing a method for producing a weather-stable pearlescent pigment, comprising the following steps: (i) suspending the base pearlescent pigment in a solvent; (iia) coating the base pearlescent pigment from step (i) in a solvent with a rare earth metal oxide precursor at a predetermined pH1 to obtain a rare earth metal oxide layer; or (iib) coating the base pearlescent pigment from step (i) in a solvent by one of the following methods: (iib1) obtaining a layer of rare earth metal oxide using a rare earth metal oxide precursor at a predetermined pH1, and then coating this pearlescent pigment from the step with a precursor of a second metal oxide at a predetermined pH2 to obtain a second metal oxide; or (iib2) forming a second oxide using a precursor of a second metal oxide at a predetermined pH2, and then coating this pearlescent pigment with a rare earth metal oxide precursor at a predetermined pH1 to obtain a layer of rare earth metal oxide; or (iib3) using a rare earth metal oxide precursor together with a precursor of a second metal oxide at a predetermined pH3 for coating, where pH3 is equal to pH1 and pH2, or preferably between pH1 and pH2; (iii) coating the pearlescent pigment from step (iia) or (iib) in a solvent with an organofunctional silane or an aqueous precondensed organofunctional silane; (iv) Separating the coated nacreous pigment, optionally washing it with a solvent, and drying it at a temperature in the range of 80 °C to 160 °C.

[0082] The basic nacreous pigment can be produced according to known methods, and many products are commercially available.

[0083] The solvent can be water or an organic solvent. Preferred organic solvents are alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-methylpropanol, 2-methoxypropanol, and butyl glycol. Also, mixtures of any desired proportions of these alcohols are possible. Preferred alcoholic solvents are ethanol, isopropanol, or mixtures thereof.

[0084] Water is preferred as the solvent, and in this case, the precursor material of the rare earth metal oxide is preferably M 1 An appropriate water-soluble salt of a cation, which is typically a chloride, nitrate, sulfate, acetate, etc. The pH value is stabilized by administering an appropriate amount of a base such as NaOH or KOH, or an acid such as HCl or HNO3.

[0085] For the second metal oxide coating, preferably, water glass for SiO2 and chlorides or nitrites of Al, Zn, Zr, Mg, or Sn are used.

[0086] M 1 The cation is preferably 50 to 100 mol% of M 1 (III) cations, more preferably 80 to 100% of M 1 (III) cations, each M 1 Based on the total amount of cations. These are an appropriate amount of M 1 (IV) cations and may be mixed. Generally, M 1 (IV) cations are less preferred because these cations often have distinct colors.

[0087] When the solvent is an alcoholic solvent, the precursor material of the rare earth metal oxide is also preferably a corresponding salt of the M cation having sufficient solubility in the solvent (for example, chloride, nitrate, acetate, octanoate, acetyl-acetonate). Here, water is often added to hydrolyze the metal cation. 1 Regarding the precursor of the second metal oxide, typically, silanes such as tetramethoxysilane or tetraethoxysilane are used to form SiO2, and other metals of salts such as chloride, nitrate or acetonato are typically used.

[0088] For the precursor of the second metal oxide, typically, silanes such as tetramethoxysilane or tetraethoxysilane are used to form SiO2, and other metals of salts such as chloride, nitrate or acetonato are typically used. 2 Regarding the precursor of the second metal oxide, typically, silanes such as tetramethoxysilane or tetraethoxysilane are used to form SiO2, and other metals of salts such as chloride, nitrate or acetonato are typically used.

[0089] The catalyst used in the alcoholic solvent is preferably a nitrogen-containing base. Examples thereof include, for example, ammonia, hydrazine, methylamine, ethylamine, triethanolamine, dimethylamine, diethylamine, methylethylamine, trimethylamine, triethylamine, ethylenediamine, trimethylenediamine, tetramethylenediamine, 1-propylamine, 2-propylamine, 1-butylamine, 2-butylamine, 1-propylmethylamine, 2-propylmethylamine, 1-butylmethylamine, 2-butylmethylamine, 1-propylethylamine, 2-propylethylamine, 1-butylethylamine, 2-butylethylamine, piperazine, pyridine and the like.

[0090] The pH1 value for precipitating the rare earth metal oxide precursor is preferably in the range of 4.5 to 9.0, more preferably in the range of 5.0 to 8.5. The pH2 value for precipitating the second metal oxide precursor is preferably in the range of 5.0 to 9.0.

[0091] The temperature for the coating reaction is preferably in the range from 50 °C to the boiling point of the solvent used, more preferably in the range of 55 °C to 80 °C.

[0092] The drying step (vi) can be carried out under ambient pressure or under vacuum.

[0093] A further object of the present invention is solved by the use of weather-resistant nacreous pigments in coatings, printing inks, plastics, powder coatings, and especially automotive base coatings.

[0094] A further embodiment of the present invention is a formulation comprising a weather-resistant nacreous pigment, especially an automotive basecoat formulation.

Examples

[0095] Example: Example 1: 100 g of a commercially available silver nacreous pigment based on synthetic mica with a fineness of 10 - 40 μm (Symic C604, Eckart) was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 °C, and a solution consisting of 1.90 g of EuCl3 dissolved in 50 mL of water was added at a pH of 5.2. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, the pH value was raised to 7.5 with a 5 wt% KOH solution and stirred for 15 minutes. *

[0096] Next, a water glass solution (mixed with 51.4 g of water glass solution, 3.0 wt% SiO2 (theoretical value based on the initial nacreous pigment), and 20.7 g of demineralized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 7.5.

[0097] After the solution was completely added, the suspension was stirred for 1 h, then a solution of 7.1 g of Hydrosil 2627 diluted with 24.3 g of demineralized water was added. After stirring for an additional 180 minutes, the suspension was filtered, the filter cake was washed with demineralized water, and then dried at 95 °C under a vacuum of 100 mbar (millibar).

[0098] Example 2: 100 g of a commercially available silver nacreous pigment based on synthetic mica with a fineness of 10 - 40 μm (Symic C604, Eckart) was suspended in 900 g of water. Then, the dispersion was heated to 70 °C, and 2.61 g of PrCl3 dissolved in 42 mL of water was added at a pH of 6.7.​* A solution consisting of 6H2O was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, the pH value was raised to 7.5 with a 5wt% KOH solution and stirred for 15 minutes.

[0099] Next, a water glass solution (a mixture of 51.4 g of water glass solution, 3.0 wt% SiO2 (theoretical value referring to the initial nacreous pigment), and 20.7 g of demineralized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 7.5.

[0100] After the solution was completely added, the suspension was stirred for 1 h, and then a solution of 2.1 g of Dynasilan 1189 diluted with 14.7 g of isopropyl alcohol was added. After stirring for another 180 minutes, the suspension was filtered off, the filter cake was washed with demineralized water, and then dried at 75 °C under a vacuum of 100 mbar.

[0101] Example 3: 100 g of a silver nacreous pigment (Symic C604, Eckart) based on synthetic mica with a particle size of 10 - 40 μm commercially available was suspended in 900 g of water. Then, the dispersion was heated to 70 °C, and at pH 8.5, a solution of 3.06 g of Sm(NO3)3 * consisting of 6H2O was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, a water glass solution (a mixture of 51.4 g of water glass solution, 3.0 wt% SiO2, and 20.7 g of demineralized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 8.5.

[0102] After the solution was completely added, the suspension was stirred for 1 h, and then a solution of 1.9 g of Dynasilan 6490 diluted with 14.7 g of isopropyl alcohol was added. After stirring for another 180 minutes, the suspension was filtered off, the filter cake was washed with demineralized water, and then dried at 75 °C under a vacuum of 100 mbar.

[0103] Example 4: 100 g of a commercially available silver mica pearlescent pigment (Symic C604, Eckart) based on synthetic mica with a fineness of 10 - 40 μm was suspended in 900 g of water. Then, the dispersion was heated to 70 °C, and a solution consisting of 2.99 g of Gd(NO3)3 * 6H2O dissolved in 65 mL of water was added at a pH of 5.5. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, the pH value was raised to 7.5 with a 5 wt% KOH solution and stirred for 15 minutes.

[0104] Next, a water glass solution (mixed with 51.4 g of water glass solution, 3.0 wt% SiO2, and 20.7 g of deionized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 7.5.

[0105] After the solution was completely added, the suspension was stirred for 1 h, and then a solution of 5.7 g of Hydrosil 2776 diluted with 24.3 g of deionized water was added. After stirring for another 180 minutes, the suspension was filtered off, the filter cake was washed with deionized water, and then dried at 95 °C under a vacuum of 100 mbar.

[0106] Example 5: 100 g of a commercially available silver mica pearlescent pigment (Symic C604, Eckart) based on synthetic mica with a fineness of 10 - 40 μm was suspended in 900 g of water. Then, the dispersion was heated to 70 °C, and a solution consisting of 2.37 g of YbCl3 * 6H2O dissolved in 65 mL of water was added at a pH of 6.7. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, the pH value was raised to 7.5 with a 5 wt% KOH solution and stirred for 15 minutes.

[0107] Next, a water glass solution (mixed with 51.4 g of water glass solution, 3.0 wt% SiO2, and 20.7 g of deionized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 7.5.

[0108] After adding the solution completely, the suspension was stirred for 1 h, and then a solution of 7.1 g of Hydrosil 2627 diluted with 24.3 g of deionized water was added. After further stirring for 180 min, the suspension was filtered off, and the filter cake was washed with deionized water.

[0109] Example 6: 150 g of a commercially available silver mica pearlescent pigment (Symic C604, Eckart) based on synthetic mica with a fineness of 10 - 40 μm was suspended in 1200 g of water. Subsequently, the dispersion was heated to 70 °C, and a solution of 2.87 g of NdCl3 * consisting of H2O dissolved in 60 mL of water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, the pH value was raised to 7.5 with a 5 wt% KOH solution and stirred for 15 min.

[0110] Next, a water glass solution (mixed with 77.1 g of water glass solution, 3.0 wt% SiO2, and 31.0 g of deionized water) was slowly introduced into the suspension while keeping the pH value constant at pH 7.5.

[0111] After adding the solution completely, the suspension was stirred for 1 h, and then a solution of 9.65 g of Hydrosil 2627 diluted with 36.5 g of deionized water was added. After further stirring for 180 min, the suspension was filtered off, the filter cake was washed with deionized water, and then dried at 95 °C under a vacuum of 100 mbar.

[0112] Example 7 (alcohol route): 100 g of a commercially available silver mica pearlescent pigment (Symic C604, Eckart) based on synthetic mica with a fineness of 10 - 40 μm was suspended in 500 ml of isopropanol and brought to the boiling point.

[0113] While mixing gently, first 2.0 g of H2O was added, and then within 1 hour, 3.96 g of EuCl3 in 20 g of isopropyl alcohol *A solution of H2O was added. Subsequently, a mixture of 0.45 g of ethylenediamine and 3.0 g of H2O was added. Then, 8.9 g of tetraethoxysilane and 21.0 g of isopropyl alcohol were continuously introduced over 2 hours by use of a dosing pump. Next, the suspension was reacted for an additional 6 hours. Then, a solution of 2.1 g of Dynasilan 1189 in 12.9 g of isopropyl alcohol was added and heating was stopped. The mixture was stirred overnight at room temperature, filtered, washed, and then dried at 95 °C under a vacuum of 100 mbar.

[0114] Example 8: 100 g of a commercially available silver mica-based pearlescent pigment (Symic C604, Eckart) with a particle size of 10 - 40 μm was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 °C and a solution consisting of 5.6 g of Gd(NO3)3 * 6H2O dissolved in 75 mL of water was added at a pH of 5.5. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, the pH value was raised to 7.5 with a 5 wt% KOH solution and stirred for 15 minutes.

[0115] Next, a water glass solution (mixed with 42.8 g of a water glass solution, 2.5 wt% SiO2, and 13.8 g of demineralized water) was slowly introduced into the suspension while keeping the pH value constant at pH 7.5.

[0116] After the solution was completely added, the suspension was stirred for 1 h and then a solution of 5.7 g of Hydrosil 2776 diluted with 24.3 g of demineralized water was added. After stirring for an additional 180 minutes, the suspension was filtered off, the filter cake was washed with demineralized water, and then dried at 95 °C under a vacuum of 100 mbar.

[0117] Example 9: 100 g of a commercially available silver mica-based pearlescent pigment (Symic C604, Eckart) with a particle size of 10 - 50 μm was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 °C and a solution consisting of 2.4 g of EuCl3 *A solution consisting of H2O was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Subsequently, the pH value was raised to 7.5 with a 5 wt% KOH solution and stirred for 15 minutes.

[0118] Next, a water glass solution (mixed with 42.8 g of water glass solution, 6.0 wt% SiO2, and 13.8 g of deionized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 7.5.

[0119] After the solution was completely added, the suspension was stirred for 1 h, and then a solution of 2.0 g of Dynasilan 4148 diluted with 24.3 g of deionized water was added. After further stirring for 180 minutes, the suspension was filtered off, the filter cake was washed with deionized water, and then dried at 95 °C under a vacuum of 100 mbar.

[0120] Example 10: 100 g of a commercially available silver mica pearlescent pigment (Symic C604, Eckart) based on synthetic mica with a fineness of 10 - 50 μm was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 °C, and at a pH of 5.5, 4.0 g of EuCl3 dissolved in 75 mL of water * A solution consisting of H2O was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Subsequently, the pH value was raised to 7.5 with a 5 wt% KOH solution and stirred for 15 minutes.

[0121] Next, a water glass solution (mixed with 42.8 g of water glass solution, 6.0 wt% SiO2, and 13.8 g of deionized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 7.5.

[0122] After the solution was completely added, the suspension was stirred for 1 h, and then a solution of 5.7 g of Hydrosil 2776 diluted with 24.3 g of deionized water was added. After further stirring for 180 minutes, the suspension was filtered off, the filter cake was washed with deionized water, and then dried at 95 °C under a vacuum of 100 mbar.

[0123] Example 11: 100 g of a commercially available red nacreous pigment (Luxan C241, Eckart) based on glass flakes with a fineness of 10 - 60 μm coated with titanium dioxide was suspended in 800 g of water. Then, the dispersion was heated to 70 °C, and a solution consisting of 3.06 g of Sm(NO3)3 * dissolved in 67 mL of water was added at pH 8.5. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, a water glass solution (mixed with 51.4 g of water glass solution, 6.0 wt% SiO2, and 20.7 g of deionized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 8.5. After the solution was completely added, the suspension was stirred for 1 h, and then a solution of 1.7 g of Dynasilan 6490 diluted with 14.7 g of isopropyl alcohol was added. After further stirring for 180 min, the suspension was filtered off, the filter cake was washed with deionized water, and then dried at 75 °C under a vacuum of 100 mbar.

[0124] Example 12: 100 g of a commercially available silver nacreous pigment (Symic C604, Eckart) based on synthetic mica with a fineness of 10 - 50 μm was suspended in 900 g of water. Subsequently, the dispersion was heated to 70 °C, and a solution consisting of 2.4 g of EuCl3 * dissolved in 75 mL of water was added at a pH of 5.5. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, the pH value was raised to 7.5 with a 5 wt% KOH solution and stirred for 15 min.

[0125] Next, a water glass solution (mixed with 51.4 g of water glass solution, 6.0 wt% SiO2, and 13.8 g of deionized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 7.5.

[0126] After the solution was completely added, the suspension was stirred for 1 h, and then a solution of 2.0 g of Dynasilan 1189 diluted with 24.3 g of isopropyl alcohol was added. After further stirring for 180 min, the suspension was filtered off, the filter cake was washed with deionized water, and then dried at 95 °C under a vacuum of 100 mbar.

[0127] Example 13: 100 g of a commercially available silver mica-based pearlescent pigment (Symic C001, Eckart) with a particle size of 10 - 50 μm coated with titanium dioxide was suspended in 900 g of water. Then, the dispersion was heated to 70 °C, and a solution consisting of 2.2 g of Gd(NO3)3 * 6H2O dissolved in 75 mL of water was added at a pH of 5.5. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, the pH value was raised to 7.5 with a 5 wt% KOH solution and stirred for 15 minutes.

[0128] Next, a water glass solution (mixed with 11.4 g of water glass solution, 6.0 wt% SiO2, and 13.8 g of deionized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 7.5. After the solution was completely added, the suspension was stirred for 1 h, and then a solution of 2.0 g of Dynasilan 1189 diluted with 24.3 g of isopropyl alcohol was added. After stirring for an additional 180 minutes, the suspension was filtered off, the filter cake was washed with deionized water, and then dried at 95 °C under a vacuum of 100 mbar.

[0129] Example 14: 150 g of a commercially available silver mica-based pearlescent pigment (Symic C604, Eckart) with a particle size of 10 - 40 μm was suspended in 1200 g of water. Subsequently, the dispersion was heated to 70 °C, and a solution consisting of 1.27 g of ZnCl2 dissolved in 60 mL of water was added at a pH of 6.5. At the same time, the pH value was kept constant by adding a water glass solution (mixed with 28.2 g of water glass solution, 6.0 wt% SiO2, and 31.0 g of deionized water).

[0130] Subsequently, a solution consisting of 3.47 g of Sm(NO3)3 * 6H2O dissolved in 67 mL of water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution.

[0131] After completely adding the solution, the suspension was stirred for 1 h and then a solution of 9.65 g of Hydrosil 2627 diluted with 36.5 g of demineralized water was added. After further stirring for 180 min, the suspension was filtered off, the filter cake was washed with demineralized water and then dried at 95 °C under a vacuum of 100 mbar.

[0132] Example 15: Based on 100 g of commercially available titanium dioxide and based on synthetic mica with a particle size of 10 - 50 μm coated with iron oxide (Symic C604, Eckart), 900 g of pearlescent pigment was suspended in water. Then, the dispersion was heated to 70 °C and a solution of 2.4 g of EuCl3 * consisting of H2O was added. At the same time, the pH value was kept constant by adding 10% KOH solution. Then, the pH value was raised to 7.5 with 5 wt% KOH solution and stirred for 15 min. 12.0 g of a solution of zinc chloride w(ZnCl2) = 7.0% was added, and an aqueous glass solution of 8.5 wt% SiO2 was added simultaneously while maintaining the pH at 7.5.

[0133] After completely adding the solution, the suspension was stirred for 90 min and then a solution of 6.43 g of Hydrosil 2627 diluted with 30 g of demineralized water was slowly added. The suspension was continuously stirred at 70 °C for a further 17 h, then filtered, the filter cake was washed with demineralized water and then dried at 95 °C under a vacuum of 100 mbar.

[0134] Example 16: Based on 100 g of commercially available titanium dioxide and based on synthetic mica with a particle size of 10 - 50 μm coated with iron oxide (Symic C604, Eckart), 900 g of silver pearlescent pigment was suspended in water. Then, after heating the dispersion to 70 °C, 12.0 g of a solution of zinc chloride w(ZnCl2) = 7.0% was added. The pH was adjusted to 7.0 by continuously adding an aqueous glass solution of 8.5 wt% SiO2.

[0135] After adding the solution completely, the suspension was stirred for 1 hour and then the pH was adjusted to 8.5. Thereafter, a solution consisting of 3.06 g of Sm(NO3)3 dissolved in 67 mL of VE water was added. * A solution consisting of 6H2O was added. At the same time, the pH value was kept constant by adding 10% KOH solution. After adding the solution completely, the suspension was stirred for 1 hour and then a solution of 1.9 g of Dynasilan 6490 diluted with 10 g of isopropyl alcohol was added. After stirring for a further 180 minutes, the suspension was filtered off, the filter cake was washed with demineralized water and then dried at 95 °C under a vacuum of 100 mbar.

[0136] Example 17: 900 g of a pearlescent pigment with red interference (Symic C241, Eckart), based on coated synthetic mica with a particle size of 10 - 50 μm based on 100 g of commercially available titanium dioxide, was suspended in 900 g of water. Thereafter, the dispersion was heated to 70 °C, the pH was adjusted to 7.5, and then a solution consisting of 1.28 g of Sm(NO3)3 dissolved in 28 mL of demineralized water was added. * A solution consisting of 6H2O was added. At the same time, the pH value was kept constant by adding 10% KOH solution. After 15 minutes and additional stirring, 12.0 g of a solution of zinc chloride w(ZnCl2)=7.0% was added while simultaneously adding an aqueous glass solution of 8.5 wt% SiO2 to maintain a pH of 7.5. After adding the solution completely, the suspension was stirred for a further 90 minutes and then a solution of 6.43 g of Hydrosil 2627 diluted with 30 g of demineralized water was slowly added. The suspension was stirred at 70 °C for a further 17 hours, then filtered, the filter cake was washed with demineralized water and then dried at 95 °C under a vacuum of 100 mbar.

[0137] Comparative Example 1: (Conforming to EP1682622A1) 150 g of a commercially available silver pearlescent pigment based on synthetic mica with a particle size of 10 - 50 μm (Symic C604, Eckart) was suspended in 1200 g of water. Subsequently, the dispersion was heated to 70 °C and at a pH of 6.5, 4.76 g of CeNO3 dissolved in 60 mL of water was added. *A solution consisting of 6H2O was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Subsequently, the pH value was raised to 7.5 with a 5wt% KOH solution and stirred for 15 minutes.

[0138] Next, a water glass solution (a mixture of 77.1 g of a water glass solution containing 6.0 wt% SiO2 and 31.0 g of deionized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 7.5.

[0139] After the solution was completely added, the suspension was stirred for 1 h and then a solution of 9.65 g of Hydrosil 2627 diluted with 36.5 g of deionized water was added. After further stirring for 180 minutes, the suspension was filtered off, the filter cake was washed with deionized water, and then dried at 95 °C under a vacuum of 100 mbar.

[0140] Comparative Example 2: (According to US2014 / 018439A1) 150 g of a commercially available silver mica pearlescent pigment (Symic C001, Eckart) based on synthetic mica with a fineness of 10 - 50 μm coated with titanium dioxide was suspended in 1200 g of water. Subsequently, the dispersion was heated to 70 °C, and a solution of 3.60 g of CeNO3 * consisting of 6H2O was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. The dispersion was stirred for an additional 1 hour, and then the pH value was raised to pH 7.5 by adding a 10% KOH solution. 5.7 g of a solution of Hydrosil 2776 diluted with 24.3 g of deionized water was added. After further stirring for 180 minutes, the suspension was filtered off, the filter cake was washed with deionized water, and then dried at 95 °C under a vacuum of 100 mbar.

[0141] Comparative Example 3: A commercially available silver mica pearlescent pigment, Symic C001, Eckart (D of 22 μm) based on synthetic mica with a fineness of 10 - 50 μm coated with titanium dioxide without a weather-resistant top coat. 50 )

[0142] Comparative Example 4: A commercially available silver opaque nacreous pigment having synthetic mica with a fineness of 10 to 50 μm as a substrate without a weather-resistant top coat, Symic C604, Eckart (D of 22 μm 50 ).

[0143] Comparative Example 5: (According to EP1682622A1) 150 g of a commercially available silver nacreous pigment Symic C604, Eckart) was suspended in 1200 g of water. Then, the dispersion was heated to 70 °C, and at pH 6.5, a solution consisting of 1.19 g of CeNO3 * 6H2O dissolved in 50 mL of VE water was added. At the same time, the pH value was kept constant by adding a 10% KOH solution. Then, the pH value was raised to 7.5 with a 5 wt% KOH solution and stirred for 15 minutes.

[0144] Next, a water glass solution (mixed with 25.7 g of a water glass solution, 6.0 wt% of SiO2, and 31.0 g of demineralized water) was slowly introduced into the suspension, and the pH value was kept constant at pH 7.5.

[0145] After the solution was completely added, the suspension was stirred for 1 h and then a solution of 2.25 g of Dynasilan 6490 diluted with 36.5 g of demineralized water was added. After further stirring for 180 minutes, the suspension was filtered off, the filter cake was washed with demineralized water, and then dried at 95 °C under a vacuum of 100 mbar.

[0146] Comparative Example 6: A commercially available red nacreous pigment based on titanium dioxide-coated glass flakes with a fineness of 10 to 60 μm, Luxan C241, Eckart (D50 of 29 μm) without a weather-resistant top coat.

[0147] All experimental results regarding the composition of the outermost layer are summarized in Table 1.

[0148]

Table 1

[0149] Test method B: B1 Photocatalytic activity: To determine the photocatalytic activity of the pigment powder, a special gas-phase photoreactor schematically shown in Figure 1 was used.

[0150] 150 mg of the pigment powder was weighed at the center of a Petri dish and then placed at the bottom of the photoreactor. The temperature of the photoreactor was adjusted and kept constant at 50 °C.

[0151] The photoactivity of the sample was measured in the ambient air circulating back to the photoreactor through the FTIR measurement system using a gas pump. The initial moisture and CO2 contents of the air were approximately 0.2% and 400 ppm, respectively.

[0152] As a model contaminant, 1 μL of acetone was injected across the septum inside the system. After the contaminant was evenly distributed, the UV lamp (90 mW / cm at 405 nm 2 ) was switched on and the acetone began to decompose, forming CO2 quantitatively.

[0153] The decomposition of acetone and the formation of CO2 were monitored with an FTIR spectrometer as a function of time, fitted to the first-order reaction kinetics, and the first-order rate constant was obtained. The initial production rates of acetone and carbon dioxide were linearly approximated and the production rates were obtained in units of ppm / h.

[0154] The higher the CO2 formation in ppm per hour, the higher the photocatalytic activity of the pigment powder. If the CO2 formation rate was less than 3 ppm / h, the test passed.

[0155] For each test series, it was necessary to pre-calibrate the zero spectrum by using the same procedure without pigment and acetone injection. The value of this blank test was subtracted from the value of the sample containing the pigment.

[0156] B2: Color consistency and optical properties of the sample compared to the starting material without top coating: The samples were applied as doctor blade drawdowns on a black and white opacity chart (Byko - Chart 2853, Byk Gardner) using a 40 - μm spiral bar for samples based on synthetic mica and a 50 - μm spiral bar for samples based on glass flakes. The effect pigments were dispersed in a conventional nitrocellulose coating (Dr. Renger Erco bronzing blend varnish 2615e from Morton; 6.0 wt% content based on the total weight of the wet varnish). The color change was determined using a MINOLTA CM - 700d in diffuse reflection, comparing each sample without a weathering top - coating. The color values of the white part of the opacity chart were measured and the difference was expressed in the well - known Hunter formula: ΔE * =(ΔL *2 +Δa *2 +Δb *2 ) 1 / 2 Such differences are characteristic of the overall tone change of the pearlescent pigments. An overall color change ΔE * of 2.25 or less was within the acceptable range.

[0157] B3 2 - coat air - gun application: White - ground aluminum test panels were coated with a 1K aqueous base test base - coat varnish containing an acrylate - polyurethane binder and the pearlescent pigments of the examples and comparative examples in an amount of 1.5 wt% using an Oerter APL1.2 spray - gun application. The wet thickness of the coating was 13 - 17 μm and the coated panels were dried at 80°C for 12 minutes.

[0158] A 1K conventional acrylate - based lacquer was used as a clear - coat with a thickness of 37 - 43 μm and dried at 140°C for 30 minutes. Using a 1K clear - coat instead of the conventionally used 2K clear - coat improves the test conditions.

[0159] B4 Enhanced weathering test (xenon and dew - water combination test): The panel was subjected to a xenon accelerated weathering test for 1000 hours in accordance with SAE J 2527. Immediately afterwards, the panel was subjected to a dew condensation test at a temperature of 40 °C for 72 hours in accordance with DIN EN ISO 6270-2.

[0160] The gloss was measured before and after the test using a 20° gloss meter (Micro-TRI-Gloss by BYK Gardener) in accordance with DIN EN ISO 2813 and expressed as the difference in % with respect to the gloss before the test. A decrease of less than -40% in relative gloss was within the acceptable range.

[0161] In some cases, this test was only applied if the photocatalytic activity test and the color change test were passed.

[0162] B5 Carbon content measurement: The carbon content of all samples was determined by combustion of the sample in an oxygen stream and detection of the generated CO2 by IR spectroscopy using an analyzer from LECO Instruments (Germany).

[0163] B6 XRF analysis: The metal oxides of the rare earth metals and the Zn content of Example 14 of the sample, as well as some of the pigments from the comparative examples, were determined by means of X-ray fluorescence analysis (XRF). For this purpose, each pigment was incorporated into a lithium tetraborate glass tablet mold, fixed in a solid sample measurement cup, and analyzed therefrom. The measuring instrument used was the Advantix ARL system from Thermo Scientific. First, the measured values were calibrated by an appropriate standard method. The results are shown in Table 1.

[0164] Since the transparent synthetic mica or glass substrate already has a large amount of silica, the Si content of the top coating of the sample could not be determined by this method. Instead, the theoretical values assuming a 100% reaction rate are shown in Table 1.

[0165] C Results: The results of the test are shown in Table 2.

[0166]

Table 2

[0167] D Discussion: All examples of the present invention passed the photoactivity test very well and had a low change ΔE * and passed the combined test of xenon and dew water. The photoactivity test was significantly failed in Comparative Example 7, which had no weathering top coating and was a green nacreous pigment. Also, Comparative Examples 3 and 4, which represent silver nacreous pigments, were clearly failed in this test.

[0168] Comparative Examples 1 and 5 were prepared according to EP 1682622 A1, and both comparative examples passed the photoactivity test. Comparative Example 1 also passed the combined test of xenon and dew water, but Comparative Example 5 did not pass this test. However, Comparative Example 1 had a neutral anthrasite color tone and did not pass the color change ΔE * test, especially when compared with Examples 1 to 8 and Example 10. This is considered to be due to the fact that the amount of Ce2O3 used here is quite large and the yellowish color of this cerium oxide. Comparative Example 5 passed the color change test (ΔE * was comparable to that of Example 12 having the same basic nacreous pigment), which is clearly due to the small amount of Ce2O3 used. However, this amount of Ce2O3 seems to be too low to pass the combined test of xenon and condensed water.

[0169] Example 13 showed a silver nacreous pigment coated with only a single metal oxide layer (Gd2O3) as a rare earth metal in the top coating. This sample also passed all the tests, but the photoactivity was slightly higher than that of most of the other examples. In contrast, Comparative Example 2 had a single Ce2O3 top coating and did not pass the photoactivity test.

[0170] Examples 15 and 17 showed particularly good results in the combined test of xenon and dew water.

[0171] The carbon content of all the examples was quite low, indicating that only a part of the silane used for surface modification was actually bonded to the surface of the pigment. Without being bound to any theory, the inventors believe that this quite low C content results in a non-hydrophobic surface that helps pass the combination test of xenon and condensed water.

Claims

1. A weather-resistant nacreous pigment having a basic nacreous luster with an interference color, comprising a transparent platelet-shaped substrate and at least one metal oxide layer having a refractive index > 1.8, and having a weathering top coating having at least one metal oxide and an organic functional surface modification on this basic nacreous pigment, Regarding the basic nacreous luster pigment having a silver interference color, the weather-resistant top coating is composed of a first metal oxide of a rare earth metal M selected from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof, or １ consists of, or Regarding the basic nacreous luster pigment having an interference color of coloring or silver interference color, the weathering top coating contains a rare earth metal M selected from the group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixtures thereof １ of the first metal oxide, and a second metal M selected from the group consisting of Si, Al, Zn, Mg, Zr, Sn, and mixtures or combinations thereof ２ contains the second metal oxide from, and in each case of (a) or (b), the organic functional surface modification comprises an organofunctional silane or a water-based precondensed organofunctional silane, weather-resistant nacreous pigment.

2. The weather-resistant nacreous pigment according to claim 1, wherein the weathering top coating comprises a metal oxide of a rare earth metal from the group consisting of La, Pr, Nd, Sm, Eu, Gd, Ho, Yb, and mixtures thereof.

3. The weather-resistant nacreous pigment according to claim 1 or 2, wherein the weathering top coating comprises a metal oxide of a rare earth metal from the group consisting of Nd, Sm, Yb, Eu, Ga and mixtures thereof.

4. Metal M ２ wherein the second metal oxide is SiO ２ , Al ２ O ３ , ZnO, MgO, ZrO ２ , SnO ２ and a weather-resistant nacreous pigment according to any one of claims 1 to 3 selected from the group consisting of mixtures or combinations thereof.

5. M １ Based on the total amount of ions, the rare earth metal M １ 50 to 100 atomic% of the metal oxide is M １ The weather-resistant nacreous pigment according to any one of claims 1 to 4, based on the oxidation state of (III).

6. Rare earth metal M １ The weather-resistant nacreous pigment according to any one of claims 1 to 5, wherein the amount of the first metal oxide is in the range of 0.3 to 3.0% by weight based on the whole of the nacreous pigment.

7. The weather-resistant top coating is M １ ２ O ３ When calculated as the total amount of the rare earth weather-resistant top coating calculated as, the weather-resistant nacreous pigment according to any one of claims 1 to 6, further comprising cerium metal oxide in an amount of 0.0 to 30% by weight when calculated as Ce ２ O ３ ​

8. Metal M ２ The weather-resistant nacreous pigment according to any one of claims 1 to 7, wherein the amount of the second metal oxide is in the range of 1.0 to 4.0% by weight based on the whole of the nacreous pigment.

9. The weather-resistant nacreous pigment according to any one of claims 1 to 8, wherein the weathering top coating (b) has a structure in which the first coating located on the high refractive index metal oxide coating is the first rare earth metal oxide coating and the second metal oxide coating follows this.

10. The weather-resistant nacreous pigment according to any one of claims 1 to 9, wherein the weathering top coating (b) has a structure characterized in that both the first rare earth metal oxide and the second metal oxide are produced by co-precipitation of metal oxide precursors.

11. The transparent platelet-shaped substrate from the basic nacreous luster pigment is selected from the group consisting of natural mica, synthetic mica platelets, glass platelets, SiO ２ platelets, Al ２ O ３ platelets, synthetic boehmite platelets, BiOCl platelets, and mixtures thereof, the weather-resistant nacreous luster pigment according to any one of claims 1 to 10.

12. The following steps: (i) suspending the basic nacreous pigment in a solvent, (iia) coating the basic nacreous pigment from step (i) in the solvent using a rare earth metal oxide precursor at a predetermined pH1 to obtain a rare earth metal oxide layer, or, (iib) coating the basic nacreous pigment from step (i) in the solvent by one of the following methods: (iib1) obtaining a layer of rare earth metal oxide using a rare earth metal oxide precursor at a predetermined pH1, and then coating this nacreous pigment from the step with a precursor of the second metal oxide at a predetermined pH2 to obtain a second metal oxide, or, (iib2) forming the second metal oxide using the precursor of the second metal oxide at a predetermined pH2, and then coating this nacreous pigment with a rare earth metal oxide precursor at a predetermined pH1 to obtain a layer of rare earth metal oxide; or, (iib3) using the rare earth metal oxide precursor together with the precursor of the second metal oxide for the coating at a predetermined pH3, where pH3 is equal to pH1 and pH2, or preferably between pH1 and pH2, (iii) coating the nacreous pigment from step (iia) or step (iib) with an organofunctional silane or a water-based precondensed organofunctional silane in the solvent, and (iv) separating the coated nacreous pigment, optionally washing it with a solvent, and drying it at a temperature in the range of 80°C to 160°C. A method for producing a weather-resistant nacreous pigment according to any one of claims 1 to 11, comprising the above steps.

13. The solvent may be water or an organic solvent, preferably an alcoholic solvent. Regarding the aqueous solvent, the rare earth metal M １ The salt of the (III) cation is M １ is used in an amount of 50 to 100 mol% based on the total amount of the cations, and regarding the organic solvent, the rare earth metal M １ The salt of the (III) cation or any of the metal organic compounds of the rare earth metal M １ The production method according to claim 12, wherein (III) any of the metal organic compounds of the cation is used as a precursor material.

14. Use of the weather-resistant nacreous pigment according to any one of claims 1 to 11 in coatings, printing inks, plastics, powder coatings, particularly automotive base coatings.

15. A formulation, particularly an automotive base coat formulation, comprising the weather-resistant nacreous pigment according to any one of claims 1 to 11.

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