Metallic interference pigments, methods for producing same and uses thereof - Patents.com

Abstract

The present invention relates to a metallic interference pigment comprising aluminum platelets having an average thickness in the range of 5 nm to 600 nm, which are optionally passivated and coated, in that order, by Layer A and Layer B, wherein Layer A consists of silicon dioxide and Layer B consists of iron(III) oxide doped with a dopant element selected from the group consisting of tungsten, indium, gallium, and titanium, the molar fraction of the dopant element in Layer B relative to the total molar amount of iron and the dopant element being 0.5 mol % to 10 mol %, and 60 to 85 parts by weight of iron(III) oxide is present per 10 parts by weight of aluminum. Furthermore, the present invention relates to a method for producing the metallic interference pigment according to the present invention and to uses of the metallic interference pigment.

Description

[Technical Field]

[0001] The present invention relates to a metallic interference pigment that is yellow with a greenish tint, a method for producing it and its uses.

[0002] In recent years, metal interference pigments have been established for use in colored coatings, printing inks, inks, plastics, glass, ceramics and decorative cosmetic formulations.Metal interference pigments are characterized by a metal substrate, such as aluminum metal substrate (can be stabilized by providing a silicon dioxide layer on it), covered with a highly refractive metal oxide layer, such as iron (III) oxide layer.Because metal substrates are opaque, metal interference pigments have high hiding power, in contrast to pearlescent pigments that contain translucent substrates.

[0003] When light is incident on a metal interference pigment, a portion of the incident light is transmitted through the high-refractive-index metal oxide layer, while another portion is reflected from the surface of the high-refractive-index metal oxide layer. The portion of the incident light that transmits through the high-refractive-index metal oxide layer is finally reflected from the surface of the metal substrate. The light reflected from the surface of the metal substrate and the light reflected from the surface of the high-refractive-index metal oxide layer form an optical path difference, resulting in an interference phenomenon that ultimately causes the color of the metal interference pigment. The desired color tone can be set by appropriately selecting the high-refractive-index metal oxide layer, and therefore the refractive index and layer thickness also affect the color tone.

[0004] For diverse applications, the metallic interference pigments used have a hue angle of at least 85 h ab Preferably, the metallic interference pigment has a yellow hue with a greenish tint corresponding to an angle of 15°. At the same time, the metallic interference pigment has a hue (chroma) C of at least 55. * ab It is desirable to have a high color saturation corresponding to 15°.

[0005] Currently available metallic interference pigments do not meet the above requirements.

[0006] For example, the metallic interference pigments Zenexo® Golden Shine from Schlenk Metallic Pigments GmbH, Meoxal® Taklamakan Gold from Merck KGaA, and Paliocrom® Gold from Sun Chemical Colors & Effects GmbH only exhibit a yellow hue without any greenish tint. In this regard, reference is also made to the metallic interference pigments disclosed in WO 2019 / 063372 A1, whose hue angles are only in the range of 68-78 and are still not greenish yellow.

[0007] The present invention therefore aims to provide metallic interference pigments that are yellow with a greenish tint, on the basis that the metallic interference pigments provided should also have high color saturation.

[0008] The object of the present invention is to provide a metallic interference pigment comprising aluminum platelets having an average thickness in the range of 5 nm to 600 nm, optionally passivated and coated by a layer A and a layer B in this order, wherein Layer A is made of silicon dioxide, and layer B is made of iron (III) oxide doped with a dopant element selected from the group consisting of tungsten, indium, gallium, and titanium; the molar fraction of the dopant element in Layer B relative to the total molar amount of iron and the dopant element is 0.5 mol % to 10 mol %; 60 to 85 parts by mass of iron (III) oxide is present per 10 parts by mass of aluminum. This is accomplished by providing a metallic interference pigment.

[0009] The metallic interference pigments according to the present invention, which can be obtained by the manufacturing process according to the present invention described below, are characterized by a greenish yellow color. This is achieved by doping the highly refractive metal oxide layer with iron(III) oxide and small amounts of specific dopant elements. Doping can shift the hue angle of the metallic interference pigments toward higher values ​​without compromising the hue.

[0010] The metallic interference pigments according to the present invention are described in more detail below.

[0011] As already mentioned above, the metal interference pigment according to the present invention comprises aluminum platelets. The aluminum platelets serving as the metal substrate may be passivated, i.e., they may be covered with a native oxide layer. The thickness of the native oxide layer is typically in the range of 3 nm to 5 nm, and as shown below, is included in the thickness of the aluminum platelets in the context of the present invention.

[0012] According to the present invention, the aluminum platelets have an average thickness in the range of 5 nm to 600 nm, preferably in the range of 5 nm to 400 nm, more preferably in the range of 5 nm to 200 nm, and even more preferably in the range of 5 nm to 100 nm, for example, in the range of 10 nm to 50 nm or 15 nm to 30 nm. By using thin aluminum platelets, a larger surface area to be covered with the metal interference pigment can be covered with the same mass of aluminum, thereby achieving particularly high hiding power. The average thickness of the aluminum platelets is their average thickness and should be understood as the arithmetic mean of all measured thicknesses. The average thickness of the aluminum platelets is determined by measurements based on scanning transmission electron microscope (STEM) images. The average thickness of the aluminum platelets is the average of at least 200 measurements of different aluminum platelets.

[0013] Regarding the size of the aluminum platelets, i.e., their diameter, the present invention is not subject to any further limitations. The diameter of the aluminum platelets in the present case is the so-called d 50 This refers to the value at which 50% of the aluminum platelets from a random sample are smaller than the specified value. 50 The diameter d of the aluminum platelet is typically 5 μm to 100 μm, for example, 5 μm to 50 μm or 10 μm to 30 μm. 50 is determined by measurements based on laser light diffraction according to DIN ISO 13320:2020-01 using a commercially available particle size distribution analyzer (Helios BF, Quixel wet dispersion, with lens 3) available, for example, from Sympatec GmbH.

[0014] The diameter of the aluminum platelet, d, also known as the aspect ratio 50 The ratio between the average thickness of the aluminum platelets and the average thickness of the aluminum platelets is also not subject to any particular limitation in the present invention, which can be in the range of, but is not limited to, 50 to 5000, 100 to 2000 or 200 to 1000.

[0015] Ideally, the aluminum platelets have a thickness SPAN(t) in the range of 0.1 to 0.4, preferably in the range of 0.1 to 0.3, for example in the range of 0.1 to 0.2. SPAN ) The thickness SPAN is obtained from the width of the thickness distribution and is calculated according to the following formula:

number

[0016] diameter d 50 Similarly, the exponents in the above formula represent the respective values ​​in the cumulative distribution curve. 10 is the temperature at which 10% of the aluminum platelets 10Correspondingly, 90% of the aluminum platelets are thinner than their t 10 Similar considerations apply to thicknesses of t 50 Thickness and t 90 This also applies to thickness.

[0017] Finally, the thickness variation (Δh) is obtained as a percentage from the thickness SPAN:

number

[0018] Therefore, a thickness SPAN in the range of 0.1 to 0.4 means a thickness variation in the range of 10% to 40%.

[0019] Aluminum platelets can be obtained by wet milling. Judging from their appearance, aluminum platelets obtained by wet milling are also called "corn flakes" or "silver dollars." "Corn flake" type aluminum platelets, also known as lamellar type, have irregular, sawtoothed side edges, while "silver dollar" type aluminum platelets, also known as lenticular type, usually have circular edges.

[0020] Instead of wet milling, aluminum platelets can also be obtained by physical vapor deposition (PVD). Aluminum platelets obtained in this manner are also called vacuum metallized pigments (VMP). Judging from their appearance, they are polygonal with straight side edges. Due to their manufacturing process, vacuum metallized pigments have extremely low thickness variations and are much smoother than aluminum platelets from wet milling. Metal interference pigments based on vacuum metallized pigments not only have excellent color saturation, but also superior hiding power. Therefore, preferably, the aluminum platelets of the metal interference pigments according to the present invention are vacuum metallized pigments. Vacuum metallized pigments are commercially available from various suppliers. In this regard, mention may be made, for example, of vacuum metallized pigments such as Decomet® from Schlenk Metallic Pigments GmbH, METALURE® from Eckart GmbH, and Metasheen® from Sun Chemical Colors & Effects GmbH.

[0021] According to the present invention, the aluminum platelet is coated with Layer A and Layer B in this order. Thus, Layer A is applied to the aluminum platelet first. Subsequently, Layer B is applied to this layer. Thus, Layers A and B encase the aluminum platelet, with Layer A being arranged between the aluminum platelet and Layer B. Typically, the aluminum platelet is coated with Layer A and Layer B in such a way that the coating is completed in each case.

[0022] Layer A, made of silicon dioxide with a low refractive index (refractive index n≦1.8), serves to stabilize the aluminum platelets, thus preventing them from being directly exposed to the conditions that are present during the subsequent formation of layer B.

[0023] Layer A may have an average thickness in the range of, but not limited to, 5 nm to 200 nm, for example, 10 nm to 100 nm. The same explanation given above for determining the average thickness of aluminum platelets applies to determining the average thickness of Layer A, except that 100 samples are measured and evaluated by scanning electron microscope (SEM) images.

[0024] The highly refractive layer B (refractive index n>1.8) is primarily responsible for the interference and thus the color of the metallic interference pigment. In the present invention, layer B is composed of iron(III) oxide doped with a dopant element selected from the group consisting of tungsten, indium, gallium, and titanium. The presence of the dopant element in layer B influences the refractive index of layer B in such a way that the hue angle of the metallic interference pigment shifts toward higher values, resulting in the metallic interference pigment having a final greenish yellow color. Preferably, the dopant element is tungsten, since it is readily available in the form of the corresponding compound.

[0025] Regarding the amount of dopant element, the molar fraction of the dopant element in Layer B relative to the total molar amount of iron and dopant element is 0.5 mol% to 10 mol%, preferably 1.0 to 8 mol%, and even more preferably 1.5 to 7 mol%. If the amount of dopant element is too low, a greenish yellow color will still not be achieved. If the amount of dopant element is too high, the color saturation will decrease, resulting in a significant decrease in the hue of the metal interference pigment. The molar fraction of the dopant element in Layer B relative to the total molar amount of iron and dopant element is determined using energy dispersive X-ray spectroscopy (EDX).

[0026] As already mentioned at the beginning, the thickness of layer B affects not only the refractive index but also the color tone. Typically, layer B has an average thickness in the range of 15 nm to 300 nm, and therefore the average thickness of layer B can be, for example, in the range of 25 nm to 200 nm or in the range of 50 nm to 150 nm. To determine the average thickness of layer B, the explanation given above for determining the average thickness of aluminum platelets applies, with the only difference being that 100 samples are measured and evaluated by scanning electron microscope (SEM) images.

[0027] In both the case of Layer A and Layer B, the thickness of each layer can be adjusted by the amount of each precursor compound added. When the same amount of aluminum platelet is provided, the thickness of each layer increases as more of each precursor compound is added. Therefore, the amount of precursor compound added is adjusted so that Layer A and Layer B have appropriate thicknesses, for example, thicknesses within the above ranges. The precursor compounds for Layer A and Layer B will be discussed in more detail below in the description of the manufacturing method of the present invention.

[0028] According to the present invention, the metal interference pigment contains 60 to 85 parts by weight, e.g., 60 to 80 parts by weight or 60 to 75 parts by weight, of iron(III) oxide per 10 parts by weight of aluminum. Those skilled in the art will recognize that as the aluminum platelets become thinner, the amount of iron(III) oxide must be increased to achieve a certain layer thickness, provided that the aluminum mass remains constant. This is because the thinner the aluminum platelets become, the greater their surface area to be coated. The above discussion, of course, applies equally to layer A as well as layer B.

[0029] Layer B may be provided with a surface coating as layer C. The surface coating may be formed, for example and without limitation, from an organic polymer, a silane, or a siloxane. The surface coating may also consist of silicon dioxide, as will be described later in connection with the manufacturing process according to the invention. In principle, a combination of silicon dioxide and a silane is also possible.

[0030] Applying such a surface coating to Layer B can further enhance the mechanical and chemical resistance of the metal interference pigment, which is also referred to as surface functionalization. However, such a surface coating is not necessarily required. Thus, the metal interference pigment can also consist of aluminum platelets having an average thickness ranging from 5 nm to 600 nm, which may be passivated and are coated with Layer A and Layer B in this order. Therefore, in this embodiment, apart from Layer A and Layer B, there are no other layers on the optionally passivated aluminum platelets.

[0031] Due to this special structure, as described above, the metal interference pigment according to the present invention simultaneously has a greenish yellow hue and high color saturation. In other words, the metal interference pigment according to the present invention has a hue C of at least 55. * ab 15° with a hue angle of at least 85° ab It has a 15° angle.

[0032] Color characteristic, i.e., hue angle h ab 15° and hue C * abTo determine the 15° angle, a coating formulation (8.5% solids by weight) is first prepared, consisting of 0.7 g of metal interference pigment and 9.3 g of a coating containing butanol-moistened nitrocellulose and polycyclohexanone resin as well as another resin based on butyl acrylate-isobutyl vinyl ether. The pigment loading is therefore 7% by weight. The coating formulation is mixed using a speed mixer manufactured by Hauschild & Co. KG, which disperses the metal interference pigment in the coating formulation. The coating formulation is then applied to black and white test cardboard (DIN A5, containing optical brightener) manufactured by TQC Sheen GmbH using a film applicator manufactured by Zehntner GmbH and a 38 μm squeegee manufactured by TQC Sheen GmbH. After squeegee application and subsequent drying, first at room temperature (i.e., 25°C) and then at 60°C, the spectral reflectance of light incident at a 45° angle on the measurement surface and emitted by a D65 light source was measured at six different detection angles (15°, 15°, 25°, 45°, 75°, and 110°) relative to a 10° observer using a commercially available multi-angle spectrophotometer in accordance with DIN EN ISO 18314-3:2018-12 and converted to corresponding values ​​in the CIELAB color space. Here, measurements were performed on a Color Partner GmbH "Color Scout A+" vacuum measuring table equipped with a BYK-Gardner GmbH "BYK-mac i" multi-angle spectrophotometer. This was also used to determine the color difference ΔE110°, as described below.

[0033] In addition to their color properties, the metal interference pigments of the present invention can also be characterized by their color difference ΔE110°. The color difference ΔE110° is a measure of the hiding power of the metal interference pigment, with a smaller color difference ΔE110° indicating a higher hiding power. To determine the color difference ΔE110°, as described above, a squeegee application is again first required, and the pigment loading is again 7% by weight. The color difference is then measured using a commercially available multi-angle spectrophotometer in accordance with DIN 6175:2019-07 in a 45° / 110° geometry.

[0034] Due to the opacity of the aluminum platelets that serve as the metal substrate, the metal interference pigments according to the present invention typically have a color difference ΔE110° of less than 1.5, which is even more true when thin aluminum platelets are used, for example aluminum platelets with an average thickness in the range of 5 nm to 30 nm, and / or when vacuum metallized pigments are used for this purpose.

[0035] Furthermore, the present invention provides a method for producing the metal interference pigment according to the present invention as described above, the production method according to the present invention comprising the following steps (a) to (c): (a) providing aluminum platelets having an average thickness in the range of 5 nm to 600 nm, which are optionally passivated; (b) coating the aluminum platelets provided in step (a) with a layer A of silicon dioxide by hydrolysis of an organosilicon compound or precipitation of water glass; and (c) coating the layer A obtained in step (b) with a layer B of iron(III) oxide doped with a dopant element selected from the group consisting of tungsten, indium, gallium and titanium by precipitation of an iron salt in the presence of a dopant salt selected from the group consisting of tungsten, indium, gallium and titanium salts.

[0036] The metallic interference pigments obtainable by the manufacturing process according to the invention have a yellow color with a greenish tint and a high color saturation.

[0037] The manufacturing process according to the invention is explained in more detail below, but the definitions made in relation to the metallic interference pigments according to the invention apply equally, unless otherwise stated below.

[0038] In step (a) of the manufacturing process according to the present invention, optionally passivated aluminum platelets having an average thickness in the range of 5 nm to 600 nm are provided. For this purpose, the aluminum platelets can be provided in suspended form. To suspend the aluminum platelets, an organic solvent such as isopropanol can be used, which is particularly suitable for the subsequent coating operation in step (b).

[0039] In step (b) of the manufacturing process of the present invention, the aluminum platelet provided in step (a) is coated with a silicon dioxide layer A. This can be achieved by hydrolysis of an organosilicon compound. An example of an organosilicon compound is tetraethyl orthosilicate (TEOS), also known as tetraethoxysilane. However, in principle, any other organosilicon compound can be used as long as it has a hydrolyzable group. Alternatively, the coating in step (b) can be carried out by precipitation of water glass.

[0040] For the coating step (b), hydrolysis is preferably carried out in the presence of a base or acid as a catalyst. Suitable basic catalysts include alkaline solutions such as sodium hydroxide solution or potassium hydroxide solution, particularly aqueous ammonia solution. Suitable acid catalysts include phosphoric acid and carboxylic acids (such as acetic acid and oxalic acid). For hydrolysis, water must be present in at least the stoichiometrically required amount; therefore, excess water is usually used. For temperature control, it is desirable to gradually heat the reaction mixture to 70°C to 75°C within 10 to 48 hours.

[0041] When the coating in step (b) is carried out by precipitation of water glass, typically a solution of sodium silicate (DAB6) is added at 70°C within 2 hours. Depending on the size of the reactor and the pigment surface, the addition is carried out at a flow rate of 0.1-0.2 l / min, while the pH is kept constant at 8.0 with dilute sulfuric acid. Stirring is then continued for 15 minutes, during which the pH remains almost unchanged.

[0042] After hydrolysis of the organosilicon compound or precipitation of the water glass, the aluminum platelets coated with layer A are separated from the other components of the reaction mixture using a filter press and washed. Further details regarding the coating operation of step (b) are known to those skilled in the art and can be found, for example, in WO 2015 / 014484 A1.

[0043] In step (c) of the manufacturing process of the present invention, layer A obtained in step (b) is coated with layer B of iron(III) oxide doped with a dopant element selected from the group consisting of tungsten, indium, gallium, and titanium. This is achieved by precipitation of an iron salt in the presence of a dopant salt selected from the group consisting of tungsten, indium, gallium, and titanium salts. The iron salt is typically iron(III) chloride, but other iron salts may be used as long as they can ultimately be precipitated as iron(III) oxide. The dopant salt may be selected, but is not limited to, from the group consisting of sodium tungstate (dihydrate), indium(III) chloride, gallium(III) nitrate, and titanium(IV) oxychloride (hydrogen chloride). Sodium tungstate (dihydrate), in particular, has proven advantageous for doping due to its ready availability. However, in principle, dopant salts other than those mentioned above are also contemplated, as long as they can be used for appropriate doping.

[0044] In step (c), the aluminum platelets from step (b) coated with the silicon dioxide layer A (present as an aqueous slurry after washing) can be used immediately. Therefore, resuspension is not necessary. The pH is then adjusted to about 3.4 by adding acid. An aqueous solution of an iron salt is then added. At the same time, aqueous ammonia or a similar solution is added. This causes precipitation and maintains the pH constant; otherwise, the pH would drop as a result of the precipitation reaction, as would occur with iron(III) chloride due to the release of hydrogen chloride. The dopant salt can be provided by an aqueous solution of an iron salt, for example, in the case of indium(III) chloride, gallium(III) nitrate, and titanium(IV) oxychloride (xHCl), or by an aqueous ammonia solution, for example, in the case of sodium tungstate (dihydrate). The amount of iron salt is selected so that 60 to 85 parts by weight of iron(III) oxide is present per 10 parts by weight of aluminum in the metallic interference pigment. The amount of dopant salt is selected so that the molar fraction of the dopant element in Layer B relative to the total molar amount of iron and the dopant element is 0.5 mol % to 10 mol %. This allows the metallic interference pigment to have a hue C of at least 55. * ab A hue angle of at least 85° with high color saturation corresponding to 15° ab It definitely has a yellow hue with a greenish tint corresponding to 15°.

[0045] In principle, the iron salts used are quantitatively converted during the coating operation of step (b). The same applies to the dopant salts.

[0046] After precipitation of the iron salt in the presence of the dopant salt, the pH is adjusted to about 5. After cooling and washing the aluminum platelets coated with Layers A and B, they are vacuum dried at a temperature of 60°C. The aluminum platelets coated with Layers A and B are then subjected to a heat treatment characterized by holding the platelets at a temperature of 250°C to 400°C for a period of 30 minutes to 2 hours. This converts the initially formed iron(III) hydroxide doped with a dopant element selected from the group consisting of tungsten, indium, gallium, and titanium into the corresponding iron(III) oxide. Further details regarding the precipitation of step (c) are known to those skilled in the art and can be found, for example, in WO 2015 / 014484 A1.

[0047] The metal interference pigment obtained in step (c) can now be used immediately. If necessary, in the subsequent step (d), layer B can be provided with a surface coating, for example, made of an organic polymer, silane or siloxane. The procedure for this is described in detail, inter alia, in WO 2015 / 044188 A1. If the surface coating is made of silicon dioxide, the method can be carried out in the same manner as in step (b).

[0048] Finally, the present invention provides the use of the metal interference pigments according to the present invention for pigmenting paints, printing inks, inks, plastics, glass, ceramics and decorative cosmetic preparations.By using the metal interference pigments according to the present invention to color these products, they simultaneously acquire a greenish yellow hue and high color saturation, which is not possible with the metal interference pigments known from the prior art. [Example]

[0049] The following examples serve to further illustrate the present invention without, however, limiting it.

[0050] In each of the following examples and comparative examples, 600 g of an aqueous suspension of passivated aluminum platelets coated with an approximately 40 nm thick silicon dioxide layer was used. Commercially available aluminum platelets (Decomet® from Schlenk Metallic Pigments GmbH) have an average thickness of about 25 nm and a diameter d of about 12 μm. 50 The aqueous suspension contained 45 g of passivated aluminum platelets coated with a silicon dioxide layer, of which the aluminum platelets accounted for approximately 15 g.

[0051] The SiO2 layer was formed on the passivated aluminum platelet as follows: 153.5 g of a 14.6 wt.% solids suspension of vacuum-metallized pigment in isopropanol was placed in a vessel, diluted with 100.5 g of ethanol, and heated to 70°C. Next, 3.5 g of a 10% potassium hydroxide solution in ethanol was added. At 70°C, 53.4 g of TEOS and a mixture of 170 g of water and 10.9 g of 25% aqueous ammonia were added sequentially. After a 30-minute reaction time, a second addition of 46.6 g of TEOS was made, followed by a further 30-minute reaction time, followed by a third addition of 41.3 g of TEOS, followed by a further 30-minute reaction time, followed by a fourth addition of 17.0 g of TEOS, followed by a final reaction time of 1 hour. Then, 300 g of water was added, and the mixture was transferred to a larger vessel. The mixture was then further diluted by adding 2200 g of water while stirring. 0.5 g of citric acid was then added, followed by precipitation for a period of 12 to 24 hours. The supernatant was removed, and water was added again. A new precipitation was carried out for a period of 12 to 24 hours, after which the supernatant was again removed. Finally, water was added until an aqueous suspension with a solids content of 7.5% (by mass) was obtained, as shown above.

[0052] Example A The aqueous suspension was heated to a temperature of around 75°C, the pH adjusted to around 3.4, and then 518.0 g of 40% aqueous iron(III) chloride solution was added. In parallel, 365.8 g of 18.25% aqueous ammonia solution was added to induce precipitation and maintain a constant pH. The dopant salt used was sodium tungstate (dihydrate), which had been added to the aqueous ammonia solution in advance. The dopant salt accounted for 8.2 g of the aqueous ammonia solution, corresponding to a mass fraction of sodium tungstate (dihydrate) in the aqueous ammonia solution of approximately 2.25% by weight. Coating with Layer B was carried out so that 68.0 g of iron(III) oxide was present per 10 g of aluminum in the metal interference pigment. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0053] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0054] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and hue C * ab The results are shown in Table 1.

[0055] Example B The aqueous suspension was heated to a temperature of approximately 75°C, the pH was adjusted to approximately 3.4, and then 540.8 g of a 40% aqueous solution of iron(III) chloride was added. In parallel, 382.0 g of an 18.25% aqueous ammonia solution was added to induce precipitation and maintain a constant pH. The dopant salt used was sodium tungstate (dihydrate), which had been added to the aqueous ammonia solution in advance. The dopant salt accounted for 8.6 g of the aqueous ammonia solution, corresponding to a mass fraction of sodium tungstate (dihydrate) in the aqueous ammonia solution of approximately 2.25% by weight. Coating with Layer B was carried out so that the metal interference pigment contained 71.0 g of iron(III) oxide per 10 g of aluminum. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0056] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0057] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and Hue C* ab The results are shown in Table 1.

[0058] Example C The aqueous suspension was heated to a temperature of approximately 75°C, the pH was adjusted to approximately 3.4, and then 492.8 g of a 40% aqueous solution of iron(III) chloride was added. In parallel, 364.9 g of an 18.25% aqueous ammonia solution was added to induce precipitation and maintain a constant pH. The dopant salt used was sodium tungstate (dihydrate), which had been added to the aqueous ammonia solution in advance. The dopant salt accounted for 24.7 g of the aqueous ammonia solution, corresponding to a mass fraction of sodium tungstate (dihydrate) in the aqueous ammonia solution of approximately 6.76% (by mass). Coating with Layer B was carried out so that the metal interference pigment contained 64.7 g of iron(III) oxide per 10 g of aluminum. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0059] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0060] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and hue C * ab The results are shown in Table 1.

[0061] Example D The aqueous suspension was heated to a temperature of approximately 75°C, the pH was adjusted to approximately 3.4, and then 519.5 g of a 40% aqueous solution of iron(III) chloride was added. In parallel, 384.7 g of an 18.25% aqueous ammonia solution was added to induce precipitation and maintain a constant pH. The dopant salt used was sodium tungstate (dihydrate), which had been added to the aqueous ammonia solution in advance. The dopant salt accounted for 26.0 g of the aqueous ammonia solution, corresponding to a mass fraction of sodium tungstate (dihydrate) in the aqueous ammonia solution of approximately 6.76% (by mass). Coating with Layer B was carried out so that 68.2 g of iron(III) oxide per 10 g of aluminum was present in the metal interference pigment. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0062] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0063] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and hue C * ab The results are shown in Table 1.

[0064] Example E The aqueous suspension was heated to a temperature of approximately 75°C, the pH was adjusted to approximately 3.4, and then 537.0 g of a 40% aqueous solution of iron(III) chloride was added. In parallel, 397.6 g of an 18.25% aqueous ammonia solution was added to induce precipitation and maintain a constant pH. The dopant salt used was sodium tungstate (dihydrate), which had been added to the aqueous ammonia solution in advance. The dopant salt accounted for 26.9 g of the aqueous ammonia solution, corresponding to a mass fraction of sodium tungstate (dihydrate) in the aqueous ammonia solution of approximately 6.76% (by mass). Coating with Layer B was carried out so that 70.5 g of iron(III) oxide was present per 10 g of aluminum in the metal interference pigment. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0065] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0066] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and hue C * ab The results are shown in Table 1.

[0067] Example F The aqueous suspension was heated to a temperature of approximately 75°C, the pH was adjusted to approximately 3.4, and then 542.1 g of 40% aqueous iron(III) chloride solution was added. In parallel, 368.1 g of 18.25% aqueous ammonia solution was added to induce precipitation and maintain a constant pH. Indium(III) chloride, which had been added to the aqueous iron(III) chloride solution beforehand, was used as the dopant salt. The dopant salt accounted for 8.9 g of the aqueous iron(III) chloride solution, corresponding to a mass fraction of indium(III) chloride in the aqueous iron(III) chloride solution of approximately 1.65% (by mass). Coating with Layer B was carried out so that 70.0 g of iron(III) oxide was present per 10 g of aluminum in the metal interference pigment. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0068] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0069] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and hue C * ab The results are shown in Table 1.

[0070] Example G The aqueous suspension was heated to a temperature of approximately 75°C, the pH was adjusted to approximately 3.4, and then 493.1 g of a 40% aqueous solution of iron(III) chloride was added. In parallel, 333.9 g of an 18.25% aqueous ammonia solution was added to induce precipitation and maintain a constant pH. Gallium(III) nitrate, which had been added to the aqueous solution of iron(III) chloride beforehand, was used as the dopant salt. The dopant salt accounted for 9.4 g of the aqueous solution of iron(III) chloride, corresponding to a mass fraction of gallium(III) nitrate in the aqueous solution of iron(III) chloride of approximately 1.91% (by mass). Coating with Layer B was carried out so that 63.5 g of iron(III) oxide was present per 10 g of aluminum in the metal interference pigment. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0071] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0072] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and hue C * ab The results are shown in Table 1.

[0073] Example H The aqueous suspension was heated to a temperature of approximately 75°C, the pH was adjusted to approximately 3.4, and then 548.3 g of 40% aqueous iron(III) chloride solution was added. In parallel, 371.3 g of 18.25% aqueous ammonia solution was added to induce precipitation and maintain a constant pH. Gallium(III) nitrate, which had been added to the aqueous iron(III) chloride solution beforehand, was used as the dopant salt. The dopant salt accounted for 10.5 g of the aqueous iron(III) chloride solution, corresponding to a mass fraction of gallium(III) nitrate in the aqueous iron(III) chloride solution of approximately 1.91% (by mass). Coating with Layer B was carried out so that 70.6 g of iron(III) oxide was present per 10 g of aluminum in the metal interference pigment. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0074] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0075] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and hue C * ab The results are shown in Table 1.

[0076] Example I The aqueous suspension was heated to approximately 75°C, the pH adjusted to approximately 3.4, and then 569.4 g of 40% aqueous iron(III) chloride solution was added. In parallel, 356.6 g of 18.25% aqueous ammonia solution was added to induce precipitation and maintain a constant pH. Titanium(IV) oxychloride (x hydrogen chloride), which had been added previously to the aqueous iron(III) chloride solution, was used as the dopant salt. The dopant salt accounted for 53.0 g of the aqueous iron(III) chloride solution, corresponding to a mass fraction of titanium(IV) oxychloride (x hydrogen chloride) in the aqueous iron(III) chloride solution of approximately 9.30% by weight. Coating with Layer B was carried out so that 67.8 g of iron(III) oxide was present per 10 g of aluminum in the metallic interference pigment. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0077] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0078] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and hue C * ab The results are shown in Table 1.

[0079] Comparative example A The aqueous suspension was heated to a temperature of about 75°C, the pH was adjusted to about 3.4, and then 490.6 g of a 40% aqueous solution of iron(III) chloride was added. At the same time, 338.7 g of an 18.25% aqueous solution of ammonia was added to induce precipitation and maintain a constant pH. Coating with Layer B was carried out so that the metallic interference pigment contained 64.4 g of iron(III) oxide per 10 g of aluminum. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0080] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0081] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and hue C * ab The results are shown in Table 1.

[0082] Comparative example B The aqueous suspension was heated to a temperature of about 75°C, the pH was adjusted to about 3.4, and then 518.7 g of a 40% aqueous solution of iron(III) chloride was added. At the same time, 358.1 g of an 18.25% aqueous solution of ammonia was added to induce precipitation and maintain a constant pH. Coating with Layer B was carried out so that 68.1 g of iron(III) oxide was present per 10 g of aluminum in the metal interference pigment. For this purpose, appropriate preliminary tests were first carried out, taking into account the aluminum platelets used.

[0083] The pH value was then adjusted to around 5. After cooling and washing, vacuum drying was carried out at a temperature of around 60° C. Finally, the solid thus obtained was subjected to a heat treatment by first heating from room temperature to 270° C. at a heating rate of 1.5° C. / min, then heating from 270° C. to 370° C. at a heating rate of 0.5° C. / min, followed by holding at 370° C. for 1 hour.

[0084] After heat treatment, the resulting metallic interference pigment is then subjected to the measurement of its color properties, i.e., hue angle h, as described above. ab 15° and hue C * ab The results are shown in Table 1.

[0085] [Table 1]

[0086] As is evident from Examples A to I above, a hue angle h of at least 85 ab 15° and at least 55 hue C * ab A hue angle of 15° can be achieved by doping with a dopant element selected from the group consisting of tungsten, indium, gallium, and titanium. Therefore, the metallic interference pigments of Examples A to I were characterized by a greenish yellow hue and high color saturation. In contrast, without doping, as is evident from Comparative Examples A and B above, a hue angle h of just under 80° can be achieved. ab Only 15° could be achieved. Therefore, the metallic interference pigments of Comparative Examples A and B did not exhibit a greenish yellow hue.

Claims

1. 1. A metallic interference pigment comprising aluminum platelets having an average thickness in the range of 5 nm to 600 nm, optionally passivated and coated by a layer A and a layer B in that order, Layer A is made of silicon dioxide, and Layer B is made of iron (III) oxide doped with a dopant element selected from the group consisting of tungsten, indium, gallium, and titanium; the molar fraction of the dopant element in Layer B relative to the total molar amount of iron and the dopant element is 0.5 mol % to 10 mol %; A metallic interference pigment in which 60 to 85 parts by weight of iron(III) oxide is present per 10 parts by weight of aluminum.

2. Diameter d of aluminum platelet ５０ 2. The metal interference pigment of claim 1, wherein the average particle size is 5 μm to 100 μm.

3. 3. The metallic interference pigment of claim 1, wherein the aluminum platelets have a thickness variation in the range of 10% to 40%.

4. The metallic interference pigment of any one of claims 1 to 3, wherein the aluminum platelets are vacuum metallized pigments.

5. 5. The metallic interference pigment according to claim 1, wherein Layer A has an average thickness in the range of 5 nm to 200 nm.

6. 6. The metallic interference pigment according to claim 1, wherein the dopant element is tungsten.

7. 7. The metallic interference pigment according to claim 1, wherein Layer B has an average thickness in the range of 15 nm to 300 nm.

8. The metallic interference pigment according to any one of claims 1 to 7, wherein Layer B is provided with a surface coating.

9. Hue C of at least 55 ＊ ａｂ Hue angle h of at least 85 at 15° ａｂ 9. The metallic interference pigment of claim 1, wherein the .alpha.

10. 10. The metallic interference pigment according to any one of claims 1 to 9, having a color difference ΔE110° of less than 1.

5.

11. A method for producing the metal interference pigment of any one of claims 1 to 10, comprising the following steps (a) to (c): (a) providing aluminum platelets having an average thickness in the range of 5 nm to 600 nm, which are optionally passivated; (b) coating the aluminum platelets provided in step (a) with a layer A of silicon dioxide by hydrolysis of an organosilicon compound or precipitation of water glass; and (c) coating the layer A obtained in step (b) with a layer B of iron(III) oxide doped with a dopant element selected from the group consisting of tungsten, indium, gallium and titanium by precipitation of an iron salt in the presence of a dopant salt selected from the group consisting of tungsten, indium, gallium and titanium salts.

12. 12. The method of claim 11, wherein the dopant salt is selected from the group consisting of sodium tungstate (dihydrate), indium (III) chloride, gallium (III) nitrate, and titanium (IV) oxychloride (x hydrogen chloride).

13. 13. The method of claim 12, wherein the dopant salt is sodium tungstate (dihydrate).

14. The method of any one of claims 11 to 13, further comprising the following step (d): (d) providing a surface coating on Layer B obtained in step (c);

15. Use of the metallic interference pigments according to any one of claims 1 to 10 for pigmented paints, printing inks, inks, plastics, glass, ceramics and decorative cosmetic preparations.

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