Metal interference pigments, methods for producing them, and their use

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] This invention relates to a greenish-yellow metal interference pigment, a method for producing the same, and its use.

[0002] In recent years, metal interference pigments have become established for use in colored paints, printing inks, inks, plastics, glass, ceramics, and decorative cosmetic formulations. Metal interference pigments are characterized by a metal substrate, such as an aluminum substrate (which can be stabilized by providing a layer of silicon dioxide on top), being covered with a highly refractive metal oxide layer, such as a layer of iron(III) oxide. Because the metal substrate is opaque, metal interference pigments have high opacity, in contrast to pearlescent pigments which contain translucent substrates.

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

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

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

[0006] For example, the metallic interference pigments of Zenexo® GoldenShine manufactured by Schlenk Metallic Pigments GmbH, Meoxal® Taklamakan Gold manufactured by Merck KGaA, and Paliocrom® Gold manufactured by Sun Chemical Colors & Effects GmbH do not have a greenish hue and only exhibit a yellow phase. In this regard, reference is also made to the metallic interference pigments disclosed in WO 2019 / 063372 A1, but its hue angle is only in the range of 68 to 78 and is still not a yellowish green.

[0007] Therefore, the object of the present invention is to provide a yellow metallic interference pigment with a greenish hue, and it is based on the fact that the provided metallic interference pigment should also have a high color saturation.

[0008] The above object is achieved by a metallic interference pigment according to the present invention, which comprises aluminum platelets having an average thickness in the range of 5 nm to 600 nm, optionally passivated, and coated in this order by layer A and layer B, where layer A is composed of silicon dioxide and 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 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 relative to 10 parts by mass of aluminum, by providing the metallic interference pigment.

[0009] The metal interference pigment according to the present invention that can be obtained by the manufacturing process according to the present invention described below is characterized by a yellow color tone with a greenish tint. This is achieved by doping the high refractive index metal oxide layer with a small amount of a specific dopant element in addition to iron(III) oxide. Doping makes it possible to shift the hue angle of the metal interference pigment towards a higher value without incurring damage in terms of hue.

[0010] The metal interference pigment according to the present invention will be described in more detail below.

[0011] As already described above, the metal interference pigment according to the present invention includes aluminum platelets. The aluminum platelets serving as the metal substrate may be passivated, that is, they may be coated with a natural oxide layer. The thickness of the natural oxide layer typically ranges from 3 nm to 5 nm and is included in the thickness of the aluminum platelets in the context of the present invention as shown below.

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

[0013] The present invention is not further limited with respect to the size of the aluminum platelet, i.e., its diameter. The diameter of the aluminum platelet in the case of the present invention is the so-called d 50 which means that 50% of the aluminum platelets from a random sample have a value smaller than its specified value. Although not limited, the diameter d 50 of the aluminum platelet is typically 5 μm to 100 μm, for example, 5 μm to 50 μm or 10 μm to 30 μm. The diameter d 50 of the aluminum platelet is determined by measurement based on laser light diffraction in accordance with DIN ISO 13320:2020-01 using a commercially available particle size distribution measuring device (Helios BF, Quixel wet dispersion, using lens 3) commercially available from Sympatec GmbH, for example.

[0014] The ratio between the diameter d 50 of the aluminum platelet, also referred to as the aspect ratio, and the average thickness of the aluminum platelet is also not subject to any specific restrictions in the case of the present invention. It can be in the range of 50 to 5000, 100 to 2000 or 200 to 1000, but is not limited thereto.

[0015] Ideally, the aluminum platelet has a thickness SPAN (t SPAN ) 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, but is not limited thereto. The thickness SPAN is obtained from the width of the thickness distribution and is calculated according to the following formula:

Equation

[0016] Similar to the diameter d 50 , the exponents in the above formula represent the respective values in the cumulative distribution curve. Therefore, t 10 is such that 10% of the aluminum platelets have a t 10It means thinner than the thickness. In response to that, 90% of aluminum plates are thinner than their thickness. 10 Having a thickness equal to or greater than the thickness. A similar consideration is, t 50 Thickness and t 90 This also applies to thickness.

[0017] Finally, the thickness variation (Δh) is obtained as a percentage of 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 from wet grinding. Judging from their appearance, aluminum platelets obtained by wet grinding are also called "cornflake" or "silver dollar." Cornflake-type aluminum platelets, also known as lamellar-type, have irregular, serrated lateral edges, while silver dollar-type aluminum platelets, also known as lenticular-type, usually have circular edges.

[0020] Instead of wet grinding, aluminum platelets can also be obtained by physical vapor deposition (PVD). Aluminum platelets obtained by this method are also called vacuum metallized pigments (VMPs). Judging from their appearance, they are polygonal with straight side edges. Due to their manufacturing process, vacuum metallized pigments have extremely low thickness variation and are much smoother than aluminum platelets from wet grinding. Metal interference pigments based on vacuum metallized pigments not only have excellent color saturation but also excellent opacity. Preferably, the aluminum platelets of metal interference pigments according to the present invention are therefore vacuum metallized pigments. Vacuum metallized pigments are commercially available from various suppliers. In this regard, for example, Decomet® from Schlenk Metallic Pigments GmbH, METALURE® from Eckart GmbH, and Metasheeen® from Sun Chemical Colors & Effects GmbH should be mentioned.

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

[0022] Layer A, made from silicon dioxide and having a low refractive index (refractive index n ≤ 1.8), helps stabilize the aluminum platelet. Therefore, layer A prevents the aluminum platelet from being directly exposed to the conditions that are being carried out during the subsequent formation of layer B.

[0023] While not limited, layer A can have an average thickness in the range of 5 nm to 200 nm, for example, in the range of 10 nm to 100 nm. The explanation given above for determining the average thickness of aluminum platelets applies directly to determining the average thickness of layer A, except that 100 samples are measured and evaluated using scanning electron microscope (SEM) imaging.

[0024] In this case, layer B, with high refractive index (refractive index n > 1.8), is primarily involved in interference and, consequently, in the color scheme of the metal interference pigment. In this invention, layer B consists 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 allows for an influence on the refractive index of layer B, such that the hue angle of the metal interference pigment shifts toward a larger value, resulting in the metal interference pigment ultimately having a greenish-yellow hue. Preferably, the dopant element is tungsten, as it is readily available in the form of the corresponding compound.

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

[0026] As mentioned earlier, the thickness of layer B affects not only the refractive index but also the color. 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 50 nm to 150 nm. Determining the average thickness of layer B is the same as the explanation given above for determining the average thickness of aluminum platelets, except that 100 samples are measured and evaluated using scanning electron microscope (SEM) imaging.

[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. Given the same amount of aluminum platelets, 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 layers A and B have appropriate thicknesses, for example, within the range shown above. The precursor compounds of layers A and B are discussed in more detail below in the description of the manufacturing method according to the present invention.

[0028] According to the present invention, the metal interference pigment contains 60 to 85 parts by mass, for example, 60 to 80 parts by mass or 60 to 75 parts by mass of iron(III) oxide per 10 parts by mass of aluminum. Those skilled in the art will recognize that when the aluminum platelet becomes thinner, the mass of iron(III) oxide must be increased to achieve a certain layer thickness, provided that the mass of aluminum remains constant. This is because, as the aluminum platelet becomes thinner, the surface area covered increases. The above considerations naturally apply equally to layer A as well as layer B.

[0029] A surface coating can be provided as layer C in layer B. While not limited to these, the surface coating can be formed from, for example, an organic polymer, silane, or siloxane. The surface coating may also be composed of silicon dioxide, as will be described later in relation to the manufacturing process according to the present invention. In principle, combinations of silicon dioxide and silane are also possible.

[0030] By applying such a surface coating to layer B, the mechanical and chemical resistance of the metal interference pigment can be further enhanced, which is also referred to as surface functionalization. However, such a surface coating is not always necessary. Therefore, the metal interference pigment may also consist of an aluminum platelet having an average thickness in the range of 5 nm to 600 nm, which may also be passivated and coated in this order by layers A and B. Thus, apart from layers A and B, in this embodiment there are no other layers on the optionally passivated aluminum platelet.

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

[0032] Color characteristics, i.e., hue angle ab 15° and hue C * abTo determine the 15°, a coating formulation (8.5% by mass solids) is first prepared, consisting of 0.7 g of a 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. Therefore, the pigment addition is 7% (by mass). After mixing the coating formulation using a speed mixer from Hauschild & Co KG to disperse the metal interference pigment in the coating formulation, the coating formulation is applied to black and white test cardboard (DIN A5, containing fluorescent whitening agent) from TQC Sheen GmbH using a film applicator from Zehntner GmbH and a 38 μm squeegee from TQC Sheen GmbH. After squeegee coating and subsequent drying at room temperature (i.e., 25°C) followed by drying at 60°C, the spectral reflectance of light emitted by a D65 light source, incident at a 45° angle on the measurement surface, is measured at six different detection angles (15°, 15°, 25°, 45°, 75°, and 110°) for a 10° observer, using a commercially available multi-angle spectrophotometer according to DIN EN ISO 18314-3:2018-12, and converted to corresponding values ​​in the CIELAB color space. Here, the measurements are performed on a ColorPartner GmbH "Color Scout A+" vacuum measuring table equipped with a BYK-Gardner GmbH "BYK-mac i" multi-angle spectrophotometer. This is also used to determine the color difference ΔE110°, as described later.

[0033] In addition to its color characteristics, the metal interference pigment according to the present invention can also be characterized by its color difference ΔE110°. The color difference ΔE110° is a measure of the opacity of the metal interference pigment, where a smaller color difference ΔE110° indicates higher opacity. In determining the color difference ΔE110°, as described above, squeegee coating is required first, and the pigment addition is again 7% by mass. The color difference is then measured using a commercially available multi-angle spectrophotometer in accordance with DIN 6175:2019-07, in a geometric arrangement of 45° / 110°.

[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. This is even more true when thin aluminum platelets, for example, aluminum platelets having an average thickness in the range of 5 nm to 30 nm, are used 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) A step of providing an aluminum platelet having an average thickness in the range of 5 nm to 600 nm, which is optionally passivated; (b) A step of coating the aluminum platelet provided in step (a) with a layer A of silicon dioxide by hydrolysis of an organosilicon compound or precipitation of water glass; and (c) A step of coating layer A obtained in step (b) with 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 iron salt in the presence of a dopant salt selected from the group consisting of tungsten salt, indium salt, gallium salt, and titanium salt.

[0036] The metal interference pigment obtainable by the manufacturing process according to the present invention has a greenish-yellow hue and high color saturation.

[0037] The manufacturing process according to the present invention is described in more detail below, and unless otherwise specified, the definitions made in relation to metal interference pigments according to the present invention apply equally.

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

[0039] In step (b) of the manufacturing process according to the present invention, the aluminum platelet provided in step (a) is coated with a layer A of silicon dioxide. This can be done 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 hydrolyzable groups. Alternatively, the coating in step (b) can be carried out by precipitation of water glass.

[0040] Regarding the coating in 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 acidic catalysts include phosphoric acid and carboxylic acids (such as acetic acid and oxalic acid). In hydrolysis, water must be present in at least the stoichiometrically required amount, and therefore, excess water is usually used. In terms of temperature control, it is desirable to gradually heat the reaction mixture to 70°C to 75°C within 10 to 48 hours.

[0041] If the coating in step (b) is carried out by precipitation of water glass, typically a solution of sodium silicate (DAB6) is added within 2 hours at 70°C. 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, where the pH value is kept constant at 8.0 by dilute sulfuric acid. Stirring is then continued for 15 minutes, during which the pH value hardly changes.

[0042] Following the hydrolysis of the organosilicon compound or the precipitation of 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 in 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 according to 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 done by precipitation of an iron salt in the presence of a dopant salt selected from the group consisting of tungsten salts, indium salts, gallium salts, and titanium salts. The iron salt is typically iron(III) chloride, but other iron salts may be used as long as they can ultimately precipitate as iron(III) oxide. The dopant salt can be selected from the group consisting of sodium tungstate (dihydrate), indium(III) chloride, gallium(III) nitrate, and titanium(IV) oxychloride (x hydrogen chloride), although this is not limited to these. In particular, sodium tungstate (dihydrate) has proven advantageous for doping due to its easy availability. However, in principle, other dopant salts other than those mentioned above are also conceivable as long as they can be used for appropriate doping.

[0044] In the coating of step (c), the aluminum platelets from step (b), coated with silicon dioxide layer A (which exist as an aqueous slurry after washing), can be used immediately. Therefore, resuspension is not necessary. The pH is then adjusted to approximately 3.4 by adding acid. Next, an aqueous solution of iron salt is added. Simultaneously, an aqueous solution of ammonia or an equivalent is added. This causes precipitation while maintaining a constant pH; otherwise, a decrease in pH would occur as a result of the precipitation reaction, such as the release of hydrogen chloride when iron(III) chloride is used. The dopant salt can be supplied as an aqueous solution of iron salt in the case of, for example, indium(III) chloride, gallium(III) nitrate, and titanium(IV) oxychloride (x hydrogen chloride), or as an aqueous solution of ammonia in the case of, for example, sodium tungstate (dihydrate). The amount of iron salt is selected so that 60 to 85 parts by mass of iron(III) oxide are present in the metal interference pigment per 10 parts by mass of aluminum. The amount of dopant salt is selected such that the mole 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%. This ensures that the metal interference pigment has at least 55 hue C * ab Along with a high color saturation equivalent to 15°, at least a hue angle of 85 h ab It definitely has a greenish-yellow hue corresponding to 15°.

[0045] In principle, the iron salts used are quantitatively converted during the coating operation in 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 approximately 5. After cooling and washing the aluminum plates coated with layers A and B, they are vacuum-dried at a temperature of 60°C. The aluminum plates coated with layers A and B are then subjected to a heat treatment characterized by being held 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 in 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 be used immediately here. If necessary, a surface coating can be provided on layer B in the subsequent step (d), which may be formed from, for example, an organic polymer, silane, or siloxane. The procedure for this is described in detail, in particular, in WO 2015 / 044188 A1. If the surface coating is composed 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 metal interference pigments according to the present invention for colored paints, printing inks, inks, plastics, glass, ceramics, and decorative cosmetic formulations. By coloring with metal interference pigments according to the present invention, each product is simultaneously given a greenish-yellow hue and high color saturation. This is not possible with metal interference pigments known from the prior art. [Examples]

[0049] The following examples may be helpful in further illustrating the present invention, but are not limited thereto.

[0050] In each of the following examples and comparative examples, 600 g of an aqueous suspension of passivated aluminum platelets coated with a silicon dioxide layer approximately 40 nm thick was used. Commercially available aluminum platelets (Decomet®, manufactured by Schlenk Metallic Pigments GmbH) have an average thickness of approximately 25 nm and a diameter of approximately 12 μm. 50 It was a vacuum metallized pigment having [specific properties]. The solid content of the aqueous suspension was 7.5% (by mass). Therefore, the aqueous suspension contained 45 g of passivated aluminum platelets coated with a silicon dioxide layer, with approximately 15 g of which was aluminum platelets.

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

[0052] Example A The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 518.0 g of 40% iron(III) chloride aqueous solution was added. In parallel, 365.8 g of 18.25% ammonia aqueous solution was added to induce precipitation and maintain a constant pH. Sodium tungstate (dihydrate), pre-added to the ammonia aqueous solution, was used as the dopant salt. The dopant salt accounted for 8.2 g of the ammonia aqueous solution, which corresponds to approximately 2.25% by mass of sodium tungstate (dihydrate) in the ammonia aqueous solution. 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 conducted considering the aluminum platelets to be used.

[0053] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0054] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C * ab We investigated the value of 15°. The results are shown in Table 1.

[0055] Example B The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 540.8 g of 40% iron(III) chloride aqueous solution was added. In parallel, 382.0 g of 18.25% ammonia aqueous solution was added to induce precipitation and maintain a constant pH. Sodium tungstate (dihydrate), pre-added to the ammonia aqueous solution, was used as the dopant salt. The dopant salt accounted for 8.6 g of the ammonia aqueous solution, which corresponds to approximately 2.25% by mass of sodium tungstate (dihydrate) in the ammonia aqueous solution. 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 conducted considering the aluminum platelets to be used.

[0056] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0057] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C* ab We investigated the value of 15°. The results are shown in Table 1.

[0058] Example C The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 492.8 g of 40% iron(III) chloride aqueous solution was added. In parallel, 364.9 g of 18.25% ammonia aqueous solution was added to induce precipitation and maintain a constant pH. Sodium tungstate (dihydrate), pre-added to the ammonia aqueous solution, was used as the dopant salt. The dopant salt accounted for 24.7 g of the ammonia aqueous solution, which corresponds to approximately 6.76% (by mass) of the sodium tungstate (dihydrate) in the ammonia aqueous solution. 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 conducted considering the aluminum platelets to be used.

[0059] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0060] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C * ab We investigated the value of 15°. The results are shown in Table 1.

[0061] Example D The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 519.5 g of 40% iron(III) chloride aqueous solution was added. In parallel, 384.7 g of 18.25% ammonia aqueous solution was added to induce precipitation and maintain a constant pH. Sodium tungstate (dihydrate), pre-added to the ammonia aqueous solution, was used as the dopant salt. The dopant salt accounted for 26.0 g of the ammonia aqueous solution, which corresponds to approximately 6.76% (by mass) of the sodium tungstate (dihydrate) in the ammonia aqueous solution. Coating with layer B was carried out so that 68.2 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 conducted considering the aluminum platelets to be used.

[0062] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0063] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C * ab We investigated the value of 15°. The results are shown in Table 1.

[0064] Example E The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 537.0 g of 40% iron(III) chloride aqueous solution was added. In parallel, 397.6 g of 18.25% ammonia aqueous solution was added to induce precipitation and maintain a constant pH. Sodium tungstate (dihydrate), pre-added to the ammonia aqueous solution, was used as the dopant salt. The dopant salt accounted for 26.9 g of the ammonia aqueous solution, which corresponds to approximately 6.76% (by mass) of the sodium tungstate (dihydrate) in the ammonia aqueous solution. 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 conducted considering the aluminum platelets to be used.

[0065] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0066] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C * ab We investigated the value of 15°. The results are shown in Table 1.

[0067] Example F The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 542.1 g of 40% iron(III) chloride aqueous solution was added. In parallel, 368.1 g of 18.25% ammonia aqueous solution was added to induce precipitation and maintain a constant pH. Indium(III) chloride, pre-added to the iron(III) chloride aqueous solution, was used as the dopant salt. The dopant salt accounted for 8.9 g of the iron(III) chloride aqueous solution, which corresponds to approximately 1.65% (by mass) of indium(III) chloride in the iron(III) chloride aqueous solution. 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 conducted considering the aluminum platelets to be used.

[0068] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0069] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C * ab We investigated the value of 15°. The results are shown in Table 1.

[0070] Example G The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 493.1 g of 40% iron(III) chloride aqueous solution was added. In parallel, 333.9 g of 18.25% ammonia aqueous solution was added to induce precipitation and maintain a constant pH. Gallium(III) nitrate, pre-added to the iron(III) chloride aqueous solution, was used as the dopant salt. The dopant salt accounted for 9.4 g of the iron(III) chloride aqueous solution, which corresponds to approximately 1.91% (by mass) of gallium(III) nitrate in the iron(III) chloride aqueous solution. 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 conducted considering the aluminum platelets to be used.

[0071] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0072] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C * ab We investigated the value of 15°. The results are shown in Table 1.

[0073] Example H The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 548.3 g of 40% iron(III) chloride aqueous solution was added. In parallel, 371.3 g of 18.25% ammonia aqueous solution was added to induce precipitation and maintain a constant pH. Gallium(III) nitrate, pre-added to the iron(III) chloride aqueous solution, was used as the dopant salt. The dopant salt accounted for 10.5 g of the iron(III) chloride aqueous solution, which corresponds to approximately 1.91% (by mass) of gallium(III) nitrate in the iron(III) chloride aqueous solution. 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 conducted considering the aluminum platelets to be used.

[0074] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0075] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C * ab We investigated the value of 15°. The results are shown in Table 1.

[0076] Example I The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 569.4 g of 40% iron(III) chloride aqueous solution was added. In parallel, 356.6 g of 18.25% ammonia aqueous solution was added to induce precipitation and maintain a constant pH. Titanium(IV) oxychloride (x hydrogen chloride), pre-added to the iron(III) chloride aqueous solution, was used as the dopant salt. The dopant salt accounted for 53.0 g of the iron(III) chloride aqueous solution, which corresponds to approximately 9.30% by mass of titanium(IV) oxychloride (x hydrogen chloride) in the iron(III) chloride aqueous solution. 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 metal interference pigment. For this purpose, appropriate preliminary tests were first conducted considering the aluminum platelets to be used.

[0077] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0078] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C * ab We investigated the value of 15°. The results are shown in Table 1.

[0079] Comparative example A The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 490.6 g of 40% iron(III) chloride aqueous solution was added. Simultaneously, 338.7 g of 18.25% ammonia aqueous solution was added to induce precipitation and maintain a constant pH. Coating with layer B was carried out so that the metal interference pigment contained 64.4 g of iron(III) oxide per 10 g of aluminum. For this purpose, appropriate preliminary tests were first conducted considering the aluminum platelets to be used.

[0080] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0081] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C * ab We investigated the value of 15°. The results are shown in Table 1.

[0082] Comparative example B The aqueous suspension was heated to approximately 75°C, and the pH was adjusted to approximately 3.4. Then, 518.7 g of 40% iron(III) chloride aqueous solution was added. Simultaneously, 358.1 g of 18.25% ammonia aqueous solution 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 conducted considering the aluminum platelets to be used.

[0083] Next, the pH value was adjusted to around 5. After cooling and washing, vacuum drying was performed at a temperature of around 60°C. Finally, the resulting solid was subjected to a heat treatment in which it was first heated from room temperature to 270°C at a heating rate of 1.5°C / min, then heated from 270°C to 370°C at a heating rate of 0.5°C / min, and then held at 370°C for 1 hour.

[0084] After heat treatment, the resulting metal interference pigment is subjected to the color characteristics, i.e., the hue angle h, as described above. ab 15° and hue C * ab We investigated the value of 15°. The results are shown in Table 1.

[0085] [Table 1]

[0086] As is clear from the above examples A to I, the hue angle h is 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 metal interference pigments of Examples A-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, the hue angle was slightly less than 80°. ab Only 15° was achieved. Therefore, the metal interference pigments of Comparative Examples A and B did not exhibit a greenish-yellow hue.

Claims

1. A metal interference pigment comprising an aluminum platelet having an average thickness in the range of 5 nm to 600 nm, which is optionally passivated and coated in this order by layers A and B, Layer A is composed of silicon dioxide, and 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 mole fraction of the dopant element in layer B relative to the total molar amount of iron and dopant elements is between 0.5 mol% and 10 mol%. A metal interference pigment containing 60 to 85 parts by mass of iron(III) oxide per 10 parts by mass of aluminum.

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

3. The metal interference pigment according to claim 1, wherein the aluminum platelet has a thickness variation in the range of 10% to 40%.

4. The metal interference pigment according to claim 1, wherein the aluminum platelet is a vacuum metallized pigment.

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

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

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

8. The metal interference pigment according to claim 1, wherein a surface coating is provided on layer B.

9. At least 55 hue C ＊ ａｂ At 15°, the h-angle is at least 85. ａｂ A metal interference pigment according to claim 1, having an angle of 15°.

10. A metal interference pigment according to claim 1, having a color difference ΔE of 110° of less than 1.

5.

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

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

14. The method according to claim 11, further comprising the following step (d): (d) A step of applying a surface coating to layer B obtained in step (c).

15. Use of a metal interference pigment according to any one of claims 1 to 10 for colored paints, printing inks, inks, plastics, glass, ceramics and decorative cosmetic formulations.

Images