Effect pigments having reflective core

Abstract

To provide a thin effect pigment that has a rather simple structure that shows some very favourable optical properties.SOLUTION: The present invention relates to an effect pigment having optically active layers consisting of a flake of a highly reflective material with a layer of a semiconducting material directly adjacent to one side or both sides, the semiconducting material having a bandgap of 0.1 to 3.5 eV. The effect pigment may be further coated with a coating which is optically non-active in the visible wavelength region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to effect pigments with a reflective core. Generally, effect pigments can be described as flakes with a plate-like structure that reflect, scatter, absorb, or otherwise exhibit different optical appearances depending on the viewing angle relative to the substrate on or in which they are applied. Effect pigments are used, for example, in coatings in the automotive industry or in cosmetics. [Background technology]

[0002] Effect pigments are known in the art and can generally be classified based on the core material for the platelet-like structure, which may be metallic or non-metallic. Typically, this core material is coated with a number of different layers to provide the desired optical effect.

[0003] WO 1999 / 035194 discloses thin metallic effect pigments, which comprise a thin, typically metallic, reflective layer with a dielectric coating disposed on both flat surfaces. Other layers may be added to this structure. Examples of suitable dielectric materials include silicon dioxide (SiO2) and magnesium fluoride (MgF2). However, the required thickness of the dielectric layer is >50 nm, and the resulting saturation effect is low. The flakes also exhibit color flop due to path-dependent interference effects. Furthermore, all claimed layers adjacent to the metal core are dielectric layers with a band gap of >3.5 eV and a refractive index of <2.0.

[0004] U.S. Patent Application Publication Nos. 20140368918 and 20150309231 disclose high-chroma color pigments in the form of multilayer stacks. U.S. Patent Application Publication No. 20140368918 describes pigments consisting of at least a reflective core layer, a semiconductor absorbing layer, and a dielectric absorbing layer, but suggests additional dielectric and semiconductor layers for optimal chroma performance. U.S. Patent Application Publication No. 20150309231 describes pigments consisting of at least a reflective core layer, a semiconductor absorbing layer, a dielectric absorbing layer, and a high refractive index layer. These types of pigments are said to exhibit a low red hue shift when viewed from low angles (0 to 45 degrees). Such a hue shift is not observed in the pigments disclosed in International Publication No. 1999 / 035194, which uses a dielectric stack as an adjacent material. WO 200 / 022418 describes seven layers of pigments that shift color depending on the angle of incidence of incident light. The stack is described as a central reflective layer, followed by an isotropic selective absorbing layer, a dielectric layer, and an absorbing layer. However, the structure of these pigments is very complex, and the manufacturing process is quite involved. Summary of the Invention [Problem to be solved by the invention]

[0005] There is a need for effect pigments that have attractive optical properties such as color, flop, and high gloss combined with high hiding power, but which are structurally simple.

[0006] Another object is to provide a method for producing such effect pigments. [Means for solving the problem]

[0007] The present invention relates to thin effect pigments with a fairly simple structure that exhibit several very advantageous optical properties. In one embodiment, the invention relates to effect pigments having an optically active layer consisting of thin flakes of highly reflective material immediately adjacent on one or both sides to a layer of semiconductor material having a bandgap of 0.1 to 3.5 eV.

[0008] Further preferred embodiments are disclosed in claims 2-9.

[0009] A further object of the present invention is solved by providing a method for producing an effect pigment using a PVD process, the method comprising the following steps: (a) coating a thin flexible substrate with a release coating; (b) depositing the semiconductor layer 1 onto a flexible substrate using a roll-to-roll process; (c) depositing a layer of reflective metal onto the semiconductor layer 1; (d) depositing a second semiconductor layer 2 onto the reflective metal layer; (e) peeling the material stack from the flexible substrate in a solvent; and (f) Optionally, further steps include particle sizing, particle classification, and solvent dispersion.

[0010] Further preferred embodiments of the method are disclosed in claims 11-13. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows the normalized spectral response at 15 degrees for materials 3a-3f. DETAILED DESCRIPTION OF THE INVENTION

[0012] A particularly advantageous property of the thin effect pigments according to the invention is their particularly high flop index compared to known high flop index pigments, such as Metalure Liquid Black. The flop index is a measure of the change in reflectance of a metallic color when rotated over a range of viewing angles. The effect pigments according to the invention may have a flop index greater than 25, more particularly greater than 30. The effect pigments according to the invention may have a flop index in the range of 25 to 250, more particularly in the range of 30 to 200, preferably 35 to 200.

[0013] In addition, unlike many interference-based pigments, the effect pigments according to the invention exhibit little viewing angle dependent color shift.

[0014] In a further embodiment, the highly reflective material is selected from the group consisting of aluminum, copper, chromium, titanium, or gold. Preferably, the highly reflective material is aluminum.

[0015] In a further embodiment, the semiconductor material has a band gap in the range of 0.1 to 2.5 eV, more preferably in the range of 0.2 to 1.5 eV. Preferably, the semiconductor material is germanium, silicon, alloys of germanium and silicon, silicon monoxide, non-stoichiometric chromium oxide (CrO x ), or non-stoichiometric aluminum oxide (AlO x ). More preferably, the semiconductor material is selected from germanium, silicon, alloys thereof, and non-stoichiometric aluminum oxide (AlO x ), even more preferably selected from germanium, silicon, or alloys thereof, and most preferably the semiconductor material is selected from silicon. The average molecular stoichiometric ratio x of oxygen is in the range of 0.05 to 2.50.

[0016] The effect pigments according to the present invention can be described as multilayered AB, ABA, or ABC systems, where B is a highly reflective material and adjacent layers A and C are semiconductor materials with a bandgap of 0.1 to 3.5 eV. In one embodiment of the present invention, adjacent layers A or C are semiconductor materials with a bandgap in the range of 0.1 to 1.5 eV. The highly reflective material B is typically a flake- or platelet-like material with an average thickness in the range of 5 to 500 nm, more preferably in the range of 5 to less than 100 nm, even more preferably in the range of 7 to less than 75 nm, and most preferably in the range of 10 to 50 nm.

[0017] For the purposes of the present invention, the average thickness of the platelet-shaped material, as well as the thickness of the semiconducting layer, is determined by scanning electron microscopy (SEM). For effect pigments without an additional encapsulation layer, the method described in WO 2004 / 087816 A2 can be used. For effect pigments with an additional encapsulation layer, the cross section is preferably prepared by incorporating the effect pigment in a two-component clear coat (Autoclear Plus HS from Sikkens GmbH) at a concentration of about 10% by weight with a sleeved brush, applying a film with the aid of a spiral applicator (wet film thickness 26 μm), drying, and cutting to obtain a cross section. Using this method, the cross sections of an appropriate number of particles should be measured to achieve a representative statistical evaluation. Customarily, about 100 particles are measured.

[0018] The effect pigments according to the invention, as considered above, may consist of only two or three layers as a multilayer structure AB or ABC system, where B is a highly reflective material and the adjacent layers A and C are semiconducting materials with a band gap of 0.1 to 3.5 eV. Such layers are optically active in the visible light wavelength range.

[0019] When both adjacent A and C layers are present, they may be the same material, resulting in an ABA layer stack, or they may be different materials. Preferably, the A and C layers are the same material. The average thickness of layers A and C may be the same or different. Typically, the average thickness of layers A and C may be in the range of 5 to 200 nm. Ideally, the thickness is <200 nm, more ideally, the thickness is <100 nm, and most ideally, the thickness is <75 nm.

[0020] For the purposes of the present invention, the average thickness of layers A and C is determined by scanning electron microscopy (SEM). Using this method, the thickness of layers A and C should be measured in the cross section of an adequate number of particles to achieve a representative statistical evaluation. Customarily, about 100 particles are measured.

[0021] Within the scope of the present invention, dielectric materials are insulators (weak electrical conductors) that typically have a bandgap greater than about 4 eV, such as ceramics, diamond, etc. Dielectric materials are typically optically transparent, i.e., have very low absorption in the visible region of the electromagnetic spectrum.

[0022] In a highly preferred embodiment, the effect flake of highly reflective material is made from aluminum and the semiconductor material having a bandgap of 0.1 to 3.5 eV is selected from the group consisting of germanium, silicon, and alloys thereof.

[0023] Most preferred are effect pigments having an ABA layer stack, in which the central layer B is aluminum and the adjacent layers A are silicon.

[0024] The effect pigments according to the present invention can be produced using a physical vapor deposition (PVD) process. In such a process, a thin, flexible substrate, such as a PET film, is coated with a release coating, which allows subsequent layers to delaminate or "peel" during subsequent processing steps. The release coating step can be omitted if peeling of the stack material is not intended and a metallized film is to be produced. Semiconductor layer 1 is deposited on the flexible substrate using a roll-to-roll process with a suitable semiconductor at an appropriate thickness (Thickness 1) to produce the desired color for the web side. In the next step, a 5-500 nm layer of reflective metal is subsequently deposited on semiconductor layer 1. In a further step, a second semiconductor layer 2 is subsequently metallized on the reflective metal layer at an appropriate thickness (Thickness 2) to produce the desired color for the metal side. Semiconductor layers 1 and 2 can be composed of the same or different semiconductor materials. Additionally, Thickness 1 and Thickness 2 can also be the same or different thicknesses. If the semiconductor layers 1 and 2 are both made of the same semiconductor material and have the same thickness, the coloring on both sides of the reflective metal will be the same.

[0025] The above process produces a material stack that can be peeled from the flexible substrate in a subsequent step. The above process can be repeated on the other side of the film, and multiple stacks can be deposited on a single film by repeating the process. Additionally, by removing one of the semiconductor layers, one side can be colored while the other side maintains the optical properties of metal. If semiconductor layer 1 is removed, the metal side will be colored, while if semiconductor layer 2 is removed, the web side will be colored.

[0026] For pigment production, the deposited material is typically stripped from the substrate using a solvent or mechanical stripping process, followed by post-processing steps that may include particle sizing, particle classification, and solvent dispersion.

[0027] The color and other optical properties of the effect pigments according to the invention can be made visible and measurable by incorporating the effect pigments into a colorless binder system and using the resulting composition to coat a substrate. For example, an ink composition can be obtained by mixing about 6% by weight of the effect pigments according to the invention with a colorless nitrocellulose binder and preparing a drawdown on a sample card, e.g., a BYK Gardner drawdown card.

[0028] The optical properties of the material on the drawdown card can be measured using BYK-mac i MetallicColor.

[0029] In general, it has been found that in effect pigments according to the invention, the color of the pigment shifts from the reddish to the bluish part of the color spectrum by increasing the layer thickness of the semiconductor material deposited on the highly reflective material. A similar effect has been found by keeping the layer thickness of the semiconductor material constant and replacing the semiconductor material with one of higher refractive index.

[0030] In certain embodiments, the effect pigments may be encapsulated with a further layer of optically inactive material. Such encapsulation may be necessary, for example, to ensure outgassing stability in aqueous coating systems or aqueous printing inks. At least the edge portions of the effect pigments are not covered by the semiconducting layer and may therefore be subject to attack by corrosive media.

[0031] By optically inactive material is meant within the scope of the present invention a layer that reflects less than 20%, or preferably less than 10%, of the incident light in the optical wavelength region. In addition, it does not change the chroma response. In particular, the outer optically inactive layer, when applied in a nitrocellulose lacquer as described in the experimental section, results in a ΔC * 15° is ≦2.0, and / or ΔH * 15°is ≦10°, preferably ≦5°, and / or ΔL * 15° exhibits a change in the coated effect pigment of ≦10.

[0032] In a preferred embodiment, the optically inactive layer encapsulates essentially the entire effect pigment and consists of a layer of Mo oxide, SiO, AlO, or a surface modifier such as an organofunctional silane, phosphate ester, phosphonate ester, phosphite ester, and combinations thereof.

[0033] More preferably, the optically inactive layer encapsulates the entire effect pigment and consists of a layer of Mo oxide, SiO2, and optionally a surface modifier such as an organofunctional silane. Such a system is described, for example, in WO 2019 / 110490 A1. In another preferred embodiment, the optically inactive layer consists of a layer of SiO2 and, optionally, a layer of organofunctional silane. The organofunctional silane is required here primarily as a surface modifier to adjust the chemical compatibility of the effect pigment with the binder medium of the final application, as described, for example, in EP 1 084 198 A1.

[0034] Organofunctional silanes with suitable functional groups, preferably used as surface modifiers, are commercially available, for example, manufactured by Evonik, Rheinfelden, Germany, and sold under the trade name "Dynasylan™". Further products can be purchased from OSi Specialties (Silquest™ silanes) or Wacker (Genosil™ silanes).

[0035] Examples of suitable organofunctional silanes are 3-methacryloxypropyltrimethoxysilane (Dynasylan MEMO), vinyltri(meth)ethoxysilane (Dynasylan VTMO or VTEO), 3-mercaptopropyltri(meth)ethoxysilane (Dynasylan MTMO or 3201), 3-glycidyloxypropyltrimethoxysilane (Dynasylan GLYMO), tris(3-trimethoxysilylpropyl)isocyanurate (Silquest Y-11597), gamma-mercaptopropyltrimethoxysilane (Silquest A-189), bis(3-triethoxysilylpropyl)polysulfide (Silquest A-1289), bis(3-triethoxysilyl)disulfide (Silquest A-1589), beta(3,4-epoxycyclohexyl)ethyltri-methoxysilane (Silquest A-186), gamma-isocyanatopropyl-trimethoxysilane (Silquest A-Link 35, Genosil GF40), (methacryloyloxymethyl)trimethoxysilane (Genosil XL 33), and (isocyanatomethyl)trimethoxysilane (Genosil XL 43).

[0036] In one preferred embodiment, the organofunctional silane mixture modifying the SiO layer contains at least one aminofunctional silane. The aminofunctional group is a functional group that can participate in chemical interactions with most of the groups present in the binder. This interaction can involve covalent bonding with, for example, isocyanate or carboxylate functional groups of the binder, or hydrogen bonding with, for example, OH or COOR functional groups, or other ionic interactions. Therefore, it is highly suitable for chemically bonding effect pigments with different types of binders.

[0037] The following compounds are preferably used for this purpose: aminopropyltrimethoxysilane (Dynasylan AMMO), aminopropyltriethoxysilane (Dynasylan AMEO), N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (Dynasylan DAMO), N-(2-aminoethyl)-3-aminopropyltriethoxysilane, triaminofunctional trimethoxysilane (Silquest A-1130), bis(gamma-trimethoxysilylpropyl)amine (Silquest A-1170), N-ethyl-gamma-aminoisobutyltrimethoxysilane (Silquest A-Link 15), N-phenyl-gamma-diaminopropyltrimethoxysilane (Silquest Y-9669), 4-amino-3,3-dimethylbutyltrimethoxysilane (Silquest Y-11637), (N-cyclohexylaminomethyl)-triethoxysilane (Genosil XL 926), (N-phenylaminomethyl)-trimethoxysilane (Genosil XL 973), and mixtures thereof. In another embodiment, pre-hydrolyzed and pre-condensed organofunctional silanes may be used, as described in EP 3080209 B1.

[0038] In other embodiments, organofunctional silanes or other corrosion inhibitors such as, for example, phosphate esters, phosphonate esters, phosphite esters, and combinations thereof, may be coated directly onto the effect pigment to impart corrosion and gassing stability, particularly to the edge portions of the effect pigment.

[0039] The effect pigments according to the present invention can be used in a wide range of applications, such as coatings, inks, cosmetics, etc., typically for metallic effect pigments.

[0040] Coating or ink compositions containing these effect pigments can exhibit very high flop indices, for example flop indices in the range of 30-200, or preferably in the range of 35-200.

[0041] Some further aspects of the present invention relate to coating films of the above-mentioned material stacks. Such films can be considered as precursor materials for producing the final effect pigments.

[0042] Embodiment 1 relates to a film coated on a flexible substrate, comprising a first layer of a semiconductor having a bandgap of 0.1 to 3.5 eV and a layer of a reflective material coated thereon.

[0043] Embodiment 2 relates to embodiment 1, wherein an additional layer of semiconductor material is coated onto the layer of highly reflective material.

[0044] Aspect 3 relates to aspect 1 or 2, wherein the highly reflective material is selected from the group consisting of aluminum, copper, chromium, titanium, or gold.

[0045] In a third aspect, the semiconductor material having a band gap of 0.1 to 3.5 eV is germanium, silicon, an alloy of germanium and silicon, silicon monoxide, non-stoichiometric chromium oxide (CrO x ), or non-stoichiometric aluminum oxide (AlO x ) is selected from the group consisting of:

[0046] A fourth embodiment relates to the third embodiment, wherein the semiconductor material having a band gap of 0.1 to 3.5 eV is selected from the group consisting of germanium, silicon, and alloys thereof.

[0047] Aspect 5 relates to any one of Aspects 1 to 4, wherein the flakes of highly reflective material have an average thickness in the range of 5 to 500 nm.

[0048] Example 6 relates to any one of Examples 1 to 5, wherein the layer of semiconductor material has an average thickness in the range of 5 to 200 nm.

[0049] Aspect 7 relates to any one of Aspects 1 to 6, wherein the highly reflective material is aluminum and the semiconductor material is selected from the group consisting of germanium, silicon, and an alloy of germanium and silicon. [Example]

[0050] Preliminary Example 1: Two-layer material (Al-Ge) An aluminum layer with an optical density (OD) of 1.0–1.5 was deposited onto a 30 cm-wide transparent polyester film coated with a CAB (cellulose acetobutylate)-based release agent using electron beam PVD deposition. Enough Al was deposited onto the web to complete the following second step and to obtain an Al-only web for comparison. The electron beam source was positioned 36 cm below the web during the process, and the web speed was maintained constant at 9 m / min. The electron beam source accelerating voltage was maintained constant at 10 kV throughout the experiment. In the second step, a Ge layer was deposited on top of the aluminum layer. The electron beam current was varied depending on the conditions. When the conditions were changed, the web was stopped and the shutter was closed, thereby obtaining a clear, visible outline when observing the web after the experiment.

[0051] Using the setup described above, different thicknesses of Ge were deposited onto the aluminum layer, resulting in colorations ranging from blue (thicker layers) to red (thinner layers). The results are summarized in Table 1. [Table 1]

[0052] Example 2: Three-layer material (Ge-Al-Ge) A three-layer material was fabricated using the same setup as in Example 1. The electron beam source was positioned 36 cm below the web during the process, and the web speed was maintained constant at 10 m / min. The accelerating voltage of the electron beam source was maintained constant at 10 kV throughout the experiment. In the first step, a Ge layer was deposited using PVD electron beam evaporation on a transparent polyester film with a release coat layer. The Ge thickness was determined using a rudimentary in-situ optical transmission sensor, and the electron beam current was manipulated to target the appropriate Ge thickness. In the next step, an Al layer equivalent to approximately 0.9–1.5 OD was deposited. The optical transmission sensor, combined with current adjustment, was used to target the appropriate Al thickness. In the third process step, an additional layer of Ge was deposited. Again, the Ge thickness was determined using an in-situ optical transmission sensor, and the electron beam current was manipulated to target the appropriate Ge thickness. The thickness of the two Ge layers was targeted to be identical, so that the web side and metal side of each condition would have the same color. Three separate sets of colors were successfully produced, targeting orange, purple, and blue colorations. The coloration of the web side and metal side of the film was highly comparable for each set of materials.

[0053] The process conditions are summarized in Table 2. [Table 2]

[0054] All materials from Example 2 were stripped from the polyester film and milled / ground to the particle sizes (D50 values) listed below. Pigments were prepared at 20% by weight in GEPM. Inks were prepared with Eckart's in-house LQ5797 nitrocellulose binder system with the total metal content specified below. Samples were drawn down onto flat BYK drawdown cards. Gloss data was collected using a BYK Micro Tri-gloss meter. Additional optical data was collected using a BYK Mac meter. The results of these measurements are summarized in Table 3. [Table 3]

[0055] Example 3: Three-layer material (Ge-Al-Ge) and effect pigments A three-layer material was fabricated using the same setup as in Example 2. The electron beam source was positioned 36 cm below the web during the process, and the web speed was maintained constant at 10 m / min. The accelerating voltage of the electron beam source was maintained constant at 10 kV throughout the experiment. In the first step, a Ge layer was deposited using PVD electron beam evaporation onto a transparent polyester film with a release coat layer. The electron beam current was set at the beginning of the experiment, and the web speed was used to control the Ge layer thickness. In the second step, an Al layer equivalent to approximately 1.0-1.5 OD was deposited. An optical transmission sensor was used in combination with current adjustment to target the appropriate Al thickness. In the third process step, an additional layer of Ge was deposited using the same parameters as the first step. Again, the electron beam current was set at the beginning of the experiment, but in this example, the web speed was used to control the Ge layer thickness. The goal was to achieve identical thicknesses for the two Ge layers, so that the web side and metal side of each condition would have the same color. Yellow, orange, burgundy, royal blue, and teal colorations were produced well. Coloration on the web side and metal side of the film was fairly comparable for each set of materials.

[0056] All materials from Example 3 were stripped from the polyester film and milled / ground to a particle size of approximately 20 microns (20 μm) (D50 value). Pigments were prepared at 20% by weight in GEPM. Inks were prepared with Eckart's in-house LQ5797 nitrocellulose binder system, using the total metal content specified below. Samples were drawn down onto flat BYK drawdown cards. Gloss data was collected using a BYK Micro Tri-gloss meter. A comparison with commercially available Metalure Liquid Black is shown in Table 4 under Comparative Example 3f. Additional optical data was collected using a BYK Mac meter. The results of these measurements are summarized in Table 4. Additionally, the normalized spectral response at 15 degrees for Materials 3a-3f is shown in Figure 1. [Table 4]

[0057] Example 4: Three layer material (Ge-Cu-Ge) A three-layer material was fabricated using a setup similar to that of Example 1, with Cu as the central metal layer. The electron beam source was positioned 36 cm below the web during the process, and the web speed was maintained constant at 10 m / min. The accelerating voltage of the electron beam source was maintained constant at 10 kV throughout the experiment. In the first step, a Ge layer was deposited using PVD electron beam evaporation onto a transparent polyester film with a release coat layer. The Ge thickness was determined using a rudimentary in-situ optical transmission sensor, and the electron beam current was manipulated to target the appropriate Ge thickness. To target a red color, a Ge thickness of approximately 10 nm was targeted using SEM and optical data obtained from Example 2. In the next step, a Cu layer equivalent to approximately 2.0-3.0 OD was deposited. The optical transmission sensor, combined with current adjustment, was used to target the appropriate Cu thickness. SEM microscopy images showed that a Cu thickness of approximately 50 nm was achieved. In the third process step, an additional layer of Ge was deposited. Again, an in-situ optical transmission sensor was used to determine the germanium thickness, and the electron beam current was manipulated to target the appropriate germanium thickness. The thickness of the two germanium layers was targeted to be identical, so that the web side and metal side of each condition would have the same color. Red coloration was targeted, and three separate conditions were successfully produced. The coloration of the web side and metal side of the film was highly comparable for each material set.

[0058] All materials from Example 4 were stripped from the polyester film and milled / ground to a particle size of approximately 15 microns (15 μm) (D50 value). The pigment was prepared at 23 wt% in GEPM. While Cu-based PVD pigments are typically difficult to stabilize, the germanium surface coating appears to impart at least some chemical stability, allowing for post-processing of the pigment without significant optical degradation. Inks were prepared with Eckart's in-house LQ5797 nitrocellulose binder system using a total metal content of 6.0%. Samples were drawn down onto flat BYK drawdown cards. For comparison, optical data is shown for a sample of Metalure Liquid Black (4b) at 3.2% solids. Gloss data was collected using a BYK Micro Tri-gloss meter. Additional optical data was collected using a BYK Mac meter. The results of these measurements are summarized in Tables 5a and 5b. [Table 5] [Table 6]

[0059] Preliminary Example 5: Two-layer film (Cr-CrOx) Using a setup similar to that in Example 1, a two-layer film was fabricated with Cr as the first metal layer. The electron beam source was positioned 36 cm below the web during the process. The electron beam source acceleration voltage was maintained constant at 10 kV throughout the experiment. A Cr layer equivalent to approximately 1.0-2.0 OD was deposited as the first reflective metal layer. A second layer of Cr was deposited with oxygen flowing through the plume to create a CrOx layer on top of the Cr metal layer. The web speed was held constant at 36 m / min, and the current was varied from 150 mA to 290 mA in 20 mA increments. The shutter was closed between beam source current changes. This process was repeated at web speeds of 18 m / min and 9 m / min, achieving increasing CrOx thickness with increasing web speed and increasing electron beam current. In a separate experiment, SEM microscopy images showed that a CrOx thickness of approximately 70-80 nm corresponds to a strong blue coloration.

[0060] The resulting film color change (from thinnest CrOx to thickest CrOx) is in the following order: light yellow, orange, burgundy, purple, royal blue, blue, blue-green, green, yellow-green. Gloss data was collected using a BYK Micro Tri-gloss meter. Additional optical data was collected using a BYK Mac meter. The results of these measurements are summarized in Table 6. [Table 7]

[0061] Example 6: Two-layer film (Si-Al) Using the same setup as in Example 1, a bilayer film was fabricated with Si as the first semiconductor layer. The electron beam source was positioned 36 cm below the web during the process. The accelerating voltage of the electron beam source was maintained constant at 10 kV throughout the experiment. The Si layer was deposited at a fixed current of 332 mA, and the web speed was varied non-continuously from 6 to 34 m / s to control the Si layer thickness. A shutter was closed between web speed changes to signal the change in conditions during film analysis. Previous silicon depositions using this current setting at a web speed of 11 m / s resulted in a Si thickness of 29 + / - 2 nm. Therefore, the expected Si thickness range is 7 nm to 60 nm for the end points of web speeds of 34 m / s and 6 m / s, respectively. A second layer of metallic Al was deposited on top of the Si semiconductor layer to a thickness corresponding to an optical density of approximately 1.0 to 1.5 OD.

[0062] The resulting films exhibited a silver coloration on the Al metal side, and the color change on the Si side, from the thinnest deposited Si (highest web speed) to the thickest deposited Si (lowest web speed), was in the following order: pale yellow, gold, orange, purple, royal blue, blue, blue-green, and blue-green-green. All films exhibited highly reflective visual properties with excellent clarity on both the silver and colored sides. Optical color measurement data for the colored film sides were collected using a BYK Mac meter. The results of these measurements are summarized in Table 7. [Table 8]

[0063] Example 7: Three layer material (Si-Al-Si) A three-layer material was fabricated using the same setup as in Example 2. The electron beam source was positioned 36 cm below the web during the process, and the web speed was maintained constant at 19 m / min for Si deposition and 11 m / min for Al deposition. The electron beam source acceleration voltage was maintained constant at 10 kV throughout the experiment. In the first step, a Si layer was deposited using PVD electron beam evaporation on a transparent polyester film with a release coat layer. The electron beam current was set at the beginning of the experiment, and the web speed was used to manipulate the silicon layer thickness. In the second step, an Al layer equivalent to approximately 1.0-1.5 OD was deposited. An optical transmission sensor was used in combination with current adjustment to target the appropriate Al thickness. In the third process step, an additional layer of Si was deposited using the same parameters as the first step. Again, the electron beam current was set at the beginning of the experiment to manipulate the silicon layer thickness. The target thickness for the two silicon layers was identical, so that the web side and metal side of each condition would have the same color. Si thicknesses corresponding to yellow and gold colors were targeted for materials 7a and 7b, respectively. Yellow and gold colored films and subsequent pigmentation were successfully produced. The coloration of the web side and metal side of the film was highly comparable for each material set.

[0064] All materials from Example 7 were stripped from the polyester film and milled / ground to a particle size of approximately 14 microns (14 μm) (D50 value). Pigments were prepared at 10% by weight in ethanol. Inks were prepared with a nitrocellulose binder system using a total metal content of 3.0% by weight. Samples were drawn down onto flat BYK drawdown cards. Gloss data was collected using a BYK Micro Tri-gloss meter. Additional optical data was collected using a BYK Mac meter. A comparison with Metalure L51010AE (a commercially available aluminum PVD pigment from Eckart America) is shown in Table 8, section 7c. The results of these measurements are summarized in Table 8. [Table 9]

Claims

1. Effect pigments having an optically active layer consisting of flakes of highly reflective material immediately adjacent on one or both sides to a layer of semiconductor material having a band gap of 0.1 to 3.5 eV.

2. The effect pigment of claim 1 , wherein the effect pigment is further encapsulated with an outer optically inactive layer.

3. 3. The effect pigment of claim 1 or claim 2, wherein the highly reflective material is selected from the group consisting of aluminum, copper, chromium, titanium, or gold.

4. The semiconductor material having a band gap of 0.1 to 3.5 eV is selected from the group consisting of germanium, silicon, alloys of germanium and silicon, silicon monoxide, non-stoichiometric chromium oxide (CrO ｘ ), or non-stoichiometric aluminum oxide (AlO ｘ 4. The effect pigment according to claim 1, wherein the pigment is selected from the group consisting of:

5. 5. The effect pigment of claim 4, wherein the semiconductor material having a bandgap of 0.1 to 3.5 eV is selected from the group consisting of germanium, silicon, and alloys thereof.

6. 6. The effect pigment according to claim 1, wherein the flakes of highly reflective material have an average thickness in the range of 5 to 500 nm.

7. 7. The effect pigment according to claim 1, wherein the layer of semiconductor material has an average thickness in the range of 5 to 200 nm.

8. The optically inactive layer is made of Mo oxide, SiO ２ , Al ２ O ３ 8. The effect pigment of claim 1, which comprises a layer of a surface modifier, such as an organofunctional silane, a phosphate ester, a phosphonate ester, a phosphite ester, or a combination thereof.

9. 9. The effect pigment according to claim 1, wherein the flakes of highly reflective material are made of aluminum and the semiconductor material having a bandgap of 0.1 to 3.5 eV is selected from the group consisting of germanium, silicon, and alloys thereof.

10. 10. A method for producing the effect pigments according to any one of claims 1 to 9 using a PVD process, comprising the steps of: (g) coating the thin flexible substrate with a release coat; (h) depositing a semiconductor layer 1 onto said flexible substrate using a roll-to-roll process; (i) depositing a layer of a reflective metal onto said semiconductor layer 1; (j) depositing a second semiconductor layer 2 onto the reflective metal layer; (k) peeling the material stack from the flexible substrate in a solvent; and (l) optionally further steps including particle sizing, particle classification, and solvent dispersion; A manufacturing method comprising:

11. The method of claim 10, wherein the reflective metal has a thickness in the range of 5 to 500 nm.

12. The manufacturing method according to claim 10 or 11, wherein the semiconductor layer 1 and the semiconductor layer 2 are made of the same material.

13. The method according to any one of claims 10 to 12, wherein the semiconductor layers 1 and 2 have the same thickness.

14. A coating or ink composition comprising the effect pigment according to any one of claims 1 to 9.

15. 15. The coating or ink composition of claim 14, having a flop index in the range of 30 to 200.

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