DE102015112412A1 - The color non-altering multi-layer structures and protective coating thereon - Google Patents

Abstract

An omnidirectional interference pigment with a protective coating. The pigment comprises a first layer of a first material and a second layer of a second material, wherein the second layer extends over the first layer. In addition, the pigment reflects a band of electromagnetic radiation having a predetermined full width half maximum (FWHM) of less than 300 nm and a predetermined color shift of less than 30 ° when the pigment is exposed to broad band electromagnetic radiation and from angles between 0 and 45 ° is considered. The pigment has a weather resistant coating which covers its outer surface and reduces a relative photocatalytic activity of the pigment by at least 50%.

Description

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part (CIP) of U.S. Patent Application Serial No. 14 / 242,429, filed April 1, 2014, which in turn is a CIP application of US Patent Application Serial No. 14 / 138,499, which in turn is a CIP application of U.S. Patent Application Serial No. 13 / 913,402 filed on Jun. 8, 2013, which in turn filed a CIP application of U.S. Patent Application filed on Feb. 6, 2013 Serial No. 13 / 760,699, which in turn is a CIP application of U.S. Patent Application Serial No. 13 / 572,071, filed on August 10, 2012, which in turn is a CIP application of U.S. Patent Application Serial No. 5 filed on Feb. 5, 2011 No. 13 / 021,730, which in turn is a CIP application of U.S. Patent Application Serial No. 12 / 793,772, filed June 4, 2010 (US Pat. No. 8,736,959), which in turn filed a CIP application filed on Feb. 18,2002 009 filed US Patent Application Serial No. 12 / 388,395 (US Pat. No. 8,749,881), which in turn is a CIP application of US Patent Application Serial No. 11 / 837,529 filed on August 12, 2007 (US Pat. No. 7,903,339). U.S. Patent Application Serial No. 13 / 913,402, filed on Jun. 28, 2013, is a CIP application of 13 / 014,398 filed Jan. 26, 2011, which is a CIP application of 12 / 793,772 filed June 4, 2010. U.S. Patent Application Serial No. 13 / 014,398, filed January 26, 2011, is a CIP application of 12 / 686,861 filed on January 13, 2010 (U.S. Patent No. 8,593,728), which filed a CIP application filed on Feb. 19, 2009 12 / 389,256 (U.S. Patent 8,329,247); all are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to multilayer thin film structures bearing protective coatings and, more particularly, to multilayer thin film structures having a protective coating which exhibit minimal or imperceptible color shift when exposed to broad band electromagnetic radiation and viewed from various angles.

BACKGROUND OF THE INVENTION

Pigments consisting of multilayer structures are known. In addition, pigments are also known which show or cause a highly saturated omnidirectional structure or interference color. However, such prior art pigments require at least 39 thin film layers to obtain desired color properties.

Note that costs associated with the production of multilayer thin film pigments are proportional to the number of layers required. Thus, the cost associated with the production of highly saturated omnidirectional structural inks using multilayer stacks of dielectric materials may be prohibitive. Therefore, there is a need for a high chrominance omnidirectional feature color that requires a minimum number of thin film layers.

In addition, it is known that pigments can fade, change color, etc. when exposed to sunlight, and especially ultraviolet light. Thus, there is also a need for a high chrominance omnidirectional interference pigment which is weather resistant.

SUMMARY OF THE INVENTION

An omnidirectional interference pigment is provided which has a protective coating. The pigment comprises a first layer of a first material and a second layer of a second material, wherein the second layer extends over the first layer. In addition, the pigment reflects a band of electromagnetic radiation having a predetermined full width half maximum (FWHM) of less than 300 nm and a predetermined color shift of less than 30 ° when the pigment is exposed to broad band electromagnetic radiation and from angles between 0 and 45 ° is considered. Similarly, the pigment has a weather resistant coating which covers its outer surface and reduces a relative photocatalytic activity of the pigment by at least 50%.

The weather resistant coating may comprise an oxide layer and the oxide layer may be selected from silica, alumina, zirconia, titania and / or ceria. In addition, the weather resistant coating may include a first oxide layer and a second oxide layer, wherein the second oxide layer is different from the first oxide layer. Furthermore, the second oxide layer may be a hybrid oxide layer which is a combination of at least two different oxide layers. Finally, the pigment itself, ie the pigment without the protective coating, contains no oxide layer.

There is also disclosed a method of producing omnidirectional colored interference pigments having a protective coating. The method includes providing a plurality of pigment particles having a structure and properties as indicated above, and suspending the plurality of pigment particles in a first liquid to form a pigment suspension. In addition, an oxide precursor is provided which forms a second liquid and an oxide-forming element such as silicon, aluminum, zirconium, titanium or cerium. The pigment suspension and the oxide precursor are mixed and result in deposition of a weather resistant oxide coating on the plurality of pigment particles, which coating reduces a relative photocatalytic activity of the pigment particles by at least 50%.

In some cases, the first liquid is a first organic solvent and the second liquid is a second organic solvent. In addition, the first and second organic solvents may be organic polar solvents such as n-propyl alcohol, isopropyl alcohol, ethanol, n-butanol and acetone. In other cases, the first organic solvent and the second organic solvent may be organic polar protic solvents.

As regards the oxide precursor, the oxide-forming element may be silicon in the form of tetraethoxysilane, the oxide-forming element aluminum may be in the form of aluminum sulfate and / or aluminum tri-sec-butoxide, the oxide-forming element zirconium may be in the form of zirconium butoxide Oxide-forming element Cer may be in the form of cerium nitrate hexahydrate and / or ceric sulfate, and the oxide-forming element titanium may be in the form of titanium ethoxide and / or titanium isopropoxide and / or titanium butoxide.

In other cases, the first liquid is a first aqueous liquid and the second liquid is a second aqueous liquid. In addition, the oxide-forming element may be silicon in the form of sodium silicate, the oxide-forming element aluminum may be in the form of aluminum sulphate and / or aluminum sulphate hydrate and / or sodium aluminate, the oxide-forming element zirconium may be in the form of zirconyl chloridoctahydrate, the oxide-forming element cerium may be in the form of Cernitrathexahydrat before and the oxide-forming element titanium may be present in the form of titanium tetrachloride.

BRIEF DESCRIPTION OF THE FIGURES

1A is a schematic representation of a dielectric layer (DL) that reflects and transmits incident electromagnetic radiation.

1B is a schematic representation of a reflector layer (RL), which reflects incident electromagnetic radiation.

1C is a schematic representation of an absorbing layer (A1) that absorbs incident electromagnetic radiation.

1D is a schematic representation of a selective absorbing layer (SAL) that absorbs and transmits incident electromagnetic radiation.

2 is a schematic representation of reflection and transmission of incident electromagnetic radiation through a multi-layer, an omnidirectional structure color thin film of a 1st generation, which consists of a plurality of dielectric layers;

3 Fig. 12 is a schematic representation of a multi-layer, omnidirectional structural ink thin film of the 1st generation consisting of a plurality of dielectric layers;

4 Fig. 12 is a graph showing a comparison of 0.2% area-to-area average of electromagnetic radiation for the transversal magnetic mode and the trans-electric mode;

5 is a graphical representation of the reflectance as a function of wavelength for the in 4 illustrated case II;

6 FIG. 4 is a graph of the center wavelength dispersion in cases I, II and III, which in FIG 4 are shown;

7 is a schematic representation of reflection and absorption of incident electromagnetic radiation through a multi-layer, an omnidirectional structure color thin film of a 2nd generation, which consists of a plurality of dielectric layers and an absorbent layer;

8th Fig. 12 is a schematic representation of a multilayered omnidirectional structural ink of the 2nd generation thin film consisting of a plurality of dielectric layers and an absorbing layer and / or reflective layer;

9A Fig. 12 is a schematic representation of a 2-generation thin film of an omnidirectional structure color consisting of a plurality of dielectric layers and an absorbing / reflecting layer, with a chroma (C *) of 100 and a reflectance (Max R). of 60%;

9B is a plot of reflectance versus wavelength for the in 9A illustrated second-generation 5-layer multilayer stack thin film compared to a 1st generation 13-layer multilayer thin film and for viewing angles of 0 and 45 degrees;

10 Fig. 12 is a schematic representation of a multi-layered, omnidirectional structural paint, 3rd generation thin film consisting of a plurality of dielectric layers, a selective absorbing layer (SAL), and a reflector layer;

11A Fig. 12 is a schematic representation of a zero or near zero of an electric field within a ZnS dielectric layer exposed to 500 nm electromagnetic radiation (EMR);

11B is a graphical representation of the absolute value of electric field squared (| E | ² ) versus thickness of in 1A ZnS dielectric layer when exposed to an EMR having wavelengths of 300, 400, 500, 600 and 700 nm;

12 Fig. 12 is a schematic representation of a dielectric layer extending over a substrate or reflector layer exposed to electromagnetic radiation at an angle θ with respect to a normal to the outer surface of the dielectric layer;

13 Figure 3 is a schematic representation of a ZnS dielectric layer having a Cr absorber layer located at the zero or near zero of the electric field within the ZnS dielectric layer for incident EMR having a wavelength of 434 nm;

14 Figure 4 is a plot of percent reflection versus reflected EMR wavelength for a multilayer stack without a Cr absorber layer (e.g. 1A ) and a multilayer stack with a Cr absorber layer (e.g. 3A ) exposed to white light;

15A FIG. 12 is a first harmonic and second harmonic plot shown by a ZnS dielectric layer extending over an A1 reflector layer (eg, FIG. 4A );

15B FIG. 12 is a plot of percent reflection versus reflected EMR wavelength for a multilayer stack having a ZnS dielectric layer extending over an A1 reflector layer plus a Cr absorber layer located within the ZnS dielectric layer such that the in 8A be absorbed second harmonic shown;

15C FIG. 12 is a plot of percent reflection versus reflected EMR wavelength for a multilayer stack having a ZnS dielectric layer extending over an A1 reflector layer plus a Cr absorber layer located within the ZnS dielectric layer such that the in 8A absorbed first harmonic shown;

16A Fig. 12 is a graph of electric field squared versus thickness of the dielectric layer and showing the angular dependence of a Cr absorber layer on an electric field under irradiation with incident light at 0 and 45 degrees.

16B Figure 3 is a graph of percent absorption by a Cr absorber layer versus reflected EMR wavelength when irradiated with white light at angles of 0 and 45 ° with respect to a normal of the outer surface (where 0 ° is normal to the surface);

17A is a schematic representation of an omnidirectional, a red structure color having multilayer stack according to an embodiment of the present invention;

17B is a graphical representation of the percent absorption of in 10A shown Cu absorber layer against reflected EMR wavelength for irradiation of the in 10A illustrated multilayer stack with white light at angles of incidence of 0 and 450;

18 Figure 3 is a graphical comparison of computational / simulation data and experimental data for a percent reflection versus reflected EMR wavelength for an omnidirectional red-textured multilayer stack for a feasibility study irradiated with white light at an incidence angle of 0 °;

19 FIG. 13 is a plot of percent reflection versus wavelength for an omnidirectional structural color multilayer stack according to one embodiment of the present invention; FIG.

20 FIG. 13 is a plot of percent reflection versus wavelength for an omnidirectional structural color multilayer stack according to one embodiment of the present invention; FIG.

21 FIG. 13 is a plot of percent reflection versus wavelength for an omnidirectional structural color multilayer stack according to one embodiment of the present invention; FIG.

22 FIG. 13 is a plot of percent reflection versus wavelength for an omnidirectional structural color multilayer stack according to one embodiment of the present invention; FIG.

23 12 is a graphical representation of a portion of an a * b * color map using the CIELAB color space in which the chroma and hue shift between a conventional paint and a paint consisting of pigments according to an embodiment of the present invention (sample (b)) ) are compared;

24 FIG. 12 is a schematic representation of an omnidirectional structural color multi-layer stack according to an embodiment of the present invention; FIG.

25 FIG. 12 is a schematic representation of an omnidirectional structural color multi-layer stack according to an embodiment of the present invention; FIG.

26 FIG. 12 is a schematic representation of an omnidirectional structural color multi-layer stack according to an embodiment of the present invention; FIG.

27 Fig. 12 is a schematic representation of an omnidirectional structural-color four-layer pigment according to an embodiment of the present invention;

28 Fig. 12 is a schematic representation of an omnidirectional structural colored seven-layer pigment according to an embodiment of the present invention;

29 Figure 3 is a schematic representation of an omnidirectional structural colored seven-layer pigment having a protective coating according to an embodiment of the present invention;

30 Figure 3 is a schematic representation of a protective coating having two or more layers, according to one embodiment of the present invention;

31 Fig. 10 is a graph showing a normalized relative photocatalytic activity for an omnidirectional, textured-color pigment having a number of different protective coatings;

32A is one of two Scanning Electron Microscope (SEM) images for a plurality of omnidirectional, textured-color seven-layer pigments without protective coating; and

32B is one of two Scanning Electron Microscope (SEM) images for a plurality of omnidirectional, textured-color seven-layer pigments having a protective coating of silica and zirconia-alumina.

DETAILED DESCRIPTION OF THE INVENTION

An omnidirectional structure or interference color is created. The omnidirectional structure color is in the form of a multilayer thin film (also referred to herein as a multilayer stack) which reflects a narrow band of electromagnetic radiation in the visible spectrum and has little or no discernible color shift when the multilayer thin film is viewed from angles between 0 to 45 degrees , The multilayer thin film can be used as a pigment in a paint composition, as a continuous thin film on a pattern, and the like.

The multilayer thin film includes a multilayer stack having a first layer and a second layer overlying the first layer. In some cases, the multilayer stack reflects a narrow band of electromagnetic radiation having an FWHM of less than 300 nm, preferably less than 200 nm, and in some cases less than 150 nm. The multilayer thin film also has a color shift of less than 50 nm, preferably less than 40 nm, and more preferably less than 30 nm, when the multilayer stack of broad band electromagnetic radiation, e.g. B. white light, exposed and viewed from angles between 0 and 45 degrees. In addition, the multilayer stack could have a separate reflected band of electromagnetic radiation in the UV range and / or in the IR range.

The total thickness of the multilayer stack is less than 2 μm, preferably less than 1.5 μm, and even more preferably less than 1.0 μm. Thus, the multilayer stack can be used as a paint pigment in thin film paint coatings.

The first and second layers may be made of dielectric material or, alternatively, the first and / or the second layer may be made of an absorbent material. Absorbent materials include selective absorbing materials such as Cu, Au, Zn, Sn, alloys thereof, and the like, or alternatively, colorful dielectric materials such as Fe ₂ O ₃ , Cu ₂ O, combinations thereof, and the like. The absorbent material may also be a non-selective absorbent material such as Cr, Ta, W, Mo, Ti, Ti-nitride, Nb, Co, Si, Ge, Ni, Pd, V, iron oxides, combinations or alloys thereof and the like. The thickness of an absorbent layer consisting of selective absorbent material is between 20 to 80 nm, while the thickness of an absorbent layer consisting of non-selective absorbent material is between 5 to 30 nm.

The multilayer stack may also include a reflector layer over which the first layer and the second layer extend, the reflector layer may be made of metals such as Al, Ag, Pt, Cr, Cu, Zn, Au, Sn, alloys thereof and the like. The reflector layer generally has a thickness between 30 and 200 nm.

The multilayer stack may comprise a narrow band of reflected electromagnetic radiation having the shape of a symmetrical peak within the visible spectrum. Alternatively, the narrow reflected band of electromagnetic radiation in the visible spectrum may be so adjacent to the UV region that a portion of the reflected band of electromagnetic radiation, ie the UV part, is not visible to the human eye. Alternatively, the reflected band of electromagnetic radiation may have a part in the IR region, so that the IR part is also not visible to the human eye.

Whether the reflected band of electromagnetic radiation lying in the visible spectrum now adjoins the UV or IR region or has a symmetric peak within the visible spectrum - the multilayer thin films disclosed herein have a narrow band of reflected electromagnetic radiation in the visible spectrum that has a low, small or imperceptible color shift. The low or imperceptible color shift may be in the form of a slight shift of center wavelength for a narrow reflected band of electromagnetic radiation. Alternatively, the low or imperceptible color shift may take the form of a slight shift of a UV-side edge or an IR-side edge of a reflected band of electromagnetic radiation adjacent to the IR region and the UV region, respectively. Such a small shift of a center wavelength, a UV-side edge and / or an IR-side edge is typically less than 50 nm, in some cases less than 40 nm and in other cases less than 30 nm when using the multilayer thin film viewed from angles between 0 and 45 degrees.

In addition, the omnidirectional structural paint may be in the form of a multi-layered thin film in the form of a plurality of pigment particles having a protective coating. Thus, a weather resistant pigment is created. The protective coating may include one or more oxide layers which reduce the relative photocatalytic activity of the pigment particles. The oxide layer may be any oxide layer known to those skilled in the art and includes, for example, a silicon oxide layer, an aluminum oxide layer, a zirconium oxide layer, a titanium oxide layer, a ceria layer, combinations thereof, and the like. In some cases, the protective coating includes a first oxide layer and a second oxide layer. In addition, the first oxide layer and / or the second oxide layer may be a hybrid oxide layer, i. H. an oxide layer that is a combination of two different oxides. Likewise, and as stated above, the pigment per se may be in the form of a multi-layered thin film which does not have an oxide layer.

A method of producing an omnidirectional interference pigment could involve the use of an acid, an acidic compound, an acidic solution, and the like. In other words, the plurality of omnidirectional interference pigment particles could be treated in an acidic solution. Additional teachings and details of the omnidirectional interference pigment and method of making the pigment will be discussed later in this document.

It will open 1 Referred to where the 1A to 1D represent the basic components of an omnidirectional textured color design. Exactly shows 1A a dielectric layer exposed to incident electromagnetic radiation. In addition, the dielectric layer (DL) reflects and transmits a portion of the incident electromagnetic radiation. In addition, the incident electromagnetic radiation is the same to the transmitted part and the reflected part, and usually the transmitted part is much larger than the reflected part. Dielectric layers may be made of dielectric materials such as SiO ₂ , TiO ₂ , ZnS, MgF _2, and the like.

In sharp contrast shows 1B a reflective layer (RL) in which all incident electromagnetic radiation is reflected and which has substantially zero transmittance. Reflector layers are typically made of materials such as aluminum, gold and the like.

1C shows an absorbing layer (AL), wherein incident electromagnetic radiation is absorbed by the layer and not reflected or transmitted. Such an absorbent layer may consist of graphite, for example. Likewise, all of the incident electromagnetic radiation is absorbed and the transmission and reflectance are approximately zero.

1D shows a partially absorbing or selective absorbing layer (SAL) in which a portion of the incident electromagnetic radiation is absorbed by the layer, a portion is transmitted and a portion is reflected. Thus, the amount of transmitted, absorbed and reflected electromagnetic radiation is equal to the amount of incident electromagnetic radiation. In addition, such selective absorbing layers may be made of materials such as a thin layer of chromium, layers of copper, brass, bronze, and the like.

As for the present invention, three generations of the design and manufacture of omnidirectional interference thin films are disclosed.

First generation

It will be up now 2 Referring to Figure 2, there is shown a schematic representation of a multilayer thin film having a plurality of dielectric layers. In addition, the reflection and the transmission of an incident electromagnetic radiation are shown schematically. As stated above, the typical transmission for incident electromagnetic radiation is much larger than its reflection, and therefore many layers are required.

3 shows a part of a multilayer thin film consisting of dielectric layers having a first refractive index (DL ₁ ) and a second refractive index (DL ₂ ). Note that the double lines between the layers simply represent a boundary layer between the different layers.

Without wishing to be bound by theory, one method or approach for designing and producing a desired multilayer stack is as follows.

When electromagnetic radiation strikes a material surface, waves of the radiation may be reflected from the material or transmitted through the material. When electromagnetic radiation at the angle θ ₀ to the first end 12 the multi-layer structure 10 , the reflected angles forming the electromagnetic waves with the surface of the high and low refractive index layers are θ _H and θ _L, respectively. Apply the Snellian law: n ₀ Sinθ ₀ = n _L Sinθ _L = n _H Sinθ _H (1) then the angles θ _H and θ _L can be determined if the refractive indices n _H and n _{L are} known.

undAs for the omnidirectional reflectance, a necessary but insufficient condition for the TE mode and the TM mode of the electromagnetic radiation requires that the maximum refraction angle (θ _{H, MAX} ) within the first layer be smaller than the Brewster angle (θ _B ) at the interface between the first layer and the second layer. If the condition is not satisfied, the TM mode of electromagnetic waves is not reflected at the second and all subsequent boundaries and thus passes through the structure. It follows:

and

Which is why the following is necessary:

was auch folgendermaßen ausgedrückt werden kann:

und wobei:

undIn addition to the necessary condition illustrated by Equation 4, if the electromagnetic radiation of wavelength λ having an angle θ _{0 is} incident on a multilayer structure and the individual bilayers of the multilayer structure may have thicknesses d _H and d _L with refractive indices n _H and _H, respectively n _L , the characteristic translation matrix (F _T ), θ _{0 are} expressed as:

which can also be expressed as follows:

and wherein:

and

wobei

undIn addition, applies

in which

and

undSolve ρ _T expressly for TE and TM:

and

An angle-dependent band structure can be obtained from a boundary condition for the edge, the so-called bandgap, of the entire reflection zone. For the purposes of the present invention, bandgap is defined as the equation for the line separating the total reflection zone from the transmission zone for the given band structure.

A boundary condition which determines the band gap frequencies of the highly reflected band can be given by: Trace | F _T | = -1 (16)

oder, anders ausgedrückt:

Thus, from +3 follows:

or in other words:

By combining Equations 15 and 7, the following bandgap equation is obtained:

In which: L ₊ = n _H d _H Cos θ _H + n _L d _L Cos θ _L (20) and: L _- = n _H d _H Cos θ _H - n _L d _L Cos θ _L (21)

für den TE-Modus, und:

für den TM-Modus.The "+" sign in the bandgap equation shown above represents the band gap for the long wavelength (λ _long ), and the "-" sign represents the band gap for the short wavelength (λ _short ) 21 um, you get:

for TE mode, and:

for the TM mode.

An approximate solution for the bandgap can be determined by the following expression: L = n _H d _H Cos _H - n _L d _L ~ _L Cos 0 (24)

für den TE-Modus und:

für den TM-Modus.This approach is useful when considering a quarter-wave design (described in more detail below) and choosing optical thicknesses of the alternating layers to be equal to each other. In addition, relatively small differences in the optical thicknesses of the alternating layers provide a cosine that is close to one. Thus, Equations 23 and 24 provide bandgap approximation equations:

for TE mode and:

for the TM mode.

Values for L ₊ and ρ _TM as a function of the angle of incidence can be obtained from equations 7, 8, 14, 15, 20, and 21, thereby allowing calculations of λ _long and λ _short in the TE and TM modes as a function of the angle of incidence are.

The central wavelength of an omnidirectional reflector (λ _c ) can be determined from the relationship: λ _c = 2 (n _H d _H Cos θ _H + n _L d _L Cos θ _L ) (27)

für den TE-Modus, und:

für den TM-Modus. Man beachte, dass das Verhältnis von Bereich zu Bereichsmitte in Prozent ausgedrückt werden kann, und für die Zwecke der vorliegenden Erfindung werden die Begriffe Verhältnis von Bereich zu Bereichsmitte und Verhältnis von Bereich zu Bereichsmitte in Prozent austauschbar verwendet. Man beachte ferner, dass ein hierin angegebener Wert für, Verhältnis von Bereich zu Bereichsmitte', auf den ein ,%'-Zeichen folgt, ein Prozentwert des Verhältnisses von Bereich zu Bereichsmitte ist. Die Verhältnisse von Bereich zu Bereichsmitte für den TM-Modus und den TE-Modus können numerisch aus Gleichungen 28 und 29 berechnet werden und grafisch als Funktion eines hohen Brechungsindex und eines niedrigen Brechungsindex dargestellt werden.The central wavelength may be an important parameter because its value indicates an approximate range of the electromagnetic wavelength and / or color spectrum that is to be reflected. Another important parameter that can give an indication of the width of a reflection band is defined as the ratio of a range of wavelengths within the omnidirectional reflection band to the mid-range of the wavelengths within the omnidirectional reflection band. This "ratio of area to area center" (η) is expressed mathematically as:

for TE mode, and:

for the TM mode. Note that the ratio of area to area center may be expressed in percent, and for purposes of the present invention, the terms area to area center ratio and area to area center ratio are used interchangeably. It should also be noted that a range-to-area-center-ratio value given herein, followed by a '%' sign, is a percentage of the area-to-area ratio. The area-to-area center ratios for the TM mode and the TE mode can be computed numerically from Equations 28 and 29 and plotted graphically as a function of high refractive index and low refractive index.

wobei:

und F_c, der Streuungsfaktor der Zentralwellenlänge, kann ausgedrückt werden als:

Note that the scatter of the central wavelength must be minimized to obtain the narrow omnidirectional band. Thus, from Equation 27, the scatter of the central wavelength can be expressed as:

in which:

and F _c , the scattering factor of the central wavelength, can be expressed as:

As a result, a multilayer stack having a desired low central wavelength shift (Δλ _c ) can be made of an optically low density material having a refractive index of n _L and one or more layers having a thickness of d _L and an optically dense material having a refractive index of n _H and one or more layers having a thickness of d _{H are} designed.

Exact supplies 4 FIG. 4 is a graph of a comparison of the 0.2% region by region ratio for the transversal magnetic mode and the trans-electrical electromagnetic radiation mode plotted as a function of high refractive index to low refractive index. FIG. In the figure, three cases are shown, of which Case I relates to a large difference between the transversal magnetic mode and the transversal electric mode, Case II relates to a situation in which a smaller difference between the transversal magnetic mode and the trans-electric mode and Case III concerns a situation in which there is a very small difference between the transversal magnetic mode and the transversal electric mode. Also shows 5 a percent reflection versus wavelength for a reflected electromagnetic radiation for a case analogous to Case II.

In 5 For example, a small scatter of the center wavelength for a multilayer thin film is shown in accordance with Case III. Besides, and as in 6 Case II shows a shift of the center wavelength of less than 50 nm (Case II) when considering a multilayer thin film structure between 0 and 45 degrees, and Case III gives a shift of the center wavelength of less than 25 nm when the thin film structure is electromagnetic Radiation between 0 and 45 degrees is exposed.

Second generation

It will open 7 Reference is made where an illustrative structure / conception according to a second generation is shown. In the 7 The multilayer structure shown has a plurality of dielectric layers and an underlying absorbent layer. In addition, none of the incident electromagnetic radiation is transmitted through the structure, ie, all incident electromagnetic radiation is reflected or absorbed. Such a structure as in 7 allows to reduce the number of dielectric layers necessary to obtain a suitable level of reflection.

For example, supplies 8th a schematic representation of such a structure in which a multilayer stack of a central absorbent layer of Cr, a first layer of dielectric material (DL ₁ ), which is located over the absorbent Cr layer, a second layer of dielectric material (DL ₂ ), the above the DL ₁ layer, and then another DL ₁ layer overlying the DL ₂ layer. With such a design, the thicknesses of the first dielectric layer and the third dielectric layer could be the same.

Exactly shows 9A a graphical representation of a structure in which two TiO ₂ layers adjacent to a central Cr layer and on the other hand adjacent to two SiO ₂ layers. As in the diagram is shown, the layers of TiO ₂ and SiO _{2 are} not the same thickness. Also shows 9B Reflectance against wavelength spectrum of in 9A 5-layered structure and compared to a 13-layer structure made according to the first generation design. As in 9B When the structures are viewed at 0 and 45 degrees, there is a shift in the center wavelength of less than 50 nm, and preferably less than 25 nm. Also in 9B the fact is shown that a 5-layer structure according to the second generation behaves substantially the same as a 13-layer structure of the first generation.

Third generation

It will open 10 Referring to Figure 3, there is shown a third generation design in which a first layer of dielectric material DL ₁ extends over a reflective layer (RL) pad and a selective absorbing layer SAL extends over the DL ₁ layer. In addition, a further DL ₁ layer may be provided which extends over the selective absorbing layer. Also shown in the figure is that all incidental electromagnetic radiation is either reflected or selectively absorbed by the multilayer structure.

A design like it in 10 is another approach that is used to design and manufacture a desired multilayer stack. Specifically, a thickness at a zero or near-zero energy point is used for a dielectric layer and discussed below.

For example 11A a schematic representation of a dielectric ZnS layer, which lies over an A1 reflector layer. The dielectric ZnS layer has a total thickness of 143 nm, and for incident electromagnetic radiation having a wavelength of 500 nm, an energy point of zero or almost zero is 77 nm. In other words, the dielectric ZnS layer exhibits incidental EMR Wavelength of 500 nm an electric field of zero or almost zero at a distance of 77 nm from the A1 reflector layer. There are also 11B a plot of the energy field over the ZnS dielectric layer for a number of different incident EMR wavelengths. As shown in the graph, the dielectric layer for the 500 nm wavelength has a zero electric field at a thickness of 77 nm, but for EMR wavelengths of 300, 400, 600, and 700 nm, an electric field at 77 nm is not zero.

As far as the calculation of a zero or almost zero point of the electric field is concerned, it shows 12 a dielectric layer 4 with a total thickness 'D', an incremental thickness 'd' and a refractive index 'n' on a backing or core layer 2 with a refractive index n _s . Incident light hits the outside surface 5 the dielectric layer 4 at an angle θ with respect to a line 6 which is perpendicular to the outer surface 5 , and reflected from the outer surface 5 with the same angle. Incident light is through the outer surface 5 and in the dielectric layer 4 with an angle θ _F with respect to the line 6 transmitted and hits with an angle θ _s on the surface 3 the underlying layer 2 ,

wobei k = 2π / λ und λ eine gewünschte Wellenlänge ist, die reflektiert werden soll. Außerdem ist α = n_ssinθ_s, wobei 's' der Unterlage in 5 entspricht, und (z) ist die Permittivität der Schicht als Funktion von z. Somit gilt |E(d)|² = u(z)|²exp(2ikαy)|_z=d (36) für die s-Polarisation und

für die p-Polarisation.For a single dielectric layer, θ _s = θ _F and the energy / electric field (E) can be expressed as E (z) when z = d. From the Maxwell equations, the electric field for an s-polarization can be expressed as: E - (d) = {u (z), 0, 0} exp (ikαy) | _{z = d} (34) and for a p-polarization as:

in which k = 2π / λ and λ is a desired wavelength to be reflected. In addition, α = n _s sin θ _s , where 's' of the pad in 5 and (z) is the permittivity of the layer as a function of e.g. Thus applies | E (d) | ² = u (z) | ² exp (2ikαy) | _{z = d} (36) for the s-polarization and

for the p-polarization.

Note that a change in the electric field along the Z direction of the dielectric layer 4 can be estimated by calculating the unknown parameters u (z) and v (z) where it can be shown that:

und

Of course, i 'is the square root of -1. Based on the boundary conditions u | _{z = 0} = 1, v | _{z = 0} = q _s and the following equations: q _s = n _s cos θ _s for the s-polarization (39) q _s = n _s / cos θ _s for the p-polarization (40) q = ncosθ _F for the s-polarization (41) q = n / cosθ _F for p-polarization (42) φ = k · n · d cos (θ _F ) (43) u (z) and v (z) can be expressed as:

and

für die s-Polarisation mit φ = k·n·dcos (θ_F), und:

für die p-Polarisation, wobei:

und

Therefore:

for s-polarization with φ = k · n · d cos (θ _F ), and:

for the p-polarization, where:

and

was es möglich macht, nach Dicke ,d' aufzulösen, d. h. nach der Position oder der Lage innerhalb der dielektrischen Schicht, wo das elektrische Feld null ist.For a simple situation where θ _F = 0 or a normal incidence, φ = k · n · d and α = 0, then:

which makes it possible to resolve by thickness, d ', that is, the position or location within the dielectric layer where the electric field is zero.

It will be up now 13 Referring to where equation 52 was used to calculate that the zero or near zero of the electric field in the in 11A When exposed to an EMR having a wavelength of 434 nm, the dielectric ZnS layer shown is at 70 nm (instead of 77 nm at a wavelength of 500 nm). In addition, a 15 nm-thick Cr absorber layer was inserted at a thickness of 70 nm from the Al reflector layer to obtain a ZnS-Cr boundary layer having a zero or near zero electric field. Such a structure of the present invention allows passage of 434 nm wavelength light through the Cr-ZnS interfaces, but absorbs light that does not have a wavelength of 434 nm. In other words, the Cr-ZnS barrier layers have an electric field of zero or almost zero with respect to light having a wavelength of 434 nm, and therefore 434 nm light passes through the barrier layer. However, the Cr-ZnS barrier layers do not have a zero or near zero electric field for light having no wavelength of 434 nm, and thus such light is absorbed by the Cr absorber layer and / or Cr-ZnS barrier layers, and by the A1 reflector layer is not reflected.

Note that a certain percentage of light passes through the Cr-ZnS interface within +/- 10 nm of the desired 434 nm. But note also that such a narrow band of reflected light, e.g. B. 434 +/- 10 nm for the human eye still provides a sharp structure color.

The result of the Cr absorber layer in the multilayer stack in 13 is in 14 where the percent reflection against the reflected EMR wavelength is shown. As shown by the dotted line, the one in 13 A ZnS dielectric layer without a Cr absorber layer is shown to have a narrow reflected peak at about 400 nm, but a much broader peak is present at about 550+ nm. In addition, there is still a significant amount of light in the 500 nm wavelength region reflected. Thus, a double peak is present which prevents the multilayer stack from having or showing a structural color.

In contrast, the solid line in 14 the in 13 shown structure, where the Cr absorber layer is present. As shown in the figure, a sharp peak is present at about 434 nm and a sharp drop in reflectance for wavelengths above 434 nm is provided by the Cr absorber layer. Note that the sharp peak represented by the solid line appears optically as a sharp / structural color. Likewise shows 14 where the width of a reflected peak or band is measured, ie, the width of the band is determined at 50% reflection of the maximum reflected wavelength, also referred to as full width at half maximum (FWHM).

As for the omnidirectional behavior of the 13 As to the illustrated multilayer structure, the thickness of the ZnS dielectric layer may be designed or adjusted to provide only the first harmonic of reflected light. Note that this is sufficient for a "blue" color, but producing a "red" color requires extra consideration. For example, control of angular independence for red light is difficult because thicker dielectric layers are needed, which in turn results in a highly harmonic design, ie the presence of the second and possibly third harmonic is essential. In addition, the dark red color space is very narrow. Thus, a red-colored multilayer stack has a higher angular variance.

To overcome the higher angular variance for red color, the present application discloses a unique and novel design / structure that provides a red color that is angle independent. For example, shows 15A a dielectric layer showing first and second harmonics for incident white light when viewing an outer surface of the 0 and 45 degree dielectric layer. As shown in the graph, a low angle dependence (small Δλ _c ) is provided by the thickness of the dielectric layer, but such a multilayer stack has a combination of blue color (1st harmonic) and red color (2nd harmonic) and is suitable thus not for a desired "only red" color. Therefore, the concept / structure of using an absorber layer to absorb an undesired harmonic series has been developed. 15A Fig. 12 also shows an example of the position of the central wavelength of the reflected band (λ _c ) for a given reflection peak and the scattering or shift of the central wavelength (Δλ _c ) when the sample is viewed from 0 and 45 degrees.

Now it will open 15B Referenced where the second harmonic in 15A is absorbed with a Cr absorber layer at the appropriate thickness of the dielectric layer (e.g., 72 nm) and a sharp blue color is provided. More important for the present invention is that 15C shows that by absorbing the first harmonic with the Cr absorber at a different thickness of the dielectric layer (e.g., 125 nm), a red color is provided. However, shows 15C also that the use of the Cr absorber layer leads to an angle dependence of the multilayer stack which is higher than desired, ie greater than the desired Δλ _c .

Note that the relatively large shift in λ _c for the red color compared to the blue color is due to the fact that the dark red color space is very narrow, and to the fact that the Cr absorber layer absorbs wavelengths that are with an electric field is not associated with zero, that is, that it does not absorb light when the electric field is zero or almost zero. So shows 16A in that the zero or non-zero point for the wavelengths of light is different at different angles of incidence. Such factors lead to the angle-dependent absorption, which in 16B that is, the difference in the 0 ° and 45 ° absorption curves. In order to further refine the design and the angle independence of the multilayer stack, therefore, an absorber layer, the z. B. blue light is absorbed regardless of whether the electric field is zero or not used.

Exactly shows 17A a multilayer stack having a Cu absorber layer instead of a Cr absorber layer extending over a ZnS dielectric layer. The results of using such a "colored" or "selective" absorber layer is in 17B shown a much "closer" grouping of the 0 ° and 45 ° absorption lines for the multilayer stack shown in FIG 17A demonstrated. Thus, a comparison between 16B and 16B the significant improvement in absorption angle independence when using a selective absorber layer rather than a non-selective absorber layer.

On this basis, a multi-layer stack was designed and manufactured for a feasibility study. In addition, computational / simulation results and actual experimental data for the feasibility sample were compared. More precisely, and as from the graph in 18 was shown a sharp produces red color (wavelengths greater than 700 nm are typically not seen by the human eye), and good agreement was obtained between the computational / simulation and experimental light data obtained from the actual sample. In other words, calculations / simulations may be used and / or they may be used to simulate the results of multilayer stack designs according to one or more embodiments of the present invention and / or multilayer stacks of the prior art.

A list of simulated and / or actually produced multilayer stack samples is given in Table 1 below. As shown in the table, the multilayer structures disclosed herein include at least 5 different layered structures. In addition, the samples were simulated and / or manufactured from a wide range of materials. Samples were created which showed high chrominance, low hue shift and excellent reflectance. In addition, the three- and five-layered samples had a total thickness between 120 and 200 nm, the seven-layered samples had a total thickness between 350 and 600 nm, the nine-layered samples had a total thickness between 440 and 500 nm, and the eleven-layered samples had a total thickness between 600 and 660 nm. Table 1 Avg. Chrominance (0-45) Δh (0-65) Max. Reflectance sample name 3 layers 90 2 96 3-1 5-layers 91 3 96 5-1 7-ply 88 1 92 7-1 91 3 92 7-2 91 3 96 7-3 90 1 94 7-4 82 4 75 7-5 76 20 84 7-6 9-ply 71 21 88 9-1 95 0 94 9-2 79 14 86 9-3 90 4 87 9-4 94 1 94 9-5 94 1 94 9-6 73 7 87 9-7 11-ply 88 1 84 11-1 92 1 93 11-2 90 3 92 11-3 89 9 90 11-4

It will be up now 19 Referring to FIG. 5, where is shown a graph of percent reflection versus reflected EMR wavelength for an omnidirectional reflector when exposed to white light at angles of 0 and 45 degrees with respect to the surface of the reflector. As shown in the diagram, both the 0 ° and 45 ° curves show a very low reflectance, e.g. Below 20%, which is obtained from the omnidirectional reflector for wavelengths greater than 500 nm. However, as shown by the curves, the reflector provides a sharp increase in the reflection band at wavelengths between 400-500 nm and reaches a maximum at about 90% at 450 nm. Note that the portion or region of the graph is on the left (UV side) of the curve represents the UV portion of the reflection band provided by the reflector.

The sharp increase in reflectivity afforded by the omnidirectional reflector is characterized by an IR-side edge of each curve ranging from a weakly-reflected portion at wavelengths greater than 500 nm to a highly-reflected portion, e.g. B.> 70% is enough. A linear portion 200 of the IR side edge is inclined at an angle (β) of over 60 ° with respect to the x axis, has a length L of about 50 on the reflectance axis, and a gradient of 1.2. In some cases, the linear portion is inclined at an angle of over 70 ° with respect to the x-axis, while in other cases β is greater than 75 °. Likewise, the reflection band has a visible FWHM of less than 200 nm and in some cases a visible FWHM of less than 150 nm and in other cases a visible FWHM of less than 100 nm. In addition, the central wavelength λ _{c is} the visible reflection band as in 19 represented as the wavelength equidistant between the IR-side edge of the reflection band and the UV edge of the UV spectrum in the visible FWHM.

Note that the term "visible FWHM" denotes the width of the reflection band between the IR side edge of the curve and the edge of the UV spectrum region, beyond which the reflection provided by the omnidirectional reflector is not visible to the human eye is. In this way, the inventive designs and multilayer stacks disclosed herein utilize the non-visible UV portion of the electromagnetic radiation spectrum to provide a sharp or textured color. In other words, the omnidirectional reflectors disclosed herein utilize the non-visible UV portion of the electromagnetic radiation spectrum to create a narrow band of reflected visible light, despite the fact that the reflectors can reflect a much wider band of electromagnetic radiation entering the UV Region.

Now it will open 20 Referring to Figure 1, there is shown a generally symmetrical reflection band provided by a multilayer stack according to an embodiment of the present invention and viewed at 0 ° and 45 °. As shown in the figure, the reflection band provided by the multilayer stack, when viewed at 0 °, has a wavelength shift (λ _c (0 °)) of less than 50 nm when the multilayer stack is at 45 ° (FIG. is considered λ _c (45 °)), ie Δλ _c (0-45 °) <50 nm. In addition, the FWHM of both the 0 ° and the 45 ° -Reflexionsbands -Reflexionsbands less than 200 nm.

21 Figure 4 shows a graph of percent reflection versus reflected EMR wavelength for another omnidirectional reflector design when irradiated with white light from angles of 0 and 45 ° with respect to the surface of the reflector. Similar to in 19 and, as shown in the diagram, both the 0 ° and 45 ° curves exhibit a very low reflectance, e.g. Below 10% provided by the omnidirectional reflector for wavelengths greater than 550 nm. However, as shown by the curves, the reflector provides a sharp increase in the reflection band at wavelengths between 560-570 nm and reaches a maximum at about 90% at 700 nm. Note that the portion or region of the graph is on the right Side (IR side) of the curve represents the IR portion of the reflection band provided by the reflector.

The sharp increase in reflectance provided by the omnidirectional reflector is characterized by a UV-side edge of each curve ranging from a low-reflectance portion at wavelengths greater than 550 nm to a highly reflective portion, e.g. B.> 70% is enough. A linear portion 200 of the UV-side edge is inclined at an angle (β) of over 60 ° with respect to the x-axis, has a length L of about 40 on the reflectance axis, and a gradient of 1.4. In some cases, the linear portion is inclined at an angle of over 70 ° with respect to the x-axis, while in other cases β is greater than 75 °. Likewise, the reflection band has a visible FWHM of less than 200 nm and in some cases a visible FWHM of less than 150 nm and in other cases a visible FWHM of less than 100 nm. In addition, the central wavelength λ _c for the visible reflection band, as in 18 defined as the wavelength that is equidistant from the visible FWHM to the UV-side edge of the reflection band and to the IR edge of the IR spectrum.

Note that the term "visible FWHM" denotes the width of the reflection band between the UV-side edge of the curve and the edge of the IR spectrum range, beyond which the reflection provided by the omnidirectional reflector is not visible to the human Eye. In this way, the inventive designs and multilayer stacks disclosed herein utilize the non-visible IR portion of the electromagnetic radiation spectrum to provide a sharp or textured color. In other words, the omnidirectional reflectors disclosed herein utilize the non-visible IR portion of the electromagnetic radiation spectrum to form a narrow band of reflected light visible light, despite the fact that the reflectors can reflect a much broader band of electromagnetic radiation reaching into the IR region.

It will be up now 22 Referring to Figure 1, where a percentage reflection versus wavelength graph for another seven-layer omnidirectional reflector is shown when exposed to white light at angles of 0 and 45 ° with respect to the surface of the reflector. In addition, a definition or characterization of omnidirectional properties provided by omnidirectional reflectors disclosed herein is shown. More specifically, and when a reflection band provided by a reflector according to the present invention has a maximum, ie, a peak, as shown in the figure, each curve has a central wavelength (λ _c ) defined as the wavelength, which is a maximum reflection shows or experience The term maximum reflected wavelength can also be used for λ _c .

As in 22 is shown, there is a shift or displacement of when an outer surface of the omnidirectional reflector from an angle of 45 ° (λ _c (45 °)) is considered, z. For example, the outer surface is inclined at 45 ° with respect to the human eye viewing the surface, compared to when the surface is viewed at an angle of 0 ° (((0 °)), ie perpendicular to the surface The displacement of λ _c (Δλ _c ) provides a measure of the omnidirectional property of the omnidirectional reflector Of course, zero displacement, ie, zero displacement, would be a perfectly omnidirectional reflector, however, omnidirectional reflectors disclosed herein may have a Δλ _c of less than 50 nm, which may appear to the human eye as if the surface of the reflector did not change the color, and thus the reflector is omnidirectional from a practical point of view In some cases, omnidirectional reflectors disclosed herein may have a Δλ _c of less than 40 nm, in other cases a Δλ _c of less than 30 nm and in still other cases a Δλ _c of less than s are 20 nm, while in yet other cases they have a Δλ _c of less than 15 nm. Such a shift in Δλ _c may be determined by a graph of actual reflectance versus wavelength for a reflector and / or alternatively by modeling the reflector when the materials and layer thicknesses are known.

Another definition or characterization of omnidirectional properties of a reflector may be determined by the displacement of a side edge for a given set of angular reflection bands. For example, and as in 19 , provides a shift or shift of an IR side edge (ΔS _IR ) for reflection from an omnidirectional reflector viewed from 0 ° (S _IR (0 °)) as compared to the IR side edge for reflection by the same reflector, which is considered from 45 ° (S _IR (45 °)), a measure of the omnidirectional property of the omnidirectional reflector. In addition, when using ΔS _IR as a measure of omnidirectionality, it may be preferable to use Δλ _c , e.g. B. for reflectors that create a reflection band, the in 19 is similar, ie a reflection band with a peak corresponding to a maximum reflected wavelength and which is not in the visible range (see 19 and 21 ). Note that the shift of the IR-side edge (ΔS _IR ) is at the visible FWHM and / or can be measured.

As in 21 , provides displacement or displacement of a UV-side edge (ΔS _IR ) for reflection from an omnidirectional reflector viewed from 0 ° (S _UV (0 °)) as compared to the IR-side edge for reflection by the same reflector viewed from 45 ° (S _UV (45 °)), a measure of the omnidirectional property of the omnidirectional reflector. Note that the shift of the UV-side edge (ΔS _UV ) is at the visible FWHM and / or can be measured.

Of course, a zero displacement, ie no displacement (ΔS _i = 0 nm, i = IR, UV) would characterize a perfectly omnidirectional reflector. However, omnidirectional reflectors disclosed herein can provide a ΔS _L of less than 50 nm, which may appear to the human eye as if the surface of the reflector did not change color, and thus the reflector is omnidirectional from a practical point of view. In some cases, omnidirectional reflectors disclosed herein may have a ΔS _i of less than 40 nm, in other cases a ΔS _i of less than 30 nm, and in yet other cases a ΔS _i of less than 20 nm, while in FIG still quite different cases have a ΔS _i of less than 15 nm. Such a shift in ΔS _i can be determined by a graph of actual reflectance versus wavelength for a reflector and / or alternatively by modeling the reflector when the materials and layer thicknesses are known.

The shift of an omnidirectional reflection can also be measured by a slight hue shift. For example, the hue shift of the pigments consisting of multilayer stacks according to one embodiment of the present invention, 30 ° or less, as in 23 is shown (see Δθ ₁ ), and in some cases, the hue shift is 25 ° or less, preferably less than 20 °, more preferably less than 15 °, and even more preferably less than 10 °. In contrast, conventional pigments show a hue shift of 45 ° or more (see Xθ ₂ ).

Summarized in 24 a schematic representation of an omnidirectional multilayer thin film according to an embodiment of the present invention, in which a first layer 110 a second layer 120 which extends over it. An optical reflector layer 100 can be included. Likewise, two symmetric layers may be on an opposite side of the reflector layer 100 be present, ie the reflector layer 100 can be a first layer 110 have, which is arranged opposite to the layer shown in the figure, so that the reflector layer 100 between two first layers 110 is arranged. In addition, a second layer 120 opposite to the reflector layer 100 be arranged so that a five-layer structure is created. Therefore, it should be understood that the discussion of the multilayer thin films given herein also includes the possibility of a mirror structure with respect to one or more central layers. Thus, can 24 to serve as an illustration for one-half of a five-layered multilayer stack.

The first shift 110 and the second layer 120 may be dielectric layers, ie consist of a dielectric material. Alternatively, one of the layers may be an absorbent layer, e.g. A selective absorbing layer or a non-selective absorbing layer. For example, the first layer 110 a dielectric layer and the second layer 120 may be an absorbent layer.

25 shows half of a seven-layered design at reference numerals 20 , The multilayer stack 20 has an additional layer 130 on, which is above the second layer 120 extends. For example, the additional layer 130 a dielectric layer extending over an absorbent layer 110 extends. Note that the layer 130 from the same or different material as the layer 110 can exist. In addition, the layer can 130 using the same or a different method as it is used to the layers 100 . 110 and / or 120, to the multilayer stack 20 be added, for example by a sol-gel method.

26 shows one half of a nine-layered design at reference numerals 24 , where a still further layer 105 between the optional reflector layer 100 and the first layer 110 is arranged. For example, the additional layer 105 an absorbent layer 105 be that between the reflector layer 100 and a dielectric layer 110 lies. A non-exhaustive list of materials from which the various layers can be made is shown in Table 2 below. Table 2 Refractive index materials (visible region) Refractive index materials (visible region) material Refractive index material Refractive index Germanium (Ge) 4.0-5.0 Chrome (Cr) 3.0 Tellurium (Te) 4.6 Tin sulfide (SnS) 2.6 Gallium antimonite (GaSb) 4.5-5.0 little porous Si 2.56 Indium arsenide (InAs) 4.0 chalcogenide glass 2.6 Silicon (Si) 3.7 Cerium oxide (CeO ₂ ) 2.53 Indium phosphate (InP) 3.5 Tungsten (W) 2.5 Gallium arsenate (GaAs) 3.53 Gallium nitride (GaN) 2.5 Gallium phosphate (GaP) 3.31 Manganese (Mn) 2.5 Vanadium (V) 3 Niobium oxide (Nb ₂ O ₃ ) 2.4 Arsenic selenide (As ₂ Se ₃ ) 2.8 Zinc telluride (ZnTe) 3.0 CuAlSe ₂ 2.75 Chalcogenide glass + Ag 3.0 Zinc selenide (ZnSe) 2.5-2.6 Zinc sulfide (ZnS) 2.5-3.0 Titanium dioxide (TiO ₂ ) sol gel 2.36 Titanium dioxide (TiO ₂ ) vacuum deposited 2.43 Alumina (Al ₂ O ₃ ) 1.75 Hafnium oxide (HfO ₂ ) 2.0 Yttrium oxide (Y2O3) 1.75 Sodium aluminum fluoride (Na3AlF6) 1.6 polystyrene 1.6 Polyethersulfone (PES) 1.55 Magnesium fluoride (MgF2) 1.37 highly porous Si 1.5 Lead fluoride (PbF2) 1.6 Indium Tin Oxide Nanorods (ITO) 1.46 Potassium fluoride (KF) 1.5 Lithium fluoride (LiF4) 1.45 Polyethylene (PE) 1.5 calcium fluoride 1.43 Barium fluoride (BaF2) 1.5 Strontium fluoride (SrF2) 1.43 Silica (SiO 2) 1.5 Lithium fluoride (LiF) 1.39 PMMA 1.5 PKFE 1.6 Aluminum arsenate (AlAs) 1.56 Sodium fluoride (NaF) 1.3 Sol-gel silica (SiO 2) 1.47 Nanoporous silica (SiO2) 1.23 N, N'-bis (1-naphthyl) 4,4'-diamine (NPB) 1.7 Sputtered silica (SiO 2) 1.47 Polyamide-imide (PEI) 1.6 Vacuum-deposited silica (SiO 2) 1.46 Zinc sulfide (ZnS) 2.3 + i (0.015) Niobium oxide (Nb ₂ O ₅ ) 2.1 Titanium nitride (TiN) 1.5 + i (2.0) Aluminum (Al) 2.0 + i (15) Chrome (Cr) 2.5 + i (2.5) Silicon nitride (SiN) 2.1 Niobium pentoxide (Nb2O5) 2.4 mica 1.56 Zirconium oxide (ZrO2) 2.36 polyallomer 1.492 Hafnium oxide (HfO2) 1.9-2.0 polybutylene 1.50 Fluorocarbon (FEP) 1.34 ionomers 1.51 Polytetrafluoroethylene (TFE) 1.35 Polyethylene (low density) 1.51 Fluorocarbon (FEP) 1.34 Nylons (PA) Type II 1.52 Polytetrafluoroethylene (TFE) 1.35 Acrylic multipolymer 1.52 Chlorotrifluoroethylene (CTFE) 1.42 Polyethylene (medium density) 1.52 cellulose propionate 1.46 Styrene butadiene thermoplastic 1.52 to 1.55 cellulose acetate butyrate 1.46-1.49 PVC (rigid) 1.52 to 1.55 cellulose acetate 1.46 to 1.50 Nylons (polyamide) type 6/6 1.53 Methylpentene polymer 1,485 urea formaldehyde 1.54 to 1.58 Acetal homopolymer 1.48 Polyethylene (High Density) 1.54 acrylics 1.49 Styrene-acrylonitrile copolymer 1.56 to 1.57 cellulose nitrate 1.49 to 1.51 Polystyrene (heat and chemistry) 1.57-1.60 ethylcellulose 1.47 Polystyrene (general purpose) 1.59 polypropylene 1.49 Polycarbornate (unfilled) 1.586 polysulfone 1,633 SnO2 2.0

Methods of making the multilayer stacks disclosed herein may be any methods or processes known to those skilled in the art, or methods that are not known to those skilled in the art. Typical known methods include wet processes such as sol-gel processing, layered processing, spin coating and the like. Other known dry processes include chemical vapor deposition processing and physical vapor deposition processing such as sputtering, electron beam deposition, and the like.

The multilayer stacks disclosed herein can be used for almost any color application, for example, as pigments for paints, thin films applied to surfaces, and the like.

As stated above, omnidirectional interference pigments are provided which have a protective / weather resistant coating. For example, in the 27 and 28 shown exemplary pigments that can be coated. Is more accurate 27 a schematic representation of a 3-layer pigment 12 with a core layer 100 , a first non-oxide layer 112 , a selective absorbent layer 114 and an additional non-oxide layer 116 extending above the selective absorbent layer 114 extends. 28 is a schematic representation of a pigment 12a that the pigment 12 resembles except that layers 112a . 114a as in 28A and an additional non-oxide layer 116a have been added. Note that the layers 112 - 112a . 114 - 114a and or 116 / 116a could consist of the same material and could have the same thickness.

29 is a schematic representation of a pigment 22 that is a pigment 12a with a protective coating 200 shows. Also shows 30 that the protective coating 200 may be a single layer or, alternatively, may consist of two layers, e.g. B. from a first layer 202 and a second layer 204 , Note that the first layer 202 and / or the second layer 204 may be a single oxide layer or alternatively may be a hybrid oxide layer consisting of two or more oxides or containing two or more oxides. For example, the protective coating 200 a single oxide layer, for example a single layer of silica, alumina, zirconia or ceria. Alternatively, the protective coating 200 the first layer 202 and the second layer 204 include, and the first layer 202 and the second layer 204 are each a single oxide layer of silicon oxide, alumina, zirconia, titania or ceria. As another alternative, the first layer 202 a single oxide layer and the second layer 204 may be a hybrid oxide layer which is a combination of at least two of silica, alumina, zirconia, titania and ceria. As yet another alternative, the second layer 204 a single oxide layer and the first layer 204 may be a hybrid oxide layer which is a combination of at least two of silica, alumina, zirconia, titania and ceria.

To make the invention more understandable, but not to limit its scope in any way, examples of weather resistant omnidirectional structural paint pigments and process protocols for the production of such pigments are discussed below.

Protocol 1 - 7-layer pigments, which are etched with phosphoric acid and coated with a SiO ₂ layer.

To a suspension containing 10 g of 7-layered pigments dispersed in 110 ml of acetone was added 0.13 ml of phosphoric acid (85%) and stirred for 30 minutes at room temperature. The suspension was then filtered and washed twice with acetone. Solid particles were filtered off and phosphoric acid treated 7-layer pigments were obtained. The 7-ply pigments had a structure as in 28B shown, with a core layer of Al, two ZnS layers, each adjacent to the Al layer, two selectively absorbing Cr layers, each adjacent to the two ZnS layers, and another two ZnS layers, each to the adjacent to two Cr layers.

The phosphoric acid-treated 7-layer pigments were then suspended in 160 ml of ethanol in a round bottom flask equipped with a reflux condenser. The suspension was heated to 65 ° C after 35 g of water and 3.5 g of a 28% aqueous ammonia solution were added. Then, a solution of 10 g of tetraethoxysilane diluted with 13 ml of ethanol was added in small portions to the heated suspension with stirring. The reaction mixture was stirred at 65 ° C for 14 hours, then solid particles were filtered from the liquid, washed with ethanol and then washed with isopropyl alcohol (IPA). Seven-layer SiO ₂ coated pigments were obtained after the solid particles had been dried at 100 ° C for 24 hours.

Protocol 1A - 7-layered pigments coated with an SiO ₂ layer

An amount of 10 g of 7-layer pigments was suspended in 160 ml of ethanol in a round bottom flask equipped with a reflux condenser without first being treated with phosphoric acid as in Protocol 1. The suspension was heated to 65 ° C after 35 minutes g of water and 3.5 g of a 28% aqueous ammonia solution were added. Then, a solution of 10 g of tetraethoxysilane diluted with 13 ml of ethanol was added in small portions to the heated suspension with stirring. The reaction mixture was stirred at 65 ° C for 14 hours, then solid particles were filtered from the liquid, washed with ethanol and then washed with isopropyl alcohol (IPA). Seven-layer SiO ₂ coated pigments were obtained after the solid particles had been dried at 100 ° C for 24 hours.

Protocol 2-7-layered pigments coated with an SiO ₂ layer using an aqueous solution

Fifteen grams of 7-layer pigments were placed in a 250 ml three-necked flask. Then, 100 ml of DI water was added and the solution was stirred in an ethylene glycol bath heated to 80 ° C. The solution was adjusted to a pH of 7.5 by adding a few drops of a 1 M NaOH solution. Then, 20 ml of Na ₂ SiO ₃ (13 wt% SiO ₂ ) was added to the solution at a constant flow rate of 0.1 ml / min by a syringe pump. While the Na ₂ SiO _{3 was} added, 1 M HCl solution was also added by means of an automatic pH control system to maintain the pH of 7.5. The mixture was allowed to cool to room temperature, filtered off, washed with IPA and dried at 100 ° C for 24 hours. The coated material may be further annealed at 200 ° C for 24 hours.

Protocol 3-7-layered pigments coated with an SiO ₂ layer and an SiO ₂ -Al ₂ O ₃ hybrid layer

Two grams of pigments coated with SiO ₂ by protocol 1 or 1A were suspended in 20 ml of a water solution and had a pH of about 10 (adjusted by dilute NaOH solution). The suspension was heated to 60 ° C. with constant stirring in a 100 ml round bottom flask. Then, 0.5 ml of an 18 wt% Na ₂ SiO ₃ solution and 1 ml of 0.5 M Al ₂ (SO ₄ ) ₃ solution were both titrated simultaneously into the pigment suspension at a constant rate in 1 hour. The pH of the slurry was not controlled. After titration the suspension became 30 Aging for a few minutes while stirring. The mixture was filtered and residual solid particles were washed with DI water and then washed with IPA. Seven-layered pigments having an SiO ₂ layer and an Al ₂ O ₃ layer were obtained after the remaining solid particles were dried at 100 ° C for 24 hours.

Protocol 4-7-layered pigments coated with an SiO ₂ layer and a ZrO ₂ + Al ₂ O ₃ hybrid layer

Three grams of pigments coated with SiO ₂ according to Protocol 1 or 1A were coated in a 100 ml round bottom flask with 20 ml of ethanol and stirred at room temperature. In addition, 0.66 g of aluminum tri-sec-butoxide and 2.47 ml of zirconium butoxide were dissolved in 15 ml of IPA. The mixture of aluminum tri-sec-butoxide + zirconium butoxide was titrated into the pigment suspension at a constant rate in 2 hours. At the same time, 0.66 ml of DI water diluted in 2 ml of ethanol was added. After titration, the suspension was stirred for a further 30 minutes. The mixture was filtered and the remaining solid particles were washed with ethanol and then washed with IPA. Seven-layered pigments having an SiO ₂ layer and a ZrO ₂ + Al ₂ O ₃ hybrid layer were obtained after the remaining particulate matter had been dried at 100 ° C for 24 hours or alternatively further annealed at 200 ° C for 24 hours ,

Protocol 5-7-layered pigments coated with an SiO2 layer and a ZrO2 + Al2O3 hybrid layer

Three grams of pigments coated with SiO ₂ by protocol 1 or 1A were suspended in 20 ml DI 8 pH water (adjusted by dilute NaOH solution) in a 100 ml round bottom flask and heated to 50 ° with constant stirring C heated. Then, 0.5 ml of a 5 wt% NaAlO ₂ solution and 0.5 ml of 10 wt% ZrOCl ₂ solution were both titrated simultaneously into the pigment suspension at a constant rate in 30 minutes. The pH of the slurry was controlled to 8 by the addition of dilute HCl or NaOH solution. After titration, the suspension was left for 30 minutes with stirring. The mixture was filtered off, washed with DI water and then washed with IPA. The coated pigments were obtained after being dried at 100 ° C for 24 hours or, alternatively, annealed at 200 ° C for 24 hours.

Protocol 6-7-layered pigments which are coated with an SiO ₂ layer, a CeO ₂ layer and a ZrO ₂ + Al ₂ O ₃ hybrid layer

Pigments (3.5 g) coated with silica (SiO ₂ ) by protocol 1 or 1A were suspended in 26.83 mL of water in a 100 mL round bottom flask and stirred at 70 ° C for 20 minutes. Then, 0.33 g of Ce (NO ₃ ) 3 .6H ₂ O in 1.18 ml of H ₂ O was titrated into the pigment suspension at a constant rate of 2 ml / hr and the mixture became titrated for an additional 1.5 hours kept stirring. During the reaction, the pH of the solution was kept constant at 7.0 using a dilute NaOH solution. The mixture was filtered and the remaining solid particles were washed three times with water and then washed three more times with IPA. Seven-layered pigments having an SiO ₂ layer and a layer of CeO ₂ were obtained after the remaining solid particles were dried at 100 ° C for 24 hours.

Then, 3 g of the coated pigments were suspended in 20 ml of ethanol in a 100 ml round bottom flask and stirred at room temperature. A mixture of 0.66 g of aluminum tri-sec-butoxide and 2.47 ml of zirconium butoxide dissolved in 15 ml of IPA was titrated into the pigment suspension at a constant rate in 2 hours. At the same time, 0.66 ml DI water, diluted in 2 ml ethanol, was added. After titration, the suspension was stirred for a further 30 minutes. The mixture was filtered and the remaining solid particles were washed with ethanol and then washed with IPA. Seven-layered pigments having an SiO ₂ layer, a layer of CeO 2, and a ZrO ₂ + Al ₂ O ₃ hybrid layer were obtained after the remaining solid particles were dried at 100 ° C for 24 hours.

Protocol 7-7-layered pigments coated with a CeO ₂ layer and a ZrO ₂ + Al ₂ O ₃ hybrid layer

Three grams of pigments with a 7-layer design were suspended in 20 ml of ethanol in a 100 ml round bottomed flask and stirred at 75 ° C. A solution of 0.44 g of Ce (NO ₃ ) ₃ .6H ₂ O dissolved in 20 ml of IPA was titrated at a constant rate in 1 hour. At the same time, 0.15 ml of ethylenediamine (EDA), diluted in 0.9 ml of DI water, was added. Thereafter, an additional 0.15 ml of EDA diluted in 0.9 ml DI water was added. After titration, the suspension was stirred for an additional 15 minutes. The mixture was filtered and the remaining solid particles were washed with IPA. Seven-layered pigments having a CeO ₂ layer were obtained after the remaining solid particles were dried at 100 ° C for 5 hours.

Then, the CeO ₂ -coated pigments were suspended in 20 ml of ethanol in a 100 ml round-bottomed flask and stirred at room temperature. Then, a mixture of 0.66 g of aluminum tri-sec-butoxide and 2.47 ml of zirconium butoxide dissolved in 15 ml of IPA was titrated into the pigment suspension at a constant rate in 2 hours. At the same time, 0.66 ml of DI water diluted in 2 ml of ethanol was added. After titration, the suspension was stirred for a further 30 minutes. The mixture was filtered and the remaining solid particles were washed with ethanol and then washed with IPA. Seven-layered pigments having a CeO ₂ layer and a ZrO ₂ + Al ₂ O ₃ hybrid layer were obtained after the remaining solid particles were dried at 100 ° C for 24 hours, or alternatively annealed at 200 ° C for 24 hours ,

Protocol 8 - 7-layered pigments coated with a ZrO ₂ layer

Two grams of pigments with a 7-layer design were suspended in 30 mL of ethanol in a 100 mL round bottom flask and stirred at room temperature. A solution of 2.75 ml of zirconium butoxide (80% in 1-butanol) diluted in 10 ml of ethanol was titrated at a constant rate in 1 hour. At the same time, 1 ml of DI water, which had been diluted in 3 ml of ethanol, was added. After titration, the suspension was stirred for an additional 15 minutes. Seven-layered pigments with a layer of ZrO ₂ were obtained after the remaining solid particles were filtered from the solution, washed with ethanol and dried at 100 ° C for 5 hours, or alternatively annealed at 200 ° C for 24 hours.

Protocol 9-7-layered pigments coated with an SiO ₂ layer and an Al ₃ O ₃ layer

Two grams of pigments coated with SiO ₂ by protocol 1 or 1A were suspended in 20 ml of water solution having a pH of about 8 (adjusted by dilute NaOH solution) in a 100 ml round bottom flask and heated to 50 with constant stirring ° C heated. Then, 0.5 ml of 5 wt% NaAlO ₂ solution was titrated into the pigment suspension at a constant rate in 30 minutes. The pH of the slurry was adjusted to 8 using a HCl 1M solution. After titration, the suspension was left for 30 minutes with stirring. The mixture was filtered off, washed with DI water and then washed with IPA. The coated pigments were obtained after being dried at 100 ° C for 24 hours.

Protocol 10 - 7-layered pigments coated with an SiO ₂ layer and a TiO ₂ layer

A 250 ml three necked round bottom flask was placed in an ethylene glycol oil bath set at 80 ° C. Then, 15 g of leaflets coated with SiO ₂ according to Protocol 1 or 1A and 100 ml of DI water were added to the flask and stirred at 400 rpm. The solution was adjusted to a pH of 2 by adding a few drops of concentrated HCl solution. A prediluted 35% TiCl ₄ solution was then titrated at a constant flow rate of 0.1 ml / min via a syringe pump. To keep the pH constant, a base solution in the form of NaOH solution (8M) was titrated into the flask by an automatic pH control system. During the deposition, leaflet samples were extracted at certain time intervals to determine the layer thickness. The mixture was allowed to cool to room temperature, then filtered, washed with IPA and dried at 100 ° C for 24 hours or alternatively annealed at 200 ° C for 24 hours.

The weatherability of the coated pigments was tested in the following manner. Seven cylindrical Pyrex flasks (capacity about 120 ml) were used as photoreactive vessels. Each flask contained 40 ml of a solution of a fluorescent red dye (Eosin B) (1 x 10 ^-5 M) and 13.3 mg of a pigment to be tested. The pigment-eosin B solution were stirred magnetically for 30 min in the dark and then exposed to light from a sunlight simulator (Oriel ^® Sol2A ^TM Class ABA solar simulator) was irradiated. For each pigment, the same type of pigment wrapped with an aluminum foil was used as a direct control. In addition, commercially available TiO ₂ (Degussa P25) was used as a reference to compare the photocatalytic activity under the same experimental conditions. UV / Vis absorption spectra were recorded after 65 hours exposure to light to verify the photocatalytic activity of each sample.

The results of the test were recorded as relative photocatalytic activity against pigment type as in 31 is shown. In addition, the 7-layer pigments without protective coating were set as those exhibiting 100% photocatalytic activity and used as a comparison for the coated pigment samples. As in 31 is shown, all coated pigment samples showed a reduced compared to the uncoated sample photocatalytic activity. In addition, the 7-layered pigment having an SiO ₂ coating (designated P / S), the 7-layered pigment having an SiO ₂ coating layer, and a ZrO ₂ + Al ₂ O ₃ hybrid coating layer exhibited the 7-layered pigment having a SiO ₂ coating layer, a CeO ₂ coating layer and a ZrO ₂ + Al ₂ O ₃ hybrid coating layer (designation P / S / C / ZA) and the 7-layered pigment having a CeO ₂ coating layer and a ZrO ₂ + Al ₂ O ₃ hybrid coating layer a reduction in photocatalytic activity of at least 50% compared to the uncoated pigments. In contrast, the 7-layered pigment having an SiO ₂ coating layer and an SiO ₂ + Al ₂ O ₃ hybrid coating layer showed a reduction in photocatalytic activity of only 33.8%.

Scanning electron micrographs of the 7-layer pigments before and after coating with an SiO ₂ layer and a ZrO ₂ -Al ₂ O ₃ layer (protocol 4) are described in US Pat 32A respectively. 32B shown. As shown by the pictures, the surfaces of the pigments are smooth and the physical form and structural integrity of the pigments after coating are the same as the pigments before coating. In addition, EDX dot-map images of a 7-layer omnidirectional structure pigment with an outer ZnS layer which has been coated with a first SiO ₂ layer and a second ZrO ₂ -Al ₂ O ₃ hybrid protective layer (Protocol 4) , as expected, relatively higher concentrations of Zn, S, Si, Zr and Al in the coating structure.

An overview of coatings, the method used to form a coating, the coating thickness, the uniformity of the coating thickness and the photocatalytic activity can be found in Table 3 below. Table 3 sample Core* layer material Coating protocol Thickness (mm) uniformity Photocatalytic Atity ** 1 P7 1. SiO2 1.1A 80 G 51% 2 P7 1. SiO2 1.1A 80 G 3 P7 1. SiO2 1.1A 80 G 4 P7 1. SiO2 1.1A 30 G 5 P7 1. SiO2 1.1A 40 G 6 P7 1. SiO2 1.1A 50 G 7 P7 1. SiO2 1.1A 15 G 8th P7 1. SiO2 1.1A 10 G 9 P7 1. SiO2 1.1A 30 G 50% 10 P7 1. SiO2 1.1A 30 G Second Al2O3 9 <10 G 11 P7 1. SiO2 1.1A 30 G Second ZrO2-Al2O3 5 15 NG 12 P7 1. SiO2 1.1A 30 G Second ZrO2-Al2O3 6 15 G 13 P7 1. SiO2 1.1A 80 G Second CeO2 7 NG 14 P7 1. SiO2 1.1A 80 G 66% Second SiO2-Al2O3 3 10 G 15 P7 1. SiO2 1.1A 80 G Second SiO2-Al2O3 3 10 G 16 P7 1. SiO2 1.1A 80 G Second SiO2-Al2O3 3 10 G 17 P7 1. SiO2 1.1A 80 G Second Al2O3 9 10 G 18 P7 1. SiO2 1.1A 80 G 33% Second ZrO2-Al2O3 6 15 G 19 P7 1. SiO2 1.1A 80 G 33% Second CeO2 6 3 G Third ZrO2-Al2O3 6 15 G 20 P7 1. CeO2 7 3 G 21% Second ZrO2-Al2O3 6 15 G 21 P7 1. CeO2 7 3 G Second ZrO2-Al2O3 6 15 G 22 P7 1. CeO2 7 3 G Second ZrO2-Al2O3 6 15 G 27 P7 1. ZrO2 11 20 G * P7 = 7-layer pigment
** compared to the uncoated 7-layer pigment

On this basis, Table 4 provides a listing of various oxide layers, substrates that can be coated, and areas of coating thicknesses included in the present teachings. Table 4 oxide substratum Coating thickness range (nm) SiO ₂ Mica, P7, metal, oxides 10-160 TiO ₂ Mica, P7, metal, oxides 20-100 ZrO ₂ Mica, P7, metal, oxides 20-100 Al ₂ O ₃ Mica, P7, metal, oxides 5-30 CeO ₂ Mica, P7, oxides ~ 5-40 SiO ₂ -Al ₂ O ₃ Mica, P7, oxides 20-100 ZrO ₂ -Al ₂ O ₃ Mica, P7, metal, oxides 10-50

In addition, the omnidirectional structural color pigments having a protective coating may be subjected to an organosilane surface treatment. For example, according to one example of treatment according to an organosilane protocol, 0.5 g of pigments coated with one or more of the protective coatings discussed above were dissolved in 10 ml of a solution of EtOH / water (4: 1) having a pH of about 5.0 (adjusted by dilute acetic acid solution) in a 100 ml round bottom flask. The slurry was sonicated for 20 seconds and then stirred for 15 minutes at 500 rpm. Then, 0.1 to 0.5% by volume of organosilane as an active ingredient was added to the slurry, and the solution was stirred at 500 rpm for further 2 hours. The slurry was then centrifuged or filtered using DI water, and the remaining pigments redispersed in 10 ml EtOH / water (4: 1) solution. The pigmented EtOH / water slurry was heated to 65 ° C to reflux and stirred for 30 minutes at 500 rpm. The slurry was then centrifuged or filtered using DI water and then IPA to produce a cake of pigment particles. Finally, the cake was dried at 100 ° C for 12 hours.

The organosilane protocol may utilize any organosilane coupling agent known to those skilled in the art, including, for example, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane (APTMS), N- [3- (trimethoxysilyl) propyl] ethylenediamine, 3-methacryloxypropyltrimethoxysilane (MAPTMS), N - [2 (vinylbenzylamino) ethyl] -3-aminoproplyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane and the like.

The above examples and embodiments are for illustration only, and changes, modifications and the like which are nevertheless within the scope of the invention will be apparent to those skilled in the art. Thus, the scope of the invention is defined by the claims and their equivalents.

Claims (7)

Omnidirectional structural pigment having a protective coating comprising: a pigment comprising a first layer of a first material and a second layer of a second material, the second layer overlying the first layer, wherein the pigment comprises a band of electromagnetic radiation having a predetermined full width at half maximum (FWHM) of less than 300 nm and a predetermined color shift of less than 30 ° in the CIELAB color space, when the pigment is exposed to broad band electromagnetic radiation and viewed from angles between 0 and 45 °; a weather resistant coating which coats an outer surface of the pigment and reduces at least 50% of the photocatalytic activity of the pigment as compared to the pigment which does not have the weather resistant coating. An omnidirectional structural color pigment having a protective coating according to claim 1, wherein the weather resistant coating comprises an oxide layer. An omnidirectional structural color pigment having a protective coating according to claim 2, wherein said oxide layer is selected from the group consisting of silica, alumina, zirconia, titania and ceria. An omnidirectional structural color pigment having a protective coating according to claim 3, wherein the weather resistant coating comprises a first oxide layer and a second oxide layer, the second oxide layer being different from the first oxide layer. An omnidirectional structural color pigment having a protective coating according to claim 4, wherein the second oxide layer is a hybrid oxide layer which is a combination of two different oxides. The omnidirectional structural color pigment having a protective coating of claim 5 wherein the first oxide layer is silicon oxide and the second oxide layer is at least two selected from the group consisting of silica, alumina, zirconia, titania and ceria. An omnidirectional structural color pigment having a protective coating according to claim 1 wherein the pigment does not have an oxide layer.

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