HK1182730A - Diffractive pigment blend and composition - Google Patents

Description

Diffractive pigment mixtures and compositions

Technical Field

The present invention relates to diffractive pigment mixtures and compositions comprising diffractive pigment flakes, and more particularly, all-dielectric diffractive pigment flakes.

Background

Generally, the pigment composition comprising all-dielectric pigment flakes is substantially transparent and allows for overprinting. Such pigment compositions can be applied over an image or underlying color so that the image or underlying color is visible through the pigment composition. In contrast, pigment compositions comprising common metal-dielectric pigment flakes (e.g., fabry-perot type pigment flakes) can darken or obscure an image or underlying color.

Colored and substantially transparent pigment compositions can be formed using the colored all-dielectric pigment flakes. For example, the colored all-dielectric pigment flakes may include alternating layers of high index dielectric material and low index dielectric material (i.e., a two-color stack). As a result of the thin film interference, certain color components of light incident on such pigment flakes are reflected by the dielectric layer while other color components are transmitted, so that the pigment flakes appear to have a color known as the background color. In other words, the dielectric layer provides the background color. Examples of colored all-dielectric pigment flakes are disclosed in U.S. Pat. No. 3, 7,238,424 to Raksha et al, entitled 7/3 in 2007, Phillips et al, US6,524,381, entitled 2/25 in 2003, Phillips et al, US 5,569,535, entitled 10/29 in 1996, and Phillips et al, US 5,059,245, entitled 10/22 in 1991, which are incorporated herein by reference.

Diffractive and substantially transparent pigment compositions can be formed using all-dielectric diffractive pigment flakes. For example, an all-dielectric diffractive pigment flake may include at least one dielectric layer that includes a diffractive structure, such as a diffraction grating. Light incident on such pigment flakes is diffracted by the diffractive structure into its chromatic components, i.e. is angularly dispersed according to wavelength, so that the pigment flakes appear to have different colors at different viewing angles, which is called a diffractive effect. In other words, the diffractive structure provides a diffractive effect. An example of all-dielectric diffractive pigment flakes is disclosed in U.S. patent No. US6,815,065 to Argoitia et al, entitled 11/9/2004, which is incorporated herein by reference.

In some cases, there is a need for achromatic diffractive pigment compositions that provide white, i.e., neutral, background color and white diffractive effects. The neutral white background color substantially maintains the underlying color of the object coated with the pigment composition, while the neutral white diffraction effect essentially exhibits a full-color rainbow over the underlying color at different viewing angles. Achromatic all-dielectric pigment flakes providing a white background color and a white diffractive effect are disclosed in US patent US6,815,065. However, such pigment flakes have a relatively complex optical design, requiring several layers of different thicknesses.

Achromatic diffractive pigment compositions comprising ordinary metal-dielectric pigment flakes typically provide a gray or black background color as well as a iridescent diffractive effect. Examples of achromatic diffractive metal-dielectric pigment flakes are disclosed in U.S. patent nos. US6,749,936, 6,749,777 to Argoitia et al, entitled 6/15, 2004 and 6,692,830 to Argoitia et al, entitled 2/17, 2004, which are incorporated herein by reference. Examples of colored diffractive metal-dielectric pigment flakes are disclosed in U.S. patent No. US6,902,807 to Argoitia et al, entitled 6/7/2005, and US6,841,238 to Argoitia et al, entitled 1/11/2005, which are incorporated herein by reference.

Disclosure of Invention

The present invention relates to a diffractive pigment composition comprising: a pigment medium; and a plurality of sets of all-dielectric diffractive pigment flakes mixed and dispersed in the pigment medium, wherein each set of all-dielectric diffractive pigment flakes includes one or more dielectric layers that provide a background color, and wherein at least one of the one or more dielectric layers includes a diffractive structure that provides a diffractive effect; wherein each set of all-dielectric diffractive pigment flakes provides a different diffractive effect; and wherein the diffractive pigment composition provides a combined diffractive effect that is a combination of different diffractive effects provided by the plurality of sets of all-dielectric diffractive pigment flakes.

The present invention also relates to a diffractive pigment mixture comprising: a plurality of sets of all-dielectric diffractive pigment flakes, wherein each set of all-dielectric diffractive pigment flakes includes one or more dielectric layers that provide a background color, and wherein at least one of the one or more dielectric layers includes a diffractive structure that provides a diffractive effect; wherein each set of all-dielectric diffractive pigment flakes provides a different diffractive effect; and wherein the diffractive pigment mixture provides a combined diffractive effect that is a combination of different diffractive effects provided by the plurality of sets of all-dielectric diffractive pigment flakes.

In some embodiments, the diffractive pigment composition or mixture provides a combined diffractive effect that is a neutral white diffractive effect. In other embodiments, the combined diffractive effect comprises an inverted color change (inverted flop). In general, a single set of all-dielectric diffractive pigment flakes has difficulty achieving this and similar combined diffractive effects.

Drawings

The invention will now be described in more detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of a cross-section of an all-dielectric diffractive pigment flake having a multilayer structure;

FIG. 2A is a photograph of a paint cast film (paintawdown) of the diffractive and non-diffractive pigment composition of example 1 under diffuse illumination;

FIG. 2B is a photograph of the cast film of FIG. 2A under direct illumination at a first angle of incidence;

FIG. 2C is a photograph of the cast film of FIG. 2A under direct illumination at a second angle of incidence;

FIG. 2D is a photograph of the cast film of FIG. 2A under direct illumination at a third angle of incidence;

FIG. 3 is a reflectance spectrum plot of the diffractive and non-diffractive pigment compositions of example 1;

FIG. 4 is a color locus curve for the diffractive pigment composition of example 1;

FIG. 5 is a reflectance spectrum plot of the diffractive pigment composition of example 2;

FIG. 6A is a color locus curve for the diffractive pigment composition of example 2 under a first set of illumination and viewing conditions;

FIG. 6B is a color locus curve for the diffractive pigment composition of example 2 under a second set of illumination and viewing conditions;

FIG. 7 is a color locus curve for the diffractive pigment composition of example 3; and

fig. 8 is a schematic diagram of a cross-section of an all-dielectric diffractive pigment flake having an encapsulated structure.

Detailed Description

The present invention provides diffractive pigment mixtures and compositions formed by mixing different types of all-dielectric pigment flakes that provide different diffractive effects. Advantageously, the diffractive pigment mixtures and compositions provide a combined diffractive effect that is a combination of different diffractive effects.

Generally, all dielectric diffractive pigment flakes have an aspect ratio of at least 2:1 and an average particle size of about 5 μm to about 200 μm, depending on the coating application selected. The pigment flakes may be single layer or multilayer flakes. Each pigment flake includes one or more dielectric layers, typically one or more thin film dielectric layers. Typically, each pigment flake is composed of one or more dielectric layers. Preferably, each pigment flake comprises or consists of a plurality of dielectric layers.

The one or more dielectric layers may be formed of any suitable dielectric material. Typically, the dielectric material is substantially transparent. Also typically, the dielectric material is an inorganic material. Alternatively, the dielectric material is an organic or organic-inorganic material. The dielectric material may be a high index dielectric material having a refractive index higher than about 1.65 or a low index dielectric material having a refractive index lower than about 1.65.

Non-limiting examples of suitable high refractive index dielectric materials include zinc sulfide (ZnS), zinc oxide (ZnO), zirconium oxide (ZrO)₂) Titanium dioxide (TiO)₂) Diamond-like carbon, indium oxide (In)₂O₃) Indium Tin Oxide (ITO) and tantalum pentoxide (Ta)₂O₅) Cerium oxide (CeO)₂) Yttrium oxide (Y)₂O₃) Europium oxide (Eu)₂O₃) Such as ferroferric oxide (Fe)₃O₄) And ferric oxide (Fe)₂O₃) Iron oxide, hafnium nitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO) of₂) Lanthanum oxide (La)₂O₃) Magnesium oxide (MgO), neodymium oxide (Nd)₂O₃) Praseodymium oxide (Pr)₆O₁₁) Samarium oxide (Sm)₂O₃) Antimony trioxide (Sb)₂O₃) Silicon, silicon monoxide (SiO), selenium oxide (Se)₂O₃) Tin oxide (SnO)₂)、Tungsten trioxide (WO)₃) And combinations thereof, and the like. Examples of other suitable high index dielectric materials include mixed oxides such as those described in U.S. patent No. US 5,989,626 to Coombs et al, issued 11/23 1999, which is incorporated herein by reference. When the dielectric materials in US 5,989,626 are used for the dielectric layer, they are most commonly oxidized to form oxides such as ZrTiO₄Stoichiometric state (stoichiometric state). Non-limiting examples of such mixed oxides include titanium zirconium oxide, titanium niobium oxide, combinations thereof, and the like.

Non-limiting examples of suitable low index dielectric materials include silicon dioxide (SiO)₂) Aluminum oxide (Al)₂O₃) Such as magnesium fluoride (MgF)₂) Aluminum fluoride (AlF)₃) Cerium fluoride (CeF)₃) Lanthanum fluoride (LaF)₃) Sodium aluminum fluoride (e.g., Na)₃AlF₆Or Na₅Al₃F₁₄) Neodymium fluoride (NdF)₃) Samarium fluoride (SmF)₃) Barium fluoride (BaF)₂) Calcium fluoride (CaF)₂) Lithium fluoride (LiF), combinations thereof, and the like. Examples of other suitable low index dielectric materials include organic monomers and polymers including olefins such as dienes, acrylates (e.g., methacrylates), perfluoroolefins (perfluoroolefins), polytetrafluoroethylene (Teflon), Fluorinated Ethylene Propylene (FEP), combinations thereof, and the like.

It should be appreciated that the several dielectric materials described above are typically present in non-stoichiometric forms, often depending on the particular method used to deposit the dielectric material as a coating, and thus the compound names described above refer to near-stoichiometric relationships. For example, silicon monoxide and silicon dioxide have nominal (nominal) silicon to oxygen ratios of 1:1 and 1:2, respectively, but the actual silicon to oxygen ratio of a particular coating may vary slightly from these nominal values. Such non-stoichiometric dielectric materials are also within the scope of the present invention.

In some cases, the dielectric material is selectively absorptive to visible lightAbsorbing dielectric materials in specific color bands of the spectrum, e.g., absorbing metal compounds such as metal oxides, nitrides, carbides or sulfides, cermets, dielectric materials including radiation-induced color centers, and combinations thereof, and the like. Non-limiting examples of suitable absorbing metal compounds include titanium suboxide (TiO)_x) Chromium oxide (e.g., Cr)₂O₃) Iron oxides (e.g., Fe)₂O₃) Cobalt oxide (e.g., CoO), silicon monoxide (SiO), titanium nitride (TiN), titanium carbide (TiC), titanium carbonitride (TiC)_xN_1-x) Such as aluminum metal oxide (e.g., AlCrO)_xOr AlCoO_x) Mixed phase oxides of (a), calcium sulfide (CdS), combinations thereof, and the like.

When the pigment flakes include multiple dielectric layers, the dielectric layers may be formed of the same or different dielectric materials and may have the same or different physical thicknesses. Typically, each of the one or more dielectric layers has a physical thickness of about 30nm to about 1000nm, respectively. In general, the physical thickness is selected to correspond to the optical thickness required for a particular optical design.

The pigment flakes can have various optical designs. The optical design of the preferred embodiment will be described in more detail below. A particular optical design may be centered at different design wavelengths in the visible spectrum (e.g., by varying layer thicknesses or compositions) to provide different background colors corresponding to bands in the visible spectrum characterized or preferably centered at the particular design wavelengths, referred to as color bands. Typically, the colored diffractive pigment composition has a reflection of at least 50% at a design wavelength corresponding to a background color.

In some embodiments, the background color is provided by thin film interference. When white light is incident on such an embodiment, the background color band of the white light is reflected by the dielectric layer or layers and the other color bands are transmitted, causing the pigment flakes to appear to have a background color. In some cases, such embodiments may provide a color shifting effect such that pigment flakes appear to have a first background color at a first viewing or incident angle and a second background color at a second viewing or incident angle.

In other embodiments, the background color is provided by selective absorption. In such embodiments, the one or more dielectric layers comprise at least one layer of absorbing dielectric material. When white light is incident on such an embodiment, a particular color band of the white light is selectively absorbed by the one or more dielectric layers, while the background color band is reflected, causing the pigment flake to appear to have a background color. In still other embodiments, the background color is provided by a combination of thin film interference and selective absorption.

It should be noted that since the pigment flakes are all dielectric and generally substantially transparent, the final visible appearance of an object coated with the diffractive pigment composition will be affected by both the underlying color of the object and the background color provided by the pigment flakes.

The pigment flakes can have various layer structures. The layer structure of the preferred embodiment will be described in further detail below. For example, the pigment flakes may have a multilayer structure or an encapsulated structure, which may be symmetrical or asymmetrical.

The pigment flakes also include diffractive structures that provide diffractive effects. In general, the background color band is diffracted by the diffractive structure into its color components, i.e., is angularly dispersed according to wavelength, such that the pigment flakes appear to have different colors at different viewing angles. In other words, the thin film interference provided by the dielectric layer "filters" the diffractive effect provided by the diffractive structure. It should be noted that diffraction effects are most pronounced under direct illumination. Under diffuse illumination, the background color is mainly observed.

At least one of the one or more dielectric layers has a diffractive structure formed therein or thereon. Typically, the diffractive structure is a diffraction grating, with regular lines or lines generated by holography. Preferably, the diffraction grating has a line profile, such as a notch or square, or sinusoidal profile, which increases the diffraction efficiency of one or more high diffraction orders while decreasing the diffraction efficiency of the zero diffraction order. Typically, the diffractive structure has a line frequency of about 500 lines/mm to about 4000 lines/mm, preferably about 1200 lines/mm to about 3500 lines/mm. Increasing the line frequency will increase the angular dispersion, i.e. the "width", at each diffraction order, according to the grating equation.

Examples of all dielectric diffractive pigment flakes and methods of making such pigment flakes are disclosed in U.S. patent No. US6,815,065. Examples of full color dielectric pigment flakes and methods of making such pigment flakes are disclosed in U.S. Pat. Nos. 7,238,424, 6,524,381, 5,569,535, and 5,059,245. The all-dielectric diffractive pigment flakes used to form the diffractive pigment mixtures and compositions of the present invention can be one of the disclosed embodiments and modifications or compositions thereof, or new embodiments. Also, the pigment flakes can be produced by one of the disclosed manufacturing methods, modifications or combinations thereof, or new manufacturing methods. The manufacturing method used to produce the preferred embodiment of the present invention will be described in more detail below.

Typically, a substrate, such as a foil or plastic sheet, is provided which is patterned with diffractive structures. Some or all of the one or more dielectric layers are then sequentially deposited on the patterned substrate using a deposition technique such as Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD), or electrolytic deposition to form a single or multi-layer coating. Thus, at least one of the one or more dielectric layers is patterned with a diffractive structure. The single or multiple layer coating is sequentially peeled or milled from the substrate and the bottom surface to form all dielectric diffractive pigment flakes or preformed flakes. If a pre-fabricated sheet is formed, the remaining one or more dielectric layers are then sequentially deposited on the pre-fabricated sheet to form the all-dielectric diffractive pigment flakes.

The diffractive pigment mixtures and compositions of the present invention comprise a plurality of sets of all-dielectric diffractive pigment flakes. Typically, the mixtures and compositions comprise two to four groups. Each group consists of only one type of pigment flake, unlike the other groups. Generally, all types of pigment flakes have the same optical design, centered on substantially the same design wavelength or different design wavelengths. Also generally, all types of pigment flakes have the same layer structure, e.g., the same multilayer or encapsulated structure. Each set may provide substantially the same background color or a different background color. Furthermore, each group provides a different diffractive effect. In some cases, the groups are formed together in one batch. In other cases, the groups are formed separately in different batches and then mixed.

In some embodiments, each set of all-dielectric diffractive pigment flakes provides a different background color and has substantially the same line frequency. That is, each set of pigment flakes has an optical design centered at a different design wavelength in the visible spectrum, but includes diffractive structures having substantially the same line frequency. Thus, each set provides a diffraction effect having a different spectral profile but substantially the same angular dispersion at each diffraction order. In such embodiments, the diffractive pigment mixture or composition provides a combined background color that is a combination of the different background colors provided by the groups, and a combined diffractive effect that is a combination of the different diffractive effects provided by all of the groups. Typically, combining the background color and the combined diffraction effect is additive combining.

In either the neutral or non-colored embodiments, the different background colors are selected according to the additive color principle such that the diffractive pigment mixture or composition provides a white, i.e., neutral, background, and white diffractive effect. The neutral white background color substantially retains the underlying color of an object coated with the diffractive pigment mixture or composition, while the neutral white diffractive effect exhibits substantially all of the colors of a rainbow (all colors of therainbow) above the underlying color at different viewing angles. Any suitable combination of background colors may be selected. Suitable combinations of background colors include three primary colors, three secondary colors, and two complementary colors. For example, a neutral diffractive pigment mixture or composition can be formed using red, green, blue all-dielectric diffractive pigment flakes, or magenta, yellow, cyan all-dielectric diffractive pigment flakes.

In other embodiments, each set of dielectric diffractive pigment flakes provides substantially the same background color and has a different line frequency. That is, each set of pigment flakes has an optical design centered at substantially the same design wavelength in the visible spectrum, but includes diffractive structures having different line frequencies. Thus, each set provides a diffractive effect having substantially the same spectral profile but a different angular dispersion at each diffraction order. In such embodiments, the diffractive pigment mixture or composition provides a background color that is substantially the same as the background color provided by all of the groups, and a combined diffractive effect that is a combination of the different diffractive effects provided by all of the groups. For example, the combined diffraction effect may include an gonioapparent color. Typically, the combined diffraction effect is additive combining.

In still other embodiments, each set of all-dielectric diffractive pigment flakes provides a different background color and has a different line frequency. In such embodiments, the diffractive pigment mixture or composition provides a combined background color that is a combination of the different background colors provided by all of the groups, and a combined diffractive effect that is a combination of the different diffractive effects provided by all of the groups. Typically, combining the background color and the combined diffraction effect is additive combining.

In the absence of pigment medium, sets of all-dielectric diffractive pigment flakes can be mixed to form a diffractive pigment mixture. Alternatively, the groups may be mixed and dispersed in a pigment medium to form the diffractive pigment composition. The pigment medium may be any suitable type of pigment medium. Typically, the pigment medium includes a binder or resin that can be cured, for example, by evaporation, heating, or exposure to Ultraviolet (UV) radiation. Non-limiting examples of suitable resins include alkyd resins, polyester resins, acrylic resins, polyurethane resins, vinyl resins, epoxy resins, styrene resins, and melamine formaldehyde resins. Alternatively, the pigment medium may include a carrier or solvent such as an organic solvent or water, a set retarder such as clove oil, or other additives.

The diffractive pigment compositions are useful as coatings or inks and are applied to a variety of objects, for example, currency and security documents, product packaging, textiles, automotive, sporting goods, electronic housings, household appliances, architectural structures, and flooring.

Examples having a multilayer Structure

In some embodiments, the all-dielectric diffractive pigment flakes have a multilayer structure, which can be symmetric or asymmetric. In other words, the pigment flakes are composed of a multi-layer stack (i.e., a two-color stack). Each multilayer stack comprises a plurality of dielectric layers, typically 3 to 9 layers. More particularly, each multilayer stack comprises alternating layers of high index dielectric material (H) and low index dielectric material (L), i.e. one or more HL pairs and optionally additional H or L layers.

In a preferred embodiment, the H layers are composed of the same high index dielectric material and have substantially the same physical and optical thickness. Similarly, the L layers are composed of the same low index dielectric material and have substantially the same physical and optical thickness. Both the H and L layers have 1/4 wavelength optical thickness (QWOT) at the design wavelength. Thus, as a result of thin film interference, the multilayer stack provides a background color characterized or preferably centered at the design wavelength. Generally, when light having a wavelength other than the design wavelength is reflected at the interface between the H layer and the L layer, interference tends to be destroyed, whereas when light having a wavelength of the design wavelength is reflected, interference is advantageously generated, thereby providing a background color. By adjusting the QWOT, different background colors can be achieved. In addition, by adjusting the number of HL pairs, the width and intensity of the background color band can be adjusted. A large number of HL pairs can achieve a narrower and stronger background color band.

Referring to fig. 1, an exemplary all-dielectric diffractive pigment flake 100 having a symmetrical multi-layer structure is composed of a seven-layer stack. The seven-layer stack includes four H layers 110 alternating with three L layers 120. The four H layers 110 are made of TiO₂And the three L layers 120 are made of SiO₂And (4) forming. Both the H layer 110 and the L layer 120 have QWOT at the design wavelength. Further, both the H layer 110 and the L layer 120 include a diffraction grating 130.

Example 1

In the neutral or achromatic color example, the combined diffractive pigment composition of example 1 includes four sets of all-dielectric diffractive pigment flakes 100 as shown in fig. 1. Each of the four groups is centered at a different design wavelength, i.e., 400nm, 500nm, 600nm, or 700 nm. In each of the four groups, diffraction grating 130 has substantially the same line frequency, i.e., 1440 lines/mm.

For ease of understanding, the diffractive pigment compositions are compared below with their non-diffractive counterparts (analogues). Sets of diffractive and non-diffractive all-dielectric pigment flakes centered at each of four different design wavelengths are formed together. A foil embossed with a diffraction grating and a square frame that was easily broken into 25 μm by 25 μm square flakes was provided as the substrate for the diffractive all-dielectric pigment flakes. A flat foil is provided as a substrate for the non-diffractive all-dielectric pigment flakes. Then, seven dielectric layers were sequentially deposited on the substrate using vacuum evaporation (vacuum evaporation) in a box coater. The seven-layer coating was peeled from the substrate and ultrasonically agitated to produce diffractive and non-diffractive all-dielectric pigment flakes having an average particle size of about 25 μm. These groups can also be manufactured separately in a similar manner.

Each set of diffractive or non-diffractive all-dielectric pigment flakes centered at a particular design wavelength is dispersed in a coating vehicle (paint vehicle). Thus, separate diffractive and non-diffractive all-dielectric pigment flakes centered at 400nm, 500nm, 600nm or 700nm are formed. Four sets of diffractive all-dielectric pigment flakes were mixed in a 1:1:1:1 weight ratio (i.e., 25 weight percent of each) to form a diffractive pigment mixture and dispersed in a coating vehicle in a pigment flake to coating vehicle weight ratio of 0.2:3.9 to form a combined diffractive pigment composition. Similarly, four sets of non-diffractive all-dielectric pigment flakes were mixed in a 1:1:1:1 weight ratio (i.e., 25 weight percent of each) to form a non-diffractive pigment mixture and dispersed in a coating vehicle in a pigment flake to coating vehicle weight ratio of 0.2:3.9 to form a combined non-diffractive pigment composition.

Referring to fig. 2, four separate cast films (drawdown) 210, 211, 212 and 213 of diffractive pigment composition centered at 400nm, 500nm, 600nm or 700nm, respectively, and a combined cast film 214 of diffractive pigment composition were coated on a black and white Laneta card. Similarly, four cast films 220, 221, 222, and 223 of non-diffractive pigment blends centered at 400nm, 500nm, 600nm, or 700nm, respectively, and a cast film 224 of the combined non-diffractive pigment composition were coated on a black and white Laneta card.

FIG. 2A is a photograph of the coating casting films 210 and 220 under diffuse illumination 224. Generally, non-diffractive pigment compositions are more colored and have a more metallic appearance. As the wavelength increased, the color of the four separate cast films 220-223 of non-diffractive pigment composition changed on the black matrix from blue at 400nm to green at 500nm, to orange at 600nm, to red at 700 nm. Complementary colors were observed on a white base. As the wavelength increases, the color of the casting film 220-223 changed from yellow at 400nm to purple at 500nm, to blue at 600nm, to cyan at 700nm on the white substrate. Although not chromatic, the same general color trend was observed for the four separate cast films 210-213 of diffractive pigment compositions. The cast film 214 of the combined diffractive pigment composition and the cast film 224 of the combined non-diffractive pigment composition are neutral in nature, i.e., achromatic. The combined diffractive and non-diffractive pigment composition exhibits silver on a black background and white on a white background.

The reflection of the dope cast films 210 & 214 & 220 & 224 on the black matrix under diffuse illumination was characterized using a DataColor SF600 + spectrophotometer that uses an integrating sphere with specular reflection included to create the diffuse/8 illumination/viewing geometry. Referring to fig. 3, the reflectance spectra of four separate diffractive pigment compositions and a combined diffractive pigment composition centered at 400nm, 500nm, 600nm and 700nm, 310, 311, 312, 313 and 314, respectively. Similarly, 320, 321, 322, 323, and 324 are the reflectance spectra of four non-diffractive pigment compositions centered at 400nm, 500nm, 600nm, and 700nm, respectively, and a combined non-diffractive pigment composition. Generally, diffractive and non-diffractive pigment compositions centered at different design wavelengths have higher reflectivities at wavelengths near the design wavelength. Thus, the observed color of the separate diffractive and non-diffractive pigment compositions is primarily the background color corresponding to the design wavelength under diffuse illumination.

In particular, the reflection spectra 314 and 324 of the combined diffractive and non-diffractive pigment compositions are relatively flat over the visible wavelength range (i.e., across 400nm to 700 nm), respectively, exhibiting neutral color under diffuse illumination. The combined diffractive and non-diffractive pigment compositions each have a reflection of at least 30% over the entire visible wavelength range, respectively. The "white" color of the observed combined diffractive and non-diffractive pigment composition is essentially the combination of the different background colors of the separate diffractive and non-diffractive pigment compositions, according to the additive color principle.

FIG. 2B is a photograph of the casting films 210 and 220 under direct illumination at a first incident angle 224; fig. 2C and 2D are photographs of the casting films 213, 214, 223, and 224 under direct illumination at the second and third left-tilt incident angles, respectively. Under direct illumination, the diffractive and non-diffractive pigment compositions differ more significantly in appearance. Generally, non-diffractive pigment compositions are darker, whereas diffractive pigment compositions are brighter due to reflecting relatively more light. In particular, the diffractive pigment composition acts as a retroreflector, sending diffracted light (i.e., light of a non-zero diffraction order) back to the light source. In contrast, non-diffractive pigment compositions only specularly reflect light.

The angular dependent color of the dope casting film 210 and 214 on the black matrix was characterized by a Murakami angle spectrophotometer under direct illumination at an incident angle of 45 ℃ and an observation angle of-33 ℃ to 80 ℃ with a step size of 1 ℃. Referring to fig. 4, 410, 411, 412, 413, and 414 are the color traces of four separate diffractive pigment compositions and a combined diffractive pigment composition centered at 400nm, 500nm, 600nm, and 700nm, respectively.

The color locus 413 of the diffractive pigment composition centered at 700nm is confined to the first quadrant, positive a and b, indicating that only wavelengths between yellow (i.e., about 580 nm) and red (i.e., about 700 nm) are diffracted. At this design wavelength, only wavelengths around 700nm are favorably interfered when reflected from the seven-layer stack. In general, the thin film interference provided by the seven-layer stack filters the diffraction effects provided by the diffraction grating. In other words, the seven-layer stack acts as an interference filter placed in front of the "white" diffractive effect (i.e. the full-color rainbow), so that the "colored" diffractive effect, i.e. the filtered rainbow, can be observed.

Similarly, the color locus 412 of the diffractive pigment composition centered at 600nm is confined to the first and second quadrants, the color locus 411 of the diffractive pigment composition centered at 500nm is primarily located in the second and third quadrants, and the color locus 410 of the diffractive pigment composition centered at 400nm is primarily located in the third quadrant.

On the other hand, the color traces 414 of the combined diffractive pigment composition are distributed almost equally around the origin of the a × b plot, indicating that all colors of the rainbow can be observed. For a given angle of incidence, a particular diffraction order will pass through the visible spectrum as the viewing angle changes. In other words, the combination diffractive pigment composition provides a white diffractive effect, i.e., a neutral diffractive effect.

Advantageously, the combined diffractive pigment composition is not only a neutral color under diffuse illumination, as shown in fig. 3, but also a neutral color under direct illumination, as shown in fig. 4. Unexpectedly, not only the background color provided by the thin film interference addition is additive, but also the color provided by the diffractive interference. In other words, the combined diffractive effect of the combined diffractive pigment composition is an additive combination of the different diffractive effects provided by the separate diffractive pigment compositions.

Examples 2 and 3

In both color-reversal examples, each of the combined diffractive pigment compositions of examples 2 and 3 included two sets of all-dielectric diffractive pigment flakes 100 as shown in fig. 1. The two groups are centered around substantially the same design wavelength, i.e., either 550nm (example 2) or 700nm (example 3). In each of the two groups, diffraction grating 130 has a different line frequency, i.e., 1440 lines/mm or 2000 lines/mm.

Sets of all dielectric diffractive pigment flakes centered at 550nm (example 2) or 700nm (example 3) and having two different line frequencies were made together. Two pieces of foil embossed with a diffraction grating having two line frequencies and a square frame that was conveniently broken into 25 μm by 25 μm square flakes were provided as the substrate for the all-dielectric diffractive pigment flakes. Then, seven dielectric layers were sequentially deposited on the substrate using vacuum evaporation in a box coater. The seven-layer coating was peeled off the substrate and ultrasonically agitated to produce all-dielectric diffractive pigment flakes having an average particle size of about 25 μm with two line frequencies. The groups may also be manufactured separately in a similar manner.

Each set of all dielectric diffractive pigment flakes having a particular line frequency is dispersed in the coating vehicle. Thus, separate diffractive pigment compositions were formed having line frequencies of 1440 lines/mm and 2000 lines/mm centered at 550nm (example 2) or 700nm (example 3). Two sets of all dielectric diffractive pigment flakes centered at 550nm were mixed in a 1:1 weight ratio, i.e., 50 weight percent of each set, to form a diffractive pigment mixture centered at 550nm, and the pigment flakes to coating vehicle weight ratio was dispersed in the coating vehicle of 0.14:3.9 to form a combined diffractive pigment composition centered at 550 nm. Similarly, two sets of all-dielectric diffractive pigment flakes centered at 700nm were mixed in a 1:1 weight ratio, i.e., 50 weight percent of each set, to form a diffractive pigment mixture centered at 700nm, and the pigment flakes to coating vehicle weight ratio of 0.14:3.9 were dispersed in the coating vehicle to form a combined diffractive pigment composition centered at 700 nm.

Two separate cast films of diffractive pigment composition centered at 550nm and having line frequencies of 1440 lines/mm and 2000 lines/mm and a cast film of the combined diffractive pigment composition centered at 550nm were coated on a black and white Laneta card (example 2). Similarly, cast films of two separate diffractive pigment compositions centered at 700nm and having line frequencies of 1440 lines/mm and 2000 lines/mm and a cast film of a combined diffractive pigment composition centered at 700nm were coated on a black and white Laneta card (example 3).

The reflectance of the dope cast film on the black substrate was characterized using a DataColor SF600 + spectrophotometer under diffuse illumination. Referring to FIG. 5, the reflectance spectra of 510, 511, and 512 are respectively for two separate diffractive pigment compositions centered at 550nm and having line frequencies of 1440 lines/mm and 2000 lines/mm and a combined diffractive pigment composition centered at 550nm (example 2). The pigment composition has a maximum reflection at a wavelength of 530nm to 550nm, corresponding to a green background color. Thus, under diffuse illumination, the observed color of the separate and combined diffractive pigment compositions is primarily the background color corresponding to the design wavelength. Further, the reflection spectrum 512 of the combined diffractive pigment composition is essentially the average of the reflection spectra 510 and 511 of the separate diffractive pigment compositions.

The flop of the cast film of dope under direct illumination on the black matrix was characterized by a Murakami angle spectrophotometer. With respect to fig. 6A, 610, 611, and 612 are the color locus of two separate diffractive pigment compositions centered at 550nm and having line frequencies of 1440 lines/mm and 2000 lines/mm and the color locus of a combined diffractive pigment composition centered at 550nm, respectively, obtained at an incident angle of 0 ° and an observation angle of 12 ° to 80 ° in 1 ° steps (example 2).

The color traces 610, 611, and 612 for the two separate diffractive pigment compositions and the combined diffractive pigment composition, respectively, centered at 550nm, lie primarily in the second quadrant, indicating wavelengths between yellow (i.e., about 580 nm) and green (i.e., about 510 nm) that are primarily diffracted.

In particular, the color locus 610 of the diffractive pigment composition having a line frequency of 1440 lines/mm changes from yellow to green from 12 ° to 34 °, where only specular reflection, i.e., zero diffraction order, is desired. At higher angles, where a-1 diffraction order is desired, the color locus 610 is in the second quadrant, from 34 ° to about 60 ° corresponding to a yellow-green hue, and in the first quadrant, from about 60 ° to 80 ° corresponding to a yellow-red hue. In general, the thin film interference provided by the seven-layer stack filters the diffraction effects provided by the diffraction grating.

The color locus 611 of the diffractive pigment composition having a line frequency of 2000 lines/mm shows similarity, except through a smaller color range. This behavior is consistent with what the grating equation predicts. At an incident angle of 0 deg., wavelengths of 400nm to 500nm are predicted to be diffracted by a diffraction grating having a line frequency of 2000 lines/mm on the-1 diffraction order at 53 deg. to 90 deg.. In contrast, at an incident angle of 0, wavelengths from 400nm to 694nm are predicted to be diffracted by a diffraction grating having a line frequency of 1440 lines/mm on the-1 diffraction order from 35 ° to 90 °.

For all viewing angles, e.g., 63 °, the color locus 612 of the combined diffractive pigment composition lies between the color loci 610 and 611 of the separate diffractive pigment compositions, indicating that the colors provided by the diffractive interference are additive, i.e., consistent with the additive color principle. In other words, the combined diffractive effect provided by the combined diffractive pigment composition is an additive combination of the different diffractive effects provided by the separate diffractive pigment compositions.

Note that the color locus 612 of the combined diffractive pigment composition smoothly moves from 12 ° to 63 °, but it abruptly changes direction from 63 ° to 80 ° and moves to a greener hue. In other words, the combination diffractive pigment composition exhibits an inverse flop, which will produce interesting optical effects.

With respect to fig. 6B, 620, 621 and 622 are the color locus of two separate diffractive pigment compositions centered at 550nm and having line frequencies of 1440 lines/mm and 2000 lines/mm and the color locus of a combined diffractive pigment composition centered at 550nm, respectively, obtained at a 45 ° incident angle and at a 1 ° step size at-33 ° to 80 ° observation angles (example 2).

Also under this set of illumination and viewing angle conditions, the color locus 622 of the combined diffractive pigment composition lies between the color loci 620 and 621 of the two separate diffractive pigment compositions for all viewing angles, e.g., 0 ° and-13 °, indicating that the colors provided by the diffractive interference are additive. The color locus 622 of the combined diffractive pigment composition includes a loop. The color locus 622 moves in one direction from about 5 to-13, but it abruptly changes direction and moves in the opposite direction from-13 to about-20. In other words, the combination diffractive pigment composition exhibits an inverse flop, which will produce interesting optical effects.

With respect to fig. 7, 710, 711, and 712 are the color locus of two separate diffractive pigment compositions centered at 700nm and having line frequencies of 1440 lines/mm and 2000 lines/mm and the color locus of a combined diffractive pigment composition centered at 700nm, respectively, obtained at an incident angle of 0 ° and an observation angle of 12 ° to 80 ° in 1 ° steps (example 3).

The color traces 710, 711, and 712 of the two separate diffractive pigment compositions and the combined diffractive pigment composition, respectively centered at 700nm, are limited to the first quadrant, representing diffraction of only wavelengths between yellow (i.e., about 580 nm) and red (i.e., about 700 nm). In general, the thin film interference provided by the seven-layer stack filters the diffraction effects provided by the diffraction grating. For all viewing angles, the color locus 712 of the combined diffractive pigment composition centered at 700nm for the combined diffractive pigment composition centered at 550nm is located between the color loci 710 and 711 of the two separate diffractive pigment compositions centered at 700nm, indicating that the colors provided by the diffractive interference are additive.

Embodiments with Package Structure

In some embodiments, the all-dielectric diffractive pigment flakes have an encapsulated structure. In other words, the pigment flakes consist of encapsulated preformed flakes. Each encapsulated pre-fabricated sheet comprises a plurality of dielectric layers, typically 2 to 5 dielectric layers. More specifically, each packaged pre-fabricated sheet comprises alternating layers of high index dielectric material (H) and low index dielectric material (L), i.e., one or more HL pairs, and optionally additional H or L layers. The alternating layers include a core layer or pre-formed sheet, which may be H or L layers, and one or more encapsulation layers. At least the core layer includes a diffraction grating.

In a first preferred embodiment, the H layers are composed of the same high index dielectric material and have substantially the same physical and optical thickness. Similarly, the L layers are composed of the same low index dielectric material and have substantially the same physical and optical thickness. Both the H and L layers have 1/4 wavelength optical thickness (QWOT) at the design wavelength. Thus, as a result of thin film interference, the encapsulated pre-fabricated sheet provides a background color that is characterized or preferably centered at the design wavelength. By adjusting the QWOT, different background colors can be achieved. According to the present invention, in order to manufacture a neutral color diffractive pigment composition or a mixed color diffractive pigment composition, it is necessary to mix separate encapsulated prefabricated flake sets centered at different design wavelengths.

In a second preferred embodiment, the H layers are typically, but not necessarily, composed of the same high index material, and the L layers are typically, but not necessarily, composed of the same low index material. The core layer has a physical thickness selected for a particular design wavelength, and the encapsulation layer has substantially the same physical thickness for all design wavelengths. Thus, as a result of thin film interference, the encapsulated pre-fabricated sheet provides a background color that is characterized or preferably centered at the design wavelength. By adjusting the physical thickness of the core layer, different background colors can be achieved. Varying the optical path through the core layer can produce different thin film interference conditions.

Advantageously, such embodiments are particularly convenient for making neutral and mixed color diffractive pigment compositions. Starting from a core layer or pre-fabricated flakes having different physical thicknesses, it is not necessary to separately manufacture sets of all-dielectric diffractive pigment flakes centered at different design wavelengths in different batches and sequentially mix the sets to provide a diffractive pigment mixture, but instead sets of all-dielectric diffractive pigment flakes having different colorations can be manufactured together in a single batch to provide a diffractive pigment mixture. In other words, the set of all-dielectric diffractive pigment flakes is automatically mixed.

Referring to fig. 8, an exemplary all-dielectric diffractive pigment flake 800 having an encapsulated structure is composed of a preformed flake or core layer 821 encapsulated by three layers 810 and 820. More particularly, pigment flake 800 includes a core L layer 821 surrounded by an encapsulation H layer 810, encapsulation H layer 810 is surrounded by an encapsulation L layer 820, and encapsulation L layer 820 is in turn surrounded by another encapsulation H layer 810. From TiO₂Two H layers 810 of SiO₂The two L layers 820 and 821 of composition alternate. Core L-layer 821 has a physical thickness selected for a particular design wavelength, and package H-layer 810 and L-layer 820 have substantially fixed physical thicknesses for all design wavelengths. Further, both the H layer 810 and the L layers 820 and 821 include a diffraction grating 830.

An exemplary neutral diffractive pigment composition includes a set of all-dielectric diffractive pigment flakes 800 as shown in fig. 8. Each set having a core L-layer 821 of different physical thickness (e.g., between about 50nm and about 300 nm), and a package H-layer 810, e.g., about 60nm, and an L-layer 820, e.g., about 90nm, of substantially the same physical thickness. Thus, the group had a coloration varying from red, to yellow, to green, to blue, to violet. In each set, diffraction gratings 830 have substantially the same line frequency, for example 1440 lines/mm. Thus, the diffractive pigment composition provides a background color of white, i.e., a neutral color, as well as a white diffractive effect, as described above in reference example 1.

In an alternative embodiment, each set of all-dielectric diffractive pigment flakes 800 has a different line frequency, e.g., 1440 lines/mm and 2000 lines/mm, in addition to the core L layer 821 of a different physical thickness, such that the diffractive pigment composition provides a neutral white background color and a combined diffractive effect.

Preferred neutral diffractive pigment compositions can be made in a manner similar to that in example 1, i.e., by sequentially depositing encapsulating dielectric layers on sets of all-dielectric diffractive pre-fabricated platelets having different physical thicknesses. The encapsulation layer may be deposited under fixed deposition conditions by using various deposition techniques to achieve substantially the same physical thickness for all sets. Suitable deposition techniques include fluidized bed thermal or plasma assisted CVD, PVD on particle curtains (curtains) between sputtering targets or on particles moving on a vibrating conveyor, CVD or PVD on tumbling particles in a cylinder, remote plasma CVD, and wet chemical deposition.

Of course, various other embodiments may be devised without departing from the spirit and scope of the invention.

Claims (20)

1. A diffractive pigment composition comprising:

a pigment medium; and

a plurality of sets of all-dielectric diffractive pigment flakes mixed and dispersed in the pigment medium, wherein each of the sets of all-dielectric diffractive pigment flakes includes one or more dielectric layers for providing a background color, and wherein at least one of the one or more dielectric layers includes a diffractive structure for providing a diffractive effect;

wherein each of the sets of all-dielectric diffractive pigment flakes provides a different diffractive effect; and is

Wherein the diffractive pigment composition provides a combined diffractive effect that is a combination of the different diffractive effects provided by the set of all-dielectric diffractive pigment flakes.

2. The diffractive pigment composition according to claim 1, wherein each of the sets of all-dielectric diffractive pigment flakes provides a different background color and has substantially the same line frequency.

3. The diffractive pigment composition according to claim 2, wherein the diffractive pigment composition provides a combined background color that is a combination of the different background colors provided by the set of all-dielectric diffractive pigment flakes.

4. The diffractive pigment composition according to claim 3, wherein the combined background color is a white background color, and wherein the combined diffractive effect is a white diffractive effect.

5. The diffractive pigment composition according to claim 1, wherein each of the sets of all-dielectric diffractive pigment flakes provides substantially the same background color and has a different line frequency.

6. The diffractive pigment composition according to claim 5, wherein the diffractive pigment composition provides a background color that is substantially the same as a background color provided by the all-dielectric diffractive pigment flake set, and wherein the combined diffractive effect comprises an inverse flop.

7. The diffractive pigment composition according to claim 1, wherein each set of all-dielectric diffractive pigment flakes provides a different background color and has a different line frequency.

8. The diffractive pigment composition according to claim 7, wherein the diffractive pigment composition provides a combined background color that is a combination of the different background colors provided by the set of all-dielectric diffractive pigment flakes, and the combined diffractive effect comprises an inverse flop.

9. The diffractive pigment composition according to claim 1, wherein said one or more dielectric layers consists of a plurality of dielectric layers.

10. The diffractive pigment composition according to claim 9, wherein the plurality of dielectric layers comprises alternating layers of a high index of refraction dielectric material and a low index of refraction dielectric material.

11. The diffractive pigment composition according to claim 10 wherein each of said alternating layers has an 1/4 wavelength optical thickness corresponding to a design wavelength, and wherein said background color is centered at said design wavelength.

12. The diffractive pigment composition according to claim 11, wherein each set of all-dielectric diffractive pigment flakes has a different 1/4 wavelength optical thickness corresponding to a different design wavelength such that each set of all-dielectric diffractive pigment flakes provides a different background color.

13. The diffractive pigment composition according to claim 10, wherein the alternating layers comprise a core layer and one or more encapsulation layers.

14. The diffractive pigment composition according to claim 13, wherein each set of all-dielectric diffractive pigment flakes has the core layer having a different physical thickness and the one or more encapsulation layers having substantially the same physical thickness such that each set of all-dielectric diffractive pigment flakes provides a different background color.

15. The diffractive pigment composition according to claim 1, wherein said one or more dielectric layers comprises at least one layer of an absorbing dielectric material and said background color is provided at least in part by selective absorption.

16. The diffractive pigment composition according to claim 15, wherein said absorbing dielectric material is an absorbing metal compound, a cermet, a dielectric material including a radiation induced color center, or a combination thereof.

17. The diffractive pigment composition according to claim 1, wherein said background color is provided by thin film interference, selective absorption, or a combination thereof.

18. The diffractive pigment composition according to claim 1, wherein each set of all-dielectric diffractive pigment flakes has the same optical design.

19. The diffractive pigment composition according to claim 1, wherein each set of all-dielectric diffractive pigment flakes has the same layer structure.

20. A diffractive pigment mixture comprising:

a plurality of sets of all-dielectric diffractive pigment flakes, wherein each of the sets of all-dielectric diffractive pigment flakes includes one or more dielectric layers for providing a background color, and wherein at least one of the one or more dielectric layers includes a diffractive structure for providing a diffractive effect;

wherein each of the sets of all-dielectric diffractive pigment flakes provides a different diffractive effect; and

wherein the diffractive pigment mixture provides a combined diffractive effect that is a combination of the different diffractive effects provided by the set of all-dielectric diffractive pigment flakes.