Bifunctional pigments

Abstract

The present disclosure relates to bifunctional pigments. The pigment sheet may include a multi-layer optical structure. The multilayer optical structure may have a first surface with a first modulation corresponding to the relief of the diffraction grating. The multi-layer optical structure may have a second surface having a second modulation, where the second surface is opposite the first surface, and the second modulation is less than the first modulation such that the second surface is relatively flatter than the first surface. The multi-layer optical structure may exhibit a diffractive color for the multi-layer optical structure with respect to a first angular range of incident light angles, and may exhibit an interference color for the multi-layer optical structure with respect to a second angular range of incident light angles.

Description

Background Art

[0001] Conventional interference effect pigment flakes comprise relatively thin layers of different optical materials coated in a specific order on a carrier. If the carrier is made of a transparent material, such as mica or glass, the pigment flakes are colored and transparent. In one example, both sides of a substrate comprising mica or glass are coated with a set of layers (referred to herein as an optical stack) comprising different optical materials of varying thicknesses. The combination of optical materials with different refractive indices and different thicknesses creates an interference structure in which the substrate acts as a plane of symmetry (i.e., an imaginary plane that divides the structure of the pigment flake into two mirror-imaged halves). The symmetry of the optical stack means that similar layers in the pigment flake, in the same order, face each other, with one layer acting as a plane of symmetry.

[0002] Optically variable pigment flakes include a layer of reflective metal (rather than mica or glass), which makes the flakes colored and opaque. In one example, each optical stack in an optically variable pigment flake includes a translucent chromium absorber layer and a transparent, colorless magnesium fluoride (MgF2) layer formed on a reflective aluminum (Al) substrate. In this case, the optical stack is symmetrical with respect to the Al substrate. Summary of the Invention

[0003] In some implementations, a pigment flake comprises: a multilayer optical structure comprising: a first surface having a first modulation, the first modulation corresponding to a relief of a diffraction grating; and a second surface having a second modulation, the second surface opposite the first surface and the second modulation being less than the first modulation, such that the second surface is relatively flatter than the first surface, wherein the multilayer optical structure exhibits a diffraction color for a first angular range of the multilayer optical structure with respect to an angle of incident light, and exhibits an interference color for a second angular range of the multilayer optical structure with respect to an angle of incident light.

[0004] In some implementations, a method of forming a dual-functional pigment flake includes: providing a substrate having a diffraction grating structure on a surface of the substrate; forming a release layer on the surface of the substrate; forming a first optical stack on the release layer, the first optical stack being formed such that a surface of the first optical stack has a relief of the diffraction grating structure; forming a magnetizable layer above the first optical stack; forming a second optical stack above the magnetizable layer, the second optical stack being formed such that a modulation of a surface of the second optical stack is less than a modulation of a surface of the first optical stack having the relief of the diffraction grating structure; and removing the release layer to separate the substrate from a multilayer optical structure, the multilayer optical structure including the first optical stack, the magnetizable layer, and the second optical stack.

[0005] In some implementations, a dual-functional pigment flake comprises: a first optical stack, wherein a surface of the first optical stack has a first modulation; a magnetizable layer positioned above the first optical stack; and a second optical stack positioned above the magnetizable layer, wherein a surface of the second optical stack has a second modulation, the second modulation being less than approximately half the first modulation, wherein the first optical stack and the second optical stack cause the pigment flake to exhibit a diffraction color for a first angular range of the dual-functional pigment flake with respect to an angle of incident light, and to exhibit an interference color for a second angular range of the dual-functional pigment flake with respect to an angle of incident light. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1A-1B is a diagram illustrating an example of conventional pigment flakes oriented in a planar structure.

[0007] Figure 2 is a diagram illustrating an example of conventional magnetizable pigment flakes oriented in a cylindrical structure.

[0008] Figure 3 is a diagram illustrating an example of a bifunctional pigment flake described herein.

[0009] Figure 4 is a graph illustrating a specific example of modulation reduction of a surface of a multilayer optical structure of a bifunctional pigment flake.

[0010] Figure 5A-5B is a diagram associated with an example implementation of a bifunctional pigment flake comprising a multilayer optical structure including a first optical stack and a second optical stack.

[0011] Figures 6A-6C is a diagram associated with another example implementation of a dual-function pigment flake that includes a multilayer optical structure including a first optical stack and a second optical stack.

[0012] Figure 7 is a diagram associated with another example implementation of a dual-function pigment flake that includes a multilayer optical structure including a first optical stack and a second optical stack.

[0013] Figure 8 is a flow chart of an example process associated with the formation of bifunctional pigment flakes described herein. DETAILED DESCRIPTION

[0014] The following detailed description of example implementations refers to the accompanying drawings, in which the same reference numerals in different drawings may identify the same or similar elements.

[0015] The pigment flakes that exhibit diffraction of incident light can be multilayer flakes with symmetrical optical stacking on opposite sides of a reflective substrate. The symmetrical optical stacking may include an interference structure that provides goniochromatic characteristics. Some goniochromatic diffraction pigment flakes include a magnetizable core. In a specific example, depositing nickel on a diffraction grating pattern produces magnetic needles along a linear grating pattern that allow the diffraction pigment flakes dispersed in an organic binder to be magnetically aligned. Here, the pigment flakes can have an optical stack (e.g., a thin film optical structure) that is symmetrical with the magnetizable layer. In some cases, the diffraction grating can be embossed onto a roller-coated substrate. The surface relief on both sides of this pigment flake repeats the surface relief of the substrate used for pigment manufacturing.

[0016] Magnetizable diffraction pigment flakes with high-frequency diffraction gratings have high diffraction efficiency but low total reflectivity. The total reflectivity of such pigment flakes is affected by the height of the protruding elements of the diffraction grating. In fact, as the height of the protruding elements of the diffraction grating increases, the light is more scattered. Cross gratings are two-dimensional periodic diffraction gratings with periodicity along two directions. The orientation of the gratings relative to each other can be in the range of 45 degrees (°) to 90°. In one particular case, a high-frequency diffraction cross grating pigment flake with more than 3800 lines per millimeter (mm) provides an iridescent blue color at an incident angle of about 75°. For a grating of 3800 lines per mm and an incident angle of about 75°, only wavelengths shorter than about 525 nanometers (nm) (blue) are diffracted back in the direction of the incident light beam.

[0017] The structure of some interference pigment flakes is asymmetric. In one example, a magnetic interference pigment flake can include a metal or oxide magnetic layer with Fabry-Perot (FP) structures formed on both sides of the magnetic layer, each FP structure including a thin chromium absorption layer, a dielectric MgF2 spacer layer, and an Al2O3 coating layer. The two Fabry-Perot structures can be different (e.g., having different thicknesses or layers), in which case the color shift effect is shown from opposite sides of the pigment flake. In fact, in pigments with different colors on different sides, the colors mix together, which produces a third color with a poor color shift appearance. Therefore, pigments containing pigment flakes with different colors on opposite sides can reduce the color performance of the pigment.

[0018] Some pigment flakes have a single-cavity design—meaning that in a given interference structure, the pigment flake includes a single layer of optical spacer between the reflector layer and the semi-transparent absorber layer. Thus, the optical stack of such a pigment flake has a single-cavity thin-film structure, which can be expressed as M1 / D / M2, where M1 is an opaque layer of a highly reflective metal (e.g., Al, silver (Ag), gold (Au), platinum (Pt), etc.), M2 is a semi-transparent layer of a transition metal (e.g., chromium (Cr), titanium (Ti), tungsten (W), etc.), and D is a layer of a dielectric or semiconductor material (e.g., MgF2, silicon dioxide (SiO2), titanium dioxide (TiO2), zinc sulfide (ZnS), etc.). Some pigment flakes have a multi-cavity (e.g., two-cavity) design. The dual-cavity design of the optical stack can be expressed as M1 / D / M2 / D / M2. The complete design of a dual-cavity pigment flake includes a dual-cavity optical stack on each side and can therefore be expressed as M2 / D / M2 / D / M1 / D / M2 / D / M2.

[0019] Color-shifting pigment flakes dispersed in an organic binder and printed on a flat surface appear in several colors at different viewing angles. Figure 1A The brightest colors appear when the non-specular 10° geometry shown in Figure 1A In the example, article 100 includes pigment flakes 101 dispersed in an organic binder 102 printed on a substrate 103. An incident light beam from a light source 104 strikes pigment flake 101 along a direction 105 at a 15° angle from a normal 106. According to the law of reflection, the angle of reflection equals the angle of incidence. Therefore, the light reaching pigment flake 101 is reflected in a direction 108 at a 15° angle from normal 106. However, at this angle, observer 107 sees the image of light source 104 but cannot see the color of pigment flake 101 due to its high reflectivity. To see the color of pigment flake 101 without seeing the light from light source 104, observer 107 can be mounted at a 5° angle from normal 106. At this angle, light reaching observer 107 along a direction 109 represents a bright appearance of the first color of the pigment. For example, for a green to blue pigment, the first color may be green.

[0020] The color shifting pigment changes color (e.g., from green to blue) due to a change in viewing angle. The angle can be changed in three ways—moving the light source 104, moving the viewer 107, or by tilting the article 100 (without moving the light source 104 or viewer 107). Figure 1B An example of tilting the article 100 is schematically shown in FIG. Figure 1B As shown in FIG, the light source 104 and the observer 107 are located at Figure 1A Here, the article 100 on the substrate 103 is tilted (rotated) counterclockwise in the plane of the page. Figure 1A In contrast, light incident in direction 105 is reflected in direction 110 away from viewer 107. Instead, viewer 107 sees scattered light from pigment flake 101 in direction 109. In this example, the color of the light at viewer 107 is dark blue (rather than blue as in the example above). Figure 1A Green in the orientation shown in ).

[0021] For magnetizable color shifting pigments, the magnetizable pigment flakes are dispersed in a liquid organic binder and printed on a surface, and the pigment flakes align along the magnetic field lines of an applied external magnetic field (along their longest dimension). Manipulating the magnets enables the magnetic field to be controlled so that it can be parallel to the surface or curved relative to the surface and have a concave or convex configuration. This enables the magnetizable pigment flakes to be oriented to form a Fresnel mirror. The Fresnel mirror can be cylindrical, parabolic, annular, conical, etc., depending on the magnetic field configuration. In this arrangement, the incident light reflected from the pigment flakes generates different interactive optical effects. Figure 2 An example of magnetizable pigment flakes oriented in a cylindrical structure is shown in .

[0022] exist Figure 2 In the embodiment shown in FIG2 , article 200 is exposed to light source 204 and light ray 205 reflects from pigment flakes 201, causing light ray 205′ to be directed toward viewer 207. In contrast, light rays 206 and 208, which are substantially parallel to light ray 205, are reflected, causing light rays 206′ and 208′ to be directed away from viewer 207. This is because pigment flakes 201 are aligned in the direction of the magnetic field (rather than parallel to substrate 203 of article 200). In this case and with this orientation of article 200 relative to light source 204 and viewer 207, the element formed by pigment flakes 201 in organic binder 202 appears as bright, reflective bands in the areas corresponding to light rays 205 / 205′, and as dark, non-reflective areas (e.g., black) in the areas corresponding to light rays 206 / 206′ and 208 / 208′.

[0023] What is desirable is an article that exhibits both a primary interference color and a color other than dark or black (for example, to enhance security). At normal viewing angles, the reflectivity of an angle-dependent pigment on a diffraction grating is lower than that of a pigment deposited on a flat substrate. On the other hand, articles printed with diffractive pigments produce a rainbow of colors at high viewing angles, while articles with pigment flakes are dark. Therefore, it is desirable to develop a pigment that exhibits both a primary interference color and a diffraction color at normal viewing angles. In practice, such pigment flakes should have a diffraction efficiency that is relatively balanced with the overall reflectivity.

[0024] Some implementations described herein provide dual-functional pigment flakes. In some implementations, the dual-functional pigment flakes include a multilayer optical structure comprising a first surface having a first modulation corresponding to a relief of a diffraction grating and a second surface having a second modulation that is less than the first modulation (e.g., such that the second surface is relatively flatter than the first surface). In some aspects, the dual-functional pigment flakes having this multilayer optical structure exhibit diffraction colors for a first angular range of incident light angles of the multilayer optical structure and interference colors for a second angular range of incident light angles of the multilayer optical structure. In the dual-functional pigment flakes described herein, diffraction efficiency and total reflectivity are relatively balanced because the first surface of the dual-functional pigment flakes has a relatively high modulation (e.g., to provide sufficient diffraction efficiency but low total reflectivity) and the second surface of the dual-functional pigment flakes has a relatively low modulation (e.g., to provide low diffraction efficiency but high total reflectivity). In some implementations, dual-functional pigment flakes having these properties are formed by intentionally increasing the thickness of the pigment flake, which results in the modulation of the second surface of the dual-functional pigment flake being less than the modulation of the first surface of the dual-functional pigment flake (e.g., the surface adjacent to the grating substrate). More details are provided below.

[0025] Figure 3 is a diagram illustrating an example of a dual-function pigment flake 300 on a substrate 350. In some implementations, as Figure 3 As shown in FIG, the dual-function pigment flake 300 includes a multilayer optical structure 302 having a first surface 302s1 and a second surface 302s2.

[0026] The multilayer optical structure 302 is a multilayer structure including multiple optical stacks that cause the dual-functional pigment flake 300 to exhibit diffraction colors within a first angular range and interference colors within a second angular range. In some implementations, the first angular range can include angles greater than about 45°, while the second angular range can include angles less than about 45°. Typically, the first angular range can include angles greater than angle α, while the second angular range can include angles less than angle α. Figure 5A-5B 6A-6C provide more details about the multilayer optical structure 302. In some implementations, the thickness of the multilayer optical structure 302 can be in a range from about 400 nanometers (nm) to about 3 micrometers (μm).

[0027] In some implementations, such as Figure 3 As shown in FIG, a multilayer optical structure 302 of a dual-function pigment flake 300 is formed on a surface of a substrate 350 including a diffraction grating structure (e.g., a periodic structure including a series of ridges and valleys). Figure 3As shown in FIG, first surface 302s1 has a modulation corresponding to the relief of the diffraction grating structure of substrate 350. That is, first surface 302s1 may have a modulation that is a mirror image of the modulation of the diffraction grating structure of substrate 350. As used herein, the term "modulation" refers to the distance between a given high point (e.g., a ridge) and a given low point (e.g., a valley) on a surface. In other words, the modulation may refer to the depth of the profile of the surface.

[0028] like Figure 3 As shown in FIG, a first surface 302s1 of the multilayer optical structure 302 (as well as a surface of the substrate 350) has a modulation m1, while a second surface 302s2 has a modulation identified as m2. As shown, the modulation m2 is less than the modulation m1. That is, the second surface 302s2 is relatively flatter than the first surface 302s1. In some implementations, the modulation m2 is at least about 50% less than the modulation m1. That is, in some implementations, the modulation m2 is less than half of the modulation m1. In some implementations, the difference in modulation between the first surface 302s1 and the second surface 302s2 enables the dual-function pigment flake 300 to exhibit diffraction colors for a first range of angles of the multilayer optical structure 302 relative to the angle of incident light, and to exhibit interference colors for a second range of angles of the multilayer optical structure 302 relative to the angle of incident light, as described below.

[0029] In some implementations, the thickness of the multilayer optical structure 302 (e.g., the thickness of one or more layers of the multilayer optical structure 302) causes the modulation m2 of the second surface 302s2 to be less than the modulation m1 of the first surface 302s1. Thus, in some implementations, the thickness of the multilayer optical structure 302 (e.g., the thickness of one or more layers of the multilayer optical structure 302) can be controlled or selected to achieve a desired reduction in modulation of the second surface 302s2 (relative to the modulation of the first surface 302s1).

[0030] As indicated above, Figure 3 Provided as an example. Other examples may be related to Figure 3 Different than described. Figure 3 The number of layers and their arrangement shown in the figure are provided as examples. In practice, there may be more than Figure 3 More layers, fewer layers, different layers, or differently arranged layers than shown in FIG. Figure 3 Two or more layers shown in can be implemented in a single layer, or Figure 3 The single layer shown in can be implemented as multiple distributed layers. Additionally or alternatively, Figure 3 A set of layers (eg, one or more layers) shown in FIG. 1 may perform the operations described as being performed by Figure 3 One or more functions performed by another set of layers shown in .

[0031] Figure 4 is a diagram illustrating a specific example of a reduction in modulation of the second surface 302s2 (relative to the first surface 302s1), which can be achieved by increasing the thickness of the multilayer optical structure 302. Figure 4 In the example of FIG. 3 , a multilayer optical structure 302 comprising thin film MgF2 layers (with varying thicknesses) is deposited on a polyester cross-grating substrate 350 comprising a surface having a modulation of 80 nm. Figure 4 As shown in , the modulation of the second surface 302s2 decreases from 80 nm to 19 nm when the thickness of the multilayer optical structure 302 approaches 2900 nm. In some implementations, the reduction in modulation of the second surface 302s2 (e.g., compared to the modulation of the first surface 302s1) can depend on one or more characteristics of the multilayer optical structure 302, such as the thickness of one or more layers of the multilayer optical structure 302, the porosity of one or more layers of the multilayer optical structure 302, the crystallinity of one or more layers of the multilayer optical structure 302, or the presence (or absence) of columnar structures within one or more layers of the multilayer optical structure 302, etc.

[0032] As indicated above, Figure 4 Provided as an example. Other examples may be related to Figure 4 Different than described.

[0033] In some implementations, the multilayer optical structure 302 includes a pair of optical stacks. Figure 5A-5B is a diagram associated with an example implementation of a dual-function pigment flake 300 that includes a multilayer optical structure 302 that includes a first optical stack 504a and a second optical stack 504b. Figure 5A In the example shown in FIG, the first optical stack 504a includes an absorbing layer 506a (e.g., a first semi-transparent Cr layer), a transparent layer 508a (e.g., a first dielectric MgF2 layer), and a reflective layer 510a (e.g., a first opaque Al layer). Similarly, the second optical stack 504b includes a reflective layer 510b (e.g., a second opaque Al layer), a transparent layer 508b (e.g., a second dielectric MgF2 layer), and an absorbing layer 506b (e.g., a second semi-transparent Cr layer). As further shown, the multilayer optical structure 302 also includes an intermediate layer 512 (e.g., a third MgF2 layer) and a magnetizable layer 514 between the first optical stack 504a and the second optical stack 504b.

[0034] In some implementations, such as Figure 5A As shown in , the multilayer optical structure 302 is formed on a release layer 550 on a surface of a substrate 350. In some implementations, the release layer 550 is a removable layer (eg, a layer that dissolves in the presence of a solvent) that enables separation of the dual-function pigment flake 300 from the substrate 350.

[0035] exist Figure 5A In the example shown in , the first optical stack 504a and the second optical stack 504b are single-cavity optical stacks (i.e., the first optical stack 504a includes a single cavity, and the second optical stack 504b includes a single cavity). In addition, the first optical stack 504a is symmetrical to the second optical stack 504b (e.g., the intermediate layer 512 and the magnetizable layer 514 serve as planes of symmetry). In some implementations, the first optical stack 504a and / or the second surface 302s2 can be a multi-cavity optical stack (e.g., the first optical stack 504a and / or the second optical stack 504b can be a dual-cavity optical stack, examples of which are described below with respect to Figures 6A-6C Additionally or alternatively, in some implementations, the first optical stack 504a and the second optical stack 504b can be asymmetric (e.g., such that the layer structure of the first optical stack 504a is different from the layer structure of the second optical stack 504b about a center plane formed by the intermediate layer 512 and the magnetizable layer 514).

[0036] In some implementations, such as Figure 5A As shown in and described herein, the modulation m1 of the first surface 302s1 of the multilayer optical structure 302 is greater than the modulation m2 of the second surface 302s2 of the multilayer optical structure 302. Figure 5A As shown in FIG, the surface of the layer between the first surface 302s1 and the second surface 302s2 of the multilayer optical structure 302 has a modulation that is smaller than the modulation m1 of the first surface 302s1 and larger than the modulation m2 of the second surface 302s2. Figure 5A As shown in FIG, the modulation m3 of the surface of the intermediate layer 512 is greater than the modulation m2 of the second surface 302s2 and less than the modulation m1 of the first surface 302s1. In some implementations, the modulation of the surface within the multilayer optical structure 302 decreases along a direction moving from the first surface 302s1 to the second surface 302s2 (e.g., the modulation of the surface decreases in a direction away from the relief of the diffraction grating (i.e., the first surface 302s1)).

[0037] exist Figure 5A In the example shown in , the thickness of the dual-function pigment flake 300 is controlled by the thickness of the intermediate layer 512. Thus, in some implementations, the incorporation of the intermediate layer 512 (e.g., between the first optical stack 504a and the second optical stack 504b) can be used to provide a thickness that makes the second surface 302s2 flatter than the first surface 302s1. In some implementations, the intermediate layer 512 is a layer of insignificant material (e.g., a dielectric material such as MgF2). In some implementations, such as Figure 5AAs shown in FIG, the intermediate layer 512 is located between the first optical stack 504a and the second optical stack 504b (eg, near the middle of the single cavity dual function pigment flake 300).

[0038] In some implementations, Figure 5A The dual-function pigment flake 300 shown in FIG can be formed using vacuum deposited layers over a substrate 350. For example, the surface of the substrate 350 including the diffraction grating structure can be coated with layers of different materials by thermal evaporation in a vacuum. In this example, the substrate 350 is coated with a release layer 550. Next, an absorber layer 506a is deposited on the release layer 550. A transparent layer 508a is deposited on the absorber layer 506a, and then a reflective layer 510a is deposited on the transparent layer 508a. Here, the transparent layer 508a (e.g., the layer between the absorber layer 506a and the reflective layer 510a) defines the color of the angularly heterochromatic interference thin film structure of the first optical stack 504a.

[0039] Next, an intermediate layer 512 is deposited over the reflective layer 510a. In some implementations, the intermediate layer 512 can include a dielectric material such as MgF2. In some implementations, the thickness of the intermediate layer can be in a range of about 100 nm to about 2000 nm. Notably, the intermediate layer 512 does not define the color of the dual-function pigment flake 300. Here, the purpose of the intermediate layer 512 is to increase the physical thickness of the multilayer optical structure 302 in order to control (e.g., reduce) the modulation m2 of the second surface 302s2. In other words, the intermediate layer 512 can act as a spacer that controls the overall thickness of the dual-function pigment flake 300 while reducing the modulation m2 of the second surface 302s2 relative to the modulation m1 of the first surface 302s1.

[0040] A magnetizable layer 514 (e.g., a layer comprising any suitable magnetizable material) is formed on the intermediate layer 512, and a second optical stack 504b is formed on the magnetizable layer 514. In this example, the formation of the second optical stack 504b includes the formation of a reflective layer 510b, followed by the formation of a transparent layer 508b, and then the formation of an absorbing layer 506b. Here, the top surface of the absorbing layer 506b is the second surface 302s2. In some implementations, the thickness of the absorbing layer 506b can match the thickness of the absorbing layer 506a, the thickness of the transparent layer 508b can match the thickness of the transparent layer 508a, and / or the thickness of the reflective layer 510b can match the thickness of the reflective layer 510a. Additionally or alternatively, the thickness of the absorber layer 506b can be different from the thickness of the absorber layer 506a, the thickness of the transparent layer 508b can be different from the thickness of the transparent layer 508a, and / or the thickness of the reflective layer 510b can be different from the thickness of the reflective layer 510a. The thickness of the transparent layers 508a and 508b determines the color exhibited by the dual-function pigment flake 300. In some implementations, the transparent layers 508 (e.g., transparent layers 508a, 508b) can include a material with a low refractive index (e.g., MgF2, SiO2, etc.). Additionally or alternatively, the transparent layer 508 can include a material with a high refractive index (e.g., ZnS, TiO2, etc.). Figure 5A The multilayer optical structure 302 shown in FIG can be expressed as follows:

[0041] Second optical stack 504b

[0042] Magnetizable layer 514

[0043] Middle layer 512

[0044] First optical stack 504a

[0045] Each optical stack 504 includes a corresponding absorption layer 506 , a transparent layer 508 , and a reflective layer 510 .

[0046] In a specific example implementation, the multilayer optical structure 302 can be a symmetrical structure of a gold to green single cavity interference pigment thin film deposited on a crossed diffraction grating with a frequency of 3500 lines / mm and a modulation of 80 nm. Here, the structure has the following configuration:

[0047] Second optical stack 504b (510 nm, see below)

[0048] Magnetizable layer 514 (80nm nickel)

[0049] Intermediate layer 512 (600nm MgF2)

[0050] First optical stack 504a (510 nm, see below)

[0051] Release layer 550

[0052] Substrate 350

[0053] Each optical stack 504 includes an absorbing layer 506 (10 nm Cr), a transparent layer 508 (420 nm MgF2), and a reflective layer 510 (80 nm Al). In this example, the total thickness of the multilayer optical structure 302 is 1700 nm. Figure 5B 3 is a graph illustrating spectral characteristics of a first side (e.g., the side of the multilayer optical structure 302 having the first surface 302s1) and a second side (e.g., the side of the multilayer optical structure 302 having the second surface 302s2) of the multilayer optical structure 302 under a diffuse (e.g., 8°) geometry. Here, the first surface 302s1 has a modulation m1 of 80 nm, and due in part to the structure of the multilayer optical structure 302 (e.g., the thickness of the intermediate layer 512), the second surface 302s2 has a modulation m2 of 30 nm.

[0054] like Figure 5B As illustrated in FIG, over a wavelength range from 350 nm to 950 nm, the reflectivity of the first side of the multilayer optical structure 302 (i.e., the side having the first surface 302s1 with an 80 nm modulation) is generally lower than the reflectivity of the second side of the multilayer optical structure 302 (e.g., the side having the second surface 302s2 with a 30 nm modulation). In addition, the chromaticity (C*) and hue (h*) of the first side are lower than those of the second side, as shown in the following table:

[0055] C* h* First surface 302s1 side 49.26 17.96 Second surface 302s2 side 58.6 16.06

[0056] As indicated above, Figure 5A-5B Provided as an example. Other examples may be related to Figure 5A-5B Different than described. Figure 5A The number and arrangement of layers shown in the diagram are provided as examples only. In practice, there may be more than Figure 5A More layers, fewer layers, different layers, or differently arranged layers than shown in FIG. Figure 5A Two or more layers shown in can be implemented in a single layer, or Figure 5A The single layer shown in can be implemented as multiple distributed layers. Additionally or alternatively, Figure 5A A set of layers (eg, one or more layers) shown in FIG. 1 may perform the operations described as being performed by Figure 5A Another set of layers shown in FIG performs one or more functions.

[0057] In some implementations, the thickness of the multilayer optical structure 302, and therefore the thickness used to control the modulation of the second surface 302s2, can be defined at least in part by the design of the multilayer optical structure 302. That is, in some implementations, the dual-function pigment flake 300 can be designed such that the thickness of the pigment itself causes the second surface 302s2 to be flatter than the first surface 302s1. In some implementations, the multilayer optical structure 302 including one or more dual-cavity optical stacks 504 can be designed to achieve such a multilayer optical structure 302.

[0058] Figures 6A-6C is a diagram associated with another example implementation of a dual-function pigment flake 300 that includes a multilayer optical structure 302 that includes a first optical stack 504a and a second optical stack 504b. Figure 6A In the example shown in , the first optical stack 504a and the multilayer optical structure 302 are dual-cavity optical stacks. Figure 6A In the example shown in FIG, the first optical stack 504a includes an absorbing layer 506a1 (e.g., a first semi-transparent Cr layer), a transparent layer 508a1 (e.g., a first dielectric MgF2 layer), an absorbing layer 506a2 (e.g., a second semi-transparent Cr layer), a transparent layer 508a2 (e.g., a second dielectric MgF2 layer), and a reflective layer 510a (e.g., a first opaque Al layer). Similarly, the second optical stack 504b includes a reflective layer 510b (e.g., a second opaque Al layer), a transparent layer 508b1 (e.g., a third dielectric MgF2 layer), an absorbing layer 506b1 (e.g., a third semi-transparent Cr layer), a transparent layer 508b2 (e.g., a fourth dielectric MgF2 layer), and an absorbing layer 506b2 (e.g., a fourth semi-transparent Cr layer). As further shown, the multilayer optical structure 302 also includes an intermediate layer 512 (e.g., a fifth MgF2 layer) and a magnetizable layer 514 between the first and second optical stacks 504a, 504b. Notably, in this example embodiment, the multilayer optical structure 302 does not include the intermediate layer 512. Here, the thickness of the multilayer optical structure 302 is increased via the thickness of the dual cavity design (rather than through the use of the intermediate layer 512).

[0059] In some implementations, control over the thickness of the multilayer optical structure 302 can be provided by the thickness of the one or more transparent layers 508. For example, the thickness of the one or more transparent layers 508 can be used to reduce the modulation m2 of the second surface 302s2 (compared to the modulation m1 of the first surface 302s1) by increasing the overall thickness of the multilayer optical structure 302. In some implementations, the thickness of such transparent layers 508 can be in the range of about 50 nm to about 1500 nm. Figure 6A The multilayer optical structure 302 in the example shown in FIG can be expressed as follows:

[0060] Second optical stack 504b

[0061] Magnetizable layer 514

[0062] Middle layer 512

[0063] First optical stack 504a

[0064] The first optical stack 504a includes an absorption layer 506a1, a transparent layer 508a1, an absorption layer 506a2, a transparent layer 508a2 and a reflective layer 510a; and the second optical stack 504b includes a reflective layer 510b, a transparent layer 508b1, an absorption layer 506b1, a transparent layer 508b2 and an absorption layer 506b2.

[0065] In a specific example implementation, the multilayer optical structure 302 can form a symmetrical red to gold color where a pair of dual cavity optical stacks 504 have Figure 6B . In this example, the substrate 350 is coated with a release layer 550 in the form of water-soluble sodium chloride. The release layer 550 is then coated with an absorbing layer 506a1, followed by a transparent layer 508a1, an absorbing layer 506a2, a transparent layer 508a2, and a reflective layer 510a. As shown, these layers form a dual-cavity first optical stack 504a of the multilayer optical structure 302. A magnetizable layer 514 (e.g., stainless steel or another suitable ferromagnetic material) is then deposited on the reflective layer 510a. Notably, in this example, the magnetizable layer 514 serves as a face of the multilayer optical structure 302. A second optical stack 504b is then formed on the magnetizable layer 514 by forming a reflective layer 510b, a transparent layer 508b1, an absorbing layer 506b1, a transparent layer 508b2, and an absorbing layer 506b2. In Figure 6B Example thicknesses of the various layers are illustrated in the table shown in , which provides a total structure thickness of approximately 1400 nm. Here, the modulation m1 of the first surface 302s1 is 80 nm, while the modulation m2 of the second surface 302s2 is 34 nm. This difference in the surface modulation of the multilayer optical structure 302 results in differences in the optical properties.

[0066] Figure 6C 3 is a graph illustrating spectral characteristics of a first side (e.g., a side of the multilayer optical structure 302 having the first surface 302s1) and a second side (e.g., a side of the multilayer optical structure 302 having the second surface 302s2) of the multilayer optical structure 302. Here, as described above, the first surface 302s1 has a modulation m1 of 80 nm, and due in part to the structure of the multilayer optical structure 302 (e.g., the thickness of the intermediate layer 512), the second surface 302s2 has a modulation m2 of 34 nm.

[0067] like Figure 6C As illustrated in FIG, within the wavelength range of 350 nm to 950 nm, the reflectivity of the first side of the multilayer optical structure 302 (i.e., the side having the first surface 302s1 with an 80 nm modulation) is generally lower than the reflectivity of the second side of the multilayer optical structure 302 (e.g., the side having the second surface 302s2 with a 30 nm modulation). In addition, the diffraction efficiency of the first side is different from the diffraction efficiency of the second side. The following table summarizes the reflection and diffraction efficiencies of the first and second sides of this example multilayer optical structure 302:

[0068]

[0069] As illustrated in this example, the chromaticity C* of a sample with an 80nm modulation at a -80° observation angle is 24 units. For a sample with a 36nm modulation at the same observation angle, the chromaticity C* is 17 units. In other words, the first surface 302s1 side (e.g., the side with the 80nm modulation) reflects approximately 69% of the incident light and has a higher diffraction efficiency of 24 chromaticity units. In contrast, the second surface 302s2 side (e.g., the side with the 34nm modulation) reflects approximately 78% of the light and has a lower diffraction efficiency of 17 units. The example experimental results in the table above indicate that the first surface 302s1 side (e.g., the side adjacent to the substrate 350) of the multilayer optical structure 302 with the higher modulation m1 provides lower reflectivity and higher diffraction efficiency, while the second surface 302s2 side of the multilayer optical structure 302 with the lower modulation m2 provides higher reflectivity, lower diffraction efficiency, and brighter color.

[0070] As indicated above, Figures 6A-6C Provided as an example. Other examples may be related to Figures 6A-6C Different than described. Figure 6A-6B The number and arrangement of layers shown in the diagram are provided as examples only. In practice, there may be more than Figure 6A-6B More layers, fewer layers, different layers, or differently arranged layers than shown in FIG. Figure 6A-6B Two or more layers shown in can be implemented in a single layer, or Figure 6A-Figure 6B The single layer shown in can be implemented as multiple distributed layers. Additionally or alternatively, Figure 6A-6B A set of layers (eg, one or more layers) shown in FIG. 1 may perform the operations described as being performed by Figure 6A-6B Another set of layers shown in FIG performs one or more functions.

[0071] In some cases, the thickness of the dual cavity optical design may not be sufficient to reduce the modulation m2 of the second surface 302s2 of the multilayer optical structure 302. In such cases, the thickness of both the dual cavity design and the intermediate layer 512 may be used to provide a thickness that reduces the modulation m2 of the second surface 302s2. Figure 7 is a diagram illustrating an example of a gold dual-function pigment flake 300 formed using this combination of techniques.

[0072] In this example, a release layer 550 is coated on the substrate 350, which is then coated with an absorption layer 506a1, which is then coated with a transparent layer 508a1, an absorption layer 506a2, a transparent layer 508a2, and a reflective layer 510a. As shown, these layers form a dual-cavity first optical stack 504a of the multilayer optical structure 302. A magnetizable layer 514 (e.g., stainless steel or other suitable ferromagnetic material) is then deposited on the reflective layer 510a, and an intermediate layer 512 is formed on the magnetizable layer 514. It is noteworthy that in this example, the magnetizable layer 514 and the intermediate layer 512 serve as the faces of the multilayer optical structure 302. A second optical stack 504b is then formed on the magnetizable layer 514 by forming a reflective layer 510b, a transparent layer 508b1, an absorption layer 506b1, a transparent layer 508b2, and an absorption layer 506b2. Figure 7 Example thicknesses of the various layers are illustrated in the table shown in , which provides a total structure thickness of 1866 nm. Here, the modulation m1 of the first surface 302s1 is 80 nm, while the modulation m2 of the second surface 302s2 is 28 nm. This difference in the modulation of the surfaces of the multilayer optical structure 302 results in differences in the optical properties.

[0073] As indicated above, Figure 7 Provided as an example. Other examples may be related to Figure 7 The description is different. Figure 7 The number and arrangement of layers shown in FIG are provided as examples. In practice, there may be more than Figure 7 More layers, fewer layers, different layers, or differently arranged layers than shown in FIG. Figure 7 Two or more layers shown in can be implemented in a single layer, or Figure 7 The single layer shown in can be implemented as multiple distributed layers. Additionally or alternatively, Figure 7 A set of layers (eg, one or more layers) shown in FIG. 1 may perform the operations described as being performed by Figure 7 Another set of layers shown in FIG performs one or more functions.

[0074] Figure 8 is a flow chart of an example process 800 associated with the formation of the dual-function pigment flakes 300 described herein.

[0075] like Figure 8 As shown in , process 800 may include providing a substrate having a diffraction grating structure on a surface of the substrate (block 810). For example, substrate 350 may be provided having a diffraction grating structure on a surface of substrate 350, as described above.

[0076] like Figure 8 As further shown in FIG, process 800 may include forming a release layer on a surface of the substrate (block 820). For example, release layer 550 may be formed on a surface of substrate 350, as described above.

[0077] like Figure 8 As further shown in FIG, process 800 may include forming a first optical stack on a release layer, the first optical stack being formed such that a surface of the first optical stack has a relief of a diffraction grating structure (block 830). For example, the first optical stack 504a may be formed on the release layer 550, the first optical stack 504a being formed such that a first surface 302s1 of the first optical stack 504a has a relief of a diffraction grating structure, as described above.

[0078] like Figure 8 As further shown in FIG, process 800 may include forming a magnetizable layer over the first optical stack (block 840). For example, the magnetizable layer 514 may be formed over the first optical stack 504a, as described above.

[0079] like Figure 8 As further shown in FIG, process 800 may include forming a second optical stack over the magnetizable layer, the second optical stack being formed such that a modulation of a surface of the second optical stack is less than a modulation of a surface of the relief having a diffraction grating structure of the first optical stack (block 850). For example, a second optical stack 504b may be formed over the magnetizable layer 514, the second optical stack 504b being formed such that a modulation m2 of a second surface 302s2 of the second optical stack 504b is less than a modulation m1 of a first surface 302s1 of the relief having a diffraction grating structure of the first optical stack 504a, as described above.

[0080] like Figure 8 As further shown in FIG, process 800 may include removing a release layer to separate the substrate from the multilayer optical structure including the first optical stack, the magnetizable layer, and the second optical stack (block 860). For example, the release layer may be removed to separate substrate 350 from multilayer optical structure 302 including the first optical stack 504a, the magnetizable layer 514, and the second optical stack 504b, as described above.

[0081] Process 800 may include additional implementations, such as any single implementation or any combination of implementations described below and / or implementations related to one or more other processes described elsewhere herein.

[0082] In a first embodiment, the modulation m2 of the second surface 302s2 of the second optical stack 504b is at least 50% smaller than the modulation m1 of the first surface 302s1 of the first optical stack 504a having the diffraction grating structure relief.

[0083] In a second embodiment, either alone or in combination with the first embodiment, the process 800 includes forming an intermediate layer 512 associated with increasing the thickness of the dual-function pigment flake 300, the intermediate layer 512 being positioned between the first optical stack 504a and the second optical stack 504b.

[0084] In a third embodiment, alone or in combination with one or more of the first and second embodiments, process 800 includes forming an intermediate layer 512 associated with increasing the thickness of the dual-functional pigment sheet 300, the intermediate layer 512 being integrated into at least one of the first optical stack 504a or the second optical stack 504b.

[0085] although Figure 8 Example blocks of process 800 are shown, but in some embodiments, process 800 includes more Figure 8 More blocks, fewer blocks, different blocks, or differently arranged blocks than shown in . Additionally or alternatively, two or more blocks of process 800 can be executed in parallel.

[0086] In some implementations, the multilayer optical structure 302 described herein (e.g., a multilayer optical structure 302 having a thickness such that the second surface 302s2 is flatter than the first surface 302s1) enables the dual-function pigment flake 300 to exhibit diffraction colors within a first angular range (e.g., angles greater than approximately 45°) and interference colors within a second angular range (e.g., angles less than approximately 45°). This capability is provided because diffraction efficiency and total reflectivity are relatively balanced due to the first surface 302s1 having a relatively high modulation (e.g., to provide sufficient diffraction efficiency but low total reflectivity) and the second surface 302s2 having a relatively low modulation (e.g., to provide low diffraction efficiency but high total reflectivity), and the difference in modulation is due to the thickness of the dual-function pigment flake 300 such that the modulation m2 of the second surface 302s2 is less than the modulation m1 of the first surface 302s1.

[0087] The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the implementation to the precise form disclosed. Modifications and variations are possible in light of the above disclosure and can also be acquired from practice of the implementation.

[0088] As used herein, the term "component" is intended to be broadly interpreted as hardware, firmware, or a combination of hardware and software. Obviously, the systems and / or methods described herein can be implemented in different forms of hardware, firmware, and / or a combination of hardware and software. The actual dedicated control hardware or software code used to implement these systems and / or methods does not limit these implementations. Therefore, the operation and behavior of the systems and / or methods are described herein without reference to specific software code - it should be understood that the systems and / or methods can be implemented using software and hardware based on the description herein.

[0089] Although particular combinations of features are recited in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of the various implementations. In fact, many of these features can be combined in ways that are not explicitly recited in the claims and / or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of the various implementations includes the combination of each dependent claim with all other claims in the claim set. As used herein, a phrase referring to "at least one" in a list of items refers to any combination of those items, including single members. For example, "at least one of a, b, or c" is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination with multiples of the same item.

[0090] Unless clearly described, otherwise any element, action or instruction used in this article should not be interpreted as key or necessary.In addition, as used in this article, the article " one " and " an " are intended to include one or more projects, and can be used interchangeably with " one or more ".In addition, as used in this article, the article " the " is intended to include one or more projects quoted in relation to the article " the ", and can be used interchangeably with " the one or more ".In addition, as used in this article, the term " group " is intended to include one or more projects (for example, related projects, unrelated projects or the combination of related and unrelated projects), and can be used interchangeably with " one or more ".When referring only to a project, phrase " only one " or similar language is used.In addition, as used in this article, the term " has ", " has ", " has " etc. are intended to be open term.In addition, unless otherwise clearly stated, phrase " based on " is intended to mean " at least partially based on ".In addition, as used in this article, the term " or " is intended to have inclusiveness when used in a series, and can be used interchangeably with " and / or ", unless otherwise clearly stated (for example, if used in combination with " either " or " only one of them ").

Claims

1. A pigment flake comprising: Multi-layer optical structure, including: a first surface having a first modulation corresponding to a relief of a diffraction grating; and a second surface having a second modulation, the second surface being opposite to the first surface and the second modulation being smaller than the first modulation, such that the second surface is relatively flatter than the first surface, The multilayer optical structure exhibits diffraction colors for a first angle range of the multilayer optical structure with respect to an angle of incident light, and exhibits interference colors for a second angle range of the multilayer optical structure with respect to an angle of incident light. 2 . The pigment flake of claim 1 , wherein the second modulation is at least 50% smaller than the first modulation. 3 . The pigment flake of claim 1 , wherein a surface of a layer of the multilayer optical structure located between the first surface and the second surface has a third modulation that is less than the first modulation and greater than the second modulation.

4. The pigment flake of claim 1, wherein the multilayer optical structure comprises an intermediate layer positioned between a first optical stack of the multilayer optical structure and a second optical stack of the multilayer optical structure. 5 . The pigment flake of claim 4 , wherein the intermediate layer has a thickness in a range from about 100 nanometers (nm) to about 2000 nm.

6. The pigment flake of claim 1, wherein the multilayer optical structure comprises an optical stack including a transparent layer having a thickness selected to reduce the second modulation of the second surface compared to the modulation of the first surface. 7 . The pigment flake of claim 6 , wherein the transparent layer of the optical stack has a thickness in a range from about 50 nanometers (nm) to about 1500 nm.

8. The pigment flake of claim 1, wherein the multilayer optical structure has a thickness in a range from about 400 nanometers to about 3 micrometers.

9. The pigment flake of claim 1, wherein the first angular range includes angles greater than about 45 degrees.

10. The pigment flake of claim 1, wherein the second angular range comprises angles less than about 45 degrees.

11. The pigment flake of claim 1 , wherein the multilayer optical structure comprises at least one pair of symmetrical optical stacks.

12. The pigment flake of claim 1, wherein the multilayer optical structure comprises at least one pair of asymmetric optical stacks.

13. The pigment flake of claim 1, wherein the multilayer optical structure comprises at least one single cavity optical stack.

14. The pigment flake of claim 1, wherein the multilayer optical structure comprises at least one dual-cavity optical stack.

15. A method of forming a dual-function pigment flake, comprising: providing a substrate having a diffraction grating structure on a surface of the substrate; forming a release layer on the surface of the substrate; forming a first optical stack on the release layer, the first optical stack being formed such that a surface of the first optical stack has a relief of the diffraction grating structure; forming a magnetizable layer over the first optical stack; forming a second optical stack over the magnetizable layer, the second optical stack being formed such that a modulation of a surface of the second optical stack is smaller than a modulation of a surface of the first optical stack having the relief of the diffraction grating structure; as well as The release layer is removed to separate the substrate from a multilayer optical structure including the first optical stack, the magnetizable layer, and the second optical stack.

16. The method of claim 15, wherein the modulation of the surface of the second optical stack is at least 50% less than the modulation of the surface of the first optical stack having the relief of the diffraction grating structure.

17. The method according to claim 15, further comprising: An intermediate layer associated with increasing the thickness of the dual-function pigment flake is formed, the intermediate layer being positioned between the first optical stack and the second optical stack.

18. The method according to claim 15, further comprising: An intermediate layer associated with increasing the thickness of the bifunctional pigment flake is formed, the intermediate layer being integrated into at least one of the first optical stack or the second optical stack.

19. A dual-function pigment flake comprising: a first optical stack, wherein a surface of the first optical stack has a first modulation; a magnetizable layer positioned above the first optical stack; as well as a second optical stack over the magnetizable layer, wherein a surface of the second optical stack has a second modulation that is less than about half of the first modulation, The first optical stack and the second optical stack enable the dual-functional pigment sheet to exhibit diffraction color for a first angle range of the dual-functional pigment sheet with respect to the incident light angle, and to exhibit interference color for a second angle range of the dual-functional pigment sheet with respect to the incident light angle.

20. The dual-function pigment flake of claim 19, wherein the modulation of a surface within the pigment flake decreases in a direction from a surface of the first optical stack to a surface of the second optical stack.

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