CN113881272A

CN113881272A - Pigment flakes, coatings and security articles

Info

Publication number: CN113881272A
Application number: CN202111070802.6A
Authority: CN
Inventors: 徐明权; 向杰; 石斌; 牛亮亮; 潘硕
Original assignee: Huizhou Foryou Optical Technology Co ltd
Current assignee: Huizhou Foryou Optical Technology Co ltd
Priority date: 2021-09-13
Filing date: 2021-09-13
Publication date: 2022-01-04

Abstract

Pigment flakes, coatings, and security articles are disclosed. The pigment flake includes at least one optical interference structure; wherein the reflective properties of the optical interference structures are configured such that at least some of the reflective peaks of the pigment flakes shift from a predetermined band of visible light to outside the band of visible light when the viewing angle changes from a first angle to a second angle, such that the pigment flakes appear colored at the first angle and the pigment flakes appear uncolored at the second angle. The application can increase the color change range of the pigment flakes.

Description

Pigment flakes, coatings and security articles

Technical Field

The application relates to the technical field of optical discoloration, in particular to pigment flakes, paint and anti-counterfeiting products.

Background

The optically variable structure has a color change phenomenon related to the observation angle, and the observer can observe different colors at different angles, particularly, the optically variable structure can show obviously different colors when observing at an angle of 0 degree or 60 degrees or so with the normal direction of the surface of the optically variable structure, and the phenomenon is called flop. For example, color change phenomena such as green to red, red to green, green to blue, etc. can be obtained according to specific optical designs. And the color change phenomenon cannot be reproduced by common counterfeiting methods such as color reproduction equipment, electronic color separation plate making, rubbing and the like. Therefore, the optical color-changing material can be used as an effective anti-counterfeiting means for currency, bank notes, secret documents and anti-counterfeiting labels. Most of the printed currency in the world is protected against forgery by the photochromic material.

During long-term research and development, the inventors of the present application found that the demand for pigment flakes having color flop is increasing, and the color change range of the pigment flakes in the prior art is smaller.

Disclosure of Invention

It is a primary object of the present application to provide pigment flakes, coatings and security articles that increase the color shifting range of the pigment flakes.

In order to achieve the purpose, the technical scheme adopted by the application is as follows: providing a pigment flake comprising at least one optical interference structure;

wherein the reflective properties of the optical interference structures are configured such that at least some of the reflective peaks of the pigment flakes shift from a predetermined band of visible light to outside the band of visible light when the viewing angle changes from a first angle to a second angle, such that the pigment flakes appear colored at the first angle and the pigment flakes appear uncolored at the second angle.

Wherein,

under a first angle of observation, the reflectivity of the pigment flakes in the visible light band is higher than the reflectivity outside the visible light band;

the pigment flakes have a reflectivity outside the visible band that is higher than the reflectivity in the visible band at a second angle of view.

Wherein,

under the observation angle of a second angle, the pigment flake does not have a main reflection peak in a visible light wave band, the reflectivity of a secondary reflection peak is less than 15%, and the number of the secondary reflection peaks is less than 5.

Wherein,

under a first angle of observation, the pigment flake has a main reflection peak with a reflectivity of more than 50% in a visible light wave band, and the number of secondary reflection peaks is less than 5.

Wherein the visible light wave band is 400nm-630 nm.

The optical interference structure comprises metal layers and dielectric layers which are alternately stacked, and the metal layers and the dielectric layers are matched to form a Fabry-Perot interference structure.

Wherein the thickness of the metal layer is 1-12nm, and the thickness of the dielectric layer is 200-400 nm.

Wherein, the total number of layers of the metal layer and the dielectric layer is 5-21.

Wherein the pigment flake further comprises a reflective layer having an optical interference structure disposed on at least one major surface thereof.

The pigment flake further comprises at least two magnetic layers, the magnetic layers are arranged between two adjacent layers of the reflecting layers, and the optical interference structure is arranged on the main surface of the reflecting layer on the outermost side, which is far away from the magnetic layers.

The optical interference structure comprises a first medium layer and a second medium layer which are alternately stacked, and the absolute value of the difference value of the refractive index of the first medium layer and the refractive index of the second medium layer is within the range of 0.2-1.5.

The optical thickness of the first dielectric layer is 0.5-5 QWOT of 380-780 nanometer, and/or the optical thickness of the second dielectric layer is 0.5-5 QWOT of 380-780 nanometer.

Wherein the first angle is between 0 and 15 degrees of an angle of intersection between the viewing angle and a direction normal to the major surfaces of the pigment flakes and the second angle is between 30 and 60 degrees of an angle of intersection between the viewing angle and a direction normal to the major surfaces of the pigment flakes.

Wherein the ratio of the L value of the pigment flakes as measured by the colorimeter at a first angle of view to the L value of the flakes as measured by the colorimeter at a second angle of view is greater than 6.

In order to achieve the above object, the present application also provides a coating material comprising a base solvent and the above pigment flakes doped in the base solvent.

In order to achieve the purpose, the application also provides a false proof product which comprises a product body and the paint applied on the product body.

Compared with the prior art, the application realizes the non-color change by setting the reflection characteristics of the optical interference structures in the pigment flakes, namely when the observation angle is changed from a first angle to a second angle, at least part of reflection peaks of the pigment flakes are shifted to the outside of a preset visible light wave band, so that the pigment flakes can present color at the first angle and present non-color at the second angle; therefore, the pigment flake has better cleaning, environmental protection and weather resistance due to the characteristic of structural color, has the advantage of stronger controllability in the attenuation process of a reflection peak in a visible light spectrum region in the process from color to non-color, and has the characteristic of being more natural in the color changing process.

Drawings

Fig. 1 is a schematic structural view of one embodiment of a pigment flake of the present application;

fig. 2 is a graph of the reflectance spectrum of the pigment flake shown in fig. 1;

fig. 3 is a schematic structural view of another embodiment of a pigment flake according to the present application;

fig. 4 is a graph of the reflectance spectrum of the pigment flake shown in fig. 3.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It should be noted that if directional indications (such as up, down, left, right, front, and back … …) are referred to in the embodiments of the present application, the directional indications are only used to explain the relative positional relationship between the components, the movement situation, and the like in a specific posture (as shown in the drawings), and if the specific posture is changed, the directional indications are changed accordingly.

In addition, if there is a description of "first", "second", etc. in the embodiments of the present application, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present application.

The present application provides pigment flakes that can achieve a color change from chromatic to achromatic with a change in viewing angle, with an increased color shift range over prior art pigment flakes that can only change between colors (e.g., red to green, green to blue, or red to gold, etc.).

It will be understood that "achromatic" in the present application refers to white, black and various shades of grey, which may form a series of colors, gradually from white to light grey, then to medium grey and then to dark grey, until black, and that this series, called black and white series, may be represented by a line, one end being pure white, the other end being pure black, and the middle being various intermediate shades of grey. Chromatic refers to colors other than the black and white series, including all colors in the visible spectrum and gray with some color propensity.

Although there are optical variable units that can realize black front view and color side view. However, this kind of light-variable unit is formed by adding selective absorptive material into a common light-variable structure (the common light-variable structure refers to a light-variable structure whose color-variable range can only be changed in the color range), so that under the front-view condition, the visible spectral components reflected by the light-variable pigment under the vertical incidence angle are shielded, and the black appearance is displayed under the front-view condition, and the color appearance is displayed under the side-view condition.

The non-color change achieved by the selective absorbing material is more by the perception of the human eye, is not true color black in nature, can also be understood as the functional perception of common optical effect produced by the combination of the light absorbing material and the optically variable pigment, and can only achieve the front view black effect by adding a few and kinds of selective absorbing materials, which is not a matter easy to control per se, and the process is complicated, is not beneficial to industrial production, and in the non-color change achieved by the non-color changing material, such as black to color, either the front side is not black enough, the texture is lacking, or the bright side color cannot be guaranteed, and the color changing process is very abrupt, and the aesthetic requirement of the pigment cannot meet the requirement of high-end application; in addition, the color saturation of the optically variable unit is relatively low, because the selective absorptive pigment cannot completely realize the selective absorption, namely, the pigment can only realize the full absorption for a certain wavelength under a certain viewing angle, but when the angle is changed, the optical path difference is changed, and the pigment must generate different degrees of absorption for other wavelengths, so that when the color is required to be displayed, the pigment is inevitably influenced by the absorptivity of an absorbing material, and the color saturation, even the hue, of the optically variable pigment is reduced; in addition, since the absorption effect of the selective absorbing material needs to be reduced in the side view, so that the optical variable unit can be colored in the side view, the selective absorbing material needs to be prevented from being flaky, otherwise, the selective absorbing material can cover the side view, and the color display in the side view is affected, so that strong diffuse reflection can be generated on a non-colored display surface (namely, when the optical variable unit is viewed frontwards), the non-colored texture is greatly reduced, particularly the metal feeling is reduced, and the application of the pigment in high-end fields such as piano lacquer and the like is limited; and the cleaning, environmental protection and weather resistance of the optical variable unit are not enough. The pigment (selective absorbing material) has inevitable defects in oxidation resistance and severe environments such as acid resistance and alkali resistance, so the technical scheme in the prior art has obvious defects in cleanliness and weather resistance compared with the pigment with a structural color structure because of the existence of the pigment (selective absorbing material).

Unlike the above-described approach of achieving achromatic color by selective absorption of materials, the present application achieves achromatic color by setting the reflection characteristics of the optical interference structures in the flakes such that at least some of the reflection peaks of the flakes shift from a predetermined visible band to outside the visible band when the viewing angle changes from a first angle to a second angle, thereby achieving chromatic color at the first angle and achromatic color at the second angle; therefore, the pigment flake has better cleaning, environmental protection and weather resistance due to the characteristic of structural color, has the advantage of stronger controllability in the attenuation process of a reflection peak in a visible light spectrum region in the process from color to non-color, and has the characteristic of being more natural in the color changing process.

Taking as an example that "first angle" and "second angle" are used to describe angles between the viewing angle and the normal to the major surfaces of the flakes, the first angle can be greater than the second angle, and the second angle can be greater than the first angle, without limitation, with respect to the optical interference structures of the flakes. For example, when viewing a pigment flake at an angle of 0 ° to 15 ° from normal to a major surface of the a pigment flake, the a pigment flake appears colored, and when viewing the a pigment flake at an angle of 30 ° to 60 ° from normal to a major surface of the a pigment flake, the a pigment flake appears achromatic, the a pigment flake can have a first angle in the range of 0 ° to 15 °, and the a pigment flake can have a second angle in the range of 30 ° to 60 °, i.e., the first angle of the a pigment flake is less than the second angle. For another example, when viewing B flakes at an angle of 20 ° to 60 ° from normal to the major surfaces of the B flakes, the B flakes appear colored, and when viewing the B flakes at an angle of 0 ° to 10 ° from normal to the major surfaces of the B flakes, the B flakes appear uncolored, the first angle of the B flakes can range from 20 ° to 30 °, the second angle of the B flakes can range from 0 ° to 10 °, i.e., the first angle of the B flakes is greater than the second angle.

In addition, as can be seen from the above description, the present application shifts the reflection spectrum by the change of the optical path difference, that is, by adjusting the frequency shift range of the reflection spectrum when the pigment flakes change from the first angle to the second angle, at least a part of the reflection peaks of the pigment flakes shift from the preset visible light band to outside the visible light band when the observation angle changes from the first angle to the second angle, thereby realizing the change from color to non-color. To ensure that the flakes achieve a chromatic to achromatic color cross-over, the flakes of the present application can have a wide range of frequency shifts from a first angle to a second angle. For example, the flakes exhibit a blue color at a first angle (e.g., 0 °), and the flakes can shift in frequency by greater than or equal to 50nm to ensure that at least a portion of the emission peak can blue-shift from within the visible band of light to outside the visible band of light, such that the flakes can exhibit an achromatic color at a second angle (e.g., 60 °), where the color of the flakes would otherwise only change in the chromatic region, and no chromatic to achromatic change is achieved. As another example, the flakes can exhibit an orange color at a first angle (e.g., 50 °), and the flakes can shift in frequency in a range greater than or equal to 100nm to ensure that at least a portion of the emission peak can be red-shifted from within the visible band of light to outside the visible band of light, such that the flakes can exhibit an achromatic color at a second angle (e.g., 0 °), where the color of the flakes would otherwise only change in the chromatic region, and no chromatic to achromatic change would be achieved.

It is understood that the preset visible light band of the present application may be a commonly understood visible light band, i.e. 400-700 nm; or may be a predetermined wavelength band, such as 400nm to 630 nm.

Alternatively, the flakes can have a reflectivity in the visible wavelength band that is higher than a reflectivity outside the visible wavelength band at a first angle of view, i.e., the flakes can exhibit a distinct color at the first angle by configuring the reflective properties of the optical interference structures such that the flakes reflect a substantial amount of visible light at the first angle.

Further, at a first angle of view, the reflectivity of all peaks of the pigment flake in the visible wavelength band can be higher than the reflectivity of any peak outside the visible wavelength band, i.e., the light reflected by the pigment flake at the first angle is almost visible.

In addition, the inventors have found, through long-term research, that, under the observation angle of the first angle, the stronger the interference main peak at the visible light wavelength band (for example, more than 50%), the smaller the number of secondary peaks, the narrower the half-peak width, the purer the hue of the color to be displayed, the higher the color saturation, and when there are more secondary peaks, for example, 5, the composite color appears, which is reflected in poor color purity and lightness. The reflection properties of the optical interference structures of the present application can thus be set as: the pigment flakes have primary reflection peaks with a reflectivity of greater than 50% in a visible light band at a first angle, and the number of secondary reflection peaks is less than 5, such that the pigment flakes exhibit purer color and higher color saturation at the first angle.

Optionally, the reflectivity of the pigment flakes outside the visible light band is higher than the reflectivity of the pigment flakes within the visible light band at the viewing angle of the second angle by setting the reflective properties of the optical interference structure to increase the reflectivity of the pigment flakes outside the visible light band at the second angle and suppress the reflectivity of the pigment flakes within the visible light band at the second angle, such that a substantial amount of non-visible light is reflected by the pigment flakes at the second angle, such that the pigment flakes appear substantially achromatic at the second angle. Further, at the viewing angle of the second angle, the reflectance of all the reflection peaks of the pigment flakes outside the visible light band may be higher than the reflectance of any one of the reflection peaks in the visible light band, i.e., the light reflected by the pigment flakes at the second angle is almost invisible.

In addition, the inventor has found through long-term research that, under the observation angle of the second angle, the number of the appearing secondary peaks in the visible light variable waveband is less or no secondary peak, and the lower the highest reflectivity of the secondary peak in the visible light variable waveband is, the higher the displayed non-chromatic degree is, for example, when 5 secondary peaks appear, the highest reflectivity of which is 15%, the color displayed in side view is gray which is slightly colorful in the primary color, and when no secondary peak exists, the color displayed in side view is black. The reflection properties of the optical interference structures of the present application can thus be set as: the pigment flakes do not have a primary reflection peak within the visible light band at the second angle, the reflectivity of the secondary reflection peak is less than 15%, and the number of the secondary reflection peaks is less than 5, so that the pigment flakes exhibit a high degree of non-colorfulness at the second angle.

The present application provides the following two embodiments for changing between achromatic and chromatic regions of a pigment flake by frequency shifting of the reflection spectrum, which are not limited to these embodiments.

The first embodiment:

the optical interference structure includes metal layers and dielectric layers alternately stacked. The metal layer and the dielectric layer are matched to form a Fabry-Perot interference structure.

Although the macroscopic structure is a common optical interference structure, the difficulty of the existing process must be overcome, and the delicate thickness and material of each layer must be matched, because in the multilayer optical film, the influence of the material, the number of layers and the thickness on the interference effect is extremely large, and the influence is more obvious as the number of layers increases, so that the proper material, the optical interference structure and the thickness of each interference layer need to be selected, and the synergistic effect of all the factors can be combined to realize the spectrum curve of the special color change effect of the pigment.

Further, the inventors have found in practice that the order of the color changes generally follows a blue shift law, i.e. generally in the order red, orange, yellow, green, indigo, blue, violet, when viewed from a front to a side view. To achieve that only a specific color appears during the front-view to side-view process, such as red changing to green, and orange, yellow, etc., do not appear in the middle, it is often very difficult, and therefore the inventors of the present application precisely control the setting parameters (e.g., the number of layers, the thickness and material of each layer, etc.) of the pigment flakes, so that only a specific color appears during the front-view to side-view process, and no intermediate color appears. Specifically, the pigment flakes of example 1 tend to have a purple color when changing from blue to black, and by providing two dielectric layers on the outer surfaces of the pigment flakes of example 1 (i.e., the pigment flakes of example 2), only blue and black colors are present and intermediate colors such as purple (i.e., colors other than blue and black) are not present when viewing from front to side, i.e., the present application can suppress the presence of intermediate colors by precisely controlling the setting parameters of the pigment flakes. The pigment flakes for suppressing the appearance of the intermediate color are not limited to the pigment flakes of embodiment 2, and are not repeated herein.

Specifically, in the embodiment, the reflection spectrum characteristics of the fabry-perot interference structure are controlled by controlling the structural characteristics such as the thicknesses and the number of layers of the metal layers and the dielectric layers in the fabry-perot interference structure, so that the reflection of the pigment flakes in the visible light band at the second angle is suppressed, and the reflection of the pigment flakes outside the visible light band at the second angle is enhanced, so that when the observation angle is changed from the first angle to the second angle, at least part of the reflection peak of the pigment flakes shifts from the preset visible light band to the outside of the visible light band, and thus the pigment flakes realize the change from color to non-color.

The thickness of the metal layer may be 1-12nm, for example, 3nm, 5nm or 8 nm. The thickness of the dielectric layer may be 200-400nm, such as 210nm, 270nm or 350 nm.

The total number of the metal layers and the dielectric layers in the Fabry-Perot interference structure is 4-20, and the Fabry-Perot interference structure can be 2 layers, 4 layers, 6 layers, 8 layers, 10 layers and the like.

By setting the thicknesses and the number of layers of the metal layer and the dielectric layer to the above conditions, at least part of the reflection peak of the pigment flake shifts from a preset visible light waveband to the outside of the visible light waveband when the observation angle is changed from a first angle to a second angle, so that the pigment flake realizes the change from color to non-color.

In addition, the metal layer may be made of at least one of chromium, nickel, titanium, copper, germanium, silicon, and the like. The dielectric layer may be made of at least one of silicon dioxide, magnesium fluoride, titanium dioxide, aluminum oxide, magnesium oxide, silicon monoxide, and the like.

In addition, the pigment flake in this embodiment may further include a reflective layer, and at least one major surface of the reflective layer is provided with an optical interference structure, so as to ensure that light emitted to the reflective layer through the optical interference structure is reflected by the reflective layer, thereby improving color brightness of the pigment flake.

The reflecting layer can be made of at least one of aluminum, silver, copper, chromium, iron, cobalt, nickel, titanium, silicon and silver.

The thickness of the reflective layer may be between 10-30nm, for example 12nm, 16nm, 18nm, 23nm, 27nm, or the like.

Optionally, in this embodiment, a magnetic layer may be further added to achieve the optical change characteristic from chromatic to achromatic, and the magnetic layer may also have magnetic properties, so that the pigment flakes may be oriented by a dynamic magnetic field during printing, thereby achieving a 3D effect, and further having a magnetic recording function. The magnetic layer of this embodiment may be provided in the vicinity of the reflective layer, but is not limited thereto. For example, the number of the reflecting layers in the pigment flake is at least two, the magnetic layer is arranged between two adjacent reflecting layers, and the optical interference structure is arranged on the main surface of the outermost reflecting layer away from the magnetic layer.

The magnetic layer can be made of iron, cobalt, nickel, gadolinium, terbium, dysprosium, erbium, alloys thereof or oxides thereof, and the like. For example, the magnetic layer may be an iron-silicon alloy, an iron-aluminum alloy, an iron/silicon/chromium alloy, or an iron/nickel/molybdenum alloy.

The thickness of the magnetic layer may be between 10-60nm, for example, 13nm, 16nm, 18nm, 26nm, 32nm, 40nm, 48nm, 56nm, or the like.

In addition, in this embodiment, at least one of the optical interference structure and the reflective layer may be doped with materials such as electrochromic material, photochromic material, temperature-sensitive material, fluorescent material, or infrared absorbing material, or may be replaced with materials such as electrochromic material, photochromic material, temperature-sensitive material, fluorescent material, or infrared absorbing material, so that the pigment flake of this embodiment has a function of displaying different colors under excitation of specific wavelengths such as ultraviolet light in addition to the function of changing colors into non-colors.

The second embodiment:

the optical interference structure includes first and second dielectric layers alternately stacked. Wherein the absolute value of the difference between the refractive index of the first dielectric layer and the refractive index of the second dielectric layer is 0.2-1.5 (e.g., 0.4 or 0.9, etc.). When the interference structure completely selects all dielectric materials, the difference value of the refractive index of the first dielectric layer and the refractive index of the second dielectric layer is controlled, so that when the observation angle is changed from a first angle to a second angle, at least part of reflection peaks of the pigment flakes shift from a preset visible light waveband to the outside of the visible light waveband, and the pigment flakes realize the change from color to non-color.

The first dielectric layer and the second dielectric layer can be made of at least one of lanthanum titanate, titanium dioxide, hafnium dioxide, zinc sulfide, silicon dioxide, magnesium fluoride, magnesium oxide, aluminum fluoride and cryolite.

In addition, the optical thickness of each of the first dielectric layer and the second dielectric layer is controlled within the range of 0.5-5 QWOT (quarter-wavelength optical thickness) of 380-780 nm, so that the reflection and cut-off band characteristics of the pigment sheet in a visible light wave band at a second angle are inhibited, the number of secondary peaks and the highest reflection peak of the secondary peaks are regulated and controlled, and the uncolored degree of the pigment sheet at the second angle is high. Wherein, the relation between QWOT and the physical thickness d is as follows: QWOT is 4nd/λ, n is the refractive index, d is the physical thickness, and λ is the reference wavelength.

The following specific examples of pigment flakes are provided to illustrate the pigment flakes of the present application. Wherein examples 1 and 2 describe the pigment flake of the first embodiment and examples 3 and 4 describe the pigment flake of the second embodiment.

The pigment flakes of the above embodiments can be prepared by physical vapor deposition, chemical vapor deposition, sol-gel, dipping, and the like.

Alternatively, the pigment flakes of the various embodiments described above can be dispersed in a liquid phase system, i.e., can be mixed with a base solvent to form a coating or ink, etc.

Of course, the paint or ink containing the pigment flakes can be coated on the body of the product to prepare anti-counterfeiting products such as currency, invoices, securities, certificates, trademarks and the like. Alternatively, the coatings or inks containing the pigment flakes of the present application can be used as colorants for application to articles such as toys.

Further, the coatings or inks comprising the pigment flakes of the present application can be used to make … …, for example, nail polish, eye shadow, automotive or architectural coatings, and the like, but are not limited thereto.

Example 1:

as shown in fig. 1, the pigment flake 100 has a structure of metal layer 110, dielectric layer 120, reflective layer 130, dielectric layer 120, metal layer 110, dielectric layer 120, and metal layer 110.

Wherein the dielectric layer 120 is made of SiO₂The metal layer 110 is made of Cr and the reflective layer is made of Al.

The thicknesses are respectively as follows: 5nm/320nm/6nm/310nm/13nm/320nm/50nm/320nm/13nm/310nm/6nm/320nm/5 nm.

After the film plated according to the film system is crushed, the front surface (namely the first angle is 0-15 ℃) is blue, and the side surface (namely the first angle is 30-60 ℃) is black. The spectral curve of example 1 is shown in fig. 2, and when viewed from the front, the reflectance is strongest near 450nm, showing blue; in the side view, the reflection peak at 450nm under the front view observation angle is blue-shifted to be within the range of 300-380nm, and the reflection peak at about 840nm under the front view observation angle is blue-shifted to be 780nm, namely the overall reflectivity of the visible light wave band in the side view is less than 10 percent, and the visible light wave band is black, although the reflectivity is enhanced near 720nm, the wave band is a near infrared wave band which is invisible to human eyes, so that the color observed in the side view is black. That is, the pigment flake of example 1 appeared blue on the front and black on the sides, with essentially no secondary peaks. In addition, through multiple tests, when the reflectivity of the secondary peak is less than 15 percent and the total number is less than 5, the black color is kept when viewed from side. The embodiment utilizes the synergistic effect of multiple Fabry-Perot interference cavities, so that constructive interference in a specific waveband of visible light is enhanced in front view, reflection in the visible waveband is reduced in side view, and absorption is enhanced.

Example 2:

pigment flake 100 has the structure of dielectric layer 120/metal layer 110/dielectric layer 120/reflective layer 130/dielectric layer 120/metal layer 110/dielectric layer 120/metal layer 110/dielectric layer 120.

The thicknesses are respectively as follows: 160nm/5nm/320nm/6nm/310nm/13nm/320nm/50nm/320nm/13nm/310nm/6nm/320nm/5nm/160 nm.

In this example, a dielectric layer was added to each of the opposite outer surfaces of the pigment flake of example 1, and compared to example 1, the pigment flake of this example, when pulverized as a thin film plated in this film system, exhibited a blue color on the front side (i.e., first angle of 0 to 15 °), and a black color on the side (i.e., first angle of 30 to 60 °), and only blue and black colors appeared and no intermediate colors such as violet (i.e., colors other than blue and black colors) appeared during the viewing angle from front to side.

Example 3:

the pigment flake has the structure of metal layer/dielectric layer/reflective layer/dielectric layer/metal layer/dielectric layer/metal layer. The dielectric layer material is WO₃The metal material is Ti, the reflecting layer material is Al, and the thicknesses are respectively as follows: 4nm/340nm/5nm/330nm/10nm/310nm/50nm/320nm/10nm/330nm/5nm/340nm/4nm, the front side of the film is yellow, the side is black, and the front side of the film is green and the side is dark green or gray after being irradiated by ultraviolet light. The intensity of the color produced by light excitation is stronger by applying a difference in the intensity of the ultraviolet light.

Example 4:

as shown in fig. 3, the pigment flake 200 has a structure of first dielectric layer 210/second dielectric layer 220/first dielectric layer 210.

The dielectric layer is made of SiO₂The dielectric layer is made of TiO₂I.e., the pigment flake 200 is SiO in structure₂/TiO₂/SiO₂/TiO₂/SiO₂/TiO₂/SiO₂。

The thicknesses of the layers in the pigment flake 200 are, in order: 100nm/210nm/210nm/40nm/210nm/210nm/100 nm.

Plating multiple layers of films according to the film system structure, breaking after separation, and obtaining the pigment with blue front view and black side view. As shown in fig. 4, the front view spectral reflectance curve of example 3 exhibited a peak reflectance of 85% at 410nm, only one secondary peak between 450 and 700nm, and a secondary peak reflectance of 15% at 510nm, so that the pigment flake of example 4 appeared blue at a front view viewing angle. As can be seen by comparing the front view spectral reflectance curve and the side view spectral reflectance curve in FIG. 4, the pigment flake of example 4 was seen to have a 780nm peak blue-shifted to 720nm at a front view angle, a 510nm peak blue-shifted to 460nm at a front view angle, and a 410nm peak blue-shifted to 340nm at a front view angle. Thus, the side-view spectral reflectance curve of example 4 has only a small secondary peak within the predetermined visible light band (e.g., at 630nm 400-), i.e., a 12% secondary peak at 460nm, such that the pigment flake of example 4 appears gray under side-view viewing angles. The pigment flakes of example 4 were viewed as blue and as gray from the side.

Example 5:

the structure of the pigment flake is first dielectric layer/second dielectric layer/first dielectric layer.

The dielectric layer is made of SiO₂The dielectric layer is made of TiO₂I.e. the structure of the pigment flakes is SiO₂/TiO₂/SiO₂/TiO₂/SiO₂/TiO₂/SiO₂。

The optical thickness of each layer in the pigment flake is 1.0\3.6\2.3\0.7\2.3\3.6\1.0 QWOT at 550nm in sequence.

Plating multiple layers of films according to the film system structure, breaking after separation, and obtaining the pigment with blue front view and black side view.

In addition, the pigment flakes of the above examples have an L value greater than 90 when measured with a BYK colorimeter at a first angle of view (e.g., 0 °), and less than 15 when measured with a BYK colorimeter at a second angle of view (e.g., 50 °). I.e., the ratio of the L value of the pigment flakes as measured by the colorimeter at a first angle of view to the L value of the flakes as measured by the colorimeter at a second angle of view is greater than 6.

The above embodiments are merely examples, and not intended to limit the scope of the present application, and all modifications, equivalents, and flow charts using the contents of the specification and drawings of the present application, or those directly or indirectly applied to other related arts, are included in the scope of the present application.

Claims

1. A pigment flake, comprising:

at least one optical interference structure;

2. The pigment flake of claim 1,

the pigment flakes have a reflectivity in the visible light band that is higher than a reflectivity outside the visible light band at the first angle of view;

the pigment flakes have a reflectivity outside the visible wavelength band that is higher than a reflectivity within the visible wavelength band at the second angle of view.

3. The pigment flake of claim 2,

under the observation angle of the second angle, the pigment flake does not have a main reflection peak in the visible light wave band, the reflectivity of a secondary reflection peak is less than 15%, and the number of the secondary reflection peaks is less than 5.

4. The pigment flake of claim 3,

under the observation angle of the first angle, the pigment flake has main reflection peaks with the reflectivity higher than 50% in the visible light wave band, and the number of the secondary reflection peaks is less than 5.

5. The pigment flake of claim 4, wherein the visible wavelength range is from 400nm to 630 nm.

6. The pigment flake of claim 1, wherein the optical interference structures comprise alternating stacked layers of metal and dielectric that cooperate to form a fabry-perot interference structure.

7. The pigment flake of claim 6, wherein the metal layer has a thickness of 1-12nm and the dielectric layer has a thickness of 200-400 nm.

8. The pigment flake of claim 7, wherein the total number of metal layers and dielectric layers is from 5 to 21.

9. The pigment flake of claim 6, further comprising a reflective layer having the optical interference structure disposed on at least one major surface.

10. The pigment flake of claim 9, further comprising at least two magnetic layers, wherein the magnetic layers are disposed between two adjacent reflective layers, and wherein the optical interference structure is disposed on a major surface of the outermost reflective layer facing away from the magnetic layers.

11. The pigment flake of claim 1, wherein the optical interference structure comprises alternating layers of first and second dielectric layers, the first dielectric layer having a refractive index that differs from the second dielectric layer by an absolute value in a range of 0.2-1.5.

12. The pigment flake of claim 11, wherein the first dielectric layer has an optical thickness of 0.5-5 QWOT at 380-780 nm and/or the second dielectric layer has an optical thickness of 0.5-5 QWOT at 380-780 nm.

13. The pigment flake of claim 1, wherein the first angle is between 0 degrees and 15 degrees at an angle of intersection between the viewing angle and a direction normal to a major surface of the flake and the second angle is between 30 degrees and 60 degrees at an angle of intersection between the viewing angle and a direction normal to a major surface of the flake.

14. The pigment flake of claim 1, wherein the pigment flake exhibits a ratio of L-value measured with a colorimeter at a first angle of view to L-value measured with a colorimeter at a second angle of view of greater than 6.

15. A coating comprising a base solvent and the pigment flake of any of claims 1-14 doped in the base solvent.

16. A security article comprising an article body and the coating of claim 15 applied to the article body.