CN111823749B

CN111823749B - Optical anti-counterfeiting element, manufacturing method thereof and optical anti-counterfeiting product

Info

Publication number: CN111823749B
Application number: CN201910319695.2A
Authority: CN
Inventors: 张巍巍; ***; 朱军
Original assignee: China Banknote Printing and Minting Corp; Zhongchao Special Security Technology Co Ltd
Current assignee: Zhongchao Special Security Technology Co Ltd; China Banknote Printing and Minting Group Co Ltd
Priority date: 2019-04-19
Filing date: 2019-04-19
Publication date: 2022-02-25
Anticipated expiration: 2039-04-19
Also published as: CN111823749A

Abstract

The embodiment of the invention provides an optical anti-counterfeiting element, a manufacturing method thereof and an optical anti-counterfeiting product, and belongs to the field of anti-counterfeiting. The optical security element comprises: a substrate; the surface relief structure layer is positioned on the substrate and comprises at least a first area and a second area which are not overlapped with each other, the first area comprises a first grating microstructure, the second area comprises a second grating microstructure, the first grating microstructure is composed of a third grating microstructure and a filling layer covered on the surface of the third microstructure, the depth-to-width ratio of the third grating microstructure is larger than that of the second grating microstructure, the refractive index of the filling layer and the refractive index of the third grating microstructure meet preset conditions, a second reflection coating is covered on the first grating microstructure in the same shape, and a first reflection coating different from the second reflection coating is covered on the second grating microstructure in the same shape. The optical anti-counterfeiting device can simultaneously form two or more than two different optical anti-counterfeiting characteristics, and the different optical anti-counterfeiting characteristics do not interfere with each other.

Description

Optical anti-counterfeiting element, manufacturing method thereof and optical anti-counterfeiting product

Technical Field

The invention relates to the field of anti-counterfeiting, in particular to an optical anti-counterfeiting element, a manufacturing method thereof and an optical anti-counterfeiting product.

Background

The human eye is very sensitive to color and color variations and is able to distinguish small differences between two colors. Therefore, the color change as an optical anti-counterfeiting element is an extremely efficient anti-counterfeiting feature. Optical anti-counterfeiting elements based on color and color change have been used as important optical anti-counterfeiting features in various fields such as banknote anti-counterfeiting and brand protection. The anti-counterfeiting element can realize color change through an optical principle, namely, when the optical anti-counterfeiting element is inclined, the color in the optical anti-counterfeiting element changes along with the change of an observation angle. This change in color is very easily discernable and does not require extensive training of the user.

Human eyes also have extremely sensitive perception and resolution capability to dynamic characteristics, so that in the field of optical anti-counterfeiting, a common optical anti-counterfeiting form is provided by forming a unique visual effect by using dynamic elements. When the observer changes the viewing angle, for example by tilting the optical security element or by changing the illumination direction of the light source or by changing the viewing direction of the observer, the position of certain graphic elements in the optical security element changes and/or the shape changes. Such a change in position, shape, etc. is simple to identify and does not require excessive training of the viewer, who may experience significant dynamic effects in a very short time, e.g., a few seconds. The color and the color change can be realized in various ways, for example, the color is obtained by using the metal reflective coating or the color layer is coated on the metal reflective coating to obtain the color, and the obtained color does not change along with the change of the observation angle. The principle of Fabry-Perot interferometer can also be adopted, and the optical variable coating with the color changing along with the change of the observation angle can be formed by adopting a structure of absorbing layer/dielectric layer/reflective coating or a mode of laminating high refractive index material/low refractive index material/high refractive index material/… ….

In the existing products and processes, dynamic image-text information is formed by adopting a grating. The microstructure of the grating can be a diffraction type holographic grating, and the change of the light transmission direction is realized through different periods and arrangement directions; the reflecting direction of the light can be changed by the blazed gratings with different inclination angles and direction angles; the cylindrical lens can also be adopted to modulate incident light, and special change of reflected light is realized through arrangement in different directions.

The dynamic microstructure can form dynamic characteristics which are easy to observe and recognize only by increasing a reflective coating on the surface of the dynamic microstructure to improve the diffraction or reflection efficiency of the dynamic microstructure. Generally, diffraction type microstructures such as holographic gratings need to be combined with a metal reflective coating because the diffraction type microstructures have a dispersion effect on the gratings, dynamic characteristics and color characteristics of the diffraction type microstructures are formed by the gratings, and the reflective coating only improves diffraction efficiency. The reflective elements such as blazed gratings or micro mirrors are generally combined with the optically variable coating to form an optically variable effect, wherein the dynamic characteristics are determined by the reflective elements with specific arrangement, and the color and color change are determined by the optically variable reflective coating.

The combination of two different colors (different colors or color change) or different dynamic types (diffraction and reflection) forms the combined effect of multiple characteristics, and can further improve the anti-counterfeiting performance of the optical anti-counterfeiting element. Different color features or different dynamic type features are difficult to combine through the traditional mode, especially, strict positioning relation exists among different features, and the traditional printing and hollowing mode has the problem of registration precision, so that the method cannot be obtained through the traditional printing and hollowing mode.

Disclosure of Invention

An object of the embodiments of the present invention is to provide an optical anti-counterfeiting element, a manufacturing method thereof, and an optical anti-counterfeiting product, which are used to solve or at least partially solve the above technical problems.

In order to achieve the above object, an embodiment of the present invention provides a method for manufacturing an optical security element, including: step S11, providing a substrate; step S12, forming an optical microstructure on one surface of the substrate, wherein the optical microstructure includes at least a first region and a second region that do not overlap with each other, wherein the first region includes a third grating microstructure, the second region includes a second grating microstructure, and an aspect ratio of the third grating microstructure is greater than that of the second grating microstructure; step S13, depositing a first reflective coating on the surface of the optical microstructure; step S14, removing the first reflective plating layer covering the third grating microstructure, and leaving the first reflective plating layer covering the second grating microstructure; step S15, coating a filling layer on the surface of the structure formed according to steps S11 to S14, wherein the refractive index of the filling layer and the refractive index of the optical microstructure satisfy preset conditions so that the filling layer and the third grating microstructure can form a first grating microstructure; and step S16, depositing a second reflective plating layer different from the first reflective plating layer on the filling layer.

Correspondingly, the embodiment of the invention also provides an optical anti-counterfeiting element, which comprises: a substrate; the surface relief structure layer is positioned on the substrate and comprises at least a first area and a second area which are not overlapped with each other, the first area comprises a first grating microstructure, the second area comprises a second grating microstructure, the surface relief structure layer is composed of a third grating microstructure and a filling layer covering the surface of the third microstructure, the depth-to-width ratio of the third grating microstructure is larger than that of the second grating microstructure, the refractive index of the filling layer and the refractive index of the third grating microstructure meet preset conditions, a second reflection coating is covered on the first grating microstructure in the same shape, and a first reflection coating different from the second reflection coating is covered on the second grating microstructure in the same shape.

Correspondingly, the embodiment of the invention also provides an optical anti-counterfeiting product which comprises the optical anti-counterfeiting element.

The optical anti-counterfeiting element provided by the embodiment of the invention can simultaneously form two or more than two different optical anti-counterfeiting characteristics, and the different optical anti-counterfeiting characteristics do not interfere with each other.

Additional features and advantages of embodiments of the invention will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the embodiments of the invention without limiting the embodiments of the invention. In the drawings:

FIG. 1 shows a schematic cross-sectional view of an optical security element according to an embodiment of the invention;

fig. 2a shows a schematic surface view of an optical security element according to an embodiment of the invention;

FIG. 2b shows a schematic cross-sectional view of the optical security element shown in FIG. 2 a; and

fig. 3a to 3f show a schematic flow chart of a method for producing an optical security element according to an embodiment of the invention.

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration and explanation only, not limitation.

According to an embodiment of the present invention, an optical security element is provided, which may include a substrate and a surface relief structure layer on the substrate, where the surface relief structure layer includes at least a first region and a second region that are not overlapped with each other, the first region may include a first grating microstructure, the second region may include a second grating microstructure, the first grating microstructure may be composed of a third grating microstructure and a filling layer covering a surface of the third microstructure, an aspect ratio of the third grating microstructure is greater than that of the second grating microstructure, and a refractive index of the filling layer and a refractive index of the third grating microstructure satisfy a preset condition. The first grating microstructure is covered with a second reflection coating in the same shape, and the second grating microstructure is covered with a first reflection coating different from the second reflection coating in the same shape.

The first region and the second region are only used for illustration and are not used to limit the present invention, and the surface relief structure layer may include a plurality of regions, wherein the depth ratio of the grating microstructures of two adjacent regions has a relatively obvious difference.

Due to the fact that the reflection coatings on the areas are different, the optical anti-counterfeiting element provided by the embodiment of the invention can form two or more different optical anti-counterfeiting features, and mutual interference does not exist between the different optical anti-counterfeiting features.

In order to facilitate an observer to observe the optical anti-counterfeiting element through the substrate, the first grating microstructure, the second grating microstructure and the filling layer are transparent or semitransparent.

Any grating microstructure of any area of the optical anti-counterfeiting element provided by the embodiment of the invention can be one or more of the following: a sub-wavelength grating, a holographic grating, a blazed grating, a spherical lens, or a cylindrical lens.

The structural characteristic size range of any grating microstructure in any area of the optical anti-counterfeiting element provided by the embodiment of the invention can be 100nm to 100 μm. The depth of any grating microstructure of any region may range from 10nm to 40 μm. For example, the holographic grating typically has a feature width of 1 μm and a depth of 100 nm; the characteristic width of the blazed grating is generally 9 μm, and the depth is 1.5 μm; the characteristic width of the sub-wavelength grating is generally 350nm and the depth is 140 nm.

The aspect ratio of any grating microstructure in any area of the optical anti-counterfeiting element provided by the embodiment of the invention is generally less than 0.4, and preferably 0.05 to 0.2. This is because when the aspect ratio is large, although the corresponding diffraction or reflection effect can be generated, because the depth of the grating is too deep, the intensity of the generated diffraction or reflection spectrum is too low, the overall visual perception is too dim, and the bright and easily-recognizable optical effect cannot be generated, so that the grating cannot be used for the anti-counterfeiting characteristics of products, especially optical anti-counterfeiting products.

Any reflective coating in embodiments of the invention may be one or more of: a metal layer, a metal compound layer, a stack of high and low index materials, or a fabry-perot interferometer.

The material of the reflective coating can be a metal reflective material, the metal reflective coating requires a metal material with high reflectivity, and the metal reflective coating can be a full spectrum reflective material and a corresponding alloy, such as aluminum, silver, tin, nickel, chromium, platinum, and can also be a reflective material with a specific color and a corresponding alloy material, such as copper, gold, and the like, which can generate a fixed color while providing high reflectivity. The metal reflective coating mainly has the function of improving diffraction or reflection efficiency, and the reflective coating does not have the effect of color change.

When the metal reflecting material is combined with a diffraction type holographic grating (for example, a sine type one-dimensional grating with the period of 1 mu m and the depth of 100 nm), the diffraction efficiency can be improved, and dynamic characteristics and rainbow colors can be formed. When the metal reflective material is combined with a reflective grating (for example, a blazed grating having a period of 13 μm and a depth of 2 μm), the reflection efficiency is improved, and a bright reflection effect is obtained.

The material of the reflective coating layer may also be a metal compound, and the metal compound layer may be a metal oxide, such as titanium dioxide, silicon dioxide, zirconium dioxide, or the like; metal sulfides such as zinc sulfide; other metal compounds are also possible.

The material of the reflective coating layer can also be a stack of materials with high and low refractive indexes, in which the refractive index n of the material with high refractive index is more than or equal to 1.8, including but not limited to ZnS, TiN, TiO₂、TiO、Ti₂O₃、Ti₃O₅、Ta₂O₅、Nb₂O₅、CeO₂、Bi₂O₃、Cr₂O₃、Fe₂O₃Any material or combination of (a); the refractive index n of the low refractive index material is less than 1.8, including but not limited to SiO₂、MgF₂、Na₃AlO₆、Al₂O₃Any material or combination thereof. The high-refractive index material and the low-refractive index material are arranged in an overlapped mode to form a film system structure of 'high-refractive index material/low-refractive index material/high-refractive index material/… …/high-refractive index material'. This configuration enables selective reflection of a specific spectral wavelength, resulting in a first color when viewed from the front. When the light is obliquely incident, the light path traveled by the light in the high/low refractive index material stack is different from the light path traveled by the light when the light is perpendicularly incident, forming a second color, thereby creating a color change effect.

Meanwhile, when the laminated structure of "high refractive material/low refractive index material/high refractive index material/… …/high refractive index material" is combined with a one-dimensional sub-wavelength grating (for example, with a period of 350nm and a depth of 110nm), a third color different from the laminated structure can be formed.

The reflective coating may also be a "fabry-perot" interferometer. The Fabry-Perot interferometer is a wavelength selective structure with higher reflection efficiency and is a film system structure of an absorption layer/a dielectric layer/a reflection coating. The absorption layer is made of metal material and has a small thickness, when light passes through the absorption layer, about half of the light is reflected, and the other half of the light is transmitted, so the absorption layer can be called as a semi-reflective semi-transparent film, including but not limited to chromium, nickel, copper, cobalt, titanium, vanadium, tungsten, tin, silicon, germanium and combinations thereof, and the thickness of the absorption layer can be 2nm-30 nm. Half of the dielectric layer is a metal compound, the dielectric layer material can be a low refractive index dielectric material with a refractive index less than 1.8, including but not limited to silicon dioxide, magnesium fluoride, cryolite, alumina and a combination thereof, and the thickness can be 100-1000 nm; the dielectric material may also be a high index material with a refractive index greater than 1.8, including but not limited to ZnS, TiN, TiO₂、TiO、Ti₂O₃、Ti₃O₅、Ta₂O₅、Nb₂O₅、CeO₂、Bi₂O₃、Cr₂O₃、Fe₂O₃Any material or combination. The reflective coating material is generally a metal material with high reflectivity, and may also be a non-metal material, including but not limited to any material of aluminum, silver, tin, nickel, chromium, platinum, copper, gold, silicon, or a combination thereof, and has a thickness of 10nm or more.

In a "fabry-perot" interferometer configuration, the absorbing layer acts as a beam splitter, reflecting the ordinary light (called beam 1), and transmitting half of it. The transmitted light is reflected by the reflecting coating after passing through the dielectric layer and then is emitted out through the absorbing layer (called as a light beam 2), and the light beam 1 and the light beam 2 interact to generate interference, so that the selection of specific wavelength is enhanced, and the color can be observed. When the incident direction of the light is changed, the optical path of the light beam in the medium layer is changed, if the medium material is a high-refractive-index material, the color is unchanged or is not obviously changed, and if the medium material is a low-refractive-index material, the color is obviously changed, so that the light-changing effect is achieved. For example, the "fabry-perot" interferometer structure may be chrome metal/silica metal/aluminum metal or aluminum metal/alumina trioxide metal/aluminum metal, the color of which can be changed when the viewing angle is changed.

The micro-grating structure of the surface relief structure layer and the reflective coating can be combined and matched at will to form various optical effects.

Fig. 1 shows a schematic cross-sectional view of an optical security element 1 according to an embodiment of the invention. As shown in fig. 1, a surface relief layer 3 is present on a substrate 2, the surface relief layer comprising at least two regions, region 31 and region 32 respectively. The region 31 has a grating microstructure 311, and the region 32 has a grating microstructure 321.

The grating microstructure 311 is a deep holographic diffraction grating with a period width of 1.2 μm and a depth of 0.7 μm; the grating microstructure 311 is formed with a filling layer 5, the refractive index of the filling layer 5 is substantially the same as the refractive index of the surface relief layer 3, and the filling layer 5 directly contacts with the grating microstructure 311, so that the interface between the filling layer 5 and the grating microstructure 311 in the first region 31 disappears or substantially disappears, thereby forming a transparent whole. The filling layer 5 and the grating microstructure 311 form a new grating microstructure 51. A reflective coating of aluminum is deposited over the grating microstructure 51 to a thickness of about 30 nm.

The grating microstructure 321 is a blazed grating, the period depth is 13 μm, and the depth is 0.8 μm. The blazed grating is deposited with a Fabry-Perot resonant cavity type reflection coating 42, which comprises an absorption layer aluminum, a dielectric layer aluminum oxide and a reflection coating aluminum in sequence from the surface of the blazed grating, wherein the thickness of the absorption layer aluminum is about 10nm, the thickness of the dielectric layer aluminum oxide is about 377nm, and the thickness of the reflection coating aluminum is about 20 nm. The reflective coating 42 appears yellow in front view, with a hue angle h of about 80 ° and a saturation C of about 72 in CIE coordinates.

In the manufacture of the optical security element 1 shown in fig. 1, the surface relief layer 3 may be formed on the substrate 2, the reflective coating 42 is coated on the surface relief layer 3, and the reflective coating on the grating microstructures 311 in the first region 31 is removed by a suitable method, so that only the reflective coating 42 of the grating microstructures 321 in the second region 32 remains. A filling layer 5 is formed over the grating microstructures 311 of the first region 31 and the reflective plating 42 of the second region 32. The filling layer 5 can be formed by wet coating, and because the filling layer has certain fluidity, the same morphology as the

grating microstructures

311 and 321 of the first and

second regions

31 and 32 cannot be maintained, i.e. the same type of coverage property is not provided. Due to its fluidity, the filling material tends to flow to a position where the potential energy is low, and thus fills the bottom of the grating. And because the filling material has certain surface tension, the filling material still adheres to the surface of the grating microstructure flowing through to form a new filling layer surface positioned in the first area and a new filling layer surface positioned in the second area. Since the filling layer 5 mainly fills the bottom of the

grating microstructures

311 and 321, the new surface has a shallower depth while maintaining the same period and width as the

grating microstructures

311 and 321, respectively. Since the refractive index n of the filling layer 5 is the same as or close to the refractive index of the surface relief layer 3, and the filling layer 5 is in direct contact with the surface relief layer 3, the interface 311 between the filling layer 5 and the surface relief layer 3 in the first region 31 disappears or substantially disappears, forming a transparent whole. The surface of the filling layer 5 forms new

grating microstructures

51 and 52 on the first region 31 and the second region 32, respectively. The new grating microstructure 51 has a period width of 1.2 μm and a depth of 0.15 μm. And then depositing a reflective coating of aluminum with a thickness of about 30nm on the

grating microstructures

51 and 52 to form the optical anti-counterfeiting element shown in fig. 1.

When an observer observes the security element 1 through the substrate 2, the first region 31 exhibits a holographic effect with iridescence, and various effects such as dynamic sense, switching, relief, three-dimensional stereo and the like can be realized through proper arrangement. Because the new grating microstructure 51 formed by the filling layer has the period of 1.2 mu m and the depth of 0.15 mu m, and is provided with the reflective coating aluminum, the grating microstructure has higher diffraction efficiency, and the holographic characteristics have high brightness and strong dynamic sense and are easy to be identified by the public. In the second region 32, the reflective plating layer 62 is blocked by the reflective plating layer 42 due to the reflective plating layer 42, so that only the reflective plating layer 42 is visible to an observer. When the anti-counterfeiting element 1 is inclined, the color changes due to the optical path difference of light propagating in the reflective coating 42, and the color changes from golden yellow to green. Because the grating microstructure 321 is a reflective blazed grating, the reflective coating 42 can maintain the original color after being attached to the blazed grating without interference. And by changing the arrangement mode of the blazed grating, various effects such as dynamic effect, switching, relief, three-dimensional stereo and the like can be obtained. The first region 31 is a diffraction-type hologram, and the second region is a reflection-type light variation-sensitive feature, which are significantly different from each other in terms of color expression and dynamic effect, for example, in the first region 31 of the diffraction-type hologram, since the reflective plating 61 is aluminum, the full-spectrum reflection effect of aluminum still bright to the observer is exhibited, and due to the characteristics of the hologram grating, the first region generally cannot form a stable vivid color effect, but rather, exhibits a rainbow color peculiar to the hologram, that is, exhibits a plurality of colors at a small variation angle. The second region 32 of the reflective dynamic light changes, due to the existence of the fabry-perot interference layer, can form a stable color with high brightness and high saturation, and the color does not change suddenly, even if the blazed grating 321 exists, the whole second region still presents golden yellow of the reflective coating 42. Because the first region 31 and the second region 32 have a strict positioning and registration relationship, the reflective plating layer 61 is strictly formed on the grating microstructure 51, the reflective plating layer 62 is strictly attached to the grating microstructure 321, the grating microstructure 51 and the grating microstructure 321 are not covered with each other, the plating layer 61 is not attached to the grating microstructure 321, and the plating layer 42 is not attached to the grating microstructure 51, so that two different accurate combinations of dynamic and color characteristics can be realized.

Furthermore, the manufacturing method of the optical anti-counterfeiting element provided by the embodiment of the invention is suitable for combining two distinct features which have positioning and registration relations. As shown in fig. 2a, the security element 1 is composed of a region 31 and a region 32, wherein the region 31 is composed of holographic gratings with different directions, and the region 32 is composed of blazed gratings with different inclination angles and directions. Fig. 2b shows a schematic cross-sectional view of the security element 1 from fig. 2a at the parting line 7.

By suitably arranging the blazed gratings in the area 32 as shown in fig. 2b, a pentagram as in the middle of fig. 2a can be obtained, e.g. the blazed grating at the middle 321 of the pentagram 32 is oriented in the direction d1 and the blazed grating at the middle 322 of the pentagram 32 is oriented in the direction d 2. The two directions are different, and a macroscopic three-dimensional relief effect can be formed. By specifically adjusting the inclination and orientation of the blazed gratings in the area 32, a five-pointed star with a three-dimensional relief can be obtained. A reflective coating 42, such as a "fabry-perot" resonator structure, e.g., aluminum/silicon dioxide/aluminum, with a 10nm thickness of aluminum, a 400nm thickness of silicon dioxide, and a 50nm thickness of aluminum, is deposited over the surface of the five-pointed star 32 (i.e., the blazed grating).

The structure of the region 31 is similar to that of the region 31 in fig. 1.

In the production of the optical security element 1 shown in fig. 1, the surface relief layer 3 may be formed on the substrate 2, and the surface relief layer 3 may be coated with a reflective coating 42, such as aluminum/silica/aluminum, wherein the aluminum has a thickness of 10nm, the silica has a thickness of 400nm, and the aluminum has a thickness of 50 nm. The aluminium-containing Fabry-Perot resonant cavity on the region 31 can be corroded by means of alkali liquor corrosion, and the coating 42 on the region 32 is not easy to be corroded by alkali liquor and then reserved due to the fact that the surface structure is flat and the thickness of the aluminium layer is thick. A filling layer 5 is formed over the grating microstructures 311 of the first region 31 and the reflective plating 42 of the second region 32. The filling layer 5 may be formed by means of wet coating. Due to the presence of the filling layer, and the refractive index of the filling layer is similar to that of the surface relief layer 3, the height of the grating microstructure 311 can be reduced by properly adjusting the thickness of the filling layer, and the grating microstructure 311 can be lowered to a proper height, for example, in the case of a period of 1 μm of the grating microstructure 311, the depth is 50nm-150nm, and a holographic diffraction effect with high brightness can be obtained. If the depth is deeper, the light of the holographic grating can be absorbed more strongly, the diffraction efficiency is influenced, and the brightness is reduced; if the depth is shallow, the diffraction efficiency is not high, and a good holographic effect cannot be produced. On the basis of which a coating is formed, here a reflective coating 61 on the area 31 and a reflective coating 62 on the area 32, both of which are made of the same material, for example a metallic copper reflective coating, by a single deposition.

The five-pointed star has a three-dimensional visual effect, when the anti-counterfeiting product is inclined, different faces of the five-pointed star can reflect light rays and have different brightness, so that the visual effect of a real three-dimensional image as shown in the figure is brought to an observer, and because a Fabry-Perot resonant cavity structure, such as aluminum/silicon dioxide/aluminum, is arranged on the microstructure of the five-pointed star region, wherein the thickness of the aluminum is 10nm, the thickness of the silicon dioxide is 400nm, and the thickness of the aluminum is 50nm, the whole embossed five-pointed star is golden yellow when the anti-counterfeiting product is observed perpendicular to the surface of the optical anti-counterfeiting product. When viewed obliquely, the color of the five-pointed star changed to green. Around the five-pointed star is a holographic zoom area 31 with rainbow color, and the whole area presents the color of the metal copper because the metal copper is deposited on the surface of the holographic zoom area. Because the coating is precisely hollowed by adopting the microstructure, and the color of the coating is determined, the colors of different dynamic/relief backgrounds are different, and the colors and the dynamic/relief are strictly positioned and registered without mutual interference. When the anti-counterfeiting element is observed perpendicularly, the relief pentagram is golden yellow, the zooming area 31 (namely, the background area) is superposed by metal copper and iridescent color, the colour of the metal copper is absent on the pentagram, and the gold color formed by the Fabry-Perot resonant cavity structure is present and only exists; no golden color formed by a Fabry-Perot resonant cavity structure exists on the background area, and the color of the Fabry-Perot resonant cavity structure is the same as that of the copper. The pattern and color have a precisely registered relationship. The holographic gratings in the regions 31 are arranged appropriately, when the security element is tilted, the holographic gratings of different regions diffract light into the eyes of an observer, and the shape of the region seen by the observer each time is exactly the same as the outline of the pentagon formed by the regions 32 by appropriate design, and when the security element is tilted, the outline expands outwards in the region of the regions 31 from the outermost edges of the pentagon formed by the regions 32, and the outline of the pentagon of the regions 32 is maintained all the time while expanding.

Meanwhile, the types of materials in the Fabry-Perot resonant cavity structure can be changed by changing the properties of the etching solution. For example, if the "Fabry-Perot" resonator structure is "aluminum/silicon dioxide/aluminum, wherein the thickness of aluminum is 10nm, the thickness of silicon dioxide is 400nm, and the thickness of aluminum is 50 nm", the etching and hollowing needs to be performed by using alkali liquor. If the Fabry-Perot resonant cavity structure is sequentially changed into chromium/silicon dioxide/aluminum from the surface of the microstructure upwards, wherein the thickness of the chromium is 8nm, the thickness of the silicon dioxide is 380nm, and the thickness of the aluminum is 50nm, a dechroming solution is adopted to remove hollowing.

Alternatively, the microstructures 311 of the region 31 may also be blazed gratings with a high aspect ratio. The

reflective coatings

61 and 62 on the optical security element may also be coatings of a "fabry-perot" resonator structure.

The optical security element according to embodiments of the invention is particularly suitable for being made as a windowed security thread. The security thread has a thickness of no more than 50 microns. The anti-counterfeiting paper with the windowing safety line is used for anti-counterfeiting of various high-safety products such as bank notes, credit cards, passports and securities and high-value-added products, various packaging papers, packaging boxes and the like.

The optical security element according to the invention can also be used as labels, logos, wide strips, transparent windows, overlaminates, etc., which can be adhered to various articles by various adhesion mechanisms, for example to high security products and high value-added products such as banknotes, credit cards, etc.

It can be known from the content introduced in the background art that the anti-counterfeiting capability of the optical anti-counterfeiting element can be effectively improved by combining two different colors or two dynamic characteristics. However, there are many problems in the process of combining two different types of anti-counterfeiting features, and the main problem is how to accurately place the two dynamic microstructures together and simultaneously deposit reflective coatings with different properties on different areas. Due to the precise positioning of at least two microstructures and two coatings, it is difficult to achieve the positioning accuracy required above using conventional printing overprinting.

In view of the above process difficulties, an embodiment of the present invention further provides a method for manufacturing an optical anti-counterfeiting element, as shown in fig. 3a to 3f, the method mainly includes the following steps:

as shown in fig. 3a, in step S11, a substrate 2 is provided.

The substrate is formed of at least one material selected from the group consisting of polyethylene terephthalate, polyvinyl chloride, polyethylene, polycarbonate, and polypropylene. The substrate may be transparent.

As shown in fig. 3b, in step S12, optical microstructures 3 are formed on one surface of the substrate 2.

The material of the optical microstructure can be ultraviolet curing polyester acrylic resin and epoxy acrylic resin. The optical microstructures may be transparent.

The optical microstructure comprises at least a first region 31 and a second region 32 which do not overlap with each other, wherein the first region 31 comprises a grating microstructure 311 and the second region 32 comprises a grating microstructure 321.

The sub-grating structure can be formed by laser double-beam interference exposure, laser direct-writing exposure or electron beam direct writing, or can be copied in batch by ultraviolet casting, mould pressing and nano-imprinting. For example, the sub-wavelength micro-relief structure and the holographic grating can be manufactured into a master plate by a holographic interference method, a laser direct etching technology, an electron beam etching technology and the like, a working plate is manufactured by an electroforming process, and then the working plate is transferred onto a base material by a production process such as mould pressing, ultraviolet casting and the like.

For example, the grating microstructure 311 may be a reflective mirror or a blazed grating as the reflective element, the region 32 may be configured to realize a holographic effect, and the grating microstructure 321 may be a holographic grating with a large aspect ratio.

The aspect ratio of the grating microstructure 311 may be greater than or equal to 0.4, and the aspect ratio of the grating microstructure 321 may be less than 0.4.

As shown in fig. 3c, in step S13, a reflective coating is deposited on the surface of the optical microstructure.

The formation of the reflective coating on the surface of the grating microstructure is realized by at least one of a thermal evaporation deposition method, an electron beam evaporation deposition method and a magnetron sputtering deposition method. Due to the requirements of the subsequent process, it is necessary to ensure that the reflective coating deposited on the surface of the microstructure has the property of same type coverage, i.e. the deposited coating needs to keep the original microstructure morphology as much as possible, so that a wet coating or printing method cannot be adopted.

The reflective coating may be a dielectric stack formed by sequentially stacking a high refractive index material layer and a low refractive index material layer, or a single-layer reflective coating (metal or high refractive index medium), or a reflective coating with a fabry-perot (F-P) structure, where the deposition layer on the grating microstructure 311 of the region 31 is referred to as a reflective coating 41, and the deposition layer on the grating microstructure 321 of the region 32 is referred to as a reflective coating 42.

As shown in fig. 3d, in step S14, the reflective plating 41 covering the grating microstructure 311 is removed, and the reflective plating 42 covering the grating microstructure 321 is remained.

The grating microstructure 311 and the grating microstructure 321 have different aspect ratios. A larger aspect ratio indicates a steeper grating microstructure and a larger slope. The smaller the aspect ratio, the flatter the grating microstructure and the smaller the slope. In step 13, a reflective coating can be evaporated by vacuum evaporation, the quality of the deposition material in the same unit solid angle in unit time is fixed in vacuum, and when the surface of the substrate has a fluctuant microstructure, the coating thickness of the microstructure area is smaller than that of the flat area under the same time and process conditions. The larger the aspect ratio of the microstructure area, the smaller the thickness of the coating layer covered on the microstructure area relative to the thickness of the coating layer in the flat area. When the structure formed in step S13 is immersed in an etching solution capable of etching the reflective coating, the etching solution will simultaneously etch the reserved area 32 and the hollow area 31. However, since the grating microstructure in the hollow area 31 has a larger aspect ratio, the reflective coating deposited thereon is thinner, and therefore is more easily corroded by the corrosive liquid. Therefore, in the same processing time, the reflective coating of the hollow area 31 is completely corroded to leak the grating microstructure 311, while the reflective coating of the reserved area 32 is only corroded to a small extent due to the thicker reflective coating, and most of the reflective coating is still reserved, and the properties of the original reflective coating are maintained. The key parameter for determining the hollowing or reserving of the plating layer in each area is the depth-to-width ratio of the grating microstructure in each area. When the depth-to-width ratio is more than or equal to 0.4, the reflective coating on the upper layer of the grating microstructure is easier to be corroded and hollowed out under the action of corresponding corrosive liquid; when the aspect ratio is less than 0.4, the reflective coating on the upper layer of the grating microstructure is more easily retained. Of course, the larger the depth-to-width ratio difference between the hollowed-out area and the reserved area, the better the depth-to-width ratio difference is, the higher the contrast of the hollowed-out speed can be obtained, and the process is easier to realize.

As shown in fig. 3e, in step S15, a filling layer 5 is coated on the surface of the structure formed in steps S11 to S14, wherein the refractive index of the filling layer 5 and the refractive index of the optical microstructure satisfy the predetermined conditions so that the filling layer and the grating microstructure 311 can form the grating microstructure 51.

The filling layer may be transparent and have a refractive index that is the same as or similar to the refractive index of the optical microstructures. When the filling layer material is coated on the reflective coating layer of the reserved area and the grating microstructure layer of the hollow area in a wet coating mode, the filling layer is used as a protective layer to be attached to the reflective coating layer in the reserved area. And the surface of the grating microstructure in the hollow area has no reflection coating, so that the filling material is directly contacted with the grating microstructure. And because the filling layer has certain fluidity by adopting a wet coating mode, the filling layer does not have the property of same-type coverage, but more filling layers flow to a region with lower potential energy, namely the filling layers are deposited and filled at the bottom of the grating microstructure, so that the depth of the grating microstructure in the original hollow region is reduced, the original depth-to-width ratio is reduced to be less than 0.4, and a better optical effect is achieved.

Optionally, the absolute value of the difference between the refractive index of the filling layer material and the refractive index of the optical microstructure is less than 0.5.

As shown in fig. 3f, a reflective plating layer different from the reflective plating layer 42 is deposited on the filling layer 5 at step S16.

And depositing a reflective coating on the side with the filling layer. The reflective coating may be a dielectric stack formed by sequentially stacking a high refractive index material layer and a low refractive index material layer, or a single reflective coating (metal or high refractive index dielectric), or a reflective coating of a fabry-perot (F-P) structure, in which a portion above the region 31 is 61 and a portion above the region 32 is 62.

In the optical anti-counterfeiting element manufactured by the method, the grating microstructure 321 and the reflection coating 42 act together to form a first dynamic color effect, the grating microstructure 51 and the reflection coating 61 act together to form a second dynamic color effect, and the two dynamic color effects are not interfered with each other.

It should be noted that the preparation method of the optical anti-counterfeiting element of this embodiment is the same as or similar to the specific implementation details of the optical anti-counterfeiting element of the above embodiment, and therefore, the details are not repeated herein.

Embodiments of the present invention also provide security products, such as banknotes, credit cards, passports and securities, and the like, comprising the above-described optical security element.

Although the embodiments of the present invention have been described in detail with reference to the accompanying drawings, the embodiments of the present invention are not limited to the details of the above embodiments, and various simple modifications can be made to the technical solutions of the embodiments of the present invention within the technical idea of the embodiments of the present invention, and the simple modifications all belong to the protection scope of the embodiments of the present invention.

It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. In order to avoid unnecessary repetition, the embodiments of the present invention do not describe every possible combination.

Those skilled in the art will understand that all or part of the steps in the method according to the above embodiments may be implemented by a program, which is stored in a storage medium and includes several instructions to enable a single chip, a chip, or a processor (processor) to execute all or part of the steps in the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.

In addition, any combination of various different implementation manners of the embodiments of the present invention is also possible, and the embodiments of the present invention should be considered as disclosed in the embodiments of the present invention as long as the combination does not depart from the spirit of the embodiments of the present invention.

Claims

1. A method for making an optical security element, comprising:

step S11, providing a substrate;

step S12, forming an optical microstructure on one surface of the substrate, wherein the optical microstructure includes at least a first region and a second region that do not overlap with each other, wherein the first region includes a third grating microstructure, the second region includes a second grating microstructure, and an aspect ratio of the third grating microstructure is greater than that of the second grating microstructure;

step S13, depositing a first reflective coating on the surface of the optical microstructure;

step S14, removing the first reflective plating layer covering the third grating microstructure, and leaving the first reflective plating layer covering the second grating microstructure;

step S15, coating a filling layer on the surface of the structure formed according to steps S11 to S14, wherein the refractive index of the filling layer and the refractive index of the optical microstructure satisfy preset conditions so that the filling layer and the third grating microstructure can form a first grating microstructure; and

step S16, depositing a second reflective plating layer different from the first reflective plating layer on the filler layer.

2. The method of claim 1, wherein the substrate, the first grating microstructure, the second grating microstructure, the filler layer are transparent or translucent.

3. The method of claim 1, wherein the refractive index of the filling layer and the refractive index of the optical microstructure satisfy the following preset conditions: the absolute value of the difference between the refractive index of the filling layer and the refractive index of the optical microstructure is less than 0.5.

4. The method of claim 1, wherein the third grating microstructure has an aspect ratio of not less than 0.4, and the first and second grating microstructures have an aspect ratio of less than 0.4.

5. The method of claim 4, wherein the first and second grating microstructures have an aspect ratio of 0.05 to 0.2.

6. The method of claim 1, wherein,

the range of the structure characteristic dimension of the first grating microstructure and the second grating microstructure is 100nm to 100 μm; and/or

The depth range of the first grating microstructure and the second grating microstructure is 10nm to 40 μm.

7. The method of claim 1, wherein,

the first grating microstructure and/or the second grating microstructure is one or more of: a sub-wavelength grating, holographic grating, blazed grating, spherical lens, or cylindrical lens; and/or

The first grating microstructure and/or the second grating microstructure are periodic or non-periodic.

8. The method of claim 1, wherein the first and/or second reflective plating is one or more of: a metal layer, a metal compound layer, a stack of high and low index materials, or a fabry-perot interferometer.

9. An optical security element comprising:

a substrate;

a surface relief structure layer on the substrate, the surface relief structure layer including at least a first region and a second region that do not overlap with each other, the first region including a first grating microstructure, the second region including a second grating microstructure, wherein the first grating microstructure is composed of a third grating microstructure and a filling layer covering a surface of the third grating microstructure, an aspect ratio of the third grating microstructure is greater than that of the second grating microstructure, a refractive index of the filling layer and a refractive index of the third grating microstructure satisfy a predetermined condition so that the filling layer and the third grating microstructure can form a first grating microstructure, wherein the first grating microstructure is conformally covered with a second reflective coating, and the second grating microstructure is conformally covered with a first reflective coating different from the second reflective coating, the filling layer also covers the first reflection coating, and the second reflection coating covers the filling layer in a conformal manner.

10. The optical security element according to claim 9, wherein the substrate, the first grating microstructure, the second grating microstructure, the filler layer are transparent or translucent.

11. The optical security element according to claim 9, wherein the refractive index of the filling layer and the refractive index of the third grating microstructure satisfy the following preset conditions: the absolute value of the difference between the refractive index of the filling layer and the refractive index of the third grating microstructure is less than 0.5.

12. The optical security element according to claim 9,

the range of the structure characteristic dimension of the first grating microstructure and the second grating microstructure is 100nm to 100 μm;

the depth range of the first grating microstructure and the second grating microstructure is 10nm to 40 μm; and/or

The aspect ratio of the first grating microstructure and the second grating microstructure is less than 0.4.

13. The optical security element according to claim 12, wherein the first grating microstructure and the second grating microstructure have an aspect ratio of 0.05 to 0.2.

14. The optical security element according to claim 9,

15. The optical security element according to claim 9, wherein the first and/or second reflective coating is one or more of: a metal layer, a metal compound layer, a stack of high and low index materials, or a fabry-perot interferometer.

16. The optical security element according to claim 9, wherein the third grating microstructure has an aspect ratio of not less than 0.4, and the first and second grating microstructures have an aspect ratio of less than 0.4.

17. The optical security element according to claim 16, wherein the first grating microstructure and the second grating microstructure have an aspect ratio of 0.05 to 0.2.

18. An optical security product comprising an optical security element according to any one of claims 9 to 17.