CN110450560B

CN110450560B - Optical anti-counterfeiting element, preparation method thereof and optical anti-counterfeiting product

Info

Publication number: CN110450560B
Application number: CN201810430518.7A
Authority: CN
Inventors: 张巍巍; 张宝利; 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: 2018-05-08
Filing date: 2018-05-08
Publication date: 2020-12-25
Anticipated expiration: 2038-05-08
Also published as: CN110450560A

Abstract

The invention provides an optical anti-counterfeiting element, a preparation method thereof and an optical anti-counterfeiting product, and belongs to the technical field of optical anti-counterfeiting. The optical security element comprises a substrate, a relief layer on the substrate, and a reflective layer at least partially covering the relief layer, the relief layer comprising: the non-image-text area is composed of a plurality of non-overlapping micro-relief units, each micro-relief unit is provided with a plurality of grating micro-relief structures, the reflecting layer covers the grating micro-relief structures, and the reflecting layer has a modulation effect on incident light; and the image-text area is not overlapped with the non-image-text area to form transparent image-text. The non-image-text area is formed into the grating micro-relief structure, so that the character pattern and the background have no obvious boundary, and the identification effect and the overall aesthetic degree are greatly improved.

Description

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

Technical Field

The invention relates to an optical anti-counterfeiting technology, in particular to an optical anti-counterfeiting element, a preparation method thereof and an optical anti-counterfeiting product.

Background

Human eyes have extremely sensitive perception and resolution capability to dynamic characteristics, so that in the technical field of optical anti-counterfeiting, a common optical anti-counterfeiting form is to form a unique visual effect by utilizing dynamic elements. When a viewer looks from a different viewing angle (e.g., tilting the optical security element, changing the illumination direction of the light source, or changing the viewing direction of the viewer), the position of certain graphic elements in the optical security element changes and/or changes shape. Such a change in position, shape, etc. is characterized by simple recognition, and the observer can feel a significant dynamic effect in a very short time, for example, several seconds, without much education on the observer.

Meanwhile, human eyes are very sensitive to color and color change, and can distinguish the small difference between the two colors, so that the color change serving as an optical anti-counterfeiting element is also an anti-counterfeiting feature with extremely high efficiency. When the optical security element is tilted, the color in the optical security element changes with the change in the viewing angle.

In some existing products and processes, dynamic graphic and text information is formed by using gratings. The microstructure forming the grating can be a diffraction type holographic grating or a reflective blazed grating, the diffraction type holographic grating realizes the change of the light propagation direction through different periods and arrangement directions, and the reflective blazed grating changes the reflection direction of the light through the blazed gratings with different inclination angles and direction angles. In the existing products, the above-mentioned grating is generally adopted to form the character pattern, and the background is a flat surface without grating, so that the formed character has high brightness and a glaring flicker effect, and the character pattern and the background have a high contrast, however, the character pattern and the background have an obvious boundary line, so that the recognition effect and the overall aesthetic degree are poor, and the color of the character pattern and the color of the background are generally the same, which greatly reduces the recognition.

Disclosure of Invention

The embodiment of the invention aims to provide an optical anti-counterfeiting element, a preparation method thereof and an optical anti-counterfeiting product, which are used for improving the identifiability of the optical anti-counterfeiting element.

In order to achieve the above object, the present invention provides an optical security element comprising a substrate, a relief layer on the substrate, and a reflective layer at least partially covering the relief layer, the relief layer comprising: the non-image-text area is composed of a plurality of non-overlapping micro-relief units, each micro-relief unit is provided with a plurality of grating micro-relief structures, the reflecting layer covers the grating micro-relief structures, and the reflecting layer has a modulation effect on incident light; and the image-text area is not overlapped with the non-image-text area to form transparent image-text.

Preferably, in the multiple micro-relief units, the grating micro-relief structures in different micro-relief units have different reflection directions for incident light, and the grating micro-relief structures in the same micro-relief unit have the same reflection direction for the incident light.

Preferably, the micro-relief unit is one or more of a sawtooth grating, a sine grating and a rectangular grating.

Preferably, the characteristic dimension of the grating micro-relief structure is 3 μm to 100 μm.

Preferably, the size of any of the grating microrelief structures is at least an order of magnitude smaller than the size of the non-image-text regions.

Preferably, the reflective layer comprises at least one of a metal layer, a metal compound layer, a stack of high and low refractive index materials and a fabry-perot interferometer.

Preferably, the image-text area is a flat area.

Preferably, the image area is formed by a plurality of light absorbing microstructures having a light trapping effect on incident light.

Preferably, the light absorbing microstructures have any one of a circular, sinusoidal, rectangular, triangular cross-section.

Preferably, the light absorbing microstructures have a feature size of 0.1 μm to 1 μm and an aspect ratio of greater than 0.3.

Preferably, the picture and text area is covered with a coloring layer.

Preferably, the coloured layer and the relief layer are in contact with the surface of different sides of the substrate.

Preferably, the relief layer is between the coloured layer and the substrate.

Preferably, the image-text area has a plurality of image-text sub-areas, and the coloring layers covered on different image-text sub-areas have different colors.

Preferably, the reflective layer also covers the light absorbing microstructures.

Correspondingly, the invention also provides an optical anti-counterfeiting product which is characterized by comprising the optical anti-counterfeiting element.

Correspondingly, the invention also provides a preparation method of the optical anti-counterfeiting element, which comprises the following steps: forming a relief layer on a substrate, the relief layer having a non-image-text region and a flat image-text region formed by a grating micro-relief structure; depositing a reflective layer on the relief layer; and removing the reflective layer deposited on the image-text area.

Preferably, the method further comprises: and coating a coloring layer on the image-text area of the relief layer.

Preferably, the method further comprises: forming a light absorption microstructure in the image-text area; wherein, in case the image-text area of the relief layer is formed by a light-absorbing microstructure, the reflective layer deposited on the image-text area is not removed.

Through the technical scheme, the non-image-text area is formed into the grating micro-relief structure, so that the character pattern and the background have no obvious boundary, and the identification effect and the overall aesthetic degree are greatly improved.

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 is a schematic cross-sectional view of an optical security element provided by the present invention;

FIG. 2 is a schematic diagram of the principle of forming dynamic patterns and texts under different observation angles by the optical anti-counterfeiting element provided by the invention;

FIG. 3 is a schematic diagram of the principle of imaging of different micro-relief units provided by the present invention;

FIG. 4 is a schematic diagram of the present invention providing a dynamic effect that floats above the surface of an optical security element;

FIG. 5 is a schematic diagram showing the dynamic effect of the present invention sinking below the surface of an optical security element;

FIG. 6 is a schematic diagram of rendering a zoom dynamic effect provided by the present invention;

FIG. 7 is a schematic diagram of the present invention providing a dynamic effect of rotation;

FIG. 8 is a schematic cross-sectional view of a Fabry-Perot structure as a reflective layer according to the present invention;

FIG. 9 is a schematic cross-sectional view of an optical security element with a light-absorbing microstructure as an image-text region according to the present invention;

FIG. 10 is a schematic cross-sectional view of an optical security element provided by the present invention with a colored layer and a relief layer on different side surfaces of a substrate;

FIG. 11 is a schematic cross-sectional view of an optical security element provided by the present invention having a colored layer on the surface of the same side of the substrate as the embossed layer;

fig. 12 is a schematic cross-sectional view of an optical anti-counterfeiting element with different colors of colored layers covering different image-text subregions, provided by the invention;

FIG. 13 is a schematic diagram of different colors of different texts according to the present invention;

FIG. 14 is a schematic diagram of different colors of the same text;

FIG. 15 is a schematic diagram of a character with color variation;

FIG. 16 is a flow chart of a method of making an optical security element provided by the present invention; and

fig. 17 is a schematic view of an optical security element provided by the present 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.

Fig. 1 is a schematic cross-sectional view of an optical security element provided by the present invention, as shown in fig. 1, the optical security element includes a substrate 1, a relief layer 2 disposed on the substrate 1, and a reflective layer 3 at least partially covering the relief layer 2, the relief layer 2 includes a non-image-text region 21 and an image-text region 22, wherein the non-image-text region 21 is formed by a plurality of non-overlapping

micro-relief units

211, 212, 213, each micro-relief unit has a plurality of grating micro-relief structures, the reflective layer 3 covers the grating micro-relief structures, and the reflective layer 3 has a modulation effect on incident light; the image-text area 22 is not overlapped with the non-image-text area 21, and forms transparent images and texts.

Wherein, taking fig. 1 as an example, the micro-relief unit 211 has grating

micro-relief structures

2111 and 2112, the micro-relief unit 212 has grating

micro-relief structures

2121 and 2122, and the micro-relief unit 213 has grating

micro-relief structures

2131 and 2132, it should be understood by those skilled in the art that fig. 1 is a schematic diagram only, only three

micro-relief units

211, 212, 213 are exemplarily shown in fig. 1, and only two grating micro-relief structures are exemplarily shown in each micro-relief unit.

The substrate 1 has an upper surface and a lower surface, and typically the relief layer 2 and the reflective layer 3 are on the same side surface of the substrate 1, e.g. the relief layer 2 and the reflective layer 3 are both on the upper surface of the substrate 1 or both on the lower surface of the substrate 1.

The "micro-relief unit" is used to describe a kind of grating micro-relief structure having the same reflection direction to the incident light, and it should be noted that the reflection directions described herein may be completely the same or substantially the same, that is, although the grating micro-relief structures in the same micro-relief unit are required to have the same reflection direction to the incident light in the manufacturing process, errors are also allowed.

In the optical anti-counterfeiting element described above, the reflective layer 3 covering the grating micro-relief structure of the non-image-text area 21 can modulate incident light, the image-text area 22 not covering the reflective layer 3 can form transparent image-text information with specific meaning, and the image-text area 22 can be a flat area. As shown in fig. 1, the non-image-text area 21 is covered with the reflective layer 3, and the image-text area 22 is not covered with the reflective layer 3. The teletext area 22 shown in fig. 1 has two

teletext sub-areas

221, 222 which can be used to form different teletext, the two teletext sub-areas being shown merely by way of example in fig. 1.

In the multiple micro-relief units, the grating micro-relief structures in different micro-relief units have different reflection directions to incident light, and the grating micro-relief structures in the same micro-relief unit have the same reflection direction to the incident light. The micro-relief unit is a combination of one or more of a sawtooth grating, a sine grating and a rectangular grating. That is to say, there is no specific requirement for the specific structural shape of the grating micro-relief structure, as long as the requirements that the grating micro-relief structure in the same micro-relief unit has the same reflection direction of the incident light and the grating micro-relief structures in different micro-relief units have different reflection directions of the incident light are met, and the specific form of the micro-relief unit can be determined according to the optical effect and the grating property which are required to be realized. It will be appreciated by those skilled in the art that the grating microrelief structure shown in figure 1 can be referred to as a blazed grating.

The relief layer 2 can be obtained by micro-nano processing modes such as optical exposure, electron beam exposure and the like, and can be copied in batches by processing modes such as ultraviolet casting, mould pressing, nano imprinting and the like.

The grating micro-relief structures in the same micro-relief unit may be periodic or aperiodic, and taking the micro-relief unit 211 in fig. 1 as an example, the cross sections of the two grating

micro-relief structures

2111 and 2112 may be the same or different. In the case where the cross sections of the two grating

micro-relief structures

2111 and 2112 are the same, it is referred to as a grating micro-relief structure being periodic, and in the case where the cross sections of the two grating

micro-relief structures

2111 and 2112 are different, it is referred to as a grating micro-relief structure being non-periodic.

The feature size of the grating micro-relief structure should be 3 μm to 100 μm, regardless of whether the grating micro-relief structure is periodic or aperiodic. The characteristic dimension of the grating micro-relief structure refers to the width of the grating micro-relief structure, and takes the grating micro-relief structure 2111 in fig. 1 as an example, that is, the width of the grating micro-relief structure 2111.

The size of any grating micro-relief structure should be at least an order of magnitude smaller than the size of the non-image-text area. The size (also referred to as dimension) of the grating micro-relief structure may be the length, width, height or area of the grating micro-relief structure, and the size (also referred to as dimension) of the non-image area may be the length, width, height or area of the non-image area.

Fig. 2 is a schematic diagram illustrating a principle that a non-image-text area 21 of the optical anti-counterfeiting element provided by the present invention forms dynamic images and texts under different viewing angles, in the optical anti-counterfeiting element provided by the present invention, a plurality of

micro-relief units

211, 212, 213 are provided in the non-image-text area 21 of the relief layer 2, and each of the

micro-relief units

211, 212, 213 has a plurality of grating micro-relief structures with different parameters, including but not limited to 2111, 2112, 2121, 2122, 2131, 2132, etc. By taking the grating micro-relief structure as the blazed grating as an example, the reflection direction of the incident light can be modulated by adjusting the inclination angle of the blazed grating and the orientation of the blazed grating, and the incident light can be reflected to a specific direction. In the non-image-text area 21, the grating micro-relief structures with the same parameters form a micro-relief unit, e.g. 211, 212, 213. Each micro-relief unit comprises a grating micro-relief structure which has the same parameters, has a modulation effect on incident light and is provided with a reflecting layer. The blazed grating structure with the same parameters in the non-image-text area 21 can be taken out, for example as a subunit 211, to form the pattern shown in fig. 2 (c). The pattern shown in fig. 2(c) can be seen as composed of a blazed grating background (formed by non-image areas) with a reflective layer and image areas without a reflective layer, and since the grating micro-relief structure as the background has a reflective layer, the reflectivity of the background is much higher than that of the image areas without a reflective layer, so that a bright background and darker characters appear when viewed from the outside, forming a shadow image. However, one micro-relief unit is only a part of the non-image-text area, so one micro-relief unit cannot occupy all the space, but occupies a part, and the rest is occupied by other micro-relief units, assuming that a "mask" as shown in fig. 2(a) is the position occupied by one micro-relief unit 211, wherein a white area is the effective occupied area of the micro-relief unit 211, and a black area is the position occupied by other micro-relief units (e.g. 212, 213) except the micro-relief unit 211. The "text" shown in fig. 2(b) is the text formed by the complete background and the corresponding text area formed by the micro-relief unit 211.

Fig. 2(a) can be considered as a "mask", black being the inactive part, white being the active part, and the viewer seeing the "active part" (fig. 2(c)) selected to act behind the "image (fig. 2(b)) through the" mask "(fig. 2 (a)). Still taking the micro-relief unit 211 as an example, it should be understood by those skilled in the art that this process is a process of composition on a computer, and it can be considered from the aspects of mathematics and graphics processing that, for example, the combination of the micro-relief unit 211 and the image-text sub-area 221 is actually obtained by superimposing the image-text shown in fig. 2(b) and the mask shown in fig. 2(a), wherein the white area in the mask shown in fig. 2(a) is assigned with 1, the black area is assigned with 0, and then performing the and operation with the image-text shown in fig. 2(b), so as to obtain the micro-relief unit 211. Taking the blazed grating as an example, when the observer is just in the reflection direction of the blazed grating, the micro-embossed unit 211 in the non-image-text area 21 of the optical anti-counterfeiting element can be observed. In the micro-relief unit 211, although the effective part of the grating micro-relief structure does not occupy the whole space, the blazed grating with the reflective layer 3 in the background formed by the non-image-text area has sufficient reflectivity to support the image without the reflective layer, and thus the negative image information, such as the number "1", can be observed.

Fig. 3 is a schematic diagram of the principle of imaging of different micro-relief units provided by the present invention, where an image-text area 21 of an optical anti-counterfeiting element has a plurality of micro-relief units (9 in fig. 3), as shown in fig. 3, in the process of synthesizing on a computer, an embossed layer can be regarded as being formed by overlapping different image-text information and masks, that is, the position occupied by each micro-relief unit is determined by a corresponding "mask" picture, and the image-text situation formed by the complete background formed by the micro-relief units and the corresponding image-text area at the corresponding position is determined by a corresponding "image-text" picture, as shown in fig. 3, the image-text "and" mask "schematic diagram of each micro-relief unit is given, and as shown in fig. 3, the optical anti-counterfeiting element is formed by 9" masks "image-text" at the corresponding positions. By combining the 9 "masks" shown in fig. 3 and the 9 "images and texts" at corresponding positions in an overlapping manner, a final optical anti-counterfeiting element is formed, and those skilled in the art should understand that this process is to obtain a combination by overlapping each "mask" and the corresponding "image and text" and then to superimpose the obtained 9 combinations to form the final optical anti-counterfeiting element.

Because the orientation of the background blazed grating in each micro-relief unit is different, the information of different micro-relief units can be observed under different angles, for example, the information of the micro-relief unit 211 can be observed from the upper left, and by analogy, the image-text information can be observed in the whole space coordinate. The pictures and texts in each micro-relief unit are in different positions, and when the micro-relief unit is observed from different angles, an observer feels the change of the positions of the pictures and texts, so that the dynamic effect is realized. As shown in fig. 4, when viewed from the upper left, the blazed grating in the background (i.e. non-image-text area) of the micro-relief unit 211 just reflects the incident light to be observed by human eyes, and the background is bright, while the character "1" (i.e. image-text area) in the micro-relief unit 211 has no reflective layer, so its reflectivity is much lower than that of the background, and thus, it is contrasted with the background to form the shadow "1" of the bright background and dark character. At the moment, the graphic and text information '1' is positioned at the upper left side of the anti-counterfeiting element; when viewed from above, a "1" is located on the upper side of the security element; when viewed from the top right, "1" is on the top right of the security element, and so on. Because the parameters of the grating micro-relief structures in different micro-relief units are different, when one micro-relief unit reflects light rays into human eyes, the reflected light rays of other micro-relief units cannot be observed by the human eyes, and therefore the problem of mutual interference among the micro-relief units does not exist. Therefore, as long as human eyes can observe bright background and shadow texts, only one micro-relief unit plays a role in reflection, so that the phenomenon that the multiple texts are interfered with each other is avoided, and clear recognition of the texts is ensured. It should be noted that the graph in fig. 3 is for more clearly explaining the motion generation process and various relationships between the micro-relief units, and the resolution of the schematic diagram is much smaller than that of the actual design diagram, so that the phenomenon of blurring or frame missing does not occur during actual observation.

Fig. 4 is a schematic diagram showing a dynamic effect floating on the surface of the optical security element provided by the present invention, and fig. 5 is a schematic diagram showing a dynamic effect sinking below the surface of the optical security element provided by the present invention. The observation effect formed in fig. 4 is homodromous, that is, during the process of horizontally changing the observation angle, the image (i.e. the image-text information "1") synchronously moves horizontally along with the movement of human eyes in the same direction. In this case, the human eyes will also simultaneously obtain a floating feature in which the pattern floats above the surface on which the optical security element 1 is located. If the position of the image in fig. 4 is changed in the horizontal direction as in the case shown in fig. 5, the observation effect can be obtained as a reverse dynamic feature, that is, the image moves horizontally in synchronization with the opposite direction of the movement of the human eyes in horizontally changing the observation angle. In this case, the human eyes will also acquire a characteristic of the sinking that the pattern sinks below the surface on which the optical security element is located. The depth of the float and sink features in fig. 4 and 5 are positively correlated to the intensity of the dynamic sense of the image (i.e., the distance moved per horizontal viewing angle range). Similarly, the same sense of motion and the reverse sense of motion can be formed in the same way in the vertical direction, and the description is omitted here.

Fig. 6 is a schematic diagram of the present invention for showing dynamic zooming effect, when a pattern "1" with different sizes is adopted, a full parallax pattern feature with zooming feature can be obtained. Fig. 7 is a schematic diagram showing a dynamic effect of rotation provided by the present invention, and when a pattern "1" with different rotation angles is adopted, a full parallax pattern feature with a rotation feature can be obtained. The principle of fig. 6 and 7 is similar to that of fig. 4, and will not be described herein.

The reflective layer 3 described in the present invention comprises at least one of a metal layer, a metal compound layer, a stack of high and low refractive index materials and a fabry-perot interferometer.

The reflective layer may be an Al layer, which may have a thickness of, for example, 40 nm. The reflective layer is not limited to the Al layer in practical applications, and may include any one or a combination of the following various coatings:

a single-layer metal plating layer;

a plurality of metal coatings;

a coating formed by sequentially stacking an absorption layer, a low-refractive-index dielectric layer and a reflection layer, wherein the reflection layer or the absorption layer is in contact with the grating micro-relief structure (and possibly the light absorption microstructure);

a multi-medium layer coating formed by sequentially stacking a high-refractive-index medium layer, a low-refractive-index medium layer and a high-refractive-index medium layer;

and a coating layer formed by sequentially stacking an absorption layer, a high refractive index medium layer and a reflection layer, wherein the reflection layer or the absorption layer is in contact with the grating micro-relief structure (and possibly the light absorption microstructure).

The structure of the reflective layer may be referred to as an interference multilayer film structure, and the interference multilayer film structure may form a fabry-perot (FP) resonator, which has a selective effect on incident white light, so that the emergent light only includes certain wavelength bands, thereby forming a specific color, when the incident angle changes, the optical path relative to the incident angle changes, and the interference wavelength band also changes, thereby causing the color presented to an observer to change accordingly, thereby forming a color-changing light variable effect. In the embodiment according to the present invention, the high refractive index dielectric layer refers to a dielectric layer having a refractive index of 1.7 or more, and the material thereof may be ZnS, TiN, TiO2, TiO, Ti2O3, Ti3O5, Ta2O5, Nb2O5, CeO2, Bi2O3, Cr2O3, Fe2O3, HfO2, ZnO, or the like, and the low refractive index dielectric layer refers to a dielectric layer having a refractive index of less than 1.7, and the material thereof may be MgF2, SiO2, or the like. The material of the reflecting layer can be metal such as Al, Cu, Ni, Cr, Ag, Fe, Sn, Au, Pt and the like or mixture and alloy thereof; the absorbing layer material can be metal such as Al, Cr, Ni, Cu, Co, Ti, V, W, Sn, Si, Ge, etc. or their mixture and alloy. The reflecting layer is used for enhancing the diffraction and/or reflection intensity of the grating micro-relief structure and providing the color characteristics of the reflecting layer, so that the optical anti-counterfeiting element has richer color selection and higher anti-counterfeiting capability.

The reflective layer may be formed on the grating micro-relief structure by physical and/or chemical deposition methods, such as, but not limited to, thermal evaporation, magnetron sputtering, MOCVD, molecular beam epitaxy, and the like. Preferably, the reflective layer may be formed on the grating micro-relief structure in the form of a conformal coating.

The specific structure of the reflective layer will be explained below with reference to fig. 8, taking as an example the reflective layer formed on the grating micro-relief structure. Fig. 8 is a schematic cross-sectional view of a fabry-perot structure as a reflective layer according to the present invention, and as shown in fig. 8, when the reflective layer according to the present invention is a multilayer film structure, especially a fabry-perot (FP) cavity, for example, a stack structure of chromium 31 (absorption layer), magnesium fluoride 32 (dielectric layer), and aluminum 33 (reflective layer) from top to bottom is formed to form a reflective layer 3, which is deposited on the relief layer 2, thereby forming the entire background region. The color of the reflective layer changes when the viewing direction is changed. For example, when the chromium layer 61 is 9nm, the magnesium fluoride layer 62 is 470nm, and the aluminum layer 63 is 70nm, when an observer observes the surface of the element 1 perpendicularly, the non-image-text area of the optical anti-counterfeiting element presents magenta color; when obliquely observed, the non-image-text area of the optical anti-counterfeiting element presents green. Therefore, the viewer will have an overall look and feel that the distance between the number "1" and the number "0" changes as the color of the background (i.e., the non-image-text area) changes during the process of changing the viewing angle. The integration of the color change effect and the dynamic effect is realized.

In order to improve the contrast with the reflective layer of the background formed by the non-image-text area, a light absorption microstructure can be used as a light trap to absorb incident light in the image-text area, so that the whole spectrum of visible light can be absorbed, reflected light can be inhibited, and a so-called optical black structure can be formed. Fig. 9 is a schematic cross-sectional view of an optical security element of the present invention, in which the image-text region is a light-absorbing microstructure, and as shown in fig. 9, the image-text region 22 is formed by a plurality of light-absorbing microstructures, and the light-absorbing microstructures have a light-trapping effect on incident light. The image-text area 22 shown in fig. 9 has two image-

text sub-areas

221, 222 which can be used to form the different images-text, which are only exemplarily shown in fig. 9, but of course each of which is formed by a plurality of light-absorbing microstructures. The light absorbing microstructures have a high aspect ratio (i.e., a ratio of depth to width), and when light is incident on the light absorbing microstructures, since the light absorbing microstructures have a high aspect ratio, the incident light undergoes multiple reflections, absorption, resonance, etc. between the light absorbing microstructures, no light "escapes" the light absorbing microstructures or little light exits the light absorbing microstructures, and a "trap" of light is formed, thereby forming black ("optical black").

It will be appreciated that where the image area 22 is formed of light absorbing microstructures (that is, the image area is not a flat area), a reflective layer also overlies the light absorbing microstructures, i.e. there may be a reflective layer over the image area 22, whereas where the image area 22 is a flat area, there is no reflective layer in the image area 22 to reduce reflection of light.

It will be appreciated by those skilled in the art that the light absorbing microstructures are similar to the grating micro-relief structures (e.g., 2111, 2112, etc.) in shape and size, and the light absorbing microstructures have a feature size of 0.1 μm to 1 μm and an aspect ratio greater than 0.3. The characteristic dimension of the light absorbing microstructures is the width of the light absorbing microstructures.

In one embodiment, the light absorbing microstructures may have a feature size of 1 μm and a depth of 0.8 μm. Of course, the feature size of the light absorbing microstructures can be less than 1 μm or less than 0.5 μm, and the aspect ratio can be greater than 0.8.

In another embodiment, the light absorbing microstructure has a feature size of 330nm and a depth of 180nm, in which case the light absorbing microstructure regions appear dark brown, whether the microimages are viewed microscopically or the macroscopic images are viewed directly.

The light absorption microstructure can be obtained through micro-nano processing modes such as optical exposure, electron beam exposure and the like, and is copied in batches through processing modes such as ultraviolet casting, mould pressing, nano imprinting and the like. The area covered by the light-absorbing microstructures in the above general process is deterministically determined by the original plate and is not affected by the batch process, and has unique advantages over conventional ink-printed microimage layers, such as complete reduction of design size, no expansion, higher contrast and resolution, and the fineness of the light-absorbing microstructures is determined by their characteristic size, which can be in the order of microns or less, and higher resolution than ink-printed microimages.

The cross section of the light absorbing microstructure is any one of circular, sinusoidal, rectangular and triangular, and the top view shape can be any geometrical shape, such as circular, polygonal and the like. Similar to the grating microrelief structure, the light absorbing microstructures can be periodic or aperiodic.

The absorption of different wave bands of incident light can be realized by adjusting the parameters of the light absorption microstructure to obtain various colors, and when aluminum is used as a reflecting layer (the reflecting layer covers the grating micro-relief structure and the light absorption microstructure), the color of characters of pictures and texts observed by naked eyes is red when the depth of the light absorption microstructure is 100nm and the width of the light absorption microstructure is 300 nm; when the depth of the light absorption microstructure is 180nm and the width of the light absorption microstructure is 345nm, the color of the characters of the pictures and texts observed by naked eyes is brown; when the depth of the light absorption microstructure is 300nm and the width is 250nm, the color of the characters of the pictures and texts observed by naked eyes is black.

Because the background area formed by the non-image-text area has the grating micro-relief structure, and the reflecting layer is deposited on the grating micro-relief structure, the reflectivity is higher and can reach more than 50 percent, even approach 90 percent. The surface of the text area 22 is not provided with a reflective layer, and the reflectivity is generally less than 10%. Therefore, the reflectivity difference between the two is large, and clear negative image and text information can be formed. In order to further improve the difference of the reflectivity between the background reflective layer and the characters without the reflective layer and increase the contrast of the negative image, an absorption layer can be coated on the image-text area or the other surface of the image-text area substrate, so that the absorption of the character area to incident light is further increased, the reflectivity is reduced, and the contrast of the negative image is improved.

The optical anti-counterfeiting element provided by the invention can be covered with a coloring layer on the image-text area. The colored layer and the relief layer may be on different side surfaces of the substrate or on the same side surface of the substrate.

Fig. 10 is a schematic cross-sectional view of an optical security element provided by the present invention, in which the colored layer and the relief layer are on different side surfaces of the substrate, and as shown in fig. 10, the colored layer 4 and the relief layer 2 are in contact with different side surfaces of the substrate 1, that is, the colored layer 4 and the relief layer 2 are on different side surfaces of the substrate 1, and the reflective layer 3 and the relief layer 2 are on the same side surface of the substrate 1. For example, the embossed layer 2 is on the upper surface of the substrate 1, and the colored layer 4 is on the lower surface of the substrate 1. In the presence of the colored layer 4, the colored layer 4 can absorb the light passing through the image-text area 2, so as to prevent the light from reflecting through a bearing object (such as paper and other materials at the lower part of the optical anti-counterfeiting element) to interfere the reflection modulation of the

micro-embossed units

211, 212 and 213 in the non-image-text area 21 on the light. As shown in fig. 10, in the case that the text area 22 includes two text sub-areas 221, 222 (i.e. the first text sub-area 221 and the second text sub-area 222), the coloring layer 4 may also include two coloring sub-layers 41, 42 (i.e. the first coloring sub-layer 41 and the second coloring sub-layer 42), wherein the first coloring sub-layer 41 can absorb the light passing through the first text sub-area 221, and the second coloring sub-layer 42 can absorb the light passing through the second text sub-area 222.

Fig. 11 is a schematic cross-sectional view of the optical security element provided by the present invention, in which the colored layer and the relief layer are on the surface of the same side of the substrate, and as shown in fig. 11, the relief layer 2 is located between the colored layer 4 and the substrate 1, that is, the colored layer 4 and the relief layer 2 are on the surface of the same side of the substrate 1, that is, the relief layer 2, the reflective layer 3, and the colored layer 4 are on the surface of the same side of the substrate 1, that is, all on the upper surface of the substrate 1 or all on the lower surface of the substrate 1. In this case, the observer needs to see through the substrate 3 for observation, and in this embodiment, because the colored layer 4 and the embossed layer 2 are located at the same side, interference of light rays at different interfaces is avoided, which is more favorable for absorption of light rays and improvement of text contrast, and is favorable for observation.

Fig. 12 is a schematic cross-sectional view of an optical anti-counterfeiting element provided by the present invention, in which the colors of colored layers covered on different image-text sub-areas are different, and as shown in fig. 12, the image-text area has a plurality of image-text sub-areas, and the colors of the colored layers covered on different image-text sub-areas are different. Taking fig. 12 as an example, the image-text area 22 has two image-

text sub-areas

221, 222, and correspondingly, the coloring layer 4 has two

coloring sub-layers

41, 42, a first image-text sub-area 221 covers the first coloring sub-layer 41, and a second image-text sub-area 222 covers the second coloring sub-layer 42, wherein the first coloring sub-layer 41 and the second coloring sub-layer 42 have different colors.

The colors of the coloring layers 4 at different positions of the text area (i.e. different text sub-areas) may be different, as shown in fig. 11, a first coloring sub-layer 41 is below the position of the first text sub-area 221, a second coloring sub-layer 42 is below the position of the second text sub-area 222, and the colors of the first coloring sub-layer 41 and the second coloring sub-layer 42 are different. When the observer views from the relief layer 2 side, the reflected light of the reflective layer 3 on the non-image-text region 21 can be observed, and the reflected light of the colored layer 4 can be observed through the image-text region 22. Since the coloured layer 4 is capable of absorbing most of the spectral energy of the incident light, the energy distribution of the remaining wavelengths in the spectrum of the reflected light constitutes the colour that is ultimately perceived by the human eye.

Fig. 13 is a dynamic diagram that different characters have different colors, as shown in fig. 13, the first image-text sub-region 221 and the second image-text sub-region 222 form two different images, and taking fig. 13 as an example, it is assumed that the first coloring sub-layer 41 is red and is located below the first image-text region 221, and the image-text formed by the first image-text region 221 is a number "1"; the second coloring sublayer 42 is blue and is located under the second text region 222, and the text formed by the second text region 222 is the number "0". The situation as shown in fig. 13 is finally formed. When the optical anti-counterfeiting element 1 is tilted or the observation angle of an observer is changed or the incident direction of incident light is changed, the distance between the number "1" and the number "0" can be observed to change, and a dynamic effect is formed. Also, due to the presence of the first and

second pigmented sublayers

41, 42, the number "1" represents the color of the first pigmented sublayer 41, in this embodiment red, and the number "0" represents the color of the second pigmented sublayer 42, in this embodiment blue. Finally, the dynamic characteristics of the characters with different colors and texts are formed. Such multi-colored animation effects are difficult to achieve with a single microstructure or reflective layer or pigment. Fig. 13 shows the effects observed from 40 ° (-40 °), 15 ° (-15 °), 15 ° (15 °), and 40 ° (40 °) to the left, respectively.

Fig. 14 is a dynamic diagram of the same text having different colors, as shown in fig. 14, different text sub-areas 221, 222 of the text area 22 are located at different positions of the formed text, taking fig. 14 as an example, the first coloring layer 41 is red and is located below the first text sub-area 221, wherein the first text sub-area 221 forms an upper half of the number "10"; the second coloured layer 42 is blue and is located below the second teletext sub-region 222, wherein the second teletext sub-region 222 forms the lower half of the number "10". Resulting in the situation shown in fig. 14. When the optical anti-counterfeiting element 1 is tilted or the observation angle of an observer is changed or the incident direction of incident light is changed, the distance between the number "1" and the number "0" can be observed to change, and a dynamic effect is formed. Also, due to the presence of the first colored layer 41 and the second colored layer 42, the upper half of the number "10" shows the color of the first colored layer 41, red in this embodiment, and the lower half of the number "10" shows the color of the second colored layer 42, blue in this embodiment. Finally, dynamic characteristics of different positions of the same image-text are formed. Fig. 14 shows the effects observed from 40 ° (-40 °), 15 ° (-15 °), 15 ° (15 °), and 40 ° (40 °) to the left, respectively.

In the optical anti-counterfeiting element provided by the invention, the coloring layer can also select color-changing ink with the color changing along with the observation angle, such as OVI ink, besides the pigment with fixed color. Fig. 15 is a dynamic schematic diagram of the characters with color change provided by the present invention, as shown in fig. 15, when the optical anti-counterfeiting element is tilted or the observation angle of the observer is changed, or the incident direction of the incident light is changed, the distance between the number "1" and the number "0" can be observed to change, so as to form a dynamic effect, and the color of the number "10" changes with the change of the observation angle because the colored layer 4 is the color-changing ink. Fig. 15 shows the effects observed from 40 ° (-40 °), 15 ° (-15 °), 15 ° (15 °), and 40 ° (40 °) to the left, respectively.

Correspondingly, the invention also provides a preparation method of the optical anti-counterfeiting element, which comprises the following steps: forming a relief layer on the substrate, wherein the relief layer is provided with a non-image-text area and a flat image-text area which are formed by the grating micro-relief structure; depositing a reflective layer on the relief layer; and removing the reflective layer deposited on the image-text area. In order to provide the contrast of the image displayed in the image area, the method for preparing the optical anti-counterfeiting element provided by the invention may further include coating a coloring layer on the image area of the relief layer, where the specific position, color and other characteristics of the coloring layer have been described above in detail, and are not described herein again. As can be seen from the above description, the image-text region of the relief layer can also be formed by a light-absorbing microstructure, and thus the present invention provides a method further comprising: forming a light absorption microstructure in the image-text area; wherein, in case that the image-text area of the relief layer is formed by the light-absorbing microstructure, the reflective layer deposited on the image-text area is not removed.

Fig. 16 is a flowchart of a method for manufacturing an optical security element according to the present invention, as shown in fig. 16, the method includes:

step 1601, forming a relief layer on a substrate, wherein the substrate may be a transparent substrate or a translucent substrate and includes two surfaces, and the relief layer has a non-image area and a flat image area formed by a grating micro-relief structure. The grating micro-relief structure can be manufactured by an electron beam direct etching method or a laser direct etching method, the parameters of the grating micro-relief structure are configured in the manufacturing process, and then the relief layer formed by the grating micro-relief structure is formed on one surface of the base material.

Step 1602, a reflective layer is deposited on the relief layer, where the reflective layer 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 layer (metal or high refractive index medium), or a reflective layer of a fabry-perot (F-P) structure.

Step 1603, the reflective layer deposited in the image area is removed to reduce the attenuation of light, and it should be noted that if the light absorbing microstructures are formed in the image area, this step, i.e. the reflective layer in the image area, need not be removed. In addition, it should be noted that the light absorbing microstructures formed in the image-text area may be high-aspect-ratio light absorbing microstructures or large-depth light absorbing microstructures, and the parameters of the light absorbing microstructures are configured during the process of manufacturing the light absorbing microstructures, which is combined with step 1601, that is, the relief layer formed by the grating micro-relief structure and the light absorbing microstructures is formed on one surface of the substrate.

And 1604, coating a coloring layer on the image-text area of the relief layer, wherein the characteristics of the coloring layer such as specific position and color can be obtained according to the description above. Specifically, the colored layer may be coated on the surface of the other side of the substrate or the surface of the same side as the relief layer, depending on the properties of the deposited reflective layer. For example, when the reflective layer is a "microstructure/absorber/dielectric/reflective film" or "high index/low index" stack, the colored layer and the relief layer can be on the same side surface of the substrate; when the reflective layer is other types of "microstructure/reflective film/dielectric film/absorbing film" or "high refractive index/low refractive index" or metallic reflective layer, the colored layer and the embossed layer may be on different side surfaces of the substrate.

After the optical anti-counterfeiting element is prepared by the method, protective layers can be coated on two sides of the optical anti-counterfeiting element, and the protective layers can protect the anti-counterfeiting element from being influenced by the external environment and protect the corrosion resistance of the reflecting layer, wherein the protective layers are required to have certain transparency and cannot interfere incident light and reflected light.

For an intuitive effect, the inventors have shown a schematic representation of an optical security element by way of fig. 17, from which fig. 17 the non-image area 21 and the image area 22 can be seen, the image area 22 forming the number "10".

Correspondingly, the invention also provides an optical anti-counterfeiting product comprising the optical anti-counterfeiting 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.

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. An optical security element comprising a substrate, a relief layer on the substrate, and a reflective layer at least partially covering the relief layer, the relief layer comprising:

the non-image-text area is composed of a plurality of non-overlapping micro-relief units, each micro-relief unit is provided with a plurality of grating micro-relief structures, the reflecting layer covers the grating micro-relief structures, and the reflecting layer has a modulation effect on incident light; and

and the image-text area is not overlapped with the non-image-text area to form transparent image-text.

2. An optical security element according to claim 1, wherein in the plurality of micro-relief units, the grating micro-relief structures in different micro-relief units reflect incident light in different directions, and the grating micro-relief structures in the same micro-relief unit reflect incident light in the same direction.

3. An optical security element according to claim 1, wherein the micro-relief elements are a combination of one or more of a sawtooth grating, a sinusoidal grating, a rectangular grating.

4. An optical security element according to claim 2, wherein the characteristic dimension of the grating micro-relief structure is from 3 μm to 100 μm.

5. An optical security element according to claim 1, wherein the size of any of the grating microrelief structures is at least an order of magnitude smaller than the size of the non-image-text regions.

6. An optical security element according to claim 1, wherein the reflective layer comprises at least one of a metal layer, a metal compound layer, a stack of high and low index materials and a fabry-perot interferometer.

7. An optical security element according to claim 1, wherein the image-text region is a flat region.

8. An optical security element according to claim 1 wherein the image area is formed from a plurality of light absorbing microstructures having a light trapping effect on incident light.

9. An optical security element according to claim 8, wherein the light absorbing microstructures have any one of a circular, sinusoidal, rectangular, triangular cross-section.

10. An optical security element according to claim 8, wherein the light absorbing microstructures have a feature size of 0.1 μm to 1 μm and an aspect ratio of greater than 0.3.

11. An optical security element according to claim 8, wherein the image-text area is covered with a coloured layer.

12. An optical security element according to claim 11, wherein the coloured layer and the relief layer are in contact with surfaces on different sides of the substrate.

13. An optical security element according to claim 11, wherein the relief layer is between the coloured layer and the substrate.

14. An optical security element as claimed in claim 11, wherein the image-text area has a plurality of image-text sub-areas, the coloured layer overlying different image-text sub-areas being of different colours.

15. An optical security element according to claim 8, wherein the reflective layer also overlies the light absorbing microstructures.

16. An optical security product comprising an optical security element according to any one of claims 1 to 15.

17. A method of making an optical security element, the method comprising:

forming a relief layer on a substrate, the relief layer having a non-image-text region and a flat image-text region formed by a grating micro-relief structure;

depositing a reflective layer on the relief layer; and

and removing the reflecting layer deposited on the image-text area.

18. The method of claim 17, further comprising:

and coating a coloring layer on the image-text area of the relief layer.

19. The method of claim 17, further comprising:

forming a light absorption microstructure in the image-text area;

wherein, in case the image-text area of the relief layer is formed by a light-absorbing microstructure, the reflective layer deposited on the image-text area is not removed.