EP4331857A1

EP4331857A1 - Optical anti-counterfeiting element, design method therefor, and anti-counterfeiting product

Info

Publication number: EP4331857A1
Application number: EP22794222.4A
Authority: EP
Inventors: Kai Sun; Jun Zhu
Original assignee: China Banknote Printing and Minting Corp; Zhongchao Special Security Technology Co Ltd
Current assignee: China Banknote Printing and Minting Corp; Zhongchao Special Security Technology Co Ltd
Priority date: 2021-04-25
Filing date: 2022-01-25
Publication date: 2024-03-06
Also published as: CN115230363B; WO2022227741A1; CN115230363A

Abstract

The present invention provides an optical anti-counterfeiting element and a design method therefor, and an anti-counterfeiting product. The optical anti-counterfeiting element has a roughly smooth diffuse reflective curved surface. Incident light is reflected by the diffuse reflective curved surface and then may form a roughly uniform brightness distribution in a range no less than a preset observation angle set Ωv. the diffuse reflective curved surface comprises modified curved surface regions and unmodified curved surface regions, the modified curved surface regions and the unmodified curved surface regions have different reflective properties, and the modified curved surface regions correspond to the pattern regions of animation frames. When the diffuse reflective curved surface is irradiated by the incident light, the modified curved surface regions collectively appear as a pattern of a dynamic feature, and the unmodified curved surface regions collectively appear as a background of the dynamic features. The fabrication process therefor is simple, and dynamic features such as color and/or bright and dark contrast may be flexibly achieved.

Description

Cross-Reference to Related Disclosure

The present invention claims priority to Chinese Patent Disclosure No. 202110449712.1, filed to the China National Intellectual Property Administration on April 25, 2021 and entitled "Optical Anti-Counterfeiting Element and Design Method Therefor, and Anti-Counterfeiting Product", which is incorporated herein by reference in its entirety.

Technical Field

The present invention relates to the technical field of anti-counterfeiting, and specifically relates to an optical anti-counterfeiting element and a design method therefor, and an anti-counterfeiting product.

Background

In order to prevent counterfeiting generated by means such as scanning and copying, etc., optical anti-counterfeiting technology has been widely applied in various high-security or high-value-added products such as banknotes and financial bills, and has obtained a very good effect.
Currently, an attractive technique is to combine micro-structures determined by plate-making with an optically variable layer; as disclosed in Chinese patents CN 102712207 A and CN 107995894 A , the brightness distribution of reflected light is modulated by a pre-designed reflective micro-surface, to achieve a dynamic effect, and an interference plating layer may be superimposed to achieve a combination of color change and dynamic effect. This can generally produce patterns, such as a variety of motion effects, e.g., lines, circles, curves or characters, and can produce a three-dimensional stereoscopic sense. However, in most cases, color tones of a pattern and a background can only be the same, and a bright-dark contrast relationship is also basically single, and thus it is difficult to achieve dynamic features of multiple colors or any bright-dark relationship.
A Moire amplification construction based on micro-lenses and micro-patterns can also generate a display image having a three-dimensional depth effect, for example as described in patent WO 2005/052650 A2 . Here, a periodic display image composed of many small micro-patterns is amplified by grids composed of micro-lenses with similar but not exactly the same periods. In this way, a stereoscopic sense obviously located before or after an actual surface may be generated, or so-called orthogonal parallax motion may be generated. However, such a Moire amplification construction has a disadvantage that the manufacturing thereof is complicated, two imprint steps for the micro-lenses and the micro-patterns are required, and precise alignment is required between the two steps.
Finally, for example, as described in patent WO 2014/108303 A1 , a magnetically arranged reflective pigment is aligned with a magnet having a corresponding shape, thereby generating a bright (in particular annular) dynamic effect which includes a certain depth effect. This effect is very bright and easy to see clearly, but the required magnetic ink is relatively expensive, and the type and resolution of the effect are limited by the available magnet and cannot be adjusted at will.
In addition to the listed deficiencies, all the described disclosures use a structure in the form of "unit", such as the reflective micro-surface, the pigment sheet and the micro-lens unit; a sudden change in slope between units and gaps between units inevitably render that a display area of an element cannot be sufficiently represented, thereby reducing the resolution of an image. Therefore, it is necessary to develop an optical anti-counterfeiting element which has detailed enough expressive force, a simple manufacture process and can flexibly achieve dynamic features of color and/or bright-dark contrast, etc.

Summary

Some embodiments of the present invention provide an optical anti-counterfeiting element and a design method therefor, and an anti-counterfeiting product, which have a simple manufacture process, and can flexibly achieve dynamic features such as color and/or bright-dark contrast, etc.
In order to achieve the object, the embodiments of the present invention provide an optical anti-counterfeiting element; the optical anti-counterfeiting element presents a dynamic feature, the dynamic feature is pre-designed as reproduction of a group of animation frames visible at a preset observation angle set Ωv, and each of the group of animation frames includes a pattern region and a background region forming an optical contrast with the pattern region; the optical anti-counterfeiting element has a roughly smooth diffuse reflective curved surface, incident light is reflected by the diffuse reflective curved surface and then may form a roughly uniform brightness distribution in a range no less than the preset observation angle set Ωv; the diffuse reflective curved surface includes modified curved surface regions and unmodified curved surface regions, the modified curved surface regions and the unmodified curved surface regions have different reflective properties, wherein the modified curved surface regions correspond to the pattern regions; and when the diffuse reflective curved surface is irradiated by the incident light, the modified curved surface regions collectively present a pattern of dynamic feature, and the unmodified curved surface regions collectively present a background of the dynamic feature.
In an embodiment mode, the diffuse reflective curved surface is periodic in at least one direction.
In an embodiment mode, the diffuse reflective curved surface is aperiodic in at least one direction.
In an embodiment mode, an average distance between adjacent peaks and valleys of the diffuse reflective curved surface is 5 µm to 100 µm, preferably 10 µm to 30 µm.
In an embodiment mode, an average height difference between adjacent peaks and valleys of the diffuse reflective curved surface is 1 µm to 10 µm.
In an embodiment mode, at least a part of each of the unmodified curved surface regions is smooth or has secondary structures.
In an embodiment mode, each of the modified curved surface regions is modified by one or more of the following manners: adding secondary structures to each of the modified curved surface regions; making each of the modified curved surface regions smooth; making each of the modified curved surface regions flat; configuring each of the modified curved surface regions to have protrusions or concavities compared with the unmodified curved surface regions; adjusting an angle of each of the modified curved surface regions, so that the incident light is reflected to a range exceeding the preset observation angle set Ωv; or adjusting a thickness of plating layer or coating layer of each of the modified curved surface regions to be different from those of the unmodified curved surface regions.
In an embodiment mode, in cases where each of the modified curved surface regions is modified by two or more of the following manners, the two or more of the following manners exist in a parallel combination manner and/or a serial combination manner.
In an embodiment mode, a transverse feature size of the secondary structures is 0.2 µm to 5 µm.
In an embodiment mode, a width of each of the modified curved surface regions is 0.5 µm to 20 µm, preferably 2 µm to 10 µm.
In an embodiment mode, the different reflective properties mean that when irradiated by the incident light, the modified curved surface regions and the unmodified curved surface regions have one or a combination of different reflected colors, different reflected brightness, or different reflected textures.
Embodiments of the present invention further provide a design method for an optical anti-counterfeiting element, the design method comprising: designing a dynamic feature, wherein the dynamic feature is reproduction of a group of animation frames visible at a preset observation angle set Ωv, and each of the group of animation frames includes a pattern region and a background region forming an optical contrast with the pattern region; designing a roughly smooth diffuse reflective curved surface for the optical anti-counterfeiting element, such that after incident light is reflected by the diffuse reflective curved surface, a roughly uniform brightness distribution is formed in a range no less than the preset observation angle set Ωv; modifying regions corresponding to the pattern region of each of the group of animation frames on the basis of an observation angle of each of the group of animation frames, to form modified curved surface regions, so that the modified curved surface regions and unmodified curved surface regions have different reflective properties; and when the diffuse reflective curved surface is irradiated by the incident light, the modified curved surface regions collectively presenting a pattern of the dynamic feature, and the unmodified curved surface regions collectively presenting a background of the dynamic feature.
In an embodiment mode, the diffuse reflective curved surface is periodic in at least one direction.
In an embodiment mode, the diffuse reflective curved surface is aperiodic in at least one direction.
In an embodiment mode, an average distance between adjacent peaks and valleys of the diffuse reflective curved surface is 5 µm to 100 µm, preferably 10 µm to 30 µm.
In an embodiment mode, an average height difference between adjacent peaks and valleys of the diffuse reflective curved surface is 1 µm to 10 µm.
In an embodiment mode, modifying regions corresponding to the pattern region of each of the group of animation frames on the basis of an observation angle of each of the group of animation frames, to form modified curved surface regions, includes: pixelating each of the group of animation frames and the diffuse reflective curved surface; determining a first azimuth angle and a first pitch angle of each of the group of animation frames, the first azimuth angle and the first pitch angle being determined according to an observation angle of each of the group of animation frames; determining a second azimuth angle and a second pitch angle of each pixel of the diffuse reflective curved surface, the second azimuth angle and the second pitch angle being determined according to a normal vector at the each pixel of the diffuse reflective curved surface; and executing the following steps regarding each of the group of animation frames: finding, at positions corresponding to pixels of a pattern region in each of the group of animation frames in the diffuse reflective curved surface, pixels corresponding to the second azimuth angle and the second pitch angle that match the first azimuth angle and the first pitch angle of each of the group of animation frames, to form a region that corresponds to the pattern region of each of the group of animation frames in the diffuse reflective curved surface; and modifying the region formed in the diffuse reflective curved surface and corresponding to the pattern region of each of the group of animation frames.
In an embodiment mode, finding, at positions corresponding to pixels of a pattern region in each of the group of animation frames in the diffuse reflective curved surface, pixels corresponding to the second azimuth angle and the second pitch angle that match the first azimuth angle and the first pitch angle of the pixels of the pattern region, includes: within a preset distance range between the diffuse reflective curved surface and the pixels of the pattern region in each of the group of animation frames, finding pixels which correspond to the second azimuth angle of which an angular difference between the second azimuth angle and half of the first azimuth angle is within a first preset angular difference range, and the second pitch angle of which an angular difference between the second pitch angle and the first pitch angle is within a second preset angular difference range.
In an embodiment mode, the preset distance range means that the distance from the positions where the pixels of the pattern region in each of the group of animation frames are located is less than 100 µm, preferably less than 50 µm; and/or the first preset angular difference range means that the angular difference from the first azimuth angle is less than 3°, preferably less than 0.5°; and/or the second preset angular difference range means that the angular difference from the first pitch angle is less than 3°, preferably less than 0.5°.
In an embodiment mode, modifying regions corresponding to the pattern region of each of the group of animation frames to form modified curved surface regions includes executing one or more of the following manners: adding secondary structures to each of the modified curved surface regions; making each of the modified curved surface regions smooth; making each of the modified curved surface regions flat; configuring each of the modified curved surface regions to have protrusions or concavities compared with the unmodified curved surface regions; adjusting an angle of each of the modified curved surface regions, so that the incident light is reflected to a range exceeding the preset observation angle set Ωv; or adjusting a thickness of plating layer or coating layer of each of the modified curved surface regions to be different from those of the unmodified curved surface regions.
In an embodiment mode, the dynamic feature is one or a combination of translation, rotation, scaling, deformation, looming, and Yin/Yang transformation; and/or the optical contrast is one or a combination of different colors, different brightness, and different textures visible to human eyes.
In an embodiment mode, the width of each of the modified curved surface regions is 0.5 µm to 20 µm, preferably 2 µm to 10 µm.
In an embodiment mode, embodiments of the present invention further provide an anti-counterfeiting product using the optical anti-counterfeiting element.
In an embodiment mode, embodiments of the present invention further provide a data carrier; the data carrier has the optical anti-counterfeiting element or has the anti-counterfeiting product.
The optical anti-counterfeiting element provided in the embodiments of the present invention has a simple manufacture process and can flexibly realize dynamic features such as color and/or bright-dark contrast, etc.; in addition, while various multi-color dynamic features are presented on a macroscopic scale, there is no directly-recognizable arrangement rule on a microscopic scale, thereby enhancing the difficulty of counterfeiting in multi-dimensions such as micro-structure design and manufacture process.
Other features and advantages of embodiments of the present invention will be described in detail in the following part of specific embodiments.

Brief Description of the Drawings

The accompanying drawings are used for providing further understanding of the embodiments of the present invention and constitute a part of the description, and are used for explaining the embodiments of the present invention together with the following specific embodiments, rather than constitute limitation to the embodiments of the present invention. In the accompanying drawings, for clarity, the illustrations are not drawn to scale. In the accompanying drawings:

Fig. 1 is a schematic diagram illustrating a diffuse reflection effect of a diffuse reflective curved surface region of an optical anti-counterfeiting element on incident light;
Fig. 2 is a design sample diagram showing a periodic diffuse reflective curved surface region;
Fig. 3 is a design sample diagram showing an aperiodic diffuse reflective curved surface region;
Fig. 4 is an embodiment in which a curved surface region to be modified is determined according to animation frames;
Fig. 5 is another embodiment in which a curved surface region to be modified is determined according to animation frames;
Fig. 6 is a schematic diagram of modification manners of a part or the whole of modified curved surface regions; and
Fig. 7 is a schematic diagram of the use of an optical anti-counterfeiting element on a banknote.

Detailed Description of the Embodiments

Hereinafter, specific embodiments of the present invention will be described in detail in combination with the accompanying drawings. It should be understood that the specific embodiments described herein are only configured to illustrate and explain embodiments of the present invention, and are not intended to limit embodiments of the present invention.
The embodiments of the present invention provide an optical anti-counterfeiting element; the optical anti-counterfeiting element presents a dynamic feature, the dynamic feature is pre-designed as reproduction of a group of animation frames visible at a preset observation angle set Ωv, and each of the group of animation frames includes a pattern region and a background region forming an optical contrast with the pattern region; the optical anti-counterfeiting element has a roughly smooth diffuse reflective curved surface, incident light is reflected by the diffuse reflective curved surface and then forms a roughly uniform brightness distribution in a range no less than the preset observation angle set Ωv; the diffuse reflective curved surface includes modified curved surface regions and unmodified curved surface regions, the modified curved surface regions and the unmodified curved surface regions have different reflective properties, wherein the modified curved surface regions correspond to the pattern regions; and when the diffuse reflective curved surface is irradiated by the incident light, the modified curved surface regions collectively present a pattern of the dynamic feature, and the unmodified curved surface regions collectively present a background of the dynamic feature, that is, the modified reflective surface elements collectively reproduce the pattern of the dynamic feature, and the unmodified reflective surface elements collectively reproduce the background of the dynamic feature.
The different reflective properties mean that when irradiated by the incident light, the modified curved surface regions and the unmodified curved surface regions have one or a combination of different reflected colors, different reflected brightness, or different reflected textures.
When the diffuse reflective curved surface is irradiated by the incident light, at an observation angle corresponding to an animation frame, the animation frame is observed, wherein a pattern of an observed animation frame is presented by the modified curved surface regions, and a background of the observed animation frame is presented by the unmodified curved surface regions.
In the embodiments of the present invention, "a group of animation frames visible at a preset observation angle set Ωv" means that observation angles are in one-to-one correspondence with each of the group of animation frames, and one observation angle corresponds to one animation frame.
The dynamic feature in the embodiments of the present invention roughly refers to a dynamic feature appearing when an observation angle changes. In principle, the observation angle may be an angle of one or more of three elements, i.e. a light source (i.e. the incident light), an element and an observer. For example, in cases where the positions of illumination light source and human eyes remain unchanged, by holding the optical anti-counterfeiting element or an article having the optical anti-counterfeiting element in hands, and by shaking the element back and forth or left and right, i.e. by changing the angle of the optical anti-counterfeiting element, the designed dynamic feature is seen. To simplify the statement, some embodiments of the present invention define an observation direction by a line connecting the eyes of an observer and an observed point, thereby defining an observation angle. It should be noted that this definition does not materially affect or limit any relevant content of the embodiments of the present invention. The observation angle is a three-dimensional spatial parameter, and therefore needs to be decomposed into at least two angles for accurate description. For example, a pitch angle and an azimuth angle is configured together for description, and angles between an observation direction and three coordinate axes, i.e. x, y, and z may also be configured together for description.
The patterns of the animation frames may be designed as letters, numbers, characters, symbols or geometric shapes (in particular a circle, an ellipse, a triangle, a rectangle, a hexagon or a star, etc.). The dynamic feature generally refers to one of any translation, rotation, scaling, deformation, looming, and Yin/Yang transformation of a design pattern presented by the element and directly visible to human eyes, and may also be any combination of these dynamic features. The translation may be designing such that a design pattern translates in a specific direction, or may be designing such that the design pattern translates in multiple directions, and the translation direction thereof is associated with the observation direction. A common combination feature is designing that while the position of a pattern of an animation frame changes, the shape thereof also changes, for example, transforming from circle into square. The dynamic feature may have an orthogonal parallax motion behavior of the pattern, that is, the motion direction of the pattern is always perpendicular to the change of the observation direction, which further attracts the attention of an observer by a counterintuitive situation. The motion of the patterns of the animation frames may generate a stereoscopic sense of floating above or below the plane where the element is located by the principle of horizontal parallax between two eyes. The pattern also includes a plurality of sub-patterns presenting the same or different motion behaviors and/or the same or different floating heights or floating depths. In particular, the pattern includes at least a first curve and a second curve; when observed in a first or second observation direction respectively, these curves respectively present a first or second target curve located at a central position of a first or second region. When the anti-counterfeiting element is tilted, it is preferred that the two curves move in different (preferably opposite) directions, thereby producing a particularly dynamic appearance. It should be appreciated that in the same manner, the pattern of the anti-counterfeiting element also includes more than two curves; and when the anti-counterfeiting element is tilted, these curves may move in the same or different directions. For example, curves in the form of alphanumeric character strings may alternately exhibit different motion behaviors, e.g. alternately floating above or below the plane of a planar pattern region and moving according to the floating heights thereof when the anti-counterfeiting element is tilted. For the specific principles of various dynamic features, reference may be made to the available patent texts CN 102712207 A , CN 107995894 A , WO 2005/052650 A2 , etc. In the embodiments of the present invention, the terms "pattern" and "pattern region" may be used interchangeably.
During specific design, the dynamic feature may be represented by a group of pictures generated by computer software, such as mathematical calculation software, pattern processing software, etc. For example, a bitmap having a bmp format is used, and design patterns of different colors and a common background of the patterns are reflected by grayscale values of 0-255. Each of the group of pictures corresponds to visual information presented to human eyes at a specific observation angle, and is referred to as an animation frame of the designed dynamic feature.
The preset observation angle set Ωv means that all preset dynamic features is seen when the observation angle of human eyes varies in this set. The optical anti-counterfeiting element may reflect the illumination light out of the set, but these reflected light rays may not be associated with designed animation features, and may also provide relatively dark or black visual information for the dynamic feature. The preset observation angle set Ωv may be described by an azimuth angle and a pitch angle, for example, the azimuth angle is designed to be 0-360°, and the pitch angle is 0-35° or 10-50°, etc., that is, the dynamic feature is seen as long as the human eyes are located in this conical region. The setting of the angle parameters depends on the designer's object, the lighting environment where the observer is located, observation habits, etc.
For a diffuse reflective curved surface S, pitch angle and azimuth angle are configured to determine an orientation of a curved surface region at each position of the diffuse reflective curved surface S. Of course, other parameters can also be configured to determine the orientation of the curved surface region, in particular parameters that are orthogonal to each other are used, such as two orthogonal components of the direction of the curved surface region. In order to produce sufficiently fine patterns and continuously changing dynamic features, the length of fluctuating features of the diffuse reflective curved surface S, i.e. an average distance between adjacent peaks and valleys, is preferably less than the recognition capability of human eyes; and the recognition capability is generally about 100 µm at a distance of distinct vision, and the closer the distance, the higher the resolution capability. Accordingly, the average distance between adjacent peaks and valleys should not exceed 100 µm. On the other hand, an excessively small distance may generate obvious diffraction of light, which affects color stability of the dynamic feature. A transverse size at a distance of 5 µm to 100 µm may not produce obvious diffraction iridescence while producing sufficiently fine features, and the transverse size may further preferably be 10 µm to 30 µm. The average distance between peaks and valleys in the diffuse reflective curved surface S may be calculated by the following method. Selecting a square region with an area A in the diffuse reflective curved surface S, finding the number N of peaks included in the area A, and considering that the number of peaks and the number of valleys are substantially the same, then the average distance is $\overline{a} = \sqrt{A} / 2 N$
.
In the embodiments of the present invention, the diffuse reflective curved surface S is continuous and smooth, that is, the diffuse reflective curved surface S has no break point or crack, and the diffuse reflective curved surface S has no corners. A curved surface satisfies that first derivatives ∂S/∂x and ∂S/∂y are both substantially continuous. For example, a curved surface defined by equation S(x, y)=sin(2πx/p_x)sin(2πy/p_y) is continuous and smooth in both x and y directions, P_x and P_y being periods in the x and y directions. The actual manufacturing precision is certainly limited, and the purpose of some embodiments of the present invention may be achieved if the diffuse reflective curved surface S is roughly smooth. In addition, in practical use, it is not necessary that all positions of the diffuse reflective curved surface S are smooth, and the purpose of some embodiments of the present invention may be achieved if most regions of the diffuse reflective curved surface S, such as 80% or more of the area, have a smooth characteristic. The diffuse reflective curved surface S may be periodic in at least one direction, for example, the diffuse reflective curved surface S is periodic in both x and y directions, for example, a curved surface determined by the following expression: $S (x, y) = \sin (2 πx / p_{x}) \sin (2 πy / p_{y}),$
where p _x represents a period in the x direction, p_y represents a period in the y direction, and x and y represent independent variables.
Of course, it is also possible to have periodicity in only one direction (for example, in the x direction), for example, a curved surface determined by the following expression also satisfies the requirement of smoothness. $S (x, y) = \sin (2 πx / p_{x}) .$
Generally, considering that a function with a period P may be decomposed by using a Fourier series manner, and a one-dimensional periodic function S(x) is taken as an example, $S (x) = \sum_{n = - N}^{N} c_{n} \cdot \exp (i \frac{2 πnx}{P}), where c_{n} = \frac{1}{P} \int_{x_{0}}^{x_{0} + P} S (x) \cdot \exp (- i \frac{2 πnx}{P}) dx .$
Conversely, coefficients C_n and N are set, and a periodic function is constructed by using the following formula, where N is a positive integer. $S (x) = \sum_{n = - N}^{N} c_{n} \cdot \exp (i \frac{2 πnx}{P})$
For an aperiodic diffuse reflective curved surface S, a computer program may be configured to generate a matrix random height matrix, and numerical values of the height matrix represent multiple scatter points on the aperiodic diffuse reflective curved surface S. By performing certain difference processing or blurring processing on the height matrix, the aperiodic diffuse reflective curved surface SS is obtained.
A main function of the diffuse reflective curved surface S is to generate uniform reflected light in the predetermined preset observation angle set Ωv, which is similar to visual impression of diffuse reflection generated by common office paper. For achieving the purpose, the orientation of each curved surface region needs to be selected within a continuous angle set Ωs, and the orientation may be defined by an azimuth angle and a pitch angle, for example. The choice of the continuous angle set Ωs needs to allow for the incident light to be at least evenly reflected into the preset observation angle set Ωv, and thus Ωs must cover a minimum set co-determined by the direction of the incident light ω1, and Ωv. Equivalently, the reflective curved surface S reflects the incident light to an angle set Ωr, Ωr covers the preset observation angle set Ωv, i.e., Ωv being a subset or proper subset of Ωr. In particular, Ωs is designed as a minimum set co-determined by the direction of the incident light ω1, and Ωv, i.e. Ωv is the same as Ωr. For example, when the incident light is normally incident on the surface of an element, that is, when the element is in an xy plane, the incident light is along a z direction; and according to a geometric law of reflection, an azimuth angle of an element of Ωs is the same as an azimuth angle of an element of Ωv, and a pitch angle of the element thereof is half of a pitch angle of the element of Ωv.
In order to realize the dynamic feature, it is necessary to modify the diffuse reflective curved surface according to each pixel point of each of the group of animation frames, so as to change uniform reflection light distribution in the preset observation angle set Ωv. The size of the diffuse reflective curved surface should be greater than the size of the area occupied when all of the group of the animation frames are presented together, so that each of the group of animation frames can correspond to the diffuse reflective curved surface without scaling, and thus each pixel in the pattern region of each of the group of animation frames can find a corresponding position point on the diffuse reflective curved surface, and the position point will be modified.
According to the position Pv where a pattern region contained in a certain animation frame is located and the observed angle ωv thereof, a position Ps and an angle ωs of a curved surface region to be modified are found, for example, a position and an angle of a curved surface region to be modified may be found per pixel. In principle, Pv and Ps should be the same position, and among ωv, ωs and an angle of the incident light ω1, reflection law of geometric optics needs to be satisfied, that is, the incident light, the reflected light and a normal line of the curved surface region are located in the same plane, and the incident angle is equal to a reflected angle. Here, ωs=f(ωv, ωi) is configured to represent that there is a quantitative relationship among the three. The specific calculation formula may be found on a general optical textbook, for example, Bohn's "Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light". In practical design, when Pv=Ps, the angle ωs of the curved surface region at the position, ωv and ωi may not exactly satisfy the geometric law of reflection. Therefore, the curved surface region is modified within a certain range of positions and a certain range of angles, i.e. $Ps \in (Pv - Δ P, Pv + ΔP)$
$ω s \in (f (ω v, ωi) - Δω, f (ω v, ωi) + Δω)$
wherein the selection of position deviation ΔP and angle deviation Δω is specifically determined according to the size of the curved surface region, the resolution of human eyes for angle and size, and the designed dynamic feature; and the principle thereof is that at least one curved surface region to be modified is found, and said curved surface region and a design pattern do not produce a difference distinguishable by human eyes. Generally, the position deviation ΔP is less than 100 µm, preferably less than 50 µm; and the angle deviation Δω is defined as an angle between a normal direction of a modified curved surface region and a normal direction of the curved surface region corresponding to a preset observation angle of the pattern; and the angle deviation Δω should be less than 3°, preferably less than 0.5°.
Generally, assume that the pitch angles of two curved surface regions are θ₁ and θ₂ respectively, and the azimuth angles are respectively cp, and ϕ₂.
The angle between normal lines of the two curved surface regions is calculated by the following formula: $\begin{matrix} Δω = \\ (180 / π) [(sinθ)] {[{(_{1} {cosφ}_{1} - {sinθ}_{2} {cosφ}_{2})}^{2} + {({sinθ}_{1} {sinφ}_{1} - {sinθ}_{2} {sinφ}_{2})}^{2} + {({cosθ}_{1} - {cosθ}_{2})}^{2}]}^{1 / 2} . \end{matrix}$
During specific execution, each of the group of animation frames may be pixelized, and the diffuse reflective curved surface may be pixelized. In optional cases, pixelation may be performed only regarding the pattern region of each of the group of animation frames. The nature of pixelation is to divide an animation frame into, for example, N×M small regions, and the area occupied by each of the small regions may be very small, for example. Similarly, small regions divided after pixelation of the diffuse reflective curved surface may also be very small. For example, in the embodiments of the present invention, a width of each of the small regions is 0.5 µm to 10 µm, preferably 2 µm to 4 µm; and correspondingly, a length of each of the small regions is 0.5 µm to 10 µm, preferably 2 µm to 4 µm.
Further, a first azimuth angle and a first pitch angle of each of the group of animation frames may be determined, and each of the group of animation frames corresponds to a specific observation angle in a one-to-one manner, so that the first azimuth angle and the first pitch angle may be determined according to the observation angle of each of the group of animation frames. In the embodiments of the present invention, the observation angle is a direction vector in a rectangular coordinate system. The angle between the direction vector and the xy-plane is defined as the pitch angle (which can also be said to be a complement angle of an angle between the direction vector and the z-axis). The direction vector is projected onto the xy plane to form a projection vector, in which the angle between the projection vector and the x axis is defined as the azimuth angle.
Further, a second azimuth angle and a second pitch angle of each pixel of the diffuse reflective curved surface may be determined, the second azimuth angle and the second pitch angle being determined according to a normal vector at the each pixel of the diffuse reflective curved surface. In the diffuse reflective curved surface, the azimuth angle of the pixel may be defined as an angle between a normal vector at the pixel and the x axis, and the pitch angle is defined as an angle between the normal vector at the pixel and the z axis. In xyz coordinates defined in the embodiments of the present invention, the xy plane is a plane where the optical anti-counterfeiting element is located, the x axis may be a longitudinal direction of the optical anti-counterfeiting element, the y axis may be a transverse direction of the optical anti-counterfeiting element, and the z axis may be an axis perpendicular to the optical anti-counterfeiting element.
The following steps may be executed regarding each of the group of animation frames: finding, at positions corresponding to pixels of a pattern region in each of the group of animation frames in the diffuse reflective curved surface, pixels corresponding to the second azimuth angle and the second pitch angle that match the first azimuth angle and the first pitch angle of each of the group of animation frames, to form a region that corresponds to the pattern region of each of the group of animation frames in the diffuse reflective curved surface. For example, a group of animation frames may be projected vertically on a diffuse reflective curved surface in the same proportion, so that a position corresponding to each pixel in each of the group of animation frames on the diffuse reflective curved surface may be determined. Finding pixels corresponding to the second azimuth angle and the second pitch angle that match the first azimuth angle and the first pitch angle of each of the group of animation frames, includes: within a preset distance range between the diffuse reflective curved surface and the pixels of the pattern region in each of the group of animation frames, finding pixels which correspond to the second azimuth angle of which an angular difference between the second azimuth angle and the first azimuth angle is within a first preset angular difference range, and the second pitch angle of which an angular difference between the second pitch angle and half of the first pitch angle is within a second preset angular difference range. In an embodiment mode, in cases where the pitch angle is very small, the difference in azimuth angles becomes no longer important. Therefore, in cases where the pitch angle is relatively small, the azimuth angle may not be considered, and only within the preset distance range, pixels corresponding to the second pitch angle of which an angular difference between the second pitch angle and half of the first pitch angle is within the second preset angular difference range may be found. The preset distance range means that the distance from the positions where the pixels of the pattern region in each of the group of animation frames are located is less than 100 µm, preferably less than 50 µm; and/or the first preset angular difference range means that the angular difference from the first azimuth angle is less than 3°, preferably less than 0.5°; and/or the second preset angular difference range means that the angular difference from half of the first pitch angle is less than 3°, preferably less than 0.5°. For one pixel in the pattern region, one or more pixels complying with conditions may be found in the diffuse reflective curved surface, and the one or more pixels complying with conditions can all be modified. After pixels matching each pixel of the pattern region of each of the group of animation frames are found in the diffuse reflective curved surface, these matching pixels form a region corresponding to the pattern region of each of the group of animation frames. The region formed in the diffuse reflective curved surface and corresponding to the pattern region of each of the group of animation frames is modified, and then a modified curved surface region is formed.
Modification to the curved surface region may be adding a secondary structure to the modified curved surface region, and the feature size of the secondary structure is obviously smaller than the feature size of the curved surface region, and thus the secondary structure is spread on the surface of the curved surface region along the direction of the curved surface region. The feature size of the curved surface region of the diffuse reflective curved surface may be characterized by an average distance between adjacent peaks and valleys. A transverse feature size of the secondary structure is 0.2 µm to 5 µm, and can produce a diffraction effect or an absorption effect on visible light. The absorption effect may be absorbing incident light of a specific frequency set by a grating structure of a sub-wavelength scale by means of the principle of surface plasma resonance absorption, thereby changing the color of reflected light while maintaining the original reflection direction. Generally, when the depth of the sub-wavelength structure is relatively deep, for example, 300 nm to 700 nm, effective absorption is generated in a wider frequency set, thereby significantly reducing the brightness of reflected light in this direction, that is, the sub-wavelength structure becomes an optical absorption or optical black structure.
The modified curved surface region may be entirely provided with secondary structures before modification, so that while a uniform reflection light distribution is generated in the preset observation angle set Ωv, a specific color or brightness feature is provided. Accordingly, modification to the curved surface region may make a part or the whole of the modified curved surface region smooth. For example, the secondary structures of the modified curved surface region are removed, so as to generate specular reflection with a higher reflectivity for the whole visible light band. In an embodiment mode, at least a part of the unmodified curved surface region may be provided to be smooth or have a secondary structure.
The modification to the curved surface region may be making the modified curved surface region flat, so that the modified curved surface region can only reflect the incident light to a specific opposite direction. At other observation angles, the modified region does not provide or only provides little reflected light, thereby causing darker or blacker visual perception than other regions.
Modification to the curved surface region may be adjusting an angle of the modified curved surface region, so that the modified curved surface region reflects all light rays incident on the modified curved surface region to a direction exceeding the preset observation angle set Ωv. Generally, the pitch angle of the curved surface region is increased and exceeds a minimum set co-determined by the direction of the incident light ω1, and Ωv, so that the incident light is reflected to exceed the set determined by Ωv. The modified curved surface region does not provide or only provides little reflected light, thereby causing darker or blacker visual perception than other regions.
To generate a pattern of a sufficient contrast, the surface on which the modified curved surface region is located or the surface opposite the surface on which the modified curved surface region is located (e.g. the unmodified curved surface region) may have a plating layer or coating layer. The plating layer or coating layer includes a reflection-enhancement coating layer (in particular a metallization layer), a reflection-enhancement plating layer, a reflective ink layer, an absorption ink layer, a coating layer of a high-refractive index material, and a plating layer of a high-refractive index material. The reflection-enhancement coating layer, plating layer or the reflective ink layer preferably has a color migration effect, i.e. having a color tone change in different observation angles, for example using a Fabry-Perot interference structure. Alternatively, a reflection region and a curved surface region may also be impressed in the reflective ink layer or the absorption ink layer.
Modification to the curved surface region may be that the modified curved surface region forms a protrusion or a concavity compared with the surrounding unmodified curved surface region; or modification to the curved surface region may be that the thickness of the plating layer or the coating layer of the modified curved surface region is different from that of the unmodified curved surface region. For example, there is a reflective plating layer, coating layer or ink in the modified curved surface region, while there is no reflective plating layer, coating layer or ink in the unmodified curved surface region; or there is no reflective plating layer, coating layer or ink in the modified curved surface region, while there is a reflective plating layer, coating layer or ink in the unmodified curved surface region.
Modification to the curved surface region may be serial combined use of the plurality of modification manners. For example, a concavity lower than the unmodified curved surface region is formed in the modified curved surface region, then a secondary structure is added to the concavity, and finally a reflective plating layer of the secondary structure region is removed (i.e. having a thickness different from that of the reflective plating layer of the unmodified curved surface region); or a concavity lower than the unmodified curved surface region is formed in the modified curved surface region, and color ink is filled in the concavity, and the thickness of the color ink is obviously greater than the thickness of the ink in the unmodified curved surface region. Modification to the curved surface region may be parallel combined use of the plurality of modification manners. For example, a flat concavity is formed in a part of the modified curved surface region, and a secondary structure is added to another part of the modified curved surface region along an orientation of the curved surface region. Modification to the curved surface region may be re-combined use of the serial combination manner and the parallel combination manner of the modification manners.
In the embodiments of the present invention, according to the visibility degree of the generated pattern, the width of the modified curved surface region is 0.5 µm to 20 µm, preferably 2 µm to 10 µm. Compared with the unmodified curved surface region, the modified curved surface region has one or a combination of different reflected colors, different reflected brightness, or different reflected textures.
Regarding the optical anti-counterfeiting element, within the preset observation angle set Ωv, the modified curved surface regions collectively present patterns of animation frames, and the unmodified curved surface regions collectively present backgrounds of each of the group of animation framess. The pattern region has different optical contrast from the background region, which may specifically be one or a combination of different colors, different brightness, and different textures visible by human eyes.
The embodiments of the present invention further provide a design method for an optical anti-counterfeiting element, the design method includes: designing a dynamic feature, wherein the dynamic feature is a group of animation frames visible at a preset observation angle set Ωv, and each of the group of animation frames includes a pattern region and a background region forming an optical contrast with the pattern region; designing a roughly smooth diffuse reflective curved surface for the optical anti-counterfeiting element, such that after incident light is reflected by the diffuse reflective curved surface, a roughly uniform brightness distribution is formed in a range no less than the preset observation angle set Ωv; modifying regions corresponding to the pattern region of each of the group of animation frames on the basis of an observation angle of each of the group of animation frames, to form modified curved surface regions, so that the modified curved surface regions and unmodified curved surface regions have different reflective properties; and when the diffuse reflective curved surface is irradiated by the incident light, the modified curved surface regions collectively presenting a pattern of the dynamic feature, and the unmodified curved surface regions collectively presenting a background of the dynamic feature.
During specific design, the dynamic feature may be represented by a group of pictures generated by computer software, such as mathematical calculation software, pattern processing software, etc. For example, a bitmap having a bmp format is used, and design patterns of different colors and a common background of the patterns are reflected by grayscale values of 0-255. Each of the group of pictures corresponds to visual information presented to human eyes at a specific observation angle, and is referred to as an animation frame of the designed dynamic feature. For the specific working principle and benefits of the design method for an optical anti-counterfeiting element in the embodiments of the present invention, reference may be made to the description of the optical anti-counterfeiting element in the embodiments of the present invention, and it will not be repeated here.
The embodiments of the present invention further provide an anti-counterfeiting product using the optical anti-counterfeiting element of any embodiment of the present invention. The anti-counterfeiting product may be in the forms of for example, an anti-counterfeiting thread, an anti-counterfeiting strip, an anti-counterfeiting label, etc. The embodiments of the present invention further provide a data carrier having the anti-counterfeiting element of any embodiment of the present invention or the anti-counterfeiting product of any embodiment of the present invention. The anti-counterfeiting element or the anti-counterfeiting product may be arranged in an opaque region of the data carrier, and a transparent window region or a through opening in the data carrier, or above the transparent window region or through opening. The data carrier may especially be a valuable document, e.g., a banknote (especially a paper banknote, a polymeric material banknote or a thin film composite banknote), stocks, warrant, certificate, ticket, check and a high-value entry ticket, but also an identification card, e.g. a credit card, a bank card, a cash card, an authorization card, a personal identity card, or personal information page of a passport, etc.
Hereinafter, the optical anti-counterfeiting element and the manufacturing method therefor provided in embodiments of the present invention will be further described in conjunction with the accompanying drawings.
Fig. 1 is a schematic diagram illustrating a diffuse reflection effect of a diffuse reflective curved surface region of an optical anti-counterfeiting element on incident light. The plane where the optical anti-counterfeiting element 1 is located is defined as an xy plane, and the diffuse reflective curved surface S is composed of a plurality of curved surface regions 3 connected smoothly. In the embodiments of the present invention, smooth connection means that first derivatives of two connected surfaces are continuous, that is to say, there is no junction between the two but the two are connected, there is neither break nor broken line. The curved surface regions 3 may have protrusions and concavities. In Fig. 1, the optical anti-counterfeiting element 1 has a substrate 6, and the diffuse reflective curved surface S is located on one side of the substrate. However, the presence of the substrate 6 is a requirement for the processing process, and may not belong to a part of the optical anti-counterfeiting element 1 itself. The substrate 6 may serve as a part of an anti-counterfeiting product formed by the optical anti-counterfeiting element 1. Of course, the substrate 6 may also be removed in the anti-counterfeiting product, such as a hot stamping product, a structural layer is transferred to other carriers, and the substrate 6 does not become a part of the anti-counterfeiting product. The substrate 6 does not become an essential constituent part of the optical anti-counterfeiting element 1. Incident light 4 is incident to the side of the substrate 6 provided with the diffuse reflective curved surface S, and the incident light 4 forms a plurality of reflected light rays 5 in different directions through the reflection effect of the diffuse reflective curved surface S. Angular (for example, the angle defined by an azimuth angle and a pitch angle) distribution of the plurality of curved surface regions 3 is controlled, so that a roughly uniform diffuse reflective visual effect covers a preset observation angle set Ωv of a predetermined dynamic feature. For simplifying the statement and without loss of generality, the direction of the incident light 4 is set as a z direction, which is a direction perpendicular to the xy plane. Moreover, the azimuth angles of the elements of the set Ωv are predetermined to be 0° to 360°, and the pitch angles are predetermined to be 0° to 35°. Accordingly, an average distance between peaks and valleys of the diffuse reflective curved surface may be controlled within a range of 20 µm to 50 µm, and the longitudinal height is set to be 0 µm to 10 µm, so that the diffuse reflective curved surface S reflects the incident light 4 to an angle set Ωr, and Ωr covers the preset observation angle set Ωv. In practical designs, a finite numerical value is usually configured to represent a continuous curved surface, and thus the coverage in some embodiments of the present invention specifically means that any element in the set Ωv can find a corresponding element close enough thereto in Ωr, for example, an angle between the two does not exceed 1°. In practical designs, a reflective smooth curved surface should include at least 3000 peaks and valleys, preferably more than 50000, so as to generate a sufficiently fine and uniform reflection light distribution. Fig. 1 only shows that the diffuse reflective curved surface of the optical anti-counterfeiting element can generate a diffuse reflection effect on the incident light, and does not relate to specific dynamic features and modification manners for the curved surface regions.
To further illustrate the specific forms which the diffuse reflective curved surface S can adopt, Fig. 2 exemplifies a design manner of a periodic diffuse reflective curved surface. An analytic equation is used: $S (x, y) = \sin (2 πx / p_{x}) + \sin (2 πy / p_{y}) + 3 \sin (2 πx / p_{x}) \sin (2 πy / p_{y})$
where P_x and P_y are periods in the x and y directions, P_x=20 µm and P_y=30 µm are set. This formula can make a smooth diffuse reflective curved surface with periodicity in both the x and y directions. According to requirements, the pitch angle of each region of the diffuse reflective curved surface may be adjusted as a whole by adjusting the overall fluctuation height of the diffuse reflective curved surface S. Both sine and cosine functions are infinitely derivable, and thus the equation S(x, y) completely satisfies the requirements of continuity and smoothness. Set F(x, y,z)=z-S(x, y)=0, and a normal equation and a normal vector n of any pixel point (x₀, y₀, z₀ ) on the diffuse reflective curved surface S may be calculated from the following formulas, respectively: $(x - x_{0}) / F_{x} (x_{0}, y_{0}, z_{0}) = (y - y_{0}) / F_{y} (x_{0}, y_{0}, z_{0}) = (z - z_{0}) / F_{z} (x_{0}, y_{0}, z_{0})$
$\vec{n} = (F_{x} (x_{0}, y_{0}, z_{0}) F_{y} (x_{0}, y_{0}, z_{0}), F_{z} (x_{0}, y_{0}, z_{0}))$
here F_x represents a first derivative of function F(x, y, z) to x, F_y represents a first derivative of the function F(x, y, z) to y, and F_z represents a first derivative of the function F(x, y, z) to z.
The azimuth angle φ (defined as the angle between the normal vector and the x axis) and the pitch angle θ (defined as the angle between the normal vector and the z axis) of a curved surface region at (x₀, y₀, z₀ ) may be directly obtained via the normal vector: $\cos (θ) = F_{z} / \sqrt{{F_{x}}^{2} + F_{y}^{} + F_{z}^{}} | (x_{0}, y_{0}, z_{0});$
$\tan (ϕ) = F_{y} / F_{x} | (x_{0}, y_{0}, z_{0}) .$
Fig. 3 exemplifies a design manner of an aperiodic diffuse reflective curved surface. For an aperiodic diffuse reflective curved surface S, one method is that a computer program is configured to generate a matrix random height matrix, and numerical values of the height matrix represent multiple scatter points on the diffuse reflective curved surface S. By performing certain difference processing or blurring processing on the matrix, the aperiodic diffuse reflective curved surface S is obtained. The difference processing may be performed by using manners such as a bilinear interpolation, resampling by using a pixel region relationship, bicubic interpolation in a 4×4 pixel neighborhood, or Lanczos interpolation in an 8×8 pixel neighborhood; and the blurring processing may be performed by using manners such as average blur, defocus blur, motion blur, or Gaussian blur. By the difference processing or blurring processing, it may be ensured that no abrupt change or break exist between heights, and therefore the smooth characteristic of the diffuse reflective curved surface is ensured, that is, the first derivative is roughly continuous. Random heights may be generated using pseudo-random numbers, which are number strings that appear random but are calculated by a deterministic algorithm, and thus in a strict sense, they are not true random numbers. However, pseudo-random numbers are widely used, because the statistic features of pseudo-random selection (e.g. equal probability of each number or statistical independence of successive numbers) are generally sufficient to meet the requirements of practical use, and unlike true random numbers, pseudo-random numbers are easily generated by a computer.
According to the animation frames constituting the dynamic features, a specific curved surface region of a diffusely reflected reflection region is modified, so as to generate partially differentiating reflective properties. The angle of the incident light ωi is set to be along the z-axis direction, Figs. 4 and 5 provide two embodiments illustrating how to determine a curved surface region to be modified.
Fig. 4 is an embodiment in which a curved surface region to be modified is determined according to animation frames. The two tables of Fig. 4 represent pitch angles and azimuth angles of a local curved surface region, respectively. As the sampling density of discrete data is limited, the data of the pitch angles and the azimuth angles in Fig. 4 does not clearly reflect the smooth characteristic of the diffuse reflective curved surface S, which does not affect illustration of the principle of how to determine a curved surface region to be modified by using animation frames in this embodiment.
As shown in Fig. 4, 7 is an animation frame of a dynamic feature; the animation frame is defined as being observed in a direction of pitch angle=0° and azimuth angle=0°. 71 is a pattern region of the animation frame, and 72 is a background region of the animation frame. 71 and 72 have optical contrast visible to human eyes. On the diffuse reflective curved surface S, the size of a reflection region 21 corresponding to the animation frame 7 is at least not less than the size of a region where the animation frame 7 is located, so that visual information of the animation frame 7 is completely presented. Taking any point Pv (which may also be considered as any pixel point) on the pattern region 71 as an example, a corresponding point of Pv is determined in the reflection region 21. In the reflection region 21, by taking Pv as a center point, within the range of ΔP, a curved surface region of which the pitch angle=0° or deviation between the curved surface region and the curved surface region of which the pitch angle=0° is smaller than Δω is found. In cases where the pitch angle is very small, the difference in azimuth angles becomes no longer important, and thus the azimuth angle is not taken into account here. By suitably controlling the magnitude of ΔP and Δw, it is always possible to find a corresponding point of any point Pv in the reflection region 21, i.e. finding a curved surface region to be modified. For example, an average distance between adjacent peaks and valleys of the curved surface region is 30 µm, and ΔP=60 µm and Δω=1° are set, so that a point (0.4°, 75.2°) is found at a lower right position of the point Pv in the reflection region 21; and modification to a curved surface region corresponding to the point can generate a predicted visual contrast at the point Pv of the animation frame 7.
Fig. 5 is another embodiment in which a curved surface region to be modified is determined according to animation frames. The two tables of Fig. 5 represent pitch angles and azimuth angles of a local curved surface region, respectively. As the sampling density of discrete data is limited, the data of the pitch angles and the azimuth angles in Fig. 5 does not clearly reflect the smooth characteristic of the curved surface S, which does not affect illustration of the principle of how to determine a curved surface region to be modified by using animation frames in this embodiment.
As shown in Fig. 5, in an animation frame 8, 81 is a pattern region of the animation frame 8, and 82 is a background region of the animation frame 8. The pattern region 81 and the background region 82 have an optical contrast visible to human eyes. The pattern region 81 has a position change relative to the pattern region 71 in Fig. 4, and the animation frame 8 is defined to be observed in a direction of pitch angle=20° and azimuth angle=90°. On the diffuse reflective curved surface S, the size of a reflection region 22 corresponding to the animation frame 8 is at least not less than the size of the region where the animation frame 8 is located, so that visual information of the animation frame 8 is completely presented. Taking any point Pw (which may also be considered as any pixel point) on the pattern region 81 as an example, a corresponding point of Pw is determined in the reflection region 22. In the reflection region 22, by taking Pw as a center point, within the range of ΔP, a curved surface region which is the same as a curved surface region determined by the angle (pitch angle=10° and azimuth angle=90°) or which has an angular deviation less than Δω is found. By suitably controlling the magnitude of ΔP and Δω, it is always possible to find a curved surface region to be modified in the reflection region 22. For example, an average distance between adjacent peaks and valleys of the curved surface region is 30 µm, and ΔP=60 µm and Δω=1° are set, so that points (10.1°, 92.2°) and (9.8°, 89.7°) are found near the point Pw in the reflection region 22; and modification to curved surface regions respectively corresponding to the two points can generate a predicted visual contrast at the point Pw of the animation frame 8.
The curved surface region may be modified in multiple manners. A part or the whole of a modified curved surface region 31 in Fig. 6 is modified in a particular manner to produce reflective properties different from an unmodified curved surface region 32. 9 is an example of modification manners, wherein
As shown in Fig. 6, 91 represents that modification to the curved surface region is that the modified curved surface region forms a concavity compared with the periphery (e.g., unmodified curved surface region); the depth of the concavity is selected within 0.5 µm to 3 µm, and is related to the width of the modified region. In addition, the modification to the curved surface region may be making the modified curved surface region flat, so that the modified curved surface region can only reflect the incident light to a specific direction. At other observation angles, the modified curved surface region does not provide or only provides little reflected light, thereby causing darker or blacker visual perception than other regions.
As shown in Fig. 6, 92 represents that modification to the curved surface region may be adding a secondary structure to the modified region, and the feature dimension of the secondary structure is obviously smaller than the size of the curved surface region, and thus the secondary structure may be spread on the surface of the curved surface region along the direction of the curved surface region. A transverse feature size of the secondary structure is 0.2 µm to 5 µm, and can produce a diffraction effect or an absorption effect on visible light. The absorption effect may be absorbing incident light of a specific frequency set by a grating structure of a sub-wavelength scale by means of the principle of surface plasma resonance absorption, thereby changing the color of reflected light while maintaining the original reflection direction. Generally, when the depth of the sub-wavelength structure is relatively deep, for example, 300 nm to 700 nm, effective absorption is generated in a wider frequency set, thereby significantly reducing the brightness of reflected light in this direction, that is, the sub-wavelength structure becomes an optical absorption or optical black structure.
As shown in Fig. 6, 93 represents that the modified curved surface region may be entirely provided with secondary structures before modification, so that while a uniform reflection light ray distribution is generated in the observation angle set Ωv, a specific color or brightness feature is provided. Accordingly, modification to the curved surface region may make the modified curved surface region smooth. That is, the secondary structures of the modified curved surface region are removed, so as to generate specular reflection with a higher reflectivity for the full band of visible light.
As shown in Fig. 6, 94 represents that to generate a pattern of a sufficient contrast, the surface on which the modified curved surface region is located or the surface opposite the surface on which the modified curved surface region is located (e.g. the unmodified curved surface region) may have a plating layer or coating layer. The plating layer or coating layer includes a reflection-enhancement coating layer (in particular a metallization layer), a reflection-enhancement plating layer, a reflective ink layer, an absorption ink layer, a coating layer of a high-refractive index material, and a plating layer of a high-refractive index material. The reflection-enhancement coating layer, plating layer or the reflective ink layer preferably has a color migration effect, i.e. having a color tone change in different observation angles, for example using a Fabry-Perot interference structure, e.g. a Cr(5 nm)/MgF₂(500 nm)/AI(50 nm) structure. Alternatively, the reflection region and the curved surface region may also be impressed in the reflective ink layer or the absorption ink layer.
Modification to the curved surface region may be that the thickness of the plating layer or the coating layer of the modified curved surface region is different from that of the unmodified curved surface region. For example, there is a reflective plating layer, coating layer or ink in the modified curved surface region, while there is no reflective plating layer, coating layer or ink in the unmodified curved surface region; or there is no reflective plating layer, coating layer or ink in the modified curved surface region, while there is a reflective plating layer, coating layer or ink in the unmodified curved surface region.
As shown in Fig. 6, 95 represents that modification to the curved surface region may be adjusting an angle of the modified curved surface region, so that the incident light is reflected to a direction exceeding the preset observation angle set Ωv. Generally, the pitch angle of the curved surface region is increased and exceeds a minimum set co-determined by the direction of the incident light ω1, and Ωv, so that the incident light may be reflected to exceed the set determined by Ωv. The modified curved surface region does not provide or only provides few reflected light rays, thereby causing darker or blacker visual perception than other regions.
As shown in Fig. 6, 96 represents that modification to the curved surface region may be serial combined use of the plurality of modification manners. For example, a concavity lower than the periphery region is formed in the modified curved surface region, then a secondary structure is added to the concavity, and finally a reflective plating layer of the secondary structure region is removed (i.e. having a thickness different from that of the unmodified curved surface region); or a concavity lower than the periphery region is formed in the modified curved surface region, and color ink is filled in the concavity, and the thickness of the color ink is obviously greater than the thickness of the ink in the unmodified curved surface region.
As shown in Fig. 6, 97 represents that modification to the curved surface region may be parallel combined use of the plurality of modification manners. For example, a flat concavity is formed in a part of the modified curved surface region, and a secondary structure is added to another part of the modified curved surface region along an orientation of the curved surface region. Modification to the curved surface region may be re-combined use of a serial combination manner and a parallel combination manner of the modification manners.
The modified part may be present partly or wholly within the modified curved surface region. For an ideal planar curved surface region, the modified part will be equal to the modified curved surface region. While for a bent curved surface region, the modified part will exist partly in the modified curved surface region. The width of the modified region is 0.5 µm to 10 µm, preferably 2 µm to 4 µm. Compared with the unmodified curved surface region, the modified curved surface region has one or a combination of different reflected colors, different reflected brightness, or different reflected textures.
Curved surface regions 31 and 32 of parts of the diffuse reflective curved surface S in Fig. 6 reflect the incident light 4 to directions 51 and 52, respectively. Reflected light rays of the modified curved surface region 31 generate a pattern of an animation frame, that is, modified curved surface regions collectively present patterns of animation frames; reflected light rays of the unmodified curved surface region 32 generate a background of the animation frame, that is, unmodified curved surface regions collectively present backgrounds of the animation frames. The pattern region has different optical contrast from the background region, which may specifically be one or a combination of different colors, different brightness, and different textures visible by human eyes.
Fig. 7 shows a schematic diagram of a banknote 10. The banknote 10 has the optical anti-counterfeiting element of some embodiments of the present invention, and the optical anti-counterfeiting element is embedded in the banknote 10 in the form of a window anti-counterfeiting thread 101. In addition, the optical anti-counterfeiting element can also be used in a manner of a label 102, and an open region 103 is formed in the banknotes 10, so as to facilitate light transmittance for observation. It should be understood that some embodiments of the present invention are not limited to an anti-counterfeiting thread and a banknote, and may be used in various anti-counterfeiting products, such as in labels on goods and packages, or in anti-counterfeiting documents, identity cards, passports, credit cards, healthcare cards, and the like. In bank notes and similar documents, in addition to anti-counterfeiting threads and labels, for example, wider anti-counterfeiting strips or transfer elements can also be used.
Embodiments of the present invention provide a storage medium, on which a program is stored, and the program, when executed by a processor, implements the design method for an optical anti-counterfeiting element in any embodiment of the present invention.
Embodiments of the present invention provide a processor, the processor is used for running a program, wherein the program, when running, executes the design method for an optical anti-counterfeiting element in any embodiment of the present invention.
Embodiments of the present invention provide an electronic device; the device includes a processor, a memory, and a program stored on the memory and running on the processor, and the program, when executed by the processor, implements the design method for an optical anti-counterfeiting element in any embodiment of the present invention.
Some embodiments of the present invention further provide a computer program product, which, when executed on a data processing device, is suitable for executing a program in which steps of the design method for an optical anti-counterfeiting element in any embodiment of the present invention are initialized.
As will be appreciated by a person skilled in the art, embodiments of the present invention may be provided as a method, a system, or a computer program product. Therefore, the present invention may take the form of entirely hardware embodiments, entirely software embodiments or embodiments combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to a disk memory, a CD-ROM, an optical memory, etc.) containing computer-usable program codes.
Some embodiments of the present invention are described with reference to the flowcharts and/or block diagrams of the method, device (system), and computer program product according to the embodiments of the present invention. It should be understood that computer program instructions may be configured to implement each process and/or block in a flowchart and/or a block diagram and a combination of processes and/or blocks in the flowchart and/or the block diagram. These computer program instructions may be provided to a general-purpose computer, a special-purpose computer, an embedded processor, or a processor of other programmable data processing devices to generate a machine, so that instructions executed by a processor of a computer or other programmable data processing devices generate an apparatus for realizing a designated function in one or more flows in a flowchart and/or in one or more blocks in a block diagram.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing devices to operate in a particular manner, such that the instructions stored in the computer-readable memory produce a manufacture comprising an instruction apparatus, the instruction apparatus implementing functions specified in one or more flows of a flowchart and/or one or more blocks of a block diagram.
These computer program instructions may also be loaded onto a computer or other programmable data processing devices, so that a series of operation steps are executed on the computer or other programmable devices to generate processing implemented by the computer, so that the instructions executed on the computer or other programmable data processing devices provide steps for implementing functions specified in one or more flows in the flowchart and/or one or more blocks in the block diagram.
In a typical configuration, a computing device includes one or more processors (CPU), an input/output interface, a network interface, and a memory.
The memory includes forms such as a non-permanent memory, a random access memory (RAM), and/or a non-transitory memory such as a read-only memory (ROM) or a flash RAM, in a computer-readable medium. The memory is an example of a computer-readable medium.
The computer-readable medium, comprising both permanent and non-permanent, and removable and non-removable medium, may achieve information storage by any method or technology. The information may be computer-readable instructions, data structures, modules of a program, or other data. Examples of the computer storage medium include but are not limited to, phase change access memory (PRAM), static random-access memory (SRAM), dynamic random-access memory (DRAM), other types of random-access memories (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices, or any other non-transmission media, which may be configured to store information that may be accessed by the computing device. As defined herein, the computer-readable media do not include transitory computer-readable media, such as modulated data signals and carriers.
It should also be noted that the terms "include", "includes", or any other variations thereof are intended to cover a non-exclusive inclusion, so that a process, method, commodity, or device that includes a series of elements not only includes those elements, but also includes other elements that are not explicitly listed, or further includes inherent elements of the process, method, commodity, or device. Without further limitation, an element defined by a sentence "include a ..." does not exclude other same elements existing in the process, method, commodity, or device that includes the element.
The described content merely relates to embodiments of the present invention, and is not intended to limit some embodiments of the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall belong to the scope of the claims of the present invention.

Claims

An optical anti-counterfeiting element, wherein the optical anti-counterfeiting element presents a dynamic feature, and the dynamic feature is pre-designed as reproduction of a group of animation frames visible at a preset observation angle set Ωv, and each of the group of animation frames comprises a pattern region and a background region forming an optical contrast with the pattern region;
the optical anti-counterfeiting element has a roughly smooth diffuse reflective curved surface, incident light is reflected by the diffuse reflective curved surface and then forms a roughly uniform brightness distribution in a range no less than the preset observation angle set Ωv;

the diffuse reflective curved surface comprises modified curved surface regions and unmodified curved surface regions, the modified curved surface regions and the unmodified curved surface regions have different reflective properties, wherein the modified curved surface regions correspond to the pattern regions; and

when the diffuse reflective curved surface is irradiated by the incident light, the modified curved surface regions collectively present a pattern of the dynamic feature, and the unmodified curved surface regions collectively present a background of the dynamic feature.
The optical anti-counterfeiting element as claimed in claim 1, wherein the diffuse reflective curved surface is periodic in at least one direction.
The optical anti-counterfeiting element as claimed in claim 1, wherein the diffuse reflective curved surface is aperiodic in at least one direction.
The optical anti-counterfeiting element as claimed in claim 1, wherein an average distance between adjacent peaks and valleys of the diffuse reflective curved surface is 5 µm to 100 µm, preferably 10 µm to 30 µm.
The optical anti-counterfeiting element as claimed in claim 1, wherein an average height difference between adjacent peaks and valleys of the diffuse reflective curved surface is 1 µm to 10 µm.
The optical anti-counterfeiting element as claimed in claim 1, wherein at least a part of each of the unmodified curved surface regions is smooth or has secondary structures.
The optical anti-counterfeiting element as claimed in claim 1, wherein each of the modified curved surface regions is modified by one or more of the following manners:
adding secondary structures to each of the modified curved surface regions;

making each of the modified curved surface regions smooth;

making each of the modified curved surface regions flat;

configuring each of the modified curved surface regions to have protrusions or concavities compared with the unmodified curved surface regions;

adjusting an angle of each of the modified curved surface regions, so that the incident light is reflected to a range exceeding the preset observation angle set Ωv; or

adjusting a thickness of plating layer or coating layer of each of the modified curved surface regions to be different from those of the unmodified curved surface regions.
The optical anti-counterfeiting element as claimed in claim 7, wherein in cases where each of the modified curved surface regions is modified by two or more of the following manners, the two or more of the following manners exist in a parallel combination manner and/or a serial combination manner.
The optical anti-counterfeiting element as claimed in any of claims 6-8, wherein a transverse feature size of the secondary structures is 0.2 µm to 5 µm.
The optical anti-counterfeiting element as claimed in claim 1, wherein a width of each of the modified curved surface regions is 0.5 µm to 20 µm, preferably 2 µm to 10 µm.
The optical anti-counterfeiting element as claimed in claim 1, wherein the different reflective properties mean that when irradiated by the incident light, the modified curved surface regions and the unmodified curved surface regions have one or a combination of different reflected colors, different reflected brightness, or different reflected textures.
A design method for an optical anti-counterfeiting element, wherein the design method comprises:
designing a dynamic feature, wherein the dynamic feature is reproduction of a group of animation frames visible at a preset observation angle set Ωv, and each of the group of animation frames comprises a pattern region and a background region forming an optical contrast with the pattern region;

designing a roughly smooth diffuse reflective curved surface for the optical anti-counterfeiting element, such that after incident light is reflected by the diffuse reflective curved surface, a roughly uniform brightness distribution is formed in a range no less than the preset observation angle set Ωv;

modifying regions corresponding to the pattern region of each of the group of animation frames on the basis of an observation angle of each of the group of animation frames, to form modified curved surface regions, so that the modified curved surface regions and unmodified curved surface regions have different reflective properties; and

when the diffuse reflective curved surface is irradiated by the incident light, the modified curved surface regions collectively presenting a pattern of the dynamic feature, and the unmodified curved surface regions collectively presenting a background of the dynamic feature.
The design method as claimed in claim 12, wherein the diffuse reflective curved surface is periodic in at least one direction.
The design method as claimed in claim 12, wherein the diffuse reflective curved surface is aperiodic in at least one direction.
The design method as claimed in claim 12, wherein an average distance between adjacent peaks and valleys of the diffuse reflective curved surface is 5 µm to 100 µm, preferably 10 µm to 30 µm.
The design method as claimed in claim 12, wherein an average height difference between adjacent peaks and valleys of the diffuse reflective curved surface is 1 µm to 10 µm.
The design method as claimed in claim 12, wherein modifying regions corresponding to the pattern region of each of the group of animation frames on the basis of an observation angle of each of the group of animation frames, to form modified curved surface regions, comprises:
pixelating each of the group of animation frames and the diffuse reflective curved surface;

determining a first azimuth angle and a first pitch angle of each of the group of animation frames, the first azimuth angle and the first pitch angle being determined according to an observation angle of each of the group of animation frames;

determining a second azimuth angle and a second pitch angle of each pixel of the diffuse reflective curved surface, the second azimuth angle and the second pitch angle being determined according to a normal vector at the each pixel of the diffuse reflective curved surface; and

executing the following steps regarding each of the group of animation frames:
finding, at positions corresponding to pixels of a pattern region in each of the group of animation frames in the diffuse reflective curved surface, pixels corresponding to the second azimuth angle and the second pitch angle that match the first azimuth angle and the first pitch angle of each of the group of animation frames, to form a region that corresponds to the pattern region of each of the group of animation frames in the diffuse reflective curved surface; and

modifying the region formed in the diffuse reflective curved surface and corresponding to the pattern region of each of the group of animation frames.
The design method as claimed in claim 17, wherein finding, at positions corresponding to pixels of a pattern region in each of the group of animation frames in the diffuse reflective curved surface, pixels corresponding to the second azimuth angle and the second pitch angle that match the first azimuth angle and the first pitch angle of the pixels of the pattern region, comprises:
within a preset distance range between the diffuse reflective curved surface and pixels of the pattern region in each of the group of animation frames, finding pixels which correspond to the second azimuth angle of which an angular difference between the second azimuth angle and the first azimuth angle is within a first preset angular difference range, and the second pitch angle of which an angular difference between the second pitch angle and half of the first pitch angle is within a second preset angular difference range.
The design method as claimed in claim 18, wherein
the preset distance range means that the distance from the positions where the pixels of the pattern region in each of the group of animation frames are located is less than 100 µm, preferably less than 50 µm; and/or

the first preset angular difference range means that the angular difference from the first azimuth angle is less than 3°, preferably less than 0.5°; and/or

the second preset angular difference range means that the angular difference from the first pitch angle is less than 3°, preferably less than 0.5°.
The design method as claimed in claim 12 or 17, wherein modifying regions corresponding to the pattern region of each of the group of animation frames to form modified curved surface regions comprises executing one or more of the following manners:
adding secondary structures to each of the modified curved surface regions;

making each of the modified curved surface regions smooth;

making each of the modified curved surface regions flat;

configuring each of the modified curved surface regions to have protrusions or concavities compared with the unmodified curved surface regions;

adjusting an angle of each of the modified curved surface regions, so that the incident light is reflected to a range exceeding the preset observation angle set Ωv;

adjusting a thickness of plating layer or coating layer of each of the modified curved surface regions to be different from those of the unmodified curved surface regions.
The design method as claimed in claim 12, wherein
the dynamic feature is one or a combination of translation, rotation, scaling, deformation, looming, and Yin/Yang transformation; and/or

the optical contrast is one or a combination of different colors, different brightness, and different textures visible to human eyes.
The design method as claimed in claim 12, wherein the width of each of the modified curved surface regions is 0.5 µm to 20 µm, preferably 2 µm to 10 µm.
An anti-counterfeiting product using the optical anti-counterfeiting element as claimed in any of claims 1-11.
A data carrier, wherein the data carrier has the optical anti-counterfeiting element as claimed in any of claims 1-11 or the anti-counterfeiting product as claimed in claim 23.