Light absorption imaging type optical anti-counterfeiting element based on micro Fresnel lens and preparation method of light absorption imaging type optical anti-counterfeiting element

Abstract

The invention discloses a light absorption imaging type optical anti-counterfeiting element based on a micro Fresnel lens and a preparation method of the light absorption imaging type optical anti-counterfeiting element. Firstly, a micro image-text array and a micro Fresnel lens array are synthesized into a three-dimensional microstructure, and micro image-text information corresponds to a light absorption area of the three-dimensional microstructure; in the finally prepared optical anti-counterfeiting film, the micro image-text array is of a'convex 'structure, the micro Fresnel lens array is of a'groove' structure, when light enters from the side, far away from the base film, of the three-dimensional microstructure formed through ultraviolet curing, the depth of the micro image-text array and the micro Fresnel lens array in the structure leads to an optical path difference, and the optical path difference is reduced. Light rays are continuously reflected by multiple interfaces at the micro image-text array part, and energy is consumed due to medium absorption or scattering to form dark fringes. According to the method, the optical anti-counterfeiting film with the naked-eye visible three-dimensional image-text can be obtained only through one-time processing, the influence of the alignment precision and the thickness of the base film on imaging does not need to be considered any more, the preparation process is simplified, the cost is reduced, and meanwhile the anti-counterfeiting reliability and stability are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of anti-counterfeiting packaging, and in particular to a method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens. Background Art

[0002] In the packaging industry, anti-counterfeiting remains a key concern. Packaging and anti-counterfeiting are closely linked, working together to protect products and maintain market order. As a protective barrier to products, packaging provides the foundation for anti-counterfeiting technology. Anti-counterfeiting technology not only adds value to product packaging but also significantly enhances its safety and reliability. Packaging that utilizes advanced anti-counterfeiting technology often creates a sense of high quality and sophistication, positively impacting brand image and product quality.

[0003] Microlens imaging technology, which uses a microlens array to refract and focus light to create a three-dimensional image, plays a crucial role in the field of anti-counterfeiting packaging. Through the careful design of a specific microlens array and micro-image array, microlens imaging technology can create a stunning naked-eye 3D effect on the packaging surface. When consumers view the packaging from different angles, they can see a three-dimensional pattern or text. This not only adds interest and visual appeal to the packaging, but also significantly enhances its anti-counterfeiting effectiveness.

[0004] As one of the most advanced anti-counterfeiting technologies, microlens anti-counterfeiting technology has many unique advantages in the field of anti-counterfeiting. However, it also has some shortcomings that cannot be ignored: First, the manufacturing process for microlens anti-counterfeiting elements is extremely complex and sophisticated, requiring the sequential production of microlenses and micro-image arrays. This process places stringent demands on the precision of production equipment and precise control of the process. Compared to traditional anti-counterfeiting technologies, microlens anti-counterfeiting technology requires not only initial investment in equipment purchase, but also ongoing maintenance costs and material loss, resulting in relatively high overall manufacturing costs.

[0005] Furthermore, the actual design and implementation of microlens anti-counterfeiting technology requires careful consideration of numerous complex factors. As for the product base film, different products require widely varying types of base films, and the thickness of the base films also varies. The key to microlens imaging lies in precise focal length adaptation. Even the slightest change in the thickness of the product base film will disrupt the originally designed imaging focal length, thereby interfering with the optical presentation of the entire microlens anti-counterfeiting system. If the packaging material is temporarily replaced, or the packaging thickness changes due to design adjustments, the pre-set microlens anti-counterfeiting effect will be greatly reduced, and it will be impossible to present the ideal flawless optical effect, resulting in severe challenges to the reliability and stability of the anti-counterfeiting system. Summary of the Invention

[0006] In order to overcome the shortcomings of the existing technology, the purpose of the present invention is to provide a method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens. An optical anti-counterfeiting film with three-dimensional images visible to the naked eye can be obtained with only one processing. There is no need to consider the influence of alignment accuracy and base film thickness on imaging. While simplifying the preparation process and reducing costs, the reliability and stability of anti-counterfeiting can also be guaranteed.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows: a method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens, comprising the following steps: Step S100, producing a photolithography file for an optical anti-counterfeiting three-dimensional microstructure: separately designing a micro-Fresnel lens array and a micro-graphic array, combining the micro-Fresnel lens array and the micro-graphic array into a three-dimensional microstructure in optical software, and outputting a photolithography file corresponding to the three-dimensional microstructure, wherein the micro-graphic information corresponds to the light absorption region of the three-dimensional microstructure; Step S200, forming a three-dimensional microstructure on the photolithographic glass: using the photolithographic file prepared in step S100, performing exposure and development processing on the photolithographic glass to form a three-dimensional microstructure on the photolithographic glass, wherein the portion corresponding to the micro-image array forms a "groove", and the portion corresponding to the micro-Fresnel lens array forms a "protrusion"; Step S300, making a resin master: using the photolithography glass obtained in step S200, embossing on a resin film to obtain a resin master, wherein, in the three-dimensional microstructure on the resin master, the portion corresponding to the micro-graphic array forms a "protrusion", and the portion corresponding to the micro-Fresnel lens array forms a "groove"; Step S400, making a metal nickel plate: electroplating the resin master plate made in step S300 to obtain a metal nickel plate; Step S500, producing an optical anti-counterfeiting film: using the metal nickel plate produced in step S400, embossing the base film to obtain an optical anti-counterfeiting film, wherein, in the three-dimensional microstructure on the optical anti-counterfeiting film, the portion corresponding to the micro-graphic array forms a "protrusion", and the portion corresponding to the micro-Fresnel lens array forms a "groove"; Step S600 , forming a reflective metal layer: a reflective metal layer is provided on the surface of the three-dimensional microstructure of the optical anti-counterfeiting film prepared in step S500 .

[0008] Compared to the prior art, the present invention has the following advantages: The preparation method first combines a micro-graphic array with a micro-Fresnel lens array to form a three-dimensional microstructure, with the micro-graphic information corresponding to the light absorption area of the three-dimensional microstructure, while the retained portion of the micro-Fresnel lens array serves as the background information of the micro-graphic array. In the resulting optical anti-counterfeiting film, the micro-graphic array has a "protrusion" structure, while the micro-Fresnel lens array has a "groove" structure. When light is incident from the side of the base film away from the three-dimensional microstructure formed by UV curing, the light passes through the base film to the micro-graphic array portion. The structural depth of the micro-graphic array and the micro-Fresnel lens array results in an optical path difference. Light is continuously reflected at multiple interfaces in the micro-graphic array portion, and energy is consumed by medium absorption or scattering, forming dark patterns. This facilitates the observation of images with a stronger depth of field without increasing the thickness of the photoresist layer. The three-dimensional microstructure obtained in this preparation method can fully exert the effect of binding and absorbing light, so that the unique dark pattern can be seen directly with the naked eye. An optical anti-counterfeiting film with three-dimensional images visible to the naked eye can be obtained with only one processing. There is no need to consider the influence of alignment accuracy and base film thickness on imaging. Even if the packaging material is temporarily replaced or the packaging thickness is changed due to design adjustments, it will not affect the pre-set anti-counterfeiting effect. While simplifying the preparation process and reducing costs, it also ensures the reliability and stability of anti-counterfeiting.

[0009] In the above-mentioned method for preparing the light-absorbing imaging optical anti-counterfeiting element based on the micro-Fresnel lens, in step S500, the optical anti-counterfeiting film is manufactured by ultraviolet light curing imprint replication.

[0010] In the above-mentioned method for preparing the light-absorbing imaging optical anti-counterfeiting element based on the micro-Fresnel lens, in step S500, the optical anti-counterfeiting film is obtained by hot pressing replication.

[0011] In the above-mentioned method for preparing the light-absorbing imaging optical anti-counterfeiting element based on the micro-Fresnel lens, step S200 includes the following steps: Step S210: Importing the photolithography file prepared in step S100 into a photolithography machine, exposing the photolithography glass on the photolithography machine, and transferring the three-dimensional microstructure to the photoresist layer of the photolithography glass, wherein the micro-image array corresponds to the etched portion of the photoresist layer, and the micro-Fresnel lens array corresponds to the non-etched portion of the photoresist layer; Step S220: Place the exposed photoresist glass into a developer to dissolve the photosensitive portion of the photoresist layer so that a three-dimensional microstructure appears on the photoresist glass. After development, the etched portion of the photoresist layer is dissolved and removed to form a "groove", while the non-etched portion is retained to form a "bump".

[0012] In the above-mentioned method for preparing the light-absorbing imaging optical anti-counterfeiting element based on the micro-Fresnel lens, step S300 includes the following steps: Step S310: selecting a suitable resin film; Step S320: placing the resin film on the photolithography glass on a panelizing machine, squeezing in panelizing oil, and applying a certain pressure to make the resin film and the photolithography glass closely adhere to each other; Step S330: Fix the shape of the three-dimensional microstructure by ultraviolet light irradiation, and obtain a resin master after peeling.

[0013] In the above-mentioned method for preparing the light-absorbing imaging optical anti-counterfeiting element based on the micro-Fresnel lens, in step S310 , the thickness of the resin film is between 100 μm and 300 μm.

[0014] In the above-mentioned method for preparing the light-absorbing imaging optical anti-counterfeiting element based on the micro-Fresnel lens, step S400 includes the following steps: Step S410: uniformly depositing a layer of metallic silver on the resin master obtained in step S300 through a silver mirror reaction; Step S420: Using the resin master plate with metallic silver attached as a cathode in an electrolytic cell, nickel is deposited on the cathode by electroplating in an electrolyte containing nickel ions to obtain a metallic nickel plate with a three-dimensional microstructure.

[0015] In the above-mentioned method for preparing the light-absorbing imaging optical anti-counterfeiting element based on the micro-Fresnel lens, in step S500 , the thickness of the base film is between 15 μm and 50 μm.

[0016] The above-mentioned method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens further includes the following steps after step S600: Step S700, laminating and producing an optical anti-counterfeiting product: laminating the optical anti-counterfeiting film produced in step S600 to the surface of a desired article to obtain the desired optical anti-counterfeiting product.

[0017] The present invention also provides a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens, which is manufactured using the aforementioned method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens, and comprises a base film, a light-absorbing imaging three-dimensional microstructure array, a metal reflective layer, an adhesive layer, paper, and a back coating layer, which are sequentially connected. This optical anti-counterfeiting element has a three-dimensional microstructure composed of a micro-image array and a micro-Fresnel lens array. The three-dimensional microstructure forms a light absorption area, and the micro-image information corresponds to the light absorption area of the three-dimensional microstructure. The portion retained by the micro-Fresnel lens array serves as the background information of the micro-image array. When light is incident, the three-dimensional microstructure can fully exert its light-binding and light-absorbing effects, allowing the naked eye to directly perceive the unique dark pattern. This optical anti-counterfeiting element is manufactured using the aforementioned method, and its preparation process is simple, the cost is lower, and the anti-counterfeiting effect is more stable and reliable.

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of a method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to an embodiment of the present invention; Figure 2 Schematic diagram of the principle of a method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to an embodiment of the present invention; Figure 3 This is a layered structure diagram of a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to an embodiment of the present invention; Figure 4 This is a visual effect diagram of a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to an embodiment of the present invention; Figure 5 This is a partial top view of the three-dimensional microstructure array of the light-absorbing imaging optical anti-counterfeiting element based on the micro-Fresnel lens according to an embodiment of the present invention, wherein the black portion is the light absorption area.

[0020] Description of Figure Numbers: 01: Base film, 02: Light-absorbing imaging three-dimensional microstructure array, 03: Metal reflective layer, 04: Adhesive layer, 05: Paper, 06: Back coating. DETAILED DESCRIPTION

[0021] Reference Figure 1 and Figure 2 The present invention provides a method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens, comprising the following steps: Step S100, producing a photolithography file for an optical anti-counterfeiting three-dimensional microstructure: separately designing a micro-Fresnel lens array and a micro-graphic array, combining the micro-Fresnel lens array and the micro-graphic array into a three-dimensional microstructure in optical software, and outputting a photolithography file corresponding to the three-dimensional microstructure, wherein the micro-graphic information corresponds to the light absorption area of the three-dimensional microstructure, and the micro-graphic information corresponds to the light absorption area of the three-dimensional microstructure. At the same time, the magnification after the graphic image is formed should meet the following requirements: Magnification M: M= , where is the lens period, For the graphic cycle; Lens curvature radius r: , where h is the lens height and Φ1 is the lens diameter; Lens focal length : , where n is the refractive index; Step S200, forming a three-dimensional microstructure on the photolithographic glass: using the photolithographic file prepared in step S100, performing exposure and development processing on the photolithographic glass to form a three-dimensional microstructure on the photolithographic glass, wherein the portion corresponding to the micro-image array forms a "groove", and the portion corresponding to the micro-Fresnel lens array forms a "protrusion"; Step S300, making a resin master: using the photolithography glass obtained in step S200, embossing on a resin film to obtain a resin master, wherein, in the three-dimensional microstructure on the resin master, the portion corresponding to the micro-graphic array forms a "protrusion", and the portion corresponding to the micro-Fresnel lens array forms a "groove"; Step S400, making a metal nickel plate: electroplating the resin master plate made in step S300 to obtain a metal nickel plate; Step S500, producing an optical anti-counterfeiting film: using the metal nickel plate produced in step S400, embossing the base film to obtain an optical anti-counterfeiting film, wherein, in the three-dimensional microstructure on the optical anti-counterfeiting film, the portion corresponding to the micro-graphic array forms a "protrusion", and the portion corresponding to the micro-Fresnel lens array forms a "groove"; Step S600 , forming a reflective metal layer: a reflective metal layer is provided on the surface of the three-dimensional microstructure of the optical anti-counterfeiting film prepared in step S500 .

[0022] Reference Figures 3 to 5This preparation method first combines a micro-image array and a micro-Fresnel lens array into a three-dimensional microstructure, where the micro-image information corresponds to the light absorption area of the three-dimensional microstructure, while the retained portion of the micro-Fresnel lens array serves as the background information of the micro-image array. In the resulting optical anti-counterfeiting film, the micro-image array has a "convex" structure, while the micro-Fresnel lens array has a "groove" structure. When light is incident from the side of the base film away from the three-dimensional microstructure formed by UV curing, the light passes through the base film to reach the micro-image array. The structural depth between the micro-image array and the micro-Fresnel lens array results in an optical path difference. The light is continuously reflected at multiple interfaces in the micro-image array, and energy is consumed by medium absorption or scattering, forming dark patterns. This allows for the observation of images with a stronger depth of field without increasing the thickness of the photoresist layer. The three-dimensional microstructure obtained in this preparation method can fully exert the effect of binding and absorbing light, so that the unique dark pattern can be seen directly with the naked eye. An optical anti-counterfeiting film with three-dimensional images visible to the naked eye can be obtained with only one processing. There is no need to consider the influence of alignment accuracy and base film thickness on imaging. Even if the packaging material is temporarily replaced or the packaging thickness is changed due to design adjustments, it will not affect the pre-set anti-counterfeiting effect. While simplifying the preparation process and reducing costs, it also ensures the reliability and stability of anti-counterfeiting.

[0023] Example 1 Reference Figure 1 and Figure 2 Embodiment 1 of the present invention provides a method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens, comprising the following steps: Step S100: preparing a photolithography file of an optical anti-counterfeiting three-dimensional microstructure: The software converts the preset graphic information into a micrographic array. Simultaneously, a microFresnel lens array is fabricated based on the designed microFresnel lens parameters. In optical software, the microFresnel lens array and the micrographic array are combined by superimposing them to create a three-dimensional microstructure. A corresponding photolithography file is then output. This three-dimensional microstructure has a light-absorbing region, where the micrographic information corresponds to the light-absorbing region of the three-dimensional microstructure. The portion of the microFresnel lens array retained during the overlapping synthesis serves as the background information for the micrographic information. When light is incident on the micrographic array, a strong contrast is formed between the background information and the background information, generating a unique dark pattern.

[0024] Step S200: fabricating a three-dimensional microstructure on the photolithographic glass: Step S210: Importing the photolithography file prepared in step S100 into a photolithography machine, exposing the photolithography glass on the photolithography machine, and transferring the three-dimensional microstructure to the photoresist layer of the photolithography glass, wherein the micro-image array corresponds to the etched portion of the photoresist layer, and the micro-Fresnel lens array corresponds to the non-etched portion of the photoresist layer; Step S220: Place the exposed photoresist glass in a developer to dissolve the photosensitive portions of the photoresist layer, revealing the three-dimensional microstructure on the glass. After development, the etched portions of the photoresist layer are dissolved and removed, forming "grooves," while the unetched portions remain, forming "bumps." The micro-graphic array and the micro-Fresnel lens array have opposite etched portions during the photolithography process, resulting in two different visual effects: direct imaging results in a white or bright image, while absorption imaging results in a black or gray image.

[0025] Step S300: Making a resin master: Step S310: Select a suitable resin film. The resin film may be polyethylene terephthalate (PET) with a thickness between 100 μm and 300 μm, preferably a PET film with a thickness of 188 μm. Step S320: placing a resin film on the photolithography glass having the three-dimensional microstructure array obtained in step S200 on a panelizing machine, squeezing in panelizing oil, and applying a certain pressure to tightly adhere the resin film to the photolithography glass. Specifically, the panelizing oil is a liquid material with a certain degree of peelability and UV curability; Step S330: Fix the shape of the three-dimensional microstructure by ultraviolet light irradiation, and obtain a resin master after peeling. In the three-dimensional microstructure on the resin master, the portion corresponding to the micro-graphic array forms a "protrusion", and the portion corresponding to the micro-Fresnel lens array forms a "groove".

[0026] Step S400: Making a metal nickel plate: Step S410: uniformly depositing a layer of metallic silver on the resin master obtained in step S300 through a silver mirror reaction to form a conductive layer so that the insulating resin master film can smoothly conduct electrons; Step S420: Using the resin master plate with metallic silver attached as a cathode in an electrolytic cell, nickel is deposited on the cathode by electroplating in an electrolyte containing nickel ions to obtain a metallic nickel plate with a three-dimensional microstructure.

[0027] Step S500: producing an optical anti-counterfeiting film: An optical anti-counterfeiting film is obtained by selecting a suitable base film material and replicating the three-dimensional microstructure of the metal nickel plate onto a base film surface with a thickness of 15μm to 50μm using an embossing and replicating unit on a rotary embossing device. Within the three-dimensional microstructure on the optical anti-counterfeiting film, the portion corresponding to the micro-graphic array forms a "bump," and the portion corresponding to the micro-Fresnel lens array forms a "groove." When light is incident from the side of the base film away from the side where the three-dimensional microstructure is formed by UV curing, the light passes through the base film to the micro-graphic array portion. The structural depth between the micro-graphic array and the micro-Fresnel lens array results in an optical path difference. The light is continuously reflected at multiple interfaces in the micro-graphic array portion, and energy is consumed by medium absorption or scattering, forming dark patterns. The dark patterns of this optical anti-counterfeiting film are observable to the naked eye on base film surfaces with a thickness of 15μm to 50μm. Therefore, even if the packaging material is temporarily replaced or the packaging thickness is changed due to design adjustments, the pre-set anti-counterfeiting effect will not be affected.

[0028] Furthermore, an optical anti-counterfeiting film is produced by UV-curing embossing replication: the UV-curing coating is evenly coated on one side of the base film in the coating unit, and the embossing replication unit and the metal plate roller complete the replication, transfer and curing of the three-dimensional microstructure under the action of the roller and UV light to obtain an optical anti-counterfeiting film. During the embossing process, a certain amount of pressure needs to be applied to ensure that the UV-curing varnish can fully fill the structural grooves of the nickel plate and ensure the integrity of the transfer of the three-dimensional microstructure array. The base film material needs to have good flatness and surface properties to ensure that the pattern can be well replicated. A PET chemical base film with a pre-coated layer is preferred.

[0029] Step S600: making a reflective metal layer: A reflective metal layer is formed on the surface of the three-dimensional microstructure of the optical anti-counterfeiting film produced in step S500 by vacuum evaporation. Specifically, the reflective metal layer can be made of a metal such as Al, Au, Ag, Cu, Cr, Sn, Pt, or a mixture or alloy thereof, preferably Al.

[0030] Example 2 Example 2 of the present invention provides a method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens. This method differs from Example 1 in that, in step S500, the optical anti-counterfeiting film is produced by hot pressing replication: the thermoplastic coating on the surface of the base film is softened at high temperature and squeezed into the grooves of the three-dimensional microstructure array under a certain pressure. After cooling and setting, the optical anti-counterfeiting film is obtained. Specifically, the thermoplastic coating can be a peelable transfer coating or a composite coating.

[0031] Example 3 Example 3 of the present invention provides a method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens. The method differs from Example 1 or Example 2 in that, after step S600, the method further includes the following steps: Step S700: Laminating and manufacturing optical anti-counterfeiting products: The optical security film produced in step S600 is affixed to the surface of a desired article to obtain the desired optical security product. For example, the optical security film produced in step S600 can be affixed to paper of a predetermined specification using glue, and then a back coating is applied to the side of the paper away from the optical security film to obtain optical security paper. The optical security paper can be mass-produced for use by packagers. Of course, in some applications, the optical security film can also be directly affixed to certain products.

[0032] Example 4 Reference Figure 3 Embodiment 4 of the present invention provides a micro-Fresnel lens-based light-absorbing imaging optical anti-counterfeiting element, manufactured using the aforementioned method for preparing a micro-Fresnel lens-based light-absorbing imaging optical anti-counterfeiting element. The element comprises a base film 01, a light-absorbing imaging three-dimensional microstructure array 02, a metal reflective layer 03, an adhesive layer 04, paper 05, and a back coating layer 06, all connected in sequence. This optical anti-counterfeiting element comprises a three-dimensional microstructure composed of a micro-image array and a micro-Fresnel lens array. The three-dimensional microstructure forms a light-absorbing region, and the micro-image information corresponds to the light-absorbing region of the three-dimensional microstructure. The portion retained by the micro-Fresnel lens array serves as the background information of the micro-image array. When light is incident, the three-dimensional microstructure fully exerts its light-binding and light-absorbing effects, allowing the naked eye to directly perceive the unique dark pattern. This optical anti-counterfeiting element, manufactured using the aforementioned method, has a simple production process, lower costs, and a more stable and reliable anti-counterfeiting effect.

[0033] It should be noted that, in the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0034] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens, characterized in that: The steps include: Step S100, producing a photolithography file for an optical anti-counterfeiting three-dimensional microstructure: separately designing a micro-Fresnel lens array and a micro-graphic array, combining the micro-Fresnel lens array and the micro-graphic array into a three-dimensional microstructure in optical software, and outputting a photolithography file corresponding to the three-dimensional microstructure, wherein the micro-graphic information corresponds to the light absorption region of the three-dimensional microstructure; Step S200, forming a three-dimensional microstructure on the photolithographic glass: using the photolithographic file prepared in step S100, performing exposure and development processing on the photolithographic glass to form a three-dimensional microstructure on the photolithographic glass. In the three-dimensional microstructure on the photolithographic glass, the portion corresponding to the micro-image array forms a "groove", and the portion corresponding to the micro-Fresnel lens array forms a "protrusion". Step S300, making a resin master: using the photolithography glass obtained in step S200, embossing on a resin film to obtain a resin master, wherein, in the three-dimensional microstructure on the resin master, the portion corresponding to the micro-graphic array forms a "protrusion", and the portion corresponding to the micro-Fresnel lens array forms a "groove"; Step S400, making a metal nickel plate: electroplating the resin master plate made in step S300 to obtain a metal nickel plate; Step S500, producing an optical anti-counterfeiting film: using the metal nickel plate produced in step S400, embossing the base film to obtain an optical anti-counterfeiting film, wherein, in the three-dimensional microstructure on the optical anti-counterfeiting film, the portion corresponding to the micro-graphic array forms a "protrusion", and the portion corresponding to the micro-Fresnel lens array forms a "groove"; Step S600 , forming a reflective metal layer: a reflective metal layer is provided on the surface of the three-dimensional microstructure of the optical anti-counterfeiting film prepared in step S500 .

2. The method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to claim 1, characterized in that: In step S500, an optical anti-counterfeiting film is produced by ultraviolet light curing imprint replication.

3. The method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to claim 1, characterized in that: In step S500, an optical anti-counterfeiting film is produced by hot pressing replication.

4. The method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to claim 1, wherein: Step S200 includes the following steps: Step S210: Importing the photolithography file prepared in step S100 into a photolithography machine, exposing the photolithography glass on the photolithography machine, and transferring the three-dimensional microstructure to the photoresist layer of the photolithography glass, wherein the micro-image array corresponds to the etched portion of the photoresist layer, and the micro-Fresnel lens array corresponds to the non-etched portion of the photoresist layer; Step S220: Place the exposed photoresist glass in a developer to dissolve the photosensitive portion of the photoresist layer, so that the three-dimensional microstructure appears on the photoresist glass. After development, the etched portion of the photoresist layer is dissolved and removed to form a "groove", while the non-etched portion is retained to form a "bump".

5. The method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to claim 1, characterized in that: Step S300 includes the following steps: Step S310: selecting a suitable resin film; Step S320: placing the resin film on the photolithography glass on a panelizing machine, squeezing in panelizing oil, and applying a certain pressure to make the resin film and the photolithography glass closely adhere to each other; Step S330: Fix the shape of the three-dimensional microstructure by ultraviolet light irradiation, and obtain a resin master after peeling.

6. The method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to claim 5, characterized in that: In step S310 , the thickness of the resin film is between 100 μm and 300 μm.

7. The method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to claim 1, characterized in that: Step S400 includes the following steps: Step S410: uniformly depositing a layer of metallic silver on the resin master obtained in step S300 through a silver mirror reaction; Step S420: Using the resin master plate with metallic silver attached as a cathode in an electrolytic cell, nickel is deposited on the cathode by electroplating in an electrolyte containing nickel ions to obtain a metallic nickel plate with a three-dimensional microstructure.

8. The method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to claim 1, wherein: In step S500 , the thickness of the base film is between 15 μm and 50 μm.

9. The method for preparing a light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens according to claim 1, wherein: After step S600, the following steps are also included: Step S700, laminating and producing an optical anti-counterfeiting product: laminating the optical anti-counterfeiting film produced in step S600 to the surface of a desired article to obtain the desired optical anti-counterfeiting product.

10. A light-absorbing imaging optical anti-counterfeiting element based on a micro-Fresnel lens, characterized in that: The optical anti-counterfeiting element is made by the preparation method of the light-absorbing imaging type optical anti-counterfeiting element based on the micro-Fresnel lens as described in any one of claims 1 to 9, and includes a base film, a light-absorbing imaging type three-dimensional microstructure array, a metal reflective layer, an adhesive layer, paper and a back coating layer connected in sequence.

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