Composite film with dynamic optical anti-counterfeiting function, preparation method and application

Abstract

The invention discloses a composite film with a dynamic optical anti-counterfeiting function, which belongs to the technical field of optical anti-counterfeiting, and comprises a base material layer, a release layer, an imaging layer, a plating layer, a dynamic optical function layer, a protective layer and an adhesive layer which are sequentially laminated, the imaging layer is provided with a static holographic pattern formed by compression molding; the dynamic optical functional layer comprises a photo-thermal response type semi-crystalline polymer and near-infrared absorption dye dispersed in the photo-thermal response type semi-crystalline polymer, has a three-dimensional cross-linked network structure formed by ultraviolet curing, and can generate a dynamic anti-counterfeiting effect by triggering reversible phase change through irradiation of laser with set wavelength. The invention also discloses a preparation method of the composite film. Through integration of dual anti-counterfeiting mechanisms of static holography and dynamic response, the comprehensive requirements of high safety, low cost, easy verification and environmental adaptability are met, and the method is particularly suitable for high-end anti-counterfeiting application which needs to be embedded into a card through a lamination process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical anti-counterfeiting technology, and particularly relates to a composite film with dynamic optical anti-counterfeiting function, a preparation method and application, in particular, an anti-counterfeiting film suitable for high-end certificates and cards and a preparation method thereof, which realizes reversible dynamic display through photo-thermal effect. BACKGROUND

[0002] Optical anti-counterfeiting technology is an important means to ensure the security of certificates, bank cards, brand commodities and the like. At present, the mainstream technology still mainly relies on static holographic anti-counterfeiting. This technology produces a rainbow luster effect that changes with the angle by molding micro-nano optical structures (such as diffraction gratings) on the surface of a plastic film. Although the static holographic technology is mature and has a low cost, the pattern is fixed and unchangeable, and it is easy to be scanned and copied by high-precision equipment, and the security of anti-counterfeiting is increasingly insufficient. The static holographic pattern cannot enhance the identification difficulty through visual changes or dynamic effects, resulting in that counterfeiters can obtain images by using high-resolution equipment and make copies, which weakens the non-reproducibility of anti-counterfeiting. At the same time, the existing technology cannot realize dynamic changes through physical and chemical mechanisms, and only relies on the pattern design itself, which is difficult to cope with increasingly advanced copying technology.

[0003] Although dynamic information anti-counterfeiting technologies such as two-dimensional codes have appeared at present, their verification relies on electronic devices, and needs to be scanned or networked for inquiry, which destroys the intuitiveness of anti-counterfeiting. Users cannot directly observe the anti-counterfeiting effect with their naked eyes, and need to use external tools, which reduces the convenience and experience of use. In addition, technologies such as two-dimensional codes are susceptible to environmental interference, and may not be read normally when they are dirty, blocked or lack of light, which further affects the reliability of anti-counterfeiting.

[0004] Some advanced tunable photonic material technologies are also being explored, such as CN109830175A discloses an anti-counterfeiting mark comprising a photonic crystal layer and a holographic pattern layer, which forms an anti-counterfeiting effect by combining the diffraction of the holographic pattern with the bandgap reflection of the photonic crystal layer; WO2020192579A1 discloses an anti-counterfeiting mark combining a photonic crystal layer and a holographic pattern layer, which produces a photo-variable effect by changing the angle. However, they have problems such as complex preparation, high cost, poor environmental stability and the like. Liquid crystal and photonic crystal materials require precise packaging and driving circuits, and the process is complex and costly, which is difficult to meet the needs of commercial anti-counterfeiting labels for low cost, high stability and mass production; at the same time, photonic materials are sensitive to environmental factors such as temperature and humidity, and are prone to performance degradation, resulting in unstable dynamic effects and affecting long-term use effects.

[0005] In summary, the existing anti-counterfeiting technology is difficult to balance between security, convenience and process feasibility. Static hologram is easy to copy, digital verification is not intuitive, and new dynamic materials face the bottleneck of cost and stability. Therefore, an innovative anti-counterfeiting solution is needed, which can integrate the high intuitiveness of static hologram and the high security of dynamic anti-counterfeiting, and the preparation process is compatible with traditional film technology and the cost is controllable. SUMMARY

[0006] In view of one or more of the above defects or improvement needs of the prior art, the present application provides a composite film with dynamic optical anti-counterfeiting function, preparation method and application, to solve the problems of easy copying of existing static holographic anti-counterfeiting technology, electronic device-dependent dynamic two-dimensional code verification, and high cost and poor stability of tunable photonic materials. Through the integration of the dual anti-counterfeiting mechanism of "static hologram and dynamic response", the comprehensive needs of high security, low cost, easy verification and environmental adaptability are realized, which is especially suitable for high-end anti-counterfeiting applications that need to be embedded inside the card through lamination process.

[0007] To achieve the above-mentioned purpose, according to the first aspect of the present application, a composite film with dynamic optical anti-counterfeiting function is provided, comprising a substrate layer, a release layer, an imaging layer, a plating layer, a dynamic optical function layer, a protective layer and a glue layer arranged in sequence. The imaging layer has a mold-formed static holographic pattern. The dynamic optical function layer comprises a photothermal responsive semi-crystalline polymer and a near-infrared absorbing dye dispersed therein, and has a three-dimensional cross-linked network structure formed by ultraviolet curing. The dynamic optical function layer is configured to undergo reversible crystallization-melting phase transition when irradiated by laser with a wavelength matching the absorption band of the near-infrared absorbing dye, thereby producing a dynamic optical anti-counterfeiting effect.

[0008] As a further improvement of the present application, the photothermal responsive semi-crystalline polymer is an aliphatic polyester polymer or a modified substance thereof, which includes but is not limited to one or more of polycaprolactone (PCL), polybutylene adipate (PBA), polyhydroxyalkanoate (PHA), preferably the polymer is polycaprolactone (PCL).

[0009] Preferably, the number average molecular weight (Mn) of the photothermal responsive semi-crystalline polymer is 30,000-100,000, more preferably 50,000-80,000; the melting point is 50-65℃, more preferably 55-60℃. The photothermal responsive semi-crystalline polymer has a reversible crystallization-melting phase transition property with a melting point in the range of 50-65℃.

[0010] As a further improvement of the present application, the near-infrared absorbing dye includes, but is not limited to, one or more of rare earth doped upconversion nanoparticles (such as NaYF4:Yb3 + , Er3 + ), carbon nanotubes, phthalocyanine dyes, merocyanine dyes, or indocyanine green dyes.

[0011] Preferably, the near-infrared absorbing dye has an absorption wavelength range of 800-1100 nm. This range corresponds to common near-infrared laser sources (such as 808 nm, 980 nm), and the use of a near-infrared absorbing dye that can be excited by near-infrared light can reduce the influence of ambient visible light.

[0012] The near-infrared absorbing dye in the dynamic optical functional layer, upon absorbing laser of a set wavelength, converts light energy into heat energy, causing the photo-thermal responsive semi-crystalline polymer in the local area to undergo a phase transition from crystalline to amorphous, causing the material refractive index (Δn) to reversibly change (typically in the range of 0.01-0.05), forming a temporary phase modulation area (temporary optical pattern). After the laser is removed, the temporary area dissipates heat and returns to its original state through low-temperature crystallization, thereby producing a dynamic optical anti-counterfeiting effect.

[0013] As a further improvement of the present application, the three-dimensional crosslinked network structure is formed by photo-thermal responsive semi-crystalline polymer under the action of a crosslinking agent and is cured by ultraviolet light. Preferably, the crosslinking agent is selected from one or more of the following categories: thiol compounds (such as pentaerythritol tetra(3-mercaptopropionate)), benzophenone photoinitiators, acrylate monomers or prepolymers (such as dipentaerythritol pentaacrylate), and epoxy acrylate resins.

[0014] The three-dimensional crosslinked network structure is preferably formed by thiol-ene click chemistry or benzophenone photocrosslinking and other light-triggered chemical reactions. Thiol-ene click chemistry occurs between thiol groups (-SH) and olefin groups (C=C), and the photo-thermal responsive semi-crystalline polymer can be chemically modified to introduce functional groups (such as terminal alkenyl, hydroxyl, or carboxyl) to enhance crosslinking efficiency. For example, when the polymer matrix (such as terminal alkenyl modified PCL) contains olefins, the crosslinking agent (such as pentaerythritol tetra(3-mercaptopropionate)) provides thiol groups, and under ultraviolet light excitation, the thiol and olefin undergo addition reaction to form a stable C-S bond crosslinked structure. The benzophenone photocrosslinking reaction is that the benzophenone crosslinking agent transitions to the excited state under ultraviolet light irradiation, abstracts hydrogen to generate free radicals, which abstracts hydrogen atoms from the polymer (such as PCL) to form polymer radicals, which then couple to form a C-C bond crosslinked structure. The crosslinked network structure of the present application gives the dynamic optical functional layer good mechanical strength and durability.

[0015] In the dynamic optical functional layer, the near-infrared absorbing dye absorbs light energy and converts it into heat energy; the photothermal responsive semi-crystalline polymer utilizes thermally induced phase transitions to generate optical changes; and the three-dimensional cross-linked network structure ensures that this process is reversible and durable. This invention, through the combination of these three elements, forms a stable, reversible, and durable dynamic anti-counterfeiting system, solving the industry problem of balancing stability and reversibility in dynamic anti-counterfeiting technology.

[0016] As a further improvement of the present invention, to enhance the anti-counterfeiting level, the dynamic optical functional layer is further provided with a pattern code, which can be formed by existing technology, including but not limited to: Multi-wavelength dye distribution coding: Doping different absorption wavelengths of dyes in different regions (such as 808nm and 1064nm dye composites) to achieve selective laser response; Crosslinking density gradient encoding: By controlling UV curing parameters (such as intensity and time) to form crosslinking density differences within the dynamic optical functional layer, the phase change response threshold is adjusted; Thickness gradient coating coding: The film thickness (1~50μm) of the region is controlled by precise coating, and the photothermal effect is modulated by the thickness difference.

[0017] As a further improvement of the present invention, the thickness of the dynamic optical functional layer is 1~50μm, preferably 5~20μm. If the thickness is too high or too low, it is difficult to ensure coating uniformity, leading to response differences and easily causing light scattering, thus affecting the visual effect.

[0018] As a further improvement of the present invention, the material of the substrate layer includes, but is not limited to, one or more of polyethylene terephthalate (PET), polycarbonate (PC), polypropylene (PP), or polyvinyl chloride (PVC); more preferably, polyethylene terephthalate (PET) or polycarbonate (PC). The thickness of the substrate layer is preferably 12~100μm. The substrate layer serves as a carrier to ensure the smooth progress of subsequent coating, molding, and other processes. This layer will be peeled off after the film is thermally transferred to the card substrate.

[0019] As a further improvement of the present invention, the release layer is disposed on the substrate layer, and its surface tension is preferably 40~52 dyn / cm. This surface tension optimizes the peeling force and ensures complete transfer. Its thickness is preferably 0.1~0.5μm. The release layer ensures that during card lamination, all functional layers can be separated from the substrate layer as a whole and firmly transferred to the card substrate, achieving precise thermal transfer.

[0020] As a further improvement of the present invention, the imaging layer is disposed on the release layer, and its material includes acrylic resin, and its thickness is preferably 0.5~2.0μm; a permanent static holographic pattern (such as a diffraction grating, microtext, etc.) is formed on the side of the imaging layer opposite to the release layer by a molding process.

[0021] As a further improvement of the present invention, the coating is a metal layer (such as aluminum) or a transparent dielectric layer (such as zinc sulfide), preferably with a thickness of 300-600 Å, used to enhance the optical contrast and brightness of the holographic pattern. The imaging layer and the coating together constitute the basis of static anti-counterfeiting information.

[0022] As a further improvement of the present invention, the material of the protective layer includes one or more of polyurethane, nano-silica, polyacrylate, or fluorocarbon resin, and its glass transition temperature (Tg) after curing is not lower than 220°C. The Tg of the protective layer is higher than the card lamination temperature (usually 180~190°C), which is used to prevent the deformation of each layer of the dynamic anti-counterfeiting film during the high-temperature lamination process of the card. The thickness of the protective layer is preferably 0.8~1.5μm.

[0023] As a further improvement of the present invention, the adhesive layer is preferably a hot melt adhesive with a softening point of 95~150℃ and a thickness of 4~8μm. It is activated during lamination to bond the entire dynamic anti-counterfeiting film to the card substrate. The softening point of the adhesive layer is lower than the card lamination temperature to ensure the activation and bonding performance of the adhesive layer.

[0024] According to a second aspect of the present invention, a method for preparing the composite thin film with dynamic optical anti-counterfeiting function is provided, comprising the following steps: S1 applies release layer material to the substrate layer, which is cured to form a release layer. S2 coats the imaging layer material onto the release layer, and forms a static holographic pattern by molding to obtain the imaging layer; S3 vapor-deposits a coating onto the imaging layer; S4 applies a coating liquid containing a photothermal responsive semi-crystalline polymer, a near-infrared absorbing dye, and a crosslinking agent to the coating layer, and forms a dynamic optical functional layer after drying and ultraviolet curing. S5 applies a protective layer material onto the dynamic optical functional layer, which is then cured to form a protective layer. S6 applies adhesive material to the protective layer, which cures to form an adhesive layer.

[0025] As a further improvement of the present invention, in the coating liquid of the dynamic optical functional layer, the amount of the near-infrared absorbing dye added is 0.1% to 3% of the mass of the photothermal responsive semi-crystalline polymer, preferably 0.5% to 2%; the amount of the near-infrared absorbing dye added can be adjusted according to the absorption peak value, thereby controlling costs while ensuring balanced photothermal conversion efficiency. The amount of the crosslinking agent added is 1% to 10% of the mass of the photothermal responsive semi-crystalline polymer, preferably 3% to 6%, to balance mechanical strength and phase transition reversibility.

[0026] As a further improvement of the present invention, the coating liquid of the dynamic optical functional layer further includes a solvent, and the solid content of the coating liquid is 10% to 30%, preferably 15% to 20%.

[0027] Preferably, the solvent includes, but is not limited to, one or more of tetrahydrofuran, acetone, ethyl acetate, N-methylpyrrolidone, or propylene glycol methyl ether acetate, and more preferably tetrahydrofuran or ethyl acetate to ensure compatibility.

[0028] In step S4, a coating liquid is applied to the surface of the static holographic layer using a coating process (such as microgravure coating, slot coating, or blade coating). By controlling the coating thickness in each area, as well as the light intensity and time during UV curing, the dynamic optical functional layer is formed.

[0029] Preferably, the coating speed is 2~5 m / min, the wet film thickness is 15~50 μm, and the viscosity of the coating liquid is 500~2000 cP to ensure coating uniformity.

[0030] Preferably, the drying method is to dry at 40~50℃ for 3~5 minutes to remove the solvent; the ultraviolet curing method is to cure for 10~60 seconds at a wavelength of 300~400 nm and an intensity of 50~200 mW / cm²; preferably, the intensity is 80~120 mW / cm² and the time is 15~30 seconds.

[0031] Preferably, in step S4, a pattern code is further formed using existing technologies, including but not limited to multi-wavelength dye distribution coding, crosslink density gradient coding, and thickness gradient coating coding.

[0032] According to a third aspect of the present invention, an application of the composite film with dynamic optical anti-counterfeiting function in card anti-counterfeiting is provided, wherein the composite film with dynamic optical anti-counterfeiting function is embedded in the card by hot pressing transfer.

[0033] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art: (1) The composite film with dynamic optical anti-counterfeiting function of the present invention constructs a dual anti-counterfeiting mechanism of "static holographic pattern carrying + near-infrared laser triggered dynamic display". The dynamic effect is generated by the physical and chemical changes of the material itself, which is difficult to copy by scanning, greatly increasing the difficulty of counterfeiting and greatly improving the anti-counterfeiting security.

[0034] (2) The composite film with dynamic optical anti-counterfeiting function of the present invention can be dynamically verified without any electronic equipment. The dynamic effect can be directly observed with the naked eye by simply irradiating it with a low-power laser pen of a set wavelength. The verification process is simple and intuitive. Moreover, the near-infrared laser verification method is safe and reliable and is not affected by ambient light.

[0035] (3) The composite film with dynamic optical anti-counterfeiting function of the present invention first forms a static holographic pattern and coating on a substrate, then coats and cures the dynamic optical functional layer, and finally combines a protective layer and an adhesive layer. By matching the layer thickness and curing conditions, the dynamic optical functional layer can be made compatible with the multi-layer structure and process of general holographic anti-counterfeiting film. Through the design of the temperature-resistant protective layer and adhesive layer, it can be adapted to the harsh process conditions of internal lamination of ID cards, and realize built-in, permanent anti-counterfeiting. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of a composite film with dynamic optical anti-counterfeiting function according to an embodiment of the present invention.

[0037] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 110, substrate layer; 120, release layer; 130, imaging layer; 140, coating; 150, dynamic optical functional layer; 160, protective layer; 170, adhesive layer. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared by conventional methods in the art. In the following embodiments, unless otherwise described in detail, conventional experimental methods in the art can be used.

[0040] Example 1 This embodiment provides a built-in dynamic anti-counterfeiting film suitable for high-security cards such as passport chip pages. This film needs to be embedded inside the polycarbonate (PC) card body after lamination, and has high requirements for temperature resistance, durability, and anti-counterfeiting level.

[0041] The substrate layer is a 100μm thick transparent polycarbonate (PC) film, which has good dimensional stability and high temperature resistance, and can withstand subsequent lamination processes. The release layer uses a hydroxyl acrylic resin system with a coating thickness of 0.5μm and a surface tension controlled at 42 dyn / cm to ensure complete transfer during card lamination. The imaging layer is made of thermoplastic acrylic resin, and a static pattern of the national emblem diffraction grating with a depth of about 1.2μm is formed by hot pressing. Vacuum evaporation of metallic aluminum forms a coating with a thickness of about 400 Å to provide a strong metallic luster and diffraction effect.

[0042] The dynamic optical functional layer uses terminal alkenyl-modified polycaprolactone (PCL, Mn=80,000, melting point 60℃) as the matrix, in which rare earth-doped nanoparticles (NaYF4:Yb³) with a uniformly dispersed absorption peak at 808nm are embedded. + Er³ + The thiol-ene click chemistry system was adopted, and the crosslinking agent was pentaerythritol tetra(3-mercaptopropionate), with a mass ratio of PCL: crosslinking agent: rare earth doped nanoparticles = 100:5:1.5.

[0043] The protective layer is made of polyurethane coating with a glass transition temperature (Tg) of not less than 220℃ after curing and a thickness of 1.0μm. It is used to protect the layers of the dynamic anti-counterfeiting film from damage during the high-temperature lamination of the ID card (usually 180-190℃). The adhesive layer is made of hot melt adhesive with a softening point of 115℃ and a thickness of 5μm. It is used to firmly bond with the passport card base during lamination.

[0044] The preparation steps are as follows: (1) Static pattern and coating preparation: After coating the release layer on the PC substrate, the imaging layer resin is coated. Then, at 125°C and 8MPa pressure, a nickel plate with the national emblem pattern is hot-pressed for 1-3 seconds to form a static holographic pattern; after completion, an aluminum layer is deposited in a vacuum coating machine.

[0045] (2) Preparation of dynamic optical functional layer coating solution: Dissolve terminal alkenyl PCL, pentaerythritol tetra(3-mercaptopropionate) and rare earth nanoparticles in tetrahydrofuran solvent in the above proportion to prepare a uniform coating solution with a solid content of 20%.

[0046] (3) Coating and pre-drying of dynamic optical functional layer: The above coating liquid was precisely coated onto the surface of the aluminum layer using a slit coater at a coating speed of 2 m / min, and the wet film thickness was controlled to be 50 μm. The film was then passed through a hot air drying oven at 50°C for 5 minutes to completely remove the solvent.

[0047] (4) UV curing crosslinking: The pre-dried film is placed in a nitrogen-protected environment and irradiated for 20 seconds with a UV-LED surface light source (main wavelength 365nm, intensity 100 mW / cm²) to cause the thiol and olefin to undergo a click chemical reaction and form a stable three-dimensional crosslinked network structure.

[0048] (5) Composite of protective layer and adhesive layer: Polyurethane raw material is coated on the cured dynamic optical functional layer and then thermosetting to form a protective layer. Finally, hot melt adhesive raw material is coated on the protective layer to form an adhesive layer, thus obtaining the dynamic anti-counterfeiting film of the present invention.

[0049] (6) Hot pressing transfer: The prepared film is laminated onto the PC chip page substrate of the electronic passport at 150°C and 0.5MPa using a hot pressing transfer device to form an embedded anti-counterfeiting layer.

[0050] Verification results: When illuminated with an 808nm laser pointer with an output power of 500mW, a dynamic pattern of golden wheat ears appeared within the national emblem within 1 second. After the laser was removed, the dynamic pattern completely disappeared within 30 seconds, and the material returned to its initial state.

[0051] Example 2 This embodiment provides a low-cost dynamic anti-counterfeiting film suitable for bank cards. The differences from Embodiment 1 in materials and preparation steps are: the substrate layer is replaced with a 50μm thick BOPET film; in the dynamic optical functional layer formulation, the polymer matrix is ​​ordinary PCL (Mn=45,000), the photothermal dye is a cyanine organic dye with an absorption peak of 980nm, and the crosslinking system uses benzophenone photocrosslinking with a mass ratio of PCL:benzophenone:dye = 100:3:0.8; during the preparation process, UV curing is carried out in air using a medium-pressure mercury lamp (80 mW / cm²) for 15 seconds, simplifying the production process. The prepared film is then laminated onto a bank card using a hot-pressing transfer device.

[0052] Verification results: When illuminated with a 980nm laser pointer, the anti-counterfeiting pattern appears within 1.5 seconds and recovers in 35 seconds.

[0053] Example 3 This embodiment provides a multi-wavelength responsive anti-counterfeiting film suitable for sticker-type anti-counterfeiting such as visas. The difference from Embodiment 1 in materials and preparation steps lies in the addition of 0.5% carbon nanotubes with an absorption peak of 808 nm and 1.0% phthalocyanine dye with an absorption peak of 1064 nm to the formulation of the dynamic optical functional layer. During the coating process of the dynamic optical functional layer, the dye is regionally distributed and encoded using coating technology. The resulting film is then laminated onto the visa using a hot-press transfer device.

[0054] Verification results: Using two lasers, 808nm and 1064nm, to trigger the process, different dynamic information can be displayed, achieving dual verification.

[0055] Comparative Example 1 Compared with Example 1, the difference is that no crosslinking agent was added to the coating liquid of the dynamic optical functional layer.

[0056] Results: The film exhibited permanent deformation after 5 laser irradiation cycles and failed after 50 cycles. This demonstrates that the cross-linked network is crucial for structural stability.

[0057] Comparative Example 2 Compared to Example 1, amorphous polymer polystyrene (PS) was used instead of PCL as the matrix for the dynamic optical functional layer.

[0058] Result: No dynamic effects were produced. This proves that the reversible phase transition of semi-crystalline polymers is the basis for dynamic anti-counterfeiting measures.

[0059] Comparative Example 3 Compared to Example 1, the rare earth nanoparticles were replaced with the visible light absorbing dye Rhodamine B (absorption peak 570 nm).

[0060] Results: The film rapidly photodegraded under ambient light, and visible laser light posed a safety risk. This demonstrates the necessity and superiority of near-infrared absorbing dyes.

[0061] Comparative Example 4 Compared to Example 1, the amount of near-infrared absorbing dye (rare earth doped nanoparticles) added was increased to 5% of the PCL mass.

[0062] Results: The mechanical properties of the dynamic layer deteriorated and it was prone to cracking, proving that the dye content needs to be optimized within a reasonable range.

[0063] The films prepared in the above embodiments and comparative examples were further tested as follows, and the results are shown in Table 1: 1. Phase Change Cycle Test: Referring to the cyclic fatigue test principle in ASTM D638, a customized test method for the phase change durability of optical anti-counterfeiting films was developed. The sample was fixed on the test platform, and a near-infrared laser (output power 500mW, spot diameter 2mm) was used to irradiate it at a frequency of once per second. Each cycle consisted of 2 seconds of irradiation (triggering the phase change) and 30 seconds of rest (completion of recovery). The test was terminated when the dynamic pattern contrast decreased to 50% of its initial value or when permanent deformation of the material occurred.

[0064] 2. Response Time Test: A high-speed photoelectric detection system (response time < 1ms) was used for measurement. A timer was synchronously triggered at the start of laser irradiation. The detector captured the light intensity changes of the dynamic pattern, and the time interval was recorded when the light intensity reached 90% of its stable value. The test was repeated 10 times, and the average value was taken. The laser power density was uniformly controlled at 100mW / cm².

[0065] 3. Recovery Time Test: Using the same high-speed detection system, start timing the instant the laser is removed, and monitor the time required for the intensity of the dynamic pattern to decay to 10% of its initial value. The test must be conducted in a vibration-free environment to avoid external interference.

[0066] 4. Weather resistance rating: Accelerated aging test was conducted according to ASTM D7869 standard, with an irradiance of 0.55W / m², a blackboard temperature of 70°C, and continuous irradiation for 1000 hours. After the test, the following grades were applied: Grade 0: No visible defects; Grade 1: Slight discoloration or deformation; Grade 2: Obvious defects; Grade 3: Severe deterioration.

[0067] Table 1. Performance Comparison of Each Embodiment and Comparative Example

[0068] The results show that: In Example 1, the optimized formulation (PCL matrix + appropriate amount of dye / crosslinking agent) can achieve >1000 cycles and a fast response of 0.5 seconds, exhibiting the best overall performance and meeting the requirements of high-end cards; In Example 2, the low-cost solution (ordinary PCL + organic dye) can still maintain >800 cycles, verifying its practicality under controllable cost; In Example 3, the dual anti-counterfeiting effect achieved through multi-wavelength encoding can achieve >900 cycles, demonstrating the potential for functional expansion. In contrast, in Comparative Examples 1 and 2, the function failed when there was no crosslinking network or the polymer was not in a semi-crystalline state, proving that both the crosslinking structure and phase transition capability are indispensable; In Comparative Examples 3 and 4, visible light dyes or excessive dyes led to a sharp drop in durability, highlighting the necessity of near-infrared dyes and precise dosage control.

[0069] In summary, by combining a dynamic anti-counterfeiting mechanism with a universal film structure, the resulting film can be completely embedded inside the card through thermal transfer technology. While maintaining the advantages of traditional holographic anti-counterfeiting, it achieves reversible, high-security dynamic verification that requires laser triggering, thus solving the problems of easy replication of static patterns and unintuitive dynamic verification in existing technologies.

[0070] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite film with dynamic optical anti-counterfeiting function, characterized in that, It includes a substrate layer, a release layer, an imaging layer, a coating layer, a dynamic optical functional layer, a protective layer, and an adhesive layer that are stacked in sequence. The imaging layer has a molded static holographic pattern; The dynamic optical functional layer includes a photothermal responsive semi-crystalline polymer and near-infrared absorbing dyes dispersed therein, and has a three-dimensional cross-linked network structure formed by ultraviolet light curing. The dynamic optical functional layer is configured to undergo a reversible crystallization-melting phase transition when irradiated with a laser whose absorption band matches that of the near-infrared absorbing dye, thereby producing a dynamic optical anti-counterfeiting effect.

2. The composite film with dynamic optical anti-counterfeiting function according to claim 1, characterized in that, The photothermal responsive semi-crystalline polymer includes one or more of polycaprolactone, polybutylene adipate, and polyhydroxyalkanoate. Preferably, the number-average molecular weight of the photothermal responsive semi-crystalline polymer is 30,000 to 100,000, and the melting point of the photothermal responsive semi-crystalline polymer is 50 to 65°C.

3. The composite film with dynamic optical anti-counterfeiting function according to claim 1, characterized in that, The near-infrared absorbing dyes include one or more of the following: rare earth-doped upconversion nanoparticles, carbon nanotubes, phthalocyanine dyes, cyanine dyes, and indocyanine green dyes. Preferably, the absorption wavelength of the near-infrared absorbing dye is in the range of 800~1100nm.

4. The composite film with dynamic optical anti-counterfeiting function according to claim 1, characterized in that, The dynamic optical functional layer also has pattern coding, including multi-wavelength dye distribution coding, cross-linking density gradient coding, or thickness gradient coating coding.

5. The composite film with dynamic optical anti-counterfeiting function according to claim 1, characterized in that, The thickness of the dynamic optical functional layer is 1~50μm; and / or, The substrate layer is made of one or more of polyethylene terephthalate, polycarbonate, polypropylene, or polyvinyl chloride, and has a thickness of 12-100 μm; and / or, The surface tension of the release layer is 40~52 dyn / cm, and its thickness is 0.1~0.5μm; And / or, The imaging layer is made of acrylic resin and has a thickness of 0.5~2.0 μm; and / or, The coating is a metal layer or a transparent dielectric layer with a thickness of 300~600 Å; and / or, The protective layer is made of one or more of polyurethane, nano-silica, polyacrylate, or fluorocarbon resin, with a glass transition temperature of not less than 200°C after curing and a thickness of 0.8~1.5μm; and / or, The adhesive layer is made of hot melt adhesive with a softening point of 95~150℃ and a thickness of 4~8μm.

6. A method for preparing a composite thin film with dynamic optical anti-counterfeiting function as described in any one of claims 1-5, characterized in that, Includes the following steps: S1 applies release layer material onto the substrate layer to form a release layer; S2 coats the imaging layer material onto the release layer, and forms a static holographic pattern by molding to obtain the imaging layer; S3 vapor-deposits a coating on the imaging layer; S4 applies a coating liquid containing a photothermal responsive semi-crystalline polymer, a near-infrared absorbing dye, and a crosslinking agent to the coating layer, and forms a dynamic optical functional layer after drying and ultraviolet curing. S5 coats a protective layer material onto the dynamic optical functional layer to form a protective layer; S6 applies adhesive material to the protective layer to form an adhesive layer.

7. The method according to claim 6, characterized in that, The amount of the near-infrared absorbing dye added is 0.1% to 3% of the mass of the photothermal responsive semi-crystalline polymer, and the amount of the crosslinking agent added is 1% to 10% of the mass of the photothermal responsive semi-crystalline polymer. Preferably, the coating liquid of the dynamic optical functional layer further includes a solvent, and the solid content of the coating liquid is 10% to 30%; the solvent includes one or more of tetrahydrofuran, acetone, ethyl acetate, N-methylpyrrolidone or propylene glycol methyl ether acetate.

8. The method according to claim 6 or 7, characterized in that, The crosslinking agent is selected from one or more of thiol compounds, benzophenone photoinitiators, acrylate monomers or prepolymers, and epoxy acrylate resins.

9. The method according to claim 6 or 7, characterized in that, In step S4, The drying conditions are: drying temperature 40~50℃, drying time 3~5 minutes; and / or, The conditions for UV curing are: wavelength 300~400 nm, intensity 50~200 mW / cm², and curing time 10~60 seconds.

10. The application of a composite film with dynamic optical anti-counterfeiting function in card anti-counterfeiting, characterized in that, The composite film with dynamic optical anti-counterfeiting function as described in any one of claims 1-5, or the composite film with dynamic optical anti-counterfeiting function prepared by the method described in any one of claims 6-9.

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