Liquid crystal polymer film based on dynamic covalent chemical bond, preparation method of liquid crystal polymer film and application of liquid crystal polymer film in dynamic anti-counterfeiting and self-repairing

Abstract

The invention discloses a liquid crystal polymer film based on dynamic covalent chemical bonds as well as a preparation method and application of the liquid crystal polymer film in dynamic anti-counterfeiting and self-repairing, and belongs to the technical field of stimuli-responsive fluorescent materials. According to the invention, the problems of single response mode, lack of reconfigurability, weak physical damage resistance and the like of the existing stimuli-responsive fluorescent material are solved. According to the invention, the photoresponsive fluorescent switch based on a fluorescence resonance energy transfer mechanism is constructed through synergistic compounding of spiropyrane and tetraphenyl ethylene, and a time-color two-dimensional key identification function is realized. By means of the excellent dynamic exchange performance of diselenide bond dynamic covalent chemistry, the polymer network is endowed with self-repairing capability and topological structure remodeling characteristic, so that the film has programmable information writing, erasing and rewriting functions and physical damage self-repairing capability, an innovative technical path is provided for the high-end anti-counterfeiting field, and the application prospect is wide. The safety and reliability of an anti-counterfeiting system can be remarkably improved, and the core requirement of the market for a high-performance anti-counterfeiting material can be precisely met.

Description

Technical Field

[0001] This invention relates to a liquid crystal polymer film based on dynamic covalent chemical bonds, its preparation method, and its application in dynamic anti-counterfeiting and self-healing, belonging to the field of stimulus-responsive fluorescent materials technology. Background Technology

[0002] In today's digital age, the need for information security and product anti-counterfeiting and traceability is becoming increasingly urgent. This is especially true in high-end luxury goods, specialty pharmaceuticals, and important documents, where security requirements are extremely high, leading to frequent issues of forgery and tampering. Compared to traditional information encryption materials (such as static optical encryption materials like static fluorescent inks and infrared absorbing dyes, and physical encryption materials like photonic crystals) and ordinary QR codes, the core advantage of stimulus-responsive fluorescent materials lies in their ability to generate dynamically adjustable, multi-dimensional, and time-controlled optical signals.

[0003] However, the application of existing stimulus-responsive fluorescent materials in high-end encryption, anti-counterfeiting, and traceability fields still faces several key technical bottlenecks, significantly restricting their widespread application in these high-security scenarios. Specific technical shortcomings are as follows: First, the response mode is limited; most materials can only switch between two colors (e.g., colorless and colored) or binary fluorescence states (e.g., fluorescence on and off), resulting in limited information storage capacity and making anti-counterfeiting labels easily counterfeited, leading to insufficient security. Second, they lack dynamic reconfigurability; once information is written, it is difficult to erase or reprogram, failing to meet the core requirements of dynamic information updates and cyclical use in high-security scenarios. Third, the materials have weak resistance to physical damage; after scratching, folding, or other physical actions, their anti-counterfeiting function may permanently fail, seriously affecting practical applications. Therefore, developing novel stimulus-responsive fluorescent materials with both self-healing and dynamic anti-counterfeiting properties is expected to overcome existing technical bottlenecks, providing superior solutions for high-end encryption, anti-counterfeiting, and traceability fields, and has significant application implications. Summary of the Invention

[0004] This invention addresses the shortcomings of existing stimulus-responsive fluorescent materials, such as limited response modes, lack of reconfigurability, and weak resistance to physical damage. It provides a method for preparing liquid crystal polymer films based on dynamic covalent chemical bonds and their application in dynamic anti-counterfeiting and self-healing.

[0005] The technical solution of the present invention: One objective of this invention is to provide a method for preparing a liquid crystal polymer film, the method comprising the following steps: Step 1: Mix the liquid crystal material, spiropyran, tetraphenylethylene derivative, crosslinking agent, chain extender and photoinitiator, dissolve the mixed raw materials in a solvent and stir evenly to obtain liquid crystal prepolymer mother liquor; Step 2: Coat the liquid crystal prepolymer mother liquor onto the pretreated PET film layer, dry at 40-60℃, cool to room temperature, peel off the PET film to obtain an uncured liquid crystal film; Step 3: The uncured liquid crystal film is subjected to photocuring treatment to obtain a liquid crystal polymer film.

[0006] Further specifying, the proportions of liquid crystal material, spiropyran, tetraphenylethylene derivative, crosslinking agent, chain extender and photoinitiator in the mixed raw materials of step one are 75-85 wt%, 5-10 wt%, 1-2 wt%, 8-10 wt%, 1-10 wt% and 1-2 wt%, respectively.

[0007] Further specifying, in step one, the liquid crystal material is RM257, the tetraphenylethylene derivative is TPE, and the crosslinking agent is 3,3'-diselenobis(propionylhydrazine).

[0008] Further specifying, the chain extender is EDDET, the photoinitiator is photoinitiator 784, and the solvent is THF.

[0009] Further specifying, the concentration of the liquid crystal prepolymer mother liquor obtained in step one is 20-40 wt%.

[0010] Further specifying, the PET film pretreated in step two is a friction-treated polyimide-oriented PET film.

[0011] Furthermore, the preparation method of the friction-treated polyimide-oriented PET film is as follows: First, polyimide adhesive is uniformly coated on the surface of the PET substrate, and the wet film thickness is controlled at 1-3 μm through the coating process. Then, it is placed in an environment of 70-85℃ for thermosetting treatment. Next, the PI layer is oriented by friction alignment equipment, and the friction speed of the equipment is set to 1000-1500 r / min. Finally, a pre-oriented PI alignment layer is formed on the surface of the PET substrate, and a pre-treated PET film is obtained.

[0012] Further specifying, the coating thickness of the liquid crystal prepolymer mother liquor in step two is 50-300 μm.

[0013] Further specifying, the thickness of the uncured liquid crystal film obtained in step two is 50-200 μm.

[0014] Further specifying, the irradiation intensity of the photocuring treatment in step three is 5-10 mW / cm². 2 The wavelength is 500 nm and the time is 10-20 min.

[0015] The second objective of this invention is to provide a liquid crystal polymer film that possesses both self-healing and fluorescence-stimulated response properties.

[0016] The third objective of this invention is to provide an application of the above-mentioned liquid crystal polymer film in the preparation of dynamic anti-counterfeiting films.

[0017] The fourth objective of this invention is to provide a method for preparing a dynamic anti-counterfeiting film, which includes the following steps: (1) Masks containing different encrypted information patterns are sequentially applied to the surface of the liquid crystal polymer film, and after each application of the mask, an irradiation with a wavelength of 365 nm and an intensity of 5-20 mW / cm is applied. 2 Irradiation with ultraviolet light yields thin films inscribed with different encrypted information; (2) Irradiate the film with different encrypted information patterns at 365 nm for 30-60 s. The film changes color as a whole, thus completing the hiding of the encrypted information patterns and obtaining a dynamic anti-counterfeiting film.

[0018] The fifth objective of this invention is to provide a dynamic anti-counterfeiting film prepared by the above method. Specifically, under 500 nm visible light, the film exhibits different encrypted information patterns as the duration of illumination changes.

[0019] The sixth objective of this invention is to provide a dynamic anti-counterfeiting film prepared by the above method, specifically, the dynamic anti-counterfeiting film can erase encrypted information patterns under heating and green light irradiation.

[0020] Furthermore, the dynamic anti-counterfeiting film, after the encrypted information pattern has been erased, can be rewritten with new encrypted information.

[0021] Beneficial effects: This invention constructs a photoresponsive fluorescent switch based on the fluorescence resonance energy transfer (FRET) mechanism through the synergistic compounding of spiropyran (SP) and tetraphenylethylene (TPE), achieving a dual-dimensional "time-color" key recognition function. Furthermore, leveraging the excellent dynamic exchange properties of diselenate bonds, it endows the polymer network with self-healing capabilities and topological reshaping characteristics, enabling the film to possess programmable information writing, erasing, and rewriting functions, as well as self-healing capabilities for physical damage. This provides an innovative technological path for the high-end anti-counterfeiting field, significantly improving the security and reliability of anti-counterfeiting systems and precisely matching the market's core demand for high-performance anti-counterfeiting materials. Compared with existing technologies, it also has the following advantages: (1) This invention utilizes the aggregation-induced emission properties of TPE, which can efficiently transfer the absorbed energy to SP units through the fluorescence resonance energy transfer (FRET) mechanism, thereby making the color change of SP more obvious. Moreover, the FRET effect formed by SP and TPE units can break through the limitation of the single color change of traditional fluorescent materials, realize multi-color tunable fluorescent materials, and simultaneously meet the function of information storage. Furthermore, 3,3'-diselenobis(propionylhydrazine) is used as a "smart switch" for the molecular motion environment: on the one hand, the degree of isomerization of SP is precisely controlled, thereby realizing the on-demand adjustment of the photochromic performance of the system; on the other hand, this dynamic crosslinking network also functions as a crosslinking agent, while endowing the material with self-healing ability, effectively extending the service life and fatigue resistance of the film.

[0022] (2) The liquid crystal polymer film prepared by the present invention can make the hidden information appear, change or disappear sequentially by switching between ultraviolet light and visible light. This dynamic and programmable display mode greatly increases the difficulty of counterfeiting, and raises the level of anti-counterfeiting from visible to controllable change, realizing high-security dynamic anti-counterfeiting and multiple information encryption.

[0023] (3) This invention utilizes the interaction between the dynamic exchange of diselenide bonds and the isomerization of spiropyran molecules to enable anti-counterfeiting information to be erased and rewritten, giving anti-counterfeiting labels flexibility and breaking through the limitations of fixed information in traditional anti-counterfeiting labels. It provides a brand-new design idea and implementation path for the development of next-generation smart materials. Attached Figure Description

[0024] Figure 1 For the FRET effect of SP and TPE; Figure 2 The information writing and storage process of the liquid crystal polymer film prepared in Example 1 in an anti-counterfeiting scenario; Figure 3 This is a schematic diagram of the information reading process of the liquid crystal polymer film prepared in Example 1 in an anti-counterfeiting scenario; Figure 4 Comparison of POM (Polymer Oxide Material) for fracture and self-repair of the liquid crystal polymer film prepared in Example 1; Figure 5 This is a schematic diagram of the static color of the TPE anti-counterfeiting liquid crystal film without SP modification prepared for Comparative Example 1. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0026] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art may make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0027] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0028] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0029] Example 1: The method for preparing the liquid crystal polymer thin film in this embodiment includes the following steps: (1) Weigh RM257 of liquid crystal monomers ( 1.2 g, 2 mmol), spiropyran (SP, 6.5 mg, 0.018 mmol), diselenoyl crosslinking agent (3,3'-diselenoylbis(propionylhydrazine), 20.0 mg, 0.060 mmol), chain extender (EDDET, 300 mg, 1.64 mmol), tetraphenylethylene derivative (TPE, 4 mg (0.009 mmol) and photoinitiator Irgacure 784 (2 mg) were placed in a sample vial.

[0030] (2) Add 2 mL of THF to the bottle and sonicate for 10 min to obtain a clear prepolymer solution.

[0031] (3) Polyimide (PAA) adhesive is uniformly coated onto the surface of the PET substrate using a precision coating process, with the dry film thickness strictly controlled to be 2 μm. Subsequently, the PET substrate coated with PAA adhesive is placed in a constant temperature environment of 80℃ for thermosetting to obtain a polyimide (PI) layer. The PI layer is subjected to directional friction treatment using a special friction orientation equipment, with the friction speed set to 1000 r / min. By optimizing the friction parameters, the orientation uniformity is ensured, and a PI orientation layer with a pre-oriented structure is formed on the surface of the PET substrate, finally obtaining a pre-treated PET film. (4) The prepolymer solution obtained in (2) above is coated onto the surface of the friction-treated polyimide-oriented PET film by a doctor blade coating (300 μm gap between the doctor blades), and dried at 60 °C for 24 h to form a functional layer with a thickness of about 200 μm.

[0032] (5) After cooling to room temperature, remove the liquid crystal film from the PET substrate and then cure it with 500 nm green light (10 min, 5 mW / cm²). 2 A light yellow liquid crystal polymer film with uniform orientation was obtained.

[0033] The application of the aforementioned liquid crystal polymer film in dynamic anti-counterfeiting using a two-dimensional "time-color" system; (6) The first step is the information writing process: a digital photomask template with partitionable and adjustable characteristics (such as...) is used. Figure 2 As shown, a photomask containing partitions ①②③④⑤⑥⑦ is used to design three different encrypted information patterns: State 1: Number 5, composed of partitions ①⑦③④⑤; State 2: Number 6, composed of partitions ①⑦③④⑤⑥; State 3: Number 8, composed of partitions ①②③④⑤⑥⑦. The different encrypted information patterns are written in stages using an ultraviolet irradiation strategy. The specific operation is as follows: <1> Writing to state 1 (digit 5): Directional irradiation of mask sections ①⑦③④⑤ using 365 nm ultraviolet light (irradiation duration 60 s, light intensity 5 mW / cm²). 2 Partitions ② and ⑥ are shielded with aluminum foil to prevent ultraviolet light exposure, completing the initial writing of status 1 information; <2> State 2 (digit 6) writing: Based on the information already written in State 1, remove the foil covering partition 6 and maintain 365 nm ultraviolet light irradiation (light intensity 5 mW / cm²). 2 Continue irradiating partitions ①⑦③④⑤⑥ for 150 seconds (partition ② is still covered with tin foil) to achieve the superimposed writing of state 2 information; <3> State 3 (Number 8) Writing: Based on the information already written in State 2, completely remove the foil masking from all partitions, and continue to use 365 nm ultraviolet light (illuminance 5 mW / cm²) on mask partitions ①②③④⑤⑥⑦. 2 Irradiate for 2 minutes to complete the final writing of state 3 information and obtain a thin film with different encrypted information written on it.

[0034] (7) The second step is information hiding: In order to ensure the security of encrypted information, after the information is written, the photomask template is removed and the patterned film is irradiated with 365 nm ultraviolet light in the whole area (irradiation time is 30 s) so that the film presents a uniform reddish-brown appearance, thereby achieving efficient hiding of encrypted information patterns and obtaining dynamic anti-counterfeiting film.

[0035] (8) The above dynamic anti-counterfeiting film was tested by using 500 nm green light as a stimulus source. Spiropyran molecules undergo the following reversible isomerization reaction under ultraviolet (UV) and visible (Vis) light (Equation I below). Based on the differentiated control of the degree of isomerization, during the information decryption process excited by visible light, the film can present a digital code corresponding to the degree of isomerization; the digital code that appears only within a preset precise time window is the target valid information, while the digital codes outside this time window are invalid false information. The relevant test results are shown in Figure 3. By dynamically adjusting the duration of green light irradiation, the film can present different information display forms. This scheme designates the number "6" as valid encrypted information. Tests showed that: after irradiation for 10 s, the film outputs the error information pattern "8"; after irradiation for 100 s, the film stably presents the valid encrypted information "6"; and after irradiation for 240 s, the film outputs the error information pattern "5". This confirms that the dynamic anti-counterfeiting film possesses time-information dual-dimensional key anti-counterfeiting characteristics.

[0036]

[0037] Formula I Furthermore, by utilizing the dynamic nature of the diselenide bond in the anti-counterfeiting film as shown in Formula II, the dynamic anti-counterfeiting film is heat-treated, specifically heated at 100°C for 2 hours and then irradiated with 500 nm green light for 10 minutes. This allows the previously written encrypted information pattern to be erased, and a new anti-counterfeiting pattern can be rewritten in a new location. This realizes the programmability and reconfigurability of the anti-counterfeiting information, which is suitable for occasions where the anti-counterfeiting information needs to be replaced periodically.

[0038]

[0039] Formula II (9) To test the self-healing properties of the liquid crystal polymer film, a sample was cut into two parts and then heated at 100°C for 3 hours. The parts then recombined, as shown in the image. Figure 4 As shown.

[0040] Comparative Example 1: The difference between this comparative example and Example 1 is that step (1) involves weighing liquid crystal monomer RM257 ( 1.2 g, 2 mmol), diselenyl bond crosslinking agent (3,3'-diselenylbis(propionylhydrazine), 20.0 mg, 0.060 mmol), chain extender (EDDET, 300 mg, 1.64 mmol), tetraphenylethylene derivative (TPE, 4 mg (0.009 mmol) and photoinitiator Irgacure 784 (2 mg) were placed in sample vials; the remaining process steps and parameter settings were the same as in Example 1.

[0041] When the thin film prepared in this comparative example was irradiated at 365 nm, it was found that the film showed only two colors: colorless and cyan. Figure 5 As shown, this indicates that the encrypted information of the film is not time-dependent and lacks dynamic light and chemical response performance, resulting in a low level of anti-counterfeiting and easy counterfeiting.

[0042] Comparative Example 2: The difference between this comparative example and Example 1 is that pentaerythritol tetraacrylate is used instead of diselenylene bond crosslinking agent in step (1), while the remaining process steps and parameter settings are the same as in Example 1.

[0043] Although the thin film prepared in this comparative example exhibits photochromic and fluorescent switching properties, it lacks self-healing and thermal reconstruction capabilities. Once scratched, the damage is permanent, and the written pattern cannot be effectively erased after heat treatment.

[0044] The above description is only a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a liquid crystal polymer film, characterized in that, include: Step 1: Mix the liquid crystal material, spiropyran, tetraphenylethylene derivative, crosslinking agent, chain extender and photoinitiator, dissolve the mixed raw materials in a solvent and stir evenly to obtain liquid crystal prepolymer mother liquor; Step 2: Coat the liquid crystal prepolymer mother liquor onto the pretreated PET film layer, dry at 40-60℃, cool to room temperature, peel off the PET film to obtain an uncured liquid crystal film; Step 3: The uncured liquid crystal film is subjected to photocuring treatment to obtain a liquid crystal polymer film.

2. The preparation method according to claim 1, characterized in that, In the mixed raw materials of step one, the proportions of liquid crystal material, spiropyran, tetraphenylethylene derivative, crosslinking agent, chain extender and photoinitiator are 75-85 wt%, 5-10 wt%, 1-2 wt%, 8-10 wt%, 1-10 wt% and 1-2 wt%, respectively.

3. The preparation method according to claim 1, characterized in that, In step one, the liquid crystal material is RM257, the tetraphenylethylene derivative is TPE, the crosslinking agent is 3,3'-diselenobis(propionylhydrazine), the chain extender is EDDET, the photoinitiator is photoinitiator 784, and the solvent is THF.

4. The preparation method according to claim 1, characterized in that, The PET film pretreated in step two is a friction-treated polyimide-oriented PET film.

5. The preparation method according to claim 1, characterized in that, The irradiation intensity of the photocuring treatment in step three is 5-10 mW / cm². 2 The wavelength is 500 nm and the time is 10-20 min.

6. A liquid crystal polymer film according to any one of claims 1 to 5, characterized in that, It possesses both self-healing and fluorescence-stimulated response properties.

7. The application of the liquid crystal polymer film according to claim 6 in the preparation of dynamic anti-counterfeiting film.

8. A method for preparing a dynamic anti-counterfeiting film, characterized in that, include: (1) A mask containing different encrypted information patterns is sequentially applied to the surface of the liquid crystal polymer film described in claim 6, and after each application of the mask, an irradiation with a wavelength of 365 nm and an intensity of 5-20 mW / cm is applied. 2 Irradiation with ultraviolet light yields thin films inscribed with different encrypted information; (2) Irradiate the thin film with different encrypted information patterns at 365 nm for 30-60 s. The film changes color, thus completing the hiding of the encrypted information patterns and obtaining a dynamic anti-counterfeiting film.

9. A dynamic anti-counterfeiting film prepared by the method of claim 8, characterized in that, Under 500 nm visible light, the dynamic anti-counterfeiting film displays different encrypted information patterns as the duration of illumination changes.

10. A dynamic anti-counterfeiting film prepared by the method of claim 8, characterized in that, The dynamic anti-counterfeiting film can erase the encrypted information pattern under heating and green light irradiation, and the dynamic anti-counterfeiting film with the encrypted information pattern erased can be rewritten with new encrypted information.

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