Polyimide film, method for preparing the same, and use thereof

Abstract

This application relates to a polyimide film, its preparation method, and its application, falling within the field of polymer film preparation technology. The preparation method includes: dissolving calix[n]aromatics, monoacyl chloride monomers, and diacyl chloride monomers in an organic solvent at a specific molar ratio to form a hyperbranched structure; adding a diamine monomer to generate an amino-terminated hyperbranched structure; then adding a dianhydride monomer and a diacyl chloride monomer to obtain a polyamic acid solution; and finally, chemical imidization and film-forming treatment to obtain a polyimide film. This application effectively solves the problem that existing polyimide films struggle to simultaneously possess excellent bending resistance and creep resistance, significantly improving the film's applicability in the field of flexible displays.

Description

Technical Field

[0001] This application relates to the field of polymer film technology, specifically to a polyimide film, its preparation method, and its application. Background Technology

[0002] Polyimide films have become an important choice for core substrate materials of flexible display devices due to their excellent heat resistance, mechanical properties, and dimensional stability. As flexible display technology accelerates towards ultra-thinness and foldability, more stringent requirements are placed on the comprehensive performance of polyimide films: they must not only possess high light transmittance (e.g., >88%) and low yellowness index to meet the optical quality requirements of displays; they must also withstand hundreds of thousands of dynamic bends at extremely small radii of curvature (e.g., 0.5 mm or even 0.25 mm) without plastic deformation or creases; at the same time, they must maintain a low coefficient of thermal expansion (CTE < 15 ppm / K) during high-temperature processes to match other functional layers.

[0003] To address these challenges, existing technologies have explored various molecular structures and processes. For example, Chinese invention patent CN116162244B discloses a polyimide film with a "spring-like structure" folded macromolecular chain segment constructed by introducing anthracene-1,8-diamine. This design utilizes recoverable elastic deformation generated by changes in bond length and bond angle, which to some extent improves the film's bending resistance under extreme curvature. However, the deformation capability of this "spring-like" chain segment mainly relies on the local bond angle adjustment of the main chain, and its energy dissipation pathway is relatively singular. During long-term or high-frequency dynamic bending, it is difficult to fully dissipate the accumulated stress, leading to molecular chain slippage and accumulation of plastic deformation, ultimately resulting in creases or a decline in mechanical properties.

[0004] On the other hand, Chinese patent application CN120383731A discloses a polyamide-imide and its preparation method, which uses a diamine monomer containing amide bonds to copolymerize with dianhydrides such as 6FDA and BPDA, and supplements it with a gradient active polymerization process and a LiCl dynamic solubilization system to achieve a balance between high light transmittance and high mechanical properties. However, this technical solution mainly strengthens the film through linear copolymerization and intermolecular hydrogen bond network, and its crosslinking density and energy dissipation mechanism are limited. When dealing with ultra-low curvature bending at extremely small bending radii (such as 0.25 mm), this linear or slightly crosslinked molecular chain network is still difficult to effectively suppress the relative slippage of molecular chains, and there is a risk of stress concentration and creep failure, manifested as insufficient bending life or excessive coefficient of thermal expansion.

[0005] In summary, while existing polyimide films achieve high light transmittance and low thermal expansion, their energy dissipation mechanisms and stress transfer networks still have shortcomings. This makes it difficult to simultaneously achieve excellent bending resistance and creep resistance under the extreme bending conditions required for ultra-thin flexible display applications. How to construct more efficient and diverse non-destructive energy dissipation channels through molecular engineering design, and optimize the balance between elasticity and toughness of the cross-linked network structure, thereby overcoming the bottleneck of the trade-off between mechanical properties, creep resistance, and bending resistance in polyimide films, is a pressing technical problem to be solved in this field. Summary of the Invention

[0006] This application provides a polyimide film, its preparation method, and its application, which can solve the technical problem that existing polyimide films are difficult to have both excellent bending resistance and creep resistance.

[0007] To achieve the above objectives, this application provides the following technical solution: The first aspect of this application provides a method for preparing a polyimide film, comprising dissolving calix[n]arene, monoacyl chloride monomer, and diacyl chloride monomer in an organic solvent at a molar ratio of 1:m:(nm) to form a hyperbranched structure; wherein n is any integer between 4 and 10, and m is any integer between 0 and n; adding a diamine monomer to generate an amino-terminated hyperbranched structure; adding a dianhydride monomer and a diacyl chloride monomer to obtain a polyamic acid solution; adding a dehydrating agent and a catalyst to perform chemical imidization to obtain a polyamide-imide solution; and performing a film-forming treatment on the polyamide-imide solution to obtain a polyimide film.

[0008] In one alternative embodiment, the reaction time for forming the hyperbranched structure is 1-3 h; and / or the reaction time for generating the amino-terminated hyperbranched structure is 1-3 h; and / or the reaction time for obtaining the polyamic acid solution is 6-10 h.

[0009] In one optional embodiment, the reaction temperature in the chemical imidization reaction to obtain the polyamic acid solution is 5°C; and / or, the reaction conditions in the chemical imidization reaction are: reacting at room temperature for 3-7 h, followed by reacting at 60-80°C for 0.5-1 h.

[0010] In one optional embodiment, the film-forming process includes the steps of sequentially performing a coating, solvent removal, and heat treatment.

[0011] In one optional embodiment, the heat treatment conditions are: treatment at 240-280°C for 0.5-1.5 h.

[0012] In an optional embodiment, the diamine monomer is selected from any one or more of formulas (1) to (22): ; The dianhydride monomer is selected from any one or more of formulas (23) to (33): ; The diacyl chloride monomer is selected from any one or more of formulas (34) to (39): ; The monoacyl chloride monomer is selected from any one or more of formulas (40) to (45): ; calix[n]aromatics are selected from any one or more of formulas (46)-(50): .

[0013] In one optional embodiment, the organic solvent is selected from one or more of N,N'-dimethylethanolamine, N,N-dimethylformamide, and N-methyl-2-pyrrolidone; and / or, the catalyst is selected from one or more of imidazole, isoquinoline, quinoline, triethylamine, pyridine, piperidine, and ethanolamine; and / or, the dehydrating agent is one or more of acetic anhydride, N,N'-dicyclohexylcarbodiimide, anhydrous sodium acetate, and anhydrous calcium acetate.

[0014] In one optional embodiment, a dehydrating agent and a catalyst are added, and the ratio of carboxyl groups, catalyst and dehydrating agent in the mixture is 1:1:3-10.

[0015] A second aspect of this application provides a polyimide film prepared by the above-described preparation method.

[0016] The third aspect of this application provides the application of the aforementioned polyimide film in the field of flexible displays.

[0017] This application provides a polyimide film, its preparation method, and its application. The method involves dissolving calix[n]arene, monoacyl chloride monomer, and diacyl chloride monomer in an organic solvent at a specific molar ratio to form a hyperbranched structure. The calix[n]arene is used as a macrocyclic crosslinking core, and its reaction with monoacyl chloride and diacyl chloride constructs a three-dimensional network with controllable branching. Then, a diamine monomer is added to generate an amino-terminated hyperbranched structure, which is further reacted with dianhydride monomer and diacyl chloride monomer to obtain a polyamic acid solution. Subsequently, chemical imidization is performed by adding a dehydrating agent and a catalyst to obtain a polyamide-imide solution. Finally, a polyimide film is obtained through film formation. By adjusting the molar ratio of calix[n]arene to acyl chloride monomer, the elasticity of the hyperbranched crosslinked network and the brittleness caused by excessive crosslinking can be precisely balanced. This allows the macrocyclic cavity compound calix[n]arene to undergo reversible conformational inversion under external force, thereby effectively dissipating energy. Furthermore, the hyperbranched structure, with its covalent links between calix[n]arene and macromolecular chains, radially transmits stress, providing multiple non-destructive energy dissipation channels. This effectively solves the problems of existing polyimide films easily generating creases during bending and creeping under static loads, significantly improving the film's mechanical strength, creep resistance, and bending resistance, ensuring its high reliability and long lifespan in flexible display applications.

[0018] In summary, this application constructs a hyperbranched polyimide system with a unique energy dissipation mechanism through the synergistic effect of molecular structure design and process control, achieving full-process optimization from raw material ratio to final film formation, forming a complete technical closed loop, and providing a systematic solution for the preparation of high-performance flexible display substrate materials. Attached Figure Description

[0019] Figure 1 It is the 1H NMR spectrum of the reaction between calix[8] aromatic hydrocarbons and benzoyl chloride.

[0020] Figure 2 This is a schematic diagram of the static bending resistance test of polyimide film.

[0021] Figure 3 This is a schematic diagram of the dynamic bending resistance test of polyimide film. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit the invention.

[0023] To achieve the above-mentioned objectives, this invention provides a method for preparing a polyimide film, the resulting film, and its applications. The overall technical solution is as described in the embodiments of this application, mainly including the following core technical elements: using calix[n]arene as a macrocyclic crosslinking core, a hyperbranched structure with controllable branching degree is constructed by adjusting the molar ratio of calix[n]arene with monoacyl chloride monomers and diacyl chloride monomers; after end-capping with the amino groups of a diamine monomer, it is polymerized with dianhydride or diacyl chloride monomer to generate a polyamic acid solution; subsequently, chemical imidization is performed to obtain a polyamide-imide solution; finally, a polyimide film is obtained through coating, solvent removal, and heat treatment. The above technical elements work together to constitute the overall technical solution of this invention.

[0024] The first aspect of this invention provides a method for preparing a polyimide film. A calix[n]arene, a monoacyl chloride monomer, and a diacyl chloride monomer are dissolved in an organic solvent at a molar ratio of 1:m:(nm) to form a hyperbranched structure; wherein n is any integer between 4 and 10, and m is any integer between 0 and n; a diamine monomer is added to generate an amino-terminated hyperbranched structure; a dianhydride monomer and / or a diacyl chloride monomer are added to obtain a polyamic acid solution; a dehydrating agent and a catalyst are added to perform chemical imidization to obtain a polyamide-imide solution; the polyamide-imide solution is subjected to a film-forming treatment to obtain a polyimide film. In this invention, by setting calix[n]arene as the core of a macrocyclic compound with ring strain energy, and by precisely controlling the branching degree of the hyperbranched structure using the ratio of monoacyl chloride to diacyl chloride, the resulting polymer network possesses both the radial stress transmission capability brought by the hyperbranched structure and avoids the brittleness caused by excessive cross-linking. At the same time, the macrocyclic cavity of calix[n]arene can undergo reversible conformational inversion under external force, providing multiple non-destructive energy dissipation channels. This collaboratively solves the problems of poor mechanical properties, insufficient creep resistance, and insufficient bending resistance of polyimide films in the prior art, and significantly improves the applicability of the film in the field of flexible displays.

[0025] Specifically, the hyperbranched polyimide prepared in the embodiments of this application has the general molecular formula structure shown in formula (51): Equation (51); Wherein, A1 is a diacyl chloride monomer, A2 is a dianhydride monomer, A3 is a monoacyl chloride monomer, R is a diamine monomer, the value of a ranges from 1 to 1000, and the value of b ranges from 0 to 1000. For calix[n] aromatics, n ranges from 4 to 10, which also represents a calix[n] aromatics grafted with n chains. Equation (51) shows a calix[8] aromatics grafted with 8 molecular chains, and the grafted chains on the calix[n] aromatics in the hyperbranched structure have the above four general molecular chain formulas.

[0026] In one specific implementation, the reaction time for forming the hyperbranched structure is 1-3 h; the reaction time for generating the amino-terminated hyperbranched structure is 1-3 h; and the reaction time for obtaining the polyamic acid emulsion is 6-10 h. By limiting the reaction time of each stage, the construction rate of hyperbranched nodes and the growth degree of polyamic acid molecular chains can be precisely controlled, avoiding gelation due to excessively rapid reaction in the early stage or insufficient molecular weight due to insufficient reaction in the later stage, thereby ensuring that the final film has a uniform microstructure and excellent mechanical stability.

[0027] In one specific implementation, the reaction temperature for obtaining the polyamic acid solution is 5°C; the chemical imidization reaction conditions are: reacting at room temperature for 3-5 h, followed by reacting at 60-80°C for 0.5-1 h. This staged heating chemical imidization strategy first completes most of the cyclization initiation and intermediate conversion at room temperature, then accelerates the ring-closing reaction and removes small molecule byproducts under mild heating conditions. This process effectively avoids main chain degradation or yellowing that may result from prolonged high-temperature reactions, ensuring high light transmittance and high imidization conversion rate of the film.

[0028] As a specific implementation method, the film-forming process includes sequentially performing coating, solvent removal, and heat treatment. By breaking down the film-forming process into ordered coating, solvent gradient evaporation, and high-temperature curing steps, internal stress in the adhesive can be effectively eliminated, bubble formation can be prevented, and molecular chain rearrangement and hyperbranching network densification can be promoted, thereby obtaining a high-quality film with uniform thickness, smooth surface, and no defects.

[0029] As a specific implementation method, the heat treatment conditions are: treatment at 240-280℃ for 0.5-1.5 h. Performing heat treatment within this temperature window ensures complete cyclization of residual carboxyl groups to achieve thorough imidization, promotes further densification of hyperbranched nodes to enhance network rigidity, and avoids thermal degradation caused by excessively high temperatures, thus enabling the film to maintain high strength while possessing excellent bending resistance.

[0030] As a specific implementation method, the present invention does not limit the specific selection of diamine monomers, which can be any one or more of formulas (1) to (22); the present invention does not limit the specific selection of dianhydride monomers, which can be any one or more of formulas (23) to (33); the present invention does not limit the specific selection of diacyl chloride monomers, which can be any one or more of formulas (34) to (39); the present invention does not limit the specific selection of monoacyl chloride monomers, which can be any one or more of formulas (40) to (45); the present invention does not limit the specific selection of calix[n]arene, which can be any one or more of formulas (46) to (50). By selecting monomers with the above-mentioned specific structures, and by using fluorine-containing, biphenyl, or ether groups to adjust the rigidity and free volume of the molecular chain, and by combining calix[n]arene with different cavity sizes, the optimal matching of hyperbranched node density and chain segment mobility can be achieved, thereby optimizing the overall performance of the film at the molecular level.

[0031] As a specific implementation method, this invention does not limit the specific selection of the organic solvent, which can be one or more of N,N'-dimethylethanolamine, N,N-dimethylformamide, and N-methyl-2-pyrrolidone; similarly, this invention does not limit the specific selection of the catalyst, which can be one or more of imidazole, isoquinoline, quinoline, triethylamine, pyridine, piperidine, and ethanolamine; this invention does not limit the specific selection of the dehydrating agent, which can be one or more of acetic anhydride, N,N'-dicyclohexylcarbodiimide, anhydrous sodium acetate, and anhydrous calcium acetate. Using the above-mentioned high-boiling-point polar solvents can ensure the stable dissolution of hyperbranched intermediates and high molecular weight polyamic acid, while the specific combination of catalyst and dehydrating agent can significantly improve the selectivity and rate of the imidization reaction, ensuring that the reaction system proceeds efficiently without side reaction interference.

[0032] As a specific embodiment, the present invention provides a method for preparing a polyimide film. After adding a dehydrating agent and a catalyst, the ratio of carboxyl groups, catalyst, and dehydrating agent in the mixture is 1:1:3-10. By controlling the molar ratio of carboxyl groups, catalyst, and dehydrating agent, the catalytic active centers are ensured to be saturated, while excess dehydrating agent is used to completely remove the water generated in the reaction, pushing the imidization equilibrium towards the forward reaction direction, thereby achieving near-complete conversion and reducing the adverse effects of residual carboxyl groups on the film's heat resistance and dielectric properties.

[0033] A second aspect of the present invention provides a polyimide film prepared by the preparation method in any of the above embodiments. This film contains a hyperbranched network structure composed of covalently linked calix[n]arenes, exhibiting excellent tensile strength, low creep characteristics, and superior bending resistance. Its performance indicators are significantly better than those of traditional linear polyimide films, making it particularly suitable for flexible electronic devices with extremely high mechanical reliability requirements.

[0034] A third aspect of this invention provides an application of the polyimide film in any of the above embodiments in the field of flexible displays. Experimental results show that the polyimide film prepared by this invention exhibits extremely low bulging height and excellent static recovery ability in repeated bending tests. Therefore, it can be used to prepare cover plate materials or substrate materials that solve the problems of creases and bulging in flexible display screens, meeting the needs of high-end applications such as foldable screen phones and rollable displays.

[0035] Unless otherwise specified, all materials, reagents and instruments used in the embodiments of this invention can be obtained through commercial channels.

[0036] Key raw materials include: calix[n]aromatics (n=4,6,8, etc., purity ≥98%), monoacyl chloride monomers (such as benzoyl chloride, purity ≥99%), diacyl chloride monomers (such as terephthaloyl chloride, purity ≥99%), diamine monomers (such as 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, purity ≥99%), and dianhydride monomers (such as 4,4'-(hexafluoroisopropene) phthalic anhydride, purity ≥99%); solvents include N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP); catalysts include isoquinoline, imidazole, etc.; and dehydrating agents include acetic anhydride, etc.

[0037] The instruments and equipment include: a constant temperature magnetic stirrer, a vacuum degassing machine, a precision coating machine, a programmable temperature oven, an Instron 5967 universal testing machine (for mechanical property testing), and a TA Q800 dynamic mechanical analyzer (for creep resistance testing).

[0038] Example 1: This embodiment provides a method for preparing a polyimide film (A1-CPAI).

[0039] Benzoyl chloride (BC), terephthaloyl chloride (TPC), and calixarene (C8) [8] were dissolved in N,N-dimethylacetamide (DMAc) under a nitrogen protective atmosphere. The molar ratio of C8, BC, and TPC was controlled to be 1:5:3. The reaction was carried out for 3 h to form a hyperbranched structure. Figure 1 As shown, Figure 1 The figure shows the 1H NMR spectrum of the reaction between calix[8]arene and benzoyl chloride. It can be seen from the figure that the characteristic peak of the C8 terminal hydroxyl group has basically disappeared, indicating that the terminal hydroxyl group of calix[8]arene has basically completely reacted with the acyl chloride, and the hyperbranched structure of acyl chloride end capping has been successfully constructed.

[0040] 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) was added to the above reaction system, and the molar ratio of C8 to TFMB was controlled at 0.04:1. After reacting for 1 h, an amino-terminated hyperbranched structure was generated.

[0041] TPC and 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA) were added. The reaction temperature was controlled at 5°C by adding an ice-water bath. The molar ratio of 6FDA to TPC was controlled at 2:3. The reaction was stopped after stirring for 8 hours to obtain a polyamic acid (PAA) solution with a solid content of 10 wt%.

[0042] Isoquinoline and acetic anhydride were added to the PAA adhesive solution, and the molar ratio of carboxyl groups, isoquinoline and acetic anhydride in the PAA was controlled to be 1:1:5. The reaction was stirred at room temperature for 6 h, followed by chemical imidization at 60 °C for 1 h to obtain a polyamide-imide (CPAI) solution.

[0043] After vacuum degassing and filtration, the CPAI solution was uniformly coated onto a clean glass plate using a coating machine. The plate was first treated at 90°C for 2 hours to remove the solvent, and then heat-treated at 280°C for 0.5 hours to finally obtain an Al-polyamide-imide film (Al-CPAI).

[0044] The prepared Al-CPAI film is transparent and uniform in appearance, without bubbles or cracks.

[0045] This embodiment successfully prepared a polyimide film based on the hyperbranched structure of calix[8]arene, confirming the feasibility of the technical route of the present invention.

[0046] Example 2: This embodiment aims to verify the effect of the change in the molar ratio of calix[n]aromatic, monoacyl chloride and diacyl chloride monomers on the film performance, and to support the feasibility of the range of m values.

[0047] With all other preparation conditions the same as in Example 1, only the molar ratio of C8, BC and TPC was adjusted from 1:5:3 to 1:4:4 (i.e., the m value was changed) to obtain A2-polyamide-imide film (A2-CPAI).

[0048] The results show that the product can still achieve the technical effects of the present invention, with a slight improvement in tensile strength and bending resistance. This proves that within a limited molar ratio range, the degree of branching can be effectively controlled by adjusting the ratio of monoacyl chloride to diacyl chloride, and the technical solution has good feasibility and stability.

[0049] Example 3: This embodiment aims to verify the effect of another boundary value on the molar ratio of calix[n]aromatic, monoacyl chloride and diacyl chloride monomers on film performance.

[0050] With all other preparation conditions the same as in Example 1, only the molar ratio of C8, BC and TPC was adjusted from 1:5:3 to 1:2:6 to obtain A3-polyamide-imide film (A3-CPAI).

[0051] The results show that even with a high proportion of diacyl chloride, the resulting film still maintains good mechanical properties and bending resistance. Although the elongation at break fluctuates, the overall performance is still significantly better than the comparative film without the introduction of hyperbranched structure, demonstrating the wide adaptability of the parameter range.

[0052] Example 4: This embodiment aims to verify the effects of different types of calix[n]aromatics (n value variation) and the lower limit of heat treatment temperature on film performance.

[0053] Benzoyl chloride (BC), terephthaloyl chloride (TPC) and calix[6] aromatic hydrocarbon (C6) were dissolved in DMAc, and the molar ratio of C6, BC and TPC was controlled to be 1:3:3. The reaction was carried out for 3 h.

[0054] TFMB was added, and the molar ratio of C6 to TFMB was controlled at 0.02:1. The reaction was carried out for 1 h.

[0055] TPC and 6FDA were added, and the molar ratio of 6FDA to TPC was controlled at 4:1. The mixture was heated in an ice-water bath at 5°C and stirred for 8 hours to obtain a PAA adhesive with a solid content of 10 wt%.

[0056] Isoquinoline and acetic anhydride (ratio 1:1:5) were added, and the mixture was reacted at room temperature for 6 h and then at 60 °C for 1 h to obtain a CPAI solution.

[0057] After coating, the film was treated at 90℃ for 2 h, followed by heat treatment at 240℃ for 0.5 h (using the lower limit of the heat treatment temperature) to obtain A4-polyamide-imide film (A4-CPAI).

[0058] The results show that the film prepared by using calix[6] aromatics and a lower heat treatment temperature still has excellent bending resistance, which confirms the effectiveness of the scheme when the n value is in the range of 4-10 and the heat treatment temperature is at the lower limit.

[0059] Example 5: This embodiment aims to verify the effect of different molar ratios on the performance of the cup[6] aromatic system.

[0060] With all other preparation conditions the same as in Example 4, only the molar ratio of C6, BC and TPC was adjusted to 1:2:4 to obtain A5-polyamide-imide film (A5-CPAI).

[0061] The results show that the product performance is stable under this parameter adjustment, further supporting the limitation on the molar ratio range.

[0062] Example 6: This embodiment is intended to verify the feasibility of another extreme molar ratio condition in the cup [6] aromatic system.

[0063] With all other preparation conditions the same as in Example 4, only the molar ratio of C6, BC and TPC was adjusted to 1:1:5 to obtain A6-polyamide-imide film (A6-CPAI).

[0064] The results show that even at high diacyl chloride ratios, the hyperbranched structure based on calix[6]arene can still impart good overall performance to the film.

[0065] Example 7: This embodiment aims to verify the effects of different solid contents and amine end-capping ratios on film performance.

[0066] Under a nitrogen atmosphere, BC, TPC and C8 were dissolved in DMAc in a molar ratio of 1:5:3 and reacted for 3 h.

[0067] TFMB was added, and the molar ratio of C8 to TFMB was controlled at 0.06:1. The reaction was carried out for 1 h.

[0068] Add 6 FDA (without adding additional TPC), control the temperature in an ice-water bath at 5°C, and stir for 8 hours to obtain a PAA adhesive with a solid content of 20 wt%.

[0069] Isoquinoline and acetic anhydride (ratio 1:1:5) were added, and the reaction was carried out at room temperature for 6 h and at 60 °C for 1 h.

[0070] After coating, the film was treated at 90℃ for 2 h and then at 260℃ for 0.5 h to obtain A7-polyamide-imide film (A7-CPAI).

[0071] The results showed that the process remained smooth and the film quality was good even after increasing the solid content and adjusting the amino end-capping ratio.

[0072] Example 8: This embodiment aims to verify the effect of different molar ratios in a high solids content system.

[0073] With all other preparation conditions the same as in Example 7, only the molar ratio of C8, BC and TPC was adjusted to 1:4:4 to obtain A8-polyamide-imide film (A8-CPAI).

[0074] The results show that the properties of the thin film prepared under these conditions meet expectations, demonstrating the robustness of the process parameters.

[0075] Example 9: This embodiment aims to verify the influence of another molar ratio boundary in a high solids content system.

[0076] With all other preparation conditions the same as in Example 7, only the molar ratio of C8, BC and TPC was adjusted to 1:2:6 to obtain A9-polyamide-imide film (A9-CPAI).

[0077] The results show that, under all parameter boundary conditions, the method of the present invention can successfully prepare polyimide films with excellent properties.

[0078] Example 10: To verify the inventiveness and significant technical effects of the polyimide film prepared by this invention, the following comparative tests were conducted: Comparative Example 1 (B1-CPAI): Linear polyamide-imide films were prepared directly by polymerization of TFMB, TPC, and 6FDA (molar ratio corresponding to the total amount in Example 1) without the addition of calix[n]arene, monoacyl chloride, and amino end-capping steps.

[0079] Comparative Example 2 (B2-CPAI): Same as Comparative Example 1, but the ratio of dianhydride to diacyl chloride was adjusted to correspond to Example 4.

[0080] Comparative Example 3 (B3-CPI): Conventional linear polyimide films were prepared by polymerization of only TFMB and 6FDA, without acyl chloride monomers and calixarenes.

[0081] Test items and methods: 1. Mechanical properties: Tensile strength, modulus and elongation at break were tested using an Instron 5967 universal testing machine in accordance with GB / T 1040.3-2006.

[0082] 2. Creep resistance: The maximum strain was tested after 60 minutes at 150℃ and 60 MPa constant stress using a TA Q800 dynamic mechanical analyzer.

[0083] 3. Static bending resistance: such as Figure 2 As shown, Figure 2 This is a schematic diagram of the static bending resistance test of polyimide film. The film is folded 180° (radius 1 mm) between two planar glass plates and held for 24 h. After unfolding for 1 h, the unfolding angle is measured. The larger the unfolding angle, the smaller the plastic deformation and the better the bending resistance.

[0084] 4. Dynamic bending resistance: such as Figure 3 As shown, Figure 3 This is a schematic diagram of the dynamic bending resistance test of polyimide film. Through the U-shaped dynamic bending test, the film is repeatedly folded 200,000 times at a folding radius of 1.0 mm, and the bulge height at the bending center is measured. The lower the height, the better the dynamic bending resistance.

[0085] The test results are shown in Table 1 below: Table 1. Comprehensive performance test results of polyimide films prepared in the examples and comparative examples. As shown in Table 1, compared with Comparative Examples 1-3 which did not introduce the hyperbranched structure of calix[n]arene, the films prepared in Examples 1-9 of this invention exhibit significant advantages in all performance indicators. In particular, Example 2 has a tensile strength as high as 211.8 MPa, an elongation at break of 23.58%, a maximum strain of only 2.68%, a static bending unfolding angle of 175°, and a dynamic bending arch height as low as 19.54 μm.

[0086] Combination Figure 2 and Figure 3 The testing principle and results analysis show that Comparative Example 3 (traditional linear PI) exhibited an arch height exceeding 1000 μm after dynamic bending, indicating severe plastic deformation and irreversible creases. In contrast, Example 2 of this invention showed an arch height of only 19.54 μm. This confirms that the reversible conformational inversion mechanism of the calix[n]arene macrocyclic cavity under external force effectively dissipates bending energy, and the hyperbranched structure achieves radial stress transmission, avoiding stress concentration. Furthermore, although Example 2 has a similar chemical composition to Comparative Example 1, the introduction of a controlled hyperbranched crosslinking network significantly improves its creep resistance (maximum strain) and dynamic bending resistance, demonstrating the unexpected technical effects of this invention.

[0087] In this application example, the test samples covered the products prepared under different calix[n] aromatic hydrocarbon types, different molar ratios, different solid contents and different heat treatment conditions in Examples 1 to 9. The test results consistently showed that, within the above parameter range, the polyimide films prepared by this invention exhibited excellent mechanical properties, creep resistance and bending resistance.

[0088] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for preparing a polyimide film, characterized in that, Calico[n]aromatic hydrocarbon, monoacyl chloride monomer and diacyl chloride monomer are dissolved in an organic solvent in a molar ratio of 1:m:(nm) to form a hyperbranched structure; where n is any integer between 4 and 10, and m is any integer between 0 and n. Adding a diamine monomer generates an amino-terminated hyperbranched structure; Adding dianhydride monomer and diacyl chloride monomer yields a polyamic acid solution; Chemical imidization was carried out by adding a dehydrating agent and a catalyst to obtain a polyamide-imide solution; The polyamide-imide adhesive solution is subjected to a film-forming process to obtain the polyimide film.

2. The preparation method according to claim 1, characterized in that, In the reaction that forms the hyperbranched structure, the reaction time is 1-3 h; And / or, in the reaction that generates the amino-terminated hyperbranched structure, the reaction time is 1-3 h; And / or, in the reaction to obtain the polyamic acid solution, the reaction time is 6-10 h.

3. The preparation method according to claim 1, characterized in that, In the reaction to obtain the polyamic acid solution, the reaction temperature is 5°C; And / or, in the chemical imidization reaction, the reaction conditions are: reacting at room temperature for 3-7 h, followed by reacting at 60-80℃ for 0.5-1 h.

4. The preparation method according to claim 1, characterized in that, The film-forming process includes the following steps: sequentially performing film coating, solvent removal, and heat treatment.

5. The preparation method according to claim 4, characterized in that, The heat treatment conditions are: treatment at 240-280℃ for 0.5-1.5 h.

6. The preparation method according to claim 1, characterized in that, The diamine monomer is selected from any one or more of formulas (1) to (22): ； The dianhydride monomer is selected from any one or more of formulas (23) to (33): ； The diacyl chloride monomer is selected from any one or more of formulas (34) to (39); ； The monoacyl chloride monomer is selected from any one or more of formulas (40) to (45); ； The calix[n] aromatic hydrocarbon is selected from any one or more of formulas (46) to (50); 。 7. The preparation method according to claim 1, characterized in that, The organic solvent is selected from N,N'-dimethylethanolamine, N,N-Dimethylformamide One or more of N-methyl-2-pyrrolidone; And / or, the catalyst is selected from one or more of imidazole, isoquinoline, quinoline, triethylamine, pyridine, piperidine, and ethanolamine; And / or, the dehydrating agent is one or more of acetic anhydride, N,N'-dicyclohexylcarbodiimide, anhydrous sodium acetate, and anhydrous calcium acetate.

8. The preparation method according to claim 1, characterized in that, After adding the dehydrating agent and catalyst, the ratio of carboxyl groups, catalyst and dehydrating agent in the mixture is 1:1:3-10.

9. A polyimide film prepared by the preparation method according to any one of claims 1-8.

10. The application of the polyimide film according to claim 9 in the field of flexible displays.

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