Photosensitive polyimide precursor, photosensitive polyimide film formed therefrom, and use thereof

Abstract

The application discloses a photosensitive polyimide precursor, a photosensitive polyimide film formed by the photosensitive polyimide precursor and application thereof, and belongs to the technical field of photosensitive polyimide film materials. The photosensitive polyimide precursor is formed by copolymerization of an aromatic dianhydride compound, an aromatic diamine compound, a photosensitive diamine compound I and a photosensitive diamine compound II, wherein the ratio of the number of moles of the aromatic dianhydride compound to the total number of moles of the aromatic diamine compound, the photosensitive diamine compound I and the photosensitive diamine compound II is 1:1, and the ratio of the number of moles of the photosensitive diamine compound I to the number of moles of the photosensitive diamine compound II is 1:1. The photosensitive polyimide film formed by the photosensitive polyimide precursor has both 1,4-dihydropyridine photosensitive groups and o-nitrobenzyl ether photosensitive groups, can produce a synergistic enhancement effect after ultraviolet light irradiation, and thus can significantly improve the height and stability of a surface relief grating structure, and can be directly applied to the fields of high-safety optical encryption labels, information anti-counterfeiting and the like.

Description

Technical Field

[0001] This application belongs to the field of photosensitive polyimide film material technology, and specifically discloses a photosensitive polyimide precursor, the photosensitive polyimide film formed therefrom, and its application. Background Technology

[0002] Photosensitive polyimide (PSPI) is a polymer material that combines excellent mechanical properties, superior thermal stability, electrical insulation, and photosensitivity. It can be self-patterned through molecular functionalization, significantly simplifying photolithography paths and eliminating interface defects. It has been widely used in semiconductor packaging, flexible displays, and microelectronics. In diffraction optics, PSPI is considered an ideal substrate for fabricating diffraction gratings due to its excellent film-forming properties and dimensional stability. However, the diffraction efficiency of a diffraction grating is directly related to its height. Increasing the grating groove depth is expected to achieve higher optical performance, but existing PSPI materials are limited by factors such as photosensitivity characteristics, development structure fidelity, and post-baking shrinkage, resulting in generally low grating heights that cannot meet the performance requirements of high-end applications such as holographic anti-counterfeiting and high-temperature encrypted marking.

[0003] Currently, various technical routes for fabricating polyimide-based gratings have been reported in related studies. For example, Qiu Keqiang et al. used holographic lithography and electroplating transfer technology to fabricate a phase-type gold transmission grating with a groove depth of 200 nm on a 300 nm polyimide film, verifying the feasibility of high line density transmission gratings. Other studies have used PSPI containing cinnamic acid groups as "ink" to fabricate photocrosslinkable surface-undulating gratings through soft printing technology, enriching the grating patterning fabrication system. Among these, the PSPI thin film system based on 1,4-dihydropyridine (DHP) photosensitive diamine units has attracted the most attention. It can construct surface-embossed holographic gratings through photolithography combined with solvent engineering, effectively adapting to applications such as holographic anti-counterfeiting and high-temperature stable encrypted labels.

[0004] However, while existing PSPI thin film systems based on 1,4-dihydropyridine (DHP) photosensitive diamine units can be used to construct surface-embossed holographic gratings for anti-counterfeiting encryption tags via photolithography-solvent engineering, the photoreaction driving force of the DHP groups is insufficient, making it difficult to drive effective migration of polymer chains. The resulting grating height is generally only about 200 nm. Furthermore, the industry lacks effective strategies for actively enhancing grating height through molecular structure design. Grating height remains constrained by multiple factors, including material photosensitivity, development retention, and post-baking shrinkage, making it difficult to effectively increase to higher levels. Therefore, there is an urgent need to develop a photosensitive polyimide material that can actively enhance grating height through molecular structure design. Summary of the Invention

[0005] This application effectively solves the technical problem of low grating height in existing PSPI film systems based on 1,4-dihydropyridine (DHP) photosensitive diamine units by disclosing a photosensitive polyimide precursor, the photosensitive polyimide film formed therefrom, and its application.

[0006] To achieve the above objectives, the technical solution provided in this application is as follows: A first aspect of this application provides a photosensitive polyimide precursor, which is formed by copolymerization of a monomer composition comprising: (a) Aromatic dianhydrides; (b) Aromatic diamine compounds; (c) Photosensitive diamine compound I, having the chemical structure shown in formula (1); (d) Photosensitive diamine compound II, having the chemical structure shown in formula (2); (1); (2); The ratio of the molar number of the aromatic dianhydride compound to the total molar number of the aromatic diamine compound, the photosensitive diamine compound I, and the photosensitive diamine compound II is 1:1, and the molar ratio of the photosensitive diamine compound I to the photosensitive diamine compound II is 1:1.

[0007] In the disclosure of the first aspect, the aromatic dianhydride compound described in this application is selected from at least one of pyromellitic dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, benzophenone dianhydride, and hexafluorodianhydride.

[0008] In the disclosure of the first aspect, the aromatic diamine compound described in this application is selected from at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, and 4,4'-diaminodiphenyl sulfone.

[0009] The second aspect of this application discloses a method for preparing the above-mentioned photosensitive polyimide precursor, which includes the following steps: Under inert gas protection, the aromatic dianhydride compound, the aromatic diamine compound, the photosensitive diamine compound I, and the photosensitive diamine compound II are dissolved in an organic solvent and polymerized at a temperature of -10 to 60°C for 4 to 48 hours to obtain a solution containing the photosensitive polyimide precursor.

[0010] In the disclosure of aspect 2, the organic solvent described in this application is selected from... N,N- dimethylformamide, N,N- dimethylacetamide, N- At least one of methylpyrrolidone and dimethyl sulfoxide.

[0011] A third aspect of this application discloses a photosensitive polyimide film with highly stable diffraction properties, which is formed from the photosensitive polyimide precursor described above. The surface of the photosensitive polyimide film has a surface relief grating structure. Under exposure conditions of 8μm × 8μm linewidth / line spacing, the average grating height of the surface relief grating structure is not less than 650nm; and Under exposure conditions of 8μm×8μm linewidth / line spacing, the average grating height of the surface relief grating structure is not less than 710nm.

[0012] The fourth aspect of this application discloses a method for preparing the aforementioned photosensitive polyimide film with highly stable diffraction properties, which includes the following steps: Preparation of a solution containing a photosensitive polyimide precursor; The solution containing the photosensitive polyimide precursor is coated onto the substrate surface to form a coating. Dry the coating to form a photosensitive polyimide precursor film; The photosensitive polyimide precursor film is subjected to patterned exposure and development treatment to form a surface relief grating structure on the film surface. After drying and curing, a photosensitive polyimide film with high stable diffraction performance is obtained.

[0013] In the fourth aspect of the disclosure, the patterned exposure described in this application includes ultraviolet light exposure of the photosensitive polyimide precursor film using a mask.

[0014] In the fourth aspect of the disclosure, the developing process described in this application includes placing the exposed photosensitive polyimide precursor film in a developing solution for developing.

[0015] In the disclosed embodiment of aspect 4, the wavelength of the ultraviolet light exposure described in this application is 254nm~405nm, and the exposure dose is 10~500mJ / cm².

[0016] In the fourth aspect of the disclosure, the developer described in this application comprises a mixture selected from... N,N -Dimethylformamide, N,N -Dimethylacetamide, N- At least one organic solvent selected from methylpyrrolidone, dimethyl sulfoxide, and anhydrous ethanol.

[0017] The fifth aspect of this application also discloses the application of the photosensitive polyimide film with high stable diffraction performance described above, specifically the application of the photosensitive polyimide film with high stable diffraction performance in fields such as optical encryption, multi-level grayscale lithography, or information anti-counterfeiting.

[0018] Compared with the prior art, the advantages or beneficial effects of this application include at least: This application employs an aromatic dianhydride compound, an aromatic diamine compound, a photosensitive diamine compound I containing a 1,4-dihydropyridine group on its side chain, and a photosensitive diamine compound II containing an o-nitrobenzyl ether group on its side chain to copolymerize a photosensitive polyimide precursor. The photosensitive polyimide film formed based on this precursor possesses both a 1,4-dihydropyridine (DHP) photosensitive group and an o-nitrobenzyl ether photosensitive group that can generate a synergistic enhancement effect after ultraviolet light irradiation. This solves the problems of insufficient grating height and poor structural stability of the single DHP photosensitive system from the perspective of molecular structure design. Specifically, the DHP photosensitive group undergoes photo-induced dehydration upon irradiation, initially forming a hydrogen bond network. Simultaneously, the o-nitrobenzyl ether photosensitive group undergoes photolysis upon irradiation, releasing phenolic hydroxyl groups and detaching o-nitrosobenzaldehyde small molecules in situ. The phenolic hydroxyl groups provide high-density hydrogen bond acceptor / donor active sites, which can recombine with the photolysis products of 1,4-dihydropyridine to form a high-density secondary hydrogen bond cross-linking network, significantly enhancing the internal cohesion of the grating relief structure. The photoly detached o-nitrosobenzaldehyde small molecules then play a transient plasticizing role between chain segments, effectively reducing the local glass transition temperature, significantly improving the mobility of the polymer backbone, and effectively promoting the formation of a stronger hydrogen bond network. Based on the above synergistic effects, the solvent elution rate and expansion stress instability process during development are significantly accelerated, ultimately resulting in a macroscopic increase in the height of the grating relief. In addition, the phenolic hydroxyl groups that are covalently fixed on the molecular chain after photolysis can significantly enhance the polarity difference between the exposed and unexposed areas, so that the surface relief grating structure formed after development can still be effectively maintained in harsh environments such as high temperature and high humidity, giving the grating structure better long-term stability and environmental tolerance, significantly extending the maintenance time of the grating structure and ensuring its diffraction stability. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is the proton NMR spectrum of the photosensitive diamine compound II of this application; Figure 2 Infrared spectra of the polyimide precursor film and the film cured by step temperature increase in this application. Figure 3 The UV-Vis absorption spectra of the photosensitive polyimide precursor film and the film after UV irradiation are shown in this application. Figure 4AFM height diagrams of the surface relief gratings formed on the photosensitive polyimide film of this application under linewidth / spacing conditions of 4μm×4μm, 6μm×6μm, 8μm×8μm and 10μm×10μm respectively; Figure 5 This is a height histogram of the surface relief grating formed by the photosensitive polyimide film of this application under linewidth / spacing conditions of 4μm×4μm, 6μm×6μm, 8μm×8μm and 10μm×10μm; Figure 6 This is a diagram showing the period and height data of the surface relief grating formed by the photosensitive polyimide film of this application under the condition of 6μm×6μm linewidth / line spacing; Figure 7 This is a diagram showing the period and height data of the surface relief grating formed by the photosensitive polyimide film of this application under the condition of 8μm×8μm linewidth / line spacing; Figure 8 The image shows the period and height data of the surface relief grating formed on the photosensitive polyimide film of Comparative Example 1 under the condition of 6μm×6μm linewidth / spacing. Figure 9 A digital photograph of the photosensitive polyimide film with a surface relief grating structure (6μm×6μm) of this application under white light; Figure 10 The test diagrams show the grating diffraction intensity at the theoretical first-order diffraction angle for the photosensitive polyimide film with a surface relief grating structure (6μm×6μm) of this application and the photosensitive polyimide film with a surface relief grating structure (6μm×6μm) of Comparative Example 1. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments described in this application without creative effort are within the scope of protection of this application.

[0022] In the descriptions related to this application, the term "and / or" is used to describe the relationship between related objects, indicating the existence of three relationships. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. Here, A and B can be singular or plural; the symbol " / " means "or".

[0023] In the descriptions related to this application, the term "at least one" refers to one or more, and "multiple" refers to two or more; the term "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of A, B, or C" or "at least one of A, B, and C" can mean any one of A, B, and C, or A+B, or A+C, or B+C, or A+B+C, where A, B, and C can be single or multiple.

[0024] In the description of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be specifically determined by its function and internal logic, and does not constitute any limitation on the execution process of this embodiment.

[0025] In the description of this application, the numerical range should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Any intermediate value within a stated range, as well as any other stated value or each smaller range between intermediate values ​​within a stated range, are also included in this embodiment, and the upper and lower limits of the smaller ranges may be independently included or excluded from the range.

[0026] Unless otherwise stated, the technical / scientific terms used in this application have the meanings commonly understood by one of ordinary skill in the art. While this application describes only preferred materials and methods, similar or equivalent methods and materials may be used in specific embodiments or test cases. All references to this application are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this application shall prevail.

[0027] To address the issue of low grating height in PSPI thin film systems based on 1,4-dihydropyridine (DHP) photosensitive diamine units, this application provides a photosensitive polyimide precursor in a first aspect. This photosensitive polyimide precursor is formed by copolymerization of a monomer composition comprising: (a) an aromatic dianhydride compound; (b) an aromatic diamine compound; (c) a photosensitive diamine compound I having the chemical structure shown in formula (1); and (d) a photosensitive diamine compound II having the chemical structure shown in formula (2). (1); (2); The ratio of the molar number of the aromatic dianhydride compound to the total molar number of the aromatic diamine compound, the photosensitive diamine compound I, and the photosensitive diamine compound II is 1:1, and the molar ratio of the photosensitive diamine compound I to the photosensitive diamine compound II is 1:1.

[0028] It should be noted that the aromatic dianhydride compound refers to a monomer whose molecular structure contains an aromatic ring and two anhydride groups directly attached to the aromatic ring, and which can undergo a polycondensation reaction with an aromatic diamine monomer to form polyamic acid. This includes, but is not limited to, one or more of pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), diphenyl ether dianhydride (ODPA), benzophenone dianhydride (BTDA), and hexafluorodianhydride (6FDA). In this application, pyromellitic dianhydride is used as an example to illustrate the mechanism of synthesizing photosensitive polyamic acid using aromatic dianhydride compounds as monomers, facilitating understanding by those skilled in the art. This does not constitute any limitation on the scope of protection. The aforementioned biphenyl dianhydride, diphenyl ether dianhydride, benzophenone dianhydride, and hexafluorodianhydride are also applicable to the technical solution of this application and can achieve the same or equivalent technical effects. This application will not provide examples of each of them individually.

[0029] It should be noted that the aromatic diamine compound refers to a monomer containing an aromatic ring and two amino groups (-NH2) directly attached to the aromatic ring in its molecular structure, and capable of forming polyamic acid through a condensation reaction with an aromatic dianhydride monomer. This includes, but is not limited to, one or more of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (p-PDA), m-phenylenediamine (m-PDA), 4,4'-diaminodiphenylmethane (MDA), and 4,4'-diaminodiphenyl sulfone (DDS). In this application, 4,4'-diaminodiphenyl ether is used as an example to illustrate the mechanism of synthesizing photosensitive polyamic acid using aromatic diamine compounds as monomers, facilitating understanding by those skilled in the art. This does not constitute any limitation on the scope of protection. The aforementioned p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, and 4,4'-diaminodiphenyl sulfone are also applicable to the technical solutions of this application and can achieve the same or equivalent technical effects. Therefore, this application will not provide examples of each of them individually.

[0030] It should be noted that the photosensitive diamine compound I has the chemical structure shown in formula (1). This application does not specifically limit the source of the photosensitive diamine compound I; it can be stably prepared by referring to the synthetic route described in the published literature (“Palladium-assisted MetalPatterning on Polyimide Surfaces” Chinese J. Polym. Sci. 2022, 40, 1287–1296).

[0031] It should be noted that the photosensitive diamine compound II has the chemical structure shown in formula (2). This application also discloses a method for synthesizing the photosensitive diamine compound II, specifically comprising the following steps: Step 1: Add 200mL of anhydrous... N,N- Dimethylformamide (DMF) was added to a two-necked flask. While stirring magnetically, 23.763 g of o-nitrobenzyl bromide (0.11 mol) was added and allowed to dissolve completely. Then, 40.728 g of cesium carbonate (Cs₂CO₃, 0.125 mol) and 25.981 g of cesium iodide (CsI, 0.11 mol) were slowly added in three portions. After each addition, the flask neck was rinsed with a small amount of DMF (approximately 5 mL). A reflux condenser and a constant-pressure dropping funnel were installed, and the oil bath was heated to 70°C.

[0032] Step 2: Dissolve 27.719 g of 3,5-dibromophenol (0.11 mol) in 150 mL of anhydrous DMF and add the solution to a constant pressure dropping funnel. Under nitrogen protection, add the solution from this step dropwise to the double-necked flask at a rate of approximately 1 drop per second. After the addition is complete, continue the reaction at 70 °C under nitrogen protection for 12 hours.

[0033] Step 3: After the reaction is complete, filter while hot and collect the filtrate. Slowly pour the filtrate into 4L of deionized water and let it stand overnight. Filter to precipitate the solid product, and dry the solid product in a vacuum oven at 55℃ for 24 hours to obtain the intermediate o-DMN.

[0034] Step 4: Add 19.35 g of intermediate o-DMN and 200 mL of tetrahydrofuran (THF) to a 100 mL double-necked flask. Add 0.6 g of tetratriphenylphosphine palladium (Pd(PPh3)4) and 20.73 g of potassium carbonate under magnetic stirring. After adding, wash the mouth of the flask with a small amount of THF and reflux at 70 °C for 10 minutes.

[0035] Step 5: Add 27.710 g of p-aminophenylborate acid salt, 200 mL of THF, and 100 mL of deionized water in portions to a centrifuge tube. Sonicate until the solid is completely dissolved, then transfer the solution to a constant-pressure dropping funnel. Evacuate the reaction flask and purge it with nitrogen for protection. Slowly add the solution described in this step dropwise through the constant-pressure dropping funnel at 70°C. After the addition is complete, continue the reaction for 24 hours.

[0036] Step 6: After the reaction is complete, filter to remove insoluble matter, extract the filtrate with 200 mL of ethyl acetate and separate the organic phase, wash the organic phase three times with saturated brine (50 mL each time), dry with anhydrous sodium sulfate, filter and remove the solvent by rotary evaporation, and dry the obtained solid in a vacuum oven at 50 °C for 24 hours to obtain the photosensitive diamine compound II shown in formula (2).

[0037] (2); in, Figure 1 The proton NMR spectrum of the photosensitive diamine compound II is shown below. (¹H NMR,400MHz,DMSO-d6) δ 8.11 (d,J= 8.2Hz,1H), 7.87 (d,J=7.7Hz,1H), 7.79(t,J= 6.6Hz,1H),7.62 (t,J= 6.6Hz,1H),7.42(d,J= 6.5Hz,4H),7.29(s,1H),7.00(s,2H),6.64(d,J= 6.4Hz,4H),5.57(s,2H),5.23(s,4H).

[0038] This application employs an aromatic dianhydride compound, an aromatic diamine compound, a photosensitive diamine compound I containing a 1,4-dihydropyridine group on its side chain, and a photosensitive diamine compound II containing an o-nitrobenzyl ether group on its side chain to copolymerize a photosensitive polyimide precursor. The photosensitive polyimide film formed based on this precursor possesses both a 1,4-dihydropyridine (DHP) photosensitive group and an o-nitrobenzyl ether photosensitive group that can generate a synergistic enhancement effect after ultraviolet light irradiation. This solves the problems of insufficient grating height and poor structural stability of the single DHP photosensitive system from the perspective of molecular structure design. Specifically, the DHP photosensitive group undergoes photo-induced dehydration upon irradiation, initially forming a hydrogen bond network. Simultaneously, the o-nitrobenzyl ether photosensitive group undergoes photolysis upon irradiation, releasing phenolic hydroxyl groups and detaching o-nitrosobenzaldehyde small molecules in situ. The phenolic hydroxyl groups provide high-density hydrogen bond acceptor / donor active sites, which can recombine with the photolysis products of 1,4-dihydropyridine to form a high-density secondary hydrogen bond cross-linking network, significantly enhancing the internal cohesion of the grating relief structure. The photoly detached o-nitrosobenzaldehyde small molecules then play a transient plasticizing role between chain segments, effectively reducing the local glass transition temperature, significantly improving the mobility of the polymer backbone, and effectively promoting the formation of a stronger hydrogen bond network. Based on the above synergistic effects, the solvent elution rate and expansion stress instability process during development are significantly accelerated, ultimately resulting in a macroscopic increase in the height of the grating relief. In addition, the phenolic hydroxyl groups that are covalently fixed on the molecular chain after photolysis can significantly enhance the polarity difference between the exposed and unexposed areas, so that the surface relief grating structure formed after development can still be effectively maintained in harsh environments such as high temperature and high humidity, giving the grating structure better long-term stability and environmental tolerance, significantly extending the maintenance time of the grating structure and ensuring its diffraction stability.

[0039] It should be noted that the molar ratio of the aromatic dianhydride compound to the total molar ratio of the aromatic diamine compound, the photosensitive diamine compound I, and the photosensitive diamine compound II is preferably 1:1, and the molar ratio of the photosensitive diamine compound I to the photosensitive diamine compound II is preferably 1:1. This ensures the stoichiometric balance between the anhydride and amino groups in the polycondensation reaction, effectively improves the degree of polymerization, and yields photosensitive polyamic acid (polyimide precursor) with good structural properties.

[0040] This application provides a method for preparing the photosensitive polyimide precursor of this application in a second aspect, preferably comprising the following steps: Under inert gas protection, the aromatic dianhydride compound, the aromatic diamine compound, the photosensitive diamine compound I, and the photosensitive diamine compound II are dissolved in an organic solvent and polymerized at a temperature of -10 to 60°C for 4 to 48 hours to obtain a solution containing the photosensitive polyimide precursor.

[0041] It should be noted that this application does not specifically limit the type of organic solvent, and polar aprotic solvents known in the art can be used, including but not limited to... N,N- Dimethylformamide (DMF) N,N- Dimethylacetamide (DMAc) N- Methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), etc. In the embodiments of this application, [the following is used] N,N- The above example of dimethylacetamide is used to illustrate the concept, aiming to facilitate understanding and implementation by those skilled in the art, and does not constitute any limitation on the scope of protection. N,N- dimethylformamide, N- Methylpyrrolidone and dimethyl sulfoxide are also applicable to the technical solutions of this application and can achieve the same or equivalent technical effects. This application will not provide examples of each of them.

[0042] It should be noted that this application does not specifically limit the type of inert gas. Inert gases known in the art, such as nitrogen and argon, can be used, as long as the polycondensation reaction can be carried out under conditions that isolate oxygen throughout.

[0043] In a third aspect, this application provides a photosensitive polyimide film with highly stable diffraction properties, which is formed from the photosensitive polyimide precursor described above. The surface of the photosensitive polyimide film has a surface relief grating structure. Under exposure conditions of 6μm × 6μm linewidth / spacing, the average grating height of the surface relief grating structure is not less than 650nm; and Under exposure conditions of 8μm×8μm linewidth / line spacing, the average grating height of the surface relief grating structure is not less than 710nm.

[0044] This application provides a method for preparing a photosensitive polyimide film with high stable diffraction properties as described above in aspect 4, preferably comprising the following steps: Step 1: Prepare a solution containing the photosensitive polyimide precursor according to the aforementioned method; Step 2: Coat the substrate surface with the solution containing the photosensitive polyimide precursor to form a coating; Step 3: Dry the coating to form a photosensitive polyimide precursor film; Step 4: The photosensitive polyimide precursor film is subjected to patterned exposure and development treatment to form a surface relief grating structure on the film surface. After drying and curing, a photosensitive polyimide film with high stable diffraction performance is obtained.

[0045] It should be noted that this application does not specifically limit the solid content of the solution containing the photosensitive polyimide precursor. Those skilled in the art can adjust it according to actual needs, as long as it meets the coating process requirements and obtains the required film thickness and photosensitivity. This application preferably uses a solid content of 5-30%, for example, 5%, 10%, 15%, 20%, 30%, etc., to ensure that a coating with good coatability and photosensitivity can be obtained. In this application, a solid content of 10% is used as an example in the embodiments, which does not constitute any limitation on the scope of protection. Other solid content values ​​falling within the above preferred range are also applicable to the technical solutions of this application, and will not be exemplified individually.

[0046] It should be noted that this application does not particularly limit the coating method for forming the coating. The method should be designed to enable the solution containing the photosensitive polyimide precursor to form a uniform, defect-free coating on the substrate surface. Spin coating, blade coating, spray coating, and other coating methods known in the art can be used. In this application, spin coating is used as an example in the embodiments, which does not constitute any limitation on the scope of protection. Other coating methods are equally applicable to the technical solutions of this application, and will not be exemplified one by one.

[0047] It should be noted that this application does not specifically limit the drying method of the coating. The drying method should be designed to effectively remove the organic solvent from the solution containing the photosensitive polyimide precursor, forming a solid film with good smoothness. Known heat treatment methods, including but not limited to vacuum drying and oven drying, can be used. In this embodiment, drying at 80°C for 120 minutes is used as an example, which does not constitute any limitation on the scope of protection. Other drying methods and parameters are also applicable to the technical solution of this application, and will not be exemplified one by one.

[0048] It should be noted that the patterned exposure refers to selectively irradiating the photosensitive polyimide precursor film with ultraviolet light using a mask, causing a photochemical reaction in the exposed area to form a latent image pattern. This allows for the selective removal of unexposed or exposed areas by the developing solution in the subsequent development step to obtain the desired pattern. In a possible implementation, the wavelength of the ultraviolet light exposure is 254nm~405nm, and the exposure dose is 10~500mJ / cm², thereby ensuring sufficient exposure and the formation of a clear pattern. In this application, a wavelength of 365nm and an exposure dose of 500mJ / cm² are used as an example to illustrate the principle of balancing commercially available ultraviolet light sources and sufficient exposure. This does not constitute a limitation on the scope of protection of this application. Other combinations of wavelengths and exposure doses are also applicable to the technical solutions of this application, and will not be exemplified individually.

[0049] It should be noted that the developing process refers to impregnating the exposed photosensitive polyimide precursor film with a developing solution. The developing solution selectively dissolves and removes unexposed or exposed areas to obtain the desired pattern. The developing solution contains ingredients selected from... N,N -Dimethylformamide (DMF) N,N -Dimethylacetamide (DMAc) N- At least one organic solvent selected from methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and anhydrous ethanol (EtOH). Anhydrous ethanol is used as the developing solution in the embodiments of this application for the purpose of facilitating understanding and implementation by those skilled in the art, and does not constitute a limitation on the scope of protection of this application. Other developing solutions are equally applicable to the technical solutions of this application, and will not be exemplified one by one in this application.

[0050] It should be noted that the drying and curing refers to subjecting the developed patterned photosensitive polyimide precursor film to a stepped heating heat treatment under an inert atmosphere, causing the photosensitive polyimide precursor to undergo an imidization reaction (dehydration cyclization), ultimately obtaining a polyimide film with a complete pattern. In this embodiment, the following heating procedure (first heating to 150°C and holding for 30 minutes, then sequentially heating to 200°C and holding for 30 minutes, 250°C and holding for 30 minutes, and 300°C and holding for 30 minutes) is used as an example. This does not constitute a limitation on the scope of protection of this application. Other stepped heating heat treatments are also applicable to the technical solutions of this application, and will not be exemplified one by one.

[0051] In its fifth aspect, this application also provides the application of the photosensitive polyimide film with high diffraction performance described in this application. Specifically, the photosensitive polyimide film with high diffraction performance is applied to fields such as optical encryption, multi-level grayscale lithography, or information anti-counterfeiting. Because the photosensitive polyimide film of this application has high diffraction performance, on the one hand, micro-nano structures with specific diffraction characteristics can be fabricated on its surface, thereby utilizing the uniqueness of the diffraction pattern to achieve information encoding and optical encryption, and utilizing the viewpoint dependence of the diffraction structure to achieve visual anti-counterfeiting effects; on the other hand, a single exposure and development using a grayscale mask can directly form three-dimensional microstructures with continuous or stepped height distributions, meeting the application requirements of multi-level grayscale lithography.

[0052] The technical solution of this application will be further described below with reference to specific embodiments.

[0053] Example 1 This example provides a method for preparing a photosensitive polyimide film with highly stable diffraction properties. The specific steps are as follows: Step 1: Under nitrogen protection, dissolve 1 mmol pyromellitic dianhydride (PMDA), 0.5 mmol 4,4'-diaminodiphenyl ether (ODA), 0.25 mmol photosensitizing diamine compound I (PM), and 0.25 mmol photosensitizing diamine compound II (NBDT) in 10 mL of water. N,N- In dimethylacetamide (DMAc), the mixture was stirred and reacted in an ice-water bath at 0-5°C for 24 hours to obtain a solution containing a photosensitive polyimide precursor with a solid content of approximately 10%. The chemical structure of the photosensitive polyimide precursor is shown in formula (3):

[0054] Where x:y:z=1:1:2.

[0055] Step 2: Spin-coat 100 μL of the solution containing the photosensitive polyimide precursor described in the previous step evenly onto the clean glass slide surface, so that a uniform and defect-free coating is formed on the glass slide surface.

[0056] Step 3: Dry the coating at 80°C for 120 minutes to obtain a photosensitive polyimide precursor film.

[0057] Step 4: The photosensitive polyimide precursor film is exposed to ultraviolet light (wavelength 365nm, exposure dose 500mJ / cm²) using a mask with a 6μm×6μm linewidth / spacing pattern. The exposed film is then immersed in anhydrous ethanol for 60 seconds and rinsed three times with deionized water to remove residual solvent, forming a surface relief grating structure on the film surface. Finally, the film with the surface relief grating structure is cured in a nitrogen atmosphere using a stepped heating process to obtain a photosensitive polyimide film with highly stable diffraction properties. The stepped heating program is as follows: first, the temperature is raised to 150℃ and held for 30 minutes, then successively raised to 200℃ and held for 30 minutes, 250℃ and held for 30 minutes, and 300℃ and held for 30 minutes.

[0058] Test Example 1 To verify the successful preparation of the photosensitive polyimide precursor and the photosensitive polyimide, the photosensitive polyimide precursor film prepared in Example 1 and the film cured by step temperature rise were characterized by infrared spectroscopy. The results were as follows: Figure 2 As shown.

[0059] according to Figure 2 This demonstrates the successful synthesis of the photosensitive polyamic acid precursor (polyamic acid) and its efficient conversion into photosensitive polyimide.

[0060] Test Example 2 To verify the photosensitivity of the photosensitive polyimide precursor film described in this application, the photosensitive polyimide precursor film prepared in Example 1 and the film after ultraviolet light irradiation were characterized by ultraviolet-visible absorption spectroscopy. The results are as follows: Figure 3 As shown.

[0061] according to Figure 3 It is known that the photosensitive polyimide precursor film has stable absorption characteristics within a specific wavelength range. However, after irradiation with ultraviolet light at a wavelength of 365 nm, the absorption peak of the film in the range of 300 nm to 400 nm changes significantly, and the overall absorption peak intensity decreases. This confirms that the DHP photosensitive group underwent a photoinduced dehydration reaction after irradiation, and that the o-nitrobenzyl ether group underwent a photolysis reaction. This confirms that the photosensitive polyimide precursor film described in this application has good ultraviolet photosensitivity, and that both the DHP photosensitive group and the o-nitrobenzyl ether photosensitive group can effectively undergo photochemical reactions under ultraviolet light irradiation.

[0062] Test Example 3 To investigate the effect of pattern linewidth / spacing on the surface relief grating structure formed on the surface of the photosensitive polyimide film, the linewidth / spacing of the mask in Example 1 was changed to 4μm×4μm, 8μm×8μm, and 10μm×10μm, respectively. Following the same preparation steps as in Example 1, the corresponding photosensitive polyimide films were prepared. The surface relief grating structure formed on the surface of each film was characterized using atomic force microscopy (AFM). The scanning range was 80μm×80μm, and the scanning rate was 0.5Hz. The results were as follows: Figure 4 As shown. Among them, Figure 4 (a) to (d) are AFM height maps of the surface relief gratings formed under linewidth / spacing conditions of 4μm×4μm, 6μm×6μm, 8μm×8μm and 10μm×10μm respectively.

[0063] according to Figure 4 It can be seen that the photosensitive polyimide film prepared in this application forms a clear, regular and uniform periodic surface relief grating stripe structure under different linewidth / line spacing conditions, indicating that the photosensitive polyimide film material of this application has good photolithographic patterning capability.

[0064] Further quantitative analysis was conducted on the surface relief grating structures formed under the above linewidth / spacing conditions, and specific statistics were compiled. Figure 4 The height of the surface relief grating formed under various line width / spacing conditions is the result. Figure 5 As shown.

[0065] according to Figure 5 It can be seen that as the linewidth / spacing increases from 4μm×4μm to 10μm×10μm, the surface relief grating height first increases and then decreases. Specifically, when the linewidth / spacing is 4μm×4μm, the surface relief grating height is approximately 150nm; when the linewidth / spacing increases to 6μm×6μm, the surface relief grating height reaches over 680nm; when the linewidth / spacing further increases to 8μm×8μm, the surface relief grating height continues to increase to approximately 710nm; while when the linewidth / spacing continues to increase to 10μm×10μm, the surface relief grating height drops back to approximately 350nm. This indicates that both 6μm×6μm and 8μm×8μm linewidth / spacing conditions are favorable for forming a surface relief grating structure with a high grating height, especially 8μm×8μm, which is the optimal exposure linewidth / spacing condition for this application.

[0066] To further quantify and analyze the periodic integrity and structural uniformity of surface relief grating structures formed under different linewidth / spacing conditions, this application statistically analyzed the period and height of surface relief gratings formed under 6μm×6μm and 8μm×8μm linewidth / spacing conditions. The results are as follows: Figure 6 and Figure 7 As shown.

[0067] according to Figures 6 to 7 It can be seen that the actual period of the surface relief grating formed under the condition of 6μm×6μm linewidth / spacing is about 6.0μm, and the average height reaches about 680nm. The actual period of the surface relief grating formed under the condition of 8μm×8μm linewidth / spacing is about 8.0μm, and the average height reaches about 710nm. The above results show that the photosensitive polyimide film prepared in this application can form a high aspect ratio surface relief grating structure with a height of more than 650nm under both 6μm×6μm and 8μm×8μm linewidth / spacing conditions. Moreover, the actual period of the grating is consistent with the linewidth / spacing height designed by the mask, indicating that the photosensitive polyimide film of this application has excellent pattern transfer fidelity.

[0068] Test Example 4 To verify the synergistic enhancement effect of the photosensitive polyimide precursor film described in this application, Comparative Example 1 is provided.

[0069] Comparative Example 1 The difference between this comparative example and Example 1 is that the photosensitive diamine compound II (NBDT) was not added to the monomer component used to prepare the photosensitive polyimide precursor. The specific steps included: Step 1: Under nitrogen protection, dissolve 1 mmol pyromellitic dianhydride, 0.5 mmol 4,4'-diaminodiphenyl ether, and 0.5 mmol photosensitizing diamine compound I in 10 mL of water. N,N- In dimethylacetamide, the mixture was stirred and reacted for 24 hours under ice-water bath conditions at 0-5°C to obtain a solution containing a photosensitive polyimide precursor with a solid content of approximately 10%.

[0070] Step 2: Spin-coat 100 μL of the solution containing the photosensitive polyimide precursor described in the previous step evenly onto the clean glass slide surface to form a coating on the glass slide surface; Step 3: Dry the coating at 70°C for 120 minutes to obtain a photosensitive polyimide precursor film; Step 4: The photosensitive polyimide precursor film is exposed to ultraviolet light (wavelength 365nm, exposure dose 500mJ / cm²) using a photomask with a 6μm × 6μm linewidth / spacing pattern. The exposed film is then immersed in anhydrous ethanol for 60 seconds and rinsed three times with deionized water to remove residual solvent, forming a surface relief grating structure on the film surface. Finally, the film with the surface relief grating structure is cured in a nitrogen atmosphere using a stepped temperature increase process to obtain the photosensitive polyimide film. The stepped temperature increase program is as follows: first, the temperature is increased to 150℃ and held for 30 minutes, then sequentially increased to 200℃ and held for 30 minutes, 250℃ and held for 30 minutes, and finally 300℃ and held for 30 minutes. The height of the surface relief grating of the photosensitive polyimide film prepared in Comparative Example 1 was measured according to the method in Test Example 3, and the result was as follows: Figure 8 As shown.

[0071] according to Figure 8 It can be seen that the surface relief grating height formed by the photosensitive polyimide film prepared in Comparative Example 1 under the condition of 6μm×6μm linewidth / spacing is only about 200nm, which is much lower than the surface relief grating height formed by the photosensitive polyimide film prepared in Example 1. This confirms that a single DHP photosensitive group cannot provide sufficient photoreaction driving force. However, by introducing both DHP photosensitive group and side chain containing o-nitrobenzyl ether photosensitive group, the o-nitrobenzyl ether photosensitive group can be used to generate phenolic hydroxyl groups in situ through photolysis to increase hydrogen bond active sites. At the same time, the plasticizing effect of the o-nitrosobenzaldehyde small molecule can be used to improve the chain segment mobility. Thus, based on the synergistic effect of the two, the grating height can be effectively increased from 200nm to 680nm.

[0072] Test Example 5 To verify the diffraction optical properties and encryption effect of the surface relief grating structure formed by the photosensitive polyimide film of this application, the photosensitive polyimide film prepared in Example 1 was observed and photographed under a white light source. The results are as follows: Figure 9 As shown.

[0073] according to Figure 9 As can be seen, under white light illumination, the surface of the photosensitive polyimide film prepared in this application exhibits bright and vivid rainbow colors (structural colors) due to the grating diffraction effect. Specifically, the surface relief grating area formed under the condition of 6μm×6μm linewidth / spacing shows obvious rainbow diffraction fringes, and the colors change regularly with the observation angle.

[0074] Further, an in-situ measurement of the diffraction intensity of the surface relief grating was performed using a fiber optic spectrometer at the theoretical first-order diffraction angle, and the results were as follows: Figure 10 As shown.

[0075] according to Figure 10 As can be seen, the diffraction intensity of the photosensitive polyimide film prepared in this application reached 0.63 at 600 nm, while the diffraction intensity of the photosensitive polyimide film prepared in Comparative Example 1 was only 0.14 under the same conditions. The significant improvement in diffraction intensity directly proves the ability of the high-undulation (712 nm) surface relief grating to suppress light signals, and can provide a brighter holographic anti-counterfeiting visual effect.

[0076] The above results demonstrate that the photosensitive polyimide film prepared by this invention can form a diffraction grating pattern with high diffraction efficiency through mask exposure, and can reveal structural colors under illumination, with the structural colors exhibiting angle-dependent characteristics. Since these structural colors originate from physical micro-nano structures, they possess advantages such as resistance to fading and difficulty in replication and counterfeiting. Therefore, the photosensitive polyimide film of this application can be directly applied to fields such as high-security optical encryption tags and information anti-counterfeiting devices.

[0077] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0078] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A photosensitive polyimide precursor, characterized in that, Formed by copolymerization of the following monomer composition, wherein the monomer composition comprises: (a) Aromatic dianhydrides; (b) Aromatic diamine compounds; (c) Photosensitive diamine compound I, having the chemical structure shown in formula (1); (d) Photosensitive diamine compound II, having the chemical structure shown in formula (2); ； (1) (2) The ratio of the molar number of the aromatic dianhydride compound to the total molar number of the aromatic diamine compound, the photosensitive diamine compound I, and the photosensitive diamine compound II is 1:1, and the molar ratio of the photosensitive diamine compound I to the photosensitive diamine compound II is 1:

1.

2. The photosensitive polyimide precursor according to claim 1, characterized in that, The aromatic dianhydride compound is selected from at least one of pyromellitic dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, benzophenone dianhydride, and hexafluorodianhydride.

3. The photosensitive polyimide precursor according to claim 1, characterized in that, The aromatic diamine compound is selected from at least one of 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, and 4,4'-diaminodiphenyl sulfone.

4. A method for preparing the photosensitive polyimide precursor according to any one of claims 1 to 3, characterized in that, Includes the following steps: Under inert gas protection, the aromatic dianhydride compound, the aromatic diamine compound, the photosensitive diamine compound I, and the photosensitive diamine compound II are dissolved in an organic solvent and polymerized at a temperature of -10 to 60°C for 4 to 48 hours to obtain a solution containing the photosensitive polyimide precursor.

5. The preparation method according to claim 4, characterized in that, The organic solvent is selected from N,N- dimethylformamide, N,N- dimethylacetamide, N- At least one of methylpyrrolidone and dimethyl sulfoxide.

6. A photosensitive polyimide film with highly stable diffraction properties, characterized in that, Formed using the photosensitive polyimide precursor according to any one of claims 1 to 3; The surface of the photosensitive polyimide film has a surface relief grating structure; Under exposure conditions of 6μm × 6μm linewidth / spacing, the average grating height of the surface relief grating structure is not less than 650nm; and Under exposure conditions of 8μm×8μm linewidth / line spacing, the average grating height of the surface relief grating structure is not less than 710nm.

7. A method for preparing a photosensitive polyimide film with high stable diffraction properties according to claim 6, characterized in that, Includes the following steps: Preparation of a solution containing a photosensitive polyimide precursor; The solution containing the photosensitive polyimide precursor is coated onto the substrate surface to form a coating. Dry the coating to form a photosensitive polyimide precursor film; The photosensitive polyimide precursor film is subjected to patterned exposure and development treatment to form a surface relief grating structure on the film surface. After drying and curing, a photosensitive polyimide film with high stable diffraction performance is obtained.

8. The preparation method according to claim 7, characterized in that, The patterned exposure includes ultraviolet light exposure of the photosensitive polyimide precursor film using a mask; And / or, the developing process includes placing the exposed photosensitive polyimide precursor film in a developing solution for development.

9. The preparation method according to claim 8, characterized in that, The wavelength of the ultraviolet light exposure is 254nm~405nm, and the exposure dose is 10~500mJ / cm²; And / or, the developer contains a selection from... N,N -Dimethylformamide, N,N -Dimethylacetamide, N- At least one organic solvent selected from methylpyrrolidone, dimethyl sulfoxide, and anhydrous ethanol.

10. The application of the photosensitive polyimide film with high stable diffraction performance as described in claim 6 in the fields of optical encryption, multi-level grayscale lithography, or information anti-counterfeiting.

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