A high-toughness polyimide composite film for flexible copper-clad plate and a preparation method thereof

Abstract

This invention discloses a high-toughness polyimide composite film applicable to flexible copper-clad laminates and its preparation method, belonging to the technical field of polyimide film materials. It includes: a support layer, an adhesive layer disposed on at least one side of the support layer, and a toughening interface layer embedded between the support layer and the adhesive layer. The support layer is formed by the polycondensation of a diamine monomer and an aromatic dianhydride, the diamine monomer including flexible aromatic diamines and rigid fused-ring aromatic diamines. The polymer molecular chain of the adhesive layer contains end groups, the end groups including benzotriazole ring structures capable of forming stable complexes with copper. The toughening interface layer is formed by reacting terminal amino-terminated hyperbranched polyimide grafted with mica powder particles and polyamic acid resin used to form the support layer. The toughness and dimensional stability of the support layer are controlled by the combination of flexible and rigid diamines, the interlayer bonding is optimized and the overall flexural strength of the film is improved by utilizing hyperbranched grafted mica powder particles, and the adhesion is enhanced by the complexation of the benzotriazole ring with copper.

Description

Technical Field

[0001] This invention belongs to the field of polyimide film material technology, specifically relating to a high-toughness polyimide composite film that can be used in flexible copper-clad laminates and its preparation method. Background Technology

[0002] Flexible copper clad laminate (FCCL) is the core substrate of flexible printed circuit board (FPC). Among them, two-layer flexible copper clad laminate (2L-FCCL) has become the mainstream development direction of FCCL because it eliminates the epoxy / silicone adhesive layer of traditional three-layer products and uses a thermoplastic polyimide layer directly composited with copper foil. It has the advantages of being thinner, lighter, more heat-resistant, and having a lower dielectric constant.

[0003] As the insulating and adhesive substrate for 2L-FCCL, the performance of polyimide film directly determines the reliability and service life of FPC. The industry has put forward core requirements for it, such as high adhesion, high dimensional stability, high heat resistance, and low glass transition temperature (Tg). With the development of electronic devices towards miniaturization and wearability, high toughness and resistance to repeated bending have become new key performance indicators.

[0004] Currently, there are still many technical bottlenecks in the use of polyimide films for 2L-FCCL: 1) It is difficult to balance toughness and adhesion: The rigid aromatic heterocyclic structure introduced to improve adhesion will lead to a decrease in film flexibility, making it prone to cracking during bending, and the number of bending cycles is generally less than 3000. 2) Imbalance between dimensional stability and flexural strength: Although using rigid diamine alone to prepare the support layer can reduce the coefficient of linear expansion (CTE), the film becomes severely brittle; while fully flexible diamine will lead to excessively high CTE, making the copper clad laminate prone to delamination and cracking. 3) Defects of inorganic particle modification: In the existing technology, the inorganic reinforcing particles are prone to agglomeration, and rigid particles will reduce the toughness of the film. At the same time, the particles have poor compatibility with organic resins, which can easily lead to insufficient interlayer bonding. 4) Poor processability: Some products, in pursuit of heat resistance, have a Tg exceeding 290℃, resulting in a narrow hot pressing processing window, low production efficiency, and low yield. 5) Performance degradation under high temperature and high humidity: The polyamic acid precursor has poor end group stability, and the amino group is easily oxidized and the anhydride group is easily hydrolyzed, which leads to a significant decrease in the peel strength of the film from the copper foil under high temperature and high humidity conditions.

[0005] Existing patent applications, such as CN103739842A, disclose thermoplastic polyimide films with adhesion of only 1.1-1.2 N / mm and poor bending resistance; patent application CN115746351A presents films with a low coefficient of thermal expansion (Tg) approaching 300℃, making processing difficult; while patent application CN119858367A improves adhesion, its elongation is low, and its toughness still fails to meet the requirements of high-end wearable devices. Therefore, developing a polyimide composite film with synergistically optimized toughness and adhesion and balanced overall performance is key to solving current technical challenges. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a high-toughness polyimide composite film that can be used in flexible copper-clad laminates and its preparation method, thereby solving the problems in the prior art.

[0007] The objective of this invention can be achieved through the following technical solutions: A polyimide composite film includes a support layer, an adhesive layer disposed on at least one side of the support layer, and a toughening interface layer embedded between the support layer and the adhesive layer; The support layer is formed by polycondensation of a diamine monomer and an aromatic dianhydride, wherein the diamine monomer includes flexible aromatic diamines and rigid fused-ring aromatic diamines; The polymer molecular chain of the adhesive layer contains end groups, and the end groups include a benzotriazole ring structure that can form a stable complex with copper. The toughened interface layer is formed by reacting amino-terminated hyperbranched polyimide grafted with mica powder particles with polyamic acid resin used to form the support layer.

[0008] Furthermore, the molar ratio of flexible aromatic diamine to rigid fused-ring aromatic diamine is (8-42):(58-92).

[0009] Further, the flexible aromatic diamine is selected from one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 1,3-bis(3-aminophenoxy)benzene; the rigid fused-ring aromatic diamine is selected from one or more of 1,5-diaminonaphthalene, 2,6-diaminoanthraquinone, and 2,7-diaminofluorene; and the aromatic dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-diphenyl ethertetracarboxylic dianhydride. The adhesive layer is formed by polycondensation of a diamine monomer, a dianhydride monomer and a monoamine containing a benzotriazole structure, wherein the monoamine containing a benzotriazole structure is selected from one or more of 5-aminobenzotriazole, 2-aminobenzotriazole and 4-aminomethylbenzotriazole.

[0010] Furthermore, the terminal amino hyperbranched polyimide grafted mica powder particles are prepared by addition and condensation reactions of surface-amino-treated mica powder, acrylate monomers, and aliphatic diamines.

[0011] Furthermore, the mass ratio of the surface-aminated mica powder, acrylate monomers, and aliphatic diamine is 1:(1.1-3.6):(0.7-4.6).

[0012] Furthermore, the particle size of the terminal amino hyperbranched polyimide grafted mica powder particles is 0.15-9 μm, and the amount added is 0.06%-1.3% of the mass of the support layer.

[0013] The above-mentioned method for preparing polyimide composite films includes the following steps: S1, a flexible aromatic diamine, a rigid fused-ring aromatic diamine and an aromatic dianhydride are subjected to a polycondensation reaction to generate polyamic acid resin A; S2, surface-aminated mica powder undergoes an addition reaction with acrylate monomers, followed by a polycondensation reaction with an aliphatic diamine to prepare terminal amino hyperbranched polyimide-grafted mica powder particles; the particles are dispersed in a chemical casting composite reagent, and then mixed with the polyamic acid resin A to obtain a mixed dispersion. S3, a polycondensation reaction is carried out between a diamine monomer, a dianhydride monomer and a monoamine containing a benzotriazole structure to generate polyamic acid resin B; S4. Using the mixed dispersion as the support layer material and the polyamic acid resin B as the adhesive layer material, a film is formed to obtain the polyimide composite film.

[0014] Furthermore, the chemical casting composite reagent includes: a catalyst, a dehydrating agent, and an organic solvent; The catalyst is selected from one or more of imidazole and its derivatives, triethylamine, and N-methylimidazolium; the dehydrating agent is selected from one or more of acetic anhydride, propionic anhydride, and benzoic anhydride.

[0015] Furthermore, the molar ratio of the sum of the molar amounts of the flexible aromatic diamine and the rigid fused-ring aromatic diamine to the molar ratio of the aromatic dianhydride is 100:(100.08-100.55).

[0016] The molar ratio of the diamine monomer, the dianhydride monomer, and the monoamine containing the benzotriazole structure is (98.2-99.7):100:(0.3-3.8).

[0017] A flexible copper-clad laminate includes a copper foil layer and a polyimide layer, wherein the polyimide layer is the aforementioned polyimide composite film, and the adhesive layer of the polyimide composite film is directly disposed on the surface of the copper foil layer.

[0018] The beneficial effects of this invention are: 1. In existing technologies, using only rigid diamines to prepare the support layer leads to film embrittlement, while using fully flexible diamines results in excessively high coefficient of linear expansion (CTE), causing delamination and delamination of the copper clad laminate. This invention, in a toughened thermosetting polyimide support layer, strictly controls the molar ratio of flexible aromatic diamines to rigid fused-ring aromatic diamines to be 8-42:58-92. The rigid fused-ring structure maintains extremely low thermal expansion characteristics, ensuring the film's CTE remains stable at ≤20ppm / ℃, achieving excellent thermal expansion matching with the copper foil. Simultaneously, the ether bonds or flexible segments in the flexible diamine provide stress buffering, effectively avoiding the embrittlement defects caused by high rigidity. This structural design allows the film to achieve an elongation of ≥45% while maintaining high dimensional stability, balancing the contradiction between rigidity and flexibility.

[0019] 2. Addressing the problems of traditional inorganic modified particles easily agglomerating, reducing film toughness, and having poor compatibility with resins leading to insufficient interlayer bonding, this invention introduces amino-terminated hyperbranched polyimide grafted with mica powder particles, which then react with thermosetting polyamic acid to form a toughening interface layer. On one hand, the hyperbranched polyimide chains on the mica powder surface form highly complex molecular chain entanglements and chemical bonds with the matrix resin, greatly improving compatibility, completely avoiding particle agglomeration, and achieving strong interlayer bonding without peeling. On the other hand, combining the lamellar slip characteristics of mica powder and the flexibility of the hyperbranched chains, the film can effectively dissipate stress when subjected to external forces, giving the composite film excellent flexural strength, allowing it to withstand more than 5000 cycles of repeated 180° bending, fully meeting the high-frequency bending requirements of high-end wearable devices.

[0020] 3. Addressing the shortcomings of existing 2L-FCCL precursors with unstable end groups (amino groups are easily oxidized, and anhydride groups are easily hydrolyzed), leading to a significant decrease in the peel strength of the film from copper foil under high temperature and humidity conditions, and the conventional introduction of rigid aromatic heterocycles for adhesion enhancement sacrificing film toughness, this invention employs a monoamine containing a benzotriazole structure as an end-capping agent in the synthesis of a functional thermoplastic polyimide adhesive layer. The heteroatoms abundant in the benzotriazole ring can form extremely stable coordination complexes with Cu²⁺ on the copper foil surface, successfully transforming traditional physical adsorption into a strong chemical bond. This mechanism results in a film peel strength of ≥1.6 N / mm, and after being placed in a high temperature and humidity environment of 85℃ / 85%RH for 1000 hours, the peel strength retention rate remains as high as ≥85%, completely eliminating delamination and delamination phenomena. Furthermore, since this group exists only at the molecular chain end and has a low proportion, it significantly improves the adhesive force without interfering with the flexibility and thermoplasticity of the polyimide backbone.

[0021] 4. Addressing the issue that some existing products, in pursuit of heat resistance, result in excessively high glass transition temperatures (Tg) (>290℃), leading to a narrow hot-pressing processing window and low production yield, this invention, through overall molecular weight control and the selection of specific monomers, successfully and precisely controls the Tg of the adhesive layer within the 220-285℃ range while maintaining the film's long-term resistance to 260℃ high temperatures and excellent mechanical properties (tensile strength ≥210MPa, modulus ≥7.0GPa). This significantly broadens the hot-pressing processing window for downstream lamination with copper foil. More importantly, the accompanying chemical casting coating or multilayer composite extrusion process is 100% seamlessly compatible with existing polyimide film and 2L-FCCL production lines, requiring no additional or modified equipment. Process parameters are easily controlled, and product yield can be consistently maintained at ≥95%, demonstrating strong industrialization potential. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] A high-toughness polyimide composite film for use in flexible copper-clad laminates includes a toughened thermosetting polyimide support layer, a functional thermoplastic polyimide adhesive layer, and a toughened interface layer between the two layers. The design and core function of each layer are as follows: 1) Toughened thermosetting polyimide support layer: It is prepared by polycondensation of flexible aromatic diamine and rigid fused-ring aromatic diamine with aromatic dianhydride. The molar ratio of flexible to rigid diamine is 8-42:58-92. While ensuring low CTE (dimensional stability), the ether bond / flexible segment of the flexible diamine improves the flexural strength and elongation of the support layer and avoids embrittlement. 2) Functional thermoplastic polyimide adhesive layer: Benzotriazole rings are introduced into the end groups. The N and N heteroatoms contained therein can form stable coordination complexes with Cu²⁺ on the surface of copper foil to achieve chemical bonding. Compared with physical adsorption bonding, it is stronger and can still maintain high peel strength under high temperature and high humidity. Moreover, the proportion of benzotriazole rings as end groups is low, which does not affect the thermoplasticity and flexibility of polyimide. 3) Toughened interface layer: It is formed by the reaction of terminal amino hyperbranched polyimide grafted mica powder particles with thermosetting polyamic acid. Mica powder is a layered inorganic particle with both rigidity and toughness. The hyperbranched polyimide chains grafted on its surface can form molecular chain entanglement and chemical bonding with thermosetting / thermoplastic polyimide, which not only increases the interlayer contact area and improves the interlayer bonding force, but also improves the overall folding resistance of the film through the flexibility of the hyperbranched chains and the interlayer slippage of mica powder, while avoiding the agglomeration of inorganic particles.

[0024] The present invention also provides a method for preparing the above-mentioned high-toughness polyimide composite film, comprising the following steps: S1, Synthetic thermosetting polyamic acid resin A Flexible aromatic diamines and rigid fused-ring aromatic diamines are dissolved in a molar ratio of 8-42:58-92 in a strongly polar aprotic organic solvent (one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone). Under nitrogen protection and at 0-40°C, aromatic dianhydrides are added in batches (total molar amount of flexible and rigid diamines: molar amount of dianhydrides = 100:100.08-100.55). The mixture is stirred and reacted for 4-7 hours to obtain thermosetting polyamic acid resin A with a viscosity of 1500-2500 P and a solid content of 16-25%.

[0025] Preferably, the flexible aromatic diamine is selected from one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 1,3-bis(3-aminophenoxy)benzene; the rigid fused-ring aromatic diamine is selected from one or more of 1,5-diaminonaphthalene, 2,6-diaminoanthraquinone, and 2,7-diaminofluorene; and the aromatic dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-diphenyl ethertetracarboxylic dianhydride.

[0026] S2. Prepare amino-terminated hyperbranched polyimide-grafted mica powder particles and formulate a mixed dispersion. Preparation of modified particles: Surface-aminated mica powder (particle size 0.15-9 μm), acrylate monomers (one or more of methyl acrylate and ethyl acrylate), and aliphatic diamines (one or more of ethylenediamine and propylenediamine) are added to methanol / ethanol solvent at a mass ratio of 1:(1.1-3.6):(0.7-4.6). An addition reaction is first carried out at 45-60℃ for 3-5 h, followed by vacuum filtration to remove unreacted small molecules. Then, aliphatic diamines are added, and a polycondensation reaction is carried out at 50-65℃ for 4-6 h. The mixture is then vacuum filtered again and dried to obtain terminally amino hyperbranched polyimide-grafted mica powder particles. Preparation of mixed dispersion: Add the above particles to the chemical casting composite reagent at 0.06%-1.3% of the mass of toughened thermosetting polyimide (mixed dispersion), and ultrasonically disperse for 30-60 min; then mix with polyamic acid resin A from step S1 at low temperature (e.g., -10℃ to -3℃) and high speed of 1800-2800 rpm for 5-10 min to obtain mixed dispersion.

[0027] Preferably, the chemical casting composite reagent is composed of a catalyst, a dehydrating agent, and an organic solvent in a mass ratio of (1.2-5.8):(16-38):(60-80), which can reduce the resin viscosity, promote uniform particle dispersion, and simultaneously rapidly gel and lock the particle distribution to avoid sedimentation and agglomeration. The catalyst is selected from one or more of imidazole and its derivatives, triethylamine, and N-methylimidazolium, and its amount is 1.2%-5.8% of the mass of the thermosetting polyamic acid resin A. The dehydrating agent is selected from one or more of acetic anhydride, propionic anhydride, and benzoic anhydride, and its amount is 16%-38% of the mass of the thermosetting polyamic acid resin A.

[0028] S3, Synthetic functional thermoplastic polyamic acid resin B Diamine monomer and dianhydride monomer are dissolved in a strongly polar aprotic organic solvent at a molar ratio of (98.2-99.7):100, and prepolymerized at 20-50℃ for 2-3 hours under nitrogen protection. Then, a monoamine containing a benzotriazole structure (dianhydride monomer:monoamine molar ratio = 100:0.3-3.8) is added as a capping agent, and the reaction is continued for 3-5 hours to obtain functional thermoplastic polyamic acid resin B with a viscosity of 450-650P and a solid content of 7-11%.

[0029] Preferably, the monoamine containing the benzotriazole structure is 5-aminobenzotriazole or 2-aminobenzotriazole, which, as a capping agent, can control the molecular chain length, improve the uniformity of molecular weight distribution, and at the same time introduce benzotriazole end groups to achieve complexation and adhesion with copper.

[0030] S4, Film Forming Process Both chemical casting coating and multilayer composite extrusion processes are compatible with existing polyimide film production lines, requiring no major equipment modifications. Chemical casting coating process: The mixed dispersion from step S2 is used to prepare a toughened thermosetting polyimide support layer with a thickness of 18-22 μm using a casting machine; polyamic acid resin B from step S3 is coated on one or both sides of the support layer, and then placed in a vacuum oven for thermal imidization reaction by heating at a program of 150℃→250℃→350℃→460℃ (heating rate 5-10℃ / min) to obtain a composite film with a total thickness of 20-25 μm and an adhesive layer thickness of 2-3 μm; Multilayer composite extrusion process: The mixed dispersion from step S2 and the polyamic acid resin B from step S3 are respectively fed to a multilayer composite die head (the middle layer is the support layer and the two sides are the adhesive layers). After extrusion, the film is cast, biaxially stretched (stretch ratio 1.2-1.5:1), and cured at a high temperature of 300-450℃ to obtain a composite film.

[0031] The technical solution of the present invention will be described below through the following embodiments, wherein all relevant raw materials in the embodiments and comparative examples are sourced as follows: Aminated mica powder: Zhejiang Fenghong New Material Co., Ltd., FHM-8000 series; 18um rolled copper foil: Tongling Nonferrous Metals Jinwei Copper Co., Ltd.

[0032] Example 1 A method for preparing a high-toughness polyimide composite film includes the following steps: 1. Synthetic Resin A: 32.5 kg of 4,4'-diaminodiphenyl ether (flexible) and 65.8 kg of 1,5-diaminonaphthalene (rigid) were dissolved in 800 kg of N,N-dimethylformamide. Under nitrogen protection, 52.6 kg of pyromellitic dianhydride and 40.3 kg of 3,3',4,4'-biphenyltetracarboxylic dianhydride were added in batches. The mixture was stirred at 25°C for 5 h to obtain resin A with a viscosity of 1850 P and a solid content of 19.28%. 2. Preparation of modified particles and formulation of dispersion: 1 kg of aminated mica powder with a particle size of 0.5 μm, 2.3 kg of methyl acrylate, and 3.5 kg of ethylenediamine were added to 10 kg of methanol and reacted at 50 °C for 4 h. After filtration, the reaction was continued for 5 h, and the particles were dried to obtain modified particles. 1.7 kg of modified particles, 20 kg of N-methylimidazole, and 24 kg of acetic anhydride were added to 80 kg of N,N-dimethylformamide and ultrasonically dispersed for 40 min. The mixture was then mixed with resin A at -9 °C and 1900 rpm for 5 min to obtain a dispersion. 3. Synthetic Resin B: 12.6 kg of 4,4'-diaminodiphenyl ether and 30.5 kg of 1,3-bis(4-aminophenoxy)benzene were dissolved in 420 kg of N,N-dimethylacetamide. After prepolymerization for 2.5 h, 0.5 kg of 5-aminobenzotriazole was added, and the mixture was reacted at 40 °C for 4 h to obtain resin B with a viscosity of 560 P and a solid content of 9.40%. 4. Film formation: The mixed dispersion from step S2 is used to prepare a 20 μm thick toughened thermosetting polyimide support layer using a casting machine. Then, the polyamic acid resin B from step S3 is coated on both sides of the support layer. The layer is placed in a vacuum oven and heated according to the program of 150℃ (25 min) → 250℃ (25 min) → 350℃ (25 min) → 460℃ (25 min) (heating rate 5℃ / min) to obtain a composite film with a total thickness of 26 μm and a 3 μm thickness of the adhesive layer on each side.

[0033] Examples 2-7 The difference between Examples 2-7 and Example 1 lies only in adjusting parameters such as the type of flexible / rigid diamine, the amount / size of modified particles, the type of end-capping agent, and the film-forming process. The specific core parameters are shown in Table 1, and the remaining steps are the same as in Example 1.

[0034] Table 1 Core parameters of Examples 2-7 Comparative Examples 1-7 To verify the rationality of the structure and parameter design of the present invention, seven comparative examples were set up, all of which were compared with Example 1, with only a single variable changed. The specific variable is shown in Table 2, and the remaining steps are the same as in Example 1.

[0035] Table 2 Comparative Examples 1-7 Core Variables Performance testing The polyimide composite films prepared in Examples 1-7 and Comparative Examples 1-7 were rolled with 18µm calendered copper foil to form two-layer adhesive-free double-sided copper-clad laminates, and their performance was tested according to the following standards: Mechanical properties: Tensile strength, modulus, and elongation are tested according to ASTM D882. Coefficient of linear expansion (CTE): Tested using the TMA method (50-200℃); Glass transition temperature (Tg): Tested using the DMA method (heating rate 5℃ / min); Peel strength: tested by IPC-TM-650, and the retention rate after 1000 hours of high temperature and high humidity at 85℃ / 85%RH was also tested; Bending resistance: GB / T13022 test for the number of repeated 180° bends (bending radius 1mm).

[0036] The test results are shown in Table 3.

[0037] Table 3 Performance test results of the examples and comparative examples Note: Comparative Example 6 showed film embrittlement and fracture during peel strength testing, resulting in no data; high temperature and high humidity retention rate was not meaningful for testing.

[0038] Results Analysis As shown in Table 3, the polyimide composite films prepared in Examples 1-7 of this invention exhibit excellent overall performance and all meet the high-end application requirements of 2L-FCCL. In contrast, the comparative examples show a significant decrease in performance due to parameter deviations or structural deficiencies. Comparative Example 1: Without modified particles and benzotriazole end-capping agent, the interlayer bonding strength and adhesion are greatly reduced, the peel strength is only 0.8 N / mm, and the bending resistance is only 1100 times. Comparative Example 2: The modified particles had an excessively large particle size (10 μm), resulting in poor dispersibility, decreased mechanical properties and dimensional stability of the film, a tensile strength of only 163 MPa, and a CTE of 26 ppm / ℃. Comparative Example 3: Excessive addition of modified particles resulted in severe film embrittlement, with an elongation of only 25% and a bending resistance of only 550 cycles. Comparative Example 4: The support layer was entirely made of flexible diamine, with a CTE as high as 29ppm / ℃, poor thermal expansion matching with copper foil, and a peel strength of only 0.5N / mm; Comparative Example 5: The lack of modified particles resulted in insufficient interlayer bonding, leading to a significant decrease in peel strength and flexural strength. Comparative Example 6: Excessive use of acrylate and aliphatic diamine resulted in excessive hyperbranching of particles, causing the film to become brittle and unusable. Comparative Example 7: Without benzotriazole end-capping agent, relying solely on physical adhesion, the peel strength is only 1.0 N / mm, and the high temperature and high humidity retention rate is only 75%.

[0039] The above results fully demonstrate that the present invention, through the synergistic design of a support layer composed of flexible diamine, an adhesive layer with benzotriazole end groups, and a toughening interface layer of amino-terminated hyperbranched polyimide grafted with mica powder particles, as well as the precise control of various preparation parameters, has successfully achieved the synergistic performance of polyimide composite films with high toughness, high adhesion, high dimensional stability, high heat resistance, and low Tg, thus solving the core pain points of the prior art.

[0040] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0041] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A polyimide composite film, characterized in that, It includes a support layer, an adhesive layer disposed on at least one side of the support layer, and a toughening interface layer embedded between the support layer and the adhesive layer; The support layer is formed by polycondensation of a diamine monomer and an aromatic dianhydride, wherein the diamine monomer includes flexible aromatic diamines and rigid fused-ring aromatic diamines; The polymer molecular chain of the adhesive layer contains end groups, and the end groups include a benzotriazole ring structure that can form a stable complex with copper. The toughened interface layer is formed by reacting amino-terminated hyperbranched polyimide grafted with mica powder particles with polyamic acid resin used to form the support layer.

2. The polyimide composite film according to claim 1, characterized in that, The molar ratio of flexible aromatic diamine to rigid fused-ring aromatic diamine is (8-42):(58-92).

3. The polyimide composite film according to claim 1, characterized in that, The flexible aromatic diamine is selected from one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, and 1,3-bis(3-aminophenoxy)benzene; the rigid fused-ring aromatic diamine is selected from one or more of 1,5-diaminonaphthalene, 2,6-diaminoanthraquinone, and 2,7-diaminofluorene; the aromatic dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 3,3',4,4'-diphenyl ethertetracarboxylic dianhydride. The adhesive layer is formed by polycondensation of a diamine monomer, a dianhydride monomer and a monoamine containing a benzotriazole structure, wherein the monoamine containing a benzotriazole structure is selected from one or more of 5-aminobenzotriazole, 2-aminobenzotriazole and 4-aminomethylbenzotriazole.

4. The polyimide composite film according to claim 1, characterized in that, The terminal amino hyperbranched polyimide-grafted mica powder particles are prepared by addition and condensation reactions of surface-amino-treated mica powder, acrylate monomers, and aliphatic diamines.

5. A polyimide composite film according to claim 4, characterized in that, The mass ratio of the surface-aminated mica powder, acrylate monomers and aliphatic diamine is 1:(1.1-3.6):(0.7-4.6).

6. The polyimide composite film according to claim 4, characterized in that, The particle size of the terminal amino hyperbranched polyimide grafted mica powder particles is 0.15-9 μm, and the amount added is 0.06%-1.3% of the mass of the support layer.

7. The method for preparing the polyimide composite film according to any one of claims 1-6, characterized in that, Includes the following steps: S1, a flexible aromatic diamine, a rigid fused-ring aromatic diamine and an aromatic dianhydride are subjected to a polycondensation reaction to generate polyamic acid resin A; S2, surface-aminated mica powder undergoes an addition reaction with acrylate monomers, followed by a polycondensation reaction with an aliphatic diamine to prepare terminal amino hyperbranched polyimide-grafted mica powder particles; the particles are dispersed in a chemical casting composite reagent, and then mixed with the polyamic acid resin A to obtain a mixed dispersion. S3, a polycondensation reaction is carried out between a diamine monomer, a dianhydride monomer and a monoamine containing a benzotriazole structure to generate polyamic acid resin B; S4. Using the mixed dispersion as the support layer material and the polyamic acid resin B as the adhesive layer material, a film is formed to obtain the polyimide composite film.

8. The method for preparing the polyimide composite film according to claim 7, characterized in that, The chemical casting composite reagent includes: a catalyst, a dehydrating agent, and an organic solvent; The catalyst is selected from one or more of imidazole and its derivatives, triethylamine, and N-methylimidazolium; the dehydrating agent is selected from one or more of acetic anhydride, propionic anhydride, and benzoic anhydride.

9. The method for preparing the polyimide composite film according to claim 7, characterized in that, The molar ratio of the sum of the molar amounts of the flexible aromatic diamine and the rigid fused-ring aromatic diamine to the aromatic dianhydride is 100:(100.08-100.55). The molar ratio of the diamine monomer, the dianhydride monomer, and the monoamine containing the benzotriazole structure is (98.2-99.7):100:(0.3-3.8).

10. A flexible copper-clad laminate, comprising a copper foil layer and a polyimide layer, characterized in that, The polyimide layer is the polyimide composite film according to any one of claims 1-6, and the adhesive layer of the polyimide composite film is directly disposed on the surface of the copper foil layer.

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