High-adhesion polyimide composite film applicable to flexible copper clad laminate, and preparation method therefor

Abstract

Disclosed are a high-adhesion polyimide composite film applicable to a flexible copper clad laminate, and a preparation method therefor. The polyimide composite film is composed of a thermosetting polyimide support layer and a thermoplastic polyimide adhesive layer provided on at least one surface of the thermosetting polyimide support layer. An interface layer formed by reacting amino-terminated hyperbranched polyamide-grafted silica particles with thermosetting polyamic acid is embedded between the thermosetting polyimide support layer and the thermoplastic polyimide adhesive layer, and the terminal group of the thermoplastic polyimide contains an imidazole ring capable of forming a complex with copper. In the present invention, by embedding the amino-terminated hyperbranched polyamide-grafted silica particles into the interface between the thermosetting layer and the thermoplastic layer, the contact area between the support layer and the adhesive layer is increased; moreover, by means of the complexation effect of the imidazole ring and copper, a polyimide composite film having high adhesion, high dimensional stability, high heat resistance and a low glass transition temperature is prepared.

Description

A high-adhesion polyimide composite film for use in flexible copper-clad laminates and its preparation method. Technical Field

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

[0002] Flexible printed circuit boards (FPCs) are widely used in electronics, home appliances, medical, automotive, aerospace, and military fields due to their lightweight, thinness, and flexibility. Flexible copper clad laminates (FCCLs) are the key substrate of FPCs. Traditional three-layer FCCLs consist of copper foil, thermosetting polyimide film, and epoxy or silicone adhesive, while two-layer FCCLs use a thermoplastic polyimide layer instead of epoxy or silicone adhesive, resulting in thinner, lighter, and more heat-resistant copper clad laminates, gradually becoming the industry mainstream.

[0003] Chinese patent application CN103739842A proposes a thermoplastic polyimide film for a two-layer FCCL. In order to ensure a certain dimensional stability, diamines containing benzoxazole, benzimidazole aromatic heterocycles, etc. are introduced, which reduces the overall thermoplasticity of the molecular chain, resulting in an adhesion of only 1.1-1.2 N / mm, which poses a hidden danger to subsequent applications.

[0004] Chinese patent application CN115746351A proposes a method for preparing thermoplastic polyimide films with low coefficient of thermal expansion. By introducing double bonds into the polyimide molecular chain and achieving photo-crosslinking under the action of crosslinking agents and photoinitiators, the coefficient of thermal expansion of the film is reduced. However, the crosslinking structure restricts the movement of the molecular chain, making its glass transition temperature close to 300℃, which is not conducive to hot pressing and is difficult to commercialize.

[0005] Chinese patent application CN1957051A discloses an adhesive film and its preparation method. The method uses co-extrusion-cast coating to laminate a thermoplastic polyimide adhesive layer onto one or both sides of a thermosetting polyimide core layer, thereby obtaining a heat-adhesive composite film. However, both thermosetting and thermoplastic polyamic acid precursors use diamine or dianhydride polycondensation. The amino end group can lead to oxidation upon heating, reducing the film's heat resistance, especially its adhesion after heating. On the other hand, the anhydride end group is prone to ring-opening hydrolysis, resulting in uneven molecular weight distribution of polyimide, which in turn affects the uniformity of performance.

[0006] As can be seen from the above, in order to meet the increasingly demanding application requirements of two-layer FCCL for thin film substrates, such as high adhesion, high dimensional stability, high heat resistance and low glass transition temperature, existing technologies need to be improved. Summary of the Invention

[0007] To overcome the problems in the prior art, the present invention provides a highly adhesive polyimide composite film that can be used in flexible copper clad laminates and a method for preparing the same, thereby obtaining a polyimide composite film with high adhesion, high dimensional stability, high heat resistance and low glass transition temperature.

[0008] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0009] This invention provides a highly adhesive polyimide composite film for flexible copper-clad laminates. The polyimide composite film includes a thermosetting polyimide support layer and a thermoplastic polyimide adhesive layer disposed on at least one side of the thermosetting polyimide support layer. An interface layer formed by the reaction of terminal amino hyperbranched polyamide grafted silica particles with thermosetting polyamic acid is embedded between the thermosetting polyimide support layer and the thermoplastic polyimide adhesive layer.

[0010] In this invention, by embedding amino-terminated hyperbranched polyamide grafted with silica particles into the interface between the thermosetting layer and the thermoplastic layer, the contact area between the support layer and the adhesive layer is increased, thereby improving the peel strength and adhesion of the composite film.

[0011] As an optional implementation, in the polyimide composite film provided by the present invention, the interface layer is formed by: dispersing the terminal amino hyperbranched polyamide grafted silica particles in a chemical casting agent, mixing them with a thermosetting polyamic acid resin, and then obtaining the film through a polymerization reaction.

[0012] As an optional implementation, in the polyimide composite film provided by the present invention, the thermosetting polyimide support layer is prepared by reacting a flexible aromatic diamine and a rigid aromatic diamine with an aromatic dianhydride, wherein the molar ratio of the flexible aromatic diamine to the rigid aromatic diamine is 5-35:65-95.

[0013] In this invention, the precursor polyamic acid resin is formed by the polycondensation reaction of flexible aromatic diamine, rigid aromatic diamine, and aromatic dianhydride. Using rigid aromatic diamine monomers can reduce the coefficient of linear expansion, and the close molecular packing can control the water absorption rate, reducing the risk of copper-clad laminate delamination and delamination caused by film moisture absorption. However, excessive rigid aromatic diamine can lead to a further decrease in film flexibility, failing to meet application requirements. Therefore, this invention also simultaneously introduces flexible aromatic diamine monomers to improve elongation and enhance application performance.

[0014] As an optional implementation, in the polyimide composite film provided by the present invention, the end groups of the thermoplastic polyimide adhesive layer contain imidazole rings that can form complexes with copper.

[0015] Based on the same technical concept, the present invention also provides a method for preparing the above-mentioned high-adhesion polyimide composite film for flexible copper-clad laminates, comprising the following steps:

[0016] S1. A polyamic acid resin A is generated by polycondensation of a flexible aromatic diamine, a rigid aromatic diamine, and an aromatic dianhydride.

[0017] S2. The surface-aminated silica undergoes an addition reaction with acrylate or its homologues, and then reacts with aliphatic diamine or its homologues to prepare terminal amino hyperbranched polyamide-grafted silica particles. Finally, these particles are dispersed in a chemical casting agent and rapidly mixed with the polyamic acid resin A prepared in step S1 to obtain a mixed solution. The mass ratio of the surface-aminated silica, acrylate or its homologues, and aliphatic diamine or its homologues is 1:1-3:0.7-4.

[0018] S3. Polycondensation reaction of diamine, dianhydride and monoamine produces polyamic acid resin B.

[0019] S4. Using the mixed solution in step S2 as the thermosetting polyimide support layer and the polyamic acid resin B prepared in step S3 as the thermoplastic polyimide adhesive layer, a polyimide composite film is prepared by a film-forming process.

[0020] In this invention, the branching degree of the terminal-amino hyperbranched polyamide-grafted silica particles is controlled by adjusting the amounts of acrylate or its homologues and aliphatic diamine or its homologues. Too low a branching degree results in a small number of amino groups, leading to minimal improvement in resin compatibility; too high a branching degree causes polymer crosslinking, also affecting film performance. The terminal-amino hyperbranched polyamide-grafted silica particles are dispersed in a chemical casting agent and mixed with thermosetting polyamic acid resin. The liquid chemical casting agent significantly reduces resin viscosity, facilitating uniform dispersion of the terminal-amino hyperbranched polyamide-grafted silica particles. The chemical casting agent promotes resin gelation in a short time, locking in the distribution of the terminal-amino hyperbranched polyamide-grafted silica particles in the film and preventing sedimentation and secondary agglomeration of the particles due to excessive storage or reaction time. The unique hyperbranched molecular structure, low-chain entanglement, and abundant amino groups on the silica surface enhance the compatibility between the inorganic silica particles and the organic system. During high-speed mixing and casting, it reacts with the terminal anhydride groups of thermosetting polyamic acid molecular chains to eliminate residual active groups and form a cross-linked network structure, improving the dimensional stability and heat resistance of the film. In the field of chemistry, homologues refer to organic compounds with similar structures and molecular compositions differing by one or more "CH2" atomic groups.

[0021] As an optional implementation, in the preparation method provided by the present invention, in step S2, the amount of the amino-terminated hyperbranched polyamide-grafted silica particles added is 0.05-1% of the mass of the thermosetting polyimide support layer, and the particle size of the amino-terminated hyperbranched polyamide-grafted silica particles is 0.1-10 μm.

[0022] Furthermore, the particle size of the terminal amino hyperbranched polyamide grafted silica particles is preferably 0.2-6 μm.

[0023] In this invention, the amount of amino-terminated hyperbranched polyamide-grafted silica particles added is calculated based on the total amount of powder added. By controlling the particle size and amount of amino-terminated hyperbranched polyamide-grafted silica particles, the amino-terminated hyperbranched polyamide-grafted silica particles can increase the contact area between the support layer and the adhesive layer by embedding them into the interface between the thermosetting layer and the thermoplastic layer, thereby improving the peel strength of the composite film without affecting other properties.

[0024] As an optional implementation, in the preparation method provided by the present invention, in step S2, the chemical casting agent consists of a catalyst, a dehydrating agent, and an organic solvent; the catalyst is selected from one or more of pyridine and its derivatives, quinoline, isoquinoline, and triethylamine, and the amount of the catalyst is 1-5% of the mass of polyamic acid resin A; the dehydrating agent is selected from one or more of acetic anhydride, propionic anhydride, and benzoic anhydride, and the amount of the dehydrating agent is 15-35% of the mass of polyamic acid resin A. In the field of chemistry, a derivative refers to a more complex product derived from the substitution of atoms or groups of atoms in a compound molecule by other atoms or groups of atoms, or it can be a new substance generated by the transformation of the original substance through a chemical reaction.

[0025] As an optional implementation, in the preparation method provided by the present invention, the film-forming process in step S4 includes the following steps: using the mixed solution in step S2 as a support layer and the polyamic acid resin B prepared in step S3 as a bonding layer, the polyimide composite film is obtained after being co-extruded through two or three layers through a die and then subjected to high temperature treatment.

[0026] As an optional implementation, in the preparation method provided by the present invention, the film-forming process in step S4 further includes the following steps: preparing a thermosetting polyimide support layer by chemical casting, then coating polyamic acid resin B on one or both sides, and preparing a polyimide composite film by high-temperature imidization.

[0027] As an optional implementation, in the preparation method provided by the present invention, in step S1, the molar ratio of the sum of the flexible aromatic diamine and the rigid aromatic diamine to the molar ratio of the aromatic dianhydride is 100:100.05-100.5.

[0028] As an optional implementation, in the preparation method provided by the present invention, the monoamine is a monoamine containing an imidazole structure.

[0029] As an optional implementation, in the preparation method provided by the present invention, the monoamine containing an imidazole structure is selected from one or more of 2-aminoimidazole, 4-aminoimidazole, 5-amino-4-imidazolium carboxamide, and 2-aminobenzimidazole; the molar ratio of the diamine, dianhydride and the monoamine containing an imidazole structure is 98-99.5:100:0.5-4.

[0030] As an optional implementation, in the preparation method provided by the present invention, in step S1, the molar ratio of the sum of the flexible aromatic diamine and the rigid aromatic diamine to the molar ratio of the aromatic dianhydride is 100:100.05-100.5.

[0031] As an optional implementation, in the preparation method provided by the present invention, in step S1, the flexible aromatic diamine is selected from one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)diphenyl sulfone, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

[0032] As an optional implementation, in the preparation method provided by the present invention, in step S1, the rigid aromatic diamine is selected from one or more of 4,4'-diaminobiphenyl, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, p-phenylenediamine, m-phenylenediamine, p-phenylenediamine, and 4,4'-diaminobenzophenone.

[0033] As an optional implementation, in the preparation method provided by the present invention, in step S1, the aromatic dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride.

[0034] As an optional implementation, in the preparation method provided by the present invention, in step S3, the diamine is selected from one or more of 4,4'-diaminodiphenyl ether (4,4'-ODA), 3,4'-diaminodiphenyl ether (3,4'-ODA), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,3-bis(3-aminophenoxy)benzene (TPE-M), 1,4-bis(4-aminophenoxy)benzene (TPE-Q), 4,4'-bis(4-aminophenoxy)diphenyl sulfone (BAPS), and 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP).

[0035] As an optional implementation, in the preparation method provided by the present invention, in step S3, the dianhydride is selected from one or more of pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride (α-ODPA).

[0036] Based on the same technical concept, the present invention also provides a two-layer flexible copper-clad laminate, comprising a copper foil layer and a polyimide layer, wherein the polyimide layer is the above-mentioned high-adhesion polyimide composite film.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] (1) In this invention, a thermoplastic polyimide adhesive layer is provided on at least one side of the thermosetting polyimide support layer, and an interface layer formed by the reaction of terminal amino hyperbranched polyamide grafted silica particles is embedded between the thermosetting polyimide support layer and the thermoplastic polyimide adhesive layer, which can increase the contact area between the support layer and the adhesive layer, improve the peel force of the composite film, and increase the adhesion.

[0039] (2) In this invention, the terminal amino hyperbranched polyamide grafted silica particles are mixed with chemical casting reagents and thermosetting polyamic acid resin solution, which can make the inorganic particles uniformly distributed in the film and avoid the problems of sedimentation and agglomeration. At the same time, the terminal amino hyperbranched polyamide grafted silica particles have a large number of amino groups on their surface, which can enhance the compatibility of silica particles with organic systems. During high-speed mixing and casting, they react with the terminal anhydride groups of thermosetting polyamic acid molecular chains to eliminate residual active groups and form a cross-linked network structure, which can improve the dimensional stability of the film.

[0040] (3) The monoamine containing imidazole structure in this invention is used as a capping agent for thermoplastic polyamic acid. On the one hand, it can control the endpoint of the polycondensation reaction, avoid excessive growth of molecular chains in the later stage, and improve the uniformity of molecular weight distribution. On the other hand, it can improve the adhesion of the composite film by forming a complex with copper through the imidazole ring. Moreover, the imidazole ring is introduced as an end group and accounts for a small proportion in the molecular chain, so it will not reduce the overall thermoplasticity.

[0041] (4) By further optimizing the film, the present invention can significantly improve the adhesion, dimensional stability and heat resistance of the material, while maintaining a low glass transition temperature. Attached Figure Description

[0042] Figure 1 shows the microscopic examination results of the polyimide composite film prepared in Example 7;

[0043] Figure 2 is a schematic diagram of the reaction of amino-terminated hyperbranched polyamide grafted silica particles prepared in the example.

[0044] Figure 3 shows a planar view of the polyimide composite film prepared in Comparative Example 1. The left side shows the observation results under a 500x microscope, and the right side shows the observation results under a 1500x microscope.

[0045] Figure 4 is a planar view of the polyimide composite film prepared in Example 3. The left side shows the observation results under a 500x microscope, and the right side shows the observation results under a 1500x microscope.

[0046] Figure 5 shows a planar view of the polyimide composite film prepared in Comparative Example 3. The left side shows the observation results under a 500x microscope, and the right side shows the observation results under a 1500x microscope. Detailed Implementation

[0047] To facilitate understanding of the present invention, a more comprehensive and detailed description of the invention will be provided below in conjunction with the accompanying drawings and preferred embodiments. However, the scope of protection of the present invention is not limited to the specific embodiments described below. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0048] Example 1

[0049] A method for preparing a highly adhesive polyimide composite film includes the following steps:

[0050] 1. Aggregation

[0051] 31.7 kg of ODA and 36.4 kg of p-PDA were dissolved in 800 kg of dimethylformamide. 54.4 kg of PMDA, 31.9 kg of BTDA and 43.7 kg of BPDA were added in batches and reacted for 5 hours to obtain a thermosetting polyamic acid resin with a viscosity of 1850 P.

[0052] 11.7 kg of ODA and 31.2 kg of TPE-R were dissolved in 420 kg of dimethylformamide. 36.4 kg of PMDA was added in batches, and finally 0.48 kg of 2-aminoimidazole was added and reacted for 4 hours to obtain a thermoplastic polyamic acid resin with a viscosity of 550 P.

[0053] 1 kg of amino-modified silica with a particle size of 0.4 μm and 2.2 kg of methyl acrylate were added to 10 kg of methanol. After reacting at 50 °C, the mixture was vacuum filtered. Then, 3.35 kg of ethylenediamine was added, and the mixture was reacted in methanol and vacuum filtered again to obtain amino-terminated hyperbranched polyamide-grafted silica particles. The reaction diagram is shown in Figure 2.

[0054] 2. Film Forming

[0055] 1.6 kg of amino-terminated hyperbranched polyamide grafted silica particles, 19 kg of pyridine, and 22 kg of acetic anhydride were added to a high-speed mixer and mixed evenly with thermosetting polyamic acid resin at 1850 rpm. The mixture was then conveyed through a pipeline to a die head for extrusion molding. After further processes such as casting, longitudinal and transverse stretching, and high-temperature heating, a thermosetting polyimide film with a thickness of 19 μm was obtained.

[0056] 3. Coating

[0057] Thermoplastic polyamic acid resin was coated on both sides of a thermosetting polyimide film, and the temperature was programmed to rise within the range of 150℃-450℃ to obtain a composite film with a total thickness of 25μm and adhesive layers on both sides with a thickness of 3μm.

[0058] Example 2

[0059] A method for preparing a highly adhesive polyimide composite film includes the following steps:

[0060] The polymerization process is the same as in Example 1.

[0061] 1.58 kg of 0.5 μm terminal amino hyperbranched polyamide grafted silica particles, 18 kg of pyridine, and 21 kg of acetic anhydride were added to a high-speed mixer and mixed uniformly with thermosetting polyamic acid resin at 1850 rpm to obtain thermosetting polyamic acid precursor resin. The precursor resin was then simultaneously conveyed to a three-layer co-extrusion die with thermoplastic polyamic acid resin for extrusion molding. After casting, longitudinal and transverse stretching, and high-temperature heating, a composite film with a total thickness of 25 μm was obtained, with the adhesive layers on both sides having a thickness of 3 μm.

[0062] Example 3

[0063] A method for preparing a highly adhesive polyimide composite film includes the following steps:

[0064] 1. Aggregation

[0065] 12.7 kg of ODA, 12.4 kg of TPE-M and 67.5 kg of 4,4'-diamino-2,2'-dimethylbiphenyl were dissolved in 800 kg of dimethylformamide. 65.2 kg of PMDA and 41 kg of BTDA were added in batches and reacted for 6 hours to obtain a thermosetting polyamic acid resin with a viscosity of 2370 P.

[0066] 14.4 kg of ODA and 25.9 kg of BAPP were dissolved in 420 kg of dimethylformamide. 9.4 kg of PMDA and 29.6 kg of α-BPDA were added in batches. Finally, 0.57 kg of 2-aminobenzimidazole was added and the reaction was carried out for 4.5 hours to obtain a thermoplastic polyamic acid resin with a viscosity of 510 P.

[0067] 1 kg of amino-modified silica with a particle size of 3 μm and 2.2 kg of methyl acrylate were added to 10 kg of methanol. After reacting at 50 °C, the mixture was vacuum filtered. Then, 3.35 kg of ethylenediamine was added, and the mixture was reacted in methanol and vacuum filtered again to obtain amino-terminated hyperbranched polyamide-grafted silica particles. The reaction diagram is shown in Figure 2.

[0068] 2. Film Forming

[0069] 1 kg of terminal amino hyperbranched polyamide grafted silica particles, 19 kg of pyridine, and 22 kg of acetic anhydride were added to a high-speed mixer and mixed evenly with the resin at a speed of 2250 rpm. The mixture was then conveyed through a pipeline to a die head for extrusion molding. After further processes such as casting, longitudinal and transverse stretching, and high-temperature heating, a thermosetting polyimide film with a thickness of 19 μm was obtained.

[0070] 3. Coating

[0071] Thermoplastic polyamic acid resin was coated on both sides of a thermosetting polyimide film, and the temperature was programmed to rise within the range of 150℃-450℃ to obtain a composite film with a total thickness of 25μm and adhesive layers on both sides with a thickness of 3μm.

[0072] Example 4

[0073] A method for preparing a highly adhesive polyimide composite film includes the following steps:

[0074] The polymerization process is the same as in Example 2.

[0075] 1 kg of 3.2 μm terminal amino hyperbranched polyamide grafted silica particles, 19 kg of pyridine, and 22 kg of acetic anhydride were added to a high-speed mixer and mixed uniformly with thermosetting polyamic acid resin at 2350 rpm to obtain thermosetting polyamic acid precursor resin. The precursor resin was simultaneously conveyed to a three-layer co-extrusion die with thermoplastic polyamic acid resin and extruded. After casting, longitudinal and transverse stretching, and high-temperature heating, a composite film with a total thickness of 25 μm was obtained, with the adhesive layers on both sides having a thickness of 3 μm.

[0076] Example 5

[0077] A method for preparing a highly adhesive polyimide composite film includes the following steps:

[0078] 1. Aggregation

[0079] 18.2 kg of BAPP, 8.9 kg of 3,4'-ODA, and 75.3 kg of 4,4'-diamino-3,3'-dimethylbiphenyl were dissolved in 800 kg of dimethylformamide. 97.2 kg of PMDA was added in batches and reacted for 4 hours to obtain a thermosetting polyamic acid resin with a viscosity of 1580 P.

[0080] 35.3 kg of BAPS and 10.7 kg of BAPP were dissolved in 420 kg of dimethylformamide. 16.9 kg of ODPA and 16.0 kg of BPDA were added in batches. Finally, 0.23 kg of 3-aminoimidazole was added and the mixture was reacted for 5.5 hours to obtain a thermoplastic polyamic acid resin with a viscosity of 450 P.

[0081] 1 kg of amino-modified silica with a particle size of 2.8 μm and 2.2 kg of methyl acrylate were added to 10 kg of methanol. After reacting at 50 °C, the mixture was vacuum filtered. Then, 3.35 kg of ethylenediamine was added, and the mixture was reacted in methanol and vacuum filtered again to obtain amino-terminated hyperbranched polyamide-grafted silica particles. The reaction diagram is shown in Figure 2.

[0082] 2. Film Forming

[0083] 0.4 kg of terminal amino hyperbranched polyamide grafted silica particles, 19 kg of pyridine, and 22 kg of acetic anhydride were added to a high-speed mixer and mixed uniformly with thermosetting polyamic acid resin at 2550 rpm to obtain thermosetting polyamic acid precursor resin. The precursor resin was simultaneously conveyed to a three-layer co-extrusion die along with thermoplastic polyamic acid resin and extruded. The resulting composite film, with a total thickness of 25 μm, was obtained through processes such as casting, longitudinal and transverse stretching, and high-temperature heating. The thickness of the adhesive layers on both sides was 4 μm.

[0084] Example 6

[0085] A method for preparing a highly adhesive polyimide composite film includes the following steps:

[0086] 1. Aggregation

[0087] 10.2 kg of BAPS, 16.1 kg of BAPP and 69.9 kg of 4,4'-diaminobenzophenone were dissolved in 800 kg of dimethylformamide. 69.4 kg of BPDA and 34.2 kg of PMDA were added in batches and reacted for 6 hours to obtain a thermosetting polyamic acid resin with a viscosity of 2030 P.

[0088] 8.9 kg of BAPS and 33.7 kg of TPE-Q were dissolved in 420 kg of dimethylformamide. 15 kg of PMDA and 22.1 kg of BTDA were added in batches. Finally, 0.18 kg of 2-aminobenzimidazole was added and reacted for 5.5 hours to obtain a thermoplastic polyamic acid resin with a viscosity of 620 P.

[0089] 1 kg of amino-modified silica with a particle size of 1.5 μm and 2.2 kg of methyl acrylate were added to 10 kg of methanol. After reacting at 50 °C, the mixture was vacuum filtered. Then, 3.35 kg of ethylenediamine was added, and the mixture was reacted in methanol and vacuum filtered to obtain amino-terminated hyperbranched polyamide-grafted silica particles.

[0090] 2. Film Forming

[0091] 0.2 kg of amino-terminated hyperbranched polyamide grafted silica particles, 19 kg of pyridine, and 22 kg of acetic anhydride were added to a high-speed mixer and mixed uniformly with thermosetting polyamic acid resin at 2550 rpm to obtain thermosetting polyamic acid precursor resin. The precursor resin was simultaneously conveyed to a three-layer co-extrusion die with thermoplastic polyamic acid resin and extruded. The resulting composite film, with a total thickness of 20 μm, was obtained through processes such as casting, longitudinal and transverse stretching, and high-temperature heating. The thickness of the adhesive layers on both sides was 3 μm.

[0092] Example 7

[0093] A method for preparing a highly adhesive polyimide composite film includes the following steps:

[0094] 1. Aggregation

[0095] 9.3 kg of TPE-M and 72.8 kg of 4,4'-diaminodiphenylmethane were dissolved in 800 kg of dimethylacetamide, and 117.8 g of BPDA was added in batches and reacted for 7 hours to obtain a thermosetting polyamic acid resin with a viscosity of 1730 P.

[0096] 44.2 kg of TPE-M was dissolved in 420 kg of dimethylacetamide. 16.6 kg of PMDA, 14.2 kg of α-ODPA and 4.9 kg of BTDA were added in batches. Finally, 0.14 kg of 2-aminobenzimidazole was added and the reaction was carried out for 4.7 hours to obtain a thermoplastic polyamic acid resin with a viscosity of 520 P.

[0097] 1 kg of amino-modified silica with a particle size of 1 μm and 2.2 kg of methyl acrylate were added to 10 kg of methanol. After reacting at 50 °C, the mixture was vacuum filtered. Then, 3.35 kg of ethylenediamine was added, and the mixture was reacted in methanol and vacuum filtered again to obtain amino-terminated hyperbranched polyamide-grafted silica particles. The reaction diagram is shown in Figure 2.

[0098] 2. Film Forming

[0099] 0.14 kg of terminal amino hyperbranched polyamide grafted silica particles, 19 kg of pyridine, and 22 kg of acetic anhydride were added to a high-speed mixer and mixed uniformly with thermosetting polyamic acid resin at 2650 rpm to obtain thermosetting polyamic acid precursor resin. The precursor resin was simultaneously conveyed to a three-layer co-extrusion die with thermoplastic polyamic acid resin and extruded. After casting, longitudinal and transverse stretching, and high-temperature heating, a composite film with a total thickness of 25 μm was obtained, with the adhesive layers on both sides having a thickness of 3 μm.

[0100] Comparative Example 1

[0101] The difference from Example 1 is that 2-aminoimidazole is not added, nor are terminal amino hyperbranched polyamide grafted silica particles added; otherwise, it is the same as in Example 1.

[0102] Comparative Example 2

[0103] 1. Aggregation

[0104] 85.8 kg of ODA was dissolved in 800 kg of dimethylacetamide, and 47.1 kg of PMDA, 27.6 kg of BTDA and 37.8 kg of BPDA were added in batches and reacted for 6 hours to obtain a thermosetting polyamic acid resin with a viscosity of 2030 P.

[0105] 11.7 kg of ODA and 31.3 kg of TPE-R were dissolved in 420 kg of dimethylacetamide. 36.5 kg of PMDA was added in batches, and finally 0.48 kg of 2-aminoimidazole was added. The reaction was carried out for 4.5 hours to obtain a thermoplastic polyamic acid resin with a viscosity of 580 P.

[0106] 1 kg of amino-modified silica with a particle size of 11.5 μm and 2.2 kg of methyl acrylate were added to 10 kg of methanol. After reacting at 50 °C, the mixture was vacuum filtered. Then, 3.35 kg of ethylenediamine was added, and the mixture was reacted in methanol and vacuum filtered to obtain amino-terminated hyperbranched polyamide-grafted silica particles.

[0107] 2. Film Forming

[0108] 1.6 kg of terminal amino hyperbranched polyamide grafted silica particles, 18 kg of pyridine, and 21 kg of acetic anhydride were added to a high-speed mixer and mixed evenly with thermosetting polyamic acid resin at 2250 rpm to obtain thermosetting polyamic acid precursor resin. The precursor resin was then simultaneously conveyed to a three-layer co-extrusion die with thermoplastic polyamic acid resin for extrusion molding. After casting, longitudinal and transverse stretching, and high-temperature heating, a composite film with a total thickness of 25 μm was obtained, with the adhesive layers on both sides having a thickness of 3 μm.

[0109] Comparative Example 3

[0110] 1. Aggregation

[0111] 55.4 kg of m-PDA was dissolved in 770 kg of dimethylacetamide, and 56.3 kg of PMDA, 33 kg of BTDA and 45.2 kg of BPDA were added in batches and reacted for 6.5 hours to obtain a thermosetting polyamic acid resin with a viscosity of 2350 P.

[0112] 10.7 kg of ODA and 30.7 kg of TPE-M were dissolved in 420 kg of dimethylacetamide. 37.5 kg of PMDA was added in batches, and finally 1.142 kg of 2-aminoimidazole was added. The reaction was carried out for 4.5 hours to obtain a thermoplastic polyamic acid resin with a viscosity of 580 P.

[0113] 1 kg of amino-modified silica with a particle size of 3.5 μm and 2.2 kg of methyl acrylate were added to 10 kg of methanol. After reacting at 50 °C, the mixture was vacuum filtered. Then, 3.35 kg of ethylenediamine was added, and the mixture was reacted in methanol and vacuum filtered to obtain amino-terminated hyperbranched polyamide-grafted silica particles.

[0114] 2. Film Forming

[0115] 3 kg of terminal amino hyperbranched polyamide grafted silica particles, 18 kg of pyridine, and 21 kg of acetic anhydride were added to a high-speed mixer and mixed evenly with thermosetting polyamic acid resin at 2250 rpm to obtain thermosetting polyamic acid precursor resin. The precursor resin was then simultaneously conveyed to a three-layer co-extrusion die along with thermoplastic polyamic acid resin for extrusion molding. After further processing such as casting, longitudinal and transverse stretching, and high-temperature heating, a composite film with a total thickness of 25 μm was obtained, with adhesive layers on both sides having a thickness of 3 μm.

[0116] Comparative Example 4

[0117] 1. Aggregation

[0118] 85.8 kg of ODA was dissolved in 770 kg of dimethylacetamide, and 47.1 kg of PMDA, 27.6 kg of BTDA and 37.8 kg of BPDA were added in batches and reacted for 5.8 hours to obtain a thermosetting polyamic acid resin with a viscosity of 1750 P.

[0119] 22.2 kg of ODA and 20.7 kg of BAPP were dissolved in 420 kg of dimethylacetamide. 36.7 kg of PMDA was added in batches, and finally 0.419 kg of 2-aminoimidazole was added and reacted for 3 hours to obtain a thermoplastic polyamic acid resin with a viscosity of 500 P.

[0120] 1 kg of amino-modified silica with a particle size of 3.5 μm and 2.2 kg of methyl acrylate were added to 10 kg of methanol. After reacting at 50 °C, the mixture was vacuum filtered. Then, 3.35 kg of ethylenediamine was added, and the mixture was reacted in methanol and vacuum filtered to obtain amino-terminated hyperbranched polyamide-grafted silica particles.

[0121] 2. Film Forming

[0122] 1.6 kg of terminal amino hyperbranched polyamide grafted silica particles, 18 kg of pyridine, and 21 kg of acetic anhydride were added to a high-speed mixer and mixed evenly with thermosetting polyamic acid resin at a speed of 2030 rpm to obtain thermosetting polyamic acid precursor resin. The precursor resin was then simultaneously conveyed to a three-layer co-extrusion die with thermoplastic polyamic acid resin for extrusion molding. After casting, longitudinal and transverse stretching, and high-temperature heating, a composite film with a total thickness of 25 μm was obtained, with the adhesive layers on both sides having a thickness of 3 μm.

[0123] Comparative Example 5

[0124] The difference from Example 1 is that no terminal amino hyperbranched polyamide grafted silica particles are added; otherwise, it is the same as in Example 1.

[0125] Comparative Example 6

[0126] 1. Aggregation

[0127] 31.7 kg of ODA and 36.4 kg of p-PDA were dissolved in 800 kg of dimethylformamide. 54.4 kg of PMDA, 31.9 kg of BTDA and 43.7 kg of BPDA were added in batches and reacted for 5 hours to obtain a thermosetting polyamic acid resin with a viscosity of 1850 P.

[0128] 11.7 kg of ODA and 31.2 kg of TPE-R were dissolved in 420 kg of dimethylformamide. 36.4 kg of PMDA was added in batches, and finally 0.48 kg of 2-aminoimidazole was added and reacted for 4 hours to obtain a thermoplastic polyamic acid resin with a viscosity of 550 P.

[0129] 1 kg of amino-modified silica with a particle size of 0.5 μm and 3.8 kg of methyl acrylate were added to 10 kg of methanol. After reacting at 50 °C, the mixture was vacuum filtered. Then, 3 kg of ethylenediamine was added, and the mixture was reacted in methanol and vacuum filtered to obtain amino-terminated hyperbranched polyamide-grafted silica particles.

[0130] The remaining steps are the same as in Example 1.

[0131] Comparative Example 7

[0132] The difference from Example 1 is that 2-aminoimidazole was not added; otherwise, it is the same as in Example 1.

[0133] Performance testing

[0134] The polyimide composite film prepared in Example 7 was examined using a microscope. Its cross-section is shown in Figure 1. The core layer is a thermosetting polyimide layer 1, and the two sides are thermoplastic polyimide layers 2. The two layers are interleaved to form an interface layer 3. The interior contains terminal amino hyperbranched polyamide grafted silica particles 4.

[0135] The polyimide composite films prepared in Comparative Example 1, Example 3, and Comparative Example 3 were examined using a microscope, and their core layer film planes are shown in Figures 3-5. In Comparative Example 1, no terminal amino-terminated hyperbranched polyamide-grafted silica particles were added; as shown in Figure 3, the core layer surface is smooth. Figure 4 shows the layer film plane of the polyimide composite film in Example 3, and Figure 5 shows the layer film plane of the polyimide composite film in Comparative Example 3. With the increase in the amount of terminal amino-terminated hyperbranched polyamide-grafted silica particles added, the core layer surface becomes significantly rougher, thereby increasing the contact area between the core layer and the adhesive layer and improving the peel strength.

[0136] The polyimide films prepared in the above examples and comparative examples were tested for mechanical properties according to ASTM D882, linear expansion coefficient according to TMA method, and glass transition temperature according to DMA method (heating rate 5℃ / min). They were then rolled with 18μm rolled copper foil to form two-layer adhesive-free double-sided copper-clad laminates according to industrial methods, and peel strength was tested according to IPC-TM-650. The results are shown in Table 1 below.

[0137] Table 1: Overall performance of the polyimide films obtained in the examples and comparative examples

[0138] When testing the peel strength in Comparative Example 6, the film broke brittlely, making it impossible to obtain a specific value.

[0139] As shown in Table 1, compared with Example 1, Comparative Example 1 did not use terminal amino hyperbranched polyamide grafted silica particles and 2-aminoimidazole, resulting in a slight increase in the coefficient of thermal expansion (CTE) of the film and a significant decrease in peel strength. In Comparative Example 2, the thermosetting layer diamine was entirely flexible ODA and used 11.5 μm amino-modified silica, leading to insufficient molecular chain rigidity and excessively large silica particle size, significantly reducing the mechanical properties of the polyimide film and increasing the coefficient of thermal expansion (CTE). In Comparative Example 3, the thermosetting layer diamine was entirely rigid PDA, with high molecular chain regularity and increased intermolecular forces, hindering the internal rotation and movement of the molecular chains. Furthermore, the excessive addition of silica particles caused a sharp decrease in the flexibility of the film, failing to meet application requirements. In Comparative Example 4, the thermosetting layer consisted entirely of flexible ODA, with excessive content leading to decreased tensile strength and poor dimensional stability of the film. Additionally, the thermoplastic layer had an excessively high Tg and poor peel strength. In Comparative Example 5, the absence of terminally amino hyperbranched polyamide grafted onto silica particles resulted in an increased coefficient of thermal expansion and a sharp decrease in peel strength. In Comparative Example 6, the excessive use of methyl acrylate and ethylenediamine led to over-hybridization and an excessive number of amino groups on the silica particle surface, causing excessive PI crosslinking and a significant decrease in film elongation, making it prone to brittle fracture during processing and application. In Comparative Example 7, the absence of 2-aminoimidazole in the thermoplastic layer resulted in reduced film peel strength.

[0140] As can be seen from the above, the introduction of imidazole-containing monoamine and amino-terminated hyperbranched polyamide grafted silica particles into the structure of polyimide composite films in this invention can significantly improve the film's adhesion, dimensional stability, and heat resistance, while maintaining a low glass transition temperature, thus meeting the processing and application requirements of materials such as two-layer FCCL.

[0141] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A high-adhesion polyimide composite film for use in flexible copper-clad laminates, the polyimide composite film comprising a thermosetting polyimide support layer and a thermoplastic polyimide adhesive layer disposed on at least one side of the thermosetting polyimide support layer, characterized in that, An interface layer is embedded between the thermosetting polyimide support layer and the thermoplastic polyimide adhesive layer, formed by the reaction of terminal amino hyperbranched polyamide-grafted silica particles with thermosetting polyamic acid.

2. The high-adhesion polyimide composite film according to claim 1, characterized in that, The interface layer is formed by dispersing the terminal amino hyperbranched polyamide grafted silica particles in a chemical casting agent, mixing them with a thermosetting polyamic acid resin, and then obtaining the layer through a polymerization reaction.

3. The high-adhesion polyimide composite film according to claim 1, characterized in that, The thermosetting polyamic acid resin is prepared by reacting flexible aromatic diamines and rigid aromatic diamines with aromatic dianhydrides, wherein the molar ratio of the flexible aromatic diamines to the rigid aromatic diamines is 5-35:65-95.

4. The high-adhesion polyimide composite film according to claim 1, characterized in that, The end groups of the thermoplastic polyimide contain imidazole rings that can form complexes with copper.

5. The method for preparing the high-adhesion polyimide composite film according to any one of claims 1-4, characterized in that, Includes the following steps: S1. A polyamic acid resin A is generated by polycondensation of a flexible aromatic diamine, a rigid aromatic diamine, and an aromatic dianhydride. S2. Surface-aminated silica undergoes an addition reaction with methyl acrylate or its homologues, followed by a reaction with an aliphatic diamine or its homologues to prepare terminally aminated hyperbranched polyamide-grafted silica particles. These particles are then dispersed in a chemical casting agent and rapidly mixed with the polyamic acid resin A prepared in step S1 to obtain a mixed solution. The mass ratio of the surface-aminated silica, acrylate, and aliphatic diamine is 1:1-3:0.7-4. S3. Polycondensation reaction of diamine, dianhydride and monoamine produces polyamic acid resin B; S4. Using the mixed solution in step S2 as the thermosetting polyimide support layer and the polyamic acid resin B prepared in step S3 as the thermoplastic polyimide adhesive layer, a polyimide composite film is prepared by a film-forming process.

6. The method for preparing the highly adhesive polyimide composite film according to claim 5, characterized in that, In step S2, the amount of the terminal amino hyperbranched polyamide grafted silica particles added is 0.05%-1% of the mass of the thermosetting polyimide, and the particle size of the terminal amino hyperbranched polyamide grafted silica particles is 0.1-10 μm.

7. The method for preparing the highly adhesive polyimide composite film according to claim 5, characterized in that, In step S2, the chemical casting agent consists of a catalyst, a dehydrating agent, and an organic solvent; the catalyst is selected from one or more of pyridine and its derivatives, quinoline, isoquinoline, and triethylamine, and the amount of the catalyst used is 1-5% of the mass of polyamic acid resin A; the dehydrating agent is selected from one or more of acetic anhydride, propionic anhydride, and benzoic anhydride, and the amount of the dehydrating agent used is 15-35% of the mass of polyamic acid resin A.

8. The method for preparing the highly adhesive polyimide composite film according to claim 5, characterized in that, In step S1, the polyamic acid resin A is generated by the polycondensation reaction of a flexible aromatic diamine, a rigid aromatic diamine and an aromatic dianhydride; the ratio of the sum of the molar amounts of the flexible aromatic diamine and the rigid aromatic diamine to the molar amount of the aromatic dianhydride is 100:100.05-100.

5.

9. The method for preparing the high-adhesion polyimide composite film for flexible copper-clad laminates according to claim 5, characterized in that, In step S3, the monoamine is a monoamine containing an imidazole structure.

10. The method for preparing the high-adhesion polyimide composite film for flexible copper-clad laminates according to claim 9, characterized in that, The monoamine containing an imidazole structure is selected from one or more of 2-aminoimidazole, 4-aminoimidazole, 5-amino-4-imidazolium carboxamide, and 2-aminobenzimidazole; the molar ratio of the diamine, dianhydride and the monoamine containing an imidazole structure is 98-99.5:100:0.5-4.

11. The method for preparing the highly adhesive polyimide composite film according to claim 5, characterized in that, In step S3: The diamine is selected from one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)diphenyl sulfone, and 2,2-bis[4-(4-aminophenoxy)phenyl]propane; The dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride.

12. A two-layer flexible copper-clad laminate, comprising a copper foil layer and a polyimide layer, characterized in that, The polyimide layer is a high-adhesion polyimide composite film as described in any one of claims 1-4.

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