Intrinsic black polyimide, preparation method and application thereof

Abstract

This application relates to the field of polymer materials technology, and discloses an intrinsic black polyimide, its preparation method, and its application. The preparation method includes: dissolving diamine monomers M and N in a solvent under an inert atmosphere, then adding a dianhydride monomer and stirring to obtain a first polyamic acid solution; adding an oxidant and a melanin monomer to the first polyamic acid solution, mixing thoroughly, and oxidizing to obtain a second polyamic acid solution; coating the second polyamic acid solution onto a substrate and drying to obtain a precursor film; and performing an imidization treatment on the precursor film to obtain an intrinsic black polyimide film. This application prepares a novel type of intrinsic black polyimide by chemically bonding melanin-like structural units with strong visible light absorption capabilities into the polyimide molecular backbone; it achieves its light-shielding effect without the need for adding black light-shielding substances or coating the surface with a black coating, and exhibits excellent visible light absorption performance.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and in particular to an intrinsic black polyimide, its preparation method, and its application. Background Technology

[0002] Polyimide, with its excellent thermal stability, mechanical strength, and low dielectric loss, is widely used in integrated circuit packaging and flexible electronics as a dielectric layer, stress buffer layer, and packaging substrate material, effectively ensuring the reliable operation of devices under high-frequency and high-power conditions. As display technology evolves towards higher contrast and higher precision, such as using polyimide in OLED pixel definition layers to suppress ambient light reflection and improve visual contrast, and as advanced packaging demands higher signal integrity, there is a clear need for improved optical blackness in polyimide. However, traditional polyimide has high transmittance in the visible light band and lacks inherent light-shielding capabilities, limiting its application in scenarios requiring optical isolation or visual shielding.

[0003] To impart a black appearance to polyimides, current technologies primarily employ physically blended carbon black, carbon nanotubes, or other black fillers, or the addition of organic dyes. However, black fillers are prone to agglomeration due to uneven dispersion, leading to decreased film density, increased interface defects, and significantly deteriorated dielectric properties. Dyes, on the other hand, suffer from poor heat resistance and easy migration, making them unsuitable for the high-temperature imidization of polyimides and subsequent processes. Introducing intrinsic light-absorbing structures into the molecular chain to prepare black polyimides represents a more promising new technological approach. Such materials achieve broad-spectrum visible light absorption while maintaining the inherent high thermal stability, low dielectric constant, and good mechanical properties of polyimides, demonstrating significant potential in high-end display light-shielding layers, high-frequency and high-speed packaging substrates, and electromagnetic shielding.

[0004] Therefore, there is an urgent need to develop black polyimides that combine high intrinsic blackness, excellent overall performance, and good process adaptability. Summary of the Invention

[0005] This application provides an intrinsic black polyimide, its preparation method, and its application, aiming to solve the technical problems of low thermal stability, deteriorated dielectric properties, and low mechanical properties of existing black polyimides.

[0006] To achieve the above objectives, the present application adopts the following technical solution.

[0007] A first aspect of this application provides an intrinsic black polyimide with the chemical structural formula shown in formula (I):

[0008] ;

[0009] Where n is an integer from 10 to 300;

[0010] Structural unit A can be any of the following structures:

[0011] ;

[0012] Structural unit B can be any of the following structures:

[0013] ;

[0014] Structural unit C can be any of the following structures:

[0015] ;

[0016] Structural unit R is a colored structural unit, which is a catechol derivative or an indole derivative.

[0017] Preferably, the coloring structural unit R is any one of the following structures: .

[0018] Preferably, its number-average molecular weight is 3,000 to 100,000;

[0019] The structural unit B accounts for 0.2% to 40% of the molar percentage of the polyimide backbone.

[0020] A second aspect of this application provides a method for preparing the aforementioned intrinsic black polyimide, comprising:

[0021] S1, under an inert atmosphere, diamine monomer M and diamine monomer N are dissolved in a solvent, and then dianhydride monomer is added. The reaction is stirred to obtain the first polyamic acid solution.

[0022] Wherein, the diamine monomer M comprises structural unit B and coloring structural unit R; the diamine monomer N comprises structural unit C; and the dianhydride monomer comprises structural unit A.

[0023] S2, add an oxidant and a melanin monomer containing a coloring structural unit R to the first polyamic acid solution, mix them evenly and oxidize them to obtain a second polyamic acid solution;

[0024] The oxidant includes any one of hydrogen peroxide, potassium iodate, ammonium persulfate, or sodium periodate;

[0025] S3, the second polyamic acid solution is coated onto the substrate and dried to obtain a precursor film; the precursor film is subjected to imidization treatment to obtain an intrinsic black polyimide film.

[0026] Preferably, the diamine monomer M comprises any one of the following compounds:

[0027] ;

[0028] The diamine monomer N includes any one of the following compounds:

[0029] ;

[0030] The dianhydride monomer includes any one of the following compounds:

[0031] ;

[0032] The melanin monomer includes any one of the following compounds:

[0033]

[0034] Preferably, the molar ratio of diamine monomer M, diamine monomer N, and dianhydride monomer is (0.1~1):(0.8~8):(1~10);

[0035] The mass ratio of the first polyamic acid solution, oxidant, and melanin monomer is 100 : (2~20) : (1~10).

[0036] Preferably, the solvent is a polar solvent, or an aqueous solution of an organic base and a surfactant;

[0037] The polar solvent includes any one of N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, γ-butyrolactone, m-cresol, dimethyl sulfoxide, N,N-dimethylformamide, or N,N-dimethylacetamide;

[0038] The organic base includes 1,2-dimethylimidazolium or 4-(dimethylamino)idine; the surfactant includes sodium dodecyl sulfate.

[0039] The total mass fraction of the diamine monomer M, diamine monomer N, and dianhydride monomer in the solvent is 5-40 wt%.

[0040] Preferably, the imidization treatment includes gradient heating imidization or low-temperature imidization;

[0041] The gradient heating imidization includes: holding the precursor film at 25~100℃ for 0.5~3h, raising the temperature to 100~200℃ and holding for 0.5~3h, and then raising the temperature to 200~300℃ and holding for 0.2~2h.

[0042] The low-temperature imidization includes:

[0043] The imidization catalyst was sprayed onto the precursor film and kept at 190°C for 1 hour; the imidization catalyst was a dispersion of aminoquinoline-modified attapulgite nanosheets.

[0044] More preferably, the imidization catalyst is obtained by dispersing attapulgite nanosheets and aminoquinoline into DMAC;

[0045] The mass ratio of the attapulgite nanosheets to aminoquinoline is 1:2.

[0046] A third aspect of this application provides the application of the above-described intrinsic black polyimide or the intrinsic black polyimide prepared by the above-described preparation method in the fields of flexible circuit boards, display encapsulation light shielding, and electromagnetic shielding.

[0047] Compared with the prior art, the beneficial effects of this application are as follows:

[0048] This application prepares a novel type of intrinsically black polyimide by chemically bonding melanin-like structural units with strong visible light absorption capabilities into the main chain of a polyimide molecule. It does not require the addition of black light-blocking substances or the coating of a black layer on the surface to achieve a light-blocking effect and has excellent visible light absorption performance.

[0049] The intrinsic black polyimide of this application exhibits broad-spectrum, high-intensity intrinsic absorption in the visible light region. It possesses excellent blackness, high thermal stability, good mechanical properties, and a controllable dielectric constant, making it valuable for applications in high-end flexible circuit boards, display packaging light-shielding layers, and electromagnetic shielding. Attached Figure Description

[0050] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0051] Figure 1 This is a photograph of the intrinsic black polyimide film A.

[0052] Figure 2 The image shows the UV-Vis absorption spectrum of the intrinsic black polyimide film A.

[0053] Figure 3 This is the ultraviolet transmission spectrum of the intrinsic black polyimide film B. Detailed Implementation

[0054] 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 of this application without creative effort are within the scope of protection of this application.

[0055] In the following description of this embodiment, the terms "including", "comprising", "having", and "containing" are all open-ended terms, meaning that they include but are not limited to.

[0056] In the following description of this embodiment, the term "and / or" is used to describe the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0057] In the following description of this embodiment, the term "at least one" means one or more, and "more than one" means two or more. "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 both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0058] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms "a" and "the" as used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0059] Those skilled in the art should understand that, in the following description of the embodiments 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 determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0060] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood as each intermediate value between the upper and lower limits of the specifically disclosed range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0061] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification 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 specification shall prevail.

[0062] Firstly, this application provides an intrinsic black polyimide. Through molecular structure design, this application introduces strongly light-absorbing chromophores into the polyimide backbone via chemical bonds, endowing the material with intrinsic broad-spectrum visible light absorption characteristics and high optical density.

[0063] Its chemical structural formula is shown in formula (Ⅰ):

[0064]

[0065] Where n is an integer from 10 to 300;

[0066] Structural unit A can be any of the following structures:

[0067]

[0068] Structural unit B can be any of the following structures:

[0069]

[0070] Structural unit C can be any of the following structures:

[0071]

[0072] Structural unit R is a coloring structural unit, which is either a catechol derivative or an indole derivative. Specifically, the coloring structural unit R is any one of the following structures:

[0073] .

[0074] The intrinsic black polyimide of this application has a number-average molecular weight of 3,000 to 100,000. The structural unit B accounts for 0.2% to 40% of the molar percentage of the polyimide backbone.

[0075] Secondly, this application provides a method for preparing the aforementioned intrinsically black polyimide. This application prepares a novel type of intrinsically black polyimide by chemically bonding melanin-like structural units with strong visible light absorption capabilities into the polyimide molecular backbone. Specifically, it includes:

[0076] S1, under an inert atmosphere, diamine monomers M and N are dissolved in a solvent, and then dianhydride monomers are added. The reaction is stirred to obtain a light-colored intrinsic black polyamic acid solution, denoted as the first polyamic acid solution; wherein, the reaction temperature is preferably -10~35℃.

[0077] In this application, the diamine monomer M comprises structural unit B and coloring structural unit R. Specifically, the diamine monomer M includes any one of the following compounds:

[0078] ;

[0079] The diamine monomer N comprises the structural unit C. Specifically, the diamine monomer N includes any one of the following compounds:

[0080]

[0081] The dianhydride monomer comprises structural unit A. Specifically, the dianhydride monomer includes any one of the following compounds:

[0082] .

[0083] In this application, the molar ratio of diamine monomer M, diamine monomer N and dianhydride monomer is preferably (0.1~1):(0.8~8):(1~10).

[0084] In this application, the solvent is a polar solvent, or an aqueous solution of an organic base and a surfactant.

[0085] Specifically, the polar solvent is selected from any one of N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, γ-butyrolactone, m-cresol, dimethyl sulfoxide, N,N-dimethylformamide, or N,N-dimethylacetamide;

[0086] Specifically, the organic base is selected from 1,2-dimethylimidazole or 4-(dimethylamino)idine; the surfactant is sodium dodecyl sulfate;

[0087] In this application, the total mass fraction of the diamine monomer M, diamine monomer N, and dianhydride monomer in the solvent is 5-40 wt%.

[0088] S2, add an oxidant and a melanin monomer containing a coloring structural unit R to the first polyamic acid solution, mix them evenly and oxidize them to obtain a second polyamic acid solution;

[0089] Specifically, the oxidant includes any one of hydrogen peroxide, potassium iodate, ammonium persulfate, or sodium periodate;

[0090] In this application, the melanin monomer includes any one of the following compounds:

[0091]

[0092] The mass ratio of the first polyamic acid solution, oxidant, and melanin monomer is 100 : (2~20) : (1~10).

[0093] S3, the second polyamic acid solution is coated onto the substrate and dried to obtain a precursor film; the precursor film is subjected to imidization treatment to obtain an intrinsic black polyimide film.

[0094] In this application, the imidization treatment can be selected as gradient heating imidization or low temperature imidization;

[0095] The gradient heating imidization includes: holding the precursor film at 25~100℃ for 0.5~3h, raising the temperature to 100~200℃ and holding for 0.5~3h, and then raising the temperature to 200~300℃ and holding for 0.2~2h.

[0096] The low-temperature imidization includes: spraying an imidization catalyst onto a precursor film and holding it at 190°C for 1 hour. The imidization catalyst is a dispersion of aminoquinoline-modified attapulgite nanosheets, obtained by dispersing attapulgite nanosheets and aminoquinoline in DMAC; the preferred mass ratio of attapulgite nanosheets to aminoquinoline is 1:2.

[0097] The intrinsic black polyimide of this application achieves its light-shielding effect without the need for added black light-shielding materials or a black coating on its surface, exhibiting excellent visible light absorption performance. It displays broad-spectrum, high-intensity intrinsic absorption in the visible light region, possessing excellent blackness, high thermal stability, good mechanical properties, and a controllable dielectric constant. It can be used in high-end flexible circuit substrates, display packaging light-shielding layers, and electromagnetic shielding. For example, the intrinsic black polyimide of this application can be used in high-frequency, high-speed electronic packaging substrates or micro-interconnect circuits, demonstrating significant application value.

[0098] The present application will be further described below through specific embodiments.

[0099] The diamine monomer M used in the examples, which includes structural unit B and coloring structural unit R, has the following chemical structure:

[0100]

[0101] Example 1

[0102] This embodiment provides a method for preparing intrinsic black polyimide, including:

[0103] In a three-necked round-bottom flask, 4.0855 g (42.5 mmol) of 1,2-dimethylimidazole and 0.075 g (0.23 mmol) of sodium dodecyl sulfate were dissolved in 900 mL of deionized water and stirred for 30 min under nitrogen protection until completely dissolved. Then, 3.4041 g (17.0 mmol) of 4,4'-diaminodiphenyl ether and 1.50 g (4.32 mmol) of diamine monomer M were added sequentially, and the mixture was stirred at 25 °C for 30 min. Subsequently, 5.0017 g (17.0 mmol) of BPDA was added, and 200 mL of deionized water was added to the mixture. The temperature of the reaction system was gradually increased to 70 °C, and the reaction was stirred for 18 h to obtain a viscous, light black aqueous solution of polyamic acid salt.

[0104] At room temperature, a black polyamic acid aqueous solution was filtered and defoamed, and then a solution containing 10 g of 30% hydrogen peroxide (H2O2) and 4.5 g (30 mmol) of 5,6-dihydroxyindole (DHI) was added. The mixture was stirred for 24 h to carry out oxidative polymerization and obtain a second polyamic acid solution.

[0105] A second polyamic acid solution was coated onto a glass substrate using a blade coating method. The substrate was then placed in a forced-air heating device and heated at 60°C for 2 hours to evaporate part of the solvent, yielding a precursor film. Subsequently, aminoquinoline-modified attapulgite (QL-REC) was sprayed onto the precursor film using a spray coating method, and imidized at 190°C for 1 hour to obtain an intrinsic black polyimide film A, denoted as PI-A. The aminoquinoline-modified attapulgite was obtained by dispersing attapulgite nanosheets and aminoquinoline in DMAC at a mass ratio of 1:2.

[0106] The synthetic route for intrinsic black polyimide film A is shown below:

[0107]

[0108] Example 2

[0109] This embodiment provides a method for preparing intrinsic black polyimide, including:

[0110] 19.9 g (108 mmol) of benzidine and 5.0 g (11.2 mmol) of diamine monomer M were added to a reaction vessel equipped with a mechanical stirrer and cooled to -10 °C in an ice-salt bath. Then, 1925.5 g of dimethyl sulfoxide (DMSO) was added, and the mixture was stirred until the diamine monomer was completely dissolved. Next, 50.0 g (230 mmol) of pyromellitic anhydride was added to the vessel, and the mixture was stirred at -10 °C for 24 h under nitrogen protection to obtain a light black first polyamic acid solution.

[0111] At room temperature, the first polyamic acid solution was filtered and defoamed, and then a solution containing 10 g of 30% hydrogen peroxide (H2O2) and 4.5 g (30 mmol) of 5,6-dihydroxyindole (DHI) was added. The mixture was stirred for 24 h to carry out oxidative polymerization and obtain the second polyamic acid solution.

[0112] The second polyamic acid solution was coated onto a glass substrate by a blade coating method, and the substrate was placed in a blower heating device and heated at 60°C for 2 hours to evaporate part of the solvent, thus obtaining a precursor film. Subsequently, it was placed in a nitrogen atmosphere and kept at 50°C for 0.5 hours, then heated to 150°C for 0.5 hours, and then heated to 250°C for 0.2 hours to perform imidization, thus obtaining an intrinsic black polyimide film B, denoted as PI-B.

[0113] The synthetic route for intrinsic black polyimide film B is shown below:

[0114]

[0115] Example 3

[0116] This embodiment provides a method for preparing intrinsic black polyimide, including:

[0117] 9.7 g (90.0 mmol) of p-phenylenediamine and 21.4 g (47.8 mmol) of diamine monomer M were added to a reaction vessel equipped with a mechanical stirrer, and the temperature was controlled at 25 °C. Then, 800.0 g of N,N-dimethylacetamide (DMAc) was added, and the mixture was stirred until the diamine monomer was completely dissolved. Next, 21.8 g (100 mmol) of pyromellitic anhydride was added to the vessel, and the mixture was stirred at 25 °C for 24 h under nitrogen protection to obtain a light black first polyamic acid solution.

[0118] At room temperature, the first polyamic acid solution was filtered and defoamed, and then a solution containing 10 g of 30% hydrogen peroxide (H2O2) and 2.25 g (15 mmol) of 5,6-dihydroxyindole (DHI) was added. The mixture was stirred for 24 h to carry out oxidative polymerization and obtain the second polyamic acid solution.

[0119] The second polyamic acid solution was coated onto a glass substrate by a blade coating method, and the substrate was placed in a blower heating device and heated at 60°C for 2 hours to evaporate part of the solvent, thus obtaining a precursor film. Subsequently, it was placed in a nitrogen atmosphere and kept at 50°C for 0.5 hours, then heated to 150°C for 0.5 hours, and then heated to 250°C for 0.2 hours to perform imidization, thus obtaining an intrinsic black polyimide film C, denoted as PI-C.

[0120] The synthetic route for the intrinsic black polyimide film C is shown below:

[0121]

[0122] Comparative Example 1

[0123] 3.4041 g (17.0 mmol) of 4,4'-diaminodiphenyl ether was added to a reaction vessel equipped with a mechanical stirrer, and the temperature was controlled at 25 °C. Then, 22.76 g of N,N-dimethylacetamide (DMAc) was added, and the mixture was stirred until the diamine monomer was completely dissolved. Next, 5.0017 g (17.0 mmol) of pyromellitic anhydride was added to the vessel, and the mixture was stirred at 25 °C for 24 h under nitrogen protection to obtain a light yellow, transparent polyamic acid solution.

[0124] At room temperature, the polyamic acid solution is filtered and defoamed, then coated onto a glass substrate by a scraping method. The substrate is then placed in a blower heating device and heated at 60°C for 2 hours to evaporate part of the solvent, thus obtaining a precursor film. Subsequently, it is placed in a nitrogen atmosphere and kept at 100°C for 3 hours, then heated to 200°C for 3 hours, and then heated to 300°C for 2 hours to perform imidization, thus obtaining a polyimide film D, denoted as PI-D.

[0125] The synthetic route for polyimide film D is shown below:

[0126]

[0127] The intrinsic black polyimide film prepared in this application was subjected to performance tests, as detailed below:

[0128] A physical image of the intrinsic black polyimide film A prepared in Example 1 is shown below. Figure 1 As shown, it appears uniformly black. Its UV-Vis absorption spectrum is as follows: Figure 2 As shown, the film exhibits strong absorption in a wide wavelength range of 200-1000 nm, especially in the visible light region of 400-800 nm where the absorbance remains consistently high, indicating that this intrinsic polyimide film possesses excellent broadband light-shielding properties.

[0129] The ultraviolet transmission spectrum of the intrinsic black polyimide film B prepared in Example 2 is as follows: Figure 3 As shown. By Figure 3 It can be seen that the intrinsic black polyimide film B has low transparency. Under visible light at a wavelength of 650nm, its transmittance is as low as 0.45%, and the highest transmittance in the visible light range is only 48.2%, indicating that it has good light-blocking properties.

[0130] The optical performance test data of the polyimide films in Examples 1-3 and the comparative examples are shown in Table 1.

[0131] Table 1. Optical performance test data of polyimide films

[0132]

[0133] As shown in Table 1, under visible light at a wavelength of 650 nm, the transmittance of the intrinsic black polyimide films in Examples 1-3 is all less than 0.5%, exhibiting excellent light-shielding properties. In contrast, the transmittance of the comparative polyimide film is 84.8%, and its light-shielding properties are far lower than those of the intrinsic black polyimide film of this application. Excellent light-shielding properties are of great significance for the application of polyimide films in cutting-edge fields such as high-end display packaging light-shielding layers and high-frequency circuit substrates.

[0134] Table 2. Test data of electrical and mechanical properties of polyimide films.

[0135]

[0136] The intrinsic black polyimides prepared in Examples 1-3 of this application were subjected to electrical and mechanical property tests, and the results are shown in Table 2. The dielectric strength of PI-A to PI-C is 268~275 kV / mm, and the volume resistivity is (7.2~8.6)×10⁻⁶. 14 Ω·m, surface resistivity (3.8~4.5)×10 14 Ω; tensile strength 108~115 MPa, tensile modulus 4.0~4.3 GPa. Compared with comparative PI-D, the intrinsic black polyimide exhibits more than twice the volume and surface resistivity, and more than 60% higher tensile modulus. The results demonstrate that the intrinsic black polyimide prepared in this application achieves excellent light-shielding properties while also possessing high electrical insulation and high mechanical strength, exhibiting superior overall performance compared to traditional polyimide films.

[0137] Although this application has been described in detail in this specification with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, such modifications or improvements made without departing from the spirit of this application are all within the scope of protection claimed in this application.

Claims

1. An intrinsically black polyimide, characterized in that, Its chemical structural formula is shown in formula (Ⅰ): ； Where n is an integer from 10 to 300; Structural unit A can be any of the following structures: ； Structural unit B can be any of the following structures: ； Structural unit C can be any of the following structures: ； Structural unit R is a colored structural unit, which is a catechol derivative or an indole derivative.

2. The intrinsic black polyimide according to claim 1, characterized in that, The coloring structural unit R can be any of the following structures: 。 3. The intrinsic black polyimide according to claim 1, characterized in that, Its number-average molecular weight is 3,000 to 100,000; The structural unit B accounts for 0.2% to 40% of the molar percentage of the polyimide backbone.

4. The method for preparing the intrinsic black polyimide according to claim 1, characterized in that, include: S1, under an inert atmosphere, diamine monomer M and diamine monomer N are dissolved in a solvent, and then dianhydride monomer is added. The reaction is stirred to obtain the first polyamic acid solution. Wherein, the diamine monomer M comprises structural unit B and coloring structural unit R; the diamine monomer N comprises structural unit C; and the dianhydride monomer comprises structural unit A. S2, add an oxidant and a melanin monomer containing a coloring structural unit R to the first polyamic acid solution, mix them evenly and oxidize them to obtain a second polyamic acid solution; The oxidant includes any one of hydrogen peroxide, potassium iodate, ammonium persulfate, or sodium periodate; S3, the second polyamic acid solution is coated onto the substrate and dried to obtain a precursor film; the precursor film is subjected to imidization treatment to obtain an intrinsic black polyimide film.

5. The preparation method according to claim 4, characterized in that, The diamine monomer M comprises any one of the following compounds: ； The diamine monomer N includes any one of the following compounds: ； The dianhydride monomer includes any one of the following compounds: ； The melanin monomer includes any one of the following compounds: 。 6. The preparation method according to claim 4, characterized in that, The molar ratio of diamine monomer M, diamine monomer N and acid anhydride monomer is (0.1~1):(0.8~8):(1~10); The mass ratio of the first polyamic acid solution, oxidant, and melanin monomer is 100 : (2~20) : (1~10).

7. The preparation method according to claim 4, characterized in that, The solvent is a polar solvent, or an aqueous solution of an organic base and a surfactant; The polar solvent includes any one of N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, γ-butyrolactone, m-cresol, dimethyl sulfoxide, N,N-dimethylformamide, or N,N-dimethylacetamide; The organic base includes 1,2-dimethylimidazolium or 4-(dimethylamino)idine; the surfactant includes sodium dodecyl sulfate. The total mass fraction of the diamine monomer M, diamine monomer N, and dianhydride monomer in the solvent is 5-40 wt%.

8. The preparation method according to claim 4, characterized in that, The imidization process includes gradient heating imidization or low-temperature imidization; The gradient heating imidization includes: holding the precursor film at 25~100℃ for 0.5~3h, raising the temperature to 100~200℃ and holding for 0.5~3h, and then raising the temperature to 200~300℃ and holding for 0.2~2h. The low-temperature imidization includes: The imidization catalyst was sprayed onto the precursor film and kept at 190°C for 1 hour; the imidization catalyst was a dispersion of aminoquinoline-modified attapulgite nanosheets.

9. The preparation method according to claim 8, characterized in that, The imidization catalyst was obtained by dispersing pizosite nanosheets and aminoquinoline into DMAC; The mass ratio of the attapulgite nanosheets to aminoquinoline is 1:

2.

10. The intrinsic black polyimide of claims 1-3 or any one of claims 4-9 is used in the fields of flexible circuit boards, display encapsulation light shielding, and electromagnetic shielding.

Images