A black polyimide film and a method for manufacturing the same

Abstract

The present application relates to the field of organic materials, in particular to a black polyimide film and a preparation method thereof.The black polyimide film provided by the present application has a polyimide with a structure shown in formula (L).In the preparation method provided by the present application, an aniline oligomer diamine shown in formula (II) is used, wherein each bridging nitrogen atom is coupled with a protective group, such as benzyloxy carbonyl or tert-butyloxy carbonyl; the above-mentioned diamine monomer is homopolymerized or copolymerized with a diamine monomer shown in formula (III) and a dianhydride monomer to form a resin solution; then, a polyimide / polyamic acid film is prepared through a film forming process; and then, a deprotection group treatment is performed, so that an intrinsic black polyimide film is obtained.The polymer prepared by the present application has excellent solubility, and after the deprotection, the material exhibits uniform black properties, excellent solvent resistance and mechanical properties, thereby solving the contradiction between the processing performance and the solvent resistance and mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of organic materials, and in particular to a black polyimide film and its preparation method. Background Technology

[0002] In recent years, the pace of product iteration in the communications industry has accelerated. Flexible displays, with their unique advantage of being able to retract and unfold screens, can significantly save space and are therefore highly favored by the market. Polyimide film, as an important high-temperature resistant insulating material, and with its good compatibility with copper foil, has been widely used in this field.

[0003] However, with rapid technological advancements and increasingly fierce industry competition, protecting intellectual property and technological achievements has become an inevitable choice for enterprises. Technicians discovered that when using traditional yellow transparent polyimide film as a coating, printed circuit design schemes are easily cracked and copied. To address this issue, many manufacturers have begun using black polyimide film to replace traditional transparent polyimide film.

[0004] In high-end fields such as aerospace, to ensure the stable operation of imaging systems, sensors, and other sensitive devices, it is necessary to prevent them from being interfered with by stray light. These devices are typically placed within light-shielding fixtures. With the continuous advancement of aerospace technology, the performance requirements for these light-shielding fixtures are becoming increasingly stringent, such as strong absorption capacity in the visible light region, lightweight construction, and excellent space resistance. Therefore, many engineers have begun exploring the use of black polyimide films to fabricate such fixtures.

[0005] At the same time, in order to meet the manufacturing needs of complex parts and respond to the development trend of low carbon and environmental protection, the market has also put forward more stringent requirements for the solubility and processability of materials.

[0006] In conclusion, the market demand for black polyimide films is showing an increasingly strong trend. Developing black polyimide films with excellent optical shielding, mechanical, and processing properties not only has broad market prospects but also profound strategic significance.

[0007] Currently, there are three main methods for preparing black polyimide films. The first is the in-situ dyeing method, which involves adding black pigments or dye particles to a polyimide solution and then using a film-forming process to obtain the target film. The second is the composite method, which involves coating a black resin onto a polyimide film and then curing it at a higher temperature to obtain a black film. The third is the intrinsic method, which involves adding a special monomer to the polyimide system, and the introduced structure has strong absorption in the visible light region.

[0008] Patent CN109867786B uses 4'-bis(4-aminoaniline)benzene and 1,3'-bis(4-aminoaniline)phenylenediamine monomers as diamine monomers, and one or more of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA), and pyromellitic tetracarboxylic dianhydride (PMDA) as dianhydride monomers. Polymerization is carried out in an aprotic polar solvent to obtain a polyamic acid solution, which is then cast, coated, and thermocured to obtain a black polyimide film. This intrinsically black polyimide film has excellent electrical insulation properties and can be used in applications requiring high insulation, such as insulating protective films for wireless charging antennas, FPC cover films, and lithium battery connector cover films, as well as black high-temperature resistant labels, black polyimide-based films for tapes, and solar energy absorption and storage films.

[0009] Patent CN109180936A describes a polyamic acid film prepared by using pyromellitic dianhydride (PMDA), 4,4'-diaminodiphenyl ether (ODA), and 4,4'-diaminodiphenylamine (NDA) as raw materials to prepare a polyamic acid solution, followed by high-temperature imidization. Performance testing results show that this black polyimide film exhibits excellent light-blocking properties.

[0010] Patent CN113563212B uses anthraquinone derivative tetraamine monomers, in which only two amine groups can undergo polycondensation, thus yielding linear polymers. The black polyimide obtained by this invention has good light-shielding properties, excellent mechanical properties, thermal stability, and dielectric properties, and its optical transmittance across the entire wavelength range is less than 1%.

[0011] Patent CN111574426A synthesizes a deep red or black diamine monomer containing an isoindigo structure. This monomer (with the possibility of adding other diamines) is then subjected to a polycondensation reaction with an aromatic dianhydride to obtain a polyamic acid solution. Black polyimide is then prepared by thermal or chemical imidization. The large planar conjugated, strongly electron-withdrawing isoindigo structure endows the material with its black color.

[0012] Patent CN115873250B describes the preparation of a novel intrinsic black polyimide material by introducing a pyrrolopyrrole-dione structure with coplanar and highly conjugated characteristics into the polyimide molecular chain. The coplanarity and highly conjugated pyrrolopyrrole-dione structure effectively lowers the π→π* excitation energy of electronic transitions, causing a redshift in the absorption spectrum, broadening its visible light absorption range, and improving the visible light absorption capacity of polyimide.

[0013] Currently, the publicly available intrinsic methods for preparing black polyimide materials typically employ monomers with high absorbance coefficients for polymerization to obtain stable polyimides. These polyimides often contain large conjugated systems or numerous chromophores. This limits the solubility of the resulting polyimide, often requiring the use of high-boiling-point solvents such as N,N'-dimethylacetamide as the reaction solvent. Even so, the solubility remains low, making high-concentration application difficult. Furthermore, subsequent solvent removal consumes significant energy. Additionally, some researchers have attempted to improve the solubility by coupling alkyl chains to the main structure, but this method usually reduces the material's mechanical properties, making it difficult to balance solubility and mechanical properties. Simultaneously, because these polymerized systems are black, defects such as foreign matter and bubbles are difficult to detect during polymerization and coating, increasing the difficulty of quality control. Summary of the Invention

[0014] In view of this, the present invention provides a black polyimide film and a method for preparing the same. The polymer obtained by the present invention has excellent solubility. Furthermore, after deprotection, the material exhibits uniform black color, excellent solvent resistance, and mechanical properties, resolving the contradiction between processability, solvent resistance, and mechanical properties. In addition, the polymerization system remains a traditional transparent amber solution, making it easy to observe and detect defects, thus effectively controlling product quality.

[0015] This invention provides a black polyimide film, wherein the polyimide has the structure shown in formula (L):

[0016]

[0017] in:

[0018] n, m1, m2, and For the range of choices, please refer to the previous text; for detailed explanations, please refer to the following text.

[0019] The present invention also provides a method for preparing the black polyimide film described in the above technical solution, comprising the following steps:

[0020] A) The dianhydride monomer, diamine monomer and solvent are mixed and polymerized to obtain a polyamic acid precursor solution;

[0021] B) Film Formation:

[0022] The polyamic acid precursor solution was cast into a film, dried, and heat-treated to obtain a black polyimide film.

[0023] or

[0024] The polyamic acid precursor solution is subjected to imidization treatment to obtain polyimide powder; then, the polyimide powder is dissolved in a solvent, cast into a film, dried, and deprotected to obtain a black polyimide film.

[0025] The types, amounts, and conditions of each substance are detailed below.

[0026] This invention provides a black polyimide film and its preparation method. The preparation method uses an aniline oligomer diamine as shown in formula (II), wherein each bridging nitrogen atom is coupled with a protecting group, such as benzylic acid carbonyl (Cbz) or tert-butoxy carbonyl (Boc). The above-mentioned diamine monomer is homopolymerized or copolymerized with a diamine monomer and a dianhydride monomer as shown in formula (III) to form a resin solution. Then, through a film-forming process, this solution can be made into a polyimide / polyamic acid film. Subsequently, the film is subjected to deprotection treatment to obtain an intrinsically black polyimide film with excellent performance. The introduction of protecting groups significantly improves the solubility of polyimide, enabling it to dissolve in low-boiling-point solvents such as tetrahydrofuran and chloroform, greatly improving the material's processing performance. After deprotection treatment, abundant hydrogen bonds are formed intramolecularly and intermolecularly, giving the material excellent mechanical properties and effectively resolving the contradiction between solubility and mechanical properties. Furthermore, the solution system and precursor film retain the traditional yellow and transparent properties of polyimide, facilitating process quality control. Only in the final step does it transform into a black film, resulting in a product exhibiting uniform black color, excellent solvent resistance, and superior mechanical properties. This invention cleverly resolves the contradiction between processing performance, solvent resistance, and mechanical properties, and has broader application prospects. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the reaction route of the preparation method of the present invention;

[0029] Figure 2 These are appearance diagrams of the black polyimide films obtained in various embodiments of the present invention;

[0030] Figure 3 Visible light absorption spectra of black polyimide films obtained in some embodiments of the present invention;

[0031] Figure 4Thermogravimetric diagrams of precursor resin powders PI-2 and PI-6;

[0032] Figure 5 Infrared images of the precursor films (PI-2 and PIF-2) before and after heat treatment in Example 2;

[0033] Figure 6 Infrared images of the precursor films (PI-6 and PIF-6) before and after heat treatment in Case 6. Detailed Implementation

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0035] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0036] The term “and / or” as used herein includes any and all combinations of one or more of the related listed items.

[0037] In this document, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0038] In this article, when referring to units for data ranges, if the unit is only followed by the right endpoint, it means that the units for the left and right endpoints are the same. For example, 50~100℃ means that the units for the left endpoint "50" and the right endpoint "100" are both in℃.

[0039] This invention provides a black polyimide film, wherein the polyimide has the structure shown in formula (L):

[0040]

[0041] in:

[0042] n can be 3 to 8, specifically 3, 4, 5, 6, 7, or 8;

[0043] The ratio of m2 / (m1+m2) is 0% to 90%; specifically, it can be 0% (i.e., m2=0), 10% (i.e., m2 / m1=1 / 9), 20% (i.e., m2 / m1=2 / 8), 30% (i.e., m2 / m1=3 / 7), 40% (i.e., m2 / m1=4 / 6), 50% (i.e., m2 / m1=5 / 5), 60% (i.e., m2 / m1=6 / 4), 70% (i.e., m2 / m1=7 / 3), 80% (i.e., m2 / m1=8 / 2), 90% (i.e., m2 / m1=9 / 1), and more preferably 70% to 90%; the value of m1 is not limited, and preferably 5 to 1000.

[0044] Selected from the structures shown in equations (Ⅰ-1') to (Ⅰ-11'):

[0045]

[0046] In formula (Ⅰ-3'), A is selected from the following groups:

[0047]

[0048] Selected from the structures shown in equations (Ⅲ-1') to (Ⅲ-12'):

[0049]

[0050] in,

[0051] R1 is selected from: H, F, CF3; n in formula (Ⅲ-1') is 1 to 4, specifically 1, 2, 3, 4; R2 is selected from: CF3, CH3;

[0052] Y is selected from: O, S, NH;

[0053] X is selected from the following groups:

[0054]

[0055] The present invention also provides a method for preparing the black polyimide film described in the above technical solution, comprising the following steps:

[0056] A) The dianhydride monomer, diamine monomer and solvent are mixed and polymerized to obtain a polyamic acid precursor solution;

[0057] B) Film Formation:

[0058] The polyamic acid precursor solution was cast into a film, dried, and heat-treated to obtain a black polyimide film.

[0059] or

[0060] The polyamic acid precursor solution is subjected to imidization treatment to obtain polyimide powder; then, the polyimide powder is dissolved in a solvent, cast into a film, dried, and deprotected to obtain a black polyimide film.

[0061] in:

[0062] The dianhydride monomer is selected from the compounds shown in formulas (I-1) to (I-11):

[0063]

[0064] In formula (Ⅰ-3), A is selected from the following groups:

[0065]

[0066] The diamine monomer is the diamine monomer shown in formula (II), or the diamine monomer shown in formula (II) and the diamine monomer shown in formula (III);

[0067]

[0068] In formula (II):

[0069] n is 3 to 8;

[0070] Selected from, but not limited to, the following groups:

[0071] The diamine monomer represented by formula (III) is selected from the compounds represented by formulas (III-1) to (III-12):

[0072]

[0073] in,

[0074] R1 is selected from: H, F, CF3; n in equation (Ⅲ-1) is 1 to 4;

[0075] R2 is selected from: CF3, CH3;

[0076] Y is selected from: O, S, NH;

[0077] X is selected from the following groups:

[0078]

[0079] The reaction route for the formation of polyimide from dianhydride monomers and diamine monomers is shown in the following equation:

[0080]

[0081] The reaction route of the preparation method of the present invention is as follows: Figure 1 As shown.

[0082] [Regarding step A]:

[0083] A) The dianhydride monomer, diamine monomer, and solvent are mixed and polymerized to obtain a polyamic acid precursor solution.

[0084] Regarding dianhydride monomers :

[0085] In this invention, the dianhydride monomer is selected from compounds of formulas (I-1) to (I-11):

[0086]

[0087] In formula (Ⅰ-3), A is selected from the following groups:

[0088]

[0089] The present invention does not impose any special restrictions on the source of the dianhydride monomer, which may be a commercially available product or prepared according to known methods in the art.

[0090] Regarding diamine monomers :

[0091] In this invention, the diamine monomer is the diamine monomer shown in formula (II), or the diamine monomer shown in formula (II) and the diamine monomer shown in formula (III).

[0092] Regarding the diamine monomer shown in formula (II):

[0093] In this invention, the diamine monomer represented by formula (II) is as follows:

[0094]

[0095] in:

[0096] n is 3 to 8, specifically 3, 4, 5, 7, 7, 8. When n = 3, the above monomer is aniline tetramer diamine; when n = 4, the above monomer is aniline pentamer diamine; when n = 5, the above monomer is aniline hexamer diamine; and so on.

[0097] Selected from, but not limited to, the following groups: (i.e., the Boc group) (i.e., the Cbz group).

[0098] when When the diamine monomer is a Boc group, taking n=4 as an example, the diamine monomer can be prepared by the following method:

[0099] S1. The compound shown in formula (1) reacts with p-phenylenediamine reactants to form the compound shown in formula (2);

[0100] The p-phenylenediamine reactants are p-phenylenediamine and / or p-phenylenediamine hydrochloride;

[0101] S2. The compound shown in formula (2) undergoes a Boc coupling reaction with ditert-butyl dicarbonate to form the compound shown in formula (3).

[0102] S3, the compound shown in formula (3) undergoes deprotection and hydrogenation reactions to obtain the diamine monomer shown in formula (II);

[0103]

[0104] Regarding step S1:

[0105] The reaction route for this step is as follows:

[0106]

[0107] In this invention, the compound shown in formula (1) is [(4-aminophenyl)(4-bromophenyl)amino]methane-2-methylpropyl-2-yl ester, and its source is not particularly limited, being a commercially available product or prepared according to known methods in the art.

[0108] In this invention, the p-phenylenediamine reactants are p-phenylenediamine and / or p-phenylenediamine hydrochloride, and their sources are not particularly limited, being commercially available products or prepared according to methods known in the art.

[0109] In this invention, the molar ratio of the compound shown in formula (1) to the p-phenylenediamine reactant is preferably (2.0 to 2.5):1, specifically 2.0:1, 2.05:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, and more preferably 2.05:1.

[0110] In this invention, the reaction is preferably carried out in the presence of a catalyst, a ligand, an alkaline substance, and a solvent medium.

[0111] The catalyst is preferably at least one of a ruthenium compound, a rhodium compound, and a palladium compound, more preferably a palladium compound. The palladium compound is preferably at least one of Pd(PPh3)4, Pd(OAc)2, PdCl2, PdCl2(dppf), PdCl2(PPh3)2, and Pd2(dba)3. In this invention, the molar ratio of the catalyst to the compound shown in formula (I) is preferably (0.0002–0.001):1, specifically 0.0002:1, 0.0003:1, 0.0004:1, 0.0005:1, 0.0006:1, 0.0007:1, 0.0008:1, 0.0009:1, or 0.001:1, more preferably (0.0005–0.001):1.

[0112] The ligand is preferably a phosphine-containing ligand, including but not limited to trimethylphosphine, triethylphosphine, tripropylphosphine, triisopropylphosphine, tributylphosphine, tricyclohexylphosphine, triphenylphosphine, triisopropylphosphine, bis(2-diphenylphosphine) ether (DPEPhos), 1,1′-binaphthyl-2,2′-bisdiphenylphosphine (BINAP), 2-dicyclohexylphosphine-2′,4′,6′-triisopropylbiphenyl (X-Phos), 4,5-bisdiphenylphosphine-9,9-dimethyloxanthracene (XANTPhos), 2-(dicyclohexylphosphine)-3,6-dimethoxy-2′,4′,6′-tri-1-propyl-11′-biphenyl (BrettPhos), 2-dicyclohexylphosphine-2′,6′-diisopropoxy-1,1′-biphenyl (RuPhos), 2-di-tert-butylphosphine-2′,4′,6′- At least one of the following: triisopropylbiphenyl (tBuXPhos), 2-(di-tert-butylphosphine)-3,6-dimethoxy-2′,4′,6′tri-1-propyl-1,1′-bisphenyl (tBuBrettPhos), 1,1′-bis(diphenylphosphine)ferrocene (Dppf), (R)-(-)-1-[(S)-2-(dicyclohexylphosphine)ferrocene]ethyldi-tert-butylphosphine (CyPFt-Bu), 5-di-tert-butylphosphine-1′,3′,5′-triphenyl-1′H-[1,4′]dipyrazole (BippyPhos), and N-[2-di(1-adamantane)phosphophenyl]morpholine (Mor-DalPhos), more preferably at least one of DPEPhos, BINAP, X-Phos, XANTPhos, and BrettPhos. In this invention, the molar ratio of the ligand to the catalyst is preferably (1-10):1, more preferably (1-4):1.

[0113] The alkaline substance comprises at least one of a metal compound, an organic base, an inorganic base, and an inorganic salt, preferably at least one of sodium tert-butoxide, potassium tert-butoxide, sodium amino, lithium diisopropylamino, sodium bis(trimethylsilyl)amino, lithium bistrimethylsilylamino, 4-dimethylaminopyridine, triethylamine, KOH, NaOH, K2CO3, Na2CO3, and Cs2CO3, more preferably at least one of sodium tert-butoxide, potassium tert-butoxide, and Cs2CO3. In this invention, the molar ratio of the alkaline substance to the compound shown in formula (1) is preferably (1.5–10):1, specifically 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

[0114] The reaction is preferably carried out in a solvent medium. The solvent is preferably an organic solvent, or a mixture of an organic solvent and water. The organic solvent is preferably an oxygen-removing organic solvent, and is preferably at least one of dichloromethane, trichloromethane, tetrahydrofuran, dioxane, toluene, and benzene. In this invention, the solvent is more preferably at least one of tetrahydrofuran, dioxane, toluene, a dioxane-water mixture, or a toluene-water mixture. In this invention, the volume ratio of the organic solvent to water in the mixed solvent is preferably (5-20):1. In this invention, the mass of the solvent is preferably 5-20 times the mass of the compound shown in formula (1), more preferably 10-15 times.

[0115] In this invention, the reaction is preferably carried out under a protective atmosphere, more preferably under a nitrogen atmosphere and / or an argon atmosphere.

[0116] In this invention, the reaction temperature is preferably 50–100°C, specifically 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, and 100°C, more preferably 60–80°C. In this invention, the reaction time is preferably 6–10 hours. In this invention, the reaction is preferably accompanied by stirring. Based on the Buchwald-Hartwig cross-coupling reaction, the compound shown in formula (1) reacts with p-phenylenediamine reactants to form the aniline pentamer shown in formula (2). In the structure shown in formula (2), the Ph- group is a conventional abbreviation in the art, representing phenyl.

[0117] In this invention, preferably, step S1 specifically includes: mixing the compound shown in formula (1), p-phenylenediamine reactants, catalyst, ligand, basic substance and solvent under a protective atmosphere, and heating to react and form the compound shown in formula (2).

[0118] In this invention, after the reaction is completed, the following post-processing is preferably performed: solid-liquid separation, washing, and drying. The solid-liquid separation is preferably performed by filtration. The washing involves rinsing the precipitate with an organic solvent, which can be done while filtration is being performed, or by centrifugation. The organic solvent is preferably the solvent used in the reaction. The drying is preferably performed under vacuum. The drying temperature is preferably 80–100°C; the drying time is preferably 5–12 hours. After the above post-processing, the aniline pentamer solid product shown in formula (2) is obtained.

[0119] Regarding step S2:

[0120] The reaction route for this step is as follows:

[0121]

[0122] In this invention, the source of the di-tert-butyl dicarbonate (abbreviated as DIBOC, chemical formula abbreviation (Boc)2O) is not particularly limited, and it can be a commercially available product or prepared according to known preparation methods in the art.

[0123] In this invention, the molar ratio of the compound shown in formula (II) to ditert-butyl dicarbonate is preferably 1:(3-6), specifically 1:3, 1:4, 1:5, 1:6, and more preferably 1:(4-5).

[0124] In this invention, the reaction is preferably carried out in the presence of an alkaline substance and a solvent medium.

[0125] The alkaline substance includes at least one of a metal compound, an organic base, an inorganic base, and an inorganic salt, preferably at least one of sodium tert-butoxide, potassium tert-butoxide, sodium amino, lithium diisopropylamino, sodium bis(trimethylsilyl)amino, lithium bistrimethylsilylamino, 4-dimethylaminopyridine, triethylamine, KOH, NaOH, K2CO3, Na2CO3, and Cs2CO3, more preferably 4-dimethylaminopyridine. In this invention, the molar ratio of the alkaline substance to the compound shown in formula (2) is preferably (0.05~5):1, specifically 0.05:1, 0.1:1, 0.25:1, 0.5:1, 0.75:1, 1:1, 2:1, 3:1, 4:1, or 5:1.

[0126] The solvent is preferably an organic solvent, more preferably at least one selected from dichloromethane, chloroform, tetrahydrofuran, dioxane, acetone, butanone, toluene, ethyl acetate, xylene, methanol, ethanol, and diethyl ether, and even more preferably at least one selected from chloroform and tetrahydrofuran. In this invention, the amount of the solvent is preferably 3 to 10 times the mass of the compound shown in formula (2).

[0127] In this invention, the reaction temperature is preferably 40–100°C, specifically 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C; more preferably, 60–70°C, which is also a milder temperature condition. The reaction time is preferably 4–12 hours. The compound shown in formula (II) undergoes a Boc coupling reaction with di-tert-butyl dicarbonate to obtain the aniline pentamer-Boc shown in formula (3).

[0128] In this invention, preferably, step S2 specifically includes: mixing the compound shown in formula (2), di-tert-butyl dicarbonate, an alkaline substance and a solvent, and refluxing the reaction to form the compound shown in formula (3).

[0129] In this invention, after the above reaction is completed, the following post-processing is preferably performed: solid-liquid separation, washing, and drying. The solid-liquid separation is preferably performed by filtration. The washing is performed by rinsing with an organic solvent; the organic solvent is preferably ethanol. The drying is preferably performed by vacuum drying. The drying temperature is preferably 80–100°C; the drying time is preferably 5–12 hours. After the above post-processing, the aniline pentamer-Boc solid product shown in formula (3) is obtained.

[0130] Regarding step S3:

[0131] The reaction route for this step is as follows:

[0132]

[0133] In this invention, the Ph2CN- groups at both ends of the compound of formula (3) are deprotected and hydrogenated to obtain the diamine monomer shown in formula (II).

[0134] In this invention, the reaction in step S3 is preferably carried out in the presence of a hydrogen source reagent, an alkaline substance, and a solvent medium.

[0135] The hydrogen source reagent includes, but is not limited to, H2, hydroxylamine hydrochloride, ammonium formate, sodium borohydride, etc., and is preferably at least one of H2, hydroxylamine hydrochloride, and ammonium formate. In this invention, the molar ratio of the hydrogen source reagent to the compound shown in formula (3) is preferably (3-10):1, more preferably (3-5):1.

[0136] In this invention, when hydroxylamine hydrochloride is used as the hydrogen source reagent, the reaction in step C) can be carried out in the presence of an alkaline substance. The alkaline substance includes at least one of an organic base and an inorganic base, preferably at least one of sodium acetate, dimethylaminopyridine, triethylamine, pyridine, KOH, and NaOH, more preferably pyridine and triethylamine. When the alkaline substance is pyridine and triethylamine, the molar ratio of pyridine to triethylamine is preferably 1:(2-5). In this invention, the molar ratio of the alkaline substance to the compound shown in formula (3) is preferably (10-20):1.

[0137] In this invention, when H2 and ammonium formate are used as hydrogen source reagents, the reaction in step C) can be carried out under the action of a catalyst. The catalyst is preferably at least one of a palladium-containing catalyst and a nickel-containing catalyst, more preferably at least one of a Pd / C catalyst and a Pd(OH)2 / C catalyst. In this invention, the molar ratio of the catalyst to the compound shown in formula (3) is preferably (0.05–0.2):1.

[0138] The solvent is preferably an organic solvent, more preferably at least one selected from dichloromethane, chloroform, tetrahydrofuran, dioxane, acetone, butanone, toluene, ethyl acetate, xylene, methanol, ethanol, and diethyl ether, and even more preferably at least one selected from dichloromethane, chloroform, and tetrahydrofuran. In this invention, the amount of the solvent is preferably 5 to 20 times the mass of the compound shown in formula (3).

[0139] In this invention, the reaction temperature is preferably room temperature to the solvent boiling point, more preferably 20 to 50°C, meaning the reaction can occur at room temperature / room temperature. The reaction time is preferably 1 to 6 hours. After the reaction, the aniline pentameric diamine monomer of formula (II) is formed.

[0140] In this invention, preferably, step S3 specifically includes: mixing the compound shown in formula (3), the hydrogen source reagent, the alkaline substance / catalyst, and the solvent, and carrying out a deprotection and hydrogenation reaction to form the diamine monomer shown in formula (II).

[0141] In this invention, when hydroxylamine hydrochloride is used as the hydrogen source reagent, after the above reaction is completed, the resulting reaction solution is preferably subjected to the following post-treatment: solid-liquid separation, washing, and drying. The solid-liquid separation is preferably performed by filtration or centrifugation. The washing is performed by rinsing with an organic solvent; the organic solvent includes, but is not limited to, at least one of dichloromethane, chloroform, tetrahydrofuran, dioxane, acetone, butanone, toluene, ethyl acetate, xylene, methanol, ethanol, and diethyl ether, more preferably at least one of dichloromethane, chloroform, and tetrahydrofuran. The drying is preferably vacuum drying. The drying temperature is preferably 80–100°C; the drying time is preferably 5–12 hours. After the above post-treatment, the solid product of the aniline pentameric diamine monomer shown in formula (II) is obtained.

[0142] In this invention, when H2 and ammonium formate are used as hydrogen source reagents, after the above reaction is completed, the resulting reaction solution is preferably subjected to the following post-treatment: solid-liquid separation, washing, extraction, and drying. The solid-liquid separation is preferably performed by filtration or centrifugation. The washing is performed by rinsing with an organic solvent; the organic solvent includes, but is not limited to, at least one of dichloromethane, chloroform, tetrahydrofuran, dioxane, acetone, butanone, toluene, ethyl acetate, xylene, methanol, ethanol, and diethyl ether, more preferably at least one of dichloromethane, chloroform, and tetrahydrofuran. The extraction is performed using, but is not limited to, a Soxhlet extractor. Specifically, the obtained solid is placed in the extractor, and an organic solvent such as dichloromethane, chloroform, or tetrahydrofuran is used for reflux extraction. The resulting extract is further concentrated to a solid state using a rotary evaporator. Drying is preferably vacuum drying. The drying temperature is preferably 80–100°C; the drying time is preferably 5–12 hours. After the above post-treatment, the aniline pentameric diamine monomer solid product shown in formula (II) is obtained.

[0143] when When n is a Boc group, and n takes other values, the preparation method described above for n=4 can be followed.

[0144] when When it is a Cbz group, refer to The preparation method for the diamine monomer with the Boc group is the same, the main difference being the reaction conditions when coupling the Cbz group. The conditions are as follows: At 0–10°C, a certain amount of saturated sodium bicarbonate aqueous solution is added to the organic solution of the compound to which the Cbz group is to be added, followed by the addition of benzyl chloroformate. The reaction mixture is stirred at 0–10°C for 0.5–1 hour, then heated to 25°C and stirred further at 25°C for 0.5–1 hour. The reaction is quenched with water, and then extracted with ethyl acetate. The combined organic extracts are dried over anhydrous sodium sulfate, filtered, and concentrated under reduced pressure to obtain the target product. Preferably, the molar ratio of the compound to which the Cbz group is to be added to benzyl chloroformate is 1:1–2. The molar ratio of the compound to which the Cbz group is to be added to sodium bicarbonate is 1:1–2. The organic solvent is preferably a commonly used reagent such as tetrahydrofuran, toluene, or ethyl acetate.

[0145] Regarding the diamine monomer shown in formula (Ⅲ):

[0146] In this invention, the diamine monomer represented by formula (III) is selected from compounds represented by formulas (III-1) to (III-12):

[0147]

[0148] in,

[0149] R1 is selected from: H, F, CF3; n in equation (Ⅲ-1) is 1 to 4, specifically 1, 2, 3, 4;

[0150] R2 is selected from: CF3, CH3;

[0151] Y is selected from: O, S, NH;

[0152] X is selected from the following groups:

[0153]

[0154] The present invention does not impose any special restrictions on the source of the diamine monomer shown in formula (III), which can be a commercially available product or prepared according to known preparation methods in the art.

[0155] In this invention, the molar ratio of the diamine monomer shown in formula (II) to the diamine monomer shown in formula (III) is preferably 10:0 to 1:9, specifically 10:0, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9, and more preferably 1:9 to 3:7.

[0156] In this invention, the molar ratio of the diamine monomer to the dianhydride monomer is preferably 1:(0.95-1.05), specifically 1:0.95, 1:0.96, 1:0.97, 1:0.98, 1:0.99, 1:1.00, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, and more preferably 1:(0.98-1.02).

[0157] In this invention, the solvent is preferably an organic solvent, more preferably including at least one selected from N,N'-dimethylformamide (DMF), N,N'-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), m-cresol (m-Cresol), dichloromethane (DCM), chloroform (CF), tetrahydrofuran (THF), dioxane (DX), acetone (ACE), butanone (MEK), toluene (TOL), ethyl acetate (EA), xylene (Xylene), and diethyl ether (EE), and even more preferably at least one selected from DCM, CF, DMF, DMAc, DMSO, and NMP. In this invention, the amount of solvent used is preferably such that the system concentration is 5wt% to 40wt%, specifically 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, and 40wt%.

[0158] In this invention, the preferred temperature for the polymerization reaction is -20 to 40°C, specifically -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, and 40°C. The preferred reaction time is 1 to 70 hours, specifically 1 hour, 10 hours, 20 hours, 30 hours, 40 hours, 50 hours, 60 hours, and 70 hours.

[0159] In this invention, the atmosphere for the polymerization reaction is air or an inert atmosphere. There are no particular limitations on the type of inert atmosphere; any conventional inert atmosphere in the art, such as nitrogen or argon, is acceptable.

[0160] Step A) The dianhydride monomer and the diamine monomer are polymerized in a solvent to obtain a polyamic acid precursor solution.

[0161] [Regarding step B]:

[0162] B) Film Formation:

[0163] In this invention, after obtaining the polyamic acid precursor solution in step A), a film is formed. The film can be formed in two ways: firstly, the polyamic acid precursor solution is cast into a film, dried, and heat-treated to obtain a black polyimide film; secondly, the polyamic acid precursor solution is imidized to obtain polyimide powder; then, the polyimide powder is dissolved in a solvent, cast into a film, dried, and deprotected to obtain a black polyimide film.

[0164] Regarding the first film-forming method:

[0165] In this invention, the film casting is performed by direct film casting or by biaxial stretching after casting. There are no particular limitations on the casting and biaxial stretching methods; any conventional casting and biaxial stretching methods known to those skilled in the art can be used.

[0166] In this invention, after the film is cast, it is dried. The drying temperature is preferably between room temperature and 160°C, and can be selected within this range depending on the type of solvent, but must not exceed the boiling point of the solvent. After drying, a polyamic acid precursor film is obtained.

[0167] In this invention, after drying to obtain a polyamic acid precursor film, a heat treatment is performed. This heat treatment comprises two steps: deprotection treatment and thermal imidization treatment.

[0168] in:

[0169] The preferred temperature for the deprotection treatment is 140–250°C, specifically 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C; the temperature can be programmed or fixed. The preferred treatment time is 4–12 hours, specifically 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours. The preferred atmosphere for the deprotection treatment is a vacuum atmosphere or an inert atmosphere; the inert atmosphere is not particularly limited, such as a nitrogen atmosphere or an argon atmosphere.

[0170] The preferred temperature for the thermal imidization treatment is 150–350°C, specifically 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, and 350°C. The preferred treatment time is 5–90 minutes, specifically 5 minutes, 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, and 90 minutes. The atmosphere for the thermal imidization treatment can be air, vacuum, or an inert atmosphere; the inert atmosphere is not particularly limited, such as a nitrogen atmosphere or an argon atmosphere. After the above two heat treatment steps, a black polyimide film is obtained.

[0171] Regarding the second film-forming method:

[0172] In this invention, the polyamic acid precursor solution is first subjected to imidization treatment. Preferably, the imidization treatment is a chemical imidization treatment; the process preferably includes: mixing the polyamic acid precursor solution with an imidizing agent, then precipitating the precipitate in a poor solvent, performing solid-liquid separation, and drying to obtain polyimide powder.

[0173] in:

[0174] The imidizing agent is preferably a nitrogen-containing compound and acetic anhydride; wherein the nitrogen-containing compound is preferably at least one of triethylamine, pyridine, and methylpyridine. The molar ratio of the nitrogen-containing compound to the diamine monomer used in step A) is preferably (0.5–3.5):1, specifically 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, or 3.5:1. The molar ratio of the acetic anhydride to the diamine monomer used in step A) is preferably (0.5–5.5):1, specifically 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, or 5.5:1.

[0175] The mixing process is preferably agitated. The stirring speed is preferably 300-1000 rpm, specifically 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, or 1000 rpm; the stirring time is preferably 0.5-36 h, specifically 0.5 h, 1 h, 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, or 36 h.

[0176] After mixing, a poor solvent is added to precipitate the precipitate. The poor solvent includes, but is not limited to, at least one selected from water, methanol, ethanol, and ethylene glycol. Preferably, the water is deionized water. After precipitation, solid-liquid separation is performed. The method of solid-liquid separation is not particularly limited and can be any conventional method in the art, such as filtration. After solid-liquid separation, rinsing is preferably performed; the rinsing is preferably performed using the same poor solvent used for precipitation. After rinsing, drying is performed. After drying, polyimide powder is obtained.

[0177] In this invention, after obtaining polyimide powder, it is dissolved in a solvent to form a solution. The solvent is preferably an organic solvent, more preferably at least one selected from DMF, DMAc, DMSO, NMP, m-Cresol, DCM, CF, THF, DX, ACE, MEK, TOL, EA, Xylene, and EE, and most preferably at least one selected from DCM, CF, DMF, DMAc, DMSO, and NMP. The amount of solvent used is preferably such that the solid content of the resulting solution is 10% to 40%, specifically 10%, 15%, 20%, 25%, 30%, or 35%.

[0178] In this invention, after dissolving polyimide powder in a solvent to form a solution, a film is cast. The film casting can be direct casting or biaxial stretching after casting. There are no particular limitations on the casting and biaxial stretching methods; any conventional casting and biaxial stretching methods known to those skilled in the art can be used.

[0179] In this invention, after the film is cast, it is dried. The drying temperature is preferably between room temperature and 160°C, and can be selected within this range depending on the type of solvent, but must not exceed the boiling point of the solvent. After drying, a polyimide precursor film is obtained.

[0180] In this invention, after drying to obtain the polyimide precursor film, only a one-step deprotection treatment is required. The deprotection treatment can be carried out using a chemical method or a thermal treatment method, preferably a thermal treatment method.

[0181] The chemical method involves immersing the precursor film in a solution containing a deprotection agent, treating it at a specific temperature, followed by washing and drying to obtain the target product. The solution containing the deprotection agent includes acidic solutions, alkaline solutions, or solutions containing a catalyst. Acidic solutions include solutions of hydrochloric acid, sulfuric acid, or trifluoroacetic acid. Alkaline solutions include solutions of alkaline substances such as sodium hydroxide, potassium hydroxide, or potassium carbonate. The catalyst in the catalyst-containing solution includes platinum catalysts and palladium catalysts. The specific temperature is preferably room temperature to the solvent boiling point; the heating method is not limited, such as electric heating or microwave heating. The treatment time is preferably 30 min to 12 h, more preferably 1 to 5 h. The solvent used for washing includes, but is not limited to, deionized water (H2O), DMF, DMAc, DMSO, NMP, m-Cresol, DCM, CF, THF, DX, ACE, MEK, TOL, EA, Xylene, EE, methanol (MeOH), or ethanol (Ethanol), preferably at least one of H2O, MeOH, and Ethanol.

[0182] The heat treatment method involves heat-treating the precursor film at a specific temperature and atmosphere for a certain period of time. The preferred heat treatment temperature is 140–250°C, specifically 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C; the temperature can be programmed or fixed. The preferred heat treatment time is 4–12 hours, specifically 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours. The preferred heat treatment atmosphere is a vacuum atmosphere or an inert atmosphere; the inert atmosphere is not particularly limited, such as a nitrogen atmosphere or an argon atmosphere. After the above treatment, a black polyimide film is obtained.

[0183] In the preparation method provided by this invention, an aniline oligomer diamine of formula (II) is used, wherein each bridging nitrogen atom is coupled with a protecting group, such as benzylic acid carbonyl (Cbz) or tert-butoxy carbonyl (Boc). The above-mentioned diamine monomer is homopolymerized or copolymerized with the diamine monomer and dianhydride monomer of formula (III) to form a resin solution. Then, through a film-forming process, the solution can be made into a polyimide / polyamic acid film. Subsequently, the film is subjected to deprotection treatment to obtain an intrinsically black polyimide film with excellent performance. The introduction of protecting groups significantly improves the solubility of polyimide, enabling it to dissolve in low-boiling-point solvents such as tetrahydrofuran and chloroform, greatly improving the processing performance of the material. After deprotection treatment, abundant hydrogen bonds are formed intramolecularly and intermolecularly, giving the material excellent mechanical properties and effectively solving the contradiction between solubility and mechanical properties. In addition, the solution system and the precursor film still retain the traditional yellow and transparent characteristics of polyimide, which facilitates process quality control. Only in the final step is it transformed into a black film.

[0184] This invention belongs to the intrinsic method, which features stable color and excellent overall performance, making it a relatively ideal preparation method. The principle behind the intrinsic black color of the polyimide film prepared by this invention is as follows: after the decomposition of the protecting groups in the molecular chain, the main chain transforms into reduced polyaniline segments; these segments are further oxidized to form oxidized polyaniline segments. Due to the wide absorption range of the polyaniline structure with its large conjugation characteristics in the visible light region, the material is endowed with excellent visible light absorption capabilities, thus exhibiting intrinsic black properties.

[0185] Traditional polyimide films, due to the abundance of aromatic rings within the polyimide molecule and the resulting charge transfer between molecules, exhibit strong absorption characteristics in the visible light region, typically appearing golden yellow or dark brown. This single color greatly limits their application scenarios and scope. This invention, however, develops a method for preparing intrinsically black polyimide films. This method effectively overcomes the problem of insufficient absorption capacity in the visible light region of existing polyimide films, fully meeting the stringent technical requirements for optical performance in special fields such as light shielding and security.

[0186] Compared with the prior art, the present invention has the following beneficial effects:

[0187] In the preparation process of this invention, a large number of solubilizing groups are cleverly introduced, successfully solving the problems of poor solubility and poor processing performance of traditional intrinsic black polyimide films, and significantly improving the operability of the film during processing. Particularly noteworthy is that this invention innovatively proposes a deprotecting group coloring process, enabling the prepared black polyimide film to possess excellent mechanical properties and solvent resistance, thereby further broadening its application possibilities in various fields. Furthermore, based on the unique intrinsic characteristics of intrinsic black polyimide films, black color can be achieved without the addition of color fillers, fundamentally avoiding the adverse effects of color fillers on the overall performance of dyed black films. Simultaneously, it also avoids the cracking phenomenon that occurs in composite films under extreme environments such as high temperature and high frequency due to adhesive failure and mismatch of thermal expansion coefficients, thus affecting their functionality and service life.

[0188] In addition to the aforementioned black polyimide film, any equivalent substitutions or modifications made to the technical solution and inventive concept of this invention, including materials such as fibers, profiles, composites, and foams, should be covered within the scope of protection of this invention.

[0189] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0190] Example 1

[0191] A) Boc-protected aniline pentameric diamine (i.e., the diamine monomer shown in formula (II), n=4, PG group is Boc; 0.02mol, 17.46g) and 4,4'-terephthalodioxydiphthalic anhydride, i.e. 4,4'-HQDPA (i.e., the dianhydride monomer shown in formula (I-3); 0.02mol, 8.05g) were added to N,N'-dimethylacetamide (154mL) and stirred at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0192] B) Add the imidizing agent triethylamine (0.042 mol, 4.24 g) and acetic anhydride (0.05 mol, 5.10 g) to the above polyamic acid solution, stir at room temperature for 5 h, then precipitate in ethanol, pulverize, filter, wash, and dry to obtain white polyimide powder PI-1 (23.55 g, yield 95%). Take 10 g of the above powder and dissolve it in 40 g of chloroform to obtain a solution with a solid content of 20%; cast the solution onto a glass substrate, level it with a scraper, and dry it at 50 °C for 5 h. Then, place the entire substrate in a 3 mol / L sulfuric acid solution, soak it at 50 °C for 5 h, wash it with deionized water, and dry it at 100 °C for 30 min to obtain a black polyimide film PIF-1 (thickness δ = 41 μm).

[0193] Example 2

[0194] A) Add Boc-protected aniline pentameric diamine (i.e., the diamine monomer shown in formula (II), n=4, PG group is Boc; 0.02mol, 17.46g) and hexafluorodianhydride, i.e. 6FDA (i.e., the dianhydride monomer shown in formula (I-3); 0.02mol, 8.88g) to N,N'-dimethylacetamide (159mL), stir at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0195] B) Add the imidizing agent triethylamine (0.042 mol, 4.24 g) and acetic anhydride (0.05 mol, 5.10 g) to the above polyamic acid solution, stir at room temperature for 5 h, then precipitate in ethanol, pulverize, filter, wash with ethanol, and dry to obtain white polyimide powder PI-2 (24.08 g, yield 94%). Take 10 g of the above powder and dissolve it in 40 g of N,N'-dimethylacetamide to obtain a solution with a solid content of 20%; cast the solution onto a glass substrate, level it with a scraper, and dry it at 120 °C for 5 h. Then, place the entire substrate in a high-temperature oven under vacuum conditions and maintain the temperature at 230 °C for 4 h to obtain a black polyimide film PIF-2 (thickness δ = 33 μm).

[0196] Example 3

[0197] A) Add Boc-protected aniline pentameric diamine (i.e., the diamine monomer shown in formula (II), n=4, PG group is Boc; 0.02mol, 17.46g) and pyromellitic dianhydride, i.e. PMDA (i.e., the dianhydride monomer shown in formula (I-1); 0.02mol, 4.36g) to N,N'-dimethylacetamide (120mL), stir at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0198] B) The above polyamic acid solution was cast onto a glass substrate and leveled with a scraper. It was dried at 120°C for 5 hours. Then, the entire substrate was placed in a high-temperature oven under vacuum conditions and kept at 230°C for 4 hours. After that, it was kept at 300°C for 1 hour to obtain a black polyimide film PIF-3 (thickness δ=35μm).

[0199] Example 4

[0200] A) Add Boc-protected aniline pentameric diamine (i.e., the diamine monomer shown in formula (II), n=4, PG group is Boc; 0.02mol, 17.46g) and ketone anhydride, i.e. BTDA (i.e., the dianhydride monomer shown in formula (I-3); 0.02mol, 6.45g), to N,N'-dimethylacetamide (130mL), stir at room temperature for 24h, and obtain a pale yellow viscous polyamic acid solution.

[0201] B) The above polyamic acid solution was cast onto a glass substrate and leveled with a scraper. It was dried at 120°C for 5 hours. Then, the entire substrate was placed in a high-temperature oven under vacuum conditions and kept at 230°C for 4 hours. After that, it was kept at 300°C for 1 hour to obtain a black polyimide film PIF-4 (thickness δ=21μm).

[0202] Example 5

[0203] A) Boc-protected aniline heptameric diamine (i.e., the diamine monomer shown in formula (II), n=6, PG group is Boc; 0.02mol, 25.11g) and 4,4'-terephthalodioxydiphthalic anhydride, i.e. 4,4'-HQDPA (i.e., the dianhydride monomer shown in formula (I-3); 0.02mol, 8.05g) were added to N,N'-dimethylacetamide (180mL) and stirred at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0204] B) Add the imidizing agent triethylamine (0.042 mol, 4.24 g) and acetic anhydride (0.05 mol, 5.10 g) to the above polyamic acid solution, stir at room temperature for 5 h, then precipitate in ethanol, pulverize, filter, wash with ethanol, and dry to obtain white polyimide powder PI-5 (30.42 g, yield 94%). Take 10 g of the above powder and dissolve it in 40 g of chloroform to obtain a solution with a solid content of 20%; cast the solution onto a glass substrate, level it with a scraper, and dry it at 50 °C for 5 h. Then, place the entire substrate in a 3 mol / L sulfuric acid solution, soak it at 50 °C for 5 h, wash it with deionized water, and dry it at 100 °C for 30 min to obtain a black polyimide film PIF-5 (thickness δ = 32 μm).

[0205] Example 6

[0206] A) Boc-protected aniline heptameric diamine (i.e., the diamine monomer shown in formula (II), n=6, PG group is Boc; 0.02mol, 25.11g) and hexafluorodianhydride, i.e. 6FDA (i.e., the dianhydride monomer shown in formula (I-3); 0.02mol, 8.88g) were added to N,N'-dimethylacetamide (190mL) and stirred at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0207] B) Add the imidizing agent triethylamine (0.042 mol, 4.24 g) and acetic anhydride (0.05 mol, 5.10 g) to the above polyamic acid solution, stir at room temperature for 5 h, then precipitate in ethanol, pulverize, filter, wash with ethanol, and dry to obtain white polyimide powder PI-6 (30.66 g, yield 93%). Take 10 g of the above powder and dissolve it in 40 g of N,N'-dimethylacetamide to obtain a solution with a solid content of 20%; cast the solution onto a glass substrate, level it with a scraper, and dry it at 120 °C for 5 h. Then, place the entire substrate in a high-temperature oven under vacuum conditions and maintain the temperature at 230 °C for 4 h to obtain a black polyimide film PIF-6 (thickness δ = 25 μm).

[0208] Example 7

[0209] A) Boc-protected aniline heptameric diamine (i.e., the diamine monomer shown in formula (II), n=6, PG group is Boc; 0.02mol, 25.11g) and pyromellitic dianhydride, i.e. PMDA (i.e., the dianhydride monomer shown in formula (I-1); 0.02mol, 4.36g), were added to N,N'-dimethylacetamide (120mL) and stirred at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0210] B) The above polyamic acid solution was cast onto a glass substrate and leveled with a scraper. It was dried at 120°C for 5 hours. Then, the entire substrate was placed in a high-temperature oven under vacuum conditions and kept at 230°C for 4 hours. After that, it was kept at 300°C for 1 hour to obtain a black polyimide film PIF-7 (thickness δ=28μm).

[0211] Example 8

[0212] A) Boc-protected aniline heptameric diamine (i.e., the diamine monomer shown in formula (II), n=6, PG group is Boc; 0.02mol, 25.11g) and ketone anhydride i.e. BTDA (i.e., the dianhydride monomer shown in formula (I-3); 0.02mol, 6.45g) were added to N,N'-dimethylacetamide (130mL) and stirred at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0213] B) The above polyamic acid solution was cast onto a glass substrate and leveled with a scraper. It was dried at 120°C for 5 hours. Then, the entire substrate was placed in a high-temperature oven under vacuum conditions and kept at 230°C for 4 hours. After that, it was kept at 300°C for 1 hour to obtain a black polyimide film PIF-8 (thickness δ=29μm).

[0214] Example 9

[0215] A) Cbz-protected aniline tetramer diamine (i.e., the diamine monomer shown in formula (II), n=3, PG group is Cbz; 0.02mol, 13.64g) and 4,4'-terephthalodioxydiphthalic anhydride, i.e. 4,4'-HQDPA (i.e., the dianhydride monomer shown in formula (I-3); 0.02mol, 8.05g) were added to N,N'-dimethylacetamide (154mL) and stirred at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0216] B) Add the imidizing agent triethylamine (0.042 mol, 4.24 g) and acetic anhydride (0.05 mol, 5.10 g) to the above polyamic acid solution, stir at room temperature for 5 h, then precipitate in ethanol, pulverize, filter, wash, and dry to obtain white polyimide powder PI-9 (21.61 g, yield 96%). Take 10 g of the above powder and dissolve it in 40 g of N,N'-dimethylacetamide to obtain a solution with a solid content of 15%; cast the solution onto a glass substrate, level it with a scraper, and dry it at 50 °C for 5 h. Then, place the entire substrate in a 3 mol / L hydrobromic acid solution, soak it at 50 °C for 5 h, wash it with deionized water, and dry it at 100 °C for 30 min to obtain a black polyimide film PIF-9 (thickness δ = 23 μm).

[0217] Example 10

[0218] A) The Cbz-protected aniline hexameric diamine (i.e., the diamine monomer shown in formula (II), n=5, PG group is Cbz; 0.02mol, 21.28g) and the ketone anhydride, i.e. BTDA (i.e., the dianhydride monomer shown in formula (I-3); 0.02mol, 6.45g), were added to N,N'-dimethylacetamide (170mL) and stirred at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0219] B) The above polyamic acid solution was cast onto a glass substrate and leveled with a scraper. It was dried at 120°C for 5 hours. Then, the entire substrate was placed in a high-temperature oven under vacuum conditions and kept at 230°C for 4 hours. After that, it was kept at 300°C for 1 hour to obtain a black polyimide film PIF-10 (thickness δ=34μm).

[0220] Example 11

[0221] A) Boc-protected aniline heptameric diamine (i.e., the diamine monomer shown in formula (II), n=6, PG group is Boc; 0.002mol, 2.511g), 4,4'-diaminodiphenyl ether (i.e., the diamine monomer shown in formula (III-3); 0.018mol, 3.60g) and hexafluorodianhydride, i.e. 6FDA (i.e., the dianhydride monomer shown in formula (I-3); 0.02mol, 8.88g), were added to N,N'-dimethylacetamide (85mL) and stirred at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0222] B) Add the imidizing agent triethylamine (0.042 mol, 4.24 g) and acetic anhydride (0.05 mol, 5.10 g) to the above polyamic acid solution, stir at room temperature for 5 h, then precipitate in ethanol, pulverize, filter, wash with ethanol, and dry to obtain white polyimide powder PI-11 (10.62 g, yield 93.6%). Dissolve 6 g of the above powder in 40 g of N,N'-dimethylacetamide to obtain a solution with a solid content of 15%; cast the solution onto a glass substrate, level it with a scraper, and dry at 120 °C for 5 h. Then, place the entire substrate in a high-temperature oven under vacuum conditions and maintain the temperature at 230 °C for 4 h to obtain a black polyimide film PIF-11 (thickness δ = 17 μm).

[0223] Example 12

[0224] A) Boc-protected aniline pentameric diamine (i.e., the diamine monomer shown in formula (II), n=4, PG group is Boc; 0.01mol, 8.73g), p-phenylenediamine (i.e., the diamine monomer shown in formula (III-1); 0.01mol, 1.08g) and hexafluorodianhydride, i.e. 6FDA (i.e., the dianhydride monomer shown in formula (I-3); 0.02mol, 8.88g), were added to N,N'-dimethylacetamide (106mL) and stirred at room temperature for 24h to obtain a pale yellow viscous polyamic acid solution.

[0225] B) The above polyamic acid solution was cast onto a glass substrate and leveled with a scraper. It was dried at 120°C for 5 hours. Then, the entire substrate was placed in a high-temperature oven under vacuum conditions and kept at 230°C for 4 hours. After that, it was kept at 300°C for 1 hour to obtain a black polyimide film PIF-12 (thickness δ=18μm).

[0226] Product Testing :

[0227] (1) Mechanical property testing

[0228] The tensile properties of the black polyimide films obtained in each embodiment were tested, and the results are shown in Table 1.

[0229] Table 1: Tensile properties of the black polyimide films obtained in each example

[0230] sample Tensile strength (MPa) Tensile modulus (GPa) Example 1 (PIF-1) 139.6 2.86 Example 2 (PIF-2) 107.2 2.52 Example 3 (PIF-3) 111.4 2.84 Example 4 (PIF-4) 125.6 2.76 Example 5 (PIF-5) 108.4 2.65 Example 6 (PIF-6) 103.1 2.63 Example 7 (PIF-7) 99.6 2.53 Example 8 (PIF-8) 108.5 2.58 Example 9 (PIF-9) 134.6 2.94 Example 10 (PIF-10) 121.3 2.77 Example 11 (PIF-11) 105.6 2.08 Example 12 (PIF-12) 107.3 2.24

[0231] As can be seen from the test results in Table 1, the black polyimide film obtained by this invention has a tensile strength of over 99 MPa and a modulus of over 2 GPa, exhibiting excellent mechanical properties.

[0232] (2) Product appearance

[0233] The black polyimide films obtained in each embodiment are as follows: Figure 2 As shown, samples 1 to 12 are the appearance images of films PIF-1 to PIF-12 obtained in Examples 1 to 12, respectively. Among them, PIF-1 to 10 are homopolymer films, and PIF-11 to 12 are copolymer films (the ratio of the special diamine monomer shown in Formula (II) to the conventional diamine monomer shown in Formula (III) is 5:5 and 1:9, respectively). As can be seen from the figures, the homopolymer films are all black and the color is uniform; the copolymer films are thinner and the proportion of special diamine monomer is lower, so the blackness of the films is not as good as that of the homopolymer method, but the overall color is still black.

[0234] (3) Visible light absorption test

[0235] Visible light absorption tests were performed on some of the resulting thin films, and the results are as follows: Figure 3 As shown in the figure, when the thickness (δ) of the homopolymer film is greater than 40 μm, almost all visible light is absorbed in the 400–800 nm range, and the transmittance is close to 0. Films with a thickness less than 40 μm exhibit strong absorption in the 400–700 nm range, and the transmittance is also close to 0. Copolymer films have relatively strong absorption in the 400–600 nm range, and the transmittance in the 600–700 nm range is higher than that of copolymer films.

[0236] (4) Solubility test of intermediates

[0237] The solubility of the intermediate product polyimide resin powder in the examples was tested, and the results are shown in Table 2.

[0238] Table 2: Solubility of precursor polyimide resin powder (10% solid content)

[0239] DMAc DMF NMP THF EA m-Cresol CF TOL ACE MEK PI-1 ++ ++ ++ ++ + ++ ++ + + + PI-2 ++ ++ ++ ++ ++ ++ ++ + ++ ++ PI-5 ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ PI-6 ++ ++ ++ ++ ++ ++ ++ + ++ ++

[0240] Note: ++ indicates complete dissolution, + indicates partial dissolution, and - indicates insoluble.

[0241] As can be seen from the test results in Table 2, the precursor polyimide resin powder in this invention can be dissolved by a variety of organic solvents, which can realize a variety of operation schemes. Among them, solvents with low boiling points are more conducive to achieving low-energy operation.

[0242] (5) Solvent resistance test of thin film products

[0243] Solvent resistance tests were conducted on the black polyimide films obtained in each embodiment. A small amount of the film was placed in a solvent and heated under reflux for 12 hours, and the film condition was observed. The results are shown in Table 3.

[0244] Table 3: Solvent resistance of black polyimide film products (solid content 0.2%)

[0245] DMAc DMF NMP THF EA m-Cresol CF TOL ACE MEK Ethanol PIF-1 - - - - - - - - - - - PIF-2 - - - - - - - - - - - PIF-3 - - - - - - - - - - - PIF-4 - - - - - - - - - - - PIF-5 - - - - - - - - - - - PIF-6 - - - - - - - - - - - PIF-7 - - - - - - - - - - - PIF-8 - - - - - - - - - - - PIF-9 - - - - - - - - - - - PIF-10 - - - - - - - - - - - PIF-11 - - - - - - - - - - - PIF-12 - - - - - - - - - - -

[0246] Note: ++ indicates dissolution, + indicates swelling, and - indicates insolubility.

[0247] As can be seen from the test results in Table 3, the black polyimide film obtained by this invention does not dissolve or swell in a variety of organic solvents, exhibiting excellent solvent resistance.

[0248] (6) Thermogravimetric analysis and infrared testing

[0249] The heat treatment process of precursor polyimide resin powder is a thermal decomposition process, with typical thermal weight loss processes such as... Figure 4 As shown. The resin powder decomposes under heat, forming a polyimide with aniline segments in its main chain. Infrared results are shown below. Figure 5 and Figure 6 As shown.

[0250] This invention provides a black polyimide film and its preparation method. Compared to other intrinsic methods, the polymer obtained by this invention exhibits excellent solubility, dissolving not only in aprotic polar solvents such as N,N'-dimethylformamide, N,N'-dimethylacetamide, and dimethyl sulfoxide, but also in low-boiling-point solvents such as chloroform and tetrahydrofuran, enabling green, environmentally friendly, and energy-saving operation. Furthermore, the polymerization system remains a traditional transparent amber solution, facilitating observation and defect detection (such as foreign matter and bubbles), and effectively controlling product quality. After deprotection, due to the transformation of the molecular chain structure, the material exhibits uniform black properties, excellent solvent resistance, and mechanical properties. This invention cleverly resolves the contradiction between processing performance, solvent resistance, and mechanical properties, and has broader application prospects.

[0251] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention, including the best mode, and also to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. However, the scope of protection of the present invention is not limited thereto. It should be noted that, for example, equivalent substitutions or changes made according to the technical solution and inventive concept of the present invention, and material forms including fibers, profiles, composites, foams, etc., should all be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a black polyimide film, characterized in that, Includes the following steps: A) The dianhydride monomer, diamine monomer and solvent are mixed and polymerized to obtain a polyamic acid precursor solution; B) Film Formation: The polyamic acid precursor solution is subjected to imidization treatment to obtain polyimide powder; then, the polyimide powder is dissolved in a solvent, cast into a film, dried, and deprotected to obtain a black polyimide film. in: The dianhydride monomer is 4,4'-terephthalodioxydiphthalic anhydride or hexafluorodianhydride; The diamine monomer is the diamine monomer shown in formula (II), or the diamine monomer shown in formula (II) and 4,4'-diaminodiphenyl ether; Equation (II); In formula (II): n is 3 to 8; Selected from the following groups: , .

2. The preparation method according to claim 1, characterized in that, In step A), the molar ratio of the diamine monomer shown in formula (II) to 4,4'-diaminodiphenyl ether is 10:0 to 1:

9.

3. The preparation method according to claim 1, characterized in that, In step A), the molar ratio of the diamine monomer to the dianhydride monomer is 1:(0.95~1.05).

4. The preparation method according to claim 1, characterized in that, In step A), the solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, m-cresol, dichloromethane, chloroform, tetrahydrofuran, dioxane, acetone, butanone, toluene, ethyl acetate, xylene, and diethyl ether.

5. The preparation method according to claim 1, characterized in that, In step A), the polymerization reaction is carried out at a temperature of -20 to 40°C for 1 to 70 hours.

6. The preparation method according to claim 1, characterized in that, In step B), the imidization treatment is a chemical imidization treatment, which includes: mixing the polyamic acid precursor solution with an imidizing agent, then precipitating the precipitate in a poor solvent, separating the solid and liquid, and drying to obtain polyimide powder.

7. The preparation method according to claim 6, characterized in that, The imidizing agent is a nitrogen-containing compound and acetic anhydride; wherein the nitrogen-containing compound is at least one selected from triethylamine, pyridine, and methylpyridine. The molar ratio of the nitrogen-containing compound to the diamine monomer used in step A) is (0.5~3.5):1; The molar ratio of the acetic anhydride to the diamine monomer used in step A) is (0.5~5.5):

1.

8. The preparation method according to claim 1, characterized in that, In step B), the deprotection treatment is performed by a chemical method or a heat treatment method; The heat treatment method is performed at a temperature of 140~250℃ for 4~12 hours.

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